CENOZOIC DUST ACCUMULATION IN THE SOUTH PACIFIC RECORDED AT IODP SITE U1369

Eolian dust that accumulates in pelagic sediment reflects ancient wind patterns and dust fluxes to the atmosphere. Variations in sedimentary dust accumulation rates are used to reconstruct changes in overall wind “gustiness” and the aridity of the source region. One method to measure ancient dust fluxes is through Thorium-232 concentrations found in pelagic sediment. Abundant Thorium-232 values in marine sediments are primarily associated with sediments derived from continental weathering processes. In the open ocean, far removed from the continents, the only source of Thorium-232 is from wind blown dust.

In order to investigate the long-term record of dust accumulation in the South Pacific during the Cenozoic, we analyzed the Thorium-232 concentration in samples recovered at IODP Site U1369. Site U1369 contains a sediment record spanning the last 58 Mya. Preliminary Thorium-232 based dust flux rates range from a maximum 20.47 mg/cm²/kyr to a minimum value of 14.02 mg/cm²/kyr. This range of values is similar to data from South Pacific DSDP Site 596 to the northwest, but lower than new data from nearby Site U1370 to the west. The relatively low dust fluxes estimated from Thorium-232 are consistent with with relatively humid conditions in Southern Hemisphere dust sources and relatively sluggish atmospheric circulation over the time interval ~ 58 Mya to 22 Mya. However additional data are needed to reconcile differences between Sites U1370 and the new data from Site U1369 and to better compare the dust reconstructions to the Cenozoic record of global climate.