Search

The recent completion of drilling at Vostok station in East Antarctica has allowed the extension of the ice record of atmospheric composition and climate to the past four glacial-interglacial cycles. The succession of changes through each climate cycle and termination was similar, and atmospheric and climate properties oscillated between stable bounds. Interglacial periods differed in temporal evolution and duration. Atmospheric concentrations of carbon dioxide and methane correlate well with Antarctic air-temperature throughout the record. Present-day atmospheric burdens of these two important greenhouse gases seem to have been unprecedented during the past 420,000 years.

Author(s): EPICA Community Members; EPICA Community Members; C. Barbante [1, 2]; J.-M. Barnola [3]; S. Becagli [4]; J. Beer [5]; M. Bigler [6, 7]; C. Boutron [3]; T. Blunier [6]; [...]

Author(s): O. Watanabe [1]; J. Jouzel (corresponding author) [2]; S. Johnsen [3]; F. Parrenin [2, 4]; H. Shoji [5]; N. Yoshida [6, 7] Recent ice core studies have raised the [...]

Author(s): D. Genty (corresponding author) [1]; D. Blamart [1]; R. Ouahdi [1]; M. Gilmour [2]; A. Baker [3]; J. Jouzel [1]; Sandra Van-Exter [4] The signature of Dansgaard-Oeschger events--millennial-scale abrupt [...]

A deuterium-excess history has been obtained from ice cores from Vostok, East Antarctica, covering the glacial-interglacial cycle of the past 150,000 years. A strong anticorrelation with the orbital obliquity of the Earth was found and values are higher during the cold stage 5d, possibly driven by relatively less moisture from high latitudes and more from low latitudes. The deuterium-excess is thus able to give long-term, spatially integrated data on ocean surface conditions.

An understanding of how climate events in the Northern and Southern hemispheres are related is one of the main issues of climate dynamics. A new study uses the atmospheric methane concentrations of air bubbles trapped in ice cores from Greenland and Antarctica to determine the timing of temperature change in the two regions. It is found that, on average, climate change in Greenland lagged that of the Antarctic by 1000-2500 years during the last interglacial period. Such a time delay suggests that the oceans play an important part in transmitting climate changes.

A new glaciological time-scale that is consistent with ocean records has been established for the Vostok station in Antarctica. Ice-core records which reveal local temperature, dust accumulation and air composition extend the glaciological time-scale to the penultimate glacial period, approximately 140,000 to 200,000 years ago. Vostok's penultimate glacial period was colder t the most recent one, and concentrations of carbon dioxide and CH4 correlate well in relation to temperature throughout the record.

The climate in the Holocene period in Greenland fluctuating between stable and unstable, as revealed by the results obtained from the Greenland Ice-core Project (GRIP) studies. The unstable climatic conditions are represented by the cores which formed during the two glaciations and the Eemian interglacial which occurs between the two glaciations. The stability of the climate is determined by the estimation of the oxygen isotope record from the ice cores. The climatic changes are caused by variations in the atmospheric temperature.

Analysis of an ice core from Greenland indicates that interglacial periods do not normally have as stable a climate as the current Holocene period displays. The stable-isotope record indicates that climate can change drastically within as little as a few decades. This implies that the current climate may not stay stable as pollutants and greenhouse gasses are added. The last interglacial may also have lasted longer than previously thought.

Oxygen isotope levels from an ice core taken from the summit of Greenland's ice sheet confirmed previous evidence for the episodic occurrence of interstadials or periods of comparatively warm climate during the last glaciation. These interstadials, which were from 500 to 2,000 years in duration, developed sporadically probably because of the highly complex and variable circulation of the North Atlantic.

An ice core drilled at Dome C, Antarctica, is the oldest ice core so far retrieved. On the basis of ice flow modelling and a comparison between the deuterium signal in the ice with climate records from marine sediment cores, the ice at a depth of 3,190 m in the Dome C core is believed to have been deposited around 800,000 years ago, offering a rare opportunity to study climatic and environmental conditions over this time period. However, an independent determination of this age is important because the deuterium profile below a depth of 3,190 m depth does not show the expected correlation with the marine record. Here we present evidence for enhanced 10Be deposition in the ice at 3,160–3,170 m, which we interpret as a result of the low dipole field strength during the Matuyama–Brunhes geomagnetic reversal, which occurred about 780,000 years ago. If correct, this provides a crucial tie point between ice cores, marine cores and a radiometric timescale. [ABSTRACT FROM AUTHOR]

Presents the complete oxygen isotope record for the Greenland Ice Sheet Project (GISP2) core, drilled 28 kilometers west of the GRIP core. Large, rapid climate fluctuations throughout the glacial period, which closely match those reported for the GRIP core; Significant differences between the two records in the bottom 10 percent of the cores; Alteration due to ice flow.

Changes in past atmospheric carbon dioxide concentrations can be determined by measuring the composition of air trapped in ice cores from Antarctica. So far, the Antarctic Vostok and EPICA Dome C ice cores have provided a composite record of atmospheric carbon dioxide levels over the past 650,000 years. Here we present results of the lowest 200 m of the Dome C ice core, extending the record of atmospheric carbon dioxide concentration by two complete glacial cycles to 800,000 yr before present. From previously published data and the present work, we find that atmospheric carbon dioxide is strongly correlated with Antarctic temperature throughout eight glacial cycles but with significantly lower concentrations between 650,000 and 750,000 yr before present. Carbon dioxide levels are below 180 parts per million by volume (p.p.m.v.) for a period of 3,000 yr during Marine Isotope Stage 16, possibly reflecting more pronounced oceanic carbon storage. We report the lowest carbon dioxide concentration measured in an ice core, which extends the pre-industrial range of carbon dioxide concentrations during the late Quaternary by about 10 p.p.m.v. to 172-300 p.p.m.v.

The Milankovitch theory of climate change proposes that glacial-interglacial cycles are driven by changes in summer insolation at high northern latitudes. The timing of climate change in the Southern Hemisphere at glacial-interglacial transitions (which are known as terminations) relative to variations in summer insolation in the Northern Hemisphere is an important test of this hypothesis. So far, it has only been possible to apply this test to the most recent termination, because the dating uncertainty associated with older terminations is too large to allow phase relationships to be determined. Here we present a new chronology of Antarctic climate change over the past 360,000 years that is based on the ratio of oxygen to nitrogen molecules in air trapped in the Dome Fuji and Vostok ice cores. This ratio is a proxy for local summer insolation, and thus allows the chronology to be constructed by orbital tuning without the need to assume a lag between a climate record and an orbital parameter. The accuracy of the chronology allows us to examine the phase relationships between climate records from the ice cores and changes in insolation. Our results indicate that orbital-scale Antarctic climate change lags Northern Hemisphere insolation by a few millennia, and that the increases in Antarctic temperature and atmospheric carbon dioxide concentration during the last four terminations occurred within the rising phase of Northern Hemisphere summer insolation. These results support the Milankovitch theory that Northern Hemisphere summer insolation triggered the last four deglaciations.

Two deep ice cores from central Greenland, drilled in the 1990s, have played a key role in climate reconstructions of the Northern Hemisphere, but the oldest sections of the cores were disturbed in chronology owing to ice folding near the bedrock. Here we present an undisturbed climate record from a North Greenland ice core, which extends back to 123,000 years before the present, within the last interglacial period. The oxygen isotopes in the ice imply that climate was stable during the last interglacial period, with temperatures 5 degrees C warmer than today. We find unexpectedly large temperature differences between our new record from northern Greenland and the undisturbed sections of the cores from central Greenland, suggesting that the extent of ice in the Northern Hemisphere modulated the latitudinal temperature gradients in Greenland. This record shows a slow decline in temperatures that marked the initiation of the last glacial period. Our record reveals a hitherto unrecognized warm period initiated by an abrupt climate warming about 115,000 years ago, before glacial conditions were fully developed. This event does not appear to have an immediate Antarctic counterpart, suggesting that the climate see-saw between the hemispheres (which dominated the last glacial period) was not operating at this time.

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.