Perennial Ice Research Articles

The Global 2000-2020 Land Cover and Land Use Change Dataset Derived From the Landsat Archive: First Results

Recent advances in Landsat archive data processing and characterization enhanced our capacity to map land cover and land use globally with higher precision, temporal frequency, and thematic detail. Here, we present the first results from a project aimed at annual multidecadal land monitoring providing critical information for tracking global progress towards sustainable development. The global 30-m spatial resolution dataset quantifies changes in forest extent and height, cropland, built-up lands, surface water, and perennial snow and ice extent from the year 2000 to 2020. Landsat Analysis Ready Data served as an input for land cover and use mapping. Each thematic product was independently derived using locally and regionally calibrated machine learning tools. Thematic maps validation using a statistical sample of reference data confirmed their high accuracy (user’s and producer’s accuracies above 85% for all land cover and land use themes, except for built-up lands). Our results revealed dramatic changes in global land cover and land use over the past 20 years. The bitemporal dataset is publicly available and serves as a first input for the global land monitoring system.

RADIOCARBON CONSTRAINTS ON PERIODS OF POSITIVE CAVE ICE MASS BALANCE DURING THE LAST MILLENNIUM, JULIAN ALPS (NW SLOVENIA)

ABSTRACTCaves containing perennial ice deposits make up a little-known, but emerging part of the cryosphere under increasing scrutiny from the scientific community. M-17, a sag-type ice cave opening at 1879 m asl in the Tolminski Migovec massif of the Julian Alps (NW Slovenia) contains a perennial underground ice deposit whose paleoclimate sensitivity is poorly understood and whose longevity under current climate change is at risk. The past mass balance of this cave is constrained using wood macro-remains embedded in ice. Accelerator mass spectrometry radiocarbon dating of 18 wood samples embedded in ice provides the largest currently available dataset for a subterranean ice deposit in the southern European Alps. The reconstructed chronostratigraphy reveals three main phases of likely positive ice balance around 900–1100 AD, 1200–1300 AD, and 1700–1800 AD, as well as a period of negative mass balance around 1300–1400 AD. The onset of cave glaciation is deemed to have occurred no later than about 900 AD, with evidence of overall positive ice mass balance during multi-decadal periods characterized by cooler-than-average summers and wetter-than-average springs. Conversely, negative mass balance is recorded during a period warmer-than-average summers and dry springs. The cave has experienced ice mass loss since its discovery in the 1980s.

Heat Shock Response of the Active Microbiome From Perennial Cave Ice.

Ice caves constitute the newly investigated frozen and secluded model habitats for evaluating the resilience of ice-entrapped microbiomes in response to climate changes. This survey identified the total and active prokaryotic and eukaryotic communities from millennium-old ice accumulated in Scarisoara cave (Romania) using Illumina shotgun sequencing of the ribosomal RNA (rRNA) and messenger RNA (mRNA)-based functional analysis of the metatranscriptome. Also, the response of active microbiome to heat shock treatment mimicking the environmental shift during ice melting was evaluated at both the taxonomic and metabolic levels. The putatively active microbial community was dominated by bacterial taxa belonging to Proteobacteria and Bacteroidetes, which are highly resilient to thermal variations, while the scarcely present archaea belonging to Methanomicrobia was majorly affected by heat shock. Among eukaryotes, the fungal rRNA community was shared between the resilient Chytridiomycota and Blastocladiomycota, and the more sensitive Ascomycota and Basidiomycota taxa. A complex microeukaryotic community highly represented by Tardigrada and Rotifera (Metazoa), Ciliophora and Cercozoa (Protozoa), and Chlorophyta (Plantae) was evidenced for the first time in this habitat. This community showed a quick reaction to heat shock, followed by a partial recovery after prolonged incubation at 4°C due to possible predation processes on the prokaryotic cluster. Analysis of mRNA differential gene expression revealed the presence of an active microbiome in the perennial ice from the Scarisoara cave and associated molecular mechanisms for coping with temperature variations by the upregulation of genes involved in enzyme recovery, energy storage, carbon and nitrogen regulation, and cell motility. This first report on the active microbiome embedded in perennial ice from caves and its response to temperature stress provided a glimpse into the impact of glaciers melting and the resilience mechanisms in this habitat, contributing to the knowledge on the functional role of active microbes in frozen environments and their response to climatic changes.

An empirical algorithm to map perennial firn aquifers and ice slabs within the Greenland Ice Sheet using satellite L-band microwave radiometry

Abstract. Perennial firn aquifers are subsurface meltwater reservoirs consisting of a meters-thick water-saturated firn layer that can form on spatial scales as large as tens of kilometers. They have been observed within the percolation facies of glaciated regions experiencing intense seasonal surface melting and high snow accumulation. Widespread perennial firn aquifers have been identified within the Greenland Ice Sheet (GrIS) via field expeditions, airborne ice-penetrating radar surveys, and satellite microwave sensors. In contrast, ice slabs are nearly continuous ice layers that can also form on spatial scales as large as tens of kilometers as a result of surface and subsurface water-saturated snow and firn layers sequentially refreezing following multiple melting seasons. They have been observed within the percolation facies of glaciated regions experiencing intense seasonal surface melting but in areas where snow accumulation is at least 25 % lower as compared to perennial firn aquifer areas. Widespread ice slabs have recently been identified within the GrIS via field expeditions and airborne ice-penetrating radar surveys, specifically in areas where perennial firn aquifers typically do not form. However, ice slabs have yet to be identified from space. Together, these two ice sheet features represent distinct, but related, sub-facies within the broader percolation facies of the GrIS that can be defined primarily by differences in snow accumulation, which influences the englacial hydrology and thermal characteristics of firn layers at depth. Here, for the first time, we use enhanced-resolution vertically polarized L-band brightness temperature (TVB) imagery (2015–2019) generated using observations collected over the GrIS by NASA's Soil Moisture Active Passive (SMAP) satellite to map perennial firn aquifer and ice slab areas together as a continuous englacial hydrological system. We use an empirical algorithm previously developed to map the extent of Greenland's perennial firn aquifers via fitting exponentially decreasing temporal L-band signatures to a set of sigmoidal curves. This algorithm is recalibrated to also map the extent of ice slab areas using airborne ice-penetrating radar surveys collected by NASA's Operation IceBridge (OIB) campaigns (2010–2017). Our SMAP-derived maps show that between 2015 and 2019, perennial firn aquifer areas extended over 64 000 km2, and ice slab areas extended over 76 000 km2. Combined together, these sub-facies are the equivalent of 24 % of the percolation facies of the GrIS. As Greenland's climate continues to warm, seasonal surface melting will increase in extent, intensity, and duration. Quantifying the possible rapid expansion of these sub-facies using satellite L-band microwave radiometry has significant implications for understanding ice-sheet-wide variability in englacial hydrology that may drive meltwater-induced hydrofracturing and accelerated ice flow as well as high-elevation meltwater runoff that can impact the mass balance and stability of the GrIS.

The tale of an ice-preserved Alpine Long-Eared Bat in the Pyrenees

The Alpine Long-eared Bat Plecotus macrobullaris (Kuzjakin, 1965) is a relatively recently defined species and one of the few bats able to occupy the high-mountain environment. The phylogenetic studies of this species suggest that it originated before the Middle Pleistocene. However, it has never been reported in ancient chronologies, no fossils are known, and the older recognized specimens are those from museum collections. One of the main reasons for this lack of ancient and fossil record is that the skeletal anatomy of this species has not been described in detail yet, making difficult the correct assignation of skeletal remains. We present a Long-eared Bat individual that was ice-preserved within the perennial ice in a high-mountain ice cave, SO-01, in the Pyrenees. The bat skin was radiocarbon dated, pointing that the specimen died more likely in a timeframe between 1760 and 1800 AD. Following previously published criteria based on cranial diagnostic features the recovered specimen was assigned to P. macrobullaris, which represents the most ancient record of this species in the Pyrenees and probably worldwide. In addition, some new observations have been described on both cranial and postcranial anatomical traits.

Thyroid-Mediated Metabolic Differences Underlie Ecological Specialization of Extremophile Salmonids in the Arctic Lake El’gygytgyn

El’gygytgyn, the only “ancient lake” in the Arctic (3.6 MY), is a deep (176 m) and extremely cold (always ≤ 4°C) waterbody inhabited by unique salmonids, which colonized the ecosystem stepwise during the global fluctuations of the Quaternary climate. The descendant of the first-wave-invaders (long-finned charr) dwells in the deep waters and feeds on amphipods. The second-wave-invaders (smallmouth charr) consume copepods in the mid-waters. Recent third-wave-invaders (Boganida charr) are spread throughout the ecosystem and feed on insects when they are young shifting to piscivory at an older age. Here, we present the data on the charrs’ thyroid status and metabolic characteristics, confirming their ecological specialization. The long-finned charr exhibits an extremely low thyroid content, the substitution of carbohydrates for lipids in the cellular respiration, an increased hemoglobin level and a high antioxidant blood capacity. These traits are likely to be the legacy of anaerobic survival under perennial ice cover during several Quaternary glaciations. Moderate thyroid status and reduced metabolic rate of the smallmouth charr, along with an inactive lifestyle, could be regarded as a specialization to saving energy under the low food supply in the water column. The piscivorous Boganida charr could be sub-divided into shallow-water and deep-water groups. The former demonstrates a significantly elevated thyroid status and increased metabolism. The latter is characterized by a reduced thyroid level, metabolic rate, and lipid accumulation. Thus, the endemic El’gygytgyn charrs represent a wide spectrum of contrast physiological adaptation patterns essential to survive in sympatry under extremely cold conditions.

The influence of snow on sea ice as assessed from simulations of CESM2

Abstract. We assess the influence of snow on sea ice in experiments using the Community Earth System Model version 2 for a preindustrial and a 2xCO2 climate state. In the preindustrial climate, we find that increasing simulated snow accumulation on sea ice results in thicker sea ice and a cooler climate in both hemispheres. The sea ice mass budget response differs fundamentally between the two hemispheres. In the Arctic, increasing snow results in a decrease in both congelation sea ice growth and surface sea ice melt due to the snow's impact on conductive heat transfer and albedo, respectively. These factors dominate in regions of perennial ice but have a smaller influence in seasonal ice areas. Overall, the mass budget changes lead to a reduced amplitude in the annual cycle of ice thickness. In the Antarctic, with increasing snow, ice growth increases due to snow–ice formation and is balanced by larger basal ice melt, which primarily occurs in regions of seasonal ice. In a warmer 2xCO2 climate, the Arctic sea ice sensitivity to snow depth is small and reduced relative to that of the preindustrial climate. In contrast, in the Antarctic, the sensitivity to snow on sea ice in the 2xCO2 climate is qualitatively similar to the sensitivity in the preindustrial climate. These results underscore the importance of accurately representing snow accumulation on sea ice in coupled Earth system models due to its impact on a number of competing processes and feedbacks that affect the melt and growth of sea ice.

A sedimentary record from the Makarov Basin, Arctic Ocean, reveals changing middle to Late Pleistocene glaciation patterns

Sediment core ARC5-ICE6 from the Makarov Basin was used to reconstruct circum-Arctic glaciation and surface-ocean circulation history for the Middle to Late Pleistocene, ∼0.5–0.7 Ma. Sedimentary proxies include elemental composition, coarse grain content, clay mineralogy, and radiogenic isotopes (Sr-Nd-Pb). Earlier studied records from the central Arctic Ocean were compared with ICE6 for a broader paleoceanographic context. Results indicate predominant sediment delivery from the Eurasian shelves and glaciated mainland with intermittent glacial inputs from North America. Low proxy variability prior to Marine Isotope Stage (MIS) 6 (∼0.2 Ma) suggests persistent sediment transport by sea ice via the Transpolar Drift and limited glaciation at the Eurasian margin. Since MIS 6, sediment inputs and provenance exhibit large shifts between glacial- and interglacial-type environments. The overall northern Eurasian Ice Sheet (EAIS) expansion was possibly related to climatic cooling and growth of a perennial sea ice in the Arctic Ocean. Provenance indicators from MIS 6, 5b and 4/3 reflect EAIS expansions followed by deglacial meltwater discharge from west Siberia. This provenance indicates a strong cyclonic circulation in the Arctic Ocean characterized by a significantly eastward-extended Transpolar Drift. Different glaciogenic sourcing and attendant circulation are proposed for several events within MIS 5 and 3, where proxies indicate increased sediment inputs from North America rather than Eurasian ice sheets. Overall limited glacial influence inferred for MIS 3 is consistent with relatively high sea level reconstructed for this interstadial. The Last Glacial Maximum is barely identifiable in the ICE6 record due to low glacial inputs and/or depositional hiatus.

First Observations of a Transient Polynya in the Last Ice Area North of Ellesmere Island

AbstractThe area to the north of Ellesmere Island and Greenland contains the Arctic's thickest ice and it is predicted to be the last to lose its perennial ice, thus providing an important refuge for ice‐dependent species. There is however evidence that this Last Ice Area is, like the entire Arctic, undergoing rapid changes that may reduce its suitability as a refuge. During May 2020, a polynya developed to the north of Ellesmere Island in a region where there are no reports of a previous development. We use a variety of remotely sensed data as well as an atmospheric reanalysis to document the evolution and the dynamics responsible for the polynya. In particular, we argue that anomalously strong divergent winds associated with an intense and long‐lived Arctic anti‐cyclone contributed to the development of the polynya as well as similar previously unreported events in May 1988 and 2004.

What Antarctic Plants Can Tell Us about Climate Changes: Temperature as a Driver for Metabolic Reprogramming.

Global warming is strongly affecting the maritime Antarctica climate and the consequent melting of perennial snow and ice covers resulted in increased colonization by plants. Colobanthus quitensis is a vascular plant highly adapted to the harsh environmental conditions of Antarctic Peninsula and understanding how the plant is responding to global warming is a new challenging target for modern cell physiology. To this aim, we performed differential proteomic analysis on C. quitensis plants grown in natural conditions compared to plants grown for one year inside open top chambers (OTCs) which determine an increase of about 4 °C at midday, mimicking the effect of global warming. A thorough analysis of the up- and downregulated proteins highlighted an extensive metabolism reprogramming leading to enhanced photoprotection and oxidative stress control as well as reduced content of cell wall components. Overall, OTCs growth seems to be advantageous for C. quitensis plants which could benefit from a better CO2 diffusion into the mesophyll and a reduced ROS-mediated photodamage.

Archaeal lipids reveal climate‐driven changes in microbial ecology at Lake El'gygytgyn (Far East Russia) during the Plio‐Pleistocene

ABSTRACTIsoprenoid glycerol dialkyl glycerol tetraethers (iGDGTs) are commonly preserved molecular biomarkers of archaea whose distributions can be used to reconstruct past temperature, and possibly, methane and nitrogen cycling. To date, iGDGT systematics have not been widely investigated in Arctic lacustrine environments. Here, we analyze iGDGTs in sediments of Lake El'gygytgyn, located in the Russian Arctic, to reconstruct the paleoenvironmental conditions from the Pliocene to today using TEX86 and other indices. The TEX86‐inferred temperature history shows a long‐term warming trend, in stark contrast to other Arctic records and other proxies from Lake El'gygytgyn, suggesting that non‐temperature factors obfuscate the use of TEX86 at this site. Other GDGT‐based indices including the BIT Index, ΔRing Index, Methane Index and the GDGT‐0/crenarchaeol ratio suggest that TEX86 is strongly influenced by archaeal community changes. The most significant community shifts are observed c. 2.4 Ma and record an increase in Euryarchaeota production and/or a decrease in Thaumarchaeota production, which was driven by the establishment of permafrost and perennial lake ice during the early Pleistocene. Overall, this study demonstrates an important interpretative framework for iGDGTs in lacustrine systems and describes variations in Arctic climate and lake biogeochemistry over timescales of thousands to millions of years.

Upper ocean variability off NE Greenland (79°N) since the last glacial maximum reconstructed from stable isotopes in planktic foraminifer morphotypes

We report on stable oxygen and carbon isotope data obtained on two different morphotypes of polar planktic foraminifers, i.e., fully encrusted and minor encrusted Neogloboquadrina pachyderma, from a sediment core taken on the NE Greenland continental margin. These morphotypes are supposed to live at different water depths of the upper water column in the area which today is strongly stratified, with a low-saline, cold-water layer at the surface. The paired isotopic data sets inform on temporal variations of past water salinity and temperature in the preferred water depth ranges of the investigated morphotypes and allow conclusions on the stratification of the upper water column. The radiocarbon-dated sediment core covers the time interval from 21 to 4 cal-ka, but the early part of the deglacial interval (18.5–12.7 cal-ka) is not represented, probably due to intense erosion by bottom currents. In sediments from the late last glacial maximum, oxygen isotope differences between thin-shelled and thick-shelled N. pachyderma are low and point at a weaker stratification with less freshwater than today near the surface. The carbon isotopes indicate a dense, perennial sea ice cover, very limited bioproduction, and the presence of a subsurface Atlantic Water layer. In the late deglaciation until ∼10.3 cal-ka, the stable isotope values of both analyzed morphotypes are considerably lower, with significantly stronger amplitudes in the record of thin-shelled specimens than later on. The high-amplitude record stems from a laminated sediment sequence whose older part was deposited within just a few decades. The data are evidence of a strong freshwater event in the research area that probably started before 12.7 ka and may have reduced sea surface salinities by 4–5 practical salinity units. As freshwater sources we discuss both the disintegration of NE Greenland shelf ice and export from the Arctic Ocean interior. The event may have contributed to the weakening of the Atlantic meridional overturning circulation during the Younger Dryas cold event. For the early and mid-Holocene (10-4 cal-ka), the isotope data suggest a structure of the upper water column similar to today, with a well-developed halocline separating low-saline near-surface waters from the underlying Atlantic Water layer. A seasonally disintegrated sea ice cover allowed for a considerable planktic bioproduction.

Thinner Sea Ice Contribution to the Remarkable Polynya Formation North of Greenland in August 2018

In August 2018, a remarkable polynya was observed off the north coast of Greenland, a perennial ice zone where thick sea ice cover persists. In order to investigate the formation process of this polynya, satellite observations, a coupled ice-ocean model, ocean profiling data, and atmosphere reanalysis data were applied. We found that the thinnest sea ice cover in August since 1978 (mean value of 1.1 m, compared to the average value of 2.8 m during 1978−2017) and the modest southerly wind caused by a positive North Atlantic Oscillation (mean value of 0.82, compared to the climatological value of −0.02) were responsible for the formation and maintenance of this polynya. The opening mechanism of this polynya differs from the one formed in February 2018 in the same area caused by persistent anomalously high wind. Sea ice drift patterns have become more responsive to the atmospheric forcing due to thinning of sea ice cover in this region.

Achievements and Developing Suggestions of Sinopec’s Drilling Technologies in Arctic Sea

The Arctic area is rich in oil and gas resources. However, its geological and environmental factors such as low temperature, shallow hazards, permafrost and extreme temperature change in wellbore bring many challenges to drilling operation. For this reason, during the Thirteenth Five-Year Plan period, Sinopec took safety, environmental protection and efficient drilling as its overall goals and focused on solving the problem of cold adaptability of drilling equipments and tools, drilling technologies and measures, wellbore working fluids. Research was performed on key technologies regarding drilling hazard assessment and control, environmental protection, key drilling equipments and tools, drilling techniques, wellbore working fluids, etc. Impressive progresses were made in the quantitative risk assessment method for hazards to shallow gas and gas hydrate formations, the orbital drilling rigs and tools utilized at −50 °C, stability evaluation and borehole stability control in permafrost, and engineering technologies related to drilling fluid and cement slurry under low temperature conditions. As a result, the key technology system of drilling in the Arctic sea was preliminarily developed. As the Arctic oil and gas development enters higher latitudes and thicker permafrost regions on land, and the oceans will advance to deeper waters, perennial ice or thicker ice floes, drilling in Arctic sea will face greater challenges and requires further progress. Therefore, it is necessary to build a complete drilling and completion technology system in the Arctic sea by improving the theories and methods and developing new key equipments and tools. With the system, the demands of efficient exploration and development of oil and gas reservoirs in the Arctic region can be realized, thereby enhancing the economic benefits and core competitiveness of China’s oil companies in international cooperation projects of oil and gas development in this area.

On the Origin of Discrepancies Between Observed and Simulated Memory of Arctic Sea Ice

AbstractTo investigate the inherent predictability of sea ice and its representation in climate models, we compare the seasonal‐to‐interannual memory of Arctic sea ice as given by lagged correlations of sea‐ice area anomalies in large model ensembles (Max Planck Institute Grand Ensemble and Coupled Model Intercomparison Project phase 6) and multiple observational products. We find that state‐of‐the‐art climate models significantly overestimate the memory of pan‐Arctic sea‐ice area from the summer months into the following year. This cannot be explained by internal variability. We further show that the observed summer memory can be disentangled regionally into a reemergence of positive correlations in the perennial ice zone and negative correlations in the seasonal ice zone; the latter giving rise to the discrepancy between observations and model simulations. These findings could explain some of the predictability gap between potential and operational forecast skill of Arctic sea‐ice area identified in previous studies.

Record summer rains in 2019 led to massive loss of surface and cave ice in SE Europe

Abstract. Glaciers worldwide are shrinking at an accelerated rate as the climate changes in response to anthropogenic influence. While increasing air temperature is the main factor behind glacier mass and volume loss, variable patterns of precipitation distribution also play a role, though these are not as well understood. Furthermore, while the response of surface glaciers (from large polar ice sheets to small alpine glaciers) to climatic changes is well documented and continuously monitored, little to nothing is known about how cave glaciers (perennial ice accumulations in rock-hosted caves) react to atmospheric warming. In this context, we present here the response of cave and surface glaciers in SE Europe to the extreme precipitation events occurring between May and July 2019 in SE Europe. Surface glaciers in the northern Balkan Peninsula lost between 17 % and 19 % of their total area, while cave glaciers in Croatia, Greece, Romania and Slovenia lost ice at levels higher than any recorded by instrumental observations during the past decades. The melting was likely the result of large amounts of warm water delivered directly to the surface of the glaciers, leading to rapid reduction in the area of surface glaciers and the thickness of cave glaciers. As climate models predict that such extreme precipitation events are set to increase in frequency and intensity, the presence of cave glaciers in SE Europe and the paleoclimatic information they host may be lost in the near future. Moreover, the same projected continuous warming and increase in precipitation extremes could pose an additional threat to the alpine glaciers in southern Europe, resulting in faster-than-predicted melting.

Latest Holocene paleoenvironmental and paleoclimate reconstruction from an alpine bog in the Western Mediterranean region: The Borreguil de los Lavaderos de la Reina record (Sierra Nevada)

Several organic and inorganic geochemical analyses have been carried out in the sedimentary record of the Borreguil de los Lavaderos de la Reina (BdlR-03), an alpine peat bog located on the north face of the Sierra Nevada (southern Iberian Peninsula). This study permitted a high-resolution reconstruction of paleoenvironmental evolution for the last ~2700 cal yr BP in the highest mountain range of southern Iberian Peninsula. An overall trend towards a climatic aridification and a reduction of aquatic environments is observed in this record. Insolation and long-term positive North Atlantic Oscillation trends were the most important factors controlling this aridification, forcing regional and local environmental changes. Four phases are differentiated within the paleoenvironmental evolution of BdlR-03: (1) a pre-bog environment from 2700 to 2600 cal yr BP with important siliciclastic sedimentation and low organic content; (2) a bog environment with important presence of terrestrial vascular plant, water availability and maximum humid conditions between ~2600 and ~1870 cal yr BP, coinciding with the Iberian-Roman Humid Period; (3) a subsequent drier bog environment, between ~1870 and ~300 cal yr BP during the Dark Ages, the Medieval Climate Anomaly and the first stages of the Little Ice Age, characterized by lower productivity that affected the development of terrestrial vascular plants and aquatic environments; and (4) a wetland environment with an increase of aquatic algae, development of ephemeral pools and unstable climate conditions between ~300 cal yr BP and the present, coinciding with the final stages of the Little Ice Age and the Modern Global Warming. This recent environmental pattern, which is opposite to the general aridification trend in the western Mediterranean, is likely explained by the gradual melting of the perennial ice and/or snow packs at higher elevations in the last centuries. Aeolian inputs would have continuously contributed nutrients to these nutrient-impoverished alpine environments. High dust inputs are especially noticed during the last ~200 years, which can be explained by human-induced enhanced aridification and the development of the commercial agriculture in some North African regions. In addition, the environmental signal in the last century seems to be significantly affected by human activities.

Late Quaternary paleoceanographic history based on ostracode records from the Chukchi Plateau, western Arctic Ocean

Fossil ostracode assemblages were investigated in three sediment cores from the Chukchi Plateau, in the western Arctic Ocean, in order to reconstruct its late Quaternary paleoceanographic history. The cores were obtained from water depths of 435–741 m, within the range of modern Atlantic Water (AW). The ostracode abundance shows distinct glacial/interglacial fluctuations, suggesting the suppression of benthic bioproductivity during glacial periods, probably associated with the development of perennial sea ice. Based on the modern ostracode distribution in the Arctic Ocean, 11 common ostracode taxa out of a total of 33 are related to specific water mass or sea ice conditions. Analyses of key ostracode species and a benthic foraminifera species, Cassidulina teretis, reveal a pronounced faunal turnover between MIS 3 and MIS 1. A distinct assemblage dominated by Polycope spp. and accompanied by other species preferring Arctic Intermediate Water (AIW) (Microcythere medistriatum, Pseudocythere caudata, Cytheropteron sedovi, C. scoresbyi, and Pedicythere spp.) characterizes the period between late MIS 5 and MIS 3, whereas MIS 1 is characterized by a rise in Krithe spp. and two species associated with AW (Cytheropteron perlaria and Cassidulina teretis). The faunal turnover indicates an upward shift of AIW and a decline of the influence of warm AW during the period between late MIS 5 and MIS 3, presumably caused by a weakening or cessation of the westward dispersion of AW. The distributions of two sea-ice related species, Acetabulastoma arcticum and Rabilimis mirabilis, indicate minimal perennial sea-ice cover and probably summer sea-ice-free conditions throughout MIS 1 and the development of a summer sea-ice margin environment during interglacial/interstadial periods.

Cryogenic cave carbonate and implications for thawing permafrost at Winter Wonderland Cave, Utah, USA

Winter Wonderland Cave contains perennial ice associated with two types of cryogenic cave carbonate (CCC) formed during the freezing of water. CCCfine is characterized by relatively high δ13C values, whereas CCCcoarse exhibits notably low δ18O values indicating precipitation under (semi)closed-system conditions in a pool of residual water beneath an ice lid. Previous work has concluded that CCCcoarse forms during permafrost thaw, making the presence of this precipitate a valuable indicator of past cryospheric change. Available geochronologic evidence indicates that CCC formation in this cave is a Late Holocene or contemporary process, and field observations suggest that the cave thermal regime recently changed in a manner that permits the ingress of liquid water. This is the first documented occurence of CCCcoarse in the Western Hemisphere and one of only a few locations where these minerals have been found in association with ice. Winter Wonderland Cave is a natural laboratory for studying CCC genesis.

First investigation of perennial ice in Winter Wonderland Cave, Uinta Mountains, Utah, USA

Abstract. Winter Wonderland Cave is a solution cave at an elevation of 3140 m above sea level in Carboniferous-age Madison Limestone on the southern slope of the Uinta Mountains (Utah, USA). Temperature data loggers reveal that the mean annual air temperature (MAAT) in the main part of the cave is −0.8 ∘C, whereas the entrance chamber has a MAAT of −2.3 ∘C. In contrast, the MAAT outside the cave entrance was +2.8 ∘C between August 2016 and August 2018. Temperatures in excess of 0 ∘C were not recorded inside the cave during that 2-year interval. About half of the accessible cave, which has a mapped length of 245 m, is floored by perennial ice. Field and laboratory investigations were conducted to determine the age and origin of this ice and its possible paleoclimate significance. Ground-penetrating-radar (GPR) surveys with a 400 MHz antenna reveal that the ice has a maximum thickness of ∼ 3 m. Samples of rodent droppings obtained from an intermediate depth within the ice yielded radiocarbon ages from 40±30 to 285±12 years. These results correspond with median calibrated ages from CE 1560 to 1830, suggesting that at least some of the ice accumulated during the Little Ice Age. Samples collected from a ∼ 2 m high exposure of layered ice were analyzed for stable isotopes and glaciochemistry. Most values of δ18O and δD plot subparallel to the global meteoric waterline with a slope of 7.5 and an intercept of 0.03 ‰. Values from some individual layers depart from the local waterline, suggesting that they formed during closed-system freezing. In general, values of both δ18O and δD are lowest in the deepest ice and highest at the top. This trend is interpreted as a shift in the relative abundance of winter and summer precipitation over time. Calcium has the highest average abundance of cations detectable in the ice (mean of 6050 ppb), followed by Al (2270 ppb), Mg (830 ppb), and K (690 ppb). Most elements are more abundant in the younger ice, possibly reflecting reduced rates of infiltration that prolonged water–rock contact in the epikarst. Abundances of Al and Ni likely reflect eolian dust incorporated in the ice. Liquid water appeared in the cave in August 2018 and August 2019, apparently for the first time in many years. This could be a sign of a recent change in the cave environment.