GNOM v1.0: an optimized steady-state model of the modern marine neodymium cycle

Abstract

Abstract. Spatially distant sources of neodymium (Nd) to the ocean that carry different isotopic signatures (εNd) have been shown to trace out major water masses and have thus been extensively used to study large-scale features of the ocean circulation both past and current. While the global marine Nd cycle is qualitatively well understood, a complete quantitative determination of all its components and mechanisms, such as the magnitude of its sources and the paradoxical conservative behavior of εNd, remains elusive. To make sense of the increasing collection of observational Nd and εNd data, in this model description paper we present and describe the Global Neodymium Ocean Model (GNOM) v1.0, the first inverse model of the global marine biogeochemical cycle of Nd. The GNOM is embedded in a data-constrained steady-state circulation that affords spectacular computational efficiency, which we leverage to perform systematic objective optimization, allowing us to make preliminary estimates of biogeochemical parameters. Owing to its matrix representation, the GNOM model is additionally amenable to novel diagnostics that allow us to investigate open questions about the Nd cycle with unprecedented accuracy. This model is open-source and freely accessible, is written in Julia, and its code is easily understandable and modifiable for further community developments, refinements, and experiments.

Simulating marine neodymium isotope distributions using Nd v1.0 coupled to the ocean component of the FAMOUS–MOSES1 climate model: sensitivities to reversible scavenging efficiency and benthic source distributions

“…Both Rempfer et al (2011) and Gu et al (2019) simplified this method by applying spatially uniform sediment Nd fluxes, also limited to the upper 3000 m. In more recent work, Pöppelmeier et al (2020b) removed the depth limitation (as we have done), and incorporated a geographically varying scaling factor to try to capture more localised features through increased benthic fluxes (Abbott et al, 2015b;Blaser et al, 2020;Grenier et al, 2013;Lacan and Jeandel, 2005;Rahlf et al, 2020). Pasquier et al (2022) presented the first inverse model of global marine cycling of Nd, and the strength of the sediment Nd flux to the ocean was imposed with an exponential depth function, resembling eddy kinetic energy and particulate organic matter fluxes, which are characteristically larger near the surface and in coastal regions.…”

“…Numerical models are useful tools for investigating Nd cycling since they can specify the processes that govern the spatiotemporal variability in Nd isotope distributions in the ocean. Neodymium isotopes have been simulated in a range of different modelling studies testing specific hypotheses relating to Nd fluxes and thermohaline redistribution (Pöppelmeier et al, 2020a;Arsouze et al, 2009;Rempfer et al, 2011;Siddall et al, 2008;Jones et al, 2008;Roberts et al, 2010;Tachikawa et al, 2003;Ayache et al, 2016;Gu et al, 2019;Oka et al, 2021Oka et al, , 2009Pöppelmeier et al, 2022;Ayache et al, 2023;Pasquier et al, 2022;Du et al, 2020). However, recent work suggests that a seafloor-wide benthic flux, resulting from early diagenetic reactions, may dominate the marine Nd cycle (Haley et al, 2017;Abbott, 2019;Abbott et al, 2015aAbbott et al, , b, 2019Du et al, 2016).…”

Influence of GEOTRACES data distribution and misfit function choice on objective parameter retrieval in a marine zinc cycle model

“…6c, f), resulting in globally higher surface-ocean Zn concentrations. Additionally, reduced surface Southern Ocean nutrient uptake and export decrease concentrations in deep waters of the Southern Ocean through reduced nutrient trapping (Sarmiento et al, 2004;Marinov et al, 2006;Primeau et al, 2013), and, because reduced Zn uptake is a consequence of a decrease in the uptake stoichiometry parameter r Zn : P , it leads to a strengthening of the global Zn-PO 4 correlation, while the Zn-Si correlation is weakened (Vance et al, 2017;de Souza et al, 2018). The shape of the RMAE-optimised uptake curve in synObs_IDP_circ is unique in our optimisation ensemble (Fig.…”

“…Although there are modelling studies of marine trace metal cycling that objectively calibrate a variety of their model pa- rameters (e.g. Frants et al, 2016;Weber et al, 2018;Pasquier et al, 2022), the impact of data distribution, model imperfections, or choice of the misfit function on optimisation results are often not discussed. In this study, we have separately assessed how optimisation results are impacted by these sources of uncertainty.…”

Neodymium budget in the Mediterranean Sea: evaluating the role of atmospheric dusts using a high-resolution dynamical-biogeochemical model

“…Later, the same authors investigated the evolution of the AMOC as it responds to freshwater perturbations under improved LGM boundary conditions in the Bern3D intermediate complexity model (Pöppelmeier et al, 2021). Pasquier et al (2022) presented the first inverse model of the global marine biogeochemical cycle of Nd using the Global Neodymium Ocean Model (GNOM) v1.0. This relatively simple model compares well to previous models; however, the GNOM model does not represent scavenging by calcium carbonate (CaCO 3 ) which could have a very important impact on the vertical cycle of Nd.…”