AMOC- vs. gyre-driven heat transport variability: a new method for attributing North Atlantic ocean heat transport

Abstract:

Interannual to decadal variability in North Atlantic sea surface temperatures is thought to have a broad-reaching impact on climate. Ocean heat content variability in the subpolar North Atlantic is predominantly driven by ocean heat transport through 45⁰N. It is still unclear what fraction of this ocean heat transport variability is controlled by the wind-driven gyres, and what fraction is controlled by the Atlantic Meridional Overturning Circulation (AMOC). In this work, we present a new physically-based method for separating these two components of the heat transport. This method makes use of isopycnal coordinates and identifies physical boundaries between the upper AMOC, the deep western boundary current, and the gyre, to produce a new division of ocean heat transport while still respecting mass conservation. We apply this new method to the CESM large ensemble and evaluate the importance of gyre-driven vs. overturning-driven heat transport on multiple timescales. Results have important implications for the behavior of the AMOC, which plays a key role in regulating surface temperatures around the North Atlantic.