CENOZOIC RECORD OF DUST ACCUMULATION IN THE SOUTH PACIFIC FROM 232TH ANALYSES OF IODP SITE U1371

The accumulation of dust in remote, pelagic sediments is controlled by aridity in the source regions as well as the gustiness of the transporting winds. Models and theory predict lower zonal wind intensities and gustiness in climates characterized by diminished meridional gradients such as the Late Cretaceous and Early Paleogene. The few published long-term data indicate overall lower dust accumulation in the northern Pacific and southern Indian Ocean during the Late Cretaceous and Early Paleogene than during the Neogene, as well as higher dust accumulation in the northern hemisphere than that in the south during the Late Cretaceous and Early Paleogene. However, the existing dust reconstruction likely is biased by sparse coverage, particularly from the Pacific with data limited to the northern low and subtropical latitudes.

Here we present new Thorium-232 based dust flux estimates from South Pacific IODP Site U1371. Thorium can be used as a proxy for dust because the dominant source of ²³²Th to the oceans is through terrigenous sediments. The primary transport mechanism for terrigenous sediments to the open ocean is wind. We analyzed the ²³²Th concentration in samples from Site U1371 and applied a linear sedimentation rate to calculate the flux of dust for samples dating between ~57-69 Ma. The preliminary data indicate a decrease in dust flux to Site U1371 from ~69 Ma to 57 Ma. This trend is consistent with a decrease in the aridity of the source region over the time interval, which likely was Australia at the time. However the data are also consistent with an overall decrease in wind gustiness during the study interval period. Additional data will enable us to correlate the record of dust at Site U1371 to the record of global climate to test potential relationships between global warmth and South Pacific dust supply.