Contribution of ocean physics and dynamics at different scales to heat uptake in low-resolution aogcms

Abstract

Using an ensemble of atmosphere-ocean general circulation models (AOGCMs) in an idealized climate change experiment, this study quantifies the contributions to ocean heat uptake (OHU) from ocean physical parameterizations and resolved dynamical processes operating at different scales. Analysis of heat budget diagnostics reveals a leadingorder global heat balance in the subsurface upper ocean in a steady state between the large-scale circulation warming it and mesoscale processes cooling it, and shows that there are positive contributions from processes on all scales to the subsurface OHU during climate change. There is better agreement among the AOGCMs in the net OHUthan in the individual scales/ processes contributing to it. In the upper ocean and at high latitudes,OHUis dominated by small-scale diapycnal processes. Below 400 m,OHUis dominated by the superresidual transport, representing large-scale ocean dynamics combined with all parameterized mesoscale and submesoscale eddy effects. Weakening of the AMOC leads to less heat convergence in the subpolar NorthAtlantic and less heat divergence at lower latitudes, with a small overall effect on the netAtlantic heat content. At low latitudes, the dominance of advective heat redistribution is contrary to the diffusive OHU mechanism assumed by the commonly used upwelling-diffusion model. Using a density water-mass framework, it is found that most of the OHU occurs along isopycnal directions. This feature ofOHUis used to accurately reconstruct the global vertical oceanwarming profile from the surface heat flux anomalies, supporting advective (rather than diffusive) models of OHU and sea level rise.