Gulf Stream transport and pathway variability: the importance of air-sea fluxes

Abstract

Understanding the various mechanisms that control path and transport variability of the Gulf Stream (GS) is important due to its major role in the global redistri- bution of heat. This work provides evidence that localised surface heat fluxes can induce changes in the path and strength of the GS.
Interannual path and transport variability of the GS are calculated here using different methods in a range of observational products, which are compared to high resolution (eddy-resolving) ocean model output. It is shown that changes in the baroclinic transport, i.e. the density-driven component, are crucial in controlling total GS transport variability. Furthermore, observational and model evidence was found that intense air-sea fluxes during severe winters alters the cross-stream density structure and in turn the GS transport compared to the previous year. The investigation found that these years were also associated with deeper mixed layers, strengthened meridional temperature gradients (to the north and south of the GS core) and an intensified westward component of the southern recirculation.
Lagrangian analysis is performed to examine GS pathway variability. Distinctive characteristics of the recirculating and Subpolar Gyre (SPG)-bound pathways are revealed. In particular, a more direct, faster, subsurface pathway to the SPG is revealed than has been found previously. By demonstrating that this pathway had increased throughput to this region during the 1990s, it is possible for the first time to reconcile the 1990s SPG warming with a Lagrangian approach. The influx of warm water during this decade is related to air-sea fluxes associated with the North Atlantic Oscillation (NAO). Additionally, near-surface pathways are significantly correlated to the wind stress curl over the STG.

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