The radiocarbon age of calcite dissolving at the sea floor: estimates from pore water data Academic Article uri icon

abstract

  • We measured the radiocarbon content and stable isotopic composition of pore water and bottom water sCO sub(2), sedimentary organic carbon, and CaCO sub(3) at two sites on the Ceara Rise, one underlying bottom water that is supersaturated with respect to calcite (Site B), the other underlying undersaturated bottom water (Site G). The results were combined with pore water O sub(2), sCO sub(2), and Ca super(2+) profiles and Sayles, 1996) to estimate the radiocarbon content of the CaCO sub(3) that is dissolving in the sediment mixed layer. At Site G, the CaCO sub(3) that is dissolving in the upper 2 cm of the sediments is clearly younger (richer in super(14)C) than the bulk sedimentary CaCO sub(3), indicating that nonhomogeneous CaCO sub(3) dissolution occurs there. The case for nonhomogeneous dissolution is much weaker at the site underlying supersaturated bottom water. The results indicate that nonhomogeneous dissolution occurs in sediments underlying undersaturated bottom water, that the dissolution is rapid relative to the rate of homogenization of the CaCO sub(3) in the mixed layer by bioturbation, and that the dissolution rate of CaCO sub(3) decreases as it ages in the sediment mixed layer. The results support the hypothesis, based on solid phase analyses, that the preferential dissolution of young (i.e., radiocarbon-rich) CaCO sub(3) leads to a pattern of increasing radiocarbon age of mixed-layer CaCO sub(3) as the degree of undersaturation of bottom water increases 1984; Broecker et al., 1991).

publication date

  • April 2000