EVIDENCE OF A DISSOLUTION EFFECT ON BENTHIC FORAMINIFERAL SHELL CHEMISTRY - DELTA-C-13, CD CA, BA/CA, AND SR/CA RESULTS FROM THE ONTONG JAVA PLATEAU/

Core-top benthic foraminifera (Cibicidoides wuellerstorfi) from a dept h transect of Soutar box cores from the Ontong-Java Plateau (1.6 - 4.4 km) were analyzed for cadmium, barium, and strontium (Cd/Ca, Ba/Ca, a nd Sr/Ca) and for their stable isotopic composition (delta(13)C and de lta(18)O). We also measured bottom water delta(13)C, Cd, and Ba at the se sites. Foraminiferal delta(13)C values remain roughly constant over the entire depth range while bottom water delta(13)C values increase slightly, such that the delta(13)C difference between C, wuellerstorfi and bottom water ranges from about +0.2 parts per thousand in cores a bove 2.5 km to about -0.2 parts per thousand in cores below 4 km. This apparent depth dependence has not been previously reported, but this range in Delta delta(13)C values is comparable to the uncertainty in p ublished delta(13)C calibration studies. We observe strong decreases i n foraminiferal Cd/Ca, Ba/Ca, and Sr/Ca ratios (50, 25, and 15 percent , respectively) at water depths greater than about 2.5 km. These decre ases are substantially larger than the corresponding changes in bottom water trace element concentrations, and they are not correlated with variations in pore water Cd and Ba concentrations at these sites. Toge ther, the foraminiferal and bottom water Cd/Ca, Ba/Ca, and Sr/Ca data yield decreases in the apparent distribution coefficients for these me tals into calcite with increasing water depth, again a pattern which h as not been previously reported. These results when combined with the data from published core-top calibration studies suggest that a prefer ential loss of Cd, Ba, and Sr occurs during the dissolution of benthic foraminiferal calcite on the sea floor and raise the possibility of a dissolution-driven decrease in benthic foraminiferal delta(13)C value s.