Proposing a mechanistic understanding of atmospheric CO2 during the last 740,000 years

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Köhler, P. and Fischer, H. (2005): Proposing a mechanistic understanding of atmospheric CO2 during the last 740,000 years , Geophysical Research Abstracts, Vol. 7, 02397, 2005. European Geosciences Union, 2nd General Assembly, 24-29 April 2005, Vienna, Austria. .
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Paleo-climate records in ice cores revealed high variability in temperature, atmospheric dust content and CO2. The longest CO2 record from the Antarctic ice core of the Vostok station went back in time as far as about 410 kyr BP showing a switch of glacials and interglacials in all those parameters approximately every 100 kyr during the last four glacial cycles with CO2 varying between 180 280 parts ppmv. New measurements of dust and the isotopic temperature proxy deuterium of the EPICA Dome C ice core covered the last 740 kyr, however, revealed glacial cycles of reduced temperature amplitude. These new archives offer the possibility to propose atmospheric CO2 for the pre-Vostok time span as called for in the EPICA challenge. Here, we contribute to this challenge using a box model of the isotopic carbon cycle (Khler et al., submitted to GBC) based on process understanding previously derived for Termination I and show that major features of the Vostok period are reproduced while prior to Vostok our model predicts significantly smaller amplitudes in CO2 variations. While most processes which impact on CO2 were reduced in their magnitude during the terminations of the pre-Vostok period, the absolute contribution of iron fertilisation changed only slightly. Thus, the relative importance of biological and biogeochemical processes is enhanced (approximately doubling their relative share) in the pre-Vostok period. The contribution of physical processes (SST, sea level, sea ice) to the CO2 rise during terminations stayed always below 25%, while ocean circulation contributed up to 75% during the Vostok era but less than 50% before.

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