Enhancement of new production in the northeast subarctic Pacific Ocean during negative North Pacific index events

We examined interannual variability in the 1965–1990 winter‐summer differences in surface nitrate (ΔNO 3 ) in the northeast subarctic Pacific Ocean (Station P, 50°N, 145°W). Increases in ΔNO 3 , of 30–70% above the mean value occurred during four events (1969, 1971‐1972, 1979, 1983). The ΔNO 3 time series was highly correlated ( r = 0.86) with the spring‐summer nitrate utilization rate from 1970 to 1980. The ΔNO 3 time series was negatively correlated with the North Pacific index (NPI) ( r = ‐0.72) and positively correlated with solar radiation in the spring ( r = 0.48) and summer ( r = 0.46). A simple ecosystem model forced with observed incident solar radiation and mixed‐layer depth during the spring‐summer period predicted increases in export production that were 50% of the observed increase for 1970–1972 and 1977–1979. Comparison between the ΔNO 3 and sedimenting particulate organic nitrogen (PON) showed that the high ΔNO 3 event of 1983 was associated with a dramatic increase in PON fluxes. A simple ecosystem model underpredicts observed interannual variations in export production, and this result combined with the observed PON fluxes suggests that a combination of increased phytoplankton production and increased f ratio produced the observed increase in ΔNO 3 . The increase in f ‐ratio implies a change in the community structure of the phytoplankton during the elevated ΔNO 3 events that appears connected to changes in the NPI.