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Anthropogenic Forcing of the Baltic Sea Thallium Cycle
... It is well-established that basins poorly connected with the open ocean can have seawater ε 205 Tl values that do not match the open ocean. Seawater ε 205 Tl values are still recorded in sediments formed in these basins, but these values are skewed toward local, oftentimes freshwater-dominated inputs (ε 205 Tl ≈ -2‱; e.g., the Black and Baltic seas; Owens et al., 2017;Ostrander et al., 2024). ...
... Seawater ε 205 Tl values are oftentimes directly transferred to siliciclastic sediments (e.g., Owens et al., 2017;Wang et al., 2022;Ostrander et al., 2024), and apparently also some carbonate sediments according to the results of this study. Consistent capture of seawater isotope compositions by both siliciclastic and carbonate sediments is a unique quality of the Tl isotope paleoredox proxy. ...
... For example, past seawater U isotope compositions are sensitive to global ocean oxygenation levels and can be transferred to some carbonates, but shales are nearly always strongly and variably fractionated (Lau et al., 2019 and references therein). Past seawater Mo isotope compositions are also sensitive to global ocean oxygenation levels but are rarely transferred to any sediment type (Kendall et al., 2017 Neubert et al., 2008Ostrander et al., 2024). Nor are sedimentary ε 205 Tl values strongly affected by shelf-to-basin oxide "shuttling" across a redoxcline (Chen et al., 2022). ...
... Wykazuje skłonność do sorpcji na cząsteczkach gleby i osadów oraz do bioakumulacji w roślinach, bezkręgowcach i rybach [2;3]. Analizy przeprowadzone przez Woods Hole Oceanographic Institution (WHOI) wykazały, że poziom talu w Morzu Bałtyckim znacząco wzrasta, co stanowi poważne zagrożenie dla ekosystemu morskiego oraz zdrowia ludzi [4]. W warunkach beztlenowych, które panują w wielu częściach Bałtyku, tal wiąże się z minerałami siarczkowymi, co prowadzi do jego akumulacji w osadach dennych [5]. ...
Thallium (Tl) is a highly toxic element that threatens human health and the environment. Although it occurs naturally, industrial activities such as chemical production significantly increases its concentration in the environment. In addition, climate change, such as rising temperatures and more frequent extreme weather events, can exacerbate the release and transport of thallium in the environment, increasing the risk of negative health and ecological consequences for living organisms (Karbowska 2016).
The aim of this work was to review the literature on environmental Tl contamination and its impact on plants. Special focus has been placed on analyzing the mechanisms of Tl interaction with key physiological and biochemical processes in plants. Understanding these aspects is crucial for assessing the potential ecological consequences and developing strategies to mitigate its negative impact on the environment.
Tl is easily absorbed by plants, and its high concentration in plant tissues can lead to serious metabolic disorders. It negatively affects plant growth, reducing shoot and root length. In addition, it can interfere with the uptake and transport of essential nutrients (Espinosa et al. 2023). It also influences oxidative stress and lipid peroxidation, leading to damage to cell membranes (Babić et al. 2009). Furthermore, Tl reduces photosynthetic efficiency by decreasing chlorophyll content and the efficiency of photosystem II (Canturk 2023).
Tl contamination poses an increasing threat to the natural environment and human health, highlighting the need for further research on the mechanisms of its toxicity and the long-term consequences of its presence in the environment.
The short sediment core EMB201/7-4 retrieved from the East Gotland Basin, central Baltic Sea, is explored here as a candidate to host the stratigraphical basis for the Anthropocene series and its equivalent Anthropocene epoch, still to be formalized in the Geological Time Scale. The core has been accurately dated back to 1840 CE using a well-established event stratigraphy approach. A pronounced and significant change occurs at 26.5 cm (dated 1956 ± 4 CE) for a range of geochemical markers including ²³⁹⁺²⁴⁰ Pu, ²⁴¹ Am, fly-ash particles, DDT (organochlorine insecticide), total organic carbon, and bulk organic carbon stable isotopes. This stratigraphic level, which corresponds to a change in both lithology and sediment colour related to early anthropogenic-triggered eutrophication of the central Baltic Sea, is proposed as a Global Boundary Stratotype Section and Point for the Anthropocene series.
Plain Language Summary
Although less prevalent in the environment than toxic metals such as lead and cadmium, thallium is a highly toxic metal even at very low levels. Because reliable measurements are difficult at such low concentrations, thallium pollution is far less documented than other toxic metals. Cement production originally was estimated to be the primary source of thallium pollution at the global scale, but it was later recognized that coal burning was likely the main source. These previous estimates refer to the recent decades but no longer‐term inventories were available. Furthermore, no inventories were established at the scale of the European continent. Detailed measurements in Alpine ice cores show that thallium pollution after the late 19th century primarily was the result of coal burning in western Europe, and was largest between 1920 and 1965 as expected from coal consumption records. The rapid growth of cement production that took place after World War II had only limited impact on thallium pollution in Europe.
Thallium is a highly poisonous heavy metal. Since Tl pollution control has been neglected worldwide until the present, countless Tl pollutants have been discharged into the environment, endangering the safety of drinking water, farmland soil, and food chain, and eventually posing a great threat to human health. However, the source, occurrence, pathway and fate of Tl in the environment remains understudied. As Tl in non-contaminated systems and from anthropogenic origin exhibits generally different isotopic signatures, which can provide fingerprint information and a novel way for tracing the anthropogenic Tl sources and understanding the environmental processes. This review summarizes: (i) the state-of-the-art development in highly-precise determination analytical method of Tl isotopic compositions, (ii) Tl isotopic fractionation induced by the low-temperature surface biogeochemical process, (iii) Tl isotopic signature of pollutants derived from anthropogenic activities and isotopic fractionation mechanism of Tl related to the high-temperature industrial activities, and (iv) application of Tl isotopic composition as a new tracer emerging tracer for source apportionment of Tl pollution. Finally, the limitations and possible future research about Tl isotopic application in environmental contamination is also proposed: (1) Tl fractionation mechanism in different environmental geochemistry processes and industrial activities should be further probed comprehensively; (2) Tl isotopes for source apportionment should be further applied in other different high Tl-contaminated scenarios (e.g., agricultural systems, water/sediment, and atmosphere).
Major Baltic inflow events (MBI) transport large amounts of saline water into the Baltic. They are the solely source for deep water ventilation in the central Baltic basins, and control to a large extent the environmental conditions below the permanent halocline. Available series of MBI frequency and intensity depict strong decrease of MBI frequency after the 1980s, followed by long lasting stagnation periods in the central Baltic basins. However, the expected decrease in mean salinity of the Baltic was not observed. Also the frequency of large volume changes of the Baltic has not changed, and recent model studies predict a slight increase of MBI frequency with warming climate. Using long term data series of sea level, river discharge, and salinity from the Belt Sea and the Sound a continuous series of barotropic inflows was reconstructed for the period from 1887 till present. A comparison with the MBI series of Fischer and Matthäus (1996) revealed significant differences in the period since the 1980s. The reasons for the deviations are mainly the lack of appropriate data between 1976 and 1991, and the change in observation methods afterward, which caused a bias in the inflow statistics. In contrast to earlier investigations the revised MBI series depicts no significant long term trend in MBI frequency and intensity, contradicting the hypothesis that climate change caused a decreasing MBI frequency. There exists a decadal variability of MBI with a main period of 25–30 years. Periods with reduced MBI frequency were identified. The revised MBI series was proved with observations of dissolved oxygen and salinity in the bottom layer of the Bornholm basin. Until today climate change has no obvious impact on the MBI related oxygen supply to the central Baltic Sea. The increased eutrophication during the last century is most probably the main driver for temporal and spatial spreading of suboxic and anoxic conditions in the deep layer of the Baltic Sea.
The deep basins of the Baltic Sea, including the Gotland and Landsort Deeps, are well-known for the exceptional occurrence of sedimentary Mn carbonate. Although the details of the mechanisms of Mn carbonate formation are still under debate, a close relationship with episodic major Baltic inflows (MBIs) is generally assumed, at least for the Gotland Basin. However, the few studies on Mn cycling during MBIs suffer from a limited temporal resolution. Here we report on Mn dynamics in the water column and sediments of the Gotland Deep following an MBI that entered the Baltic Sea in December 2014. Water column profiles of dissolved Mn were obtained at a monthly to bi-monthly resolution between February 2015 and March 2017 and revealed an impact of the MBI on the Gotland Deep bottom waters beginning in March 2015. Water column profiles and budget estimates provided evidence for remarkable losses of dissolved Mn associated with the enhanced deposition of Mn oxide particles, as documented in sediment trap samples and surface sediments. In July 2015, subsequent to the nearly full oxygenation of the water column, clear signals of the re-establishment of bottom water anoxia appeared, interrupted by a second inflow pulse around February 2016. However, dissolved Mn concentrations of up to 40 μM in the bottom waters in June 2016 again indicated a pronounced reduction of Mn oxide and the escape of dissolved Mn back into the open water column. The absence of substantial amounts of Mn carbonate in the surface sediments at the end of the observation period suggested that the duration of bottom water oxygenation plays an important role in the formation of this mineral. Data from both an instrumental time series and a dated sediment core from the Gotland Deep supported this conclusion. Enhanced Mn carbonate formation occurred especially between the 1960s and mid-1970s, when several MBIs caused a long-lasting oxygenation of the water column. By contrast, Mn carbonate layers were much less pronounced or even missing after single MBIs in 1993, 2003, and 2014, each of which provided a comparatively short-term supply of O2 to the deeper water column.
Beneath the waves, oxygen disappears
As plastic waste pollutes the oceans and fish stocks decline, unseen below the surface another problem grows: deoxygenation. Breitburg et al. review the evidence for the downward trajectory of oxygen levels in increasing areas of the open ocean and coastal waters. Rising nutrient loads coupled with climate change—each resulting from human activities—are changing ocean biogeochemistry and increasing oxygen consumption. This results in destabilization of sediments and fundamental shifts in the availability of key nutrients. In the short term, some compensatory effects may result in improvements in local fisheries, such as in cases where stocks are squeezed between the surface and elevated oxygen minimum zones. In the longer term, these conditions are unsustainable and may result in ecosystem collapses, which ultimately will cause societal and economic harm.
Science , this issue p. eaam7240
The rates of marine deoxygenation leading to Cretaceous Oceanic Anoxic Events are poorly recognized and constrained. If increases in primary productivity are the primary driver of these episodes, progressive oxygen loss from global waters should predate enhanced carbon burial in underlying sediments—the diagnostic Oceanic Anoxic Event relic. Thallium isotope analysis of organic-rich black shales from Demerara Rise across Oceanic Anoxic Event 2 reveals evidence of expanded sediment-water interface deoxygenation ~43 ± 11 thousand years before the globally recognized carbon cycle perturbation. This evidence for rapid oxygen loss leading to an extreme ancient climatic event has timely implications for the modern ocean, which is already experiencing large-scale deoxygenation.
Thallium is released into the biosphere from
both natural and anthropogenic sources. It is generally
present in the environment at low levels; however, human
activity has greatly increased its content.
Atmospheric emission and deposition from industrial
sources have resulted in increased concentrations of
thallium in the vicinity of mineral smelters and coalburning
facilities. Increased levels of thallium are found
in vegetables, fruit and farm animals. Thallium is toxic
even at very low concentrations and tends to accumulate
in the environment once it enters the food chain.
Thallium and thallium-based compounds exhibit higher
water solubility compared to other heavy metals. They
are therefore also more mobile (e.g. in soil), generally
more bioavailable and tend to bioaccumulate in living
organisms. The main aim of this review was to summarize
the recent data regarding the actual level of thallium
content in environmental niches and to elucidate the
most significant sources of thallium in the environment.
The review also includes an overview of analytical
methods, which are commonly applied for determination
of thallium in fly ash originating from industrial
combustion of coal, in surface and underground waters,
in soils and sediments (including soil derived from
different parent materials), in plant and animal tissues
as well as in human organisms.
Significance
Oxygen-deficient waters are expanding globally in response to warming and coastal eutrophication. Coastal ecosystems provide valuable services to humans, but these services are severely reduced with decreasing oxygen conditions. In the Baltic Sea, oxygen-deficient waters have expanded from 5,000 to over 60,000 km ² with large decadal fluctuations over the last century, reducing the potential fish yield and favoring noxious algal blooms. This increase is due to the imbalance between oxygen supply from physical processes and oxygen demand from consumption of organic material, enhanced by nutrient inputs and temperature increases. Further nutrient reductions will be necessary to restore a healthier Baltic Sea and counteract effects from warming.
The sedimentary geochemistry of manganese is dominated by the redox control of its speciation, higher oxidation states (Mn3+ and 4+) occurring as insoluble oxyhydroxides in well-oxygenated environments and the lower oxidation state (Mn2+) being much more soluble in oxygen-deficient settings. Its geochemical behavior is therefore quite different in oxic and anoxic environments, and where oxic and anoxic conditions are juxtaposed, Mn is recycled between the two environments. In modern marine sediments, Mn is present above its crustal abundance as an oxyhydroxide in all slowly accumulating (pelagic) sediments of the deep ocean and in surficial deposits of continental margin environments. Diagenetic recycling of Mn in the latter causes surficial deposits to have larger Mn enrichments than in many pelagic sediments. Bottom sediments of permanently anoxic basins show no enrichments and have Mn concentrations that are controlled solely by the aluminosilicate fraction. Manganese carbonates (kutnohorite and calcic rhodochrosite) are found only in anoxic sediments accumulating beneath surface oxic horizons (and therefore under oxygenated bottom waters) in many nearshore environments. Such enrichments are due to delivery of Mn by burial of surface oxyhydroxides into the subsurface anoxic environment where they are dissolved. Pore-water Mn levels can reach saturation with respect to a mixed Mn-Ca carbonate phase in such sediments. The diagenetic origin for these phases is shown by their carbon isotope compositions, which typically indicate a carbon source from decomposing organic matter. The presence of Mn carbonates therefore signifies that the host sediment must have accumulated under oxygenated bottom waters. On the basis of this information it is proposed that, in contrast to several current explanations for the formation of Mn carbonates (kutnohorite and rhodochrosite) in ancient organic-rich shales, limestone, and marl sequences and in many Mn ore deposits, the occurrence of these mineral phases indicates that the sediments originally accumulated beneath oxygenated bottom waters. By analogy with the present, Mn carbonates could not have formed in the bottom waters of anoxic basins. These diagenetic phases, however, did form where Mn was supplied at a high rate, namely, by the burial of oxyhydroxide-enriched surface sediments, to a subsurface anoxic environment. This situation could only have occurred under oxygenated bottom waters. The presence of Mn carbonates in ancient black shales (and in some carbonate-rich rocks) lends strong support to the notion that these rocks did not necessarily form in anoxic basins but owe their carbon richness to a high supply of organic matter to sediments deposited under oxygenated bottom waters, probably in continental margin settings.
Eutrophication is one of the most severe and widespread forms of disturbance affecting coastal marine systems. Whilst there are general models of effects on benthos, such as the Pearson-Rosenberg (P-R) model, the models are descriptive rather than predictive. Here we first review the process of increased organic matter production and the ensuing sedimentation to the seafloor. It is shown that there is no simple relationship between nutrient inputs and the vertical flux of particulate organic matter (POM). In particular, episodic hydrographic events are thought to be the key factor leading to high rates of sedimentation and accompanying hypoxia. We extend an earlier review of effects of hypoxia to include organisms living in the water column. In general, fishes are more sensitive to hypoxia than crustaceans and echinoderms, which in turn are more sensitive than annelids, whilst molluscs are the least sensitive. Growth is affected at oxygen concentrations between 6.0 and 4.5 mg O-2 1(-1), other aspects of metabolism are affected at between 4 and 2 mg O-2 1(-1) and mortality occurs where concentrations are below 2.0 to 0.5 mg O-2 1(-1). Field studies, however, show that complex behavioural changes also occur as hypoxia increases, and these are described herein. The areas where hypoxia occurs are frequently areas that are stagnant or with poor water exchange. Thus again, hydrographic factors are key processes determining whether or not hypoxia and eutrophication occur. Tolerance to ammonia and hydrogen sulphide is also reviewed, as these substances are found at near zero concentrations of oxygen and are highly toxic to most organisms. However, the effects of interactions between oxygen, ammonia and hydrogen sulphide only occur below oxygen concentrations of ca. 0.5 mg O-2 1(-1), since only below this concentration are hydrogen sulphide and oxygen released into the water. Models of eutrophication and the generation of hypoxia are discussed, and in particular the P-R model is analysed. Although agreement with the model is widely reported the actual predictions of the model have rarely been tested. Our review suggests that the major effects on benthic fauna result from hypoxia rather than organic enrichment per se and suggests that the P-R model is descriptive rather than predictive. Finally, a managerial tool is proposed, based on the stages of effects of hypoxia and organic enrichment suggested by the P-R model and on an earlier study. The proposed strategy involves rapid assessment tools and indicates where more detailed surveys are needed. Managers are advised that remedial action will not produce rapid results and that recovery from eutrophication will probably take decades. Thus it is essential to detect potential hypoxia and eutrophication effects at early stages of development.
Euxinic ocean conditions accompanied significant events in Earth history, including several Phanerozoic biotic crises. By critically ex-amining modern and ancient euxinic environments and the range of hypotheses for these sulfidic episodes, we elucidate the primary factors that influenced the generation of euxinia. We conclude that periods of global warmth promoted anoxia because of reduced sol-ubility of oxygen, not because of ocean stagnation. Anoxia led to phosphate release from sediments, and continental configurations with expansive nutrient-trapping regions focused nutrient recycling and increased regional nutrient buildup. This great nutrient supply would have fueled high biological productivity and oxygen demand, enhancing oxygen depletion and sulfide buildup via sulfate reduc-tion. As long as warm conditions prevailed, these positive feedbacks sustained euxinic conditions. In rare, extreme cases, euxinia led to biotic crises, a hypothesis best supported by evidence from the end-Permian mass extinction.
A study of the water-mass circulation of the Baltic has been undertaken by making use of a three dimensional Baltic Sea model simulation. The saline water from the North Atlantic is traced through the Danish Sounds into the Baltic where it upwells and mixes with the fresh water inflow from the rivers forming a Baltic haline conveyor belt. The mixing of the saline water from the Great Belt and Oresund with the fresh water is investigated making use of overturning stream functions and Lagrangian trajectories. The overturning stream function was calculated as a function of four different vertical coordinates (depth, salinity, temperature and density) in order to understand the path of the water and where it upwells and mixes. Evidence of a fictive depth overturning cell similar to the Deacon Cell in the Southern Ocean was found in the Baltic proper corresponding to the gyre circulation around Gotland, which vanishes when the overturning stream function is projected on density layers. A Lagrangian trajectory study was performed to obtain a better view of the circulation and mixing of the saline and fresh waters. The residence time of the water masses in the Baltic is calculated to be 26-29 years and the Lagrangian dispersion reaches basin saturation after 5 years.
Thallium (Tl) is a rare but widely dispersed element. All forms of thallium are soluble enough to be toxic to living organisms. Thallium is more toxic to humans than mercury, cadmium, lead, copper or zinc and has been responsible for many accidental, occupational, deliberate, and therapeutic poisonings since its discovery in 1861. Its chemical behavior resembles the heavy metals (lead, gold and silver) on the one hand and the alkali metals (K, Rb, Cs) on the other. It occurs almost exclusively in natural waters as monovalent thallous cation. The solubility of thallous compounds is relatively high so that monovalent thallium is readily transported through aqueous routes into the environment. Tl can be transferred from soils to crops readily and accrues in food crops. The fascinating chemistry and high toxicity potential make thallium and its compounds of particular scientific interest and environmental concern. Thallium was detected in base-metal mining effluents. The conventional removal of heavy metals from wastewater has little effect on thallium. In this review, various treatment options and removal technologies are enumerated in order to protect the environment from thallium toxicity.
The accumulation and tissue distribution of toxicants in aquatic biota can be determinative of their toxic impact to both the exposed organism, and their potential human consumers. In the current study the accumulation of the trace metal thallium (Tl) in gill, muscle, plasma and otoliths of rainbow trout (Oncorhynchus mykiss) following acute (96-h) and sub-chronic (28-d) waterborne exposures was investigated. Owing to known interactions between Tl and potassium ions (K+ ), plasma and muscle K+ concentrations were also determined. Branchial Tl accumulated in a dose-dependent manner in both acute and sub-chronic exposures, while plasma Tl was rapidly mobilized to tissues, and accumulated only at exposure concentrations of 141 µg L-1 or higher. For muscle tissue, Tl concentrations at 28-d were markedly lower than those at 96-h at comparable exposure concentrations (0.9 µg L-1 ), indicating the presence of mechanisms that act to reduce Tl accumulation over time. However, after acute exposure muscle Tl reached concentrations that, if consumed, would exceed acceptable daily intake values for this element, indicating some risk to human health from the consumption of fish from waters heavily contaminated with Tl. Otoliths showed Tl concentrations that reflected exposure concentration and length, confirming their capacity to provide insight into fish exposure history. No changes in tissue K+ concentrations were observed, suggesting that the accumulation of Tl in rainbow trout plasma and muscle does not occur at the expense of K+ homeostasis. In addition to highlighting the capacity of rainbow trout to accumulate Tl to levels that exceed recommended dietary doses to human consumers, this study provides the first data of tissue-specific Tl accumulation in an important regulatory species.
The thallium isotopic composition (ε²⁰⁵Tl) of seawater has been identified as a promising proxy for global oceanic redox conditions due to its close association with Mn oxide burial. Currently the preferred archives for past seawater Tl isotope reconstructions are from anoxic (no oxygen detected) and/or sulfidic (no oxygen detected and free sulfide present) environments that may suffer from basin restriction. Here we conduct a comprehensive modern calibration of authigenic sedimentary ε²⁰⁵Tl with core tops covering a wide range of bottom water oxygenation and sediment compositions. We show that quantitative Tl removal in the reducing porewaters (e.g., Mn reduction) at/near the sediment-water interface could allow the sediments to track the water column ε²⁰⁵Tl. Even if the bottom water is not anoxic, a shallow oxygen penetration depth under high export productivity and/or high sedimentation rates may still allow rapid oxygen consumption and buildup of reducing porewaters conducive for complete Tl removal. Thus, applications of the Tl isotope redox proxy can be greatly expanded beyond the anoxic conditions into places with open-ocean connections and high mass accumulation rates for high-resolution temporal reconstructions. We present a decision tree using the sediment enrichment factors of Mn, Ba, and U to determine whether sediment archives are likely to record the seawater ε²⁰⁵Tl. We additionally provide an estimate of authigenic Tl burial fluxes in environments with quantitative Tl removal, which is roughly double the size of the ‘euxinic/anoxic’ sink in previously published global marine Tl mass balance estimates.
Thallium andV isotopes in organic-rich sediments have recently been explored for reconstructing marine oxygenation by tracking the burial ofMn oxides either locally or globally. The ‘Fe and Mn shuttle’ is a well known mechanism that can transport elements associated with Fe and Mn oxide phases formed under mildly oxidizing shallow water environments both laterally and vertically to euxinic (sulfidic water column) deep waters. The Fe and Mn shuttle has been demonstrated to strongly affect Fe andMo isotope compositions of sediments accumulating beneath anoxic and euxinic settings. Similar to Mo, Tl and V are also enriched in oceanic ferromanganese crust and nodules, which impart the largest isotopic offsets from modern seawater for Tl and V. Thus, the mechanism of an Fe and Mn shuttle has the potential to, but currently unconstrained, affect Tl and V isotopic compositions (ε²⁰⁵Tl and δ ⁵¹V) in organic-rich sediments in the modern and ancient records.
We have used Black Sea sediments that are known to preserve enrichment and sedimentary isotope signatures for an Fe shuttle. This is due to an Fe transport from the more oxic margin to the deep euxinic basin and corresponding enrichment in the underlying sediments. These samples were used to test for a potential Fe and Mn shuttle effect on ε ²⁰⁵Tl and δ ⁵¹V in sediments deposited under oxic, suboxic, and euxinic water columns. Authigenic ε ²⁰⁵Tl from all three depositional settings is indistinguishable (–2.7 ± 0.3, –2.4 ± 0.5, and –2.4 ± 0.3), which is within error of the Black Sea surface seawater (–2.2 ± 0.3). In contrast, oxic and suboxic sediment have similar δ ⁵¹V values (–1.06 ± 0.33 ‰ and –1.04 ± 0.30 ‰), which are significantly more negative than euxinic sediments (–0.57 ± 0.06 ‰).
All the sediments deposited under oxic, suboxic, and euxinic water columns in the Black Sea capture ε ²⁰⁵Tl of the surface seawater because there is almost no permanent burial of Mn oxides in this basin. This finding is consistent with the indistinguishable ε ²⁰⁵Tl between the surface seawater and the riverine input. Sedimentary δ ⁵¹V appears to be controlled predominantly by the redox state of the depositional environments with little effect from an Fe or Mn shuttle. The lack of Fe and Mn shuttle effect on ε ²⁰⁵Tl and δ ⁵¹V in the Black Sea is likely due to the shallow (∼100 m) chemocline in the strongly, 2000-m deep redox-stratified water column of this basin and very slow deep-water renewal rate. Iron and Mn in oxides are not delivered to the sediments, instead, they are dissolved and captured in the water column as iron sulfide and reduced Mn mineral phases. Our results suggest that Fe and Mn shuttle transport mechanisms may not strongly affect Tl and V isotopes, at least in extreme cases of water column redox stratification. Further work is required to constrain the isotopic signals using other modern and, by inference, diverse ancient settings for additional shuttling mechanisms.
The deep basins of the Baltic Sea experienced dramatic climate- and eutrophication-induced redox changes between oxic and euxinic water column conditions. Irregularly appearing Major Baltic Inflows (MBI) carrying North Sea waters to the Baltic Sea are partly able to oxygenate euxinic bottom waters within several weeks. After an absence of ∼10 years, an exceptional strong inflow event in December 2014 reached the Gotland Basin in early March 2015 providing the opportunity of detailed studies on the impact of fast redox shifts on elemental cycles. Here we report on P and trace metal (Co, Mo, U, V and W) dynamics in the water column, pore water, and sediment of the central Gotland Basin over a 4.5 year-long observation period. These time series record the entire redox development including the primary MBI-related oxygenation, the transitional development to anoxia before a second inflow pulse, and the final re-establishment of euxinia. Samples obtained in August 2012 represent the previous euxinic stagnation period not affected by MBI's since nearly a decade. Concentration measurements and a budget calculation suggest only a limited impact of the MBI on the water column P inventory and the corresponding eutrophication level of the Gotland Basin. This is due to insufficient Fe availability preventing efficient trapping of phosphate during water column oxygenation. In addition, the fast recovery of reducing conditions allowed only a short-term storage of deposited Mn–Fe–P mineral phases in the surface sediment. Due to pronounced scavenging by Mn oxides, substantial water column depletion occurred intermittently for V and W, but again, re-establishing reducing conditions favored Mn oxide dissolution and the release especially of W back into the water column. Mo and U were less affected by Mn and Fe shuttling and Mo even showed an increasing water column inventory due to replenishment by intruding North Sea waters. In contrast, the water column inventory of Co remained on an approx. 50% level about 4.5 years after the inflow suggesting a significant sedimentary burial of Co within the course of the inflow event. Although sedimentary Mn carbonate layers, which were commonly formed in concert with the frequent inflows between ∼1960 and 1980, were missing or only weakly developed after the single inflow events in 1994, 2003, and 2014, dated short cores from the study area reveal clear Co and less pronounced V enrichments during the latter inflows. Because Mo, U and W are synchronously depleted compared with their normal sapropel levels, the combination of these trace metals and Co may help to identify past MBIs not reflected by Mn carbonate presence.
Pore water data of thallium (Tl) in marine environments are scarce. It has been suggested that anoxic sediments are a sink for dissolved Tl likely due to its incorporation into Fe sulfides. However, recent studies indicated that Tl is removed from solution prior to the onset of sulfidic conditions and that Tl is involved in biological cycles in coastal seawater. To assess the Tl behavior in marine sediments, pore waters of a high energy beach (Spiekeroog Island, Germany) were sampled during different seasons and on different spatial scales. The study site provides a perfect set of samples to assess trace metal behavior under various redox conditions.
Samples were analyzed for dissolved trace metals Tl, molybdenum (Mo), uranium (U), and rhenium (Re). Additionally, sediments were incubated to monitor trace metal removal or release under controlled conditions. On-site redox conditions were characterized using dissolved oxygen (O2), manganese (Mn), and iron (Fe) concentrations.
Our results indicated high enrichments of Tl in pore waters concurrently to aerobic organic matter (OM) degradation, exceeding seawater concentrations up to 6-fold. In contrast, Tl was completely removed in weakly reducing pore water characterized by more than 1 µM Mn or Fe. The spatial Tl distribution in intertidal pore waters responded to the present dissolved Mn and Fe level, which varied in space and with season. We suggest, Tl release to be attributed to OM degradation, particle desorption, or reoxidation, whereas Tl removal is likely related to the presence of traces amounts of dissolved sulfide.
In conclusion, the fast reaction kinetics of Tl led to fast and complete removal in comparison to Mo, U, and Re and we suggest the following order of removal: Tl>Re>U>Mo. The removal behavior as well as the high enrichments of Tl in pore waters implicate that sinks and sources in the marine environment are not yet fully understood. Although the intertidal sediments form an overall sink for Tl (U and Re), especially under mostly anoxic conditions in summer, sediments turn into a Tl net source in winter, when sediments are more oxic.
For global marine Tl balances, Tl fluxes have been estimated based on pore water Tl/Mn ratios. Contrastingly, Tl removal from pore waters at low threshold concentrations of Mn at our site indicates that these Tl flux estimations may not be applicable in permeable sandy beach sediments and in many other types of sediments, which host mildly sulfidic conditions.
Ediacaran sediments record an unusual global carbon cycle perturbation that has been linked to widespread oceanic oxygenation, the Shuram negative C isotope excursion (NCIE). However, proxy‐based estimates of global ocean redox conditions during this event have been limited largely due to proxy specificity (e.g., euxinic sediments for Mo and U isotopes). Modern global seawater documents a homogenous Tl isotope composition (ε205Tl = −6.0) due to significant manganese oxide burial, which is recorded in modern euxinic sediments. Here, we provide new data documenting that sediments deposited beneath reducing but a non‐sulfidic water column from the Santa Barbara Basin (ε205Tl = −5.6 ± 0.1) also faithfully capture global seawater Tl isotope values. Thus, the proxy utilization of Tl isotopes can extend beyond strictly euxinic settings. Second, to better constrain the global redox conditions during the Shuram NCIE, we measured Tl isotopes of locally euxinic and ferruginous shales of the upper Doushantuo Formation, South China. The ε205Tl values of these shales exhibit a decreasing trend from ≈−3 to ≈−8, broadly coinciding with the onset of Shuram NCIE. There are ε205Tl values (−5.1 to −7.8) during the main Shuram NCIE interval that approach values more negative than modern global seawater. These results suggest that manganese oxide burial was near or even greater than modern burial fluxes, which is likely linked to an expansion of oxic conditions. This ocean oxygenation may have been an important trigger for the Shuram NCIE and evolution of Ediacaran‐type biota. Subsequently, Tl isotopes show an increasing trend from the modern ocean value to values near the modern global inputs or even heavier (ε205Tl ≈ −2.5 ~ 0.4), occurring prior to recovery from the NCIE. These records may suggest that there was a decrease in the extent of oxygenated conditions in the global oceans during the late stage of the Shuram NCIE.
Thallium (Tl) is typical rare element with severe toxicity comparable to Hg and Pb. To track Tl pollution, isotopic fractionation of Tl was evaluated during pyrite smelting for sulfuric acid production. Large variations in Tl isotope compositions were observed among the pyrite ore (PO) and its four different smelting wastes. The starting raw PO had an ε205Tl value of +1.28. The fluidized-bed furnace slag generated by high-temperature smelting had the heaviest ε205Tl (+16.24) in the system. Meanwhile, the boiler fly ash (ε205Tl = +8.34), cyclone fly ash (ε205Tl = +2.17), and electrostatic precipitation fly ash (ε205Tl = -1.10), with decreasing grain sizes during the treatment processes, were characterized by elevated levels of Tl contents and substantial enrichment in the light Tl isotopes relative to the furnace slag. Further calculation and high-resolution transmission electron microscopy indicated that Tl isotope fractionation could be governed by both Rayleigh-type fractionation and adsorption of volatilized Tl by particles of various grain sizes. According to the substantial differences in the PO from its smelting wastes and the measurement precision of isotopic fractionation, it is suggested that Tl isotopes can serve as a new tool for tracing pollution of Tl.
Redox-sensitive trace metals are powerful tools for the reconstruction of modern and past redox conditions in aquatic ecosystems. The most prominent example is molybdenum (Mo), which behaves conservatively as soluble molybdate in the oxygenated ocean, but forms particle-reactive thiomolybdates at sufficiently high sulfide concentrations. Previous studies proposed that the redox behavior of tungsten (W), the geochemical twin of Mo, is also affected by sulfide, suggesting its potential as a promising new redox proxy. Here we present a comprehensive W dataset from the highly sulfidic Black Sea and the weakly sulfidic Landsort Deep (Baltic Sea), as the type localities of modern euxinic basins, that combines water column, pore water, and sediment records. A dataset from the Gotland Basin obtained following oxygenation of the formerly euxinic water column during the major Baltic inflow in 2014 is used as the hypoxic example. The even stronger adsorption of W than Mo on Mn and Fe oxides at pelagic redoxclines identified these particles as important carrier transferring W from the oxygenated surface ocean to euxinic bottom waters. This shuttling was most pronounced during the inflow event in the Gotland Basin causing substantial deposition of Mn oxides that were highly enriched in W. Compared to the oxygenated surface waters, dissolved Mo was severely depleted in the highly sulfidic water column of the Black Sea, whereas the bottom water levels of dissolved W were elevated. An additional W source derived from pore-water reflux, as indicated by the exceptionally high concentrations of W in highly sulfidic pore waters from the Landsort Deep sediments. In addition to the decoupling from Mn, the pore water W enrichments are compatible with the previously proposed greater solubility of thiotungsate species than of tungstate. Despite the absence of a substantial sedimentary accumulation of authigenic W in the sapropels of the Black Sea, the comparable patterns of S, Fe, and W in an Eemian record may suggest sorption of internally cycled (thio)tungstate onto pyrite. Unexpected W enrichments in modern and medieval sediments from the central Landsort Deep indicate a close relationship with Mn carbonate formation occurring during long-lasting bottom water hypoxia. In contrast to the highly variable Mo content, the near-background variation of W in the sapropels of euxinic basins questions the utility of W as a redox proxy in euxinic systems. However, given the strong affinity between W and the Mn/Fe cycle, this element may be a useful proxy in hypoxic systems, especially its isotopic signature.
The Black Sea is the world’s largest anoxic basin and a model system for studying processes across redox gradients. In between the oxic surface and the deeper sulfidic waters there is an unusually broad layer of 10–40 m, where neither oxygen nor sulfide are detectable. In this suboxic zone, dissolved phosphate profiles display a pronounced minimum at the upper and a maximum at the lower boundary, with a peak of particulate phosphorus in between, which was suggested to be caused by the sorption of phosphate on sinking particles of metal oxides. Here we show that bacterial polyphosphate inclusions within large magnetotactic bacteria related to the genus Magnetococcus contribute substantially to the observed phosphorus peak, as they contain 26–34% phosphorus compared to only 1–5% in metal-rich particles. Furthermore, we found increased gene expression for polyphosphate kinases by several groups of bacteria including Magnetococcaceae at the phosphate maximum, indicating active bacterial polyphosphate degradation. We propose that large magnetotactic bacteria shuttle up and down within the suboxic zone, scavenging phosphate at the upper and releasing it at the lower boundary. In contrast to a passive transport via metal oxides, this bacterial transport can quantitatively explain the observed phosphate profiles.
An accurate and complete emission inventory for atmospheric trace metals on a global scale is needed for both modeler community and policy makers to assess the current level of environmental contamination by these pollutants, major emission sources and source regions, and the contribution of the atmospheric pathway to the contamination of terrestrial and aquatic environments. Major progress has been made in assessing emissions of trace metals in various countries and even regions, e.g., Europe, since the first global emission estimate for these pollutants was made by Nriagu and Pacyna (1988). These improved national and regional emission inventories have been used in this work to assess the global trace metal emissions from anthropogenic sources in the mid-1990s. The results of this work conclude that stationary fossil fuel combustion continues to be the major source of Cr, Hg, Mn, Sb, Se, Sn, and Tl with respect to the coal combustion and the major source of Ni and V with respect to oil combustion. Combustion of leaded, low-leaded, and unleaded gasoline continues to be the major source of atmospheric Pb emissions. The third major source of trace metals is non-ferrous metal production, which is the largest source of atmospheric As, Cd, Cu, In, and Zn. The largest anthropogenic emissions of atmospheric trace metals were estimated in Asia. This can be explained by growing demands for energy in the region and increasing industrial production. As a result, the Asian emissions are not only larger than the emissions on other continents, but also show an increasing trend. Another factor contributing to high emissions in Asia is the efficiency of emission control, which is lower than in Europe and North America. Concerning the two latter continents, emissions of trace metals show a decreasing tendency over the last two decades.
In open ocean waters thallium (Tl) belongs to the group of conservative elements, even though deviations from this trend have been observed in NW German coastal waters. Here, we report on tidal, seasonal and spatial dynamics of Tl along with Mo and Mn in the water column of a backbarrier tidal flat close to the island of Spiekeroog, the Jade system (Inner Jade and Jade Bay) and the adjacent offshore region. Dissolved thallium (Tldiss) displays strong tidal and seasonal variations (∼25–60 pM) unrelated to salinity. In all study areas, Tldiss clearly deviates from conservative behavior. In general, Tldiss is low during low tide (with a loss of up to 50%) and inversely related to Mndiss, except in summer. The tidal Tl variations as well as the loss of Tl in the water column may be due to Tl removal from pore waters in reducing sediments and drainage of Tl-free but Mn-rich pore waters into the water column during low tide. The negative Tl anomaly can be traced offshore for more than 40 km to the island of Helgoland.
The redox chemistry of Tl is not well studied, and Tl removal from pore waters was previously suggested to only occur under anoxic/sulfidic conditions. By contrast, our preliminary pore water results suggest that Tl could be removed already under slightly reducing (suboxic) conditions, likely along with microbially induced Mn reduction in the sediments. Therefore, this study supports the biological involvement in the aqueous cycling of Tl. We propose the use of Tldiss next to Mndiss as valuable indicator of suboxic or anoxic pore water discharge to the coastal realm.
Thallium (Tl) isotopes are a new and potentially powerful paleoredox proxy that may track bottom water oxygen conditions based on the global burial flux of manganese oxides. Thallium has a residence time of ∼20 thousand years, which is longer than the ocean mixing time, and it has been inferred that modern oxic seawater is conservative with respect to both concentration and isotopes. Marine sources of Tl have nearly identical isotopic values; therefore, the Tl sinks, adsorption onto manganese oxides and low temperature oceanic crust alteration (the dominant seawater output) are the primary controls of the seawater isotopic composition. For relatively short-term, ∼million years, redox events it is reasonable to assume that the dominant mechanism that alters the Tl isotopic composition of seawater is associated with manganese oxide burial because large variability in low temperature ocean crust alteration is controlled by long-term, multi-million years, average ocean crust production rates.
Thallium is a non essential and highly toxic metal listed by USEPA and the European Water Framework Directive as a priority pollutant. It is present in the environment mainly as Tl(I) and Tl(III) usually at very low concentrations, which makes it a challenging element requiring high sensitive instrumental techniques to measure it in complex matrices. The average concentration of thallium in the Earth's crust is generally below 1 ppm and its geochemical behaviour and mobility is often compared to that of potassium. In non-contaminated freshwater, the thallium concentration is generally below 1 μg/L and rarely exceeds 20 ng/L in the open ocean. The affinity of thallium for iron and manganese oxyhydroxides is often observed in soil and sediment where its concentrations normally remain in the low ppm except for mine and contaminated areas. Thallium is present at low ng/m³ in aerosols and air particulates but can increase to higher levels in highly urbanized areas and in mining and industrialized zones. For this review, more than 285 papers containing information of thallium in natural waters, soils, sediments and air particulates have been consulted but only a low number of them present information on the speciation of the metal.
Here, for the first time, we report the thallium (Tl) isotope record in moderately contaminated soils with contrasting land management (forest and meadow soils), which have been historically affected by emissions from coal-fired power plants. Our findings clearly demonstrate that Tl of anthropogenic (high-temperature) origin with light isotope composition was deposited onto the studied soils, where heavier Tl (205Tl ~ 1) naturally occurs. The results show a positive linear relationship (R2 = 0.71) between 1/Tl and the isotope record, as determined for all the soils and bedrocks, also indicative of binary Tl mixing between two dominant reservoirs. We also identified significant Tl isotope variations within the products from coal combustion and thermo-desorption experiments with local Tl-rich coal pyrite. Bottom ash exhibited the heaviest Tl isotope composition (205Tl ~0), followed by fly ash (205Tl between 2.5 and 2.8) and volatile Tl fractions (205Tl between 6.2 and 10.3), suggesting partial Tl isotope fractionations. Despite the evident role of soil processes in the isotope redistributions, we demonstrate that Tl contamination can be traced in soils, and propose that the isotope data represent a possible tool to aid our understanding of post-depositional Tl dynamics in surface environments for the future.
Thallium stable isotope data are used in this study, for the first time, to apportion Tl contamination in soils. In the late 1970's, a cement plant near Lengerich, Germany, emitted cement kiln dust (CKD) with high Tl contents, due to co-combustion of Tl-enriched pyrite roasting waste. Locally contaminated soil profiles were obtained down to 1 m depth and the samples are in accord with a binary mixing relationship in a diagram of Tl isotope compositions (expressed as ε(205)Tl, the deviation of the (205)Tl/(203)Tl ratio of a sample from the NIST SRM 997 Tl isotope standard in parts per 10(4)) versus 1/[Tl]. The inferred mixing endmembers are the geogenic background, as defined by isotopically light soils at depth (ε(205)Tl ≈ -4), and the Tl emissions, which produce Tl-enriched topsoils with ε(205)Tl as high as ±0. The latter interpretation is supported by analyses of the CKD, which is also characterized by ε(205)Tl ≈ ±0, and the same ε(205)Tl value was found for a pyrite from the deposit that produced the co-combusted pyrite roasting waste. Additional measurements for samples from a locality in China, with outcrops of Tl sulphide mineralization and associated high natural Tl backgrounds, reveal significant isotope fractionation between soils (ε(205)Tl ≈ +0.4) and locally grown green cabbage (ε(205)Tl between -2.5 and -5.4). This demonstrates that biological isotope fractionation cannot explain the isotopically heavy Tl in the Lengerich topsoils and the latter are therefore clearly due to anthropogenic Tl emissions from cement processing. Our results thus establish that isotopic data can reinforce receptor modelling for the toxic trace metal Tl.
The ecotoxicological importance of thallium stems from its acute toxicity, the effects of which are as harmful to living organisms as those of lead and mercury. The main anthropogenic sources of thallium are the emissions from coal combustion processes, underlining the need to control this element in coal and coal by-products. Despite the threat posed by thallium, very little information has been published on its behaviour in coal-fired power plants or on its modes of occurrence in coal, its mobilisation and its distribution. Although thallium is highly toxic, the environmental risk presented by this element in coal utilisation have been studied to a much lesser degree than in the case of other toxic elements such as lead, cadmium or mercury. The present work addresses the issue of thallium in coal, focussing on its origin, modes of occurrence, the analytical methods commonly used for its determination and its behaviour during coal utilisation for energy production.
This paper presents the first study of Tl isotopes in early diagenetic pyrite. Measurements from two sections deposited during the Toarcian Ocean Anoxic Event (T-OAE, ∼183 Ma) are compared with data from Late Neogene (<10 Ma) pyrite samples from ODP legs 165 and 167 that were deposited in relatively oxic marine environments. The Tl isotope compositions of Late Neogene pyrites are all significantly heavier than seawater, which most likely indicates that Tl in diagenetic pyrite is partially sourced from ferromanganese oxy-hydroxides that are known to display relatively heavy Tl isotope signatures. One of the T-OAE sections from Peniche in Portugal displays pyrite thallium isotope compositions indistinguishable from Late Neogene samples, whereas samples from Yorkshire in the UK are depleted in the heavy isotope of Tl. These lighter compositions are best explained by the lack of ferromanganese precipitation at the sediment–water interface due to the sulfidic (euxinic) conditions thought to be prevalent in the Cleveland Basin where the Yorkshire section was deposited. The heavier signatures in the Peniche samples appear to result from an oxic water column that enabled precipitation of ferromanganese oxy-hydroxides at the sediment–water interface.
The trace elements (As, B, Ba, Be, Bi, Cd, Co, Cr, Cs, Cu, Ga, Ge, Hg, Li, Mn, Mo, Ni, Pb, Rb, Sb, Se, Sn, Sr, Ta, Th, Tl, U, V, W, Y, Zn, Zr and REE) in a subbituminous coal and their behaviour during combustion in a large power station were characterized by their content and distribution in the fuel (organic and/or inorganic affinities) and in the combustion wastes (partition and volatility). Samples were fractionated by density and magnetic separations and cascade impactors. Quantitative analyses were performed by X-ray diffraction, ICP-MS, ICP-AES, AAS and ICP-AES with hydride generation. Among the findings is the important role of anhydrite (CaSO4) in the sorption of trace elements such as As, B, Ge, Se, Pb, Mo, Zn and Tl from flue gas and in the reduction of emissions of these potentially toxic elements. Calcium oxide has a high sorption capacity for some of the elements studied. This sorption phenomenon and the condensation, mainly as fine fly ash particles, of important fractions of the trace elements during the cooling of flue gas significantly reduce the gaseous emissions of potentially toxic trace elements from coal combustion in the power station studied.
Saline water from the North Sea, which is able to enter the deep water of the central parts of the Baltic Sea, must unavoidably pass two shallow sill areas: the Darss Sill in the Belt Sea area and the Drogden Sill in the Sound. Both sills restrict considerably the inflow of highly saline and oxygen-rich water known as major Baltic inflows. Long-term observations of salinity and current made at light vessels Gedser Rev and Drogden in the sill areas are used to evaluate the role of the Drogden Sill in major inflow of events. The different contributions of the two passages are documented on the basis of 90 events that took place between 1897 and 1976.Based on the volume and salt transports across the two sills the intensity of major inflows is re-assessed. The significance of each sill varies considerably from event to event. The volume crossing the Drogden Sill during major events is, on average, one third of that crossing the Darss Sill and usually far more salt enters the Baltic across the latter. However, in some cases, the amounts of salt transported across the sills are equal (e.g. January 1993) or the amount crossing the Drogden Sill is even the larger fraction (e.g. January 1925, January 1908).The re-assessed intensity of the 1993 event showed that the inflow in January 1993 must be characterized as very strong owing to the considerable salt transport across the Drogden Sill.
The precision of Tl isotopic measurements by thermal ionization mass spectrometry (TIMS) is severely limited by the fact that Tl possesses only two naturally occurring isotopes, such that there is no invariant isotope ratio that can be used to correct for instrumental mass discrimination. In this paper we describe new chemical and mass spectrometric techniques for the determination of Tl isotopic compositions at a level of precision hitherto unattained. Thallium is first separated from the geological matrix using a two-stage anion-exchange procedure. Thallium isotopic compositions are then determined by multiple-collector inductively coupled plasma-mass spectrometry with correction for mass discrimination using the known isotopic composition of Pb that is admixed to the sample solutions. With these procedures we achieve a precision of 0.01–0.02% for Tl isotope ratio measurements in geological samples and this is a factor of ≥3–4 better than the best published results by TIMS. However, without adequate precautions, experimental artifacts can be generated that result in apparent Tl isotopic fractionations of up to one per mil.
Manganese and iron reduction in marine sediments are known to play important roles in the biogeochemical cycles of many elements, including carbon, sulfur, phosphorus and several trace elements. These reduction reactions affect these cycles on a variety of time scales, ranging from those as short as seasonal time scales (e.g., nutrient cycling in coastal ecosystems), to those as long as thousands to tens of thousands of years (e.g., glacial—interglacial transformations in deep sea sediments). In this review article I will briefly summarize the results of laboratory studies on the types of manganese and iron reduction that are known to occur in marine sediments, and then discuss the occurrence of these processes in different sedimentary environments. Particular efforts will be given to examining the rates and mechanisms of sedimentary manganese and iron reduction in relationship to other biogeochemical processes in sediments.
The need to understand local effects of global climate change is most urgent in the Large Marine Ecosystems (LMEs) since marine ecosystem-based management requires information on the LME scale. Reported here is a study of sea surface temperature (SST) change in the World Ocean LMEs in 1957–2006 that revealed strong regional variations in the rate of SST change. The rapid warming in 1982–2006 was confined to the Subarctic Gyre, European Seas, and East Asian Seas. These LMEs warmed at rates 2–4 times the global mean rate. The most rapid warming was observed in the land-locked or semi-enclosed European and East Asian Seas (Baltic Sea, North Sea, Black Sea, Japan Sea/East Sea, and East China Sea) and also over the Newfoundland–Labrador Shelf. The Indian Ocean LMEs’ warming was slow, while two major upwelling areas – California and Humboldt Currents – experienced a slight cooling. The Subarctic Gyre warming was likely caused by natural variability related to the North Atlantic Oscillation. The extremely rapid surface warming in the enclosed and semi-enclosed European and East Asian Seas surrounded by major industrial/population agglomerations may have resulted from the observed terrestrial warming directly affecting the adjacent coastal seas. Regions of freshwater influence in the European and East Asian Seas seem to play a special role in modulating and exacerbating global warming effects on the regional scale.
The thallium (Tl) concentrations and isotope compositions of various river and estuarine waters, suspended riverine particulates and loess have been determined. These data are used to evaluate whether weathering reactions are associated with significant Tl isotope fractionation and to estimate the average Tl isotope composition of the upper continental crust as well as the mean Tl concentration and isotope composition of river water. Such parameters provide key constraints on the dissolved Tl fluxes to the oceans from rivers and mineral aerosols.The Tl isotope data for loess and suspended riverine detritus are relatively uniform with a mean of ε205Tl = −2.0 ± 0.3 (ε205Tl represents the deviation of the 205Tl/203Tl isotope ratio of a sample from NIST SRM 997 Tl in parts per 104). For waters from four major and eight smaller rivers, the majority were found to have Tl concentrations between 1 and 7 ng/kg. Most have Tl isotope compositions very similar (within ±1.5 ε205Tl) to that deduced for the upper continental crust, which indicates that no significant Tl isotope fractionation occurs during weathering. Based on these results, it is estimated that rivers have a mean natural Tl concentration and isotope composition of 6 ± 4 ng/kg and ε205Tl = −2.5 ± 1.0, respectively.In the Amazon estuary, both additions and losses of Tl were observed, and these correlate with variations in Fe and Mn contents. The changes in Tl concentrations have much lower amplitudes, however, and are not associated with significant Tl isotope effects. In the Kalix estuary, the Tl concentrations and isotope compositions can be explained by two-component mixing between river water and a high-salinity end member that is enriched in Tl relative to seawater. These results indicate that Tl can display variable behavior in estuarine systems but large additions and losses of Tl were not observed in the present study.
Hydrothermal fluids expelled from the seafloor at high and low temperatures play pivotal roles in controlling seawater chemistry. However, the magnitude of the high temperature water flux of mid-ocean ridge axes remains widely disputed and the volume of low temperature vent fluids at ridge flanks is virtually unconstrained. Here, we determine both high and low temperature hydrothermal fluid fluxes using the chemical and isotopic mass balance of the element thallium (Tl) in the ocean crust. Thallium is a unique tracer of ocean floor hydrothermal exchange because of its contrasting behavior during seafloor alteration at low and high temperatures and the distinctive isotopic signatures of fresh and altered MORB and seawater.The calculated high temperature hydrothermal water flux is (0.17–2.93) × 1013 kg/yr with a best estimate of 0.72 × 1013 kg/yr. This result suggests that only about 5 to 80% of the heat available at mid-ocean ridge axes from the crystallization and cooling of the freshly formed ocean crust, is released by high temperature black smoker fluids. The residual thermal energy is most likely lost via conduction and/or through the circulation of intermediate temperature hydrothermal fluids that do not alter the chemical budgets of Tl in the ocean crust.The Tl-based calculations indicate that the low temperature hydrothermal water flux at ridge flanks is (0.2–5.4) × 1017 kg/yr. This implies that the fluids have an average temperature anomaly of only about 0.1 to 3.6 °C relative to ambient seawater. If these low temperatures are correct then both Sr and Mg are expected to be relatively unreactive in ridge-flank hydrothermal systems and this may explain why the extent of basalt alteration that is observed for altered ocean crust appears insufficient to balance the oceanic budgets of 87Sr/86Sr and Mg.
We present optimised analytical protocols for the precise and accurate determination of Tl concentrations and isotope compositions (IC) for water samples by multiple collector inductively coupled plasma mass spectrometry (MC-ICPMS). The Tl abundance measurements utilise the isotope dilution (ID) technique. About 50 ml of seawater or river water, with ∼150 to 500 pg of Tl, are spiked with a ²⁰³Tl tracer and thallium is then separated from the sample matrix using a single anion-exchange column. The isotope compositions of spiked samples are measured by MC-ICPMS using either admixed Pb or Pt for mass bias correction. Replicate analyses of three natural water samples with Tl contents of 3 to 10 pg/g displayed external reproducibilities (1 S.D.) of 0.2% to 1.5%.
Results are presented for the first in-depth investigation of Tl isotope variations in marine materials. The Tl isotopic measurements were conducted by multiple collector-inductively coupled plasma mass spectrometry for a comprehensive suite of hydrogenetic ferromanganese crusts, diagenetic Fe–Mn nodules, hydrothermal manganese deposits and seawater samples. The natural variability of Tl isotope compositions in these samples exceeds the analytical reproducibility (±0.05‰) by more than a factor of 40. Hydrogenetic Fe–Mn crusts have ϵ205Tl of +10 to +14, whereas seawater is characterized by values as low as −8 (ϵ205Tl represents the deviation of the 205Tl/203Tl ratio of a sample from the NIST SRM 997 Tl isotope standard in parts per 104). This ∼2‰ difference in isotope composition is thought to result from the isotope fractionation that accompanies the adsorption of Tl onto ferromanganese particles. An equilibrium fractionation factor of α∼1.0021 is calculated for this process. Ferromanganese nodules and hydrothermal manganese deposits have variable Tl isotope compositions that range between the values obtained for seawater and hydrogenetic Fe–Mn crusts. The variability in ϵ205Tl in diagenetic nodules appears to be caused by the adsorption of Tl from pore fluids, which act as a closed-system reservoir with a Tl isotope composition that is inferred to be similar to seawater. Nodules with ϵ205Tl values similar to seawater are found if the scavenging of Tl is nearly quantitative. Hydrothermal manganese deposits display a positive correlation between ϵ205Tl and Mn/Fe. This trend is thought to be due to the derivation of Tl from distinct hydrothermal sources. Deposits with low Mn/Fe ratios and low ϵ205Tl are produced by the adsorption of Tl from fluids that are sampled close to hydrothermal sources. Such fluids have low Mn/Fe ratios and relatively high temperatures, such that only minor isotope fractionation occurs during adsorption. Hydrothermal manganese deposits with high Mn/Fe and high ϵ205Tl are generated by scavenging of Tl from colder, more distal hydrothermal fluids. Under such conditions, adsorption is associated with significant isotope fractionation, and this produces deposits with higher ϵ205Tl values coupled with high Mn/Fe.
Hypoxia, a growing worldwide problem, has been intermittently present in the modern Baltic Sea since its formation ca. 8000 cal. yr BP. However, both the spatial extent and intensity of hypoxia have increased with anthropogenic eutrophication due to nutrient inputs. Physical processes, which control stratification and the renewal of oxygen in bottom waters, are important constraints on the formation and maintenance of hypoxia. Climate controlled inflows of saline water from the North Sea through the Danish Straits is a critical controlling factor governing the spatial extent and duration of hypoxia. Hypoxia regulates the biogeochemical cycles of both phosphorus (P) and nitrogen (N) in the water column and sediments. Significant amounts of P are currently released from sediments, an order of magnitude larger than anthropogenic inputs. The Baltic Sea is unique for coastal marine ecosystems experiencing N losses in hypoxic waters below the halocline. Although benthic communities in the Baltic Sea are naturally constrained by salinity gradients, hypoxia has resulted in habitat loss over vast areas and the elimination of benthic fauna, and has severely disrupted benthic food webs. Nutrient load reductions are needed to reduce the extent, severity, and effects of hypoxia.
Toxicity and pollution potential of thallium are reviewed. Thallium is slightly more acutely toxic to mammals than mercury, and as acutely toxic as copper to fish. Its present industrial uses are too limited to generate pollution, but thallium, discharged in wastes from mines, ore-processing, and coal-burning plants, is contaminating the environment.
Thallium (T1+) is a toxic heavy metal which was accidentally discovered by Sir William Crookes in 1861 by burning the dust from a sulfuric acid industrial plant. He observed a bright green spectral band that quickly disappeared. Crookes named the new element 'Thallium' (after thallos meaning young shoot). In 1862, Lamy described the same spectral line and studied both the physical and chemical properties of this new element (Prick, J.J.G., 1979. Thallium poisoning. In: Vinkrn, P.J., Bruyn, G.W. (Eds.), Intoxication of the Nervous System, Handbook of Clinical Neurology, vol. 36. North-Holland, New York. pp. 239-278).
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