Spatiotemporal Variability of Aragonite Saturation State in the Northern East China Sea

Abstract

In order to evaluate the spatiotemporal distribution of the carbonate system in the northern East China Sea (ECS), we first measured the seasonal dissolved inorganic carbon (DIC) and total alkalinity (TA), from which the aragonite saturation state (Ωarag) was calculated for the years 2015–2017. The DIC, TA, and Ωarag were 1,680.9–2,211.4 μmol kg−1, 2,145.1–2,312.8 μmol kg−1, and 1.2–6.0, respectively. The spatiotemporal variability of Ωarag in the northern ECS was mainly controlled by seasonal water mass, such as Yellow Sea Surface Water, Changjiang Dilute Water, and Yellow Sea Bottom Water (YSBW). The lowest Ωarag (∼1.4) in bottom layer was observed in high primary production areas caused by the extension of the Changjiang River plume with the higher Ωarag (up to 6) and was closely linked to the YSBW with low Ωarag expanded southward from Yellow Sea near bottom. Although this area was not a hypoxia zone unlike western shelf region (Chinese region) of the northern ECS, YSBW near bottom could enhance the suppression of bottom aragonite without hypoxia. In eastern region of northern ECS, higher production at surface, YSBW with lower Ωarag extension, and longer respiration product accumulations near bottom tend to lower Ωarag, as compared with western region where the summer hypoxia led to lower Ωarag. Therefore, this result indicates that the eastern region of the northern ECS is also susceptible to ocean acidification, along with the summer hypoxic zone of the western region.