Benthic community response to seasonal variations in the pelagic-benthic coupling: In situ high-resolution studies of the benthic oxygen uptake in Arctic deep-sea sediments

Frank Wenzhofer, Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Bremerhaven, HGF-MPG Group for Deep Sea Ecology and Technology, Bremerhaven, Germany, Eva-Maria Nothig, Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Bremerhaven, Germany, Autun Purser, Alfred-Wegener-Institute Helmholtz-Centrum for Polar and Marine Research, Germany, Melanie Bergmann, Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Bremerhaven, Bremerhaven, Germany and Thomas Soltwedel, Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research, Bremerhaven, Germany
Polar regions play a central role within the global carbon cycle. Rapidly changing physical and chemical conditions, as currently observed and predicted to continue into the future, will affect numerous aspects of ecosystem functioning, including productivity, remineralisation, and energy flow between ecosystem compartments. Benthic communities in the deep-sea depend entirely on the supply of organic matter from the surface. A large fraction of the annual carbon deposition to the seafloor can arrive in substantial pulses following surface phytoplankton blooms. However, how the Arctic deep-sea community structure and activity respond to these seasonal variations is not yet known. A critical research gap is also the balance between food supply and demand of the benthic community.

Here we present the first seasonal study on in situ benthic oxygen consumption of the Arctic seafloor in relation to particle fluxes and data on fauna community structure derived from time series seafloor imagery. Weekly measurements of the sediment oxygen uptake rates between summer 2017 and 2018 at the LTER deep-sea observatory HAUSGARTEN were used as a proxy for organic carbon mineralization, with sinking POC flux used to estimate the food supply to the sea floor. Benthic oxygen consumption doubled in May following a spring bloom in surface waters. This elevated activity coincided with the advent of fluffy material on the seafloor. A higher abundance of benthic fauna was observed after a time lag of a few days. High-resolution measurements of benthic oxygen consumption are crucial to achieve a better understanding of the marine carbon cycle and to improve evaluations of the impact of climate change on these remote ecosystems. This study is part of the Arctic long-term observatory FRAM (Frontiers of Arctic Marine Monitoring).