Articles | Volume 15, issue 16
Research article
16 Aug 2018
Research article |  | 16 Aug 2018

Deep-sea benthic communities and oxygen fluxes in the Arctic Fram Strait controlled by sea-ice cover and water depth

Ralf Hoffmann, Ulrike Braeckman, Christiane Hasemann, and Frank Wenzhöfer

Abstract. Arctic Ocean surface sea-ice conditions are linked with the deep sea benthic oxygen fluxes via a cascade of interdependencies across ecosystem components such as primary production, food supply, activity of the benthic community, and their functions. Additionally, each ecosystem component is influenced by abiotic factors such as light availability, temperature, water depth, and grain size structure. In this study, we investigated the coupling between surface sea-ice conditions and deep-sea benthic remineralization processes through a cascade of interdependencies in the Fram Strait. We measured sea-ice concentrations, a variety of different sediment characteristics, benthic community parameters, and oxygen fluxes at 12 stations of the LTER HAUSGARTEN observatory, Fram Strait, at water depths of 275–2500 m. Our investigations reveal that the Fram Strait is bisected into two long-lasting and stable regions: (i) a permanently and highly sea-ice-covered area and (ii) a seasonally and low sea-ice-covered area. Within the Fram Strait ecosystem, sea-ice concentration and water depth are two independent abiotic factors, controlling the deep-sea benthos. Sea-ice concentration correlated with the available food and water depth with the oxygen flux. In addition, both abiotic factors sea-ice concentration and water depth correlate with the macrofauna biomass. However, at water depths > 1500 m the influence of the surface sea-ice cover is minimal with water depth becoming more dominant. Benthic remineralization across the Fram Strait on average is  ∼ 1 mmol C m−2 d−1. Our data indicate that the portion of newly produced carbon that is remineralized by the benthos is 5 % in the seasonally low sea-ice-covered eastern part of Fram Strait but can be 14 % in the permanently high sea-ice-covered western part of Fram Strait. Here, by comparing a permanently sea-ice-covered area with a seasonally sea-ice-covered area, we discuss a potential scenario for the deep-sea benthic ecosystem in the future Arctic Ocean, in which an increased surface primary production may lead to increasing benthic remineralization at water depths < 1500 m.

Short summary
Our study links surface sea-ice cover and benthic oxygen fluxes in the Fram Strait via primary production, food supply, benthic community, and their functions. We show that sea-ice cover and water depth are the most important factors influencing the ecosystem. However, in water depths > 1500 m, the effect of sea ice fades out. Further, we discuss primary production and benthic remineralization patterns and developed a potential scenario for the benthic remineralization in a future Arctic Ocean.
Final-revised paper