Seasonal variability of carbonate chemistry and decadal changes in waters of a marine sanctuary in the Northwestern Gulf of Mexico


We report seasonal water column carbonate chemistry data collected over a three-year period (late 2013 to 2016) at Flower Garden Banks National Marine Sanctuary (FGBNMS) located on the subtropical shelf edge of the northwestern Gulf of Mexico. The FGBNMS hosts the northernmost tropical coral species in the contiguous United States, with over 50% living coral cover. Presented here are results from samples of the upper 25 m of the water column collected from September 2013 to November 2016. Additionally, following a localized mortality event likely associated with major continental flooding in summer 2016, water samples from up to ~250 m depth were collected in the broader FGBNMS area on a rapid response cruise to examine the seawater carbonate system. Both surface (<5 m) total alkalinity (TA) and total dissolved inorganic carbon (DIC) vary over small ranges (2391 ± 19 μmol kg−1 and 2060 ± 19 μmol kg−1, respectively) for all times-series samples. Temperature and salinity both played an important role in controlling the surface water carbonate system dynamics, although temperature was the sole significant factor when there was no flooding. The FGBNMS area acted as a sink for atmospheric CO2 in winter and a CO2 source in summer, while the time-integrated CO2 flux is close to zero (−0.14 ± 1.96 mmol-C m−2 yr−1). Results from three cruises, i.e., the Gulf of Mexico and East Coast Carbon Project (GOMECC-1) in 2007, the rapid response study, and the Gulf of Mexico Ecosystems and Carbon Cruise (GOMECC-3), revealed decreases in both pH and saturation state with respect to aragonite (Ωarag) in subsurface waters (~100–250 m) over time. These decreases are larger than those observed in other tropical and subtropical waters. Based on reaction stoichiometry, calculated anthropogenic CO2 contributed 30–41% of the overall DIC increase, while elevated respiration accounted for the rest.



coral reef, ocean acidification, gulf of mexico, flower garden banks national marine sanctuary, anthropogenic co2


XH was supported by a Gulf of Mexico Research Initiative grant (GOMRI-220). Data collected using this grant are publicly available through the Gulf of Mexico Research Initiative Information & Data Cooperative (GRIIDC) at;;sdata=%2FfFnpWMvLVjKrO8VckHfeDGFrL1XjQmxen3WXqh%2FSdo%3D&amp;reserved=0 (UDI: R2.x220.000:0006). Quarterly sampling that was part of the Stetson Bank long-term monitoring program was funded through Interagency Agreement E14PG00052 between the U.S. Department of the Interior (DOI), Bureau of Safety and Environmental Enforcement (BSEE) and the National Oceanic and Atmospheric Administration's National Ocean Service (NOAA-NOS), Office of National Marine Sanctuaries (ONMS), through FGBNMS, as well as the National Marine Sanctuary Foundation(NMSF). Quarterly sampling that was part of the long-term monitoring program at EFGB and WFGB was funded through Interagency Agreements M14PG00020 and M16PG00018 between U.S. DOI, Bureau of Ocean Energy Management and the NOAA-NOS, ONMS, through FGBNMS. The samples were collected under permits FGBNMS-2009- 001 and FGBNMS-2014-001. NCRMP is co-funded by NOAA's Coral Reef Conservation Program (NCRMP) and Ocean Acidification Program (OAP). NCRMP sample collection and processing were conducted by T. Burton, R. Carlton, R. Clark, K. Edwards, and D. Graham. The GOMECC1 study was supported by NOAA Global Carbon Cycle Program, and the GOMECC-3 study was supported by NOAA OAP.


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Hu, X., Nuttall, M.F., Wang, H., Yao, H., Staryk, C.J., McCutcheon, M.R., Eckert, R.J., Embesi, J.A., Johnston, M.A., Hickerson, E.L. and Schmahl, G.P., 2018. Seasonal variability of carbonate chemistry and decadal changes in waters of a marine sanctuary in the Northwestern Gulf of Mexico. Marine Chemistry, 205, pp.16-28.