This buoy is located in Fagatele Bay along the southwestern point of Tutuila Island in American Samoa within the National Marine Sanctuary of American Samoa. The buoy is located just offshore of Fagatele Bay's coral reef ecosystem in 23 m (75 ft) of water. Data are recorded every 3 hours and transmitted daily. This Moored Autonomous Partial Pressure of Carbon Dioxide (MAPCO2) buoy was primarily established to monitor ocean acidification within a tropical coral reef ecosystem in the Southern Hemisphere, complementing a national array of moored carbon dioxide buoys across the Pacific, Atlantic, and Caribbean. Other important physical parameters are also monitored, including water temperature, salinity, turbidity, chlorophyll, dissolved oxygen, pH, and air pressure. The buoy is primarily funded by NOAA's Ocean Acidification Program and supported by NOAA's Pacific Marine Environmental Laboratory (PMEL), Atlantic Oceanographic and Meteorological Laboratory (AOML), Coral Reef Conservation Program (CRCP), and the National Marine Sanctuary of American Samoa. Local partners include the National Park Service of American Samoa, American Samoa Department of Marine and Wildlife Resources, and the Coral Reef Advisory Group of American Samoa. The Pacific Islands Ocean Observing System (PacIOOS) supports the maintenance of the buoy and instrumentation. Data are managed by PMEL at the NOAA Western Regional Center in Seattle, Washington. PMEL enables data streaming into the PacIOOS website for visualization purposes only: the near real-time data have not been post-calibrated or quality controlled and are therefore not of the climate quality that PMEL is required to achieve. Only post-calibrated and quality-controlled data should be used for scientific publications and are available for download separately at the NOAA Ocean Carbon Data System (OCADS) website in a delayed-mode capacity.