INTERANNUAL VARIABILITY IN NITRATE SUPPLY TO SURFACE WATERS OF THE NORTHEAST PACIFIC-OCEAN

In the past decade, the upper ocean in the NE Pacific has undergone ch anges in physical and chemical properties which are similar to the rec ent El Nino/La Nina cycle. During the 1989 La Nina, winter waters at O cean Station Papa (OSP) were relatively cool, saline and nitrate rich. With the onset of the 1991 El Nino period, however, winter waters at OSP were more saline by 0.3 psu, warmer by over 2 degrees C and nitrat e depleted by 30 %. In 1994, oceanic winter temperatures were the warm est ever observed in over 40 yr of sampling. The decrease in winter nu trient supply persisted eastward from OSP to the coast of Vancouver Is land, and resulted in an expanded area of nitrate depletion in summer. Lower winter nitrate supply is estimated to have reduced new producti on through spring and summer by 40% (2 million tonnes C) in a 290 000 km(2) patch of ocean west of Vancouver Island. We suggest that decline s in phytoplankton production of this magnitude affect both the produc tivity and composition of higher trophic levels.