Observations of contrasted glacial-interglacial dissolution of foraminifera above the lysocline in the Bay of Bengal, northeastern Indian Ocean
Observations of contrasted glacial-interglacial dissolution of foraminifera above the lysocline in the Bay of Bengal, northeastern Indian Ocean
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DOI：
10.1007/s13131-021-1821-3
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发表时间：
2021-01
影响因子：
1.4
通讯作者：
Duo Wang;Xuan Ding;Franck Bassinot
中科院分区：
文献类型：
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作者：
Duo Wang;Xuan Ding;Franck Bassinot
U1446（19°50′n, 85°44′e，水深1430 m）是国际海洋发现计划（IODP）第353次考察（印度季风降雨）期间钻探的。它位于孟加拉湾北部的Mahanadi海上盆地。在这个相对较浅的地点，沉积速率和生物碳酸盐含量很高。利用微古生物学方法，我们研究了该遗址上40米左右的浮游和底栖有孔虫，时间跨度约为190ka。有孔虫记录的一个显著特征是发生了强烈但变化的溶解，尽管地点远高于现代溶斜层。如此强的溶解度在本地区从未见过报道。我们估计了有孔虫的通量，并量化了底栖有孔虫与总有孔虫的比例（底栖/总有孔虫）以及有孔虫破碎化指数，以表征溶解层上溶蚀的过去变化。该研究揭示了明显的冰期-间冰期对比，在海洋同位素阶段（MISs） 1和5比MISs 2-4和6溶解更强。这种保存差异可能会对有孔虫地球化学指标产生强烈影响。我们的新观察结果要求对该地区溶斜上溶蚀的原因进行深入研究，并评估其对用于古环境重建的基于有孔虫的代用物的影响。
Site U1446 (19°50′N, 85°44′E, at water depth 1 430 m) was drilled during Expedition 353 (Indian monsoon rainfall) of the International Ocean Discovery Program (IODP). It is located in the Mahanadi offshore basin, on the northern Bay of Bengal. Sedimentation rates and contents of biocarbonates are high at this relatively shallow site. Using a micropaleontological approach, we examined planktonic and benthic foraminifera in the upper around 40 m of this site, spanning the last around 190 ka. A striking feature of the foraminiferal record is the occurrence of strong but varying dissolution although the site is located well above the modern lysocline. Such strong dissolution has never been reported in this area. We estimated the flux of foraminifera and quantified the ratio of benthic foraminifera over total foraminifera (benthic/total foraminifera) along with the foraminifer fragmentation index in order to characterize past changes in this above-lysocline dissolution. This study reveals a clear glacial-interglacial contrast, with a stronger dissolution during marine isotope stages (MISs) 1 and 5 than during MISs 2–4 and 6. Such a difference in preservation is likely to have a strong impact on geochemical proxies measured on foraminifera. Our new observations call for an in-depth study of the causes of such above-lysocline dissolution in the region, and an evaluation of its impact on the foraminifera-based proxies used for paleoenvironmental reconstruction.