Ice-water Interface Research Articles

Methane dynamics in three different Siberian water bodies under winter and summer conditions

Abstract. Arctic regions and their water bodies are affected by a rapidly warming climate. Arctic lakes and small ponds are known to act as an important source of atmospheric methane. However, not much is known about other types of water bodies in permafrost regions, which include major rivers and coastal bays as a transition type between freshwater and marine environments. We monitored dissolved methane concentrations in three different water bodies (Lena River, Tiksi Bay, and Lake Golzovoye, Siberia, Russia) over a period of 2 years. Sampling was carried out under ice cover (April) and in open water (July–August). The methane oxidation (MOX) rate and the fractional turnover rate (k′) in water and melted ice samples from the late winter of 2017 was determined with the radiotracer method. In the Lena River winter methane concentrations were a quarter of the summer concentrations (8 nmol L−1 vs. 31 nmol L−1), and mean winter MOX rate was low (0.023 nmol L−1 d−1). In contrast, Tiksi Bay winter methane concentrations were 10 times higher than in summer (103 nmol L−1 vs. 13 nmol L−1). Winter MOX rates showed a median of 0.305 nmol L−1 d−1. In Lake Golzovoye, median methane concentrations in winter were 40 times higher than in summer (1957 nmol L−1 vs. 49 nmol L−1). However, MOX was much higher in the lake (2.95 nmol L−1 d−1) than in either the river or bay. The temperature had a strong influence on the MOX (Q10=2.72±0.69). In summer water temperatures ranged from 7–14 ∘C and in winter from −0.7 to 1.3 ∘C. In the ice cores a median methane concentration of 9 nM was observed, with no gradient between the ice surface and the bottom layer at the ice–water interface. MOX in the (melted) ice cores was mostly below the detection limit. Comparing methane concentrations in the ice with the underlaying water column revealed methane concentration in the water column 100–1000 times higher. The winter situation seemed to favor a methane accumulation under ice, especially in the lake with a stagnant water body. While on the other hand, in the Lena River with its flowing water, no methane accumulation under ice was observed. In a changing, warming Arctic, a shorter ice cover period is predicted. With respect to our study this would imply a shortened time for methane to accumulate below the ice and a shorter time for the less efficient winter MOX. Especially for lakes, an extended time of ice-free conditions could reduce the methane flux from the Arctic water bodies.

Roughness and storage capacity of freshwater ice in the Straits of Mackinac

In the event of a maritime oil spill in winter conditions, the fate of oil released under ice presents considerable difficulties with respect to detection, containment and recovery compared to spills that form slicks in open water. This study presents the first quantification of roughness and associated storage capacity of the ice-water interface for freshwater ice in the Laurentian Great Lakes in North America. Ground Penetrating Radar (GPR) observations are used to retrieve ice thicknesses every 2.5 cm on a grid over ice ranging between 0.26 and 0.48 m in the Straits of Mackinac to derive a digital elevation model of the ice bottom. The root mean square of height deviations of the ice underside is observed to be 0.03 m (over a correlation length of approximately 20 m) with a storage capacity of 0.03 m3/m2. The observed physical characteristics relevant to oil entrainment at the ice underside are similar to those reported for first year sea ice and may store similar quantities of oil during the initial spill. However, the difference in the physical structure between first year ice (with brine channels) and freshwater ice (consolidated ice cap) may result in a disparity in the timing of oil appearance, and require considerably different remediation treatment.

Turbulent convection in subglacial lakes

Abstract

Rapid Manipulation in Irradiance Induces Oxidative Free-Radical Release in a Fast-Ice Algal Community (McMurdo Sound, Antarctica).

Sea ice supports a unique assemblage of microorganisms that underpin Antarctic coastal food-webs, but reduced ice thickness coupled with increased snow cover will modify energy flow and could lead to photodamage in ice-associated microalgae. In this study, microsensors were used to examine the influence of rapid shifts in irradiance on extracellular oxidative free radicals produced by sea-ice algae. Bottom-ice algal communities were exposed to one of three levels of incident light for 10 days: low (0.5 μmol photons m−2 s−1, 30 cm snow cover), mid-range (5 μmol photons m−2 s−1, 10 cm snow), or high light (13 μmol photons m−2 s−1, no snow). After 10 days, the snow cover was reversed (either removed or added), resulting in a rapid change in irradiance at the ice-water interface. In treatments acclimated to low light, the subsequent exposure to high irradiance resulted in a ~400× increase in the production of hydrogen peroxide (H2O2) and a 10× increase in nitric oxide (NO) concentration after 24 h. The observed increase in oxidative free radicals also resulted in significant changes in photosynthetic electron flow, RNA-oxidative damage, and community structural dynamics. In contrast, there was no significant response in sea-ice algae acclimated to high light and then exposed to a significantly lower irradiance at either 24 or 72 h. Our results demonstrate that microsensors can be used to track real-time in-situ stress in sea-ice microbial communities. Extrapolating to ecologically relevant spatiotemporal scales remains a significant challenge, but this approach offers a fundamentally enhanced level of resolution for quantifying the microbial response to global change.

Heat flux balance description of unidirectional freezing and melting dynamics on a translational temperature gradient stage

Directional solidification occurs in industrial and natural processes, such as freeze-casting, metal processing, biological cryopreservation and freezing of soils. Translational temperature gradient stage allows to control the process of directional solidification and to visualize it with optical microscope. In this stage freezing velocity and temperature gradient are decoupled and are independently controlled. Here we study the dynamics of the phase transition interface in thin water samples using translational temperature gradient stage. We follow position of the ice–water interface with optical microscopy and compare it to solution of one dimensional Stefan problem in the low velocity limit. We find an agreement between experimental observations and theoretical predictions for constant velocity and during acceleration of the ice front. This work presents a practical framework for analysis and design of experiments on a translational temperature gradient stage.

Estimates of spectral wave attenuation in Antarctic sea ice, using model/data inversion

A model-data inversion is applied to an extensive observational dataset collected in the Southern Ocean north of the Ross Sea during late autumn to early winter, producing estimates of the frequency-dependent rate of dissipation by sea ice. The modeling platform is WAVEWATCH III® which accounts for non-stationarity, advection, wave generation, and other relevant processes. The resulting 9477 dissipation profiles are co-located with other variables such as ice thickness to quantify correlations which might be exploited in later studies to improve predictions. An average of dissipation profiles from cases of thinner ice near the ice edge is fitted to a simple binomial. The binomial shows remarkable qualitative similarity to prior observation-based estimates of dissipation, and the power dependence is consistent with at least three theoretical models, one of which assumes that dissipation is dominated by turbulence generated by shear at the ice-water interface. Estimated dissipation is lower closer to the ice edge, where ice is thinner, and waveheight is larger. The quantified correlation with ice thickness may be exploited to develop new parametric predictions of dissipation.

Compositional differences of fluorescent dissolved organic matter in Arctic Ocean spring sea ice and surface waters north of Svalbard

We assessed the qualitative composition of fluorescent dissolved organic matter (FDOM) in Arctic Ocean surface water and in sea ice north of the Svalbard Archipelago (in the Sophia Basin, the Yermak Plateau and the north Spitsbergen shelf) in May and June 2015, during the “TRANSSIZ” expedition (Transitions in the Arctic Seasonal Sea Ice Zone). Samples collected in open lead waters (OW), under-ice waters (UIW) and from the sea ice (ICE) were analyzed by fluorescence spectroscopy and subsequently by multivariate statistical methods using Parallel Factor Analysis (PARAFAC). Statistical analyses of all measured DOM fluorescence excitation and emission matrices (EEMs) enabled four components to be identified and validated. The spectral characteristics of the first component C1 (λEx/λEm 282(270)/335) corresponded to those of tryptophan. The spectral properties of the other three components corresponded to those of humic-like substances: components two (C2 − λEx/λEm 315(252)/395) and three (C3 − λEx/λEm 357(258)/446) corresponded to humic-like substances of marine origin, whereas component four (C4 − λEx/λEm 261(399)/492) resembled terrestrial humic-like substances. Changes in FDOM composition were recorded in OW, in contrast to UIW and sea ice. In the OW the sum of fluorescence intensities of humic-like components (C2, C3 and C4) was two times higher than the fluorescence intensity of protein-like component (C1). Component C2 exhibited the highest fluorescence intensity. In the UIW and particularly in the sea ice the fluorescence intensity of the protein-like component, IC1, was the highest. The IC1 in the sea ice increased toward the sea ice bottom, reaching maximum values at the sea ice-water interface. The calculated spectral indices (SUVA(254) and HIX) and ratios of fluorescence intensities of protein-like to humic-like components, Ip/Ih, suggested that FDOM in water and sea ice was predominantly autochthonous, characterized by low molecular weight organic compounds and low aromatic ring saturation. Enrichment factors Dc, calculated from salinity-normalized values of the optical DOM properties and dissolved organic carbon concentrations, indicated the significant fractionation of FDOM in the sea ice relative to the parent open waters. The humic-like terrestrial component C4 was enriched the least, whereas the protein-like component C1 was enriched the most. A statistically significant (p < 0.0001) and relatively strong (R = 63) correlation between IC1 and the total chlorophyll a concentration Tchla was found in the sea ice, which suggests that sympagic algal communities were producers of the protein-like FDOM fraction.

High-Density Liquid Water at a Water-Ice Interface.

Because ice surfaces catalyze various key chemical reactions impacting nature and human life, the structure and dynamics of interfacial layers between water vapor and ice have been extensively debated with attention to the quasi-liquid layer. Other interfaces between liquid water and ice remain relatively underexplored, despite their importance and abundance on the Earth and icy extraterrestrial bodies. By in situ optical microscopy, we found that a high-density liquid layer, distinguishable from bulk water, formed at the interface between water and high-pressure ice III or VI, when they were grown or melted in a sapphire anvil cell. The liquid layer showed a bicontinuous pattern, indicating that immiscible waters with distinct structures were separated on the interfaces in a similar manner to liquid-liquid phase separation through spinodal decomposition. Our observations not only provide a novel opportunity to explore ice surfaces but also give insight into the two kinds of structured water.

Modelling dynamic ice-sheet boundaries and grounding line migration using the level set method

AbstractComputing predictions of future sea level that include well-defined uncertainty bounds requires models that are capable of robustly simulating the evolution of ice sheets and glaciers. Ice flow behaviour is known to be sensitive to the location and geometry of dynamic ice boundaries such as the grounding line (GRL), terminus position and ice surface elevation, so that any such model should track these interfaces with a high degree of accuracy. To address this challenge, we implement a numerical approach that uses the level-set method (LSM) that accurately models the evolution of the ice–air and ice–water interface as well as capturing topological changes in ice-sheet geometry. This approach is evaluated by comparing simulations of grounded and marine-terminating ice sheets to various analytical and numerical benchmark solutions. A particular advantage of the LSM is its ability to explicitly track the moving margin and GRL while using a fixed grid finite-difference scheme. Our results demonstrate that the LSM is an accurate and robust approach for tracking the ice surface interface and terminus for advancing and retreating ice sheets, including the transient marine ice-sheet interface and GRL positions.

Water freezing characteristics in granular soils: Insights from pore-scale simulations

It has been observed in both laboratory and field studies that unfrozen soil moisture content is hysteretic between freezing and thawing conditions. While a few explanations have been provided for the causes of this hysteresis, there is no general agreement in the literature on underlying causal mechanisms. In this study, we use pore-scale simulations to investigate the role that contact angle hysteresis during freezing and thawing conditions may play in the observed differences in soil moisture content during freezing and thawing conditions. We also use these pore-scale simulations to better assess the similarities between freezing and water drainage processes in pore space as such realistic assessments are very limited in the literature. Specifically, we use 3D images of natural sand packs and synthetic silicates to generate pore-scale model domains and to simulate water drainage and water freezing in the soil pore space. The simulated water drainage curve and relative permeability-saturation relations for the sand packs agrees well with measured data available in the literature for sandy soils. The simulated soil freezing curves were successfully converted to simulated water drainage curve confirming conclusions of previous studies on coarse granular soils. Water freezing simulations using different contact angles for freezing (water receding) and thawing (water advancing) showed that the hysteresis in soil freezing curves could be driven by a hysteresis in the contact angle of water-ice interface at the pore wall (i.e. grain surface). In addition, simulations of water drainage in partially frozen soils revealed that soil freezing enhances liquid water retention in pore space due to reduction of mean active pore radius and increased frequency of pore corners which agrees with the observations of published studies in laboratory and field conditions.

Sympagic Fauna in and Under Arctic Pack Ice in the Annual Sea-Ice System of the New Arctic

A strong decline and thinning of the Arctic sea-ice cover over the past five decades has been documented. The former multiyear sea-ice system has largely changed to an annual system and with it the dynamics of sea-ice transport across the Arctic Ocean. Less sea ice is reaching the Fram Strait and more ice and ice-transported material is released in the northern Laptev Sea and the central Arctic Ocean. This trend is expected to have a decisive impact on ice associated (“sympagic”) communities. As sympagic fauna plays an important role in transmitting carbon from the ice-water interface to the pelagic and benthic food webs, it is important to monitor its community composition under the changing environmental conditions. We investigated the taxonomic composition, abundance and distribution of sea-ice meiofauna (here heterotrophs >10 μm; eight stations) and under-ice fauna (here metazoans >300 μm; fourteen stations) in Arctic 1.5 year-old pack ice north of Svalbard. Sampling was conducted during spring 2015 by sea-ice coring and trawling with a Surface and Under-Ice Trawl. We identified 42 taxa associated with the sea ice. The total abundance of sea-ice meiofauna ranged between 580 and 17,156 ind.m–2 and was dominated by Ciliophora (46%), Copepoda nauplii (29%), and Harpacticoida (20%). In contrast to earlier studies in this region, we found no Nematoda and few flatworms in our sea-ice samples. Under-ice fauna abundance ranged between 15 and 6,785 ind.m–2 and was dominated by Appendicularia (58%), caused by exceptionally high abundance at one station. Copepoda nauplii (23%), Calanus finmarchicus (9%), and Calanus glacialis (6%) were also very abundant while sympagic Amphipoda were comparatively rare (0.35%). Both sympagic communities showed regional differences in community composition and abundance between shelf and offshore stations, but only for the under-ice fauna those differences were statistically significant. Selected environmental variables moderately explained variations in abundances of both faunas. The results of this study are consistent with predictions of diversity shifts in the new Arctic.

Demonstration of the cryoprotective properties of the fucose-containing polysaccharide FucoPol

We report the cryoprotective potential of FucoPol, a fucose-containing bacterial exopolysaccharide produced by Enterobacter A47. In vitro cryopreservation assays of Vero, Saos-2, HFFF2 and C2C12 cell lines exposed to a validated non-cytotoxic 2.5 mg/mL FucoPol concentration demonstrated a consistent post-thaw metabolic viability increase. Calorimetric analysis showed a non-colligative, FucoPol concentration-dependent increase of the freezing point (Tf), with minimal change in melting point (Tm). Freezing point variation was corroborated by Polarized Optical Microscopy studies, also showing a reduction of ice crystal dimensions. Its proven shear-thinning behaviour and polyanionicity favour interactivity between the polysaccharide and the water-ice interface, resulting in ice growth inhibition. These findings demonstrate FucoPol’s high promise as a bio-based, biodegradable approach to be implemented into cryopreservation formulations.

Laboratory tests to investigate the initial phase of ice ridge consolidation

During lake/sea ice ridging and river ice jamming, broken ice blocks experience transient heat conduction. In present work, this process is represented by submerging a cold fresh-ice block into fresh water at freezing point. The thermal behavior of ice was investigated both experimentally in the cold laboratory of Norwegian University of Science and Technology and numerically with Finite Differential Method (FDM). Most thermal properties of fresh water and fresh ice are well known except the heat transfer between ice and water (convective flux). Ice pieces with varying initial thicknesses and temperatures were applied while ice growth and temperature histories were measured. The physical experiments were performed to obtain a heat transfer coefficient (h), which was essential to calculate the convective flux. The two dimensionless numbers, Fourier and Stefan numbers, were used to study the development of ice temperatures and the ice growth. During the process the convective flux has limited influence on ice temperature while it reduced the maximum ice growth. This is because new ice that forms on the water-ice interface insulates the original ice from the water. In other words, the dimensionless temperature development is governed by the Fourier number alone. The ice growth, on the other hand, is influenced by the convective flux, so that a higher initial thickness and/or a lower initial temperature decreases the ice growth fraction. A balance of latent heat, inertia and convective flux shows that an increase of convective flux directly reduces latent flux and consequently the ice growth. The overall results from simulation and experiments demonstrate that an areal scalar (convective flux) and a volumetric scalar (latent energy flux) cannot be scaled simultaneously. Therefore, the dimensionless ice growth is a function of Stefan number and modified by convective flux, which is parameterized by initial temperature and thickness.

An Ice-Binding Protein from an Antarctic Ascomycete Is Fine-Tuned to Bind to Specific Water Molecules Located in the Ice Prism Planes.

Many microbes that survive in cold environments are known to secrete ice-binding proteins (IBPs). The structure–function relationship of these proteins remains unclear. A microbial IBP denoted AnpIBP was recently isolated from a cold-adapted fungus, Antarctomyces psychrotrophicus. The present study identified an orbital illumination (prism ring) on a globular single ice crystal when soaked in a solution of fluorescent AnpIBP, suggesting that AnpIBP binds to specific water molecules located in the ice prism planes. In order to examine this unique ice-binding mechanism, we carried out X-ray structural analysis and mutational experiments. It appeared that AnpIBP is made of 6-ladder β-helices with a triangular cross section that accompanies an “ice-like” water network on the ice-binding site. The network, however, does not exist in a defective mutant. AnpIBP has a row of four unique hollows on the IBS, where the distance between the hollows (14.7 Å) is complementary to the oxygen atom spacing of the prism ring. These results suggest the structure of AnpIBP is fine-tuned to merge with the ice–water interface of an ice crystal through its polygonal water network and is then bound to a specific set of water molecules constructing the prism ring to effectively halt the growth of ice.

Remote sensing northern lake methane ebullition

Northern lakes are considered a major source of atmospheric methane (CH4), a potent GHG1,2. However, large uncertainties in their emissions (7–26 Tg CH4 yr–1; ref. 2) arise from challenges in upscaling field data, including fluxes by ebullition (bubbling), the dominant emission pathway2. Remote sensing of ebullition would allow detailed mapping of regional emissions but has hitherto not been developed. Here, we show that lake ebullition can be imaged using synthetic aperture radar remote sensing during ice-cover periods by exploiting the effect of ebullition on the texture of the ice–water interface. Applying this method to five Alaska regions and combining spatial remote sensing information with year-round bubble-trap flux measurements, we create ebullition-flux maps for 5,143 Alaskan lakes. Regional lake CH4 emissions, based on satellite remote sensing analyses, were lower compared to previous estimates based on upscaling from individual lakes2,3 and were consistent with independent airborne CH4 observations. Thermokarst lakes formed by thaw of organic-rich permafrost had the highest fluxes, although lake density and lake size distributions also controlled regional emissions. This new remote sensing approach offers an opportunity to improve knowledge about Arctic CH4 fluxes and helps to explain long-standing discrepancies between estimates of CH4 emissions from atmospheric measurements and data upscaled from individual lakes. Arctic lake methane emissions, which occur primarily by ebullition, are difficult to quantify from extrapolating in situ data due to spatial and temporal variability. Remote sensing can detect ebullition, through changes in frozen lake surface properties, reducing uncertainty in emission fluxes.

Turbulence in the stratified boundary layer under ice: observations from Lake Baikal and a new similarity model

Abstract. Seasonal ice cover on lakes and polar seas creates seasonally developing boundary layer at the ice base with specific features: fixed temperature at the solid boundary and stable density stratification beneath. Turbulent transport in the boundary layer determines the ice growth and melting conditions at the ice–water interface, especially in large lakes and marginal seas, where large-scale water circulation can produce highly variable mixing conditions. Since the boundary mixing under ice is difficult to measure, existing models of ice cover dynamics usually neglect or parameterize it in a very simplistic form. We present the first detailed observations on mixing under ice of Lake Baikal, obtained with the help of advanced acoustic methods. The dissipation rate of the turbulent kinetic energy (TKE) was derived from correlations (structure functions) of current velocities within the boundary layer. The range of the dissipation rate variability covered 2 orders of magnitude, demonstrating strongly turbulent conditions. Intensity of mixing was closely connected to the mean speeds of the large-scale under-ice currents. Mixing developed on the background of stable density (temperature) stratification, which affected the vertical structure of the boundary layer. To account for stratification effects, we propose a model of the turbulent energy budget based on the length scale incorporating the dissipation rate and the buoyancy frequency (Dougherty–Ozmidov scaling). The model agrees well with the observations and yields a scaling relationship for the ice–water heat flux as a function of the shear velocity squared. The ice–water heat fluxes in the field were the largest among all reported in lakes (up to 40 W m−2) and scaled well against the proposed relationship. The ultimate finding is that of a strong dependence of the water–ice heat flux on the shear velocity under ice. The result suggests large errors in the heat flux estimations when the traditional “bulk” approach is applied to stratified boundary layers. It also implies that under-ice currents may have much stronger effect on the ice melt than estimated by traditional models.

Numerical Simulation on the Influence of the Longitudinal Fins on the Enhancement of a Shell-and-Tube Ice Storage Device

The theoretical model of the solidification process of a shell-and-tube ice storage (STIS) device with longitudinal fins is established. The liquid fraction, the energy-discharging rate and the ice storage ratio are investigated, with particular focus on the effects of the fin structure parameters on the solidification process. Furthermore, the temperature and the streamline distributions are discussed to reveal the mechanism of the solidification process in the STIS device and the negative effect of natural convection (NC). It is indicated that the solidification process of the STIS device is dominated by the heat transfer via the fins at the beginning, and then by the heat transfer at the water–ice interface. The ice storage is negatively affected by the NC, for the reason that the water with a higher temperature stays in the lower part of the STIS device and the temperature gradient at the water–ice interface is small. The ice storage performance can be enhanced by increasing the fin structure parameters, including height, thickness and number.

Entropic Origin of the Attenuated Width of the Ice–Water Interface

The solid–liquid interface of water is ∼50% narrower (or thinner) than that of argon. With the help of molecular dynamics simulations, we compare two water models, namely, TIP4P/ice and mW, with Le...

Heightened Cold-Denaturation of Proteins at the Ice-Water Interface.

The process of freezing proteins is widely used in applications ranging from processing and storage of biopharmaceuticals to cryo-EM analysis of protein complexes. The formation of an ice-water interface is a critical destabilization factor for the protein, which can be offset by the use of cryo-protectants. Using molecular dynamics simulation, we demonstrate that the presence of the ice-water interface leads to a lowering of the free-energy barrier for unfolding, resulting in rapid unfolding of the protein. The unfolding process does not require direct adsorption of the protein to the surface, but is rather mediated by nearby liquid molecules that show an increased tendency for hydrating nonpolar groups. The observed enhancement in the cold denaturation process upon ice formation can be mitigated by addition of glucose, which acts as a cryoprotectant through preferential exclusion from side chains of the protein.

Computational Study of Differences between Antifreeze Activity of Type-III Antifreeze Protein from Ocean Pout and Its Mutant.

The antifreeze activity of a type-III antifreeze protein (AFP) expressed in ocean pout (Zoarces americanus) is compared with that of a specific mutant (T18N) using all-atom molecular dynamics simulations. The antifreeze activity of the mutant is only 10% of the wild-type AFP. The results from this simulation study revealed the following insights into the mechanism of antifreeze action by type-III AFPs. The AFP gets adsorbed to the advancing ice front due to its hydrophobic nature. A part of the hydrophobicity is caused by the presence of clathrate structure of water molecules near the ice-binding surface (IBS). The mutation in the AFP disrupts this structure and thereby reduces the ability of the mutant to adsorb to the ice-water interface leading to the loss of antifreeze activity. The mutation, however, has no effect on the ability of the adsorbed protein to bind to the growing ice phase. Simulations also revealed that all surfaces of the protein can bind to the ice phase, although the IBS is the preferred surface.