07 Oct 2022
07 Oct 2022
Status: this preprint is open for discussion.

Optimisation of the marine Nd isotope scheme in the ocean component of the FAMOUS general circulation model

Suzanne Robinson1, Ruza Ivanovic1, Lauren Gregoire1, Lachlan Astfalck2, Tina van de Flierdt3, Yves Plancherel3, Frerk Pöppelmeier4, and Kazuyo Tachikawa5 Suzanne Robinson et al.
  • 1School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK
  • 2School of Physics, Mathematics and Computing, The University of Western Australia, Crawley, Western Australia, Australia
  • 3Department of Earth Science and Engineering, Imperial College London, London, SW7 2AZ, UK
  • 4Climate and Environmental Physics, Physics Institute and Oeschger Center for Climate Change Research, University of Bern, 3012 Bern, Switzerland
  • 5Aix Marseille Univ, CNRS, IRD, INRAE, Coll France, CEREGE, Aix-en-Provence, France

Abstract. The neodymium (Nd) isotope composition (εNd) 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 × 1012 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 εNd properties under the modern vigorous circulation condition. On the other hand, Nd isotope distributions in the North Pacific are 3 to 4 εNd-units too unradiogenic compared to water measurements, and our simulations indicate that a spatially uniform flux of bulk sediment εNd 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 εNd signal, in part relating to the complex interplay of Nd addition and water advection.

Suzanne Robinson et al.

Status: open (until 28 Dec 2022)

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Suzanne Robinson et al.

Suzanne Robinson et al.


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Short summary
The neodymium (Nd) isotope (εNd) scheme in the ocean model of FAMOUS is used to explore a benthic Nd flux to seawater. Our results demonstrate that sluggish modern Pacific waters are sensitive to benthic flux alterations, whereas the well-ventilated North Atlantic displays a much weaker response. In closing, there are distinct regional differences in how seawater acquires its εNd signal, in part relating to the complex interactions of Nd addition and water advection.