Insights into the spatial and vertical distribution of extant planktonic foraminifera in the Bay of Bengal

Abstract

Planktonic foraminifera provide essential palaeoceanographic proxies, as their shells are used to characterise past ocean conditions. The accurate interpretation of palaeorecords depends on a thorough understanding of the species-specific ecological preferences. While global distribution patterns are well documented, regional analysis are sparser, which limits our understanding of the response of planktonic foraminiferal distribution to local environmental conditions. This study synthesises data of extant planktonic foraminiferal abundances to determine their spatial and vertical distributions in the Bay of Bengal, using available and published plankton net and sediment trap data. Our analysis highlights the dominance of six species that exhibit distinctive spatial and vertical distribution patterns. Globigerinoides ruber and Trilobatus sacculifer are associated with oligotrophic waters, and nutrient-rich areas, respectively. They consistently inhabit the upper 40 m of the water column, within the mixed layer. Neogloboquadrina dutertrei and Globigerina bulloides thrive in stratified waters near the Ganges-Brahmaputra River mouth and in the upwelling system south of India. While abundant in the mixed layer, their high numbers in the subsurface in stratified conditions and associated subsurface nutrient availability highlights their capacity to dwell in both surface and subsurface environments. Globorotalia cultrata and Globigerinita glutinata are abundant in the northern Bay of Bengal, with G. cultrata inhabiting the upper thermocline, while G. glutinata has the broadest vertical distribution, from the mixed layer to the deep thermocline. These findings help constraining the regional response of key species to local conditions and hence their use in palaeoenvironmental reconstructions from this critical sector of the global ocean.