Contrasting effects of temperature and biological processes on aragonite saturation state at the A4HDYD station in the North Yellow Sea

To explore the effects of seawater temperature and biological processes on aragonite saturation state (Klarag), eight field surveys were conducted from December 2014 to November 2015 at A4HDYD station in the North Yellow Sea (NYS). Low regional yearly initial values of seawater Klarag (1.26-1.76) were obtained in winter due to low seawater temperature. During spring to early autumn, surface-water Klarag increased from 2.02 to 3.47 for the increasing seawater temperature and biological production, whereas bottom-water Klarag remained as low as 1.44-1.79 due to low seawater temperature, net community respiration and the influence of the North Yellow Sea Cold Water Mass (NYSCWM). Following the collapse of stratification in late autumn, the seawater was wellmixed with an average Klarag of 2.17. The annual cycle of seawater temperature dominated the seasonal variations of Klarag, counteracted by biological production increasing Klarag of 0.49 in surface water in March and strengthened by net community respiration decreasing Klarag of 0.11-0.41 below the pycnocline during summer and autumn. It is, therefore, mid-to-high latitude coastal areas impacted by human activities are likely subject to ocean acidification due to the combined effects of low seawater temperature and net community respiration.