Resumen:
First videographic indication of an Antarctic cold
seep ecosystem was recently obtained from the collapsed
Larsen B ice shelf, western Weddell Sea (Domack et al.,
2005). Within the framework of the R/V Polarstern expedition
ANTXXIII-8, we revisited this area for geochemical,
microbiological and further videographical examinations.
During two dives with ROV Cherokee (MARUM, Bremen),
several bivalve shell agglomerations of the seep-associated,
chemosynthetic clam Calyptogena sp. were found in the
trough of the Crane and Evans glacier. The absence of living
clam specimens indicates that the flux of sulphide and
hence the seepage activity is diminished at present. This impression
was further substantiated by our geochemical observations.
Concentrations of thermogenic methane were moderately
elevated with 2μM in surface sediments of a clam
patch, increasing up to 9μM at a sediment depth of about
1m in the bottom sections of the sediment cores. This correlated
with a moderate decrease in sulphate from about 28mM
at the surface down to 23.4 mM, an increase in sulphide to up
to 1.43mM and elevated rates of the anaerobic oxidation of
methane (AOM) of up to 600 pmol cm−3 d−1 at about 1m
below the seafloor. Molecular analyses indicate that methanotrophic
archaea related to ANME-3 are the most likely candidates
mediating AOM in sediments of the Larsen B seep.
Descripción:
This study was conducted within the framework
of the Research Center/Cluster of Excellence MARUM
“The Ocean in the Earth System” (funded by the Deutsche
Forschungsgemeinschaft – DFG) as well as the Census of Marine
Life projects Census for Antarctic Marine Life (CAML) and
Chemosynthetic Ecosystem Science (CHESS). We thank captain,
crew and shipboard scientists of R/V Polarstern cruise ANTXXIII-
8 for excellent support with work at sea. We thank J.-H. Lott and
E. Pugacheva from the Alfred Wegener Institute, Bremerhaven and
Vernadsky Institute of Geochemistry and Analytical Chemistry,
Moscow, respectively, for bathymetric measurements and georeferencing.
Furthermore, we thank W. Dimmler and H. Bohlmann
from FIELAX and ISITEC, Bremerhaven, respectively, for ROV
maintenance and operation as well as N. R¨odiger from the Max
Planck Institute for Marine Microbiology, Bremen for molecular
analyses. We would also like to express our special thanks to
E. Domack from the Hamilton College, New York for providing
the coordinates and video footage of seafloor observations made in
the Larsen B area during the US Antarctic Program cruise in March
2005. Further support was provided by the Helmholtz Association,
Max Planck Society and the University of Bremen.