Hilde Snoeckx

Late Cenozoic Eolian deposition in the North Pacific: Asian drying, Tibetan uplift, and cooling of the northern hemisphere

A newly constructed record of eolian dust accumulation from the central North Pacific shows that dust deposition increased by an order of magnitude quite rapidly at 3.6 Ma. We associate this sudden drying with the uplift of at least the northern portion of the Tibetan Plateau, shutting off the Indian Ocean moisture source to central and western China. This ten-fold increase in atmospheric dust loading appears to be associated with the 1-m.y.-long shift toward heavy δ18O values that occurred at 3.6–2.6 Ma. The dust grain-size record of wind intensity begins its late Cenozoic coarsening a million years before the drying event, at ∼4.5 Ma. The northern hemisphere cooling that results in intensification of the subpolar westerly winds may have as its ultimate cause the drawdown of atmospheric CO2 in the latest Miocene and the early Pliocene closing of the Panamanian Seaway.

Late Quaternary CaCO3 stratigraphy of the eastern equatorial Pacific

Four patterns of CaCO3 abundance occur in cores retrieved from the eastern equatorial Pacific during the Venture 01 expedition. Core locations lie along a north-south transect at 110°W underneath the different currents of the equatorial current system and along an east-west transect from 110° to 90°W, at approximately 3°S, underneath the South Equatorial Current. The “classic” or central equatorial Pacific pattern of CaCO3 abundance maxima associated with glacial stages as defined by the δ18O record characterizes only a small portion of the area studied. In the area where the Peru current turns west to join the South Equatorial Current, the carbonate record is characterized by a broad low, centered on interglacial carbonate stage B-3 (approximately stage 5 in δ18O stratigraphy) overlying a broad mid-Brunhes maximum. Low-amplitude variations in CaCO3 percentages are superimposed on this pattern. This pattern extends westward in a long-wavelength pattern in which the B-3 carbonate low becomes decreasingly pronounced away from the equator. The fourth pattern, observed north of 10°N, is erratic and may be only local in extent.

Dry bulk density and CaCO3 relationships in upper Quaternary sediments of the eastern equatorial Pacific

Abstract Results from 1110 paired CaCO3 and bulk density measurements from cores raised from the eastern equatorial Pacific permit formulation of well constrained CaCO3-DBD relationships for that region. The cores lie along a N-S transect at 110°W from 10°N to 3°S underneath the different currents of the equatorial current system and along an E-W transect from 110° to 90°W, at approximately 3°S. Two distinct, crescent-shaped dry bulk density-CaCO3 relationships are observed. For equal CaCO3 percentages, sediments from those sites at 110°W, which are situated in the high productivity zone, have lower dry bulk density. Cores raised from closer to shore have relatively greater DBD.