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Antarctic climate cooling and terrestrial ecosystem response
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The average air temperature at the Earth's surface has increased by 0.06 degrees C per decade during the 20th century, and by 0.19 degrees C per decade from 1979 to 1998. Climate models generally predict amplified warming in polar regions, as observed in Antarctica's peninsula region over the second half of the 20th century. Although previous reports suggest slight recent continental warming, our spatial analysis of Antarctic meteorological data demonstrates a net cooling on the Antarctic continent between 1966 and 2000, particularly during summer and autumn. The McMurdo Dry Valleys have cooled by 0.7 degrees C per decade between 1986 and 2000, with similar pronounced seasonal trends. Summer cooling is particularly important to Antarctic terrestrial ecosystems that are poised at the interface of ice and water. Here we present data from the dry valleys representing evidence of rapid terrestrial ecosystem response to climate cooling in Antarctica, including decreased primary productivity of lakes (6-9% per year) and declining numbers of soil invertebrates (more than 10% per year). Continental Antarctic cooling, especially the seasonality of cooling, poses challenges to models of climate and ecosystem change.
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... A significant extent of permafrost occurs in the Antarctic Peninsula region where ice-free areas occupy about 6500km 2 (Brooks et al., 2019). The Antarctic Peninsula region has been exposed to accelerated atmospheric warming in the last decades of the 20th century when the air temperatures locally increased by >3°C (e. g. Doran et al., 2002;Vaughan et al., 2003;Turner et al., 2020). The warming of the Antarctic Peninsula region has been confirmed on the basis of numerous studies especially in its western part, which shows mean annual air temperatures ranging from −2 to −4°C (Turner et al., 2020). ...
... Likewise, the results from other regions in Antarctica reported rather stable conditions without any notable trend (Carshalton et al., 2022) or warming and thickening trends (Cannone et al., 2021). Seasonality of cooling thus presents challenges for models dealing with climate change and ecosystems (Doran et al., 2002). ...
Climate change and its impacts on sensitive polar ecosystems are relatively little studied in Antarctic regions. Permafrost and active layer changes over time in periglacial regions of the world are important indicators of climate variability. These changes (e. g. permafrost degradation, increasing of the active layer thickness) can have a significant impact on Antarctic terrestrial ecosystems. The study site (AWS-JGM) is located on the Ulu Peninsula in the north of James Ross Island. Ground temperatures at depths of 5, 50, and 75 cm have been measured at the site since 2011, while air temperature began to be measured in 2004. The main objective is to evaluate the year-to-year variability of the reconstructed temperature of the top of the permafrost table and the active layer thickness (ALT) since 2004 based on air temperature data using TTOP and Stefan models, respectively. The models were verified against direct observations from a reference period 2011-2021 showing a strong correlation of 0.95 (RMSE = 0.52) and 0.84 (RMSE = 3.54) for TTOP and Stefan models, respectively. The reconstructed average temperature of the permafrost table for the period 2004-2021 was -5.8 °C with a trend of -0.1 °C/decade, while the average air temperature reached -6.6 °C with a trend of 0.6 °C/decade. Air temperatures did not have an increasing trend throughout the period, but in the first part of the period (2004/05-2010/11) showed a decreasing tendency (-1.3 °C/decade). In the period 2011/12-2020/21, it was a warming of 1.9 °C/decade. The average modelled ALT for the period 2004-2021 reached a value of 60cm with a trend of -1.6 cm/decade. Both models were found to provide reliable results, and thus they significantly expand the information about the permafrost and ALT, which is necessary for a better understanding of their spatiotemporal variability and the impact of climate change on the cryosphere.
... Increasing longwave radiation over the glaciers added little to the meltwater runoff. We argue that the near-surface air temperature lapse rate is different near the coast due to the higher humidity (Doran, Priscu, et al., 2002). Modeled lapse rate is assumed to be the dry adiabatic everywhere in the valley, an accurate assumption for environments up valley, westward of and including Canada Glacier (Doran, Priscu, et al., 2002;Hoffman et al., 2014). ...
... We argue that the near-surface air temperature lapse rate is different near the coast due to the higher humidity (Doran, Priscu, et al., 2002). Modeled lapse rate is assumed to be the dry adiabatic everywhere in the valley, an accurate assumption for environments up valley, westward of and including Canada Glacier (Doran, Priscu, et al., 2002;Hoffman et al., 2014). Near the coast, east of Canada Glacier we applied the wet adiabatic lapse rate. ...
The McMurdo Dry Valleys, Antarctica, are a polar desert populated with numerous closed‐watershed, perennially ice‐covered lakes primarily fed by glacial melt. Lake levels have varied by as much as 8 m since 1972 and are currently rising after a decade of decreasing. Precipitation falls as snow, so lake hydrology is dominated by energy available to melt glacier ice and to sublimate lake ice. To understand the energy and hydrologic controls on lake level changes and to explain the variability between neighboring lakes, only a few kilometers apart, we model the hydrology for the three largest lakes in Taylor Valley. We apply a physically based hydrological model that includes a surface energy balance model to estimate glacial melt and lake sublimation to constrain mass fluxes to and from the lakes. Results show that lake levels are very sensitive to small changes in glacier albedo, air temperature, and wind speed. We were able to balance the hydrologic budget in two watersheds using meltwater inflow and sublimation loss from the ice‐covered lake alone. A third watershed, closest to the coast, required additional inflow beyond model uncertainties. We hypothesize a shallow groundwater system within the active layer, fed by dispersed snow patches, contributes 23% of the inflow to this watershed. The lakes are out of equilibrium with the current climate. If the climate of our study period (1996–2013) persists into the future, the lakes will reach equilibrium starting in 2300, with levels 2–17 m higher, depending on the lake, relative to the 2020 level.
... In the Antarctic, at least 80 per cent of the sea ice in winter is thin, first-year ice, suggesting that this ice will be unstable with warming; however, the complexity of feedback mechanisms related to open water, salinity and depth of warmer water suggest that this thin ice might be resilient (Wadhams 1991). Further, warming in the Peninsula area and cooling in the continent has been confirmed by temperature records from 1966 to 2000 (Doran et al. 2002). ...
... These ecosystems are characterised by low species diversity and high adaptation, leaving them vulnerable to environmental change (International Arctic Science Committee 1994). Warming in the Antarctic Peninsula and the sub-Antarctic islands will lead to changes in species, while summer cooling evident in the continent suggests that biologic declines will result (see Doran et al. 2002). ...
... Differently from the large increase in temperature over the Arctic and the Third Pole, the variations in Antarctic temperature show regional differences and are sensitive to the selected time period. For the second half of the 20th century, the Antarctic Peninsula and West Antarctica displayed rapid warming, whereas the analysis of Antarctic meteorological data reflects a net cooling on the Antarctic continent in this period [23][24][25][26]. However, the spatial distribution of changes in Antarctic temperature has changed since the beginning of the 21st century. ...
Polar amplification appears in response to greenhouse gas forcing, which has become a focus of climate change research. However, polar amplification has not been systematically investigated over the Earth’s three poles (the Arctic, Antarctica, and the Third Pole). An index of polar amplification is employed, and the annual and seasonal variations of land surface temperature over the Earth’s three poles are examined using MODIS (Moderate Resolution Imaging Spectroradiometer) observations for the period 2001–2018. As expected, the warming of the Arctic is most conspicuous, followed by the Third Pole, and is weakest in Antarctica. Compared to the temperature changes for the global land region, positive polar amplification appears in the Arctic and the Third Pole on an annual scale, whereas Antarctic amplification disappears, with a negative amplification index of −0.72. The polar amplification for the Earth’s three poles shows seasonal differences. Strong Arctic amplification appears in boreal spring and winter, with a surface warming rate of more than 3.40 times the global mean for land regions. In contrast, the amplification of the Third Pole is most conspicuous in boreal summer. The two poles located in the Northern Hemisphere have the weakest amplification in boreal autumn. Differently from the positive amplification for the Arctic and the Third Pole in all seasons, the faster variations in Antarctic temperature compared to the globe only appear in austral autumn and winter, and the amplification signal is negative in these seasons, with an amplification index of −1.68 and −2.73, respectively. In the austral winter, the strong negative amplification concentrates on West Antarctica and the coast of East Antarctica, with an absolute value of amplification index higher than 5 in general. Generally, the polar amplification is strongest in the Arctic except from June to August, and Antarctic amplification is the weakest among the Earth’s three poles. The Earth’s three poles are experiencing drastic changes, and the potential influence of climate change should receive attention.
... Unlike more temperate desert environments on Earth, the MDVs host significant reservoirs of water stored as glacial ice, shallow subsurface ice (i.e., permafrost), and surficial snow deposits. Climate models predict significant warming over East Antarctica through the year 2100 at a projected rate of +0.03 • C yr −1 [79], despite the modest cooling observed in the MDVs in the 1990s and early 2000s [80]. Ref. [47] demonstrates how some of these reservoirs are only metastable under current Antarctic environmental conditions, not only due to rising temperatures, but also due to the complex interplay between soil thermophysics and sediment/albedo feedback, resulting in insolation-driven melting. ...
Available soil moisture is thought to be the limiting factor for most ecosystem processes in the cold polar desert of the McMurdo Dry Valleys (MDVs) of Antarctica. Previous studies have shown that microfauna throughout the MDVs are capable of biological activity when sufficient soil moisture is available (~2–10% gravimetric water content), but few studies have attempted to quantify the distribution, abundance, and frequency of soil moisture on scales beyond that of traditional field work or local field investigations. In this study, we present our work to quantify the soil moisture content of soils throughout the Fryxell basin using multispectral satellite remote sensing techniques. Our efforts demonstrate that ecologically relevant abundances of liquid water are common across the landscape throughout the austral summer. On average, the Fryxell basin of Taylor Valley is modeled as containing 1.5 ± 0.5% gravimetric water content (GWC) across its non-fluvial landscape with ~23% of the landscape experiencing an average GWC > 2% throughout the study period, which is the observed limit of soil nematode activity. These results indicate that liquid water in the soils of the MDVs may be more abundant than previously thought, and that the distribution and availability of liquid water is dependent on both soil properties and the distribution of water sources. These results can also help to identify ecological hotspots in the harsh polar Antarctic environment and serve as a baseline for detecting future changes in the soil hydrological regime.
... They are considered important refuges for species during extreme temperature and drought events and support microbial interactions, element cycling and ecosystem functions (Dupraz et al., 2009). Antarctic glacier ecosystems are characterized by low annual average temperatures (below −19.8°C) and precipitation (below 100 mm/year water equivalent) and a dry atmosphere (rapid evaporation is driven by low humidity due to katabatic winds), which place severe limitations on biological activity (Doran et al., 2002). However, the potential role of microbial mats in the alteration of Earth's biogeochemical cycling is challenging to determine because these mats are generally not well studied (Bolhuis & Stal, 2011;Liu et al., 2011). ...
Glaciers cover nearly 10% of the Earth's surface and are unique biomes dominated by microbial communities that support key ecosystem processes. The melting of glaciers is among the most conspicuous consequences of global climate change, with impacts on microbial ecology and associated biogeochemistry. However, we are still missing an integrative understanding of microbial biodiversity from divergent habitats associated with glaciers.
Here, we compiled global microbiome metadata from 93 representative glaciers over 180 locations and used random forest, microbial ecological networks and structural equation modelling to evaluate the biodiversity and environmental factors associated with the glacier microbiomes of seven contrasting habitats: water, epilithic biofilm, cryoconite, mat, ice, sediment and permafrost soil.
The results showed that microbial diversity largely changed across habitats, with the highest in permafrost soil, followed by sediment, ice, mat, cryoconite, water and epilithic biofilm. More importantly, we provided critical evidence that the environmental and climatic factors associated with the microbiomes of glaciers varied with glacier habitats. Microbial diversity in water was highly correlated with latitude, cryoconite microbial diversity was significantly ( p = 0.01) correlated with pH, and permafrost soil and sediment microbial diversity were mainly explained by temperature (17.05% and 13.37% respectively).
Using ecological association network analysis, we identified some tightly linked common microbial taxa (e.g. Proteobacteria and Bacteroidetes) that were present in all the habitats and were vulnerable to climatic factors, such as temperature and precipitation. This study demonstrated that microbial diversity, drivers and co‐occurrence patterns differ among glacier habitats globally, and diverse habitat‐dependent glacier microbiomes could serve as early warning sentinels for the study of life on glaciers and its potential future in a warming world.
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... Low temperatures, rapid freeze/thaw cycles, aridity, variations in light regimes, steep chemical and salt gradients, and nutrient bioavailability all pose challenges to life in this evolving landscape [2][3][4][5][6][7]. In the early 1990's the MDVs experienced a decadal cooling trend [8]. In 2006 this cooling trend terminated and the MDVs have since experienced higher and more variable temperatures with highflow and flood events occurring more frequently [9,10]. ...
The meltwater streams of the McMurdo Dry Valleys are hot spots of biological diversity in the climate-sensitive polar desert landscape. Microbial mats, largely comprised of cyanobacteria, dominate the streams which flow for a brief window of time (~10 weeks) over the austral summer. These communities, critical to nutrient and carbon cycling, display previously uncharacterized patterns of rapid destabilization and recovery upon exposure to variable and physiologically detrimental conditions. Here, we characterize changes in biodiversity, transcriptional responses and activity of microbial mats in response to hydrological disturbance over spatiotemporal gradients. While diverse metabolic strategies persist between marginal mats and main channel mats, data collected from 4 time points during the austral summer revealed a homogenization of the mat communities during the mid-season peak meltwater flow, directly influencing the biogeochemical roles of this stream ecosystem. Gene expression pattern analyses identified strong functional sensitivities of nitrogen-fixing marginal mats to changes in hydrological activities. Stress response markers detailed the environmental challenges of each microhabitat and the molecular mechanisms underpinning survival in a polar desert ecosystem at the forefront of climate change. At mid and end points in the flow cycle, mobile genetic elements were upregulated across all mat types indicating high degrees of genome evolvability and transcriptional synchronies. Additionally, we identified novel antifreeze activity in the stream microbial mats indicating the presence of ice-binding proteins (IBPs). Cumulatively, these data provide a new view of active intra-stream diversity, biotic interactions and alterations in ecosystem function over a high-flow hydrological regime.
... In 2002 the climate regime of MCM soil ecosystems dramatically shifted from a decadal cooling trend (Doran et al., 2002) to a warmer, wetter, climate with greater interannual variability (Gooseff et al., 2017). To account for potential effects of this climate shift on habitat suitability and nematode growth and development, we measured adult S. lindsayae of each sex from each till type (N = 118 (1999), 94 (2004) for Ross Sea till and N = 46 (1999), 54 (2004) for Taylor II till) sampled from 6 different soil monitoring plots per till type during the 1999/2000 and 2004/2005 seasons. ...
Ecological stoichiometry is a useful theoretical framework for understanding the sources and controls on nutrient availability that structure the composition and diversity of biotic communities. One such relationship is that organismal development rate is positively linked to cellular Phosphorus (P). We hypothesized that P availability, relative to other nutrients, e.g., nitrogen and carbon, would drive the evolution of traits associated with organismal growth and development. We examined the effects of P availability both in situ and in vitro, on free-living soil nematodes. We found that P-deficient environments produce predictable changes in the ecology and evolution of important life history traits. Our results identify altered rRNA gene copy number and subsequent changes in gene expression and protein synthesis as mechanisms by which P-deficiency influences these traits. These findings have important implications for explaining soil ecological and evolutionary patterns across multiple levels of organization, including the structure and functioning of organisms, populations, communities, and ecosystems.
The McMurdo Dry Valleys form the largest relatively ice-free area on the Antarctic continent. The perennially ice-covered lakes, ephemeral streams and extensive areas of exposed soil are subject to low temperatures, limited precipitation and salt accumulation. The dry valleys thus represent a region where life approaches its environmental limits. This unique ecosystem has been studied for several decades as an analog to environments on other planets, particularly Mars. For the first time, the detailed terrestrial research of the dry valleys is brought together here, presented from an astrobiological perspective. Chapters include a discussion on the history of research in the valleys, a geological background of the valleys, setting them up as analogs for Mars, followed by chapters on the various sub-environments in the valleys such as lakes, glaciers and soils. Includes concluding chapters on biodiversity and other analog environments on Earth.
Soils in the Antarctic Dry Valleys have been significantly influenced by soil formation factors such as parent material, climate, and topography. Factors common in more temperate zones, including chemical weathering and leaching of minerals, occur to a much lesser extent in these cold arid soils, leading to an accumulation of salts and bases, which will likely affect the distribution of soil biota. Since the intensity of these factors may vary with topography, this study examined the soil properties and soil invertebrate communities along an elevational gradient in Taylor Valley, Antarctica. We sampled from two spatial scales (1 X 1 m and 10 X 10 m) at three sites (83, 121, and 188 m a.s.l) on the south side of Lake Hoare in Taylor Valley, and examined soil moisture, nitrogen, carbon, pH, and electrical conductivity (which provides an estimation of soil salinity), as well as the distribution and community structure of soil invertebrates. We found significant differences in soil properties with elevation, along with associated differences in soil communities. Biodiversity was greatest at the lowest elevation, closest to the shore of Lake Hoare, where soil moisture, carbon, and nitrogen were highest, and salinity was lowest. Scottnema lindsayae dominated the nematode communities found at all sites. Electrical conductivity was higher and carbon and nitrogen contents were lower at the upper elevations. The distribution of both Eudorylaimus and Plectus appeared to be influenced by soil moisture; electrical conductivity affected the mortality of all three nematode genera found. Soil properties did differ with sampling scale, suggesting that changes in microhabitats not detected at sampling intervals of a meter or more may be more reliably detected by sampling at a smaller scale.
We are studying the distribution, biodiversity, and abundance of nematodes in the most extreme terrestrial environment on earth, the Dry Valley region of Antarctica. Here we report that the nematode community structure of 1-3 species in two functional groups may be the simplest soil food web of any terrestrial ecosystem. Nematodes were widespread and not correlated with moisture, C, or N, factors that define soil biotic complexity elsewhere. In a field experiment, treatments increasing soil water, carbon, and temperature, alone or in combination, generally decreased the abundance of the single omnivore-predator species and increased the abundance of its microbivorous prey species. These low-diversity nematode communities, limited to ≤3 species, apparently lack species redundancy and appear sensitive to environmental change. Our findings suggest that Antarctic soil ecosystems are sensitive to anthropogenic disturbance.