THE INFLUENCE OF ORGANIC-MATTER DIAGENESIS ON CACO3 DISSOLUTION AT THE DEEP-SEA FLOOR

In situ benthic flux chamber measurements were performed at seafloor locations in the Atlantic and Pacific oceans where the bottomwaters were supersaturated, approximately saturated, and undersaturated with respect to calcite. There was no evidence of significant dissolution at or above the saturation horizon. Below the saturation horizon, however, significant benthic fluxes of titration alkalinity and calcium out of the sediments were observed indicating appreciable dissolution. Where observed, the rate of dissolution is consistent with a rate expression of reaction order 4.5 and a rate constant in the range of 0.05 to 0.5% per day. A numerical simulation was constructed to represent organic matter and CaCO3 diagenesis at the seafloor. At the supersaturated and near-saturation sites, the model over-predicts the influence of metabolically produced CO2 on the extent of CaCO3 dissolution. It is possible that these results can be reconciled by a better understanding and parameterization of organic matter mineralization and porewater transport processes in surface sediments. The primary factors to be considered include (1) the oxidation state of the carbon being oxidized, (2) the vertical distribution of oxidation rates including the role of DOC in sediment remineralization, (3) the influence of nondiffusive transport of near-surface porewaters, and (4) the influence of episodic depositional events on organic and inorganic carbon cycling.