230Thを用いたチリ沖中緯度域における第四紀後期生物起源粒子フラックス変動

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概要

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•  Throughout geologic time, variations of atmospheric CO2 partial pressures (pCO2) have been associated with climate change. During glacial periods, increased productivity and an efficient biological pump in the North Pacific, equatorial Pacific, and Southern Oceans may have contributed to low atmospheric pCO2. Furthermore, changes in global ocean ventilation would have been considered to be among the most effective controllers of variations of atmospheric pCO2 glacial-interglacial time scale. However, there is still some controversy as to whether ventilation was effective everywhere during glacial periods, and whether intensification of marine productivity resulted in a decrease of atmospheric pCO2. Resolving this controversy requires more data from many regions regarding temporal changes in past export fluxes of biogenic materials, especially in the upwelling area, where active ocean ventilation and biological production are observed. The aim of this study is to identify changes in the 230Th-normalized export flux of biogenic components commonly used as proxies for paleoproductivity—namely total organic carbon (TOC), calcium carbonate (CaCO3), biogenic opal (SiOPAL), and opal and CaCO3 ratio (SiOPAL/CaCO3)—as recorded in a sediment core from 36°S off the central–south Chilean coast. The 230Th-normalized fluxes of biogenic components were low from 22,000 to 15,000 calendar years before the present (cal yr BP), indicating reduced primary productivity. From 13,000 to 10,000 cal yr BP, the 230Th-normalized flux of biogenic components increased, thereafter dropping between 8000 and 5000 cal yr BP, and again increasing slightly in the late Holocene (< 5000 cal yr BP). The changing 230Th-normalized fluxes of biogenic components are linked to upwelling activity, which was at its maximum during the late deglaciation during the past 22,000 yr. The high fluxes off the central–south Chilean coast might in part be not only due to enhanced coastal upwelling but also related to enhanced upwelling at higher latitudes of the polar frontal zone in the entire Southern Ocean, which would be related to the north-south migration of Southern Westerly Winds.

著者

• 宮下 航

  高速炉技術サービス株式会社

• 福田 美保

  （独）海洋研究開発機構地球環境変動領域

• 原田 尚美

  （独）海洋研究開発機構地球環境変動領域

• 川上 創

  （独）海洋研究開発機構むつ研究所

• 松本 剛

  琉球大学理学部物質地球科学科

関連論文

• 230Thを用いたチリ沖中緯度域における第四紀後期生物起源粒子フラックス変動
• ^Thを用いたチリ沖中緯度域における第四紀後期生物起源粒子フラックス変動

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