Abstract:
Prydz Bay Antarctica is an embayment situated at the ocean-ward end of the Lambert
Glacier/Amery Ice Shelf complex East Antarctica. This study aims to document the
palynological assemblages of 58 surface sediment samples from Prydz Bay, and to
compare these assemblages with ancient palynomorph assemblages recovered from
strata sampled by drilling projects in and around the bay.
Since the early Oligocene, terrestrial and marine sediments from the Lambert Graben
and the inner shelf areas in Prydz Bay have been the target of significant glacial
erosion. Repeated ice shelf advances towards the edge of the continental shelf
redistributed these sediments, reworking them into the outer shelf and Prydz Channel
Fan. These areas consist mostly of reworked sediments, and grain size analysis
shows that finer sediments are found in the deeper parts of the inner shelf and the
deepest areas on the Prydz Channel Fan. Circulation within Prydz Bay is dominated
by a clockwise rotating gyre which, together with coastal currents and ice berg
ploughing modifies the sediments of the bay, resulting in the winnowing out of the
finer 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 which
is reflected in the palynomorph distribution. Assemblages consist of Holocene
palynomorphs recovered mostly from the Mid Shelf and Coastal areas and reworked
palynomorphs recovered mostly from the North Shelf and Prydz Channel Fan. The
percentage of gravel to marine palynomorph and pollen counts show a relationship
which may reflect a similar source from glacially derived debris but the percentage
of mud to marine palynomorph and pollen counts has no relationship.
Reworked palynomorphs consist of Permian to Eocene spores and pollen and Eocene
dinocysts which are part of the Transantarctic Flora. Holocene components are a
varied assemblage of acritarchs, dinoflagellate cysts (dinocysts), prasinophyte algae,
red algae and large numbers of Zooplankton sp. and foraminifera linings. In situ
dinocysts are dominated by the heterotroph form Selenopemphix antarctica and none of the Holocene dinocyst species found in Prydz Bay have been recorded in the
Arctic. In contrast acritarchs, prasinophytes and red algae are all found in the Arctic
and reflect a low salinity and glacial meltwater environment. Comparison with
modern surface samples from the Arctic and Southern Ocean show there is a strong
correlation to reduction in the autotroph:heterotroph dinocyst ratio with increasing
latitude.
Todays assemblage of marine palynomorphs are more complex than those recorded
in 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 Antarctica
as well as surface sediments in Prydz Bay, but there are very low numbers of
Leiosphaeridia spp. and Sigmopollis spp. present today in comparison to the ancient
record. Dinocysts in situ and recovered in Prydz Bay are endemic to the Antarctic
but have not been recorded in the ancient record.
