Wave-Driven Geomorphology of Pacific Carbonate Coastlines: From landscape to Wavelength Scale

James Bramante, Ph.D., 2019
Jeffrey Donnelly, Advisor

Coral atoll ecosystems and the humans they support are among the most vulnerable to anthropogenic climate change. Unfortunately, the sediment dynamics that shape coral reefs and reef islands are poorly understood. Here, I apply eclectic methods to produce insights into the ways tropical cyclones and waves move sediment on fringing reefs. First, I use a numerical model of hydrodynamics to demonstrate that end-of-century sea-level rise will increase the importance of sediment produced on reef flats relative to that produced on fore reefs for island sediment budgets. Second, I execute a series of oscillating flow tunnel experiments to constrain the rate at which sediment erodes reef surfaces under waves. I find that the erosion rate increases as a power law of wave orbital velocity. Finally, from analysis of sediment cores retrieved from the Marshall Islands, I reconstruct tropical cyclogenesis in the Marshall Islands over the past 3000 years. Using the results from an ensemble of climate models, I demonstrate that enhanced tropical cyclogenesis during the Little Ice Age may have been driven by anomalous climate mode behavior. This thesis demonstrates the importance of sediment dynamics on the morphology of fringing reefs and the sensitivity of those dynamics to centennial climate variability.