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

The ( super(231)Pa/ super(230)Th) sub(xs,0) records obtained from two cores from the western (MD97-2138; 1 degree 25'S, 146 degree 24'E, 1900 m) and eastern (Ocean Drilling Program Leg 138 Site 849, 0 degree 11.59'N, 110 degree 31.18'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 super(230)Th-normalized biogenic preserved and terrigenous fluxes, as well as major and trace elements concentrations, in both cores. The ( super(231)Pa/ super(230)Th) sub(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 ( super(231)Pa/ super(230)Th) sub(xs,0) variations in the western equatorial Pacific also seem to be controlled by productivity (carbonate and/or opal). The generally high ( super(231)Pa/ super(230)Th) sub(xs,0) ratios (>0.093) of the profile could be due to opal and/or MnO sub(2) in the sinking particles. The profiles of ( super(231)Pa/ super(230)Th) sub(xs,0) and super(230)Th-normalized fluxes indicate a decrease in exported carbonate, and possibly opal, during isotopic stages 2 and 4 in MD97-2138. Using super(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.