Little is known about how biogeochemical processes in permeable sediments affect the pH of coastal waters. We demonstrate that seawater recirculation in permeable sands can play a major role in proton (H +) cycling in a coral reef lagoon. The diel pH range (up to 0.75 units) in the Heron Island lagoon was the broadest ever reported for reef waters, and the night-time pH (7.69) was comparable to worst-case scenario predictions for seawater pH in 2100. The net contribution of coarse carbonate sands to the whole system H + fluxes was only 9% during the day, but approached 100% at night when small scale (i.e., flow and topography-induced pressure gradients) and large scale (i.e., tidal pumping as traced by radon) seawater recirculation processes were synergistic. Reef lagoon sands were a net sink for H +, and the sink strength was a function of porewater flushing rate. Our observations suggest that the metabolism of advection-dominated carbonate sands may provide a currently unknown feedback to ocean acidification.
Santos, IR, Glud, RN, Maher, DT, Erler, DV & Eyre, BD 2011, 'Diel coral reef acidification driven by porewater advection in permeable carbonate sands, Heron Island, Great Barrier Reef', Geophysical Research Letters, vol. 38, art. no. L03604, pp. 1-5.
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