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Promising regions for detecting the overturning circulation in Atlantic Pa/Th: a model-data comparison
The Atlantic Meridional Overturning Circulation (AMOC) is a critical component of the climate system, strongly influencing the climate via ocean heat transport. The AMOC had different characteristics during glacial periods and is expected to change under anthropogenic climate forcing. To reconstruct past AMOC strength, the Pa/Th (protactinium-231 to thorium-230) ratio measured in marine sediments serves as a unique proxy. However, this ratio reflects not only circulation changes, but also effects from biological particle export and benthic nepheloid layers. Therefore, it remains an open question which regions exhibit a reliable AMOC signal in their sedimentary Pa/Th. This study, utilising the Bern3D model and a compilation of sediment cores with 11 newly published cores, suggests that equatorial West Atlantic Pa/Th is as sensitive to AMOC changes as the Bermuda Rise region. Additionally, the Pa/Th response to AMOC changes observed in part of the northern North Atlantic, which is opposite to regions further south, is caused by AMOC-induced changes in particle production. Cores in this region are promising to reconstruct AMOC strength, despite exhibiting an AMOC-to-Pa/Th relationship opposite from usual and high levels of opal. Additional cores in the North Atlantic at 40-60°N between 1 and 2 km depth are desirable for the application of Pa/Th. Our results suggest a new focus of Pa/Th reconstructions on the equatorial West Atlantic and the northern North Atlantic, which appear to be better suited to quantify past AMOC strength.