Subsurface pH and carbonate saturation state of aragonite on the Chinese side of the North Yellow Sea: seasonal variations and controls

[摘要] Based upon eight field surveys conducted between May 2011 and May 2012, weinvestigated seasonal variations in pH, carbonate saturation state ofaragonite (Ω_arag), and ancillary data on the Chinese side ofthe North Yellow Sea, a western North Pacific continental margin of majoreconomic importance. Subsurface waters were CO₂-undersaturated in Mayand nearly in equilibrium with atmospheric CO₂ in June. From July toOctober, the fugacity of CO₂ (fCO₂) of bottom water graduallyincreased from 438 ± 44 μatm to 630 ± 84 μatm, andpH_T decreased from 8.02 ± 0.04 to 7.88 ± 0.06 due to localaerobic remineralization of primary-production-induced biogenic particles.The subsurface community respiration rates in summer and autumn wereestimated to be from 0.80 to 1.08 μmol-O₂ kg⁻¹ d⁻¹ within arelatively high salinity range of 31.63 to 32.25. From November to May inthe next year, however, subsurface fCO₂ gradually decreased and pHincreased due to cooling and water column ventilation. The correspondingbottom water Ω_arag 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 Ω_arag values (from 1.13 to 1.40) wereobserved mainly in subsurface waters within the high salinity range of 31.63to 32.25, which covered a major fraction of the study area in October andNovember. Of the China seas, the North Yellow Sea represents one of the systemsmost vulnerable to the potential negative effects of ocean acidification.

[学科分类] 地球化学与岩石