This talk comprises the public portion of the PhD dissertation defense from approximately 9:00-10:00 AM.
Department: Earth System Science
Graduate Student: Daniel Ibarra
Advisor: Dr. Page Chamberlain
Title: Paleoclimate Constraints on Terrestrial Hydroclimate, Silicate Weathering and the Carbon Cycle
Abstract: Maintenance of a habitable planet requires connections and balance among Earth’s biogeochemical cycles. Further, the strength of these links determines the stability of habitable conditions in the climate system conducive for the evolution of life. Signatures of Earth’s past climate, paleoclimate records, provide constraints beyond the reach of the instrumental record on the directionality, strength and co-evolution of key Earth system cycles.
Crucially, the geography, topography and lithology of Earth’s continents have two important features that are the focus of this dissertation. First, the continents provide boundary conditions that determine global circulation and hydroclimate patterns that couple Earth’s water and carbon cycles (Chapters 1 and 2). For example, I have used mass and energy balance constraints (sensu Budyko) to forward model pluvial lake distributions to demonstrate that the now-arid western North America was wetter during past colder and warmer than present periods during the Pliocene-Pleistocene. Second, the land surface provides a stabilizing negative feedback in the form of silicate weathering fluxes (Chapters 3-5), balancing the long-term carbon cycle through alkalinity delivery to the oceans. Using reactive transport models, I have placed new constraints on the role of land plants and lithology in determining the coupling between terrestrial hydroclimate and weathering. Further, using lithium isotope measurements, I have investigated the terrestrial weathering response to a large carbon cycle perturbation that produced widespread ocean anoxia.
In this dissertation I have used data, observations and modeling to place mechanistic constraints on how interactions between Earth’s surface and long-term biogeochemical cycles maintain balance and habitable conditions in our climate system. Collectively these results suggest that the surface Earth system, our planet’s fluid envelope, has been progressively tuned and stabilized by the advent of continents and the evolution of life.