Journal of Oceanography, Vol. 60 (No. 1), pp. 75-91, 2004
Joaquim I. Goes1*, Kosei Sasaoka2, Helga do R. Gomes1, Sei-ichi Saitoh3 and Toshiro Saino2,4,5
1Bigelow Laboratory for Ocean Sciences, West Boothbay Harbor, ME 04575, U.S.A.
2Earth Observation Research Centre, National Space Development Agency of Japan, Tokyo 106-0032, Japan
3Graduate School of Fisheries Sciences, Hokkaido University, Hakodate 041-8611, Japan
4Hydrospheric-Atmospheric Research Centre, Nagoya University, Nagoya 464-8601, Japan
5Frontier Research System for Global Change, 3173-25, Yokohama 236-0001, Japan
(Received 8 October 2003; in revised form 22 November 2003; accepted 24 November 2003)
Abstract: This study documents the results of a multi-sensor satellite investigation aimed at comparing the seasonality and interannual variability of phytoplankton biomass and primary productivity (PP) in the western and eastern gyres of the subarctic Pacific. Satellite data helped discern several features, most importantly the existence of significant east-west gradients in the supply of nitrate in winter, in the consumption of nitrate by phytoplankton and in phytoplankton production and biomass accumulation over the growth season. In the western subarctic gyre many of these features appear to be regulated by the strength of sea surface winds through increased iron and nitrate inputs. Multiple regression analysis of data extracted from 12 boxes spanning different hydrographic regimes in the subarctic Pacific, showed that over 65% of the variations in PP in the subarctic Pacific could be explained solely on the basis of changes in the strength of sea surface winds and the intensity of incident irradiance (PAR). The dependence of PP on sea surface wind stress was far greater in the western subarctic Pacific Gyre (WSG), than in the Alaskan Gyre (ALG) due to diminishing impact of surface winds towards the east. Spring accumulation of phytoplankton biomass was greater in the WSG than in the ALG despite the higher rates of PP in the latter. This study assumes particular significance because it helps ascertain the existence of several sub-regions within the two broader domains of the WSG and the ALG. In addition, large interannual variations in phytoplankton biomass and PP were observed in the subarctic Pacific following the onset of the El-Niño event of 1997 and the transition to La-Niña conditions in 1999. These variations were largely the result of differences in meteorological and oceanographic conditions across the subarctic Pacific following the development of the El-Niño.