An updated global ocean chromium biogeochemical cycle


Based on i) new data from regeneration incubations and ii) an exhaustive compilation of total chromium (Cr) and stable isotope composition (δ53Cr) data, among them a significant number of new profiles collected as part of different oceanographic cruises, Janssen and co-authors (2021, see reference below) propose a comprehensive description of the different processes that might affect the Cr/δ53Cr distribution. Those are:

  • Cr release from biogenic particles, which may be driven by Cr oxidation, is mechanistically independent from the regeneration of major elements in organic matter (e.g. C, N, P). This Cr release could occur either in the water column or oxic sediments, and can explain the [Cr]-rich side of the Cr/δ53Cr array (figure A below)
  • In oxygen minimum zones, dissolved Cr can occur under its reduced form Cr(III), not soluble and thus easily scavenged in the water column or in the sediment, as illustrated in the figure D below,
  • large benthic Cr fluxes can be locally important, and are possibly a globally-important component of the ocean’s Cr budget,
  • hydrothermal inputs effects are not well constrained yet,
  • as for all the oceanic tracers, mixing will generally lead to an homogenization of the variabilities due to the biogeochemical processes but also of the source effects (margins being locations where local inputs might be significant), and
  • however, water masses that are mixing might also be imprinted by a specific signature, that could be superimposed on the other effects.

In the end, the authors warn us about the complexity and role of these biogeochemical processes shaping the Cr/δ53Cr array before using them as paleo-proxies.

Figure: Map showing locations of Pacific and Southern Ocean intermediate and deep water Cr data, including new data (open circles) and literature data (closed circles), along with new pore water Cr data (star). Superimposed is the global array of δ53Cr data (data from: this study; Goring-Harford et al., 2018; Janssen et al., 2020; Moos & Boyle, 2019; Moos et al., 2020; Nasemann et al., 2020; Rickli et al., 2019; Scheiderich et al., 2015), along with a mechanistic breakdown showing how biological productivity and release from biogenic particles (lower left), benthic fluxes (lower center), and Cr removal in OMZs (lower right) shape the global array.

Reference:

Janssen, D. J., Rickli, J., Abbott, A. N., Ellwood, M. J., Twining, B. S., Ohnemus, D. C., Nasemann, P., Gilliard, D., & Jaccard, S. L. (2021). Release from biogenic particles, benthic fluxes, and deep water circulation control Cr and δ53Cr distributions in the ocean interior. Earth and Planetary Science Letters, 574, 117163. Access the paper: 10.1016/j.epsl.2021.117163

Latest highlights

Science Highlights

Tracing dust deposition with aluminium and silicate at a resolution never reached before

Benaltabet and his colleagues propose a study of the dissolved aluminium and silicate fate in the Gulf of Aqaba (Red Sea).

24.01.2023

Science Highlights

Actinium-227 distribution traces at least three processes in the North Atlantic Ocean

Le Roy and colleagues report an oceanic section of Actinium-227 in the North Atlantic Ocean.

23.01.2023

Science Highlights

Do you want to know more about iron and its isotopes? This review is for you!

Authors present a comprehensive review of iron and iron isotope sources, internal cycling, and sinks in the ocean.

17.01.2023

Science Highlights

Different fates of four poorly soluble trace elements in the Pacific Ocean

Zheng and co-authors present the full-depth distributions of aluminum, lead, manganese and copper in the western South Pacific.

24.11.2022

Rechercher