The importance of air-sea fluxes on the variability of Gulf Stream pathways from a Lagrangian perspective
The throughput of subtropical waters to the subpolar region in the North Atlantic is evident in both observations and models. Using Lagrangian methods, this throughput has been found to be much less than North Atlantic Current (NAC) transport of around 20 Sv. Water parcels residing in the subtropical gyre (STG) are understood to largely recirculate within this region before entrainment into the NAC, reaching the subpolar gyre (SPG) after about 5 years, while faster (<1 year) direct transport of Gulf Stream (GS) waters into the SPG, via the NAC, has remained elusive. Here, large ensembles of particle trajectories are computed using currents from a 31-year eddy-resolving model hindcast, to explore the direct pathways of GS waters, starting from the Florida Straits at 26oN at depths ranging from the surface to 300 m. The variability of these pathways is quantified with depth and on seasonal and interannual timescales with strong air-sea fluxes found to be imperative for near-surface and sub-surface pathways. The trajectory density (i.e. the number of trajectories passing through each grid cell), depth, temperature and age are also examined in order to assess the potential impact from decadal variability in throughput to the SPG.