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 (Ω _arag ), 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 Ω _arag (1.26-1.76) were obtained in winter due to low seawater temperature. During spring to early autumn, surface-water Ω _arag increased from 2.02 to 3.47 for the increasing seawater temperature and biological production, whereas bottom-water Ω _arag 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 well-mixed with an average Ω _arag of 2.17. The annual cycle of seawater temperature dominated the seasonal variations of Ω _arag , counteracted by biological production increasing Ω _arag of 0.49 in surface water in March and strengthened by net community respiration decreasing Ω _arag 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.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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