THE IMPACT OF CHANGING WINDS ON ESTUARINE EVOLUTION, COPANO BAY, TX

Over 160 high-resolution 2-D seismic lines and 6 sediment cores up to 16 m in length were collected from Copano Bay along the northwestern Gulf of Mexico in order to study the impact of climate change on estuarine systems over the last 10 k.y. Both core and seismic data reveal that the history of the bay was punctuated by major flooding events. These flooding events represent a landward shift of estuarine environments and changes in the rate of sediment accretion. Possible causes for the formation of the flooding events include sea-level fluctuations, climate changes, and autocyclic events. Most climatically-driven mechanisms for environmental changes within estuaries focus on changes in the amount of sediment delivered to the estuarine system. One very important and often overlooked aspect of climate change is changes in wind strength and direction. Previous studies suggest that most shallow lagoons and estuaries are in equilibrium with sediment input and wave-energy dissipation. Due to this equilibrium, most modern accumulation rates equal the rate of relative sea-level rise within shallow estuaries. Using grain-size data as a proxy for paleo-wind strength from central-basin deposits, we test whether a disruption in the equilibrium between accumulation rates and wave energy is an overlooked cause for para-sequence development within estuaries and incised valleys. We suggest that with stronger winds or increased fetch, shallow estuaries become deeper and accumulating sediments become coarser and better sorted. With weaker winds or decreased fetch, estuaries become shallower and accumulating sediments become finer and exhibit poorer sorting.