ALBERT

Description: We investigate the effect of a projected reduction in the Atlantic Ocean meridional heat transport (OHT) on changes in its seasonal cycle. We analyze a climate projection experiment with the Max-Planck Institute Earth System Model (MPI-ESM) performed for the Coupled Model Intercomparison Project phase 5 (CMIP5). In the RCP8.5 climate change scenario, the OHT declines in MPI-ESM in the North Atlantic by 30–50 % by the end of the 23rd century. The decline in the OHT is accompanied by a change in the seasonal cycle of the total OHT and its components. We decompose the OHT into overturning and gyre component. For the total OHT seasonal cycle, we find a northward shift of 5 degrees and latitude dependent temporal shifts of 1 to 6 months that are mainly associated with changes in the meridional velocity field. We find that the shift in the OHT seasonal cycle predominantly results from changes in the wind-driven surface circulation which projects onto the overturning component of the OHT in the tropical and subtropical North Atlantic. This leads to latitude dependent shifts of 1 to 6 months in the overturning component. In the subpolar North Atlantic, we find that the reduction of the North Atlantic Deep Water formation in RCP8.5 and changes in the gyre heat transport result in a strongly weakened seasonal cycle with a weakened seasonal amplitude by the end of the 23rd century and thus changes the OHT seasonal cycle in the SPG.