Impact of Shifting Subpolar Front on Phytoplankton Dynamics in the Western Margin of East/Japan Sea

Abstract

A subpolar front (SPF) generated between the East Korea Warm Current (EKWC) and the North Korea Cold Current (NKCC) in the western margin of the East/Japan Sea has shifted northward in recent decades. This study investigated the biomass and composition of the phytoplankton assemblage in relation to hydrological and biogeochemical features in the shallow shelf and slope off the Korean coast from January to June in 2016 and 2017, to determine the mechanistic effects of SPF on spring–summer phytoplankton bloom dynamics. Monthly average depth-integrated chlorophyll a (Chl a) levels and the contribution of phytoplankton classes revealed bimodal diatom blooms in early spring and summer in the frontal zone. Canonical correspondence analysis showed that the distribution of high Chl a was associated with cold, low-salinity NKCC water in March 2016. No Chl a peak was observed in March 2017 when the warm saline EKWC water mass invaded. These results suggest that the NKCC intrusion acts as a forcing mechanism leading to enhanced phytoplankton biomass in the frontal zone. In contrast, positive correlations of Chl a concentration with water density and nutrient concentrations suggest that summer blooms were fed by the subsurface chlorophyll maximum (SCM) driven by shoaling of the pycnocline and nitracline. Varying water-column stratification determined the thickness of the SCM layer, driving year-to-year variability in the magnitude of diatom blooms. These findings further suggest that seasonal/interannual variability in the timing of algal blooms affects regional trophodynamics and hence could be an important factor in explaining ecosystem changes in this region.

Carbon cycling in the East Sea (Japan Sea): A review

“…Several water masses are present in the upper layer, down to a depth of ~500 m, and they show associated horizontal variations in biogeochemical properties (Kim et al, 2004;Kim et al, 2008). For example, in the southwestern part of the EJS, the East Sea Intermediate Water (ESIW) occurs below the TWC at around 200-400 m (Yoon and Kawamura, 2002;Kim D. et al, 2021). A salinity minimum (<34.06 psu), low temperatures (1-5°C…”

Spatial Dynamics of Demersal Fish Assemblages off the Korean Coast in the East Sea

“…Consequently, fish fauna in the northern part of the eastern Korean coast exhibit distinctly different species compositions compared with the southern and southeastern fish assemblages influenced by the Tsushima Warm Current (TWC) [ 19 ]. Marine communities in the East Sea can be vertically divided into shallower and deeper groups owing to the different influences of the East Korea Warm Current in the surface layer and the North Korea Cold Current in the deeper layer [ 20 ].…”