Self-limiting geothermal convection in marine carbonate platforms

Large scale inward and upward density-driven convective circulations occur in the porous structure of many marine carbonate platforms. Their geochemic al implications are of prime importance for a variety of problems where a s ubstantial transport of chemical species is required. In the present study we show, using simple thermal and hydraulic arguments, that there is a nega tive feedback between convective flow and heat transfer. This results in an upper limit on geothermally-driven vertical fluxes, irrespective of the hy draulic conductivity of the medium. This concept is potentially applicable to a variety of problems. Taking the example pf two on-going debated questi ons in the reef scientific community, i.e., diagenesis and nutrient cycling , we show unambiguously that whereas convective circulations in coral reefs are compatible with dolomitization models, they are too low by at least on e to two orders of magnitude to be a significant process in the nutrient bu dget of coral reefs.