Glacial to Holocene changes in the surface and deep waters of the northeast Indian Ocean

Stable carbon and oxygen isotopic investigations are carried out on planktonic and benthic foraminifera from an AMS-dated sediment core of the northeast Indian Ocean (NEIO) to infer glacial to Holocene changes in surface and deep waters. The chronology of this gravity core (SK157-14; water-depth 3306 m; lat. 5°11′N; long. 90°05′E) was established using six AMS radiocarbon ages and oxygen isotope stratigraphy. Variations in δ18O and δ13C values of planktonic (Globigerinoides ruber) and benthic foraminifera (Cibicidoides spp.) are suggestive of large changes in the surface and deep water characteristics during the last ~ 60 ka. The δ18Opl values in core SK157-14 are significantly higher compared to the sediment cores in the northern Bay of Bengal and the Andaman Sea because of the diminished influence of riverine fresh water fluxes. Large variations in planktonic δ18Opl are noticed during the marine isotopic stage (MIS) 3.1 and 3.3. Glacial to Holocene Δδ18Opl amplitude (1.8‰) is consistent with other published oxygen isotope records from the nearby locations. Maximum enrichment in δ18Opl occurs at 24–19 and the minimum during 7–6 ka BP. Spectral analysis of planktonic δ18Opl time series suggests a teleconnection between surface water δ18O and North Atlantic climate oscillations.

Benthic foraminiferal δ18Oben values indicate deep water cooling of ~ 1.5 °C during the last glacial maximum. The δ13Cben values are generally higher for the Holocene foraminifera suggesting greater contribution from the North Atlantic deep water (NADW). However glacial benthic foraminifera are characterized by lower δ13Cben values. Highly depleted δ13Cben values during the ~ 60–50, 21–17 and 13–11 ka BP intervals suggest decrease contribution from the North Atlantic deep water (NADW) and increase influx from the Southern Ocean Deep Water (SODW). In addition, oxidation of organic matter and ageing of the deep water may have contributed in the pronounced decrease in δ13Cben during the glacial intervals.