Determining the Source of Methane in Arctic Ocean Waters Adjacent to Subsea Permafrost

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Methane is a potent greenhouse gas that is present in large amounts in frozen soils and marine sediments in the Arctic. Both natural and anthropogenic climate change are influencing the methane dynamics in the Arctic Ocean, through thawing of subsea permafrost as well as the decreasing sea-ice extent; several recent investigations have documented seemingly elevated methane concentrations in seawater and releases of methane to the atmosphere associated with both of these processes. Release of stored methane can lead to further warming and then to further methane releases in a reinforcing cycle. Both subsea permafrost thaw and sea-ice melt can influence several methane reservoirs such as the stability of ancient methane stored within and below sediments as well as the production of methane by microorganisms both in the seafloor in recently deposited sediments and thawed permafrost and in subsurface ocean waters associated with phytoplankton blooms. Given the diverse sources of methane to ocean waters and the atmosphere in the continental margins of the Arctic Ocean, it is currently unknown which source is contributing most of the observed methane in Arctic waters and thus how the magnitude of this methane source may change. Measurements of the natural radiocarbon content of methane dissolved in ocean waters and sediments can be used to identify its source. For example, methane emitted from seeps and clathrate hydrates is radiocarbon-free, methane formed in recently deposited anoxic sediments or in the subsurface ocean as a result of phytoplankton blooms contains more modern levels of radiocarbon, and degrading permafrost is of Pleistocene age (27,000-43,000 years old). The work proposed here will aim to elucidate these sources through natural radiocarbon measurements of methane dissolved in ocean waters and sediments collected during transects across the continental margin of the Beaufort Sea. The major challenge associated with measuring the natural radiocarbon content of methane dissolved in seawater is collecting enough methane carbon for a quantitative Accelerator Mass Spectrometry (AMS) analysis. Previously published procedures have recently been modified enabling the extraction and collection of methane from approximately 10,000 liters of seawater in less than two hours. These new procedures will enable roughly 100 samples to be collected during a one week oceanographic expedition. Measured horizontal and vertical distributions of the natural radiocarbon content of methane dissolved in ocean waters will determine how the source of methane changes from the coast to the open ocean and from the seafloor to the sea surface. These methane isotopic distributions will also provide a solid test of the hypothesis that the aerobic oxidation of methane will provide a counterbalancing feedback removing the increased quantities of methane leaving the seafloor before it reaches the atmosphere. Graduate and undergraduate students will be involved in the entire scientific process with opportunities not only in their home lab, but also with visits to other facilities. The investigators will leverage firmly established pathways with the University of Rochester and the Rochester Museum and Science Center to promote educational programs within the Rochester City School District to serve underrepresented minority K-12 students.