Benthic C fixation and cycling in diffuse hydrothermal and background sediments in the Bransfield Strait, Antarctica

• Main Authors: Woulds, Clare, Bell, James B., Glover, Adrian G., Bouillon, Steven, Brown, Louise S.
• Format: Text
• Language: English
• Published: 2019
• Subjects: Bransfield Strait; Antarc*; Antarctica
• Online Access: https://doi.org/10.5194/bg-2019-198; https://www.biogeosciences-discuss.net/bg-2019-198/

Sedimented hydrothermal vents are likely to be widespread compared to hard substrate hot vents. They host chemosynthetic microbial communities which fix inorganic C at the seafloor, as well as a wide range of macroinfauna, including vent-obligate and background non-vent taxa. There are no previous direct observations of Carbon cycling at a sedimented hydrothermal vent. We conducted 13 C isotope tracing experiments at 3 sedimented sites in the Bransfield Strait, Antarctica, which showed different degrees of hydrothermalism. Two experimental treatments were applied, with 13 C added as either algal detritus (photosynthetic C), or as bicarbonate (substrate for benthic C fixation). Algal 13 C was taken up by both bacteria and metazoan macrofaunal, but its dominant fate was respiration, as observed at deeper and more food limited sites elsewhere. Rates of 13 C uptake and respiration suggested that the diffuse hydrothermal site was not the hotspot of benthic C-cycling that we hypothesised it would be. Fixation of inorganic C into bacterial biomass was observed at all, and was measurable at 2 out of 3 sites. At all sites, newly fixed C was transferred to metazoan macrofauna. Fixation rates were relatively low compared to similar experiments elsewhere, thus C fixed at the seafloor was a minor C source for the benthic ecosystem. However, as the greatest amount of benthic C fixation occurred at the off vent (non-hydrothermal) site (0.077 ± 0.034 mg C m −2 fixed during 60 h), we suggest that benthic fixation of inorganic C is more widespread than previously thought, and warrants further study.