Cold Seeps in a Warming Arctic: Insights for Benthic Ecology

Abstract

Cold-seep benthic communities in the Arctic exist at the nexus of two extreme environments; one reflecting the harsh physical extremes of the Arctic environment and another reflecting the chemical extremes and strong environmental gradients associated with seafloor seepage of methane and toxic sulfide-enriched sediments. Recent ecological investigations of cold seeps at numerous locations on the margins of the Arctic Ocean basin reveal that seabed seepage of reduced gas and fluids strongly influence benthic communities and associated marine ecosystems. These Arctic seep communities are mostly different from both conventional Arctic benthic communities as well as cold-seep systems elsewhere in the world. They are characterized by a lack of large specialized chemo-obligate polychetes and mollusks often seen at non-Arctic seeps, but, nonetheless, have substantially higher benthic abundance and biomass compared to adjacent Arctic areas lacking seeps. Arctic seep communities are dominated by expansive tufts or meadows of siboglinid polychetes, which can reach densities up to >3 × 10 5 ind.m −2. The enhanced autochthonous chemosynthetic production, combined with reef-like structures from methane-derived authigenic carbonates, provides a rich and complex local habitat that results in aggregations of non-seep specialized fauna from multiple trophic levels, including several commercial species. Cold seeps are far more widespread in the Arctic than thought even a few years ago. They exhibit in situ benthic chemosynthetic production cycles that operate on different spatial and temporal cycles than the sunlight-driven counterpart of photosynthetic production in the ocean's surface. These systems can act as a spatio-temporal bridge for benthic communities and associated ecosystems that may otherwise suffer from a lack of consistency in food quality from the surface ocean during seasons of low production. As climate change impacts accelerate in Arctic marginal seas, photosynthetic primary production cycles are being modified, including in terms of changes in the timing, magnitude, and quality of photosynthetic carbon, whose delivery to the seabed fuels benthic communities. Furthermore, an increased northward expansion of species is expected as a consequence of warming seas. This may have implications for dispersal and evolution of both chemosymbiotic species as well as for background taxa in the entire realm of the Arctic Ocean basin and fringing seas.

A chemosynthetic ecotone—“chemotone”—in the sediments surrounding deep‐sea methane seeps

“…That a distinct chemotone fauna, potentially with habitat endemic species, appears to surround methane seeps reaffirms this perception. Seeps are also associated with the provision of a number of valuable ecosystem services, including carbon sequestration through the production of authigenic carbonates, biogeochemical cycling, habitat provision to commercially important species, and bioprospecting potential (Boetius and Wenzhöfer 2013; Levin et al 2016; Åström et al 2020). However, seep habitats are under increasing direct and indirect pressure from current and projected anthropogenic activities including fishing (German et al 2011; Bowden et al 2013), oil and gas extraction (German et al 2011; Cordes et al 2016), mining, and climate change (Levin and Le Bris 2015; Sweetman et al 2017).…”

“…Deep-sea methane seeps are physiologically stressful environments, yet host highly productive communities that are fueled predominantly by chemical energy via chemosynthesis (Levin 2005;Demopoulos et al 2010;Levin et al 2016;Åström et al 2018). They are patchily distributed along continental margins worldwide and are associated with the provision of a number of ecosystem services of global significance, including carbon sequestration through the production of authigenic carbonates, high rates of biogeochemical cycling, habitat provision to commercially important species, and bioprospecting potential (Boetius and Wenzhöfer 2013;Levin et al 2016;Åström et al 2020). Levin et al (2016) proposed that the biological and chemical influence of methane seeps extends out vertically and horizontally from the seep center into the overlying water column and down into underlying sediments to form a "sphere of influence" (Fig.…”

Effectiveness of Fluorescent Viability Assays in Studies of Arctic Cold Seep Foraminifera

“…This observation suggests that "inhospitable" conditions are temporary variations rather than permanent constraints. Instability/variability of the environment can be related to the ephemeral nature of methane seeps, which are strongly dependent on methane flux (Levin, 2005;Åström et al, 2020). As shown by Yao et al (2019), the Lomvi (MC893) and Lunde (MC886) pockmarks are characterized by two different types of methane transport: advective and dominated by methane diffusion (Lomvi and Lunde, respectively).…”

“…The combined usage of the fluorogenic probes together with the Rose Bengal staining can be used to separate live foraminifera from recently dead individuals, and thus be a useful tool to build up a more detailed picture of benthic foraminiferal distribution patterns and ecology. It might be especially useful in studies of heterogeneous and variable environments such as cold seeps, which depend on the highly variable flux of methane and can evolve and change rapidly over time (Levin, 2005;Cordes et al, 2006;Åström et al, 2020).…”

Methane-Derived Authigenic Carbonates on the Seafloor of the Laptev Sea Shelf

“…To date, many studies have investigated various aspects of authigenic carbonate mineralization and overall methane seepage system functioning. These studies have been reviewed in several papers (Lein, 2004;Judd and Hovland, 2007;Roberts and Feng, 2013;Suess, 2014;Levin et al, 2016;Åström et al, 2020).…”