Metabarcoding data reveal vertical multitaxa variation in topsoil communities during the colonization of deglaciated forelands.

Ice-free areas are expanding worldwide due to dramatic glacier shrinkage and are undergoing rapid colonization by multiple lifeforms, thus representing key environments to study ecosystem development. It has been proposed that the colonization dynamics of deglaciated terrains is different between surface and deep soils but that the heterogeneity between communities inhabiting surface and deep soils decreases through time. Nevertheless, tests of this hypothesis remain scarce, and it is unclear whether patterns are consistent among different taxonomic groups. Here, we used environmental DNA metabarcoding to test whether community diversity and composition of six groups (Eukaryota, Bacteria, Mycota, Collembola, Insecta, and Oligochaeta) differ between the surface (0-5 cm) and deeper (7.5-20 cm) soil at different stages of development and across five Alpine glaciers. Taxonomic diversity increased with time since glacier retreat and with soil evolution. The pattern was consistent across groups and soil depths. For Eukaryota and Mycota, alpha-diversity was highest at the surface. Time since glacier retreat explained more variation of community composition than depth. Beta-diversity between surface and deep layers decreased with time since glacier retreat, supporting the hypothesis that the first 20 cm of soil tends to homogenize through time. Several molecular operational taxonomic units of bacteria and fungi were significant indicators of specific depths and/or soil development stages, confirming the strong functional variation of microbial communities through time and depth. The complexity of community patterns highlights the importance of integrating information from multiple taxonomic groups to unravel community variation in response to ongoing global changes.

Global warming accelerates uptake of atmospheric mercury in regions experiencing glacier retreat.

As global climate continues to warm, melting of glaciers releases a large quantity of mercury (Hg) originally locked in ice into the atmosphere and downstream ecosystems. Here, we show an opposite process that captures atmospheric Hg through glacier-to-vegetation succession. Our study using stable isotope techniques at 3 succession sites on the Tibetan Plateau reveals that evolving vegetation serves as an active "pump" to take up gaseous elemental mercury (Hg0) from the atmosphere. The accelerated uptake enriches the Hg pool size in glacier-retreated areas by a factor of ∼10 compared with the original pool size in the glacier. Through an assessment of Hg source-sink relationship observed in documented glacier-retreated areas in the world (7 sites of tundra/steppe succession and 5 sites of forest succession), we estimate that 400 to 600 Mg of Hg has been accumulated in glacier-retreated areas (5‰ of the global land surface) since the Little Ice Age (∼1850). By 2100, an additional ∼300 Mg of Hg will be sequestered from the atmosphere in glacier-retreated regions globally, which is ∼3 times the total Hg mass loss by meltwater efflux (∼95 Mg) in alpine and subpolar glacier regions. The recapturing of atmospheric Hg by vegetation in glacier-retreated areas is not accounted for in current global Hg models. Similar processes are likely to occur in other regions that experience increased vegetation due to climate or land use changes, which need to be considered in the assessment of global Hg cycling.

Disappearance of the last tropical glaciers in the Western Pacific Warm Pool (Papua, Indonesia) appears imminent.

The glaciers near Puncak Jaya in Papua, Indonesia, the highest peak between the Himalayas and the Andes, are the last remaining tropical glaciers in the West Pacific Warm Pool (WPWP). Here, we report the recent, rapid retreat of the glaciers near Puncak Jaya by quantifying the loss of ice coverage and reduction of ice thickness over the last 8 y. Photographs and measurements of a 30-m accumulation stake anchored to bedrock on the summit of one of these glaciers document a rapid pace in the loss of ice cover and a ∼5.4-fold increase in the thinning rate, which was augmented by the strong 2015-2016 El Niño. At the current rate of ice loss, these glaciers will likely disappear within the next decade. To further understand the mechanisms driving the observed retreat of these glaciers, 2 ∼32-m-long ice cores to bedrock recovered in mid-2010 are used to reconstruct the tropical Pacific climate variability over approximately the past half-century on a quasi-interannual timescale. The ice core oxygen isotopic ratios show a significant positive linear trend since 1964 CE (0.018 ± 0.008‰ per year; P < 0.03) and also suggest that the glaciers' retreat is augmented by El Niño-Southern Oscillation processes, such as convection and warming of the atmosphere and sea surface. These Papua glaciers provide the only tropical records of ice core-derived climate variability for the WPWP.

Assessment of snout analysis of Himalayan glaciers: impact studies on Pindari, Kafni, Sundardhunga, and Baljuri base camp glaciers.

There are several causes for the increasing rate of deglaciation, such as global warming, increase in the concentration of black carbon, and extensive use of fossil fuels which causes the change in the overall climate system and shifting glacier ecosystem. This study was conducted on Pindari valley glaciers part of lesser Himalaya in Uttarakhand. This study investigates to (1) monitor and map change in the frontal length or the snout region of a glacier that can be studied with the help of remote sensing techniques and (2) evaluate the decadal and annual retreat rate of the glacier from 1972 to 2018. The study applies both the maximum likelihood classifier and NDSI spectral indices based classification for extracting the glacier region for different periods. This study reveals a significant amount of retreats taking place in the selected glaciers, Pindari, Sundardhunga, Kafni, and Baljuri base camp glaciers, from 1972 to 2018 as 1719.95 m, 1751.21 m, 1057.01 m, and 810.78 m, respectively. The highest amount of change is noticed in Pindari and Sundardhunga glaciers, higher than ~ 1700 m. The study analyses temporal variation of the annual and decadal retreat rate in the Pindari valley glaciers, which would be helpful for the further study of the other glaciers.

Blue carbon gains from glacial retreat along Antarctic fjords: What should we expect?

Rising atmospheric CO2 is intensifying climate change but it is also driving global and particularly polar greening. However, most blue carbon sinks (that held by marine organisms) are shrinking, which is important as these are hotspots of genuine carbon sequestration. Polar blue carbon increases with losses of marine ice over high latitude continental shelf areas. Marine ice (sea ice, ice shelf and glacier retreat) losses generate a valuable negative feedback on climate change. Blue carbon change with sea ice and ice shelf losses has been estimated, but not how blue carbon responds to glacier retreat along fjords. We derive a testable estimate of glacier retreat driven blue carbon gains by investigating three fjords in the West Antarctic Peninsula (WAP). We started by multiplying ~40 year mean glacier retreat rates by the number of retreating WAP fjords and their time of exposure. We multiplied this area by regional zoobenthic carbon means from existing datasets to suggest that WAP fjords generate 3,130 tonnes of new zoobenthic carbon per year (t zC/year) and sequester >780 t zC/year. We tested this by capture and analysis of 204 high resolution seabed images along emerging WAP fjords. Biota within these images were identified to density per 13 functional groups. Mean stored carbon per individual was assigned from literature values to give a stored zoobenthic Carbon per area, which was multiplied up by area of fjord exposed over time, which increased the estimate to 4,536 t zC/year. The purpose of this study was to establish a testable estimate of blue carbon change caused by glacier retreat along Antarctic fjords and thus to establish its relative importance compared to polar and other carbon sinks.

Detection and Assessment of a Large and Potentially Tsunamigenic Periglacial Landslide in Barry Arm, Alaska.

The retreat of glaciers in response to global warming has the potential to trigger landslides in glaciated regions around the globe. Landslides that enter fjords or lakes can cause tsunamis, which endanger people and infrastructure far from the landslide itself. Here we document the ongoing movement of an unstable slope (total volume of 455 × 106 m3) in Barry Arm, a fjord in Prince William Sound, Alaska. The slope moved rapidly between 2010 and 2017, yielding a horizontal displacement of 120 m, which is highly correlated with the rapid retreat and thinning of Barry Glacier. Should the entire unstable slope collapse at once, preliminary tsunami modeling suggests a maximum runup of 300 m near the landslide, which may have devastating impacts on local communities. Our findings highlight the need for interdisciplinary studies of recently deglaciated fjords to refine our understanding of the impact of climate change on landslides and tsunamis.

Declining glacier cover threatens the biodiversity of alpine river diatom assemblages.

Climate change poses a considerable threat to the biodiversity of high altitude ecosystems worldwide, including cold-water river systems that are responding rapidly to a shrinking cryosphere. Most recent research has demonstrated the severe vulnerability of river invertebrates to glacier retreat but effects upon other aquatic groups remain poorly quantified. Using new data sets from the European Alps, we show significant responses to declining glacier cover for diatoms, which play a critical functional role as freshwater primary producers. Specifically, diatom α-diversity and density in rivers presently fed by glaciers will increase with future deglaciation, yet ß-diversity within and between sites will reduce because declining glacier influence will lower the spatiotemporal variability of glacier cover and its associated habitat heterogeneity. Changes in diatom assemblage composition as glacier cover declined were associated strongly with increasing riverbed stability and water temperature. At the species level, diatoms showed a gradation of responses; for example, Eunotia trinacria, found exclusively at river sites with high (≥52%) catchment glacier cover, may be affected negatively by ice loss. Conversely, seven taxa confined to sites with no glacier cover, including Gomphonema calcareum, stand to benefit. Nineteen (22%) taxa were noted as threatened, endangered, rare or decreasing on the Red List of Algae for Germany, with most at sites ≤26% glacier cover, meaning further ice loss may benefit these diatoms. However, six taxa found only in rivers ≥28% glacier cover may require reclassification of their Red List conservation status, as this habitat is threatened by deglaciation. Our identification of clear links between decreasing glacier cover and river diatom biodiversity suggests there could be significant reorganization of river ecosystems with deglaciation, for example, through alterations to primary production, biogeochemical cycles, and the shifting resource base of alpine freshwater food webs which lack significant allochthonous energy inputs.

Vulnerability of Southeast Greenland Glaciers to Warm Atlantic Water From Operation IceBridge and Ocean Melting Greenland Data.

We employ National Aeronautics and Space Administration (NASA)'s Operation IceBridge high-resolution airborne gravity from 2016, NASA's Ocean Melting Greenland bathymetry from 2015, ice thickness from Operation IceBridge from 2010 to 2015, and BedMachine v3 to analyze 20 major southeast Greenland glaciers. The results reveal glacial fjords several hundreds of meters deeper than previously thought; the full extent of the marine-based portions of the glaciers; deep troughs enabling warm, salty Atlantic Water (AW) to reach the glacier fronts and melt them from below; and few shallow sills that limit the access of AW. The new oceanographic and topographic data help to fully resolve the complex pattern of historical ice front positions from the 1930s to 2017: glaciers exposed to AW and resting on retrograde beds have retreated rapidly, while glaciers perched on shallow sills or standing in colder waters or with major sills in the fjords have remained stable.

Vertical distribution of the soil microbiota along a successional gradient in a glacier forefield.

Spatial patterns of microbial communities have been extensively surveyed in well-developed soils, but few studies investigated the vertical distribution of micro-organisms in newly developed soils after glacier retreat. We used 454-pyrosequencing to assess whether bacterial and fungal community structures differed between stages of soil development (SSD) characterized by an increasing vegetation cover from barren (vegetation cover: 0%/age: 10 years), sparsely vegetated (13%/60 years), transient (60%/80 years) to vegetated (95%/110 years) and depths (surface, 5 and 20 cm) along the Damma glacier forefield (Switzerland). The SSD significantly influenced the bacterial and fungal communities. Based on indicator species analyses, metabolically versatile bacteria (e.g. Geobacter) and psychrophilic yeasts (e.g. Mrakia) characterized the barren soils. Vegetated soils with higher C, N and root biomass consisted of bacteria able to degrade complex organic compounds (e.g. Candidatus Solibacter), lignocellulolytic Ascomycota (e.g. Geoglossum) and ectomycorrhizal Basidiomycota (e.g. Laccaria). Soil depth only influenced bacterial and fungal communities in barren and sparsely vegetated soils. These changes were partly due to more silt and higher soil moisture in the surface. In both soil ages, the surface was characterized by OTUs affiliated to Phormidium and Sphingobacteriales. In lower depths, however, bacterial and fungal communities differed between SSD. Lower depths of sparsely vegetated soils consisted of OTUs affiliated to Acidobacteria and Geoglossum, whereas depths of barren soils were characterized by OTUs related to Gemmatimonadetes. Overall, plant establishment drives the soil microbiota along the successional gradient but does not influence the vertical distribution of microbiota in recently deglaciated soils.

Terricolous Lichens in the Glacier Forefield of the Morteratsch Glacier (Eastern Alps, Graubünden, Switzerland).

Three sampling sites were established at increasing distance from the Morteratsch glacier to investigate lichen communities on soil in the glacier forefield. The survey yielded 13 lichen species and one lichenicolous fungus. Peltigera extenuata (Nyl. ex Vain.) Lojka (Peltigerales) is new to the canton of Graubünden.

Terricolous Lichens in the Glacier Forefield of the Pasterze (Eastern Alps, Carinthia, Austria).

The investigation of lichens on soil, plant debris and terricolous mosses in the glacier forefield of the Pasterze yielded 35 lichen species. Placidiopsis oreades Breuss (Verrucariales) is new to Austria. Three sampling sites were established at increasing distance from the glacier, in order to compare species diversity, abundance and composition within the forefield and with four other glacier forefields of the Eastern Alps.

Terricolous Lichens in the Glacier Forefield of the Rötkees (Eastern Alps, South Tyrol, Italy).

The investigation of lichens on soil, plant debris and terricolous mosses in the glacier forefield of the Rötkees yielded 31 lichen taxa (29 species and 2 varieties) and one lichenicolous fungus. Micarea incrassata Hedl. (Lecanorales) is new to Italy. Three sampling sites were established at increasing distance from the glacier, in order to compare species diversity, abundance and composition.

Terricolous Lichens in the Glacier Forefield of the Gaisbergferner (Eastern Alps, Tyrol, Austria).

The investigation of lichens on soil, plant debris and terricolous mosses in the glacier forefield of the Gaisbergferner yielded 41 lichen taxa (39 species and 2 varieties) and one lichenicolous fungus. Three sampling sites were established at increasing distance from the glacier, in order to compare species diversity, abundance and composition.

Cold mountain stream chironomids (Diptera) of the genus Diamesa indicate both historical and recent climate change.

Chironomids of the genus Diamesa (Meigen, 1835, Diptera: Chironomidae) inhabit cold, oxygen-rich running waters. We have investigated the presence of Diamesa and other freshwater macroinvertebrates at 22 stream sampling sites in 3 European high mountain regions (the Central Pyrenees, the Ötztal Alps, and the Tatra Mountains) to establish suitable temperature conditions for Diamesa dominance. It has been generally accepted that their high abundance was linked to the presence of glaciers; however, we have shown that in the Tatra Mountains, where there are no glaciers, the conditions for the dominance of Diamesa species are created due to permanent snowfields, the geographical orientation of the valley and shading by the surrounding high peaks. The historical connection of Diamesa to glaciers was investigated from the paleolimnological records of subfossil chironomid assemblages from the Bohemian Forest, where glaciers disappeared before or during the Late Glacial period. As expected, water temperature seems to be the main driver of Diamesa distribution, and we determined that the relative abundance of Diamesa species was significantly higher at the sites with a mean July water temperature below 6.5 °C. The Diamesa-dominated stream communities seems to be endangered due to ongoing climate warming and this assumption is supported by our paleolimnological results from the Bohemian Forest lakes, where Diamesa has disappeared due to warming of lake inflows at the beginning of the Holocene. These findings strengthen the former suggestions that some Diamesa species could be used as an indicator for tracking recent environmental changes in vulnerable ecosystems of cold mountain streams.

Linking microbial biogeochemical cycling genes to the rhizosphere of pioneering plants in a glacier foreland.

Glacier retreat raises global concerns but brings about the moment to study soil and ecosystem development. In nutrient-limited glacier forelands, the adaptability of pioneering plant and microbial species is facilitated by their interactions, including rhizosphere effects, but the details of this adaptability are not yet understood. In the rhizosphere of five pioneering plants, we comprehensively deciphered the microbial taxonomic and functional compositions. Two nitrogen-fixing microbial genera, Bradyrhizobium and Mesorhizobium, were among the most abundant taxa in the rhizomicrobiome. Moreover, several rhizobial genera, including Rhizobium, Pararhizobium, Allohrizobium, and Sinorhizobium, head the list of major modules in microbial co-occurrence networks, highlighting the vital roles of nitrogen-cycling taxa in the rhizomicrobiome of pioneering plants. Microbial genes involved in nitrogen, sulfur, phosphorus, and methane cycles were simultaneously correlated with microbial community dissimilarity, and 12 functional pathways were detected with distinct relative abundances among soils. Zooming in on the nitrogen-cycling genes, nifW, narC, nasA, nasB, and nirA were mainly responsible for the significant differences between soils. Furthermore, soil pH and the carbon/nitrogen ratio were among the topsoil properties interacting with nitrogen and sulfur cycling gene dissimilarity. These results explicitly linked biogeochemical cycling genes to the rhizomicrobiome and soil properties, revealing the roles of these genes as microbial drivers in mediating rhizosphere soil-plant-microbiome interactions.

Potential macroalgal expansion and blue carbon gains with northern Antarctic Peninsula glacial retreat.

The West Antarctic Peninsula (WAP) is a hotspot of physical climate change, especially glacial retreat, particularly in its northern South Shetland Islands (SSI) region. Along coastlines, this process is opening up new ice-free areas, for colonization by a high biodiversity of flora and fauna. At Potter Cove, in the SSI (Isla 25 de Mayo/King George Island), Antarctica, colonization by macroalgae was studied in two newly ice-free areas, a low glacier influence area (LGI), and a high glacier influence area (HGI) differing in the presence of sediment run-off and light penetration, which are driven by levels of glacial influence. We installed artificial substrates (tiles) at 5 m depth to analyze benthic algal colonization and succession for four years (2010-2014). Photosynthetic active radiation (PAR, 400-700 nm), temperature, salinity, and turbidity were monitored at both sites in spring and summer. The turbidity and the light attenuation (Kd) were significantly lower at LGI than at HGI. All tiles were colonized by benthic algae, differing in species identity and successional patterns between areas, and with a significantly higher richness at LGI than HGI in the last year of the experiment. We scaled up a quadrat survey on the natural substrate to estimate benthic algal colonization in newly deglaciated areas across Potter Cove. Warming in recent decades has exposed much new habitat, with macroalgae making up an important part of colonist communities 'chasing' such glacier retreat. Our estimation of algal colonization in newly ice-free areas shows an expansion of ∼0.005-0.012 km2 with a carbon standing stock of ∼0.2-0.4 C tons, per year. Life moving into new space in such emerging fjords has the potential to be key for new carbon sinks and export. In sustained climate change scenarios, we expect that the processes of colonization and expansion of benthic assemblages will continue and generate significant transformations in Antarctic coastal ecosystems by increasing primary production, providing new structures, food and refuge to fauna, and capturing and storing more carbon.

Mass balance of Nehnar glacier from 2000 to 2020, using temperature indexed-IAAR approach.

Glacier mass balance is inextricably linked to annual meteorological conditions and is a key indicator for assessing the ice reserves of a glacier. As a result, a number of studies have estimated glacier mass balance using different methods. Here, we have used the improved accumulation area-ratio (IAAR) method to study the mass balance of the Nehnar glacier from 2000 to 2020. This study also aims to study the spatiotemporal behavior and other dynamics of the glacier. Results have shown that the glacier has continuously lost its ice reserves throughout the studied period though at a lower rate since 2010. Its annual specific mass balance has changed from - 50.10 ± 3 cm w.e in 2000 to - 59.46 ± 3 cm w.e. in 2020. The equilibrium line altitude (ELA) of the glacier rose by 90 m and has shifted from 4260 masl in 2000 to 4350 masl in 2020. The glacier has shrunk from an area of 1.64 km2 in 2000 to 1.38 km2 in 2020 losing nearly 16% of its area. The study highlights the need for continued monitoring of glacier mass balance to better understand and predict the effects of climate change. These findings have important implications for the future of glacier retreat and water reserves of the Jhelum basin.

Sedimentary organic molecular compositions reveal the influence of glacier retreat on ecology on the Tibetan Plateau.

Global warming and glacier retreat have significant impacts on the structure and function of natural ecosystems. However, little is known about how glacier retreat affects the long-term evolution of ecosystems at high-altitude regions. In this study, we explored the possible effects of glacier retreat on catchment vegetation and lake productivity in Lake Puma Yumco, southeastern Tibetan Plateau, based on detailed organic molecular compositions determined by an ultra-high-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), and combined with various sedimentary geochemical indicators. The glaciers in the catchment keep retreating since 1870 CE, as inferred from the multiple indices of total organic carbon content (TOC), total nitrogen content (TN), C/N ratios, and carbonate contents. Accompanying modern global warming and glacier shrinkage, the relative abundance of soil- and vegetation-derived large molecular compounds (e.g., vascular plant-derived polyphenols, highly unsaturated and phenolic compounds, and condensed aromatics) increased gradually in lake sediments, suggesting that ice-covered land was exposed under warming condition, and gradually revegetation occurred. Both increases in relative abundance of nitrogen-containing compounds (e.g., CHNO) and chlorophyll derivative contents in the lake sediments were observed since 1870 CE, suggesting that stronger catchment weathering and increasing terrestrial nutrient loads enhanced the downstream lake productivity after glacier retreat. Our results imply that continued global warming and alpine glacier retreat in the future may further promote vegetation expansion and increases in lake productivity on the Tibetan Plateau.

Vascular plant and cryptogam abundance as well as soil chemical properties shape microbial communities in the successional gradient of glacier foreland soils.

In the glacier forelands, microbes play a fundamental role in soil development and shaping the vegetation structure. Such ecosystems represent various stages of soil development and are, therefore, an excellent place to study the interrelationship between soil, plants, and microorganisms. The aim of the study was to assess the effects of vegetation and soil physicochemical properties developing after glacier retreat on soil microbial communities. Specifically, abundance, species richness and the composition of arbuscular mycorrhizal fungi (AMF), as well as microbial biomass and community structure in soils were compared between plots established in 800-meter transects of three glacier forelands in northern Sweden. The cover of vascular plants and cryptogams, soil C content, AMF spore density and species richness, AMF biomass indicators, total microbial biomass, and bacterial phospholipid fatty acids (PLFA) were significantly and positively related to the distance from the glacier terminus. On the other hand, macronutrient concentrations and pH decreased along with increasing distance. No significant impact of the distance from the glacier terminus on the ratio fungal/bacterial PLFA was observed. Moreover, we found a significant effect of both glacier and the distance from the glacier terminus on the microbial community structure. AMF species richness and spore density in the glacier forelands were generally low, which is probably due to a limited supply of inoculum in primary successional ecosystems. Most microbial biochemical markers and AMF parameters were positively associated with the number of arbuscular mycorrhizal plant species and vascular plant and lichen cover as well as C content in soil, whereas negatively with soil macronutrients and pH. This could be related to an increase in plant cover and a decrease in soil nutrient levels as plant succession progresses. Our results showed that vegetation, soil C content, and microbial communities are interlinked and exhibit concordant patterns along successional gradients.

Dissolved organic matter defines microbial communities during initial soil formation after deglaciation.

Ecosystem succession and pedogenesis reshuffle the composition and turnover of dissolved organic matter (DOM) and its interactions with soil microbiome. The changes of these connections are especially intensive during initial pedogenesis, e.g. in young post-glacial areas. The temporal succession and vertical development of DOM effects on microbial community structure remains elusive. Using Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS), high-throughput sequencing, and molecular ecological networks, we characterized the molecular diversity of water-extractable DOM and identified its links to microbial communities in soil profiles along deglaciation chronosequence (12, 30, 40, 52, 80, and 120 years) in the southeastern Tibetan Plateau. Low-molecular-weight compound content decreased, whereas the mid- and high-molecular-weight compounds increased with succession age and soil depth. This was confirmed by the increase in double bond equivalents and averaged oxygen-to­carbon ratios (O/C), and decrease in hydrogen-to­carbon ratios (H/C), which reflect DOM accumulation and stabilization. Microbial community succession shifted towards the dominance of oligotrophic Acidobacteria and saprophytic Mortierellomycota, reflecting the increase of stable DOM components (H/C < 1.5 and wider O/C). Less DOM-bacterial positive networks during the succession reduced specialization of labile DOM production (such as lipid- and protein-like compounds), whereas more DOM-fungal negative networks increased specialization of stable DOM decomposition (such as tannin- and condensed aromatic-like compounds). Consequently, DOM stability is not intrinsic during initial pedogenesis: stable DOM compounds remain after fast bacterial utilization of labile DOM compounds, whereas fungi decompose slowly the remaining DOM pools.