This dataset contains carbonate system data collected by scientists from the U.S. Geological Survey (USGS) St. Petersburg Coastal and Marine Science Center to investigate the effects of carbon cycling, coastal and ocean acidification in the Gulf of Mexico near the Tampa Bay estuary located in west central Florida, USA. These data were collected using an autonomous instrument called the Ocean Carbon System version 3 (OCSv3) deployed on the University of South Florida (USF), Coastal Ocean Monitoring and Prediction System (COMPS) Buoy C12. The OCSv3 consists of four sensors integrated into a Sea-Bird Scientific STOR-X submersible data logger including a Sea-Bird SeapHOx sensor for measurement of pH that incorporates a Sea-Bird SBE 37-SMP-ODO MicroCAT C-T-ODO (P) Recorder for measurement of conductivity (for calculation of salinity), temperature, depth, and dissolved oxygen; a Pro-Oceanus CO2-Pro CV CO2 sensor; and a Wetlabs Eco-PAR sensor for measurement of photosynthetically active radiation. The dataset is a time series of carbonate system parameters including: water temperature (Celsius, °C), pressure (decibar, dbar), salinity, pHT (pH on the total scale), carbon dioxide (parts per million, ppm), pressure from the CO2-Pro Infrared Gas Analyzer (IRGA) (millibars, mbar), dissolved oxygen (milligrams per liter, mg/L) and photosynthetically active radiation (microEinsteins). Each parameter was measured every hour for 24-hour time periods throughout the duration of deployment.