Site: California Current Ecosystem LTER
North Pacific Gyre Oscillation (NPGO) and three co-variates (salinity, dissolved nitrate, and phytoplankton chlorophyll a), from the CCE-LTER and CalCOFI region.
Emanuele Di Lorenzo et al. (2008)

Research in the CCE LTER site led to the discovery of a new mode of climate variability that has been named the North Pacific Gyre Oscillation (NPGO, Di Lorenzo et al. 2008). The NPGO was initially uncovered through the analysis of a computer model of ocean circulation, developed to reproduce and diagnose long-term climate measurements in the North Pacific. The study revealed variation in sea surface height that is closely related to other changes in the North Pacific, such as long-term variations in ocean salinity, dissolved nutrients (including nitrate, an important nutrient limiting phytoplankton growth at the base of the food web), and chlorophyll-a, a measure of the total biomass of phytoplankton.

Interannual variations in the NPGO appear to be related to year-to-year variations in the large-scale wind system that sets up coastal upwelling, and to changes in the intensity of North Pacific ocean circulation. When positive, the NPGO represents an increase in the transport of both the Alaskan Coastal Current and California Current. The NPGO helps explain the variability in the coastal upwelling that influences the flux of dissolved nutrients into sunlit surface waters, which stimulates the production of phytoplankton. This phytoplankton growth affects the production of zooplankton and influences the feeding success and survival of many species of plankton-feeding fishes in the Northeast Pacific.

Considerable previous work focused on an index of climate variability known as the Pacific Decadal Oscillation (PDO), and its co-variability with biological properties of the North Pacific. The PDO is derived from sea surface temperature variation north of the tropics. The PDO is thought to shift from a predominately positive to predominately negative state approximately every 20-30 years, and the abundance of a number of types of marine organisms, such as krill, salmon, and others, varies in concert with these changes. However, both satellite data and computer models suggest that since about 1990 the NPGO has intensified relative to the PDO (Di Lorenzo et al. 2008). Thus, future changes in Northeast Pacific ocean food webs may become increasingly influenced by this newly discovered mode of climate variability.