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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 07 Jun 2019

Research article | 07 Jun 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

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

Clare Woulds1, James B. Bell1,2, Adrian G. Glover3, Steven Bouillon4, and Louise S. Brown1,2 Clare Woulds et al.
  • 1water@leeds, School of Geography, University of Leeds, Leeds, LS2 9JT, UK
  • 2Cefas, Pakefield Road, Lowestoft, Suffolk, NR33 0HT, UK
  • 3Life Sciences Dept., Natural History Museum, Cromwell Rd, London SW7 5BD, UK
  • 4Department of Earth and Environmental Sciences, KU Leuven, Leuven, Belgium

Abstract. 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 13C isotope tracing experiments at 3 sedimented sites in the Bransfield Strait, Antarctica, which showed different degrees of hydrothermalism. Two experimental treatments were applied, with 13C added as either algal detritus (photosynthetic C), or as bicarbonate (substrate for benthic C fixation).

Algal 13C 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 13C 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.

Clare Woulds et al.
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Clare Woulds et al.
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Short summary
Sedimented hydrothermal vents occur where heated, mineral rich (hydrothermal) water seeps through seafloor sediments. They host chemosynthetic microbes, which use chemical energy to fix dissolved carbon dioxide into sugars (chemosynthesis). We conducted carbon tracing experiments, and observed chemosynthesis at both vent and non-vent sites. Thus, chemosynthesis occurred over a much larger area of than expected, suggesting it is more widespread than previously thought.
Sedimented hydrothermal vents occur where heated, mineral rich (hydrothermal) water seeps...