Substantial invasion of Antarctic Intermediate Water into the Arabian Sea during Younger Dryas and Heinrich Stadials

Abstract

Antarctic Intermediate Water (AAIW) is an important component of the global thermohaline circulation and an essential limb of the Atlantic Meridional Overturning Circulation (AMOC), which redistributes heat, oxygen, and nutrients in the global ocean. Understanding the dynamics of intermediate water circulation over a millennial timeframe is essential to determine the impact of AMOC changes on ocean heat transport during abrupt climatic events. However, the precise relationship between global ocean intermediate water circulation and abrupt climate events, such as the Younger Dryas (YD) and Heinrich Stadials (HS), is not yet fully understood, particularly in tropical regions. Here, we present a ∼29 ka high-resolution record of Neodymium isotope (Ɛ_Nd) in authigenic phases, a water mass tracer, of a sediment core collected from the intermediate depth (840 m) in the eastern Arabian Sea (off Goa) to understand the past variability in AAIW circulation in the northern Indian Ocean on a millennial time scale. Our new Ɛ_Nd record reveals the pronounced temporal variation (−9.5 to −6.1) throughout the core, marked with enhanced radiogenic Nd signature during the YD, HS1, and HS2. These episodes of enhanced radiogenic Nd signatures signify an increased northward penetration of Antarctic Intermediate Water into the Northern Indian Ocean. The intervals of northward progression of AAIW coincide with the Northern Hemisphere cold events which could have resulted from the enhanced formation of AAIW in the Southern Ocean that occurred due to the warming-induced deceleration of the AMOC. This correlation underscores a robust connection between the formation of North Atlantic Deep Water (NADW) and Southern Ocean climate dynamics through the "bipolar seesaw" mechanism. Our study emphasizes that tracking changes in AAIW in the Arabian Sea can provide insights into the past and future variations in AMOC.