EGUsphere EGUsphere EGUsphere EGUsphere Copernicus Publications Göttingen, Germany 10.5194/egusphere-2022-937 Optimisation of the marine Nd isotope scheme in the ocean component of the FAMOUS general circulation model Robinson Suzanne https://orcid.org/0000-0003-4035-800X 1 Ivanovic Ruza https://orcid.org/0000-0002-7805-6018 1 Gregoire Lauren https://orcid.org/0000-0003-0258-7282 1 Astfalck Lachlan 2 van de Flierdt Tina 3 Plancherel Yves 3 Pöppelmeier Frerk https://orcid.org/0000-0003-4050-2550 4 Tachikawa Kazuyo 5 School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK School of Physics, Mathematics and Computing, The University of Western Australia, Crawley, Western Australia, Australia Department of Earth Science and Engineering, Imperial College London, London, SW7 2AZ, UK Climate and Environmental Physics, Physics Institute and Oeschger Center for Climate Change Research, University of Bern, 3012 Bern, Switzerland Aix Marseille Univ, CNRS, IRD, INRAE, Coll France, CEREGE, Aix-en-Provence, France 07 10 2022 2022 1 46 Copyright: © 2022 Suzanne Robinson et al. 2022 This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/4.0/ This article is available from https://egusphere.copernicus.org/preprints/2022/egusphere-2022-937/ The full text article is available as a PDF file from https://egusphere.copernicus.org/preprints/2022/egusphere-2022-937/egusphere-2022-937.pdf

<p>The neodymium (Nd) isotope composition (&epsilon;<sub>Nd</sub>) of seawater can be used to trace large-scale ocean circulation features. Yet, due to the elusive nature of marine Nd cycling, particularly in discerning non-conservative particle-seawater interactions, there remains considerable uncertainty surrounding a complete description of marine Nd budgets. Here, we present an optimisation of the Nd isotope scheme within the fast coupled atmosphere-ocean general circulation model (FAMOUS), using a statistical emulator to explore the parametric uncertainty and optimal combinations of three key model inputs relating to: (1) the efficiency of reversible scavenging, (2) the magnitude of the seafloor benthic flux, and (3) a riverine source scaling, accounting for release of Nd from river sourced particulate material. Furthermore, a suite of sensitivity tests provide insight on the regional mobilisation and spatial extent (i.e., testing a margin-constrained versus a seafloor-wide benthic flux) of certain reactive sediment components. In the calibrated scheme, the global marine Nd inventory totals 4.27 &times; 10<sup>12</sup> g and has a mean residence time of 727 years. Atlantic Nd isotope distributions are represented well, and the weak sensitivity of North Atlantic Deep Water to highly unradiogenic sedimentary sources implies an abyssal benthic flux is of secondary importance in determining the water mass &epsilon;<sub>Nd</sub> properties under the modern vigorous circulation condition. On the other hand, Nd isotope distributions in the North Pacific are 3 to 4 &epsilon;<sub>Nd</sub>-units too unradiogenic compared to water measurements, and our simulations indicate that a spatially uniform flux of bulk sediment &epsilon;<sub>Nd</sub> does not sufficiently capture the mobile sediment components interacting with seawater. Our results of sensitivity tests suggest that there are distinct regional differences in how modern seawater acquires its &epsilon;<sub>Nd</sub> signal, in part relating to the complex interplay of Nd addition and water advection.</p>

 Natural Environment Research Council NE/L002574/1