Laurent Augustin

Eight glacial cycles from an Antarctic ice core

The Antarctic Vostok ice core provided compelling evidence of the nature of climate, and of climate feedbacks, over the past 420,000 years. Marine records suggest that the amplitude of climate variability was smaller before that time, but such records are often poorly resolved. Moreover, it is not possible to infer the abundance of greenhouse gases in the atmosphere from marine records. Here we report the recovery of a deep ice core from Dome C, Antarctica, that provides a climate record for the past 740,000 years. For the four most recent glacial cycles, the data agree well with the record from Vostok. The earlier period, between 740,000 and 430,000 years ago, was characterized by less pronounced warmth in interglacial periods in Antarctica, but a higher proportion of each cycle was spent in the warm mode. The transition from glacial to interglacial conditions about 430,000 years ago (Termination V) resembles the transition into the present interglacial period in terms of the magnitude of change in temperatures and greenhouse gases, but there are significant differences in the patterns of change. The interglacial stage following Termination V was exceptionally long—28,000 years compared to, for example, the 12,000 years recorded so far in the present interglacial period. Given the similarities between this earlier warm period and today, our results may imply that without human intervention, a climate similar to the present one would extend well into the future.The Antarctic Vostok ice core provided compelling evidence of the nature of climate, and of climate feedbacks, over the past 420,000 years. Marine records suggest that the amplitude of climate variability was smaller before that time, but such records are often poorly resolved. Moreover, it is not possible to infer the abundance of greenhouse gases in the atmosphere from marine records. Here we report the recovery of a deep ice core from Dome C, Antarctica, that provides a climate record for the past 740,000 years. For the four most recent glacial cycles, the data agree well with the record from Vostok. The earlier period, between 740,000 and 430,000 years ago, was characterized by less pronounced warmth in interglacial periods in Antarctica, but a higher proportion of each cycle was spent in the warm mode. The transition from glacial to interglacial conditions about 430,000 years ago (Termination V) resembles the transition into the present interglacial period in terms of the magnitude of change in temperatures and greenhouse gases, but there are significant differences in the patterns of change. The interglacial stage following Termination V was exceptionally long—28,000 years compared to, for example, the 12,000 years recorded so far in the present interglacial period. Given the similarities between this earlier warm period and today, our results may imply that without human intervention, a climate similar to the present one would extend well into the future.

The Hans Tausen drill: design, performance, further developments and some lessons learned

Abstract In the mid-1990s, excellent results from the GRIP and GISP2 deep drilling projects in Greenland opened up funding for continued ice-coring efforts in Antarctica (EPICA) and Greenland (NorthGRIP). The Glaciology Group of the Niels Bohr Institute, University of Copenhagen, was assigned the task of providing drilling capability for these projects, as it had done for the GRIP project. The group decided to further simplify existing deep drill designs for better reliability and ease of handling. The drill design decided upon was successfully tested on Hans Tausen Ice Cap, Peary Land, Greenland, in 1995. The 5.0m long Hans Tausen (HT) drill was a prototype for the ~11m long EPICA and NorthGRIP versions of the drill which were mechanically identical to the HT drill except for a much longer core barrel and chips chamber. These drills could deliver up to 4m long ice cores after some design improvements had been introduced. The Berkner Island (Antarctica) drill is also an extended HT drill capable of drilling 2 m long cores. The success of the mechanical design of the HT drill is manifested by over 12 km of good-quality ice cores drilled by the HT drill and its derivatives since 1995.

Erosion record in Lake La Thuile sediments (Prealps, France): Evidence of montane landscape dynamics throughout the Holocene:

Lake La Thuile, in the Northern French Prealps (874 m a.s.l.), provides an 18-m long sedimentary sequence spanning the entire Lateglacial/Holocene period. The high-resolution multi-proxy (sedimentological, palynological, and geochemical) analysis of the uppermost 6.2 m reveals the Holocene dynamics of erosion in the catchment in response to landscape modifications. The mountain belt is at relevant altitude to study past human activities, and the watershed is sufficiently disconnected from large valleys to capture a local sedimentary signal. From 12,000 to 10,000 cal. BP (10–8 kyr cal. BC), the onset of hardwood species triggered a drop in erosion following the Lateglacial/Holocene transition. From 10,000 to 4500 cal. BP (8–2.5 kyr cal. BC), the forest became denser and favored slope stabilization, while erosion processes were very weak. A first erosive phase was initiated at ca. 4500 cal. BP without evidence of human presence in the catchment. Then, the forest declined at approximately 3000 cal. BP, suggesting the first human influence on the landscape. Two other erosive phases are related to anthropic activities: approximately 2500 cal. BP (550 cal. BC) during the Roman period and after 1600 cal. BP (350 cal. AD) with a substantial accentuation in the Middle Ages. In contrast, the lower erosion produced during the ‘Little Ice Age’, when climate deteriorations are generally considered to result in an increased erosion signal in this region, suggests that anthropic activities dominated the erosive processes and completely masked the natural effects of climate on erosion in the late Holocene.

Extending The Ice Core Record Beyond Half A Million Years

Ice cores have been a crucial source of information about past changes in the climate and atmosphere. The Vostok ice core from Antarctica has provided key global change data sets extending 400,000 years in the past [Petit et al., 1999], while Japanese scientists drilling at Dome Fuji have obtained records extending to 330,000 years. Now, a new core being drilled by a consortium of European laboratories has surpassed these ages, and looks like its extending the ice core record several hundred thousand years into the past. Ice cores are unique: of all the paleo-records, they have the most direct linkage with the atmosphere. At some sites, the time resolution is sufficient to study extremely fast climate changes; and they have information about many forcing factors for climate (including greenhouse gas concentrations) displayed in the same cores as the resulting climate changes. Ice cores have already played a central role in informing the debate about global change, providing the only direct evidence of historical changes in greenhouse gas concentrations, the clearest evidence of past linkage between greenhouse gases and climate, and the first indication that very rapid climate changes (linked to changes in thermohaline circulation) occurred in recent Earth history Both European and U.S. ice core scientists scored major successes with the completion of cores to bedrock in central Greenland in the early 1990s (the Greenland Ice Core Project (GRIP), and the Greenland Ice Sheet Project Two (GISP2)) [Hammer et al., 1997]. To follow this up, the next challenge was to produce a series of equally definitive records from Antarctica. The European team turned their eyes to central Antarctica, and formed the European Project for Ice Coring in Antarctica (EPICA). This is a consortium of laboratories from 10 European nations, under the auspices of the European Science Foundation (ESF), and funded by the European Union (EU) and national organizations. EPICA aims to drill two cores to bedrock, one at Concordia Station, Dome C (75°06’S, 123°24’E), the other at Kohnen Station in Dronning Maud Land (DML) (75°00’S, 00°04’E). The Dome C drilling aims to retrieve a record covering a time period that is as long as possible, while the DML drilling aims to retrieve a high-resolution record of one complete glacial-interglacial cycle at a site facing the Atlantic Ocean. The DML drilling made a successful start during the 2001-2002 austral summer, completing the drill installation, and penetrating to a depth of 450.94 m, which means the core has reached early Holocene ice. At Dome C, this was a major year of drilling, with the drill reaching 2864 m below the surface, just 400 m above the estimated depth of bedrock. This article describes the work at Dome C during the past season.