Benthic-pelagic coupling in the Barents Sea: an integrated data-model framework

Abstract

The Barents Sea is experiencing long-term climate-driven changes, e.g. modification in oceanographic conditions and extensive sea ice loss, which can lead to large, yet unquantified disruptions to ecosystem functioning. This key region hosts a large fraction of Arctic primary productivity. However, processes governing benthic and pelagic coupling are not mechanistically understood, limiting our ability to predict the impacts of future perturbations. We combine field observations with a reaction-transport model approach to quantify organic matter (OM) processing and disentangle its drivers. Sedimentary OM reactivity patterns show no gradients relative to sea ice extent, being mostly driven by seafloor spatial heterogeneity. Burial of high reactivity, marine-derived OM is evident at sites influenced by Atlantic Water (AW), whereas low reactivity material is linked to terrestrial inputs on the central shelf. Degradation rates are mainly driven by aerobic respiration (40–75%), being greater at sites where highly reactive material is buried. Similarly, ammonium and phosphate fluxes are greater at those sites. The present-day AW-dominated shelf might represent the future scenario for the entire Barents Sea. Our results represent a baseline systematic understanding of seafloor geochemistry, allowing us to anticipate changes that could be imposed on the pan-Arctic in the future if climate-driven perturbations persist. This article is part of the theme issue ‘The changing Arctic Ocean: consequences for biological communities, biogeochemical processes and ecosystem functioning’.

Climate-driven benthic invertebrate activity and biogeochemical functioning across the Barents Sea polar front

“…To minimize the effect of non-climatic drivers of change, stations were selected with comparable water depths (200–400 m), sediment type and bottom fishing activity [69,70]. Bottom fishing activity was minimized by selecting locations that showed low levels of activity (based on VMS tracking data, visualized at: ) and we verified that there was no recent activity at the point of station occupancy using sediment surface imagery [71] and geochemical profiles [72,73].…”

The changing Arctic Ocean: consequences for biological communities, biogeochemical processes and ecosystem functioning

“…They find direct links between aerobic processes, reactive organic carbon and highest abundances of bacteria and archaea in the uppermost sediment layer followed by dominance of microbes involved in nitrate/nitrite and iron/manganese reduction across the oxic-anoxic redox boundary and sulphate reducers at depth. Using an original approach, Freitas et al [47] combine field observations from the Barents Sea with a Reaction-Transport model to quantify organic matter processing and its drivers. Their results indicate that, at sites influenced by Atlantic Water, there is a clear burial of highly reactive marine derived organic matter.…”

Advancing on large-scale trends of apparent organic matter reactivity in marine sediments and patterns of benthic carbon transformation

“…As such, it is likely that the majority of sediment load and OM are delivered during late fall and early winter flood events, and the diagenetic system close to the river mouth reaches a mature state during early spring when the typical porewater and benthic-pelagic fluxes have established. A surprisingly similar steady benthic cycling has been observed along a sea-sea-ice gradient at the Barents Sea shelf, which is a very seasonally dominated environment (Freitas et al, 2020). Thus, for the purpose of our investigations, we assume that on longer time/depth scales those sediments reach steady state and the limitations imposed should be minimal.…”

“…This pattern can be explained by the fact that highly reactive (i.e. low ) OM is predominantly degraded in the uppermost sediment layers, thus increasing the relative contribution of oxygen, if oxygen is the dominant electron acceptor at these sediment depths (Freitas et al, 2020;Glud, 2008). In contrast, a decrease in apparent reactivity leads to a higher burial of OM to sub-oxic or anoxic sediments (e.g., Meister et al, 2013).…”

“…Here, we do not consider the degradation pathways mediated by metal oxides due to a lack of SWI data that would allow constraining boundary conditions of metal oxides. While this might result in a slightly overrepresentation of sulfate reduction (e.g., at the Skagerrak; Canfield et al, 1993;Rysgaard et al, 2001), it has been demonstrated that metal oxide pathways represent a minor contribution to total OM heterotrophic degradation on a global scale (Freitas et al, 2020;Thullner et al, 2009), albeit in continental margin sediments iron hydroxide reduction may represents an important OM degradation pathway (Beckler et al, 2016).…”