| dc.description.abstract | The ocean is absorbing an increasing amount of carbon dioxide (CO2), which is rapidly changing seawater chemistry. As seawater CO2 increases, ecosystem calcification is hindered by the resulting decline in pH, aragonite saturation state (Ωar), and carbonate ion concentration. The Flower Gardens Bank National Marine Sanctuary (FGB) coral reef ecosystem, which is in the northwestern Gulf of Mexico (GoM) off the Texas coast, is one of the healthiest tropical coral reefs in the Caribbean and GoM with over 50 percent coral coverage. The West Texas continental shelf also hosts a number of different ecologically and economically important calcifying ecosystems, such as oyster reefs, and represents an area that is currently understudied with respect to carbonate chemistry. The GoM is frequented by large tropical storms, including Hurricane Harvey, a category four storm that made landfall on August 25th, 2017, which have been shown to alter the carbonate chemistry of nearshore ecosystems. Although Hurricane Harvey did not hit the FGB directly, there has been concern about indirect but potentially damaging impacts of storm runoff on the FGB coral reefs. Hurricane Harvey produced a record rainfall event that caused extensive flooding and elevated freshwater discharge and terrestrial runoff into the coastal areas off the Texas coast. Hurricane Harvey’s strong and prolonged winds may have also enhanced upwelling that brought cold, acidified deep waters toward the surface. This study investigates the effects of the freshwater storm plume and upwelling produced by Hurricane Harvey on the carbonate and nutrient seawater chemistry of the Texas continental shelf. I present water chemistry data from five cruises, two before Harvey (June and August 2017) and three after (September, October, and November 2017). These five cruises were located across the continental shelf of Texas and seawater samples were collected and analyzed for total alkalinity (TA) and dissolved inorganic carbon (DIC), and the remaining carbonate chemistry parameters (partial pressure of CO2 (pCO2), pH, and Ωar) were calculated. Nutrient concentrations (nitrate (NO-3), nitrite (NO-2), ammonium (NH+4), phosphate (HPO2-3), and silicate (HSiO3-) were also analyzed to further characterize how Hurricane Harvey affected seawater chemistry. The floodwaters from Hurricane Harvey delivered a substantial influx of nutrients and rainwater into Galveston Bay and the surrounding coastal region. The rainwater lowered the TA of coastal surface water while the excess nutrients stimulated photosynthesis. The increase in primary production decreased pCO2 and DIC while increasing pH and Ωar. The runoff from Hurricane Harvey lowered coastal water pCO2 to below atmospheric CO2 levels, even though coastal waters are normally a summertime source of CO2 to the atmosphere. Further, all carbonate chemistry parameters on the outer continental shelf below ~50 m depth in the September data, collected soon after Hurricane Harvey, have lower temperature, pH, Ωar, and higher pCO2 and temperature normalized pCO2, indicating that the strong prolonged winds from Hurricane Harvey enhanced upwelling that brought deep water to shallower depths. As large tropical storms continue to intensify with global climate change, it is imperative to understand how these storms both aid and hinder the health of calcifying communities and to further understand and characterize how coastal acidification is shaping GoM ecosystems. | en |
