Marine barite: Recorder of variations in ocean export productivity

摘要

Marine barite (BaSO_4) is produced in the water column in association with decaying organic matter; its distribution in the water column and in core-top sediments closely corresponds with the organic carbon flux from the surface ocean to the deep ocean (export production). Barite preservation in non-sulfate-reducing sediments is high, compared to other proxies used to reconstruct both export carbon fluxes (export production) and carbon burial rates. Thus the accumulation rate of marine barite is one of the most promising methods (or proxy variables) for export production and has been used to understand and reconstruct past biogeochemical processes in the ocean, including export productivity. Like any other paleoceanographic proxy, there are assumptions and complications associated with the application of barite accumulation rates in reconstructing export production. Specifically, because barite constitutes only a small fraction of the total sediment (< 1%), computing precise barite accumulation rates depends on accurate estimates of bulk sediment mass accumulation rates which are hard to determine, particularly at high temporal resolution. Moreover, the significance of variable barite preservation depends on seawater saturation levels with respect to barite and sedimentation rates, which have not yet been fully investigated. Several studies have demonstrated the utility of this proxy, and if used wisely, marine barite accumulation rates in marine sediments can provide valuable information about changes in carbon export to depth and the response of the carbon cycle to climate perturbations in the geological record. Ideally, to achieve higher confidence in paleo-reconstructions of export production, several independent proxies should be applied simultaneously at any given site or time interval.