2010 Annual Science Report
Arizona State University Reporting | SEP 2009 – AUG 2010
Stoichiometry of Life, Task 4: Biogeochemical Impacts on Planetary Atmospheres
Oxygenation of Earth’s early atmosphere must have involved an efficient mode of carbon burial. In the modern ocean, carbon export of primary production is dominated by fecal pellets and aggregates produced by the animal grazer community. But during most of Earth history the oceans were dominated by unicellular, bacteria-like organisms (prokaryotes) causing a substantially altered biogeochemistry. The NASA Ocean Biogechemical Model (NOBM) is applied using cyanobacteria (blue-green algae) as the only photosynthetic group in the oceans. The analyses showed that the early Earth ocean had 19% less primary production and 35% more nitrate due to slower growth by the cyanobacteria, and reduced nutrient uptake efficiency relative to modern phytoplankton Additionally there was 8% more total carbon in the oceans as a result of higher atmospheric pCO2. We plan to optimize this early Proterozoic ocean model in combination with a 1 D model to account for changes in aggregate formation and sinking speed in response to varying nutrients.
The ocean biogeochemistry module affords simulation of such phenomena as photosynthesis on the Early Earth, the stratification of dominant photosynthetic pigments by light quality, and potential variations in the 50% of net primary productivity of life on the modern Earth. The NASA Ocean Biogeochemistry Model (NOBM) was applied to questions relating to early life on Earth in an effort to understand possible scenarios on other planets. Watson Greg, working with Suzanne Neuer, Ariel Anbar and Graduate Student Steven Romaniello, conducted a first-order global “experiment” using cyanobacteria as the only photosynthetic group in the oceans (i.e., modern diatoms, chlorophytes, and coccolithophores were removed from the standard NOBM configuration), and assuming modern ocean physical dynamics. The cyanobacteria were consumed by primitive heterotrophic bacteria. There was no iron limitation, assuming that volcanic sources of iron were abundant. Also the atmospheric carbon partial pressure was assumed to be 1000 uatm. The analyses suggest that the early Earth ocean might have had ~ 20% less primary production and ~ 35% more nitrate available due to slower growth by cyanobacteria, and reduced nutrient uptake efficiency relative to modern phytoplankton. Silica concentrations were of course much higher than the modern Earth since cyanobacteria do not uptake silica. Additionally there was 8% more total carbon in the oceans as a result of higher atmospheric pCO2. The results of this preliminary experiment continue to be analyzed to inform further efforts.
PROJECT INVESTIGATORS:Susanne Neuer
PROJECT MEMBERS:Ariel Anbar
RELATED OBJECTIVES:Objective 1.1
Formation and evolution of habitable planets.
Earth's early biosphere.
Production of complex life.
Co-evolution of microbial communities
Effects of environmental changes on microbial ecosystems
Biosignatures to be sought in nearby planetary systems