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Abstract

Previous work showed that South Atlantic sediments have lower glacial than Holocene (231)pa/Th-230, which was attributed to a switch in the flow direction of Atlantic deep-water. Debate exists, however as to the degree to which two processes - circulation and scavenging - determine sedimentary Pa-231/Th-230, making this interpretation contentious. Here we address this issue using 145-kyr records of paleocirculation proxies. Benthic foraminiferal delta C-13, neodymium isotopes (epsilon(Nd)) and sedimentary Pa-231/Th-230 were all measured in a single sediment core from the South Atlantic subtropical gyre. This site largely excludes the influence of local productivity changes on Pa-231/Th-230 records. Measured Pa-231/Th-230 ranges between similar to 0.041 during glacials and similar to 0.055 during interglacial periods and is consistently lower than the production ratio, indicating export of Pa-231 from the central South Atlantic for the entire duration of the record. The lower glacial Pa-231/Th-230 is regionally consistent, suggesting that basin-scale oceanographic processes cause the decrease. In turn, less radiogenic epsilon(Nd) and lower benthic delta C-13 confirm the classical picture of an increase in Southern Component Water (SCW) influence in the Atlantic during glacial periods and point to a circulation control on the observed (231)pa/Th-230 decrease rather than a local productivity change. We suggest that associated with this change in water mass distribution the dominant sink for Pa-231 shifted from the margins of the South Atlantic and/or the Southern Ocean during interglacials, to the North Atlantic during glacial periods. Indeed, elevated Pa-231/Th-230 in the deep North Atlantic during glacials supports this mechanism of northward transport of Pa-231 by SCW. (C)2015 Elsevier B.V. All rights reserved.