Surface hydrodynamic variations and their forcing mechanisms over the past ~412,000 years from the western equatorial Indian Ocean

Abstract

Indian Ocean's tropical region receives the most insulation and is influenced by factors such as the intensity of trade winds, global walker circulations, and teleconnections. The western equatorial Indian Ocean (WEIO) is crucial for studying the variability of Indian monsoons in the past. To better understand the changes in mixed layer hydrodynamics and productivity over the past ~ 412 ka, we examined the planktonic foraminifera Globigerinoides ruber (G. ruber) oxygen and carbon isotope record (δ¹⁸O_G.ruber, δ¹³C_G.ruber) in core VM29045-PC taken from the WEIO (6° 00’ S, 69° 02’ E; 2860 m water depth). The chronology was established using five radiocarbon (¹⁴C) dates and δ¹⁸O_G.ruber compared with global isostack LR04. The values of δ¹⁸O_G.ruber were lower during Marine isotopic stage (MIS )11, MIS 5, and MIS 1, indicating higher SST, precipitation, and a strong summer monsoon. In contrast, MIS 10 and MIS 2 showed much higher values corresponding to cool and dry periods. The cooling intensities and interstadial cycles in MIS 10 and MIS 2 would be due to the Indian Ocean Dipole (IOD)/ equatorial westerly wind variability. The record (δ¹⁸O_G.ruber and δ¹³C_G.ruber) was compared globally with the western Pacific warm pool (WPWP), Southern Agulhas Bank (SAB), and southeast Atlantic (SEA), which showed coherency with Indian and other Ocean basins and interstadial warming during the glacial periods MIS 10 and MIS 2. It showed less cooling during MIS 6, MIS 8, and lower productivity. Higher productivity was observed during mid-MIS 10 and 9, and MIS 3 − 1, corresponding to higher δ¹³C_G.ruber values.