Geochemistry of eolian dust in Pacific pelagic sediments: Implications for paleoclimatic interpretations

Abstract

Geochemical data (REEs, Th, Sc) were determined for the operationally defined eolian dust (ODED) fraction (n = 57) from the north and equatorial Pacific Ocean. Paleoclimate studies commonly have assumed that this sediment fraction represents eolian materials from continental source regions. This study shows, on the basis of geochemical data, published mineralogical data, and mixing models, that the ODED fraction actually is a mixture of materials from two endmember sources: the continental crust (eolian-transported weathering products) and the oceanic crust (primarily volcanogenic material). Mixing model results show that the average ash content is significant in the ODED fraction (equatorial Pacific = 43%; north Pacific = 24%). We have used this information to reconsider and refine the results of previous paleoclimate studies. In the northwest Pacific the flux of the eolian fraction is greater during glacial stages and shows a latitudinal maximum between 35[deg]N and 42 [deg]N. Eolian fluxes are greatest during interglacial periods in the equatorial Pacific. These results are consistent with previous interpretations. In contrast to previous assumptions, eolian mass accumulation rates may not be a valid indicator of paleo-aridity because they are correlated with grain size. Furthermore, the relative abundance of the two endmembers is correlated with the average grain size of the dust fraction (the continental crust component is associated with larger grains). This compositional effect should be considered in future studies which commonly utilize grain size as a proxy indicator of paleo-wind intensity.