title: Cyanobacterial Diazotrophy and Earth's Delayed Oxygenation.
abstract: The redox landscape of Earth's ocean-atmosphere system has changed dramatically throughout Earth history. Although Earth's protracted oxygenation is undoubtedly the consequence of cyanobacterial oxygenic photosynthesis, the relationship between biological O2production and Earth's redox evolution remains poorly understood. Existing models for Earth's oxygenation cannot adequately explain the nearly 2.5 billion years delay between the origin of oxygenic photosynthesis and the oxygenation of the deep ocean, in large part owing to major deficiencies in our understanding of the coevolution of O2and Earth's key biogeochemical cycles (e.g., the N cycle). For example, although possible links between O2and N scarcity have been previously explored, the consequences of N2limitation for net biological O2production have not been examined thoroughly. Here, we revisit the prevailing view that N2fixation has always been able to keep pace with P supply and discuss the possibility that bioavailable N, rather than P, limited export production for extended periods of Earth's history. Based on the observation that diazotrophy occurs at the expense of oxygenesis in the modern ocean, we suggest that an N-limited biosphere may be inherently less oxygenic than a P-limited biosphere-and that cyanobacterial diazotrophy was a primary control on the timing and tempo of Earth's oxygenation by modulating net biogenic O2fluxes. We further hypothesize that negative feedbacks inhibit the transition between N and P limitation, with the implication that the pervasive accumulation of O2in Earth's ocean-atmosphere system may not have been an inevitable consequence of oxygenic photosynthesis by marine cyanobacteria.
authors.affiliation: Department of Earth Sciences, University of California, Riverside, Riverside, CA USA.
authors.forename: Stephanie L
authors.initials: SL
authors.lastname: Olson
authors.affiliation: School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA USA.
authors.forename: Christopher T
authors.initials: CT
authors.lastname: Reinhard
authors.affiliation: Department of Earth Sciences, University of California, Riverside, Riverside, CA USA.
authors.forename: Timothy W
authors.initials: TW
authors.lastname: Lyons
keywords: boring billion; cyanobacteria; denitrification; diazotrophy; oxygen