Paleo-Productivity reconstruction based on Ba content in marine sediments

Productivity changes in the tropical-subtropical East-Atlantic are reconstructed using a multiproxy approach. This involves comparing the barium content of the marine surface sediment and sediment core records with other export productivity proxies.
Recent biogenic barium accumulation rates (Babio-AR) are shown to generally reflect export productivity (Pexp) in the modern East Atlantic. This relationship may also depend on the planktonic ecology of the surface water, which is dominated by the Ba-rich skeletons (celestite of acantharians) in the open marine environment. Coastal and open marine transfer functions are derived by calibrating Babio-AR with export productivity. However, the sedimentary Ba signal is found to decrease with depth below 1850 m, probably due to increased dissolution. Results also show that Ba preservation is not dependent on the amount of fine fraction (< 2µm). lt remains uncertain whether increased silica dissolution through open marine aeolian Fe-input (Bishop, 1988; Takeda, 1998) favours a decreased Ba-flux.
Longterm Pexp-changes determined using the new Ba transfer functions significantly agree with those derived from other methods (i.e. TOC) in open marine locations in the northern margin of the North Atlantic subtropical gyre over the last 40 ka and the last 330 ka in the equatorial divergence zone. Export productivity is shown to be 2-3 times higher than today during cold periods in the equatorial high productivity zone and possibly up to 6 times higher during stages 6 and 8. Productivity cycles are evidently controlled by the lateral advection of nutrient-rich intermediate waters from high southern latitudes.