Using chromium isotopes to reconstruct the oxygenation history of the oceans is challenged by modern data

Analyses of seawater chromium (Cr) concentrations and isotopes in diverse marine environments (Arctic, Pacific, and Atlantic Oceans) reveal a strong correlation between Cr isotope composition (δ53Cr) and Cr concentration. High δ53Cr values and low Cr concentration reflect losses of isotopically light Cr in neritic environments. Contrastingly, open ocean waters with low δ53Cr values and high Cr concentration are hypothesized to reflect the addition of seawater-derived Cr released from marine sediments or settling particles. Although reductive removal of Cr in oxygen minimum zones (OMZs) may explain low Cr concentrations in subsurface north Pacific waters, the heterogeneity in δ53Cr values in the modern (oxic) ocean entails that redox cycling of Cr isotopes in the ocean should be considered in future research.

16 Scheiderich lFigure: Correlation between chromium concentration (as ln[Cr]) and δ53Cr (‰) illustrates that samples from several locations around the world plot on a line that is consistent with closed-system Raleigh fractionation. This fractionation is probably the result of reduction of Cr(VI) is shallow and surface waters, and oxygen minimum zones, and possible reoxidation of Cr(III) at depth; observationally, Cr is “added” at depth, resulting in higher concentrations and lower δ53Cr values, and is “removed” in the surface, resulting in lower concentrations and higher d53Cr values. Click here to view the figure larger.

Reference:

Scheiderich, K., Amini, M., Holmden, C., & Francois, R. (2015). Global variability of chromium isotopes in seawater demonstrated by Pacific, Atlantic, and Arctic Ocean samples. Earth and Planetary Science Letters, 423, 87–97. doi:10.1016/j.epsl.2015.04.030

Latest highlights

A thorough estimate of the hydrothermal plumes on neodymium concentration and isotope oceanic cycles

Basak and coworkers investigated the influence of particulate matter on neodymium distributions in the Southern East Pacific Rise Hydrothermal Plume.

What are the drivers of the distributions of cadmium, nickel, zinc, copper and cobalt, manganese and aluminium in the Atlantic Ocean? Two papers are tackling this issue

The authors reveal that the distributions of dissolved tracers at depth in the South Atlantic are predominantly controlled by the mixing of North Atlantic Deep Water and waters of Antarctic origin…

Disentangling the sources and transport of iron in the Southern Ocean using a water mass mixing model analysis

Traill and co-workers used an extended optimum multiparameter analysis water‐mass mixing model…

A detailed investigation of iron complexation by organic ligands in the Western Tropical South Pacific Ocean

Léo Mahieu and his co-workers present the conditional concentration and binding-strength of iron-binding ligands during the GEOTRACES TONGA cruise.

Rechercher