Abstract:

The ongoing anthropogenic global climate change is producing severe environmental changes and is negatively impacting human society. Methane (CH4) is a potent greenhouse gas that is contributing significantly to current atmospheric and oceanic warming trends. And the current ocean warming is beginning to induce gas-hydrate decomposition, releasing CH4 to bottom waters and potentially to the atmosphere for a positive climate feedback mechanism. To investigate the sources of CH4 dissolved in waters, we developed new procedures to measure radiocarbon values of CH4 (14C-CH4) dissolved in the waters of the US-Atlantic (USAM) and US-Pacific (USPM) margins. We observed that 14C signatures in CH4 from both regions’ bottom waters were depleted relative to the sea surface and contemporary values with concentrations that were elevated. This suggests that the elevated CH4 in these bottom waters was derived from fossil sources associated with hydrocarbon seeps or gas-hydrate dissociation, rather than production from contemporary organic matter. While most surface waters displayed contemporary values of 14C-CH4 in both regions, some shallow (< 100 m) USPM sites displayed lower 14C-CH4 than its contemporary values, indicative of fossil CH4 contributions likely associated with seafloor seeps and vertical mixing. Contrasting values of 14C-CH4 in surface waters within different water depths (shallow vs. deep) indicates that fossil methane is indeed being injected into bottom waters, even if it is mostly not reaching the sea surface. This suggests that water depth and related removal rates can be important factors for determining surface methane dynamics and for the atmospheric release of fossil CH4 from the deep ocean.

Biography:

Dr. Dong Joo Joung was born and raised in Korea (South). He earned his bachelor’s degree in the Chosun University majoring in Energy Resources Engineering and pursued his master’s degree of ocean sciences at Seoul National University. He later moved to the United States of America and earned his PhD in ocean science at the University of Southern Mississippi.
Dr Joung worked as a postdoctoral research associate at University of Vermont, USA after his graduation and investigated nutrients and trace elements biogeochemistry in eutrophic lake water and sediment within Lake Champlain system. He is currently a research scientist at the Department of Earth and Environmental Sciences in University of Rochester, New York, USA, focusing on the investigation of methane dynamics, particularly fossil methane, in aquatic environments including Atlantic, Pacific, and Arctic oceans, Gulf of Mexico, and freshwater systems of Great Lakes. Dr. Joung has awarded multiple fellowships from Brain Korea (BK) 21 and Graduate Student Fellowship in Department of Marine Science, and received Outstanding Doctorate Student from the College of Science and Technology at USM. He has published 21 scientific articles and 3 are in revision, and another 2 are in preparation.

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