New paper finds ocean off US West Coast has cooled significantly over past 30 years

A paper published today in the Journal of Geophysical Research finds the summer sea surface temperatures off the US West Coast have been declining over the past 30 years at a significant rate of -0.19°C per decade. 

Related: New paper finds world's oceans have warmed only 0.09°C over past 55 years

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 117, C08012, 11 PP., 2012
doi:10.1029/2012JC008016

What determines the spatial pattern in summer upwelling trends on the U.S. West Coast?

Key Points

• Summer SST off the U.S. West Coast has been declining since the 1980s
• Cooling trend is more significant in Central and Southern California
• Ekman pumping explains the stronger cooling trend in the south

Hyodae Seo

Physical Oceanography Department, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA

Kenneth H. Brink

Physical Oceanography Department, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA

Clive E. Dorman

Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, USA

Darko Koracin

Division of Atmospheric Sciences, Desert Research Institute, Reno, Nevada, USA

Christopher A. Edwards

Ocean Sciences Department, University of California, Santa Cruz, California, USA

Analysis of sea surface temperature (SST) from coastal buoys suggests that the summertime over-shelf water temperature off the U.S. West Coast has been declining during the past 30 years at an average rate of −0.19°C decade⁻¹. This cooling trend manifests itself more strongly off south-central California than off Oregon and northern California. The variability and trend in the upwelling north of off San Francisco are positively correlated with those of the equatorward wind, indicating a role of offshore Ekman transport in the north. In contrast, Ekman pumping associated with wind stress curls better explains the stronger and statistically more significant cooling trend in the south. While the coast-wide variability and trend in SST are strongly correlated with those of large-scale modes of climate variability, they in general fail to explain the southward intensification of the trend in SST and wind stress curl. This result suggests that the local wind stress curl, often topographically forced, may have played a role in the upwelling trend pattern.