Eolian Dust Fluctuation during the Past 200,000 Years Revealed from Quartz in North Pacific Deep-sea Sediments.

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The northwest Pacific is a typical region of the world where a large amount of windborne dust falls into the sea. A deep-sea sediment core (NGC59) that was recovered from the Hess Rise in the central North Pacific under the influence of westerlies provided continuous and detailed record of eolian dust accumulation during the past 200ky. Since it is hard to extract only eolian components derived from the Asian Continent from bulk marine sediment, our study is focused on the quartz that is a major mineral in eolian dust and is unaffected by alteration. The grain size distribution of quartz extracted from the surface of the deep-sea sediments is log-normal with 1.28∅ standard deviation, comparable to that of quartz in the Chinese Loess Plateau. Using this result, eolian quartz is separated from involved volcanic quartz mathematically. High mass-accumulation rates of loess quartz occurred during glacial periods (oxygen-isotope stages 5, 2, 4, and 6), and the maximum was at stage 4. We conclude that the environment of the dust source in central Asia was very arid and that soils were easily blown up into the air from the ground surface during the glacial age. On the other hand, the median diameter of eolian quartz in the core was about 8.5∅ and did not change significantly. This may imply that the intensity of westerlies did not change over the glacial-interglacial cycle.