A comparison between excess barium and barite as indicators of carbon export

Since Dymond et al. [1992] proposed the paleoproductivity algorithm based on "Bio-Ba," which relies on a strong correlation between Ba and organic carbon fluxes in sediment traps, this proxy has been applied in many paleoproductivity studies. Barite, the main carrier of particulate barium in the water column and the phase associated with carbon export, has also been suggested as a reliable paleoproductivity proxy in some locations. We demonstrate that Ba_excess (total barium minus the fraction associated with terrigenous material) frequently overestimates Ba_barite (barium associated with the mineral barite), most likely due to the inclusion of barium from phases other than barite and terrigenous silicates (e.g., carbonate, organic matter, opal, Fe-Mn oxides, and hydroxides). A comparison between overlying oceanic carbon export and carbon export derived from Ba_excess shows that the Dymond et al. [1992] algorithm frequently underestimates carbon export but is still a useful carbon export indicator if all caveats are considered before the algorithm is applied. Ba_barite accumulation rates from a wide range of core top sediments from different oceanic settings are highly correlated to surface ocean ¹⁴C and Chlorophyll a measurements of primary production. This relationship varies by ocean basin, but with the application of the appropriate f ratio to ¹⁴C and Chlorophyll a primary production estimates, the plot of Ba_barite accumulation and carbon export for the equatorial Pacific, Atlantic, and Southern Ocean converges to a global relationship that can be used to reconstruct paleo carbon export.