Remineralization of particulate authigenic trace metals in the middle Atlantic Bight: Implications for proxies of export production

Abstract

Samples collected by time-series sediment traps deployed in the Middle Atlantic Bight were studied to better understand the formation, and preservation, of particulate authigenic forms of trace metals (Cu, Ni, Ba) That hold potential to serve as proxies in the sedimentary record of past changes in the flux of biogenic detritus sinking from the surface ocean into the deep sea (export production). Particulate biogenic and authigenic phases are extremely labile, as evidenced by the observation that as much as 70% of the particulate fluxes of organic carbon and of certain metals (Cu, Ni, and Mn), and up to 25% of the particulate fluxes of authigenic Ba and of opal collected by sediment traps are released rapidly into solution during the time period between particle collection and trap retrieval. Further remineralization on the seabed reduces concentrations of authigenic Cu and Ni in surface sediments below the limit of detection. Approximately 80% of authigenic Ba is remineralized during early diagenesis on the seabed, much more than is expected for conditions of high sediment mass accumulation rate that exist in the study area. Extensive remineralization during early diagenesis, combined with large corrections required to remove the aluminosilicate contribution to the concentrations of Cu, Ni, and Ba in sediments, preclude the successful use of down-core profiles of these trace metals to reconstruct past changes in export production of the Middle Atlantic Bight. Similar problems are likely to plague paleoproductivity reconstructions in other ocean-margin regions, or wherever high fluxes of aluminosilicate phases occur.