18 May 2021

18 May 2021

Review status: this preprint is currently under review for the journal BG.

Modeling the marine chromium cycle: New constraints on global-scale processes

Frerk Pöppelmeier1,2, David J. Janssen2,3, Samuel L. Jaccard2,3,4, and Thomas F. Stocker1,2 Frerk Pöppelmeier et al.
  • 1Climate and Environmental Physics, Physics Institute, University of Bern, 3012 Bern, Switzerland
  • 2Oeschger Center for Climate Change Research, University of Bern, 3012 Bern, Switzerland
  • 3Institute of Geological Sciences, University of Bern, 3012 Bern, Switzerland
  • 4Institute of Earth Sciences, University of Lausanne, 1015 Lausanne, Switzerland

Abstract. Chromium (Cr) and its isotopes hold great promise as tracer of past oxygenation and marine biological activity due to the different chemical properties of its two main oxidation states, Cr(III) and Cr(VI), and the associated fractionation during redox transformations. However, to date the Cr cycle remains poorly constrained due to insufficient knowledge about sources and sinks and the influence of biological activity on redox reactions. We therefore implemented the two oxidation states of Cr in the Bern3D Earth system model of intermediate complexity, in order to gain an improved understanding on the mechanisms that modulate the spatial distribution of Cr in the ocean. Due to the computational efficiency of the Bern3D model we are able to explore and constrain the range of a wide array of parameters. Our model simulates vertical, meridional, and inter-basin Cr concentration gradients in good agreement with observations. We find a mean ocean residence time of Cr between 5 and 8 kyr, and a benthic flux, emanating from all sediment surfaces, of of 0.1–0.2 nmol cm-2 yr-1, both in the range of previous estimates. We further explore the origin of regional model-data mismatches through a number of sensitivity experiments. These indicate that the benthic Cr flux may be substantially lower in the Arctic than elsewhere. In addition, we find that a refined representation of oxygen minimum zones and their Cr redox potential yields Cr(III) concentrations and Cr removal rates in much improved agreement with observational data.

Frerk Pöppelmeier et al.

Status: open (until 07 Jul 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2021-106', Anonymous Referee #1, 04 Jun 2021 reply
  • RC2: 'Comment on bg-2021-106', Catherine Jeandel, 09 Jun 2021 reply
  • RC3: 'Comment on bg-2021-106', Roger Francois, 13 Jun 2021 reply

Frerk Pöppelmeier et al.

Model code and software

Modeling the marine chromium cycle: New constraints on global-scale processes: Model output data Pöppelmeier, Frerk; Janssen, David J.; Jaccard, Samuel L.; Stocker, Thomas F.

Frerk Pöppelmeier et al.


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Short summary
Chromium (Cr) is a redox sensitive element that holds promise as a tracer of ocean oxygenation and biological activity. We here implemented the oxidation states Cr(III) and Cr(VI) in the Bern3D model to investigate the processes that shape the global Cr distribution. We find a Cr ocean residence time of 5–8 kyr and that the benthic source dominates the tracer budget. Further, regional model-data mismatches suggest strong Cr removal in oxygen minimum zones and a spatially variable benthic source.