RECORD OF HOLOCENE GLACIAL OSCILLATIONS IN BRANSFIELD BASIN AS REVEALED BY SILICEOUS MICROFOSSIL ASSEMBLAGES

Two gravity cores, Gebra-1 and Gebra-2 from the central and eastern ba sins of Bransfield Strait, West Antarctica, consist mainly of hemipela gic, laminated muds with black layers rich in sand-sized volcanic ash. Micropalaeontological (diatoms and radiolarians) and geochemical (org anic and inorganic) analyses, together with radiometric dating (U/Th, C-14 and Pb-210) have been performed on both cores. AMS analyses on To tal Organ ic Carbon yielded a C-14-age older than expected, 2810 yr sp for the core top of Gebra-1 and 2596 yr BP for Gebra-2. The downcore pattern of ages indicates a sedimentation rate of 130 cm ky(-1) for Ge bra-1 and 160 cm kyr(-1) for Gebra-2. Pb-210 anomalies suggest the cor e top of Gebra-1 is present-day sediment. The diatom and radiolarian a ssemblages are related to the sequence of neoglacial events over the l ast three millennia. The recent significant reduction in Chaetoceros r esting spores is interpreted as a reduction in palaeoproductivity. The progressive increase in sea-ice taxa for the last three millennia may indicate a cooling trend. Greater sea-ice coverage during the coldest neoglacial events in the Bransfield Basin, as well as in the Weddell Sea and Bellingshausen Sea, is documented by increases in sea-ice taxa and reductions in Thalassiosira antarctica/T. scotia resting spores, Fragilariopsis kerguelensis, the Lithomelissa group and the ''circumpo lar'' group of radiolarians. For these periods, we postulate a restric ted communication between the Weddell Sea, Bellingshausen Sea and Bran sfield basin. The millenial-scale changes are overprinted by a high fr equency cyclicity at about 200-300 yrs, which might be related to the 200-yr solar cycle.