Abstract
Concentrations and flux densities of methane were determined during a Lagrangian study of an advective filament in the permanent upwelling region off western Mauritania. Newly upwelled waters were dominated by the presence of North Atlantic Central Water and surface CH4 concentrations of 2.2±0.3nmolL−1 were largely in equilibrium with atmospheric values, with surface saturations of 101.7±14%. As the upwelling filament aged and was advected offshore, CH4 enriched South Atlantic Central Water from intermediate depths of 100–350m was entrained into the surface mixed layer of the filament following intense mixing associated with the shelf break. Surface saturations increased to 198.9±15% and flux densities increased from a mean value over the shelf of 2.0±1.1μmolm−2d−1 to a maximum of 22.6μmolm−2d−1. Annual CH4 emissions for this persistent filament were estimated at 0.77±0.64Gg which equates to a maximum of 0.35% of the global oceanic budget. This raises the known outgassing intensity of this area and highlights the importance of advecting filaments from upwelling waters as efficient vehicles for air-sea exchange.
Highlights
IntroductionPlays an important role in the Earth’s climate
Methane (CH4) is the most abundant trace organic gas in the environment [Wuebbles and Hayhoe, 2002]and plays an important role in the Earth’s climate
Upwelling waters north of ~20°N are mainly influenced by North Atlantic Central Water (NACW) while the area south of 20°N is dominated by South Atlantic Central Water (SACW) which is generally cooler, fresher and has a higher nutrient and lower oxygen content than that of NACW [Minas, et al, 1982]
Summary
Plays an important role in the Earth’s climate. The world’s oceans are a natural source of CH4 but play only a minor role in its global atmospheric budget [Wuebbles and Hayhoe, 2002], contributing up to 10% of the global atmospheric emissions [Grunwald, et al, 2009]. Coastal environments including estuaries are thought to account for approximately 75% of the marine source [Bange, et al, 1994] and coastal upwelling areas have been shown to be rich source areas [Kock, et al, 2008; Monteiro, et al, 2006; Owens, et al, 1991]. Methanogenesis is an anaerobic process, which in oceanic waters is thought to occur either in oxygen deplete waters or in anoxic micro-environments that are associated with zooplankton guts and particulate material [Bianchi, et al, 1992; Marty et al, 1997; Brooks, et al, 1981].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
