Diurnal Variations of Surface Seawater pCO₂ in Contrasting Coastal Environments

• Published in: Limnology and oceanography Vol. 54; no. 3; pp. 735 - 745
• Main Authors: Dai, Minhan, Lu, Zhongming, Zhai, Weidong, Chen, Baoshan, Cao, Zhimian, Zhou, Kuanbo, Cai, Wei-Jun, Chen, Chen-Tung Arthur
• Format: Journal Article
• Language: English
• Published: Waco, TX American Society of Limnology and Oceanography 01.05.2009
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; Earth sciences; Earth, ocean, space; Exact sciences and technology; External geophysics; Fundamental and applied biological sciences. Psychology; Marine and continental quaternary; Physical and chemical properties of sea water; Physics of the oceans; Sea water ecosystems; Surficial geology; Synecology; South China Sea; West Pacific; Asia; China; Northern China; Taiwan; Xisha Islands; Pacific Ocean; Far East; Temperature; corals; Carbon dioxide; Diurnal variation; Metabolism; Tides; Marine environment; Offshore; Reef; Hydrochemistry; Air sea interface; Partial pressure; Sea current; Surface water; Coastal environment; Bay; Invertebrata; invertebrates; Seawater
• ISSN: 0024-3590; 1939-5590
• DOI: 10.4319/lo.2009.54.3.0735

We examined diurnal variations of surface seawater pCO₂ (partial pressure of CO₂) in a suite of coastal marine environmental systems in the vicinity of the South China Sea (SCS) from inshore and nearshore settings in Xiamen Bay, Shenhu Bay, and the southwestern Taiwan Strait, to offshore sites in the basin and on the slope of the northern South China Sea as well as in a coral reef system at Xisha Islands in the middle of the SCS. There were significant diurnal changes of surface pCO₂, ranging from 1.0 Pa to 1.6 Pa (10–16 μatm) in the offshore and oligotrophic sites, ~4.1 Pa in the Taiwan Strait, 5.1–15.2 Pa in Xiamen Bay and Shenhu Bay, to as high as 60.8 Pa in the coral reef system at Xisha Islands. Processes that modulate these pCO₂ diurnal variations were temperature, tide or current, and biological controls. Temperature was a major driver of the pCO₂ diurnal variability in the oligotrophic regions, while tidal effects were important in the nearshore. In the coral reef system, biological metabolism dominated variability. Diurnal variability could have a potentially important implication on the estimate of air-sea CO₂ fluxes, which may result in an uncertainty of ± 0.48–0.77 mmol C m⁻² d⁻¹ for the offshore sites in the SCS. Such uncertainties were larger in nearshore settings.