Quantifying the areal extent and dissolved oxygen concentrations of Archean oxygen oases

Open Access
Author:
Olson, Stephanie Leigh
Graduate Program:
Geosciences
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
May 06, 2013
Committee Members:
  • Lee Kump, Thesis Advisor
Keywords:
  • oxygen oases
  • redox evolution
  • oxygenic photosynthesis
  • Archean
  • earth system model
Abstract:
Several lines of evidence indicate that the advent of oxygenic photosynthesis preceded the oxygenation of the atmosphere—perhaps by as much as 300 million years. The fate of biogenic oxygen prior to its expression in the atmosphere remains speculative, but recent work suggests that oxygen was locally available within the surface ocean to support aerobic microbial ecosystems. Simple mass balance predicts that locally oxygenated environments (oxygen oases) could exist in areas of high productivity if the local rate of oxygen production by oxygenic photosynthesis exceeds the combined rate of oxygen loss by a number of processes (e.g., exchange with the atmosphere, transport within the ocean, reaction with reduced aqueous species, biological consumption). The areal extent of these environments and the dissolved oxygen concentrations that could have persisted in an otherwise anoxic ocean, however, are key uncertainties in our understanding of the spatiotemporal redox-evolution of the early earth system. We use an earth system model of intermediate complexity (GENIE) that has been modified to simulate a theoretical Archean biosphere in order to explore redox heterogeneity in the late Archean surface ocean. We demonstrate that oxygen oases are an expected consequence of oxygenic photosynthesis beneath an essentially oxygen-devoid atmosphere—and that oxygenated surface waters need not be restricted to shallow coastal environments or microbial mats. Within oxygen oases, oxygen concentrations locally approach ~1-10 µM for a large range of plausible Archean conditions. Although oxygen concentrations in the open ocean are exceedingly low, biologically relevant dissolved oxygen concentrations are widespread in our hypothetical surface ocean.