Influence on the global environment of eolian dust : <BR>Glacial-interglacial times and the present

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  • Kawahata Hodaka
    Graduate School of Frontier Sciences and Ocean Research Institute, The University of Tokyo

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  • 風送塵の地球環境に与える影響<BR>—氷期・間氷期，完新世，現代—
  • 風送塵の地球環境に与える影響--氷期・間氷期,完新世,現代
  • フウソウジン ノ チキュウ カンキョウ ニ アタエル エイキョウ ヒョウキ カンピョウキ カンシン セイ ゲンダイ
  • Influence on the global environment of eolian dust Glacial-interglacial times and the present

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Abstract

The production/transportation of eolian dust has a mutual interaction with the climatic system. The recent estimation of eolian dust production is 1,700 Tg yr−1, with almost two-thirds from North Africa. Only 26% of the dust reaches the oceans (450 Tg yr−1). Although this amount corresponds to 3% of solid particles of total river input from terrestrial regions to oceans, eolian dust plays an important role in transporting particles to the pelagic regions in the ocean. Desert dust aerosol is dominated by particles with diameter of 0.1 to 10 μm, with the mean size being around 2 μm. Dust production is proportional to the cube of wind speed. Such aerosols have a lifetime of hours to weeks, allowing long-range transport over thousands of kilometers but producing strong gradients of dust deposition and concentrations that vary substantially over a day's time. The production and transportation of eolian dust reflects regional climate. A sedimentary core H3571 (34° 54.25′N and 179°42.18′E) showed that MAR (mass accumulation rate) of mineral aerosol varies from 156 to 732 mg cm−2 kyr−1 during the last 200 kyr with maxima in glacial times and minima during interglacials. Carbonate and phosphorus inputs with aerosol into sea surfaces have played a minor role in diminishing PCO2 in surface water during glacial times. On the other hand, the aerosol iron and silica supply to the ocean may have some potential to promote biogenic production and to enhance the MAR of organic carbon and biogenic silica into sediments. According to analysis of the Vostok Ice core, Antarctica, the concentrations of eolian dust rose from about 50 ng g-1 during interglacials to 1,000-2,000 ng g−1 during cold stages 2, 4, 6, 8, and 10. This increase is attributed to the correlation between the Vostok dust record and the climate at the Patagonian plain, which might have some link with deep ocean circulation in the Southern Atlantic. Total direct and indirect aerosol radiation forcing, as derived from models and observations, is estimated to be -0.5 [±0.4] W m−2 and −0.7 [−1.1, +0.4] W m−2, respectively, with a low level of scientific understanding. The latter effect includes the cloud albedo effect in the context of liquid water clouds.

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