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Related Experiment Video

Updated: May 13, 2026

Laboratory Simulation of an Iron(II)-rich Precambrian Marine Upwelling System to Explore the Growth of Photosynthetic Bacteria

Laboratory Simulation of an Iron(II)-rich Precambrian Marine Upwelling System to Explore the Growth of Photosynthetic Bacteria

Published on: July 24, 2016

Nitrogen cycle feedbacks as a control on euxinia in the mid-Proterozoic ocean.

R A Boyle¹, J R Clark, S W Poulton

¹Earth System Science Group, College of Life and Environmental Sciences, University of Exeter, Exeter EX4 4PS, UK. r.a.boyle@exeter.ac.uk

Nature Communications

|February 28, 2013

Summary

The mid-Proterozoic ocean had separate zones of nitrate and nitrogen fixation, leading to fluctuating hydrogen sulfide levels. These conditions persisted until the Neoproterozoic oxygenation event changed marine biogeochemistry.

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Understanding Dissolved Organic Matter Biogeochemistry Through In Situ Nutrient Manipulations in Stream Ecosystems

Understanding Dissolved Organic Matter Biogeochemistry Through In Situ Nutrient Manipulations in Stream Ecosystems

Published on: October 29, 2016

Area of Science:

Geochemistry
Marine Biogeochemistry
Paleoceanography

Background:

Earth's atmosphere was oxygenated ~2 Gyr ago, but deep oceans remained anoxic until the Neoproterozoic (~0.55 Ma).
Marine sediments indicate ferruginous (Fe(II)-rich) waters with intermittent euxinia (H2S-rich) on continental margins during this period.
Modern euxinia is rare, requiring nitrate depletion for sulfate reducers to be outcompeted by denitrifiers, and linked to nitrogen-fixing production.

Purpose of the Study:

To model a Proterozoic coastal upwelling zone and understand the feedbacks governing ocean chemistry.
To explain the spatial and temporal separation of different biogeochemical states in the mid-Proterozoic ocean.
To reconcile varying hydrogen sulfide (H2S) concentrations with existing geochemical data.

Main Methods:

Utilized a simple box model simulating a generic Proterozoic coastal upwelling system.
Incorporated biogeochemical feedbacks, including nitrate (NO3-) availability, denitrification, and nitrogen (N2)-fixation.
Analyzed the model's output to identify distinct ocean states and their transitions.

Main Results:

The model demonstrated a spatial/temporal separation between two ocean states: nitrate presence with denitrification in deeper waters, and nitrogen-fixation-driven production above euxinic conditions.
These two states represent a dynamic interplay in the Proterozoic ocean's biogeochemistry.
The model explains the fluctuating H2S concentrations observed in geological records.

Conclusions:

The mid-Proterozoic ocean exhibited a complex biogeochemical system with distinct zones driven by nutrient cycling and oxygen levels.
The interplay between denitrification and nitrogen fixation created conditions that allowed for intermittent euxinia.
This system persisted until the Neoproterozoic oxygenation event, which fundamentally altered marine biogeochemistry to its modern state.