Ice Growth Research Articles

Global Evidence of Obliquity Damping in Climate Proxies and Sea-Level Record during the Last 1.2 Ma: A Missing Link for the Mid-Pleistocene Transition

A recent research has identified an inverse amplitude link between obliquity damping and short eccentricity amplification during the Mid-Late Pleistocene based on LR04 δ18O and equatorial Pacific Site 846 sea surface temperature records that is associated with the Earth’s long-term cooling. In the present study, new evidence of this anticorrelation is presented from Antarctic δD-CO2-CH4 records, global benthic–planktic δ18O, and regional (Atlantic, Pacific, Mediterranean, and Indian) climate-related proxies. Based on a critical review of theoretical constraints (Earth’s oblateness changes and ice-volume phase lag in the obliquity band <5.0 kyr), this widespread and symmetric (bipolar) obliquity response damping has been interpreted as an effect of the obliquity–oblateness feedback, which could be the latent physical mechanism at the origin of the Mid-Pleistocene Transition (MPT). Indeed, results and considerations of the present work suggest that fast and positive/negative net variation in the Earth’s oblateness in the obliquity band was controlled by a dominant glacio-eustatic water mass component and, assuming a rapid response of the ice volume to surface temperature changes, the mean obliquity lag response is estimated to be <5.0 kyr over the past 800 kyr. These elements may explain the interglacial/glacial damping observed in the obliquity response. The consolidation of the Earth’s long-term icy state in the subtrend IV, culminating with the post-MPT obliquity damping, might have contributed to the strengthening of the short eccentricity response by mitigating the obliquity ‘ice killing’ during obliquity maxima (interglacials), favouring the obliquity-cycle skipping and a feedback-amplified ice growth in the short eccentricity band (obliquity damping hypothesis). This suggests a different impact of the climate friction than what is generally believed, which is presumably the latent physical mechanism that triggers the transient ‘competitive’ interaction between obliquity and short eccentricity started early during the Piacenzian.

Retarding ice recrystallization by tamarind seed polysaccharide: Investigation in ice cream mixes and insights from molecular dynamics simulation

Food hydrocolloids, such as naturally sourced polysaccharide stabilizers, are becoming potential candidates for retarding ice recrystallization in frozen desserts. Tamarind seed polysaccharide (TSP) and its depolymerized fraction (DTSP) possessed ice recrystallization retardation (IRR) activity by a splat cooling assay. This study is a follow-up work aiming to investigate their application effects to retard ice recrystallization in ice cream mixes (ICMs) and delve into the ice-binding behavior at the ice/water interface. Native TSP worked for or against IRR in the ICMs depending on the concentration, while DTSP possessed an increased IRR effect under the addition of higher concentration (3.0%). Compared to TSP, adding DTSP caused less of an increase in the viscosity of the ICMs. Molecular dynamics was used to simulate ice growth in the presence of TSP (oligomer) and showed that the TSP possessed activity for retarding ice growth along the prismatic planes. During the propagation of ice crystals, the TSP was bound onto the ice and caused evident structural defects of ice layers. The findings of this study proved that TSP and DTSP have a promising application to retard ice recrystallization in ice cream and shed new light on understanding the mechanism of natural polysaccharides to retard ice growth.

Numerical investigations on aero-engine icing characteristics at mixed phase conditions

Ice crystal/mixed phase icing in aero-engine will cause engine surge, stalling, thrust reduction, and even stop in extreme cases, which seriously endangers flight safety. In this paper, the characteristics of mixed phase ice accretion in aero-engines are numerically studied. The air flow field model, mixed phase trajectory model, impact model, sticking model and ice accretion model are established. Meanwhile, the sensitivity parameters of ice accretion, such as flight speed, icing time, melting rate (LWC/TWC), and relative humidity (RH), were investigated in detail. The results show that the ice thickness of nacelle surface and nosecone surface increases with the increase of flight speed. With the increase of fan span, the icing thickness of the fan surface increases significantly. The icing of the fan is mainly concentrated on the pressure side of the fan, while the suction side of the fan only has a small amount of icing in the leading edge. In the early stage of icing, the icing thickness of nacelle increases rapidly, and with the increase of icing time, the icing thickness increases, but the icing growth rate becomes slower. With the increase of the melting rate, the ice thickness of the nacelle, the nosecone and the fan pressure side surface increased significantly. When the fan span is 90 % and the melting rate is 0.05, 0.15, and 0.25, the maximum icing amount on the fan surface is 1.56, 3.85, and 5.71 mm, respectively. When the RH is high, there is more ice accumulation on the nacelle surface. At RH is 80 %, the ice thickness at the nosecone tip reaches 5.48 mm. Finally, when using the hot air deicing method, the hot air flow needs to be reasonably distributed according to the amount of icing, and the parts with less icing can appropriately reduce the distribution of hot air for rational use of energy and energy conservation.

Polycrystallinity Enhances Stress Buildup around Ice.

Damage caused by freezing wet, porous materials is a widespread problem but is hard to predict or control. Here, we show that polycrystallinity significantly speeds up the stress buildup process that underpins this damage. Unfrozen water in grain-boundary grooves feeds ice growth at temperatures below the freezing temperature, leading to fast stress buildup. These stresses can build up to levels that can easily break many brittle materials. The dynamics of the process are very variable, which we ascribe to local differences in ice-grain orientation and to the surprising mobility of many grooves-which further accelerates stress buildup. Our Letter will help understand how freezing damage occurs and in developing accurate models and effective damage-mitigation strategies.

Physical Links from Atmospheric Circulation Patterns to Barents–Kara Sea Ice Variability from Synoptic to Seasonal Timescales in the Cold Season

Abstract Previous findings show that large-scale atmospheric circulation plays an important role in driving Arctic sea ice variability from synoptic to seasonal time scales. While some circulation patterns responsible for Barents–Kara sea ice changes have been identified in previous works, the most important patterns and the role of their persistence remain unclear. Our study uses self-organizing maps to identify nine high-latitude circulation patterns responsible for day-to-day Barents–Kara sea ice changes. Circulation patterns with a high pressure center over the Urals (Scandinavia) and a low pressure center over Iceland (Greenland) are found to be the most important for Barents–Kara sea ice loss. Their opposite-phase counterparts are found to be the most important for sea ice growth. The persistence of these circulation patterns helps explain sea ice variability from synoptic to seasonal time scales. We further use sea ice models forced by observed atmospheric fields (including the surface circulation and temperature) to reproduce observed sea ice variability and diagnose the role of atmosphere-driven thermodynamic and dynamic processes. Results show that thermodynamic and dynamic processes similarly contribute to Barents–Kara sea ice concentration changes on synoptic time scales via circulation. On seasonal time scales, thermodynamic processes seem to play a stronger role than dynamic processes. Overall, our study highlights the importance of large-scale atmospheric circulation, its persistence, and varying physical processes in shaping sea ice variability across multiple time scales, which has implications for seasonal sea ice prediction. Significance Statement Understanding what processes lead to Arctic sea ice changes is important due to their significant impacts on the ecosystem, weather, and shipping, and hence our society. A well-known process that causes sea ice changes is atmospheric circulation variability. We further pin down what circulation patterns and underlying mechanisms matter. We identify multiple circulation patterns responsible for sea ice loss and growth to different extents. We find that the circulation can cause sea ice loss by mechanically pushing sea ice northward and bringing warm and moist air to melt sea ice. The two processes are similarly important. Our study advances understanding of the Arctic sea ice variability with important implications for Arctic sea ice prediction.

The roles of undercooling degree and materials surface configuration in the growth mechanism of ice layer caused by micro-droplets

Effect mechanisms of the undercooling degree and the surface configuration on the ice growth characteristics were revealed under micro-droplets icing conditions. Preferential ice crystals appear firstly on the surfaces due to the randomness of icing, and obtain growth advantages to form protruding structures. Protruding structures block the incoming droplets from contacting the substrates, causing voids around the structures. The undercooling degree mainly affects the density and the growth rate of preferential ice crystals. With the increase of undercooling degree, the preferential ice crystals have higher density and growth rate, resulting in stronger growth advantage and higher porosity. The surface configuration affects the growth mode, and the ice layer grows with uniform mode, spreading mode and structure-induced mode on the aluminum, smooth Polytetrafluoroethylene (PTFE) and rough PTFE surface respectively, causing the needle-like, ridge-like and cluster-like ice crystals. The rough structures effectively improve the porosity of the ice layer, which is beneficial for optimizing the icephobic property of the materials. This paper provides important theoretical guidance for the design of subsequent icephobic materials.

Investigating the Interaction Between Ice-Binding Proteins and Ice Surfaces Using Microfluidic Devices and Cold Stages.

Ice-binding proteins (IBPs) protect organisms living in sub-freezing conditions by inhibiting ice growth in fish and insects, limiting ice recrystallization in plants, and assisting bacteria to adhere to ice. The mechanisms by which these proteins bind to ice and inhibit its growth have been studied both experimentally and using molecular dynamic simulations. A unique experimental technique developed to test and characterize the interactions between IBPs and ice using a combination of a microfluidic device, cold stages with millikelvin temperature resolution, fluorescence-labeled IBPs, and fluorescence microscopy is described herein. The main advantage of this technique is the ability to exchange the solution around micron-sized ice crystals and characterize their binding to and inhibition of ice.

Development of a radical polymerization algorithm for molecular dynamics simulations of antifreezing hydrogels with double-network structures

The development and understanding of antifreezing hydrogels are crucial both in principle and practice for the design and delivery of new materials. The current antifreezing mechanisms in hydrogels are almost exclusively derived from their incorporation of antifreezing additives, rather than from the inherent properties of the polymers themselves. Moreover, developing a computational model for the independent yet interconnected double-network (DN) structures in hydrogels has proven to be an exceptionally difficult task. Here, we develop a multiscale simulation platform, integrating ‘random walk reactive polymerization’ (RWRP) with molecular dynamics (MD) simulations, to computationally construct a physically-chemically linked PVA/PHEAA DN hydrogels from monomers that mimic a radical polymerization and to investigate water structures, dynamics, and interactions confined in PVA/PHEAA hydrogels with various water contents and temperatures, aiming to uncover antifreezing mechanism at atomic levels. Collective simulation results indicate that the antifreezing property of PVA/PHEAA hydrogels arises from a combination of intrinsic, strong water-binding networks and crosslinkers and tightly crosslinked and interpenetrating double-network structures, both of which enhance polymer-water interactions for competitively inhibiting ice nucleation and growth. These computational findings provide atomic-level insights into the interplay between polymers and water molecules in hydrogels, which may determine their resistance to freezing.

Functional aggregation of cell-free proteins enables fungal ice nucleation.

Biological ice nucleation plays a key role in the survival of cold-adapted organisms. Several species of bacteria, fungi, and insects produce ice nucleators (INs) that enable ice formation at temperatures above -10 °C. Bacteria and fungi produce particularly potent INs that can promote water crystallization above -5 °C. Bacterial INs consist of extended protein units that aggregate to achieve superior functionality. Despite decades of research, the nature and identity of fungal INs remain elusive. Here, we combine ice nucleation measurements, physicochemical characterization, numerical modeling, and nucleation theory to shed light on the size and nature of the INs from the fungus Fusarium acuminatum. We find ice-binding and ice-shaping activity of Fusarium IN, suggesting a potential connection between ice growth promotion and inhibition. We demonstrate that fungal INs are composed of small 5.3 kDa protein subunits that assemble into ice-nucleating complexes that can contain more than 100 subunits. Fusarium INs retain high ice-nucleation activity even when only the ~12 kDa fraction of size-excluded proteins are initially present, suggesting robust pathways for their functional aggregation in cell-free aqueous environments. We conclude that the use of small proteins to build large assemblies is a common strategy among organisms to create potent biological INs.

Tracking the Eurydesma Fauna transgression across southwestern Gondwana

The cold water Eurydesma Fauna, consisting of bivalves, brachiopods, and scarce gastropods, has been associated in several basins of Gondwana with the terminal phase of the Late Paleozoic Ice Age (LPIA). The Eurydesma Fauna-bearing transgression has been identified in basins of South America and southern Africa. In western Karoo Basin of South Africa four phases of ice growth and decay have been proposed for the Dwyka Group on the basis of interstratified glaciogenic diamictites overlain by non-glaciogenic, ice rafted debris free mudstones. Each of these phases is assigned to deglaciation sequences (sensu Visser, 1997) and has been proposed to be incomplete, third order sequences made up of a basal lowstand systems tract (LST) followed by a transgressive systems tract (TST) or exclusively by a thick TST. The correlation of these deglaciation sequences has been extended to the adjacent Aranos-Kalahari basin and to the Paraná Basin (Itararé Group) in South America. Recent high-precision UPb ages on single crystal chemical abrasion, isotope dilution-thermal ionization mass spectrometry (CA-IDTIMS) have helped to refine the diachronous demise of the LPIA and the age of the Eurydesma transgression. Tentative correlations with the glaciogenic section (Sauce Grande Formation) in the Ventana Fold belt (VFB) and Malvinas/Falkland Islands (Fitzroy Tillite Formation) are supported by radiometric ages, and similar facies associations respectively. This interbasinal correlation of deglaciation sequences and radiometric ages allowed to constrain the occurrence of this fauna in southwestern Gondwana to the Asselian.The postglacial nature of the Eurydesma Fauna transgression in South American basins, particularly in the VFB-Claromecó Basin of Argentina, is in contrast with its interglacial character in the Southern African basins, where the Eurydesma transgression caps the deglaciation sequence 3 and underlies the deglaciation sequence 4.

Machine learning based classification of lake ice and open water from Sentinel-3 SAR altimetry waveforms

The aim of the study was to evaluate, for the first time, the capability of different machine learning (ML) algorithms in classifying along-track lake surface conditions (open water and ice types) across ice seasons (freeze-up, ice growth and break-up periods) from Sentinel-3 A/B synthetic aperture radar altimeter (SRAL) data. To achieve this goal, over 107,500 radar waveforms extracted from 11 large lakes across the Northern Hemisphere and three ice seasons (2018–2021) were manually labelled using complementary satellite data (Sentinel-1 imaging Synthetic Aperture Radar (SAR), Sentinel-2 Multispectral Instrument (MSI) Level 1C, and MODIS Aqua/Terra data) for the training and testing of the ML algorithms in discriminating between open water, young (thin) ice, growing ice and melting ice. The four ML algorithms tested include Random Forest (RF), Gradient Boosting Trees (GBT), K Nearest Neighbor (KNN) and Support Vector Machine (SVM). To characterize the waveforms, seven waveform parameters were derived: Leading Edge Width (LEW), Offset Center of Gravity (OCOG) Width, Pulse Peakiness (PP), backscatter coefficient (Sigma0), late tail to peak power (LTPP), early tail to peak power (ETPP) and the maximum value of the echo power (Max). Accuracies >95% were achieved across all classifiers using a 4-parameter combination (Sigma0, PP, OCOG Width, and LEW). Among all waveform parameters, Sigma0, OCOG width and PP were found to be the most important parameters for discriminating between lake ice types and open water. Despite showing comparable classification performances in the overall classification, RF and KNN are found to be a better fit for global lake ice mapping as both are less sensitive to their internal hyperparameters. Additionally, consistent results (>93.7% accuracy in all classifiers) achieved on the accuracy assessment carried out for each lake (out-of-sample testing) revealed the strength of the classifiers for spatial transferability. Implementation of RF and KNN could be valuable in a pre-or post-processing step for identifying lake surface conditions under which the retrieval of water level and ice thickness may be limited or not possible and, therefore, inform algorithms currently used for the generation of operational or research products. While the research focused on 11 of the largest lakes of the Northern Hemisphere, the classification approach presented herein has potential for application on smaller lakes too since data in SAR mode (∼300 m along-track resolution) are used.

Molecular simulation of the confined crystallization of ice in cement nanopore.

Freezing of water under nanoconfinement exhibits physical peculiarities with respect to the bulk water. However, experimental observations are extremely challenging at this scale, which limits our understanding of the effect of confinement on water properties upon freezing. In this study, we use molecular dynamic simulations to investigate how confinement affects the kinetics of growth of ice and the thermodynamic equilibrium of ice-liquid coexistence. TIP4P/Ice water model and CSH-FF model were applied to simulate ice crystallization in a confined cement system at temperatures down to 220K. We adapted an interface detection algorithm and reparameterized the CHILL/CHILL+ algorithm to capture ice growth. The confinement leads to a shift of the maximum growth rate of ice to a higher temperature than for bulk water. Both the confinement and surface impurities contribute to slowing down the ice growth. For the ice-liquid coexistence at equilibrium, we derive a formulation of Thomson's equation adapted to statistical physics quantities accessible by molecular simulation, and we show that this adapted equation predicts accurately the melting line of bulk and confined ice Ih as a function of pressure. The confinement decreases systematically the melting temperature of ice of about 5K compared with bulk ice Ih. A premelted water film about 1nm thick is observed between the solid wall and ice, and its thickness is found to decrease continuously as temperature is lowered. We note that the surface impurities are key to the formation of the premelted water nanofilm when the temperature is lower than 250K.

Effect of cryoprotectant-induced intracellular ice formation and crystallinity on bacteria during cryopreservation

Cryopreservation is widely used for the long-term storage of bacteria. Glycerol is one of the traditional cryoprotectants used widely to prevent cryoinjury during the cryopreservation of bacteria,although it may be toxic to the cells. To overcome these issues, synthetic antifreeze polymers are also used as cryoprotectants to inhibit ice formation. In the study, we compared the performance of various antifreeze synthetic polymers including poly(vinyl alcohol) (PVA), poly(vinylpyrrolidone), poly(ethylene glycol), and dextran with glycerol, among which PVA performed best on decreasing the ice growth rate.The impacts of glycerol, trehalose, combined with PVA on the survival of S. thermophilus were also explored. Notably,. S. thermophilus stored in 100 mg/mL trehalose and 1 mg/mL PVA +50 mg/mL trehalose combo showed significantly enhanced survival when compared with those in traditional cryoprotectant (20% [v/v] glycerol), which achieved the survival percentage of only 41.03 ± 0.09%. The effects of the freezing temperature and crystallinity on the survival of S. thermophilus were elucidated.

Self-Assembled Nanostructures of Homo-Oligopeptide as a Potent Ice Growth Inhibitor.

This study reports the formation of self-assembled nanostructures with homo-oligopeptides consisting of amino acids (i.e., alanine, threonine, valine, and tyrosine), the resulting morphologies (i.e., spherical shape, layered structure, and wire structure) in aqueous solution, and their potential as ice growth inhibitors. Among the homo-oligopeptides investigated, an alanine homo-oligopeptide (n = 5) with a spherical nanostructure showed the highest ice recrystallization inhibition (IRI) activity without showing a burst ice growth property and with low ice nucleation activity. The presence of nanoscale self-assembled structures in the solution showed superior IRI activity compared to an amino acid monomer because of the higher binding affinity of structures on the growing ice crystal plane. Simulation results revealed that the presence of nanostructures induced a significant inhibition of ice growth and increased lifetime of hydrogen bonding compared with unassembled homo-oligopeptide. These results envision extraordinary performance for self-assembled nanostructures as a desirable and potent ice growth inhibitor.

Surface Roughness in RANS Applied to Aircraft Ice Accretion Simulation: A Review

Experimental and numerical fluid dynamics studies highlight a change of flow structure in the presence of surface roughness. The changes involve both wall heat transfer and skin friction, and are mainly restricted to the inner region of the boundary layer. Aircraft in-flight icing is a typical application where rough surfaces play an important role in the airflow structure and the subsequent ice growth. The objective of this work is to investigate how surface roughness is tackled in RANS with wall resolved boundary layers for aeronautics applications, with a focus on ice-induced roughness. The literature review shows that semi-empirical correlations were calibrated on experimental data to model flow changes in the presence of roughness. The correlations for RANS do not explicitly resolve the individual roughness. They principally involve turbulence model modifications to account for changes in the velocity and temperature profiles in the near-wall region. The equivalent sand grain roughness (ESGR) approach emerges as a popular metric to characterize roughness and is employed as a length scale for the RANS model. For in-flight icing, correlations were developed, accounting for both surface geometry and atmospheric conditions. Despite these research efforts, uncertainties are present in some specific conditions, where space and time roughness variations make the simulations difficult to calibrate. Research that addresses this gap could help improve ice accretion predictions.

Numerical study of supercooled water droplet impacting on cold superhydrophobic surface under electric field

The process of ice formation on outdoor electrical equipment is determined by the impact of supercooled droplets on the cold surface under an electric field. Clarifying the impact-freezing of a supercooled droplet under an electric field is important for designing anti-icing surfaces in the power industry. Here, we developed a coupled electro-solidification model by combining the volume of fluid (VOF) method, a dynamic contact angle model, the two-phase electrohydrodynamic (EHD) model, the modified enthalpy solidification method and the nucleation effect. Then, the impact dynamics of a water droplet on a cold superhydrophobic surface under an electric field were studied numerically. The effects of the electric field intensity, Weber number, initial droplet temperature and conductivity on the spreading factor βm and the freezing fraction αad are analyzed. By specifically considering the effect of the electric field enhancing the water to freeze, the bottom filament is successfully recreated in the simulation. This phenomenon was first reproduced in our simulation, and it would significantly increase the probability of icing on the cold surface under the electric field, even on the superhydrophobic surface. Finally, based on the numerical results and published experimental data, we fit the freezing fraction relation of the supercooled water droplet impinging on cold superhydrophobic surface under the electric field, which can be used to predict the icing growth and prevention of icing on transmission lines. The numerical model developed here can also be directly used to simulate ice growth and guide the design of anti-icing surfaces in power transmission systems.

Models for thermal boundary layer in level ice growth and brash ice consolidation

It is important to understand the properties and parameters of ice growth models, to enable reliable assessment of the impact ice may have on facilities or to ship navigation. To improve the understanding of the different models, the theoretical formulations for ice growth are investigated and calculated results compared with laboratory and full-scale measurement data. The paper describes the ice growth models for level sea ice and how these are applied in brash ice consolidation modelling. In particular, analysis is made to account for modelling of snow cover in level ice growth models, and subsequently also salinity, porosity and the atmospheric boundary including wind effect in brash ice models. The paper presents an overview of laboratory tests and results for both level ice and brash ice. Also models for level ice growth for the case of snow cover are derived and compared with thetest results. Specifically, inclusion of snow thickness in the growth model presents some practical difficulties, as the thickness of snow cover is often not known a priori, and comparison between calculated level ice thickness and measurements suggests that a good assumption in predictive models is to assume the snow cover thickness to be proportional to level ice thickness. Further, it was observed that the wind influences much the heat transfer to atmosphere, which is not zero at the zero wind speed, a value for the heat transfer coefficient to atmosphere is derived based on laboratory tests. The findings from these analyses provide an improved understanding of the ice growth and consolidation process which can be incorporated into modelling techniques for marine design and operations.

Persistent impact of winter atmospheric circulation anomalies on Arctic sea ice

According to previous studies, the Arctic Oscillation (AO) in winter has an impact on the evolution of sea ice conditions from winter until the following September. This study explores and compares the sea ice responses to two climatic modes of variability in the winter, the positive phase of the AO and the negative phase of the Arctic Dipole (AD) patterns. This study for the first time verifies that the AD-induced sea ice thickness change is comparable in magnitude to the AO-induced change by the end of the melting season. It proves that the negative AD in winter has a persistent impact on sea ice thickness comparable to the AO has. Furthermore, the AO and AD in the winter impact sea ice conditions in different ways. The AO cannot decrease sea ice thickness until the melting season. Most decreases in sea ice thickness are found over the Beaufort and Chukchi Seas starting in May. On the other hand, the negative AD mostly inhibits sea ice growth during the growing season thermodynamically over the Atlantic sector of the Arctic Ocean. The ensemble means of 22 CMIP6 models can reasonably catch the response of sea ice thickness change to the AO and AD in spatial distribution and temporal evolution. The CMIP6 model ensemble is better at reproducing the AD-induced response of sea ice than the AO-induced response, while the spread of results from individual models is extensive.

Crystal nucleation in a vapor deposited Lennard-Jones mixture

Understanding the pathways to crystallization during the deposition of a vapor phase on a cold solid substrate is of great interest in industry, e.g., for the realization of electronic devices made of crystallites-free glassy materials, as well as in the atmospheric science in relation to ice nucleation and growth in clouds. Here we numerically investigate the nucleation process during the deposition of a glassformer by using a Lennard-Jones mixture, and compare the properties of this nucleation process with both its quenched counterpart and the bulk system. We find that all three systems homogeneously nucleate crystals in a narrow range of temperatures. However, the deposited layer shows a peculiar formation of ordered domains, promoted by the faster relaxation dynamics toward the free surface even in an as-deposited state. In contrast, the formation of such domains in the other systems occurs only when the structures are fully relaxed by quenching. Furthermore, the nucleus initially grows in an isotropic symmetrical manner, but eventually shows sub-3D growth due to its preference to grow along the basal plane, irrespective of the layer production procedure.

Identification of a common ice nucleus on hydrophilic and hydrophobic close-packed metal surfaces

Establishing a general model of heterogeneous ice nucleation has long been challenging because of the surface water structures found on different substrates. Identifying common water clusters, regardless of the underlying substrate, is one of the key steps toward solving this problem. Here, we demonstrate the presence of a common water cluster found on both hydrophilic Pt(111) and hydrophobic Cu(111) surfaces using scanning tunneling microscopy and non-contact atomic force microscopy. Water molecules self-assemble into a structure with a central flat-lying hexagon and three fused pentagonal rings, forming a cluster consisting of 15 individual water molecules. This cluster serves as a critical nucleus during ice nucleation on both surfaces: ice growth beyond this cluster bifurcates to form two-dimensional (three-dimensional) layers on hydrophilic (hydrophobic) surfaces. Our results reveal the inherent similarity and distinction at the initial stage of ice growth on hydrophilic and hydrophobic close-packed metal surfaces; thus, these observations provide initial evidence toward a general model for water-substrate interaction.