GREENCYCLESII

T5.2 Katherine Crichton

Stocks and fluxes of carbon are not well constrained in the past, and sensitivity of the carbon cycle to climate is even less known. This research project aims at constraining both aspects by combining carbon isotopes data (existing ones and/or acquired by a parallel thesis at LGGE) to a carbon-climate model of intermediate complexity (CLIMBER) in collaboration with D. Roche at LSCE. Especially, recent studies have underlined the potential of continental high latitudes to store huge quantities of carbon, partly released during the last deglaciation. Such emissions would have contributed to increasing the atmospheric CO2 level; and this requires an oceanic contribution smaller than previously thought. The CLIMBER model is equipped with the carbon cycle and the carbon isotopes, and it is well designed to test such a hypothesis.

The main initial goals are:

o to sum up the different estimates of carbon stocks for glacial period;

o to calculate the isotopic fractionation associated to each carbon flux;

o to implement different scenarios of deglaciation and associated carbon fluxes,

o and to simulate changes in carbon stocks and their isotopic compositions;

o to compare these changes with observations, in order to discuss which scenarios are likely or not.

The inferred sensitivity of the carbon stored at high continental latitudes to climatic changes will improve our understanding for the next century. New data acquired from a parallel thesis at LGGE will provide data for the last glaciation. This may also provide some constraints on terrestrial carbon dynamics during a glaciation, and may provide a means of testing 'buried carbon' hypotheses in CLIMBER.