The interaction between water flow and sediment topography (e.g., surface ripples) in shallow, permeable coral reef carbonate sediments establishes pressure gradients that increase the rate of sediment–water solute exchange relative to water flow along a flat bottom. It is unknown how this effect from surface ripples may modify the rate at which the sediment porewater is exposed to future chemical changes in the overlying water column, such as elevated pCO2 that is causing ocean acidification (OA). To address this question, this study used a series of 22-h incubations in flume aquaria with live permeable calcium carbonate sediment communities and examined the interactive effect of pCO2 (400 and 1000 µatm) and surface topography (flat and rippled sediments) on invertebrate infaunal activity, carbonate sediment microbial metabolism, and inorganic carbonate dissolution. Results show that the introduction of oxygen into flat sediments was largely driven by infaunal activity, whereas introduction of oxygen into rippled sediments was largely driven by physical flow processes. Rippled sediments exhibited rates of respiration and gross primary production that were ~ 45% and ~ 50% higher, respectively, than flat sediments. An increase in pCO2 shifted the sediments in the flat flumes from net calcifying to net dissolving, an effect that was amplified an additional ~ 60% in rippled sediments. These results suggest that current estimates of coral reef carbonate sediment calcification may be underestimating the dissolution response to OA where the carbonate sediment environment exhibits ripples in the topography.
Lantz C. A., Kessler A. J., Schulz K. G. & Eyre B. D., in press. Sediment topography enhances the response of coral reef carbonate sediment dissolution to ocean acidification. Coral Reefs. Article.
