An investigation of rapid warm transitions during MIS2 and MIS3 using Greenland ice-core data and the CLIMBER-2 model

AbstractIn the search for abetter understanding of the dominant mechanisms of the Earth’s climate system, we present a study of rapid warm-climate transitions to Dansgaard– Oeschger events as seen in the ice cores from the Greenland ice sheet. We present a continuous δ18O record from the Greenland Icecore Project (GRIP) core with a resolution of 5 years until 50 kyr BP and of 20 years until 100 kyr BP. These data are compared with other high-resolution records, i.e. the Greenland Ice Sheet Project II (GISP2) chemistry record (25 years until 50 kyr BP) and the GRIP Ca2+ record (3 years until 100 kyr BP). All records have been transformed to the GISP2 Meese/Sowers time-scale. the high-resolution records are separated into interstadials and stadials, defined by the GRIP and GISP2 δ18O records. We examine in detail the transitions into the Dansgaard–Oeschger events, and propose a scenario for the changes that occur in the different ice-core records during the approximately 50 years the transition takes. Themain difference from previous studies is the much higher-resolution datasets available until 50 kyr BP; previous high-resolution studies by Taylor and others (1997) have focused on only the Younger Dryas/Preboreal transition. the data are compared to model simulations of the Dansgaard–Oeschger events performed with the CLIMBER-2 model of intermediate complexity (Petoukhov and others, 1998 ; Ganopolski and Rahmstorf, 2001).

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Forty years later: High resolution continuous flow analysis of the Dye3 ice core

10.5194/egusphere-egu21-11820 ◽

2021 ◽

Author(s):

Helle Astrid Kjær ◽

Margaret Harlan ◽

Paul Vallelonga ◽

Anders Svensson ◽

Thomas Blunier ◽

...

Keyword(s):

High Resolution ◽

Forest Fires ◽

Continuous Flow ◽

Ice Core ◽

Flow Analysis ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Ice Cores ◽

The Core ◽

Continuous Flow Analysis

<div>The Dye-3 ice core was drilled to bedrock at the Southern part of the central Greenland ice sheet (65&#176;11'N, 43&#176;50'W) in 1979-1981. The southern location is characterized by high accumulation rates compared to more central locations of the ice sheet. Since its drilling, numerous analyses of the core have been performed, and the ice has since been in freezer storage both in the USA and in Denmark.</div><div>In October and November 2019, the remaining ice, two mostly complete sections covering the depths of 1753&#8211;1820m and 1865&#8211;1918m of the Dye-3 core, were melted during a continuous flow analysis (CFA) campaign at the Physics of Ice, Climate, and Earth (PICE) group at the University of Copenhagen. The data represents both Holocene, Younger Dryas and Glacial sections (GS 5 to 12).</div><div>&#160;</div><div>The measured data consist chemistry and impurities contained in the ice, isotopes, as well as analysis of methane and other atmospheric gases.&#160;</div><div>The chemistry measurements include NH4+, Ca2+, and Na+&#160;ions, which besides being influenced by transport, provide information about forest fires, wind-blown dust, and sea ice, respectively, as well as acidity, which aids in the identification of volcanic events contained in the core. The quantity and grain size distribution of insoluble particles was analyzed by means of an Abakus laser particle counter.</div><div>&#160;</div><div>We compare the new high-resolution CFA record of dye3 with previous analysis and thus evaluate the progress made over 40 years. Further we compare overlapping time periods with other central Greenland ice cores and discuss spatial patterns in relation to the presented climate proxies.</div>

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Tracer transport in an isochronal ice-sheet model

Journal of Glaciology ◽

10.1017/jog.2016.111 ◽

2016 ◽

Vol 63 (237) ◽

pp. 22-38 ◽

Cited By ~ 3

Author(s):

ANDREAS BORN

Keyword(s):

Ice Core ◽

Ice Sheet ◽

Vertical Motion ◽

Greenland Ice Sheet ◽

Ice Cores ◽

Model Parameters ◽

Tracer Transport ◽

Geochemical Tracers ◽

Tuning Method ◽

Polar Ice Sheets

ABSTRACTThe full history of ice sheet and climate interactions is recorded in the vertical profiles of geochemical tracers in polar ice sheets. Numerical simulations of these archives promise great advances both in the interpretation of these reconstructions and the validation of the models themselves. However, fundamental mathematical shortcomings of existing models subject tracers to spurious diffusion, thwarting straightforward solutions. Here, I propose a new vertical discretization for ice-sheet models that eliminates numerical diffusion entirely. Vertical motion through the model mesh is avoided by mimicking the real-world flow of ice as a thinning of underlying layers. A new layer is added to the surface at equidistant time intervals, isochronally, thus identifying each layer uniquely by its time of deposition and age. This new approach is implemented for a two-dimensional section through the summit of the Greenland ice sheet. The ability to directly compare simulations of vertical ice cores with reconstructed data is used to find optimal model parameters from a large ensemble of simulations. It is shown that because this tuning method uses information from all times included in the ice core, it constrains ice-sheet sensitivity more robustly than a realistic reproduction of the modern ice-sheet surface.

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Time Scale and Ice Accumulation During the Last 125,000 Years as Indicated by the Greenland 018 curve

Geological Magazine ◽

10.1017/s0016756800042229 ◽

1972 ◽

Vol 109 (1) ◽

pp. 17-24 ◽

Cited By ~ 10

Author(s):

N. A. Mörner

Keyword(s):

North America ◽

Time Scales ◽

Time Scale ◽

Ice Core ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Climatic Changes ◽

Dynamic Changes ◽

Ice Accumulation

SummaryThe 18 curve from the 1390 m long ice core from Camp Century, Greenland, shows climatic changes that are easily correlated with known glacial and non-glacial events of North America and north Europe and are thus indirectly dated. With a known chronology, the glacial dynamic changes of the Greenland Ice Sheet can be calculated for the last 125,000 years. It is concluded that the dynamics of the Greenland Ice Sheet have changed drastically during this period and that these changes are directly related to major changes of climate and extension of the Wisconsin and Weichselian glaciations. Logarithmic time scales earlier applied to this curve must therefore be incorrect.

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First continuous high-resolution aerosol record from the East Greenland Ice Core Project (EGRIP), covering the last 15,000 years

10.5194/egusphere-egu2020-15202 ◽

2020 ◽

Author(s):

Camilla Marie Jensen ◽

Tobias Erhardt ◽

Giulia Sinnl ◽

Hubertus Fischer

Keyword(s):

High Resolution ◽

Biomass Burning ◽

Forest Fires ◽

Ice Core ◽

Greenland Ice Sheet ◽

Ice Cores ◽

Background Level ◽

Volcanic Eruptions ◽

Atmospheric Conditions ◽

Data Set

Ice sheets are reliable archives of atmospheric impurities such as aerosols and gasses of both natural and anthropogenic origin. Impurity records from Greenland ice cores reveal much information about previous atmospheric conditions and long-range transport in the Northern hemisphere going back more than a hundred thousand years.Here we present the data from the upper 1,411 m from the EGRIP ice core, measuring conductivity, dust, sodium, calcium, ammonium, and nitrate. These records contain information about ocean sources, transport of terrestrial dust, soil and vegetation emissions as well as biomass burning, volcanic eruptions, etc., covering approximately the past 15,000 years. This newly obtained data set is unique as it provides the first high-resolution information about several thousands of years of the mid-Holocene period in Greenland that none of the previous impurity records from the other deep Greenland ice cores had managed to cover before due to brittle ice. This will contribute to further understanding of the atmospheric conditions for the pre-industrial period.The ammonium record contains peaks significantly higher than the background level. These peaks are caused by biomass burning or forest fires emitting plumes of ammonia large enough so that they can extend to the free troposphere and be efficiently transported all the way to the Greenland ice sheet. Here we present preliminary results of the wild fire frequency covering the entire Holocene, where the wild fires are defined as outliers in the ammonium record of annual means.

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Retrieving the paleoclimatic signal from the deeper part of the EPICA Dome C ice core

The Cryosphere ◽

10.5194/tc-9-1633-2015 ◽

2015 ◽

Vol 9 (4) ◽

pp. 1633-1648 ◽

Cited By ~ 15

Author(s):

J.-L. Tison ◽

M. de Angelis ◽

G. Littot ◽

E. Wolff ◽

H. Fischer ◽

...

Keyword(s):

High Resolution ◽

Large Scale ◽

Ice Core ◽

Ice Sheet ◽

Remote Sensing Data ◽

Ice Cores ◽

Air Content ◽

Confining Effect ◽

Chemical Profiles ◽

Subglacial Topography

Abstract. An important share of paleoclimatic information is buried within the lowermost layers of deep ice cores. Because improving our records further back in time is one of the main challenges in the near future, it is essential to judge how deep these records remain unaltered, since the proximity of the bedrock is likely to interfere both with the recorded temporal sequence and the ice properties. In this paper, we present a multiparametric study (δD-δ18Oice, δ18Oatm, total air content, CO2, CH4, N2O, dust, high-resolution chemistry, ice texture) of the bottom 60 m of the EPICA (European Project for Ice Coring in Antarctica) Dome C ice core from central Antarctica. These bottom layers were subdivided into two distinct facies: the lower 12 m showing visible solid inclusions (basal dispersed ice facies) and the upper 48 m, which we will refer to as the "basal clean ice facies". Some of the data are consistent with a pristine paleoclimatic signal, others show clear anomalies. It is demonstrated that neither large-scale bottom refreezing of subglacial water, nor mixing (be it internal or with a local basal end term from a previous/initial ice sheet configuration) can explain the observed bottom-ice properties. We focus on the high-resolution chemical profiles and on the available remote sensing data on the subglacial topography of the site to propose a mechanism by which relative stretching of the bottom-ice sheet layers is made possible, due to the progressively confining effect of subglacial valley sides. This stress field change, combined with bottom-ice temperature close to the pressure melting point, induces accelerated migration recrystallization, which results in spatial chemical sorting of the impurities, depending on their state (dissolved vs. solid) and if they are involved or not in salt formation. This chemical sorting effect is responsible for the progressive build-up of the visible solid aggregates that therefore mainly originate "from within", and not from incorporation processes of debris from the ice sheet's substrate. We further discuss how the proposed mechanism is compatible with the other ice properties described. We conclude that the paleoclimatic signal is only marginally affected in terms of global ice properties at the bottom of EPICA Dome C, but that the timescale was considerably distorted by mechanical stretching of MIS20 due to the increasing influence of the subglacial topography, a process that might have started well above the bottom ice. A clear paleoclimatic signal can therefore not be inferred from the deeper part of the EPICA Dome C ice core. Our work suggests that the existence of a flat monotonic ice–bedrock interface, extending for several times the ice thickness, would be a crucial factor in choosing a future "oldest ice" drilling location in Antarctica.

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New δ18Oatm, δ18Oice and δDice profiles from deep ice of the TALDICE core

10.5194/egusphere-egu2020-4179 ◽

2020 ◽

Author(s):

Ilaria Crotti ◽

Carlo Barbante ◽

Massimo Frezzotti ◽

Wei Jiang ◽

Amaelle Landais ◽

...

Keyword(s):

High Resolution ◽

Ice Core ◽

Ice Sheet ◽

Ice Cores ◽

Radiometric Dating ◽

The Core ◽

Climatic Signal ◽

High Frequency Variability ◽

The One ◽

Depth Relationship

The study of the deep portions of ice cores still represents a poorly explored field due to the presence of processes acting in the lowermost layers and possibly affecting the preservation of the original climatic signal. For the 1620 m TALDICE ice core, drilled at Talos Dome (East Antarctica), the high-resolution climate reconstruction and chronology definition are available only until the depth of ~1450 m (150 kyr BP) (Stenni et al., 2011, Bazin et al., 2013). Our aim is to investigate the portion below 1460 m depth to the bottom of the core, where radargrams show the presence of an unconformity in the ice sheet, to define a preliminary chronology and identify a discernible climatic signal.Here we present the new TALDICE &#948;18Oatm record in the air bubbles, in association with the new high-resolution &#948;18Oice and &#948;Dice profiles and an 81Kr radiometric date. New 46 measurements of &#948;18Oatm&#160; allowed to increase the resolution of the available profile from 1357 to 1553.95 m depth and to extend the record till the bottom of the core at 1617 m depth. The comparison between the &#948;18Oatm profile of TALDICE and the one of EPICA Dome C (EDC) ice core (Extier et al., 2018) allows to solidly define a preliminary age-depth relationship for the TALDICE core until 1500 m depth, where the gas age is estimated to be ~200 kyr BP. Below 1500 m, supplementary &#948;18Oatm measurements will be needed to identify older precession cycles and to extend the age-depth relationship further back in time. On the other hand, the high-resolution isotopic profiles in the ice (18O/16O and D/H ratios) obtained below the depth of 1528 m and compared with the EDC ones suggest that the climatic signal in the ice is preserved until to the lower level of 1547.8 m, which is dated back to 343 kyr BP. However, the lack of similarities with the EDC water isotopes record below this depth, in spite of the 81 Kr radiometric age 459 &#177; 50 kyr BP at the depth of 1574-1578 m, indicates the missing of the MIS 11 in the isotopic profiles. Moreover, the increase of high-frequency variability in the &#948;18Oice and &#948;Dice below 1547.8 m depth implies that this part of the core lays in an area of the ice sheet characterized by different properties in comparison to the ice above.Additional &#948;18Oatm, 40Ar, &#948;18Oice, and &#948;Dice measurements will be performed in the lowermost portion of the core and the results will be compared with the new 81Kr radiometric dating at the depth of 1560-1564 m and 1614-1619 m to better constrain the chronology and to investigate the ice properties in the deeper portion of the core.

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Tracing the depth of the Holocene ice in North Greenland from radio-echo sounding data

Annals of Glaciology ◽

10.3189/2013aog64a057 ◽

2013 ◽

Vol 54 (64) ◽

pp. 44-50 ◽

Cited By ~ 25

Author(s):

Nanna B. Karlsson ◽

Dorthe Dahl-Jensen ◽

S. Prasad Gogineni ◽

John D. Paden

Keyword(s):

Ice Core ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Ice Cores ◽

The Holocene ◽

Fitting Method ◽

Radio Echo Sounding ◽

North Greenland ◽

Echo Sounding

Abstract Radio-echo sounding surveys over the Greenland ice sheet show clear, extensive internal layering, and comparisons with age–depth scales from deep ice cores allow for dating of the layering along the ice divide. We present one of the first attempts to extend the dated layers beyond the ice core drill sites by locating the depth of the Bølling–Allerød transition in >400 flight-lines using an automated fitting method. Results show that the transition is located in the upper one-third of the ice column in the central part of North Greenland, while the transition lowers towards the margin. This pattern mirrors the present surface accumulation, and also indicates that a substantial amount of pre-Holocene ice must be present in central North Greenland.

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Potential for stratigraphie folding near ice-sheet centers

Journal of Glaciology ◽

10.3189/172756501781831756 ◽

2001 ◽

Vol 47 (159) ◽

pp. 639-648 ◽

Cited By ~ 29

Author(s):

Edwin D. Waddington ◽

John F. Bolzan ◽

Richard B. Alley

Keyword(s):

Transient Flow ◽

Ice Core ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Ice Cores ◽

Climate Record ◽

Bed Topography ◽

Flow Disturbances ◽

Siple Dome ◽

Ice Core Record

AbstractLack of agreement between the deep portions of the Greenland Icecore Project (GRIP) and Greenland Ice Sheet Project II (GISP2) ice cores from central Greenland suggests that folds may disrupt annual layering, even near ice divides. We use a simple kinematic flow model to delineate regions where slope disturbances (“wrinkles”) introduced into the layering could overturn into recumbent folds, and where they would flatten, leaving the stratigraphic record intact. Wrinkles are likely to originate from flow disturbances caused internally by inhomogeneities and anisotropy in the ice rheological properties, rather than from residual surface structures (sastrugi), or from open folds associated with transient flow over bed topography. If wrinkles are preferentially created in anisotropic ice under divides, where the resolved shear stress in the easy-glide direction can be weak and variable, then the deep intact climate record at Dye 3 may result from its greater distance from the divide. Alternatively, the larger simple shear at Dye 3 may rapidly overturn wrinkles, so that they are not recognizable as folds. The ice-core record from Siple Dome may be intact over a greater fraction of its depth compared to the central Greenland records if its flat bedrock precludes fluctuations in the stress orientation near the divide.

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Microstructure through an Ice Sheet

Materials Science Forum ◽

10.4028/www.scientific.net/msf.753.481 ◽

2013 ◽

Vol 753 ◽

pp. 481-484 ◽

Cited By ~ 5

Author(s):

Tobias Binder ◽

Ilka Weikusat ◽

Johannes Freitag ◽

Christoph S. Garbe ◽

Dietmar Wagenbach ◽

...

Keyword(s):

Grain Boundary ◽

Grain Boundaries ◽

Driving Forces ◽

Boundary Migration ◽

Ice Core ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Ice Cores ◽

Grain Size Analysis ◽

Size Analysis

Ice cores through an ice sheet can be regarded as a sample of a unique natural deformation experiment lasting up to a million years. Compared to other geological materials forming the earth‘s crust, the microstructure is directly accessible over the full depth. Controlled sublimation etching of polished ice sections reveals pores, air bubbles, grain boundaries and sub-grain boundaries at the surface. The microstructural features emanating at the surface are scanned. A dedicated method of digital image processing has been developed to extract and characterize the grain boundary networks. First preliminary results obtained from an ice core drilled through the Greenland ice sheet are presented. We discuss the role of small grains in grain size analysis and derive from the shape of grain boundaries the acting driving forces for grain boundary migration.

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Sea-ice feedbacks influence the isotopic signature of Greenland Ice Sheet elevation changes: Last Interglacial HadCM3 simulations

10.5194/cp-2020-40 ◽

2020 ◽

Author(s):

Irene Malmierca-Vallet ◽

Louise C. Sime ◽

Paul J. Valdes ◽

Julia C. Tindall

Keyword(s):

Sea Ice ◽

Ice Core ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Ice Cores ◽

Lapse Rate ◽

Last Interglacial ◽

Elevation Change ◽

Elevation Gradients ◽

Lapse Rates

Abstract. Changes in the Greenland ice sheet (GIS) affect global sea level. Greenland stable water isotope (δ18O) records from ice cores offer information on past changes in the surface of the GIS. Here, we use the isotope-enabled HadCM3 climate model to simulate a set of Last Interglacial (LIG) idealised GIS surface elevation change scenarios focusing on GIS ice core sites. We investigate how δ18O depends on the magnitude and sign of GIS elevation change and evaluate how the response is altered by sea ice changes. We find that modifying GIS elevation induces changes in Northern Hemisphere atmospheric circulation, sea ice and precipitation patterns. These climate feedbacks lead to ice core-averaged isotopic lapse rates of 0.49 ‰ per 100 m for the lowered GIS states and 0.29 ‰ per 100 m for the enlarged GIS states. This is lower than the spatially derived Greenland lapse rates of 0.62–0.72 ‰ per 100 m. These results thus suggest non-linearities in the isotope-elevation relationship, and have consequences for the interpretation of past elevation and climate changes across Greenland. In particular, our results suggest that winter sea ice changes may significantly influence isotopic-elevation gradients: winter sea ice effect can decrease (increase) modelled core-averaged isotopic lapse rate values by about -19 % (and +28 %) for the lowered (enlarged) GIS states respectively. The largest influence of sea ice on δ18O changes is found in coastal regions like the Camp Century site.

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