Dynamics of seawater carbonate chemistry, production, and calcification of a coral reef flat, central Great Barrier Reef

[摘要] Ocean acidification is projected to shift coral reefs from a state of netaccretion to one of net dissolution this century. Presently, our ability topredict global-scale changes to coral reef calcification is limited byinsufficient data relating seawater carbonate chemistry parameters toin situ rates of reef calcification. Here, we investigate diel andseasonal trends in carbonate chemistry of the Davies Reef flat in the centralGreat Barrier Reef and relate these trends to benthic carbon fluxes byquantifying net ecosystem calcification (nec) and net community production(ncp). Results show that seawater carbonate chemistry of the Davies Reef flatis highly variable over both diel and seasonal cycles. pH (total scale)ranged from 7.92 to 8.17, pCO₂ ranged from 272 to 542 μatm,and aragonite saturation state (Ω_arag) ranged from 2.9 to4.1. Diel cycles in carbonate chemistry were primarily driven by ncp, andwarming explained 35% and 47% of the seasonal shifts in pCO₂ andpH, respectively. Daytime ncp averaged37 ± 19 mmol C m⁻² h⁻¹ in summer and33 ± 13 mmol C m⁻² h⁻¹ in winter; nighttime ncp averaged−30 ± 25 and −7 ± 6 mmol C m⁻² h⁻¹ in summerand winter, respectively. Daytime nec averaged11 ± 4 mmol CaCO₃ m⁻² h⁻¹ in summer and8 ± 3 mmol CaCO₃ m⁻² h⁻¹ in winter, whereasnighttime nec averaged 2 ± 4 mmol and−1 ± 3 mmol CaCO₃ m⁻² h⁻¹ in summer and winter,respectively. Net ecosystem calcification was highly sensitive to changes inΩ_arag for both seasons, indicating that relatively smallshifts in Ω_arag may drive measurable shifts in calcificationrates, and hence carbon budgets, of coral reefs throughout the year.

[学科分类] 地球化学与岩石