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

2013 ◽  
Vol 54 (64) ◽  
pp. 44-50 ◽  
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.

scholarly journals Internal structure of the ice sheet between Kohnen station and Dome Fuji, Antarctica, revealed by airborne radio-echo sounding

2013 ◽  
Vol 54 (64) ◽  
pp. 163-167 ◽  
Author(s):  
Daniel Steinhage ◽  
Sepp Kipfstuhl ◽  
Uwe Nixdorf ◽  
Heinz Miller
Keyword(s):  
Internal Structure ◽  
Accumulation Rate ◽  
Ice Core ◽  
Ice Sheet ◽  
Ice Cores ◽  
Internal Layers ◽  
Radio Echo Sounding ◽  
Depth Scale ◽  
Echo Sounding

Abstract This study aims to demonstrate that deep ice cores can be synchronized using internal horizons in the ice between the drill sites revealed by airborne radio-echo sounding (RES) over a distance of >1000km, despite significant variations in glaciological parameters, such as accumulation rate between the sites. In 2002/03 a profile between the Kohnen station and Dome Fuji deep ice-core drill sites, Antarctica, was completed using airborne RES. The survey reveals several continuous internal horizons in the RES section over a length of 1217 km. The layers allow direct comparison of the deep ice cores drilled at the two stations. In particular, the counterpart of a visible layer observed in the Kohnen station (EDML) ice core at 1054 m depth has been identified in the Dome Fuji ice core at 575 m depth using internal RES horizons. Thus the two ice cores can be synchronized, i.e. the ice at 1560 m depth (at the bottom of the 2003 EDML drilling) is ∼49ka old according to the Dome Fuji age/depth scale, using the traced internal layers presented in this study.

scholarly journals Reconstructing the last interglacial at Summit, Greenland: Insights from GISP2

2016 ◽  
Vol 113 (35) ◽  
pp. 9710-9715 ◽  
Author(s):  
Audrey M. Yau ◽  
Michael L. Bender ◽  
Alexander Robinson ◽  
Edward J. Brook
Keyword(s):  
Sea Level ◽  
Accumulation Rate ◽  
Ice Core ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Cores ◽  
Credible Interval ◽  
Historical Record ◽  
Last Interglacial ◽  
North Greenland

The Eemian (last interglacial, 130–115 ka) was likely the warmest of all interglacials of the last 800 ka, with summer Arctic temperatures 3–5 °C above present. Here, we present improved Eemian climate records from central Greenland, reconstructed from the base of the Greenland Ice Sheet Project 2 (GISP2) ice core. Our record comes from clean, stratigraphically disturbed, and isotopically warm ice from 2,750 to 3,040 m depth. The age of this ice is constrained by measuring CH4 and δ18O of O2, and comparing with the historical record of these properties from the North Greenland Ice Core Project (NGRIP) and North Greenland Eemian Ice Drilling (NEEM) ice cores. The δ18Oice, δ15N of N2, and total air content for samples dating discontinuously from 128 to 115 ka indicate a warming of ∼6 °C between 127–121 ka, and a similar elevation history between GISP2 and NEEM. The reconstructed climate and elevation histories are compared with an ensemble of coupled climate-ice-sheet model simulations of the Greenland ice sheet. Those most consistent with the reconstructed temperatures indicate that the Greenland ice sheet contributed 5.1 m (4.1–6.2 m, 95% credible interval) to global eustatic sea level toward the end of the Eemian. Greenland likely did not contribute to anomalously high sea levels at ∼127 ka, or to a rapid jump in sea level at ∼120 ka. However, several unexplained discrepancies remain between the inferred and simulated histories of temperature and accumulation rate at GISP2 and NEEM, as well as between the climatic reconstructions themselves.

Do Greenland Ice Cores Reflect NW European Interglacial Climate Variations?

1995 ◽  
Vol 43 (2) ◽  
pp. 125-132 ◽  
Author(s):  
Eiliv Larsen ◽  
Hans Petter Sejrup ◽  
Sigfus J. Johnsen ◽  
Karen Luise Knudsen
Keyword(s):  
Western Europe ◽  
Ice Core ◽  
Greenland Ice Sheet ◽  
Ice Cores ◽  
High Amplitude ◽  
Atlantic Water ◽  
Polar Front ◽  
Norwegian Sea ◽  
The Holocene ◽  
Climatic Evolution

AbstractThe climatic evolution during the Eemian and the Holocene in western Europe is compared with the sea-surface conditions in the Norwegian Sea and with the oxygen-isotope-derived paleotemperature signal in the GRIP and Renland ice cores from Greenland. The records show a warm phase (ca. 3000 yr long) early in the Eemian (substage 5e). This suggests that the Greenland ice sheet, in general, recorded the climate in the region during this time. Rapid fluctuations during late stage 6 and late substage 5e in the GRIP ice core apparently are not recorded in the climatic proxies from western Europe and the Norwegian Sea. This may be due to low resolution in the terrestrial and marine records and/or long response time of the biotic changes. The early Holocene climatic optimum recorded in the terrestrial and marine records in the Norwegian Sea-NW European region is not found in the Summit (GRIP and GISP2) ice cores. However, this warm phase is recorded in the Renland ice core. Due to the proximity of Renland to the Norwegian Sea, this area is probably more influenced by changes in polar front positions which may partly explain this discrepancy. A reduction in the elevation at Summit during the Holocene may, however, be just as important. The high-amplitude shifts during substage 5e in the GRIP core could be due to Atlantic water oscillating closer to, and also reaching, the coast of East Greenland. During the Holocene, Atlantic water was generally located farther east in the Norwegian Sea than during the Eemian.

scholarly journals How warm was Greenland during the last interglacial period?

2016 ◽  
Vol 12 (9) ◽  
pp. 1933-1948 ◽  
Author(s):  
Amaelle Landais ◽  
Valérie Masson-Delmotte ◽  
Emilie Capron ◽  
Petra M. Langebroek ◽  
Pepijn Bakker ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Ice Core ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Water Isotopes ◽  
Interglacial Period ◽  
Last Interglacial ◽  
Last Interglacial Period ◽  
Ice Sheet Topography ◽  
North Greenland

Abstract. The last interglacial period (LIG, ∼ 129–116 thousand years ago) provides the most recent case study of multimillennial polar warming above the preindustrial level and a response of the Greenland and Antarctic ice sheets to this warming, as well as a test bed for climate and ice sheet models. Past changes in Greenland ice sheet thickness and surface temperature during this period were recently derived from the North Greenland Eemian Ice Drilling (NEEM) ice core records, northwest Greenland. The NEEM paradox has emerged from an estimated large local warming above the preindustrial level (7.5 ± 1.8 °C at the deposition site 126 kyr ago without correction for any overall ice sheet altitude changes between the LIG and the preindustrial period) based on water isotopes, together with limited local ice thinning, suggesting more resilience of the real Greenland ice sheet than shown in some ice sheet models. Here, we provide an independent assessment of the average LIG Greenland surface warming using ice core air isotopic composition (δ15N) and relationships between accumulation rate and temperature. The LIG surface temperature at the upstream NEEM deposition site without ice sheet altitude correction is estimated to be warmer by +8.5 ± 2.5 °C compared to the preindustrial period. This temperature estimate is consistent with the 7.5 ± 1.8 °C warming initially determined from NEEM water isotopes but at the upper end of the preindustrial period to LIG temperature difference of +5.2 ± 2.3 °C obtained at the NGRIP (North Greenland Ice Core Project) site by the same method. Climate simulations performed with present-day ice sheet topography lead in general to a warming smaller than reconstructed, but sensitivity tests show that larger amplitudes (up to 5 °C) are produced in response to prescribed changes in sea ice extent and ice sheet topography.

scholarly journals Tracer transport in an isochronal ice-sheet model

2016 ◽  
Vol 63 (237) ◽  
pp. 22-38 ◽  
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.

scholarly journals Bottom Topography and Internal Layers in East Dronning Maud Land, East Antarctica, from 179 MHz Radio Echo-Sounding

1987 ◽  
Vol 9 ◽  
pp. 221-224 ◽  
Author(s):  
Minoru Yoshida ◽  
Kazunobu Yamashita ◽  
Shinji Mae
Keyword(s):  
Cross Sections ◽  
Flow Line ◽  
Bottom Topography ◽  
Ice Core ◽  
Ice Sheet ◽  
Internal Layers ◽  
Radio Echo Sounding ◽  
Dronning Maud Land ◽  
Field Season ◽  
Echo Sounding

Extensive echo-sounding was carried out in east Dronning Maud Land during the 1984 field season. A 179 MHz radar with separate transmitting and receiving antennae was used and the echoes were recorded by a digital system to detect minute reflections. The results gave cross-sections of the ice sheet along traverse routes from lat. 69 °S. to 75°S, Detailed observations on the ground at Mizuho station showed that there was elliptical polarization in the internally reflected echoes when two antennae, kept in parallel with each other, were rotated horizontally. The internal echoes were most clearly distinguished when the antenna azimuth was oriented perpendicular to the flow line of the ice sheet. The internal echoes with a high reflection coefficient were detected at depths of 500–700 m and 1000–1500 m at Mizuho station. Since a distinct internal echo at a depth of 500 m coincides with a 5 cm thick volcanic ash-laden ice layer found in the 700 m ice core taken near the observation site, these echoes may correspond to the acidic ice layers formed by past volcanic events in east Dronning Maud Land.

scholarly journals Study of Deformations within Ice Sheets due to Bottom Undulations by Means of Radio Echo-Sounding

1979 ◽  
Vol 24 (90) ◽  
pp. 513 ◽  
Author(s):  
S. Overgaard ◽  
K. Rasmussen
Keyword(s):  
Ice Sheets ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Flow Lines ◽  
Radio Echo Sounding ◽  
Abstract Data ◽  
Surface Profiles ◽  
Technical University ◽  
Glacier Flow ◽  
Echo Sounding

Abstract In order to test the theory of glacier flow over bedrock undulations presented by S. J. Johnsen, K. Rasmussen, and N.Reeh in the accompanying abstract, data from the E.G.I.G. and the Dye-3 flow lines on the Greenland ice sheet have been analysed. The data comprise surface profiles measured by conventional techniques, and ice thicknesses and depths of internal isochronic layers obtained by the Technical University of Denmark by means of radio echo-soundings.

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

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><span><span>The Dye-3 ice core was drilled to bedrock at the Southern part of the central Greenland ice sheet (65°11'N, 43°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.</span></span></div><div><span>In October and November 2019, the remaining ice, two mostly complete sections covering the depths of 1753–1820m and 1865–1918m 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).</span></div><div> </div><div><span><span>The measured data consist chemistry and impurities contained in the ice, isotopes, as well as analysis of methane and other atmospheric gases. </span></span></div><div><span><span>The chemistry measurements include NH</span></span><span><span><sub>4</sub></span></span><span><span><sup>+</sup></span></span><span><span>, Ca</span></span><span><span><sup>2+</sup></span></span><span><span>, and Na</span></span><span><span><sup>+</sup></span></span><span><span> 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.</span></span></div><div> </div><div><span>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.</span></div>

scholarly journals Potential for stratigraphie folding near ice-sheet centers

2001 ◽  
Vol 47 (159) ◽  
pp. 639-648 ◽  
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.

Microstructure through an Ice Sheet

2013 ◽  
Vol 753 ◽  
pp. 481-484 ◽  
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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