Understanding oxygen depletion on the Oregon coastal shelf

October 9, 2013

Each spring, the winds off Oregon shift, changing ocean currents and spurring the onset of the upwelling season, an approximately 4 month period where cold, nutrient-rich, oxygen-depleted deep water is driven into the coastal region. In recent decades, measurements have shown that the concentration of oxygen in the waters off Oregon has been decreasing. More recently, seasonal hypoxia has become a concern. Although this long-term decline is well documented, the details of the annual and seasonal variability in the concentration of dissolved oxygen on the shelf are not. Using moored sensors installed off the coast of Oregon for three seasons, from 2009 to 2011, Adams et al. measured the properties of the water, including changes in the current as well as the temperature, salinity, and concentration of dissolved oxygen. They find that although the seasonal upwelling initiates the annual reduction in dissolved oxygen, it is also responsible for staving off widespread anoxia.

To understand the effect of upwelling on coastal conditions, the authors analyzed their observations for trends that occurred on a range of time scales, from subtidal to tidal to interannual. They find that because the cold is low in dissolved and because the introduction of nutrients spurs biological productivity, the onset of upwelling leads to oxygen depletion. However, upwelling also causes enhanced flushing and mixing, which prevents the oxygen from dropping as low as it otherwise would. Upwelling-induced flushing and mixing limit the annual to just 30 percent of what it should be if the infiltration of cold deep water and biological respiration were the only factors.

The authors find that changes in the winds along the coast cause weekly variability in the concentration of dissolved oxygen, while monthly variability can be caused by fluctuations in the atmospheric jet stream.

Explore further: Wind 'fights' Leeuwin to provide nutrient rich waters

More information: Adams, K. and Barth, J. Temporal variability of near-bottom dissolved oxygen during upwelling off central Oregon, Journal of Geophysical Research-Oceans, DOI: 10.1002/jgrc.20361, 2013 http://onlinelibrary.wiley.com/doi/10.1002/jgrc.20361/abstract

Related Stories

Wind 'fights' Leeuwin to provide nutrient rich waters

September 26, 2013

Researchers investigating the Ningaloo Reef's circulation patterns have discovered that periodic, local wind-driven currents are still strong enough to generate upwelling, providing important nutrients from the seabed to ...

How fish food rises from ocean depths

June 26, 2012

Research by Flinders oceanographer Associate Professor Jochen Kaempf has shed new light on the movement of nutrient-rich water generated in coastal canyons, a process which makes a fundamental contribution to the marine food ...

Oxygen isotopes improve weather predictability in Niger

May 17, 2012

For the African nation of Niger, the effect of seasonal atmospheric variability on the weather is poorly understood. Because most residents rely on local agriculture, improving the predictability of seasonal weather and precipitation ...

In hot water: Ice Age findings forecast problems

December 20, 2011

(PhysOrg.com) -- The first comprehensive study of changes in the oxygenation of oceans at the end of the last Ice Age (between about 10 to 20,000 years ago) has implications for the future of our oceans under global warming. ...

Recommended for you

Multinationals act on ocean-clogging plastics

January 16, 2017

Forty of the world's biggest companies assembled in Davos agreed on Monday to come up with cleaner ways to make and consume plastic as waste threatens the global eco-system, especially in oceans.

How the darkness and the cold killed the dinosaurs

January 16, 2017

66 million years ago, the sudden extinction of the dinosaurs started the ascent of the mammals, ultimately resulting in humankind's reign on Earth. Climate scientists have now reconstructed how tiny droplets of sulfuric acid ...

Tracking Antarctic adaptations in diatoms

January 16, 2017

Diatoms are a common type of photosynthetic microorganism, found in many environments from marine to soil; in the oceans, they are responsible for more than a third of the global ocean carbon captured during photosynthesis. ...

Study tracks 'memory' of soil moisture

January 16, 2017

The top 2 inches of topsoil on all of Earth's landmasses contains an infinitesimal fraction of the planet's water—less than one-thousandth of a percent. Yet because of its position at the interface between the land and ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.