Rapid generation of upwelling at a shelf break caused by buoyancy shutdown
Benthuysen, Jessica A.
Thomas, Leif N.
Lentz, Steven J.
MetadataShow full item record
KeywordCirculation/ Dynamics; Boundary currents; Diapycnal mixing; Ekman pumping/transport; Mixing; Topographic effects; Upwelling/downwelling
Model analyses of an alongshelf flow over a continental shelf and slope reveal upwelling near the shelf break. A stratified, initially uniform, alongshelf flow undergoes a rapid adjustment with notable differences onshore and offshore of the shelf break. Over the shelf, a bottom boundary layer and an offshore bottom Ekman transport develop within an inertial period. Over the slope, the bottom offshore transport is reduced from the shelf’s bottom transport by two processes. First, advection of buoyancy downslope induces vertical mixing, destratifying, and thickening the bottom boundary layer. The downward-tilting isopycnals reduce the geostrophic speed near the bottom. The reduced bottom stress weakens the offshore Ekman transport, a process known as buoyancy shutdown of the Ekman transport. Second, the thickening bottom boundary layer and weakening near-bottom speeds are balanced by an upslope ageostrophic transport. The convergence in the bottom transport induces adiabatic upwelling offshore of the shelf break. For a time period after the initial adjustment, scalings are identified for the upwelling speed and the length scale over which it occurs. Numerical experiments are used to test the scalings for a range of initial speeds and stratifications. Upwelling occurs within an inertial period, reaching values of up to 10 m day−1 within 2 to 7 km offshore of the shelf break. Upwelling drives an interior secondary circulation that accelerates the alongshelf flow over the slope, forming a shelfbreak jet. The model results are compared with upwelling estimates from other models and observations near the Middle Atlantic Bight shelf break.
Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 45 (2015): 294–312, doi:10.1175/JPO-D-14-0104.1.
Showing items related by title, author, creator and subject.
The Atlantic Water boundary current in the Nansen Basin : transport and mechanisms of lateral exchange Våge, Kjetil; Pickart, Robert S.; Pavlov, Vladimir; Lin, Peigen; Torres, Daniel J.; Ingvaldsen, Randi B.; Sundfjord, Arild; Proshutinsky, Andrey (John Wiley & Sons, 2016-09-22)Data from a shipboard hydrographic survey near 30°E in the Nansen Basin of the Arctic Ocean are used to investigate the structure and transport of the Atlantic Water boundary current. Two high-resolution synoptic crossings ...
Loose, Brice; Jenkins, William J.; Moriarty, Roisin; Brown, Peter; Jullion, Loic; Naveira Garabato, Alberto C.; Valdes, Sinhue Torres; Hoppema, Mario; Ballentine, Chris; Meredith, Michael P. (John Wiley & Sons, 2016-08-18)The distribution of noble gases and helium isotopes in the dense shelf waters of Antarctica reflects the boundary conditions near the ocean surface: air-sea exchange, sea ice formation, and subsurface ice melt. We use a ...
Barth, John A. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1987-10)A two-layer shallow water equation model is used to investigate the linear stability of a coastal upwelling front. The model features a surface front near a coastal boundary and bottom topography which is an arbitrary ...