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Uncovering the Neoproterozoic carbon cycle.
D T Johnston1, F A Macdonald, B C Gill
1Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, Massachusetts 02138, USA. johnston@eps.harvard.edu
Nature
|March 6, 2012
Summary
Neoproterozoic carbon isotope anomalies in rocks suggest primary changes in Earth's surface carbon cycle, not just deep ocean processes. This finding impacts our understanding of early animal evolution and ocean oxygenation.
Area of Science:
- Geochemistry
- Paleoclimatology
- Sedimentology
Background:
- Stable carbon isotopes in rocks (δ(13)C(carb) and δ(13)C(org)) are key to interpreting Earth's past climate and biology.
- Neoproterozoic records show large negative carbon isotope anomalies, challenging traditional interpretations linked to organic carbon burial and oxygen levels.
Observation:
- New δ(13)C data from Mongolia and Canada reveal tightly coupled carbonate and organic carbon isotope records during major excursions.
- Data from Namibia show decoupled δ(13)C(carb) and δ(13)C(org), explained by detrital organic matter input.
Findings:
- Quantitative analysis using a new mixing model supports a primary perturbation of the surface carbon cycle for coupled excursions.
- Previously proposed mechanisms like diagenesis or dissolved organic carbon oxidation are quantitatively ruled out for the coupled records.
Implications:
- Neoproterozoic carbon isotope excursions likely reflect direct changes in surface carbon cycling, not solely deep-ocean processes.
- Revisiting models is necessary to understand the link between these isotope anomalies, ocean oxygenation, and the evolution of early animal life.
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