STX_TA_4

The south Texas continental shelf recently revealed an unusual high-alkalinity "plume" near barrier island passes following a winter cold front. This project investigates whether this anomaly reflects event-driven export of alkaline water from low-inflow estuaries (bays where evaporation and tidal exchange dominate over freshwater discharge), superimposed on background seasonal and interannual variability, and how this affects shelf carbon chemistry and air-sea CO2 exchange. This cruise will survey total alkalinity, dissolved inorganic carbon, pH, dissolved oxygen or DO, pCO2, nutrients, and water stable isotopes across shelf stations spanning from the Colorado River mouth to Padre Island, with station spacing increasing offshore. Sampling combines CTD-rosette casts, an underway pCO2/DO/fluorescence system, and discrete water collection, spanning seasons and conditions before and after cold-front passages. Results will help identify the mechanisms controlling estuarine alkalinity export, quantify its contribution to shelf carbon cycling and CO2 flux, and constrain a coupled hydrologic-ocean-biogeochemical model. Because these naturally elevated-alkalinity waters resemble outcomes sought by ocean alkalinity enhancement (OAE) approaches for carbon dioxide removal, this work may also serve as a natural analog for studying alkalinity dispersion in coastal systems.