Response of the Gulf of Alaska 3D winter circulation to oceanic climate shifts: Ecosystem implications

Abstract

Recent measurements of zooplankton biomass and biological productivity in the Gulf of Alaska have raised a number of questions regarding possible linkages between climate and availability of renewable resources. In this article we compare 3 abrupt oceanic regime shifts in the Gulf of Alaska, the 1976–1977 warming shift, the 1998 cooling episode, and the 1998 to 1999 El Niño to La Niña transition, against concomitant changes in biological conditions reported in the literature. After the 1976–1977 warming shift, changes in the Gulf's 3D circulation, i.e., interior upwelling, onshore transport and coastal downwelling, had the same sign as their climatological means, thus providing a candidate explanation to the observed increased productivity of the upper ocean. Warming and cooling transitions have associated with them very different patterns of both horizontal and vertical circulation, where the latter is confirmed to be linked to the wind stress curl variability. Important shifts in the local biology have been reported in the literature (warming of 1976–1997 and El Niño to La Niña transition of 1998–1999) when climatological shifts in our simulated vertical velocities were large; in turn, when they were small, the ecosystem did not show significant changes and this was in part due to the resilience set by the 1976–1977 shift through the strengthening of the GOA's mean 3D circulation.