Trivalent chromium isotopes in the eastern tropical North Pacific oxygen-deficient zone

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Abstract
Significance: Chromium isotopes have been used to study ancient earth atmospheric oxygen levels and seem promising as a paleoredox proxy. However, few studies have focused on its cycling in the modern ocean. Here we analyzed samples from oxygen-deficient zones and investigated how chromium speciation and isotopes respond to extremely low oxygen environments, which helps to unravel the chromium redox cycling and the associated isotopic fractionation. The isotopic composition of trivalent chromium in the eastern tropical North Pacific oxygen-deficient zones is lighter than total dissolved chromium and residual hexavalent chromium. This finding supports the preferential reduction of isotopically light Cr found in theoretical and experimental studies and is fundamental to the usage of Cr isotopes as a paleoredox proxy.
Funding Information
  • National Science Foundation (OCE-1736996)

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