Late Quaternary variation in productivity and oxygen in the deep Central Indian Ocean based on benthic foraminiferal abundance and assemblages

The relative abundances of ecologically sensitive and dominant benthic foraminifera (> 150 µm) in a sediment core located near the southeastern boundary of the Laccadive Sea in the Central Equatorial Indian Ocean were investigated to understand the deep-water conditions of the past 19 kyrs. Faunal analysis from 14 samples spanning the last 19 kyrs were done along with geochemical analysis of the sediment and stable isotope study of foraminifera. The investigation revealed variability in export productivity and changes in bottom water dissolved oxygen concentration primarily between the Holocene and the Last Glacial Maximum (LGM), whereas the Bølling- Allerød warm event (14.7–12.9 cal kyr BP) acted as a turning point in the benthic foraminiferal assemblage. During the LGM, poorly oxygenated bottom water and high export productivity was apparent with the decreased density of species indicative of high dissolved oxygen and the dominance of species indicative of high organic carbon. Evidence of well oxygenated bottom water during the Holocene was observed with increased density of benthic foraminiferal species indicative of high dissolved oxygen. The insignificant density of the high organic carbon genus Uvigerina during the Holocene, instead of moderate food supply, infers sensitivity to the upper limit of dissolved oxygen or its increased competition with high dissolved oxygen species. This study contributes to the understanding of changes in the deep-water condition of the Central Equatorial Indian Ocean during major climatic events of the last 19 kyrs and demonstrates that the deep sea benthic foraminiferal assemblages respond to regional as well as global climate.