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Updated: May 13, 2026
09:45
Laboratory Simulation of an Iron(II)-rich Precambrian Marine Upwelling System to Explore the Growth of Photosynthetic Bacteria
Published on: July 24, 2016
Proterozoic ocean redox and biogeochemical stasis.
Christopher T Reinhard1, Noah J Planavsky, Leslie J Robbins
1Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA. reinhard@caltech.edu
Summary
Earth's oceans were largely anoxic during the Proterozoic Eon, with limited sulfidic conditions. This suggests potential molybdenum-nitrogen colimitation for marine life throughout much of Earth's history.
Area of Science:
- Geochemistry
- Paleoceanography
- Biogeochemistry
Background:
- Atmospheric oxygen increased in two steps during the Proterozoic Eon (2.5–0.543 billion years ago).
- Ocean ventilation and seafloor redox conditions during Earth's mid-Proterozoic (1.8–0.8 billion years ago) remain poorly understood.
- Mid-Proterozoic ocean chemistry influences nutrient cycling and eukaryotic life evolution.
Observation:
- Sedimentary metal enrichments provide insights into seafloor redox evolution.
- Molybdenum and chromium exhibit distinct redox behaviors, useful for paleoceanographic reconstructions.
- A large database of sedimentary metal enrichments was coupled with a mass balance model.
Findings:
- The Proterozoic deep ocean was pervasively anoxic, with anoxic seafloor covering 30–40% of the modern area.
- Euxinic (anoxic and sulfidic) seafloor conditions were limited, covering less than 1–10% of the modern seafloor area.
- The oceanic molybdenum reservoir is sensitive to sulfidic seafloor extent.
Implications:
- Seafloor redox conditions significantly impacted ocean chemistry and nutrient availability.
- The marine biosphere may have experienced molybdenum-nitrogen colimitation during many Proterozoic periods.
- Understanding Proterozoic ocean chemistry is crucial for reconstructing the evolution of early life.
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