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Rapid generation of upwelling at a shelf break caused by buoyancy shutdown


Benthuysen, J and Thomas, LN and Lentz, SJ, Rapid generation of upwelling at a shelf break caused by buoyancy shutdown, Journal of Physical Oceanography, 45, (1) pp. 294-312. ISSN 0022-3670 (2015) [Refereed Article]

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Copyright 2015 American Meteorological Society

DOI: doi:10.1175/JPO-D-14-0104.1


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.

Item Details

Item Type:Refereed Article
Keywords:circulation/dynamics, boundary currents, diapycnal mixing, Ekman pumping/transport, mixing, topographic effects, upwelling/downwelling
Research Division:Earth Sciences
Research Group:Oceanography
Research Field:Physical oceanography
Objective Division:Environmental Management
Objective Group:Marine systems and management
Objective Field:Measurement and assessment of marine water quality and condition
UTAS Author:Benthuysen, J (Dr Jessica Benthuysen)
ID Code:106817
Year Published:2015
Web of Science® Times Cited:12
Deposited By:IMAS Research and Education Centre
Deposited On:2016-02-22
Last Modified:2017-11-01

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