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A small marine biosphere in the Proterozoic
Thomas A Laakso1, Daniel P Schrag1
1Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts.
Geobiology
|November 13, 2018
Summary
Marine photosynthesis was severely limited in the Proterozoic due to low oxygen. Nutrient recycling was slow, making riverine input crucial for the limited marine biosphere.
Area of Science:
- Oceanography
- Biogeochemistry
- Paleontology
Background:
- Phosphorus is a key limiting nutrient for marine photosynthesis.
- Modern ocean productivity relies heavily on nutrient recycling by heterotrophic organisms.
- Proterozoic oceans had low oxygen levels, impacting respiration and nutrient cycling.
Purpose of the Study:
- To investigate the impact of low-oxygen Proterozoic environments on marine primary production.
- To quantify the potential rate of net primary production during the Proterozoic eon.
Main Methods:
- Utilized steady-state mass balance calculations.
- Modeled nutrient supply dynamics under varying oxygen conditions.
Main Results:
- Proterozoic net primary production was estimated to be less than 10% of modern rates, possibly below 1%.
- Nutrient recycling was significantly inhibited by low oxygen levels.
- Riverine nutrient input dominated over internal recycling.
Conclusions:
- The Proterozoic marine biosphere was likely small and concentrated in estuarine environments.
- Limited nutrient recycling in low-oxygen seas restricted global ocean productivity.
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