Le Gland G. auteur aut IRD Aumont Olivier auteur aut IRD Memery L. auteur aut IRD text journalArticle eng text/pdf reformatted digital access Thorium-234 (Th-234), an insoluble radioisotope scavenged by marine particles, can be used as a proxy of the biological carbon pump. Thorium-234 observations can constrain biogeochemical models, but a necessary first step is to estimate the poorly known partition coefficients between particulate and dissolved phases. In this study, the Th-234 partition coefficients for five particle types, differing in size and chemical composition, are estimated by fitting a global 3-D Th-234 model based on the coupled ocean general circulation-biogeochemistry model NEMO-PISCES (at a resolution of 2 degrees) to a global Th-234 data set (including GEOTRACES data). Surface partition coefficients are estimated between 0.79 and 16.7x10(6). Biogenic silica has the smallest partition coefficients. Small particulate organic carbon and lithogenic dust have the largest. Thorium-234 observations at depth cannot be recovered without allowing partition coefficients to increase by one order of magnitude from surface to 1,000m deep. In our time-dependent global 3-D model, the biases introduced by three common assumptions made in biological carbon pump studies can be quantified. First, using the C:Th-234 ratio of large particles alone leads to an overestimation of carbon export at the base of the euphotic layer, by up to a factor 2. Furthermore, assuming steady state and neglecting transport by advection and diffusion can bias fluxes by as much as 50%, especially at high latitudes and in upwellings, with a sign and intensity depending on the season. specialized thorium 234 inverse modeling partition coefficient biological carbon pump 036 032 020 124 6 3575-3606 2019 2169-9275 https://www.documentation.ird.fr/hor/fdi:010076491 10.1029/2018jc014668 2169-9275 [F B010076491] https://www.documentation.ird.fr/hor/fdi:010076491 https://horizon.documentation.ird.fr/exl-doc/pleins_textes/divers19-08/010076491.pdf IRD - Base Horizon / Pleins textes 2019-09-19 2025-02-24 fdi:010076491 fre