Lagrangian Pathways of Temperature Anomalies from the Subtropical to the Subpolar Gyre in the North Atlantic

Abstract:

We explore pathways of subtropical waters to the subpolar gyre in the North Atlantic in order to understand the extent to which temperature anomalies associated with the throughput are transported to the subpolar region. Past studies with both modeled and observed Lagrangian floats have indicated that surface throughput between the two gyres is limited and that sub-surface pathways dominate. We translate these results to the oceanic heat transport through three steps. We first use the modern SST record (1981-2013) to reconcile the lack of inter-gyre connectivity at the surface with previous findings that showed a propagation of surface thermal anomalies from the subtropics to the subpolar gyre on interannual time scales. We then use synthetic trajectories in the FLAME model launched from the Cape Hatteras region to calculate the Lagrangian integral time scales of temperature anomalies along the Gulf Stream/North Atlantic Current path. We compare these time scales to the time it takes for particles to reach the subpolar gyre in order to understand whether, on average, particles advect any memory of their anomalous temperature into the subpolar region. Finally, rather than studying the thermal anomalies for individual trajectories, we use the synthetic trajectories from FLAME to determine whether the trajectories that reach the subpolar gyre at a given time period collectively influence the upper ocean temperature of the region.