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Abrupt rise in atmospheric CO2 at the onset of the Bølling/Allerød: in-situ ice core data versus true atmospheric signals

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Köhler, P. , Knorr, G. , Buiron, D. , Lourantou, A. and Chappellaz, J. (2012): Abrupt rise in atmospheric CO2 at the onset of the Bølling/Allerød: in-situ ice core data versus true atmospheric signals , Conference Planet Under Pressure, London, 26 March 2012 - 29 March 2012 .
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During the last glacial/interglacial transition the Earth's climate underwent abrupt changes around 14.6 kyr ago. Temperature proxies from ice cores revealed the onset of the Bølling/Allerød (B/A) warm period in the north and the start of the Antarctic Cold Reversal in the south. Furthermore, the B/A was accompanied by a rapid sea level rise of about 20 m during meltwater pulse (MWP) 1A, whose exact timing is a matter of current debate. In-situ measured CO2 in the EPICA Dome C (EDC) ice core also revealed a remarkable jump of 10±1 ppmv in 230 yr at the same time. Allowing for the modelled age distribution of CO2 in firn, we show that atmospheric CO2 could have jumped by 20–35 ppmv in less than 200 yr, which is a factor of 2–3.5 greater than the CO2 signal recorded in-situ in EDC. This rate of change in atmospheric CO2 corresponds to 29–50% of the anthropogenic signal during the last 50 yr and is connected with a radiative forcing of 0.59–0.75 W m−2. Using a model-based airborne fraction of 0.17 of atmospheric CO2, we infer that 125 Pg of carbon need to be released into the atmosphere to produce such a peak. Available δ13CO2 data are neutral, whether the source of the carbon is of marine or terrestrial origin. We hypothesise that most of the carbon might have been activated as a consequence of continental shelf flooding during MWP-1A. We furthermore plan to challange our hypothesis by comparing its typical 14C signature with so far unpublished high resolution 14C data from Tahiti corals (Durant et al., 2010, Geophysical Research Abstracts, 12, EGU2010-12689-1).This potential impact of rapid sea level rise on atmospheric CO2 might define the point of no return during the last deglaciation.

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