1Institute of Oceanography, Center for Earth System Research and
Sustainability, Universität Hamburg, Bundesstrasse 53, 20146 Hamburg,
2GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany
3University of Kiel, Kiel, Germany
4Max Planck Institute for Meteorology, Hamburg, Germany
Received: 06 Jun 2016 – Discussion started: 16 Jun 2016
Abstract. We investigate changes in the seasonal cycle of the Atlantic Ocean meridional heat transport (OHT) in a climate projection experiment with the Max Planck Institute Earth System Model (MPI-ESM) performed for the Coupled Model Intercomparison Project Phase 5 (CMIP5). Specifically, we compare a Representative Concentration Pathway (RCP) RCP 8.5 climate change scenario, covering the simulation period from 2005 to 2300, to a historical simulation, covering the simulation period from 1850 to 2005. In RCP 8.5, the OHT declines by 30–50 % in comparison to the historical simulation in the North Atlantic 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 OHT seasonal cycle, we find a northward shift of 5° and latitude-dependent shifts between 1 and 6 months that are mainly associated with changes in the meridional velocity field. We find that the changes in the OHT seasonal cycle predominantly result 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 in turn to latitude-dependent shifts between 1 and 6 months in the overturning component. In comparison to the historical simulation, in the subpolar North Atlantic, in RCP 8.5 we find a reduction of the North Atlantic Deep Water formation and changes in the gyre heat transport result in a strongly weakened seasonal cycle with a weakened amplitude by the end of the 23rd century.
Revised: 17 Dec 2016 – Accepted: 04 Jan 2017 – Published: 22 Feb 2017
Fischer, M., Domeisen, D. I. V., Müller, W. A., and Baehr, J.: Changes in the seasonal cycle of the Atlantic meridional heat transport in a RCP 8.5 climate projection in MPI-ESM, Earth Syst. Dynam., 8, 129-146, doi:10.5194/esd-8-129-2017, 2017.