A regional Earth System Model has been implemented for the South Asia region. We investigate the effect of the marine biogeochemical feedback which affects the attenuation of the short-wave radiation upon the regional climate. In the experiment where the feedback is activated the average SST is lower over most of the domain. The greatest deviations (more than 1°C) in SST between the two runs occur in the summer period during the phytoplankton bloom. A significant cooling of subsurface layers occurs and the thermocline shifts upward compared to the Jerlov type absorption. The phytoplankton primary production and its deviation in the feedback-based simulation turned out to be higher, especially during periods of winter and summer phytoplankton blooms. The marine biogeochemistry feedback also affects the amount of precipitation in the model in particular during the monsoon season. The associated SST cooling leads to a reduction of the precipitation but affects it in different ways. In the Arabian Sea, the reduction of the transport of humidity across the equator leads to a reduction of the large scale precipitation in the eastern part of the basin, reinforcing reduction of the convective precipitation. In the Bay of Bengal, the feedback increases the large scale precipitation, contouring the decrease of convective precipitation. Thus, the main impacts of including the biogeochemical coupling in the Indian Ocean include the enhanced phytoplankton primary production, a shallower thermocline and decreased SST, with cascading effects upon the model ocean physics which further translates into altered atmosphere dynamics.

Deep water formation (DWF) in the North Western Mediterranean (NWMed) is a key feature of Mediterranean overturning circulation. Changes in DWF under global warming may have an impact on the regional and even on the global climate. Here we analyze the deep convection in the Gulf of Lions (GoL) in a changing climate using an atmosphere-ocean regional coupled model with a high horizontal resolution enough to represent DWF. We find that under the RCP8.5 scenario the NWMed DWF collapses by 2040-2050, leading to almost a 90% shoaling in the winter mixed layer depth by the end of the century. The collapse is mainly related to changes in sea water temperature and salinity of Modified Atlantic Water (MAW) and Levantine Intermediate Water (LIW) that strengthen the vertical stratification in the GoL. The stratification changes also alter the Mediterranean overturning circulation and the water, heat and salinity exchange with the Atlantic.

Using the depth (z) and density (ϱ) frameworks, we analyze local contributions to AMOC variability in a 900-year simulation with the AWI climate model. Both frameworks reveal a consistent interdecadal variability, however the correlation between their maxima deteriorates on year-to-year scales. We demonstrate the utility of analyzing the spatial patterns of sinking and diapycnal transformations through depth levels and isopycnals. The success of this analysis relies on the spatial binning of these maps which is especially crucial for the maps of vertical velocities which appear to be too noisy in the main regions of up- and downwelling because of stepwise bottom topography. Furthermore, we show that the AMOC responds to fast (annual or faster) fluctuations in atmospheric forcing associated with the NAO. This response is more obvious in the ϱ than in the z framework. In contrast, the link between AMOC deep water production south of Greenland is found for slower fluctuations and is consistent between the frameworks.