News brief—January 22, 2008

Subtropical oceans add oxygen to atmosphere


Researchers test a new oxygen sensor attached to a yellow Argo float used for open-ocean monitoring.

The subtropical Pacific is a net source of oxygen for the Earth’s atmosphere, according to a new paper published in the Jan. 17 issue of Nature by MBARI marine chemist Kenneth Johnson and Stephen Riser of the University of Washington. Over three-quarters of the ocean’s surface waters are clear and blue and do not sustain much life because they are nutrient poor. For decades, oceanographers have debated whether algae living in these ocean regions are net producers or consumers of oxygen. Indirect measurements indicated that these algae were producing half of the oxygen in the atmosphere, but previous attempts to measure oxygen production directly suggested that these regions were consuming oxygen. A new oxygen sensor enabled Riser and Johnson to measure oxygen production rates in the subtropical open ocean over several years. They found that each fall, the surface waters mix, creating a uniform layer of low-oxygen seawater. Starting in spring, oxygen accumulates steadily about 100 meters below the surface, at a rate that indicates marine algae are producing more oxygen than they consume over the course of the year.

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