Computational analysis of the biophysical controls on Southern Ocean phytoplankton ecosystem dynamics
MetadataShow full item record
Southern Ocean net community productivity plays an out sized role in regulating global biogeochemical cycling and climate dynamics. The structure of spatial-temporal variability in phytoplankton ecosystem dynamics is largely governed by physical processes but a variety of competing pathways complicate our understanding of how exactly they drive net population growth. Here, I leverage two coupled, 3-dimensional, global, numerical simulations in conjunction with remote sensing data and past observations, to improve our mechanistic understanding of how physical processes drive biology in the Southern Ocean. In Chapter 2, I show how different mechanistic pathways can control population dynamics from the bottom-up (via light, nutrients), as well as the top-down (via grazing pressure). In Chapters 3 and 4, I employ a higher resolution, eddy resolving, integration to explicitly track and examine closed eddy structures and address how they modify biomass at the mesoscale. Chapter 3 considers how simulated eddies drive bottom-up controls on phytoplankton growth and finds that division rates are, on average, amplified in anticyclones and suppressed in cyclones. Anomalous division rates are predominately fueled by an anomalous vertical iron flux driven by eddy-induced Ekman Pumping. Chapter 4 goes on to describe how anomalous division rates combine with anomalous loss rates to drive anomalous net population growth. Biological rate-based mechanisms are then compared to the potential for anomalies to evolve strictly via physical transport (i.e. dilution, stirring, advection). All together, I identify and describe dramatic regional and seasonal variability in when, where, and how different mechanisms drive phytoplankton growth throughout the Southern Ocean. Better understanding this variability has broad implications to our understanding of how oceanic biogeochemisty will respond to, and likely feedback into, a changing climate. Specifically, the uncertainty associated with this variability should temper recent proposals to artificially stimulate net primary production and the biological pump via iron fertilization. In Chapter 5 I argue that Southern Ocean Iron Fertilization fails to meet the basic tenets required for adoption into any regulatory market based framework.
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Applied Ocean Science & Engineering at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2019.
Suggested CitationThesis: Rohr, Tyler, "Computational analysis of the biophysical controls on Southern Ocean phytoplankton ecosystem dynamics", 2019-02, DOI:10.1575/1912/23631, https://hdl.handle.net/1912/23631
Showing items related by title, author, creator and subject.
Chen, Changsheng (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1992-06)This thesis consists of two parts: (I) variability of currents and water properties in late spring in the northern Great South Channel and (II) numerical study of stratified tidal rectification over Georges Bank. In part ...
Biological-physical interactions on Georges Bank : plankton transport and population dynamics of the ocean quahog, Arctica islandica Lewis, Craig V. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1997-06)Advective losses of bank water during winter because of strong wind forcing were hypothesized to be a significant factor limiting recruitment of Georges Bank cormnunities. This hypothesis was examined using biological-physical ...
Grozeva, Niya G. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2018-02)This thesis examines abiotic processes controlling the transformation and distribution of carbon compounds in seafloor hydrothermal systems hosted in ultramafic rock. These processes have a direct impact on carbon budgets ...