Boundary scavenging at the East Atlantic margin does not negate use of 231Pa/230Th to trace Atlantic overturning

The 231Pa/230Th method is a promising tool to reconstruct Ocean circulation over the past Glacial-Interglacial cycle. However, marine particle flux may constrain the applicability of this ratio as a direct quantitative proxy for the strength of Atlantic Meridional Overturning Circulation (AMOC) by influencing the fractionation between the in situ produced 231Pa and 230Th in ocean water. Here we present 231Pa/230Th down-core profiles from high particle flux areas off Namibia and Senegal covering the past ∼35 ka. The 231Pa/230Th profiles at these sites show very different responses to temporal variations of particle fluxes and to changes in water masses. Our results show that sedimentary 231Pa/230Th in the Eastern Atlantic margin is linked to particle flux, but controlled primarily by the mode of the AMOC. Our data suggest that during the past ∼30 ka the high productivity Eastern margin was not capable of importing and storing significant amounts of 231Pa from the open Ocean. Consequently, the applicability of the 231Pa/230Th proxy to reconstruct past ocean circulation is not hampered by this potentially additional 231Pa sink.

► We test if high productivity areas within the Atlantic Ocean lower significance of the Pa/Th proxy. ► First order influences Pa/Th are water depth and AMOC. ► Particle flux influence on Pa/Th is subordinate. ► Sensitivity of Pa/Th proxy to AMOC changes is not biased by increased glacial boundary scavenging.