Water‐Depth‐Dependent 231 Pa/ 230 Th Responses in the Central North Atlantic Since the Last Glacial Maximum

Abstract The Atlantic Meridional Overturning Circulation (AMOC) plays an important role in regulating Earth's climate through inter‐hemispheric heat transport and has undergone substantial variations during past climate transitions. Sedimentary 231 Pa/ 230 Th is widely used to reconstruct AMOC strength, yet its application is complicated by its sensitivity to changes of export productivity, hydrothermal input, and other particle sources, potentially overprinting the circulation signal. Here we present new and updated sedimentary 231 Pa/ 230 Th records spanning the last 30 kyr from a confined region in the central North Atlantic, encompassing water depths from 2,102 to 4,110 m. Despite their proximity, the records exhibit diverging trends, with 231 Pa/ 230 Th increasing at shallower sites (2,700 m) since the Last Glacial Maximum (LGM). These opposing trends are unlikely to reflect changes in particle scavenging alone, as biogenic opal fluxes show a similar pattern across sites while bulk sediment Fe/Ti and Cu/Ti indicate no significant hydrothermal influence at most sites. Including these 231 Pa/ 230 Th records into a basin‐wide North Atlantic compilation, we show that the opposing 231 Pa/ 230 Th responses across water depth are a North Atlantic‐wide feature. Idealized Bern3D simulations suggest that deep‐ocean 231 Pa/ 230 Th primarily reflects variations in southward advection of dissolved 231 Pa, whereas lower 231 Pa/ 230 Th ratios at shallower depths during the LGM result from reduced supply of 231 Pa by diminished northward transport. These results demonstrate that shallower‐depth sediments capture past overturning variability, albeit with an inverted signal relative to the deep ocean, highlighting the need for depth‐resolved, model‐supported interpretations of 231 Pa/ 230 Th.