Gulf Stream’s Induced Variations in Coastal Sea Level: Can the Same Mechanism Work From Daily to Decadal Time-Scales?

Since early on (back in the 1930s) studies have suggested that some variations in coastal sea level along the U.S. East Coast may have origin in deep ocean currents, and in particular, may relate to variations in the Gulf Stream (GS) transport and position. Recent studies confirm that interannual and decadal variations in the transport of the Atlantic Meridional Overturning Circulation (AMOC) and in the Gulf Stream contribute to coastal sea level variability. On short time-scales of days to weeks observations also show coherent sea level anomalies along the coast that seem to correlate with variations in the transport of the GS- these variations are not driven by local wind and thus are often unpredictable, causing unexpected minor tidal flooding in low-lying areas. An idealized numerical model of the GS has been set up to test the proposition that high-frequency variations in the GS can contribute to coherent variations in coastal sea level. The results show that such variations in coastal sea level can be generated by oscillations in the Florida Current transport with periods as short as 2-10 days. Fast propagating barotropic waves redistribute the GS signal to shallow regions, from the coast of Florida to the Gulf of Maine. In this idealized model, the coastal sea level variations induced by variations of ~10 Sv in the transport of the GS are equivalent to variations induced by ~5 m/s zonal wind fluctuations, though the mechanisms of wind-driven and GS-driven sea level are quite different. Variations in GS transport are related to variations in sea level gradients across the stream that can generate coastal sea level variability on a wide range of time scales, from days to decades, and even affect long-term sea level rise trends. In general, weakening GS current is thus related to increased coastal sea level independent of the time scale involved.