The Impact of fresh water flux on the Mediterranean thermohaline circulation: models inter-comparison study

Sapropels -organic matter rich layers- are common in Neogene sediments of the Mediterranean Sea. The formation of these layers is known to occur at precession minima and has been attributed to: (1) increased production of organic-matter and (2) increased preservation due to a decrease in the Thermohaline Circulation (THC) and hence oxygenation of the deep waters. In one hand, we assess the response of the Mediterranean THC to the climate system changes (Precipitation, Evaporation and Runoff), and in the other hand, we test the impact of the horizontal grid resolution on the model results. For this goal, we used ocean general circulation models (POM, MOMA and MED16) to simulate the Mediterranean THC for the present day and a precession minimum situation. POM, MOMA and MED16 have a horizontal grid mesh of 1 x 1 degrees, 1/4 x 1/4 degrees and 1/16 x 1/16 degrees respectively. The models are able to capture reasonably the Mediterranean THC components in agreement with the literature. All the experiments show that the fresh water flux (E-P-R) plays an important role in dense water formation. As the precipitation increases, the Mediterranean THC weakens which appears consistent with the "sapropel mode" of circulation. Low salinity values in the Mediterranean basin are found to be associated with the lower model resolution. The insights already gained from this study will serve as a basis for understanding the effects of climate change on a longer time scale. This work is supported by Utrecht Center of Geosciences (Netherlands); Computing was done at VMSG (Netherlands) and at IDRIS (France).