Evolution of deep water circulation in the South China Sea since 32 million years ago

Abstract

The closure of the Indonesian Gateway (IG)¹ has played a pivotal role in influencing interocean circulation, notably affecting the Indonesian Throughflow (ITF) and altering climate patterns in Southeast Asia. However, there remains controversy regarding the timing of IG closure and its impacts on climate changes. In this study, we reconstructed Nd isotope (Ɛ_Nd) time series to observe the evolution of South China Sea (SCS) deep water over the past 32 Ma from core sediments at northern SCS and to explore the deep water connection between Indian Ocean and SCS before the fully IG closure.

The Ɛ_Nd time series of SCS deep water and benthic δ¹³C composition exhibits a remarkably consistent trend with North Indian Deep Water (NIDW) from 12 to 7 Ma, indicating that NIDW once served as a potential source. This feature implies a deep-water connection between the Indian Ocean and SCS deep water during this period. The observed Ɛ_Nd increases in SCS deep water during key intervals, such as ∼ 11, ∼16, and ∼ 25 Ma, likely link to a reduced contribution of LCDW to SCS deep water. Moreover, the Luzon Strait sill became the sole deep-water pathway into the SCS after IG closure. This restriction may have limited LCDW inflow, potentially intensifying its impacts on SCS deep water, as the LCDW contribution to the SCS has been linked to deep SCS carbon reservoirs. Future studies on high-resolution Ɛ_Nd records in SCS are necessary to explore the timing and climatic implications of this tectonic transition.