Distributions and Air-Sea Exchange of Methane and Nitrous Oxide in the Levantine Basin

Jeramy Dedrick, Texas A&M University, College Station, United States, Shari Ann Yvon-Lewis, Texas A&M University College Station, Oceanography, College Station, United States, Yizhaq Makovsky, University of Haifa, Haifa, Israel, Laura Henrika Bührig, University of Haifa, Dr. Moses Strauss Department of Marine Geosciences, Mount Carmel, Haifa, Israel and Daniel Sher, University of Haifa, Leon H. Charney School of Marine Sciences, Haifa, Israel
Methane and nitrous oxide are two potent greenhouse gases with radiative forcing capabilities several times greater than carbon dioxide for a 100-year time horizon. The oceans are a source of these gases to the atmosphere. There is a dearth of measurements for these gases in the Mediterranean Sea, and in particular the highly industrial and anthropogenically-influenced Levantine Basin. The THEMO (Texas A&M – University of Haifa Eastern Mediterranean Observatory) operates two moorings in shallow and deep waters in the southeastern Mediterranean Sea where water samples were collected for two, three-month periods in 2018 and 2019. Sample analysis utilizing ECD/FID gas chromatography revealed surface waters that were supersaturated with methane and near equilibrium for nitrous oxide during all periods of measurement. Water profile observations found correlation of nitrous oxide concentrations with apparent oxygen utilization and methane concentration enhancement at mid-layer depths in proximity to the Leviathan Gas Field. Period-averaged methane fluxes were largely positive, suggesting the region acts as a significant source of the gas to the atmosphere, while low and negative nitrous oxide fluxes are indicative of a regional air-sea balance.