Antarctic Ice-free Areas Research Articles

Myxomycetes in the Antarctic: A review

This work summarize the results of Myxomycetes collections carried out by European and South American researchers on Antarctic ice free areas during the last fifty years. An annotated list and an identification key for the nine species with confirmed occurrence on the continent are presented.

Modelling and prediction of major soil chemical properties with Random Forest: Machine learning as tool to understand soil-environment relationships in Antarctica

Digital Soil Mapping includes quantitative estimations of soil attributes in areas with little or no soil information, being important in remote landscapes such as the Antarctic ice-free areas. Our objective was to predict the spatial distribution of major soil chemical attributes in two important Antarctic Peninsula regions; as well as to identify the main environmental drivers of these attributes. For this, we compiled one of the largest soil databases of Antarctica and applied the machine learning algorithm Random Forest to predict seven soil chemical attributes. We also used covariates selection and partial dependence analysis to better understand the relationships of the attributes with the environmental covariates. Bases sum was the attribute which presented the highest prediction performance, whereas Na and P predictions presented the lowest. Both accuracy and uncertainty indicators showed the difficulties of Random Forest in handling natural outliers. The soil attributes distribution was related to the mean annual temperature and annual precipitation, multispectral bands and indexes related to the vegetation response, rookeries distance expressing the birds’ activity, and topographic attributes. The attributes showed a climatic gradient, with higher values of bases sum, pH, and Na in Northern Antarctic Peninsula, and higher total organic carbon, H + Al and P in Maritime Antarctic. This shows the climate covariates influence the soil variability in a macroscale, whereas terrain predictors control the soil at local scales. This study showed the Digital Soil Mapping potential to surpass the limitations of conventional mapping and indicated the feasibility in obtaining interpretable predictions which can be directly associated with the soil forming factors. Finally, the data generated can be used as reference to monitor the impacts of the climate changes on the soils of Antarctica.

Microbial diversity in Antarctic Dry Valley soils across an altitudinal gradient.

The Antarctic McMurdo Dry Valleys are geologically diverse, encompassing a wide variety of soil habitats. These environments are largely dominated by microorganisms, which drive the ecosystem services of the region. While altitude is a well-established driver of eukaryotic biodiversity in these Antarctic ice-free areas (and many non-Antarctic environments), little is known of the relationship between altitude and microbial community structure and functionality in continental Antarctica. We analysed prokaryotic and lower eukaryotic diversity from soil samples across a 684 m altitudinal transect in the lower Taylor Valley, Antarctica and performed a phylogenic characterization of soil microbial communities using short-read sequencing of the 16S rRNA and ITS marker gene amplicons. Phylogenetic analysis showed clear altitudinal trends in soil microbial composition and structure. Cyanobacteria were more prevalent in higher altitude samples, while the highly stress resistant Chloroflexota and Deinococcota were more prevalent in lower altitude samples. We also detected a shift from Basidiomycota to Chytridiomycota with increasing altitude. Several genera associated with trace gas chemotrophy, including Rubrobacter and Ornithinicoccus, were widely distributed across the entire transect, suggesting that trace-gas chemotrophy may be an important trophic strategy for microbial survival in oligotrophic environments. The ratio of trace-gas chemotrophs to photoautotrophs was significantly higher in lower altitude samples. Co-occurrence network analysis of prokaryotic communities showed some significant differences in connectivity within the communities from different altitudinal zones, with cyanobacterial and trace-gas chemotrophy-associated taxa being identified as potential keystone taxa for soil communities at higher altitudes. By contrast, the prokaryotic network at low altitudes was dominated by heterotrophic keystone taxa, thus suggesting a clear trophic distinction between soil prokaryotic communities at different altitudes. Based on these results, we conclude that altitude is an important driver of microbial ecology in Antarctic ice-free soil habitats.

Machine learning applied for Antarctic soil mapping: Spatial prediction of soil texture for Maritime Antarctica and Northern Antarctic Peninsula

Soil texture is one of the most important soil properties as it drives several physical, chemical, biological, hydrological, and mechanical properties, and processes. In Antarctica the soil texture controls different important ecological processes, such as carbon stocks, nutrient leaching, and toxic metals retention. Thus, there is a pressing need for accurate soil data for the Antarctic ice-free areas, especially under the pressures imposed by climate changes and human disturbances on the continent. In this work, we predicted the distribution of sand, silt, and clay of the main ice-free areas of Maritime Antarctica and Northern Antarctic Peninsula, allowing novel soil texture maps to be produced for Antarctica. We used legacy soil texture data and tested different machine learning models, of which Random Forest presented the best performance to prediction. The best predictors were associated with climate, topography, and soil development degree, representing the scorpan model factors. The highest accuracy was obtained for clay prediction, mainly in the topsoil (LCCC of 0.49 and R2 of 0.31). In the mapping, the sand contents presented higher values, with a predominance of sandy loam texture, although clay contents are higher in some spots where chemical weathering is stronger. The final maps presented good spatial consistency, with soil texture distributed according to factors such as geomorphology, parent material and pedogenetic development. With our results, we aim to subsidize decision-making about soils in Antarctica, besides providing pioneer data that can be incorporated in global environmental models.

Relationships between concentrations of mercury and organic carbon in soils allow the identification of Antarctic ice-free areas with enhanced deposition of the metal

Antarctica is a sink for mercury (Hg) and plays an important role in the global Hg cycle. Knowledge about the environmental fate of Hg in Antarctic terrestrial ecosystems, however, remains highly restricted. In this study, we investigated soil Hg in samples from three areas located across a wide latitudinal range from about 62°S to over 74°S with very different climatic and environmental conditions and different potential (natural and anthropogenic) sources of Hg. The highest Hg levels were found in soils beneath mosses and ornithogenic soils in the Antarctic Peninsula, whereas extremely low values were found in coastal East Antarctica. Total Hg concentrations in soil samples from the three study areas were always closely related to those of organic carbon (OC). In corroborating the results of previous studies, this large-scale survey strongly suggests that OC is a dominant driver affecting Hg distribution in Antarctic soils. The observed linear relationship between Hg and OC concentrations, also supported by available literature data, probably, has a general relevance for Antarctic soils, and allows to identify samples affected by enhanced Hg deposition from anthropogenic or natural sources. In providing a better understanding of the biogeochemical cycle of Hg in Antarctic terrestrial ecosystems, this study suggests that soil OC content must be considered to assess Hg distribution patterns in Antarctic soils. In samples (including those of lacustrine sediments, planktonic, and benthic algal mats) unaffected by an accentuated deposition of Hg, the value of the ratio [Hg ng/g]/[OC %] appears to be less than ∼ 11.

Overexpression of Head date 1 gene (Hd1): an adaptation of antarctic hairgrass to guano input from Macronectes giganteus colonies of Antarctica

The Antarctic biodiversity, beyond the species composition, also comprises interactions between fauna and flora. M. giganteus, is one of the species that occupy the antarctic ice-free areas for reproduction. The moss Sanionia uncinata (Hedw.) Loeske and Deschampsia antarctica Desv. gress, common in Antarctica, with other species make up vast green formations and is associated with breeding areas of seabirds. These sites are large deposits of guano, because a large amount of birds those gather in colonies. Due to this large supply of guano, the soil becomes a deposit of minerals, mainly of nitrogen available in the form of ammonium and nitrate. The problem is that not all plant species tolerate high quantities of these substances so different plant species show trends in the mechanisms of tolerance to stress by ammonium, which have been proven at the molecular level. The aim of this study was to investigate the influence of breeding colonies of seabirds on plant populations in the South Shetland Islands, Antarctica, from a molecular perspective. From the analysis of the collected samples, using the RNA-Seq and qRT-PCR approach was possible to identify a single gene differential and significantly expressed in D. antarctica. The LOC_Os06g16380 gene among the sampled treatments (control, 1m and 10m), showed higher expression coming 1m near breeding areas of M. giganteus. Our results suggest that Hd1 is associated with the plants stress related to guano input since that soil analysis demonstrated a higher concentration of mineral nitrogen available near of breeding areas of seabirds.

Hydrological impact of Middle Miocene Antarctic ice-free areas coupled to deep ocean temperatures

Oxygen isotopes from ocean sediments (δ18O) used to reconstruct past continental ice volumes additionally record deep water temperatures (DWTs). Traditionally, these are assumed to be coupled (ice-volume changes cause DWT changes). However, δ18O records during peak Middle Miocene warmth (~16–15 million years ago) document large rapid fluctuations (~1–1.5‰) difficult to explain as huge Antarctic ice sheet (AIS) volume changes. Here, using climate modelling and data comparisons, we show DWTs are coupled to AIS spatial extent, not volume, because Antarctic albedo changes modify the hydrological cycle, affecting Antarctic deep water production regions. We suggest the Middle Miocene AIS had retreated substantially from previous Oligocene maxima. The residual ice sheet varied spatially more rapidly on orbital timescales than previously thought, enabling large DWT swings (up to 4 °C). When Middle Miocene warmth terminated (~13 million years ago) and a continent-scale AIS had stabilized, further ice-volume changes were predominantly in height rather than extent, with little impact on DWT. Our findings imply a shift in ocean sensitivity to ice-sheet changes occurs when AIS retreat exposes previously ice-covered land; associated feedbacks could reduce the Earth system’s ability to maintain a large AIS. This demonstrates ice-sheet changes should be characterized not only by ice volume but also by spatial extent.

Pan-Antarctic map of near-surface permafrost temperatures at 1 km2 scale

Abstract. Permafrost is present within almost all of the Antarctic's ice-free areas, but little is known about spatial variations in permafrost temperatures except for a few areas with established ground temperature measurements. We modelled a temperature at the top of the permafrost (TTOP) for all the ice-free areas of the Antarctic mainland and Antarctic islands at 1 km2 resolution during 2000–2017. The model was driven by remotely sensed land surface temperatures and downscaled ERA-Interim climate reanalysis data, and subgrid permafrost variability was simulated by variable snow cover. The results were validated against in situ-measured ground temperatures from 40 permafrost boreholes, and the resulting root-mean-square error was 1.9 ∘C. The lowest near-surface permafrost temperature of −36 ∘C was modelled at Mount Markham in the Queen Elizabeth Range in the Transantarctic Mountains. This is the lowest permafrost temperature on Earth, according to global-scale modelling results. The temperatures were most commonly modelled between −23 and −18 ∘C for mountainous areas rising above the Antarctic Ice Sheet and between −14 and −8 ∘C for coastal areas. The model performance was good where snow conditions were modelled realistically, but errors of up to 4 ∘C occurred at sites with strong wind-driven redistribution of snow.

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.

Micro-investigation of EPICA Dome C bottom ice: evidence of long term in situ processes involving acid–salt interactions, mineral dust, and organic matter

The EPICA Dome C ice core (EDC) reached a final depth of 3260 m, at a maximum height of about 15 m above the ice–bedrock interface in December 2004. We present here data gained from a detailed investigation of selected samples of the deeper part of the core located below 3200 m and referred to as bottom ice. This part of the core has been poorly investigated so far mainly because there are significant challenges in interpreting paleo-records that were very likely modified by long term in situ processes. Our study combines high resolution ion chromatography, high resolution synchrotron X-Ray micro-fluorescence (micro XRF), scanning, and transmission electron microscopy. Our aim was to identify the long term physico-chemical processes at work close to the bedrock, to determine how they have altered the initial registers, and, ultimately to extract information on the very ancient Antarctic environment.The ubiquitous presence of nanometer iron oxide crystals at the surface of wind-borne dust aggregates containing also large amount of organic matter raises the possibility that the consolidation of windborne dust clusters formed during ice recrystallization could be related to microbial iron reduction and, thus, to the progressive reactivation of dormant bacterial activity in warming ice. Inclusions of size and number density increasing with depth observed in the 12 last meters (3248–3260 m) contain liquid and solid species, among them marine biogenic acids, numerous wind-borne dust aggregates and clusters of large reversible calcium carbonate particles precipitated once the inclusion was formed and often covered by secondary gypsum. The refreezing of slush lenses is discussed as a potential cause of the formation of such heterogeneous and complex mixtures. In addition to the very fine micrometer size minerals windborne from extra-Antarctic continental sources and often accreted in large aggregates, single medium size particles (a few to ca 20 μm and among them organic debris) are commonly encountered. Their size, surface shape, and mineralogy suggest that aerosol transport from Antarctic ice-free areas played a significant role at the time EDC bottom ice was formed. Concentrations and concentration ratios of biogenic sulfur species also advocate for the strengthening of peri-Antarctic meteorological patterns that favor the inland penetration of disturbed flow carrying local material. Very large well preserved mineral particles several tens of micrometers in diameter, and biotope relics in deeper ice close to 3260 m likely come from the sub-glacial environment.

Interpreting last glacial to Holocene dust changes at Talos Dome (East Antarctica): implications for atmospheric variations from regional to hemispheric scales

Abstract. Central East Antarctic ice cores preserve stratigraphic records of mineral dust originating from remote sources in the Southern Hemisphere, and represent useful indicators of climatic variations on glacial-interglacial time scales. The peripheries of the East Antarctic Ice Sheet, where ice-free areas with the potential to emit dust exist, have been less explored from this point of view. Here, we present a new profile of dust deposition flux and grain size distributions from an ice core drilled at Talos Dome (TALDICE, Northern Victoria Land, East Antarctica), where there is a significant input of dust from proximal Antarctic ice-free areas. We analyze dust and stable water isotopes variations from the Last Glacial Maximum to the Late Holocene, and compare them to the EPICA Dome C profiles from central East Antarctica. The smaller glacial-interglacial variations at Talos Dome compared to Dome C and a distinctive decreasing trend during the Holocene characterize the TALDICE dust profile. By deciphering the composite dust signal from both remote and local sources, we show the potential of this combined proxy of source activity and atmospheric transport to give information on both regional and larger spatial scales. In particular, we show how a regional signal, which we relate to the deglaciation history of the Ross Sea embayment, can be superimposed to the broader scale glacial-interglacial variability that characterizes other Antarctic sites.

An Update on Sedimentary Pigments in Victoria Land Lakes (East Antarctica)

Antarctic ice-free areas contain lakes and ponds that have interesting limnological features and are of wide global significance as early warning indicators of climatic and environmental change. However, most limnological and paleolimnological studies in continental Antarctica are limited to certain regions. There are several ice-free areas in Victoria Land that have not yet been studied well. There is therefore a need to extend limnological studies in space and time to understand how different geological and climatic features affect the composition and biological activity of freshwater communities. With the aim of contributing to a better limnological characterization of Victoria Land, this paper reports data on sedimentary pigments (used to identify the main algal taxa) obtained through a methodology that is more sensitive and selective than that of previous studies. Analyses were extended to 48 water bodies in ice-free areas with differing lithology, latitude, and altitude, and with different morphometry and physical, chemical, and biological characteristics in order to identify environmental factors affecting the distribution and composition of freshwater autotrophic communities. A wider knowledge of lakes in a limnologically important region of Antarctica was obtained. Cyanophyta was found to be the most important algal group, followed by Chlorophyta and Bacillariophyta, whereas latitude and altitude are the main factors affecting pigment distribution.

Multiple sources supply eolian mineral dust to the Atlantic sector of coastal Antarctica: Evidence from recent snow layers at the top of Berkner Island ice sheet

The Sr and Nd isotopic composition of dust extracted from recent snow layers at the top of Berkner Island ice sheet (located within the Filchner–Ronne Ice Shelf at the southern end of the Weddell Sea) enables us, for the first time, to document dust provenance in Antarctica outside the East Antarctic Plateau (EAP) where all previous studies based on isotopic fingerprinting were carried out. Berkner dust displays an overall crust-like isotopic signature, characterized by more radiogenic 87Sr/ 86Sr and much less radiogenic 143Nd/ 144Nd compared to dust deposited on the EAP during glacial periods. Differences with EAP interglacial dust are not as marked but still significant, indicating that present-day Berkner dust provenance is distinct, at least to some extent, from that of the dust reaching the EAP. The fourteen snow-pit sub-seasonal samples that were obtained span a two-year period (2002–2003) and their dust Sr and Nd isotopic composition reveals that multiple sources are at play over a yearly time period. Southern South America, Patagonia in particular, likely accounts for part of the observed spring/summer dust deposition maxima, when isotopic composition is shifted towards “younger” isotopic signatures. In the spring, possible additional inputs from Australian sources would also be supported by the data. Most of the year, however, the measured isotopic signatures would be best explained by a sustained background supply from putative local sources in East Antarctica, which carry old-crust-like isotopic fingerprints. Whether the restricted East Antarctic ice-free areas produce sufficient eolian material has yet to be substantiated however. The fact that large (> 5 μm) particles represent a significant fraction of the samples throughout the entire time-series supports scenarios that involve contributions from proximal sources, either in Patagonia and/or Antarctica (possibly including snow-free areas in the Antarctic Peninsula and other areas as well). This also indicates that additional dust transport, which does not reach the EAP, must occur at low-tropospheric levels to this coastal sector of Antarctica.

Biogeography of terrestrial cyanobacteria from Antarctic ice-free areas

AbstractCyanobacteria inhabit the Antarctic continent and have even been observed in the most southerly ice-free areas of Antarctica (86–87° S). The highest molecular diversity of cyanobacterial communities was found in the areas located between 70° S and 80° S. Further south and further north from this zone, the diversity abruptly decreased. Seventy-nine per cent (33 of 42 operational taxonomic units) of Antarctic terrestrial cyanobacteria have a cosmopolitan distribution. Analysis of the sampling efforts shows that only three regions (southern Victoria Land, the Sør Rondane Mountains and Alexander Island) have been particularly well studied, while other areas did not receive enough attention. Although cyanobacteria possess a capacity for long-range transport, regional populations in Antarctic ice-free areas seem to exist. The cyanobacterial communities of the three most intensively studied regions, separated from each other by a distance of 3000–3400 km, had a low degree of similarity with each other. Further development of microbial biogeography demands a standardized approach. For this purpose, as a minimal standard, we suggest using the sequence of cyanobacterial 16S rRNA gene between Escherichia coli positions 405 and 780.

Nematodes from saline and freshwater lakes of the Vestfold Hills, East Antarctica, including the description of Hypodontolaimus antarcticus sp. n.

The invertebrate fauna of many Antarctic ice-free areas, even those close to permanent research stations, can be poorly known. Here we describe some nematodes from freshwater and saline, marine-derived lakes of the Vestfold Hills, East Antarctica. The freshwater lakes contained the widespread East Antarctic endemic species, Plectus frigophilus Kirjanova, 1958. The saline lakes were inhabited by two recently described species, Halomonhystera halophila Andrassy, 2006 and Halomonhystera continentalis Andrassy, 2006, and by a new species described in this report, Hypodontolaimus antarcticus sp. n. Originally marine but now brackish Highway Lake contained a nematode fauna with both freshwater and marine-derived components. The nematode fauna of Antarctica now consists of 54 named species, 22 of which are found in East Antarctica.

Depth distribution of euryhaline halophilic bacteria in Suribati Ike, a meromictic lake in East Antarctica

Euryhaline halophiles grow over a wide range of salinity, from 15% NaCl and even saturation level (about 30% NaCl). Several species of euryhaline halophiles occur worldwide, especially in marine environments and also in aquatic and terrestrial habitats of the Antarctic ice-free areas. A biogeographic view of Antarctic halophiles is that their migration among lakes on land is more difficult than in marine setting. Ponds and lakes on land may thus serve as “islands” which facilitate the selection and separation of unique species. We isolated euryhaline halophiles from the saline lake, Suribati Ike, near Syowa Station and placed them into seven groups, each demonstrating a clear depth-related distribution. Six of the seven groups probably represent new species of the genera Halomonas and Marinobacter. This result suggests that Antarctic saline lakes exhibit high selectivity of unique euryhaline halophiles and possibly of other microbial groups.