Relaxation from upwelling: The effect on dissolved oxygen on the continental shelf

• Published in: Journal of Geophysical Research: Oceans Vol. 117; no. C4
• Main Authors: Send, Uwe, Nam, SungHyun
• Format: Journal Article
• Language: English
• Published: Washington, DC Blackwell Publishing Ltd 01.04.2012; American Geophysical Union
• Subjects: continental shelf; Continental shelves; Dissolved oxygen; Earth sciences; Earth, ocean, space; Exact sciences and technology; Geophysics; Heat balance; Marine; Oceanography; Oxygen; Oxygen consumption; Physical oceanography; relaxation; Upwelling; Narrows; New York; United States; INE, USA, California, San Diego; advection; inner shelf; continental shelf; time scales; density; heat balance; Mooring; Oxygen consumption; concentration; North America; lead; currents; Mars; Relaxation; Flow regime; upwelling; temperature; heat flux; Dissolved oxygen; heat transfer; ocean circulation
• ISSN: 0148-0227; 2169-9275; 2156-2202; 2169-9291
• DOI: 10.1029/2011JC007517

Continental shelves in upwelling regimes are subject to sequences of upwelling and relaxation events, each on timescales of order 1 week typically. These episodes have pronounced impacts on the temperature and density structure on the shelves and also on the along‐shore and cross‐shore flow regimes. It had previously been demonstrated that relaxation phases advect warm water along shore (poleward) from regions of less intense upwelling, thus adding to the heat balance in upwelling locations and providing a rectification of oscillating heat fluxes. In the current paper it is shown that relaxations also modify the dissolved oxygen (DO) budget of the lower layers. On a narrow shelf, this provides enhanced DO values due to near‐surface exposure, while on a wide shelf decreased DO concentrations are created due to oxygen consumption on the inner shelf. The resulting variations along the coast can lead to along‐shore advection of high or low DO during a relaxation event. Observations are presented from moorings off San Diego and Del Mar, which show large departures from density‐correlated DO values during relaxations and which support the proposed mechanisms. Key Points Relaxations modify the dissolved oxygen budget of the lower layers Contrasting oxygen dynamics between narrow and broad shelves Alongshore advection of high or low dissolved oxygen during a relaxation event