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Study Characterizes Dissolved Organic Carbon Cycling in the Northern Gulf of Mexico

March 20, 2018

Researchers analyzed dissolved organic carbon from water column samples collected in five regions to establish baseline data about its relative persistence and cycling in the northern Gulf of Mexico. The team found that the Mississippi River exports large amounts of dissolved organic carbon with an anthropogenic 14C signature, which is removed and recycled offshore as the river plume moves offshore. The researchers observed a persistent dissolved organic carbon plume near the Macondo wellhead four years after the Deepwater Horizon incident, likely from bacteria transforming much of the spilled petroleum and methane into natural dissolved organic carbon molecules and dissolving this carbon into deep ocean water. The researchers published their findings in Geophysical Research Letters: Oceans: Stable and radiocarbon isotopic composition of dissolved organic matter in the Gulf of Mexico.

The northern Gulf of Mexico is an especially dynamic region for organic matter cycling, which is of primary importance to marine ecosystems and the global carbon cycle. An influx of carbon occurred during the Deepwater Horizon incident, and up to 25% of the released oil remains unaccounted for. A lack of Gulf of Mexico baseline data prevented a clear understanding of how the oil would be incorporated into marine foods webs, sediments, and detrital carbon reservoirs. “The main approach we used in our study to address this need was radiocarbon dating,” explained study authors Brett Walker and Brad Rosenheim. “Because terrestrial, marine, and petroleum carbon sources have very different carbon isotopic signatures, we can use these signatures to trace the sources and cycling of dissolved organic carbon in the Gulf of Mexico.”

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