HR: 12:05h
AN: C12B-08 INVITED     [Abstracts]
TI: Chemotrophic Ecosystem Beneath the Larsen Ice Shelf, Antarctica
AU: * Leventer, A
EM: aleventer@mail.colgate.edu
AF: Department of Geology, Colgate University, Hamilton, NY 13346 United States
AU: Domack, E
EM: edomack@hamilton.edu
AF: Department of Geosciences, Hamilton College, Clinton, NY 13323 United States
AU: Ishman, S
EM: sishman@geo.siu.edu
AF: Department of Geology, Southern Illinois University, Carbondale, IL 62901 United States
AU: Sylva, S
EM: ssylva@whoi.edu
AF: Woods Hole Oceanographic Institution, Mail Stop 4, Woods Hole, MA 02543 United States
AU: Willmott, V
EM: vwillmot@hamilton.edu
AF: Department of Geosciences, Hamilton College, Clinton, NY 13323 United States
AU: Huber, B
EM: bhuber@ldeo.columbia.edu
AF: Lamont Doherty Earth Observatory, 61 Route 9W, Palisades, NY 10964 United States
AU: Padman, L
EM: padman@esr.org
AF: Earth and Space Research, 3350 SW Cascade Ave., Corvallis, OR 97333 United States
AB: The first living chemotrophic ecosystem in the Southern Ocean was discovered in a region of the seafloor previously occupied by the Larsen-B Ice Shelf. A towed video survey documents an ecosystem characterized by a bottom-draping white mat that appears similar to mats of Begiattoa, hydrogen sulfide oxidizing bacteria, and bivalves, 20-30 cm large, similar to vesicomyid clams commonly found at cold seeps. The carbon source is unknown; three potential sources are hypothesized. First, thermogenically-produced methane may occur as the marine shales of this region are similar to hydrocarbon-bearing rocks to the north in Patagonia. The site occurs in an 850 m deep glacially eroded trough located along the contact between Mesozoic-Tertiary crystalline basement and Cretaceous-Tertiary marine rocks; decreased overburden could have induced upward fluid flow. Also possible is the dissociation of methane hydrates, a process that might have occurred as a result of warming oceanic bottom waters. This possibility will be discussed in light of the distribution of early diagenetic ikaite in the region. Third, the possibility of a biogenic methane source will be discussed. A microstratigraphic model for the features observed at the vent sites will be presented; the system is comprised of mud mounds with central vents and surrounding mud flow channels. A series of still image mosaics record the dynamic behavior of the system, which appears to demonstrate episodic venting. These images show the spatial relationship between more and less active sites, as reflected in the superposition of several episodes of mud flow activity and the formation of mud channels. In addition, detailed microscale features of the bathymetry of the site will be presented, placing the community within the context of glacial geomorphologic features. The Larsen-B Ice Shelf persisted through the entire Holocene, limiting carbon influx from a photosynthetic source. Tidal modeling of both pre and post breakup scenarios will be used to document oceanic circulation of the region, critical to an understanding of the role of advective processes. However, one consequence of recent ice shelf collapse is the increased downward flux of phytoplankton debris, as documented by the pockets of algal fluff observed at the sea floor and diatom counts that show a several order of magnitude increase in diatom concentration in the uppermost few cm of the sediment column. The consequences of this new source of carbon on the existing chemosynthetic community are yet to be realized, though already signs of benthic colonization are observed. Coupled to burial by dropstones, silt and clay released from glacial ice during the March 2002 ice shelf collapse, the future of this newly discovered ecosystem is uncertain. Finally, the broader implications of this discovery will be discussed, particularly with regard to the potential existence of similar ecosystems in other sub-ice settings.
DE: 4811 Chemosynthesis
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
DE: 9310 Antarctica (4207)
SC: Cryosphere [C]
MN: Fall Meeting 2005