Meridional Eddy Heat Transport Variability in the Surface Mixed Layer of the Atlantic Ocean

We analyze the interannual variability and trends of the eddy heat transport (EHT) in the surface mixed layer of the Atlantic Ocean from covariances of sea surface temperature (SST) and geostrophic velocities from satellite observations between 1993 and 2018. The EHT is largest along the path of the Gulf Stream in the Northern Hemisphere and the vicinity of the Agulhas Retroflection and Argentine basin in the Southern Hemisphere. On average, meridional EHT in the mixed layer leads to a divergence of heat away from the subtropics in both hemispheres toward the equator and higher latitudes. Depending on latitude, the divergence of the EHT accounts for around 1%-5% of the atmospheric net surface heat flux, but reaches as much as 20% for certain regions. The EHT can be linked to eddy kinetic energy (EKE) and meridional SST gradients using mixing length hypothesis, but the variability of EKE and SST gradients are not enough to capture local EHT variability. For different latitudes, the EHT shows different behavior over time, with a strong increase in northward EHT in the Gulf Stream region, and a decadal oscillation of poleward EHT in the tropical and subtropical regions. This oscillation on larger scales is highly correlated with spatially averaged EKE and the large-scale SST gradients. A comparison with climate indices indicates a relation to Atlantic climate variability, especially the meridional modes of the Tropical Atlantic Variability and the North Atlantic Oscillation (NAO).