T182 Novel Approaches for Constraining the Evolution of Essential Nutrient Cycling

Thursday, 29 October 2020
10:00 AM - 12:00 PM
Meeting Rooms

CARBON ISOTOPE EVIDENCE FOR THE GLOBAL PHYSIOLOGY OF PROTEROZOIC CYANOBACTERIA

Paper number: T182-3
Program: Technical Sessions
Time: 10:30 AM – 10:45 AM

Authors

Abstract

Ancestral cyanobacteria are assumed to dominate primary production after the Great Oxidation Event ≈2.4-2.0 Ga ago. However, carbon isotope fractionation by extant members of the dominant marine clade (α-cyanobacteria) is inconsistent with isotopic records of carbon fixation by primary producers in the mid‑Proterozoic Eon (1.8-1.0 Ga ago). To resolve this disagreement, we experimentally characterized carbon isotope fractionation by several strains of planktic β‑cyanobacteria and an engineered Proterozoic analog lacking a CO2-concentrating mechanism (CCM). We also statistically characterized carbon isotope fractionation by benthic cyanobacterial communities. At relevant mid‑Proterozoic pH and pCO2 conditions, only carbon isotope fractionation by wild-type β-cyanobacteria is consistent with the Proterozoic carbon isotope record, while carbon isotope fractionation by benthic cyanobacteria and by β-cyanobacteria lacking a CCM is not. β-Cyanobacteria with CCMs were apparently the major primary producers in the pelagic Proterozoic ocean, despite atmospheric CO2 levels up to 100-times modern. Such profound physiological stasis implies that an understanding of how modern cyanobacterial CCMs impact net carbon isotope fractionation can inform the Proterozoic C isotope record. We report an isotope flux-balance model and culturing experiments under varying environmental conditions (pCO2 and light levels) to determine the intracellular controls on carbon isotope fractionation by cyanobacteria during the Proterozoic Eon.

Geological Society of America Abstracts with Programs. Vol. 52, No. 6

doi: 10.1130/abs/2020AM-356629

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