Calcium Carbonate Preservation in the Ocean

Recent microelectrode pH and O$_{2}$ measurements across the sediment-water interface suggest CaCO$_{3}$ dissolution kinetics substantially slower than laboratory values and support a dissolution response to organic matter degradation near the sediment surface. We report a modelling exercise, motivated by these results, that indicates the pattern of calcium carbonate preservation in the equatorial Atlantic and Indian oceans is most readily reproduced using a dissolution rate constant 10 to 100 times smaller than those measured in the laboratory. The model suggests that 40% or more of the particulate CaCO$_{3}$ rain dissolves at the calcite saturation horizon in response to organic matter degradation within the sediments, and that this effect is insensitive to the choice of dissolution rate constant in ranges measured. Implications are that the dissolution flux from the sediments is greater than previously thought, and that calcium carbonate preservation in the deep sea should be strongly dependent on the particulate organic carbon to calcium carbonate rain ratio.