The latent (LHF) and sensible (SHF) heat fluxes are key components of the surface mass and energy balance in the accumulation area of the Greenland Ice Sheet, making them critical for accurate sea level projections. While Eddy-Covariance (EC) systems provide accurate measurements of the turbulent surface transport of mass and energy in the low and mid-latitudes, frequent stable boundary layer conditions in polar regions introduce uncertainties in the EC method. In addition, as EC measurements are sparse, it is critical to characterise biases in the more common bulk fluxes obtained from automatic weather stations and climate models in polar areas. In this study, we present an intercomparison of three independent EC systems from the 28 May until 31 July 2019 at the EastGRIP site at similar to 2700 m a.s.l. on the Greenland Ice Sheet to assess the accuracy of LHF and SHF measurements. A comparison of the fluxes by the three systems demonstrates excellent agreement with an absolute bias of 0.2 W m-2 and slopes between 1.01 and 1.16 for the LHF, and an absolute bias of less than 0.5Wm-2 and slopes of 1.0 for the SHF. A comparison of the validated EC fluxes against the bulk method highlights the sensitivity to the site-specific roughness length z0,m and the limitation of common parameterisations of the humidity and temperature roughness lengths z0,q and z0,t. Using improved values for z0,m, z0,q and z0,t, recomputed bulk fluxes are compared to fluxes simulated by regional climate models MAR, RACMO2.3p2 and RACMO2.4p1 for the period from 2016 to 2020. We find an overall good agreement between the measured and modelled turbulent flux magnitudes for the summer period; however, all evaluated models simulate stronger near-surface temperature gradients during winter compared to observations from automatic weather stations, leading to consistently larger modelled SHF and LHF values in winter.

Greenland's ongoing deglaciation and thawing permafrost, accompanied by an increase in ice sheet freshwater discharge and nutrient export, are significantly impacting the surrounding fjords and marine ecosystems. Understanding the geochemical linkages between ice, land, and marine environments is crucial for comprehending the effects of amplified cryosphere‐biosphere interactions on marine ecosystems. To assess dissolved organic carbon (DOC) geochemistry along Greenland's west coast, we characterized and collected water samples at twelve near‐shore stations, at depths of 5 and 50 m, in four key areas: Nuuk, Davis Strait, Disko Bay, and the Uummannaq fjord system, focusing on DOC as it represents the largest pool of organic carbon in the ocean. Analysis of DOC concentration, molecular composition, 13 C, and 14 C alongside measurements of water temperature, salinity, and stable isotopic composition, revealed that: (a) water masses were predominantly ocean water, albeit with substantial freshwater components, particularly in the most glaciated region. (b) DOC ages range from approximately 1,589 to 2,450 cal BP. (c) Despite exhibiting the greatest freshening, the Uummannaq fjord system surprisingly contained the oldest DOC among all sites. This unexpected observation is postulated to be linked to inputs of ancient carbon from discharge from marine‐terminating glaciers. Our findings underscore the potential influence of spatially heterogeneous inputs of new terrestrial sources of DOC, particularly ancient permafrost‐derived carbon, to the Arctic carbon cycle especially as glacial melt intensifies in the future. Furthermore, our study provides valuable insights into the age and composition of DOC exported from west Greenland into the adjoining marine system.

Atmospheric rivers are transient channels of intense water vapor that account for up to 90% of the poleward moisture transport from mid-latitudes. Though short-lived, these events can deliver extreme amounts of heat and rainfall that have been widely reported to accelerate ablation and ice mass loss across the Arctic. However, the impact of atmospheric river fueled snowfall has received less attention, partly due to the limited availability of empirical evidence and direct observations. Here, we explore the potential of atmospheric rivers to deliver intense snowfall to the Greenland ice sheet and thereby replenish its health through enhanced mass accumulation. Specifically, we use new firn-core isotopic analyses and glacio-meteorological datasets from Southeast Greenland to examine the origin and impact of atmospheric rivers on regional mass balance. To this end, we sampled firn core stratigraphy from the upper accumulation area of Southeast Greenland and related it to meteorological observations, to demonstrate that an intense atmospheric river in mid-March 2022 delivered up to 11.6 gigatons per day of extreme snowfall to this region of the ice sheet. We show that this immense snowfall not only recharged the snowpack and offset Greenland ice sheet net mass loss by 8% in 2022, but also raised local albedo thereby delaying the onset of summer bare-ice melt by 11 days, despite warmer than average spring temperatures. Since 2010, synoptic analysis of ERA5 data reveals that snow accumulation across Southeast Greenland increased by 20 mm water equivalent per year, driven by enhanced Atlantic cyclonicity. Depending on their seasonal timing, our study demonstrates that the impact of atmospheric rivers on the mass balance of the Greenland ice sheet is not exclusively negative. Moreover, their capacity to contribute consequential ice mass recharge may become increasingly significant under ongoing Arctic amplification and predicted poleward intrusion of mid-latitude moisture.

Mixed-phase clouds are integral to the Arctic climate system as they regulate the energy transport to and from the surface. Their ice content, which influences the cloud's optical and physical properties, is regulated by the presence of ice nucleating particles (INP). Despite this, knowledge of the sources and concentrations of INP in the Arctic is notably lacking. Here, we investigate the abundance and variability of fluorescent primary biological aerosol particles (fPBAP) within cloud residuals at a key site at 79° North over an entire year. fPBAP have been found to be active INP at warmer temperatures. Samples were continuously collected using a multiparameter bioaerosol spectrometer coupled to a ground-based counterflow virtual impactor inlet at the Zeppelin Observatory in Ny-Ålesund, Svalbard. We found that fPBAP concentrations within cloud residuals closely aligned with the expected concentration of high-temperature INP. Transmission electron microscopy confirmed the presence of fPBAP, likely bacteria, in the cloud residual samples. Seasonal analysis demonstrated a higher presence of fPBAP within cloud residuals over the summer, with water vapor isotope measurements revealing a connection between summer cloud formation and regionally sourced air masses. Low-level MPC were predominantly observed at the beginning and end of summer, possibly due to the presence of high-temperature INP. Our study - currently under interactive discussion* - provides observational evidence supporting the role of fPBAP in determining the phase of low-level Arctic clouds, with implications for the composition of respective cloud condensation nuclei sources in the future under rapid Arctic climate and environmental change.*Pereira Freitas, G., Kopec, B., Adachi, K., Krejci, R., Heslin-Rees, D., Yttri, K. E., Hubbard, A., Welker, J. M., and Zieger, P. 2023: Contribution of fluorescent primary biological aerosol particles to low-level Arctic cloud residuals, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2023-2600.

Atmospheric rivers (ARs) have been linked with extreme rainfall and melt events across the Greenland ice sheet (GrIS), accelerating its mass loss. However, the impact of AR‐fueled snowfall has received less attention, partly due to limited empirical evidence. Here, we relate new firn core stratigraphy and isotopic analyses with glacio‐meteorological data sets from SE Greenland to examine an intense AR in mid‐March 2022. We demonstrate that the associated snowfall—up to 11.6 gigatons d −1 —delayed summer melt onset by11‐days and offset Greenland's 2022 net mass loss by 8%. Since 2010, our synoptic analysis reveals that snow accumulation across SE Greenland increased by 20 mm water equivalent a −1 , driven by enhanced Atlantic cyclonicity. We find that the impact of ARs on the GrIS is not exclusively negative and their capacity to contribute mass recharge may become increasingly significant under ongoing Arctic amplification and predicted poleward intrusion of mid‐latitude moisture.

Multiple ice age cycles spanning the last three million years have fundamentally transformed the Arctic landscape. The cadence and intensity of this glacial modification underpin the stability of Arctic geosystems over geologic time scales, including its hydrology, circulation patterns, slope stability, hydrocarbon fluid flow, geochemical/sediment cycling and nutrient supply. The Barents Shelf provides a unique arena to investigate long-term landscape evolution as it has undergone significant glacial modification during the Quaternary and has an extensive stratigraphic data repository motivated by decades of hydrocarbon seismic and well exploration. Here, we assimilate new geological datasets with ice sheet erosion modelling to incrementally reconstruct the geomorphic evolution of the Eurasian Arctic domain over each of the 47 glaciations since the intensification of Northern Hemisphere glaciation -2.74 Ma. We utilise this time-transgressive framework to review hypotheses regarding the heterogenous development of the Barents Shelf and the timing of key topographic reconfiguration episodes. Our results demonstrate that up to 2.6 km of bedrock was glacially removed to the shelf margins, and though the mean rate of erosion declines over the Quaternary, the efficacy of glacial erosion has a more complex timeline. Initially, erosion was highly effective as large expanses of the Eurasian Arctic switched from subaerial exposure to marine conditions around 2 Ma. Thereafter, erosional efficacy decreased as the landscape desensitised to successive glaciations but, after 1 Ma, it increased as a dynamic, marine-based ice sheet drained by ice streams expanded, selectively eroding large outlet troughs to the shelf edge. Critically for Arctic climate, at -0.69 Ma this episode of enhanced preferential erosion opened up the Barents Seaway establishing a new circulation pathway between the Atlantic and Arctic Oceans. Our 4D landscape reconstruction provides key boundary conditions for paleoclimate models and establishes a new framework for assessing the profound impact of late-Cenozoic glaciation on the Eurasian Arctic landscape.

Mixed-phase clouds (MPCs) are key players in the Arctic climate system due to their role in modulating solar and terrestrial radiation. Such radiative interactions rely, among other factors, on the ice content of MPCs, which is regulated by the availability of ice-nucleating particles (INPs). While it appears that INPs are associated with the presence of primary biological aerosol particles (PBAPs) in the Arctic, the nuances of the processes and patterns of INPs and their association with clouds and moisture sources have not been resolved. Here, we investigated for a full year the abundance of and variability in fluorescent PBAPs (fPBAPs) within cloud residuals, directly sampled by a multiparameter bioaerosol spectrometer coupled to a ground-based counterflow virtual impactor inlet at the Zeppelin Observatory (475 m a.s.l.) in Ny-Ålesund, Svalbard. fPBAP concentrations (10−3–10−2 L−1) and contributions to coarse-mode cloud residuals (0.1 to 1 in every 103 particles) were found to be close to those expected for high-temperature INPs. Transmission electron microscopy confirmed the presence of PBAPs, most likely bacteria, within one cloud residual sample. Seasonally, our results reveal an elevated presence of fPBAPs within cloud residuals in summer. Parallel water vapor isotope measurements point towards a link between summer clouds and regionally sourced air masses. Low-level MPCs were predominantly observed at the beginning and end of summer, and one explanation for their presence is the existence of high-temperature INPs. In this study, we present direct observational evidence that fPBAPs may play an important role in determining the phase of low-level Arctic clouds. These findings have potential implications for the future description of sources of ice nuclei given ongoing changes in the hydrological and biogeochemical cycles that will influence the PBAP flux in and towards the Arctic.

The Arctic Ocean and adjacent seas are undergoing increased freshwater influx due to enhanced glacial and sea ice melt, precipitation, and runoff. Accurate delineation of these freshwater sources is vital as they critically modulate ocean composition and circulation with widespread and varied impacts. Despite this, the delineation of freshwater sources using physical oceanographic measurements (e.g., temperature, salinity) alone is challenging and there is a requirement to improve the partitioning of ocean water masses and their mixing relationships. Here, we complement traditional oceanographic measurements with continuous surface seawater isotopic analysis (delta 18O and deuterium excess) across a transect extending from coastal Alaska to Baffin Bay and the Labrador Sea conducted from the US Coast Guard Cutter Healy in Autumn 2021. We find that the diverse isotopic signatures of Arctic freshwater sources, coupled with the high freshwater proportion in these marine systems, facilitates detailed fingerprinting and partitioning. We observe the highest freshwater composition in the Beaufort Sea and Amundsen Gulf regions, with heightened freshwater content in eastern Baffin Bay adjacent to West Greenland. We apply isotopic analysis to delineate freshwater sources, revealing that in the Western Arctic freshwater inputs are dominated by meteoric water inputs-specifically the Mackenzie River-with a smaller sea ice meltwater component and in Baffin Bay the primary sources are local precipitation and glacial meltwater discharge. We demonstrate that such freshwater partitioning cannot be achieved using temperature-salinity relationships alone, and highlight the potential of seawater isotopic tracers to assess the roles and importance of these evolving freshwater sources. Freshwater inputs to the Arctic seas, including glacial and sea ice meltwater, precipitation, and river runoff, are increasing as the Arctic warms. The impacts of these changing freshwater influxes are varied depending on the type of freshwater source, and thus it is important to delineate and trace these different freshwater sources, which represents a significant challenge using only traditional physical oceanographic measurements (e.g., temperature, salinity). In this study, we utilize a new approach to identify and trace freshwater sources using continuous seawater isotopic measurements during a cruise extending from coastal Alaska, through the Canadian Archipelago, and across Baffin Bay and the Labrador Sea. We show that these isotopic measurements, which have been commonly used in other media (e.g., precipitation, water vapor, ice cores), hold important and distinct information about the source and mixing of different freshwater sources. We use these measurements to identify the freshwater sources (e.g., Mackenzie vs. Yukon River) contributing to ocean surface waters across the Arctic region. Seawater isotopic measurements (delta 18O, delta 2H, deuterium excess) show heightened freshwater content in the Beaufort Sea and Baffin Bay Isotopic observations enable freshwater source delineation not feasible from traditional physical oceanographic methods Freshwater source delineation includes the Mackenzie and Yukon Rivers around coastal Alaska and glacial meltwater in Baffin Bay

Dramatic supraglacial lake drainage events in Greenland and Antarctica are enabled by rapid hydrofracture propagation through ice over 1 km thick. Here we present a slower mode of hydrofracture, where hairline surface fractures intersect supraglacial streams, and hypothesize that penetration depth is critically limited by water supply and englacial refreezing. We develop a model of stream-fed hydrofracture, and find that under most conditions in Greenland, 2-cm-wide fractures can penetrate hundreds of metres before freezing closed. Conditions for full-depth hydrofracture are more restricted, requiring larger meltwater channels and/or warm englacial conditions. Given the abundance of streams and surface fractures across Greenland and Antarctica's expanding ablation zones, we propose that stream-driven hydrofractures are ubiquitous-even where distant from supraglacial lakes and crevasse fields. This intriguing process remains undetectable by current satellite remote sensing, yet has two major impacts that warrant further investigation. First, by driving widespread cryohydrologic warming at depths far greater than surface crevassing, it explains a consistent cold bias in modelled englacial thermal profiles. Second, the associated reduction in ice viscosity and increased damage accumulation act to enhance the vulnerability of ice sheets and shelves to dynamic instability as supraglacial drainage networks expand inland to higher elevations.

During the Last Glacial Maximum (LGM), the Patagonian Ice Sheet (PIS) was the largest Quaternary ice mass in the Southern Hemisphere outside of Antarctica. Although the margins of the LGM ice sheet are now well established through end-moraine mapping and dating, apart from a few modelling and empirical studies, there remains a lack of constraint on its thickness and three-dimensional configuration. Here, we provide a high-resolution steady-state model reconstruction of the PIS at its maximum -LGM -extent applied using Nye's perfect-plastic ice rheology. The yield-strength parameter for the perfect-plastic flow model was calibrated against independent empirical reconstructions of the Lago Pueyrred & PRIME;on Glacier, where the former vertical extent of this major outlet glacier is well constrained by cosmogenically-dated trimlines and lateral and end-moraine limits. Using this derived yield-strength parameter, the perfect-plastic model is then applied to multiple flowlines demarking each outlet across the entirety of the PIS in a GIS framework. Our results reveal that the area of the PIS was-504,500 km2 (& PLUSMN;8.5%) with a corresponding modelled ice volume of-554,500 km3 (& PLUSMN;10%), equivalent to-1.38 m (& PLUSMN;10%) of eustatic sea-level lowering at the LGM. Maximum surface elevation was at least 3500m asl although the majority of the ice sheet surface was below 2500 m asl. We find that our ice sheet reconstruction is in good general agreement with previous estimates of net PIS volume derived from transient modelling studies. We attribute the slightly lower aspect-ratio of our ice sheet (and its concomitant 5% reduction in volume and sea-level equivalent) to the lower yield strength applied, based on more temperate and dynamic ice sheet conditions.

Radio Echo Sounding (RES) surveys conducted in May 2010 and April 2011 revealed a 2 km 2 flat area with increased bed reflectivity at the base of Isunnguata Sermia at the western margin of the Greenland Ice Sheet. This flat reflector was located within a localized subglacial hydraulic potential (hydropotential) minimum, as part of a complex and elongated trough system. By analogy with comparable features in Antarctica, the initial interpretation of such a feature was a potential subglacial lake. In September 2013 a co‐located seismic survey revealed a 1,750 m by 540 and 37 m thick stratified lens‐shaped bedform at the base of a subglacial trough system. Amplitude Versus Angle (AVA) analysis yields a derived reflection coefficient R = 0.09 ± 0.14 indicative of consolidated sediments possibly overlain by dilatant till. The bed and flank on the northern side of the trough consist of unconsolidated, possibly water‐bearing sediments with R = −0.10 ± 0.08, whereas on the southern side it consists of more consolidated material. We interpret the trough as a key component of the wider subglacial drainage network, for which the sediments on its northern side act as a localized water‐storage reservoir. Given the observation of seasonally forming and rapidly draining supraglacial meltwater lakes in this area, we interpret the lens‐shaped bedform as deposited by episodically ponding meltwater within the subglacial trough system. Our results highlight the importance of transient subglacial hydrological and sedimentological processes such as drainage events for the interaction of ice sheets and their substrates, to understand ice dynamics in a warming climate.

Information from former ice sheets may provide important context for understanding the response of today’s ice sheets to forcing mechanisms. Here we present a reconstruction of the last deglaciation of marine sectors of the Eurasian Ice Sheet, emphasising how the retreat of the Norwegian Channel and the Barents Sea ice streams led to separation of the British-Irish and Fennoscandian ice sheets at c. 18.700 and of the Kara-Barents Sea-Svalbard and Fennoscandian ice sheets between 16.000 and 15.000 years ago. Combined with ice sheet modelling and palaeoceanographic data, our reconstruction shows that the deglaciation, from a peak volume of 20 m of sea-level rise equivalent, was mainly driven by temperature forced surface mass balance in the south, and by Nordic Seas oceanic conditions in the north. Our results highlight the nonlinearity in the response of an ice sheet to forcing and the significance of ocean-ice-atmosphere dynamics in assessing the fate of contemporary ice sheets.

Ice loss from the Greenland ice sheet is one of the largest sources of contemporary sea-level rise (SLR). While process-based models place timescales on Greenland’s deglaciation, their confidence is obscured by model shortcomings including imprecise atmospheric and oceanic couplings. Here, we present a complementary approach resolving ice sheet disequilibrium with climate constrained by satellite-derived bare-ice extent, tidewater sector ice flow discharge and surface mass balance data. We find that Greenland ice imbalance with the recent (2000–2019) climate commits at least 274 ± 68 mm SLR from 59 ± 15 × 10 3 km 2 ice retreat, equivalent to 3.3 ± 0.9% volume loss, regardless of twenty-first-century climate pathways. This is a result of increasing mass turnover from precipitation, ice flow discharge and meltwater run-off. The high-melt year of 2012 applied in perpetuity yields an ice loss commitment of 782 ± 135 mm SLR, serving as an ominous prognosis for Greenland’s trajectory through a twenty-first century of warming.

Whilst there has been a recent appreciation for the role of open‐system pingos in providing a fluid‐flow conduit through continuous permafrost that enables methane release, the formation and internal structure of these ubiquitous permafrost‐diagnostic landforms remains unclear. Here, we combine active‐source seismic measurements with electrical resistivity tomography to investigate the structural and subsurface characteristics of an incipient open‐system pingo actively emitting methane within the glacio‐isostatically uplifting fjord valley of Adventdalen, Svalbard. Wavefront inversion of seismic refractions delineate a spatially heterogeneous active layer, whilst deeper reflections identify the lithological boundaries between marine sediments and underlying shales at ∼68 m depth (p‐wave velocity of ∼1,790 ms −1 ). Low geometric mean inverted resistivities of 40–150 Ωm highlight the dominance of saline permafrost, whilst elevated resistivities (∼2 kΩm) occur close to the groundwater spring and in heaved areas around the pingo. Based on our results, we speculate that segregation ice dominates the pingo structure, given the absence of a notable resistivity contrast characteristic of injection ice that is typically expected within early open‐system pingo formation, and provides the most plausible geomorphic agent within the local fine‐grained sedimentology. Our results thereby indicate that sediment grain size and moisture availability can provide important controls on pingo formation. This study shows that open‐system pingos in coastal, saline permafrost environments may form differently, with implications for localized permafrost structure, its permeability to underlying gas reservoirs and consequent methane release.

The Barents Sea has experienced intense erosion throughout the Cenozoic due to uplift and repeated episodes of glaciation. This, in turn, has driven large pressure and temperature fluctuations in the sediment substrate along with rearrangement of thermogenic oil and gas accumulations. As a result, some hydrocarbon fields have relatively shallow depths, and natural gas release is widespread. This study focuses on the process of hydrocarbon leakage from the Realgrunnen reservoir - encompassing the Hanssen and Wisting discoveries - to the shallow subsurface caused by repeated cycles of glacial erosion in the central Barents Sea throughout the Quaternary. We apply 2D basin and petroleum system modeling to two seismic sections using data from two wells and run ten different scenarios that test model sensitivity to key parameters. We find that the primary factors governing gas leakage are the erosion amount, its distribution between glacial and preglacial stages, and the timing of the glaciations. Our results demonstrate that intense oil and gas leakage from the Realgrunnen reservoir occurs primarily through widespread faults activated during the first deglaciation episode. Further considerable gas leakage occurs by the seal breach after a critical overburden thickness is eroded and pressure on the reservoir decreases to ca. 9 MPa. Modeling reveals that the first deglaciation episode causes up to ca. 20% loss of oil and gas from the reservoir, whereas leakage after the seal breach yields a further ca. 15% decrease in gas. Our results are supported by seismic analyses that demonstrate hydrocarbon leakage in the study area.

Ice can sculpt extraordinary landscapes, yet the efficacy of, and controls governing, glacial erosion on geological timescales remain poorly understood and contended, particularly across Polar continental shields. Here, we assimilate geophysical data with modelling of the Eurasian Ice Sheet — the third largest Quaternary ice mass that spanned 49°N to 82°N — to decipher its erosional footprint during the entire last ~100 ka glacial cycle. Our results demonstrate extreme spatial and temporal heterogeneity in subglacial erosion, with rates ranging from 0 to 5 mm a −1 and a net volume equating to ~130,000 km 3 of bedrock excavated to depths of ~190 m. A hierarchy of environmental controls ostensibly underpins this complex signature: lithology, topography and climate, though it is basal thermodynamics that ultimately regulates erosion, which can be variously protective, pervasive, or, highly selective. Our analysis highlights the remarkable yet fickle nature of glacial erosion — critically modulated by transient ice-sheet dynamics — with its capacity to impart a profound but piecemeal geological legacy across mid- and high latitudes.

As the Arctic warms, one of the fundamental changes has been the freshening of Arctic ocean waters, impacting ocean circulation and marine ecosystems, among many other critical changes. This increase in freshwater is largely the result of increased precipitation and runoff as part of an amplified Arctic water cycle and increased influx of glacial meltwater from around the Arctic, particularly from the Greenland Ice Sheet. Tracing the sources and extent of this freshwater is critical to understanding future changes to the Arctic seas. One way of delineating these water masses is through measuring its isotopic composition (δ18O and δD), where the freshwater varies significantly from older and other ocean water sources. In order to identify these freshwater influxes, we conducted in-situ measurements aboard the USCGC Healy that transited the Chukchi and Beaufort Seas, the Northwest Passage, and performed numerous transects across Baffin Bay and the Labrador Sea, including detailed examinations of several key fjords and coastal regions of Greenland, during autumn of 2021. Over the length of this 45 day expedition, we continuously measured the isotopic composition (δ18O and δD) of surface seawater allowing us to fingerprint these sources of freshwater and assess the spatial extent of their influence. We also collected discrete samples from over 100 CTD casts, primarily in Baffin Bay, to identify how freshwater is distributed in the ocean water column. Through these measurements, we identified numerous freshwater influxes, including anomalously high proportions of freshwater in sections of the Beaufort Sea north of Alaska and in Uummannaq Fjord along the west Greenland coast. These isotopic measurements also allow for the disentangling of different freshwater sources (i.e., precipitation or glacial meltwater). Additionally, we find that the freshwater pulses along the west coast of Greenland corresponded with relatively high levels of chlorophyll and fluorescence, suggesting a possible link between this increase in biologic productivity and an increase in the proportion of freshwater.

Strong compressive and shear stresses generated by glacial loading and unloading have a direct impact on near-surface geological processes. Glacial stresses are constantly evolving, creating stress perturbations in the lithosphere that extend significant distances away from the ice. In the Arctic, periodic methane seepage and faulting have been recurrently associated with glacial cycles. However, the evolution of the Arctic glacial stress field and its impact on the upper lithosphere have not been investigated. Here, we compute the evolution in space and time of the glacial stresses induced in the Arctic lithosphere by the North American, Eurasian and Greenland ice sheets during the latest glaciation. We use glacial isostatic adjustment (GIA) methodology to investigate the response of spherical, viscoelastic Earth models with varying lithospheric thickness to the ice loads. We find that the GIA-induced maximum horizontal stress (sigma(H)) is compressive in regions characterized by thick ice cover, with magnitudes of 20-25 MPa in Fennoscandia and 35-40 MPa in Greenland at the last glacial maximum. Simultaneously, a tensile regime with sigma(H) magnitude down to -16 MPa dominates across the forebulges with a mean of -4 MPa in the Fram Strait. At present time, sigma(H) in the Fram Strait remains tensile with an East-West orientation. The evolution of GIA-induced stresses from the last glaciation to present could destabilize faults along tensile forebulges, for example, the west-coast of Svalbard. A more tensile stress regime as during the Last Glacial Maximum would have more impact on pre-existing faults that favor gas seepage from gas reservoirs.

Ice surface albedo is a primary modulator of melt and runoff, yet our understanding of how reflectance varies over time across the Greenland Ice Sheet remains poor. This is due to a disconnect between point or transect scale albedo sampling and the coarser spatial, spectral and/or temporal resolutions of available satellite products. Here, we present time-series of bare-ice surface reflectance data that span a range of length scales, from the 500 m for Moderate Resolution Imaging Spectrometer’s MOD10A1 product, to 10 m for Sentinel-2 imagery, 0.1 m spot measurements from ground-based field spectrometry, and 2.5 cm from uncrewed aerial drone imagery. Our results reveal broad similarities in seasonal patterns in bare-ice reflectance, but further analysis identifies short-term dynamics in reflectance distribution that are unique to each dataset. Using these distributions, we demonstrate that areal mean reflectance is the primary control on local ablation rates, and that the spatial distribution of specific ice types and impurities is secondary. Given the rapid changes in mean reflectance observed in the datasets presented, we propose that albedo parameterizations can be improved by (i) quantitative assessment of the representativeness of time-averaged reflectance data products, and, (ii) using temporally-resolved functions to describe the variability in impurity distribution at daily time-scales. We conclude that the regional melt model performance may not be optimally improved by increased spatial resolution and the incorporation of sub-pixel heterogeneity, but instead, should focus on the temporal dynamics of bare-ice albedo.