Date of Award
Doctor of Philosophy in Oceanography
Dr. Margaret Leinen
Dust, uplifted by wind from the continents, and transported through the atmosphere, leaves a geologic record across the earth; in loess deposits on the continents, red clays on the ocean floors and on the polar ice caps. If we can interpret the paleoclimatic and paleometeorology information preserved in these deposits, we can learn how continental climate and atmospheric circulation have varied over the course of time. Continental climate information is preserved in the composition of the dust. The mineral phases that comprise the surface of the continents are dictated by the geology of the parent rocks, but more importantly, the soils formed by the weathering of these continental rocks are extremely sensitive to the climate variables precipitation, temperature and seasonality. Records of atmospheric circulation processes are preserved in the spatial distribution patterns, flux and particle size of the deposited eolian material. In order to exploit the global paleoclimate and paleometeorology records, the relationships between the continental dust source areas, the transport process and the resulting deposits must be quantified.
In this work, sediments and aerosols from the North Pacific Ocean are studied. The North Pacific contains the most spatially and temporally contiguous record of eolian material, transported from the deserts of northern Asia by the zonal westerly winds for millions of years. Aerosols, collected from research vessels in the North Pacific, surf ace sediments from across the entire ocean basin, and a sediment core from the central North Pacific were analyzed for rock-magnetic properties, grain size and mineralogy. This study provides a data set of geological measurements that are directly related to atmospheric processes, recent sedimentation, and eolian sedimentation over the last 8 million years.
The aerosol samples record both the source region and transport history of the continental dust. Atmospheric dust concentrations are highest for those samples with the shortest transport time from Asia to the open ocean. Asian dust samples are characterized by high dust concentrations, fine grain size, and high concentrations of 2-20μm quartz and <2μm kaolinite. High latitude, Aleutian/Alaskan dust is characterized by low dust concentrations, coarse grain size and is relatively enriched in plagioclase and magnetic material. The aerosol is compositionally fractionated during the transport process, becoming relatively enriched in clay minerals at the expense of primary minerals.
The surface sediments from the North Pacific preserve the relationships between transport process and physical characteristics observed for the aerosols. The rock magnetic properties, grain size and mineralogy of the aerosols are the same as the eolian surface sediments. The sediments display a steady decrease in the grain size across the entire basin, and the composition is fractionated towards a higher coercivity, and a plagioclase-depleted and kaolinite- and chlorite- enriched composition with increasing distance from the source area.
The eolian dust preserved in the down-core sediments records the onset of major eolian sedimentation to this region 3.8 million years ago. When the flux increased, the rock magnetic grain size increased, the composition of the minerals shifted from a kaolinite-enriched mineralogy to a chlorite enriched mineralogy, suggesting acidification of the source region and acceleration of atmospheric transport.
Arnold, Eve Maureen, "The Rock Magnetic Properties, Grain Size and Mineral Composition of Winborne Dust and Sediment in the North Pacific Ocean" (1996). Open Access Dissertations. Paper 815.