MEPS 170:15-23 (1998)  -  doi:10.3354/meps170015

ABSTRACT: In the past decade, the upper ocean in the NE Pacific has undergone changes in physical and chemical properties which are similar to the recent El Niño/La Niña cycle. During the 1989 La Niña, winter waters at Ocean Station Papa (OSP) were relatively cool, saline and nitrate rich. With the onset of the 1991 El Niño period, however, winter waters at OSP were more saline by 0.3 psu, warmer by over 2°C and nitrate depleted by 30%. In 1994, oceanic winter temperatures were the warmest ever observed in over 40 yr of sampling. The decrease in winter nutrient supply persisted eastward from OSP to the coast of Vancouver Island, and resulted in an expanded area of nitrate depletion in summer. Lower winter nitrate supply is estimated to have reduced new production through spring and summer by 40% (2 million tonnes C) in a 290000 km² patch of ocean west of Vancouver Island. We suggest that declines in phytoplankton production of this magnitude affect both the productivity and composition of higher trophic levels.

KEY WORDS: Northeast Pacific · Alaskan Gyre · Mixed layer · Nitrate · Temperature · Salinity · El Niño · New production · Interannual variability