First evidence of widespread active methane seepage in the Southern Ocean, off the sub-Antarctic island of South Georgia

Abstract

25A new extensive submarine cold-seep area was discovered on the northern shelf of South Georgia during R/V Polarstern cruise ANT-XXIX/4 in spring 2013. Hydroacoustic surveys and video-based sea floor observations documented the presence of 133 individual gas bubble emissions, which were restricted to glacially-formed fjords and troughs. Effective methane transport from these emissions into the hydrosphere was proven by relative enrichments of dissolved methane in near-bottom 30 waters. Stable carbon isotopic signatures of the methane pointed to a predominant microbial origin.Although known from many continental margins in the world's oceans, this is the first report of an active area of methane seepage in the Southern Ocean. Our finding of substantial methane emission related to a trough and fjord system, a topographical setting that exists commonly in glaciallyaffected areas, opens up the possibility that methane seepage is a more widespread phenomenon in 35 polar and sub-polar regions than previously thought.

Multiple gas reservoirs are responsible for the gas emissions along the Marmara fault network

“…Intensive gas emissions are common and widespread processes in oceanic and continental marine basins. Amongst the areas on Earth where they have been densely observed, one can cite offshore Siberia (Shakhova et al, 2014), the Norwegian continental margin including the well-studied Hakon Mosby Mud Volcano (Gentz et al, 2014;Sauer et al, 2015;Westbrook et al, 2009), the North Sea (Borges et al, 2016;McGinnis et al, 2011;von Deimling et al, 2011), the Black Sea (Klaucke et al, 2006;Roemer et al, 2012a), the Sea of Marmara (Dupré et al, 2012;Dupré et al, 2010a), the Aquitaine Shelf (Dupré et al, 2014;Ruffine et al, 2017), the Central Nile Deep-Sea Fan (Dupré et al, 2010b;Roemer et al, 2014a), the US Atlantic Margin (Skarke et al, 2014;Weinstein et al, 2016), the Gulf of Mexico (Bernard et al, 1976;Hu et al, 2012), the Santa Barbara Basin (Clark et al, 2010), the Hydrate Ridge (Haeckel et al, 2004;Milkov et al, 2005;Philip et al, 2016), the Makran continental margin (Roemer et al, 2012b), the South China Sea (Di et al, 2014;Huang et al, 2009), the Japan Sea (Aoyama et al, 2007), as well as offshore New Zealand (Greinert et al, 2010) and the Southern Ocean (Roemer et al, 2014b). Such phenomena occur either as dissolved or free gases, and they lead to the formation of specific sites called cold seeps (Hovland and Judd, 1988;Suess, 2014;Talukder, 2012).…”

A quantitative assessment of methane cycling in Hikurangi Margin sediments (New Zealand) using geophysical imaging and biogeochemical modeling

“…Gas bubble rise is a particularly effective mechanism for transporting methane through the sediment and into the bottom water because gas ascension can be much faster than bubble dissolution [ Haeckel et al ., ] and methane gas cannot directly be consumed by microorganisms [ Boetius and Suess , ; Sommer et al ., ]. Many estimates of methane fluxes at the sediment surface in dissolved and gaseous form have been made in diverse locations [ Tryon and Brown , ; Leifer and MacDonald , ; Luff and Wallmann , ; Linke et al ., ; Wallmann et al ., ; Sahling et al ., ; Greinert et al ., ; Römer et al ., ; Gentz et al ., ; Geprägs et al ., ]. However, studies reporting the areal methane efflux across individual methane seep systems are rare, and are often calculated as the product of the estimated area of the seep site and the average methane flux derived from single or multiple sediment cores [e.g., Karaca et al ., ; Römer et al ., ; Smith et al ., ].…”

Carbon cycling fed by methane seepage at the shallow Cumberland Bay, South Georgia, sub‐Antarctic

“…Methane release from permafrost [Christensen, 2004;Schuur and Bockheim, 2008], gas hydrate dissociation [Jung and Vogt, 2004;Mienert et al, 2005], and sea ice melting [Walter et al, 2006;Damm et al, 2015] have all been put forward as possible factors that might accelerate methane release to the atmosphere. Most of these high-latitude studies have been conducted in the Arctic, and so far only little is known about methane dynamics in the Southern Ocean [Heeschen et al, 2004;R€ omer et al, 2014a].…”