Temperate Glaciers Research Articles

High-frequency Holocene glacier fluctuations in the Himalayan-Tibetan orogen

Holocene glacial chronostratigraphies in glaciated valleys spread throughout the Himalayan-Tibetan orogen, including the Himalaya, Tibet, Pamir, and Tian Shan, are developed using a landsystems approach, detailed geomorphic mapping, and new and published 10Be surface exposure dating. New studies in the Kulti valley of Lahul and the Parkachik valley of the Nun Kun massif of the Himalaya of northern India define three glacier advances at ∼14.7, 12.2, 0.5 ka, in addition to one historically dated late 19th Century advance in the Kulti valley, and one Late Holocene advance at ∼0.2 ka in the Parkachik valley. Three major climatic groups (subdivided into five climatic zones) are defined across the orogen using Cluster Analysis (CA) and Principal Component Analysis (PCA) to identify glaciated regions with comparable climatic characteristics to evaluate the timing, and extent of Holocene glacier advances across these regions. Our regional analyses across the Himalayan-Tibetan orogen suggest at least one Lateglacial (∼15.3–11.8 ka) and five Himalayan-Tibetan Holocene glacial stages (HTHS) at ∼11.5–9.5, ∼8.8–7.7, ∼7.0–3.2, ∼2.3–1.0, and <1 ka. The extent (amplitude) of glacier advances in 77 glaciated valleys is reconstructed and defined using equilibrium-line altitudes (ELAs). Modern glacier hypsometries are also assessed to help explain the intra-regional variations in glacier amplitudes during each regional glacier advance. A linear inverse glacier flow model is used to decipher the net changes in temperature (ΔT) between periods of reconstructed regional glacier advances in 66 glaciated valleys across different climatic regions throughout the orogen. The 10Be, ELAs, and ΔT data suggest enhanced monsoonal and increased precipitation during the Early Holocene, followed by relative cooling and increased aridity during the Mid- and Late Holocene that influenced glaciation. The sublimation-dominated cold-based glaciers in the northern regions of Himalayan-Tibetan orogen are more affected during these shifts in climate than the temperate glaciers in the south.

The Tekapo Glacier, New Zealand, during the Last Glacial Maximum: An active temperate glacier influenced by intermittent surge activity

Quaternary glaciations have created impressive landform assemblages that can be used to understand palaeo-glacier extent, character and behaviour, and hence past global and local glacier forcings. However, in the southern hemisphere and especially in New Zealand, the Quaternary glacial landform record is relatively poorly investigated with regard to glaciological properties. In this study, a 1 m digital elevation model (DEM) was generated from airborne LiDAR data and supplemented with aerial imagery and field observations to analyse the exceptionally well-preserved glacial geomorphology surrounding Lake Tekapo, New Zealand. We describe a rich suite of Last Glacial Maximum (LGM) and recessional ice-marginal, subglacial, supraglacial, glaciofluvial and glaciolacustrine landform assemblages. These represent two landsystems comprising i) fluted till surfaces with low-relief push moraine ridges; and ii) crevasse-squeeze ridges, ‘zig-zag’ eskers and attenuated lineations. The former landsystem records the behaviour of an active temperate glacier and the latter landsystem, which is superimposed upon and inset within the former, strongly suggests intermittent surge phases. The two landsystem signatures indicate a sequential change in ice-marginal dynamics during recession that was likely to have been partially non-climatically driven. Overall, we present the first evidence of surge-type glacier behaviour in New Zealand.

The glacial landsystem of Hoffellsjökull, SE Iceland: contrasting geomorphological signatures of active temperate glacier recession driven by ice lobe and bed morphology

ABSTRACTA 1:14 500 scale glacial geomorphology and surficial geology map of the foreland of Hoffellsjökull, southeast Iceland is used to assess the glacial landsystem signature of the contrasting glacier-climate interactions of two separate flow lobes within one outlet glacier. This constitutes a valuable modern analogue for employing glacial geomorphological signatures as palaeoclimate indicators in ancient deglaciated terrains. The landsystem signatures of the glacier’s two flow lobes, Svínafellsjökull and Hoffellsjökull, are distinctly different. Svínafellsjökull displays inset and seasonally climatically-tuned push moraine sequences and subglacially streamlined surfaces typical of active temperate glaciers on sloping piedmont forelands. Hoffellsjökull displays the landform-sediment assemblages typical of outwash-head/depositional overdeepening scenarios, upon which closely-spaced composite push moraines reflect a long term quasi-stationary snout at and near the Little Ice Age maximum prior to 2000. Moraine spacing on the Svínafellsjökull foreland reflects an overall trend of annual recession punctuated by quasi-stability and/or readvance in the mid-1950s-1960 and 1975–2000 as recorded by two arcuate zones of closely-spaced and partially overprinted sawtooth and hairpin moraines. The pattern of moraine distribution here also reflects spatio-temporal changes in moraine-forming processes as dictated by changes in a combination of proglacial drainage characteristics and structural glaciology or crevasse architecture. The subglacial footprint of the Svínafellsjökull foreland contains features worthy of future research attention, including an arcuate zone of overridden moraines potentially indicative of a regional Holocene ice advance, prominent flutings and debris stripes potentially indicative of groove-ploughing and point-source bedrock plucking respectively, and relatively large drumlins.

Compression characteristics of saturated re-compacted glacial tills in Tianmo Gully of Tibet, China

Glacial tills are highly compressible soils composed of loosely cemented sandy silt particles. Their role, for instance, as initial filler materials in geo-technical projects along temperate glacier regions warrant a systematic evaluation of their compressive characteristics. As such, we carry out a series of one-dimensional compression tests on re-compacted glacial till samples obtained from Tianmo Gully, Tibet, with the aims of evaluating their compressive behavior under controlled initial stress conditions. The yield stress was determined from the void ratio versus consolidation pressure (e-log sigma(v)) planes. Its compression and swelling behaviors were observed during the primary and secondary compressions of the consolidation tests. From the compression curves, a correlation can be found between the consolidation stress and the void index. In addition, we find that the compression curves of glacial tills collapse into a single curve when normalized by the compression index. The experimental results in this study provide a basic understanding of the compression characteristics of the glacial tills in Tibet, China.

Glacier sliding, seismicity and sediment entrainment

ABSTRACTThe evolution of glaciers and ice sheets depends on processes in the subglacial environment. Shear seismicity along the ice–bed interface provides a window into these processes. Such seismicity requires a rapid loss of strength that is typically ascribed to rate-weakening friction, i.e., decreasing friction with sliding or sliding rate. Many friction experiments have investigated glacial materials at the temperate conditions typical of fast flowing glacier beds. To our knowledge, however, these studies have all found rate-strengthening friction. Here, we investigate the possibility that rate-weakening rock-on-rock friction between sediments frozen to the bottom of the glacier and the underlying water-saturated sediments or bedrock may be responsible for subglacial shear seismicity along temperate glacier beds. We test this ‘entrainment-seismicity hypothesis’ using targeted laboratory experiments and simple models of glacier sliding, seismicity and sediment entrainment. These models suggest that sediment entrainment may be a necessary but not sufficient condition for the occurrence of basal shear seismicity. We propose that stagnation at the Whillans Ice Stream, West Antarctica may be caused by the growth of a frozen fringe of entrained sediment in the ice stream margins. Our results suggest that basal shear seismicity may indicate geomorphic activity.

Detecting and characterising an englacial conduit network within a temperate Swiss glacier using active seismic, ground penetrating radar and borehole analysis

ABSTRACTEnglacial hydrology plays an important role in routing surface water to the glacier's bed and it consequently affects the glacier's dynamics. However, it is often difficult to observe englacial conduit conditions on temperate glaciers because of their short-lived nature. We acquired repeated active surface seismic data over the Rhone Glacier, Switzerland to monitor and characterise englacial conduit conditions. Amplitude-versus-angle analysis suggested that the englacial conduit is water filled and between 0.5 and 4 m thick. A grid of GPR profiles, acquired during the 2018 melt season, showed the englacial conduit network persisting and covering ~ 14,000 m2. In late summer 2018, several boreholes were drilled into the conduit network. We observed generally stable water pressure, but there were also short sudden increases. A borehole camera provided images of a fast flowing englacial stream transporting sediment through the conduit. From these observations, we infer that the englacial conduit network is fed by surface meltwater and morainal streams. The surface and morainal streams merge together, enter the glacier subglacially and flow through subglacial channels along the flank. These subglacial channels flow into highly efficient englacial conduits traversing the up-glacier section of the overdeepening before connecting with the subglacial drainage system.

Surface melt‐driven seasonal behaviour (englacial and subglacial) from a soft‐bedded temperate glacier recorded by in situ wireless probes

AbstractWe investigate the spatial and temporal englacial and subglacial processes associated with a temperate glacier resting on a deformable bed using the unique Glacsweb wireless in situ probes (embedded in the ice and the till) combined with other techniques [including ground penetrating radar (GPR) and borehole analysis]. During the melt season (spring, summer and autumn), high surface melt leads to high water pressures in the englacial and subglacial environment. Winter is characterized by no surface melting on most days (‘base’) apart from a series of positive degree days. Once winter begins, a diurnal water pressure cycle is established in the ice and at the ice/sediment interface, with direct meltwater inputs from the positive degree days and a secondary slower englacial pathway with a five day lag. This direct surface melt also drives water pressure changes in the till. Till deformation occurred throughout the year, with the winter rate approximately 60% that of the melt season. We were able to show the bed comprised patches of till with different strengths, and were able to estimate their size, relative percentage and temporal stability. We show that the melt season is characterized by a high pressure distributed system, and winter by a low pressure channelized system. We contrast this with studies from Greenland (overlying rigid bedrock), where the opposite was found. We argue our results are typical of soft bedded glaciers with low englacial water content, and suggest this type of glacier can rapidly respond to surface‐driven melt. Based on theoretical and field results we suggest that the subglacial hydrology comprises a melt season distributed system dominated by wide anastomosing broad flat channels and thin water sheets, which may become more channelized in winter, and more responsive to changes in meltwater inputs. © 2019 The Authors. Earth Surface Processes and Landforms published by John Wiley &amp; Sons Ltd.

Assessing microscale anisotropy of a temperate glacier with seismic and radar borehole measurements

Assessing microscale anisotropy of a temperate glacier with seismic and radar borehole measurements

Surface melt driven summer diurnal and winter multi-day stick-slip motion and till sedimentology

Fluctuations in glacier motion are very common and are thought to be controlled by subglacial hydrology and till deformation. There are few instrumented studies that have monitored seasonal changes. We use the innovative Glacsweb subglacial in situ wireless probes, combined with dGPS and custom geophone data from an Icelandic soft-bedded temperate glacier, to show that there are two distinct seasonal styles of speed-up events. Relatively small diurnal events occur during the melt season, whilst during winter there are larger multi-day events related to positive degree days. These events are accompanied by a distinct pattern of till deformation and basal icequakes. We argue these reflect stick-slip motion which occurs when the glacier hydrological system is unable to accommodate the melt water flux generated by surface melt episodes. We show a rare fully instrumented coupled glacier/till record of contrasting summer and winter stick-slip motion and discuss its implication for till sedimentology.

Pervasive cold ice within a temperate glacier – implications for glacier thermal regimes, sediment transport and foreland geomorphology

Abstract. This study suggests that cold-ice processes may be more widespread than previously assumed, even within temperate glacial systems. We present the first systematic mapping of cold ice at the snout of the temperate glacier Midtdalsbreen, an outlet of the Hardangerjøkulen icefield (Norway), from 43 line kilometres of ground-penetrating radar data. Results show a 40 m wide cold-ice zone within the majority of the glacier snout, where ice thickness is &lt;10 m. We interpret ice to be cold-based across this zone, consistent with basal freeze-on processes involved in the deposition of moraines. We also find at least two zones of cold ice up to 15 m thick within the ablation area, occasionally extending to the glacier bed. There are two further zones of cold ice up to 30 m thick in the accumulation area, also extending to the glacier bed. Cold-ice zones in the ablation area tend to correspond to areas of the glacier that are covered by late-lying seasonal snow patches that reoccur over multiple years. Subglacial topography and the location of the freezing isotherm within the glacier and underlying subglacial strata likely influence the transport and supply of supraglacial debris and formation of controlled moraines. The wider implication of this study is the possibility that, with continued climate warming, temperate environments with primarily temperate glaciers could become polythermal in forthcoming decades with (i) persisting thinning and (ii) retreat to higher altitudes where subglacial permafrost could be and/or become more widespread. Adversely, the number and size of late-lying snow patches in ablation areas may decrease and thereby reduce the extent of cold ice, reinforcing the postulated change in the thermal regime.

Ice friction: Glacier sliding on hard randomly rough bed surface.

I present a theory for ice friction for ice sliding on a hard randomly rough surface which includes ice melting-freezing (regelation), viscoelastic energy dissipation, and cavitation. The theory is an extension of earlier work by Weertman, Lliboutry, Nye, and Kamb. I present numerical results for surfaces with realistic surface roughness power spectra. I consider both airfilled and (pressurized) waterfilled cavities. The calculated frictional shear stresses are consistent with experimental observations for temperate glaciers.

Trees record changes of the temperate glaciers on the Tibetan Plateau: Potential and uncertainty

Abstract The Tibetan Plateau and its surrounding mountains exhibit the largest concentration of glaciers at lower latitudes on earth, providing source water for the large river systems in Asia. However, glacier observations in this region are short and scarce and hence limit a better understanding of glacier behaviors under a warming climate and thereto coupled processes. The purpose of this research is to investigate the potential and the uncertainty for using pioneering trees on glacial deposits/glacier forefields as a proxy record for past glacier fluctuations in the Himalaya-Nyanqentanggula-Hengduan (H2N) area. It was found that Hippophae tibetana spent 4 years to colonize the glacier forefields at Hailuogou glacier and Pinus wallichiana germinated 11 years after glacier retreating at Gangapuna and Raikot glaciers. At deposit sites of glacier avalanche and glacial lake outburst, it took 8 years for Larix griffithii to germinate after the historical events. As shown by bootstrap resampling, the precision of the sampled maximum tree age could reach 2–14 years, which is related to the sample size to ensure the possibility of obtaining the eldest trees. However, if using the traditional sampling method at 100-cm height, errors of tree age estimation may reach up to ±20 years due to uncertainties of pith offset estimation and height-age calibration. If samples are collected with pith from ≤20 cm tree height, an error of

Microbial processes in the weathering crust aquifer of a temperate glacier

Abstract. Incident solar radiation absorbed within the ablation zone of glaciers generates a shallow perched aquifer and seasonal icebound microbial habitat. During the melt seasons of 2014 and 2015, borehole investigations were used to examine the physical, geochemical, and microbiological properties in the near-surface ice and aquifer of the temperate Matanuska Glacier (south-central Alaska). Based on temperature, solar forcing, and ice optical properties, the dissipation of shortwave radiation promoted internal melting and the formation of a weathering crust with a maximum depth of ∼2 m. Boreholes into the weathering crust provided access to water percolating through the porous ice. The water had low ion concentrations (4–12 µS cm−1), was aerobic (12 mg O2 L−1), contained 200 to 8300 cells mL−1, and harbored growing populations with estimated in situ generation times of 11 to 14 days. During the melt season, the upper 2 m of ice experienced at least 3 % of the surface photosynthetically active radiation flux and possessed a fractional water content as high as 10 %. Photosynthetic subsistence of biogeochemical reactions in the weathering crust ecosystem was supported by ex situ metabolic experiments and the presence of phototrophic taxa (cyanobacteria, golden and green algae) in the aquifer samples. Meltwater durations of ∼7.5 months coupled with the growth estimates imply biomass may increase by 4 orders of magnitude each year. Our results provide insight into how seasonal dynamics affect habitability of near-surface ice and microbial processes in a portion of the glacial biome poised to expand in extent with increasing global temperature and ablation season duration.

Direct isotopic evidence of biogenic methane production and efflux from beneath a temperate glacier

The base of glaciers and ice sheets provide environments suitable for the production of methane. High pressure conditions beneath the impermeable ‘cap’ of overlying ice promote entrapment of methane reserves that can be released to the atmosphere during ice thinning and meltwater evacuation. However, contemporary glaciers and ice sheets are rarely accounted for as methane contributors through field measurements. Here, we present direct field-based evidence of methane production and release from beneath the Icelandic glacier Sólheimajökull, where geothermal activity creates sub-oxic conditions suited to methane production and preservation along the meltwater flow path. Methane production at the glacier bed (48 tonnes per day, or 39 mM CH4 m−2 day−1), and evasion to the atmosphere from the proglacial stream (41 tonnes per day, or 32 M CH4 m−2 day−1) indicates considerable production and release to the atmosphere during the summer melt season. Isotopic signatures (−60.2‰ to −7.6‰ for δ13Cch4 and −324.3‰ to +161.1‰ for Dch4), support a biogenic signature within waters emerging from the subglacial environment. Temperate glacial methane production and release may thus be a significant and hitherto unresolved contributor of a potent greenhouse gas to the atmosphere.

Variations in the surface velocity of an alpine cirque glacier

ABSTRACTFollowing pioneering work in Norway, cirque glaciers have widely been viewed as rigidly rotating bodies. This model is incorrect for basin-filling cirque glaciers, as we have demonstrated at West Washmawapta Glacier, a small glacier in the Canadian Rocky Mountains. Here we report observations at the same glacier that assess whether complex temporal variations of flow also occur. For parts of three summers, we measured daily displacements of the glacier surface. In one year, four short-duration speed-up events were recorded. Three of the events occurred during the intervals of warmest weather, when melt was most rapid; the fourth event occurred immediately following heavy rain. We interpret the speed-up events as manifestations of enhanced water inputs to the glacier bed and associated slip lubrication by increased water volumes and pressures. No further speed-ups occurred in the final month of the melt season, despite warm temperatures and several rainstorms; the dominant subglacial water system likely transformed from one of poorly connected cavities to one with an efficient channel network. The seasonal evolution of hydrology and flow resembles behaviors documented at other, larger temperate glaciers and indicates that analyses of cirque erosion cannot rely on simple assumptions about ice dynamics.

Thermomechanical Stresses Drive Damage of Alpine Valley Rock Walls During Repeat Glacial Cycles

AbstractCycles of glaciation alter the temperature field in proximal alpine valley flanks, driving rock slope damage through thermomechanical stresses. Here we extend simplified assumptions of glacial debuttressing to quantitatively examine how paraglacial bedrock temperature changes, acting in concert with changing ice loads during Late Pleistocene and Holocene glacial cycles, create damage in adjacent rock slopes and prepare future slope instabilities. When in contact with temperate glacier ice, valley walls maintain near isothermal ~0 °C surface temperatures and are shielded from daily and annual cycles. With retreat, rock walls are rapidly exposed to strongly varying temperature boundary conditions, a transition we term “paraglacial thermal shock.” Using detailed, conceptual numerical models based on the Aletsch Glacier in Switzerland, we show that including thermomechanical stresses during simulated glacial cycles creates significantly more rock slope damage than predicted for purely mechanical ice loading and unloading. Glacier advances are especially effective in generating damage as rapid cooling drives contraction of the rock mass reducing joint normal stresses. First time exposure to annual temperature cycles during deglaciation induces a shallow damage front that follows the retreating ice margin, generating damage in a complementary process at shorter time scales. Acting on a reduced strength rock mass, modeled thermomechanical cycles enhance the development of a slope instability with similar attributes as observed in our study area. Our results demonstrate that thermomechanical stresses acting in conjunction with changing ice loads are capable of generating considerable rock slope damage with spatial and temporal patterns controlled by glacier extents.

Bacterial communities of cryoconite holes of a temperate alpine glacier show both seasonal trends and year-to-year variability

ABSTRACTCryoconite holes are small depressions of the glacier surface filled with melting water and with a wind-blown debris on the bottom. These environments are considered hot spots of biodiversity and biological activities on glaciers and host communities dominated by bacteria. Most of the studies on cryoconite holes assume that their communities are stable. However, evidence of seasonal variation in cryoconite hole ecological communities exists. We investigated the variation of the bacterial communities of cryoconite holes of Forni Glacier (Central Italian Alps) during the melting seasons (July–September) 2013 and 2016, for which samples at three and five time-points, respectively were available. Bacterial communities were characterized by high-throughput Illumina sequencing of the hypervariable V5−V6 regions of 16S rRNA gene, while meteorological data were obtained by an automatic weather station. We found consistent trends in bacterial communities, which shifted from cyanobacteria-dominated communities in July to communities dominated by heterotrophic orders in late August and September. Temperature seems also to affect seasonal dynamics of communities. We also compared bacterial communities at the beginning of the melting season across 4 years (2012, 2013, 2015 and 2016) and found significant year-to-year variability. Cryoconite hole communities on temperate glaciers are therefore not temporally stable.

Submarginal debris transport and till formation in active temperate glacier systems: The southeast Iceland type locality

Exhaustive sedimentological analysis of freshly exposed subglacial surfaces and moraines in southern Iceland provides diagnostic sedimentological signatures of: a) debris transport pathways through active temperate glacier snouts; and b) till production in subglacial traction zones dominated by deforming layers. Three till end members are recognised based on stratigraphic architecture: 1) thin and patchy tills over eroded bedrock; 2) single push moraines and complexes; and 3) overridden moraines or outwash fans. Typical till thicknesses are 0.10–1.40 m, with each till relating to a deformation event driven by the seasonally tuned processes of glacier sub-marginal shearing, freeze-on, squeezing and bulldozing. Clast form trends demonstrate progressive modification towards mature forms in subglacial traction zones with till being clearly differentiated from scree and glacifluvial deposits. Clast macrofabric strengths are variable, rarely matching those of laboratory shearing experiments, except where obviously lodged clasts are abundant. They also consistently record former glacier flow directions. But localized variability is introduced by bedrock protuberances, cavity infill, clast interference and freshly imported plucked clasts. Within tills, macrofabrics strengthen from lower (B horizon) to upper (A horizon) tills but at the outer edges of sub-marginally thickening till wedges or push moraines, seasonally-driven cycles of squeezing/flowage, freeze-on/melt-out and bulldozing give rise to a range of clast macrofabric strengths as well as superimposed deformation signatures. This reflects two extremes of till emplacement including the more mobile, flowing and often liquefied matrixes in push/squeeze moraines and, in contrast, the lodgement, deformation and ploughing at the thin end of sub-marginal till wedges.

Assimilation of ancient organic carbon by zooplankton in Tibetan Plateau lakes is depending on watershed characteristics

AbstractAncient (i.e., radiocarbon depleted) organic carbon (OC) is exported from ice sheet, glacier, and permafrost systems and may be buried, respired, or assimilated in downstream aquatic systems. Few studies have explored the potential use of this ancient OC in lake food webs. We combined natural abundance radiocarbon and stable carbon isotope data (Δ14C andδ13C) to study ancient OC utilization by zooplankton in six lakes covering a large climate gradient on the central and peripheral Tibetan Plateau. A depleted Δ14C signature of dissolved and particulate OC was found in the inflowing streams and lakes, ranging from – 49‰ to – 569‰, corresponding to radiocarbon ages between 403 yr and 6757 yr. The Δ14C values for zooplankton in the lakes ranged from – 45‰ to – 264‰, reflecting that zooplankton obtain14C‐depleted signatures through assimilation of ancient OC and/or indirectly through consumption of phytoplankton or aquatic plant utilizing14C‐depleted inorganic carbon. Moreover, ancient OC from inflowing streams contributed more to zooplankton diets in the temperate glacier area than in the cold glacier area. Assimilation of ancient OC by zooplankton in lakes is not only affected by drainage basin characteristics, such as the recharge coefficient of the lake, but also by the biogeochemical properties of OC. Use of ancient OC by zooplankton in high‐altitude lakes may constitute an important link between the contemporary aquatic food webs and the glaciated watersheds. Our findings have important implications for the contribution of ancient carbon to the modern lake food webs of high‐altitude and polar lakes.

English

The seasonal snowpack of the temperate glaciers are sources of diverse microbial inoculi. However, the microbial ecology of the tropical glacial surfaces is endangered, hence poses an extinction threat to some populations of some microbes due to rapid loss of the glacier mass. The aim of this study was to isolate and phylogenetically characterise the prokaryotes from the seasonal snow of Lewis glacier in Mt. Kenya. Snow samples were inoculated into Difco™ R2A Agar and BG-11 medium. Genomic DNA of seventeen representative axenic isolates was extracted using the mixture of MP FastDNA soil kit and the 16S rDNA gene region partially sequenced. The 16S rDNA gene sequences were blastn analyzed against the Genbank database and phylogenetic analysis was performed using MEGA 6 software. Phylogenetic analysis grouped the isolates into three phyla: Firmicutes, Proteobacteria and Actinobacteria. Isolates were affiliated with the genera Bacillus (53%), Stenotrophomonas (23.4%), Cryobacterium (5.9%), Paenibacillus (5.9%), Subtercola (5.9%) and Arthrobacter (5.9%). The results confirm that the seasonal tropical snowpack of Lewis glacier is dominated by the general terrestrial prokaryotes and a few glacier and snow specialist species. Key words: Seasonal snowpack, tropical glacier, prokaryotes, 16S rDNA.