Assessing the suitability of benthic foraminiferal morpho-groups to reconstruct paleomonsoon from Bay of Bengal

Abstract

Temporal changes in benthic foraminiferal morpho-groups were suggested as an effective proxy to reconstruct past monsoon intensity from the Arabian Sea. Here, in order to test the applicability of temporal variation in morpho-groups to reconstruct past monsoon intensity from the Bay of Bengal, we have documented recent benthic foraminiferal distribution from the continental shelf region of the northwestern Bay of Bengal. Based on the external morphology, benthic foraminifera were categorized into rounded symmetrical (RSBF) and angular asymmetrical benthic foraminifera (AABF). Additionally, a few other dominant groups were also identified based on test composition (agglutinated, calcareous) and abundance (Asterorotalids and Nonions). The relative abundance of each group was compared with the ambient physico-chemical conditions, including dissolved oxygen, organic matter, salinity and temperature. We report that the RSBF are abundant in comparatively warm and well oxygenated waters of low salinity, suggesting a preference for high energy environment, whereas AABF dominate relatively cold, hypersaline deeper waters with low dissolved oxygen, indicating a low energy environment. The agglutinated foraminifera, Asterorotalids and Nonions dominate shallow water, low salinity regions, whereas the calcareous benthic foraminiferal abundance increases away from the riverine influx regions. Food availability, as estimated from organic carbon abundance in sediments, has comparatively less influence on faunal distribution in the northwestern Bay of Bengal, as compared to dissolved oxygen, temperature and salinity. We conclude that the factors associated with freshwater influx affect the distribution of benthic foraminiferal morpho-groups in the northwestern Bay of Bengal and thus it can be used to reconstruct past monsoon intensity from the Bay of Bengal.

Abundance and Ecology of EndemicAsterorotalia trispinosafrom the Western Bay of Bengal: Implications for its Application as a Paleomonsoon Proxy

“…We do not find any relation between the relative abundance of A. trispinosa and dissolved oxygen concentration in the western Bay of Bengal. The findings based on samples collected from the wider shelf and slope of the western Bay of Bengal are in contrast with that based on samples collected from the shelf and upper slope of the northwestern Bay of Bengal, wherein a high abundance of A. trispinosa is observed in well-oxygenated waters (Manasa et al, 2016). It should, however, be noted here that the samples in the northwestern Bay of Bengal covered a limited range of physico-chemical parameters as compared to the samples used in this study (Manasa et al, 2016).…”

“…The findings based on samples collected from the wider shelf and slope of the western Bay of Bengal are in contrast with that based on samples collected from the shelf and upper slope of the northwestern Bay of Bengal, wherein a high abundance of A. trispinosa is observed in well-oxygenated waters (Manasa et al, 2016). It should, however, be noted here that the samples in the northwestern Bay of Bengal covered a limited range of physico-chemical parameters as compared to the samples used in this study (Manasa et al, 2016). The response of A. trispinosa to dissolved oxygen is, however, mixed as Frerichs (1970) found A. trispinosa in less oxygenated waters of the inner shelf regions of the Andaman Sea.…”

Multiple Ecological Parameters Affect Living Benthic Foraminifera in the River-Influenced West-Central Bay of Bengal

“…The stained sediments were stored in cold-storage (4 • C) for a minimum of 2 weeks and were then processed following the standard procedure (Manasa et al, 2016;Singh et al, 2018;Suokhrie et al, 2020). The excess ethanol rose-Bengal was removed, and the sediments were freeze-dried.…”

“…The relative influence of various factors on faunal distribution, however, varies from region to region. The salinity and temperature are the major factors in riverine influx dominated continental shelves (Manasa et al, 2016). However, the deeper depth continental slope assemblages are mainly controlled by the availability of food and dissolved oxygen concentration (Gooday, 1986;Corliss and Chen, 1988;Mackensen and Douglas, 1989;Corliss and Emerson, 1990;Barmawidjaja et al, 1992;Jorissen et al, 1992;Rosoff and Corliss, 1992;Rathburn and Corliss, 1994;Nisha and Singh, 2012;Singh et al, 2015aSingh et al, , 2018Verma et al, 2018).…”

Late-Holocene paleoceanographic and climatic changes and their impact on Indian socio-economic conditions: Benthic foraminiferal evidence from the Bay of Bengal

“…Thus, this group is used as a vital proxy for paleoclimatic reconstruction. Several studies have been conducted using foraminiferal census count around the globe to understand paleoclimatic variations (Kaiho, 1991; Manasa et al, 2016; Nigam et al, 1992; Severin, 1983; Suokhrie et al, 2018). Temporal variation in the abundance and morphology of foraminiferal tests is an evolutionary adaptation due to environmental change.…”