Carbon-related, hydrographic data collected during th NOAA Ship Ronald H. Brown 4th Gulf of Mexico Ecosystems and Carbon Cycle (GOMECC-4) cruise in Gulf of Mexico and North Atlantic Ocean from 2021-09-13 to 2021-10-21 (NCEI Accession 0294320)

This dataset contains seawater analyses conducted during the fourth Gulf of Mexico Ecosystems and Carbon Cycle (GOMECC-4) cruise on board the NOAA Ship Ronald H. Brown departing from Key West, FL into the Gulf of Mexico and then around the coastal waters of the Gulf of Mexico in a counter-clockwise direction. Samples were collected using a CTD-O2 rosette equipped with 24 niskin-style bottles. The cruise took place from September 13–October 21, 2021 and ended in St. Petersburg, FL. The effort was in support of the coastal monitoring and research objectives of NOAA’S Ocean Acidification Program. The expedition was designed to obtain a snapshot of key carbon, physical, and biogeochemical parameters as they relate to ocean acidification (OA) in the coastal realm. This was the fourth occupation of the Gulf of Mexico as part of the Ocean Acidification Program’s monitoring efforts, with the first three occurring in 2007, 2012 and 2017. The cruise included a series of 15 transects approximately orthogonal to the coast of the Gulf of Mexico and a 16th partial transect along the 27°N line between Florida and the Bahamas. On the transit between each of these transects, discrete samples were collected from the underway seawater line to obtain a comprehensive set of underway measurements.