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Recurrent photic zone euxinia limited ocean oxygenation and animal evolution during the Ediacaran
Wang Zheng1, Anwen Zhou1,2, Swapan K Sahoo3
1School of Earth System Science, Institute of Surface-Earth System Science, Tianjin University, Tianjin, 300072, China.
Nature Communications
|July 3, 2023
Summary
Mercury isotopes reveal recurrent photic zone euxinia (PZE) during the Ediacaran Period. This euxinia, linked to ocean redox changes, may have limited animal expansion and oxygen rise.
Area of Science:
- Geochemistry
- Paleoceanography
- Early Life Evolution
Background:
- The Ediacaran Period (~635-539 Ma) witnessed complex metazoan diversification, linked to ocean redox shifts.
- Mechanisms driving Ediacaran ocean redox evolution remain a subject of intense scientific debate.
- Understanding these changes is crucial for reconstructing early animal life evolution.
Purpose of the Study:
- To reconstruct Ediacaran oceanic redox conditions using mercury isotope compositions.
- To investigate the processes and dynamics of photic zone euxinia (PZE) in the Ediacaran ocean.
- To understand the impact of redox changes on early metazoan diversification.
Main Methods:
- Analysis of mercury (Hg) isotope compositions.
- Sampling of black shale sections from the Doushantuo Formation in South China.
- Reconstruction of past oceanic redox conditions based on geochemical proxies.
Main Results:
- Mercury isotopes provide compelling evidence for recurrent and spatially dynamic photic zone euxinia (PZE).
- PZE occurred on the South China continental margin during intervals of previously identified ocean oxygenation.
- PZE was likely driven by increased sulfate and nutrient availability from a transiently oxygenated ocean.
Conclusions:
- Photic zone euxinia (PZE) may have inhibited oxygen production via anoxygenic photosynthesis.
- PZE limited habitable space for eukaryotes, potentially restricting the expansion of macroscopic animals.
- These feedbacks may have abated the long-term rise of oxygen during the Ediacaran Period.
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