Metal isotope tracers of the redox and productivity states of the past oceans: Refining modern calibrations

Examples of oceanic sediment deposits Examples of oceanic sediment deposits

Trace metals play many important roles in the biogeochemistry of the oceans, and via connections with the carbon and sulfur cycles, are intrinsically linked to global climate. The oceanic distributions of trace metals are significantly influenced by the concentration of dissolved oxygen, as well as the intensity and efficiency of the ocean’s biological pump. Therefore, metal stable isotope systems have recently emerged as powerful tracers of the redox evolution and productivity status of the past and present oceans. A growing inventory of data provide (1) important boundary conditions for modelling future climate scenarios, and (2) reconstructions of the evolution of the ocean-atmosphere system throughout Earth’s history, as recorded in marine sediments. However, both applications rely on robust calibration of metal isotope cycling in the modern marine environment.

Despite recent advances, there remains an incomplete understanding regarding how trace metals are cycled through the oceans and how their dissolved isotopic signatures are transferred to the sedimentary record. To help address this knowledge gap, we have investigated the biogeochemical cycling of the iron, zinc, cadmium, and uranium isotope systems in under-constrained regions of the world’s oceans that are representative of past global ocean regimes. These datasets improve the calibration of these isotope systems in the modern ocean and facilitiate their robust application to sedimentary records in ‘deep time’ to aid environmental reconstruction efforts.