IODP航海における炭酸塩トピックス  [in Japanese] Topics on carbonate relevant topics by IODP  [in Japanese]

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<p>炭酸塩を主たるテーマとしてIODP(統合国際深海掘削計画)では4航海が実施された.310次航海でのタヒチ島の結果によると,融氷パルス(Melt water pulse=MWP)-1Aの海水準の上昇は12-22mだったが,融氷パルス-1Bは観察されなかった.325次航海では,グレートバリアリーフで更新世のサンゴ礁掘削が行なわれた.最終氷期最盛期(LGM:20,000年前)には,水温は5℃以上降温していた.307次航海は,北西太平洋の深海サンゴの内部を初めて掘削した.サンゴマウンドの発達の開始は,現代の海洋大循環が大西洋で確立した更新世の最初期に地球的規模で寒冷化した環境変動と相関していた.320/321次航海では,過去5300万年間の時間レンジをカバーする赤道太平洋の深海底より一連の堆積物が採取された.炭酸塩の沈積流量に基づき新生代の赤道域の炭酸塩補償深度(CCD)変化が復元された.</p>

<p>Integrated Ocean Drilling Program (IODP) drilled into coral reefs, deep-water coral mounds and sediments to understand the change of climate, and biogeochemical cycle. IODP Expedition 310 around Tahiti enabled to delineate the course of last deglacial sea level rise and its impact on reef growth and geometry at this island. Amplitude of the sea-level jump around melt water pulse-1A (MWP-1A) was estimated at 12-22 m (most likely 14-18 m). Sea-surface temperature variations in 20-10 kyr indicated a temperature drop of 1.5 °C at the Younger Dryas. IODP Expedition 325 recovered Pleistocene reef materials around Great Barrier Reef. More than 1,000 radiometric dates revealed detailed sea level pictures before and after the last glacial maximum (LGM: 20,000 years ago). We successfully reported more than 5℃ lowering of SST during the LGM. IODP Expedition 307 revealed the interior of a deep-water coral mound at ~800 m deep in Northern East Atlantic. Our age model based on Sr isotope recognized two growth stages; the depositionally continuous lower reef (2.6-1.7 Ma) accumulated under the low-amplitude relative sea-level change, and the discontinuous upper reef (1.0 Ma to mid-Holocene) developed under the high-amplitude relative sea-level change. The reef initiation was temporally correlated to the global cooling at the beginning of Pleistocene, when modern circulation was established in Atlantic. IODP Expedition 320/321 recovered a series of equatorial Pacific sediments covering the past 53 million years. Cenozoic evolution of carbonate compensation depth in the equatorial Pacific was reconstructed. It tracks a long-term deepening from 3.0-3.8 km during the Eocene to 4.6 km at present, which is superimposed by large fluctuations during the middle to late Eocene, and ended with a sharp >500 m deepening during the Eocene-Oligocene transition. Those variations are closely linked to changes in global climate and carbon cycle.</p>


  • The Journal of the Geological Society of Japan

    The Journal of the Geological Society of Japan 124(1), 35-45, 2018

    The Geological Society of Japan


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