231Pa in the Ocean: Research Advances and Implications for Climate Change

Protactinium-231 (231Pa), a particle-reactive radionuclide derived from 235U decay, serves as a pivotal tracer in marine geochemistry and paleoceanography, offering unique insights into particle scavenging, deep ocean circulation, and sedimentary processes. This review synthesizes significant advances in 231Pa research. A core application lies in utilizing the 231Pa/230Th ratio as a sensitive proxy for reconstructing past Atlantic Meridional Overturning Circulation (AMOC) intensity, with compelling evidence indicating a substantially weakened AMOC during the Last Glacial Maximum compared to the Holocene. Major technological breakthroughs, particularly the advent of high-precision ICP-MS and TIMS methodologies, have revolutionized the quantification of 231Pa in both dissolved and particulate phases, enabling spatial and temporal resolution. Looking forward, the integration of high-resolution sediment core analyses—featuring refined 231Pa/230Th chronologies—with advanced climate models offers a powerful pathway to significantly enhance our mechanistic understanding of the ocean’s role in global climate regulation. This synergistic approach will help constrain the dynamics of oceanic overturning circulation and its critical functions in carbon sequestration and heat redistribution across past, present, and future climate scenarios.