Neogene history of the south Pacific tradewinds: Evidence for hemispherical asymmetry of atmospheric circulation

Abstract

Eolian dust grains extracted from southeast Pacific pelagic sediments provide a Neogene record of southern hemisphere atmospheric processes. The mass accumulation rate of dust has been low and generally constant at 1-4 mg/cm2 103 y since the late Oligocene. Eolian grainsize data show an increase from 8.2[phi] (3.40 [mu]) in older sediments to 7.2[phi] (6.8o [mu]) in younger material. This shift occurred about 10.5 m.y. ago and reflects a significant increase in the intensity of atmospheric circulation then. There is no obvious response to the onset of northern hemisphere glaciation 2.5 m.y. ago in these eolian records from the South Pacific. Comparison with existing information from the northern hemisphere suggests that the southern hemisphere has had more intense atmospheric circulation throughout the Neogene and that this asymmetry reached its greatest extent between 10.5 and 2.5 Ma.