Variations in nutrients, carbon and other hydrographic parameters related to the 1976/77 and 1988/89 regime shifts in the sub-arctic Northeast Pacific

For time series at Station P (50°N, 145°W) and stations along Line P, long term changes in eight oceanographic and chemical parameters (sea surface temperature (SST), salinity, oxygen, phosphate (PO4), silicate (SiO4), nitrate (NO3), dissolved inorganic carbon (DIC), and apparent oxygen utilisation (AOU)) were influenced by climate regime shifts with a “step change” of anomalies for nutrients and carbon in the sub-arctic Pacific during the 1976/77 and 1988/89 regime shifts. The presence of regime shifts in the data in the late 1970s and the late 1980s was supported by the statistical test of [Rodionov, S.N., 2004. A sequential algorithm for testing climate regime shifts. Geophysical Research Letters 31, L09204, doi:10.1029/2004GL019448], based on the Student t-test. The response of nutrients and carbon to the regime shifts was more intensive in 1976/77 than in 1988/89. Salinity, PO4, SiO4, NO3, oxygen and DIC showed positive anomalies during 1950–1975 and negative ones during 1976–1995. The effect of La Niña on nutrients and carbon was larger than that of El Niño. Strong La Niña events (e.g. 1988/89) caused a sudden increase in nutrients and carbon. Two regime shifts (1976/77 and 1988/89) occurred just after two strong La Niña events in 1976/77 and 1988/89. At Station P, upwelling of nutrient-poor subsurface water tended to decrease the nutrients at the surface.