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

• Published in: Biogeosciences Vol. 17; no. 1; pp. 1 - 12
• Main Authors: Woulds, Clare, Bell, James B, Glover, Adrian G, Bouillon, Steven, Brown, Louise S
• Format: Journal Article
• Language: English
• Published: Katlenburg-Lindau Copernicus GmbH 02-01-2020; Copernicus Publications
• Subjects: Algae; Bacteria; Benthic environment; Benthos; Bicarbonates; Carbon; Carbon 13; Carbon cycle; Carbon fixation; Carbonates; Comparative analysis; Detritus; Ecosystems; Fate; Hydrothermal plumes; Hydrothermal springs; Hydrothermal systems (Geology); Hydrothermal vent ecosystems; Hydrothermal vents; Inorganic carbon; Isotopes; Macrofauna; Microbial activity; Microorganisms; Ocean floor; Photosynthesis; Respiration; Sediments; Sediments (Geology); Substrates; Uptake; Vents; Zoobenthos; Antarctica; Bransfield Strait
• ISSN: 1726-4189; 1726-4170; 1726-4189
• DOI: 10.5194/bg-17-1-2020

Sedimented hydrothermal vents are likely to be widespread compared to hard
substrate hot vents. They host chemosynthetic microbial communities which
fix inorganic carbon (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 three 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 hot spot of benthic C cycling that we hypothesised it would be. Fixation
of inorganic C into bacterial biomass was observed at all sites, and was
measurable at two out of three sites. At all sites, newly fixed C was transferred
to metazoan macrofauna. Fixation rates were relatively low compared with
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.