Constraining Global Marine Iron Sources and Ligand‐Mediated Scavenging Fluxes With GEOTRACES Dissolved Iron Measurements in an Ocean Biogeochemical Model

Abstract

Global marine iron model tests varying levels of atmospheric deposition, sedimentary release, ligand distributions and scavenging rates • Simulations that best reproduce observations include variable ligands and high rates of atmospheric deposition and sedimentary release • Simulations with high iron sources require high scavenging rates resulting in short residence times Accepted ArticleThis article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as

Biogeochemical feedbacks may amplify ongoing and future ocean deoxygenation: a case study from the Peruvian oxygen minimum zone

“…Iron release from continental margin sediments is probably the largest source of dissolved iron in the global ocean (Dale et al 2015;Somes et al 2021). Most of the iron is removed by scavenging before it reaches the pelagic realm (Somes et al 2021). Our model results, however, show that a significant fraction is protected by organic complexation and exported into the open ocean.…”

“…We also suggest that the benthic iron feedback may partly account for the gap between observed (Schmidtko et al 2017) and predicted trends in global ocean deoxygenation (Oschlies et al 2018). Iron release from continental margin sediments is probably the largest source of dissolved iron in the global ocean (Dale et al 2015;Somes et al 2021). Most of the iron is removed by scavenging before it reaches the pelagic realm (Somes et al 2021).…”

“…It may, thus, be possible that a decline in oxygen concentrations of bottom waters at continental margins induces wide-spread iron fertilization and deoxygenation in iron-limited offshore regions of the global ocean if the off-shelf transport is facilitated by ocean eddies and other processes. Since the residence time of dissolved iron the global ocean may be as low as 7.5 years (Somes et al 2021), changing iron fluxes may induce rapid and global scale changes in productivity and oxygen concentrations. However, a better mechanistic understanding of pelagic iron cycling is needed to evaluate this hypothesis (Tagliabue et al 2017).…”

Mechanisms driving the dispersal of hydrothermal iron from the northern Mid Atlantic Ridge

“…The NEMO-AGRIF configuration has a 1/8° (or 12.48 km) resolution regional nested grid around TAG (Figure S3 in Supporting Information S1), but the vertical resolution of NEMO-AGRIF and NEMO-ORCA2 are around three-fold lower than the particle tracking model. This set of model configurations were designed to link the very high-resolution regional modeling with the types of models used for larger scale biogeochemical modeling that tend to have horizontal resolutions of between 1 and 5° (Roshan et al, 2020;Somes et al, 2021;Tagliabue et al, 2022).…”

“…Adding further complexity is the fact that the slow spreading ridges like the mid-Atlantic ridge are typified by large axial valleys with topographic relief varying by kilometers across relatively small spatial scales. It is not known how resolving these scales of variability affects the transport of DFe into the wider basin and the implications for coarse resolution ocean biogeochemical models that are typically used to test hypothesis about hydrothermal DFe supply and cycling (Roshan et al, 2020;Somes et al, 2021;Tagliabue et al, 2022). For instance, improved understanding of the critical processes and scales regulating the dispersal from ridges would aid our understanding of the necessary process resolution for ocean models.…”