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The erosion and suspended matter/seawater interaction during and after the 1996 outburst flood from the Vatnajökull Glacier, Iceland
Abstract
The Gjálp subglacial eruption 1996 within the Vatnajökull Glacier, Iceland triggered a catastrophic outburst flood, bringing at least 180 million tonnes of suspended solids to the sea in only 42 h. This amounts to 1% of the total annual global river suspended flux to the oceans. The specific BET-surface area of the suspended solids was measured to be 11.8–18.9 m2/g, translating to the average total BET-surface area of 2.8 × 10 9 km2, providing enormous potential for adsorption/desorption and precipitation/dissolution fluxes at the suspended solids–ocean water interface. Altered basalt glass was the major constituent of the suspended matter (80%), secondary minerals such as zeolites and calcite amounted to 11%, but only 5% was fresh volcanic glass. The suspended grains were generally rounded. The glass carried by the flood is different in chemical composition from the glass produced by the Gjálp eruption. The Gjálp material has higher FeOtotal / TiO2 and TiO2 / P2O5 ratios than the suspended glass in the flood waters. The majority of the flood samples match the composition of the volcanic system, down stream from the eruption site. The large amount of altered material in the flood and its chemical composition suggests erosion conforming to a 2 m deep, 1000 m wide and 50 000 m long channel in less than 42 h. The behaviour of 28 elements on the surface of the suspended solids exposed to seawater was quantified by experiments in the laboratory. The altered basaltic glass dissolved in seawater, as recorded by the Si release from the glass. The dissolved concentrations of Na, Ca, Si, Ba, Cd, Co, Cu, Hg, Mn, Ni, and total dissolved inorganic N increased considerably when the suspended solids come into contact with the seawater, but the concentrations of Mg, K, S, Sr, Fe, Pb and Zn decreased. The experimental seawater solutions were supersaturated with respect to calcite, Mg-montmorillonite and amorphous iron-hydroxide. The rate of release (mol/m2/s) of Si, Mn, Ba, Co, Ni and Cd decreased continuously during the one week exposure to sweater. After one week, the logarithm of the dissolution rate of the altered basaltic glass was − 11.9 to − 11.6 (Si mole/m2/sec). Significantly lower than the steady-state rates for fresh basaltic glass at similar conditions. Calculated one day desorbed/dissolution suspended material fluxes are greater than the integrated dissolved flood fluxes for Mn, Ba, Ni, Co and Cd, but the Si dissolved food flux was greater than the one day desorbed/dissolved suspended material flux.
... Numerous studies have been carried out on the chemical and mechanical weathering and denudation of basalt in Iceland (i.e. Sigvaldason, 1959;Cawley et al., 1969;Ármannsson et al. 1972;Rist, 1974Rist, , 1986Árnason, 1976;Jakobsson, 1978;Raiswell and Thomas, 1984;Tómasson, 1986Tómasson, , 1991Tómasson, , 1996Gislason and Eugster, 1987b;Sigurdsson and Einarsson, 1988;Gislason and Arnórsson, 1990;Crovisier et al., 1992;Wada et al., 1992;Gislason and Arnórsson, 1993;Bluth and Kump, 1994;Gislason et al., 1996Gislason et al., , 2002Gislason et al., , 2006aGislason et al., , 2006bGislason et al., , 2008Pálsson and Vigfússon, 1996;Louvat, 1997;Louvat, et al., 1999Louvat, et al., , 2008Moulton, et al., 2000;Stefánsson and Gislason, 2001;Arnórsson et al., 2002;Snorrason et al., 2002;Russell and Knudsen, 2002;Pálsson, 2003;Hardardottir andSnorrason, 2003a andHardardóttir et al., , 2005Arnalds, 2005;Stefánsdóttir and Gislason, 2005, Kardjilov et al., 2006aGannoun et al., 2006;Pogge von Strandmann et al., 2006;Vigier et al., 2006;Sigfússon et al., 2006;2008;Georg et al., 2007;Eiríksdóttir et al., 2008). These studies dene the changes in rock chemistry and mineralogy during weathering, the chemistry of the water involved in the weathering process, the relative mobility of the elements, the saturation state of the minerals, dissolved and suspended uxes in rivers and during major oods, grain size, mineralogy and chemistry of river-suspended material, atmospheric CO 2 sequestration during chemical weath-ering, the effect of vegetation, glass content, glaciers and climate on weathering and denudation rates, the formation of soils, isotope fractionation during chemical weathering of basalts, and the time scale of the weathering. ...
... Assessments of long term mechanical denudation need to take into account major oods from the glaciers often associated with volcanic activity within the glaciers and draining of subglacial lakes, the so-called jökulhlaup (e.g. Zóphóníasson and Pálsson, 1996;Tómasson, 1996;Snorrason et al., 2002;Stefánsdóttir and Gislason, 2005;Hardardóttir et al., 2004b). ...
... The jökulhlaup in 1996, following the volcanic eruption within the Vatnajökull ice cap Russell and Knudsen, 2002;Stefánsdóttir and Gislason, 2005), resulted in at least a 180 million tonne denudation ux to the ocean in less than two days. This is more than twice the total annual mechanical denudation ux of the large and small rivers in Iceland; 60-70 million tonnes. ...
... The floods consist of a mixture of water, dissolved constituents, sediments, volcanic materials, and ice (e.g. Gislason et al., 2002;Snorrason et al., 2002;Stefánsdóttir and Gislason, 2005). Depending on their size, formation mechanism, frequency, sub-glacial topography, suspended material load and ice, the impact on the flood plain and surrounding areas can be disastrous. ...
... The total flood water volume was estimated to be 8 km 3 (Tómasson, 1996). Due to the enormous impact of these floods on ecosystems, such events have been extensively studied in terms of their hydromechanics, geomorphology and geochemistry (Björnsson, 1992(Björnsson, , 1998(Björnsson, , 2002Maizels, 1997;Snorrason et al., 1997;Kristmannsdóttir et al., 1999;Geirsdóttir et al., 2000;Roberts et al., 2000;Gislason et al., 2002;Alho et al., 2005;Stefánsdóttir and Gislason, 2005;Russell et al., 2006Russell et al., , 2010Galeczka et al., 2014a). The environmental implications of these floods have been far less studied Stefánsdóttir and Gislason, 2005;Galeczka et al., 2014a). ...
... Due to the enormous impact of these floods on ecosystems, such events have been extensively studied in terms of their hydromechanics, geomorphology and geochemistry (Björnsson, 1992(Björnsson, , 1998(Björnsson, , 2002Maizels, 1997;Snorrason et al., 1997;Kristmannsdóttir et al., 1999;Geirsdóttir et al., 2000;Roberts et al., 2000;Gislason et al., 2002;Alho et al., 2005;Stefánsdóttir and Gislason, 2005;Russell et al., 2006Russell et al., , 2010Galeczka et al., 2014a). The environmental implications of these floods have been far less studied Stefánsdóttir and Gislason, 2005;Galeczka et al., 2014a). ...
This study describes the chemical composition of dissolved, degassed and suspended fluxes of the 2002 Skaftá glacial flood, which emerged from one of the Skaftá subglacial lake due to geothermal activity beneath the Icelandic Vatnajökull glacier. The dissolved and suspended fluxes during the flood are compared with those normally observed in the Skaftá river to determine the effect of such floods on the annual fluxes of material delivered to the coastal waters. Concentrations of most dissolved elements during the flood were significantly higher than those normally observed in the Skaftá river. In addition, dissolved concentrations of nutrients such as SiO2, Fe, and V, increased more than an order of magnitude during the flood. These will affect biological processes on a local scale. The δ34S composition in the flood water suggests that the dissolved SO4 was derived from the oxidation of H2S and the geothermal fluid. The total suspended particulate load measured in the Skaftá river during the 8−day 2002 flood was approximately half of the non−flood total annual Skaftá suspended load. As particles carry the bulk of limiting nutrients to the oceans, this demonstrates the importance of glacial floods for primary production of coastal waters. The composition of the flood water and the Skaftá subglacial lake, together with reaction path modelling suggest that substantial degassing of CO2 and H2S occurred at the glacial outlet during the flood. This degassing may have released as much as 262,000 and 7,980 tonnes of CO2 and H2S, respectively, to the atmosphere having a considerable impact on the local carbon and sulphur cycle during the flood event.
... Changes in volatile release during volcanic activity influence both groundwater and surface water chemistry (Aiuppa et al., 2000;Flaathen and Gislason, 2007;Varekamp, 2008;Jones et al., 2011). For subglacial volcanoes, much of the element release is into the subglacial rivers and springs due to the confining pressure of the overlying ice restricting release as gaseous volatiles Stefánsdóttir and Gislason, 2005). ...
... Secondly, the melting of glaciers from underlying volcanic sources can lead to glacial outbreak floods, termed jökulhlaups. The two main causes of jökulhlaups are: (1) geothermal areas continuously melting an overlying glacier, leading to the accumulation and periodic draining of a subglacial lake; and (2) rapid melting of a glacier during a volcanic eruption through magma-ice interaction (Gudmundsson et al., 1997(Gudmundsson et al., , 2008Maizels, 1997;Kristmannsdóttir et al., 1999;Geirsdóttir et al., 2000;Björnsson, 2003;Alho et al., 2005;Stefánsdóttir and Gislason, 2005;Russell et al., 2006Russell et al., , 2010. The former are more common and generally of lower magnitude. ...
... Thirdly, the high mass flux and distinct chemical composition of jökulhlaups (Tómasson, 1996;Snorrason et al., 2002;Stefánsdóttir and Gislason, 2005;Galeczka et al., 2014) mean that they have the potential to play a significant role in the global geochemical cycles of elements. In particular, the high suspended particulate flux of large jökulhlaups significantly increases the water-borne particulate flux to the ocean (Gislason et al., 2006a), and an increasing number of recent studies have shown that particulate material remains reactive in the ocean, playing an integral role in the biogeochemical cycles of a number of key elements (Lacan and Jeandel, 2005;Stefánsdóttir and Gislason, 2005;Arsouze et al., 2009;Jones et al., 2012aJones et al., , 2012bJones et al., , 2014Singh et al., 2012;Pearce et al., 2013). ...
The quantification of volatile emissions from volcanoes is an integral part of understanding magmatic systems, with the exsolution and extent of volcanic degassing having a large impact on the nature of an eruption. Measurements of volatiles have traditionally focused on gas emissions into the atmosphere, but volatiles can also become dissolved in proximal water bodies en route to the surface. Thus the monitoring of rivers draining active volcanic areas can provide insights to identifying changes in activity. This process is particularly important for sub-glacial volcanoes in Iceland, where much of the volatile release is transported within glacial outbreak floods, termed jökulhlaups. Monitoring and characterising these phenomena is hampered by the dependence on spot sampling of stochastic events under challenging field conditions, which often leads to bias in the collected data. A recent technological advance is the osmotic sampler, an electricity-free pump that allows for the continuous collection of water that can subsequently be divided into time-averaged samples. This technique allows continued and unsupervised deployment of a sampler for weeks to months, representing a cost-efficient form of chemical monitoring. In this study we deployed osmotic samplers in two rivers in southern Iceland. Skálm is a proglacial river from Mýrdalsjökull glacier and Katla volcano, while Skaftá is a larger drainage system from the western part of Vatnajökull glacier. Both rivers are prone to jökulhlaups from geothermal and volcanic sources, and a small jökulhlaup of geothermal origin occurred during the second deployment in Skaftá in January 2014. The two deployments show that osmotic samplers are capable of delivering accurate chemical data in turbulent conditions for several key elements. Total dissolved fluxes for the deployment at Skaftá are calculated to be Na = 9.9 tonnes/day, Mg = 10.5 t/d, Si = 34.7 t/d, Cl = 11.0 t/d, Ca = 31.6 t/d, DIC = 50.8 t/d, and SO4 = 28.3 t/d, with significant elevations of element concentrations during the jökulhlaup. Dissolved concentrations vary considerably on temporal scales from days to seasons, so that spot sampling may miss pulses in concentrations. This is particularly important for elements such as Mn. The continuous geochemical records from the osmotic samplers make it possible to identify pulses of fluxes attributed to sea spray, groundwater, and subglacial sources. The samplers can also be combined with existing methods of river monitoring, such as conductivity and discharge, to accurately assess changes to fluvial chemistry due to volcanic inputs. Moreover, there is the potential to deploy osmotic samplers in a range of other affected water bodies (e.g. wells, springs, lakes) to gain further insights into volcanic processes.
... The specific BET-surface area of the suspended solids was measured to be 11.8-18.9 m 2 /g (Stefánsdó ttir and Gíslason, 2005). The total mass of the suspended material and its specific surface area yield the average total BET-surface area of 2.8 Â 10 9 km 2 . ...
... Seawater, used in the experiments, was collected in spring 1999 from the Selvogsgrunn section south of the Reykjanes peninsula in SW Iceland, filtrated through 0.2 Am pore cellulose acetate filter and stored in the dark before the experiments (Stefánsdó ttir and Gíslason, 2005). A total of 16 experiments were run in 250 ml polypropylene batch reactors that were placed in a temperature controlled water bath at 25 8C F 0.5 8C for 16 min to 6 days. ...
... At the end of each experiment, the water samples were filtered through 0.2 Am pore cellulose acetate filter and acidified with concentrated suprapure HNO 3 acid. The elements Ca, Mg, Na, K, S, Si, Sr were analyzed with ICP-AES (Inductively Coupled Atomic Emission Spectrometry), Al, As, Ba, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, P, Pb, Ti and Zn were analyzed with High Resolution Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and Hg was analyzed using atom fluorescence (Rodushkin and Ruth, 1997;Rodushkin et al., 1998;Stefánsdó ttir and Gíslason, 2005). ...
The objective of this study was to quantify by experiments the initial seawater–suspended basaltic glass interactions following the 1996 outburst flood from the Vatnajökull glacier, Iceland. The altered basaltic glass dissolved in seawater as recorded by the Si release from the glass. The dissolved concentrations of Na, Ca, Si, Ba, Cd, Co, Cu, Hg, Mn, Ni and total dissolved inorganic N increased with time but the concentrations of Mg, K, S, Sr, Fe, Pb and Zn decreased. Calculated 1 to 10 day fluxes for Si range from 38,000 tons/day to 70,000 tons/10 days. The fluxes for other major elements are more uncertain, but the positive flux (release from suspended matter to seawater) of Ca and Na, and negative flux of Mg, K and S are greater than the Si flux.
... They also contain very little organic carbon, both in the truly dissolved (b10 kD) fraction (0.4–0.8 mg/l,Table 1) and in the retentate (colloidal) fraction (0.14–0.37 mg/l). By contrast, estuaries which are reported to be strongly affected by U-removal in the low salinity zone have a far higher proportion of colloid-bound U and farGislason et al., 1996), Stapafell glass (Oelkers and Gislason, 2001) and samples of particulate material from an estuary in the south of Iceland (Stefansdottir and Gislason, 2005).Table 2 Element concentrations and isotope ratios of the suspended load, including major element concentrations of fresh basalt taken from the Borgarfjörður catchment (Gislason et al. 1996 Internal uncertainty is given for U activity ratios. ⁎Sample concentrations were determined from MC-ICP-MS intensities (uncertainty ± 10%). ...
... These islands dominate the suspended material flux to the oceans due to the combined effect of high-relief, high runoff, the presence of rapidly weathering volcanic rocks, and an absence of sedimentary traps. Experimental work on suspended riverine material from the 1996 outburst flood from the Vatnajokull glacier in Iceland also clearly shows that such material dissolves in seawater (Gislason et al., 2002; Stefansdottir and Gislason, 2005 ), and the Li isotope and elemental data for suspended particles presented here provide the first field-based evidence for continued weathering of basaltic particles in the estuarine environment and into the marine realm. The question then is to what extent the continued weathering and dissolution of volcanic material affects the overall U, Li and Mg isotope signal to the oceans. ...
... The question then is to what extent the continued weathering and dissolution of volcanic material affects the overall U, Li and Mg isotope signal to the oceans. Calculations based on experimentally determined basaltic glass dissolution rates at the pH and temperature range of Icelandic ocean waters (Oelkers and Gislason, 2001; Gislason and Oelkers, 2003), together with measurements of the surface area of river suspended material from Iceland (Stefansdottir and Gislason, 2005) indicate that ~ 0.05% of this material dissolves in seawater each day (Gislason et al., 2006). Crucially, even severely weathered basaltic material continues to dissolve when exposed to seawater (Stefansdottir and Gislason, 2005 ). ...
This study presents major and trace elements and uranium (U), lithium (Li) and magnesium (Mg) isotope data for dissolved and suspended particulate material from estuaries draining dominantly basaltic terrains in Iceland (Borgarfjörður) and Sao Miguel (Povoação) in the Azores archipelago. The concentrations of dissolved sodium (Na), calcium (Ca), potassium (K), sulphate (SO4), Mg and Li, and 7Li/6Li and 26Mg/24Mg isotope ratios vary directly as a function of the dissolved chloride concentration [Cl], indicating that these species are non-reactive in these estuaries. However, U appears to be affected either by colloid flocculation or the formation of Fe-oxyhydroxides in Borgarfjörður. The major element composition of suspended particulate material in the estuary at Borgarfjörður shows that the detrital silicates delivered to the estuarine mixing zone are relatively unweathered. Accordingly, the δ26Mg isotope composition of the suspended material is indistinguishable from that of the parent basalts. However, the (234U/238U) activity ratios of the suspended material are significantly different from the parent basalt indicating rapid equilibration of the U isotopes between particles and seawater. The Li concentration and δ7Li isotope composition of the suspended load are also observed to increase with increasing [Cl], consistent with ongoing weathering of detrital material and the formation of secondary minerals in seawater. Depending on the particle residence time in the estuary, this process could remove as much as 15–25% of the global riverine input of Li to the ocean.
... Depletion periods observed right after day 0.21 until day 18 for dFe, and from day 8 to day 57 for dMn were similar to observations in other studies involving riverine basalts resuspended in seawater, though those employed lower water/rock ratios than our incubation (i.e. 3.6 and 115 to 130 for Jones et al. (2012b) and Stefánsdóttir and Gíslason (2005) respectively). Jones et al. (2012b) suggested that Mn was incorporated into a precipitating secondary phase while Stefánsdóttir and Gíslason (2005) argued that dFe was consumed by formation of an Fe-phase, most likely amorphous Fe(OH) 3 . ...
... 3.6 and 115 to 130 for Jones et al. (2012b) and Stefánsdóttir and Gíslason (2005) respectively). Jones et al. (2012b) suggested that Mn was incorporated into a precipitating secondary phase while Stefánsdóttir and Gíslason (2005) argued that dFe was consumed by formation of an Fe-phase, most likely amorphous Fe(OH) 3 . Precipitating secondary phases including Mn oxyhydroxides that could have scavenged Fe were not detected by SEM analysis performed at the end of the incubation. ...
A number of trace metals play essential roles in marine ecosystem structure and biological productivity. Until recently, it has been argued that phytoplankton access primarily dissolved iron, while particulate iron was considered a refractory material with little use biologically and limited interaction with the dissolved pool. In order to assess the transfer mechanisms between sediment-sourced particulate trace metals and the dissolved pool, we conducted a 14-month incubation that reacted resuspended sediments with natural seawater, both originating from the Kerguelen area (KEOPS cruises; Southern Ocean), in the dark, and at concentrations replicating natural conditions. Three types of sediments were investigated (named BioSi, BioSi + Ca, and Basalt), mostly composed of (i) biogenic silica (bSiO2), (ii) bSiO2 and calcite, and (iii) basaltic fragments, respectively. The release of dissolved silicon (dSi), iron (dFe) and manganese (dMn) was monitored regularly throughout the incubation, as well as living bacteria density and Fe organic ligands. Depending on the origin and composition of the sediment, unique dFe and dMn fluxes were observed, including a strong decoupling between dFe and dMn. The basaltic sediment released up to 1.09 ± 0.04 nmol L⁻¹ of dFe and 0.28 ± 0.09 nmol L⁻¹ of dMn, while the biogenic sediments released a higher 3.91 ± 0.04 nmol L⁻¹ and 8.03 ± 0.42 nmol L⁻¹ of dFe and dMn, respectively. Several factors influencing the release and removal of dFe and dMn were discernable at the temporal sampling resolution of the incubation, including the structural composition of the sediment, bacterial abundance, and the formation of manganese oxides. The regular sampling over short timescales and the extended sampling over one year proved to be critical to constrain the processes and exchanges that govern the contribution of the particulate to the dissolved pools. Overall, this incubation provides a strong basis for reassessing the role of resuspended sedimentary particles in the marine biogeochemical cycles of Fe and Mn. Indeed, we show that biogenic silica, calcite-rich and basaltic particles can contribute substantial dissolved Fe and Mn to the overlying water column. In the future, the global extent of this previously overlooked external metal source should be quantified through further process studies and biogeochemical models. This article is part of a special issue entitled: “Cycles of trace elements and isotopes in the ocean – GEOTRACES and beyond” - edited by Tim M. Conway, Tristan Horner, Yves Plancherel, and Aridane G. González.
... This process stems from the weathering of Calcium-Magnesium silicates, and over the last 100 million years mainly Ca silicates. For example, the weathering of Ca-rich plagioclase, a common silicate mineral, leads to carbonate mineral precipitation according to the following reactions: Oelkers, 2003;Stefánsdóttir and Gislason, 2005;Gislason et al., 2006;Pogge von Strandmann et al., 2008). The feedback between climate and weathering has been attributed to a number of factors including the effect of temperature on 1) silicate dissolution rates, 2) runoff, 3) mechanical weathering, and 4) glacial melting (e.g. ...
... Due to their composition and rapid dissolution rates, the weathering of continental basalts has a far faster weathering rate and CO 2 consumption capacity than other major continental silicate rocks (Meybeck, 1986;Bluth and Kump, 1994;Dessert et al., 2003;Wolff-Boenisch et al., 2004. Third, Iceland is a volcanic island representative of the high-relief, volcanic and tectonically active islands that contribute over 45% of suspended material to the oceans, and the suspended material from these islands is reactive in seawater (Milliman and Syvitski, 1992;Gaillardet et al., 1999b;Stefánsdóttir and Gislason, 2005;Gislason et al., 2006). Fourth, future warming and rainfall increase is expected to be greatest over land situated at high latitudes (Alley et al., 2007). ...
... Among them, the proportion of fresh basaltic glass in Icelandic river particles was observed to span a large range, from 5% to 65% of the particle flux (Stefánsdóttir and Gíslason, 2005), but the highest values should be excluded for other islands where weathering of basaltic glass is more intense than in Iceland. For the purpose of our estimation, we consider the very low end of these observations: 15 ± 10% of basaltic particles carried by rivers to the ocean are considered to be fresh basaltic glass. ...
... The specific surface of river particles of basaltic volcanic islands was estimated to be between 11.85 and 22.26 m 2 g −1 in Iceland (Stefánsdóttir and Gíslason, 2005). For volcanic ash, the reported range is lower, typically between 0.45 and 2 m 2 g −1 (e.g. ...
... Moreover, geothermal and meltwater dissolution of glass-rich basaltic tephra releases elements into these meltwaters, enabling the delivery of biologically-limiting elements (e.g., phosphorous and iron) into the surrounding proglacial environment [66]. For example, the 1996 jökulhlaup originating from the subglacial eruption at Gjá lp had an estimated dissolved volatile and element load of 1 million tonnes [67,68], with suspended sediments comprising fresh glass, palagonite (amorphous primary product of basaltic glass alteration), alteration minerals (such as zeolite and calcite), plagioclase, augite, and olivine, and rock fragments [67]. This meltwater generated by the Gjá lp eruption had a pH ranging between 3 and 8 at the eruption site, with the resulting flood water pH ranging from 6.88 to 7.95 [68]. ...
... Moreover, geothermal and meltwater dissolution of glass-rich basaltic tephra releases elements into these meltwaters, enabling the delivery of biologically-limiting elements (e.g., phosphorous and iron) into the surrounding proglacial environment [66]. For example, the 1996 jökulhlaup originating from the subglacial eruption at Gjá lp had an estimated dissolved volatile and element load of 1 million tonnes [67,68], with suspended sediments comprising fresh glass, palagonite (amorphous primary product of basaltic glass alteration), alteration minerals (such as zeolite and calcite), plagioclase, augite, and olivine, and rock fragments [67]. This meltwater generated by the Gjá lp eruption had a pH ranging between 3 and 8 at the eruption site, with the resulting flood water pH ranging from 6.88 to 7.95 [68]. ...
The search for once-habitable locations on Mars is increasingly focused on environments dominated by fluvial and lacustrine processes, such as those investigated by the Mars Science Laboratory Curiosity rover. The availability of liquid water coupled with the potential longevity of such systems renders these localities prime targets for the future exploration of Martian biosignatures. Fluvial-lacustrine environments associated with basaltic volcanism are highly relevant to Mars, but their terrestrial counterparts have been largely overlooked as a field analogue. Such environments are common in Iceland, where basaltic volcanism interacts with glacial ice and surface snow to produce large volumes of meltwater within an otherwise cold and dry environment. This meltwater can be stored to create subglacial, englacial, and proglacial lakes, or be released as catastrophic floods and proglacial fluvial systems. Sedimentary deposits produced by the resulting fluvial-lacustrine activity are extensive, with lithologies dominated by basaltic minerals, low-temperature alteration assemblages (e.g., smectite clays, calcite), and amorphous, poorly crystalline phases (basaltic glass, palagonite, nanophase iron oxides). This paper reviews examples of these environments, including their sedimentary deposits and microbiology, within the context of utilising these localities for future Mars analogue studies and instrument testing.
... This process stems from the weathering of Calcium-Magnesium silicates, and over the last 100 million years mainly Ca silicates. For example, the weathering of Ca-rich plagioclase, a common silicate mineral, leads to carbonate mineral precipitation according to the following reactions: Oelkers, 2003;Stefánsdóttir and Gislason, 2005;Gislason et al., 2006; Pogge von Strandmann et al., 2008). The feedback between climate and weathering has been attributed to a number of factors including the effect of temperature on 1) silicate dissolution rates, 2) runoff, 3) mechanical weathering, and 4) glacial melting (e.g. ...
... Due to their composition and rapid dissolution rates, the weathering of continental basalts has a far faster weathering rate and CO 2 consumption capacity than other major continental silicate rocks (Meybeck, 1986;Bluth and Kump, 1994;Dessert et al., 2003;WolffBoenisch et al., 2004). Third, Iceland is a volcanic island representative of the high-relief, volcanic and tectonically active islands that contribute over 45% of suspended material to the oceans, and the suspended material from these islands is reactive in seawater (Milliman and Syvitski, 1992;Gaillardet et al., 1999b;Stefánsdóttir and Gislason, 2005;Gislason et al., 2006). Fourth, future warming and rainfall increase is expected to be greatest over land situated at high latitudes ( Alley et al., 2007). ...
Long-term climate moderation is commonly attributed to chemical weathering; the greater the temperature and precipitation the faster the weathering rate. To test this widely-held hypothesis, we performed a field study and determined the weathering rates of eight nearly pristine north-east Iceland river catchments with varying glacial cover over 44 y. Statistically significant linear positive correlations were found between mean annual temperature and chemical weathering in all eight catchments and between mean annual temperature and mechanical weathering and runoff in seven of the eight catchments. The runoff, mechanical weathering flux, and chemical weathering fluxes in these catchments are found to increase from 6 to 16%, 8 to 30%, and 4 to 14%, respectively, depending on the catchment for each degree of temperature increase. Positive correlations were found between time and mechanical and chemical weathering for all catchments. In summary, these results demonstrate a significant feedback between climate and Earth surface weathering, and suggest that this weathering rate is currently increasing with time due to global warming.
... Basaltic glass dissolution rates at the pH and temperature range of ocean waters suggests that $0.05% of basaltic suspended material would dissolve in seawater each day (Oelkers and Gislason, 2001;Gislason and Oelkers, 2003;Jones and Gislason, 2008). Even basaltic glass that is already severely weathered continues to dissolve when exposed to seawater (Stefánsdó ttir and Gislason, 2005). Gislason et al. (2006) and Wallmann et al. (2008) concluded that the particulate flux of Ca that subsequently dissolves in seawater is comparable to that derived from the dissolved flux. ...
... Other elements show considerable enrichment in seawater during the experiments. In particular, Mn and Ni are considerably enriched in seawater when reacted with the Hvítá River bedload (Fig. 3), similar to previous work on weathered basaltic glass/seawater experiments (Stefánsdó ttir and Gislason, 2005). Manganese concentrations increase to 0.8 and 2 ppm at 5 and 21°C, respectively, in the Hvítá River bedload experiments. ...
The riverine transport of elements from land to ocean is an integral flux for many element cycles and an important climate regulating process over geological timescales. This flux consists of both dissolved and particulate material. The world’s rivers are estimated to transport between 16.6 and 30 Gt yr-1 of particulate material, considerably higher than the dissolved flux of ∼1 Gt yr-1. Therefore, the dissolution of particulate material upon arrival in estuaries and coastal waters may be a significant flux for many elements. Here we assess the role of riverine particulate material dissolution in seawater with closed-system experiments using riverine bedload material and estuarine sediment from western Iceland mixed with open ocean seawater. Both particulate materials significantly changed the elemental concentrations of the surrounding water with substantial increases in Si concentrations indicative of silicate dissolution. Seawater in contact with bedload material shows considerable enrichment of Ca, Mg, Mn, and Ni, while Li and K concentrations decrease. Moreover, the 87Sr/86Sr of seawater decreases with time with little change in Sr concentrations, indicative of a significant two-way flux between the solid and fluid phases. Mass balance calculations indicate that 3% of the Sr contained in the original riverine bedload was released during 9 months of reaction. In contrast, the estuarine material has a negligible effect on seawater 87Sr/86Sr and transition metal concentrations, suggesting that these reactions occur when particulate material first arrives into coastal waters. Solubility calculations performed using the PHREEQC computer code confirm that primary minerals are undersaturated, while secondary minerals such as kaolinite are oversaturated in the reacted fluids. These results demonstrate that riverine transported basaltic particulate material can significantly alter the composition of seawater, although the total concentrations of many major elements in seawater are regulated by the formation of secondary phases. This behavior has important implications for nutrient supply to coastal waters and the isotopic mass balance of several elements in the oceans.
... This exchange is probably analogous to the processes that occur when Ca-Mg–rich basaltic river suspended material interacts with the ocean. Recent experimental work reported by Stefánsdóttir and Gislason (2005) and referred to by Schwartzman in his Comment, suggests that, like the alteration of mid-ocean ridges, Ca liberation from basalt and basaltic glass is concurrent with Mg consumption. The degree to which Mg consumption is required for the liberation of Ca from either the basaltic suspended material or the mid-ocean ridges is unclear. ...
... Ca release from basalt in either the mid-ocean ridges or suspended material in deltas is due to the dissolution of Ca-bearing minerals and glasses. These Ca-bearing minerals and glasses are undersaturated, and their dissolution reactions have been demonstrated to proceed in natural seawater, meteoric waters, and experimental solutions regardless of the aqueous Mg concentration (e.g., Mottle, 1983; Oelkers and Gislason, 2001; Stefánsdóttir and Gislason, 2005). These observations demonstrate that the presence of aqueous Mg is not necessary for the liberation of silicate-bound Ca. ...
... This process stems from the weathering of Calcium-Magnesium silicates, and over the last 100 million years mainly Ca silicates. For example, the weathering of Ca-rich plagioclase, a common silicate mineral, leads to carbonate mineral precipitation according to the following reactions: Oelkers, 2003;Stefánsdóttir and Gislason, 2005;Gislason et al., 2006;Pogge von Strandmann et al., 2008). The feedback between climate and weathering has been attributed to a number of factors including the effect of temperature on 1) silicate dissolution rates, 2) runoff, 3) mechanical weathering, and 4) glacial melting (e.g. ...
... Due to their composition and rapid dissolution rates, the weathering of continental basalts has a far faster weathering rate and CO 2 consumption capacity than other major continental silicate rocks (Meybeck, 1986;Bluth and Kump, 1994;Dessert et al., 2003;Wolff-Boenisch et al., 2004. Third, Iceland is a volcanic island representative of the high-relief, volcanic and tectonically active islands that contribute over 45% of suspended material to the oceans, and the suspended material from these islands is reactive in seawater (Milliman and Syvitski, 1992;Gaillardet et al., 1999b;Stefánsdóttir and Gislason, 2005;Gislason et al., 2006). Fourth, future warming and rainfall increase is expected to be greatest over land situated at high latitudes (Alley et al., 2007). ...
... Naturalraine, and glacier dams, i.e. Ruapehu, New Zealand (Carrivick et al., 2010); Bairaman, New Britain (King et al., 1989); Tam Pokhari, Nepal (Osti and Egashari, 2009); and Grimsvötn, Iceland (Stefánsdottir and Gíslason, 2005), respectively. Shown also are peak river sediment yields following volcanic eruptions; landslide episodes triggered by the 1999 Chi–Chi earthquake and several subsequent tropical cyclones, Taiwan (e.g. ...
... This yield is the highest reported for any mountain river (Fig. 3). The release of 1.8 × 10 8 m 3 of suspended sediment yield during the 1996 Grimsvötn glacial lake outburst flood, Iceland (Stefánsdottir and Gíslason, 2005), facilitated a mean specific yield of 8.1 × 10 6 t km − 2 yr − 1 for 42 h, rivalling yields reported for Taiwanese rivers impacted by earthquake-and typhoon-induced landslides. Even if averaging the contributions of these and other individual dam breaks over reference intervals of 10 3 -10 4 yr, the corresponding yields remain mostly above the median of mountain rivers (Fig. 3). ...
Earth Science Reviews, 112 (2012) 115-125. doi:10.1016/j.earscirev.2012.02.006
... This process stems from the weathering of Calcium-Magnesium silicates, and over the last 100 million years mainly Ca silicates. For example, the weathering of Ca-rich plagioclase, a common silicate mineral, leads to carbonate mineral precipitation according to the following reactions: Oelkers, 2003;Stefánsdóttir and Gislason, 2005;Gislason et al., 2006;Pogge von Strandmann et al., 2008). The feedback between climate and weathering has been attributed to a number of factors including the effect of temperature on 1) silicate dissolution rates, 2) runoff, 3) mechanical weathering, and 4) glacial melting (e.g. ...
... Due to their composition and rapid dissolution rates, the weathering of continental basalts has a far faster weathering rate and CO 2 consumption capacity than other major continental silicate rocks (Meybeck, 1986;Bluth and Kump, 1994;Dessert et al., 2003;Wolff-Boenisch et al., 2004. Third, Iceland is a volcanic island representative of the high-relief, volcanic and tectonically active islands that contribute over 45% of suspended material to the oceans, and the suspended material from these islands is reactive in seawater (Milliman and Syvitski, 1992;Gaillardet et al., 1999b;Stefánsdóttir and Gislason, 2005;Gislason et al., 2006). Fourth, future warming and rainfall increase is expected to be greatest over land situated at high latitudes (Alley et al., 2007). ...
Long-term climate moderation is commonly attributed to chemical weathering; the higher the temperature and precipitation the faster the weathering rate. Weathering releases divalent cations to the ocean via riverine transport where they promote the drawdown of CO2 from the atmosphere by the precipitation and subsequent burial of carbonate minerals. To test this widely-held hypothesis, we performed a field study determining the weathering rates of 8 nearly pristine north-eastern Iceland river catchments with varying glacial cover over 44 years. The mean annual temperature and annual precipitation of these catchments varied by 3.2 to 4.5 °C and 80 to 530%, respectively during the study period. Statistically significant linear positive correlations were found between mean annual temperature and chemical weathering in all 8 catchments and between mean annual temperature and both mechanical weathering and runoff in 7 of the 8 catchments. For each degree of temperature increase, the runoff, mechanical weathering flux, and chemical weathering fluxes in these catchments are found to increase from 6 to 16%, 8 to 30%, and 4 to 14% respectively, depending on the catchment. In contrast, annual precipitation is less related to the measured fluxes; statistically significant correlations between annual precipitation and runoff, mechanical weathering, and chemical weathering were found for 3 of the least glaciated catchments. Mechanical and chemical weathering increased with time in all catchments over the 44 year period. These correlations were statistically significant for only 2 of the 8 catchments due to scatter in corresponding annual runoff and average annual temperature versus time plots. Taken together, these results 1) demonstrate a significant feedback between climate and Earth surface weathering, and 2) suggest that weathering rates are currently increasing with time due to global warming.
... In the Skagafjö rður valley and other locations throughout Iceland, most calcite precipitates from hydrothermal waters circulating in the subsurface and is later exposed to interaction with surface runoff via erosion (Kristmannsdottir, 1979;Kristmannsdó ttir and Tó masson, 1978;Mehegan et al., 1982;Neuhoff et al., 2000;Saemundsson et al., 1980;Walker, 1960Walker, , 1964. However, in select high-temperature geothermally active areas, rivers can become temporarily supersaturated with respect to calcite during subglacial volcanic eruptions and outburst floods (Stefánsdó ttir and Gíslason, 2005;Galeczka et al., 2014Galeczka et al., , 2015, and carbonate crusts can subsequently form at the surface. The Hvanná river in southern Iceland offers a prime example of this latter pathway. ...
This study examines the Ca isotope (δ44/40Ca) geochemistry of Icelandic rivers with the overall aims of improving the δ44/40Ca tracer, constraining solute sources, and addressing the hypothesis that basalt weathering disproportionately regulates Earth’s long-term climate. We report Ca isotope and elemental data for mainstem rivers, tributary streams, thermal and non-thermal springs, basalt, calcite, soil, vegetation, and sediment collected from the Skagafjörður region in North Iceland. Waters and calcite were further analyzed for their carbon isotope (δ¹³C) composition, and we conducted experiments to characterize δ44/40Ca values of riverine colloids, the clay-size fraction (<2 µm) of soil, and exchangeable leachates obtained from soil and bedload sediment. The dataset includes analyses of travertine and coexisting water samples collected from a CO2-rich spring (Hvanná river) in South Iceland.
Samples show a ∼2‰ range, with groundwater, the ultrafiltered fraction of river water, and hydrothermal calcite producing among the highest δ44/40Ca values and travertine, soil exchangeable Ca, and vegetation the lowest. Riverine δ44/40Ca values are on average ∼0.20‰ higher than those for basalt, which shows minimal isotopic variability. Mainstem glacial-fed rivers entering the Skagafjörður valley from the soil- and vegetation-free highlands have higher δ44/40Ca values than direct-runoff tributaries draining catchments to the north where pedogenesis is more pervasive. Riverine δ44/40Ca values correlate with Sr/Ca and Na/Ca ratios, as well as the saturation index of calcite (SIcal). Riverine δ¹³C values increase from ∼-8‰ (atmospheric) to ∼-3‰ (calcite) as SIcal values increase from highly-undersaturated to near-equilibrium. One watershed (Svartá river) shows unique trends, where riverine δ44/40Ca values and Sr/Ca ratios do not correlate, and soil exchangeable leachates produced anomalously high amounts of Ca. Clay-size fractions isolated from three horizons composing a brown andosol show slightly lower δ44/40Ca values than bulk basalt, but the values overlap with those for primary minerals. Colloids appear to have lower δ44/40Ca values than truly dissolved Ca. The proxy could be developed as a tracer for colloidal contributions to riverine dissolved loads, especially in soil-mantled catchments where the inputs appear most pronounced. Groundwater δ44/40Ca values correlate with pH, temperature, distance from the coast, and Sr/Ca ratios, all consistent with fractionation control yielding varying degrees of geochemical evolution. The combined riverine patterns largely reflect three-component mixing between basalt weathering, calcite weathering, and hydrothermal water inputs. Subsurface Ca isotope fractionation indirectly impacts riverine δ44/40Ca values by elevating the δ44/40Ca values of groundwater and hydrothermal calcite. This study highlights the significance of hydrothermal water inputs of Ca and HCO3 to Icelandic rivers, which have been previously underappreciated. Mixing calculations suggest that a maximum of ∼20% of the Ca in mainstem rivers derives from surficial basalt weathering. Small tributaries draining the flanks of the valley show the clearest signals of basalt weathering by atmospheric CO2, but these waters have much lower solute concentrations than those employed in previous attempts to estimate basalt weathering rates and parameterize the climate sensitivity of the basalt weathering feedback.
... In these experiments, although several different types of clay mineral are supersaturated (see above), it may be that the clay mineralogies also consist of amorphous mixtures. Palagonite (the hydrous amorphous alteration product of basaltic glass) or iddingsite (the hydrous amorphous alteration product of olivine) may also be forming, rather than distinct clay types, as demonstrated in some experimental and natural samples (Stefansdottir and Gislason, 2005;Valle et al., 2010;Chemtob et al., 2012). ...
Lithium (Li) isotopes are a tracer of silicate weathering processes, but how they react to different components of organic and plant-assisted weathering is poorly known. To examine the effect of organic acids compared to a strong mineral acid (HCl) on Li isotope behaviour, basalt-water weathering experiments were amended with different organic acids (glycine, malic acid, cinnamic acid, and humic acid; 0.01M). The presence of the different acids significantly affects the behaviour of dissolved elemental concentrations (such as Mg, Fe, and Al), both by increasing primary rock dissolution and hindering rates of secondary mineral formation. However, the behaviour of Li isotopes appears unaffected, with all experiments following an almost identical trend of δ⁷Li versus Li/Na. This observation was consistent with a single fractionation factor during the uptake of Li into secondary minerals, yet both calculated saturation states and leaching experiments on the reacted solids indicated that Li was removed into multiple phases, suggesting that the bulk combined fractionation factor barely varied. Of the Li lost from solution in the organic experiments, we estimated that on average 76% went into neoformed clays, 16% into oxides/oxyhydroxides, and 10% into the exchangeable fraction. The fractionations observed for each phase were Δ⁷Liexch-soln = -12.7 ± 1.7‰, Δ⁷Liox-soln = -26.7 ± 0.4‰, and Δ⁷Liclay-soln = -21.6 ± 3.3‰. These fractionations were identical, within error, to those from experiments with organic-free water, implying that the Li isotope behaviour was unaffected by the presence of organic acids in the weathering reaction. This result has interesting consequences for the interpretation of Li isotopes in terms of plant-assisted weathering and the geological record of terrestrialisation. In particular, it appears to imply that seawater Li isotope records can be expected to resolve the integrated effect of plants on weathering fluxes or weathering congruence, rather than being sensitive to specific organic-mediated weathering mechanisms.
... It was thus briefly the second largest freshwater discharge on Earth, exceeded only by the Amazon, despite being generated by a comparatively small volcanic eruption (Smellie and Edwards, 2016, p. 81). The associated jökulhlaup also delivered more than 1.8 x 10 6 tonnes of suspended solids to the sea in only 42 hours (Tómasson, 1996;Stefánsdottir and Gíslason, 2005). This amounts to c. 1 % of the total annual suspended flux delivered by rivers globally to the oceans. ...
Three discrete categories of sedimentary deposits are associated with glaciovolcanism: englacial cavity, jökulhlaup and lahar. Englacial cavity deposits are found in water-filled chambers in the lee of active glaciovolcanoes or at a locus of enhanced geothermal heat flux. The cavities provide a depocentre for the accumulation of debris, either abundant fresh juvenile debris with sparse dropstones (associated with active glaciovolcanism) or polymict basal glacial debris in which dropstones are abundant (associated with geothermal hot spots). Described examples are uncommon. By contrast, volcanogenic jökulhlaup deposits are abundant, mainly in Iceland, where they form extensive sandar sequences associated with ice- covered volcanoes. Jökulhlaups form as a result of the sudden subglacial discharge of stored meltwater. Analogous deposits known as glaciovolcanic sheet-like sequences represent the ultra-proximal lateral equivalents deposited under the ice. Glaciovolcanic lahars are associated with ice- capped volcanoes. They form as a result of explosive eruptions through relatively thin ice or following dome collapse, and they trigger mainly supraglacial rather than subglacial meltwater escape. Sediment transport and depositional processes are similar in jökulhaups and lahars and are dominated by debris flow and hyperconcentrated or supercritical flow modes during the main flood stage, although the proportions of the principal lithofacies are different.
... For example, recent GLOFs in the Himalayas were documented to transport up to 200 ton-sized boulders (Richardson and Reynolds, 2000a). Remarkably, entrainment of 1.8 Â 10 8 m 3 has been documented for the 1996 Grimsvötn jokulhlaup in Iceland (Stefánsdottir and Gíslason, 2005), resulting in the highest known mean specific yield of 8.1 x 10 6 km −2 year −1 (for 42 h; Korup, 2012). GLOF depositions typically include inter-channel sand bars and bank boulder accumulation. ...
Glacial lake outburst floods (GLOFs) are sudden pulses of meltwater and sediment from lakes dammed by moraines, glacier ice, or located in bedrock overdeepenings. GLOFs had some of the highest flood volumes, discharges, sediment transport rates, and runouts from freshwater floods in Earth's history. GLOFs can cause substantial erosion, aggradation, and avulsion in river channels, accentuating their role in landscape development in glaciated regions. Their role as a natural hazard has become increasingly important in a changing cryosphere with rising exposure to population and infrastructure, retreating glaciers, and growing glacial lake volumes. In this contribution, we characterize geomorphological preconditions for, and consequences from, glacial lake outburst floods, including GLOF triggers and their hydro-dynamical properties. We review the global distribution of reported GLOFs, discuss their occurrence under ongoing atmospheric warming in past decades, and show recent progress in modeling and GLOF processes and impacts.
... The oxidized solution and the precipitated ferrihydrite, as a surface adsorbent, are mixed with seawater during a second reaction step using the composition published by Stefánsdóttir et al. [15] for North Atlantic seawater. The mixing ratio of the oxidized soil solution and the seawater is varied from 3:1 to 1:100.000 in the models to simulate the effect of increasing fluid mixing. ...
The storage of carbon, metals and nutrients in peat lands at high latitude is sensitive to climate- and land usage changes. This work shows that the thermodynamically most stable iron phases in Icelandic peat areas, like hematite or magnetite do not form, but rather the metastable ferrihydrite, which forms in abundance. Model calculations suggest that this ferrihydrite is able to adsorb high concentrations of natural derived heavy metals (Pb, As, Cr, Cu) and nutrients (P). If this ferrihydrite comes in contact with the oceans, these elements will be released through ferrihydrite-seawater interaction. This process may have significant effects to the chemistry of the near shore environments if ferrihydrite transport to the oceans increase due to future increased flooding and sea level rise.
... Volcanic hazards include degassing, volcanic gas dispersion, acid rain, pollution of surface waters, potential volcanic ash production and glacial outburst floods. These hazards have been previously investigated and used for civil-and environmental protection development in vicinities of the active volcanoes (e.g., Aiuppa, 2009;Aiuppa et al., 2006, Bagnato et al., 2013Björnsson, 2003;Bobrowski et al., 2007;Calabrese et al., 2011;Cuoco et al., 2013;D'Alessandro et al., 2013;Delmelle, 2003;Delmelle et al., 2002;Delmelle et al., 2007;Delmelle et al., 2015;Flaathen and Gislason, 2007;Floor et al.,-2011;Galeczka et al., 2014;Gislason et al., 2002;2011;Gudmundsson et al., 1997Gudmundsson et al., , 2008Jones et al., 2011;Kristmannsdóttir et al., 1999;Moune et al., 2006;Menard et al., 2014;Oppenheimer 2003;Roberts et al., 2000;Russell et al., 2006Russell et al., , 2010Snorrason et al., 2002;Stefánsdóttir and Gislason, 2005;Thordarson and Self, 2003;Thordarson and Larsen, 2007;Tómasson, 1996). ...
The chemical composition of Icelandic rain and snow is dominated by marine aerosols, however human and volcanic activity can also affect these compositions. The six month long 2014–15 Bárðarbunga volcanic eruption was the largest in Iceland for more than 200 years and it released into the atmosphere an average of 60 kt/day SO2, 30 kt/day CO2, 500 t/day HCl and 280 t/day HF. To study the effect of this eruption on the winter precipitation, snow cores were collected from the Vatnajökull glacier and the highlands northeast of the glacier. In addition to 29 bulk snow cores from that precipitated from September 2014 until March 2015, two cores were sampled in 21 and 44 increments to quantify the spatial and time evolution of the chemical composition of the snow.
The pH and chemical compositions of melted snow samples indicate that snow has been affected by the volcanic gases emitted during the Bárðarbunga eruption. The pH of the melted bulk snow cores ranged from 4.41 to 5.64 with an average value of 5.01. This is four times greater H⁺ activity than pure water saturated with the atmospheric CO2. The highest concentrations of volatiles in the snow cores were found close to the eruption site as predicted from CALPUFF SO2 gas dispersion quality model. The anion concentrations (SO4, Cl, and F) were higher and the pH was lower compared to equivalent snow samples collected during 1997–2006 from the unpolluted Icelandic Langjökull glacier. Higher SO4 and Cl concentrations in the snow compared with the unpolluted rainwater of marine origin confirm the addition of a non–seawater SO4 and Cl. The δ³⁴S isotopic composition confirms that the sulphur addition is of volcanic aerosol origin.
The chemical evolution of the snow with depth reflects changes in the lava effusion and gas emission rates. Those rates were the highest at the early stage of the eruption. Snow that fell during that time, represented by samples from the deepest part of the snow cores, had the lowest pH and highest concentrations of SO4, F, Cl and metals, compared with snow that fell later in the winter. Also the Al concentration, did exceed World Health Organisation drinking water standard of 3.7 μmol/kg in the lower part of the snow core closest to the eruption site.
Collected snow represents the precipitation that fell during the eruption period. Nevertheless, only minor environmental impacts are evident in the snow due to its interaction with the volcanic aerosol gases. In addition, the microbial communities identified in the snow that fell during the eruption were similar to those found in snow from other parts of the Arctic, confirming an insignificant impact of this eruption on the snow microecology.
... Failed moraine dams are also considered to be specific landforms associated with GLOFs ( Clague & Evans, 2000 GLOFs are capable of transporting boulders with diameters of up to several meters and an estimated mass of 200 tons. Entrainment in the order of 10 m has been documented, as in the 1996 Grimsvötn (Iceland) GLOF, while the mean specific sediment yield may reach 10 t/km /yr for a short time ( Korup, 2012;Stefánsdottir & Gíslason, 2005). Korup (2012) further showed that extreme specific sediment yields (> 10 t/km /yr) in mountain environments are typically linked to extreme events, such as volcanic eruptions, mass movements, or lake outburst floods. ...
Glacier retreat is considered to be one of the most obvious manifestations of recent and ongoing climate change in the majority of glacierized alpine and high-latitude regions throughout the world. Glacier retreat itself is both directly and indirectly connected to the various interrelated geomorphological/hydrological processes and changes in hydrological regimes. Various types of slope movements and the formation and evolution of lakes are observed in recently deglaciated areas. These are most commonly glacial lakes (ice-dammed, bedrock-dammed, or moraine-dammed lakes).
“Glacial lake outburst flood” (GLOF) is a phrase used to describe a sudden release of a significant amount of water retained in a glacial lake, irrespective of the cause. GLOFs are characterized by extreme peak discharges, often several times in excess of the maximum discharges of hydrometeorologically induced floods, with an exceptional erosion/transport potential; therefore, they can turn into flow-type movements (e.g., GLOF-induced debris flows). Some of the Late Pleistocene lake outburst floods are ranked among the largest reconstructed floods, with peak discharges of up to 107 m3/s and significant continental-scale geomorphic impacts. They are also considered capable of influencing global climate by releasing extremely high amounts of cold freshwater into the ocean. Lake outburst floods associated with recent (i.e., post-Little Ice Age) glacier retreat have become a widely studied topic from the perspective of the hazards and risks they pose to human society, and the possibility that they are driven by anthropogenic climate change.
Despite apparent regional differences in triggers (causes) and subsequent mechanisms of lake outburst floods, rapid slope movement into lakes, producing displacement waves leading to dam overtopping and eventually dam failure, is documented most frequently, being directly (ice avalanche) and indirectly (slope movement in recently deglaciated areas) related to glacial activity and glacier retreat. Glacier retreat and the occurrence of GLOFs are, therefore, closely tied, because glacier retreat is connected to: (a) the formation of new, and the evolution of existing, lakes; and (b) triggers of lake outburst floods (slope movements).
... Occurring to the north of Grímsvötn, the 1996 Gjálp eruption caused glacial meltwater to accumulate in the Grímsvötn subglacial lake for a month before it flooded to the south of Vatnajökull between 4 and 7 November 1996. This jökulhlaup reached a peak discharge rate of approximately 55,000 m 3 s -1 (Stefánsdóttir and Gíslason, 2005), draining 3.2 km 3 of meltwater from the Grímsvötn lake in about 40 hours (Bjornsson, 1998). ...
Tourists flock to southern Iceland to experience the impressive landscapes surrounding the Hekla, Eyjafjallajökull, Katla and Grímsvötn volcanoes. This chapter describes these volcanic systems and their recent activity. It also provides detail on strategies implemented by government agencies to reduce volcanic risk in this region.
... Le record a été battu en 1996, dépassant la crue de 1938 qui avait duré trois jours et charrié 40 000 m 3 .s _1 (Kristmannsdottir et al., 1999 ;Maria et al., 2000 ;Roberts et al., 2000 ;Knudsen et al., 2001 ;Russel et Knudsen, 1999 ;Smith et al., 2006 ;Stefansdóttir et Gislason, 2005). ...
Le travail s'articule autour de trois grandes questions. 1 - Comment e st née l a géomo rpholo gie paraglaciair e ? La première partie relève d'une approche épistémologique de la géomorphologie paraglaciaire. Le premier chapitre reprend les contributions scientifiques fondatrices du concept de paraglaciaire des années 1970, et les replace dans une perspective sémantique en analysant les travaux conduits depuis le 19e siècle sur les milieux englacés et leurs marges. Church et Ryder (1972) définissaient le terme de paraglaciaire comme " non-glacial processes conditioned by glaciation ". En 2002, Ballantyne a proposé une définition plus large du concept : " earth surface processes, sediments, landforms, landsystems and landscapes that are directly conditioned by former glaciation and deglaciation ". Le deuxième chapitre analyse donc les apports de trente années de recherche en géomorphologie paraglaciaire, reprend le concept de géosystème paraglaciaire et analyse les sous-systèmes (gravitaire, fluvial, lacustre, éolien, littoral, marin et socio-spatial) face aux séquences paraglaciaires. 2 - Qu'est -ce qu'une crise paraglaciaire ? La deuxième partie se propose de délimiter les contours de la géomorphologie paraglaciaire dans le cadre d'une approche spatio-temporelle. Le troisième chapitre étudie les changements climatiques susceptibles d'être à l'origine des crises temporelles paraglaciaires. Le quatrième chapitre définit les crises paraglaciaires et met l'accent sur les temporalités de ces moments clés dans l'histoire des environnements englacés. Sur le plan temporel, le paraglaciaire désigne avant tout une séquence morphologique, une crise d'érosion, qui suit la séquence glaciaire précédente. Ces crises s'illustrent par des temporalités variées, des accélérations des transferts sédimentaires surtout dans les matériaux meubles et une extension des emprises spatiales des phénomènes associées à la disparition des glaciers puisque le ruissellement redistribue les sédiments des zones proglaciaires jusqu'à la mer. Les versants sont soumis à des stress physiques générant des décohésions des parois. Les dépôts de versants sont affectés par des ravinements majeurs. Les systèmes fluviaux enregistrent des aggradations ou des dissections en fonction de la variabilité des apports, de l'énergie des processus, de la variabilité des niveaux de base locaux, régionaux ou globaux. Ils connaissent de profondes métamorphoses qu'illustrent les adaptations des variables morphologiques. Les littoraux meubles paraglaciaires bénéficient d'un apport tel en sédiments qu'ils progradent sur les marges des secteurs en phase de déglaciation. Des crises volcaniques sont également associées à ces crises climatiques et un volcanisme paraglaciaire s'observe dans des régions comme l'Islande. Les apports majeurs à la compréhension de ces crises paraglaciaires viennent des progrès technologiques pour évaluer les bilans sédimentaires et pour les dater. Une crise paraglaciaire est définie par des indicateurs comme les taux d'ablation, taux d'incision, taux de production primaire de débris, taux de transferts sédimentaires, taux de sédimentation. Ces indicateurs montrent qu'ils dépassent pendant un laps de temps t, d'un facteur n, les résultats enregistrés pendant la séquence t-1 et t +1. Cet écart est variable d'un indicateur à l'autre et d'un système à l'autre. La durée de la séquence paraglaciaire est donc d'une grande variabilité, mais doit être limitée à cette rupture temporelle dans l'évolution d'un environnement au cours duquel il est perturbé. 3 - Quels sont les apports de la géomorphologie paraglaciaire à la compréhension de l'évolution des milieux froids ? La troisième partie interroge des modelés des milieux froids pour appréhender la part du paraglaciaire ; du glaciaire et du périglaciaire dans leur évolution. Le cinquième chapitre détermine les formes paraglaciaires au sens strict. Les deux processus paraglaciaires par excellence sont d'une part la décohésion postglaciaire qui affecte les parois rocheuses et d'autre part, le ruissellement alimenté par la fonte de la glace des glaciers et celle de la glace morte qui remobilise les sédiments meubles. Ainsi, des formes d'ablation et d'accumulation associées à ces dynamiques sont elles représentatives de cette dynamique paraglaciaire (grands glissements, écroulements, éboulements massifs). En revanche, le ruissellement très actif au cours de la séquence paraglaciaire est à l'origine de la construction de formes de ravinement, d'incision et d'accumulation (cônes de déjection...). Les signatures sédimentologiques sont alors différentes et les vitesses de sédimentation sont plus élevées que lors des autres séquences morphogéniques. Toutes les zones de stockage (bas de versant, lacs, plaines alluviales, fjords...) offrent des espaces propices à l'évaluation de ces temporalités et des bilans sédimentaires associés. Le sixième chapitre reprend les grandes formes du " panthéon " glaciaire (cirques, vallées en auge, fjords, moraines, drumlins, eskers, kames) et périglaciaire (glaciers rocheux, tabliers et cônes d'éboulis) pour évaluer la part des séquences paraglaciaires dans la genèse et l'évolution de ces morphologies. Le terme de parapériglaciaire est défini. Le paraglaciaire est un concept clé pour comprendre l'évolution des milieux ayant été englacés et il recouvre une réalité très large sur le plan spatial puisqu'il peut s'appliquer à tous les espaces à la surface de la terre ayant été englacées au cours des séquences froides du Pléistocène et leurs périphéries, et qui ne le sont plus aujourd'hui, soit environ 40 % de la surface terrestre, auxquelles s'ajoutent les espaces de sédimentation offshore. Par ailleurs, il reste aujourd'hui environ 10 % d'espaces englacés, dont une fraction est susceptible de connaître une séquence de déglaciation dans le contexte actuel de réchauffement climatique. Né dans les années 1970 au Canada, le concept de paraglaciaire apporte incontestablement une clé de lecture pour la compréhension de l'évolution des paysages applicable à toutes les zones ayant connu directement ou indirectement des phases de glaciation-déglaciation. À l'heure d'une réflexion sur l'impact des changements climatiques sur les environnements, le concept de paraglaciaire ouvre des perspectives et renouvelle les approches géomorphologiques classiques en mettant l'accent sur les stocks sédimentaires, les flux, les bilans, les rythmes et les crises.
... Le record a été battu en 1996, dépassant la crue de 1938 qui avait duré trois jours et charrié 40 000 m 3 .s _1 (Kristmannsdottir et al., 1999 ;Maria et al., 2000 ;Roberts et al., 2000 ;Knudsen et al., 2001 ;Russel et Knudsen, 1999 ;Smith et al., 2006 ;Stefansdóttir et Gislason, 2005). ...
... Leaching experiments conducted on volcanic ash have shown low macronutrient:micronutrient release ratios relative to the stoichiometric requirements of phytoplankton (Frogner et al., 2001;Stefánsdóttir and Gíslason, 2005;Duggen et al., 2007;Jones and Gislason, 2008;Lin et al., 2011;Olgun et al., 2013a,b). Whilst volcanic ash likely provides a limited supply of macronutrients to LNLC regions, these vast oligotrophic systems also represent a major niche for nitrogen fixing bacteria, which have additional Fe requirements due to the presence of this element within the required nitrogenase enzyme (Berman-Frank et al., 2001). ...
Transient micronutrient enrichment of the surface ocean can enhance phytoplankton growth rates and alter microbial community structure with an ensuing spectrum of biogeochemical feedbacks. Strong phytoplankton responses to micronutrients supplied by volcanic ash have been reported recently. Here we: (i) synthesize findings from these recent studies; (ii) report the results of a new remote sensing study of ash fertilization; and (iii) calculate theoretical bounds of ash-fertilized carbon export. Our synthesis highlights that phytoplankton responses to ash do not always simply mimic that of iron amendment; the exact mechanisms for this are likely biogeochemically important but are not yet well understood. Inherent optical properties of ash-loaded seawater suggest rhyolitic ash biases routine satellite chlorophyll-a estimation upwards by more than an order of magnitude for waters with <0.1 mg chlorophyll-a m⁻³, and less than a factor of 2 for systems with >0.5 mg chlorophyll-a m⁻³. For this reason post-ash-deposition chlorophyll-a changes in oligotrophic waters detected via standard Case 1 (open ocean) algorithms should be interpreted with caution. Remote sensing analysis of historic events with a bias less than a factor of 2 provided limited stand-alone evidence for ash-fertilization. Confounding factors were poor coverage, incoherent ash dispersal, and ambiguity ascribing biomass changes to ash supply over other potential drivers. Using current estimates of iron release and carbon export efficiencies, uncertainty bounds of ash-fertilized carbon export for three events are presented. Patagonian iron supply to the Southern Ocean from volcanic eruptions is less than that of windblown dust on 1000 year timescales but can dominate supply at shorter timescales. Reducing uncertainties in remote sensing of phytoplankton response and nutrient release from ash are avenues for enabling assessment of the oceanic response to large-scale transient nutrient enrichment.
... En effet, ces phénomènes d'érosion sont importants lors des jökulhlaups, en particulier dans l'axe des chenaux de transit, qui sont vidangés de leurs sédiments à chaque débâcle. Ces phénomènes d'incorporation de sédiments plus anciens lors des crues ont été confirmés par des observations réalisées à l'occasion d'événements récents en Islande (Stephánsdóttir et Gíslason, 2005 ...
... Ca release from basalt in either the mid-ocean ridges or suspended material in deltas is due to the dissolution of Ca-bearing minerals and glasses. These Ca-bearing minerals and glasses are undersaturated, and their dissolution reactions have been demonstrated to proceed in natural seawater, meteoric waters, and experimental solutions regardless of the aqueous Mg concentration (e.g.,Mottle, 1983;Oelkers and Gislason, 2001;Stefánsdóttir and Gislason, 2005). These observations demonstrate that the presence of aqueous Mg is not necessary for the liberation of silicate-bound Ca. ...
... Broecker et al., 1992;Broecker, 1994;Alley and Macayeal, 1994;Hemming, 2004). Increased runoff due to melting, and at the extreme, glacial floods, has been demonstrated to transport huge quantities of fine-grained particulates towards the ocean (Cenderelli and Wohl, 2001;Gislason et al., 2002;Stefansdottir and Gislason, 2005;Galeczka et al., 2014). The combination of all these factors suggests that primary productivity and the subsequent burial of organic carbon may be strongly enhanced at the end of glacial cycles significantly drawing down atmospheric CO 2 , tending to moderate global warming at such times. ...
... Several processes, including dissolution, ion exchange, and desorption may each play a role. Dissolution most likely occurs as numerous primary minerals and glasses, including pyroxene, basaltic glass, and plagioclase, are undersaturated in seawater, and the Si concentrations in the fluid phase increase during the experiments (Brady and Gíslason, 1997;Jones et al., 2012a, b;Stefá nsdó ttir and Gislason, 2005). In addition, the dissolved Si isotope ratios measured in the Kerguelen plateau surface waters suggest that a lithogenic source releases Si to these waters (Fripiat et al., 2011). ...
The total mass of material globally transported to the oceans as
particulate material is as much as 30 times greater that transported to
the oceans in dissolved form. The degree to which riverine transported
particles impact ocean chemistry and influence global elemental cycles
depends on the reactivity of this particulate material in seawater and
the relative concentration of each element. The concentrations of
elements in particulate material relative to those of seawater range
from less than 1 for soluble elements such as Na, to more than
107 for insoluble elements such as Al, Fe, and the Rare
Earths. The reactivity of particulate material in seawater is difficult
to assess directly because this fluid is saturated or supersaturated
with respect to numerous elements. As such, element release from the
particulate material is commonly matched by precipitation of secondary
phases. The rates of element release can, however, be quantified by
monitoring the isotopic evolution of seawater during its reaction with a
variety of particulate material samples collected from rivers throughout
the world. This research focuses on the behavior of Sr and Nd,
representative of the most and least soluble elements transported to the
oceans. Batch experiments demonstrate that between 0.15 and 27% of Sr is
liberated from volcanic and continental particulates when interacted
with seawater over 6 months. Similarly, from 1.5 to 8.5% of Nd is
liberated from volcanic sediments over this timespan. This observed
elemental release rate from riverine particulate material has important
consequences for: (1) chemical and isotopic mass balances in the ocean;
and (2) the application of the isotopic weathering proxies to the
geological record.
... This corresponds to a flux of 1300 t/km 2 /yr, due to water infiltration though a rich weathered profile highly impacted by hydrothermalism, and a longer watererock interaction time (Rad et al., 2011a,b). Iceland is one of the volcanic regions that has been most studied with respect to alteration (Gislason and Eugster, 1987; Gislason et al., 1990 Gislason et al., , 1993; Stefansson and Gıslason, 2001; Gislason et al., 2002; Stefánsdóttir and Gíslason, 2005; Sigfusson et al., 2006; Vigier et al., 2006; Gannoun et al., 2006; Louvat et al., 2008; Gislason et al., 2009). Gislason et al. (1996) first determined chemical weathering rates of 59 t/km 2 /yr for this area. ...
Guadeloupe, Martinique and Dominica islands, like numerous tropical environments, have extreme weathering regimes. Physical denudation is mainly controlled by landslides, which reflect the torrential dynamics of the rivers. In Guadeloupe, the mechanical weathering rates vary between 800 and 4000 t/km2/yr. The lithology is very porous with high infiltration rates, which suggests that most of the element fluxes are produced in the subsurface, with chemical erosion rates 2–5 times higher than the rates from surface water. We show how the kinetics of chemical weathering rates depend on the age of the lava and subsurface circulation. In addition, erosion timescales were calculated from U-series analyses of river sediments. Our results show a broad range: 0–150 ka in Martinique and 0–60 ka in Guadeloupe. We evaluated residence times in river water on the basis of the dissolved load analyses. It appears that water circulation is globally 3-fold longer for subsurface water than for surficial water (68 and 69). Moreover, these islands are highly impacted by agriculture. However, contrary to what one might think, our results show that human activity does not disturb critical zone processes. Indeed, we show that among the combined impacts of all parameters (climate, runoff, slope, vegetation, etc.), the basin's age seems to be the control parameter for chemical weathering and land use—the younger the basin, the higher the weathering rates. We could observe a combined effect between the higher erodibility and a higher climate erosivity of the younger reliefs.
... This plain experiences transiently extremely high sediment loads (e.g. 1% of the total annual global river suspended sediment flux (180 million tonnes) in less than 42 h, Stefánsdóttir and Gíslason, 2005) as a result of jökulhlaups (sub-glacial flood outbursts as a result of volcanic activity). The most recent event occurred in 1996 (Gjálp jökulhlaup). ...
... This suggests that soil pore waters form the intermediate step between soils and riverine suspended load (aside from the unusually isotopically heavy soil samples, which may be affected by sea salts) and river waters. Some soil and suspended load samples are isotopically lighter than unaltered basalt, because they comprise a degree of secondary minerals (dominantly smectites, iddingsite (poorly crystalline smectite, chlorite, talc and micas) and kaolinite (Pogge von Strandmann et al., 2008a;Stefansdottir and Gislason, 2005)) that have preferentially taken up 6 Li. These isotope trends clearly chart the evolution from basalt, through semi-weathered material such as suspended sediment and soils, to soil pore waters, and finally to river waters, which in turn control the continental signal to the oceans. ...
Continental weathering not only plays a pivotal role for the long-term climate and CO2 regulation, it also sustains the biosphere by providing nutrients. During weathering, stable isotopes of Si, Mg and Li are fractionated, directly impacting river signatures. In a monolithological catchment, isotopic variations in rivers would rather be related to pedogenic processes such as mineral dissolution, sequestration in secondary minerals via neoformation or adsorption, and plant uptake. However, separating inorganic from biologically driven isotopic fractionation remains complex, owing the tight coupling of biology and weathering. Applying stable isotope techniques, such as Mg, can potentially provide information about those processes that control the Mg budget during weathering reactions. Existing Mg-isotope data obtained from different soils point to a contrasting picture however. Soils derived from gneissic bedrock (India) were shown to display heavier isotopic signatures relative to the bedrock, and associated fluids were enriched in light Mg isotopes, suggesting that weathering discriminates against light Mg isotopes (Tipper et al 2006). By contrast, Icelandic rivers were found to display a large range of Mg isotopic variations both lighter and heavier relative to the parental basalt, and few measured soils were shown to be isotopically lighter than basalt (Pogge von Strandmann et al 2008), suggesting isotope fractionation pattern similar to those found for other light stable isotope systems of Li and Si (e.g. Huh et al 2004; Ziegler et al 2005). This present study aims at a detailed approach to investigate the Mg isotope fractionation in Icelandic soils (Borgarfjordur catchment), in order to elucidate the potential impact of soil weathering on riverine Mg isotopic compositions. On the long run, Mg data will be complemented by Si and Li isotope measurements in order to provide a better constraint on the influence of inorganic versus biological fractionation in a natural system. The combination of these three isotope systems will contribute to a better understanding of weathering derived fluxes to rivers and hence oceans. Huh et al. (2004) Geochem. Geophys. Geosyst. 5, Q09002. Pogge von Strandmann et al. (2008) Earth Planet. Sci. Letts. 276, 187-197. Tipper et al. (2006) Earth Planet. Sci. Letts. 247, 267-279. Ziegler et al. (2005) Geochim. Cosmochim. Acta 69, 4597-4610.
... This dissolution of carbonate is enhanced by the finer grains generated through grinding at the ice sheet base. Furthermore, the discharge from such ice sheets into the ocean also carries unweathered materials into the ocean which can be weathered quickly in the seawater [Gislason et al., 2006;Stefánsdóttir and Gislason, 2005]. Another significant factor which must be considered is that large amounts of carbonate will be exposed to both physical and chemical weathering during a soft snowball state due to the fall of sea level caused by land ice development. ...
It has been suggested that a negative climate feedback may have operated during the Neoproterozoic Era as a consequence of the existence of a massive oceanic pool of dissolved organic carbon (DOC). As climate cooled so as to induce intense glaciation, the drawdown of oxygen into the Neoproterozoic ocean would have been enhanced because of the temperature dependence of the solubility of oxygen in seawater. Such increasing ventilation would have enhanced DOC remineralization, thus increasing the content of dissolved inorganic carbon (DIC) in the ocean. CO2 concentration in the atmosphere increases rapidly with DIC, thereby inhibiting further climate cooling. The model employed to illustrate the resulting climate dynamical behavior was an idealized one in which stochastic influence was assumed to be absent. However, such influence is expected to exist due to the action of processes that are not explicitly included in the model. Furthermore, the paleogeography assumed for the purpose of the published analyses was more appropriate to the Marinoan glaciation than to the earlier Sturtian event. In this paper, we fully investigate the stability of the system represented by the carbon cycle coupled climate model for both the Marinoan and Sturtian continental configurations and in the presence of stochastic perturbations. It is found that the hysteresis predicted by the ice sheet coupled model is sensitive to both continental configuration and to the strength of the negative feedback which arises due to carbon cycle coupling. Nevertheless, the very low frequency cyclic glaciation process predicted by the initial version of the model is found to persist in the presence of noise of significant amplitude. However, this cyclic behavior may be arrested entirely if the glaciation process were to result in insufficient alkalinity being delivered to the ocean basins. In this case the system would be expected to execute only a single excursion into and escape from the glacial state.
... The presence of sands of glacier origin all over the south and southeast part of Iceland is impressive. The potential mass of sediments concerned has been estimated recently: during the 1996 volcanic eruption under the Vatnajökull Glacier the suspended sediment load had reached 180 million tons in only 42 hours (Stefánsdóttir and Gislason, 2005), all the sediments accumulated beneath the glacier and down-slope have been flushed at the same time. The fate of such an enormous mass of sediments (crushed altered basalt) at sea and its impact on the global chemistry of the ocean still needs to be addressed. ...
This study investigates dissolved, suspended loads and sands of major Icelandic rivers and determines chemical and mechanical erosion rates as well as rates of CO2 consumption by the chemical weathering. A steady state model of erosion is used to locally calculate the river suspended load fluxes needed to balance chemical weathering. The total dissolved solid concentrations range from 20 to 179 mg/kg. The highest concentrations are for spring fed rivers draining young rocks in the vicinity of active volcanoes, and the lowest for direct runoff rivers draining old Tertiary rocks. Total dissolved loads, "corrected" for atmospheric, geothermal, and magmatic inputs are used together with mean annual discharges to estimate low-temperature chemical erosion rates of 16 to 111 t/km2 /yr. These rates increase with runoff but decrease with the age of the rocks. Icelandic chemical erosion rates are higher than the world average for silicate rocks, reflecting both high reactivity of the basalt and high runoff, but lower than those for other basalt-draining rivers (in Réunion, Java, Azores or Deccan). CO2 consumption rates associated to chemical denudation range between 0.18 and 2.12 106 mol/km2/yr with an average value of 0.74 106 mol/km2/yr, higher than the world average for rivers draining silicate rocks. Chemical compositions of suspended sediments and sands are similar, showing a very low weathering stage. The elements most soluble during the weathering show slightly lower concentrations in the suspended sediments. River sediment chemical compositions are assumed to reflect a mixture between 3 initially pristine rock end-members: high Mg-basalt, tholeiite and rhyolite. The most insoluble elements (REE and Th) are used to re-define the mean chemical composition of the initially unaltered rocks of each drainage basin. A mass budget between the unaltered rock of the catchments and the river dissolved and suspended loads (steady state model of erosion) is used to calculate the average annual solid load of the rivers, which range from 650 to 4300 mg/1. For some rivers there is a good agreement between calculated and measured suspended loads but for others the calculated load is much higher than the measured one. The difference stems from groundwater inputs, man-made dams and other sedimentary traps. If the relevancy of the steady state model of erosion can be questioned, the accuracy of sediment load measurements is also questionable. Pros and cons of both methods are argued. The calculated solid loads lead to very high mechanical erosion rates, ranging from 940 to 10200 t/km2 /yr. Those increase with the glacier cover but decrease with the age of the catchment rocks. Icelandic mechanical erosion rates rank among the maximum reported rates, underscoring the importance of glaciers, tectonics, glassy basaltic rocks and high runoff. In association with low chemical weathering rates, these place Icelandic rivers as an end-member in the observed anti-correlation between mechanical to chemical erosion ratios and temperature for volcanic islands.
... This suggests that soil pore waters form the intermediate step between soils and riverine suspended load (aside from the unusually isotopically heavy soil samples, which may be affected by sea salts) and river waters. Some soil and suspended load samples are isotopically lighter than unaltered basalt, because they comprise a degree of secondary minerals (dominantly smectites, iddingsite (poorly crystalline smectite, chlorite, talc and micas) and kaolinite (Pogge von Strandmann et al., 2008a; Stefansdottir and Gislason, 2005 )) that have preferentially taken up 6 Li. These isotope trends clearly chart the evolution from basalt, through semi-weathered material such as suspended sediment and soils, to soil pore waters, and finally to river waters, which in turn control the continental signal to the oceans. ...
This study presents lithium, magnesium and silicon isotope ratios from pore waters and soils from a well-characterised Histic Andosol in south-west Iceland. The soil δ7Li composition ranges between values slightly lighter than basalt, to those that are much heavier (−1.1‰ to +26.8‰), and are possibly influenced by sea salt. In contrast, precipitation-corrected dissolved (pore water) δ7Li values (1.8–10.0‰) appear to reflect preferential adsorption of 6Li onto secondary minerals, where allophane supersaturation results in high δ7Li values. Conversely low δ7Li together with high [Li] are probably due to destabilisation of allophane at low pH, and thus desorption of Li. When compared to Icelandic river values, it would appear that soil pore waters reflect an intermediate isotope composition between basalts and river waters. Precipitation corrected pore water Mg isotope ratios (δ26Mg) range between −0.46‰ and −0.12‰, and correlate with the amount of heavy Mg adsorbed onto the soil exchange complex. Silicon isotopes in the soils are isotopically lighter (δ30Si=−0.91‰ to −0.53‰) than basalt (−0.29‰), whereas pore waters are heavier (+0.13‰ to +1.03‰). Soil δ30Si values show a clear evolution between unweathered basalt and a hypothetical isotopically light endmember representing secondary minerals. Dissolved Si isotopes also respond to chemical weathering processes, and show that isotopically heavy δ30Si corresponds to high cation fluxes and high secondary mineral formation. However, comparison of all these proposed isotopic weathering tracers suggests that they respond differently to the same chemical weathering conditions. This indicates a differing behaviour during secondary mineral neoformation or adsorption depending on whether the incorporated element is a major or trace constituent. In turn, this behaviour can potentially yield important information on secondary mineral behaviour and destabilisation, and thus on the chemical weathering processes.
... Firstly, immediate response could be analysed for fluvial sub-system. Jökulhlaups are crises of strong intensity, which correspond typically to a forcing of sub-glacial volcanic origin and are often observed in Iceland (Kristmannsdóttir et al, 1999;Russell and Knudsen, 1999;Knudsen et al, 2001;Stefansdóttir and Gislason, 2005). Jökulhlaups cause sandur aggradation, which may be eroded within few years (Smith et al, 2006;Roussel, 2008). ...
The Pleistocene Earth history has been characterized by major climatic fluctuations. During glacial periods, ice may have covered around 30 per cent of the Earth surface compared to approximately 10 per cent nowadays. With global change, polar environments and other montainous glacial environments of the world are presently undergoing the most important changes since the end of the Last Glacial Maximum and are experiencing paraglacial and paraperiglacial geomorphological readjustments. Paraglacial and paraperiglacial landsystems consist of several subsystems including gravitational, fluvial, coastal, aeolian and lacustrine environments. Paraglacial and paraperiglacial landsystems can be analysed as open and complex landsystems characterized by energy, water and sediment fluxes and exchange with surrounding environments, especially with glacial and periglacial landsystems as inputs. Those cascading landsystems are likely to react to climate change because they rely on an ice-cold water stock (glacier and permafrost) that developed during a previous cold sequence (glaciation). The response of paraglacial and paraperiglacial systems to climatic forcing takes place over a long time span ranging from an immediate reaction to several millennia. The spatial limits of paraglacial and paraperiglacial landsystems are inherently dependant on the time scale over which the system is analyzed. During the Pleistocene, glaciations widely affected the high latitudes and the high altitudes of the Earth and were followed by inherited paraglacial sequences. Glacier forelands in Arctic and alpine areas experience paraglacial processes with the present warming. The expected global warming for the twenty-first century will result in significant impacts on present glacier areas in mountains and could result in the appearance of new areas for paraglacial dynamics. In permafrost terrain, landscapes underwent a similar paraperiglacial geomorphological adjustment in mountainous, continental and coastal areas, with permafrost thaw-degradation and thermokarst processes.
... Le record a été battu en 1996, dépassant la crue de 1938 qui avait duré trois jours et charrié 40 000 m 3 .s _1 (Kristmannsdottir et al., 1999 ;Maria et al., 2000 ;Roberts et al., 2000 ;Knudsen et al., 2001 ;Russel et Knudsen, 1999 ;Smith et al., 2006 ;Stefansdóttir et Gislason, 2005). ...
... Thus, the interaction of ash and water 616 mobilizes most of the environmentally available fraction of the ash very quickly 617 while the later weathering is considerably slower. Therefore, the main impact of 618 ash deposition is just after initial exposure to seawater (Duggen et al., 2007;619 Jones and Gislason, 2008;Stefansdottir and Gislason, 2005). The geochemical 620 behaviour, along with its easy physical mobilization (by air and water), dictates 621 the ephemeral character of ash deposits and the rarity of its preservation. ...
The environmental geochemical behaviour of the rhyolitic ashes from the 2008 eruption of Chaitén volcano, Southern Chile, has been studied. After the bulk characterisation, the potential contribution to the regional geochemical fluxes was examined using: i) single batch leaching tests to provide a rapid screening of the implied major and trace elements; and ii) column experiments to evaluate the temporal mobility of leached elements. The environmental concerns of these ashes are related to the fine grained component present in each sample (independent of distance from the source), in particular the presence of cristobalite, and the geochemical hazards posed by ash-water interaction. Leaching experiments show the fast dissolution of surface salts and aerosols, which dominate over glass dissolution during the first steps of the ash-water interaction. Chaitén ashes could transfer to the environment more than 1×10(10)g or 10,000 metric tonnes (mt) of Cl, S, Ca, Na, Si, and K; between 1000 and 10,000 mt of F, Mg, and Al; between 100 and 1000 mt of As, Pb, P, Fe, Sr, Zn, Mn, and Br; between 10 and 100 mt of Ba, Li, Ti, Ni, Nb, Cu, Rb, Zr, V, Mo, Co, and Sc; and less than 10 mt of Cr, Sb, Ce, Ga, Cs, and Y. These results show the fertilising potential of the ashes (e.g., providing Ca and Fe) but also the input of potentially toxic trace elements (e.g., F and As) in the regional geochemical mass balance. The Chaitén results evidence lower potentials for poisoning and fertilising than low silica ashes due to the lower contents released of practically all elements.
... The small proportion of Mo in the colloidal phase means that, even though it is isotopically lighter than the dissolved load, the complete release of Mo from this phase is unlikely to significantly affect oceanic δ 98/95 Mo. In contrast, given that high-relief and tectonically active volcanic islands such as Iceland contribute over 45% of suspended material to the oceans (Milliman and Syvitski, 1992; Gaillardet et al., 1999), and that up to 0.05% of the Icelandic suspended material dissolves in seawater each day (Stefansdottir and Gislason, 2005; Gislason et al., 2006), the release of Mo from the suspended load may have a significant impact on δ 98/95 Mo seawater . This is supported by the experimentally determined dissolution rates of basalt in seawater (Gislason and Oelkers, 2003; Oelkers et al., 2009), and evidence for Li isotopic variations in the suspended material of Borgarfjörður estuary (Pogge von Strandmann et al., 2008b). ...
The application of the molybdenum (Mo) isotope system as a proxy for determining changes in the redox state of the oceans is predicated on the assumption that the composition of continental input can be characterised from crustal rock types, and remains constant. However, it has recently been shown that the δ98/95Mo composition of global rivers varies between 0.15‰ and 2.4‰ and is therefore systematically heavier than the average composition of the continental crust (∼ 0‰). In order to understand the processes that control Mo-isotope fractionation during weathering this study presents δ98/95Mo and Mo abundance data for rivers (and estuarine samples) from Iceland that drain predominantly basaltic terrains. Resolvable differences are observed in the isotopic composition of the riverine Mo sources; ice (δ98/95Moice > 1.8‰), basaltic bedrock (δ98/95Mobedrock ∼ 0.0‰) and hydrothermal waters (δ98/95Mohydrothermal ∼−3.4‰). Systematic changes in the dissolved Mo-isotope composition are also observed within river catchments, with δ98/95Mo values increasing from ∼ 0‰ in glacial rivers (close to the source) to ∼ 1‰ downstream, consistent with Mo-isotopes being fractionated during weathering. Analysis of other riverine phases (bedload, colloids and iron-precipitates) demonstrates that these phases preferentially incorporate light Mo-isotopes, and remain coupled to the dissolved load during riverine transportation. A δ98/95Mo profile through the Borgarfjörður estuary exhibits a predominantly conservative mixing behaviour, but suggests that the release of isotopically light Mo from the particulate and/or colloidal phases may occur in the low salinity part of the estuarine mixing zone.
Iceland is a good example of the volcanic and tectonically active islands of Earth that weather at a rapid rate due to the combined effect of high relief, high runoff the presence of rapidly weathering volcanic rocks, and a lack of sedimentary traps. The annual river runoff ill Iceland is 3.9 times the world average, the average chemical denudation rate of rock-derived elements ill Iceland is 1.3 times the world average, and the average mechanical denudation rate including major floods is 5.9 times the world average. Excluding the major floods, the rate of mechanical denudation is 2.9 times the world average. Surface runoff dominates ill the Quaternary and Tertiary formations of Iceland, whereas a large part of the precipitation falling oil ice-free land it? the younger volcanic zones, covered by post-glacial lavas, infiltrates and may discharge directly as groundwater into the ocean or emerge as springs to form spring-fed streams and rivers. Temperature, discharge and chemical composition of spring-fed rivers ill Iceland are stable throughout most of the year, and the concentration of suspended particle matter is low Glacier-fed rivers are loaded with suspended matter ill the summer (aid eat-IN? autumn when their discharge is highest. Discharge and concentrations of dissolved and particulate matter of direct runoff and glacier-fed rivers respond rapidly to precipitation. Most dissolved concentrations decrease but suspended concentrations increase with increased discharge ill both direct runoff and glacier-fed rivers. The relative mobility of rock-derived major elements during chemical weathering of basalt ill Iceland varies by four orders of magnitude. The most mobile major constituents, that is, those that dissolve ill surface waters, art, F S, Na, K, Ca and Mg, whereas the least mobile major elements ill the rocks arc, Fe, Ti, Al, and Mn. The least mobile constituents arc, consumed by oxyhydroxides and Al silicates that dominate weathering minerals ill Icelandic soils. The main weathering products of basaltic glass with limited contact with soil or atmospheric CO(2) are Si-, Ca-, and Mg-rich particles with smectite structure and amorphous Fe-, Ti- and Al-rich material. The most unstable primary basaltic minerals ill the surface waters of Iceland are Mg-rich olivine and Ca-rich plagioclase: ill contrast the Fe-T-oxides are, the most stable primary minerals. The rate of chemical denudation in Iceland increases with runoff but decreases with increased age of the catchment rocks. The difference in the chemical denudation rate between river catchments in Iceland call not be explained by variation in temperature alone. At the fixed age of the rocks, vegetation cover, etc., the effect of runoff and temperature dominate. High runoff lowers the pH of surface waters where the concentration of organic acids is low and it decreases the concentration of total dissolved Al and Mg, affecting the dissolution rate of plagioclase and basaltic glass, and olivine and pyroxene at all undersaturation levels. Furthermore, high runoff results in larger undersaturation of primary minerals, decreases oversaturation of secondary weathering minerals, and increases the reactive surface area between rock and water. The higher the temperature, the higher the dissolution rate of all minerals and glasses. Where the variation in runoff and age of rocks is small, the chemical denudation rate is enhanced by vegetation and increases for most mobile elements with the rise ill glass content of catchment rocks. The mechanical denudation rates are at a maximum inthe young, glassy, glaciated catchment rocks of south-eastern Iceland but at a minimum ill the old, non-glaciated, crystalline Tertiary catchment rocks. Denudation increases with runoff, temperature, glacial cover and decreasing age of the catchment rocks. The mechanical denudation rate is less runoff-dependent ill the old catchments than ill the younger ones since the ratio of coarse to fine river-suspended matter decreases with age. The mechanical denudation rate is therefore most climate dependent ill the young glaciated catchments of Iceland. Climate warming over the last 40 Years has resulted ill increased chemical and mechanical denudation rates and therefore CO(2) sequestration ill north-eastern Iceland. The maximum increase in CO(2) fixation by chemical denudation was 40% over the last 40 Years. Runoff mechanical and chemical denudation rates ill these river catchments rose from 6 to 16%, 8 to 30%, and 4 to 14%. respectively, depending oil the catchment, for each degree of temperature increase. These observations demonstrate the importance of the negative feedback between climate and chemical and mechanical denudation.
This paper discussed the feasibility of three different dual metal (AL-Fe, AL-Cu and Fe-Cu) hydroxyl polymer modified bentonite as PRB reaction media and studied the effects of aging time, pillared temperature, suspended concentration, and aging temperature on modified bentonite using orthogonal and single factor combined experiment. Meanwhile, the structural changes of non-modified and modified bentonite were analyzed. Results showed that the four factors had different effects on modified bentonite and the effect of suspended concentration was greatest. The removal efficiencies of COD Cr and ammonia nitrogen from landfill leachate contaminated underground water was 66% and 62% respectively. And the optimal modification conditions were Fe-Cu modified bentonite, suspended concentration of 4 g/L, pillared temperature of 80°C, aging temperature of 80°C and aging time of 12 h. Moreover, the layer separation of bentonite modified by bimetal on proper conditions was expanded and the removal efficiency of COD Cr and ammonia nitrogen were improved. Therefore, the modified bentonite can be used as PRB reaction media.
Rio Colonia, a tributary of the Baker River, drains the Northern Patagonia Icefield, and is experiencing a new cycle of Glacial-Lake Outburst Floods (GLOFs). The sudden draining of c. 200 hm3 from glacier-dammed Cachet 2 Lake, results in a 3-5 fold increase in discharge in Baker River, Chile's largest. Suspended sediment concentration also increases 8-fold and load 10 to 20-fold, totalling almost 5% of the annual load.Yet baseline studies of one of the dams of a US$7 billion hydropower project to flood the confluence doesn't consider GLOF dynamics. Moreover, Patagonia, the world largest complex of icefields and temperate glaciers, is experiencing warming trends and higher glacial-river flows. And the region is one of the largest unknowns in the global sediment flux to oceans. Here we compare present morphology and dynamics with the 1967-2007 outburst-free period and the previous outburst cycle that ended in 1968, with particular focus on the Colonia/Baker river confluence. Floodplain vegetation cover shows significant changes. Implications for a recently approved Baker dam are discussed.
On May 21st, 2011, one of Iceland's most active volcano,
Grímsvötn, started its strongest eruption in a century.
Grímsvötn produced hundreds of megatonnes of fine basaltic
ash, which spread over Iceland, the North Atlantic and Europe. Such fine
grained ash can impact human activity and health both with fertilization
and with toxicity potential for aquatic environments. The purpose of
this study was: (1) to investigate the basic physical and chemical
properties of the ash from the 2011 Grímsvötn eruption, (2)
to identify surface salts deposited on the ash during the eruption, (3)
to identify which elements are released during ash–water
interactions and their release rates, (4) to characterize the secondary
phases formed during water exposure, and (5) to assess impact of the ash
on humans and the environment.
This study describes the chemical composition and fluxes of two ~ 2,000 m3/s glacial floods which emerged from the Icelandic Mýrdalsjökull and Vatnajökull glaciers into the Múlakvísl and Kaldakvísl rivers in July 2011. Water samples collected during both floods had neutral to alkaline pH and conductivity from 100 to 900 μS/cm. The total dissolved inorganic carbon (DIC), present mostly as HCO3-, was ~ 9 mmol/kg during the flood peak in the Múlakvísl but stabilized at around 1 mmol/kg; a similar behaviour was observed in the Kaldakvísl. Up to 1.5 μmol/kg of H2S was detected. Concentrations of most of the dissolved constituents in the flood waters were comparable to those commonly observed in these rivers. In contrast, the particulate suspended material concentration increased dramatically during the floods and dominated chemical transport during these events. Waters were supersaturated with respect to a number of clays, zeolites, carbonates, and Fe(oxy)hydroxides. The most soluble elements were Na, Ca, K, Sr, Mn, and Mg, whereas the least soluble were Ti, Al, and REE. This is consistent with the compositions of typical surface waters in basaltic terrains and the compositions of global rivers in general. The toxic metal concentrations were below drinking water limits, suggesting that there was no detrimental effect of flood water chemistry on the environment. Increased concentration of DOC, formate, and acetate in the flood waters suggests substantial subglacial microbiological activity in the melt water prior to the floods. Reaction path modelling of the flood water chemical evolution suggests that it experienced subglacial water-rock interaction for at least a year in the presence of limited amounts of acid gases (e.g. SO2, HCl and HF). This suggests that the heat source for glacier melting was geothermal rather than volcanic.
The reaction of Ca derived from silicate weathering with CO2 in the world's oceans to form carbonate minerals is a critical step in long-term climate moderation. Ca is delivered to the oceans primarily via rivers, where it is transported either as dissolved species or within suspended material. The relative importance for climate moderation of riverine dissolved Ca vs. suspended Ca transport stems from the total Ca flux and its climate dependence. Data in the literature suggest that, within uncertainty, global riverine dissolved Ca flux is equal to suspended material Ca flux. To determine how these fluxes depend on temperature and rainfall, a 40 yr field study was performed on 4 catchments in northeastern Iceland: Jökulsá á Fjöllum at Grímsstadir, Jökulsá á Dal at Brú, Jökulsá á Dal at Hjardarhagi, and Jökulsá í Fljótsdal at Hóll. Suspended material Ca flux depends more on seasonal and annual temperatures and rainfall variation than does dissolved Ca flux in all four catchments. For example, the average difference between the annual maximum and minimum daily suspended Ca flux for the Jökulsá á Dal at Brú is four orders of magnitude, whereas the difference for dissolved Ca flux is only approximately one order of magnitude. Similarly, the annual dissolved Ca flux for this river varies by a factor of 2.6, whereas its annual suspended Ca flux varies by a factor of 7.1. Because suspended material Ca flux is more dependent on climate, it provides a stronger negative feedback for stabilizing Earth's temperature through the greenhouse effect.
Glacial outburst floods have been observed or inferred in most glaciated regions of the world. Outburst flooding events along past ice-sheet margins have been discussed as possible causes for changes in ocean circulation while subglacial lake drainage under ice sheets may influence ice-sheet stability. The recognition of these geologically instantaneous events in the marine sediment or rock record is critical in order to characterize the magnitude and frequency of past outburst events as well as to predict the likelihood of future occurrences. In this paper, we characterize outburst lithofacies and infer depositional processes from two outburst floods within Disenchantment Bay, Alaska, and compare these deposits to other recognized outburst deposits within marine depositional settings. Here we show that the outburst deposits are lithologically similar and are composed of stratified mud, sand, and diamicton. We interpret these facies to have been formed by sediment gravity flows and hypopycnal plume sedimentation. These results show that the volume of sediment, lithofacies, and inferred depositional processes cannot be easily distinguished from normal sediment accumulation within the proximal temperate glacimarine depositional environment. The paucity of fluvial subglacial discharge in polar glacimarine environments suggests the potential for recognition of such deposits in the Antarctic.
Environmental context. Mercury (Hg) occurs at high concentrations in Arctic marine wildlife, posing a possible health risk to northern peoples who use these animals for food. We find that although the dramatic Hg increases in Arctic Ocean animals since pre-industrial times can be explained by sustained small annual inputs, recent rapid increases probably cannot, because of the existing large oceanic Hg reservoir (the ‘flywheel’ effect). Climate change is a possible alternative force underpinning recent trends.
Abstract. The present mercury (Hg) mass balance was developed to gain insights into the sources, sinks and processes regulating biological Hg trends in the Arctic Ocean. Annual total Hg inputs (mainly wet deposition, coastal erosion, seawater import, and ‘excess’ deposition due to atmospheric Hg depletion events) are nearly in balance with outputs (mainly shelf sedimentation and seawater export), with a net 0.3% year–1 increase in total mass. Marine biota represent a small fraction of the ocean’s existing total Hg and methyl-Hg (MeHg) inventories. The inertia associated with these large non-biological reservoirs means that ‘bottom-up’ processes (control of bioavailable Hg concentrations by mass inputs or Hg speciation) are probably incapable of explaining recent biotic Hg trends, contrary to prevailing opinion. Instead, varying rates of bioaccumulation and trophic transfer from the abiotic MeHg reservoir may be key, and are susceptible to ecological, climatic and biogeochemical influences. Deep and sustained cuts to global anthropogenic Hg emissions are required to return biotic Hg levels to their natural state. However, because of mass inertia and the less dominant role of atmospheric inputs, the decline of seawater and biotic Hg concentrations in the Arctic Ocean will be more gradual than the rate of emission reduction and slower than in other oceans and freshwaters. Climate warming has likely already influenced Arctic Hg dynamics, with shrinking sea-ice cover one of the defining variables. Future warming will probably force more Hg out of the ocean’s euphotic zone through greater evasion to air and faster Hg sedimentation driven by higher primary productivity; these losses will be countered by enhanced inputs from coastal erosion and rivers.
IntroductionWeathering: Definitions and ProcessesWeathering, Erosion and Atmospheric CO2Mineral Dissolution and Precipitation RatesMineral Surface AreaField Measurements of Silicate Weathering and Denudation RatesFactors Affecting Silicate Weathering and Denudation RatesThe Relative Importance of Chemical and Mechanical ProcessesWeathering and Denudation at a Global ScaleConclusions
AcknowledgementsFurther ReadingReferences
Compared to the global average, the chemical weathering rates of basalt in southwest Iceland are high and rather variable. This can be attributed to soluble rock type (basalt) and mechanical weathering, variation in runoff and age of rocks, and variable vegetative/ glacial cover. The average temperature of the catchments in this study is near constant, 5°C. Chemical weathering of the basalt is incongruent. Some of the primary minerals do not dissolve, and secondary minerals form, resulting in the fact that fluxes of all elements increase with runoff, and there is an enormous variation in the relative mobility of elements in the basalt during weathering. The relative mobility, in decreasing order, is: S > F > Na > K ≫ Ca > Si > Mg > P > Sr ⋙ Mn > Al > Ti > Fe. Relative to Na, close to 90 percent of Mg and Ca in the original rocks is left behind at the weathering site. The runoff dependence of fluxes and the variation in relative mobility is less in old rocks than in young ones. In old rocks the number of saturated minerals with respect to soil solutions has decreased because of lesser amount of soluble basaltic glass and an increased vegetative cover on old rocks. The saturation state of basaltic minerals is the most important variable for the dissolution and precipitation rate of minerals during weathering in southwest Iceland and is dictated by the pH of the weathering solutions. The overall rate of chemical denudation rate in southwest Iceland is independent of vegetative cover. However, fluxes of Ca, Mg, and Sr increase with increasing vegetative cover at constant runoff, whereas fluxes of Na and K decrease. With a continuous vegetative cover the pH of the soil solutions tends to be low (<7), and glass, olivine, pyroxene, and plagioclase are unstable, but the solutions are decreasingly saturated or more undersaturated with respect to zeolites and smectite, thus increasing the relative mobility and fluxes of Ca, Mg, and Sr. Since the weathering of Ca-Mg silicate rocks is the principal process by which CO2 is removed from the atmosphere on a geological time scale (Berner, 1992), the spread of vascular plants on the continents during the mid-Paleozoic may have resulted in a drop in CO2, not necessarily because of greatly enhanced bulk chemical weathering, as suggested by Trendall (1966) and Berner (1993), but rather due to the enhanced relative mobility and fluxes of Ca and Mg.
PHREEQC version 2 is a computer program written in the C programming language that is designed to perform a wide variety of low-temperature aqueous geochemical calculations.
A rapid method for the determination of 15 trace metals in saline water samples by high resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) was tested. The method was validated by the analysis of estuarine (SLEW-2), coastal (CASS-2) and open ocean (NASS-4) water certified reference materials. No sample pre-treatment other than acidification and dilution was carried out. Results in good agreement with certified values (where available) were obtained for all metals except for Cd and Zn. Discrepancies for these elements are explained by an unresolved MoO interference (Cd) and insufficient internal standard correction (Zn). Present data indicate that HR-ICP-MS is applicable to the rapid and accurate multi-element determination, virtually free from spectral interferences, of trace metals at pg ml–1 levels in saline water.
Volcanic eruptions under glaciers can cause dangerous floods and lahars and create hyaloclastite (fragmented glassy rock) mountains. But processes such as the rate of heat transfer between ice and magma, edifice formation, and the response of the surrounding glacier are poorly understood, because of the lack of data. Here we present observations from the fissure eruption at Vatnajökull ice cap, Iceland, in October 1996. In the 13 days of the eruption 3km3 of ice were melted and the erupted magma fragmented into glass forming a hyaloclastite ridge 6-7km long and 200-300m high under 500-750m of ice. Meltwater of temperatures of 15-20 °C flowed along a narrow channel at the glacier bed into the Grímsvötn subglacial lake for five weeks, before draining in a sudden flood, or jökulhlaup. Subsidence and crevassing of the ice cap occurred over the eruptive fissure and the meltwater path, whereas elsewhere the glacier surface remained intact, suggesting that subglacial eruptions do not trigger widespread basal sliding in warm-based glaciers.
The fertilization potential of newly erupted and well-preserved ash from the 2000 Hekla eruption in Iceland was measured for the first time by flow-through experiments. As previously shown, (1) the North Atlantic Ocean, including the subarctic seas surrounding Iceland, is the largest net sink of the world's oceans for atmospheric CO2, owing to biological drawdown during summer; (2) almost complete consumption of phosphate in chlorophyll-rich areas of the North Atlantic Ocean might limit primary production; and (3) in the southern Pacific Ocean and parts of the equatorial Pacific Ocean iron might limit primary production. We found through laboratory experiments that volcanic ash exposed to seawater initially releases large amounts of adsorbed phosphate, 1.7 mumol·g-1·h-1; iron, 37.0 mumol·g-1·h-1; silica, 49.5 mumol·g-1h-1; and manganese, 1.7 mumol·g-1·h-1. Dissolution of acid aerosols adsorbed to the surface of the ash caused the high initial release of major and trace elements. Because of the instantaneous dissolution of adsorbed components when newly erupted volcanic ash comes in contact with the ocean surface water, macronutrients and ``bioactive'' trace metals are released fast enough to become available to support primary production.
Samples of the subglacial lake in the crater of the tholeiitic basaltic caldera Grimsvotn in Iceland were obtained by using a hot-water drill to sink two boreholes through the 250-m- thick ice shelf covering the lake. The crater lake is assumed to be closed, with respect to volatile components released from subsurface magma, except for periodic draining by jokulhlaups. From the periodicity and water chemistry of the jokulhlaups, the volcano's average release rates of carbon, sulfur, chlorine and fluorine between 1954 and 1991 are estimated to be 5.3 × 107 kg C yr-1, 5.3 × 106 kg S yr-1, 6.6 × 105 kg Cl yr-1, and 1.5 × 105 kg F yr-1. The emission rate estimates for Grimsvotn, one of the most active volcanoes in Iceland, are the longest integrated estimates obtained for an active volcano and are equal to or lower than those of other major active volcanoes worldwide. This difference may imply that published release rates for other volcanoes are overestimated, because they are usually not integrated over time. -from Authors
Analysis of data from 280 rivers discharging to the ocean indicates that sediment loads/yields are a log-linear function of basin area and maximum elevation of the river basin. Other factors controlling sediment discharge (e.g., climate, runoff) appear to have secondary importance. A notable exception is the influence of human activity, climate, and geology on the rivers draining southern Asia and Oceania. Sediment fluxes from small mountainous rivers, many of which discharge directly onto active margins (e.g., western South and North America and most high-standing oceanic islands), have been greatly underestimated in previous global sediment budgets, perhaps by as much as a factor of three. In contrast, sediment fluxes to the ocean from large rivers (nearly all of which discharge onto passive margins or marginal seas) have been overestimated, as some of the sediment load is subaerially sequestered in subsiding deltas. Before the proliferation of dam construction in the latter half of this century, riv
Based on about 940,000 measurements of surface-water pCO2 obtained since the International Geophysical Year of 1956–59, the climatological, monthly distribution of pCO2 in the global surface waters representing mean non-El Niño conditions has been obtained with a spatial resolution of 4°×5° for a reference year 1995. The monthly and annual net sea–air CO2 flux has been computed using the NCEP/NCAR 41-year mean monthly wind speeds. An annual net uptake flux of CO2 by the global oceans has been estimated to be 2.2 (+22% or −19%) Pg C yr−1 using the (wind speed)2 dependence of the CO2 gas transfer velocity of Wanninkhof (J. Geophys. Res. 97 (1992) 7373). The errors associated with the wind-speed variation have been estimated using one standard deviation (about±2 m s−1) from the mean monthly wind speed observed over each 4°×5° pixel area of the global oceans. The new global uptake flux obtained with the Wanninkhof (wind speed)2 dependence is compared with those obtained previously using a smaller number of measurements, about 250,000 and 550,000, respectively, and are found to be consistent within±0.2 Pg C yr−1. This estimate for the global ocean uptake flux is consistent with the values of 2.0±0.6 Pg C yr−1 estimated on the basis of the observed changes in the atmospheric CO2 and oxygen concentrations during the 1990s (Nature 381 (1996) 218; Science 287 (2000) 2467). However, if the (wind speed)3 dependence of Wanninkhof and McGillis (Res. Lett. 26 (1999) 1889) is used instead, the annual ocean uptake as well as the sensitivity to wind-speed variability is increased by about 70%.
Sr/86Sr (0.70322) and δ
18O ( ∼2.9‰), whereas significantly lower and higher values, respectively, are found in samples from the Bárdarbunga volcanic
system (0.70307 and 3.8‰). These results strongly indicate that the Gjálp magma originated from the Grímsvötn magma system.
The 1996 magma is of an intermediate composition, representing a basaltic icelandite formed by 50% fractional crystallization
of a tholeiite magma similar in composition to that expelled by the 1998 Grímsvötn eruption. The differentiation that produced
the Gjálp magma may have taken place in a subsidiary magma chamber that last erupted in 1938 and would be located directly
beneath the 1996 eruption site. This chamber was ruptured when a tectonic fracture propagated southward from Bárdarbunga central
volcano, as indicated by the seismicity that preceded the eruption. Our geochemical results are therefore not in agreement
with lateral magma migration feeding the 1996 Gjálp eruption. Moreover, the results clearly demonstrate that isotope ratios
are excellent tracers for deciphering pathways of magma migration and permit a clear delineation of the volcanic systems beneath
Vatnajökull ice sheet.
A short eruption took place in the Grimsvotn volcano in May - June 1983. The eruption most probably started on May 28th but was first observed in the morning of May 29th. Activity was last observed on June 1st and by June 5th it was certainly over. The eruption site is within the caldera near the southern rim and a lake, about 500 m in diameter, formed in the ice shelf with a small island in the middle. The eruption was subaquatic and intermittent ash explosions 50-100 m high were observed in the lake, and a steam column rose up to about 5000 m height a.s.l. The glass phase of the ash was analyzed in a number of samples and found to be evolved basalt with a uniform chemical composition but minor variations are indicated. Samples from the 1934, 1922 and 1903 Grimsvotn eruptions and the glass phase of the eruption of the Laki craters 1783-84 are of similar composition. The Grimsvotn volcano is also the site of a major geothermal system. It appears unlikely that the heat extraction takes place in the same parts of the magmatic system as the evolution of the basalt. -from Authors
The oft-cited general correlation between net sediment accumulation and preservation of organic matter, while revealing in many ways, can be a misleading indicator of general elemental cycling processes and controls on storage of biogenic material at the continental-ocean boundary. Deltaic environments are characterized by the highest rates of net sedimentation and are the single most important class of depocenters on Earth. Available data indicate that sedimentary organic C (Corg) of both terrestrial and marine origin is efficiently decomposed in deltaic areas, with decomposition percentages reaching ≥70% and ≥90%, respectively, the latter percentage (marine) being quite comparable to deep-sea, low sedimentation environments. Despite high primary productivity associated with most deltas and evidence of substantial deposition of fresh planktonic debris, patterns of SO4= reduction indicate that the reactivity of organic material being buried is low, and that a larger proportion of Corg is often degraded compared to other marine deposits of similar net accumulation rate. As indicated by properties of the surficial Amazon delta and downdrift coastal region of northeast South America (∼1600-km extent), the primary reasons for efficient remineralization are related to intense and massive physical reworking of sediment associated with estuarine fronts, upwelling, tidal oscillation, and wind-driven waves. Fluid muds and mobile surface material cause the seafloor and continental boundary to act as a massive, suboxic, fluidized bed reactor dominated in some cases by bacterial rather than macrofaunal biomass. Reoxidation, repetitive redox successions, metabolite exchange, and continual mixing-in of fresh planktonic debris with refractory terrestrial components, result in an efficient decomposition system largely decoupled from net accumulation. Similar processes occur on smaller scales in most estuarine-shelf systems, but appear to be most dramatically expressed off the major rivers forming deltas.
The diagenesis and geochemical evolution of deep-sea sediments are controlled by the interaction between sediments and their associated pore waters. With increasing depth, the pore water of Hole 149 (DSDP) exhibits a strong depletion in Mg and a corresponding enrichment in Ca, while the alkalinity remains relatively constant. Dissolved SiO 2 is nearly constant in the upper 100 m of sediment, but is highly enriched in the deepest pore waters. The pore waters exhibit a depletion in K with increasing depth, and O 18 / O 16 pore water ratios also decrease. The sediment section has three zones of sedimentary regimes with increasing depth in the drill hole: an upper 100 m section of detrital clays, a middle section enriched in calc-akalic volcanics which have undergone submarine weathering to a smectite phase, and a lower section of siliceous ooze which still has a diagenetic smectite phase. The quartz-feldspar ratios and O 18 / O 16 composition of the silicate phases are in agreement with these interpretations. The submarine weathering of volcanics to a smectite can account for the observed pore water gradients. Volcanics release Ca and Mg to the pore waters causing the alkalinity values to increase. Smectite is formed, depletes the pore waters in Mg and O 18 and causes the alkalinity to decrease. The net reaction allows for the observed relationship between pore water Ca and Mg gradients with little net change in alkalinity. Given the abundance of volcanics in many deep-sea sediments, especially in lower sections which often form near ridge crests, the submarine formation of smectite may be an additional oceanic Mg sink which has not yet been fully considered.
A record of volcanic activity within the Vatnajökull ice cap has been obtained by combining data from three sources: tephrostratigraphic studies of two outlet glaciers, a 415-m-long ice core from northwestern Vatnajökull, and written records. The record extends back to a.d. 1200 and shows that the volcanic activity has a 130 140 yr period. Intervals of frequent eruptions with recurrence times of three to seven years alternate with intervals of similar duration having much lower eruption frequency. In comparison with other parts of the plate boundary in Iceland, eruption frequency is greater, episodes of unrest are longer, and intervals of low activity are shorter. The high eruption frequency may be the result of a more sustained supply of magma, owing to the area's location above the center of the Iceland mantle plume. When combined with historical data on eruptions and earthquakes, our data indicate that rifting-related activity in Iceland as a whole is periodic and broadly in phase with the volcanic activity within Vatnajökull.
In October 1996 a subglacial fissure to the north of the Grimsvötn caldera in W-Vatnajökull produced about 0.4km3 of Fe-rich basaltic andesite–icelandite—in an area characterized mostly by tholeiitic basalt. In this paper the chemical composition of volcanic systems in the region is discussed with the help of six new analyses and others from the literature, and a tentative model for their evolution is proposed, in which magma produced by the partial melting of a two-component mantle mixes with hydrous, silicic melt in the crust. The Vatnajökull 1996 magma belongs to a separate volcanic system, intermediate between Bardarbunga and Grimsvötn.
The article describes the petrochemical evolution of oceanic rocks in terms of plate tectonics with special reference to Iceland. The compositional variation along the rift zone is related to different production rates of mantle-derived olivine tholeiite of invariant composition which is added to the crust from below and modified by mixing with anatectic melts in the crust and concomitant crystal fractionation.The kinematic processes of crustal accretion cause rocks deposited in the rift zone to subside towards higher temperatures where they suffer hydration and progressive metamorphism before becoming a part of the stable crustal plate. Rocks deposited near the rift-centre assume the highest metamorphic grade (greatest depth) while rocks deposited at the rift-margins follow a shallow path before being carried towards lower temperatures in the stable plate. The material transport through stationary metamorphic zones produces the layering of the oceanic crust.As the hydrated rocks cross their solidus isotherm, silicic magma is formed by incongruent partial melting. The melting continues until rocks crossing the boundary between the amphibolite and granulite fades are finally dehydrated by the break-down of amphibole. This reaction boundary defines the surface of the upper mantle.The segregation and retention of crust-derived magmas within the rift zone results in chemical fractionation in the oceanic crust, for its lower sections are depleted in elements entering the early melt fractions, which are silicic and enriched in the dispersed elements. The last melt-increments from the same subsiding pile are ne-normative basalts.The rift-zone rocks are shown to be mantle-derived olivine tholeiite modified by minor amounts of crustal rhyolite and nepheline basalt, while volcanism outside the rift zone is dominated by the crust-derived magmas themselves. All mixtures undergo further mineralogical evolution towards invariant compositions in the basalt system, resembling the olivine tholeiite, quartz tholeiite, and nepheline basalt of synthetic systems. The dispersed-element geochemistry of the oceanic rocks is but slightly modified by crystal fractionation, and reflects the mixing ratios of the olivine tholeiite and the different crustal magmas.The geochemistry of radiogenic isotopes is controlled by continuous processes of crustal fractionation separating mother and daughter elements. The oxygen-isotope geochemistry can be referred to magma mixing, for rhyolites formed by anatexis in the hydrated crust are enriched in light oxygen relative to the mantle-derived melts.
Non-spectral interferences caused by a sea-water matrix diluted 5-fold on the analyte signals of 24 trace elements in ICP-MS were studied in relation to instrumental parameters. Both quadrupole (ICP-QMS) and double focusing-sector (ICP-SMS) ICP-MS were studied. The parameters were torch injector diameter, sampling depth (i.e., distance from the load coil to the sampler orifice) and rf power. A distinction was made between absolute matrix effects, expressed as integrated signal recovery over a range of nebulizer flow rates (NFR), and matrix effects monitored at a fixed NFR. For the elements studied, it was found that the degree of non-spectral interference depends on both ionization potential (IP) and atomic mass. Generally, the greater the IP and atomic mass of the analyte, the lower the recovery in the presence of the matrix. It appears that, by using optimum plasma settings in ICP-SMS, analyte signal changes may be kept to a moderate level during prolonged introduction of a sea-water matrix. The accuracy of the analytical results can be further improved by using a systematically selected set of internal standard elements.
A volcanic eruption beneath the Vatnajökull ice cap in central Iceland (Figure 1) began on September 30,1996, along a 7-km-long fissure between the volcanoes Bárdarbunga and Grímsvötn. The eruption continued for 13 days and produced ˜0.5 km3 of basaltic andesite. Meltwater from the eruption site flowed into the caldera lake of the Grímsvötn volcano, where it accumulated beneath a floating ice shelf. The lake's ice dam was lifted off the glacier bed on November 4, and in the next two days more than 3 km3 of water drained out beneath the glacier and flushed down to the south coast's alluvial plain, causing extensive flooding and damage to transportation and communication systems.
The authors present an overview of the oceanic chemistries of the bioactive trace metals, Mn, Fe, Co, Ni, Cu, and Zn; the authors combine field data with results from laboratory phytoplankton culture-trace metal studies and speculate on the potential influences of these trace metals on oceanic plankton production and species composition. Most field studies have focused on the effects of single metals. However, they propose that synergistic and antagonistic interactions between multiple trace metals could be very important in the oceans. Trace metal antagonisms that may prove particularly important are those between Cu and the potential biolimiting metals Fe, Mn, and Zn. These antagonistic interactions could have the greatest influence on biological productivity in areas of the open ocean isolated from terrestrial inputs, such as the remote high nutrient regions of the Pacific and Antarctic Oceans. The emerging picture of trace metal-biota interactions in these oceanic areas is one in which biology strongly influences distribution and chemical speciation of all these bioactive trace metals. It also seems likely that many of these bioactive trace metals and their speciation may influence levels of primary productivity, species composition, and trophic structure. Future investigations should give more complete consideration to the interactive effects of biologically important trace metals.
A rare combination of natural circumstances permits assessment of current theories on water flow beneath glaciers. Outburst floods from the subglacial lake Grímsvötn in Iceland took place before, during and after surging of Skeiarárjökull, the glacier beneath which the outburst floods drain. The observable drainage patterns associated with these floods show the different nature of the basal water conduit system of the glacier during surge and non-surge phases. During surge conditions, basal water is dispersed slowly across the bed in a distributed drainage system; but when the glacier is not surging, water is transported rapidly through a system of tunnels.
The recent volcanic history of the southwestern part of the Veidivötn fissure swarm, southern Iceland, provides a basis for assessment of volcanic risk in an area of large hydropower potential. Local tephrastratigraphy and regional tephrochronology provide relative and absolute dating of individual eruptions as well as information on the volume and distribution of the products formed in each eruption.Three large eruptions took place in this area in ∼ 1480 A.D., ∼ 900 A.D. and ∼ 150 A.D., respectively. Each eruption produced approx. 1 km3 (DRE) of basaltic, and minor amounts of silicic lava and tephra on fissures up to 42 km long. No evidence is found of smaller eruptions during this period. The estimated eruption frequency, one eruption every 600–800 years, implies that this part of the Veidivötn fissure swarm is inactive for long periods between relatively large volcanic events.A change in the mode of eruption from effusive to explosive took place during this period. The hazards posed by this area include far-reaching lava flows, widespread heavy tephra fall with thicknesses in excess of 2 m at distances of 10 km, and damming of a large glacial river with the consequent formation of unstable lakes.A volcano-tectonic model, which explains the observed eruption frequency and provides a basis for a long-term monitoring program, is proposed. Eruptions on the Veidivötn fissure swarm are interpreted as corollaries of rifting episodes initiated in the Bárdarbunga central volcano. Volcano-tectonic episodes affect the fissure swarm at an average interval of 100 years. Minor episodes are limited to the central volcano and adjacents parts of the fissure swarm. During the less frequent major episodes, rifting and volcanic activity extends to the extreme southwestern part of the fissure swarm.Seismic monitoring of the Bárdarbunga central volcano could provide an early warning of renewed activity on the Veidivötn fissure swarm. A major rifting episode resulting in eruption on its southwestern part can be expected during the next 100 to 300 years.
Experiments on seawater-basaltic glass interaction were made using a particulary high seawater-basaltic glass ratio (14.5 g/cm2; weight ratio: 50). A layered alteration skin is observed at the glass surface, while the variations in the composition of the seawater are imperceptible. Three zones of different composition and structure are distinguished: 1.1) An external zone, the composition of which evolved to saponite.2.2) A median zone of hydrotalcite-like hydroxycarbonate (Mg6Al2CO3(OH)164H2O).3.3) An internal zone, between glass and hydroxycarbonates, richer in Fe and in Mg and in which a 10 Å interval is observed (by dark field examination) compatible with a TOT type clay mineral. The composition of this zone indicates a mixing of poorly crystalline products.The principal chemical exchanges between glass and solution are the release of Ca in solution and the contribution of Mg and CO2 from seawater to form hydroxycarbonates, which are considered precursors of phyllosilicates.Comparison with natural phenomena (palagonitization) is made.
Dissolution experiments of a tholeiite basalt glass carried out at different pH and T (up to 300°C) using a rotatingdisc apparatus show that, depending on pH and T, dissolution can be controlled by one of the following steps: (1) surface reaction; (2) transport of reactants in solution; and (3) mixed reaction. The activation energies of these different processes were found to be 60, 9 and 15–50 kJ mol−1, respectively. Taking account of these results, it appears likely that surface reactions are not rate limiting for the hydrolysis of most crystalline silicate minerals in hydrothermal and metamorphic processes, and that caution should be exercised when predicting rate of reactions at high temperatures solely on the basis of activation energies measured at low temperatures.
Far-from-equilibrium dissolution rates of a suite of volcanic glasses that range from basaltic to rhyolitic in composition were measured in mixed flow reactors at pH 4 and 10.6, and temperatures from 25 to 74°C. Experiments performed on glasses of similar composition suggest that dissolution rates are more closely proportional to geometric surface areas than their BET surface areas. Measured geometric surface area normalized dissolution rates (r+,geo) at 25°C were found to vary exponentially with the silica content of the glasses. For pH 4 solutions this relation is given by:
(A1)log r+,geo(mol/m2/s)=−0.03⋅[SiO2(wt%)]−7.58, and at pH 10.6 ± 0.2 this relation is given by:
(A2)log r+,geo(mol/m2/s)=−0.02⋅[SiO2(wt%)]−7.02. These equations can be used to estimate lifetimes and metal release fluxes of natural glasses at far-from-equilibrium conditions. The lifetime at pH 4 and 25°C of a 1 mm basaltic glass sphere is calculated to be 500 yr, whereas that of a 1 mm rhyolitic glass sphere is 4500 yr. Estimated nutrient release rates from natural glasses decrease exponentially with increasing silica content.
Steady state basaltic glass dissolution rates were measured as a function of aqueous aluminum, silica, and oxalic acid concentration at 25° C and pH 3 and 11. All rates were measured in mixed flow reactors, performed in solutions that were strongly undersaturated with respect to hydrous basaltic glass, and exhibited stoichiometric Si versus Al release. Rates are independent of aqueous silica activity, but decrease with increasing aqueous aluminum activity at both acidic and basic conditions. Increasing oxalic acid concentration increased basaltic glass dissolution rates at pH 3, but had little affect at pH 11. All measured rates can be described within experimental uncertainty using
This study is aimed at quantifying surface reaction controlled basaltic glass dissolution rates at far-from-equilibrium conditions. Towards this aim, steady-state basaltic glass dissolution rates were measured as a function of pH from 2 to 11 at temperatures from 6° to 50°C, and at near neutral conditions to 150°C. All rates were measured in open system titanium mixed flow reactors. Measured dissolution rates display a common pH variation; dissolution rates decrease dramatically with increasing pH at acid conditions, minimize at near neutral pH, and increase more slowly with increasing pH at basic conditions. The pH at which basaltic glass dissolution minimizes decreases with increasing temperature.Dissolution rates were interpreted within the context of a multioxide dissolution model. Constant temperature rates are shown to be consistent with their control by partially detached Si tetrehedra at the basaltic glass surface. Regression of far-from-equilibrium dissolution rates obtained in the present study and reported in the literature indicate that all data over the temperature and pH range 6° < T < 300°C and 1 < pH < 11 can be described within uncertainty usingr+,geo = AA exp−(EA/RT)aH+3aAl3+1/3where r+,geo signifies the geometric surface area normalized steady-state basaltic glass dissolution rate at far-from-equilibrium conditions, AA refers to a constant equal to 10−5.6 (mol of Si)/cm2/s, EA, designates a pH independent activation energy equal to 25.5 kJ/mol, R stands for the gas constant, T signifies temperature in K, and ai represents the activity of the subscripted aqueous species.
Far-from-equilibrium, steady-state dissolution rates at pH 4 of a suite of natural glasses, ranging from basaltic to rhyolitic in composition, have been determined as a function of aqueous fluoride concentrations up to 1.8 × 10−4 mol/kg in mixed-flow reactors. Dissolution rates of each of these glasses increase monotonically with increasing aqueous fluoride concentration. Measured dissolution rates are found to be consistent with both the Furrer and Stumm (1986) surface coordination model and the Oelkers (2001) multi-oxide dissolution model. Application of the latter model yields the following equation that can describe all measured rates as a function of both glass and aqueous solution composition:
where r+,geo represents the far-from-equilibrium dissolution rate, normalized to geometric surface area, SiO2(wt.%) refers to weight percent of SiO2 in the glass, and ai denotes the activity of the subscripted aqueous species. Computed glass dissolution rates increase with increasing aqueous fluoride concentration due to the formation of aqueous Al-fluoride complexes, which decrease aAl3+. This rate expression can be used to predict far-from-equilibrium dissolution rates of natural glasses in a variety of natural environments. Comparison of rate predictions with the composition of natural fluids suggests that the presence of aqueous fluoride can enhance natural glass dissolution rates by an order of magnitude or more in a variety of geochemical systems.
Six Deep Sea Drilling Project (DSDP) Sites (252, 285, 315, 317, 336, 386) were examined for the chemical composition of the dissolved salts in interstitial waters, the oxygen isotopic composition of the interstitial waters, and the major ion composition of the bulk solid sediments. An examination of the concentration-depth profiles of dissolved calcium, magnesium, potassium, and H218O in conjunction with oxygen isotope mass balance calculations confirms the hypothesis that in DSDP pelagic drill sites concentration gradients in Ca. Mg. K, and H218O are largely due to alteration reactions occurring in the basalts of Layer 2 and to alteration reactions involving volcanic matter dispersed in the sediment column. Oxygen isotope mass balance calculations require substantial alteration of Layer 2 (up to 25% of the upper 1000 m). but only minor exchange of Ca, Mg, and K occurs with the overlying ocean. This implies that alteration reactions in Layer 2 are almost isochemical.
The October 1996 eruption within the Vatnajökull Glacier, Iceland, provides a unique opportunity to study the net effect of volcanic eruptions on atmospheric and oceanic CO2. Volatile elements dissolved in the meltwater that enclosed the eruption site were eventually discharged into the ocean in a dramatic flood 35 days after the beginning of the eruption, enabling measurement of 50 dissolved element fluxes. The minimum concentration of exsolved CO2 in the 1×1012 kg of erupted magma was 516 mg/kg, S was 98 mg/kg, Cl was 14 mg/kg, and F was 2 mg/kg. The pH of the meltwater at the eruption site ranged from about 3 to 8. Volatile and dissolved element release to the meltwater in less than 35 days amounted to more than one million tonnes, equal to 0.1% of the mass of erupted magma. The total dissolved solid concentration in the floodwater was close to 500 mg/kg, pH ranged from 6.88 to 7.95, and suspended solid concentration ranged from 1% to 10%. According to H, O, C and S isotopes, most of the water was meteoric whereas the C and S were of magmatic origin. Both C and S went through isotopic fractionation due to precipitation at the eruption site, creating “short cuts” in their global cycles. The dissolved fluxes of C, Ca, Na, Si, S and Mg were greatest ranging from 1.4×1010 to 1.4×109 mol. The dissolved C flux equaled 0.6 million tonnes of CO2. The heavy metals Ni, Mn, Cu, Pb and Zn were relatively mobile during condensation and water–rock interactions at the eruption site. About half of the measured total carbon flood flux from the 1996 Vatnajökull eruption will be added to the long-term CO2 budget of the oceans and the atmosphere. The other half will eventually precipitate with the Ca and Mg released. Thus, for eruptions on the ocean floor, one can expect a net long-term C release to the ocean of less than half that of the exsolved gas. This is a considerably higher net C release than suggested for the oceanic crust by Staudigel et al. [Geochim. Cosmochim. Acta, 53 (1989) 3091]. In fact, they suggested a net loss of C. Therefore, magma degassed at the ocean floor contributes more C to the oceans and the atmosphere than magma degassed deep in the oceanic crust. The results of this study show that subglacial eruptions affecting the surface layer of the ocean where either Mn, Fe, Si or Cu are rate-determining for the growth of oceanic biomass have a potential for a transient net CO2 removal from the ocean and the atmosphere. For eruptions at high latitudes, timing is crucial for the effect of oceanic biota. Eruptions occurring in the wintertime when light is rate-determining for the growth of biota have much less potential for bringing about a transient net negative CO2 flux from the ocean atmosphere reservoir.
Steady-state dissolution rates of a synthetic basaltic glass were measured in an open-system mixed flow reactor as a function of solution composition at a temperature of 90°C and over the pH range 7.8 to 8.3. The dissolution is a two-step process. The first of these steps involves the release of the cation modifier elements leading to the formation of a hydrated surface gel (HBG) of which the solubility controls the overall dissolution reaction. The glass steady-state dissolution rates were found to be independent of aqueous aluminium and silicium concentration but to depend on the chemical affinity for the overall hydrolysis reaction. The glass is a rapidly reacting solid, whose dissolution induces a dramatic change in solution concentration, which results readily in small chemical affinities for the dissolution reaction. Consequently, conditions of great undersaturation have not been investigated (affinity max. 9.8 kJ/mol). However, our results strongly suggest that the dissolution rates are controlled by the decomposition of a stoichiometric silico-aluminous surface precursor. The variation of the steady-state dissolution rates can be described using a simple expression based on the concept that the precursor is formed by the simple absorption of reactants: R (mol cm−2s−1) = 3 × 10−10 (OH−)0.39 (1−Q/8.2 × 10−5), where Q, the ion activity quotient is equal to: Q = (H4SiO4) (Al(OH)4−)0.36 (Fe(OH)3)0.18 (OH−)−0.36.
Petrology of recent basalts of the Eastern Volcanic Zone
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Flood from Grímsvötn 1972, mechanism and sediment discharge
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Non-spectral interferences caused by a saline water matrix in quadrupole and HR-ICP-MS
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The 1996 outburst flood from the Grímsvötn subglacial caldera, Iceland: composition of the caldera lake water, origin of suspended flood solids, and flux of readily dissolved nutrients and metals into the sea
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readily dissolved nutrients and metals into the sea, M.S. thesis,
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Gos í eldstö ðvum undir Vatnajö kli eftir 1200 AD (Eruptions beneath Vatnajö kull ice-cap after 1200 AD)
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after 1200 AD), in: H. Haraldsson (Ed.), Vatnajö kull: Gos og
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Hlaupid a ´ Skeidará 1996. U ´ tbreidsla, rennsli og aurburdur (The jö kulhlaup on Skeidará in the autumn 1996: the dis-tribution, discharge and sediment load
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Chemistry of river water on the Skeidará-sandur flood plane after the eruption within the Vatnajö-kull Glacier Vatnajö kull: Gos Og Hlaup
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