Modeling the relationship between 231 Pa/ 230 Th distribution in North Atlantic sediment and Atlantic meridional overturning circulation

[ 1 ] Down-core variations in North Atlantic 231 Pa xs / 230 Th xs have been interpreted as changes in the strength of the Atlantic meridional overturning circulation (AMOC). This modeling study confirms that hypothetical changes in the AMOC would indeed be recorded as changes in the distribution of sedimentary 231 Pa xs / 230 Th xs . At different sites in the North Atlantic the changes in sedimentary 231 Pa/ 230 Th that we simulate are diverse and do not reflect a simple tendency for 231 Pa xs / 230 Th xs to increase toward the production ratio (0.093) when the AMOC strength reduces but instead are moderated by the particle flux. In its collapsed or reduced state the AMOC does not remove 231 Pa from the North Atlantic: Instead, 231 Pa is scavenged to the North Atlantic sediment in areas of high particle flux. In this way the North Atlantic 231 Pa xs / 230 Th xs during AMOC shutdown follows the same pattern as 231 Pa xs / 230 Th xs in modern ocean basins with reduced rates of meridional overturning (i.e., Pacific or Indian oceans). We suggest that mapping the spatial distribution of 231 Pa xs / 230 Th xs across several key points in the North Atlantic is an achievable and practical qualitative indicator of the AMOC strength in the short term. Our results indicate that additional North Atlantic sites where down-core observations of 231 Pa xs / 230 Th xs would be useful coincide with locations which were maxima in the vertical particle flux during these periods. Reliable estimates of the North Atlantic mean 231 Pa xs / 230 Th xs should remain a goal in the longer term. Our results hint at a possible ‘‘seesaw-like’’ behavior in 231 Pa/ 230 Th in the South Atlantic.

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