Cenozoic history of atmospheric circulation intensity and climatic variability recorded by eolian deposition in the pelagic ocean.

Abstract

The overall Cenozoic record of eolian input to the Indian Ocean is one of extremely low dust flux. The largest decrease in eolian input occurred near the Paleocene/Eocene boundary and records the initial onset of extreme aridity in the desert regions of southern African. A major reduction in the grain size of eolian material also occurred at this time reflecting a significant decrease in the strength of southern hemisphere atmospheric circulation. Further reductions in dust input are recorded during the latest Eocene, during the Oligocene and in the middle Miocene and correspond to intervals of significant changes in the oxygen isotope records related to polar cooling and ice volume growth. Regional patterns of eolian deposition in the eastern equatorial Pacific track the latitudinal position of the equatorial trade winds throughout the late Neogene and suggest that, prior to about 4.0 to 5.0 Ma, the ITCZ was located farther north (at least north of about 7$\sp\circ$N) than its present location. Eolian grain size data indicate more intense southern hemisphere atmospheric circulation from about 8 to 5 Ma. Eolian flux data records a regional decrease in the supply of continental dust material near 2.4 Ma suggesting climatic conditions in Central and South America may have become relatively more humid at this time. Eolian mass accumulation rates from core V21-146 recovered from the north Pacific exhibit increased glacial dust input reflecting more arid conditions in eastern Asia at these times. Frequency domain analysis shows strong coherency to the oxygen isotope record of glaciation with no appreciable phase difference at each of the major orbital periodicities. Overall, the pattern of eolian flux closely resembles the loess-soil stratigraphy in China and can be used to link these two records. Eolian grain size data display cyclicity of 100, 41, 30-21, and 17 ky and show coherency to the oxygen isotope record of continental ice volume only at the 100 ky power with coarser eolian grains deposited during interglacial times, a pattern more clearly apparent in the older portion of the record. The data suggest relatively more intense atmospheric circulation occurred during interglacial periods. (Abstract shortened by UMI.)