Exceptionally high foraminiferal dissolution in the western Bay of Bengal

IF 3.3 2区 地球科学 Q2 ENVIRONMENTAL SCIENCES
Sudhira R. Bhadra , Rajeev Saraswat
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引用次数: 0

Abstract

The planktic foraminifera are an important component of the global carbon cycle, as they sequester the carbon, thus burying it in the sediments for ages. The burial of planktic foraminiferal shells, however, depends on the carbonate chemistry of the deep ocean. A significant fraction of foraminiferal shells dissolves well above the carbonate compensation depth. The foraminiferal lysocline is defined to delineate such zones of planktic foraminiferal dissolution well above the carbonate compensation depth. The dissolution of carbonate above the lysocline, termed supralysoclinal dissolution, has also been reported from highly productive basins. This study demarcates the extent of foraminiferal dissolution in the western Bay of Bengal. We document the distribution of planktic foraminifera and shell fragments in 100 core top samples collected from the coast perpendicular transects at depths ranging from 27 m to 2760 m. We examine the possible reasons for the foraminiferal dissolution by comparing the foraminiferal indices with the ambient bottom water parameters. The absolute abundance of planktic foraminifera is significantly low, both on the continental shelf and below ∼1000 m. The low abundance on the shelf is due to the terrigenous dilution. The fragmentation indices and the ratio between dissolution resistant and dissolution susceptible assemblage, however, confirm a significant increase in the dissolution at depths deeper than 1000 m. The foraminiferal shell dissolution at deeper depths is due to the high pressure, whereas the biogenic respiration-induced calcite under-saturation is responsible for the significant dissolution at a very shallow depth in the western Bay of Bengal, as compared to other parts of the world ocean.

孟加拉湾西部异常高的有孔虫溶解
浮游有孔虫是全球碳循环的重要组成部分,因为它们将碳隔离,从而将其埋在沉积物中很长时间。然而,浮游有孔虫壳的埋藏取决于深海的碳酸盐化学。相当一部分有孔虫壳在碳酸盐补偿深度以上溶解。有孔虫溶斜的定义是为了圈定远高于碳酸盐补偿深度的浮游有孔虫溶蚀带。在高产盆地中,碳酸盐岩在溶斜上的溶蚀也被称为超溶斜溶蚀。本研究划定了孟加拉湾西部有孔虫溶蚀的范围。我们记录了从27 ~ 2760 m深度的海岸垂直样带上采集的100个岩心顶部样品的浮游有孔虫和贝壳碎片的分布。我们通过比较有孔虫指数和环境底水参数来研究有孔虫溶解的可能原因。无论是在大陆架上还是在~ 1000 m以下,浮游有孔虫的绝对丰度都非常低。陆架上的低丰度是由于陆源稀释所致。然而,破碎指数和耐溶与易溶组合的比值证实,在深度大于1000 m时,溶蚀显著增加。较深的有孔虫壳溶解是由于高压造成的,而与世界海洋其他地区相比,孟加拉湾西部极浅深度的显著溶解是由生物呼吸引起的方解石欠饱和造成的。
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来源期刊
Anthropocene
Anthropocene Earth and Planetary Sciences-Earth and Planetary Sciences (miscellaneous)
CiteScore
6.30
自引率
0.00%
发文量
27
审稿时长
102 days
期刊介绍: Anthropocene is an interdisciplinary journal that publishes peer-reviewed works addressing the nature, scale, and extent of interactions that people have with Earth processes and systems. The scope of the journal includes the significance of human activities in altering Earth’s landscapes, oceans, the atmosphere, cryosphere, and ecosystems over a range of time and space scales - from global phenomena over geologic eras to single isolated events - including the linkages, couplings, and feedbacks among physical, chemical, and biological components of Earth systems. The journal also addresses how such alterations can have profound effects on, and implications for, human society. As the scale and pace of human interactions with Earth systems have intensified in recent decades, understanding human-induced alterations in the past and present is critical to our ability to anticipate, mitigate, and adapt to changes in the future. The journal aims to provide a venue to focus research findings, discussions, and debates toward advancing predictive understanding of human interactions with Earth systems - one of the grand challenges of our time.
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