Diagnosing eddy heat transport variability in the North Atlantic from satellite and in-situ observations

The meridional transport of heat by mesoscale eddies constitutes an important component of the total North Atlantic meridional heat transport across the northern boundary of the subtropical gyre, a region that is of vital importance to the northern branch of the Atlantic Meridional Overturning Circulation (AMOC). Temporal and spatial variations in the eddy heat transport are particularly important and can influence the hydrography and dynamics of both the subtropical and subpolar North Atlantic.
This study focuses on the interannual variability of the meridional eddy heat transport across 47°N in the North Atlantic, a latitude close to the boundary between the subpolar and the subtropical gyres. The analysis is based on the combined use of satellite observations of sea surface height anomalies (SSHA) and sea surface temperature (SST) over the 25-year period from 1993 to 2017. The vertical structure of the meridional eddy heat transport is reconstructed in 10°-longitude x 5°-latitude boxes from a composite analysis of Argo profile data and observations of mesoscale eddies in altimetric SSHA. The meridional eddy heat transport is intensified in the surface mixed layer and pycnocline and can vary immensely both zonally and vertically, in some cases reversing sign below the pycnocline. The basin-wide integrated eddy heat transport is in the order of 125 TW, with a standard deviation of 10 TW. During the observed period, the eddy heat transport increased on average by 1.1 TW/year, accelerating to 3.4 TW/year after 2005. The observed trends and variations in the eddy heat transport provide a significant contribution to the variability of the total oceanic heat transport, suggesting a potentially important forcing mechanism in the ocean component of the climate system.