A first chronology for the North Greenland Eemian Ice Drilling (NEEM) ice core

Rasmussen, S. O.; Abbott, Peter M; Blunier, Thomas; Bourne, A. J.; Brook, Edward J.; Buchardt, S. L.; Buizert, Christo; Chappellaz, J.; Clausen, Henrik; Cook, Eliza; Dahl-Jensen, Dorthe; Davies, Siwan M.; Guillevic, Myriam; Kipfstuhl, Sepp; Laepple, Thomas; Seierstad, Inger K; Severinghaus, Jeffrey P.; Steffensen, Jørgen Peder; Stowasser, C.; Svensson, Anders; Vallelonga, Paul; Vinther, Bo M.; Wilhelms, Frank; Winstrup, Mai

doi:10.5194/cp-9-2713-2013

Cited by 177 publications

(283 citation statements)

References 74 publications

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“…The EDML samples were obtained from 656 m of depth from the EPICA deep ice core drilled between 2003 to 2006 at Kohnen station (75 • 00 S, 0 • 40 E; 2892 m a.s.l.) in the Atlantic sector of East Antarctica (Oerter et al, 2009;Ruth et al, 2007;Wilhelms et al, , 2014 Rasmussen et al, 2013). Both sample depths originated from snow deposited during the Holocene (Ruth et al, 2007;Rasmussen et al, 2013) and have comparably small impurity concentrations (e.g.…”

Section: Methodsmentioning

confidence: 99%

“…in the Atlantic sector of East Antarctica (Oerter et al, 2009;Ruth et al, 2007;Wilhelms et al, , 2014 Rasmussen et al, 2013). Both sample depths originated from snow deposited during the Holocene (Ruth et al, 2007;Rasmussen et al, 2013) and have comparably small impurity concentrations (e.g. Dansgaard et al, 1982;EPICA 2004EPICA , 2006Kuramoto et al, 2011;Wegner et al, 2015).…”

Section: Methodsmentioning

confidence: 99%

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EBSD analysis of subgrain boundaries and dislocation slip systems in Antarctic and Greenland ice

et al. 2017

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Abstract. Ice has a very high plastic anisotropy with easy dislocation glide on basal planes, while glide on non-basal planes is much harder. Basal glide involves dislocations with the Burgers vector b = a , while glide on non-basal planes can involve dislocations with b = a , b = [c], and b = c + a . During the natural ductile flow of polar ice sheets, most of the deformation is expected to occur by basal slip accommodated by other processes, including non-basal slip and grain boundary processes. However, the importance of different accommodating processes is controversial. The recent application of micro-diffraction analysis methods to ice, such as X-ray Laue diffraction and electron backscattered diffraction (EBSD), has demonstrated that subgrain boundaries indicative of non-basal slip are present in naturally deformed ice, although so far the available data sets are limited. In this study we present an analysis of a large number of subgrain boundaries in ice core samples from one depth level from two deep ice cores from Antarctica (EPICA-DML deep ice core at 656 m of depth) and Greenland (NEEM deep ice core at 719 m of depth).EBSD provides information for the characterization of subgrain boundary types and on the dislocations that are likely to be present along the boundary. EBSD analyses, in combination with light microscopy measurements, are presented and interpreted in terms of the dislocation slip systems. The most common subgrain boundaries are indicative of basal a slip with an almost equal occurrence of subgrain boundaries indicative of prism [c] or c + a slip on prism and/or pyramidal planes. A few subgrain boundaries are indicative of prism a slip or slip of a screw dislocations on the basal plane. In addition to these classical polygonization processes that involve the recovery of dislocations into boundaries, alternative mechanisms are discussed for the formation of subgrain boundaries that are not related to the crystallography of the host grain.The finding that subgrain boundaries indicative of nonbasal slip are as frequent as those indicating basal slip is surprising. Our evidence of frequent non-basal slip in naturally deformed polar ice core samples has important implications for discussions on ice about plasticity descriptions, rate-controlling processes which accommodate basal glide, and anisotropic ice flow descriptions of large ice masses with the wider perspective of sea level evolution.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

EBSD analysis of subgrain boundaries and dislocation slip systems in Antarctic and Greenland ice

et al. 2017

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“…In the past, these ice core data have been used to infer the ice sheet's response to the strong warming in the early Eemian (NEEM community members, 2013) and derive ice and gas chronology (Rasmussen et al, 2013). The fabric measured from the NEEM ice core and comparisons with GRIP (Greenland Ice Core Project) and NGRIP (North Greenland Ice Core Project) ice cores may help to constrain ice flow modeling along the ridge from GRIP to NEEM and onwards to Camp Century (Weikusat and Kipfstuhl, 2010;Eichler et al, 2013;Montagnat et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

Multi-channel and multi-polarization radar measurements around the NEEM site

González

Leuschen

et al. 2018

The Cryosphere

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Abstract. Ice properties inferred from multi-polarization measurements, such as birefringence and crystal orientation fabric (COF), can provide insight into ice strain, viscosity, and ice flow. In 2008, the Center for Remote Sensing of Ice Sheets (CReSIS) used a ground-based VHF (very high frequency) radar to take multi-channel and multi-polarization measurements around the NEEM (North Greenland Eemian Ice Drilling) site. The system operated with 30 MHz bandwidth at a center frequency of 150 MHz. This paper describes the radar system, antenna configurations, data collection, and processing and analysis of this data set. Within the framework derived from uniaxial ice crystal model, we found that ice birefringence dominates the power variation patterns of co-polarization and cross-polarization measurements in the area of 100 km 2 around the ice core site. The phase shift between ordinary and extraordinary waves increases nonlinearly with depth. The ice optic axis lies in planes that are close to the vertical plane and perpendicular or parallel to the ice divide depending on depth. The ice optic axis has an average tilt angle of about 11.6 • vertically, and its plane may rotate either clockwise or counterclockwise by about 10 • across the 100 km 2 area, and at a specific location the plane may rotate slightly counterclockwise as depth increases. Comparisons between the radar observations, simulations, and ice core fabric data are in very good agreement. We calculated the effective colatitude at different depths by using azimuth and colatitude measurements of the c axis of ice crystals. We obtained an average effective c axis tilt angle of 9.6 • from the vertical axis, very comparable to the average optic axis tilt angle estimated from radar polarization measurements. The comparisons give us confidence in applying this polarimetric radio echo sounding technique to infer profiles of ice fabric in locations where there are no ice core measurements.

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“…In the updated age calculation we use the ice age found by annual layer counting of the shallow NEEM 2011 S1 core (Sigl et al, 2013). The NEEM chronology published in Rasmussen et al (2013) uses the correct, updated age estimate.Published by Copernicus Publications on behalf of the European Geosciences Union. …”

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confidence: 99%

Corrigendum to ``Gas transport in firn: multiple-tracer characterisation and model intercomparison for NEEM, Northern Greenland'' published in Atmos. Chem. Phys., 12, 4259–-4277, 2012

et al. 2014

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It was kindly pointed out to us by M. Battle that Eq. (2) on p. 4263 contains a typo, and should instead bewhere [X] corr ([X] meas ) is the gravity-corrected (measured) mixing ratio of gas species X, M = M X − M air is the molar mass difference between gas X and air, and δ grav (z) is the gravitational fractionation per unit mass difference at depth z. All calculations in the study were done correctly, following Eq. (2) as given here.Furthermore, the present-day age value for NEEM is incorrect in the orignal manuscript, and underestimates age by 6 years. The correct value is 188 +3 −9 yr. In our original, incorrect calculation we used the ice age in years before 2000 CE (b2k), while we should have used the ice age relative to the surface ice age. In the updated age calculation we use the ice age found by annual layer counting of the shallow NEEM 2011 S1 core (Sigl et al., 2013). The NEEM chronology published in Rasmussen et al. (2013) uses the correct, updated age estimate.Published by Copernicus Publications on behalf of the European Geosciences Union.

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A first chronology for the North Greenland Eemian Ice Drilling (NEEM) ice core

Cited by 177 publications

References 74 publications

EBSD analysis of subgrain boundaries and dislocation slip systems in Antarctic and Greenland ice

EBSD analysis of subgrain boundaries and dislocation slip systems in Antarctic and Greenland ice

Multi-channel and multi-polarization radar measurements around the NEEM site

Corrigendum to ``Gas transport in firn: multiple-tracer characterisation and model intercomparison for NEEM, Northern Greenland'' published in Atmos. Chem. Phys., 12, 4259–-4277, 2012

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