Oregon Shelf Hypoxia Modeling

Document Type

Book Chapter

Publication Date

5-3-2017

Department

Marine Science

School

Ocean Science and Engineering

Abstract

Bottom hypoxia on the shelf in the Northeast Pacific is caused by different processes than coastal hypoxia related to riverine inputs. Hypoxia off the coast of Oregon is a naturally occurring process as opposed to the anthropogenically forced hypoxia found in many coastal environments (e.g., Gulf of Mexico shelf, Chesapeake Bay). Off Oregon, bottom hypoxia occurs in summers that have large upwelling- driven near-bottom transport of high nitrate, low dissolved oxygen (DO) waters onto the shelf. The combination of low DO and high nitrate provides initially low (but not hypoxic) DO conditions near the bottom, and nitrate fertilization of shelf surface waters, leading to substantial phytoplankton production. Some production is grazed, and some of it sinks to the bottom where it decomposes consuming oxygen, creating bottom hypoxia in some years. Terrestrial runoff of nutrients into the system is small and not responsible for the development of bottom hypoxia. Similar processes contribute to natural hypoxia in other eastern boundary current upwelling regions, such as the Humboldt Current off Peru and the Benguela Current off Namibia and South Africa. We summarize the observational data on DO and illustrate the coupled biophysical modeling of hypoxia that has been done on the Oregon shelf. We compare hypoxia development in summer of 2002 and 2006, which differed in timing, spatial extent and intensity of hypoxia. Sensitivity analysis using various initial and boundary conditions for nitrate and dissolved oxygen reveals some of the essential conditions responsible for hypoxia development on the Oregon shelf.

Publication Title

Modeling Coastal Hypoxia: Numerical Simulations of Patterns, Controls and Effects of Dissolved Oxygen Dynamics

First Page

215

Last Page

238

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