A brief study of the force balance between a small iceberg,the ocean,sea ice,and atmosphere in the Weddell Sea

Icebergs are an important source of freshwater to the Weddell Sea. A unique set of oceanographic and other observations made during the Maud Rise Nonlinear Equation of State Study around one of the small icebergs, ubiquitous in the winter Weddell Sea, give us the opportunity to examine the dynamics of the interaction between an iceberg and the ocean. The iceberg was mapped using radar ranges and bearings from our ship, the research icebreaker Nathaniel Palmer, and found to be about 200 m wide above the water with a draft estimated to be 219 m. For this size, form drag dominates skin friction in both the atmosphere and ocean. Sea ice was ridged against the upwind side of the iceberg and thin sea ice and open water were on the downwind side. The iceberg was drifting 0.14 m s^− 1, or about 3% of the wind speed and 23° to the left. An automated CTD operating through the ship's moon-pool was used to measure temperature and salinity profiles upstream, downstream, and to the side of the iceberg. These profiles show a mixed upper layer 150 m deep upstream and 60 m deep downstream of the iceberg. The difference in density across the pycnocline was 0.05 kg m^− 3, which for the average pycnocline depth of 105 m and size of the iceberg corresponds to an interfacial internal wave speed equal to 0.166 m s^− 1. This and the upstream–downstream difference in pycnocline depth are consistent with a ± 45 m internal wave wake being generated by the motion of the iceberg. We estimate the contributions to total water drag from form drag and generation of the internal wake to be about equal. Consistent with theory, a qualitative argument using the observed pycnocline displacements suggests that internal wake drag should be a maximum when iceberg drafts are near the pycnocline depth. The drift rate of the iceberg (and sea ice) relative to wind speed was near the relative drift rate for the Weddell Sea ice we encountered during MaudNESS, but three times greater than what would result from a pure balance of atmospheric form drag against ocean form drag on the iceberg. Therefore, the force of sea ice on the iceberg, evidenced by ridging on the upwind side was dominant in moving the iceberg with the sea ice drift speed. The force transmitted through the sea ice required to drive the ice at the observed rate would be equivalent to the wind stress acting on an area of sea ice of 7.5 km². Maximum ridging forces in the 0.5 m thick sea ice should be adequate to drive the iceberg with this 219-m draft at 0.56 m s^− 1, much more than the observed drift rate but similar to the sea ice velocities during Weddell Sea storms.     

Capacitance probe measurements of brine volume and bulk salinity in first-year sea ice

First-year sea ice plays an important role in the global climate system. It changes the physical properties of the surface of the polar oceans, and modifies the energy and mass transfer between the ocean and the atmosphere. An understanding of the way sea ice affects ocean–atmosphere exchange requires detailed knowledge of the evolution of ice physical properties, which are governed by its temperature and bulk salinity. To this effect, we assessed the utility of commercially available capacitance probes in determining the salinity evolution of first-year sea ice. Measurements of the complex dielectric permittivity, ε = ε′ − iε″, at 50 MHz were carried out in land-fast ice in McMurdo Sound, Antarctica, and in the Chukchi Sea near Barrow, Alaska. For comparison, we also deployed the probes in artificial, young sea ice in an outdoor tank experiment in Fairbanks, AK. The dielectric permittivity data compare well with predictions from a dielectric mixture model.We have derived a simple relation that allows for the derivation of brine volume fraction and bulk salinity in columnar first-year sea ice from the real part of the complex dielectric permittivity. For ice at temperatures below the percolation threshold, the error in the derived bulk salinity is less than 15%. The dependence of dielectric permittivity on brine inclusion morphology needs to be taken into consideration, and measurements indicate that changes in pore morphology are recorded in the capacitance measurements.In this paper we use the real part, ε′, of the complex dielectric permittivity to study the bulk salinity of bubble-free columnar ice. Further investigations, using the imaginary part of the complex dielectric permittivity, ε″, will make it possible to use the same probes to measure the bulk salinity and pore morphology of other types of ice, e.g., frazil, platelet, and multi-year ice.     

Gravity-induced sea ice desalination under low temperature

The Bohai Rim is one of the water-scarce regions in China. But every winter, more than 1 billion m³ of sea ice formed in the sea, about 40% of which distributes within 10 km offshore and is expected to be exploited and utilized as source of freshwater. The salinity of the Bohai sea ice ranges from 4 to 11‰, under suitable ambient temperatures, gravity driven brine drainage and flushing from the melted water can convert sea ice into freshwater ice. To study the influence of ambient conditions on the process, we conducted two experiments on the coast of the Bohai Sea from January to March in 2011. The results showed that ambient temperature was a decisive and controlling factor in gravity-induced sea ice desalination, and that insulation could affect the duration, volume and salinity of the drainage. If the ambient temperature was controlled between − 4.0 and 3.0 °C, the drainage would have a low volume and high salinity. With a rise in the air temperature, the volume of the drainage increased and the salinity decreased. Sea ice desalination and freshwater production were negatively correlated: the higher the freshwater production, the lower the sea ice desalination and vice versa.     

Fracture of a ridged multi-year Arctic sea ice floe

As part of the 1994 Sea Ice Mechanics Initiative experimental program, fracture experiments were carried out on an 80 m diameter ridged multi-year (MY) ice floe in the Beaufort Sea. An edge cracked, quasi-circular ridged floe was subjected to both cyclic and ramp loading sequences using a steel flat jack. Load, crack opening displacement, acoustical and seismic measurements were made during the experiments. The objective was to gain further insight into the fracture and constitutive properties of MY sea ice. Accurate predictions of the strength of MY sea ice and the forces developed during interactions between MY sea ice and floating or fixed structures are sought. Such interactions include MY ice floe collisions with offshore structures and ships. The fracture resistance of MY ice is determined to be within the range 23 < G_c < 47 J/m² for a 80 m diameter ridged MY floe. This fracture energy is similar to values obtained for the fracture of FY sea ice both in the Arctic and the Antarctic.     

Friction of sea ice on sea ice

This paper presents the results from field tests on the friction of sea ice on sea ice performed in the Barents Sea and fjords at Spitsbergen. The effects of the sliding velocity (6 mm/s to 105 mm/s), air temperatures (− 2 °C to − 20 °C), normal load (300 N to 2000 N), presence of sea water in the interface, and ice grain orientation with respect to the sliding direction on the friction coefficient were investigated. The effect of the hold time on the static friction coefficient was also studied. The roughness of the ice surface is an important parameter that determines the value of the friction coefficient. Repeated sliding over the same track led to surface polishing and decreased the kinetic friction coefficient from 0.48 to 0.05. The studies showed that the friction coefficient is independent of the velocity when sliding occurs between natural ice surfaces. As the contacting surfaces became smoother, the kinetic friction coefficient started to depend on the velocity, as predicted by existing ice friction models. Both very high (~ 0.5) and low (~ 0.05) kinetic friction coefficients were obtained in the tests performed at high (− 2 °C) and low (− 20 °C) air temperatures. The presence of sea water in the sliding interface had very little effect on the static and kinetic friction coefficients. The static friction coefficient logarithmically increased with the hold time from ~ 0.6 at 5 s to 1.26 at 960 s. The results are discussed, and the dependences are compared with existing friction models.     

Deformation of the Arctic Ocean ice cover after the 2007 record minimum in summer ice extent

We examine the deformation of the Arctic Ocean sea ice cover after the record minimum in summer extent in 2007. The period spans ~ 2.5 months between September 15 and December 1. Ice drift and deformation inside the ice edge, within a domain that initially covers ~ 0.76 × 10⁶ km² of the western Arctic, are derived from high-resolution RADARSAT imagery from the Alaska Satellite Facility. Poleward of 80°N, we find a net convergence of more than 14% over the period. This large convergence is associated with the strength, location, and persistence of the Beaufort high-pressure pattern that led to prevailing on-shore winds north of Ellesmere Island and Greenland. This can be contrasted to the nearly 25% divergence of the ice cover, accompanied by a large regional vorticity of − 0.93 (or a clockwise rotation of ~ 53°) south of 80°N. The same atmospheric pattern produced openings as the ice cover drifts southwest towards the unconstrained ice-free part of the southern Beaufort and Chukchi Seas. These sustained strain rates, especially convergence, impacts the area and thickness distribution of the sea ice cover in the Arctic Basin. If unaccounted for, this deformation-induced decrease in ice coverage (in this region with predominantly multiyear ice) could be incorrectly ascribed to ice export with a concurrent decrease in Arctic sea ice volume, when in fact the ice volume is conserved but with a local redistribution in thickness.     

Local ice pressures for multiyear ice accounting for exposure

Local pressures are generally determined based on extreme pressures obtained in measurements. The exposure of structural components is an issue that needs attention. Exposure can be considered in everyday terms as “the longer you fish, the bigger the fish you catch.” In the case of design of offshore structures for ice environments, the more numerous the number of ice–structure interaction events, the greater the likelihood of a particular load being exceeded. The number of interactions with multiyear ice is different for say the Beaufort and Chukchi Seas, and varies with location within these areas. These differences are expressed in terms of the exposure of the structure to multiyear ice. Exposure may also vary depending on location within the structure. Structure above or below the ice belt may receive few interactions resulting in small local pressures.The paper presents a generalization of a method for accounting for exposure, originally developed for ship rams. The particular application is multiyear ice interacting with a structure. The panel data from the Beaufort Sea experience of the Molikpaq structure is used as an example. Exposure is an important parameter that can be taken into account with the method. The previous relationship α = 1.25a^− 0.7 obtained for ship rams can be reasonably applied to multiyear ice, where 10 min of multiyear ice interaction is approximately equivalent to 1 Kigoriak ship ramming event. The method is promising for use in codes, for example with the new ISO Code 19906.     

Study on optical weak absorption of borate crystals

Borate crystal is an important type of nonlinear optical crystals used in frequency conversion in all-solid-state lasers. Especially, LiB₃O₅ (LBO), CsB₃O₅ (CBO) and CsLiB₆O₁₀ (CLBO) are the most advanced. Although these borate crystals are all constructed by the same anionic group-(B₃O₇)⁵⁻, they show different nonlinear optical properties. In this study, bulk weak absorption values of three borate crystals have been studied at 1064 nm by a photothermal common-path interferometer. The bulk weak absorption values of them along [1 0 0], [0 1 0] and [0 0 1] directions were obtained, respectively, to be approximately 17.5 ppm cm⁻¹, 15 ppm cm⁻¹ and 20 ppm cm⁻¹ (LBO); 80 ppm cm⁻¹, 100 ppm cm⁻¹ and 40 ppm cm⁻¹ (CBO); 600 ppm cm⁻¹, 600 ppm cm⁻¹ and 150 ppm cm⁻¹ (CLBO) at 1064 nm. The results showed an obvious discrepancy of the values of these crystals along three axis directions. A correlation between the bulk weak absorption property and crystal intrinsic structure was then discussed. It is found that the bulk weak absorption values strongly depend on the interstitial area surrounded by the B–O frames. The interstitial area is larger, the bulk weak absorption value is higher.     

Optical and thermal properties of crystalline Tb: KLu(WO4)2

A single crystal of Tb: KLu(WO₄)₂ with dimensions of 40 mm × 40 mm × 18 mm has been grown by the top-seeded solution growth (TSSG) method. The color of the crystal is brown. Absorption and fluorescence spectra were measured at room temperature. The measured specific heat is a little lower than that of Yb: KLW (0.365 J/g K) at 90 °C. The measured mean linear coefficients of thermal expansion are α_a = 17.1643 × 10^− 6 K^− 1_, α_a^⁎ = 14.0896 × 10^− 6 K^− 1, α_b = 8.7938 × 10^− 6 K^− 1, α_c = 23.1745 × 10^− 6 K^− 1, α_c^⁎ = 20.2866 × 10^− 6 K^− 1. The results indicate that the crystal has a large anisotropy. The refractive index was measured.     

GaN epilayer on separately deposited buffer layer by hot wall epitaxy

High quality GaN epilayers were grown on a sapphire substrate using a hot wall epitaxy method. We have investigated the crystal, optical, and electrical properties of GaN epilayers grown as functions of the nitridation condition of the substrate and the growth condition of GaN buffer layer. In order to study an effective method to grow a buffer layer for the growth of high quality GaN epilayer, the buffer layers were formed on the nitridated substrate using two different methods. One is separately deposited buffer layer (SDBL), and the other is co-deposited buffer layer (CDBL). It was observed that the growth condition of the buffer layer had a strong influence on the crystal and optical properties of GaN epilayer. A strong band edge emission peak at 3.474 eV was observed from the photoluminescence spectrum measured at 5 K for GaN epilayer grown at the optimum condition of the buffer layer. The carrier concentration and mobility of undoped GaN epilayer grown with a growth rate of 0.5 μm h⁻¹ were 2 × 10¹⁸ cm⁻³ and >50 cm³ V⁻¹ s⁻¹ at room temperature, respectively.     

Extremely high surface area of ordered mesoporous MCM-41 by atrane route

Silatrane synthesized from inexpensive oxide precursor, silica and TEA was used as the precursor for MCM-41 synthesis at low temperature because of its stability in aqueous solutions. Using cationic surfactant hexadecyltrimethyl ammonium bromide (CTAB) as a template, the resulting meso-structure mimics the liquid crystal phase. Varying the surfactant concentration, ion concentration and temperature of the system, changes the structure of the liquid crystal phase, resulting in different pore structures and surface area. After heat treatment, very high surface area mesoporous silica was obtained and characterized using XRD, BET and TEM. XRD and TEM results show a clear picture of hexagonal structure. The surface area is extraordinarily high, up to more than 2400 m² g⁻¹ at a pore volume of 1.29 cm³ g⁻¹. However, the pore volume is up to 1.72 cm³ g⁻¹ when the surface area is greater than 2100 m² g⁻¹.     

Compression behaviour and micro-structure evaluation of Zr57Nb5Cu15.4Ni12.6Al10 bulk metallic glass under high pressure

Compression behaviour and micro-structure evaluation of Zr₅₇Nb₅Cu_15.4Ni_12.6Al₁₀ bulk metallic glass is investigated at room temperature up to 32.8 GPa using in-situ high pressure energy dispersive X-ray diffraction with a synchrotron radiation source. The equation of state of the bulk metallic glass is − ΔV / V = 0.012P − 2.49 × 10^− 4P² − 9.5 × 10^− 7P³ + 5.02 × 10^− 8P⁴. The result shows that the nearest atom pair of the as-quenched bulk metallic glass corresponds to Zr–Zr correlations. And with pressure increasing, the nearest atom pair changes to a new one at 32.8 GPa.     

Ice adhesion to pristine and eroded polymer matrix composites reinforced with carbon nanotubes for potential usage on future aircraft

In aircraft icing conditions, the accretion of super-cooled liquid droplets on to the surface of an aircraft is dependent on numerous factors. In particular the temperature, liquid water concentration and material properties are of crucial importance in this context. This article features results obtained upon accretion of impact ice on pristine and eroded polymeric matrix composites with and without carbon nanotube reinforcement, for potential use in aeronautical applications. Results are shown for ice shear strength of a selection of advanced materials at T = − 5 °C and T = − 10 °C for a liquid water concentration LWC ≅ 0.3 g·m^− 3, actualized in an icing tunnel. The effect of surface roughness is further examined on the considered specimens in relation to their ice shear strength characteristics.     

Temperature influence on the voltage-controlled diffractive property of Mn-doped potassium sodium tantalate niobate crystal

We report the temperature influence on the voltage-controlled diffractive property of Mn-doped potassium sodium tantalate niobate crystal. The crystal was grown by the top seeded solution growth method. Its quadratic electro-optic coefficients achieved as high as R₁₁ = 3.50 × 10⁻¹⁵ m²/V² and R₁₂ = −0.44 × 10⁻¹⁵ m²/V² near the Curie temperature, while they declined with the increasing temperature. The external electric field which correspond to the maximum diffraction efficiency of photorefractive grating moved from 166 V/mm to 512 V/mm as the temperature increased from 25 °C to 32.5 °C. The maximum diffraction efficiencies all reached the maximum value of 60% at different temperatures. The results were discussed and compared with the theoretical equations.     

Microstructure and orientation variation during cell/dendrite transition in directional solidification of a single crystal nickel-base superalloy

The crystallographic orientation and microstructure variation during cell/dendrite transition of a nickel-base single crystal superalloy have been analyzed. The crystal with the off-<0 1 1> orientation grew with a cellular interface at 6 μm s^?1 while with a dendrite interface at 100 μm s^?1. The crystal kept the orientation of bottom seed in the dendritic growth stage, and there was a short transitional zone. The deviation angle between the cellular orientation and the heat flow direction became small in the cellular growth stage. The cellular growth direction was in accordance with the heat flow direction and was independent of the crystallographic orientation. At the same crystallographic orientation, the dendrites had a large primary dendrite arm spacing during the cell/dendrite transition. The cellular crystal with a smaller orientation deviation from the cylindrical axis showed a larger primary arm spacing.     

A comprehensive analysis of the morphology of first-year sea ice ridges

A review of the morphological properties of over 300 full-scale floating first-year sea ice ridges has been made, including measurements from 1971 until the present time. Ridges were examined from the Bering and Chukchi Seas, Beaufort Sea, Svalbard waters, Barents Sea and Russian Arctic Ocean for the Arctic regions; and from the Canadian East Coast, Baltic Sea, Sea of Azov, Caspian Sea and Offshore Sakhalin for the Subarctic (or temperate) regions. Grounded ridges were excluded. A wide catalogue comprising the ridge thicknesses (sail, keel and consolidated layer), widths and angles as well as the macroporosity and the block dimensions is provided. The maximum sail height was found to be 8 m (offshore Sakhalin), and the mean peak sail height was 2.0 m, based on 356 profiles. The mean peak keel depth is 8.0 m, based on 321 profiles. The relationship between the maximum sail height, h_s, and the maximum keel depth, h_k, for all ridges is best described by the power equation h_k = 5.11h_s^0.69. The correlation differs depending on the region. For Arctic ridges a linear relationship was found to be the best fit (h_k = 3.84h_s), while for the Subarctic ridges a power relationship (h_k = 6.14h_s^0.53) best fit the data. The ratio of maximum keel to maximum sail is 5.17 on average (based on 308 values), and has also been calculated for each region mentioned above. Arctic ridges generally have a lower keel-to-sail ratio than those in Subarctic regions. The statistical distribution of keel-to-sail ratios is best represented by a gamma distribution. The average sail and keel widths were 12 and 36 m, respectively. The relationships between the sail and keel widths and other geometrical parameters were also determined. Variation of sail and keel thicknesses within individual ridges has been compared with the variability of all ridges. Ridge cross-sectional geometry can vary greatly along the length of a ridge, even over a short distance. A study was made on sail block thicknesses, and it was found that they correlate well with the sail height with a square root model. The typical macroporosity for a first-year ice ridge is 22% (based on 58 values) with an average sail macroporosity of 18% (based on 49 values) and average keel rubble macroporosity of 20% (based on 44 values). The average ridge consolidated layer thickness was 1.36 m based on 118 values. The variation of the consolidated layer was examined, and it was found that the layer tends to grow evenly with time over the width of the ridge cross section. A greater spacing between the measurements seemed to affect the variation, as it decreased with an increasing distance between each borehole. A statistical analysis based on 377 measurements of the consolidated layer of ridges in the Barents Sea showed that the gamma distribution well describes the distribution of the consolidated layer thicknesses in that area.     

Pre-industrial multiple equilibrium sea-ice flow states due to plastic ice mechanics

Because the Arctic Ocean is largely surrounded by land masses, sea ice mechanics significantly affects the outflow of ice from the Arctic Basin. An important legacy of Dr. Max Coon has been the recognition that Arctic ice pack fails and flows in a plastic manner. Building on this concept we demonstrate here that with reasonable simulation of plastic scaling of sea-ice flow through narrow channels, dynamic–thermodynamic sea ice models have the potential to yield multiple equilibrium flow and hence thickness states for appropriate seasonal daily wind and thermodynamic forcing. These multiple states are due to ‘plastic’ ice mechanics and are not ‘Budyko-Sellers’ albedo feedback multiple states. Each state consists of a mean seasonal ice thickness with annual outflow balancing net growth. Low flow states are thicker.In this paper we first demonstrate that with some caveats, a properly formulated ‘viscous plastic’ sea ice model where ‘rigid’ ice is approximated by very slow flow can successfully simulate plastic ice flow and stoppage of ice flow through narrow channels in agreement with observations and theory. The characteristics of this flow and stoppage are methodically examined by a series of initial value problems of ice flow and advection through various narrowing channels with different ice thicknesses being advected into the channel. Different rheologies are examined and the effect of different creep closure rates on stoppage is investigated using several day mechanistic simulations of flow into the channel employing explicit time stepping. In the case of parallel channels, numerical results are examined in light of analytic solutions. Together with idealized growth rates this simple channel model is used to illustrate the principle of multiple equilibrium states due to ice mechanics.Following this we utilize a 40 km resolution dynamic thermodynamic sea ice model with multiple openings from the Arctic Basin to examine the potential for multiple equilibrium flow states under pre-industrial atmospheric thermodynamic forcing together with daily wind field forcing taken from more current conditions. This potential is assessed by carrying out five year seasonal simulations initialized with different ice thicknesses. Intersection of seasonal averaged net growth and outflow thus obtained are then used to identify potential multiple states and assess their stability. With a coulombic rheology with modest cohesive strength, the results show three states two of which are stable. With an elliptical yield curve having higher cohesive strength only one low flow state is identified.Several ~ 100 year simulations are then carried out to show the existence of the two stable states and their seasonal flow and thickness characteristics. The decay time scales between pre-industrial low flow states and present high flow states are also examined via long term simulations. Finally, a simulation from 1960 to 2040 with estimated climatic warming is carried out and compared with equilibrium thickness states at discrete intervals to show the effect of inertia in the rate of ice decay due to ice mechanics.Forcing data reported in this paper are adequate to test the capability of other dynamic thermodynamic sea ice models to yield multiple flow states.     

Surface stability of potassium nitrate (KNO3) from density functional theory

Potassium nitrate has been studied by accurate DFT calculations. The bulk crystal structure and electronic structure were calculated and compared to previous studies. In addition, the surface stability of various faces was quantified, confirming that the {0 0 1} face has the lowest surface energy of 0.19 Jm⁻². Other surfaces terminated by nitrate ions exhibited reconstructions upon relaxation, rotating the ions into an orientation parallel to the surface plane.     

High-temperature electrical resistivity and heat capacity studies on nano-crystalline geikielite

We report here for the first time the temperature dependence of the electrical resistivity and heat capacity of nano-crystalline MgTiO₃ geikielite of up to 1000 K. The temperature dependence of heat capacity of nano-crystalline geikielite expressed as C_p = 46.44(5) + 0.0502(2)T − 4.56 × 10⁶T² + 1.423 × 10³T^− 0.5 − 8.672 × 10^− 6T^− 2, where C_p = is specific heat expressed in J/mol. K and T is the temperature in K. Both the electrical resistivity and heat capacity behaviour show that the geikielite (both the natural and synthetic nano-crystalline samples) are stable and remains electrically insulating up to 1000 K.     

Strain rate dependent plastic mutation in a bulk metallic glass under compression

This paper reported a strain rate dependent plasticity in a Zr-based bulk metallic glass (BMG) under axial compression over a strain rate range (1.6 × 10⁻⁵–1.6 × 10⁻¹ s⁻¹). The fracture strain decreased with increasing strain rate up to 1.6 × 10⁻³ s⁻¹. A “brittle-to-malleable” mutation occurred at strain rate of 1.6 × 10⁻² s⁻¹, subsequently, the macro plasticity vanished at 1.6 × 10⁻¹ s⁻¹. It is proposed that the result is strongly related to the combined action of the applied strain rate, the compression speed, and the propagating speed of the shear band. When the three factors coordinated in the optimal condition, multiple mature shear bands were initiated simultaneously to accommodate the applied strain, which propagated through the specimen and distributed homogeneously in space, dominating the overall plastic deformation by consuming the entire specimen effectively.