Melting Rate Research Articles

Global Climate Impacts of Greenland and Antarctic Meltwater: A Comparative Study

Abstract Both the Greenland and Antarctic ice sheets have been melting at an accelerating rate over recent decades. Meltwater from Greenland might be expected to initiate a climate response that is distinct, and perhaps different from, that associated with Antarctic meltwater. Which one might elicit a greater climate response, and what mechanisms are involved? To explore these questions, we apply climate response functions (CRFs) to guide a series of meltwater-perturbation experiments using a fully coupled climate model. In both hemispheres, meltwater drives atmospheric cooling, sea ice expansion, and strengthened Hadley and Ferrel cells. Greenland meltwater induces a slowdown of the Atlantic meridional overturning circulation (AMOC) and a cooling of the subsurface ocean in the northern high latitudes. Antarctic meltwater, instead, induces a slowdown of the Antarctic Bottom Water formation and a warming of the subsurface ocean around Antarctica. For melt rates up to 2000 Gt yr−1, the climate response is rather linear. However, as melt rates increase to 5000 Gt yr−1, the climate response becomes nonlinear. Due to a collapsed AMOC, the climate response is superlinear at high Greenland melt rates. Instead, the climate response is sublinear at high Antarctic melt rates, due to the halting of the northward expansion of Antarctic sea ice by warm surface waters. Finally, in the linear limit, we use CRFs and linear convolution theory to make projections of important climate parameters in response to meltwater scenarios, which suggest that Antarctic meltwater will become a major driver of climate change, dominating that of Greenland meltwater, as the current century proceeds. Significance Statement Melting of the Greenland and Antarctic ice sheets is one of the most uncertain potential contributors to future climate change. In this study, we address the comparative role of Greenland and Antarctic meltwater in the climate system and explore the differing mechanisms at work in each hemisphere. We find that the climate response is linear for low melt rates but becomes nonlinear for high melt rates. As the century proceeds, we speculate that Antarctic meltwater will increasingly dominate that of Greenland meltwater, leading to atmospheric cooling, Antarctic sea ice expansion, and contraction and warming of the Antarctic Bottom Water. Greenland meltwater will, instead, affect smaller changes in the Northern Hemisphere.

Migration and heat transfer modeling of a neutrally buoyant melting particle in Poiseuille flow

A computational model is developed to simulate the hydrodynamic and heat transfer behavior of a melting cylindrical solid particle in plane Poiseuille flow between horizontal parallel plates. The two-dimensional transient conservation equations for mass, momentum, and energy are solved using a finite-volume scheme implemented on a deforming mesh, accounting for the rotation and non-uniform melting of the particle. An arbitrary Lagrangian–Eulerian (ALE) method is employed to directly track the moving and deforming solid–liquid interface during the particle migration and phase change. The developed model was validated by comparison with the previously reported numerical results for migration of a non-melting neutrally buoyant cylindrical particle in plane Poiseuille flow with heat transfer. The effects of flow Reynolds (Re), Grashof (Gr), and Stefan (Ste) numbers, as well as the initial position of the melting particle across the channel on the particle trajectory, melting rate, and average Nusselt (Nu) number were investigated. It was found that the melting rate increased by increasing Gr and Ste and decreased by increasing Re. The Nu did not change more than 20% with increasing Re number from 100 to 1000, but increased significantly by increasing Gr. It was also observed that by increasing Re, the particle migrates toward the channel center because of the stronger Magnus effect. Increasing Gr, on the other hand, pushes the particle to the bottom wall due to the stronger downward flow adjacent to the particle induced by buoyancy-driven convection (natural convection).

Zonal Distribution of Circumpolar Deep Water Transformation Rates and Its Relation to Heat Content on Antarctic Shelves

AbstractWe analyze 15‐year of observational data and a 5‐year Southern Ocean model simulation to quantify the transformation rates of Circumpolar Deep Water (CDW) and the associated heat loss to the surface. This study finds that over the continental shelves of East Antarctica and the Weddell and Ross Seas, surface buoyancy fluxes transform ∼4.4 Sv of surface waters into CDW, providing a path for CDW to lose heat to the surface. In addition, ∼6.6 Sv of CDW are mixed with surface waters in the Weddell and Ross subpolar gyres. In contrast, enhanced stratification inhibits the outcropping of CDW isopycnals, reducing their transformation rates by a factor of ∼8 over the continental shelf and by a factor of ∼3 over the deeper ocean in the Amundsen and Bellingshausen Seas. The CDW retains its offshore warm properties as it intrudes over the continental shelves, resulting in elevated bottom temperatures there. This analysis demonstrates the importance of processes in subpolar gyres to erode CDW and to facilitate further transformation on the continental shelves, significantly reducing the heat able to access ice shelf fronts. This sheltering effect is strongest in the western Weddell Sea and tends to diminish toward the east, which helps explain the large zonal differences in continental‐shelf bottom temperatures and the melt rates of Antarctic ice shelves.

Strong impact of sub-shelf melt parameterisation on ice-sheet retreat in idealised and realistic Antarctic topography

AbstractFuture projections of sea-level rise under strong warming scenarios are dominated by mass loss in the marine-grounded sectors of West Antarctica, where thinning shelves as a result of warming oceans can lead to reduced buttressing. This consequently leads to accelerated flow from the upstream grounded ice. However, the relation between warming oceans and increased melt rates under the shelves is very uncertain, especially when interactions with the changing shelf geometry are considered. Here, we compare six widely used, highly parameterised formulations relating sub-shelf melt to thermal forcing. We implemented them in an ice-sheet model, and applied the resulting set-up to an idealised-geometry setting, as well as to the Antarctic ice sheet. In our simulations, the differences in modelled ice-sheet evolution resulting from the choice of parameterisation, as well as the choice of numerical scheme used to apply sub-shelf melt near the grounding line, generally are larger than differences from ice-dynamical processes such as basal sliding, as well as uncertainties from the forcing scenario of the model providing the ocean forcing. This holds for the idealised-geometry experiments as well as for the experiments using a realistic Antarctic topography.

Effect of novel concentric annular fins on the melting and solidification process of stearic acid in thermal energy storage devices

The latent heat thermal energy storage device provides an alternative solution to the problem of imbalance between energy supply and demand. To enhance heat transfer, a series of latent heat thermal energy storage devices with novel concentric annular fins are proposed, as the design accelerates the melting and solidification processes of stearic acid. Based on the finite volume method, the enthalpy-porosity approach is employed to numerical simulation the charging/discharging process. Effects of the number and arrangement of concentric annular fins on the liquid fraction, melting and solidification front, melting uniformity, temperature uniformity, velocity uniformity and total melting and solidification time during melting and solidification are studied. Results showed that the melting and solidification rate increases with increasing fin number. The total melting and solidification times were reduced by 72.83% and 86.39%, respectively, for the case with 9 concentric annular fins compared to the bare tube. Both melting performance and temperature uniformity were improved. Further, the effect of fin arrangement on the melting and solidification performance was investigated with the same total volume of fins. Results revealed that the heat transfer performance of progressively shorter fin structures < uniformly distributed fins < progressively longer fins < performance of non-uniformly distributed fin arrangement. The non-uniform fin arrangement reduces the total melting and solidification time of stearic acid by 85.46% and 90.11%, respectively, compared to bare tube. This work provides new insights into the understandings of the transient phase change process and the strategies for guiding the design for thermal energy storage devices using annular fins.

High Spatial Melt Rate Variability Near the Totten Glacier Grounding Zone Explained by New Bathymetry Inversion

AbstractTotten Glacier is a fast‐moving East Antarctic outlet with the potential for significant future sea‐level contributions. We deployed four autonomous phase‐sensitive radars on its ice shelf to monitor ice‐ocean interactions near its grounding zone and made active source seismic observations to constrain gravity‐derived bathymetry models. We observe an asymmetry in basal melting with mean melt rates along the grounding zone differing by up to 20 m/a. Our new bathymetry model reveals that this melt rate asymmetry coincides with an asymmetry in water column thickness and that the low‐melting ice‐shelf portion is shielded from the main cavity circulation. A 2‐year record yields year‐to‐year melt rate variability of 7–9 m/a with no seasonal cycle. Our results highlight the key role of bathymetry near grounding lines for accurate modeling of ice‐shelf melt, and the importance of sustained multi‐year monitoring, especially at ice‐shelf cavities where the dominant melt rate drivers vary primarily inter‐annually.

Investigation of The Physicochemical Properties of Propolis Added Ice Creams During Storage

The aim of this study is to add functional food feature to ice cream, which is a popular food, by enriching it with propolis. In addition, another aim of the study is to provide a widespread consumption potential through ice cream to propolis, which cannot be consumed raw and whose benefits and functional properties are unknown to most consumers. A mixture consisting of a total of 6 sample groups containing 0.0%, 0.1%, 0.2%, 0.3%, 0.4% and 0.5% propolis powder was prepared for the ice cream mix. Ice cream samples were prepared from these ice cream mixes. Different analyses were executed for propolis, ice cream mix and ice cream samples. While only antioxidant analysis was executed for propolis samples, Dry matter, pH, titration acidity analyzes were executed in ice cream mix samples. Volume increase index, texture analysis, melting rate, antioxidant activity and sensory analyzes in propolis added ice cream samples were carried out on different days during 2 months of storage. According to the findings, while the volume increase of the ice cream samples was not affected by the storage time, the difference between the propolis concentrations was found. It was observed that the first dripping times increased with storage, while the melting rate of the ice cream decreased. There was no significant change in the meltıng rate and first drip times depending on the propolis concentrations. The texture properties of ice cream samples have changed with the addition of propolis. The hardness and stickiness values of ice cream samples changed depending on the storage time. The addition of propolis significantly increased the antioxidant activity. Antioxidant activity was changed with the addition of propolis. The phenolic content and of ice cream did not change with storage, but FRAP value decreased slightly after 60 days of storage. Storage time had a limited effect on the physicochemical and sensory properties of ice cream. Although the addition of propolis negatively affected the physical and sensory properties of ice cream, it contributed significantly to the antioxidant activity even at the lowest concentrations. With this study, the potential of propolis-added ice cream as a functional new food for consumers of all ages has been demonstrated. In line with these results, new studies should be conducted by trying different propolis extracts and different concentrations, by revealing the functionality of propolis and adding it to new other foods.

Physical properties of hemp drink-based ice cream with different plant proteins guar gum and microbial transglutaminase

Hemp drink-based vegan ice creams were manufactured with different plant proteins (hemp, rice, almond, walnut) and texture modifiers (guar gum, microbial transglutaminase). Ice creams were analysed for pH, dry matter content, colour, melting properties, rheological properties, penetration test, thermophysical properties with Differential Scanning Calorimetry (DSC) and sensory properties. Results of this study show that the applied vegan proteins are dominating the colour of the final ice creams independent of the other ingredients. Based on melting and thermophysical properties, prepared ice cream samples can be divided into 2 groups. The almond and hemp protein containing products had higher maximum melting rate and a higher unfreezable water content, than the samples containing rice and walnut protein. In the rheological analysis the addition of microbial transglutaminase (MTG) increased the shear stress, consistency coefficient and the samples took on a more pseudoplastic character. These changes are even more pronounced and larger when guar gum was added to the samples. Penetration test revealed that the untreated samples were the hardest in case of hemp-, almond and rice protein-based vegan ice creams. Sensory panelists scores made almond protein-based vegan ice creams the best.

Lacticaseibacillus casei improves textural, functional, and sensory properties and phenolics’ bioaccessibility of frozen desserts prepared using water-soluble extract of rice by-product and Spirulina platensis

The impact of probiotic (Lacticaseibacillus casei, 8 log CFU/g) and/or prebiotic (polydextrose, 5 g/100 g) on the technological and sensory properties, phenolics bioaccessibility, and functional properties (in vitro antidiabetic, anti-hypertensive, and antioxidant activities) of frozen desserts processed with water-soluble extract of rice by-product and Spirulina platensis biomass was evaluated during storage (120 days/-18 °C). Prebiotic products were more consistent and cohesive and showed higher melting rates. Probiotic and/or synbiotic products had higher phenolic compounds bioaccessibility (gallic acid, epigallocatechin gallate, epicatechin gallate, and chlorogenic acid) and functional properties (antioxidant, ACE, ⍺-amylase, and ⍺-glucosidase inhibitory activities), lower thrombogenic and atherogenic indices and improved technological (lower firmness, consistency, cohesiveness, and viscosity) and sensory (increased mint aroma and flavor intensity) properties. L. casei survived in simulated gastrointestinal conditions (>6 log CFU/g) and did not impair sensory acceptance. In conclusion, probiotic and synbiotic frozen desserts show improved functional, technological, and sensory properties.

Numerical investigation of the air conditioning system performance assisted with energy storage of capsulated concave/convex phase change material

One of the highest energy drains in homes and businesses is the air conditioning (AC) system. Thus, any slight improvement in the AC system performance can result in considerable energy savings. This numerical study aims to boost the AC performance in hot environments via thermal energy storage. This is accomplished by directly cooling the AC condenser using capsulated phase change materials (PCM). The PCM is capsulated in a new design of concave/convex (CX) plates to reduce the lengthy PCM solidification time and also enhance the AC performance. The PCM is solidified during a relatively low nighttime temperature and then cools the AC condenser during daytime operation. The proposed encapsulated PCM design's impact on the AC performance is assessed and compared to those of used flat plates. Using ANSYS Fluent, a mathematical equations model is developed and solved and then validated via an experimental test rig of the PCM flat plates. The effects of varying the size and number of concave/convex configurations are investigated. It is found that concave/convex PCM plates greatly minimize the solidification/melting periods compared to flat plates, making them effective in AC system daily work. Rising the CX diameter and numbers enhances the PCM melting and solidification rates and decreases the air outlet temperature. Moreover, the saved percentage of the power rises with the ambient temperature and airflow rate rising. Further, the AC power usage by adopting PCM concave/convex plates is saved by a maximum value of about 16 % and 7.5 % when working for 120 and 300 min, respectively.

Hydrogen charging in AX21 activated carbon-PCM-metal foam-based industrial-scale reactor: Numerical analysis

A computational fluid dynamics (CFD) model based on the mass, momentum, and energy conservation equations is used to simulate the industrial-scale hydrogen storage in activated carbon (AC: AX-21) bottle surrounded by a layer of metal foam (MF)-phase change material (PCM: RT 22 HC) latent thermal unit. The aim is to boost the recuperation (storage) of the heat liberated from the H₂‘s exothermic (adsorption). Following the model's validation, several numerical simulations were performed to evaluate the impact of various physical features of the MF (copper), at variable porosity (ε = 0.80–1.0), on heat transfer in the hole reactor. Independently of the MF porosity, the AC-bed temperature suddenly increased (from 295 K), reaching a maximum (at about 500 s) and decreased afterward. The temperature's intensity was dependent on the probe's position in the AC-bed (i.e. several positions were studied). The H2 concentration in the AC-bed may reach 25 mmol/g. The PCM-based unit received the discharged heat from the AC-bed slowly, but with PCM incorporation in MF, the heat was quickly recovered (stored). Thanks to the MF-induced PCM's increased thermal conductivity, the heat flux, the heat transfer coefficient, and the melting rate of the PCM were all accelerated (during the charging phase) several times by decreasing the MF porosity (increasing MF mass) from 1 (pure PCM) to 0.8. The temperature and the melting contours throughout the absorption process (up 10,000 s) supported all these findings. It is obvious from the results of the current study that improving the reactor geometry and the solid bed's thermal conductivity (thermal performance) is necessary for an effective hydrogen storage system.

Firn aquifer water discharges into crevasses across Southeast Greenland

AbstractIn Southeast Greenland, summer melt and high winter snowfall rates give rise to firn aquifers: vast stores of meltwater buried beneath the ice-sheet surface. Previous detailed studies of a single Greenland firn aquifer site suggest that the water drains into crevasses, but this is not known at a regional scale. We develop and use a tool in Ghub, an online gateway of shared datasets, tools and supercomputing resources for glaciology, to identify crevasses from elevation data collected by NASA's Airborne Topographic Mapper across 29000 km2of Southeast Greenland. We find crevasses within 3 km of the previously mapped downglacier boundary of the firn aquifer at 20 of 25 flightline crossings. Our data suggest that crevasses widen until they reach the downglacier boundary of the firn aquifer, implying that crevasses collect firn-aquifer water, but we did not find this trend with statistical significance. The median crevasse width, 27 meters, implies an aspect ratio consistent with the crevasses reaching the bed. Our results support the idea that most water in Southeast Greenland firn aquifers drains through crevasses. Less common fates are discharge at the ice-sheet surface (3 of 25 sites) and refreezing at the aquifer bottom (1 of 25 sites).

Numerical study of heat transfer and melting process in a NEPCM filled 3D cuboid cavity: Application non-uniform temperature

In this numerical study, a cubic box filled with a Nanoparticle Enhanced Phase Change Material (NEPCM) (mixture “N-Octadecane/alumina (Al2O3)"), is considered. Using Comsol-Multiphysics program, the configuration is treated as a 3D symmetric numerical simulation problem under fixed boundary conditions. Besides, heat transfer fluid (HTF) generates a non-uniform temperature that varies linearly along an internal tube installed in the lowest area of the enclosure to ensure the melting of the NEPCM. Therefore, the purpose of the study is to highlight the effect of the nanoparticles volume fraction (varying from 0 to 6%) on thermal distribution and melting performances. The obtained findings figure out that the PCM melts irregularly and is affected by the non-uniform temperature of the HTF tube. Hence, the third dimension should be considered, particularly in PCM ring tank simulations, in order to obtain reliable predictions compared to practical and experimental studies. Additionally, the Al2O3 nanoparticles have a valuable effect on improving the thermal conductivity of NEPCM, where thermal resistance and melting time are reduced with the increase of the nanoparticles volume fraction. Compared to the case of pure PCM, the heat transfer enhancement yields to an augmentation in the melting rate by about 11% and 9.5% for the volume fractions of 6% and 3%, respectively. Moreover, there is a significant increase in the amount of stored thermal energy when nanoparticles are dispersed in the PCM.

Melting performance of nano-enhanced phase change materials in a triple-tube heat exchanger with zigzag-shaped tubes

This study aims at evaluating the melting behavior of nano-enhanced phase change materials (NePCM) inside a triple-tube heat exchanger with a zigzag-shape channel configuration. To assess the performance of the proposed geometry, a zigzag tube with different angles and heights is numerically simulated and the results are compared with the conventional triple-tube heat exchanger. Cu, CuO, Al2O3 and Ag nanoparticles with various concentrations are used to improve the thermal conductivity of NePCMs. The main finding of this research is a significant improvement in the melting performance of a triple-tube heat exchanger by employing a middle zigzag tube. The zigzag configuration with a 67.5° angle and 15 mm height is found as the optimum case with a great potential to (i) reduce the melting time from 4654 s in the case of a straight tube to just 827 s and (ii) increase the heat retrieval rate from just ∼47 W in case of a straight tube to ∼185 W. Among the type of nanoparticles analyzed in this research, Al2O3 has the highest melting performance with ∼14 % increase in the melting rate and heat charge rate at 4 % concentration. Increasing the concentration of Al2O3 nanoparticles from 2 % to 6 % improves the heat charge rate by ∼2.3 %.

A field study on ice melting and breakup in a boreal lake, Pääjärvi, in Finland

Abstract. Lake ice melting and breakup form a fast, nonlinear process with important mechanical, chemical, and biological consequences. The process is difficult to study in the field due to safety issues, and therefore only little is known about its details. In the present work, the field data were collected on foot, by hydrocopter, and by boat for a full time series of the evolution of ice thickness, structure, and geochemistry through the melting period. The observations were made in lake Pääjärvi in 2018 (pilot study) and 2022. In 2022, the maximum thickness of ice was 55 cm with 60 % snow ice, and in 40 d the ice melted by 33 cm from the surface and 22 cm from the bottom while the porosity increased from less than 5 % to 40 %–50 % at breakup. In 2018, the snow-ice layer was thin, and bottom and internal melting dominated the ice decay. The mean melting rates were 1.31 cm d−1 in 2022 and 1.55 cm d−1 in 2018. In 2022 the electrical conductivity (EC) of ice was 11.4 ± 5.79 µS cm−1, which is 1 order of magnitude lower than in the lake water, and ice pH was 6.44 ± 0.28, which is lower by 0.4 than in water. The pH and EC of ice and water decreased during the ice decay except for slight increases in ice due to flushing by lake water. Chlorophyll a was less than 0.5 µg L−1 in porous ice, approximately one-third of that in the lake water. The results are important for understanding the process of ice decay with consequences for lake ecology, further development of numerical lake ice models, and modeling the safety of ice cover and ice loads.

Melting characteristics of concentric and eccentric inner elliptic tube in double tube latent heat energy storage unit

Thermal energy storage is critically necessary for most solar energy applications. The phase change energy storage systems are the most promising; however, the poor thermal conductivity of the material is a major disadvantage. This work aims to simulate the melting process and investigate the optimum design parameters for a stable and high melting rate of phase-change energy storage systems. A 2-D axisymmetric numerical model has been developed using ANSYS 17. The model was validated by published experimental data. A new elliptical design of the inner tube was investigated; and the main parameters considered were eccentricity (0, 0.1, 0.2, 0.3, 0.4, and 0.5), aspect ratio (1, 0.9, 0.8, 0.7, 0.6, and angle of 0.5), and inclination (0°, 30°, 60°, and 90°) of the inner tube. The outcome of this investigation revealed that the maximum enhancement of the average melting rate was 19.14%, 42.65%, 71.3%, 105.51%, and 150.1%, for eccentricity of 0.1,0.2,0.3,0.4, and 0.5, respectively, for an aspect ratio of 1. The maximum and minimum average melting rate were 0.00516 and 0.00417 kg/min for the vertical inner elliptical tube (θ = 90°) and the horizontal inner elliptic (θ = 0°) respectively for an aspect ratio of 0.5.

Physical and sensory properties of soy-based ice cream formulated with cold-pressed high oleic low linolenic soybean oil.

The effect of cold-pressed SOYLEIC™ soybean oil (SOYLEIC) on the physical and sensory properties of soy-based ice cream was compared to commercial vegetable oil (COM-VO), commercial high oleic soybean oil (COM-HO), and heavy cream (CREAM). Fat sources had no significant effect on viscosity and fat globule size distribution of ice cream mixes. Ice cream made with COM-VO had the lowest overrun (p <0.05) and higher degree of fat destabilization; however, no difference in hardness was found. Despite similar melting rate, the shape retention behavior during melting was different for SOYLEIC, COM-VO, and COM-HO compared to CREAM. No significant differences were found in texture attributes except mouth coating, which was higher for CREAM than COM-HO and SOYLEIC (p <0.05). There was no significant difference in flavor attributes between SOYLEIC and CREAM, while COM-VO and COM-HO had higher off-flavor intensities (p <0.05). Consumer acceptability results revealed that SOYLEIC and CREAM had significantly higher flavor liking and overall liking scores than COM-VO and COM-HO (p <0.05). SOYLEIC and CREAM also had higher texture liking than COM-VO (p <0.05). Overall, liking had the highest positive significant correlation with flavor liking (r=0.996). PRACTICAL APPLICATION: Cold-pressed HOLL soybean oil has the potential to be used in formulating plant-based frozen desserts with equivalent texture but more acceptable flavor.

A model of the weathering crust and microbial activity on an ice-sheet surface

Abstract. Shortwave radiation penetrating beneath an ice-sheet surface can cause internal melting and the formation of a near-surface porous layer known as the weathering crust, a dynamic hydrological system that provides home to impurities and microbial life. We develop a mathematical model, incorporating thermodynamics and population dynamics, for the evolution of such layers. The model accounts for conservation of mass and energy, for internal and surface-absorbed radiation, and for logistic growth of a microbial species mediated by nutrients that are sourced from the melting ice. It also accounts for potential melt–albedo and microbe–albedo feedbacks, through the dependence of the absorption coefficient on the porosity or microbial concentration. We investigate one-dimensional steadily melting solutions of the model, which give rise to predictions for the weathering crust depth, water content, melt rate, and microbial abundance, depending on a number of parameters. In particular, we examine how these quantities depend on the forcing energy fluxes, finding that the relative amounts of shortwave (surface-penetrating) radiation and other heat fluxes are particularly important in determining the structure of the weathering crust. The results explain why weathering crusts form and disappear under different forcing conditions and suggest a range of possible changes in behaviour in response to climate change.

Contrasting current and future surface melt rates on the ice sheets of Greenland and Antarctica: Lessons from in situ observations and climate models

Surface meltwater production impacts the mass balance of the Greenland and Antarctic ice sheets in several ways, both directly (e.g., through runoff in Greenland) and indirectly (e.g., through cryo-hydrologic warming and frontal melt of marine-terminating glaciers in Greenland and hydrofracturing of ice shelves in Antarctica). Despite its importance, the spatial and temporal patterns in melt rates on both ice sheets are still relatively poorly understood. In this contribution we review and contrast surface melt ‘weather ‘(i.e., short term, intra- and interdiurnal variability) and surface melt ‘climate’ (i.e., longer term, interannual variability and future melt) of both ice sheets. We find that in situ observations using suitably equipped (automatic or staffed) weather stations are invaluable for a complete understanding of the melt process, which represents the complex transport of energy by radiation, turbulence, and molecular conduction between the lower atmosphere, the ice/snow surface, and the subsurface ice/snow layers. We provide example time series of ice sheet melt ‘weather’ for the marginal Greenland ice sheet, where warm and humid air masses tend to increase surface melt rate, and for coastal East Antarctica, where the opposite happens. Apart from process understanding, these in situ observations, which especially in Antarctica are scarce in space and time, are also invaluable to validate, evaluate and calibrate satellite- and model-based estimates of ice sheet surface melt rate. We provide examples of modelled melt maps for both ice sheets, and melt projections for a high-warming, fossil-fuelled development scenario. Although important milestones in melt observations (both in-situ and remotely sensed) and melt models (both global and regional) have recently been reached, we identify multiple outstanding research questions pertaining to current and future ice sheet surface melt rates.

The first cultivation of the glacier ice alga Ancylonema alaskanum (Zygnematophyceae, Streptophyta): differences in morphology and photophysiology of field vs laboratory strain cells

AbstractMelting glacier surfaces are unique ecosystems for specialized microbes, frequently harbouring blooms of microalgae with pigments contributing to the darkening of ice surfaces, reducing albedo and enhancing melt rates. The main cause of this phenomenon is algae of the genus Ancylonema. Prior investigation depended on field-collected material because these algae resisted cultivation. To enhance research on how these algae dominate melting ice, we established a strain of Ancylonema alaskanum from an alpine glacier and exposed to temperatures around the freezing point at irradiations of ~10% of full sunlight. The morphology of the culture changed, with the cells becoming longer and turning green by losing their brownish pigmentation, indicating that these dark phenols are crucial for survival in the cryosphere. Photophysiological comparisons of strain and glacial material showed adaptation of the photosynthetic apparatus to prevailing conditions. This laboratorial strain opens possibilities for a wide range of comparative ‘omics’ research.