National Oceanic and
Atmospheric Administration
United States Department of Commerce


FY 2009

The recent deoxygenation of the North Atlantic thermocline: A harbinger of the future?

Gruber, N., I. Stendardo, T. Frohlicher, and G.C. Johnson

In Goldschmidt Conference abstracts, Davos, Switzerland, 21-26 June, Geochim. Cosmochim. Acta, 73(13 (Suppl. S), A471 (2009)

Repeat measurements of the interior North Atlantic have revealed surprisingly large decreases in its oxygen content over the last few decades, primarily located at mid-depth and associated with intermediate and mode waters. This deoxygenation of the North Atlantic thermocline is driven by some combination of variations in ocean circulation/mixing and variations in the ocean's biological pump. Presently available analyses suggest that most of these changes are physically driven, owing to a climatically forced slowdown of the ventilation and circulation of these mode and intermediate waters. In the presence of a continuing biological pump, this led to a rapid consumption of the available oxygen. We will present updated analyses on the basis of a newly available data base of North Atlantic oxygen as well as new model-based results. In particular, we will investigate how the simultaneous measurements of oxygen and other constituents can help us to extract the mechanisms responsible for these changes. A better understanding of these components and processes are crucial for improving our ability to assess the vulnerability of the ocean in this century, especially since the observed oxygen changes are remarkably congruent with the changes that model projections suggest for a warming world. The ocean interior, and particularly its oxygen content, may therefore act as an early indicator of the impact that future climate change might have on ocean biogeochemistry.

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