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Modulation of an instantaneous seesaw in ice cores by CO2 pulses

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Knorr, G. , Köhler, P. and Lohmann, G. (2012): Modulation of an instantaneous seesaw in ice cores by CO2 pulses , International Partnership in ICE Core Sciences, First Open Science Conference, Giens, France, 1 October 2012 - 5 October 2012 .
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Abstract:

Abrupt climate swings that characterize the last glacial on millennial timescales are associated with major reorganizations in the Atlantic meridional overturning circulation and changes in the accompanying northward heat transport. The climatic imprint in ice cores shows that times of rapid warming in Greenland are associated with gradual cooling in Antarctica in the course of the so called Dansgaard/Oeschger (D/O) events in the north. Much of the general hemispheric interplay can be explained by the bi-polar thermal seesaw, representing one of the key concepts in paleoclimatology. This conceptual model allows several predictions that can be tested. In particular two fundamental predictions can be used for validation of the thermal seesaw, the existence of a 180° phase shifted signal between Greenland and Antarctica/South Atlantic, with a gradual characteristic in Antarctica and an abrupt signature in the South Atlantic. While recently the latter has been successfully tested against data, it is still open to reconcile the temporal relation of temperature inflections in Antarctica relative to Greenland at D/O events, since on average the associated Antarctic temperature reversals occur about two centuries later than implied by the seesaw. Here we use a comprehensive coupled atmosphere/ocean general circulation model in transient climate simulations. We apply a recently derived greenhouse gas reconstruction for the Bølling/Allerød (B/A), accounting for the modeled age distribution of CO2 in firn. These more realistic pulse like atmospheric greenhouse gas changes, relative to in- situ measurements in ice cores, can explain the temporal shape and the magnitude of temperature changes in Antarctica at the beginning of the B/A. This shows that an underlying inter-hemispheric thermal seesaw response can be reconciled with the observed lag to the predicted temperature decrease in Antarctica at the onset of the abrupt B/A warming in Greenland. In a dynamical and temporal framework of abrupt climate changes these results highlight the importance of an exact knowledge of greenhouse gas concentrations and provide further elementary evidence for the the bi-polar seesaw concept.

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