Reconstruction of Miocene to Pleistocene sea‐surface conditions in the eastern Indian Ocean on the basis of calcareous nannofossil assemblages from ODP Hole 757B
Reconstruction of Miocene to Pleistocene sea‐surface conditions in the eastern Indian Ocean on the basis of calcareous nannofossil assemblages from ODP Hole 757B
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DOI：
10.1111/iar.12373
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发表时间：
2020-01
期刊：
影响因子：
1.5
通讯作者：
Ryo Imai;Tokiyuki Sato;S. Chiyonobu;Y. Iryu
中科院分区：
文献类型：
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作者：
Ryo Imai;Tokiyuki Sato;S. Chiyonobu;Y. Iryu
我们研究了印度洋东部大洋钻探计划孔757 B的钙质超微化石组合，以重建从中新世中期到更新世的海面条件，特别是温跃层/营养层深度的变化。在海面上的营养水平重建的超微化石积累率，丰富的Discoaster，和颗石大小的变化Reticulofenestra。在11.8-7.5和6.7-6.2 Ma期间，海面条件可能是贫营养的，具有深温跃层/营养层。在7.5-6.7 Ma时从贫营养状态到富营养状态的变化是由富含营养的陆地物质的涌入或由增强的东南信风引起的富含营养的水的上涌引起的。这一结论得到了支持的磁化率的沉积物，这是一致的变化从贫营养到富营养组合的显着增加。约3.0 Ma后Discoaster丰度的减少表明此后温跃层/营养层变浅，这证实了构造限制和本格拉上升流系统的强化冷却导致的印度尼西亚洋流减少。减少模态球石大小的Reticulofenestra，表明富营养化条件下，观察到在三个视野。其中两个事件（7.5和5.0 Ma）分别对应于印度洋7.6 Ma和6.0-5.0 Ma的生物水华。
We studied the calcareous nannofossil assemblages from Ocean Drilling Program Hole 757B in the eastern Indian Ocean to reconstruct the sea‐surface conditions, especially changes in thermocline/nutricline depth, from the middle Miocene to the Pleistocene. Nutrient levels at the sea surface were reconstructed from the nannofossil accumulation rate, abundance of Discoaster, and coccolith size variations in Reticulofenestra. The sea‐surface conditions were likely to have been oligotrophic with a deep thermocline/nutricline during 11.8–7.5 and 6.7–6.2 Ma. The change from oligotrophic to eutrophic conditions at 7.5–6.7 Ma was caused by an influx of nutrient‐rich terrestrial material or upwelling of nutrient‐rich water induced by intensified southeast trade winds. This conclusion is supported by a marked increase in the magnetic susceptibility of the sediment that is coincident with the change from oligotrophic to eutrophic assemblages. The diminished abundance of Discoaster after ~ 3.0 Ma indicates shallowing of the thermocline/nutricline after that time, which confirms the reduced Indonesian Throughflow resulting from tectonic restriction and intensified cooling of the Benguela upwelling system. Decreases in the modal coccolith size of Reticulofenestra, indicating eutrophic conditions, are observed in three horizons. Two of these events (at 7.5 and 5.0 Ma) correspond to biogenic blooms in the Indian Ocean at 7.6 Ma and 6.0–5.0 Ma, respectively.