Mean Annual Air Temperature Research Articles

Expert elicitation of state shifts and divergent sensitivities to climate warming across northern ecosystems

Northern regions are warming faster than the rest of the globe. It is difficult to predict ecosystem responses to warming because the thermal sensitivity of their biophysical components varies. Here, we present an analysis of the authors’ expert judgment regarding the sensitivity of six ecosystem components – permafrost, peatlands, lakes, snowpack, vegetation, and endothermic vertebrates – across northern landscapes ranging from boreal to polar biomes. We identified 28 discontinuous component states across a 3700 km latitudinal gradient in northeastern North America and quantified sensitivity as the transition time from an initial to a contrasting state following a theoretical step change increase in mean annual air temperature of 5 °C. We infer that multiple interconnected state shifts are likely to occur within a narrow subarctic latitudinal band at timescales of 10 to more than 100 years, and response times decrease with latitude. Response times differ between components and across latitudes, which is likely to impair the integrity of ecosystems.

Distribution of Najadaceae Species in Trans-Baikal Area Due to Climatic Factors

According to data of the late 20th century in the Trans-Baikal and Baikal areas, the family Najadaceae is represented by four species known in few localities: Caulinia flexilis (4 localities), C. minor (3), and Najas major (3), N. marina (4). All of them are annuals, r-strategists, which are characterized by fluctuations in abundance. Since the 21st century, these species have been found in 20 more localities, mainly situated within the Baikal Depression. In 2015, when performing monitoring studies of aquatic flora, three more new localities of Caulinia flexilis, C. minor, and Najas major were found in the basin of the Amur River. Distribution maps of the Najadaceae species in the region were compiled, and the ecological characteristics of their habitats were given. In Trans-Baikal area, since the middle of the 20th century, warming has occurred due to an increase in the average annual temperature. For the last 70 years, aridization has increased in southern regions, which changes the habitat conditions in waterbodies. Findings of these Najadaceae species in Trans-Baikal area coincided with the periods of increase in mean annual air temperatures and with local minimums of precipitation. An increase in the number of findings of the Najadaceae species since the beginning of the 21st century, both in Trans-Baikal area and in other regions of Russia, has been occurring against the background of an increase in the average annual air temperature. In Trans-Baikal area, the trend of increasing of temperatures in the warm season since the beginning of the 21st century is favorable for these species and may contribute to their further distribution.

THE IMPACT OF EXTREME WEATHER EVENTS OF PROJECTED CANADIAN REGIONAL CLIMATE MODEL DATA ON FLEXIBLE PAVEMENT

This paper presents findings about the influence of projected data from the Canadian regional climate model on the performance of flexible pavement, building upon the results from previous work where the data was generated and published, in which a general trend of decreasing the design life was observed. Projected temperature is the most important extreme climate impact on flexible roads. Adopting a conservative approach demonstrated that two extreme events of Maximum Mean Annual Air Temperature (MMAAT) and Maximum Summer Average Air Temperature (MSAAT) resulted in significant reduction of 25 years road design life. The observed trend indicates a severity range of 7% to 15% in terms of design service life loss when considering events every year compared to every five years. The findings revealed a reduction in pavement design life by 34%, 50%, 73%, and 90% for historical, short, intermediate, and long-term life cycles in the city of Windsor, respectively.

Surface Warming Constraint Projects Less Permafrost Thawing in High Mountain Asia

AbstractReliable projections of permafrost change are crucial for estimating permafrost carbon loss. However, potential model biases in surface air temperature may yield unrealistic projections of future permafrost area. Here, by leveraging the emergent relationship between equilibrium climate sensitivity and projected changes in mean annual air temperature over High Mountain Asia (HMA), we mitigate the overestimated local warming rates and excessive thawing of permafrost associated with the “hot model” problem in models participating in the Coupled Model Intercomparison Project phase 6. After constraint, permafrost area over HMA will reduce by 37%, 64% and 99% in 2081–2100 relative to present‐day under the SSP1‐2.6, SSP2‐4.5 and SSP5‐8.5 scenarios, respectively. In contrast, the unconstrained projections tend to overestimate the loss of permafrost area by nearly 10% under the low and mid‐emission scenarios due to the overestimation of local warming rates. These findings are crucial for policymaking and provide valuable insights into global permafrost projection.

Климатические изменения годового стока рек Северного Приохотоморья

The aim of this study was to assess the climatic changes in the annual river runoff of the Northern Okhotsk Sea region within the Magadan region. In the present work the analyzed series end with data for 2019. Observation series of river runoff at eight hydrological stations were used in this work. By the method of hydrological analogy, these series were brought to a multiyear period by restoring year-on-year values. Thus, the series of annual runoff for 1958–2019 were analyzed. The research method was the analysis of runoff time series for the presence of homogeneity in the mean (Student’s criterion), as well as spectral analysis. Comparison of mean long-term values of runoff layers for two periods (1958–2000 and 2001–2019) showed that the “norm” increased by 5–37%. It should be noted that these changes are not random according to the Student’s criterion with significance level of 5%. The presence of a trend in long-term water availability fluctuations is also evidenced by the time course of the dynamic mean annual runoff. Analysis of the runoff series, mean annual air temperature and total annual precipitation made it possible to conclude that annual runoff increase is caused by climatic changes, mainly by an increase in precipitation. It is possible that runoff increase is also due to the thawing of ice in the permafrost strata. But you should pay attention to the fact that with climate warming, moisture losses for evapotranspiration increase, primarily due to the growth of trees and shrubs. Moreover, this effect is more noticeable in large catchments. A 6-year cyclicity was revealed in the long-term fluctuations of annual runoff. These fluctuations are most likely a non-stationary complex Markov process. The results of this work will be useful for hydrological calculations, long-term and ultra-long-term runoff forecasts, and studying the river – sea ecosystems. Further hydrological studies should be carried out with the obligatory study of evapotranspiration in various landscape conditions.

Assessing machine learning models to generate permafrost distribution map in Solukhumbu, Nepal

Permafrost is one of the key components of the cryosphere. Previous studies show that the extent of permafrost has shifted to higher elevations in Nepal. These researches, however, has been hampered by inconsistency in their study period. Proxies like rock glaciers and climatic variables, such as multi-decadal annual air temperature, are used to link towards the likely occurrence of permafrost. Here, the rock glacier inventory of Solukhumbu was prepared, and classified based on their activity (Intact/Relict) from Google Earth. Talus-based rock glaciers were observed more than glacier-derived ones. These rock glaciers were highly correlated with Mean Annual Air Temperature, followed by potential incoming solar radiation and slope. Three machine learning models (Logistic Regression, Random Forest and Support Vector Machines) were trained to generate permafrost probability distribution maps based on their prediction of the probability of rock glaciers being intact as opposed to relict. Logistic Regression and Support Vector Machines were able to produce a similar spatial distribution of permafrost. However, the Random Forest has low precision of spatial variation. The permafrost distribution map suggests the likely occurrence of permafrost to be above 5000 m, indicating a potential for rock and landslides should it thaw in the future. While higher-resolution input data can improve the results, this approach remains promising for application in permafrost regions where information about the ice content of rock glaciers is very limited.

Reconstructing Younger Dryas ground temperature and snow thickness from cave deposits

Abstract. The Younger Dryas stadial was characterised by a rapid shift towards cold-climate conditions in the North Atlantic realm during the last deglaciation. While some climate parameters including atmospheric temperature and glacier extent are widely studied, empirical constraints on permafrost temperature and snow thickness are limited. To address this, we present a regional dataset of cryogenic cave carbonates (CCCs) from three caves in Great Britain that formed at temperatures between −2 and 0 °C. Our CCC record indicates that these permafrost temperatures persisted for most of the Younger Dryas. By combining ground temperatures with surface temperatures from high-resolution ground-truthed model simulations, we demonstrate that ground temperatures were approximately 6.6 ± 2.3 °C warmer than the mean annual air temperature. Our results suggest that the observed temperature offset between permafrost and the atmosphere can be explained by an average snow thickness between 0.2 and 0.9 m, which persisted for 233 ± 54 d per year. By identifying modern analogues from climate reanalysis data, we demonstrate that the inferred temperature and snow cover characteristics for the British Isles during the Younger Dryas are best explained by extreme temperature seasonality, comparable to continental parts of today's Arctic Archipelago. Such a climate for the British Isles necessitates a winter sea ice margin at approximately 45° N in the North Atlantic Ocean.

Different trends in the dynamics of Arctic lakes in North Siberia under climate change in 1985–2021

The methods and results of a comparative analysis of the effects of climate changes on the dynamics of the areas of thermokarst lakes over the past 36 years in the Arctic regions on the Yamal, Gydan, and Taimyr peninsulas are considered, the areas of which are 114, 175 and 426 thousand km2, respectively. All three regions are located within the permafrost zone of the Siberian Arctic. Using images of the Landsat 4, 5, 7, and 8 satellites, time series of data on average values of lake areas for the indicated regions were obtained on the basis on averaging areas of lakes over 23 test (key) areas. The total area of the test sites is about 800 km2. Using the ERA5 reanalysis system, time series of data on the mean annual air temperature in these territories have been generated, which show a rise of the temperature over the studied period 1985–2021. A comparison of trends in changes in regional mean areas of lakes and mean annual air temperature shows that with approximately the same rate of the temperature rise on these peninsulas, different trends in the dynamics of the lake areas are observed, which are manifested, on the one hand, in a noticeable reduction in the areas of lakes in the territories of Yamal and Gydan and, on the other hand, in their growth in Taimyr. Air temperature averaged over the period 1985–2021 and coefficients of the linear trend of changes in the lake areas in each of the above regions were compared. The results show that on the territories of Yamal and Gydan, where the lake areas decrease, the mean air temperature for the same period is equal to –8.1±0.9 and –8.9±0.9 °С, respectively. On the Taimyr territory, where the lake areas increase, the mean air temperature is significantly lower: –12.8±0.94 °С. Thus, this makes possible to make a conclusion that these considered regions differ significantly from each other by values of mean air temperature, and respectively, they are characterized by different trends in changes in areas of the thermokarst lakes.

Airborne DNA reveals predictable spatial and seasonal dynamics of fungi

Fungi are among the most diverse and ecologically important kingdoms in life. However, the distributional ranges of fungi remain largely unknown as do the ecological mechanisms that shape their distributions1,2. To provide an integrated view of the spatial and seasonal dynamics of fungi, we implemented a globally distributed standardized aerial sampling of fungal spores3. The vast majority of operational taxonomic units were detected within only one climatic zone, and the spatiotemporal patterns of species richness and community composition were mostly explained by annual mean air temperature. Tropical regions hosted the highest fungal diversity except for lichenized, ericoid mycorrhizal and ectomycorrhizal fungi, which reached their peak diversity in temperate regions. The sensitivity in climatic responses was associated with phylogenetic relatedness, suggesting that large-scale distributions of some fungal groups are partially constrained by their ancestral niche. There was a strong phylogenetic signal in seasonal sensitivity, suggesting that some groups of fungi have retained their ancestral trait of sporulating for only a short period. Overall, our results show that the hyperdiverse kingdom of fungi follows globally highly predictable spatial and temporal dynamics, with seasonality in both species richness and community composition increasing with latitude. Our study reports patterns resembling those described for other major groups of organisms, thus making a major contribution to the long-standing debate on whether organisms with a microbial lifestyle follow the global biodiversity paradigms known for macroorganisms4,5.

Exploring freshwater stream bacterial communities as indicators of land use intensity

BackgroundStream ecosystems comprise complex interactions among biological communities and their physicochemical surroundings, contributing to their overall ecological health. Despite this, many monitoring programs ignore changes in the bacterial communities that are the base of food webs in streams, often focusing on stream physicochemical assessments or macroinvertebrate community diversity instead. We used 16S rRNA gene sequencing to assess bacterial community compositions within 600 New Zealand stream biofilm samples from 204 sites within a 6-week period (February–March 2010). Sites were either dominated by indigenous forests, exotic plantation forests, horticulture, or pastoral grasslands in the upstream catchment. We sought to predict each site’s catchment land use and environmental conditions based on the composition of the stream bacterial communities.ResultsRandom forest modelling allowed us to use bacterial community composition to predict upstream catchment land use with 65% accuracy; urban sites were correctly assigned 90% of the time. Despite the variation inherent when sampling across a ~ 1000-km distance, bacterial community data could correctly differentiate undisturbed sites, grouped by their dominant environmental properties, with 75% accuracy. The positive correlations between actual values and those predicted by the models built using the stream biofilm bacterial data ranged from weak (average log N concentration in the stream water, R2 = 0.02) to strong (annual mean air temperature, R2 = 0.69).ConclusionsFreshwater bacterial community data provide useful insights into land use impacts on stream ecosystems; they may be used as an additional measure to screen stream catchment attributes.

SENSITIVITY OF THE KOLYMA RIVER RUNOFF TO MODERN CLIMATE CHANGE

The Kolyma River is a large river in the continuous permafrost zone. Its basin is subject to significant climatic changes. An information-modeling complex ECOMAG is employed for the study of water regime features and dynamics. ECOMAG calculates daily water flow rates at specified points based on meteorological data with a one-day resolution.This study analyzes the actual dynamics of water runoff and runoff-forming factors during the period from 1979 to 2013. A physical-mathematical model is adapted for the Kolyma River basin. Furthermore, the study examines the sensitivity of water regime characteristics to changing climate parameters. Calibration and verification demonstrated the ECOMAG’s ability to accurately reproduce observed water discharges for two points on the Kolyma River and the satisfactory performance on its tributary, the Bolshoy Anyui River. The ECOMAG model was for the first time employed for the Kolyma River basin, thus allowing the investigation of climate-related runoff changes. The preliminary statistical analysis revealed that if the average hydrological characteristics in the Kolyma River basin from 2000 to 2013 are compared with those from 1979 to 1999 a 5,1% rise of annual river runoff is evident for the Kolymskoye river section 283 km upstream the Kolyma River mouth (from 99,4 km3 in 1979-1999 up to 104,5 km3 in 2000-2013). The ECOMAG model also effectively captures changes in the annual water runoff and its intra-annual distribution.A rise in the mean annual air temperature by 1,3°C is characteristic of the modern time period. According to weather station data, the air temperature in March, April, November, and December increased by more than 2,5°C. The total annual precipitation increased by 8,3%, with September and March experiencing the most pronounced growth.To gain a more comprehensive understanding of the mechanisms governing the Kolyma River’s response to climate changes, the sensitivity of water runoff characteristics to air temperature and precipitation changes was analyzed using the ECOMAG model to generate artificial meteorological data series. The study demonstrates that water discharge is more sensitive to a 5% increase in precipitation than to a 1ºС rise in air temperature.

Bimodalność i długoterminowe trendy wartości ekstremalnych temperatury powietrza

Histograms of air temperature with a bimodal shape are commonly observed in many regions of the world. In this study, we investigate the causes of bimodality in the histograms of daily temperature series (minimum, average, and maximum) for selected climatological stations in Slovakia. Our findings suggest that in the Central European region, the bimodal shape of air temperature histograms is mainly due to the latent heat of freezing, as the surface of snow and ice and the air are thermally coupled. The asymmetry in the air temperature histograms is due to the lower mass heat capacity of ice compared to water and air. The energy-intensive latent heat of conversion of ice to water (and vice versa) results in the more frequent occurrence of ground-layer air temperatures around the freezing point, leading to the formation of the observed local maximum. This has far-reaching implications, such as the calculation of the annual mean air temperature at climatological stations. When calculating the average air temperature, negative temperatures should be given less weight than positive temperatures. Temperatures around 0-6°C should be given higher weight. This may also explain why Arctic regions are experiencing more significant warming than equatorial regions. In the second part of this paper, we analyze the long-term trends of selected temperature indices for the climatological station at Hurbanovo (Slovakia) from 1871 to 2020. Our results indicate statistically significant changes in all temperature indices, with indices related to cold temperatures increasing more significantly than those associated with high temperatures. Finally, study examines theoretical probability distributions to estimate T-year temperatures for temperature indices at the Hurbanovo climate station in Slovakia. The analysis includes three time periods (1901–1960, 1961–2020, and 1991–2020) and reveals significant changes in temperature indices at the Hurbanovo station. The 100-year temperature of TN,min was –35.75°C in 1901–1960, –28.69°C in 1961–2020, and –26.52°C in 1991–2020. The 100-year temperature of TX,max was 39.4°C in 1901–1960 and 39.63°C in 1961–2020. TN,min showed the most significant changes, with the 100-year temperature increasing by up to 7.06°C in 1961–2020 and up to 9.23°C in 1991–2020.

Optically‐Stimulated‐Luminescence Ages and Paleo‐Environmental Implications of Relict Frost Wedges in North–Central Bohemia, Czech Republic

ABSTRACTRelict frost wedges are widespread and valuable indicators of past environmental conditions that have been extensively dated across central and western European lowlands over the past few decades, but their timing in the Czech Republic is poorly known. Here, we present optically‐stimulated‐luminescence (OSL) ages for seven relict frost wedges situated at four study sites in north–central Bohemia, Czech Republic (49.9992–50.4956°N, 13.3736–16.0011°E, 230–350 m above sea level). The OSL ages indicate that the frost wedges developed during two phases in marine isotope stage 2: an older phase that peaked at 23.6 ± 2.9 ka and a younger phase that peaked at 16.1 ± 1.3 ka. Both phases probably experienced cold, dry and windy conditions that were mostly associated with <0°C mean annual air and ground temperatures and the presence of at least discontinuous permafrost, which is in line with similar central and western European records and other paleo‐environmental archives. The new OSL ages constitute the first extended dataset on the timing of frost wedges in this undersampled area between the Fennoscandian and Alpine ice sheets, which is essential for reconstructing past permafrost extents and climate conditions, as well as for validating models of past permafrost dynamics in central Europe.

A novel indicator for equivalent mean air temperature within the tunnel considering time-varying ventilation wind speeds: Calculation and application

The study examines the coupling effect between air temperature and time-varying ventilation wind speeds within the tunnel, abstracting their influence on tunnel coldness. This investigation introduces a novel indicator—the equivalent mean air temperature within the tunnel—derived through fluid dynamics and heat transfer theories based on the principle of equivalent convective heat transfer. Case studies using the Xinjiaodong Tunnel and BSLL Tunnel illustrate the indicator's applications, including optimal anti-freezing axis identification, insulation layer thickness design, and active-controlled ventilation implementation. The optimal anti-freezing axis orientation angle for the Xinjiaodong Tunnel entrance section is 133.3°, deviating significantly by 160.8° from the actual axis, indicating a lower level of equivalent mean annual air temperature (5.5 °C) at the entrance section. This underscores the necessity to reinforce anti-freezing measures specifically at the entrance section of the Xinjiaodong Tunnel. Determining a 10 cm-thick insulation layer requirement at the Xinjiaodong Tunnel entrance section based on the equivalent mean air temperature. Through on-site investigation and published findings, it was observed that a 5 cm-thick insulation layer failed to prevent freezing, resulting in water leakage and ice formation on the lining, thus validating the calculation results. The BSLL Tunnel requires an insulation layer thickness exceeding 10 cm based on the equivalent mean air temperature, necessitating the implementation of active-controlled ventilation. Calculation results reveal that, with active-controlled ventilation wind speeds increasing from 1 m/s to 4 m/s at a temperature threshold of 4 °C, the equivalent mean air temperature during cumulative negative temperature periods within the BSLL Tunnel rises sharply from 1.0 °C to 2.7 °C. These findings demonstrate that the equivalent mean air temperature not only guides the identification of optimal anti-freezing axis, the design of insulation layer thickness considering time-varying ventilation wind speeds, and the implementation of active-controlled ventilation but also provides new methods and technologies for anti-freezing design in cold-region tunnels.

Temperature and nutrients control the presence and distribution of long-chain diols in Swiss lakes

Long-chain diols are biomarkers commonly used in the marine realm to reconstruct several environmental parameters such as sea surface temperature and salinity. However, they are also produced in lacustrine and slow-flowing river environments, a characteristic that has proved to be useful to trace past riverine inputs in coastal sedimentary records. So far, their use in lacustrine settings is sparse as their controls are not well-known. Previous studies in two lakes have shown that long-chain diol distribution is linked to changes in temperature (in a small Spanish alpine lake), but also to water column stratification (in a large deep Swiss lake). To understand the controls on i) the presence of long-chain diols in lakes, and ii) the distribution of long-chain diol isomers, surface sediments from 52 Swiss lakes were studied. Long-chain diols are present in 57% of the lakes, and machine learning (i.e., random forest model) showed that their presence is mainly controlled by mean annual air temperature, sodium and potassium concentrations and area of the lakes. Long-chain diol isomer relative distribution seems to react to temperature, nutrient (here nitrate) and oxygen concentrations in the lakes. This new insight was tested on a short sedimentary core from Lake Zurich, and compared with other biomarker proxies (based on branched and isoprenoid glycerol dialkyl glycerol tetraethers), as well as with historical record of nutrient contents and temperature. Variations in the long-chain diol index (LDI) mirror measured temperature, but also reacted to changes in nutrients and oxygenation in the lake. This study highlights the potential of long-chain diols as a proxy to trace both nutrients and temperature in lakes, potentially on geological timescales.

Assessment of branched glycerol monoalkyl glycerol tetraether (brGMGT)-based paleothermometry in the 250,000-year sediment record of Lake Chala, equatorial East Africa

Branched glycerol monoalkyl glycerol tetraethers (brGMGTs), a relatively understudied group of bacterial membrane lipids structurally similar to branched glycerol dialkyl glycerol tetraethers (brGDGTs), appear to be strongly influenced by temperature in terrestrial settings. In surficial bottom sediments of East African lakes, the abundance of brGMGTs relative to the sum of brGMGTs and brGDGTs (%brGMGT) and brGMGT distribution are strongly related to local mean annual air temperature (MAAT), stimulating development of new paleothermometers. However, applications of these methods to lake-sediment records are currently lacking. Here we investigate brGMGT concentrations and distributions in 916 samples throughout the 250,000-year (250-kyr) sediment sequence from Lake Chala, a presently fresh and permanently stratified (meromictic) tropical crater lake. All seven previously identified brGMGTs occur abundantly, reflected in a relatively high average %brGMGT of 19%. BrGMGTs and brGDGTs concentrations throughout the sequence are strongly correlated (R = 0.83, p < 0.001), suggesting that their producers and/or associated ecological niches substantially overlap. Clear distinction can be made between brGMGTs produced predominantly in the bottom sediments (H1034a and H1034c) versus the anoxic lower water column (H1020a-c and H1034b). Although a 17-month monitoring study of Lake Chala suggested brGMGTs are primarily produced in the sediments, down-core data assign greater importance to aquatic production than previously estimated. Instead of reflecting temperature, %brGMGT variations showed greatest similarity to GDGT proxies reflecting lake depth and/or mixing regime. BrGMGT-based temperature models produce ambiguous reconstructions, showing little similarity to known global temperature trends or the brGDGT-based mean summer temperature (MST) reconstruction from the same sediments.

Relation between soil glycerol dialkyl glycerol tetraethers and temperature in different climatic regions in China

AbstractTemperature variation in the past periods can provide valuable insights into the characteristics and driving mechanisms of current global warming and future changes. Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are commonly used to as a temperature proxy to quantitatively reconstruct past temperature changes. However, it still remains unclear whether the relation between brGDGTs and temperature is influenced by other environmental factors, thereby affecting the accuracy of quantitative reconstructions. A comprehensive analysis of the relation between brGDGTs and temperature across various climate regions can greatly enhance the accuracy of reconstructing past temperature changes. Here, we investigate the distribution patterns of soil brGDGTs using 28 new topsoils collected from altitudes ranging from 2100 to 4000 m.a.s.l. in the Hengduan Mountains in the southeastern margin of the Tibetan Plateau (TP), compiled previously published soil brGDGT data in China. Our results reveal distinct distribution patterns of soil brGDGTs between humid and arid regions. Furthermore, we further investigated the correlation between brGDGT indices and various environmental factors from both altitudinal and regional scales. At the altitudinal scale, brGDGT indices exhibit a stronger correlation with mean annual air temperature (MAAT) in alkaline soils (pH &gt; 7) than that in acidic soils (pH &lt; 7). At the regional scale, this correlation is higher in alkaline soils than that in acidic soils as well and is stronger in humid soils (mean annual precipitation [MAP] &gt; 800 mm) than that in semi‐humid and semi‐arid soil (400 &lt; MAP &lt; 800 mm) and arid soil (MAP &lt; 400 mm). In addition, brGDGT‐inferred temperature is more affected by MAP in humid alkaline soils but less affected in humid acidic soils. Therefore, caution is needed to use suitable brGDGT index for palaeotemperature reconstructions in various climate regions.

Distributions of bacterial branched tetraether lipids associated with bacterial communities in hummock and hollow soils from Southern Tibetan peatland

Branched glycerol dialkyl glycerol tetraethers (brGDGTs), special membrane-spanning lipids derived from some bacteria, are widely used as molecular tools in paleoenvironmental studies to reconstruct terrestrial temperature and pH conditions. However, the impact of microtopography discrepancies on the accuracy and applicability of brGDGT-based proxies remains unclear. Here we investigated the distributional patterns of brGDGTs and bacterial communities within the hummock-hollow microtopography in the mid-southern Tibetan peatlands. Our results show that the methylation index of C5-methyl brGDGTs (MBT′5ME) values are significantly correlated with the local mean annual air temperature (MAAT). However, the peat-specific temperature calibration exhibits an underestimation of MAATpeat compared to the present MAAT. We find the MBT′5ME values are significantly lower in the moist hollows than that in the drier hummocks. This discrepancy could be primarily attributed to the shifts in bacterial communities and the physiological adaptation of brGDGT-producing bacteria driven by the high soil water content. These findings highlight the remarkable variability of MBT′5ME values at small spatial scales, which holds profound implications for paleotemperature reconstruction in alpine peatlands.

A climate-driven, altitudinal transition in rock glacier dynamics detected through integration of geomorphological mapping and synthetic aperture radar interferometry (InSAR)-based kinematics

Abstract. In dry southwestern South Tyrol, Italy, rock glaciers are dominant landforms of the high-mountain cryosphere. Their spatial distribution and degree of activity hold critical information on the current state of discontinuous permafrost and consequently on the response potential to climate warming. Traditional geomorphologic mapping, however, owing to the qualitative expert-based nature, typically displays a high degree of uncertainty and variability among operators with respect to the dynamic classification of intact (permafrost-bearing) and relict (permafrost-devoid) rock glaciers. This limits the reliability of geomorphologic rock glacier inventories for basic and applied purposes. To address this limitation, (i) we conduct a systematic evaluation of the improvements that synthetic aperture radar interferometry (InSAR) can afford to the detection and dynamic classification of rock glaciers and (ii) build an integrated inventory that combines the strengths of geomorphologic- and InSAR-based approaches. To exploit fully InSAR-based information towards a better understanding of the topo-climatic conditions that sustain creeping permafrost, we further explore how velocity and the spatial distribution of moving areas (MAs) within rock glaciers may vary as a function of simple topographic variables known to exert first-order controls on incoming solar radiation, such as elevation and aspect. Starting from a geomorphologic inventory (n=789), we characterize the kinematics of InSAR-based MAs and the relevant hosting rock glaciers on 36 Sentinel-1 interferograms in the 2018–2019 period. With respect to the original inventory, InSAR analysis allowed us to identify 14 previously undetected rock glaciers. Further, it confirmed that 246 (76 %) landforms, originally interpreted as intact, do exhibit detectable movement (i.e., ≥1 cm yr−1) and that 270 (60 %) of the relict labeled counterparts do not, whereas 144 (18 %) were kinematically undefined due to decorrelation. Most importantly, InSAR proved critical for reclassifying 121 (15 %) rock glaciers, clarifying that 41 (13 %) of those interpreted as being intact do not exhibit detectable movement and that 80 (17 %) of the original relict ones do move. Reclassification (i) allowed us to identify a cluster of intact rock glaciers below 2000 m a.s.l. associated with positive mean annual air temperature (MAAT), and (ii) by increasing the altitudinal overlap between intact and relict rock glaciers, it depicts a broad transition belt in the aspect–elevation space, which varies from 50 m on west-facing slopes to 500 m on easterly ones. This finding deteriorates the significance of elevation and aspect as topographic proxies for modeling permafrost occurrence and highlights the importance of using InSAR to inform such models. From a process-oriented standpoint, InSAR information proves fundamental for imaging how this altitudinal transition manifests through changing rates and styles of rock glacier surface deformation. Specifically, we find that, as rock glaciers move faster, an increasingly larger proportion of their surface becomes kinematically involved (i.e., percent MA cover) and that this proportion increases with elevation up to 2600–2800 m, beyond which an inflection occurs and consistent average values are attained. Considering that the inflection falls between the −1 and −2 °C MAAT – the lower boundary for discontinuous permafrost – and is independent of slope gradient, we conclude that this altitudinal pattern represents a geomorphic signature: the dynamic expression of increasing permafrost distribution, from sporadic to discontinuous.

Diversity and distribution of chironomids in Central European ponds.

Ponds are common freshwater habitats in the European landscape that substantially contribute to local and regional biodiversity. Chironomids often dominate invertebrate communities in ponds but are usually disregarded in ecological studies due to relatively complicated taxonomy and identification issues. We present a comprehensive overview of the chironomid diversity in 246 ponds spanning a wide range of conditions extending from the Pannonian Plain to the Carpathians. Altogether, we recorded 225 taxa including 192 species from six subfamilies (Podonominae, Tanypodinae, Diamesinae, Prodiamesinae, Orthocladiinae and Chironominae). However, the chironomid taxa inventory is far from complete and about 16% of the total diversity of pond-dwelling chironomids remains undetected. Chironomid alpha diversity showed a significant unimodal pattern along the elevation gradient with the highest number of taxa per pond expected around 790 m a.s.l. Gamma diversity also peaked in mid-elevations (600-800 m), and the common chironomid taxa partitioned the 2100-m long altitudinal gradient relatively evenly. The heterogeneity of chironomid communities among ponds measured as beta diversity was significantly higher in elevations below 800 m. Temperature and the proportion of surrounding forests significantly influenced alpha diversity of chironomid communities, while urban land cover and pond size had no significant effect. Ponds with a mean annual air temperature of approximately 4.8°C and a low proportion of surrounding forests are expected to harbour the most diverse chironomid communities. Our study showed that chironomids represent a very diverse and often exceptionally rich group of pond-dwelling macroinvertebrates. Given the high diversity and broad range of occupied niches, chironomids should not be overlooked in pond ecology studies. On the contrary, they should be considered a potential model group.