Anthony Kirincich (WHOI)
"The Importance of Lateral Variability on Exchange Across the Inner Shelf South of Martha’s Vineyard, MA
Lateral variations in inner-shelf circulation have the potential to augment the across-shelf exchange primarily driven by the wind. This study uses a combination of high-resolution HF radar-based surface currents and a dense array of moorings south of Martha's Vineyard, MA to document the lateral variability present on the inner shelf and quantify its importance to across-shelf exchange. Averaged over an along-shelf scale of 14 km, the cumulative wind-driven across-shelf transport over the summer was less than the volume of the inner-shelf onshore of the 25-m isobath. Along-shelf variations in the wind-driven exchange were as large as the spatial mean. Independent of the wind forcing, a spatially varying time-averaged circulation, driven by a combination of tidal rectification and horizontal density gradients, resulted in along-shelf density variability, and across-shelf exchange larger than that due to wind forcing. Coherent submesoscale eddies also occurred frequently within the domain due to flow-topography effects onshore and horizontal density gradients offshore, generally with lifespans shorter than 10 hours, diameters smaller than 6 km, and vertical depths shallower than 10 meters.
The across-shelf volume transport due to eddies, estimated by seeding particles within the surface current fields, was more than half the wind-driven depth-dependent exchange. Thus, accounting for the potential coherent along-shelf variability present over the inner-shelf can significantly increase estimates of the across-shelf transfer of water masses and particles."