Decadal variability of nutrients and biomass in the southern region of Kuroshio Extension

The phytoplankton and zooplankton biomass as well as nutrients in the southern region of Kuroshio Extension (KE) presents obvious decadal variability. Both local and remote links between biomass and physical properties are investigated by comparing satellite observations and the outputs from a biological-physical coupled model. The Regional Ocean Model System (ROMS) and Carbon, Silicate, and Nitrogen Ecosystem (CoSiNE) cover the entire Pacific Ocean. The ROMS-CoSiNE model captures the spatial distribution and decadal variation of the key biological variables including phytoplankton and zooplankton biomass and nutrients in the upper ocean around the KE. The decadal variation in the region is mainly caused by the westward-propagating signals that originate from the central and eastern North Pacific. Specifically, these signals are induced by the decadal oscillation of vertical displacement related to large-scale decadal Pacific modes, such as the North Pacific Gyre Oscillation (NGPO). The evidence obtained here includes not only from surface variables (sea surface height and surface chlorophyll) but also from the variables in the deeper ocean (thermocline, subsurface nutrients, upper 100-m phytoplankton and zooplankton biomass) in the KE region. The signals of the variables in the southern KE region significantly lag that of the NPGO in the central and eastern North Pacific by about 2–4 years. The upper ocean nitrogen budget to conducted to evaluate the contribution of vertical and horizontal advection for the decadal variation of nutrients.