基于生物硅记录的孟加拉湾东南部末次冰期以来的古生产力变化

基于生物硅含量变化,结合碳酸钙和硅质生物放射虫数据,本文揭示了孟加拉湾东南部末次冰期以来的生产力演变规律及其气候响应。研究区域的古生产力演化大致分为3个阶段,即生产力相对低的末次冰期(56~18 ka)、生产力呈阶段性增加的末次冰消期(18~10 ka)以及高生产力的全新世。进一步地,研究发现末次冰期沉积物中放射虫物种主要是具有硅化程度较高的矢状环形结构的轭环虫/双篮虫属占据绝对优势(约60%)、少见硅化程度轻的纤细结构,推测末次冰期沉积物中硅质生物壳体受到明显溶解作用影响,尽管如此,末次冰期碳酸钙含量约20%、生物硅含量3.5%~4.4%、放射虫丰度1 000~6 000枚·g^-1,表明孟加拉湾东南部末次冰期以来的生产力一直处于相对较高的水平,营养盐物质丰富、生物量较高。该结论得到放射虫群落结构中罩笼虫目高相对丰度(>50%)的数据支持,其被认为是营养盐丰富的指标。此外,末次冰消期生物硅含量的阶段性波动变化现象,可能是受千年尺度气候事件的调控引起的,即Heinrich1(HS1)和新仙女木(YD)时期生产力增高、生物量增加,推测与陆源有机物质的输入带来丰富的营养物质进入上层水体、南极中层水入侵带来中层水通风增强促进硅质生物生产力的升高有关。

Productivity evolution in the southeastern Bay of Bengal since the last glaciation: Insight from biogenic silica records

Based on the biogenic silica (BSi) records, combined with the calcium carbonate (CaCO₃) and siliceous radiolarian data, the evolution of productivity and climatic response in the southeastern Bay of Bengal (SEBoB) since the last glaciation is revealed. The productivity evolution in the study area is roughly divided into three stages: relatively low productivity during the last glaciation (~56-18 ka), rapid productivity increase during the last deglaciation (~18-10 ka), and ultra high productivity during the Holocene. Radiolarian species in the sediments of the last glaciation were dominated (~60%) by highly silicified Zygocircus/Amphispyris with the sagittal ring structure, whereas slender shaped ones with low degree of silicification were few. We speculated that the shell structure of siliceous organisms in the glacial sediments were affected by dissolution. Nevertheless, the calcium carbonate content (~20%), BSi content (3.5%-4.4%), and radiolarian abundance (1000-6000 inds·g^-1) in the last glaciation indicated that productivity in the SEBoB had been relatively high, since the last glaciation with abundant nutrients and biomass. This conclusion was supported by the relatively high abundance of nassellarians (>50%)—an indicator of rich nutrients. In addition, the periodic fluctuation of Bsi contents in the last deglaciation might be controlled by millennium scale climate events. During the Heinrich Stadial 1 intervals (HS1) and Younger Dryas (YD), the climate cooled, enhanced northeast monsoon carried more terrigenous organic matter into the upper water, and the invasion of antarctic intermediate water enhanced intermediate water ventilation while biomass and productivity peaked.