Meridional and seasonal footprints of the Pacific Decadal Oscillation on phytoplankton biomass in the northwestern Pacific Ocean
We used 16 years of multiplatform-derived biophysical data to reveal the footprint of the Pacific Decadal Oscillation (PDO) on the phytoplankton biomass of the northwestern Pacific Ocean in terms of chlorophyll a concentration (Chl), and to discern the probable factors causing the observed footprint. There were meridional differences in the response of phytoplankton to changes of environmental conditions associated with deepening of the mixed layer during the positive phase of the PDO. In general, deepening of the mixed layer increased phytoplankton biomass at low latitudes (increase of Chl due to increase of nutrient supply), but lowered phytoplankton at high latitudes (decrease of Chl due to reduction of average irradiance and temperature in the mixed layer). The areas where Chl increased or decreased changed meridionally and seasonally in accord with regulation of nutrient and light/temperature limitation by changes of mixed layer depth. The observed PDO footprint on Chl in the northwestern Pacific is likely superimposed on the high-frequency component of the PDO excited by El Niño/Southern Oscillation interannual variability. On a decadal time scale, however, Chl in the northwestern Pacific were more strongly associated with the recently discovered North Pacific Gyre Oscillation.
KeywordsRemote sensing Ocean color Chlorophyll a Aleutian Low Climate changes
This work was partially supported by the Asia–Pacific Network for Global Change Research (APN, CAF2015-RR11-NMY-Siswanto). We acknowledge the Ocean Biology Processing Group (OBPG) for distributing the SeaWiFS/MODIS Chl and SST data. We thank the Physical Oceanography-Distributed Active Archive Center of the Jet Propulsion Laboratory, NCEP-Global Ocean Data Assimilation System (GODAS), and JAMSTEC Argo float team for processing and distributing the SST, GODAS MLD, and Argo float-based MLD data, respectively. We are grateful to two reviewers whose comments substantially improved the paper.
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