CLIMATE VARIABILITY IN THE TROPICAL INDIAN OCEAN DURING THE LGM AND MID-HOLOCENE

During the last decades, the western Indian Ocean has been warming faster than the other oceans [1], which impacts the mean climate state of the Tropical Indian Ocean (TIO) and the mode of climate variability events. For example, state-of-the-art climate models suggest an intimal link between a warmer TIO and an increase in the occurrence of extreme climate variability events [2]. Sediment core proxy data spanning a broad range of past mean climate states can be key to validate with real-world data these model simulations.

Here we present proxy reconstructions of past climate variability through the Last Glacial Maximum (LGM) and Middle Holocene (MH) that complement existing reconstructions to date limited to continental margin settings in the easternmost tropical Indian Ocean [3]. Our new δ¹⁸O data from individual foraminiferal analysis (IFA) document climate variability during the Late Holocene (<3 kyrs), MH (6-8 kyrs), and LGM (22-24 kyrs) time slices. We select individuals of T. trilobus and N. dutertrei to characterize the variability in the upper water column. Samples are from Ocean Drilling Program (ODP) Site 758 and from International Ocean the Discovery Program (IODP) Site U1443, both drilled at the same open ocean location in the southernmost sector of the Bay of Bengal.

At least 59 individuals of both species for each mean state were analysed to ensure a rigorous statistical analysis [4] of the data, aimed at quantifying the amplitude of variability at the upper water column. We compare our LH δ¹⁸O distributions with the predicted δ¹⁸ depth profile derived from Ocean Reanalysis System 5 time series to determine species-specific mean calcification depths, which we use to quantitatively address climate variability during the MH and LGM mean climate states. We will discuss the implications of changes in climate variability versus changes in ecological preferences of the selected foraminiferal species.

[1] Roxy et al. (2014), J. Clim. 27(22), 8501–8509; [2] Cai et al. (2018), Nat Commun. 9, 1419; [3] Thirumalai et al. (2019), Paleoceanogr. Paleoclimatol. 34(8), 1316–1327; [4] Thirumalai et al. (2013), Paleoceanogr. Paleoclimatol. 28(3), 401–412