Enhancement of new production in the northeast subarctic Pacific Ocean during negative north Pacific index events
Wong, C. S., F. A. Whitney, R. J. Matear, and K. Iseki
Limnol. Oceangr. 43:1418-1426

We examined interannual variability in the 1965-1990 winter-summer differences in surface nitrate (NO₃) in the northeast subarctic Pacific Ocean (Station P, 50°N, 145°W). Increases in NO₃, of 30-70% above the mean value occurred during four events (1969, 1971-1972, 1979, 1983). The NO₃ time series was highly correlated (r = 0.86) with the spring-summer nitrate utilization rate from 1970 to 1980. The NO₃ 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 NO₃ and sedimenting particulate organic nitrogen (PON) showed that the high NO₃ 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 NO₃. The increase in ƒ-ratio implies a change in the community structure of the phytoplankton during the elevated NO₃ events that appears connected to changes in the NPI.