Distribution of Marine Palynomorphs in Surface Sediments, Prydz Bay, Antarctica

摘要

Prydz Bay Antarctica is an embayment situated at the ocean-ward end of the LambertGlacier/Amery Ice Shelf complex East Antarctica. This study aims to document thepalynological assemblages of 58 surface sediment samples from Prydz Bay, and tocompare these assemblages with ancient palynomorph assemblages recovered fromstrata sampled by drilling projects in and around the bay.Since the early Oligocene, terrestrial and marine sediments from the Lambert Grabenand the inner shelf areas in Prydz Bay have been the target of significant glacialerosion. Repeated ice shelf advances towards the edge of the continental shelfredistributed these sediments, reworking them into the outer shelf and Prydz ChannelFan. These areas consist mostly of reworked sediments, and grain size analysisshows that finer sediments are found in the deeper parts of the inner shelf and thedeepest areas on the Prydz Channel Fan. Circulation within Prydz Bay is dominatedby a clockwise rotating gyre which, together with coastal currents and ice bergploughing modifies the sediments of the bay, resulting in the winnowing out of thefiner component of the sediment.Glacial erosion and reworking of sediments has created four differing environments(Prydz Channel Fan, North Shelf, Mid Shelf and Coastal areas) in Prydz Bay whichis reflected in the palynomorph distribution. Assemblages consist of Holocenepalynomorphs recovered mostly from the Mid Shelf and Coastal areas and reworkedpalynomorphs recovered mostly from the North Shelf and Prydz Channel Fan. Thepercentage of gravel to marine palynomorph and pollen counts show a relationshipwhich may reflect a similar source from glacially derived debris but the percentageof mud to marine palynomorph and pollen counts has no relationship.Reworked palynomorphs consist of Permian to Eocene spores and pollen and Eocenedinocysts which are part of the Transantarctic Flora. Holocene components are avaried assemblage of acritarchs, dinoflagellate cysts (dinocysts), prasinophyte algae,red algae and large numbers of Zooplankton sp. and foraminifera linings. In situdinocysts are dominated by the heterotroph form Selenopemphix antarctica and none of the Holocene dinocyst species found in Prydz Bay have been recorded in theArctic. In contrast acritarchs, prasinophytes and red algae are all found in the Arcticand reflect a low salinity and glacial meltwater environment. Comparison withmodern surface samples from the Arctic and Southern Ocean show there is a strongcorrelation to reduction in the autotroph:heterotroph dinocyst ratio with increasinglatitude.Todays assemblage of marine palynomorphs are more complex than those recordedin ancient assemblages and there is a lower level of reworked material. Acritarchs(Leiosphaeridia spp. Sigmopollis sp.) and prasinophytes (Cymatiosphaera spp.Pterospermella spp. Tasmanites spp.) are recorded in the ancient record in Antarcticaas well as surface sediments in Prydz Bay, but there are very low numbers ofLeiosphaeridia spp. and Sigmopollis spp. present today in comparison to the ancientrecord. Dinocysts in situ and recovered in Prydz Bay are endemic to the Antarcticbut have not been recorded in the ancient record.