Global simulation of dissolved <sup>231</sup>Pa and <sup>230</sup>Th in the ocean and the sedimentary <sup>231</sup>Pa∕<sup>230</sup>Th ratios with the ocean general circulation model COCO ver4.0

Abstract. Sedimentary 231Pa/230Th ratios provide clues to estimate the strength of past ocean circulation. For its estimation, understanding processes controlling distributions 231Pa and 230Th in is important. However, simulations dissolved particulate modern ocean, recently obtained from GEOTRACES project, remain challenging. Here we report a model simulation global with COCO ver4.0. Starting basic water-column reversible scavenging model, also introduced bottom dependence efficiency on particle concentration. As demonstrated previous study, incorporation improves simulated distribution deep which has been overestimated models not considering scavenging. We further demonstrate that introducing concentration results high Southern Ocean as observed data. Our best can well reproduce only oceanic but sedimentary ratios. Sensitivity analysis reveals advection primarily determines On other hand, have an opposite effect ratios, reducing their latitudinal contrast. shows realistic residence times 230Th, without significantly overestimates for both spite similar our simulation.