BIOGENIC BARIUM FLUXES TO THE DEEP-SEA - IMPLICATIONS FOR PALEOPRODUCTIVITY RECONSTRUCTION

Dymond et al. (1992) have recently proposed an algorithm to reconstruc t paleoproductivity from biogenic Ba (bio-Ba) accumulation rates in se diments. Their equation is based on sediment trap data which indicate that C-org/bio-Ba ratios in settling particles are higher in the weste rn Atlantic compared to the Pacific. From this observation they have s uggested that the flux of bio-Ba to the seafloor may depend on dissolv ed Ba concentrations in intermediate and deep waters which are signifi cantly higher in the Pacific compared to the Atlantic. Accordingly, th ey have introduced a factor related to dissolved Ba concentration in t heir equation as a variable which strongly influences paleoproductivit y estimates. In an attempt to confirm the proposed dependency of bio-B a fluxes to the seafloor on dissolved Ba concentrations in seawater we have compiled additional data on organic carbon and bio-Ba fluxes in the deep sea. These data confirm Dymond et al.'s findings that settlin g particles have significantly higher C-org/bio-Ba in the western Atla ntic compared to the Pacific. However, we also found lower ratios in t raps deployed in the North Atlantic, similar to those found in the Pac ific, while in the Panama Basin we found ratios as high as those in th e western Atlantic. From these observations we conclude that dissolved Ba concentration is not an important factor in regulating the flux of bio-Ba to the seafloor. Instead, we propose that high C-org/bio-Ba ra tios found in the western Atlantic, the Panama Basin, the Arabian Sea, and some stations in the Nordic Seas result from the addition of refr actory organic carbon from nearby continents, shelves, or slopes. If t hat is confirmed, the algorithm proposed by Dymond et al. (1992) could be simplified and could provide a powerful means to estimate paleopro ductivity. In addition, deviations from the C-org/bio-Ba ratios in set tling particles could be used to estimate the input of continental or shelf-derived refractory organic matter into the deep sea.