M. Bigler

Universität Bern, Berna, Bern, Switzerland

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Publications (105)487.47 Total impact

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  • Climate of the Past Discussions 01/2015; 11(2-2):805-830. DOI:10.5194/cpd-11-805-2015
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    The Cryosphere Discussions 01/2015; 9(1):567-608. DOI:10.5194/tcd-9-567-2015
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    ABSTRACT: We present a synchronization of the NGRIP, GRIP and GISP2 ice cores onto a master chronology extending back to 104 ka before present, providing a consistent chronological framework for these three Greenland records. The synchronization aligns distinct peaks in volcanic proxy records and other impurity records (chemo-stratigraphic matching) and assumes that these layers of elevated impurity content represent the same, instantaneous event in the past at all three sites. More than 900 marker horizons between the three cores have been identified and our matching is independently confirmed by 24 new and previously identified volcanic ash (tephra) tie-points. Using the reference horizons, we transfer the widely used Greenland ice-core chronology, GICC05modelext, to the two Summit cores, GRIP and GISP2. Furthermore, we provide gas chronologies for the Summit cores that are consistent with the GICC05modelext timescale by utilizing both existing and new gas data (CH4 concentration and δ15N of N2). We infer that the accumulation contrast between the stadial and interstadial phases of the glacial period was ∼10% greater at Summit compared to at NGRIP. The δ18O temperature-proxy records from NGRIP, GRIP, and GISP2 are generally very similar and display synchronous behaviour at climate transitions. The δ18O differences between Summit and NGRIP, however, changed slowly over the Last Glacial-Interglacial cycle and also underwent abrupt millennial-to-centennial-scale variations. We suggest that this observed latitudinal δ18O gradient in Greenland during the glacial period is the result of 1) relatively higher degree of precipitation with a Pacific signature at NGRIP, 2) increased summer bias in precipitation at Summit, and 3) enhanced Rayleigh distillation due to an increased source-to-site distance and a potentially larger source-to-site temperature gradient. We propose that these processes are governed by changes in the North American Ice Sheet (NAIS) volume and North Atlantic sea-ice extent and/or sea-surface temperatures (SST) on orbital timescales, and that changing sea-ice extent and SSTs are the driving mechanisms on shorter timescales. Finally, we observe that maxima in the Summit-NGRIP δ18O difference are roughly coincident with prominent Heinrich events. This suggests that the climatic reorganization that takes place during stadials with Heinrich events, possibly driven by a southward expansion of sea ice and low SSTs in the North Atlantic, are recorded in the ice-core records.
    Quaternary Science Reviews 11/2014; 106. DOI:10.1016/j.quascirev.2014.10.032 · 4.57 Impact Factor
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    ABSTRACT: Due to their outstanding resolution and well-constrained chronologies, Greenland ice-core records provide a master record of past climatic changes throughout the Last Interglacial–Glacial cycle in the North Atlantic region. As part of the INTIMATE (INTegration of Ice-core, MArine and TErrestrial records) project, protocols have been proposed to ensure consistent and robust correlation between different records of past climate. A key element of these protocols has been the formal definition and ordinal numbering of the sequence of Greenland Stadials (GS) and Greenland Interstadials (GI) within the most recent glacial period. The GS and GI periods are the Greenland expressions of the characteristic Dansgaard–Oeschger events that represent cold and warm phases of the North Atlantic region, respectively. We present here a more detailed and extended GS/GI template for the whole of the Last Glacial period. It is based on a synchronization of the NGRIP, GRIP, and GISP2 ice-core records that allows the parallel analysis of all three records on a common time scale. The boundaries of the GS and GI periods are defined based on a combination of stable-oxygen isotope ratios of the ice (δ18O, reflecting mainly local temperature) and calcium ion concentrations (reflecting mainly atmospheric dust loading) measured in the ice. The data not only resolve the well-known sequence of Dansgaard–Oeschger events that were first defined and numbered in the ice-core records more than two decades ago, but also better resolve a number of short-lived climatic oscillations, some defined here for the first time. Using this revised scheme, we propose a consistent approach for discriminating and naming all the significant abrupt climatic events of the Last Glacial period that are represented in the Greenland ice records. The final product constitutes an extended and better resolved Greenland stratotype sequence, against which other proxy records can be compared and correlated. It also provides a more secure basis for investigating the dynamics and fundamental causes of these climatic perturbations.
    Quaternary Science Reviews 11/2014; 106. DOI:10.1016/j.quascirev.2014.09.007 · 4.57 Impact Factor
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    ABSTRACT: The seasonal and annual representativeness of ionic aerosol proxies (among others, calcium, sodium, ammonium and nitrate) in various firn cores in the vicinity of the NEEM drill site in northwest Greenland have been assessed. Seasonal representativeness is very high as one core explains more than 60% of the variability within the area. The inter-annual representativeness, however, can be substantially lower (depending on the species) making replicate coring indispensable to derive the atmospheric variability of aerosol species. A single core at the NEEM site records only 30% of the inter-annual atmospheric variability in some species, while five replicate cores are already needed to cover approximately 70% of the inter-annual atmospheric variability in all species. The spatial representativeness is very high within 60 cm, rapidly decorrelates within 10 m but does not diminish further within 3 km. We attribute this to wind reworking of the snow pack leading to sastrugi formation. Due to the high resolution and seasonal representativeness of the records we can derive accurate seasonalities of the measured species for modern (AD 1990-2010) times as well as for pre-industrial (AD 1623-1750) times. Sodium and calcium show similar seasonality (peaking in February and March respectively) for modern and pre-industrial times, whereas ammonium and nitrate are influenced by anthropogenic activities. Nitrate and ammonium both peak in May during modern times, whereas during pre-industrial times ammonium peaked during July-August and nitrate during June-July.
    The Cryosphere 10/2014; 8(5):1855-1870. DOI:10.5194/tc-8-1855-2014 · 4.37 Impact Factor
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    ABSTRACT: Building chronological frameworks for proxy sequences spanning 130–60 ka b2k is plagued by difficulties and uncertainties. Recent developments in the North Atlantic region, however, affirm the potential offered by tephrochronology and specifically the search for cryptotephra. Here we review the potential offered by tephrostratigraphy for sequences spanning 130–60 ka b2k. We combine newly identified cryptotephra deposits from the NGRIP ice-core and a marine core from the Iceland Basin with previously published data from the ice and marine realms to construct the first tephrostratigraphical framework for this time-interval. Forty-three tephra or cryptotephra deposits are incorporated into this framework; twenty three tephra deposits are found in the Greenland ice-cores, including nine new NGRIP tephras, and twenty separate deposits are preserved in various North Atlantic marine sequences. Major, minor and trace element results are presented for the new NGRIP horizons together with age estimates based on their position within the ice-core record. Basaltic tephras of Icelandic origin dominate the framework with only eight tephras of rhyolitic composition found. New results from marine core MD99-2253 also illustrate some of the complexities and challenges of assessing the depositional integrity of marine cryptotephra deposits. Tephra-based correlations in the marine environment provide independent tie-points for this time-interval and highlight the potential of widening the application of tephrochronology. Further investigations, however, are required, that combine robust geochemical fingerprinting and a rigorous assessment of tephra depositional processes, in order to trace coeval events between the two depositional realms.
    Quaternary Science Reviews 07/2014; 106. DOI:10.1016/j.quascirev.2014.03.024 · 4.57 Impact Factor
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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; 47(21). DOI:10.1021/es402274z · 5.48 Impact Factor
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    ABSTRACT: When drilling ice cores deeper than ∼100 m, drill liquid is required to maintain ice-core quality and to limit borehole closure. Due to high-pressure air bubbles in the ice, the ice core can crack during drilling and core retrieval, typically at 600–1200 m depth in Greenland. Ice from this 'brittle zone' can be contaminated by drill liquid as it seeps through cracks into the core. Continuous flow analysis (CFA) systems are routinely used to analyse ice for chemical impurities, so the detection of drill liquid is important for validating accurate measurements and avoiding potential instrument damage. An optical detector was constructed to identify drill liquid in CFA tubing by ultraviolet absorption spectroscopy at a wavelength of 290 nm. The set-up was successfully field-tested in the frame of the NEEM ice-core drilling project in Greenland. A total of 27 cases of drill liquid contamination were identified during the analysis of 175 m of brittle zone ice. The analyses most strongly affected by drill liquid contamination include insoluble dust particles, electrolytic conductivity, ammonium, hydrogen peroxide and sulphate. This method may also be applied to other types of drill liquid used at other drill sites.
    Journal of Glaciology 07/2013; 59(215):503-506. DOI:10.3189/2013JoG12J124 · 3.21 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; 47(9). DOI:10.1021/es3047087 · 5.48 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.
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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.
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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. DOI:10.1038/nature11789 · 42.35 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; 9:749-766. DOI:10.5194/cp-9-749-2013 · 3.48 Impact Factor
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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 04/2012; 325--326:93-99. DOI:10.1016/j.epsl.2011.12.022 · 4.72 Impact Factor
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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.
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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.
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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.