South Victoria Land Research Articles

Ice Formation in an Antarctic Glacier-dammed Lake and Implications for Glacier-Lake Interactions

Perennially frozen lakes are common features in the McMurdo Dry Valleys of South Victoria Land in Antarctica. Some of them, called wet based, contain liquid water capped by a permanent ice cover between 2.5 and 6 m in thickness. The others, called dry based, are ice-block lakes. The thickness of the latter may far exceed those of the former. Their level is rising from freezing of the surface flooding of summer meltwater. However, we show here for the first time, using isotopic analyses together with an ionic and gas content and composition study, that the ice of one of these dry-based lakes has been formed by complete freezing from top to bottom of a closed water reservoir and not by successive layers of icings (aufeis) piling on top of each other. We also show how this lake, dammed by a cold-based glacier, has contributed to the formation of the basal ice layer of this glacier.

Neoproterozoic structural slices in the Ross Orogen, Skelton Glacier area, South Victoria Land, Antarctica

In the Skelton Glacier area, metasedimentary basement of the Ross Orogen comprises nine structurally and lithologically distinct fault‐bounded crustal slices containing varying proportions of limestone, greywacke, argillite, conglomerate, calc‐silicate, basaltic and felsic igneous rocks, and migmatite. Unlike metasediments elsewhere in South Victoria Land, primary sedimentary features are locally preserved in some of the slices. The various slices are characterised by greenschist to upper amphibolite facies metamorphic assemblages with the presence of andalusite and cordierite indicating relatively low pressure conditions. Deformation within the slices is commonly inhomogeneous, most sequences are transposed, and lithologic contacts are generally tectonic. Multiple folding characterises the most ductile lithologies. The original name of Skelton Group is retained, but the extent of deformation precludes lithostratigraphic mapping, and the formal lithostratigraphic nomenclature previously applied is abandoned. The range of metamorphic facies implies several kilometres or more of offset along structures bounding the slices, and assembly of the various slices is Neoproterozoic, preceding 551 ± 4 Ma igneous intrusion. This complex history of deformation and metamorphism represents the earliest stage of orogenic activity in South Victoria Land and contrasts with rocks of the Walcott and Dry Valleys areas to the north, where the structural and metamorphic history is 20–50 m.y. younger.

Trapping of aeolian sediments and build‐up of the ice cover of a dry‐based Antarctic lake

AbstractAmong the perennially frozen lakes of the Dry Valleys of South Victoria Land (Antarctica), some are dry‐based, i.e. frozen to the bottom. One of these is studied here by a multiparametric investigation (isotopic composition in δD and δ18O, ions, gas and ice texture analyses). A sediment layer about 10 cm thick appearing at a depth of 3·5 m is also studied by grain size, X‐ray diffraction and scanning electron microscope analyses. The information retrieved indicates that this ice‐block lake results from a build‐up in two steps and explains how aeolian sediments were included as a layer into the ice. Copyright © 2002 John Wiley & Sons, Ltd.

Expanded distributional records of Collembola and Acari in southern Victoria Land, Antarctica

Summary We provide new distributional records for the Collembola and Acari from south Victoria Land in the Ross Dependency, Antarctica, including the first extensive survey of Taylor Valley. We also describe the design of a modified device for the rapid sampling of Antarctic terrestrial arthropods. Sampling was carried out during the austral summers from 1998 to 2001. In several instances we found Gomphiocephalus hodgsoni, Neocryptopygus nivicolus and Stereotydeus mollis at sites where they were not reported in comprehensive surveys made some 40 years ago, which may imply recent range expansion (eg: local dispersal). By contrast, at McMurdo Station and at the former North Base (Marble Point) the distribution of G. hodgsoni and S. molliswas restricted, relative to previous records. We conclude that these latter changes may be the direct result of human activities.

Late Oligocene and early Miocene glacimarine sedimentation in the SW Ross Sea, Antarctica: the record from offshore drilling

Abstract Recent offshore drilling in the SW Ross Sea has recovered three cores with a cumulative thickness of 1500 m of Oligocene-early Miocene strata. Together with data from earlier drilling, notably from the CIROS-1 drillhole 70 km to the south (702 m of core), the cores record shallow marine glacigenic sedimentation at the margin of a rift basin bordering a mountain range that was breached by outlet glaciers from an ice sheet. This paper focuses on the late Oligocene-early Miocene record, which preserves sedimentary facies that represent warmer glacier ice and climatic conditions than are evident in the Antarctic today. Strata were cored near the South Victoria Land coast, and sedimentary facies include diamictite, conglomerate, breccia, sandstone, siltstone, mudstone and rhythmite. Facies associations, combined with seismic stratigraphic data, indicate an alternating proximal and distal marine record of glacigenic sedimentation, including phases of glacier grounding and variable degrees of iceberg rafting. Reworking by gravity-flow processes and near-shore submarine currents is also evident. These facies, together with evidence for periglacial vegetation, provide evidence of a late Oligocene-early Miocene climatic regime resembling that in the high-Arctic today. Thus, the climate was transitional between cooltemperate conditions of early Oligocene and cold-polar conditions of Quaternary time.

Direct shear tests of materials from a cold glacier: implications for landform development

The mechanical properties of materials at the ice-bed interface exert a major control on glacier behaviour and define the nature and rate of subglacial erosion. This paper presents new data on the strength and behaviour of basal ice and substrate of the Suess Glacier, south Victoria Land, Antarctica which is a small alpine dry-based glacier that has a basal temperature of −17°C. A tunnel excavated in the glacier revealed a substrate composed of frozen sand and gravel and a basal zone that was 3.8-m-thick. From bottom to top, the basal zone was composed of 1.8 m of stratified, complexly deformed layers of ice and debris-laden ice that was overlain by a 0.9-m-thick layer of frozen sediment and a 0.8-m-thick layer of discoloured ice that lies immediately beneath clean glacier ice. Direct shear tests were performed in the field on 36 samples using a strain rate of 0.85 mm/h and on replicate samples in a laboratory at strain rates of 0.08 and 0.01 mm/h. The experiments performed in the field show that the average peak shear strength of substrate samples was 2.53 MPa, which is almost twice as strong as the average value for basal ice (1.28 MPa), and the glacier ice samples (1.39 MPa). The laboratory experiments show that the behaviour and peak strength of samples sheared at the higher strain rates are considerably greater than the peak and residual strengths measured during the lower strain rate tests. The direct shear tests suggest that the glacier substrate is unlikely to deform at the current temperature.

Amalgamation of disparate crustal fragments in the Walcott Bay‐Foster Glacier area, South Victoria Land, Antarctica

Five structurally distinct crustal sub‐blocks are recognised in the Walcott Bay‐Foster Glacier area of South Victoria Land. The Radian sub‐block consists of variably deformed greenschist and amphibolite facies metasediments, some of which have original clastic textures preserved. The Riicker sub‐block is made up almost entirely of amphibolite facies marble folded into a broad synform on the 10 km scale. The Glee sub‐block is made up of three parallel belts of metasediments with northeast strike. The Renegar sub‐block consists of metasediments deformed around kilometre‐scale plutons. The Kemp sub‐block is composite, including exotic quartzofeldspathic metasediments and orthogneiss extensively altered by metamorphic muscovite. The five sub‐blocks have been amalgamated into the Walcott crustal block along amphibolite facies ductile shear zones which had dominantly strike‐slip motion. The Walcott Block has a northeast‐striking structural grain, and has been intruded by Middle Cambrian alkaline intrusions. The numerous structural discontinuities identified in the Walcott Bay‐Foster Glacier area preclude mapping of lithostratigraphy and metamorphic isograds.

Detecting human bacterial contamination in Antarctic soils

The presence of non-indigenous microbial contaminants resulting from human faecal contamination of old and currently occupied base and field camp sites in South Victoria Land, Antarctica, was assessed by PCR amplification of extracted soil DNA using species-specific PCR primers. Positive controls (samples recovered from the environs of Scott Base, including the sewage outfall) gave strong signals with Escherichia coli primers whereas Clostridium clostridiiforme primers yielded a signal only with the sewage outfall sample. A comparison was made of PCR amplification results from samples from the abandoned Canada Glacier camp site, the Lake Fryxell summer camp site, the Cape Bird Adelie penguin colony and pristine sites from relatively inaccessible regions of the Taylor Valley. Results indicated a possible residual level of E. coli contamination in the abandoned Canada Glacier camp site, but no significant contamination of the currently occupied Lake Fryxell camp site. These data may provide indirect evidence for improved awareness and standards of waste handling and disposal over the past two decades of Dry Valley field research.

UV radiation and potential biological effects beneath the perennial ice cover of an antarctic lake

High-resolution spectral scans of solar ultraviolet radiation (UVR) were obtained directly beneath the 4.0–5.0 m thick, perennial ice cover of Lake Hoare, South Victoria Land, Antarctica. Both UVA (320–400 nm) and UVB (280–320 nm) radiation were detectable beneath the ice using a diver-deployed, underwater scanning spectroradiometer which permitted accurate measurement in the 280–340 nm range, while avoiding effects of surface shading and/or hole effects. UVR at wavelengths <310 nm was not detectable below the ice. This lower wavelength UVB appears to penetrate the Lake Hoare ice to depths of no more than 1.5 m during relatively cloud-free austral summer days. Based upon estimated biologically effective UVR dosages and DNA dosimeter data, exposure of benthic and planktonic microbes to the UVR encountered immediately beneath the ice is unlikely to inhibit microbial metabolism. Although waters of oligotrophic antarctic lakes are highly transparent to UVR, the thick, high scattering and optically dense ice covers on many of these lakes offers organisms a degree of protection largely unavailable in temperate and tropical systems. Thinning or complete loss of these overlying ice covers is likely to have major consequences for the structure of antarctic lake microbial communities.

Chemical characteristics and origin of clear basal ice facies in dry-based glaciers, South Victoria Land, Antarctica

This paper describes a reconnaissance investigation of the solute chemistry of a clear basal ice facies that previous studies have suggested is the product of accretion of proglacial lake water. Clear basal ice, adjacent englacial ice, lake surface ice and lake water were sampled at six locations in the Taylor and Wright valleys. Ice from each sample location was split into five aliquots and the concentrations of sodium, potassium, calcium, magnesium and chlorides were determined using atomic absorption spectrophotometry. The clear basal ice samples can be divided into three groups on the basis of solute concentrations. Group 1 consists of six samples which have solute concentrations very similar to englacial ice, Group 2 consists of seven samples that have concentrations that are significantly greater than englacial ice and Group 3 consists of one sample which has a solute concentration that is 10 times greater than adjacent englacial ice. Four mechanisms to explain the solute enrichment are examined and it is concluded that although the chemical analysis suggests that some basal ice may have been accreted from proglacial lakes, water chemistry alone is not a reliable indicator of the origin of the clear basal ice.

Apophyllite 40Ar/39Ar and Rb‐Sr geochronology: Potential utility and application to the timing of secondary mineralization of the Kirkpatrick Basalt, Antarctica

Apophyllite (KCa4Si8O20(F, OH)·8H2O), which formed as a low‐temperature secondary mineral in the Kirkpatrick Basalt, has been examined to evaluate its potential for geochronology using the K‐Ar (by the 40Ar/39Ar technique) and Rb‐Sr methods. The 40Ar/39Ar total‐gas ages for apophyllites from the Kirkpatrick Basalt are 114–133 Ma for the central Transantarctic Mountains, 95–114 Ma for south Victoria Land, and 76–100 Ma for north Victoria Land. Within individual hand samples, apophyllite 40Ar/39Ar apparent ages show variations of up to 24 m.y., and within single large (up to ∼2 cm) crystals, differences of up to 14 m.y. are observed. The 40Ar/39Ar incremental‐heating spectra are generally flat but have lowand high‐temperature discordances attributed to 39Ar recoil. Rb‐Sr model ages for the apophyllites range from 94 to 144 Ma and vary from concordant with the 40Ar/39Ar dates to as much as 14 m.y. older. The dates are consistent with other temporal indicators of low‐temperature alteration in the basalts and are interpreted to broadly reflect the time of apophyllite precipitation. They document a geographically widespread early to middle Cretaceous secondary mineralization which is inferred to be caused by a major period of groundwater movement associated with the initiation of uplift and denudation of the Transantarctic Mountains. The results suggest that apophyllite can produce geologically meaningful ages by both Rb‐Sr and K‐Ar methods, although further work is required to fully understand the variations in age that may be attributed to Ar loss, alkali mobility, or an extended history of mineral precipitation.

A taxonomic and systematic revision of the genus Muelleria (Bacillariophyta)

The genus Muelleria (Frenguelli) Frenguelli is considered in taxonomic, systematic, and biogeographic contexts. Muelleria is a small genus composed of 15 known species. In the present report, four species are newly described (M. algida S.A. Spaulding et Kociolek sp. nov., M. luculenta S.A. Spaulding et Kociolek sp. nov., M. variolata S.A. Spaulding et Kociolek sp. nov., and M. varipunctata S.A. Spaulding et Kociolek sp. nov.) and illustrated in light microscopy and scanning electron microscopy. In addition, one new combination is made [M. holmenii (Foged) S.A. Spaulding et Kociolek comb. nov.] and three lectotypes are designated [M. linearis (O. Müller) Frenguelli, M. gibbula (Cleve) S.A. Spaulding et Stoermer, M. patagonica (O. Müller) Frenguellil. The genus Muelleria has an unusual geographic distribution. Unlike other diatom genera, most of the species [except M. terrestris (Petersen) S.A. Spaulding et Stoermer and the cosmopolitan M. gibbula] are restricted to high latitudes of either the southern or northern hemisphere. The taxa are narrowly endemic, with species restricted to isolated habitats such as oceanic islands (Iceland, Kerguelen Island, and South Shetland Islands) and arid desert lakes (South Victorialand region of Antarctica and southern Argentina). A cladistic analysis is performed based on morphological characters for 11 Muelleria species and four outgroup taxa. The results of this analysis indicate that Muelleria is a monophyletic group, lending support to the resurrection of the genus and to the hypothesis that lineages, not just individual species, share restricted distributions. Among southern hemisphere species, one lineage of Muelleria is primarily South American and the second is primarily Antarctic.

Structure and strength of basal ice and substrate of a dry-based glacier: evidence for substrate deformation at sub-freezing temperatures

AbstractThis paper presents new data and interpretations of the structure, strength and behaviour of basal ice and the substrate of Suess Glacier, south Victoria Land, Antarctica, which is a small alpine dry-based glacier that has a basal temperature of—17°C. A tunnel excavated in the glacier revealed a substrate composed of frozen sand and gravel and a basal zone that was 3.8 m thick. From bottom to top, the basal zone was composed of 1.8 m of stratified, complexly deformed layers of ice and debris overlain by a 0.9 m thick layer of frozen sediment and a 0.8 m thick layer of discoloured ice lying immediately beneath clean glacier ice. Direct shear tests performed in the field on 36 samples show that the average peak shear strength of substrate samples was 2.53 MPa, which is almost twice as strong as the average value for basal ice (1.28 MPa) and the glacier ice samples (1.39 MPa). The direct shear tests suggest that the glacier substrate is unlikely to deform at the current temperature. However, observations of the structure and composition of the basal zone suggest that the substrate contains localized weaknesses that may reduce the peak strength sufficiently to permit bed deformation and entrainment. Two observed forms of weakness are ice lenses and layers in the permafrost and lenses of unsaturated permafrost, which may be inherited from the active zone of a former land surface or produced as pore ice sublimes into cavities which have formed at the glacier bed. Interpretation of data from this study suggests that glacier beds well below the freezing point can be deformed and eroded under certain conditions.

Ice composition evidence for the formation of basal ice from lake water beneath a cold-based Antarctic glacier

AbstractEntrainment of debris by cold-based glaciers having basal temperatures as low as — 17°C can be observed in the Dry Valleys of south Victoria Land, Antarctica. The classical models developed to explain debris incorporation at the glacier base are inappropriate in such cases, since the basal temperature is well below the freezing point. An alternative model, based on the presence of ice-marginal lakes, has recently been proposed by one of the authors (S. F.). In this model, transient wet-base conditions can occur as ice flows onto the unfrozen sediments of the lake bottom, creating conditions favorable to the entrainment of sediments and to ice accretion by water freezing.Here we describe a situation where this model is consistent with an ice-composition study of the basal part of Suess Glacier, Taylor Valley. The stable isotope composition indicates that water freezing, most probably lake water, plays a major role in the formation of the basal ice layers. Total gas content of this basal ice is considerably depleted when compared to meteoric glacier ice, in accordance with a rejection mechanism during freezing. Its gas composition, strongly enriched in CO2, is also indicative of the presence of a former liquid phase.

Mercury speciation and distribution in a polar desert lake (Lake Hoare, Antarctica) and two glacial meltwater streams

Total (Hg T), reactive (Hg R) and monomethylmercury (MMHg) have been determined in unfiltered collections from Lake Hoare and two glacial meltwater streams (Canada and von Guerard streams) located in the Taylor Valley (McMurdo Dry Valleys, South Victoria Land, Antarctica). Sampling was undertaken as part of a larger project examining the origin of dissolved organic matter and trace elements in these systems. Here we evaluate the possible sources of Hg and MMHg (marine aerosols, wind blown dust and crustal weathering) to the glacial meltwater streams. Erosion of crustal material accounts for 35–75% of the inorganic Hg load in streamwater. Oceanic production and sea–air exchange of elemental Hg (Hg°) and dimethylmercury (DMHg) followed by atmospheric oxidation/decomposition, transport and deposition may deliver MMHg and inorganic Hg (in addition to crustal weathering) to glacial streams. Volcanically derived Hg may also contribute significantly to the streamwater Hg load. In Lake Hoare, Hg T ranged from 3.3 to 6.8 pM; the highest concentrations were found at 8 and 25m. MMHg levels varied from<0.4 to 2.1 pM. A peak in MMHg at 8 m follows the Hg T and Hg R distribution. Interestingly, the percent of Hg T as MMHg (%MMHg) was approx. 30% below 22 m and approx. 10% from 4 to 20 m. In situ methylation of Hg in the sediment (followed by diffusion into the overlying waters) of Lake Hoare is implied.

Late Quaternary faulting and neotectonics, South Victoria Land, Antarctica

Three Quaternary fault traces in Hidden and Garwood Valleys, South Victoria Land, provide direct evidence for neotectonic activity in the Transantarctic Mountain rift shoulder of the West Antarctic Rift system. The faults trend NE-SW and all show a large component of sinistral strike-slip displacement. The late Quaternary faults lie parallel to Palaeozoic brittle structures, suggesting that inherited anistropy has governed younger fault orientations. Sinistral displacement on NE-SW-striking Quaternary faults appears to be inconsistent with the predicted Cenozoic NW-SE dextral oblique extensional regime in South Victoria Land but can be accommodated by minor clockwise rotation of crustal blocks.

A case for Sirius Group alpine glaciation at Mount Fleming, South Victoria Land, Antarctica: A case against Pliocene East Antarctic Ice Sheet reduction

The Sirius Group comprises a suite of consolidated glacial deposits that are widespread in the Transantarctic Mountains; some of the deposits contain Pliocene marine diatoms. Because of the interpretation that the Sirius Group tills and the marine diatoms were deposited by the East Antarctic Ice Sheet, it has been inferred that the East Antarctic Ice Sheet was much reduced in area and volume during the Pliocene. These interpretations were evaluated by studying Sirius Group lodgment tills on Mount Fleming in the Dry Valleys sector of the Transantarctic Mountains. We infer that the Sirius Group lodgment tills at Mount Fleming do not support the hypothesis that the East Antarctic Ice Sheet was much reduced during the Pliocene. We demonstrate that Sirius Group lodgment tills on Mount Fleming were deposited by alpine ice. This conclusion is founded on ice-flow directions inferred from rattails, gravel fabric, and the orientation of bullet boulders, as well as on sediment and gravel characteristics of the tills. Only a very few unidentifiable diatom fragments were recovered. Better preserved, identifiable, Pliocene marine diatoms occur in moderate abundances in a 5–10-cm-thick unconsolidated and discontinuous drift that caps the lodgment tills. On the basis of the decline in diatom preservation with depth into the till, we dismiss transport of the better preserved diatoms by the ice that deposited the underlying Sirius Group lodgment till. Instead, we attribute diatom presence to eolian deposition and recycling into lodgment tills at a later stage.

Contrasting structural styles during polyphase granitoid intrusion, South Victoria Land, Antarctica

Four granitoid plutons intruded in the Walcott Bay area, South Victoria Land, during the Paleozoic Ross Orogeny, display markedly different structural styles. Bonney Pluton is a variably megacrystic hornblende‐biotite granite batholith which outcrops over an area of 1000 km2. The southern end of the body is located in the Walcott Bay area, and it is the oldest of the four granitoid bodies (530–520 Ma). The pluton synkinematically intruded Koettlitz Group metasediments under mid‐upper amphibolite facies conditions (700°C, 5 ± 1 bars). Bonney Pluton fabrics are highly variable, with weak magmatic fabrics in the pluton centre grading to well‐developed, solid‐state deformation fabrics in high strain zones at the southwestern margins. Armitage Pluton is a non‐megacrystic hornblende‐biotite body, which intruded central parts of Bonney Pluton while it was incompletely crystallised. The body forms randomly oriented dikes and stocks and is chemically distinct from Bonney Pluton. A weak magmatic fabric is developed through the body, subparallel to magmatic lineations in central parts of Bonney Pluton. Chancellor Orthogneiss is a strongly deformed biotite granite, which discordantly intrudes metasediments as randomly oriented dikes and stocks. Solid‐state deformation fabrics overprint magmatic fabrics throughout the body, indicating post‐emplacement ductile deformation. This body was emplaced into host rock close to or at the brittle‐ductile transition, at least biotite zone conditions. Hidden Granite is an undeformed biotite granite which discordantly intrudes metasediments and older granitoid bodies as randomly oriented dikes and stocks. Mafic dikes coevally intrude the granite, infilling fractures with consistent northeast—southwest orientations, at a late stage of granite crystallisation. Hidden Granite was emplaced into a brittle host rock, above the brittle‐ductile transition. The changing structural styles of the four plutons reflect intrusion during progressive uplift. The nearly parallel nature of the elongation direction of post‐emplacement ductile fabrics in Chancellor Orthogneiss, and the extension direction indicated by brittle structures in Hidden Granite, suggests a geometric relationship exists between these fabrics and structures. The northwest—southeast elongation direction also remains relatively constant during post‐emplacement deformation of the plutons.

Canada Stream: A Glacial Meltwater Stream in Taylor Valley, South Victoria Land, Antarctica

The McMurdo Dry Valleys of South Victoria Land, Antarctica, form the largest of the desert oases found along the coast of Antarctica. Although this region is an extreme cold desert, glacial meltwater streams, which flow for 6-10 wk during the austral summer, are a prominent feature of the landscape. Canada Stream is in Taylor Valley and is one of 3 major streams draining Canada Glacier. The surrounding landscape is characterized by an absence of plant life, an underlying permafrost at a depth of 0.5 m, and prominent "patterned ground" features, which are large (3-5 m across) polygonal patterns formed through freeze/thaw cycles. In contrast to the barren landscape, many of the streams contain perennial algal mats and mosses, illustrating that the presence of liquid water allows for a photosynthetically based ecosystem even under the harshest conditions. Canada Stream is one of 10 streams that flow into Lake

Diorite and gabbro of the Dromedary mafic complex, South Victoria Land, Antarctica

Abstract The syntectonic Dromedary mafic complex is a well‐preserved mafic body which was emplaced into Koettlitz Group metasediments during widespread late Proterozoic‐Paleozoic granitoid plutonism, metamorphism, and deformation in South Victoria Land, Antarctica. The 4×9 km pluton is reversely zoned. It consists of a core of calc‐alkaline cumulate and noncumulate gabbros— comprising gabbro, olivine gabbro, anorthosite, norite, and pyroxenite—surrounded by an outer margin of homogeneous pyroxene‐bearing diorite. All rocks have undergone varying degrees of metamorphic reconstitution. The resulting assemblages are strongly controlled by original rock composition. Field relationships and geochemical data suggest that the diorite and gabbro are coeval and cogenetic. The Dromedary mafic complex has geochemical signatures distinct from most other nearby dioritic bodies. It does, however, plot as an extension of syntectonic granitoids from the Dry Valley region.