MICROFOSSIL AND STABLE-ISOTOPE EVIDENCE FOR CHANGES IN LATE HOLOCENE PALAEOPRODUCTIVITY AND PALAEOCEANOGRAPHIC CONDITIONS IN THE PRYDZ BAY-REGION OF ANTARCTICA

Microfaunal and microfloral data from two gravity cores, and stable-is otope results from one of these cores taken on Fram Bank near Prydz Ba y, Antarctica indicate changes in sea-ice patterns and oceanographic c onditions which may have been linked to regional and global climate ch anges that occurred over the past 8000 yr. Modern diatom assemblages i ndicative of ice free conditions 1-2 months of the year, and dominated by Nitzschia species became prevalent some time around 2000-2700yr B. P. The occurrence of Chaetoceros spp. diatom spore-dominated assemblag es, and increased abundances of benthic and planktonic foraminifera, o stracods, and diatoms, coupled with carbon-and oxygen-isotope changes around 2700-3400 yr B.P. strongly suggests that this area of the shelf experienced conditions conducive to increased productivity during thi s time period. Based on diatom assemblage associations recognized in m odern environments, the upper water column of Fram Bank shelf waters w as probably stratified during that time due to the presence of low-sal inity melt water and a very shallow mixed layer, protected from storms , with sea-ice cover for less than 10 months per year. The close corre spondence of delta(13)C and delta(18)O values from N. pachyderma (r(2) =0.74) throughout one core suggests that whatever oceanographic condit ions influenced delta(18)O also influenced delta(13)C. Changes in Pryd z Bay microfossil abundances and isotopes may result from alterations in circulation patterns, upwelling conditions, or sea-ice patterns whi ch significantly affected benthic and planktonic productivity in the a rea. The environmental conditions indicated by older sediments in the cores are less clear, but an ice tongue may have been in place 3200-38 00 yr B.P., and minor fluctuations in productivity are indicated aroun d 6000 and 7000-7500 Sir B.P. The lower 100 cm of both cores may not r epresent in situ deposition, but if the corrected AMS dates reflect th e actual age of the sediments analysed, microfossil and isotope data i ndicate that productivity, and oceanographic conditions were very vari able around 8500-8600 yr B.P. The chronology adopted herein must be re garded as tentative until further study of the area has been undertake n. (C) 1997 Elsevier Science B.V.