Understanding oxygen depletion on the Oregon coastal shelf

Oct 09, 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

add to favorites email to friend print save as pdf

Related Stories

Wind 'fights' Leeuwin to provide nutrient rich waters

Sep 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 ...

How fish food rises from ocean depths

Jun 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 ...

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

Dec 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

NASA image: Agricultural fires in the Ukraine

11 minutes ago

Numerous fires (marked with red dots) are burning in Eastern Europe, likely as a result of regional agricultural practices. The body of water at the lower left of this true-color Moderate Resolution Imaging ...

NASA marks Polo for a hurricane

51 minutes ago

Hurricane Polo still appears rounded in imagery from NOAA's GOES-West satellite, but forecasters at the National Hurricane Center expect that to change.

NASA sees Hurricane Edouard enter cooler waters

52 minutes ago

NASA's Tropical Rainfall Measuring Mission or TRMM satellite and Aqua satellite gathered data on Hurricane Edouard's rainfall, clouds and waning power is it continued moving northward in the Atlantic into ...

First eyewitness accounts of mystery volcanic eruption

3 hours ago

New light has been shed on one of the biggest volcanic eruptions in the last 500 years—the so-called 'Unknown eruption'—thanks to an unusual collaboration between a historian and a team of earth scientists at the University ...

User comments : 0