North Pacific Gyre Oscillation links ocean climate and ecosystem change

TLDR

Decadal fluctuations in salinity, nutrients, chlorophyll, zooplankton, and fish stocks in the Northeast Pacific are poorly correlated with the Pacific Decadal Oscillation, while the NPGO pattern extends beyond the North Pacific and is part of a global‐scale mode of climate variability evident in sea level and temperature trends. The study defines the North Pacific Gyre Oscillation (NPGO) as a new climate pattern and investigates its correlation with previously unexplained fluctuations in salinity, nutrients, and chlorophyll. NPGO variability is driven by regional and basin‐scale wind‐driven upwelling and horizontal advection, which control salinity and nutrient concentrations, and these nutrient changes in turn influence phytoplankton and higher trophic levels. The NPGO serves as a strong indicator of planktonic ecosystem dynamics, and its amplified variance in observations and warming simulations suggests it may increasingly drive global‐scale decadal changes in marine ecosystems.

Abstract

Decadal fluctuations in salinity, nutrients, chlorophyll, a variety of zooplankton taxa, and fish stocks in the Northeast Pacific are often poorly correlated with the most widely‐used index of large‐scale climate variability in the region ‐ the Pacific Decadal Oscillation (PDO). We define a new pattern of climate change, the North Pacific Gyre Oscillation (NPGO) and show that its variability is significantly correlated with previously unexplained fluctuations of salinity, nutrients and chlorophyll. Fluctuations in the NPGO are driven by regional and basin‐scale variations in wind‐driven upwelling and horizontal advection – the fundamental processes controlling salinity and nutrient concentrations. Nutrient fluctuations drive concomitant changes in phytoplankton concentrations, and may force similar variability in higher trophic levels. The NPGO thus provides a strong indicator of fluctuations in the mechanisms driving planktonic ecosystem dynamics. The NPGO pattern extends beyond the North Pacific and is part of a global‐scale mode of climate variability that is evident in global sea level trends and sea surface temperature. Therefore the amplification of the NPGO variance found in observations and in global warming simulations implies that the NPGO may play an increasingly important role in forcing global‐scale decadal changes in marine ecosystems.