Iron Biogeochemical Cycle Throughout Earth History
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Iron Biogeochemical Cycle Throughout Earth History

  • Author(s): Kenlee, Bridget
  • Advisor(s): Lyons, Timothy W
  • et al.
Abstract

Iron (Fe) is present over a very wide range of redox conditions and is one of most the important nutrients for phytoplankton growth in the ocean. In a marine environment, Fe composition in the sediments is intimately linked to the chemistry of the waters from which they precipitate. Particularly, the elemental and isotopic signature of Fe recorded in sediments provide clues about the nature of the redox state and the biogeochemical cycling of bio-essential metals, both of which are associated to primary productivity, carbon cycling, and the evolution of Earth through time.In this work, I firstly evaluate Fe, a fundamental regulator of ocean primary productivity and the global carbon cycle and a limiting micronutrient for phytoplankton growth, to draw connections between win-borne bioavailable Fe distribution and its potential impact on Fe-based climate feedbacks over the last 120,000 years. Our results from sediments in the North Atlantic suggest that atmospheric processing of Saharan dust enhances the solubility and hence bioavailability of dust-borne iron independent of grain size, and this transport-dependent processing scales with atmospheric residence time and thus transport distance. These observations and inferred processes may extend to many other regions beyond the North Atlantic and enlighten the global primary productivity distribution. A second study defines natural variations in water column redox of the southern Scotia Sea basins, Dove and Pirie from scientific drilling of the Scotia Sea sedimentary record during International Ocean Discovery Program (IODP) Expedition 382. The distinct trend in the pore water and sedimentary concentrations from two basins reveal the dominant control of Fe availability on primary composition and early diagenetic signals that affects the biogeochemical signals and its effects for interpreting Fe data towards the climate evolution of the Southern Ocean. Lastly, I examine the redox state of the late-Archean and Paleoproterozoic using black shales and Banded Iron Formations (BIFs) from the San Francisco Craton, Brazil to reconstruct the O2 evolution based on redox changes of Earth's ocean. These two studies add to further evidence in the growing body of work that shows the evolution of atmospheric and marine O2 was more complex than a simple punctuated rise of oxygen.

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