The factors affecting the preservation of the isotopic fingerprint of alpine glacier meltwater in mountain groundwater systems have not been rigorously investigated. Here, we use tritium (3H), chlorine-36 ratios (36Cl/Cl), strontium-isotope ratios (87Sr/86Sr), and results from a stable isotopic mixing model to address the following questions: 1) does slope aspect affect the preservation of the isotopic fingerprint of glacial meltwater in groundwater, and 2) is the isotopic fingerprint of glacial meltwater preserved in groundwater with increasing distance from the glacier? In Glacier National Park (GNP), aspect relationships are obscured by hydrostratigraphic controls on groundwater flow, flowpath connectivity across spatial scales is limited by low-permeability rocks restricting groundwater flow to the upper carbonate rocks, and the isotopic fingerprint of glacial meltwater is preserved by 36Cl/Cl but not 3H. In Mount Hood (MH), springs emerging from north-facing slopes preserve the isotopic fingerprint of glacial meltwater, yet springs emerging from south-facing slopes provide the strongest evidence for flowpath connectivity across spatial scales. We propose an englacial mixing model (EMM) where the isotopic fingerprint of subglacial flow, and by extension, groundwater recharge from subglacial flow is a complex mixture of glacial meltwater, snowmelt, and rain that is strongly dependent on both englacial mixing processes and the stage of glacial retreat. The EMM indicates that the isotopic fingerprint of springs in GNP is becoming increasingly influenced by seasonal snowmelt relative to glacial meltwater, whereas the isotopic fingerprint of springs in MH is a dynamic mixture of sources but glacial meltwater is still preserved in some springs.

Disc-shaped pyrite suns of the Pennsylvanian age Anna Shale are thought to have formed where pressure restricted pyrite crystal growth to a flattened disc shape during diagenesis at the Anna Shale and the underlying Herrin coal boundary. Others have proposed syndepositional involvement of sulfate-reducing bacteria in the depositional environment. We hypothesize that the first steps in pyrite sun formation occur in mudflats of proglacial Alaska, with cyanobacterial mats trapping glacier silts within extracellular polymeric substances where microbial communities interact with allochthonous hydrocarbons, sulfur, and iron to precipitate amorphous iron sulfide minerals. We compared pyrite sun morphology with pyrite sun precursor formations, used 16S rRNA amplicon sequencing to investigate putative pyrite-forming bacteria, and determined iron content and mineralogy using XRD and sequential iron extraction of Matanuska Glacier mudflats sampled in June 2023. Recovered 16S rRNA sequences include EPS-generating cyanobacteria (Aphanizomenon NIES81), sulfur cycling bacteria (e.g., Thiobacillus, Sulfuritalea, Desulfovibrio), and iron cycling bacteria (e.g., Rhodoferax, Geobacter). In our proposed model, methane and hydrogen sulfide generated within anoxic mud form gas domes in benthic silt resting in a disc shape at the air-water interface. Iron sulfides precipitate below the surface of the cyanobacterial mats and are later buried and transformed into pyrite crystals with diagenesis across the disc shape. This combination of high organic carbon availability with sulfur and iron cycling and resulting iron sulfide mineral precipitation across a sharp redox gradient in depositional silt is a close match to the ancient depositional environment of the pyrite sun containing unit within the Anna Shale.

Ice-marginal lakes are increasingly common around Greenland and are important for modulating glacier runoff and dynamics. This study investigates the evolution of a ~3 km2 and up to ~100 m deep ice-dammed lake at Isunnguata Sermia, West Greenland. Satellite observations between 1987 and 2024, and field observations of a 2023 drainage using passive seismics, GNSS and time-lapse imagery reveal that the lake drains subglacially and has undergone 12 fill-drain cycles since 1987, a drainage periodicity of 1-3 years. Peak lake volume has decreased since 2010, associated with glacier thinning. Lake drainage can perturb the wider subglacial hydrology system, including triggering the release of stored subglacial water along the flood path in 2019. During the extreme melt year of 2012, the lake drained but did not refill, suggesting that subglacial leakage under the ice dam was sustained by record runoff. Transient ice flow acceleration was observed during the late season drainage in 2023 when the subglacial hydrological system was less efficient and therefore more easily overwhelmed. Our results indicate that ice-dammed lake fill-drain cycles, and the downstream impact on subglacial hydrology and ice dynamics, are modulated by ice dam thickness, melt supply and the antecedent subglacial hydraulic capacity.

High-throughput sequencing is a powerful tool for environmental microbiology and can be particularly important for examining community structure and function for organisms that are difficult to culture or environments that are difficult to mimic, like snow. Nucleic acid extraction significantly impacts these analyses, often introducing more variation between samples than PCR or sequencing. Snow algae are widespread on mountain and polar snowfields, where they contribute to biogeochemical cycling and accelerate melt. Despite increasing research on snow algae, DNA extraction remains challenging, as the thick, resilient walls of snow algal cysts can limit cell lysis, and differences among extraction methods may therefore affect the estimates of community composition and richness. Here, we compared three common extraction methods (Qiagen DNeasy PowerSoil Pro, Qiagen DNeasy PowerWater, and phenol-chloroform) alongside ultrasonication in samples with varying snow algae abundance. The extraction method strongly influenced the resulting microbial profiles assessed by amplicon sequencing of rRNA genes. Ultrasonication improved DNA yield in low-biomass samples and enhanced the recovery of DNA from resilient cells, including mature-phase snow algae, likely due to improved cell lysis. Our findings provide insights to improve standardization and facilitate comparison among studies in snow and ice environments.IMPORTANCEHigh-throughput sequencing has transformed environmental microbiology, allowing for detailed, culture-independent analyses of microbial communities. However, multiple methodological factors, including DNA extraction, can introduce variability in results, making cross-study comparisons challenging. This research contributes to improving our understanding of snow algae, which play a role in alpine and polar ecosystems by influencing biogeochemical cycles and snow reflectivity. By evaluating common DNA extraction techniques for snow algae, this study helps improve the reliability and reproducibility of sequencing data, supporting broader efforts toward methodological standardization in microbial ecology.

Abstract Snow algae darken snowpacks and accelerate melt worldwide. Although elevation strongly structures the physical conditions of mountain snowfields, its influence on snow algal traits and their effects on snowpack reflectance remains unclear. Here, we investigated snow algal composition, cellular traits, and optical properties in summer blooms across an elevational range of 1,059–3,423 m a.s.l. in the western United States, spanning two elevational gradients in the Cascade Range (CA, OR, WA) and the Rocky Mountains (UT, WY, MT). Across all samples (n = 294), snow albedo declined strongly with increasing algal cell density, indicating that total biomass, rather than pigment composition, is the dominant driver of albedo reduction. However, within Sanguina-dominated blooms (117 of 206 samples bloom samples identified across the dataset), neither relative abundance nor algal cell density varied systematically with elevation. Instead, mean cell size increased with elevation, while per-cell pigment concentrations declined, leading to higher astaxanthin:chlorophyll-a ratios driven primarily by reductions in chlorophyll-a per cell. These elevation-dependent shifts in cell size and pigment balance were consistent across both mountain ranges, indicating phenotypic acclimation to increasing environmental stress with elevation. Together, these findings link cellular-scale acclimation of a widespread snow alga to radiative processes shaping mountain snowpacks.

Abstract. In many glacial settings, winter outflows of proglacial water create stratified domed ice structures on glacial forefields. These structures, called naledi, provide an opportunity to characterise the solute fluxes of hydrological systems in winter which are poorly constrained compared to summer outflows which are dominated by supraglacial meltwater input. To characterise the different hydrological systems feeding naledi and provide conceptual models of their formation, we sampled 12 overwinter naledi and 4 supercooled summer ice accumulations (accreted ice) from the forefield of Isunnguata Sermia, a western outlet glacier of the Greenland Ice Sheet, during four field campaigns. Major ions and stable water isotopes reveal complex geochemical signatures, where the composition of successive naled layers reveal fluctuations in water source and transport throughout winter. In comparison, core analysis of summer accreted ice shows uniform geochemistry throughout, suggesting freeze-on of water from one single source in quick discrete events. These findings are supported by Electrical Resistivity Tomography (ERT) geophysical surveys, which reveal shallow hydrological pathways (1–5 m below the surface) in the glacial foreland (surveyed 400 m from the glacier terminus). Here, meltwater is transported through a saturated sediment zone feeding proglacial upwellings. Our results inform the first conceptual models of summer vs. wintertime subglacial water routing and naled formation in the proglacial zone of the Greenland Ice Sheet. We show that wintertime naledi form from a combination of top-down (unconfined) and bottom-up (confined) freezing processes which incorporates subglacial discharge, overland flow and precipitation, whereas accreted ice forms from upwellings of high velocity, highly pressurised water which freezes upon release. These seasonal changes drive different geochemical and nutrient outputs, which are critical for evaluating glacier meltwater contributions to proglacial groundwater systems and the impact of glacial discharge on downstream ecosystems.

Active and abandoned metal and coal mines generate acidic, metal-laden water that pollutes downstream areas, commonly referred to as acid mine drainage (AMD). AMD is host to microbial communities, including acidophilic iron oxidizers. Microbially mediated iron oxidation is a desirable (bio)remediation strategy for AMD. Ferrovaceae are Fe-oxidizing bacteria observed in AMD globally and thus could be an asset for bioremediation strategies. To better understand the potential for Ferrovaceae to contribute to AMD bioremediation, we analyzed 240 genomes and metagenome-assembled genomes from Ferrovaceae, including sequences from AMD sites with high iron oxidation rates. Based on our analyses, the phylogenetic and physiological diversity of this group is greater than previously known. We found that while all taxa are likely capable of iron oxidation using a cyc-2 like protein, some may also be capable of iron oxidation using an Mto-like protein. We also identified Ferrovaceae that are likely capable of anoxygenic phototrophy. Our findings indicate that multiple Ferrovaceae populations co-occur and suggest that differences in physiology may promote niche differentiation along resource axes. Physiologically diverse iron oxidizer communities could support a more resilient microbial community, resulting in higher iron oxidation rates and potentially more efficient bioremediation, and thus our results also indicate that future studies that link taxonomy with iron oxidation activity are warranted.IMPORTANCEAcid mine drainage (AMD) pollutes watersheds worldwide. Microbial communities can be leveraged to improve AMD bioremediation because they drive biogeochemical processes in these ecosystems. In AMD streams, iron-oxidizing microbial populations remove iron from the AMD effluent by precipitating iron oxides, which absorb other metals. These communities vary across sites and differ in how rapidly they oxidize iron. The factors that contribute to iron oxidation rates are not well understood, making it difficult to design effective bioremediation strategies. Ferrovaceae populations are widespread in AMD globally, including in sites with exceptionally high rates of iron oxidation. To examine the potential for Ferrovaceae to be key components of bioremediation strategies, we examined the genomic content and functional potential of Ferrovaceae in publicly available metagenomic data sets. Our analysis uncovered several new species of Ferrovaceae as well as an expanded metabolic potential for this group. Comparative genomics suggests that functional diversity leads to co-occurrence of multiple Ferrovaceae species at the same sites. The presence of multiple iron-oxidizing taxa with distinct physiology could be beneficial for bioremediation strategies.

Snow algae darken snowpacks and accelerate melt world-wide. Although elevation strongly structures mountain snowfields, its influence on snow algal traits and their effects on snowpack reflectance remains unclear. Here, we investigated snow algal blooms across an elevational range of 1059-3423 m above sea level (asl) in the Cascade Range (California, Oregon, Washington) and the Rocky Mountains (Utah, Wyoming, Montana). We analyzed 294 snow samples and quantified algal community composition, algal cell density, cell size, pigment concentrations, and snow albedo. We further examined elevation-dependent patterns within Sanguina nivaloides-dominated blooms (117 of 206 bloom samples). Across samples spanning clean snow and algal blooms, algal cell density emerged as the strongest biological predictor of albedo, whereas pigment-related variables showed no consistent effects. Within Sanguina nivaloides-dominated blooms, neither relative abundance nor algal cell density varied systematically with elevation. Instead, mean cell size increased with elevation, while per-cell pigment concentrations declined, leading to higher astaxanthin ratios driven primarily by reductions in Chla per cell. These elevation-dependent shifts in cell size and pigment balance were consistent across both mountain ranges, indicating phenotypic acclimation to increasing environmental stress with elevation. Together, these findings link cellular-scale acclimation of a widespread snow algae to radiative processes shaping mountain snowpacks.

ABSTRACT Snow algae are major biological drivers of snow darkening in polar and high-alpine environments. However, the direct contribution of algal pigmentation to snow reflectance has remained difficult to quantify because field observations cannot disentangle the effects of pigmentation from variation in biomass, species composition, and snow physical properties. Here, we characterized the optical effects of pigmentation using hyperspectral spectroradiometry to compare green, orange, and red cyst-like cells of a snow-derived Haematococcus isolate while controlling for developmental stage and cell abundance. Cysts became more red with increasing astaxanthin concentrations while chlorophyll-a concentrations remained relatively constant. Relative to green cysts, mean reflectance decreased by approximately 30% in orange cysts and 40% in red cysts. Integrated reflectance across the visible spectrum (350–800 nm) was negatively correlated with astaxanthin concentration. These results provide direct experimental evidence that algal pigmentation alone substantially reduces reflectance after controlling for cell abundance and developmental stage, and indicate that differences in snow physical properties may partly obscure this effect under natural field conditions. Our findings identify astaxanthin accumulation as an intrinsic driver of biological snow darkening and suggest that algal pigmentation, which may vary with species identity and physiological state, should be considered alongside biomass when predicting the radiative effects of snow algal blooms.

Acid mine drainage (AMD) is a global pollution problem characterized by low pH and high concentrations of metals. Active remediation is often cost-prohibitive, but Fe(II)-oxidizing microbes may be used for passive bioremediation. To leverage these species, we must understand the factors that control their distribution. Here, we examined the environmental and ecological factors that control these species with the aim of determining if microbial seeding is a viable remediation strategy. Although stochastic processes appeared to control the distribution of the majority of taxa inhabiting AMD ecosystems, the distribution of Fe(II) oxidizers appeared to be driven by environmental filtering and competition. The abundance of all the major Fe(II)-oxidizing genera had significant relationships with pH, with pH explaining 10%-38% of the variation in their abundance. The genera appeared to have pH preferences, with Acidithiobacillus and Leptospirillum preferring environments with pH below 3, Gallionella, Sideroxydans, and Ferritrophicum preferring environments with pH above 3.5, and Ferrovum preferring intermediate-pH environments. Once the effect of pH is removed, genera that share pH preferences were negatively correlated, indicating that they were likely competing for the Fe(II)-oxidizing niche in their preferred environments. Communities were also shaped by dispersal limitation, which suggests that microbial seeding may be possible in these environments. Future seeding attempts should consider species interactions and ecology more generally to inform their efforts. IMPORTANCE:Acid mine drainage (AMD) is a global pollution problem affecting streams worldwide. One method of remediating AMD is by using naturally occurring microbial communities to remove iron and other metals. However, we do not have a complete understanding of the factors that control the distribution of these species or if it is possible to seed species from one environment into another. Here, we examine the factors that control community assembly in AMD ecosystems. We find that individual species appear to be dispersal-limited; thus, microbial seeding may be a viable method for AMD remediation.

Acid mine drainage is a global pollution problem characterized by low pH and high concentrations of metals. Active remediation is often cost-prohibitive, but Fe(II) oxidizing microbes may be used for passive bioremediation. To leverage these species, we must understand the factors that control their distribution. Here, we examine the environmental and ecological factors that control these species with the aim of determining if microbial seeding is a viable remediation strategy. Although stochastic processes appear to control the distribution of majority of taxa inhabiting AMD ecosystems, the distribution of Fe(II) oxidizers is driven by environmental filtering and competition. The abundance of all the major Fe(II) oxidizing genera have significant relationships with pH, with pH explaining 10 – 38% of the variation in their abundance. The genera appear to have pH preferences with Acidithiobacillus and Leptospirillum preferring environments below pH 3, Gallionella, Sideroxydans , and Ferritrophicum preferring environments above pH 3.5, and Ferrovum preferring intermediate pH environments. Once the effect of pH is removed, genera that share pH preferences are negatively correlated, indicating that they are likely competing for the Fe(II) oxidizing niche in their preferred environments. Communities are also shaped by dispersal limitation, which suggests that microbial seeding is possible in these environments. Future seeding attempts should consider species interactions and ecology more generally to inform their efforts.

Nitrogen isotope (δ 15 N) values in ancient rocks have been used to interpret the presence of nitrogen metabolisms and fixed N availability across the Archean and Paleoproterozoic eons. However, how δ 15 N signals produced by nitrogen metabolisms of microbial communities, the impact of the geochemical environments they live in on those signals, and the fidelity of those signals through preservation in the rock record have not been fully constrained and validated. Thus, it is imperative to study modern microbial systems to test the validity of using δ 15 N signals produced by microbial communities to interpret what geochemical environments and nitrogen metabolisms influenced the production of those signals. Hydrothermal systems are an ideal place to examine the biotic and abiotic factors that impact δ 15 N signals—physical processes generate geochemical environments with wide ranges of fixed N availability and the physicochemical environments exclude multicellular eukaryotic organisms. Previous work has demonstrated the presence of nitrogen fixation genes in microbial communities across a range of temperature (16–89°C) and pH (1.9–9.8) gradients. Here, we test the validity and fidelity of using microbial community δ 15 N signals as indicators of geochemical environment and nitrogen metabolisms (specifically, biological nitrogen fixation) present in eight hydrothermal systems across Yellowstone National Park. Our results suggest that δ 15 N values measured in the ancient rock record can provide information about the N cycling and prevailing environmental conditions during deposition, but only if viewed within appropriate context.

In this study, we examined the reflectance, pigment composition, and community composition of three snow algae blooms showing distinct colors in the same snowfield in Glacier National Park (USA). Each color bloom was dominated by a different algae, each exhibiting a unique pigment signature but with astaxanthin as the predominant pigment across all three blooms. The spectral reflectance of red snow algae was consistently lower than that of green algae, while orange algae had intermediate reflectance values. Specifically, red algae reduced reflectance by approximately 55% across the PAR range, while green algae reduced reflectance by 25%. Red algae also demonstrated the highest radiative forcing, double that of green algae, leading to increased energy re-emission into the surrounding environment, which likely contributes to the localized melting of adjacent ice crystals. The high absorbance around 680 nm in cells with high astaxanthin content, such as the orange algae, suggests that semi-automatic detection methods could effectively identify these algae, as their spectral features remain distinct despite the presence of secondary carotenoids. Our data demonstrate the impact of snow algae taxonomic and pigment composition on the radiative balance of snowfields, underscoring taxonomy as a key determinant of bloom color under similar environmental conditions ### Competing Interest Statement The authors have declared no competing interest. National Science Foundation, 2113783, 2113784

Glaciers and glacially influenced ecosystems host unique biodiversity spanning all kingdoms of life, but glaciers are retreating as the global climate warms, threatening specialist species, ecosystem functions and stability. We outline the impacts and consequences of glacier retreat, identifying key drivers and mechanisms of change, focusing on biodiversity and interactions among glacier, terrestrial, freshwater and marine ecosystems. We identify global glacial biodiversity patterns and local nuances, highlighting taxa that are likely to thrive or decline with the loss of glaciers. Following glacier retreat, the availability and size of ice-free areas initially increase, leading to a ‘biodiversity peak’. However, as glaciers disappear, the formation of novel habitats decreases while communities become more homogeneous and competition increases, leading to local-to-regional biodiversity decline. Glacier loss influences multiple ecosystem functions that contribute to climate regulation, freshwater resources, carbon and nutrient cycling, soil development, primary productivity and food-web stability. Key challenges in glacier ecosystem science include improving our knowledge of the relationships between biodiversity and ecosystem functions and quantifying species interactions at local-to-global scales to improve mechanistic understanding. Such advances will enhance predictions of how biodiversity will change with the loss of glaciers, enabling informed and effective conservation and management. Glaciers are retreating with global climate warming, which threatens glacier specialists and the functions and stability of glaciers and glacially influenced ecosystems. This Review describes the impacts and consequences of glacier retreat for biodiversity, highlighting species that are likely to thrive or decline with glacier loss, and outlines key challenges and research priorities in conserving and managing biodiversity.

Terrestrial organic matter (tOM) plays a critical role in aquatic ecosystems, influencing carbon processes and greenhouse gas emissions. Here, we investigate the impact of tOM on methane production in littoral and pelagic sediments from the Mississippi River headwaters using a microcosm approach. Contrary to our expectations, tOM addition universally increased methane production across lentic sediments, with no significant difference between littoral and pelagic zones. Methane production was influenced by select sediment microorganisms, primarily methanogens and lignocellulose degrading bacteria, which responded similarly across different sediment habitats. The study highlights the role of cytochrome-containing methanogens and their syntrophic relationships with fermentative bacteria, emphasizing the significance of microbial community structure in sediment methane dynamics. Our findings suggest that increasing tOM loads to freshwater systems could have broader implications for methane emissions, driven by specific microbial interactions. ### Competing Interest Statement The authors have declared no competing interest.

Snow algae darken the surface of snow, reducing albedo and accelerating melt. However, the impact of subsurface snow algae (e.g., when cells are covered by recent snowfall) on albedo is unknown. Here, we examined the impact of subsurface snow algae on surface energy absorption by adding up to 2 cm of clean snow to surface algal blooms and measuring reflectivity. Surprisingly, snow algae still absorb significant energy across an array of wavelengths when snow-covered. Furthermore, the scale of this effect correlates with algal cell densities and chlorophyll-a concentrations. Collectively, our results suggest that darkening by subsurface snow algae lowers albedo and thus potentially accelerates snowmelt even when the algae is snow-covered. Impacts of subsurface algae on melt await assessment. This implies that snow algae play a larger role in cryosphere melt than investigations of surface-only reflectance would suggest. IMPORTANCE:This study addresses a gap in research by examining the impact of subsurface snow algae on snow albedo, which affects snowmelt rates. Previous studies have focused on visible surface blooms, leaving the effects of hidden algae unquantified. Our findings reveal that snow algae beneath the surface can still absorb energy across various wavelengths, accelerating melt even when not visible to the naked eye. This suggests that spectral remote sensing can detect these hidden algae, although their biomass might be underestimated. Understanding how subsurface snow algae influence albedo and snowmelt is crucial for accurate predictions of meltwater runoff, which impacts alpine ecosystems, glacier health, and water resources. Accurate projections are essential for managing freshwater supplies for agriculture, drinking water, and other vital uses. Thus, further investigation into subsurface snow algae is necessary to improve our understanding of their role in snow albedo reduction and water resource management.

Snow algae blooms visibly alter snow color and surface energy balance, yet the biological basis of this variability remains unclear. We investigated how pigment composition and community structure shape the optical properties of snow algae blooms of distinct colors - red, orange, and green - co-occurring within the same snowfield in Glacier National Park, USA. We measured the spectral reflectance, pigment composition (HPLC), and algal community composition (18S rRNA amplicon sequencing) of each bloom type to quantify how biological characteristics influence snow reflectance and radiative forcing. Astaxanthin dominated all blooms, while Chla was most abundant in green blooms. Distinct algal taxa characterized each color, with Sanguina dominating red blooms and Chloromonas being more abundant in green and orange. Red blooms showed the lowest reflectance and highest radiative forcing (56 W m-2), exceeding that of green (21 W m-2) and orange blooms (25 W m-2), enhancing energy absorption into the snowpack and promoting localized melting of adjacent ice crystals. Our data indicate that bloom color reflects distinct community compositions, characterized by differences in dominant taxa and pigment pools, which together drive the radiative balance of snowfields. However, these relationships may not be universal, and color is best viewed as an emergent property shaped by multiple biological and environmental factors.

Snow algal blooms decrease snow albedo and increase local melt rates. However, the causes behind the size and frequency of these blooms are still not well understood. One factor likely contributing is nutrient availability, specifically nitrogen and phosphorus. The nutrient requirements of the taxa responsible for these blooms are not known. Here, we assessed the growth of three commercial strains of snow algae under 24 different nutrient treatments that varied in both absolute and relative concentrations of nitrogen and phosphorus. After 38 days of incubation, we measured total biomass and cell size and estimated their effective albedo reduction surface. Snow algal strains tended to respond similarly and achieved bloom-like cell densities over a wide range of nutrient conditions. However, the molar ratio of nitrogen to phosphorus at which maximum biomass was achieved was between 4 and 7. Our data indicate a high requirement for phosphorus for snow algae and highlights phosphorus availability as a critical factor influencing the frequency and extent of snow algae blooms and their potential contribution to snow melt through altered albedo. Snow algae can thrive across a range of nitrogen (N) and phosphorus (P) conditions, with a higher P requirement for optimal growth. Our study suggests that increased N deposition may have a limited impact on snow algae bloom occurrence and size, emphasising P as a key factor influencing these blooms and their potential to accelerate snow melt by lowering albedo.

With more than 5500 detected exoplanets, the search for life is entering a new era. Using life on Earth as our guide, we look beyond green landscapes to expand our ability to detect signs of surface life on other worlds. While oxygenic photosynthesis gives rise to modern green landscapes, bacteriochlorophyll-based anoxygenic phototrophs can also colour their habitats and could dominate a much wider range of environments on Earth-like exoplanets. Here, we characterize the reflectance spectra of a collection of purple sulfur and purple non-sulfur bacteria from a variety of anoxic and oxic environments. We present models for Earth-like planets where purple bacteria dominate the surface and show the impact of their signatures on the reflectance spectra of terrestrial exoplanets. Our research provides a new resource to guide the detection of purple bacteria and improves our chances of detecting life on exoplanets with upcoming telescopes. Our biological pigment data base for purple bacteria and the high-resolution spectra of Earth-like planets, including ocean worlds, snowball planets, frozen worlds, and Earth analogues, are available online, providing a tool for modellers and observers to train retrieval algorithms, optimize search strategies, and inform models of Earth-like planets, where purple is the new green.