Ice-free Areas Research Articles

An inventory of glacial lakes in the South Shetland Islands (Antarctica): temporal variation and environmental patterns.

Monitoring and inventorying proglacial lakes in the Maritime Antarctica region is essential for understanding the effects of climate change on these environments. This study uses Landsat images to create a map of lakes in ice-free areas of the South Shetlands Islands (SSI) for 1986/89, 2000/03 and 2020, and verification of patterns of change in lake areas and numbers. Normalized water difference index (NDWI) products, image segmentation, field records, and cartographic products from other studies were used to validate the results. Results show a 60% increase in the number of lakes from 1986/89 to 2000/03; and a 55% increase from 2000/03 to 2020. There was a 52% increase in lake areas from 1986/89 to 2000/03; a 79% increase from 2000/03 to 2020; and a 173% increase from 1986 to 2020. From 1986 to 2020, the most significant changes were a decrease in the average elevation and distance from glaciers and an increase in distance from the sea. In 2020, SSI lakes were predominantly coastal and ice-marginal, with an E and S orientations, flat surfaces, and a low declivity.

Trends in the intensity of dense water cascading from the Arctic shelves due to ice cover reduction in the Arctic seas

The article discusses the possible relationship between changes in the ice cover area of the shelf seas of the Arctic Ocean and the intensity of dense water cascading, based on calculation data obtained with the NEMO model for the period 1986–2010, with the findings issued at 5-day intervals and a spatial resolution of 1/10°. The cascading cases were calculated using an innovative method developed by the author. The work is based on the assumption that as the ice cover in the seas retreats, the formation of cooled dense water masses is intensified, which submerge and flow down the slope from the shelf to great depths. Thus, in the Arctic shelf seas, the mechanism of water densification due to cooling is added to the mechanism of water densification during ice formation, or, replaces it for certain regions. It was found that in the Barents Sea, the Laptev Sea and the Beaufort Sea, a decrease in the ice cover area causes an increase in the number of cases of cascading. However, in most of the Arctic seas, as the area of ice cover decreases, the number of cases of cascading also decreases. As a consequence, for the whole Arctic shelf area, the number of cases of cascading also decreases with decreasing ice cover. It is shown that in the Beaufort Sea the maximum number of cascading cases was observed in the winter period of 2007–2008, which was preceded by the summer minimum of the ice cover area in the Arctic Ocean. In the Barents Sea after 2000, a situation has been observed where the ice area has been decreasing to zero values, whereas the number of cascading cases has for some time (1 month approximately) remained close to high winter values. This possibly means that the cooling and densification of the waters in ice-free areas occurs due to thermal convection. Based on the calculation of the number of cases of cascading, it can be argued that the intensification of cascading due to a reduction in the ice cover is a feature of individual seas of the Arctic Ocean, those in which there is no excessive freshening of the upper water layer due to ice melting.

Antarctolichenia onofrii gen. nov. sp. nov. from Antarctic Endolithic Communities Untangles the Evolution of Rock-Inhabiting and Lichenized Fungi in Arthoniomycetes.

Microbial endolithic communities are the main and most widespread life forms in the coldest and hyper-arid desert of the McMurdo Dry Valleys and other ice-free areas across Victoria Land, Antarctica. There, the lichen-dominated communities are complex and self-supporting assemblages of phototrophic and heterotrophic microorganisms, including bacteria, chlorophytes, and both free-living and lichen-forming fungi living at the edge of their physiological adaptability. In particular, among the free-living fungi, microcolonial, melanized, and anamorphic species are highly recurrent, while a few species were sometimes found to be associated with algae. One of these fungi is of paramount importance for its peculiar traits, i.e., a yeast-like habitus, co-growing with algae and being difficult to propagate in pure culture. In the present study, this taxon is herein described as the new genus Antarctolichenia and its type species is A. onofrii, which represents a transitional group between the free-living and symbiotic lifestyle in Arthoniomycetes. The phylogenetic placement of Antarctolichenia was studied using three rDNA molecular markers and morphological characters were described. In this study, we also reappraise the evolution and the connections linking the lichen-forming and rock-inhabiting lifestyles in the basal lineages of Arthoniomycetes (i.e., Lichenostigmatales) and Dothideomycetes.

Overlooked Species Diversity and Distribution in the Antarctic Mite Genus Stereotydeus

In the harsh Antarctic terrestrial ecosystems, invertebrates are currently confined to sparse and restricted ice free areas, where they have survived on multi-million-year timescales in refugia. The limited dispersal abilities of these invertebrate species, their specific habitat requirements, and the presence of geographical barriers can drastically reduce gene flow between populations, resulting in high genetic differentiation. On continental Antarctica, mites are one of the most diverse invertebrate groups. Recently, two new species of the free living prostigmatid mite genus Stereotydeus Berlese, 1901 were discovered, bringing the number of Antarctic and sub-Antarctic species of this genus up to 15, of which 7 occur along the coast of Victoria Land and in the Transantarctic Mountains. To examine the biodiversity of Stereotydeus spp., the present study combines phylogenetic, morphological and population genetic data of specimens collected from nine localities in Victoria Land. Genetically distinct intraspecific groups are spatially isolated in northern Victoria Land, while, for other species, the genetic haplogroups more often occur sympatrically in southern Victoria Land. We provide a new distribution map for the Stereotydeus species of Victoria Land, which will assist future decisions in matters of the protection and conservation of the unique Antarctic terrestrial fauna.

Relationship between meteoric <sup>10</sup>Be and NO<sub>3</sub><sup>−</sup> concentrations in soils along Shackleton Glacier, Antarctica

Abstract. Outlet glaciers that flow through the Transantarctic Mountains (TAM) experienced changes in ice thickness greater than other coastal regions of Antarctica during glacial maxima. As a result, ice-free areas that are currently exposed may have been covered by ice at various points during the Cenozoic, complicating our understanding of ecological succession in TAM soils. Our knowledge of glacial extent on small spatial scales is limited for the TAM, and studies of soil exposure duration and disturbance, in particular, are rare. We collected surface soil samples and, in some places, depth profiles every 5 cm to refusal (up to 30 cm) from 11 ice-free areas along Shackleton Glacier, a major outlet glacier of the East Antarctic Ice Sheet. We explored the relationship between meteoric 10Be and NO3- in these soils as a tool for understanding landscape disturbance and wetting history and as exposure proxies. Concentrations of meteoric 10Be spanned more than an order of magnitude across the region (2.9×108 to 73×108 atoms g−1) and are among the highest measured in polar regions. The concentrations of NO3- were similarly variable and ranged from ∼1 µg g−1 to 15 mg g−1. In examining differences and similarities in the concentrations of 10Be and NO3- with depth, we suggest that much of the southern portion of the Shackleton Glacier region has likely developed under a hyper-arid climate regime with minimal disturbance. Finally, we inferred exposure time using 10Be concentrations. This analysis indicates that the soils we analyzed likely range from recent exposure (following the Last Glacial Maximum) to possibly >6 Myr. We suggest that further testing and interrogation of meteoric 10Be and NO3- concentrations and relationships in soils can provide important information regarding landscape development, soil evolution processes, and inferred exposure durations of surfaces in the TAM.

Sources and sinks of perchlorate in soil in coastal ice-free areas of Antarctica

Perchlorate (ClO4−), a persistent inorganic compound, has harmful effects on human health. Natural ClO4− is formed in the atmosphere and enters into the surface environment through deposition. However, the knowledge on the occurrence, spatial variability and sinks of natural ClO4− in different environments remains limited, especially in the polar regions. Here, we investigate the sources and sinks of ClO4− in soil collected in three ice-free areas in coastal Antarctica, where the research stations and wildlife colonies are mainly distributed. No statistically significant difference in ClO4− concentrations between sites near and away from the stations suggests that local human presence is not a significant source of ClO4− in soil. Concentrations of ClO4− in soil from wildlife colonies are not significantly higher than those from sites with no intense wildlife activities, indicating that wildlife activities have no significant influences on ClO4− in soil. Thus, atmospherically formed ClO4− is the main source for soil in Antarctica. In general, ClO4− concentrations (0.1–5.1 μg kg−1) in soil in this study are much lower than those in the arid environments and comparable to those in the unsaturated zones. Leaching by snow meltwater may be the main sink for ClO4− in soil, and deeper depths for aqueous migration may contribute to the lower ClO4− concentrations in Antarctic surface soil compared to the values in the arid areas with low precipitation amount. Due to the biological origin of NO3−, no correlation between NO3− and ClO4− in soil is observed in this study, different from the observations in arid areas. In addition, no significant correlation is observed between organic matter contents and ClO4− concentrations in soil, suggesting that biological reduction is not an important sink for ClO4− in Antarctic soil.

Internal Ocean Dynamics Control the Long-Term Evolution of Weddell Sea Polynya Activity

Open-ocean polynyas effectively couple the ocean and atmosphere through large ice-free areas within the sea-ice cover, release vast quantities of oceanic heat, and impact deep ocean ventilation. Changes in polynya activity, particularly in the Weddell Sea, may be key to longer time-scale climate fluctuations, feedbacks and abrupt change. While changes in the occurrence of Weddell Sea polynyas are generally attributed to changes in the atmospheric surface forcing, the role of internal ocean dynamics for polynya variability is not well-resolved. In this study we employ a global coupled ocean-sea ice model with a repeating annual atmospheric cycle to explore changes in Weddell Sea water mass properties, stratification and ocean circulation driven by open-ocean polynyas. During the 1300-year long simulation, two large polynyas occur in the central Weddell Sea. Our results suggest that Weddell polynyas may be triggered without inter-annual changes in the atmospheric forcing. This highlights the role of ocean processes in preconditioning and triggering open-ocean polynyas on multi-centennial time-scales. The simulated polynyas form due to internal ocean-sea ice dynamics associated with a slow build-up and subsequent release of subsurface heat. A strong stratification and weak vertical mixing is necessary for building the subsurface heat reservoir. Once the water column turns unstable, enhanced vertical mixing of warm and saline waters into the surface layer causes efficient sea ice melt and the polynya appears. Subsequent, vigorous deep convection is maintained through upwelling of warm deep water leading to enhanced bottom water formation. We find a cessation of simulated deep convection and polynya activity due to long-term cooling and freshening of the subsurface heat reservoir. As subsurface waters in the Southern Ocean are now becoming warmer and saltier, we speculate that larger and more persistent Weddell polynyas could become more frequent in the future.

Dynamics of Ecological Communities Following Current Retreat of Glaciers

Glaciers are retreating globally, and the resulting ice-free areas provide an experimental system for understanding species colonization patterns, community formation, and dynamics. The last several years have seen crucial advances in our understanding of biotic colonization after glacier retreats, resulting from the integration of methodological innovations and ecological theories. Recent empirical studies have demonstrated how multiple factors can speed up or slow down the velocity of colonization and have helped scientists develop theoretical models that describe spatiotemporalchanges in community structure. There is a growing awareness of how different processes (e.g., time since glacier retreat, onset or interruption of surface processes, abiotic factors, dispersal, biotic interactions) interact to shape community formation and, ultimately, their functional structure through succession. Here, we examine how these studies address key theoretical questions about community dynamics and show how classical approaches are increasingly being combined with environmental DNA metabarcoding and functional trait analysis to document the formation of multitrophic communities, revolutionizing our understanding of the biotic processes that occur following glacier retreat.

Sea-ice, primary productivity and ocean temperatures at the Antarctic marginal zone during late Pleistocene

While Pleistocene glacial-interglacial cycles are commonly associated with strong waxing and waning of Northern Hemisphere ice sheets, the response of the Antarctic ice sheet and regional changes in oceanographic and environmental conditions to Pleistocene climate dynamics remain poorly constrained. We present a reconstruction of sea-ice cover, sea surface temperature and primary productivity off the Ross Sea margin (Adare Basin at the slope of the Drygalski Basin) during the marine isotope stages (MIS) 9 to 5 (350–70 thousands years ago, encompassing Terminations IV to II). Our multiproxy study relies on micropaleontology (diatoms, dinoflagellate cysts, benthic foraminifers), organic and inorganic geochemistry proxies (carbon and nitrogen isotopes, lipid biomarkers, XRF-data), and sedimentology (IRD) obtained from deep-sea core AS05-10. For each glacial-interglacial transition a clear succession of events can be observed: (near-)permanent sea ice cover during glacial stages is followed by ice-shelf break-up with episodic ice-free areas and surface water stratification. Notably, ice-shelf break-up precedes the increase in air temperature as measured in the Vostok ice core for each glacial-interglacial transition. Generally, air temperature over Vostok starts rising once sea-ice cover at site AS05-10 has significantly decreased, becoming seasonal, as indicated by the diatom species composition. This is also reflected by the high diatom productivity and increased water mixing at site AS05-10, which is indicative of its proximity to the Marginal Ice Zone. At the onset of Termination II (MIS6 to 5), high export productivity and dysoxic bottom water conditions occurred, while water temperature increased about 5 °C. During each interglacial spring/summer sea-ice cover is most reduced, and highest productivity occurs. Following each interglacial, the warm and cold fluctuations match the sawtooth character of the temperatures over Vostok. This record illustrates that at the Ross Sea margin, sea surface conditions and (export) productivity were strongly influenced by the natural climate variability of the Pleistocene. In light of this, current global warming may lead to increased ice-shelf break-up, water column stratification and shifts in the position/size of the Marginal Ice Zone with implications for algal species composition and diversity, and for primary productivity.

The limnology and spectral behaviour of a freshwater lake at Harmony Point, Nelson Island, Antarctica

AbstractThe present study investigates the effect of limnology on the spectral reflectance of a freshwater lake, located in an ice-free area in the Antarctic Peninsula. Field-collected samples generated limnological and spectral parameters. This fact indicates that the studied lake has an ultra-oligotrophic/oligotrophic nature based on chlorophyll a (chl a), which registered concentrations below 3 μg l-1 with no total suspended solids, almost neutral pH and transparency equalled by depth. The water spectral behaviour in each sampling station indicates that the benthic characteristics of the lake have a strong influence as the reflectance at the 705 nm wavelength being greater than that at 583 nm signals the presence of soil and/or vegetation at its bottom. Hence, it is believed that the orbital sensors with spectral bands focused on regions between the green and red edge, such as the MultiSpectral Instrument (MSI) sensor, may present better results for distinguishing the different bottom types found in the research area.

Spectral Characteristics of the Antarctic Vegetation: A Case Study of Barton Peninsula

Spectral information is a proxy for understanding the characteristics of ground targets without a potentially disruptive contact. A spectral library is a collection of this information and serves as reference data in remote sensing analyses. Although widely used, data of this type for most ground objects in polar regions are notably absent. Remote sensing data are widely used in polar research because they can provide helpful information for difficult-to-access or extensive areas. However, a lack of ground truth hinders remote sensing efforts. Accordingly, a spectral library was developed for 16 common vegetation species and decayed moss in the ice-free areas of Antarctica using a field spectrometer. In particular, the relative importance of shortwave infrared wavelengths in identifying Antarctic vegetation using spectral similarity comparisons was demonstrated. Due to the lack of available remote sensing images of the study area, simulated images were generated using the developed spectral library. Then, these images were used to evaluate the potential performance of the classification and spectral unmixing according to spectral resolution. We believe that the developed library will enhance our understanding of Antarctic vegetation and will assist in the analysis of various remote sensing data.

Variations in mineralogy of dust in an ice core obtained from northwestern Greenland over the past 100 years

Abstract. Our study is the first to demonstrate a high-temporal-resolution record of mineral composition in a Greenland ice core over the past 100 years. To reconstruct past variations in the sources and transportation processes of mineral dust in northwestern Greenland, we analysed the morphology and mineralogical composition of dust in the SIGMA-D ice core from 1915 to 2013 using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The results revealed that the ice core dust consisted mainly of silicate minerals and that the composition varied substantially on multi-decadal and inter-decadal scales, suggesting that the ice core minerals originated from different geological sources in different periods during the past 100 years. The multi-decadal variation trend differed among mineral types. Kaolinite, which generally formed in warm and humid climatic zones, was abundant in colder periods (1950–2004), whereas mica, chlorite, feldspars, mafic minerals, and quartz, which formed in arid, high-latitude, and local areas, were abundant in warmer periods (1915–1949 and 2005–2013). Comparison to Greenland surface temperature records indicates that multi-decadal variation in the relative abundance of these minerals was likely affected by local temperature changes in Greenland. Trajectory analysis shows that the minerals were transported mainly from the western coast of Greenland in the two warming periods, which was likely due to an increase in dust sourced from local ice-free areas as a result of shorter snow/ice cover duration in the Greenland coastal region during the melt season caused by recent warming. Meanwhile, ancient deposits in northern Canada, which were formed in past warmer climates, seem to be the best candidate during the colder period (1950–2004). Our results suggest that SEM–EDS analysis can detect variations in ice core dust sources during recent periods of low dust concentration.

Tidewater glacier retreat in Antarctica: The table is set for fast-growing opportunistic species, is it?

The rapid warming of the West Antarctic Peninsula (WAP) is causing an important expansion of marine coastal areas due to glacier retreat. These new ice-free areas offer additional habitats for the colonization of benthic species in areas formerly occupied by ice. The establishment of benthic species can represent important negative feedback to the warming process due to the new carbon fixed and stored. Opportunistic, fast-growing, and high turnover species are expected to colonize these new emerging areas. At Potter Cove, the glacier retreat has opened wide areas of soft bottoms, which provides an excellent study area to assess the colonization process and the success of opportunistic species. Here, we examined the population response of the opportunistic soft coral Malacobelemnon daytoni species in the soft bottom area of Potter Cove with different exposure times due to glacier retreat. Our results show a significant variation of M. daytoni population among the sampled areas in terms of presence, abundances, and distribution. In the long-term ice-free areas, opened for more than 60 years, we observed a ~20-fold increase of M. daytoni densities within just 15 years. However, this extraordinary population outburst was not observed in the newer ice-free areas (≤15 years). We registered very low densities in areas of 15 years and no colonies in areas with 10 years of open sea conditions. These were unexpected results based on colonization capabilities showed by the species and habitat suitability of the new areas. Indeed, using Species Distribution Models (SDMs) we also obtained contrasting outputs. SDMs based on long-term areas presence data predicted high habitat suitability and the potential presence of the species in the newer areas. However, when based on newer and older areas data, SDMs showed low habitat suitability and potential absence of the species in the newer areas. This work suggests that species that can be considered as fast and efficient colonizers, could not perform in that way under certain conditions. This deepens the current knowledge on species natural history and environmental relationships, especially to improve our prediction capabilities under changing environmental conditions.

Macroalgae degradation promotes microbial iron reduction via electron shuttling in coastal Antarctic sediments.

Colonization of newly ice-free areas by marine benthic organisms intensifies burial of macroalgae detritus in Potter Cove coastal surface sediments (Western Antarctic Peninsula). Thus, fresh and labile macroalgal detritus serves as primary organic matter (OM) source for microbial degradation. Here, we investigated the effects on post-depositional microbial iron reduction in Potter Cove using sediment incubations amended with pulverized macroalgal detritus as OM source, acetate as primary product of OM degradation and lepidocrocite as reactive iron oxide to mimic in situ conditions. Humic substances analogue anthraquinone-2,6-disulfonic acid (AQDS) was also added to some treatments to simulate potential for electron shuttling. Microbial iron reduction was promoted by macroalgae and further enhanced by up to 30-folds with AQDS. Notably, while acetate amendment alone did not stimulate iron reduction, adding macroalgae alone did. Acetate, formate, lactate, butyrate and propionate were detected as fermentation products from macroalgae degradation. By combining 16S rRNA gene sequencing and RNA stable isotope probing, we reconstructed the potential microbial food chain from macroalgae degraders to iron reducers. Psychromonas, Marinifilum, Moritella, and Colwellia were detected as potential fermenters of macroalgae and fermentation products such as lactate. Members of class deltaproteobacteria including Sva1033, Desulfuromonas, and Desulfuromusa together with Arcobacter (former phylum Epsilonbacteraeota, now Campylobacterota) acted as dissimilatory iron reducers. Our findings demonstrate that increasing burial of macroalgal detritus in an Antarctic fjord affected by glacier retreat intensifies early diagenetic processes such as iron reduction. Under scenarios of global warming, the active microbial populations identified above will expand their environmental function, facilitate OM remineralisation, and contribute to an increased release of iron and CO2 from sediments. Such indirect consequences of glacial retreat are often overlooked but might, on a regional scale, be relevant for the assessment of future nutrient and carbon fluxes.

Chronology and paleoclimatic implications of lacustrine sediments at Inexpressible Island, Ross Sea, Antarctica

Lacustrine sediments from ice-free areas of Antarctica record both paleoecological and paleoclimatic information. Four sediment profiles (IIL1, IIL3, IIL4 and IIL9) were collected at Inexpressible Island, Ross Sea, to establish a robust late-Holocene chronology using accelerator mass spectrometry (AMS) 14C dating and geochemical and lithological analyses. The IIL1 and IIL4 sediments were strongly affected by penguin guano, and their bottom (oldest) ages were dated to 1659 and 4820 yr BP, respectively, using a Mixed Marine SoHem mode. By contrast, the organic matter of IIL3 and IIL9 sediments were predominantly sourced from aquatic microbial mats with the bottom ages of these two cores at 3179 and 2945 yr BP, respectively, based on a SHCal13 mode. The mass accumulation rates of the four sediment profiles inferred from this chronology showed peaks during ~1400–800 yr BP, corresponding to greater mean grain size and higher sand fraction ratios in the IIL3 and IIL9 profiles, suggesting a strengthened hydrodynamic effect in this period. Our results indicate a relatively warm period occurred in the study area, in accordance with an ‘optimum’ warming in the Ross Sea region. From a regional view, this warm period was also consolidated with climatic records from the western Ross Sea, most likely corresponding to a well-recognized climate perturbation known as the Medieval Climate Anomaly (MCA) in many parts of the world.

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.

Diversity of microbial communities and genes involved in nitrous oxide emissions in Antarctic soils impacted by marine animals as revealed by metagenomics and 100 metagenome-assembled genomes

Antarctic soils generally have low temperatures and limited availability of liquid water and nutrients. However, animals can increase the nutrient availability of ice-free areas by transferring nutrients from marine to terrestrial ecosystems, mainly through their excreta. In this study, we employed shotgun metagenomics and population genome binning techniques to study the diversity of microbial communities in Antarctic soils impacted by marine pinnipeds and birds relative to soils with no evident animal presence. We obtained ~285,000 16S rRNA gene-carrying metagenomic reads representing ~60 phyla and 100 metagenome-assembled genomes (MAGs) representing eight phyla. Only nine of these 100 MAGs represented previously described species, revealing that these soils harbor extensive novel diversity. Proteobacteria, Actinobacteria, and Bacteroidetes were the most abundant phyla in all samples, with Rhodanobacter being one of the most abundant genera in the bird-impacted soils. Further, the relative abundance of genes related to denitrification was at least double in soils impacted by birds than soils without animal influence. These results advance our understanding of the microbial populations and their genes involved in nitrous oxide emissions in ice-free coastal Antarctic soils impacted by marine animals and reveal novel microbial diversity associated with these ecosystems.

Towards physical habitat characterisation in the Antarctic Sør Rondane Mountains using satellite remote sensing

Ice-free areas occupy less than 0.25% of the Antarctic surface, and mainly occur along coastlines, or as inland nunataks protruding from the extensive ice sheet. Their extreme environment and geographical isolation have contributed to the evolution of highly adapted, and largely endemic terrestrial biota. Physical habitat mapping is important to identify the main drivers of spatial variation in soil biodiversity, to predict its response to climate change and to help conservation planning. In this paper we retrieved remotely sensed Land Surface Temperature (LST) and Digital Surface Models (DSM) for the Sør Rondane Mountains in East Antarctica from respectively the Thermal InfraRed Sensor (TIRS) on Landsat 8 and the Pléiades constellation of high resolution optical imagers. Satellite data were combined with ground truth temperature and elevation measurements with the aim to assess the performance of these remotely sensed data. Over a 2 year period, satellite derived LST corresponded to in situ temperature with Mean Average Difference (MAD) of −2.5 K, and Root Mean Squared Difference (RMSD) of 6.3 K. Lower biases were observed for periods when the data loggers were frozen or snow covered (MAD −1.8K) compared to intervals where the devices were not frozen (MAD −4 K), with larger scatter (RMSD 7 K) being observed during the latter. These larger MAD and RMSD are caused by the differential heating of the top of the gravel/rocks as observed by the satellite compared to their underside, where the loggers were installed, and are also impacted by the time step of the in situ logging (3 h) and the non–linear heating of the surface. In addition, for the different study sites different biases were observed as a result of the spatial resolution of the TIRS, depending on the composition, structure, geomorphology, and the surroundings of the logger position. Sites on a narrow rock outcrop (e.g. the Perlebandet and Utsteinen nunataks) show a negative bias due to the surrounding ice fields decreasing the satellite pixel average temperature compared to the in situ measured temperatures. For sites with a more extensive rock and gravel composition further away from the ice sheet (Dry and Yuboku Valleys), a positive bias was found as a result of the temperature differential between the exposed top and covered bottom of the rocks and gravel. The DSM derived from Pléiades (without bias correction) showed in general a bias of −6 m (MAD) and scatter of 9 m (RMSD) when compared to the Reference Elevation Model of Antarctica and IceSAT-1 LIDAR data. Lowest errors were also found here for the extensive Dry and Yuboku Valley sites (respectively −5 and 3 m MAD, 7 and 4 m RMSD). Correspondence with in situ logged GPS positions was slightly worse, with a positive bias of 12 m (MAD) and scatter of 15 m (RMSD) across the sites. An analysis on the basis of these LST and DSM datasets, show a clear separability of sites by their average temperature and solar exposition (in terms of slope and aspect) at the time of Landsat overpass. Due to the Landsat overpass times, the LST datasets are however strongly biased, and further work is needed for a better understanding of the light and temperature climate in the ice-free regions. This could for example be achieved by coupling the DSM to a solar irradiance and terrain shadowing model.

Growth Forms and Functional Guilds Distribution of Soil Fungi in Coastal Versus Inland Sites of Victoria Land, Antarctica.

Simple SummaryAntarctica represents one of the most limiting environments on Earth, where exposed soils, transiently present on coastal areas and permanently exposed on McMurdo Dry Valleys, are one of the few substrata supporting microbial communities. Within these communities, fungi are one of the dominant components and play pivotal roles in recycling the extremely limited organic matter available. Despite their astonishing adaptations, the diversity of these communities and the factors determining their resistance are still poorly known. In this optic, this study aimed to give insights in the environmental parameters determining the structure of these communities and their adaptive strategies, in terms of growth forms and lifestyles. We found that abiotic conditions were the main drivers of well differentiated communities. Additionally, we highlighted that most species seemed to be highly adapted to this habitat, which may result in a relatively low resilience ability to changes in environmental condition. Both these results are of particular concern in light of global warming. Even minimal changes to environmental conditions may dramatically alter the Antarctic soil communities, risking the disappearance of many species still undescribed.In Victoria Land, Antarctica, ice-free areas are restricted to coastal regions and dominate the landscape of the McMurdo Dry Valleys. These two environments are subjected to different pressures that determine the establishment of highly adapted fungal communities. Within the kingdom of fungi, filamentous, yeasts and meristematic/microcolonial growth forms on one side and different lifestyles on the other side may be considered adaptive strategies of particular interest in the frame of Antarctic constraints. In this optic, soil fungal communities from both coastal and Dry Valleys sites, already characterized thorough ITS1 metabarcoding sequencing, have been compared to determine the different distribution of phyla, growth forms, and lifestyles. Though we did not find significant differences in the richness between the two environments, the communities were highly differentiated and Dry Valleys sites had a higher evenness compared to coastal ones. Additionally, the distribution of different growth forms and lifestyles were well differentiated, and their diversity and composition were likely influenced by soil abiotic parameters, among which soil granulometry, pH, P, and C contents were the potential main determinants.

Deep Learning Based Sea Ice Classification with Gaofen-3 Fully Polarimetric SAR Data

In this paper, the performance of C-band synthetic aperture radar (SAR) Gaofen-3 (GF-3) quad-polarization Stripmap (QPS) data is assessed for classifying late spring and summer sea ice types. The investigation is based on 18 scenes of GF-3 QPS data acquired in the Arctic Ocean in 2017. In this study, floe ice (FI), brash ice (BI) between floes and open water (OW, ice-free area) were classified based on a mini sea ice residual convolutional network, which we call MSI-ResNet. While investigating the optimal patch size for MSI-ResNet, we found that, as the patch size continues to grow, the classification accuracy first increases and then decreases. A patch size of 31 × 31 was found to achieve the best performance. The performance of classification using different polarization combinations from the QPS data was also assessed. The vertical-vertical (VV) polarization input overestimates the FI category while incorrectly identifying most of the BI as FI. The VH polarization produces a synchronous improvement in FI, BI, and OW discrimination, with a higher overall accuracy and kappa coefficient (91.09% and 0.85, respectively) than the VV polarization (83.37% and 0.70, respectively). The combination of VV and vertical-horizontal (VH) polarizations presents a modest precision improvement for BI and OW together with a slight overestimation for FI. With VV, VH, and horizontal-horizontal (HH) polarization data as the inputs, the user’s accuracy improves to 95.12%, 93.42%, and 95.17% for FI, BI, and OW, respectively. The accuracy was assessed against visual interpretation of the sea ice classes in the images using a stratified sampling method. The application of the MSI-ResNet method to data covering the Beaufort Sea and the north of the Severnaya Zemlya archipelago was found to achieve a high overall accuracy (kappa) of 94.62% (±0.92) and 94.23% (±0.90), respectively. This is similar to the classification accuracy obtained in the Fram Strait. From the results of this study, it is shown that the MSI-ResNet method performs better than the classical support vector machine (SVM) classifier for sea ice discrimination. The GF-3 QPS mode data also show more details in discriminating scattered sea ice floes than the coincident Sentinel-1A Extra Wide (EW) swath mode data.