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1. Determinants of microbial community structure in supraglacial pool sediments of monsoonal Tibetan Plateau

   https://doi.org/10.1128/spectrum.00754-24  

   Fair, Heather; Hamilton, Trinity L; Smiley, Peter C; Liu, Qiao (September 2024, Microbiology Spectrum)

   Cuomo, Christina A (Ed.)

   Abstract Supraglacial pools are prevalent on debris-covered mountain glaciers, yet only limited information is available on the microbial communities within these habitats. Our research questions for this preliminary study were: (1) What microbes occur in supraglacial pool sediments of monsoonal Tibet?; (2) Which abiotic and biotic habitat variables have the most influence on the microbial community structure?; and (3) Does microbial composition of supraglacial pool sediments differ from that of glacial-melt stream pool sediments? We collected microbial samples for 16S rRNA sequencing and invertebrates for enumeration and identification and measured 14 abiotic variables from 46 supraglacial pools and nine glacial-melt stream pools in 2018 and 2019. Generalized linear model analyses, small sample Akaike information criterion, and variable importance scores were used to identify the best predictor variables of microbial community structure. Multi-response permutation procedure (MRPP) was used to compare taxa composition between supraglacial pools and stream pools. The most abundant phyla in supraglacial pool sediments were Proteobacteria, Actinobacteria, Bacteroidota, Chloroflexi, and Cyanobacteria. Genera richness, indicator genera richness, andPolaromonasrelative abundance were best predicted by Chironomidae larvae abundance. 

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2. Diversity and co-occurrence networks of bacterial and fungal communities on two typical debris-covered glaciers, southeastern Tibetan Plateau

   https://doi.org/10.1016/j.micres.2023.127409  

   Hu, Yang; Fair, Heather; Liu, Qiao; Wang, Ziwei; Duan, Baoli; Lu, Xuyang (August 2023, Microbiological Research)

   Debris-covered glaciers (DCGs) are globally distributed and thought to contain greater microbial diversity than clean surface continental glaciers, but the ecological characteristics of microbial communities on the surface of DCGs have remained underexplored. Here, we investigated bacterial and fungal diversity and co-occurrence networks on the supraglacial debris habitat of two DCGs (Hailuogou and Dagongba Glaciers) in the southeastern Tibetan Plateau. We found that the supraglacial debris harbored abundant microbes with Proteobacteria occupying more than half (51.5%) of the total bacteria operational taxonomic units. The composition, diversity, and co-occurrence networks of both bacterial and fungal communities in the debris were significantly different between Hailuogou Glacier and Dagongba Glacier even though the glaciers are geographically adjacent within the same mountain range. Bacteria were more diverse in the debris of the Dagongba Glacier, where a lower surface velocity and thicker debris layer allowed the supraglacial debris to continuously weather and accumulate nutrients. Fungi were more diverse in the debris of the Hailuogou Glacier, which experiences a wetter monsoonal climate, is richer in calcium, has greater debris instability, and greater ice velocity than the Dagongba Glacier. These factors may provide ideal conditions for the dispersal and propagation of fungi spores on the Hailuogou Glacier. In addition, we found an obvious gradient of bacterial diversity along the supraglacial debris transect on the Hailuogou Glacier. Bacterial diversity was lower where debris cover was thin and scattered and became more diverse near the glacial terminus in thick, slow-moving debris. No such increasing bacterial pattern was detected on the Dagongba Glacier, which implies a positive relationship of debris age, thickness, and weathering on bacterial diversity. Additionally, a highly connected bacterial co-occurrence network with low modularity was found in the debris of the Hailuogou Glacier. In contrast, debris from the Dagongba Glacier exhibited less connected but more modularized co-occurrence networks of both bacterial and fungal communities. These findings indicate that less disturbed supraglacial debris conditions are crucial for microbes to form stable communities on DCGs. 

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3. Microbial communities from weathered outcrops of a sulfide‐rich ultramafic intrusion, and implications for mine waste management

   https://doi.org/10.1111/1462-2920.16489  

   Hobart, Kathryn K.; Greensky, ZhaaZhaawaanong; Hernandez, Kimberly; Feinberg, Joshua M.; Bailey, Jake V.; Jones, Daniel S. (December 2023, Environmental Microbiology)

   Abstract The Duluth Complex (DC) contains sulfide‐rich magmatic intrusions that represent one of the largest known economic deposits of copper, nickel, and platinum group elements. Previous work showed that microbial communities associated with experimentally‐weathered DC waste rock and tailings were dominated by uncultivated taxa and organisms not typically associated with mine waste. However, those experiments were designed for kinetic testing and do not necessarily represent the conditions expected for long‐term environmental weathering. We used 16S rRNA gene methods to characterize the microbial communities present on the surfaces of naturally‐weathered and historically disturbed outcrops of DC material. Rock surfaces were dominated by diverse unculturedKtedonobacteria,Acetobacteria, andActinobacteria, with abundant algae and other phototrophs. These communities were distinct from microbial assemblages from experimentally‐weathered DC rocks, suggesting different energy and nutrient resources in environmental samples. Sulfide mineral incubations performed with and without algae showed that photosynthetic microorganisms could have an inhibitory effect on autotrophic populations, resulting in slightly lower sulfate release and differences in dominant microorganisms. The microbial assemblages from these weathered outcrops show how communities develop during weathering of sulfide‐rich DC rocks and represent baseline data that could evaluate the effectiveness of future reclamation of waste produced by large‐scale mining operations. 

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4. Glacial retreat converts exposed landscapes from net carbon sinks to sources

   https://doi.org/10.1038/s43247-025-02404-z  

   Pain, A_J; Martin, J_B; Martin, E_E; Salinas-Reyes, J_T; Bennett, C. (May 2025, Communications Earth & Environment)

   Abstract Retreat of continental ice sheets exposes comminuted sediment in disequilibrium with non-glacial conditions. Weathering of this sediment may create climate feedbacks by altering exchange of greenhouse gases between atmosphere and landscapes. Here we show in a partially deglaciated watershed in southwest Greenland that glacial meltwater contains low concentrations of reactive dissolved organic carbon that enhances weathering of freshly comminuted sediment causing net sequestration of carbon dioxide. In contrast, soil water reactions enhance methanogenesis and carbon dioxide production and create greenhouse gas sources as organic carbon is remineralized. We suggest that a change from greenhouse gas sinks in glacial meltwater to greenhouse gas sources in soil water creates a switch from a negative to positive warming feedback during glacial-interglacial transitions, but a negative warming feedback may return with future anthropogenic warming, glacial retreat, and increased meltwater production. We anticipate changing weathering reactions following exposure also alter nutrient and radiogenic isotope exports. 

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5. Insights into glacial processes from micromorphology of silt-sized sediment

   https://doi.org/10.5194/tc-18-2297-2024  

   Lepp, Allison P; Miller, Lauren E; Anderson, John B; O'Regan, Matt; Winsborrow, Monica_C M; Smith, James A; Hillenbrand, Claus-Dieter; Wellner, Julia S; Prothro, Lindsay O; Podolskiy, Evgeny A (January 2024, The Cryosphere)

   Abstract. Silt-rich meltwater plume deposits (MPDs) analyzed from marine sediment cores have elucidated relationships that are clearly connected, yet difficult to constrain, between subglacial hydrology, ice-marginal landforms, and grounding-zone retreat patterns for several glacial catchments. Few attempts have been made to infer details of subglacial hydrology, such as flow regime, geometry of drainage pathways, and mode(s) of sediment transport through time, from grain-scale characteristics of MPDs. Using sediment samples from MPD, till, and grounding-zone proximal diamicton collected offshore of six modern and relict glacial catchments in both hemispheres, we examine grain shape distributions and microtextures (collectively, grain micromorphology) of the silt fraction to explore whether grains are measurably altered from their subglacial sources via meltwater action. We find that 75 % of all imaged grains (n = 9400) can be described by 25 % of the full range of measured shape morphometrics, indicating grain shape homogenization through widespread and efficient abrasive processes in subglacial environments. Although silt grains from MPDs exhibit edge rounding more often than silt grains from tills, grain surface textures indicative of fluvial transport (e.g., v-shaped percussions) occur in only a modest number of grains. Furthermore, MPD grain surfaces retain several textures consistent with transport beneath glacial ice (e.g., straight or arcuate steps, (sub)linear fractures) in comparable abundances to till grains. Significant grain shape alteration in MPDs compared to their till sources is observed in sediments from glacial regions where (1) high-magnitude, potentially catastrophic meltwater drainage events are inferred from marine sediment records and (2) submarine landforms suggest supraglacial melt contributed to the subglacial hydrological budget. This implies that quantifiable grain shape alteration in MPDs could reflect a combination of high-energy flow of subglacial meltwater, persistent sediment entrainment, and/or long sediment transport distances through subglacial drainage pathways. Integrating grain micromorphology into analysis of MPDs in site-specific studies could therefore aid in distinguishing periods of persistent, well-connected subglacial discharge from periods of sluggish or disorganized drainage. In the wider context of deglacial marine sedimentary and bathymetric records, a grain micromorphological approach may bolster our ability to characterize ice response to subglacial meltwater transmission through time. This work additionally demonstrates that glacial and fluvial surface textures are retained on silt-sized quartz grains in adequate amounts for microtexture analysis, which has heretofore been conducted exclusively on the sand fraction. Therefore, grain microtextures can be examined on silt-rich glaciogenic deposits that contain little to no sand as a means to evaluate sediment transport processes. 

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