DEEP ACCESS TO THE LARSEN ICE SHELF-B EMBAYMENT: AN INTERNATIONAL GEOLOGIC AND GEOPHYSICAL EXPEDITION (NB PALMER 2006-3)

During April to May 2006, marine geologic and geophysical work was conducted in the embayment formerly occupied by the Larsen B ice shelf, adding to observations and data collected during a February to March 2005 field season (LMG0502) in the same region. Access to this region has only been possible since catastrophic ice shelf collapse in 2002. Major accomplishments of cruise NBP0603 include:

1. Multibeam swath mapping was used to construct a bathymetric map of the trough in which a cold seep chemosynthetic community was discovered during LMG0502. Subsurface geology was analyzed using both a 3.5 kHz chirp system and single channel seismic survey and a 75 cm kasten core was recovered from the region. These data provide a geologic context for the cold seep site and a framework for continued exploration.

2. Rapid retreat of glaciers following ice shelf collapse, as predicted, is exemplified by the formation of a new fjord, Spillane Fjord, formed as the Crane Glacier retreated. At its outer reach, the previous grounding zone is delimited, a platform between 300 to 700 meters water depth, characterized by morainal features. The innermost part of the fjord reaches depths > 1200 meters; landward slopes indicate that greater water depths exist under the floating ice. This deep trough must have been carved during a previous period of expanded glaciation. Single channel seismic data record > 70 meters of basin fill. A 270 cm kasten core recovered from the deepest part of the trough, documents recent open marine turbiditic sedimentation. A suite of CTD stations along the axis of the trough reveals the presence of a subsurface cold water plume associated with low transmissivity and increased concentration of suspended particulate debris.

3. Multi-proxy data from kasten cores collected from the Larsen B embayment confirm that the recent collapse of the ice shelf is unprecedented through the Holocene. Sub ice shelf versus open marine sediments can be distinguished based on a sedimentologic, geochemical and micropaleontologic data.