Holocene 231Pa/230Th ratios, Uranium isotopes and biogenic Opal concentrations from four North Atlantic sediment cores

To investigate the variability of the Atlantic Meridional Overturning Circulation (AMOC) during the Holocene in the North Atlantic, we analyzed radioisotopes (230Th, 231Pa, 232Th, 234U, and 238U) in sediment samples from four core sites (ODP 172-1063, ODP 172-1059, ODP 162-983, and GeoB18529-2) with millennial-scale temporal resolution. From these measurements, we calculated 231Pa/230Th ratios. The isotope analyses were conducted using three instruments: a Neptune Plus MC-ICP-MS equipped with a retarding potential quadrupole filter at the Geozentrum Nordbayern, Friedrich–Alexander University, Erlangen; an ELEMENT ICP-MS at the Alfred Wegener Institute (AWI), Bremerhaven; and an iCAP TQe ICP-MS at the Institute of Earth Sciences, Heidelberg University.To assess the influence of biogenic opal (bOpal) concentrations on the 231Pa/230Th ratios, we measured bOpal concentrations from the same samples. These measurements followed an automated protocol for dissolved silica analysis using molybdate-blue spectrophotometry, conducted at Heidelberg University.