日本地球惑星科学連合2018年大会

講演情報

[JJ] ポスター発表

セッション記号 M (領域外・複数領域) » M-IS ジョイント

[M-IS10] 古気候・古海洋変動

2018年5月23日(水) 13:45 〜 15:15 ポスター会場 (幕張メッセ国際展示場 7ホール)

コンビーナ:岡崎 裕典(九州大学大学院理学研究院地球惑星科学部門)、磯辺 篤彦(九州大学応用力学研究所)、北村 晃寿(静岡大学理学部地球科学教室、共同)、佐野 雅規(早稲田大学人間科学学術院)、長谷川 精(高知大学理工学部)、岡 顕(東京大学大気海洋研究所)、加 三千宣(愛媛大学沿岸環境科学研究センター)

[MIS10-P02] 南太平洋ニュージーランド沖堆積物中の中期中新世以降の生物源オパアール変化

*垣下 涼太1岡崎 裕典1関 宰2 (1.九州大学、2.北海道大学)

The Southern Ocean is known as a high nutrient low chlorophyll (HNLC) region. In HNLC, primary production is not proportional to the supply of macro-nutrients such as nitrate, phosphate and silicate. It is suggested that iron deficiency is the reason. In the ocean other than HNLC, macro-nutrients are the limiting factor for primary production. However, in the Southern Ocean, macro-nutrients are abundantly supplied to the surface layer by upwelling. Therefore, iron, a micro-nutrient, is deficient before macro-nutrient. As a result, iron deficiency is the limiting factor for primary production in the Southern Ocean. Diatom is a phytoplankton with biogenic opal frustules and can be preserved in sediments. Therefore, sedimentary biogenic opal content is used as a proxy for past biological productivity. During Ocean Drilling Program (ODP) Leg 181 in 1998, Site 1123 was drilled in South Pacific off New Zealand (41°47.1’S, 171°29.9’W, and 3290 m water depth). In this study, biogenic opal contents for the last 10 Myrs were measured on 219 samples of ODP 1123. Biogenic opal was analyzed by extracting with an alkaline solution (2M Na2CO3) and molybdenum yellow colorimetric method. Both biogenic opal contents and fluxes were relatively high during late Miocene from 7 to 5 Ma. Alkenone sea surface temperature (SST) and alkane flux records indicated significant cooling with increased dust occurred during this period. These data were consistent with a scenario that an enhanced primary productivity occurred when increased iron supply by dust by expansion of arid regions by intensified cooling. This suggests the studied area near Site ODP 1123 was a HNLC region during 7-5 Ma.