Description: Abrupt climate changes during the last glacial period have been detected in a global array of palaeoclimate records, but our understanding of their absolute timing and regional synchrony is incomplete. Our compilation of 63 published, independently dated speleothem records shows that abrupt warmings in Greenland were associated with synchronous climate changes across the Asian Monsoon, South American Monsoon, and European-Mediterranean regions that occurred within decades. Together with the demonstration of bipolar synchrony in atmospheric response, this provides independent evidence of synchronous high-latitude–to-tropical coupling of climate changes during these abrupt warmings. Our results provide a globally coherent framework with which to validate model simulations of abrupt climate change and to constrain ice-core chronologies.

Description: Polar ice cores are unique archives recording immediate past atmospheric conditions. They provide, most prominently, reconstructions of past temperature evolution, volcanic eruptions, greenhouse gas concentrations and many other parameters that determine the environmental conditions. The dating of the ice core provides the respective chronology to the recorded past climate conditions. Here, we establish a first chronology for the East Greenland Ice-core Project (EGRIP) core based on matching of electrical conductivity peaks of volcanic origin as recorded by dielectric profiling (DEP) in the EGRIP, NGRIP and NEEM ice cores from Greenland. Our initial dating relies on the transfer of the Greenland Ice Core Chronology 2005 (GICC05) from the NGRIP and NEEM cores to the uppermost 352 m of the EGRIP core from the 2017 field season.

Description: The North East Greenland ice-stream (NEGIS) is the largest active ice-stream on the Greenland ice-sheet and is a crucial contributor to the ice-sheet mass balance. To investigate the ice-stream dynamics and to gain information about the past climate, a deep ice-core is drilled in the upstream part of the NEGIS, termed the East Greenland ice-core project (EastGRIP). Upstream flow effects introduce non-climatic bias in ice-cores and are particularly strong at EastGRIP due to high ice-flow velocities and the location in an ice-stream on the eastern flank of the Greenland ice-sheet. Understanding and ultimately correcting for such effects requires information on the source area and the local atmospheric conditions at the time of ice deposition. We use a two-dimensional Dansgaard-Johnsen model to simulate ice-flow along three approximated flow-lines between the summit of the ice-sheet and EastGRIP. Model parameters are determined using a Monte Carlo inversion by minimizing the misfit between modeled isochrones and isochrones observed in radio-echo-sounding images. We calculate backward-in-time particle trajectories to determine the source area of ice found in the EastGRIP core today and present estimates of surface elevation and past accumulation-rates at the deposition site. The thinning function and accumulated strain obtained from the modeled velocity field provide useful information on the deformation history in the EastGRIP ice. Our results indicate that increased accumulation in the upstream area is predominantly responsible for the constant annual layer thickness observed in the upper part of the ice column at EastGRIP. Inverted model parameters suggest that the imprint of basal melting and sliding is present in large parts along the flow profiles and that most internal ice deformation happens close to the bedrock. The results of this study can act as a basis for applying upstream corrections to a variety of ice-core measurements, and the model parameters can be useful constraints for more sophisticated modeling approaches in the future.

Description: We here present a synchronization of the NGRIP, GRIP, and GISP2 ice cores based mainly on volcanic events over the period 14.9-32.45 ka b2k (before AD 2000), corresponding to Marine Isotope Stage 2 (MIS 2) and the end of MIS 3. The matching provides a basis for applying the recent NGRIP-based Greenland Ice Core Chronology 2005 (GICC05) time scale to the GRIP and GISP2 ice cores, thereby making it possible to compare the synchronized palaeoclimate profiles of the cores in detail and to identify relative accumulation differences between the cores. Based on the matching, a period of anomalous high accumulation rates in the GISP2 ice core is detected within the period 16.5-18.3 ka b2k. The d18O and [Ca2+] profiles of the three cores are presented on the common GICC05 time scale and generally show excellent agreement across the stadial-interstadial transitions and across the two characteristic dust events in Greenland Stadial 3. However, large differences between the d18O and [Ca2+] profiles of the three cores are seen in the same period as the 7-9% increase in the GISP2 accumulation rate. We conclude that changes of the atmospheric circulation are likely to have occurred in this period, altering the spatial gradients in Greenland and resulting in larger variations between the records.

Description: We here report measured densities from a combination of records from the EastGRIP ice-core site. The data come from a trench and two ice cores: the shallow EGRIP-S6 core and the deep main core of the project. Based on these data, we parametrize the density as a function of depth, allowing us to provide a standard transfer function between true depth and ice-equivalent depth which is consistent with the EGRIP density measurements. EGRIP density data are only available to 117 m depth, at which depth the density is about 900 kg/m^3 and the difference between true depth and ice-equivalent depth is about 22 m. The density and overburden profiles have been extended below this depth and all the way to 1200 m in order to provide a convenient, continuous and (mostly) smooth transfer function between true depth and ice-equivalent depth. See PDF file provided under 'Documentation' for full description of data and parametrization.

Description: We here report measured densities from a combination of records from the EastGRIP ice-core site. The data come from a trench and two ice cores: the shallow EGRIP-S6 core and the deep main core of the project. Based on these data, we parametrize the density as a function of depth, allowing us to provide a standard transfer function between true depth and ice-equivalent depth which is consistent with the EGRIP density measurements. EGRIP density data are only available to 117 m depth, at which depth the density is about 900 kg/m^3 and the difference between true depth and ice-equivalent depth is about 22 m. The density and overburden profiles have been extended below this depth and all the way to 1200 m in order to provide a convenient, continuous and (mostly) smooth transfer function between true depth and ice-equivalent depth. See PDF file provided under 'Documentation' for full description of data and parametrization.

Description: We here report measured densities from a combination of records from the EastGRIP ice-core site. The data come from a trench and two ice cores: the shallow EGRIP-S6 core and the deep main core of the project. Based on these data, we parametrize the density as a function of depth, allowing us to provide a standard transfer function between true depth and ice-equivalent depth which is consistent with the EGRIP density measurements. EGRIP density data are only available to 117 m depth, at which depth the density is about 900 kg/m^3 and the difference between true depth and ice-equivalent depth is about 22 m. The density and overburden profiles have been extended below this depth and all the way to 1200 m in order to provide a convenient, continuous and (mostly) smooth transfer function between true depth and ice-equivalent depth. See PDF file provided under 'Documentation' for full description of data and parametrization.

Description: We here report measured densities from a combination of records from the EastGRIP ice-core site. The data come from a trench and two ice cores: the shallow EGRIP-S6 core and the deep main core of the project. Based on these data, we parametrize the density as a function of depth, allowing us to provide a standard transfer function between true depth and ice-equivalent depth which is consistent with the EGRIP density measurements. EGRIP density data are only available to 117 m depth, at which depth the density is about 900 kg/m^3 and the difference between true depth and ice-equivalent depth is about 22 m. The density and overburden profiles have been extended below this depth and all the way to 1200 m in order to provide a convenient, continuous and (mostly) smooth transfer function between true depth and ice-equivalent depth. See PDF file provided under 'Documentation' for full description of data and parametrization.

Description: We here report measured densities from a combination of records from the EastGRIP ice-core site. The data come from a trench and two ice cores: the shallow EGRIP-S6 core and the deep main core of the project. Based on these data, we parametrize the density as a function of depth, allowing us to provide a standard transfer function between true depth and ice-equivalent depth which is consistent with the EGRIP density measurements. EGRIP density data are only available to 117 m depth, at which depth the density is about 900 kg/m^3 and the difference between true depth and ice-equivalent depth is about 22 m. The density and overburden profiles have been extended below this depth and all the way to 1200 m in order to provide a convenient, continuous and (mostly) smooth transfer function between true depth and ice-equivalent depth. See PDF file provided under 'Documentation' for full description of data and parametrization.