| Summary: | Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2019. The architecture of coral reef ecosystems is composed of coral skeletons built from the mineral aragonite (CaCO3). Coral reefs are currently being threatened by ocean acidification (OA), which may lower calcification rates, reduce skeletal density, and increase aragonite dissolution. Crystallography and chemistry are what govern the materials properties of minerals, such solubility and strength. Thus, understanding the mineralogical nature of coral aragonite and how it forms are important for predicting bulk skeletal responses under climate change. Different models based on geochemical versus biological controls over coral skeleton biomineralization propose conflicting predictions about the fate of corals under OA. Rather than investigating the mechanism directly, I use a mineralogical approach to study the aragonite end-products of coral biomineralization. I hypothesize that coral mineralogy and crystallography will lend insights into how coral aragonite crystals form and how sensitive coral aragonite material properties may be to OA. Here I compare the crystallography, bonding environments, and compositions of coral aragonite with aragonite produced by other organisms (mollusk), synthetically (abiogenic precipitation in aragonite-supersaturated seawater and freshwater), and in natural geological settings (abiogenic). Coral aragonite crystallography does not resemble mollusk aragonite (aragonite formed with a strong biological influence), but rather is identical to abiogenic synthetic aragonite precipitated from seawater. I predict that the material properties of coral aragonite are similar to that of abiogenic synthetic seawater aragonites and that coral aragonite formation is sensitive to surrounding seawater chemistry. To test the effect OA on coral aragonites, I studied deep-sea corals from a natural Ωsw ...
|
|---|