Enhancement of new production in the northeast subarctic Pacific Ocean during negative north Pacific index events
Limnol. Oceanogr., 43(7), 1998, 1418-1426 | DOI: 10.4319/lo.19184.108.40.2068
ABSTRACT: We examined interannual variability in the 1965-1990 winter-summer differences in surface nitrate (ΔNO3) in the northeast subarctic Pacific Ocean (Station P, 50°N, 145°W). Increases in ΔNO3, of 30-70% above the mean value occurred during four events (1969, 1971-1972, 1979, 1983). The ΔNO3 time series was highly correlated (r = 0.86) with the spring-summer nitrate utilization rate from 1970 to 1980. The ΔNO3 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 ΔNO3 and sedimenting particulate organic nitrogen (PON) showed that the high ΔNO3 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 ΔNO3. The increase in -ratio implies a change in the community structure of the phytoplankton during the elevated ΔNO3 events that appears connected to changes in the NPI.