Session: Glacial Climates (LGM, Last deglaciation, Ice sheet uncertainties, Glacial-interglacial cycles)
Author: Masa Kageyama / Masa.Kageyama@lsce.ipsl.fr / LSCE-IPSL
Co-author: Tilla Roy, ECOCEANA;
Pascale Braconnot, LSCE-IPSL;
The Last Glacial Maximum (LGM) tropical sea surface temperatures (SSTs) may have a high potential to constrain the climate sensitivity to CO2 (e.g. Hargreaves et al., 2007). Careful comparison of the PMIP model results to SST reconstructions (such as MARGO, 2009) could, therefore, be crucial in our evaluation of the climate models used for prediction. The MARGO reconstructions are based on several indicators including foraminifer assemblages, alkenones and Mg/Ca. These do not always yield the same SST estimates for the LGM, and collectively show larger spatial variability than the model results. Here, we examine the changes in the habitat of coccolithophores and foraminifera (in particular G. ruber) between the Last Glacial Maximum and the pre-industrial. We use the IPSL model to represent the coccolithophores, in which a representation of nanophytoplankton is included via the PISCES ocean biogeochemistry model, and the FORAMCLIM model to compute the abundance of 8 species of foraminifera. We show that coccolithophores could record temperatures at a deeper depth than G. ruber, which could help reconstruct the thermal gradients of the upper ocean. Ultimately, this could lead to an increased knowledge of the ocean circulation, and could provide additional constraints on the atmospheric circulation since it is tightly coupled to the ocean circulation in this region. This last part of the work is based on the PMIP3 results and could be extended to PMIP4 results if available at the time of the conference.