Abstract
Abstract. Based upon eight field surveys conducted between May 2011 and May 2012, we investigated seasonal variations in pH, carbonate saturation state of aragonite (Ωarag), and ancillary data on the Chinese side of the North Yellow Sea, a western North Pacific continental margin of major economic importance. Subsurface waters were CO2-undersaturated in May and nearly in equilibrium with atmospheric CO2 in June. From July to October, the fugacity of CO2 (fCO2) of bottom water gradually increased from 438 ± 44 μatm to 630 ± 84 μatm, and pHT decreased from 8.02 ± 0.04 to 7.88 ± 0.06 due to local aerobic remineralization of primary-production-induced biogenic particles. The subsurface community respiration rates in summer and autumn were estimated to be from 0.80 to 1.08 μmol-O2 kg−1 d−1 within a relatively high salinity range of 31.63 to 32.25. From November to May in the next year, however, subsurface fCO2 gradually decreased and pH increased due to cooling and water column ventilation. The corresponding bottom water Ωarag was 1.85 ± 0.21 (May), 1.79 ± 0.24 (June), 1.75 ± 0.27 (July), 1.76 ± 0.29 (August), 1.45 ± 0.31 (October), 1.52 ± 0.25 (November), and 1.41 ± 0.12 (January). Extremely low Ωarag values (from 1.13 to 1.40) were observed mainly in subsurface waters within the high salinity range of 31.63 to 32.25, which covered a major fraction of the study area in October and November. Of the China seas, the North Yellow Sea represents one of the systems most vulnerable to the potential negative effects of ocean acidification.
Highlights
Both pH and CaCO3 saturation state ( ) are essential parameters for the health of aquatic environments
Summertime NYS cold water mass (NYSCWM) in bottom waters at a temperature of < 11 ◦C was identified in the study area (Fig. 5)
From June to August, the area occupied by NYSCWM declined considerably (Fig. 5b–d), while the lowest bottom-water temperature increased from 3.84 ◦C in June to 4.21 ◦C in July and 5.07 ◦C in August (Fig. 3b–d)
Summary
Both pH and CaCO3 saturation state ( ) are essential parameters for the health of aquatic environments. PH is the negative logarithm of the total concentration of H+ and HSO4− ions, i.e. pHT = −log10 [H+]T, where [H+]T = [H+] + [HSO−4 ]. It affects chemical/biochemical properties of seawater, including chemical reactions, equilibrium conditions, and biological toxicity. Is defined as the product of calcium and carbonate ion concentrations divided by the apparent solubility product (Ks∗p) of calcium carbonate, i.e. Since aragonite is usually the most abundant carbonate mineral in shallow sea areas (Morse et al, 2006), we adopted the carbonate saturation state of aragonite ( arag) to measure its potential to corrode CaCO3 shells and skeletons
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