Flexural and compressive strength of the landfast sea ice in the Prydz Bay, East Antarctic

A total of 25 flexural and 55 uniaxial compressive strength tests were conducted using landfast sea ice samples collected in the Prydz Bay. Three-point bending tests were performed at ice temperatures of −12 to −3 °C with force applied vertically to original ice surface, and compressive tests were performed at −3 °C with a strain-rate level of 10−6–10−2 s−1 in the directions vertical and horizontal to ice surface. Judging from crystal structure, the ice samples were divided into congelation ice, snow ice, and a mixture of the these two. The results of congelation ice showed that the flexural strength had a decreasing trend depending on porosity rather than brine volume, based on which a mathematical equation was established to estimate flexural strength. Both flexural strength and effective modulus increased with increasing platelet spacing. The uniaxial compressive strength increased and decreased with strain rate below and above the critical regime, respectively, which is 8.0 × 10−4–1.5 × 10−3 s−1 for vertically loaded samples and 2.0 × 10−3–3.0 × 10−3 s−1 for horizontally loaded samples. A drop off in compressive strength was shown with increasing sea ice porosity. Consequently, a model was developed to depict the combined effects of porosity and strain rate on compressive strength in both ductile and brittle regimes. The mechanical strength of mixed ice was lower than congelation ice, and that of snow ice was much weaker. To provide a safe guide for the transportation of goods on landfast sea ice in the Prydz Bay, the bearing capacity of the ice cover is estimated with the lower and upper envelopes of flexural strength and effective modulus, respectively, which turned out to be a function of sea ice porosity.

Variability and Formation Mechanism of Polynyas in Eastern Prydz Bay, Antarctica

Based on satellite remote sensing, several polynyas have been found in Prydz Bay, East Antarctica. Compared with the Mackenzie Bay Polynya, the only polynya in the west, the polynyas in eastern Prydz Bay have a larger area and higher ice production, but have never been studied individually. In this study, four recurrent polynyas were identified in eastern Prydz Bay from sea ice concentration data during 2002–2011. Their areas generally exhibit synchronous temporal variations and have good correlation with wind speed, which indicates that they are primarily wind-driven polynyas that need at least one stationary ice barrier to block the inflow of drifting sea ice. The components of the ice barriers of these four polynyas were identified through comparison of satellite remote sensing visible images and synthetic aperture radar images. All types of fast ice, including landfast ice, offshore fast ice and ice fingers serving as ice barriers for these polynyas are anchored by an assemblage of small icebergs and have an approximately year-round period of variations that also regulates the variability of polynyas. The movement and grounding of giant icebergs near the polynyas significantly affects the development of the polynyas. The results of this study illustrate the important impact of icebergs on Antarctic wind-driven polynyas and the formation of dense shelf water.

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

<p><b>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.</b></p> <p>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.</p> <p>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.</p> <p>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.</p> <p>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.</p> <p>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.</p>

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

<p><b>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.</b></p> <p>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.</p> <p>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.</p> <p>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.</p> <p>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.</p> <p>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.</p>

Regional Variation in Winter Foraging Strategies by Weddell Seals in Eastern Antarctica and the Ross Sea

The relative importance of intrinsic and extrinsic determinants of animal foraging is often difficult to quantify. The most southerly breeding mammal, the Weddell seal, remains in the Antarctic pack-ice year-round. We compared Weddell seals tagged at three geographically and hydrographically distinct locations in East Antarctica (Prydz Bay, Terre Adélie, and the Ross Sea) to quantify the role of individual variability and habitat structure in winter foraging behaviour. Most Weddell seals remained in relatively small areas close to the coast throughout the winter, but some dispersed widely. Individual utilisation distributions (UDi, a measure of the total area used by an individual seal) ranged from 125 to 20,825 km2. This variability was not due to size or sex but may be due to other intrinsic states for example reproductive condition or personality. The type of foraging (benthic vs. pelagic) varied from 56.6 ± 14.9% benthic dives in Prydz Bay through 42.1 ± 9.4% Terre Adélie to only 25.1 ± 8.7% in the Ross Sea reflecting regional hydrographic structure. The probability of benthic diving was less likely the deeper the ocean. Ocean topography was also influential at the population level; seals from Terre Adélie, with its relatively narrow continental shelf, had a core (50%) UD of only 200 km2, considerably smaller than the Ross Sea (1650 km2) and Prydz Bay (1700 km2). Sea ice concentration had little influence on the time the seals spent in shallow coastal waters, but in deeper offshore water they used areas of higher ice concentration. Marine Protected Areas (MPAs) in the Ross Sea encompass all the observed Weddell seal habitat, and future MPAs that include the Antarctic continental shelf are likely to effectively protect key Weddell seal habitat.

Imaging the Ice Sheet and Uppermost Crustal Structures with a Dense Linear Seismic Array in the Larsemann Hills, Prydz Bay, East Antarctica

Comprehensive geophysical surveys including magnetotelluric, seismic, and aerial gravity–magnetic surveys are essential for understanding the history of Antarctic tectonics. The ice sheet and uppermost structure derived from those geophysical methods are relatively low resolution. Although ice-penetrating radar can provide high-resolution reflectivity images of the ice sheet, it cannot provide constraints on subice physical properties, which are important for geological understanding of the Antarctic continent. To obtain high-resolution images of the ice sheet and uppermost crustal structure beneath the Larsemann Hills, Prydz Bay, East Antarctica, we conduct an ambient noise seismic experiment with 100 short-period seismometers spaced at 0.2 km intervals. Continuous seismic waveforms are recorded for one month at a 2 ms sampling rate. Empirical Green’s functions are extracted by cross correlating the seismic waveform of one station with that of another station, and dispersion curves are extracted using a new phase-shift method. A high-resolution shear-velocity model is derived by inverting the dispersion curves. Furthermore, body waves are enhanced using a set of processing techniques commonly used in seismic exploration. The stacked body-wave image clearly shows a geological structure similar to that revealed by the shear-wave velocity model. This study, which is the first of its kind in Antarctica, possibly reveals a near-vertical intrusive rock covered by an ice sheet with a horizontal extent of 4 km. Our results help to improve the understanding of the subice environment and geological evolution in the Larsemann Hills, Prydz Bay, East Antarctica.