Nitrous oxide and methane in the Atlantic Ocean between 50°N and 52°S: Latitudinal distribution and sea-to-air flux |
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| Institution: | 2. Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA;1. State Key Laboratory of Marine Resource Utilization in South China Sea, Hainan University, Haikou 570228, China;2. Shenzhen Marine Environment Monitoring Center Station, State Oceanic Administration, Shenzhen 518067, China;3. State Key Laboratory of Marine Environmental Science, College of Ocean and Earth Sciences, Xiamen University, Xiamen 361102, China;4. Marine Science Institute and Guangdong Provincial Key Laboratory of Marine Biotechnology College of Science, Shantou University, Shantou 515063, China;1. State Key Laboratory of Marine Environmental Science, Key Laboratory of the Ministry of Education for Coastal Wetland Ecosystems, College of Environment and Ecology, Xiamen University, Xiamen, Fujian 361102, China;2. Institute of Environmental Engineering, National Sun Yat-Sen University, No. 70, Lienhai Road, Kaohsiung 80424, Taiwan;3. Department of Environmental Engineering, National I-Lan University, No. 1, Sheen Lung Road, I-Lan 26047, Taiwan;4. Graduate Institute of Environmental Engineering, National Taiwan University, No. 71, Chou-Shan Road, Taipei 10673, Taiwan;1. College of Environment and Safety Engineering, Qingdao University of Science and Technology, Qingdao 266042, China;2. CAS Key Laboratory of Marine Ecology and Environmental Sciences, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China;3. Laboratory for Marine Ecology and Environmental Science, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China;4. Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao 266071, China |
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| Abstract: | We discuss nitrous oxide (N2O) and methane (CH4) distributions in 49 vertical profiles covering the upper ～300 m of the water column along two ～13,500 km transects between ～50°N and ～52°S during the Atlantic Meridional Transect (AMT) programme (AMT cruises 12 and 13). Vertical N2O profiles were amenable to analysis on the basis of common features coincident with Longhurst provinces. In contrast, CH4 showed no such pattern. The most striking feature of the latitudinal depth distributions was a well-defined “plume” of exceptionally high N2O concentrations coincident with very low levels of CH4, located between ～23.5°N and ～23.5°S; this feature reflects the upwelling of deep waters containing N2O derived from nitrification, as identified by an analysis of N2O, apparent oxygen utilization (AOU) and NO3?, and presumably depleted in CH4 by bacterial oxidation. Sea-to-air emissions fluxes for a region equivalent to ～42% of the Atlantic Ocean surface area were in the range 0.40–0.68 Tg N2O yr?1 and 0.81–1.43 Tg CH4 yr?1. Based on contemporary estimates of the global ocean source strengths of atmospheric N2O and CH4, the Atlantic Ocean could account for ～6–15% and 4–13%, respectively, of these source totals. Given that the Atlantic Ocean accounts for around 20% of the global ocean surface, on unit area basis it appears that the Atlantic may be a slightly weaker source of atmospheric N2O than other ocean regions but it could make a somewhat larger contribution to marine-derived atmospheric CH4 than previously thought. |
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