Riddles in the cold: Antarctic endemism and microbial succession impact methane cycling in the Southern Ocean

Abstract

Antarctica is estimated to contain as much as a quarter of earth's marine methane, however we have not discovered an active Antarctic methane seep limiting our understanding of the methane cycle. In 2011, an expansive (70 m × 1 m) microbial mat formed at 10 m water depth in the Ross Sea, Antarctica which we identify here to be a high latitude hydrogen sulfide and methane seep. Through 16S rRNA gene analysis on samples collected 1 year and 5 years after the methane seep formed, we identify the taxa involved in the Antarctic methane cycle and quantify the response rate of the microbial community to a novel input of methane. One year after the seep formed, ANaerobic MEthane oxidizing archaea (ANME), the dominant sink of methane globally, were absent. Five years later, ANME were found to make up to 4% of the microbial community, however the dominant member of this group observed (ANME-1) were unexpected considering the cold temperature (−1.8°C) and high sulfate concentrations (greater than 24 mM) present at this site. Additionally, the microbial community had not yet formed a sufficient filter to mitigate the release of methane from the sediment; methane flux from the sediment was still significant at 3.1 mmol CH 4 m −2 d −1 . We hypothesize that this 5 year time point represents an early successional stage of the microbiota in response to methane input. This study provides the first report of the evolution of a seep system from a non-seep environment, and reveals that the rate of microbial succession may have an unrealized impact on greenhouse gas emission from marine methane reservoirs.

Biogeography of Southern Ocean prokaryotes: a comparison of the Indian and Pacific sectors

“…Despite being persistently cold and having little to no sunlight in the winter, considerable areas of the Southern Ocean (SO) are biologically productive regions that play central roles in nutrient recirculation, supporting primary production across global ocean scales and mediating CO 2 exchange and sequestration via the biological pump (Álvarez et al ., 2002; Arrigo et al ., 2008; Lenton et al ., 2013; Legge et al ., 2015). The SO is also an important region for recirculation of climate active trace gasses such as dimethyl sulfoxide and methane (Curran and Jones, 2000; Gabric et al ., 2001; Wadham et al ., 2012; Thurber et al ., 2020). Prokaryotes (domain Bacteria and Archaea ) make up the largest proportion of microbial biomass in open SO waters and are primary drivers of biogeochemical cycling (Wilkins et al ., 2013b).…”

Antarctic ecosystems in transition – life between stresses and opportunities

“…Below the former Larsen B ice shelf, a low-activity seep (Niemann et al, 2009) with a seep-specific nematode fauna (Hauquier et al, 2011) was observed and analysed, while a small patch of bacteria occurred on the sediment at a different location (Gutt et al, 2011). In the Ross Sea at 10 m water depth a bacterial mat, based on a hydrogen sulfide and methane seep was discovered, and may have an impact on greenhouse gas emission from marine methane reservoirs (Thurber, Seabrook & Welsh, 2020). On land, geothermally active regions allow species to survive in isolation on ice-free land or in sub-ice caves, from which recolonisation of the rest of the continent could have taken place (Fraser et al, 2014).…”

Climate’s role in Earth’s shifting spheres

“…The Arctic sea ice and methane triggers and positive feedbacks were explained. There are signs the methane feedback has started, as recently methane has been found to be bubbling from the floor of the Ross Sea in the Antarctic (Thurber et al, 2020). The boreal forest situation is different.…”