Distributions of Protactinium‐231 and Thorium‐230 confirm the critical influence of meridional overturning circulation in the Indian Ocean

Abstract Sedimentary 231 Pa/ 230 Th has been used as a proxy for understanding changes in ocean circulation and productivity over the last glacial–interglacial cycle. Its application relies on the influence of meridional overturning circulation (MOC) and particle scavenging on the distribution of 231 Pa and 230 Th in the water column and sediments. While previous studies have addressed the role of MOC on the 230 Th and 231 Pa water profiles and sedimentary 231 Pa/ 230 Th in the Atlantic and Pacific Oceans, including the influence of boundary scavenging in the latter, the impact of these processes in the Indian Ocean remains unresolved. This study employs a two‐dimensional scavenging model with prescribed overturning schemes to simulate the latitudinal distribution of 230 Th and 231 Pa in the water column and sediments of the Indian Ocean. The water column profiles of both nuclides deviate from linearity, reflecting the influence of deep convection, advection, and upwelling controlled by MOC. Additionally, bottom scavenging within the nepheloid layer and boundary scavenging significantly depletes 231 Pa in the Madagascar Basin. The gradual decrease in sediment 231 Pa/ 230 Th below 1500 m in the main basins is primarily linked to MOC, while boundary scavenging contributes to systematically lowering the 231 Pa/ 230 Th. These findings point to the potential of sedimentary 231 Pa/ 230 Th as a proxy for studying the alteration of deep ocean circulation and particle flux in the Indian Ocean.