Lack of detectable chemosynthesis at a sponge dominated subarctic methane seep

Type Article
Date 2023-07
Language English
Author(s) Sinner Melina1, 2, 3, Li Hong Wei4, Michel LoïcORCID5, Vadakkepuliyambatta Sunil6, Knies Jochen7, 8, Sen Arunima9, 10
Affiliation(s) 1 : National Oceanography Center, University of Southampton, Southampton, United Kingdom
2 : Plentzia Marine Station, University of the Basque Country, Plentzia, Spain
3 : Faculty of Sciences, University of Liège, Liège, Belgium
4 : Department of Geological Sciences, Stockholm University, Stockholm, Sweden
5 : Centre national de la recherche scientifique (CNRS), Ifremer, UMR6197 BEEP (Biologie et Ecologie des Ecosystèmes marins Profonds), University Brest, Plouzané, France
6 : National Centre for Polar and Ocean Research (NCPOR), Ministry of Earth Sciences, Government of India, Vasco-da-Gama, Goa, India
7 : Geological Survey of Norway, Trondheim, Norway
8 : iC3: The Centre for ice, Cryosphere, Carbon, and Climate, The Department of Geosciences, UiT The Arctic University of Norway, Tromsø, Norway
9 : Department of Arctic Biology, The University Centre in Svalbard, Longyearbyen, Norway
10 : Department of Bioscience and Aquaculture, Nord University, Bodø, Norway
Source Frontiers In Earth Science (2296-6463) (Frontiers Media SA), 2023-07 , Vol. 11 , P. 1203998 (25p.)
DOI 10.3389/feart.2023.1203998
Keyword(s) seepage, GIS, imagery, megafauna, chemosynthesis, marine litter, benthos, sulfide
Abstract

We used high-resolution imagery within a Geographic Information System (GIS), free gas and porewater analyses and animal bulk stable isotope measurements to characterize the biotic and abiotic aspects of the newly discovered Vestbrona Carbonate Field (VCF) seep site on the Norwegian shelf (63°28′N, 6° 31′E, ∿270 m water depth). Free gas was mainly composed of microbial methane. Sediment porewater sulfide concentrations were in the millimolar range and thus high enough to sustain seep chemosymbiotrophic animals. Nonetheless, the VCF lacked chemosymbiotrophic animals despite an abundance of methane-derived carbonate crusts which are formed by the same anaerobic processes that sustain chemosymbiotrophic animals at seeps. Furthermore, none of the sampled taxa, across various trophic guilds exhibited a detectable contribution of chemosynthetically fixed carbon to their diets based on bulk stable isotope values, suggesting a predominantly photosynthetic source of carbon to the VCF seep food web. We link the absence of chemosymbiotrophic animals to highly localized methane flow pathways, which may act as a “shunt-bypass” of the anaerobic oxidation of methane (AOM) and by extension sulfide generation, thus leading to sediment sulfide concentrations that are highly heterogeneous over very short lateral distances, inhibiting the successful colonization of chemosymbiotrophic animals at the VCF seep. Instead, the seep hosted diverse biological communities, consisting of heterotrophic benthic fauna, including long lived taxa, such as soft corals (e.g., Paragorgia arborea) and stony corals (i.e., Desmophyllum pertusum, formerly known as Lophelia pertusa). Compared to the surrounding non-seep seafloor, we measured heightened megafaunal density at the seep, which we attribute to increased habitat heterogeneity and the presence of a variety of hard substrates (i.e., methane-derived authigenic carbonates, dropstones and coral rubble), particularly since the most abundant taxa all belonged to the phylum Porifera. Compared to the surrounding non-seep seafloor, marine litter was denser within the VCF seep, which we link to the more variable local topography due to authigenic carbonates, which can rip off parts of bottom trawling nets thereby making the seep act as catchment area for marine litter.

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