Front-Driven Physical–Biogeochemical–Ecological Interactions in the Yellow Sea Large Marine Ecosystem

Abstract

The Yellow Sea (YS) is among the most important large marine ecosystems (LMEs). By synthesizing a variety of physicochemical and biological data in the western SYS (Southern Yellow Sea), we provide an overview of front-driven physical–biogeochemical–ecological interactions in the Yellow Sea Large Marine Ecosystem (YSLME), mainly addressing (1) thermohaline, density, turbidity, and nutrient fronts in relation to the water-mass structure; (2) nutrient transport and light conditions associated with the fronts; (3) front-driven primary production regime; and (4) anchovy distribution and other ecological processes in the frontal zone. Generally, forced by complicated hydrodynamics under coastal water/currents, estuarine runoff, the Yellow Sea Warm Current (YSWC), and the Yellow Sea Cold Water Mass (YSCWM), robust thermohaline and density fronts are formed. Moreover, a prominent surface turbidity front forms year-round near the 30 m isobath. Three types of nutrient fronts, i.e., estuarine, coastal, and offshore, exist and change seasonally in this region; their locations generally represent the range of substance transport along with different water masses. The frontal system largely regulates the primary production regime in the SYS. Specifically, the front between the southward cold-water belt and eastern YSWC roughly shapes the western boundary of the central phytoplankton-blooming area in spring. In summer, upwelling is observed near the bottom YSCWM boundary, leading to surface cold patches, nutricline shoaling, and upward transport of nutrients. This upwelling system can extract nutrients from the YSCWM to the euphotic layer, resulting in a spatial shift in phytoplankton blooms from the central SYS in spring to the YSCWM frontal region in summer. Phytoplankton biomass also tends to peak near the autumn YSCWM front and winter YSWC front. Furthermore, anchovy distribution is closely related to the frontal system. In winter, the front adjacent to the YSWC core area at the YS entrance acts as an overwintering ground for anchovy; in spring, anchovy migrates northward for feeding, and a high biomass forms in the YSWC-affected bloom area; during summer and autumn, the YSCWM frontal region is an important spawning and nursery ground for anchovy due to food availability and suitable temperature. Overall, the frontal system may play a substantial role in shaping the YSLME via close physical–biogeochemical–ecological interactions.