Northern Victoria Land Research Articles

Pervasive, tholeiitic refertilisation and heterogeneous metasomatism in Northern Victoria Land lithospheric mantle (Antarctica)

The petrology of peridotite xenoliths in the Cenozoic volcanics from Greene Point (Northern Victoria Land, Antarctica) provides new constraints on the characterisation of the lithospheric mantle beneath the West Antarctic Rift.Based on mineral major and trace element models, this mantle domain is proposed to represent a residuum after 10% and 20% partial melting. Moreover, melting models and isotopic results for Sr and Nd systematics highlight the substantial contribution of tholeiitic melts percolating through peridotites. Close correlation with trace element contents in clinopyroxene phenocrysts from Ferrar and Karoo tholeiites allows us to ascribe this refertilisation event to the Jurassic. This asthenospheric melt was also able to transfer a garnet signature to the Northern Victoria Land mantle segment. The rare presence of glass and secondary phases indicate that Greene Point xenoliths were heterogeneously affected by alkaline metasomatism, probably related to the West Antarctic Rift System opening; this has also been widely observed in other Northern Victoria Land localities (i.e., Baker Rocks).Temperature and fO2 were calculated (950°C; Δlog fO2 (QFM), −1.70 to −0.39) at a fixed pressure of 15kbar, confirming the tendency of the anhydrous Greene Point xenolith population to have higher equilibration temperatures and comparable redox conditions, compared to the nearby amphibole-bearing peridotites from Baker Rocks.

Ferri-kaersutite, NaCa2(Mg3TiFe3+)(Si6Al2)O22O2, a new oxo-amphibole from Harrow Peaks, Northern Victoria Land, Antarctica

Ferri-kaersutite, ideally NaCa2(Mg3TiFe3+)(Si6Al2)O22O2, is a new oxo-amphibole from Harrow Peaks, Northern Victoria Land, Antarctica. It occurs as brown prismatic crystals, up to 200 μm in length, with a vitreous luster, and a perfect {110} cleavage. Ferri-kaersutite is associated with forsterite, diopside, and Cr-bearing spinel. Chemical analyses, by a combination of electron microprobe, SIMS, and 57Fe Mossbauer spectroscopy, gave the following results (in wt%): SiO2 41.69, TiO2 5.30, Al2O3 13.65, Cr2O3 0.09, Fe2O3 4.52, MgO 15.54, CaO 11.03, MnO 0.11, FeO 2.83, Na2O 2.88, K2O 0.96, H2O 0.70, F 0.24, Cl 0.08, O=(F,Cl) −0.12, sum 99.50. On the basis of 24 anions per formula unit, the formula is (Na0.816K0.179)∑0.995(Ca1.726Fe2+0.258Mn0.014)∑1.998(Mg3.383Fe2+0.088Ti0.582Fe3+0.497Al0.439Cr0.011)∑5.00 (Si6.089Al1.911)∑8.00O22[O1.187(OH)0.682F0.111Cl0.020]∑2.00. Ferri-kaersutite is monoclinic with space group C 2/ m . Its unit-cell parameters are a = 9.8378(8), b = 18.0562(9), c = 5.3027(4) A, β = 105.199(9)°, V = 908.99(13) A3, Z = 2. The five strongest reflections in its X-ray powder diffraction pattern [ d in A (relative visual intensity, hkl )] are: 8.4 (s, 110), 3.379 (ms, 131), 3.115 (ms, 310), 2.707 (s, 151), 2.598 (ms, 061). The crystal structure of ferri-kaersutite has been refined on the basis of 1783 observed reflections [ F o > 4σ( F o)] with a final R 1 = 0.038. The relatively large equivalent isotropic displacement parameter at M (1), with respect to those at M (2) and M (3) sites, together with the short M (1)–O(3) distance, suggest the occurrence of Ti4+ at the M (1) site, whereas the small octahedral distortion at this site suggests a low Fe3+ occupancy. This element is mainly hosted at the M (2) and M (3) sites. The occurrence of amphiboles in the magma source region is notably relevant. The melting of Ti-rich amphibole in the lithosphere and subsequent degrees of melt/host peridotite reactions are able to produce melts that account for the compositional spectrum ranging from extreme alkaline lavas to the most common alkaline basalts. In particular, when this amphibole is formed by reaction between a peridotite matrix and metasomatic melts/fluids with high Fe3+/Fetot ratio, its subsequent melting can influence primary volatile contents and ultimately magma rheology.

Tilt signals at Mount Melbourne, Antarctica: evidence of a shallow volcanic source

Mount Melbourne (74°21′ S, 164°43′ E) is a quiescent volcano located in northern Victoria Land, Antarctica. Tilt signals have been recorded on Mount Melbourne since early 1989 by a permanent shallow borehole tiltmeter network comprising five stations. An overall picture of tilt, air and permafrost temperatures over 15 years of continuous recording data is reported. We focused our observations on long-term tilt trends that at the end of 1997 showed coherent changes at the three highest altitude stations, suggesting the presence of a ground deformation source whose effects are restricted to the summit area of Mount Melbourne. We inverted these data using a finite spherical body source, thereby obtaining a shallow deflation volume source located under the summit area. The ground deformation observed corroborates the hypothesis that the volcanic edifice of Mount Melbourne is active and should be monitored multidisciplinarily. Keywords: Tilt monitoring; volcanic dynamics; physics volcanology; ground deformation; Victoria Land. (Published: 1 June 2016) To access the supplementary material for this article, please see the supplementary files in the column to the right (under Article Tools). Citation: Polar Research 2016, 35 , 28269, http://dx.doi.org/10.3402/polar.v35.28269

A new Eemian record of Antarctic tephra layers retrieved from the Talos Dome ice core (Northern Victoria Land)

Polar ice sheets are remarkable repositories of tephra layers. The Talos Dome ice core (72°49′S, 159°11′E), drilled at the edge of the East Antarctic Plateau, close to Late Quaternary volcanoes, offers considerable potential to extend the current tephra time-stratigraphic framework. A tephrochronological study was undertaken of the ice core sections related to the Last Interglacial and the transition to the subsequent glacial period. Thirteen macroscopically visible layers, interpreted to be related to primary deposition of fallout tephra, have been analysed for quantitative grain size and glass shard geochemistry. The layers, precisely framed within the climate (δ18O) record for the core, span in age from 111.6±1.9 to 123.3±2.2ka. Coarse particle size suggests origin from regional sources. Indeed, the vast majority of the samples display an alkaline affinity and trachytic composition that are both typical geochemical features of rifting Antarctic volcanism. Using subtle differences in the geochemical signatures and the comparison with data from previous studies, a few layers are attributed to known coeval Mt. Melbourne eruptions. Another sample subset is consistent with derivation from The Pleiades and Mt. Rittmann volcanoes. One peculiar trachytic glass population appears to be related to activity of the more distant Marie Byrd Land volcanoes. The newly detected tephras provide stratigraphic markers that could facilitate future synchronisation and dating of palaeoclimatic records. The Talos Dome tephra inventory also contributes significantly to the reconstruction of the Northern Victoria Land explosive volcanism, for which chronostratigraphic data for the Last Interglacial temporal segment are poor.

Submarine and subaerial lavas in the West Antarctic Rift System: Temporal record of shifting magma source components from the lithosphere and asthenosphere

AbstractThe petrogenesis of Cenozoic alkaline magmas in the West Antarctic Rift System (WARS) remains controversial, with competing models highlighting the roles of decompression melting due to passive rifting, active plume upwelling in the asthenosphere, and flux melting of a lithospheric mantle metasomatized by subduction. In this study, seamounts sampled in the Terror Rift region of the Ross Sea provide the first geochemical information from submarine lavas in the Ross Embayment in order to evaluate melting models. Together with subaerial samples from Franklin Island, Beaufort Island, and Mt. Melbourne in Northern Victoria Land (NVL), these Ross Sea lavas exhibit ocean island basalt (OIB)‐like trace element signatures and isotopic affinities for the C or FOZO mantle endmember. Major‐oxide compositions are consistent with the presence of multiple recycled lithologies in the mantle source region(s), including pyroxenite and volatile‐rich lithologies such as amphibole‐bearing, metasomatized peridotite. We interpret these observations as evidence that ongoing tectonomagmatic activity in the WARS is facilitated by melting of subduction‐modified mantle generated during 550–100 Ma subduction along the paleo‐Pacific margin of Gondwana. Following ingrowth of radiogenic daughter isotopes in high‐µ (U/Pb) domains, Cenozoic extension triggered decompression melting of easily fusible, hydrated metasomes. This multistage magma generation model attempts to reconcile geochemical observations with increasing geophysical evidence that the broad seismic low‐velocity anomaly imaged beneath West Antarctica and most of the Southern Ocean may be in part a compositional structure inherited from previous active margin tectonics.

Continuous Neoproterozoic to Ordovician sedimentation at the East Gondwana margin — Implications from detrital zircons of the Ross Orogen in northern Victoria Land, Antarctica

The Ross–Delamerian orogenic belt was formed along the eastern side of the Australian–East Antarctic continent during west-directed subduction of the Palaeo-Pacific Ocean in the early Palaeozoic. Northern Victoria Land (NVL) in Antarctica was located at a central position of the Ross-Delamerian system. Its metamorphic basement is formed by three lithotectonic units formerly interpreted as terranes: the Wilson, Bowers and Robertson Bay terranes (from west to east). Dating of detrital zircons from 14 metasedimentary samples of these terranes combined with petrographical and whole-rock geochemical studies give new insights into the stratigraphic and tectonic evolution of NVL. All samples show very similar zircon age spectra with two main intervals, a Ross/Pan-African-age interval (470–700Ma) and a Grenville-age interval (900–1300Ma), as well as subordinate craton-related ages dispersed over the range of ca. 1600–3500Ma. The Ross/Pan-African-age zircon population tends to get more dominant from the Priestley Formation of the Wilson Terrane to the Molar Formation of the Bowers Terrane, and finally to the Robertson Bay Group, whereas the number of craton-related ages diminishes in this direction. A common East Antarctic source area is indicated for all analyzed samples. The Priestley Formation was deposited on the Palaeo-Pacific passive continental margin of East Gondwana in the late Neoproterozoic after Rodinia breakup. The sequence was subsequently metamorphosed and intruded by the Granite Harbour Intrusives during the Ross Orogeny. The Molar Formation of the Bowers Terrane is interpreted as a turbiditic sequence deposited in an accretionary setting on the active continental margin in the Late Cambrian during and after accretion of the Glasgow island arc allochthon. The thick, homogeneous sequence of the Robertson Bay Group resulted from continuous turbiditic sedimentation in an accretionary wedge in front of the Ross Orogen after docking and imbrication of the Glasgow island arc in the Early Ordovician.

P-wave velocity structure beneath Mt. Melbourne in northern Victoria Land, Antarctica: Evidence of partial melting and volcanic magma sources

Mt. Melbourne is a late Cenozoic intraplate volcano located ∼30 km northeast of Jang Bogo Station in Antarctica. The volcano is quiescent with fumarolic activity at the summit. To monitor volcanic activity and glacial movements near Jang Bogo Station, a seismic network was installed during the 2010–11 Antarctic summer field season. The network is maintained during the summer field season every year, and the number of stations has been increased. We used continuous seismic data recorded by the network and an Italian seismic station (TNV) at Mario Zucchelli Station to develop a 3-D P-wave velocity model for the Mt. Melbourne area based on the teleseismic P-wave tomographic method. The new 3-D model presented a relative velocity structure for the lower part of the crust and upper mantle between depths of 30 and 160 km and revealed the presence of two low-velocity anomalies beneath Mt. Melbourne and the Priestley Fault. The low-velocity anomaly beneath Mt. Melbourne may be caused by the edge flow of hot mantle material at the lithospheric step between the thick East Antarctic Craton and thin Ross Sea crust. The other low-velocity anomaly along the Priestley Fault may have been beneath Mt. Melbourne and moved to the southern tip of the Deep Freeze Range, where the crustal thickness is relatively thin. The anomaly was trapped on the fault line and laterally flowed along the fault line in the northwest direction.

Oxo-amphiboles in mantle xenoliths: evidence for H2O-rich melt interacting with the lithospheric mantle of Harrow Peaks (Northern Victoria Land, Antarctica)

Amphiboles are the most widespread hydrous metasomatic phases in spinel-bearing mantle peridotites from Harrow Peaks (HP), Northern Victoria Land (Antarctica). They occur both in veinlets and disseminated in the peridotite matrix (preferentially associated with clinopyroxene and spinel grains). Four amphibole crystals were investigated by single-crystal X-ray diffraction (SC-XRD), electron microprobe analysis (EMPA), secondary ion mass spectrometry (SIMS) and micro-Mossbauer spectroscopy; these crystal-chemical data allow to constrain upper mantle conditions during growth of these amphiboles and the role of volatile circulation during metasomatic processes in the Antarctic region. The HP amphiboles have low Mg# values (69.3–84.1), high TiO2 (2.74–5.30 wt%) and FeOtot contents (3.40 to 6.90 wt%). The Fe3+/Fetot ratios are significantly high (0.53–0.66). The W-site is mainly occupied by O2- (0.984–1.187 apfu) plus OH (H2O: 0.70–1.01 wt%) and minor F (0.04–0.24 wt%) and Cl (0.03–0.08 wt%). Consequently, HP amphiboles are actually characterized by a significant oxo component. The aH2O values were calculated at 1.5 GPa by dehydration equilibrium equations written as H2O-buffering equilibria among end-member components of amphibole and coexisting peridotite phases. Three out of four HP amphibole-bearing peridotites have values of aH2O ranging from 0.122 to 0.335; whereas one sample has aH2O remarkably higher (0.782) approaching an ideal H2O basalt solubility. The HP fO2 values, determined by the olivine-spinel-orthopyroxene oxygeobarometer (ΔQFM = −1.77 : +0.01), are remarkably different from those calculated on the basis of the amphibole dehydration equilibrium and the application of the dissociation reaction (ΔQFM = −2.60 : +6.8). The high aH2O and the extremely high fO2 values, determined by the oxy-amphibole equilibrium with respect to the redox conditions recorded by the co-existing anhydrous minerals (close to QFM buffer), revealed that: i) the amphibole-forming reaction is a relatively recent process with the new phases far from having reached a potential equilibrium with the peridotite matrix; ii) amphibole seems to be formed by the precipitation of migrating H2O-rich melts with a negligible contribution of the peridotite system.

Flora and vegetation of Cape Hallett and vicinity, northern Victoria Land, Antarctica

Cape Hallett (72°19′S; 170°13′E) lies at the northern end of the western coastline of the Ross Sea region, and, to date, there appears to be no full description of its terrestrial flora despite its probable importance in understanding links between biodiversity and latitude. Here we present information about lichens and mosses from published papers, herbarium collections and personal surveys for Cape Hallett and seven nearby sites. A total of 59 lichen and 11 moss species are reported for these eight sites. Cape Hallett is one of the richest sites for terrestrial biodiversity in the Ross Sea region with about 46 lichen species and nine species of bryophytes. Lichens have their greatest diversity on the upper scree and summit area (30 species, 330 m), the least within the large penguin colony at sea level (one species). The station at Cape Hallett was established in 1957, and some of the earliest ecological and ecophysiological studies in Antarctica were carried out there. Historical comparisons are possible and have revealed considerable changes in vegetation in the lower flush area, a high level of frost heave disturbance, new lichen growth rate estimates for northern Victoria Land and extreme stability of the snow banks on the scree slopes. Cape Hallett represents a very important site for studies on links between terrestrial flora and the environment as well as on possible effects of climate change.

Shallow ice-core drilling on Styx glacier, northern Victoria Land, Antarctica in the 2014-2015 summer

Shallow ice-core drilling on Styx glacier, northern Victoria Land, Antarctica in the 2014-2015 summer

Variation in the characteristics and development of soils at Edmonson Point due to abiotic and biotic factors, northern Victoria Land, Antarctica

The lack of baseline surveys of soil environments in many areas of Antarctica provides an impediment to understanding their suitability for supporting biotic communities and limits abilities to monitor and predict impacts of environmental changes. A soil survey was conducted at Edmonson Point (Victoria Land) within representative local environments to identify their variability and drivers of soil processes and geochemistry. The soils were coarse-textured and lacked cohesion and structural development. The parent material was homogenous, and consisted of weathered and unconsolidated basaltic lavas and scoria. Despite these similarities, the soils varied significantly with the variation driven by local environmental and biotic factors. Penguins had the greatest influence, deposited guano altered soil processes leading to profound changes in soil characteristics. The ornithogenic soils were rich in penguin bio-elements, with low C/N, high EC and large variation in pH. Contents of N and C declined at comparable rates as C/N values did not change with time. Ornithogenic P was not readily lost, resulting in its high concentrations in relict soils. Abundant bacteria played a key role in these processes, but after cessation of guano inputs bacterial numbers and activity declined considerably. Alternatively, rich autotrophic microflora had a little influence on ornithogenic soil geochemistry. Characteristics and development of mineral soils were driven by hydrology and associated biological processes. Dry fellfield soils were the most immature, as indicated by more coarse-grained material, neutral pH, low EC and C/N values, scarce microflora and elemental content corresponding to typical background values. Alternatively, soils from moss communities and wetlands had higher amounts of fine-grained material, C, N and C/N values and lower pH that resulted from accumulation of organic matter. Elemental concentrations in soils from moss communities were similar to those in fellfields, but were elevated in wetland soils. While C and N contents seemed to be controlled by biotic communities, geochemistry of other elements was driven by external inputs. Although some inputs may originate from substratum weathering in the surrounding areas, marine-derived elements redistributed with penguin guano seemed to be the major source of the enrichment. Analyses of the origin and distribution of the soil elements may provide valuable records for reconstruction of geochemical and environmental processes in Antarctic terrestrial ecosystems.

Late Pleistocene-Holocene volcanic activity in northern Victoria Land recorded in Ross Sea (Antarctica) marine sediments

Eight pyroclastic fall deposits have been identified in cores of Late Pleistocene-Holocene marine sediments from the Ross Sea (Antarctica), and their components, granulometry and clast morphologies were analysed. Sedimentological, petrographic and geochemical analysis of clasts, with 40Ar-39Ar dating of alkali feldspar grains, indicate that during this period at least five explosive eruptions of mid to high intensity (plinian to subplinian) occurred, and that three of these eruptions took place from Mount Melbourne volcanic complex, between 137.1 ± 3.4 and 12 ka. Geochemical comparison of the studied tephra with micro- and crypto-tephra recovered from deep Antarctic ice cores and from nearby englacial tephra at Frontier Mountain indicates that eruptive activity in the Melbourne Volcanic Province of northern Victoria Land was intense during the Late Pleistocene-Holocene, but only a general area of provenance for the majority of the identified tephra can be identified.

An apparent population decrease, or change in distribution, of Weddell seals along the Victoria Land coast

AbstractGround counts during 1959–1968 compared with counts using high resolution (0.6 m2) satellite imagery during 2008–2012 indicated many fewer Weddell seals (Leptonychotes weddellii) at two major molting areas in the western Ross Sea: Edisto Inlet‐Moubray Bay, northern Victoria Land, and McMurdo Sound, southern Victoria Land. Breeding seals have largely disappeared from Edisto‐Moubray, though the breeding population in McMurdo Sound appears to have recovered from harvest in the 1960s. The timing of decline, or perhaps spreading (lower numbers of seals in more places), is unknown but appears unrelated to changes in sea ice conditions. We analyzed both historic and satellite‐derived ice data confirming a large expansion of pack ice mostly offshore of the Ross Sea, and not over the continental shelf (main Weddell seal habitat), and a thinning of fast ice along Victoria Land (conceivably beneficial to seals). Timing of fast ice presence and extent in coves and bays along Victoria Land, remains the same. The reduction in numbers is consistent with an altered food web, the reasons for which are complex. In the context of a recent industrial fishery targeting a seal prey species, a large‐scale seal monitoring program is required to increase understanding of seal population changes.

Highly heterogeneous soil bacterial communities around Terra Nova Bay of Northern Victoria Land, Antarctica.

Given the diminished role of biotic interactions in soils of continental Antarctica, abiotic factors are believed to play a dominant role in structuring of microbial communities. However, many ice-free regions remain unexplored, and it is unclear which environmental gradients are primarily responsible for the variations among bacterial communities. In this study, we investigated the soil bacterial community around Terra Nova Bay of Victoria Land by pyrosequencing and determined which environmental variables govern the bacterial community structure at the local scale. Six bacterial phyla, Actinobacteria, Proteobacteria, Acidobacteria, Chloroflexi, Cyanobacteria, and Bacteroidetes, were dominant, but their relative abundance varied greatly across locations. Bacterial community structures were affected little by spatial distance, but structured more strongly by site, which was in accordance with the soil physicochemical compositions. At both the phylum and species levels, bacterial community structure was explained primarily by pH and water content, while certain earth elements and trace metals also played important roles in shaping community variation. The higher heterogeneity of the bacterial community structure found at this site indicates how soil bacterial communities have adapted to different compositions of edaphic variables under extreme environmental conditions. Taken together, these findings greatly advance our understanding of the adaption of soil bacterial populations to this harsh environment.

Mass balance vs Rietveld refinement to determine the modal composition of ultramafic rocks: The case study of mantle peridotites from Northern Victoria Land (Antarctica)

This paper aims at applying the Rietveld refinement method to X-ray powder diffraction (XRPD) spectra in order to determine the mineralogical assemblages of ultramafic rocks. The results are compared to those obtained by mass balance (MB) calculations, a least squares method that reduces major element chemical analyses to the whole rock composition. This methodological work was carried out in five hydrous and anhydrous mantle xenoliths from Northern Victoria Land, Antarctica.The intrinsic goodness of the XRPD and MB results, evaluated by with Rwp and r2 respectively, shows similar values of modal compositions. Independent of the mineralogy (amphibole-bearing and amphibole-free) and textures (fine to coarse grained), good agreement (<2%) is observed for modal contents lower than 10%, whereas a discrepancy of up to 10% is recorded for phase abundances higher than 70%. The comparison of the two methods has allowed us to demonstrate that the Rietveld method is applicable even when limited amount of material (<1g) is available, and the “classical” chemical approaches (XRF and EMPA) cannot be applied. Moreover it not only provides information on rock mineral concentrations (wt.%), but also gives supplementary information on crystallographic data (i.e., mineral crystallite size, mineral lattice parameters, density, site occupancies).On the other hand, the MB procedure provides direct chemical information of both bulk rock and minerals, but requires a large amount of material (i.e., for XRF at least >1g of material is needed). Dealing with MB procedure, problems can occur if accessory minerals cannot be identified in thin sections, which are, however, part of the whole-rock analysis. Besides, the strength of XRPD, if compared with all the suitable methods for the quantitative mineralogical identification, is to provide direct information about the physical properties, and mineral site occupancies that could indirectly give a mineral chemical composition.

Paleomagnetism of the Jurassic Transantarctic Mountains revisited — Evidence for large dispersion of apparent polar wander within less than 3 Myr

The Transantarctic mountains predominantly consist of Jurassic continental flood basalts (Kirkpatrick) and sills (Ferrar) emplaced during the earliest phase of the break-up of Pangea. Published ages, based on a variety of geochronological methods all agree rather well and cluster around 180Ma suggesting emplacement during a rather short time interval of not more than 3Myr. Paleomagnetic studies, mostly carried out between the 60s and 90s of the last century, however, yield two well defined but significantly different groups of paleomagnetic pole positions plotting either in intermediate latitudes (A) or at latitudes exceeding 60°S (B). Pole positions belonging to group A are generally interpreted to be of primary origin whereas the significance of group B poles remains unclear. Here we report new data from the Kirkpatrick basalts of Northern Victoria Land, Antarctica, where 157 oriented paleomagnetic samples were taken, covering about 800m of stratigraphy and 23 volcanic flows in Gair Mesa (73.4666°S; 162.8666°E). After removal of a steep magnetic overprint with rather low coercivities straight linear segments of exclusively normal polarity trending toward the origin of projection are identified in 151 samples from 22 sites. Maximum unblocking temperatures do not exceed 580°C and maximum coercivities not 60mT. The resulting mean virtual geomagnetic pole (VGP) for the Gair Mesa plots at 66.4°S; 227.7°E (α95 of 6.2°, k=25.7) comparable to group B poles. Reflecting light microscopy reveals that the magnetic inventory of all samples analyzed is dominated by magnetite showing shrinking cracks and broad ilmenite lamellae, the latter being diagnostic for high temperature oxidation. Analysis of the distribution of the 22 pole positions obtained here shows that secular variation has successfully been averaged (Sb=15.9°) suggesting that the rocks studied here have recorded the time averaged geomagnetic field during early mid Jurassic times. Based on these new results we postulate that both clusters A and B of pole positions reflect primary magnetizations and that the Kirkpatrick basalts of Gair Mesa have been emplaced in a rather short normal polarity time interval of 3Myr. If our reasoning is correct, the apparent polar wander path for the latest early Jurassic might be more complex than previously thought. Whether this complexity is evidence for massif True Polar Wander remains speculative.

The Wilkes Land Anomaly revisited

AbstractThe Wilkes Land Gravity Anomaly, first reported in 1959–60, is located in northern Victoria Land in the Pacific Ocean sector of East Antarctica, 1400 km west of the Ross Sea and centred at 70°00'S-140°00'E. Initially described on the basis of ground-based seismic and gravity survey, and estimated at the time to have a diameter of 243 km, the original data are now supplemented by data from airborne radiosound survey, airborne gravity survey, airborne magnetic survey and satellite remote sensing. These new data enable us to expand upon the original data, and reveal that the structure has a diameter of some 510 km, is accompanied by ice streams and a chaotically disturbed region of the continental ice sheet, has a subglacial topographical relief of ≥1500 m, and exhibits a negative free air gravity anomaly associated with a larger central positive free air gravity anomaly. The feature has been described as a volcanic structure, an igneous intrusion, an ancient igneous diapir, a subglacial sedimentary basin, a glacially eroded subglacial valley, a tectonic feature and a meteorite impact crater. We re-examine the feature on the basis of these collective data, with emphasis on the free air gravity anomaly signs, magnitudes and patterns, magnetic signature magnitudes and patterns, and the size, shape, dimensions and morphology of the structure. This enhanced view adds substantially to the original description provided at the time of discovery, and suggests several explanations for the origin of the Wilkes Land Anomaly. However, the importance of this feature lies not only in determining its origin but by the fact that this part of the Wilkes Subglacial Basin is one of the most prominent regional negative geoid and associated gravity anomalies of the Antarctic continent.

Polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in Antarctic ice-free areas: Influence of local sources on lakes and soils

Antarctica is usually considered a pristine ecosystem; nevertheless it is influenced by Persistent Organic Pollutants (POPs), mainly driven by long-range atmospheric transport (LRAT). However, localized sources such as human and wildlife activities can also contribute to pollution, constituting contaminated points at a local scale. Antarctic ice-free areas, where rare lakes are located, are influenced by such sources. In this work we determine polychlorinated biphenyls (PCBs, including the non-Aroclor CB-11) and polybrominated diphenyl ethers (PBDEs) in water and sediment samples of 6 lakes in Northern Victoria Land and in soils near the Italian research station Mario Zucchelli. Determinations were performed through gas chromatography (GC) coupled both to low-resolution and high-resolution mass spectrometry (LRMS, HRMS). POP concentrations in lakes resulted low and rather similar across the sites despite their distance: ΣPCBs range between 46 and 143pgL−1 in water and 10 and 634pgg−1 in sediments, while ΣPBDEs range between 60 and 151pgL−1 in water and 193 and 1682pgg−1 in sediments. Lakes exhibited limited amplification phenomena in water during the melting season. PBDEs in the soils near the base yielded more concerning results, reaching a concentration of 33ngg−1.

Mapping the lithic colonization at the boundaries of life in Northern Victoria Land, Antarctica

The endolithic microbial communities of the Antarctic represent a borderline lifestyle in the most hostile ice-free areas of the continent. The extreme adaptation of microbes in these communities renders them very sensitive to environmental changes. To date, the actual distribution of these communities has never been investigated; yet, this information would define the geographic limits for life at present and supply a useful tool for monitoring any possible future variation related to climate change. In this study, most of the outcrops of Northern and of one site in Southern Victoria Land were recorded by altitudinal and sea distance gradients. The presence of endolithic life was determined by in situ observation, by microscopic observation of rock fragments in the laboratory, and, for doubtful samples, by culture experiment. Colonizers were present in more than 87 % of the visited sites. The presence of lithic life in Victoria Land appears to be wider than that reported 14 years earlier. The colonization trend follows climatic variation, with epiliths prevailing in coastal sites and decreasing towards the interior, while chasmoendoliths and cryptoendoliths increase and become predominant from the coast towards the inland sites. Typical cryptoendolithic colonization was exclusive on porous rocks as sandstone, chasmoendolithic colonization occurred even in less porous but translucent rocks as granite and quartz. Multivariate analysis of the combined results clearly indicates the pivotal role of the rock type in the colonization of endolithic micro-organisms; sandstone allows lithobionts to push themselves towards areas characterized by harsher conditions.

Persistent Organic Pollutants (POPs) in Antarctica: Occurrence in continental and coastal surface snow

Despite geographical isolation and almost complete absence of human settlements, Antarctica is affected by Persistent Organic Pollutants (POPs): the traces of these impacts are recorded in the snow. Although POPs were detected in Antarctica decades ago, there are still large knowledge gaps and a comprehensive understanding of their fundamental patterns is lacking. In this study, polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs, including the non-Aroclor PCB-11), polybrominated diphenyl ethers (PBDEs) and polycyclic aromatic hydrocarbons (PAHs) were measured in surface snow samples from five selected locations of Northern Victoria Land. To our knowledge this is the first study providing ground-based measurements of PCDD/Fs, PCB-11 and PBDEs in Antarctic surface snows, including the plateau. Long-range atmospheric transport (LRAT) followed by regional redistribution were hypothesized as governing sources of POPs to the Antarctic Plateau, but also local pollution from human activities was found. Sub-pgL−1 levels of PCDD/Fs were detected in the coastal samples, while PCBs (ΣPCBs 110-580pgL−1) generally showed a decrease with respect to the past decades. Similar concentrations of PBDEs (ΣBDEs 130–340pgL−1) were found, mainly attributable to the congeners BDE-47 and BDE-99. PAHs (ΣPAHs 0.65–140ngL−1) were the most abundant compounds in all sites with an unexpected high value near a refueling point. Possible source areas of contamination were investigated by means of the HYSPLIT model.