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Abstract

The strong air temperature warming between the 1950s and 2016 in the Antarctic Peninsula region¹ exceeded the global average warming²,³ with evident impacts on terrestrial ecosystems and the two native Antarctic vascular plants Deschampsia antarctica Desv. and Colobanthus quitensis (Kunth) Bartl.4, 5, 6, 7, 8, 9, 10 Subsequently, a short but intense cooling occurred from the Antarctic Peninsula to the South Orkney Islands (1999–2016),¹,11, 12, 13 impacting terrestrial ecosystems, with reduced lichen growth¹⁴ and no further expansion of D. antarctica in the Argentine Islands.⁵ The strong warming trend is predicted to resume¹⁵ with expansion of ice-free areas and continued impacts on the abiotic and biotic components of terrestrial ecosystems including the ingression of non-native species³,⁸,¹⁶,¹⁷ as recently recorded at Signy Island (South Orkney Islands).18, 19, 20 In this study we document acceleration in the expansion of D. antarctica and C. quitensis in the last decade (2009–2018) at Signy Island, where the air temperature warming trend resumed in summer after 2012. We hypothesize that the striking expansion of these plants is mainly triggered by summer air warming and release from the limitation of fur seal disturbance. We also hypothesize that the “pulse” climatic event of the strong air cooling detected in 2012 did not appear to influence the vegetation community dynamics on this island. This is the first evidence in Antarctica for accelerated ecosystem responses to climate warming, confirming similar observations in the Northern Hemisphere. Our findings support the hypothesis that future warming will trigger significant changes in these fragile Antarctic ecosystems.

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... Global climate change and human activities are having a significant impact on the Antarctic terrestrial ecosystem (Convey and Peck, 2019;Cannone et al., 2022). The Antarctic Peninsula is now experiencing some of the most rapid warming on earth (Sato et al., 2021). ...
... The ice-free areas of Antarctica is expected to increase by approximately 25% by the end of 21st century due to climate change, while most of this expansion will occur in the Antarctic Peninsula (Lee et al., 2017). Warming had caused the special phenomena of flowering plant spread and snow algae outbreak (Gray et al., 2020;Cannone et al., 2022). Similarly, a significant increase was found in biological activity over the past 50 years, measured through moss growth or accumulation rates (Amesbury et al., 2017). ...
... Similarly, a significant increase was found in biological activity over the past 50 years, measured through moss growth or accumulation rates (Amesbury et al., 2017). Currently, Antarctic plants appears to be promising models for studying the adaptation mechanism to various abiotic stresses (Convey and Peck, 2019;Perera-Castro et al., 2020;Bertini et al., 2021;Liu et al., 2021) and monitoring the regional climate changes (Amesbury et al., 2017;Lee et al., 2017;Robinson et al., 2018;Cannone et al., 2022) as well as assessing the impact of human activities (Malenovský et al., 2015;Hughes et al., 2020). Particularly, the genomic features were widely clarified in the Antarctic bacteria (Benaud et al., 2021), algae (Zhang et al., 2020b), and fishes (Kim et al., 2019), but the underpinnings remain unclear in the adaptation of mosses to extreme environments. ...
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The Antarctic climate system varies on timescales from orbital, through millennial to sub-annual, and is closely coupled to other parts of the global climate system. We review these variations from the perspective of the geological and glaciological records and the recent historical period from which we have instrumental data (the last 50 years). We consider their consequences for the biosphere, and show how the latest numerical models project changes into the future, taking into account human actions in the form of the release of greenhouse gases and chlorofluorocarbons into the atmosphere. In doing so, we provide an essential Southern Hemisphere companion to the Arctic Climate Impact Assessment.
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Reproductive allocation (reproductive biomass relative to vegetative biomass) and seed production were measured for samples of the two native phanerogams occurring in Antarctica. Material collected on South Georgia (subantarctic), Signy Island (northern maritime Antarctic) and Léonie Island (southern maritime Antarctic) allowed an initial comparison of reproduction over a wide latitudinal range. Sizes of vegetative and reproductive structures of Colobanthus quitensis were smaller in Signy Island samples than those from South Georgia or Léonie Island. This pattern was reflected in the pattern of seed production. Vegetative and reproductive structures of Deschampsia antarctica were generally similar in size at both maritime Antarctic sites, but larger at subantarctic South Georgia. Seed production was similar in each season assessed and at all three sites. In most samples of both species there were close relationships between reproductive and vegetative biomass, and seed output and reproductive biomass. Subantartic C. quitensis showed greater allocation to seed production than material from maritime Antarctic sites. D. antarctica showed the reverse pattern, with greater allocation to reproductive biomass and seed production in most samples of maritime Antarctic material, particularly those from Signy Island. Reproductive strategies do not form any specific adaptation to the Antarctic environment for these species. Reasons for the failure of other higher plants to become established in the maritime Antarctic are discussed, and it is concluded that geographical isolation is the main factor. The most important proximate factors influencing propagules which reach potential colonization sites are likely to be the short length and low temperature of the summer season in relation to the time required for establishment.
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Signy Island has experienced a dramatic increase in fur seal numbers over recent decades, which has led to the devastation of lowland terrestrial vegetation, with the eradication of moss turfs and carpets being the most prominent feature. Here we demonstrate that fur seals also affect the other major component of this region’s typical cryptogamic vegetation, the lichens, although with a lower decrease in variability and abundance than for bryophytes. Classification (UPGMA) and ordination (Principal Coordinate Analysis) of vegetation data highlight differences in composition and abundance of lichen communities between areas invaded by fur seals and contiguous areas protected from these animals. Multivariate analysis relating lichen communities to environmental parameters, including animal abundance and soil chemistry (Canonical Correspondence Analysis), suggests that fur seal trampling results in the destruction of muscicolous-terricolous lichens, including several cosmopolitan and bipolar fruticose species. In addition, animal excretion favours an increase in nitrophilous crustose species, a group which typically characterizes areas influenced by seabirds and includes several Antarctic endemics. The potential effect of such animal-driven changes in vegetation on the fragile terrestrial ecosystem (e.g. through modification of the ground surface temperature) confirms the importance of indirect environmental processes in Antarctica.
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The photosynthetic temperature response of the Antarctic vascular plants Colobanthus quitensis and Deschampsia antarctica was examined by measuring whole-canopy CO2 gas exchange and chlorophyll (Chl) a fluorescence of plants growing near Palmer Station along the Antarctic Peninsula. Both species had negligible midday net photosynthetic rates (Pn) on warm, usually sunny, days (canopy air temperature [Tc]> 20°C), but had relatively high Pn on cool days (Tc<10°C). Laboratory measurements of light and temperature responses of Pn showed that high temperature, not visible irradiance, was responsible for depressions in Pn on warm sunny days. The optimal leaf temperatures (Tl) for Pn in C. quitensis and D. antarctica were 14 and 10°C, respectively. Both species had substantial positive Pn at 0°C Tl, which were 28 (C. quitensis) and 32% (D. antarctica) of their maximal Pn, and we estimate that their low-temperature compensation points occurred at −2°C Tl (C. quitensis) and −3°C (D. antarctica). Because of the strong warming trend along the peninsula over recent decades and predictions that this will continue, we were particularly interested in the mechanisms responsible for their negligible rates of Pn on warm days and their unusually low high-temperature compensation points (i.e., 26°C in C. quitensis and 22°C in D. antarctica). Low Pn at supraoptimal temperature (25°C) appeared to be largely due to high rates of temperature-enhanced respiration. However, there was also evidence for direct impairment of the photosynthetic apparatus at supraoptimal temperature, based on Chl fluorescence and Pn/intercellular CO2 concentration (ci) response curve analyses. The breakpoint or critical temperature (Tcr) of minimal fluorescence (Fo) was ≈42°C in both species, which was well above the temperatures where reductions in Pn were evident, indicating that thylakoid membranes were structurally intact at supraoptimal temperatures for Pn. The optimal Tl for photochemical quenching (qp) and the quantum yield of photosystem II (PSII) electron transfer (φPSII) were 9 and 7°C in C. quitensis and D. antarctica, respectively. Supraoptimal temperatures resulted in lower qp and greater non-photochemical quenching (qNP), but had little effect on Fo, maximal fluorescence (Fm) or the ratio of variable to maximal fluorescence (Fv/Fm) in both species. In addition, carboxylation efficiencies or initial slopes of their Pn/ci response were lower at supraoptimal temperatures, suggesting reduced activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). Although continued warming along the peninsula will increase the frequency of supraoptimal temperatures, Tc at our field site averaged 4.3°C and was below the temperature optima for Pn in these species for the majority of diurnal periods (86%) during the growing season, suggesting that continued warming will usually improve their rates of Pn.
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Snow cover changes can have important effects on ecosystems, especially where spatial variability in cover is high, influencing the biogeochemical conditions of the underlying soil as well as the vegetation. In this study, snow thickness and areal distribution were monitored using a time lapse camera over a grid of 15 × 20 m between 2009 and 2017 at Signy Island (60°S, South Orkney Islands, maritime Antarctica). The data obtained confirmed high spatial and temporal variability in snow cover. Over the study period, the mean annual snow depth ranged between 5.6 cm (2017) and 11.1 cm (2012) while the maximum of the mean daily snow depth across the entire grid ranged between 17.1 cm (2017) and 50.1 cm (2015). No temporal trend was apparent but there was a strong correlation with mean annual air temperature, suggesting that possible future warming could decrease snow depth in the area. A negative correlation was identified between the winter Southern Oscillation Index (SOI) and mean annual snow depth, indicating an influence of El Niño–Southern Oscillation (ENSO) on snow cover in this part of Antarctica. There was considerable small-scale spatial variability in snow depth at each individual stake, with mean values between 3.9 and 25.3 cm and maximum values between 27 and 85 cm. Snow depth variability was influenced primarily by microtopography and wind direction, but also by the land cover type (vegetation). Our data highlight that spatial monitoring of snow accumulation is required at small physical scale to predict future effects of climatic changes on these sensitive maritime Antarctic terrestrial ecosystems.
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Antarctica is the last pristine environment on Earth, its biota being adapted to the harsh and extreme polar climate. Until now, soil formation and vegetation development in continental Antarctica were considered very slow due to the extreme conditions of this polar desert. Since the austral summer 2002/2003, a long-term monitoring network of the terrestrial ecosystems (soils, vegetation, active layer thickness) has been established at Victoria Land (VL) across a > 500 km latitudinal gradient of coastal sites (73°–77°S). In only one decade large ecosystem changes were detected. Climate was characterized by a significant increase of thawing degree days in northern VL and of autumn air temperature. No extreme climatic events (such as hot spells) where detected in the study period. Soil chemistry suffered large quantitative changes, clearly indicating rapid pedogenetic processes. In most soils the upper layers exhibited a strong alkalinization (pH increases up to 3 units) and increases in conductivity, anions and cations (in particular of SO4 and Na). The largest changes were observed in soils with low vegetation cover. Statistically significant differences in soil chemistry were detected between soils with high and low vegetation cover, the former showing lower pH, conductivity, Na and Cl. Most plots exhibited changes of total cover, species richness and floristic composition, with vegetation expansion in soils with low vegetation cover and the largest increase recorded at Apostrophe Island (northern VL). Principal Component Analysis (PCA) identified the main trend of vegetation change, with a shift from lower to higher cover and a secondary trend of change associated with a gradient of water availability, consistent with an increase in water instead of snow. Redundancy analysis (RDA) identified the trend of change in soil chemistry with increases in pH, conductivity, anions and cations associated with the concomitant decrease in C, N, NO3, PO4. The RDA confirmed that soil changes were associated with a gradient of vegetation change (from low to high cover) as well as of water availability, as already indirectly outlined by the PCA. Field manipulation experiments carried out at five locations of the network between 73°S and 77°S, simulating increases of precipitation from snow or water additions didn’t induce changes in soil pH, indicating that pulse events of snow accumulation or melting could not trigger persistent soil pH changes. These data allow hypothesize the occurrence of a main ecosystem change occurring at regional scale at Victoria Land. The slight air warming and its consequences on soil chemistry and vegetation, further highlight the sensitivity of the fragile Antarctic ecosystems to the consequences of even small changes in climate.
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During the past decades, the montane and subalpine belts of many European mountains experienced agricultural land abandonment followed by spontaneous recolonization of trees and shrubs on semi-natural mountain grasslands, potentially leading to severe losses in biodiversity. Here we analyse the spatial and temporal patterns of forest encroachment of a Prealpine study site in Northern Italy (Triangolo Lariano, Como) since 1954 in response to land use change and aim to assess whether this process has been accelerated by recent climate warming and atmospheric CO2 increase. To achieve a detailed reconstruction of forest encroachment dynamics, we adopted a multidisciplinary integrated approach, involving dendrochronological and phytosociological analyses, and vegetation mapping. Available maps updated with aerial photographs allowed the delineation of the forest distribution and changes of forest boundaries. Accordingly, along nine elevational transects, 60 plots were set within different forest-grassland successional stages in order to integrate vegetation mapping with phytosociological analyses and reconstruct the recruitment rates through dendrochronological analyses. Since 1954, the forest encroachment process occurred across an elevation range of 185 m, at a mean rate of 29 m per decade, although with uneven temporal and spatial trends. The forest encroachment rates increased progressively with time, from +0.8%/y (1954–1993) to +2.4%/y (1993–2015) to +4.9%/y (2015–2018). The air warming exhibited an increasing trend too, especially in the last twenty years. Betula pendula was the most abundant species responsible for this process (the only one presenting seedlings and saplings settling along the summit areas) and showed two recruitment peaks: the first in concomitance with the abandonment of the agro-silvo-pastoral practices (1950/60s), but the largest recruitment was detected with the increased air warming since early 2000s. The correlation analysis confirmed that forest encroachment was related to air warming (in particular summer warming), land use change and increase of atmospheric CO2 and that it was further accelerated in concomitance with further air warming in the recent decades. The forest encroachment process on semi-natural grasslands triggered by land use change on European mountains and its recent acceleration in response to climate warming represent an increasing threat to biodiversity, leading to potential habitat and species loss, especially of the most vulnerable habitats.
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Mid‐ to high‐latitude vegetation are experiencing changes in their seasonal cycles as a result of climate change. Although the rates of seasonal growth from winter dormancy to summer maturity have accelerated because of changes in environmental conditions, less attention has been paid to the rate of vegetation green‐up (RVG) and its dynamics, which could advance vegetation maturity. We analyzed the long‐term changes in RVG and the drivers at high northern latitudes for 35 years (1982–2016) using satellite‐retrieved leaf area index data based on partial correlation analyses and multivariable linear regression. The rates tended to increase significantly with time, particularly at high latitudes above 60°N in North America (1.8% mon‐1 decade‐1, p < 0.01) and Eurasia (1.0% mon‐1 decade‐1, p < 0.01). The increasing trend in North America was mostly because of increased heat accumulation in spring (1.2% mon‐1 decade‐1), i.e., more rapid green‐up owing to warming, with an increased carbon dioxide concentration (0.6 mon‐1 decade‐1). The trend in Eurasia, however, was induced by warming, increased carbon dioxide concentration, and stronger radiation, 1.0%, 0.7%, and 0.5% mon‐1 decade‐1, respectively, but was partly counteracted by earlier pre‐green‐up dates of ‐1.2% mon‐1 decade‐1, i.e., earlier initiation of growth which counteracted green‐up rate acceleration. The results suggested that warming was the predominant factor influencing the accelerated RVG at high latitudes; however, Eurasian vegetation exhibited different green‐up dynamics, mitigating the influence of warming with the earlier pre‐green‐up. Our findings imply that high‐latitude warming will drive vegetation seasonality toward rapid green‐up and early maturity, leading to the reinforcement of climate–vegetation interactions; however, the consequences will be more distinct in North America owing to the absence of alleviation by earlier pre‐green‐up.
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Antarctica and the Southern Ocean comprise a critical part of the Earth System. Their environments are better understood than ever before, yet the region remains poorly considered among international agreements to improve the state of the global environment. In part the situation owes to isolated regional regulation within the Antarctic Treaty System, and in part to the dated notion that Antarctica and the Southern Ocean are well conserved and relatively free from human impact. Here we review growth in knowledge of Antarctic environments and anthropogenic pressures on them. We show that the region's unusual diversity is facing substantial local and globally mediated anthropogenic pressure, on a par with environments globally. Antarctic environmental management and regulation is being challenged to keep pace with the change. Much benefit can be derived from consideration of Antarctic environmental and resource management in the context of global agreements.
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Temperature trends across Antarctica over the last few decades reveal strong and statistically significant warming in West Antarctica and the Antarctic Peninsula (AP) contrasting with no significant change overall in East Antarctica. However, recent studies have documented cooling in the AP since the late 1990s. This study aims to place temperature changes in the AP and West Antarctica into a larger spatial and temporal perspective by analyzing monthly station-based surface temperature observations since 1957 across the extratropical Southern Hemisphere, along with sea surface temperature (SST) data and mean sea level pressure reanalysis data. The results confirm statistically significant cooling in station observations and SST trends throughout the AP region since 1999. However, the full 60-year period shows statistically significant, widespread warming across most of the Southern Hemisphere mid- and high-latitudes. Positive SST trends broadly reflect these warming trends, especially in the mid-latitudes. After confirming the importance of the Southern Annular Mode (SAM) on southern high-latitude climate variability, the influence is removed from the station temperature records, revealing statistically significant background warming across all of the extratropical Southern Hemisphere. Antarctic temperature trends in a suite of climate models from the Coupled Model Intercomparison Project Phase 5 (CMIP5) are then investigated. Consistent with previous work the CMIP5 models warm Antarctica at the background temperature rate that is two times faster than that observed. However, removing the SAM influence from both CMIP5 temperatures and those observed results in Antarctic trends that differ only modestly, perhaps due to natural multidecadal variability remaining in the observations.
Article
Mosses are dominant components of high-latitude environments, and Signy Island (maritime Antarctic) provides a representative example of polar cryptogam-dominated terrestrial ecosystems. In 2011, we mapped all moss banks, their characteristics (thickness, area, floristic composition) and investigated their relationship with selected environmental factors including topography (elevation, slope, aspect), biotic disturbance (fur seals), deglaciation age of the surfaces, location on the eastern vs. western side of the island and snow cover as a proxy of water supply during the summer (December). We here identify the most important environmental factors influencing moss bank characteristics and distribution and provide a baseline for future monitoring. Moss bank abundance and distribution are the result of the interaction of multiple abiotic and biotic factors acting at different spatial scales. The most important factors are the location of moss banks on the eastern vs. western side of the island at the macroscale (with thicker and larger moss banks and a prevalence of Chorisodontium aciphyllum on the western side) and their favourable aspect (mainly N, NW) at the microscale, providing better microclimatic conditions suitable for their development. The elevation threshold detected at 120 m could indicate the occurrence of a ‘moss bank line’, analogous to the tree line, and corresponds with a threshold of mean annual temperature of −4.8 °C. The other factors examined play a subsidiary role in affecting bank distribution and characteristics. These findings allow a better understanding of this key feature of maritime Antarctic vegetation and provide quantitative information about their ecology.
Article
Antarctic terrestrial biodiversity occurs almost exclusively in ice-free areas that cover less than 1% of the continent. Climate change will alter the extent and configuration of ice-free areas, yet the distribution and severity of these effects remain unclear. Here we quantify the impact of twenty-first century climate change on ice-free areas under two Intergovernmental Panel on Climate Change (IPCC) climate forcing scenarios using temperature-index melt modelling. Under the strongest forcing scenario, ice-free areas could expand by over 17,000 km(2) by the end of the century, close to a 25% increase. Most of this expansion will occur in the Antarctic Peninsula, where a threefold increase in ice-free area could drastically change the availability and connectivity of biodiversity habitat. Isolated ice-free areas will coalesce, and while the effects on biodiversity are uncertain, we hypothesize that they could eventually lead to increasing regional-scale biotic homogenization, the extinction of less-competitive species and the spread of invasive species.
Article
Recent climate change on the Antarctic Peninsula is well documented [1-5], with warming, alongside increases in precipitation, wind strength, and melt season length [1, 6, 7], driving environmental change [8, 9]. However, meteorological records mostly began in the 1950s, and paleoenvironmental datasets that provide a longer-term context to recent climate change are limited in number and often from single sites [7] and/or discontinuous in time [10, 11]. Here we use moss bank cores from a 600-km transect from Green Island (65.3°S) to Elephant Island (61.1°S) as paleoclimate archives sensitive to regional temperature change, moderated by water availability and surface microclimate [12, 13]. Mosses grow slowly, but cold temperatures minimize decomposition, facilitating multi-proxy analysis of preserved peat [14]. Carbon isotope discrimination (Δ(13)C) in cellulose indicates the favorability of conditions for photosynthesis [15]. Testate amoebae are representative heterotrophs in peatlands [16-18], so their populations are an indicator of microbial productivity [14]. Moss growth and mass accumulation rates represent the balance between growth and decomposition [19]. Analyzing these proxies in five cores at three sites over 150 years reveals increased biological activity over the past ca. 50 years, in response to climate change. We identified significant changepoints in all sites and proxies, suggesting fundamental and widespread changes in the terrestrial biosphere. The regional sensitivity of moss growth to past temperature rises suggests that terrestrial ecosystems will alter rapidly under future warming, leading to major changes in the biology and landscape of this iconic region-an Antarctic greening to parallel well-established observations in the Arctic [20].
Article
Optimum temperature for net photosynthesis occurred at c13°C for the grass and 19°C for the pearlwort. However, both species achieved c30% of their maximum rate at 0°C, possibly their most important feature for survival in the Antarctic. The highest photosynthetic rates recorded were 8.8 mg CO 2dm -2h -1 for D. antarctica and 14.5 mg CO 2dm -2h -1 for C. quitensis. The diurnal course of assimilation in mid-summer at 60°S latitude is predicted from a combination of field microclimate data and the laboratory metabolic measurements, and net daily uptake of 55-105 and 35-73 mg CO 2dm -2 is projected for the grass and pearlwort, respectively. Neither the pearlwort nor the grass appear to have developed specialized metaoblic adaptations for survival under Antarctic conditions. Their existence in maritime Antarctic regions is dependent upon a combination of genetical, morphological and ecological strategies and occupation of relatively favourable habitats. Colobanthus and Deschampsia are most vulnerable during the few weeks following the spring melt. -from Authors
Article
Within RiSCC project both in Maritime and in northern Victoria Land the system permafrost and vegetation has been monitored during the summers 2000/2001 and 2001/2002.The results demonstrate that vegetation exerts a buffering effect on the ground thermal regime and that its role in the energy balance of the surface ground varies in respect with the different types of vegetation cover and their canopy structure. Moreover there is a direct correlation between GST, the active layerthickness and the increasing vegetation coverage and the complexity of its structure. Comparing our data with those collected in the early 1960's at Signy Island, the active layer thickening (30-50 cm) seen over the last 40 years can be coupled over the same period with an increase in distribution of the Deschampsia-Colombathus association. Such evidence demonstrates that the integrated system "permafrost and vegetation" is suitable for the monitoring of climate change effects in Antarctica.
Article
The number of individual plants and colonies of the two native Antarctic vascular plants, Colobanthus quitensis and Deschampsia antarctica, have been monitored between 1964 and 1990 on three islands in the Argentine Islands archipelago, western Antarctic Peninsula. The Deschampsia population increased by nearly 25-fold and Colobanthus by over 5-fold. Furthermore there was a considerable increase in the number of Deschampsia colonies, although no additional colonies of Colobanthus were recorded. An analysis of Colobanthus plant size in 1974 and 1990 indicated that recruitment was probably irregular although the population structure remained essentially the same. The reasons for this and the increases in population size of both species are discussed. The relatively rapid increase in the abundance and distribution of these species is considered to be a response to the increasing summer air temperatures being experienced in the region of the maritime Antarctic. In particular, there is probably improved success in reproductive behavior resulting from warmer and/or longer growing seasons.
Article
Signy Island, maritime Antarctic, lies within the region of the Southern Hemisphere that is currently experiencing the most rapid rates of environmental change. In this study, peat cores up to 2 m in depth from four moss banks on Signy Island were used to reconstruct changes in moss growth and climatic characteristics over the late Holocene. Measurements included radiocarbon dating (to determine peat accumulation rates) and stable carbon isotope composition of moss cellulose (to estimate photosynthetic limitation by CO 2 supply and model CO 2 assimilation rate). For at least one intensively 14C-dated Chorisodontium aciphyllum moss peat bank, the vertical accumulation rate of peat was 3.9 mm yr−1 over the last 30 years. Before the industrial revolution, rates of peat accumulation in all cores were much lower, at around 0.6–1 mm yr−1. Carbon-13 discrimination (Δ), corrected for background and anthropogenic source inputs, was used to develop a predictive model for CO 2 assimilation. Between 1680 and 1900, there had been a gradual increase in Δ, and hence assimilation rate. Since 1800, assimilation has also been stimulated by the changes in atmospheric CO 2 concentration, but a recent decline in Δ (over the past 50–100 years) can perhaps be attributed to documented changes in temperature and/or precipitation. The overall increase in CO 2 assimilation rate (13C proxy) and enhanced C accumulation (14C proxy) are consistent with warmer and wetter conditions currently generating higher growth rates than at any time in the past three millennia, with the decline in Δ perhaps compensated by a longer growing season.
Article
A CALM grid with a data logger system to monitor the active layer thermal regime was established on Signy Island (60°43′S, 45°38′W at 80 m a.s.l.) in December 2005. The active layer at each of the 36 nodes of the grid was monitored measuring the ground temperature at least at 4 different depths between 0.02 and 0.4 m at the end of the summer season. In addition, within the grid, we selected four sites closely spaced (in a ray of 25 m) three of which with the same topographical characteristics (north facing aspect) but different vegetation coverage (one bare ground, BG1 and two sites with different vegetation: Andreaea sp. and Sanionia uncinata) and the fourth (BG2) it is as BG1 a bare ground but with south facing aspect. In particular, 4 thermistors were located at depths of 0.02, 0.3, 0.6, and 0.9 m at BG2 and at the Andreaea sp site, 9 thermistors at 0.02, 0.3, 0.6, 1, 1.2, 1.4, 1.6, 2, and 2.5 m at BG1 and at 0.02 and 0.6 m of depth at Sanionia site. Generally, with the same aspect, a thick vegetation cover (as in Sanionia site) provides a greater insulative effect than a thinner vegetation cover (as in Andreaea site) or bare ground (BG1) because vegetation both shades and insulates the ground resulting in a reduction in summer heat flux.
Article
The terrestrial environment of Signy Island, South Orkney Islands, maritime Antarctic, is undergoing rapid and possibly irreversible change caused by a natural biological agent. During the past decade there has been a dramatic increase in the number of Antarctic fur seals Arctocephalus gazella coming ashore on the island during the short summers. It is not known whether significant numbers of seals were present on the island prior to the initiation of commercial hunting in the early 1820s. The impact that the continuing increase of these seals had made on the island's terrestrial and freshwater environments has been sudden and locally devastating. The fragile cryptogam-dominated vegetation has suffered physical damage from which it may be impossible to recover. These seals are also frequenting several of the island's freshwater lakes which are becoming increasingly eutrophic. The long-term implications of this impact are causing serious concern for the future of the lowland terrestrial and freshwater ecosystems on Signy Island if the fur seal population continues to increase.
Article
A discrete warming event (December 21, 2001–January 12, 2002) in the McMurdo Dry Valleys, Antarctica, enhanced glacier melt, stream flow, and melting of permafrost. Effects of this warming included a rapid rise in lake levels and widespread increases in soil water availability resulting from melting of subsurface ice. These increases in liquid water offset hydrologic responses to a cooling trend experienced over the previous decade and altered ecosystem properties in both aquatic and terrestrial ecosystems. Here, we present hydrological and meteorological data from the McMurdo Dry Valleys Long Term Ecological Research project to examine the influence of a discrete climate event (warming of >2 °C) on terrestrial environments and soil biotic communities. Increases in soil moisture following this event stimulated populations of a subordinate soil invertebrate species (Eudorylaimus antarcticus, Nematoda). The pulse of melt-water had significant influences on Taylor Valley ecosystems that persisted for several years, and illustrates that the importance of discrete climate events, long recognized in hot deserts, are also significant drivers of soil and aquatic ecosystems in polar deserts. Thus, predictions of Antarctic ecosystem responses to climate change which focus on linear temperature trends may miss the potentially significant influence of infrequent climate events on hydrology and linked ecological processes.
Article
We studied the development of the Antarctic herb tundra vegetation formation in relation to the history of deglaciation across a range of habitats near H. Arctowski Research Station (King George Island, South Shetland Islands). Across the three identified environmental zones (coastal, intermediate, periglacial), we quantified the total vegetation cover, cover of the two indigenous flowering plants and bryophytes, age structure and reproductive features of the two flowering plants, and species diversity of mosses and liverworts. Analysis of these data supported the recognition of the three environmental zones; however, there were few indications of systematic differences in biological features of the two higher plants across the three zones, generally supporting the view that these, and the grass Deschampsia antarctica in particular, are effective primary colonists of recently deglaciated ground in this region.