Wednesday, December 23, 2009

Coastal hypoxia tends to increase as climate warms

Oregon State University News: A new study of Pacific Ocean sediments off the coast of Chile has found that offshore waters experienced systematic oxygen depletion during the rapid warming of the Antarctic following the last “glacial maximum” period 20,000 years ago. The findings are intriguing as scientists are exploring whether climate change may be contributing to outbreaks of hypoxia – or extremely low oxygen levels – along the near-shore regions of South America and the Pacific Northwest of the United States.

Results of the study, by researchers at Oregon State University, are being published this week in Nature Geoscience. It builds on a series of field studies by researchers at OSU begun more than a decade ago through the Ocean Drilling Program, led by chief scientist Alan Mix, one of the study’s authors.

The researchers focused their study on the influence of Antarctic Intermediate Water, a huge water mass that extends outward from the Antarctic, infusing Southern Hemisphere oceans with cold, highly oxygenated water – and extending all the way to the Northern Hemisphere.

Climate models suggest that these intermediate waters should have had higher concentrations of oxygen during the last glacial period, but scant evidence backed those assertions. However, the OSU researchers were able to use core samples through the Ocean Drilling Program to analyze sediments from three sites off the Chilean coast to calculate the dissolved oxygen on the seafloor.

…It is not yet clear what effect the findings may have on understanding of the offshore hypoxia events experienced intermittently in the Pacific Northwest over the past eight years. Other researchers from Oregon State University have documented patterns of low-oxygen waters – especially off the central Oregon coast. The worst of these happened in 2006, when oxygen in near-shore waters dipped almost to zero, killing thousands of crabs and other bottom-dwelling creatures.

Similar events occur annually off central Chile and the OSU research group is working with Chilean scientists to compare the two systems. Changing wind patterns appear to be to blame for the 21st-century hypoxia – and wind may have played a role 20,000 years ago as well. Previous studies by Mix of sediment cores off Oregon revealed more oxygenation of subsurface waters during the last Glacial Maximum – and, as warming followed the last ice age, the Pacific Northwest region also experienced intervals of hypoxia, he said….

Magellanic Penguin at a colony near Punta Arenas, Chile, shot by Alastair Rae, Wikimedia Commons via Flickr, under the Creative Commons Attribution ShareAlike 2.0 License

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