Radiocarbon in Pore Water Carbon Pools in Sediments of the Eastern Equatorial Atlantic Ocean. Book uri icon

abstract

  • We analyzed the radiocarbon content of pore water dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) at 5 sites on the Sierra Leone Rise and Cape Verde Plateau in the Eastern Equatorial Atlantic. 3 of these sites lie above the calcite saturation horizon, 2 below. At all but one site, pore water DIC has radiocarbon content equal to or greater than that of bottom water DIC, to depths ranging from 2 to 7 cm below the sediment- water interface. The pore water DIC is substantially enriched in radiocarbon relative to sedimentary CaCO3 and organic carbon, indicating that radiocarbon-rich material is released preferentially from one or both of these carbon pools during early diagenesis. We do not have a direct measure of the radiocarbon content of DIC produced by organic matter oxidation, but we do know, from measurements of radiocarbon in pore water DOC, that "young" organic matter is released into pore waters during organic matter diagenesis. At all sites, pore water DOC was greatly enriched in radiocarbon relative to bottom water DOC to depths up to 8.5 cm below the interface (the maximum depth at which we made measurements); DOC in the upper 1 cm had a modern radiocarbon signature. It is likely that the organic carbon that is oxidized to DIC also is rich in radiocarbon relative to the sedimentary organic carbon pool. In situ pore water alkalinity and DIC profiles from these and other sites in the region clearly show that sedimentary CaCO3 is dissolving, both above and below the calcite saturation horizon. Thus, CaCO3 dissolution, as well as organic carbon oxidation, contributes to pore water DIC. The radiocarbon age of the CaCO3 that is dissolving can be calculated from a mass balance using pore water radiocarbon data and organic matter oxidation and CaCO3 dissolution rates derived from other pore water data. The results of these mass balance calculations will be presented.

publication date

  • February 2001