RECENT BENTHIC FORAMINIFERAL DISTRIBUTIONS ASSOCIATED WITH THE COLLAPSE OF THE LARSEN-B ICE SHELF

During the austral summer of 2001-02 marine sediment cores and surface sediment samples were collected along a transect extending from the front of the Larsen-B Ice Shelf, eastern Antarctic Peninsula. The sampling transect represents a gradient from ice shelf edge to ice distal facies. Foraminiferal analyses of the surface samples indicate three separate biofacies occurring along the transect; calcareous ice shelf edge, calcareous basin and agglutinated ice distal biofacies.

The calcareous ice shelf edge biofacies is dominated by calcareous benthic foraminifera and is characterized by Angulogerina earlandi, Cibicides lobatulus, Epistominella exigua, Ehrenbergina glabra and Globocassidulina subglobosa. Associated with this benthic assemblage are high numbers of planktonic foraminiferal tests that are dominated by Neogloboquadrina pachyderma. Agglutinated foraminifera are present but in low numbers and include Cystammina argentea. The calcareous basin biofacies also is dominated by calcareous benthic taxa. The assemblage that characterizes this biofacies includes Astrononion echolsi, Cassidulina carinata, Eponides tumidulus, Nonionella iridea and Stainforthia davisi. Although present, the planktonic foraminifers Neogloboquadrina pachyderma and Globigerina bulloides occur in lower abundances than are represented in the calcareous ice edge biofacies. Agglutinated foraminifera are present in low abundances represented by Labrospira jeffreysii and Portatrochammina antarctica. The agglutinated ice distal biofacies is dominated by agglutinated foraminifera that include Adercotryma glomeratum, Conotrochammina bullata, Cystammina argentea, Labrospira jeffreysii, Portatrochammina antarctica and Textularia weisneri. The foraminifera associated with this biofacies contain no calcareous forms.

The modern foraminiferal biofacies patterns identified along the ice shelf to ice distal gradient will be used to analyze downcore benthic foraminiferal changes to interpret temporal changes in the Larsen-B Ice Shelf. These results, in combination with forthcoming diatom, sedimentological, and geochemical analyses will provide a greater knowledge of processes related to ice shelf collapse and their application to interpreting the Holocene record.