SOUTHERN OCEAN DRIVEN δ13C MINIMA ACROSS TERMINATION I AND II IN THE EQUATORIAL INDIAN OCEAN

The δ¹³C minima at glacial terminations are a persistent feature in sediments of subtropical Indo-Pacific, eastern equatorial Pacific, south Atlantic, and sub-Antarctic. We present the first observed δ¹³C minima across Terminations I and II in the Maldives, equatorial Indian Ocean, in both subsurface and intermediate waters. Following drilling by the International Ocean Discovery Program (IODP) Expedition 359, Maldives Monsoon and Sea Level, at Site U1467, we present high-resolution stable isotope records of five planktonic foraminifera species (Globigerinoides ruber, Trilobatus sacculifer (w/o sac), Neogloboquadrina dutertrei, Globorotalia menardii, and Pulleniatina obliquiloculata (with cortex)) and one benthic species (Cibicides mabahethi) to monitor changes in the vertical thermal and nutrient profile in addition to assessing the ventilation history of the Maldivian Inner Seaway. These records span from Marine Isotope Stage (MIS) 6 to the Holocene, and reveals prominent δ¹³C decreases in the planktonic and benthic species at both Terminations.

Sub-Antarctic Mode Water and/or Antarctic Intermediate Water (SAMW/AAIW) advected northwards and propagated ¹²C-rich, well-mixed southern sourced water into all three-ocean basins during the deglaciation. The large carbon isotope excursions, measured in shells of planktonic and benthic species, are explained by increased ventilation in the Southern Ocean, reinvigorated Circumpolar Deep-Water (CDW) upwelling, and upwelling of nutrient-rich, ¹²C rich deeper water masses during the deglaciations. Yet, air-sea gas exchange also imparts the global atmospheric δ¹³C values with CO₂ outgassing and invasion on the global ocean on thermocline δ¹³C evolution. Results for Site U1467 expands on findings from the Southern Ocean indicating a combination of air-sea gas exchange and upwelling of nutrient rich, CDW during the deglaciations. These waters are also advected through the equatorial Indian thermocline except for the δ¹³C minimum seen during the MIS 4/3 transition in both the Southern Ocean and atmosphere. This would imply Termination I and II have persistent Southern Ocean sourced mode and intermediate waters entering the equatorial Indian Ocean during the deglaciations in comparison to the Modern situation where, AAIW only reaches 10°S in the Indian Ocean.