SHIFTING FORAMINIFERAL BIOFACIES AND STABLE ISOTOPES INDICATING SIGNIFICANT HOLOCENE OCEAN-ICE DYNAMICS, WESTERN ANTARCTIC PENINSULA

Foraminiferal analyses were conducted on samples collected from two sediment cores recovered from the western margin of the Antarctic Peninsula (WAP) during cruise NBP10-01 of the R/V Nathaniel B. Palmer. Kasten core KC 11 was collected from a mid-shelf location, the Hugo Island Trough, from approximately 636 m water depth. Jumbo piston core JPC 127 was collected from a coastal location, Barilari Bay, from approximately 653 m water depth. The cores extend into the Holocene approximately 11000 yBP and 8000 yBP, respectively. Calcareous benthic foraminifera dominate the foramininferal assemblages with the major taxa including Bulimina aculeata, Fursenkoina spp., Bolivina pseudopunctata and Nonionella iridea. Variation in the abundances of these major taxa result in downcore fluctuations illustrated in the principal component analyses.

In KC 11 three principal components account for ~83% of the variance in the data and represent the following: PC1is the Bulimina aculeata dominated assemblage; PC2 is the Fursenkoina spp. dominated assemblage; and PC3 is the Bolivina pseudopunctata dominated assemblage. In JPC 127 two principal components account for 89% of the variance in the data: PC1is the Fursenkoina spp. assemblage; and PC2 is the Bulimina aculeata assemblage. The B. aculeataassemblage, associated with the presence of Upper Circumpolar Deep Water (UCDW), appears on the WAP shelf in the early mid-Holocene, with its presence in Barilari Bay not occurring until the mid-Holocene.

Foraminiferal stable isotopic analyses support the foraminiferal assemblage data. In KC 11, the early Holocene Neogloboquadrina pachyderma and benthic d¹⁸O are positive, relative to core-top values, indicating greater global ice volume. Beginning ~10000 yBP, N. pachyderma and several benthic taxa d¹⁸O exhibit negative excursions of a few tenths of a per mille to ~8500 yBP. N. pachyderma and B. aculeata d¹⁸O remain relatively constant from ~8000 yBP to present. The core-top planktic-benthic d¹³C contrast in KC 11 indicates a change in oceanographic conditions occurring ~6500 yBP with a little contrast to ~8500 yBP. This is preceded by planktic and benthic d¹³C fluctuating significantly from the base of the core.