M. Bigler

University of Copenhagen, København, Capital Region, Denmark

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Publications (94)410.49 Total impact

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    ABSTRACT: Phosphorus (P) is an essential macronutrient for all living organisms. Phosphorus is often present in nature as the soluble phosphate ion PO4(3-) and has biological, terrestrial, and marine emission sources. Thus PO4(3-) detected in ice cores has the potential to be an important tracer for biological activity in the past. In this study a continuous and highly sensitive absorption method for detection of dissolved reactive phosphorus (DRP) in ice cores has been developed using a molybdate reagent and a 2-m liquid waveguide capillary cell (LWCC). DRP is the soluble form of the nutrient phosphorus, which reacts with molybdate. The method was optimized to meet the low concentrations of DRP in Greenland ice, with a depth resolution of approximately 2 cm and an analytical uncertainty of 1.1 nM (0.1 ppb) PO4(3-). The method has been applied to segments of a shallow firn core from Northeast Greenland, indicating a mean concentration level of 2.74 nM (0.26 ppb) PO4(3-) for the period 1930-2005 with a standard deviation of 1.37 nM (0.13 ppb) PO4(3-) and values reaching as high as 10.52 nM (1 ppb) PO4(3-). Similar levels were detected for the period 1771-1823. Based on impurity abundances, dust and biogenic particles were found to be the most likely sources of DRP deposited in Northeast Greenland.
    Environmental Science & Technology 10/2013; · 5.26 Impact Factor
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    ABSTRACT: The important active and passive role of mineral dust aerosol in the climate and the global carbon cycle over the last glacial/interglacial cycles has been recognized. However, little data on the most important aeolian dust-derived biological micronutrient, iron (Fe), has so far been available from ice-cores from Greenland or Antarctica. Furthermore, Fe deposition reconstructions derived from the palaeoproxies particulate dust and calcium differ significantly from the Fe flux data available. The ability to measure high temporal resolution Fe data in polar ice-cores is crucial for the study of the timing and magnitude of relationships between geochemical events and biological responses in the open ocean. This work adapts an existing flow injection analysis (FIA) methodology for low-level trace Fe determinations with an existing glaciochemical analysis system, continuous flow analysis (CFA) of ice-cores. Fe-induced oxidation of N,N'-dimethyl-p-pheylenediamine (DPD) is used to quantify the biologically more important and easily leachable Fe fraction released in a controlled digestion step at pH ∼1.0. The developed method was successfully applied to the determination of labile Fe in ice-core samples collected from the Antarctic Byrd ice-core and the Greenland Ice-Core Project (GRIP) ice-core.
    Environmental Science & Technology 04/2013; · 5.26 Impact Factor
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    ABSTRACT: The last glacial period (110 - 15 ka) has been marked by millennial scale climate variations, the trigger of which is still under debate. Such variations have been recorded in marine, ice and continental records over most of the world, but especially in the Northern Hemisphere. We first investigate the high-resolution δ18O and dust records from Greenland ice, indicating important variations in the respective moisture and dust source areas. We show that the dust concentration decrease associated with the Dansgaard-Oeschger (DO) warming events 17 to 2 happened on average within about 50 years, and that δ18O reached peak DO interstadial values faster than dust, suggesting a lag in the continental response to the abrupt warming. The individual analyzed interstadial phases lasted between 200 and 4200 years. In European eolian sequences, the different duration of the interstadials is expressed by different types of paleosols observed along a west-east transect at 50° latitude North. Discussing the paleodust cycle variations during the last climate cycle, we propose a link between European loess sequences, Chinese ones, dust records in Greenland and the variations of the North Atlantic sea ice extent and surface temperature. Changes in the dust sources are discussed (present-day deserts, but also emerged continental shelves due to sea-level lowering, dried river beds, glaciogenic dust sources along the ice-sheet edges, areas exposed to eolian erosion due to a scarce vegetation in cold climate conditions), as well as in the transport pathways in the stadial versus interstadial phases.
    04/2013;
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    ABSTRACT: During the field season in summer 2009, the first 600 m (corresponding to 3 kyr b2k (3000 years before A.D. 2000) on the GICC05 timescale) of the Greenland NEEM ice core have been analysed for a variety of aerosol constituents using Continuous Flow Analysis (CFA). Here, the records of electric conductivity, sodium (Na+), calcium (Ca2+), particle numbers of insoluble dust, ammonium (NH4+), nitrate (NO3-) and hydrogen peroxide (H2O2) are presented with an average effective resolution of 1-2 cm, depending on the component. Since the annual layer thickness ? amounts to 15cm at minimum sub-annual signals are resolved in all components over the Holocene period. We achieved to extend the aerosol record over the early Holocene period except for a large gap over the brittle zone from 5-9 kyr b2k. Seasonal variations and extreme events are preserved in great detail and all components. H2O2 is a reliable proxy for the strength of photochemical processes in the lower atmosphere and thus shows its minima and maxima at the summer and winter solstice, respectively. Dust-derived species (insoluble dust, Ca2+) show peak concentrations in early spring and minima in mid-summer. The marine-derived Na+peaks in mid-winter and is lowest during early summer. The mean annual variability in concentrations is about 20 ppbw for both Ca2+andNa+. Moreover, it is of the same order of magnitude in NH4+, butconsiderably larger in NO3- (100 ppbw), both representing continental biogenic sources peaking in spring and showing minima in autumn. The interpretation itsclimatic signal is restricted by NO3- undergoing post-depositional redistribution processes. Not only is the analysis of impurities in sub-annual resolution crucial for the accurate dating of the ice core, but also for establishing a detailed chronology of the occurrence of extreme events such as volcanic eruptions and wildfires. Furthermore, possible changes in the seasonal variability of aerosol concentrations can be investigated. First results are presented here.
    04/2013;
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    ABSTRACT: Efforts to extract a Greenland ice core with a complete record of the Eemian interglacial (130,000 to 115,000 years ago) have until now been unsuccessful. The response of the Greenland ice sheet to the warmer-than-present climate of the Eemian has thus remained unclear. Here we present the new North Greenland Eemian Ice Drilling (‘NEEM’) ice core and show only a modest ice-sheet response to the strong warming in the early Eemian. We reconstructed the Eemian record from folded ice using globally homogeneous parameters known from dated Greenland and Antarctic ice-core records. On the basis of water stable isotopes, NEEM surface temperatures after the onset of the Eemian (126,000 years ago) peaked at 8 ± 4 degrees Celsius above the mean of the past millennium, followed by a gradual cooling that was probably driven by the decreasing summer insolation. Between 128,000 and 122,000 years ago, the thickness of the northwest Greenland ice sheet decreased by 400 ± 250 metres, reaching surface elevations 122,000 years ago of 130 ± 300 metres lower than the present. Extensive surface melt occurred at the NEEM site during the Eemian, a phenomenon witnessed when melt layers formed again at NEEM during the exceptional heat of July 2012. With additional warming, surface melt might become more common in the future.
    Nature 01/2013; 493:489-494. · 38.60 Impact Factor
  • Journal of Glaciology 01/2013; 59(215):503-506. · 2.88 Impact Factor
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    ABSTRACT: The Toba eruption that occurred some 74 kyr ago in Sumatra, Indonesia, is among the largest volcanic events on Earth over the last 2 million years. Tephra from this eruption has been spread over vast areas in Asia where it constitutes a major time marker close to the Marine Isotope Stage 4/5 boundary. As yet, no tephra associated with Toba has been identified in Greenland or Antarctic ice cores. Based on new accurate dating of Toba tephra from Malaysia and on accurately dated European stalagmites the Toba event is known to occur between the onsets of Greenland Interstadials (GI) 19 and 20. Furthermore, the existing linking of Greenland and Antarctic ice cores by gas records and by the bipolar seesaw hypothesis suggests that the Antarctic counterpart is situated between Antarctic Isotope Maxima (AIM) 19 and 20. In this work we suggest a direct synchronization of Greenland (NGRIP) and Antarctic (EDML) ice cores at the Toba eruption based on matching of a pattern of bipolar volcanic spikes. Annual layer counting between volcanic spikes in both cores allows for a unique match. We first demonstrate this bipolar matching technique at the already synchronized Laschamp geomagnetic excursion (41 kyr BP) before we apply it to the suggested Toba interval. The Toba synchronization pattern covers some 2000 yr in GI-20 and AIM 19/20 and includes nine acidity peaks that are recognized in both ice cores. The suggested bipolar Toba synchronization has decadal precision. It thus allows a determination of the exact phasing of inter-hemispheric climate in a time interval of poorly constrained ice core records, and it allows for a discussion of the climatic impact of the Toba eruption in a global perspective. Furthermore, our bipolar match provides a way to place paleo-environmental records other than ice cores into a precise climatic context.
    Climate of the Past. 01/2013; 9(2):749-766.
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    ABSTRACT: Models of firn densification are a necessary requisite for dating air inclusions in polar ice cores. Previous densification models assume a homogenous firn column where densification is mainly dependent on accumulation rate, temperature and surface density. From measured density profiles with a vertical resolution of millimetres it is known that firn is a layered medium with considerable porosity variations at the firn-ice transition (sometimes more than 50 percent in adjacent layers). Very recently it turned out that the density (porosity) variations in deep firn are linked to variations of the Ca++ concentration which points to an impurity effect on densification. In our contribution we will present the first densification model for layered firn that accounts for the impurity effect. In the model the impurity effect is parameterized by the Ca++ concentration. The impurities are assumed to act like a catalyst: they increase the densification rate by reducing the activation energy. The model is applied to firn from Greenland (B26) and Antarctica (B36, EDML, EDC). The simulations are fitted on measured density profiles to find reasonable model input parameters for the impurity effect in recent firn. The derived parameterization is used to simulate the densification in Glacial periods in Antarctica and Greenland. Applying our model to Glacial conditions on the Antarctic plateau the firn column is reduced as it is suggested by d15N measurements without assuming convective zones of several tens of meters.
    04/2012;
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    ABSTRACT: Since the early 1980's methane concentrations are measured from ice cores. Air is extracted from individual ice samples by dry or wet extraction techniques and traditionally measured by gas chromatography. Over the past decades a CH4 record has been achieved with sample resolutions of down to decades and typical uncertainties of ±10 ppbv. Methane variations on time scales of decades to millennia show important correlations with climate proxies in ice cores, with remarkable correspondence between stable isotope records from Greenland ice cores and methane concentrations during the last ice age. Recent developments allow measurements of CH4 concentration directly on the drill site with very high resolution. In the frame of the NEEM (NW Greenland) ice core drilling project we measured methane concentration with a continuous flow analysis (CFA) system. The air in the CFA melt stream is extracted with a hydrophobic membrane unit, dried, and routed through two optical systems in series. The resolution of the methane data is unprecedented with excellent precision. However, the accuracy of the data is not satisfactory due to solubility of the gas in the melt stream and calibration issues. We combine precise off line measurements from several Greenland ice cores with the on line NEEM CH4 record in order to obtain an improved Greenland CH4 composite record. Further we establish a gas time scale for the NEEM ice core by synchronizing the CH4 records.
    04/2012;
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    ABSTRACT: Since the early 1980s, atmospheric CH4 records have been obtained from ice cores through discrete sampling and gas chromatographic measurements. Typical sample resolutions can reach down to decades for certain time periods, with usual uncertainties of ±10 ppbv. There are very few available CO records, using similar techniques. Recent developments of optical instruments allow now measurements of CH4 and/or CO concentration directly on the drill site or in the laboratory using continuous flow analysis (CFA) systems. The air in the CFA melt stream is extracted with a hydrophobic membrane unit, dried, and routed through the optical cavity of one or two instruments in series. We present here the first continuous measurements obtained along the NEEM (Greenland) core with an unprecedented resolution. The last 2000 years have been measured for both CH4 and CO. CH4 was also measured on older ice back to the last interglacial. Continuous measurements allow us to determine with high precision the location in depth of rapid CH4 changes and to discuss finer structures in the signal. In addition they provide a direct comparison between the chemical composition of the ice and the gas record at the same depth, thus providing information about possible local artifacts of trace-gas production within the ice.
    04/2012;
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    ABSTRACT: Analysis of air extracted from bubbles of Greenland ice results in considerably higher CO2 concentrations compared to records from Antarctic sites. This can not be explained by the inter-hemispheric gradient expected for past climatic conditions. Instead, it is attributed to chemical reactions between impurities in the ice, contributing excess CO2 to the atmospheric signal which was initially trapped in the bubbles. This is consistent with the fact that Greenland ice contains a significantly higher amount of impurities compared to Antarctic ice. Different candidates of CO2 producing chemical reactions were suggested by previous studies: (i) the acidification of carbonates, (ii) the oxidation of hydrocarbons and (iii) the photodecarboxilation of humic like substances. However, there is no agreement on how much each of the above reactions contributes. This study aims to identify the contribution from organic and inorganic sources to the Greenland CO2 excess. Compared to previous studies we base our analysis on an increased set of parameters and data points. We discuss data of CO2 and δ13C-CO2, both in high (2.5 cm) and low resolution (55 to 110 cm) along with parallel records of chemical impurities from three different sites in Greenland. The samples for the presented high resolution CO2 and δ13C of CO2 records were measured on a new set-up at the Centre for Ice and Climate (needle cracker, GC-IRMS).
    04/2012;
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    ABSTRACT: There is a strong requirement to better quantify the recurrence frequency of solar flare events of different magnitudes. One way to do that is to extend the observation of phenomena associated with the flares into the past. The idea has surfaced several times in the last 20 years that short-lived spikes of nitrate concentration observed in ice cores may be the result of solar energetic particle (SEP) events, and that their occurrence can therefore be used to extend the statistics of solar events. Despite a number of objections from the glaciological and atmospheric community, this idea is still popular in some communities, with particular emphasis placed on a large peak observed in once core in 1859, apparently contemporaneous with the Carrington Event. Here we re-examine ice core records for the period surrounding 1859, compiling more than 10 records that have the resolution required to observe such a sharp but strong nitrate signal. We show that no signal is seen in any of the cores from Antarctica for the years surrounding 1859. In Greenland, most cores have no signal in the ice dated to 1859, but some of them do have a nitrate spike within a few years of 1859. However, where other chemistry has been measured, it is found that the relevant nitrate spike (in common with most of the other nitrate spikes in the cores) is associated with an ammonium spike, which previous work has shown is characteristic of deposition from a biomass burning plume. We therefore conclude that many of the nitrate spikes seen in records to date are actually from biomass burning plumes passing over Greenland. Taking together the chemical fingerprint of the Greenland signal and the lack of spikes seen in Antarctica, we conclude that it is unlikely that there is any significant ice core nitrate enhancement that can be identified associated with the Carrington Event. While SEPs should enhance nitrate production at different layers in the atmosphere, and therefore should lead to a small broad peak in deposition to ice, it seems unlikely that the statistics of such events are accessible from ice cores.
    04/2012;
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    ABSTRACT: Ice core data from Antarctica provide detailed in-sights into the characteristics of past climate, atmospheric circulation, as well as changes in the aerosol load of the atmosphere. We present high-resolution records of solu-ble calcium (Ca 2+), non-sea-salt soluble calcium (nssCa 2+), and particulate mineral dust aerosol from the East Antarc-tic Plateau at a depth resolution of 1 cm, spanning the past 800 000 years. Despite the fact that all three parameters are largely dust-derived, the ratio of nssCa 2+ to particulate dust is dependent on the particulate dust concentration itself. We used principal component analysis to extract the joint cli-matic signal and produce a common high-resolution record of dust flux. This new record is used to identify Antarc-tic warming events during the past eight glacial periods. The phasing of dust flux and CO 2 changes during glacial-interglacial transitions reveals that iron fertilization of the Southern Ocean during the past nine glacial terminations was not the dominant factor in the deglacial rise of CO 2 concen-trations. Rapid changes in dust flux during glacial termina-tions and Antarctic warming events point to a rapid response of the southern westerly wind belt in the region of south-ern South American dust sources on changing climate con-ditions. The clear lead of these dust changes on temperature rise suggests that an atmospheric reorganization occurred in the Southern Hemisphere before the Southern Ocean warmed significantly.
    Climate of the Past 03/2012; 8(2-10.5194/cp-8-609-2012):609-623. · 3.56 Impact Factor
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    ABSTRACT: Sulphate records from Greenland ice-cores indicate that Marine Isotope Stages 4 and 5 were characterised by a higher incidence of large volcanic eruptions than other periods during the last glacial period, however, few investigations have focused on tephra deposits associated with these volcanic eruptions and the nature and origin of the events. Here we present a detailed tephrochronological framework of the products of 15 volcanic events spanning this interval; the majority of which have been preserved as cryptotephra horizons within the Greenland records. The major element compositions of individual glass shards within these horizons indicate that 13 of the eruptions originated from Iceland and 6 of these events can be correlated to the specific volcanic systems of Katla, Grímsvötn, Grímsvötn-Kverkfjöll and either Reykjanes or Veidivötn-Bárdarbunga. For the remaining Icelandic horizons a source from either the rift zone or a flank zone can be suggested based on rock suite affinities. Two horizons have been correlated to a source from the Jan Mayen volcanic system which represents the first discovery of material from this system within any Greenland ice-cores. The robust geochemical characterisations, independent ages for these horizons (derived from the GICC05 ice-core chronology) and stratigraphic positions relative to the Dansgaard-Oeschger climate events recorded in the Greenland ice-cores represent a critical framework that provides new information on the frequency and nature of volcanic events occurring in the North Atlantic region during MIS 4 and 5. This framework can now be utilised in the assessment of the differential timing and rate of response to the millennial-scale climatic events that characterised this period, through the use of the tephra horizons as time-synchronous tie-lines to other palaeoclimatic sequences.
    Quaternary Science Reviews 03/2012; · 4.08 Impact Factor
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    ABSTRACT: Using high resolution chemical impurity and dielectric profiling data annual layers have been counted on the EPICA ice core from Dronning Maud Land (EDML), Antarctica spanning the past 16700 years. The methodology used for counting Greenland ice cores and creating the Greenland Ice Core Chronology 2005 (GICC05) [Rasmussen et al., 2006] has also been implemented for the EDML counting. The estimated maximum counting error for the EDML counting is approx. 5%, but a preliminary volcanic matching with Greenland ice core records suggest differences of 1% or less during the Holocene between the EDML counting and GICC05. A comparison of cosmogenic isotope records from EDML and Greenland also suggests differences of less than 1% between the two annual layer counted chronologies. Reference: Rasmussen, S.O., Andersen, K.K., Svensson, A., Steffensen, J.P., Vinther, B.M., Clausen, H.B., Andersen, M.L.S., Johnsen, S.J., Larsen, L.B., Dahl-Jensen, D., Bigler, M., Röthlisberger R., Fischer H., Goto-Azuma K., Hansson M.E., Ruth U, A new Greenland ice core chronology for the last glacial termination, Journal of Geophysical Research Vol. 111, D06102, doi:10.1029/2005JD006079. 2006.
    Geophysical Research Abstracts. 01/2012; 14:EGU2012-13043.
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    ABSTRACT: Understanding polar firn densification is crucial for reconstructing the age of greenhouse gas concentrations extracted from ice cores, and for the interpretation of air in ice as a dating tool or as a climate proxy. Firn densification is generally modeled as a steady burial and sintering process of defined layers, where the structure of the layering is maintained along the whole firn and ice column. However, available high-resolution density data, as well as firn air samples, question this picture and point to a lack of understanding of firn densification. Based on analysis of high-resolution density and calcium concentration records from Antarctic and Greenland ice cores, we show for the first time that also impurities may have a significant impact on the densification. Analysis of firn cores shows a correlation between density and the calcium ion (Ca++) concentration, and this correlation increases with depth. The existence of this relationship is independent of the local climatic conditions at the core sites analyzed. The strong positive correlation between the density and the logarithm of Ca++ concentration indicates that impurities induce softening and lead to faster densification over a wide range of concentrations. In one core, the impurity effect manifests itself so strongly that the density develops a seasonal cycle closely following the seasonal cycle of Ca++. Our results clearly show that the structure of the firn layering changes with depth and suggest that the increased variability in density observed in deep firn, recently described as a universal feature of polar firn, may arise from the influence of Ca++ and/or other impurities. The impurity effect is likely to have direct implications on our understanding of glacial firn densification and on glacial gas age estimates.
    Earth and Planetary Science Letters 01/2012; 325--326:93-99. · 4.35 Impact Factor
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    Atmospheric Measurement Techniques 01/2012; 5:999-1013. · 3.21 Impact Factor
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    ABSTRACT: The Carrington Event of 1859 is considered to be among the largest space weather events of the last 150 years. We show that only one out of 14 well-resolved ice core records from Greenland and Antarctica has a nitrate spike dated to 1859. No sharp spikes are observed in the Antarctic cores studied here. In Greenland numerous spikes are observed in the 40 years surrounding 1859, but where other chemistry was measured, all large spikes have the unequivocal signal, including co-located spikes in ammonium, formate, black carbon and vanillic acid, of biomass burning plumes. It seems certain that most spikes in an earlier core, including that claimed for 1859, are also due to biomass burning plumes, and not to solar energetic particle (SEP) events. We conclude that an event as large as the Carrington Event did not leave an observable, widespread imprint in nitrate in polar ice. Nitrate spikes cannot be used to derive the statistics of SEPs.
    Geophysical Research Letters 01/2012; 39:L08503. · 3.98 Impact Factor

Publication Stats

3k Citations
410.49 Total Impact Points

Institutions

  • 2007–2013
    • University of Copenhagen
      • • Centre for Ice and Climate
      • • Center for Ice and Climate
      København, Capital Region, Denmark
  • 2005–2012
    • Universität Bern
      • • Climate and Environmental Physics Group
      • • Physikalisches Institut
      Berna, Bern, Switzerland