The mineralogy and chemistry of modern shallow-water and deep-sea corals
Farfan, Gabriela A.
MetadataShow full item record
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 gradient (1.15–1.44) in the Gulf of Mexico and shallow-water corals across a natural Ωsw (2.3–3.7) and pH (7.84–8.05) gradient in Palau. Minor shifts in crystallography are expressed by coral aragonite in these natural systems, likely governed by skeletal calcite contents, density, and Ω of the coral calcifying fluid. My results are most consistent with a geochemical model for biomineralization, which implies that coral calcification may be sensitive to OA. However, further work is required to determine whether the modest crystallographic shifts I observe are representative on a global scale and whether they could influence bulk skeletal material properties.
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
Suggested CitationThesis: Farfan, Gabriela A., "The mineralogy and chemistry of modern shallow-water and deep-sea corals", 2019-02, DOI:10.1575/1912/10765, https://hdl.handle.net/1912/10765
Showing items related by title, author, creator and subject.
Development of a "genome-proxy" microarray for profiling marine microbial communities, and its application to a time series in Monterey Bay, California Rich, Virginia Isabel (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2008-09)This thesis describes the development and application of a new tool for profiling marine microbial communities. Chapter 1 places the tool in the context of the range of methods used currently. Chapter 2 describes the ...
Initial settlement of marine invertebrate larvae : the role of passive sinking in a near-bottom turbulent flow environment Hannan, Cheryl Ann (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1984-02)The hypothesis that planktonic larvae of benthic invertebrates sink through the water like passive particles in turbulent flows near the seabed was tested in the field using several groups of geometrically different ...
Loewen, Mark Richard (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1991-12)Breaking waves dissipate energy, transfer momentum from the wind to surface currents and breaking enhances the transfer of gas and mass across the air-sea interface. Breaking waves are believed to be the dominant source ...