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GEOPHYSICAL RESEARCH LETTERS, VOL. 35, L03618, doi:10.1029/2007GL031745, 2008

Ocean's least productive waters are expanding

Jeffrey J. Polovina

Pacific Islands Fisheries Science Center, NOAA, Honolulu, Hawaii, USA


Evan A. Howell

Pacific Islands Fisheries Science Center, NOAA, Honolulu, Hawaii, USA


Melanie Abecassis

Joint Institute for Marine and Atmospheric Research, University of Hawaii, Honolulu, Hawaii, USA


Abstract

A 9-year time series of SeaWiFS remotely-sensed ocean color data is used to examine temporal trends in the ocean's most oligotrophic waters, those with surface chlorophyll not exceeding 0.07 mg chl/m3. In the North and South Pacific, North and South Atlantic, outside the equatorial zone, the areas of low surface chlorophyll waters have expanded at average annual rates from 0.8 to 4.3%/yr and replaced about 0.8 million km2/yr of higher surface chlorophyll habitat with low surface chlorophyll water. It is estimated that the low surface chlorophyll areas in these oceans combined have expanded by 6.6 million km2 or by about 15.0% from 1998 through 2006. In both hemispheres, evidence shows a more rapid expansion of the low surface chlorophyll waters during the winter. The North Atlantic, which has the smallest oligotrophic gyre is expanding most rapidly, both annually at 4.3%/yr and seasonally, in the first quarter at 8.5%/yr. Mean sea surface temperature in each of these 4 subtropical gyres also increased over the 9-year period. The expansion of the low chlorophyll waters is consistent with global warming scenarios based on increased vertical stratification in the mid-latitudes, but the rates of expansion we observe already greatly exceed recent model predictions.

Received 20 August 2007; accepted 16 January 2008; published 14 February 2008.

Keywords: chlorophyll; oligotrophic gyres.

Index Terms: 1615 Global Change: Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 4805, 4912); 1635 Global Change: Oceans (1616, 3305, 4215, 4513); 1640 Global Change: Remote sensing (1855).

Subscriber Access to Full Article (Nonsubscribers may purchase for $9.00, Includes print PDF, file size: 380350 bytes)

Citation: Polovina, J. J., E. A. Howell, and M. Abecassis (2008), Ocean's least productive waters are expanding, Geophys. Res. Lett., 35, L03618, doi:10.1029/2007GL031745.