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<p>Radiolarians are marine siliceous planktonic forms that are distributed in shallow to open ocean regions. These are the least attempted group of microfossils, especially in the Northwestern Bay of Bengal. This investigation focuses mainly on the systematics and distribution of radiolarians in the Northwestern Bay of Bengal (BoB) to reconstruct the paleoclimatic and paleoceanographic events of the past 7 kyr. We recorded twenty-six radiolarian species belonging to seventeen genera, six families, and two suborders. Among the twenty-six radiolarian species, eleven species (<i>Acanthosphaera actinota, Acanthosphaera pinchuda, Cenosphaera cristata, Axoprunum pierinae, Axoprunum stauraxonium, Lithopera baueri, Peripyramis circumtexta, Plectopyramis dodecomma, Plectopyramis trapezomma, Stylotrochus sol</i>, and <i>Stylotrochus sp</i>.) were reported for the first time from the Northwestern BoB. This study recorded a higher abundance of suborder Spumellaria over the Nassellaria. This dominance could be attributed to their preference for warm, low-salinity surface and subsurface waters, influenced by the enhanced riverine nutrient input triggered by the onset of the monsoon. The radiolarian analyses enabled us to record four major depth biozones: surface dwellers (0–120&#xa0;m), subsurface dwellers (120–200&#xa0;m), intermediate dwellers (200–1000&#xa0;m), and deep (&gt; 1000&#xa0;m) dwellers. The abundance of these forms varied significantly during the mid and late-Holocene periods. During the mid-Holocene, an increase in Southwest Monsoon activity brought warm, low-salinity water into the region which favored the dominance of surface-dwellers. Additionally, the influx of cold, oxygen-rich deep water and a higher supply of Total Organic Carbon (TOC) further supported an increase in abundance of deep dwellers. Whereas weakened Southwest Monsoon and enhanced nutrient supply caused by the vertical mixing resulted in a higher abundance of radiolarians. Thus, this study aims to utilize the less frequently studied radiolarian group of microfossils as the depth biozone indicators to uncover the climatic and oceanographic significance in the Northwestern Bay of Bengal.</p>

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Radiolarian Depth Biozones as Proxies for Holocene Paleoclimate in the Northwestern Bay of Bengal

  • 期刊论文

  • 发表日期：

    2025年8月27日

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  • Veena Gopika Viswam,
  • Neelakantan Ravindran Nisha

摘要

Radiolarians are marine siliceous planktonic forms that are distributed in shallow to open ocean regions. These are the least attempted group of microfossils, especially in the Northwestern Bay of Bengal. This investigation focuses mainly on the systematics and distribution of radiolarians in the Northwestern Bay of Bengal (BoB) to reconstruct the paleoclimatic and paleoceanographic events of the past 7 kyr. We recorded twenty-six radiolarian species belonging to seventeen genera, six families, and two suborders. Among the twenty-six radiolarian species, eleven species (Acanthosphaera actinota, Acanthosphaera pinchuda, Cenosphaera cristata, Axoprunum pierinae, Axoprunum stauraxonium, Lithopera baueri, Peripyramis circumtexta, Plectopyramis dodecomma, Plectopyramis trapezomma, Stylotrochus sol, and Stylotrochus sp.) were reported for the first time from the Northwestern BoB. This study recorded a higher abundance of suborder Spumellaria over the Nassellaria. This dominance could be attributed to their preference for warm, low-salinity surface and subsurface waters, influenced by the enhanced riverine nutrient input triggered by the onset of the monsoon. The radiolarian analyses enabled us to record four major depth biozones: surface dwellers (0–120 m), subsurface dwellers (120–200 m), intermediate dwellers (200–1000 m), and deep (> 1000 m) dwellers. The abundance of these forms varied significantly during the mid and late-Holocene periods. During the mid-Holocene, an increase in Southwest Monsoon activity brought warm, low-salinity water into the region which favored the dominance of surface-dwellers. Additionally, the influx of cold, oxygen-rich deep water and a higher supply of Total Organic Carbon (TOC) further supported an increase in abundance of deep dwellers. Whereas weakened Southwest Monsoon and enhanced nutrient supply caused by the vertical mixing resulted in a higher abundance of radiolarians. Thus, this study aims to utilize the less frequently studied radiolarian group of microfossils as the depth biozone indicators to uncover the climatic and oceanographic significance in the Northwestern Bay of Bengal.