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Release from biogenic particles, benthic fluxes, and deep water circulation control Cr and δ 53 Cr distributions in the ocean interior
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  • David J Janssen,
  • Jörg Rickli,
  • April N Abbott,
  • Michael J Ellwood,
  • Benjamin S Twining,
  • Daniel C Ohnemus,
  • Philipp Nasemann,
  • Delphine Gilliard,
  • Samuel L Jaccard
David J Janssen
University of Bern Institute of Geological Sciences & Oeschger Center for Climate Change Research, 8 Baltzerstrasse 1-3, 3012 Bern,

Corresponding Author:[email protected]

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Jörg Rickli
University of Bern Institute of Geological Sciences & Oeschger Center for Climate Change Research
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April N Abbott
Macquarie University
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Michael J Ellwood
Australian National University
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Benjamin S Twining
Bigelow Laboratory for Ocean Sciences, East Boothbay, ME, USA.
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Daniel C Ohnemus
University of Georgia
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Philipp Nasemann
University of Bern Institute of Geological Sciences & Oeschger Center for Climate Change Research
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Delphine Gilliard
University of Bern Institute of Geological Sciences & Oeschger Center for Climate Change Research
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Samuel L Jaccard
University of Bern Institute of Geological Sciences & Oeschger Center for Climate Change Research
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Abstract

Chromium (Cr) has shown promise as a paleoceanographic proxy due to the redox-driven control of dissolved Cr concentrations ([Cr]) and stable isotope composition (δ53Cr). However, substantial uncertainties in the biogeochemical Cr cycle have limited its paleoproxy application to date. To improve the mechanistic understanding of Cr cycling in the modern ocean and strengthen its potential proxy applications, we present new data from regeneration incubations, bottom and sediment pore waters, and a compilation of intermediate and deep water data. While Cr removal and biological export from the surface ocean is associated with organic carbon export, the deep water release of dissolved Cr from sinking particles is not directly dependent on organic carbon respiration, as indicated by differing trends between Cr, oxygen utilization and the regeneration of organic-associated macronutrients (e.g. N, P). Pore water and bottom water data demonstrate that benthic Cr fluxes are locally important and may be significant globally. The pore water dissolved Cr flux at our CaCO3-rich site is likely driven by the re-release of Cr scavenged from the water column by sinking particles, with minor contributions from lithogenic phases. We argue this is consistent with the highest open ocean [Cr] to date being found in the water column below oxygen minimum zones, likely reflecting the release of scavenged Cr in deep waters or surface sediments. Chromium released from suspended particles and surface sediments follows the global δ53Cr–[Cr] array, supporting the proposed role of biological export and regeneration in shaping global Cr and δ53Cr distributions. Global intermediate and deep water [Cr], δ53Cr and Cr:macronutrient relationships are thus shaped by a synergy of circulation patterns, water mass mixing, a deep Cr regeneration cycle, and benthic Cr sources. A biogenic control on global Cr distributions indicates that sedimentary Cr records may reflect biogenic as well as O2-dependent processes, while more research is needed to assess sediment Cr record fidelity based on an active diagenetic cycle.
Nov 2021Published in Earth and Planetary Science Letters volume 574 on pages 117163. 10.1016/j.epsl.2021.117163