Environment Counts | Vostok correlation of temperature and greenhouse gas concentrations during the last 420,000 years and four glacial-interglacial cycles
Author: Geoff Zeiss – Published At: 2012-04-07 14:33 – (2005 Reads)
In January 1998, the collaborative ice-drilling project between Russia, the United States, and France at the Russian Vostok station in East Antarctica yielded the deepest ice core ever recovered, reaching a depth of 3,623 m. The data indicate the Vostok ice-core record extends through four climate cycles, with with the oldest ice of about 420 kyr. Atmospheric concentrations of carbon dioxide and methane correlate closely with Antarctic air-temperature throughout the record. Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica, NATURE, VOL 399, 3 JUNE 1999
The late Quaternary period (the past one million years) is punctuated by a series of large glacialâ€“interglacial changes with cycles that last about 100,000 years. Glacial-interglacial climate changes are documented by complementary climate records largely derived from deep sea sediments, continental deposits of flora, fauna and loess, and ice cores. These studies have documented the wide range of climate variability on Earth. They have shown that much of the variability occurs with periodicities corresponding to that of the precession, obliquity and eccentricity of the Earthâ€™s orbit1. But understanding how the climate system responds to this initial orbital forcing is still an important issue in palaeoclimatology, in particular for the generally strong 100,000-year (100-kyr) cycle.
Ice cores give access to palaeoclimate series that includes local temperature and precipitation rate, moisture source conditions, wind strength and aerosol fluxes of marine, volcanic, terrestrial, cosmogenic and anthropogenic origin. They are also unique with their entrapped air inclusions in providing direct records of past changes in atmospheric trace-gas composition.
Figure Vostok time series and insolation. Series with respect to time (GT4 timescale for ice on the lower axis, with indication of corresponding depths on the top axis) of
- b isotopic temperature of the atmosphere
- d atmospheric delta-O18
- e mid-June insolation at 65 degrees N (in Wm-2)
Sequence of events in last four glacial terminations
Properties change in the following sequence during each of the last four glacial terminations, as recorded in Vostok. First, the temperature and atmospheric concentrations of CO2 and CH4 rise steadily, whereas the dust input decreases. During the last half of the temperature rise, there is a rapid increase in CH4. This event coincides with the start of the delta-oxygen-18 (Î´ 18O) decrease. The authors believe that the rapid CH4 rise also signifies warming in Greenland, and that the deglacial delta-oxygen-18 decrease records rapid melting of the Northern Hemisphere ice sheets.
Figure Vostok time series during glacial terminations. Variations with respect to time (GT4) of
- temperature (proxy is delta-deuterium)
These results suggest that the same sequence of climate forcing operated during each termination:
- orbital forcing (with a possible contribution of local insolation changes) followed by two strong amplifiers,
- greenhouse gases acting first, then
- deglaciation and ice-albedo feedback.
Considering the large gas-age/ice age uncertainty (1,000 years or more), the authors say it is premature to infer the sign of the phase relationship between CO2 and temperature at the start of terminations.
The authors point out an intriguing feature of the deglacial CH4 curves is that the atmospheric concentration of CH4 rises slowly, then jumps to a maximum value during the last half of the deglacial temperature rise.
Present-day atmospheric burdens of CO2 and CH4 seem to have been unprecedented during the past 420,000 years.
NATURE, VOL 399, 3 JUNE 1999