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 I. R., Glud R. N., Maher D., Erler D., & Eyre B. D., 2011. Diel coral reef acidification driven by porewater advection in permeable carbonate sands, Heron Island, Great Barrier Reef. Geophysical Research Letters 38:L03604. Article (subscription required).
