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Published Online April 15, 2004
Science DOI: 10.1126/science.1094917

Research Articles

Submitted on December 19, 2003
Accepted on March 19, 2004

Decline of Subpolar North Atlantic Circulation During the 1990s

S. Häkkinen 1* P. B. Rhines 2

1 NASA Goddard Space Flight Center, Code 971, Greenbelt, MD 20771, USA.
2 University of Washington, Box 357940, Seattle, WA 98195, USA.

* To whom correspondence should be addressed.
S. Häkkinen , E-mail: sirpa.hakkinen{at}nasa.gov

Observations of sea surface height reveal that dramatic changes have occurred over the past decade in the mid-to-high-latitude North Atlantic Ocean. TOPEX/Poseidon altimeter data show that subpolar sea surface height increased during the 1990s and the geostrophic velocity derived from altimeter data exhibits declining subpolar gyre circulation. Combining the data from earlier satellites, we find that subpolar circulation may have been weaker in the late 1990s than in the late 1970s and 1980s. Direct current-meter observations in the boundary current of the Labrador Sea support the weakening circulation trend of the 1990s and, together with hydrographic data show that the mid-to-late 1990s decline extends deep in the water column. Analysis of the local surface forcing suggests that the 1990s buoyancy forcing has a dynamic effect consistent with altimetric and hydrographic observations: a weak thermohaline forcing allows the decay of the domed structure of subpolar isopycnals and weakening of circulation.


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Science. ISSN 0036-8075 (print), 1095-9203 (online)