Snow Line Research Articles

Eccentricity Distribution beyond the Snow Line and Implications for Planetary Habitability

A fundamental question in the study of planetary system demographics is: how common is the solar system architecture? The primary importance of this question lies in the potential of planetary systems to create habitable environments, and dissecting the various components of solar system evolution that contributed to a sustainable temperate surface for Earth. One important factor in that respect is volatile delivery to the inner system and the dependence on giant planets beyond the snow line as scattering agents, particularly as such cold giant planets are relatively rare. Here, we provide an investigation of the eccentricity distribution for giant planet populations both interior and exterior to their system snow lines. We show that the median eccentricity for cold giants is 0.23, compared with a far more circular orbital regime for inner planets. We further present the results of a dynamical simulation that explores the particle scattering potential for a Jupiter analog in comparison with a Jupiter whose eccentricity matches that of the median cold giant eccentricity. These simulations demonstrate that the capacity for such an eccentric cold giant system to scatter volatiles interior to the snow line is significantly increased compared with the Jupiter analog case, resulting in a far greater volume of Earth-crossing volatiles. Thus, many of the known systems with cold giant planets may harbor water worlds interior to the snow line.

Experimental study of the binding energy of NH3 on different types of ice and its impact on the snow line of NH3 and H2O

Context. Nitrogen-bearing molecules (such as N2H+ and NH3) are excellent tracers of high-density and low-temperature regions, such as dense cloud cores. Notably, they could help advance the understanding of snow lines in protoplanetary discs and the chemical evolution of comets. However, much remains unknown about the chemistry of N-bearing molecules on grain surfaces, which could play an important role in their formation and evolution. Aims. In this work, we experimentally study the behaviour of NH3 on surfaces that mimic grain surfaces under interstellar conditions in the presence of some other major components of interstellar ices (i.e. H2O, CO2, CO). We measure the binding energy distributions of NH3 from different H2O ice substrates and also investigate how it could affect the NH3 snow line in protoplanetary discs. Methods. We performed laboratory experiments using the ultra-high vacuum (UHV) set-up VENUS (VErs des NoUvelles Syntheses). We co-deposited NH3 along with other adsorbates (H2O, 13CO, and CO2) and performed temperature programmed desorption (TPD) and temperature programmed-during exposure desorption (TP-DED) experiments. The experiments were monitored using a quadrupole mass spectrometer and a Fourier transform reflection absorption infrared spectrometer (FT-RAIRS). We obtained the binding energy distribution of NH3 on crystalline ice (CI) and compact amorphous solid water ice by analysing the TPD profiles of NH3 obtained after depositions on these substrates. Results. In the co-deposition experiments, we observed a significant delay in the desorption and a decrease of the desorption rate of NH3 when H2O is introduced into the co-deposited mixture of NH3–13CO or NH3–CO2, which is not the case in the absence of H2O. Secondly, we noticed that H2O traps roughly 5–9% of the co-deposited NH3, which is released during the phase change of water from amorphous to crystalline. Thirdly, we obtained a distribution of binding energy values of NH3 on both ice substrates instead of an individual value, as assumed in previous works. For CI, we obtained an energy distribution between 3780 K and 4080 K, and in the case of amorphous ice, the binding energy values were distributed between 3630 K and 5280 K; in both cases we used a pre-exponential factor of A = 1.94 × 1015 s−1. Conclusions. From our experiments, we conclude that the behaviour of NH3 is significantly influenced by the presence of water, owing to the formation of hydrogen bonds with water, in line with quantum calculations. This interaction, in turn, preserves NH3 on the grain surfaces longer and up to higher temperatures, making it available closer to the central protostar in protoplanetary discs than previously thought. It explains well why the NH3 freeze-out in pre-stellar cores is efficient. When present along with H2O, CO2 also appears to impact the behaviour of NH3, retaining it at temperatures similar to those of water. This may impact the overall composition of comets, particularly the desorption of molecules from their surface as they approach the Sun.

Measuring Tracers of Planet Formation in the Atmosphere of WASP-77A b: Substellar O/H and C/H Ratios, with a Stellar C/O Ratio and a Potentially Superstellar Ti/H Ratio

We present a comprehensive atmospheric retrieval study of the hot Jupiter WASP-77A b using eclipse observations from the Hubble Space Telescope (HST) and JWST. Using atmospheric retrievals, the spectral features of H2O, CO, and TiO are identified, with volume mixing ratios estimated at log10(VMR) = −4.40 −0.11+0.14 , −4.44 −0.28+0.34 , and −6.40 −0.23+0.22 , respectively. We derive the atmospheric C-to-O ratio—a key planetary formation tracer—to be C/O = 0.54 ± 0.12, which is consistent with both the stellar host value and previous studies of the planet’s atmosphere, suggesting a relatively close-in formation. Computing other elemental ratios (i.e., C/H, O/H, and Ti/H), we conclude that the general enrichment of the atmosphere (i.e., metallicity) is substellar, depleted in C and O, but that Ti appears slightly superstellar. A low C and O content could be obtained, in combination with a stellar C/O ratio if the planet formed outside of the CO2 snow line before migrating inwards. Meanwhile, a superstellar Ti/H could be obtained by late contamination from refractory rich planetesimals. While broadly in agreement with previous works, we do find some differences and discuss these while also highlighting the need for homogeneous analyses when comparative exoplanetology is conducted.

Surface mass balance and climate of the Last Glacial Maximum Northern Hemisphere ice sheets: simulations with CESM2.1

Abstract. The Last Glacial Maximum (LGM, from ∼26 to 20 ka BP) was the most recent period with large ice sheets in Eurasia and North America. At that time, global temperatures were 5–7 ∘C lower than today, and sea level ∼125 m lower. LGM simulations are useful to understand earth system dynamics, including climate–ice sheet interactions, and to evaluate and improve the models representing those dynamics. Here, we present two simulations of the Northern Hemisphere ice sheet climate and surface mass balance (SMB) with the Community Earth System Model v2.1 (CESM2.1) using the Community Atmosphere Model v5 (CAM5) with prescribed ice sheets for two time periods that bracket the LGM period: 26 and 21 ka BP. CESM2.1 includes an explicit simulation of snow/firn compaction, albedo, refreezing, and direct coupling of the ice sheet surface energy fluxes with the atmosphere. The simulated mean snow accumulation is lowest for the Greenland and Barents–Kara Sea ice sheets (GrIS, BKIS) and highest for British and Irish (BIIS) and Icelandic (IcIS) ice sheets. Melt rates are negligible for the dry BKIS and GrIS, and relatively large for the BIIS, North American ice sheet complex (NAISC; i.e. Laurentide, Cordilleran, and Innuitian), Scandinavian ice sheet (SIS), and IcIS, and are reduced by almost a third in the colder (lower temperature) 26 ka BP climate compared with 21 ka BP. The SMB is positive for the GrIS, BKIS, SIS, and IcIS during the LGM (26 and 21 ka BP) and negative for the NAISC and BIIS. Relatively wide ablation areas are simulated along the southern (terrestrial), Pacific and Atlantic margins of the NAISC, across the majority of the BIIS, and along the terrestrial southern margin of the SIS. The integrated SMB substantially increases for the NAISC and BIIS in the 26 ka BP climate, but it does not reverse the negative sign. Summer incoming surface solar radiation is largest over the high interior of the NAISC and GrIS, and minimum over the BIIS and southern margin of NAISC. Summer net radiation is maximum over the ablation areas and minimum where the albedo is highest, namely in the interior of the GrIS, northern NAISC, and all of the BKIS. Summer sensible and latent heat fluxes are highest over the ablation areas, positively contributing to melt energy. Refreezing is largest along the equilibrium line altitude for all ice sheets and prevents 40 %–50 % of meltwater entering the ocean. The large simulated melt for the NAISC suggests potential biases in the climate simulation, ice sheet reconstruction, and/or highly non-equilibrated climate and ice sheet at the LGM time.

The ghost of past climate acting on present‐day plant diversity: Lessons from a climate‐based delimitation of the tropical alpine ecosystem

AbstractHabitat stability is important for maintaining biodiversity by preventing species extinction, but this stability is being challenged by climate change. The tropical alpine ecosystem is currently one of the ecosystems most threatened by global warming, and the flora close to the permanent snow line is at high risk of extinction. The tropical alpine ecosystem, found in South and Central America, Malesia and Papuasia, Africa, and Hawaii, is of relatively young evolutionary age, and it has been exposed to changing climates since its origin, particularly during the Pleistocene. Estimating habitat loss and gain between the Last Glacial Maximum (LGM) and the present allows us to relate current biodiversity to past changes in climate and habitat stability. In order to do so, (i) we developed a unifying climate‐based delimitation of tropical alpine regions across continents, and (ii) we used this delimitation to assess the degree of habitat stability, that is, the overlap of suitable areas between the LGM and the present, in different tropical alpine regions. Finally, we discuss the link between habitat stability and tropical alpine plant diversity. Our climate‐based delimitation approach can be easily applied to other ecosystems using our developed code, facilitating macro‐comparative studies of habitat dynamics through time.

Dust color variations of comet C/2016 M1 (PanSTARRS)

Our research aims to study the dust environment of comets that are active beyond the snow line. The current work considers dust color variations in the coma of long-period comet C/2016 M1 (PanSTARRS). We observed the comet from July to October 2017 (12 epochs) using a 0.61-m telescope at the Skalnaté Pleso Observatory. The activity of the comet was stable and typical for other long-period comets. Our data show a slight bluing of the comet S'BR = −0.5 ± 0.9% per 1000 Å on August 26 and reddening to S'BR = 6.0 ± 1.4% per 1000 Å on August 28, while during the rest of the observation period, the comet mostly had red color that is typical of other comets; i.e., the average S'BR is equal to 9.5 ± 1.1% per 1000 Å. We have performed modeling of the observed color variations using model agglomerated debris particles. We could reproduce the dust color variations through changes in the dust composition; however, photometric data on their own do not allow us to make a precise conclusion. For instance, the bluest color could be induced by either water-ice, Mg-rich silicate, amorphous carbon, or their mixture. The reddest color is consistent with Mg-Fe silicates and organics. Nevertheless, further study of the comet in terms of polarimetry would yield a more robust conclusion.

Equilibrium line altitudes of alpine glaciers in Alaska suggest Last Glacial Maximum summer temperature was 2–5 °C lower than during the pre-industrial

Abstract. The lack of continental ice sheets in Alaska during the Last Glacial Maximum (LGM; 26–19 ka) has long been attributed to extensive aridity in the western Arctic. More recently, climate model outputs, a few isolated paleoclimate studies, and global paleoclimate synthesis products show mild summer temperature depressions in Alaska compared to much of the high northern latitudes. This suggests the importance of limited summer temperature depressions in controlling the relatively limited glacier growth during the LGM. To explore this further, we present a new statewide map of LGM alpine glacier equilibrium line altitudes (ELAs), LGM ΔELAs (LGM ELA anomalies relative to the Little Ice Age, LIA), and ΔELA-based estimates of temperature depressions across Alaska to assess paleoclimate conditions. We reconstructed paleoglacier surfaces in ArcGIS to calculate ELAs using an accumulation area ratio (AAR) of 0.58 and an area–altitude balance ratio (AABR) of 1.56. We calculated LGM ELAs (n= 480) in glaciated massifs in the state, excluding areas in southern Alaska that were covered by the Cordilleran Ice Sheet. The data show a trend of increasing ELAs from the southwest to the northeast during both the LGM and the LIA, indicating a consistent southern Bering Sea and northernmost Pacific Ocean precipitation source. Our LGM–LIA ΔELAs from the Alaska Range, supported with limited LGM–LIA ΔELAs from the Brooks Range and the Kigluaik Mountains, average to −355 ± 176 m. This value is much greater than the global LGM average of ca. −1000 m. Using a range of atmospheric lapse rates, LGM–LIA ΔELAs in Alaska translate to summer cooling of < 2–5 ∘C. Our results are consistent with a growing number of local climate proxy reconstructions and global data assimilation syntheses that indicate mild summer temperature across Beringia during the LGM. Limited LGM summer temperature depressions could be explained by the influence of Northern Hemisphere ice sheets on atmospheric circulation.

Investigating the past, present and future responses of Shallap and Zongo Glaciers, Tropical Andes, to the El Niño Southern Oscillation

Abstract Tropical Andean glaciers are highly sensitive to climate change and are impacted by the El Niño Southern Oscillation (ENSO). However, glaciological data are scarce, meaning that there are substantial knowledge gaps in the response of Andean glaciers to future anthropogenic and ENSO forcing and these are crucial to address, as glaciers represent a key water source for downstream populations and ecosystems. Here we integrated data from glaciological field studies, remote sensing, statistical analysis and glacier modelling to analyse the response of two Andean glaciers (Zongo and Shallap) to ENSO and their potential sensitivity to a range of climate forcing scenarios. Both glaciers retreated and experienced increasingly negative mass balance between the 1990s and the 2010s and responded strongly and rapidly to contemporary ENSO forcing, although this relationship evolved over time. Sensitivity experiments demonstrate that Shallap and Zongo are highly sensitive to ENSO forcing scenarios and the combination of ENSO and climate warming can cause rapid ice loss under the most extreme scenarios. Results also demonstrate the strong sensitivity of both glaciers to changes in the equilibrium line altitude, whereby rapid ice loss occurred when melt extended into present-day accumulation areas.

Responses of small mountain glaciers in the Maritime Alps (south-western European Alps) to climatic changes during the Last Glacial Maximum

We present new chronological data and Equilibrium Line Altitude (ELA) information for palaeoglaciers in the Maritime Alps during the Last Glacial Maximum (LGM) and the early deglaciation. Three relatively small catchments were investigated to test if the response of small (1–10 km2) glaciers to LGM climatic forcing was distinguishable from that of larger glacial systems. Palaeoglacier geometries and ELAs were reconstructed using geomorphological evidence and toolboxes in a geographic information system. Chronological control was provided through 10Be surface exposure dating of erratic boulders located on frontal and lateral moraine ridges. Our data indicate two phases of glacier advance or stabilisation in the Maritime Alps, the first occurring at ca. 25 to 24 ka and the second at ca. 20.5 to 19 ka. This is consistent with ages that have been reported from larger outlet lobes along the south-western Alpine fringe, where the second LGM advance is usually preserved in the form of a recessional moraine. Within the uncertainty of the dating technique, there are no distinguishable differences between the responses of small and large Alpine glaciers to the LGM climate. The reconstructed ELAs for palaeoglaciers in the Maritime Alps indicate a considerable variability, which appears to be linked to differences in received solar radiation, from ca. 1600 m a.s.l. for north-facing cirque glaciers to almost 2000 m a.s.l. for glaciers with a southerly aspect. We argue that such influence of solar radiation needs to be considered when using ELAs for palaeoclimatic inferences at regional scales. The calculated ELAs are up to 450 m higher than those in the northern Apennines or the Corsican mountains, indicating a relatively dry LGM climate on the Italian side of the Maritime Alps.

Glacier fluctuation chronology since the latest Pleistocene at Mount Rainier, Washington, USA

Abstract Large stratovolcanoes in the Cascade Range have high equilibrium-line altitudes that support glaciers whose Holocene and latest Pleistocene advances are amenable to dating. Glacier advances produced datable stratigraphic sequences in lateral moraines, which complement dating of end moraines. New mapping of glacial deposits on Mount Rainier using LIDAR and field observations supports a single latest Pleistocene or early Holocene advance. Rainier R tephra overlies deposits from this advance and could be as old as >11.6 ka; the advance could be of Younger Dryas age. Radiocarbon ages on wood interbedded between tills in the lateral moraines of Nisqually, Carbon, and Emmons glaciers and the South Tahoma glacier forefield suggest glacier advances between 200 and 550 CE, correlative with the First Millennium Advance in western Canada, and during the Little Ice Age (LIA) beginning as early as 1300 CE. These results resolve previous contradictory interpretations of Mount Rainier's glacial history and indicate that the original proposal of a single pre-Neoglacial cirque advance is correct, in contrast to a later interpretation of two advances of pre- and post-Younger Dryas age, respectively. Meanwhile, the occurrence of the pre-LIA Burroughs Mountain Advance, interpreted in previous work as occurring 3–2.5 ka, is questionable based on inherently ambiguous interpretations of tephra distribution.

Assessing snow cover patterns in the Indus-Ganga-Brahmaputra River Basins of the Hindu Kush Himalayas using snow persistence and snow line as metrics

This study investigates the utilization of snow persistence (SP) as a metric to assess snow cover patterns in the Upper Indus-Ganga-Brahmaputra (UIGB) river basins, an area notably susceptible to climate change. The objectives of the study are to establish seasonal snow persistence, calculate seasonal snow lines, and quantify the temporal trend of snow lines. It also underscores the importance of accounting for climate zones, elevation, and seasonal variations when investigating snow persistence. Furthermore, the study estimates the snow line elevation using the Regional Snow Line Elevation (RSLE) approach with remote sensing data. Over a span of 19 years (2003–2021), the analysis of SP% in UIGB basins indicates a notable reduction in the mean annual permanent snow zone area, decreasing by -2.61 %, -2.37 %, and -4.18 % from winter (DJF) to summer (JJA). The results uncover considerable fluctuations in snow cover across various climate zones and seasons. The impact of warming is clearly visible on snow cover, instigating a transition from permanent and seasonal snow zones towards intermittent and minimal or no snow zones. The seasonal analysis of the snow line from 2003 to 2021 illustrates fluctuation in the snow line for UIGB basins, from 2349 ± 117 m to 4802 ± 51.7 m, 3003 ± 286 m to 4871 ± 64.4 m, and 3238 ± 127 m to 5047 ± 73 m between winter and summer seasons, with the most significant fluctuation occurring in the Brahmaputra basin. A substantial increase in Snow Line Elevation (SLE) is observed for Ganga (6.67 m yr−1), and Brahmaputra (7.26 m yr−1) at the conclusion of the melting season. These findings offer invaluable insights for formulating targeted mitigation strategies in the snow accumulation regions of each river basin. They equip us with the ability to respond effectively to the spatiotemporal variability of snow cover caused by climate change.

Comparative 16s metagenomic analysis of prokaryotic diversity in freshwater and permanent snow-line glacial lakes in Türkiye

Freshwater lakes are critical to healthy ecosystems, providing vital services like drinking water and recreation for surrounding communities. Microorganisms within these ecosystems play essential roles, driving biogeochemical cycles for elements like carbon, nitrogen, and sulfur. This study utilized a metagenomic approach to examine the prokaryotic communities of three freshwater lakes in T?rkiye: the Eber and Bey?ehir lakes, located at close altitudes (967 m and 1,115 m, respectively), which serve as primary water sources for nearby communities, and Lake Uludag Buzlu (2,390 m) that lies at the permanent snow border within the Uludag glacial lake system. Metagenomics allowed us to identify species, genetic structures, and the functional roles of microorganisms. Employing high-throughput next-generation sequencing (NGS) technology, we analyzed 16S ribosomal DNA (rDNA) sequences (V3-V4 regions) from the lake samples. EzBioCloud software facilitated the analysis of prokaryotic diversity obtained using Illumina NovaSeq technology. While Eber and Bey?ehir lakes had similar diversity, Bacillota dominated in the higher-altitude Lake Uludag Buzlu. Genus-level analysis revealed Parabacteroides as the most prevalent in Lake Uludag Buzlu, contrasting with Limnohabitans dominance in Lake Eber; Lake Bey?ehir exhibited co-dominance of Limnohabitans and Planktophila.

Variability in wet and dry snow radar zones in the North of the Antarctic Peninsula using a cloud computing environment.

This work investigated the annual variations in dry snow (DSRZ) and wet snow radar zones (WSRZ) in the north of the Antarctic Peninsula between 2015-2023. A specific code for snow zone detection on Sentinel-1 images was created on Google Earth Engine by combining the CryoSat-2 digital elevation model and air temperature data from ERA5. Regions with backscatter coefficients (σ⁰) values exceeding -6.5 dB were considered the extent of surface melt occurrence, and the dry snow line was considered to coincide with the -11 °C isotherm of the average annual air temperature. The annual variation in WSRZ exhibited moderate correlations with annual average air temperature, total precipitation, and the sum of annual degree-days. However, statistical tests indicated low determination coefficients and no significant trend values in DSRZ behavior with atmospheric variables. The results of reducing DSRZ area for 2019/2020 and 2020/2021 compared to 2018/2018 indicated the upward in dry zone line in this AP region. The methodology demonstrated its efficacy for both quantitative and qualitative analyses of data obtained in digital processing environments, allowing for the large-scale spatial and temporal variations monitoring and for the understanding changes in glacier mass loss.

A glacial chronology for sub-Antarctic Marion Island from MIS 2 and MIS 3

It is increasingly apparent that local and regional factors, including geographic location, topography and climatic variability, strongly influence the timing and extent of glaciations across the Southern Hemisphere. Glacial chronologies of sub-Antarctic islands can provide valuable insights into the nature of regional climatic variability and the localised response(s) of glacial systems during periods of climatic change. With new cosmogenic 36Cl exposure ages from Marion Island in the southern Indian Ocean, we provide the oldest dated terrestrial moraine sequences for the sub-Antarctic islands. Results confirm that a local Last Glacial Maximum was reached prior to ∼56 ka when ice retreated with localised stand still events at ∼43 ka and between ∼38 and 33 ka. Evidence of ice re-advances throughout MIS 2 are limited and particularly absent for the cooling periods at ∼32 and ∼21 ka, and retreat continued until ∼17 ka ago. Any MIS 1 readvances on the island would be confined to altitudes above 900 m a.s.l. but the Holocene exposure ages remains to be documented. We compare Marion Island's glacial chronology with other sub-Antarctic islands (e.g., the Kerguelen archipelago, Auckland and Campbell islands and South Georgia) and review the evidence for a Southern Hemisphere glacial maximum in late MIS 3 (∼41 ka). At a regional scale we recognize sea surface temperatures, sea ice extent and the latitudinal position of the Southern Westerly Wind belt as key controls on equilibrium-line altitudes and ice accumulation due to their influence on air temperature and precipitation regimes. At an island scale, geomorphological mapping shows that deglaciation of individual glacier lobes was a-synchronous due to local physiographical and topographical factors controlling the island's micro-climate. We suggest that variability in deglaciation chronologies at smaller scales (particularly at the sub-Antarctic Islands) are important to consider when untangling climatic drivers across the Southern Ocean.

ВКЛАД НГМС РК В СЕЛЕВУЮ БЕЗОПАСНОСТЬ СТРАНЫ

In this paper, the scientific activities of the National Hydrometeorological Service of Kazakhstan to study the origin, development and degradation of debris flows, carried out with the aim of reducing the damage caused by debris flows, are presented over a long period. The features of precipitation, emptying of surface and intraglacial reservoirs, mineralogical and granulometric compositions of debris rocks, geomorphological conditions of debris flow formation, recurrence and characteristics of debris flows were studied. Methods for computation of the viscosity and plasticity of debris-flow mass, used in mathematical modeling of debris flow formation have been developed. A method for ultra-short-term forecasting of catastrophic debris flows caused by rainfall, based on data on preliminary soil moisture, the position of the zero isotherm and seasonal snow line, and current actual meteorological information has been developed. The feasibility of this method is tens of times greater than the feasibility of the method for short-term forecasting of debris flows caused by rainfall, which was used previously. The computation of the characteristics of debris flows is based on the discovery of an ambiguous dependence between the density of debris-flow mass and the slope of way of debris flow. A debris-flow hazard map for the territory of the Republic of Kazakhstan has been developed. A concept for protection against debris flows of Almaty city under climate changing has been proposed. A geological and geomorphological method has been developed for determining the genesis of fan, which allows optimizing the work on assessing the risk of urbanization of territories located in the mountain and foothill zones.

Reconstructions of Little Ice Age glaciers and climate in the Tanggula Mountains, Central Tibet Plateau

Mountain glaciers are one of the most sensitive indicators of climate change. Reconstructing past glacier extents provides valuable insights into the climate change for specific regions where instrumental records are not enough and even absent. In the paper we mapped the outlines for 691 Little Ice Age (LIA) glaciers in terms of prominent moraines beyond contemporary glaciers in the Tanggula Mountains, central Tibetan Plateau (TP). Based on these glacier outlines, we reconstructed the ice thicknesses and surfaces for the LIA glaciers in the region. Accordingly, we calculated the equilibrium-line altitudes (ELAs) for contemporary and LIA glaciers. By comparing the ELAs between the contemporary and LIA glaciers, we estimated the LIA summer temperature decreases in different subregions of the Tanggula Mountains. Since the LIA, the ELA have risen by 35.6 ± 18.8 m, 26.1 ± 17.6 m, and 63.1 ± 38.6 m in the respective western, central, and eastern subregions of the Tanggula Mountains. Assuming no change in precipitation, the LIA summer temperature would decrease by 0.22 ± 0.12 °C, 0.14 ± 0.09 °C, and 0.34 ± 0.21 °C in the three subregions, respectively. Moreover, glaciers in the western, central, and eastern subregions have lost 13.3%, 23.9%, and 42.8% of their area, 15.4%, 25.3%, and 39.6% of their length, and 20.8%, 39.0%, and 61.0% of their volume, respectively. By compiling the LIA ELA data from previous studies, we also estimated the LIA summer temperature changes for other regions of the TP. The LIA ELA and summer temperature changes relative to the present showed a decreasing trend from the edges towards the interior on the TP.

Consistency Analysis of Multi-Source Remote Sensing Land Cover Products in Arid Regions—A Case Study of Xinjiang

Arid regions are considered to be among the most ecologically fragile and highly sensitive to environmental change globally, and land use and land cover conditions in the region directly influence large-scale ecosystem processes. Currently, thanks to diverse remote sensing platforms, geographers have developed an array of land cover products. However, there are differences between these products due to variations in spatio-temporal resolutions. In this context, assessing the accuracy and consistency of different land cover products is crucial for rationalizing the selection of land cover products to study global or regional environmental changes. In this study, Xinjiang Uygur Autonomous Region (XUAR) is taken as the study area, and the consistency and performance (type area deviation, spatial consistency, accuracy assessment, and other indexes) of the five land cover products (GlobeLand30, FROM_GLC30, CLCD, GLC_FCS30, and ESRI) were compared and analyzed. The results of the study show that (1) the GlobeLand30 product has the highest overall accuracy in the study area, with an overall accuracy of 84.06%, followed by ESA with 75.57%, while CLCD has the lowest overall accuracy of 70.05%. (2) The consistency between GlobeLand30 and CLCD (area correlation coefficient of 0.99) was higher than that among the other products. (3) Among the five products, the highest consistency was found for water bodies and permanent snow and ice, followed by bare land. In contrast, the consistency of these five products for grassland and forest was relatively low. (4) The full-consistency area accounts for 49.01% of the total study area. They were mainly distributed in areas with relatively homogeneous land cover types, such as the north and south of the Tianshan Mountains, which are dominated by bare land and cropland. In contrast, areas of inconsistency make up only 0.03% and are mostly found in heterogeneous areas, like the transitional zones with mixed land cover types in the Altai Mountains and Tianshan Mountains, or in areas with complex terrain. In terms of meeting practical user needs, GlobeLand30 offers the best comprehensive performance. GLC_FCS30 is more suitable for studies related to forests, while FROM_GLC30 and ESRI demonstrate greater advantages in identifying permanent ice and snow, whereas the performance of CLCD is generally average.

Reconstruction of glaciers in the western boundary of the Altiplano (18.5°-19°S): Singularities and insights on potential drivers of past advances

Today, glaciers in the western Altiplano are very scarce, even on peaks exceeding 6000 m. In this mostly ice-free landscape, however, moraines and other glacial deposits are commonly found attesting to quite different climate conditions that favored the advance of glaciers in the past. Although other areas of the Altiplano have been commonly accounted for regarding paleoclimate reconstructions, western Altiplano has been often overlooked. Here we present a detailed map of glacial landforms and a paleoglacier reconstruction from a test area in the western Altiplano between 18.5° and 19°S. We reconstructed regional equilibrium line altitudes (ELA) for several moraine stages, representing extensive past glacier advances in the region. During a prominent and ubiquitous ‘Principal Moraine (PM)’ stage glaciers from most peaks and all orientations advanced to altitudes of up to 4000 m asl. Reconstructed PM ELAs along 90 valleys range from 4400 to 5000 m asl. ELA distribution reveals a strong aspect-dependency at the western boundary of the Altiplano, with ELAs 300 m lower on west-facing glaciers than east-facing glaciers. The coincidence of such steep gradient with a prominent NW-SE ridge accounts for topographic control on the precipitation and thus in the advance of glaciers along the western boundary of the Altiplano. To the east, ELAs from the peaks towering the Altiplano are comparable to ELAs from east-facing glaciers at the western Altiplano boundary but show little to no aspect-dependency. Since these patterns cannot be solely explained by increased moisture advection from the Amazon basin, we suspect that western-sourced moisture associated with increased frequency of cold fronts and cut-off events played an important role in the glacier dynamics at this latitude. Nevertheless, further investigations are required to evaluate the relative role of both precipitation regimes on the glacier dynamics from the westernmost Altiplano.

The historical Greenland Climate Network (GC-Net) curated and augmented level-1 dataset

Abstract. The Greenland Climate Network (GC-Net) consists of 31 automatic weather stations (AWSs) at 30 sites across the Greenland Ice Sheet. The first site was initiated in 1990, and the project has operated almost continuously since 1995 under the leadership of the late Konrad Steffen. The GC-Net AWS measured air temperature, relative humidity, wind speed, atmospheric pressure, downward and reflected shortwave irradiance, net radiation, and ice and firn temperatures. The majority of the GC-Net sites were located in the ice sheet accumulation area (17 AWSs), while 11 AWSs were located in the ablation area, and two sites (three AWSs) were located close to the equilibrium line altitude. Additionally, three AWSs of similar design to the GC-Net AWS were installed by Konrad Steffen's team on the Larsen C ice shelf, Antarctica. After more than 3 decades of operation, the GC-Net AWSs are being decommissioned and replaced by new AWSs operated by the Geological Survey of Denmark and Greenland (GEUS). Therefore, making a reassessment of the historical GC-Net AWS data is necessary. We present a full reprocessing of the historical GC-Net AWS dataset with increased attention to the filtering of erroneous measurements, data correction and derivation of additional variables: continuous surface height, instrument heights, surface albedo, turbulent heat fluxes, and 10 m ice and firn temperatures. This new augmented GC-Net level-1 (L1) AWS dataset is now available at https://doi.org/10.22008/FK2/VVXGUT (Steffen et al., 2023) and will continue to be refined. The processing scripts, latest data and a data user forum are available at https://github.com/GEUS-Glaciology-and-Climate/GC-Net-level-1-data-processing (last access: 30 November 2023). In addition to the AWS data, a comprehensive compilation of valuable metadata is provided: maintenance reports, yearly pictures of the stations and the station positions through time. This unique dataset provides more than 320 station years of high-quality atmospheric data and is available following FAIR (findable, accessible, interoperable, reusable) data and code practices.

Limitations of precipitation reconstructions using equilibrium-line altitudes exemplified for former glaciers in the Southern Black Forest, Central Europe

Abstract To further elucidate the Late Pleistocene glacial history of mid-elevation mountainous regions in Central Europe, 10Be cosmic-ray exposure (CRE) dating was applied to moraines in the Zastler Tal Valley in the Southern Black Forest. Periods of glacier recession from moraines in this valley began no later than 16 ka, 15 ka, and 13 ka. CRE ages of moraines in this and other parts of the Southern Black Forest cluster around 17–16 ka and 15–14 ka, thus suggesting a common forcing of glacier recession. Equilibrium-line altitudes (ELAs) during moraine formation were calculated for precipitation reconstruction. Observed spatial discrepancies in ELAs at ca. 15–14 ka are explained best by the size of snow-contributing areas. The reconstructed annual precipitation at the ELA for ca. 16 ka and ca. 15 ka is affected by large uncertainties, representing a wide range from ~50% to ~150% of present-day values. Due to various factors, such as drifting snow, the lower bounds of the estimates appear most realistic, thus concurring with the common hypothesis of less precipitation during the last glacial termination than today in Central Europe. Further research is needed before ELAs of small ice masses can be employed for precise precipitation estimates.