Glacial Influence Research Articles

The second skin of macroalgae: Unveiling the biodiversity of epiphytic microalgae across environmental gradients of the Magellan Subantarctic ecoregion

The Magellan Subantarctic ecoregion (MSE) in the Southern Hemisphere (47°-56°S; 71°-73°W) is a unique natural laboratory subject to persistent and accelerated glacial ice melt, generating a complex system of environmental gradients (e.g., salinity and temperature) that influence the ecological patterns of marine biodiversity. However, the factors influencing marine epiphytic microalgal assemblages are still poorly understood. In this context, we characterized the richness and structure of epiphytic assemblages in different benthic macroalgal hosts (Acrosiphonia arcta, Ectocarpus siliculosus, and Leptosiphonia brodiei) in sites with glaciers and estuarine characteristics (Yendegaia Bay and Fouquet Estuary) and sites without glaciers and oceanic characteristics (Batchelor River and Offing Island) of the MSE, revealing how sites, host, and environmental variables influence variation of epiphytic assemblages. In 36 samples, 67 genera of epiphytes were recorded. The dominant divisions were Bacillariophyta (50 genera), Dinophyta (7 genera) and Cyanophyta (6 genera). We observed significantly high diversity in epiphytic assemblages, with contrasting patterns of variation depending on site and/or host macroalgae. Host specificity was not evident for most epiphytes. The most factor influencing the variation of the epiphythic assemblage was the marked environmental gradient (changes in temperature, salinity, nutrients, among others) between sites with and without glacial influence. Additionally, our research identified potentially toxic and/or harmful epiphytic microalgae belonging to the divisions Dinophyta (dinoflagellates) and Cyanophyta (cyanobacteria). The data on ecological patterns of epiphyte assemblages provides valuable insights into the current state of a poorly understood microscopic biodiversity, shaped by diverse environmental factors at different sites. Under current and future climate change scenarios in the MSE, environmental gradients may become more pronounced, with important positive and/or negative consequences on epiphyte assemblages. In light of these findings, we present a baseline for future research to further develop our understanding and facilitate the monitoring and conservation of epiphytic microalgae in the MSE.

Glacier Retreat Induces Contrasting Shifts in Bacterial Biodiversity Patterns in Glacial Lake Water and Sediment

Glacial lake ecosystems are experiencing rapid changes due to accelerated glacier retreat. As glaciers recede, their influence on downstream habitats diminishes, potentially affecting the biodiversity of glacial lake microbial communities. However, there remains a knowledge gap regarding how bacterial biodiversity patterns in glacial lakes are altered by diminishing glacial influence. Here, we investigated shifts in bacterial communities in paired water and sediment samples collected from seven glacial lakes on the Tibetan Plateau, using a space-for-time substitution approach to understand the consequences of glacier retreat. Our findings reveal that bacterial diversity in lake water increases significantly with a higher glacier index (GI), whereas sediment bacterial diversity exhibits a negative correlation with GI. Both the water and sediment bacterial communities display significant structural shifts along the GI gradient. Notably, reduced glacial influence decreases the complexity of bacterial co-occurrence networks in lake water but enhances the network complexity in sediment. This divergence in diversity and co-occurrence patterns highlights that water and sediment bacterial communities respond differently to changes in glacial influence in these lake ecosystems. This study provides insights into how diminishing glacial influence impacts the bacterial biodiversity in glacial lake water and sediments, revealing contrasting patterns between the two habitats. These findings emphasize the need for comprehensive monitoring to understand the implications of glacier retreat on these fragile ecosystems.

Diatom assemblages in glacial-fed streams of Italian Western Alps

ABSTRACT The rate of glacier retreat has recently increased, with changes in the glacier discharge, river flow and water characteristics, creating specific environmental conditions for highly specialized organisms. We here investigated diatom communities in glacier-fed rivers of the Valle d’Aosta region (NW-Italy), analyzing data collected between 2010 and 2019 for the WFD monitoring programs. We present a complete checklist of the species inhabiting this region, many of which are classified as endangered in the diatom Red List. We found significant differences between sites with different catchment glacier cover (CGC), in terms of taxonomic composition, ecological guilds and abundance of Red List taxa. In particular, we observed a significant increase in species richness with the decrease in CGC, as well as significant differences in terms of taxonomic composition. We highlighted the role of Achnanthidium lineare as an indicator species for streams with the highest glacial influence, together with Hannaea arcus, Eucocconeis laevis and other oligotrophic low profile species that are well adapted to physical stress induced by glacier runoff. On the other hand, streams with lower glacial influence were characterized by motile species mostly belonging to the genera Navicula and Nitzschia, due to the nutrient increase. Didymosphenia geminata was recorded in streams with marginal glacier cover; recently observed blooms indicate that conditions may become increasingly favorable for the spread of this species in Alpine environments, as glaciers retreat. The abundance of Red List diatoms increased significantly with increasing glacier cover suggesting that glacier-fed rivers are niches for the conservation of diatom biodiversity.

Temperature-driven shifts in bacterioplankton biodiversity: Implications for cold-preferred species in warming Tibetan proglacial lakes

Recent climate warming and associated glacier retreat have dramatically changed the environmental conditions and microbial inhabitants of proglacial lakes. However, our understanding of the effects of climate warming and glacial influence on microbial biodiversity in these lakes remain relatively limited. Here, we studied bacterioplankton communities in 22 proglacial lakes on the Tibetan Plateau, spanning a range of nearly 7 °C in mean annual temperature (MAT), and examined the effects of climate and glaciers on their biodiversity by a space-to-time substitution. MAT emerged as the primary environmental driver of bacterioplankton biodiversity compared to glacial influence, increasing species richness and decreasing β-diversity. We identified 576 low-MAT (cold-preferred) species and 2,088 high-MAT (warm-preferred) species, and found that low-MAT species are less environmentally adapted, with their numbers declining as temperature increased. These results advance our understanding of temperature-driven bacterioplankton dynamics by disentangling the contrasting responses and adaptations of cold-preferred and warm-preferred species. Our findings highlight the vulnerability of cold-specialist taxa and the potential biodiversity losses associated with climate warming in the rapidly changing proglacial lakes.

Declining glacier cover drives changes in aquatic macroinvertebrate biodiversity in the Cordillera Blanca, Perú.

Ongoing climate change threatens the biodiversity of glacier-fed river ecosystems worldwide through shifts in water availability and timing, temperature, chemistry, and channel stability. However, tropical glacier-fed rivers have received little attention compared to those in temperate and Arctic biomes, despite their unique biodiversity potentially responding differently due to additional stress from higher altitude locations thus lower oxygen availability, diurnal freeze-thaw cycles, and annual monsoon rainfall disturbances. However, tropical glacier-fed rivers have received little attention compared to those in temperate and Arctic biomes, despite their unique biodiversity potentially responding differently due to additional stress from higher altitude locations thus lower oxygen availability, diurnal freeze-thaw cycles, and annual monsoon rainfall disturbances. This study quantified aquatic biodiversity responses to decreasing glacier cover in the Cordillera Blanca range of the Peruvian Andes. Ten rivers were studied along a gradient of decreasing glacier cover in the Parón, Huaytapallana, and Llanganuco basins, with a specific focus on macroinvertebrates and physicochemical parameters in both the dry and wet seasons. We found higher temperatures, more stable and lower turbidity rivers as glacier cover decreased, which were related significantly to higher local diversity and lower β-diversity. Analysis of similarity revealed significant differences in the macroinvertebrate community among rivers with high, medium, or low glacier cover, illustrating turnover from specialists to generalists as glacial influence decreased. Redundancy analysis demonstrated that there were more species found to prefer stable beds and water temperatures in medium and low glacier cover in a catchment rivers. However, certain taxa in groups such as Paraheptagyia, Orthocladiinae, Anomalocosmoecus, and Limonia may be adapted to high glacial influence habitats and at risk of glacier retreat. Although species composition was different to other biomes, the Cordillera Blanca rivers showed similar benthic macroinvertebrate biodiversity responses to glacier retreat, supporting the hypothesis that climate change will have predictable effects on aquatic biodiversity in mountain ranges worldwide.

Echo-characterization of the Sloggett Canyon and the interfluve with Valentín Canyon, Tierra del Fuego Continental Margin, Argentina

Our recent echo-character analysis of the Tierra del Fuego Continental Margin, focusing on Sloggett Canyon and the interfluve with Valentín Canyon, provides insights into contemporary sedimentary processes. Utilizing high-resolution seismic profiles obtained from the R/V Austral in 2017, we categorized sub-bottom echoes into 10 distinct types, shedding light on various processes such as hemipelagic deposition, mass wasting events, glacial influence, and the impact of bottom water masses. By integrating data from the GLORYS12V1 model (1993–2020), CTDs from the World Ocean Database, and sediment samples, we analyze the interaction between bottom currents, seafloor topography, and sediment characteristics. We conclude that the flow of the Subantarctic Water Mass acts as an active transport of coarser sediment from the continental shelf into the canyon, maintaining the Sloggett Canyon's activity, while the flows of the Upper and Lower Circumpolar Water Masses contribute to contourite formation along the eastern canyon flank and the erosion of the lower interfluve, leading to the generation of distinctive longitudinal scours. Additionally, in the continental rise, the interaction of water masses with the seafloor influences the redistribution of the deep-sea fans from the Sloggett and Valentín canyons towards the northeast. This study significantly enhances our understanding of the sedimentary dynamics in this area, establishing the basis of the sedimentary distribution for future interdisciplinary studies and for setting a new baseline in marine protected areas.

A proposed chronostratigraphic Archean–Proterozoic boundary: Insights from the Australian stratigraphic record

The Mount Bruce Supergroup (MBS) in Western Australia has been central to debates surrounding Precambrian stratigraphic subdivision and is one of the few relatively conformable successions that records both the chronometric Archean-Proterozoic boundary (APB) and the Great Oxidation Event/Episode (GOE) which has previously been proposed as the most practical basis for a chronostratigraphic boundary. Current understanding of the lithostratigraphy, chemostratigraphy, and geochronology of the MBS supports the placement of a chronostratigraphic APB in the vicinity of the contact between the Hamersley and Turee Creek Groups, although a precise boundary awaits the generation and integration of more detailed chemostratigraphic records of the GOE with the physical record. The chronometric APB as presently defined at 2500 Ma will suffice until consensus is reached regarding a revised definition based on the GOE, and reconciliation of the physical and proxy records of this event. However, the Australian stratigraphic record suggests placement of the APB either at the base of the first glacial diamictite, or at the top of the last banded iron formation (BIF) below the GOE. The first option would exclude some BIF from the Siderian, which in both cases would be the terminal period of the Archean, whereas the second option places all diamictite in a new period at the start of the Paleoproterozoic. It is further proposed that this new period be named to primarily reflect this glacial influence, rather than for the influence of the GOE which relies on less obvious laboratory-based proxies for its identification.

Wrapping a Craton: A Review of Neoproterozoic Fold Belts Surrounding the São Francisco Craton, Eastern Brazil

A synthesis of the evolution of the Neoproterozoic belts or orogens surrounding the São Francisco craton (SFC) in northeastern and southeastern Brazil is presented. Emphasis is placed on recognizing the superposition of sedimentary basins, from rift to passive margin to retroarc and foreland, as well as identifying three diachronic continental collisions in the formation of the SFC. The Tonian passive margin occurs in the southern Brasília Belt with the Vazante, Canastra, and Araxá Groups. During the Tonian, island magmatic arcs and basins developed in front and behind these arcs (fore- and back-arcs). Subsequently, in the Cryogenian–Ediacaran, a retroarc foreland basin developed with part of the Araxá Group and the Ibiá Group, and finally, a foreland basin developed, which was filled by the Bambuí Group. A tectonic structure of superimposed nappes, with subhorizontal S1–2 foliation, formed between 650 and 610 Ma, is striking. In the northern Brasília Belt, there is the Stenian passive margin of the Paranoá Group, the Tonian intrusion of the Mafic–Ultramafic Complexes, and the Mara Rosa Island magmatic arc, active since the Tonian, with limited volcanic–sedimentary basins associated with the arc. A thrust–fold belt structure is prominent, with S1 foliation and late transcurrent, transpressive tectonics characterized by the Transbrasiliano (TB) lineament. The Cryogenian–Ediacaran collision between the Paranapanema and São Francisco cratons is the first collisional orogenic event to the west. In the Rio Preto belt, on the northwestern margin of the São Francisco craton, the Cryogenian–Ediacaran Canabravinha rift basin is prominent, with gravitational sediments that represent the intracontinental termination of the passive margin that occurs further northeast. The rift basin was intensely deformed at the Ediacaran–Cambrian boundary, as was the Bambuí Group. On the northern and northeastern margins of the São Francisco craton, the Riacho do Pontal and Sergipano orogens stand out, showing a comparable evolution with Tonian and Cryogenian rifts (Brejo Seco, Miaba, and Canindé); Cryogenian–Ediacaran passive margin, where the Monte Orebe ophiolite is located; and Cordilleran magmatic arcs, which developed between 620 and 610 Ma. In the Sergipano fold belt, with a better-preserved outer domain, gravitational sedimentation occurs with glacial influence. A continental collision between the SFC and the PEAL (Pernambuco-Alagoas Massif) occurred between 610 and 540 Ma, with intense deformation of nappes and thrusts, with vergence to the south and accommodation by dextral transcurrent shear zones, such as the Pernambuco Lineament (PE). The Araçuaí belt or orogen was formed at the southeastern limit of the SFC by a Tonian intracontinental rift, later superimposed by a Cryogenian–Ediacaran rift–passive margin of the Macaúbas Group, with gravitational sedimentation and glacial influence, and distally by oceanic crust. It is overlain by a retroarc basin with syn-orogenic sedimentation of the Salinas Formation, partly derived from the Rio Doce cordilleran magmatic arc and associated basins, such as the Rio Doce and Nova Venécia Groups. A third continental collision event (SF and Congo cratons), at the end of the Ediacaran (580–530 Ma), developed a thrust–fold belt that deforms the sediments of the Araçuaí Belt and penetrates the Paramirim Corridor, transitioning to the south to a dextral strike-slip shear zone that characterizes the Ribeira Belt.

Impacts of anthropogenic activities and glacial processes on the distribution of chemical elements in Billefjord, Svalbard, Arctic

The Arctic region is undergoing rapid and extensive transformations due to global climate change. This study investigated the spatial distribution of 31 chemical elements in eight locations in Billefjord, Svalbard, Arctic, with varying degrees of anthropogenic and glacial influences. The west coast of Billefjord has experienced a greater historical anthropogenic impact, while the east coast has larger glaciers and shows less visible evidence of direct human impact. Over 450 topsoil samples collected in the west (abandoned mining town Pyramiden, and glacial valleys of Elsa, Ferdinand, Sven) and east coast of the fjord (glacial valleys of Ebba, Pollock, Ragnar and nearby the Nordenskiöld glacier). These samples were extracted and analyzed by ICP-OES. The results revealed complex distributions of elements among the locations. Nordenskiöld glacier area, along with other locations in the eastern part of the Billefjord, had significantly higher levels of most elements (20 out of 31; As, B, Ca, Cd, Co, Cr, Cu, K, Li, Mg, Mo, Sb, Se, Sn, Sr, Ti, Tl, U, V, Zr). In contrast, Ferdinand Valley and other locations on the western side of the fjord had the lowest mean concentrations of most elements (18 out of 31; B, Ca, Cu, Cd, K, Li, P, Mg, Mo, Sb, Se, Sn, Sr, Ti, Tl, U, V, Zr). These findings highlight the significant influence of glacial processes on the elemental composition of soils within the region. The meltwater flow originating from glaciers in the sampled valleys contributes to the local element load, while the loss of glacier mass is associated with decreased element concentrations within these valleys. These results underscore the complexity of element distribution in the study area and emphasize the necessity for continuous monitoring efforts in this unique and environmentally sensitive region.

Emmanuel de Martonne's glacial geomorphology research in Parâng Massif (the Southern Carpathians)

We are publishing this article in 2023, the year when the 150th anniversary of the birth of the French geographer is celebrated, the article being a tribute to Emmanuel de Martonne's work in Romania, especially for his contribution to the research of the Transylvanian Alps (the Southern Carpathians). Of the two doctoral theses that the French geographer elaborated on the territory of Romania, the last one, defended in 1905 and published in 1907 at the Sorbonne University in Paris, was dedicated to the geomorphological evolution of the Transylvanian Alps (the Southern Carpathians). Of the 14 field campaigns that Emmanuel de Martonne carried out in Romania, eight were carried out in the Southern Carpathians (Banat Massif, Transylvanian Massif) and in the neighboring regions closely related in their paleogeographical evolution to the Transylvanian Alps (the Subcarpathian area of Oltenia, the Subcarpathian area of Muntenia, and Mehedinți Plateau). For the French geographer, the transverse valleys of the Southern Carpathians were examples indicating the extensive tectonic movements that affected the territory of Romania in the Paleogene and Neogene. Glacial influences and relief forms in the high part of the Southern Carpathians became the main concern of the French geographer for at least a decade of research in Romania. More obviously, in some parts of the Southern Carpathians, the action of glaciation cut out specific shapes within the platform of the high peaks (Borăscu planation platform). In the research in Parâng Mountains, Emmanuel de Martonne aimed to identify some key evidence of glaciation: glacial cirques, lakes, valleys, thresholds, glacial grooves, glaciated knobs, and moraines. Above all, the French geographer believed that the general topography of the valleys and cirques is the fundamental element that certifies glaciation and the presence of lateral cirques justifies the succession of glacial periods.

Marine and Not Terrestrial Resources Support Nearshore Food Webs Across a Gradient of Glacial Watersheds in the Northern Gulf of Alaska

Estuaries are among the most productive ecosystems on Earth, yet they are at risk in high-latitude regions due to climate-driven effects on the connected terrestrial and marine realms. Northern Hemisphere warming exceeds the global average and accelerates the melting of glaciers. As a result, the magnitude of freshwater discharge into estuaries may increase during the peak in glacial meltwater, ultimately affecting the riverine flux of organic matter (OM) from the land to coastal environments and food webs within. We investigated the extent to which terrestrial OM subsidizes nearshore food webs in northern Gulf of Alaska watersheds and if differences in the relative proportion of terrestrial versus marine OM supporting these food webs are explained by watershed glacial cover and/or by seasonal glacial discharge regimes. A stable isotope mixing model was employed to determine the contribution of marine (phytoplankton, macroalgae) and terrestrial (vascular plant) sources to the diets of grazing/detritivore and filter/suspension-feeding coastal invertebrates at the outflows of watersheds of varying glacial influence and across three distinct discharge periods. Additionally, a distance-based redundancy analysis was conducted to investigate the effects of watershed-characteristic (e.g., slope, vegetation cover) sourcing and transport of terrestrial OM on consumer diets. The diets of both feeding groups were predominantly marine (> 90%) and varied little among estuarine study sites at watersheds of different glacial cover or glacial discharge periods. Our findings suggest that terrestrial OM is not readily used by nearshore food webs in this productive study system, presumably due to the high quantity and quality of available marine OM.

Mountain glaciers influence biogeochemical and ecological characteristics of high‐elevation lakes across the northern Rocky Mountains, USA

AbstractMountain glaciers are retreating rapidly due to climate change, leading to the formation of downstream lakes. However, little is known about the physical and biogeochemical conditions in these lakes across a range of glacial influence. We surveyed alpine lakes fed by both glacial and snowpack meltwaters and those fed by snowpack alone to compare nutrient concentrations, stoichiometry, water clarity, chlorophyll, and zooplankton communities. Total phosphorus (TP) and soluble reactive phosphorus were two times higher in glacial lakes than in non‐glacial lakes, while nitrate concentrations were three times higher. However, organic carbon concentrations in glacial lakes were two times lower than in non‐glacial lakes. The carbon‐to‐phosphorus ratio and the nitrogen‐to‐phosphorus ratio of lake seston increased with water clarity in glacial lakes, suggesting that turbidity from glacial flour increases light limitation and increases stoichiometric food quality for zooplankton in newly formed lakes. However, chlorophyll a concentrations did not differ between lake types. Through structural equation modeling, we found that glaciers exhibit a bidirectional association with nitrate and TP concentrations, perhaps mediated through landscape vegetation and lake clarity. Zooplankton communities in high‐turbidity glacial lakes were largely composed of cyclopoid copepods and rotifers (i.e., non‐filter feeders), while non‐glacial lakes tended to be dominated by calanoid copepods and cladocerans (i.e., filter feeders). Our results show that glacier‐influenced lakes have biogeochemical and ecological characteristics distinct from snow‐fed mountain lakes. Sustained studies are needed to assess the dynamics of these unique features as the influence of the alpine cryosphere fades under ongoing climate change.

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.

Massive influence of Himalayan source on sedimentation along northern Indian peninsular basin

A 39 m long sediment core (MD161-19) spanning 320 ka, collected from the intermediate water depths of (1480 m) of Mahanadi offshore was subjected to provenance analyses using Sr and Nd isotope systematics. The Sr–Nd isotope ratios of MD161-19 fall on the mixing line defined by Ganga and Brahmaputra main stem averages. Strontium and Nd isotope ratios along with Fe/Al ratio clearly show the predominance of Himalayan sediments in the study area. The significant temporal variations in the Sr–Nd isotope ratios observed for the entire depositional age (320 ka) may be attributed to changes in the relative sediment contribution by Ganga and Brahmaputra river systems draining terrains with contrasting Sr–Nd isotope ratios. The temporal geochemical profiles coupled with precipitation profile show that wet-phases during stadials led to enhanced erosion of the trans-Himalayan batholiths (THB) rocks (characterized by high εNd values) possibly due to glacial expansion in the higher reaches of the Brahmaputra catchment. The warm interstadials coupled with enhanced precipitation are accompanied by a shift towards lower εNd values which may be attributed to extensive erosion of the Ganga catchment area comprising rocks characterized by lower εNd values and diminished THB contribution due to lack of glacial influence.

Influence of Environmental Conditions on Mytilus trossulus Size Frequency Distributions in Two Glacially Influenced Estuaries

The Pacific blue mussel (Mytilus trossulus) is a foundation species in high-latitude intertidal and estuarine systems that creates complex habitats, provides sediment stability, is food for top predators, and links the water column and the benthos. M. trossulus also makes an ideal model species to assess biological responses to environmental variability; specifically, its size frequency distributions can be influenced by the environment in which it lives. Mussels that inhabit estuaries in high latitudes receive freshwater runoff from snow and glacial-fed rivers or can be under oceanic influence. These hydrographic conditions work together with local static environmental characteristics, such as substrate type, fetch, beach slope, distance to freshwater, and glacial discharge to influence mussel demographics. In 2019 and 2020, mussels were collected from two Gulf of Alaska ecoregions to determine whether mussel size frequencies change over spatial (local and ecoregional) and hydrographic scales and whether any static environmental characteristics correlate with this variability. This study demonstrated that mussel size frequencies were most comparable at sites with similar hydrographic conditions, according to the ecoregion and year they were collected. Hydrographic conditions explained approximately 43% of the variation in mussel size frequencies for both years, for the combined ecoregions. Mussel recruits (0–2 mm) were more abundant at sites with higher fetch, while large mussels (> 20 mm) were more abundant at more protected sites. Fetch and freshwater influence explained most of the variation in mussel size frequencies for both years and across both ecoregions, while substrate and slope were also important in 2019 and glacial influence in 2020. This study suggests that hydrographic and static environmental conditions may play an important role in structuring mussel sizes. Although differences in mussel size frequencies were found depending on environmental conditions, mussel sizes showed little difference across differing types of freshwater influence, and so they may be resilient to changes associated with melting glaciers.

Glacier retreat reorganizes river habitats leaving refugia for Alpine invertebrate biodiversity poorly protected.

Alpine river biodiversity around the world is under threat from glacier retreat driven by rapid warming, yet our ability to predict the future distributions of specialist cold-water species is currently limited. Here we link future glacier projections, hydrological routing methods and species distribution models to quantify the changing influence of glaciers on population distributions of 15 alpine river invertebrate species across the entire European Alps, from 2020 to 2100. Glacial influence on rivers is projected to decrease steadily, with river networks expanding into higher elevations at a rate of 1% per decade. Species are projected to undergo upstream distribution shifts where glaciers persist but become functionally extinct where glaciers disappear completely. Several alpine catchments are predicted to offer climate refugia for cold-water specialists. However, present-day protected area networks provide relatively poor coverage of these future refugia, suggesting that alpine conservation strategies must change to accommodate the future effects of global warming.

Hydrological Controls on Dissolved Organic Matter Composition throughout the Aquatic Continuum of the Watershed of Selin Co, the Largest Lake on the Tibetan Plateau.

Alpine river and lake systems on the Tibetan Plateau are highly sensitive indicators and amplifiers of global climate change and important components of the carbon cycle. Dissolved organic matter (DOM) encompasses organic carbon in aquatic systems, yet knowledge about DOM variation throughout the river-lake aquatic continuum within alpine regions is limited. We used optical spectroscopy, ultrahigh-resolution mass spectrometry (Fourier transform ion cyclotron resonance mass spectrometry), and stable water isotopic measurements to evaluate linkages between DOM composition and hydrological connection. We investigated glacial influences on DOM composition throughout the watershed of Selin Co, including upstream glacier-fed rivers and downstream-linked lakes. We found that the dissolved organic carbon concentration increased, whereas specific ultraviolet absorbance (SUVA254) decreased along the river-lake continuum. Relative to rivers, the downstream lakes had low relative abundances of polyphenolic and condensed aromatic compounds and humic-like substances but increased relative abundances of aliphatics and protein-like compounds. SUVA254 decreased while protein-like components increased with enriched stable water isotope δ2H-H2O, indicating that DOM aromaticity declined while autochthonous production increased along the flow paths. Glacier meltwater contributed to elevated relative abundances of aliphatic and protein-like compounds in headwater streams, while increased relative abundances of aromatics and humic-like DOM were found in glacier-fed lakes than downstream lakes. We conclude that changes in hydrological conditions, including glacier melt driven by a warming climate, will significantly alter DOM composition and potentially their biogeochemical function in surface waters on the Tibetan Plateau.

Glacial Influence Affects Modularity in Bacterial Community Structure in Three Deep Andean North-Patagonian Lakes.

We analyze the bacteria community composition and the ecological processes structuring these communities in three deep lakes that receive meltwater from the glaciers of Mount Tronador (North-Patagonia, Argentina). Lakes differ in their glacial connectivity and in their turbidity due to glacial particles. Lake Ventisquero Negro is a recently formed proglacial lake and it is still in contact with the glacier. Lakes Mascardi and Frías lost their glacial connectivity during the Pleistocene-Holocene transition. Total dissolved solid concentration has a significant contribution to the environmental gradient determining the segregation of the three lakes. The newly formed lake Ventisquero Negro conformed a particular bacterial community that seemed to be more related to the microorganisms coming from glacier melting than to the other lakes of the basin. The net relatedness index (NRI) showed that the bacterial community of lake Ventisquero Negro is determined by environmental filtering, while in the other lakes, species interaction would be a more important driver. The co-occurrence network analysis showed an increase in modularity and in the number of modules when comparing Lake Ventisquero Negro with the two large glacier-fed lakes suggesting an increase in heterogeneity. At the same time, the presence of modules with phototrophic bacteria (Cyanobium strains) in lakes Frías and Mascardi would reflect the increase of this functional photosynthetic association. Overall, our results showed that the reduction in ice masses in Patagonia will affect downstream large deep Piedmont lakes losing the glacial influence in their bacterial communities.

Unique benthic foraminiferal communities (stained) in diverse environments of sub-Antarctic fjords, South Georgia

Abstract. Sub-Antarctic fjords are among the environments most affected by the recent climate change. In our dynamically changing world, it is essential to monitor changes in these vulnerable settings. Here, we present a baseline study of “living” (rose-bengal-stained) benthic foraminifera from fjords of South Georgia, including fjords with and without tidewater glaciers. Their distribution is analyzed in the light of new fjord water and sediment property data, including grain size and sorting, total organic carbon, total sulfur, and δ13C of bulk organic matter. Four well-defined foraminiferal assemblages are recognized. Miliammina earlandi dominates in the most restricted, near-shore and glacier-proximal habitats, Cassidulinoides aff. parkerianus in mid-fjord areas, and Globocassidulina aff. rossensis and an assemblage dominated by Ammobaculites rostratus, Reophax subfusiformis, and Astrononion echolsi are in the outer parts of the fjords. Miliammina earlandi can tolerate strong glacial influence, including high sedimentation rates in fjord heads and sediment anoxia, as inferred from sediment color and total organic carbon / sulfur ratios. This versatile species thrives both in the food-poor inner reaches of fjords that receive mainly refractory petrogenic organic matter from glacial meltwater and in shallow-water coves, where it benefits from an abundant supply of fresh, terrestrial, and marine organic matter. A smooth-walled variant of C. aff. parkerianus, apparently endemic to South Georgia, is the calcareous rotaliid best adapted to inner-fjord conditions characterized by moderate glacial influence and sedimentation rates and showing no preference for particular sedimentary redox conditions. The outer parts of fjords with clear, well-oxygenated bottom water are inhabited by G. aff. rossensis. Ammobaculites rostratus, R. subfusiformis, and A. echolsi dominate in the deepest-water settings, with water salinities ≥ 33.9 PSU and temperatures 0.2–1.4 ∘C, characteristic of winter water and Upper Circumpolar Deep Water. The inner- and mid-fjord foraminiferal assemblages seem specific to South Georgia, although with continued warming and deglaciation, they may become more widespread in the Southern Ocean.

Multi-group biodiversity distributions and drivers of metacommunity organization along a glacial–fluvial–limnic pathway on the Tibetan plateau

Extensive global glacial retreats are threatening cryosphere ecosystem functioning and the associated biota in glacier-fed water systems. Understanding multi-group biodiversity distributions and compositional variation across diverse but hydrologically linked habitats under varying glacial influences will help explain the mechanisms underlying glacial community organization and ecosystem processes. However, such data are generally lacking due to the difficulty of obtaining biodiversity information across wide taxonomic ranges. Here, we used a multi-marker environmental DNA metabarcoding approach to simultaneously investigate the spatial patterns of community compositions and assembly mechanisms of four taxonomic groups (cyanobacteria, diatoms, invertebrates, and vertebrates) along the flowpaths of a tributary of Lake Nam Co on the Tibetan Plateau—from its glacier headwaters, through its downstream river and wetlands, to its estuary. We detected 869 operational taxonomic units: 119 cyanobacterial, 395 diatom, 269 invertebrate, and 86 vertebrate. Taxonomic richnesses consistently increased from upstream to downstream, and although all groups showed community similarity distance decay patterns, the trend for vertebrates was the weakest. Cyanobacteria, diatom, and invertebrate community compositions were significantly correlated with several environmental factors, while the vertebrate community was only correlated with waterway width. Variation partitioning analysis indicated that varying extents of environmental conditions and spatial factors affected community organizations for different groups. Furthermore, stochastic processes contributed prominently to the microorganisms' community assembly (Sloan's neutral model R2 = 0.77 for cyanobacteria and 0.73 for diatoms) but were less important for macroorganisms (R2 = 0.21 for invertebrates and 0.15 for vertebrates). That trend was further substantiated by modified stochasticity ratio analyses. This study provides the first holistic picture of the diverse biotic communities residing in a series of hydrologically connected glacier-influenced habitats. Our results both uncovered the distinct mechanisms that underlie the metacommunity organizations of different glacial organisms and helped comprehensively predict the ecological impacts of the world's melting glaciers.