Lower export production during glacial periods in the equatorial Pacific derived from ( 231 Pa/ 230 Th) xs,0 measurements in deep-sea sediments (original) (raw)

1] The ( 231 Pa/ 230 Th) xs,0 records obtained from two cores from the western (MD97-2138; 1°25 0 S, 146°24 0 E, 1900 m) and eastern (Ocean Drilling Program Leg 138 Site 849, 0°11.59 0 N, 110°31.18 0 W, 3851 m) equatorial Pacific display similar variability over the last 85,000 years, i.e., from isotopic stages 1 to 5a, with systematically higher values during the Holocene, isotopic stage 3, and isotopic stage 5a, and lower values, approaching the production rate ratio of the two isotopes (0.093), during the colder periods corresponding to isotopic stages 2 and 4. We have also measured the 230 Th-normalized biogenic preserved and terrigenous fluxes, as well as major and trace elements concentrations, in both cores. The ( 231 Pa/ 230 Th) xs,0 results combined with the changes in preserved carbonate and opal fluxes at the eastern site indicate lower productivity in the eastern equatorial Pacific during glacial periods. The ( 231 Pa/ 230 Th) xs,0 variations in the western equatorial Pacific also seem to be controlled by productivity (carbonate and/or opal). The generally high ( 231 Pa/ 230 Th) xs,0 ratios (>0.093) of the profile could be due to opal and/or MnO 2 in the sinking particles. The profiles of ( 231 Pa/ 230 Th) xs,0 and 230 Thnormalized fluxes indicate a decrease in exported carbonate, and possibly opal, during isotopic stages 2 and 4 in MD97-2138. Using 230 Th-normalized flux, we also show that sediments from the two cores were strongly affected by sediment redistribution by bottom currents suggesting a control of mass accumulation rates by sediment focusing variability.