loading page

Constraining global marine iron sources and ligand-mediated scavenging fluxes with GEOTRACES dissolved iron measurements in an ocean biogeochemical model
  • +6
  • Christopher J. Somes,
  • Andrew W. Dale,
  • Klaus Wallmann,
  • Florian Scholz,
  • Wanxuan Yao,
  • Andreas Oschlies,
  • Juan Muglia,
  • Andreas Schmittner,
  • Eric P. Achterberg
Christopher J. Somes
GEOMAR Helmholtz Centre for Ocean Research, GEOMAR Helmholtz Centre for Ocean Research, GEOMAR Helmholtz Centre for Ocean Research

Corresponding Author:[email protected]

Author Profile
Andrew W. Dale
GEOMAR Helmholtz Centre for Ocean Research Kiel, GEOMAR Helmholtz Centre for Ocean Research Kiel, GEOMAR Helmholtz Centre for Ocean Research Kiel
Author Profile
Klaus Wallmann
GEOMAR Helmholtz Centre for Ocean Research Kiel, GEOMAR Helmholtz Centre for Ocean Research Kiel, GEOMAR Helmholtz Centre for Ocean Research Kiel
Author Profile
Florian Scholz
GEOMAR Helmholtz Centre for Ocean Research, GEOMAR Helmholtz Centre for Ocean Research, GEOMAR Helmholtz Centre for Ocean Research
Author Profile
Wanxuan Yao
GEOMAR Helmholtz Centre for Ocean Research, GEOMAR Helmholtz Centre for Ocean Research, GEOMAR Helmholtz Centre for Ocean Research
Author Profile
Andreas Oschlies
Helmholtz-Zentrum für Ozeanforschung Kiel, GEOMAR, Helmholtz-Zentrum für Ozeanforschung Kiel, GEOMAR, Helmholtz-Zentrum für Ozeanforschung Kiel, GEOMAR
Author Profile
Juan Muglia
Centro para el Estudio de los Sistemas Marinos CONICET, Centro para el Estudio de los Sistemas Marinos CONICET, Centro para el Estudio de los Sistemas Marinos CONICET
Author Profile
Andreas Schmittner
College of Oceanic and Atmospheric Sciences, Oregon State University, College of Oceanic and Atmospheric Sciences, Oregon State University, College of Oceanic and Atmospheric Sciences, Oregon State University
Author Profile
Eric P. Achterberg
GEOMAR Helmholtz Centre for Ocean Research Kiel, GEOMAR Helmholtz Centre for Ocean Research Kiel, GEOMAR Helmholtz Centre for Ocean Research Kiel
Author Profile

Abstract

Iron is a key micronutrient controlling phytoplankton growth in vast regions of the global ocean. Despite its importance, uncertainties remain high regarding external iron source fluxes and internal cycling on a global scale. In this study, we used a global dissolved iron dataset, including GEOTRACES measurements, to constrain source and scavenging fluxes in the marine iron component of a global ocean biogeochemical model. Our model simulations tested three key uncertainties: source inputs of atmospheric soluble iron deposition (varying from 1.4–3.4 Gmol/yr), reductive sedimentary iron release (14–117 Gmol/yr), and compared a variable ligand parameterization to a constant distribution. In each simulation, scavenging rates were tuned to reproduce the observed global mean iron inventory for consistency. The variable ligand parameterization improved the global model-data misfit the most, suggesting that heterotrophic bacteria are an important source of ligands to the ocean. Model simulations containing high source fluxes of atmospheric soluble iron deposition (3.4 Gmol/yr) and reductive sedimentary iron release (114 Gmol/yr) further improved the model most notably in the surface ocean. High scavenging rates were then required to maintain the iron inventory resulting in relatively short surface and global ocean residence times of 0.83 and 7.5 years, respectively. The model simulates a tight spatial coupling between source inputs and scavenging rates, which may be too strong due to underrepresented ligands near source inputs, contributing to large uncertainties when constraining individual fluxes with dissolved iron concentrations. Model biases remain high and are discussed to help improve global marine iron cycle models.
Aug 2021Published in Global Biogeochemical Cycles volume 35 issue 8. 10.1029/2021GB006948