Framnes Mountains Research Articles

Distribution and Diversity of Soil Microfauna from East Antarctica: Assessing the Link between Biotic and Abiotic Factors

Terrestrial life in Antarctica has been described as some of the simplest on the planet, and mainly confined to soil microfaunal communities. Studies have suggested that the lack of diversity is due to extreme environmental conditions and thought to be driven by abiotic factors. In this study we investigated soil microfauna composition, abundance, and distribution in East Antarctica, and assessed correlations with soil geochemistry and environmental variables. We examined 109 soil samples from a wide range of ice-free habitats, spanning 2000 km from Framnes Mountains to Bailey Peninsula. Microfauna across all samples were patchily distributed, from complete absence of invertebrates to over 1600 specimens/gram of dry weight of soil (gdw), with highest microfauna abundance observed in samples with visible vegetation. Bdelloid rotifers were on average the most widespread found in 87% of sampled sites and the most abundant (44 specimens/gdw). Tardigrades occurred in 57% of the sampled sites with an abundance of 12 specimens/gdw. Nematodes occurred in 71% of samples with a total abundance of 3 specimens/gdw. Ciliates and mites were rarely found in soil samples, with an average abundance of 1.3 and 0.04 specimens/gdw, respectively. We found that microfaunal composition and abundance were mostly correlated with the soil geochemical parameters; phosphorus, NO3 − and salinity, and likely to be the result of soil properties and historic landscape formation and alteration, rather than the geographic region they were sampled from. Studies focusing on Antarctic biodiversity must take into account soil geochemical and environmental factors that influence population and species heterogeneity.

Can in-situ cosmogenic 14C be used to assess the influence of clast recycling on exposure dating of ice retreat in Antarctica?

Cosmogenic nuclide exposure dating of glacial clasts is becoming a common and robust method for reconstructing the history of glaciers and ice sheets. In Antarctica, however, many samples exhibit cosmogenic nuclide ‘inheritance’ as a result of sediment recycling and exposure to cosmic radiation during previous ice free periods. In-situ cosmogenic 14C, in combination with longer lived nuclides such as 10Be, can be used to detect inheritance because the relatively short half-life of 14C means that in-situ 14C acquired in exposure during previous interglacials decays away while the sample locality is covered by ice during the subsequent glacial. Measurements of in-situ 14C in clasts from the last deglaciation of the Framnes Mountains in East Antarctica provide deglaciation ages that are concordant with existing 26Al and 10Be ages, suggesting that in this area, the younger population of erratics contain limited inheritance.

Exposure ages from mountain dipsticks in Mac. Robertson Land, East Antarctica, indicate little change in ice-sheet thickness since the Last Glacial Maximum

Past changes in East Antarctic Ice Sheet (EAIS) volume are poorly known and diffi cult to measure, yet are critical for predicting the response of the ice sheet to modern climate change. In particular, it is important to identify the sources of sea-level rise since the Last Glacial Maximum (LGM), and ascertain the present-day stability of the world’s largest ice sheet. We present altitudinal transects of 10 Be and 26 Al exposure ages across the Framnes Mountains in Mac. Robertson Land that allow the magnitude and timing of EAIS retreat to be quantifi ed. Our data show that the coastal EAIS thinned by at most 350 m in this region during the past 13 k.y. This reduction in ice-sheet volume occurred over a ~5 k.y. period, and the present icesheet profi le was attained ca. 7 ka, in contrast to the West Antarctic Ice Sheet, which continues to retreat today. Combined with regional offshore and terrestrial geologic evidence, our data suggest that the reduction in EAIS volume since the LGM was smaller than that indicated by contemporary ice-sheet models and added little meltwater to the global oceans. Stability of the ice margin since the middle Holocene provides support for the hypothesis that EAIS volume changes are controlled by growth and decay of Northern Hemisphere ice sheets and associated global sea-level changes.

The stress distribution related to the boudinage of a visco-elastic material: examples from a polar outlet glacier

Abstract Quantitative stress measurements related to the development of mesoscale structures in rock are difficult, if not impossible. A method for determining the stress distribution and history during the development of mesoscale boudinage structures in ice is introduced here. Boudinage structures in fracture trace ice have been observed in the outlets glaciers of the Framnes Mountains, east Antarctica. Fracture traces are preserved when creasses fill with surface melt water, which freezes to form coarse-grained columnar ice. A 4.0 km flow-parallel traverse across the Central Ice Stream of the Framnes Mountains is presented to illustrate the boudinage of fracture traces with a mean width of 0.30 m. Field-based measurement of the geometric evolution of boudinage structures has been combined with surface flow rate measurements to quantitatively determine the strain rate at which the boudinage structures formed. The strain rate measurements provide boundary constraints on several two-dimensional finite difference models that have been used to analyse the stress distribution related to the formation of boudinage structures in a visco-elastic solid. The results reveal the development of pressure-shadows during the boundinage of layered rocks, and demonstrate the degree of refraction of stress across rheological boundaries, which have important ramifications for the analysis of planar and linear fabrics in rocks.

Strain localisation and incremental deformation within ice masses, Framnes Mountains, east Antarctica

Mesoscale fracture analysis of brittle features has been used to identify zones of localised ductile deformation within an ice stream, moving at ~20 ma−1 in the Framnes Mountains, east Antarctica. Ground-based survey of three strain grids has been integrated with the detailed structural analysis to develop a model of temporal and spatial variation in strain localisation within large high strain zones. Modelled strain distributions are in good agreement with the occurrence and sense of movement across zones of high ductile strain which have been inferred from observed brittle features. The major zone of high strain is 3 km wide and 15 km long and deformed dextrally at a strain rate of 6.17 × 10−3 a−1 over the two year period of observation. Despite this constant annual strain rate the internal deformation was incremental, localised and temporal in nature resulting in the development of new zones of fracturing.

Movement and structural features observed in ice masses, Framnes Mountains, Mac.Robertson Land, East Antarctica

Ice-movement surveys in the Framnes Mountains from austral summers 1993–94 and 1994–95 are presented with complementary surface elevations and structural interpretations. Surface velocities of 21 m a−1 have been recorded in Ice Stream B and 31 ma−1 in Ice Stream C. The flow rate varied between 11.6 and 21.0 m a−1 over a lateral range of 2.1 km west of Rumdoodle Peak and between 17.1 and 31.5 m a−1 over 2 km west of Mount Parsons. Two ice streams of relative high flow between the central Masson and David Ranges and several zones of incremental increase in flow rate have been identified within Ice Stream B, using shear-sense criteria based as ice-fracture geometry and subsequent deformation of crevasse traces. These zones of localized strain correlate with ice-flow survey measurements.

Movement and structural features observed in ice masses, Framnes Mountains, Mac.Robertson Land, East Antarctica

Ice-movement surveys in the Framnes Mountains from austral summers 1993–94 and 1994–95 are presented with complementary surface elevations and structural interpretations. Surface velocities of 21 m a−1 have been recorded in Ice Stream B and 31 ma−1 in Ice Stream C. The flow rate varied between 11.6 and 21.0 m a−1 over a lateral range of 2.1 km west of Rumdoodle Peak and between 17.1 and 31.5 m a−1 over 2 km west of Mount Parsons. Two ice streams of relative high flow between the central Masson and David Ranges and several zones of incremental increase in flow rate have been identified within Ice Stream B, using shear-sense criteria based as ice-fracture geometry and subsequent deformation of crevasse traces. These zones of localized strain correlate with ice-flow survey measurements.

Geology and structure of Depot Peak, MacRobertson Land. More evidence for the continuous extent of the 1000 Ma event of East Antarctica

The 1000 Ma event of East Antarctica is a granulite facies metamorphic event that affected rocks underlying more than 1000 km of the Antarctic coastline between 50°E and 70°E. The limits of the belt are defined by isotopic dating but attempts to define the belt on metamorphic grounds are sparse. Depot Peak provides an important link for determining the history of this belt as it is the only outcrop linking the Prince Charles Mountains to the Framnes Mountains and the western parts of the Rayner Complex. Much of the Prince Charles Mountains are also 1000 Ma old but much of their metamorphic history is yet to be established. The rocks at Depot Peak are garnet and cordierite‐bearing gneisses of low pressure granulite facies that were intruded by a large sheet of garnet granite prior to metamorphism and deformation. They experienced two deformation phases, D1 and D2, and they record two different metamorphic events around 560 MPa, 700°C (M1) and 510 MPa, 600°C (M2). It is difficult to demonstrate to what exte...

A Crystallographic Study of the Perennially Frozen Ice Surface of Patterned Lake, Framnes Mountains, East Antarctica

AbstractInterlocking rectangular ice patterns, with dimensions of several metres, on the surface of a perennial frozen lake in East Antarctica can be related to a strong crystallographic orientation in the underlying ice. Most of the surface patterns are characterized by parallel centimetre-scale ridges and furrows that correspond to an aggregate of tabular-shaped grains. Grain elongation is parallel to the basal plane. Thec-axis distribution within each ice pattern lies in a horizontal plane. It defines a discrete maximum perpendicular to the surface ridges and to the long axis of the rectangular pattern. Areas exhibiting no patterning are composed of variably orientated ice grains. The strongc-axis horizontal orientation and the distinctive morphology of these ice patterns are interpreted as having developed by a geometric enhancement over a long period of time.

A Crystallographic Study of the Perennially Frozen Ice Surface of Patterned Lake, Framnes Mountains, East Antarctica

AbstractInterlocking rectangular ice patterns, with dimensions of several metres, on the surface of a perennial frozen lake in East Antarctica can be related to a strong crystallographic orientation in the underlying ice. Most of the surface patterns are characterized by parallel centimetre-scale ridges and furrows that correspond to an aggregate of tabular-shaped grains. Grain elongation is parallel to the basal plane. The c-axis distribution within each ice pattern lies in a horizontal plane. It defines a discrete maximum perpendicular to the surface ridges and to the long axis of the rectangular pattern. Areas exhibiting no patterning are composed of variably orientated ice grains. The strong c-axis horizontal orientation and the distinctive morphology of these ice patterns are interpreted as having developed by a geometric enhancement over a long period of time.

Phytogeography of Antarctica

Existing schemes of phytogeographic subdivision of Antarctica and adjacent ocean are reviewed. Russian studies which commenced in the 1950s are reviewed for the first time in the Western literature. Records of lichen and moss occurrence from seventy-five scattered locations in the Australian Antarctic Territory, eastern Antarctica, are analysed for phyto- geographic patterns. Problems in the data are discussed; the main limitation is inconsistent quality of collecting. Using a polythetic agglomerative classification the localities form seven groups: large coastal outcrops of ice-free rock, Mawson Coast, Framnes Mountains, peninsulas near Casey Station, Windmill Islands, Prince Charles Mountains and floristically rich islands. The thirty-six species of lichens and five species of mosses form five groups, each with a characteristic ecological pattern. The species-groups correspond rea- sonably well with communities described from elsewhere in Antarctica. We do not erect any new subdivisions but accept the following existing phytogeographic subdivisions: Subantarctic Zone with three Regions