Coastal ocean response to summer upwelling favorable winds in a region of alongshore bottom topography variations off Oregon

Repeated mesoscale surveys of waters over the shelf and slope off Oregon were conducted during spring and summer of 2001 to study the spatial structure of the velocity and hydrographic fields. The ocean response to wind forcing is compared between a region of relatively simple topography with alongshore uniformity and a region of complex topography including a shallow submarine bank (Heceta Bank). In the simple topography region the upper water column is influenced by upwelling and fresh water from the Columbia River during spring, with the low-salinity water located farther offshore during summer. Variability in the fields is mostly confined within 30 km from the coast. Over Heceta Bank the region of higher variability is broader, spanning most of the shelf. The coastal upwelling jet is located inshore of the pinnacle of the bank during spring, moving offshore during summer. The region inshore of the bank is characterized by low velocities and flow recirculation. Near-surface fields show that the circulation evolves considerably between seasons. In both regions the area influenced by upwelled water is much broader during summer. Dense waters found over midshelf off Newport are upwelled to the north and advected south. Dense waters inshore of Heceta Bank are substantially influenced by water from the north during spring, but their source is mostly from the south during summer. South of the bank, the separation of the jet significantly increases the cross-isobath transport, constituting an efficient mechanism for transport of material from the shelf into deeper waters.