Comment on tc-2023-31

<strong class="journal-contentHeaderColor">Abstract.</strong> To investigate the mechanical properties of sea ice in the current summer Arctic, two ice blocks were lifted using ship crane during an Arctic expedition in the summer of 2021. Examination of ice crystal structure showed a granular ice layer at the top underlain by a columnar ice layer. Sea ice samples were then machined from the ice blocks for mechanical experiments performed in the laboratory. Three-point bending tests were conducted at ice temperatures of &minus;12 to &minus;3 &ordm;C, and uniaxial compressive strength tests were conducted at ice temperatures of &minus;8 to &minus;3 &ordm;C with a strain rate range of 10^&minus;6&ndash;10^&minus;2 s^&minus;1. The ice density and salinity of each sample were measured to determine brine and gas volume fraction as well as porosity. Results showed that sea ice flexural strength decreased with increasing porosity, but did not change with varying brine or gas volume fractions. A parameterization was proposed to relate sea ice flexural strength to porosity. The sea ice strain modulus was also independent on porosity and volume fractions of gas and brine. The uniaxial compressive strength decreased with increasing porosity at both ductile and brittle strain rate regimes. Furthermore, three-dimensional surfaces were obtained to depict the sea ice uniaxial compressive strength varying with porosity and strain rate, based on which the transition strain rate from ductile to brittle behaviors was determined. It was found that the transition strain rate decreased with increasing porosity. Comparisons with previous studies on sea ice strength showed that the previously reported equations for sea ice flexural strength and strain modulus did not agree with the measured data. Compared with the strength calculated using early reported sea ice porosity, the flexural strength and uniaxial compressive strength of summer Arctic sea ice decreased in recent decades, which probably brings positive feedback to the Arctic navigation.

In this research, the anisotropic behaviour of laminated sandstones, collected from southwest of Qom (central part of Iran), was evaluated using uniaxial compressive strength, point load and Brazilian tests. For this purpose, the eight rock blocks were selected. The rock samples were drilled at different direction with respect to the inclination angles (β) of 0, 30, 45, 60 and 90°. After specimen’s preparation and assessment of mineralogical and physical properties, specimens were subjected to uniaxial compressive strength, point load and Brazilian tests, and their strength and failure modes were evaluated at different inclination angles (β) between loading direction and lamination planes. Transitional angle, which indicates the change in dominant failure mode from parallel to the lamination to across the lamination, were also determined. The results indicate that the anisotropic behaviour of selected sandstones in uniaxial compressive strength test is different compared with the point load and Brazilian tests. Based on the results, the compressive strength anisotropy ratio of the studied sandstones is low, whereas for point load tests, the anisotropy ratio is obtained moderate. Finally, the different failure modes were classified for laminated sandstones.

Due to the fact that the estimation of the rock mass properties is very important in any geotechnical project, many studies have become with the aim of their determination. But, the immediate determination is very difficult because the in situ tests are time-consuming, expensive and sometimes unreliable. For this reason, many researches have attempted to calculate the rock mass characteristic through empirical equations, but only few have focused on the ultramafic rocks. The main purpose of this study is to estimate the engineering properties of the ultramafic rock masses through the uniaxial compressive strength of the intact rock, the influence of blast damage, the material constant and the Geological Strength Index with the use of Hoek and Brown criterion (Roclab Software). Thus, sixteen samples, taken from central Greece (the western part of Othrys mt and the Kallidromo mt), were tested (uniaxial compressive strength and triaxial tests) and the results were statistically described and analysed. The manuscript reveals strong positive linear correlation between the estimated (through the Hoek and Brown failure criterion) uniaxial compressive strength and the measured (determined by strength tests) uniaxial compressive strength. The values of the uniaxial rock mass compressive strength, the global rock mass compressive strength, the rock mass tensile strength, and the rock mass modulus of deformation are finally calculated and presented. Furthermore, an attempt to correlate the rock mass deformation modulus (Erm) with the tangent young modulus (Ei) results that there is high correlation between them both for peridotites and serpentinites.

Shale anisotropy characteristics have great effects on the mechanical behaviour of the rock. Understanding shale anisotropic behaviour is one of the key interests to several geo-engineering fields, including tunnel, nuclear waste disposal and hydraulic fracturing. This research adopted the finite discrete element method (FDEM) to create anisotropic shale models in ABAQUS. The FDEM models were calibrated using the mechanical values obtained from published laboratory tests on Longmaxi shale. The results show that the anisotropic features of shale significantly affect the brittleness and fracturing mechanism at the micro-crack level. The total fracture number in shale under the Uniaxial Compressive Strength (UCS) test is not only related to the brittleness of shale. It is also strongly dependent on the structure of the shale, which is sensitive to shale anisotropy. Two new brittleness indices, BIf and BICD, have been proposed in this paper. The expression for BIf directly incorporates the number of fractures formed inside of the rock, which provides a more accurate frac-ability using this brittleness index. It can be used to calculate the frac-ability of rocks in projects where there are concerns about fractures after excavation. Meanwhile, BICD links brittleness to the CD/UCS ratio in shale for the first time. BICD is easy to obtain in comparison to other brittleness indices because it is based on the Uniaxial Compressive Strength test only. In addition, it has been shown there is a relationship between tensile strength and the crack damage strength in shale. Based on this, an empirical relationship has been proposed to predict the tensile strength based on the Uniaxial Compressive Strength test.

Investigating the occurrence and accumulation of perfluoroalkylated substances and other persistent organic pollutants in snow and ice of the Earth’s Polar regions

Statistical comparisons between numerical sea ice models and an observed large‐scale strain array in the western Weddell Sea during 1992 are used to evaluate the performance of three of the more generally utilized sea ice rheology formulations. Results show that sea ice velocity is reproduced with relatively high accuracy (90% coherence, &gt;80% normalized cross correlation) in models having high‐quality atmospheric forcing fields (e.g., the European Centre for Medium‐Range Weather Forecasts). On the other hand, temporal and spatial variability of the velocity field, as exemplified by progressive vector plots and ice deformation, respectively, are reproduced less accurately (coherence and normalized cross correlation &lt;50%). In terms of model sensitivity, this means that deformation and temporal variability are more discriminating in terms of elucidating specifics about the constitutive relation and mechanical properties of sea ice on a large scale. For example, inclusion of both compressive and shear stresses is important in attaining a proper probability distribution of deformation relative to observations. Additional analysis shows that adjustments to specific model parameters improve the model results for either drift or select deformation components, but no best solution could be found, given the models examined here. Results suggest that inclusion of more physically based processes, such as subdaily tidal and inertial oscillations, reconsideration of the boundary layer formulation, and consideration of anisotropy, may be necessary to include in next‐generation sea ice models, especially those that are intended for coupling with high‐resolution (eddy resolving) ocean models.

Sea ice can be interspersed vertically with both permeable and impermeable layers. These features can be smaller than a few centimetres but are important for understanding biogeochemical cycles in sea ice. Traditionally, sea-ice samples are collected by drilling into the ice with a rotating core barrel with a cutting head. Ice cores are extracted and then cut into sections that are melted to collect the variable of interest. Drawbacks to this method include difficulty cutting sections smaller than a few centimetres thick and contamination of samples. Brines may also drain from their in-situ locations and be lost, meaning that important micro-environments in sea ice may be overlooked or misrepresented. To address these drawbacks, we developed a sea-ice melt probe that bores into sea ice and collects high-resolution samples. The capability of the melt probe to delineate a layer of dye in artificial sea ice was tested during cold laboratory-based experiments. Complementary field experiments were carried out in first-year landfast sea ice during February–March 2023 at Saroma-ko Lagoon, Japan. Experiments consisted of testing the high-vertical-resolution capability of the melt probe as well as its ability to be deployed on snow-covered sea ice. The melt probe was able to delineate a layer of dye at a finer resolution (20 mm) than traditional ice coring (approximately 50–100 mm) and could sample sea-ice brine in the field at a high vertical resolution. Melt-probe samples were also used to measure iron in sea ice without contamination. This proof-of-concept study provides an alternative method of sampling sea ice with the ability to support new research on fine-scale structures, with applications for sampling dissolved and particulate sea-ice constituents including trace metals, macro-nutrients, microplastics and gases.

&amp;lt;p&amp;gt;Investigating the temporal and spatial changes in Arctic sea ice freeboard, thickness and volume is crucial for climate and environmental research. In this study, the freeboard, thickness and volume of the Arctic sea ice between 2011 and 2020 were acquired from CryoSat-2 data and it was compared with NASA Operation IceBridge and Alfred Wegener Institue AWI datasets. The effect of wind field and temperature and itscontribution on Arctic sea ice were also investigated. The main steps of our research are as follows. 1) Selecting data points above 66 degrees north latitude and filtering out sea ice by flag value and mask; Using OSI SAF sea ice concentration (SIC) data to further constrict the area; Interpolating the latest mean sea surface data DTU21 into CryoSat-2 data; Calculating the sea ice freeboard via spatial altimetry relationship. 2) Combining with snow density, snow depth, multi-year ice density and first-year ice density to estimate the sea ice thickness respectively from freeboard according to the assumption of hydrostatic equilibrium. 3) Using the area and extent provided by NSIDC to interpret the volume. 4) Utilizing Seasonal and Trend decomposition using Loess(STL) to analyse the seasonal and interannual variations of sea ice. 5) Dividing the Arctic Ocean by its marginal sea, coupled with the HY-2B microwave scatterometer data and NCEP/NCAR reanalysis data, the impact of the Beaufort Sea, the Chukchi Sea, the East Siberian Sea, the Laptev Sea, the Kara Sea, the Barents Sea, the Greenland Sea, and the Baffin Bay wind field on the sea ice were studied. 6) Exploring the correlation between the sea surface temperature and the sea ice freeboard, thickness and volume. The result indicated that (1) the freeboard and thickness was decreasing about 9.748% and 8.80% during 2011-2020,respectively; (2) there are interlunar variations in sea ice freeboard and thickness, the freeboard and thickness of sea ice reach the minimum in August to September each year and the maximum appears in March to April; (3) Arctic sea ice is affected by both thermodynamics and dynamics, the reduction of Arctic sea ice was largely due to the sea surface wind field, one of the dynamic factors is the wind field on the sea surface. The sea ice changes in the various sea areas of the Arctic Ocean are related to the wind field to varying degrees. The changes in the sea surface wind field in recent years have further promoted the reduction of sea ice, making it possible for the Arctic to open to navigation in the summer. Fully understanding the evolution of sea ice change in the Arctic Ocean is helpful for humans to better protect the earth.&amp;lt;/p&amp;gt;

Biogeochemical characteristics of brash sea ice and icebergs during summer and autumn in the Indian sector of the Southern Ocean

As a key structural component of rockfill dams, the load-bearing capacity of large-sized concrete slabs under complex multi-axial stresses is directly related to the long-term safe operation of the dams. This study conducted uniaxial and biaxial lateral compression strength tests on C25 concrete slabs with dimensions of 1500 × 1500 × 150 mm using a large-scale bi-directional loading reaction frame test system, systematically revealing the mechanical properties and failure criteria of large-sized concrete slabs. The results indicate that the biaxial compressive strength of the concrete slabs is significantly greater than the uniaxial compressive strength. The stress–strain curves of the concrete slabs and standard specimens exhibit good consistency before failure. Based on uniaxial compressive strength data, the concrete size effect strength reduction formula proposed by Neville was modified, and a compressive strength prediction formula applicable to large-sized concrete members was established. Further integration with code-specified failure criteria led to the development of a biaxial failure envelope for large-sized concrete slabs, which was validated to agree well with measured data. The research findings can provide reliable experimental evidence and theoretical support for the strength reduction, load-bearing capacity assessment, and revisions of relevant design codes for large hydraulic components such as concrete face slabs in rockfill dams.

Abstract. Sea ice cover and thickness have substantially decreased in the Arctic Ocean since the beginning of the satellite era. As a result, sea ice strength has been reduced, allowing more deformation and fracturing and leading to increased sea ice drift speed. We use the version 3.6 of the global ocean–sea ice NEMO-LIM model (Nucleus for European Modelling of the Ocean coupled to the Louvain-la-Neuve sea Ice Model), satellite, buoy and submarine observations, as well as reanalysis data over the period from 1979 to 2013 to study these relationships. Overall, the model agrees well with observations in terms of sea ice extent, concentration and thickness. The seasonal cycle of sea ice drift speed is reasonably well reproduced by the model. NEMO-LIM3.6 is able to capture the relationships between the seasonal cycles of sea ice drift speed, concentration and thickness, with higher drift speed for both lower concentration and lower thickness, in agreement with observations. Model experiments are carried out to test the sensitivity of Arctic sea ice drift speed, thickness and concentration to changes in sea ice strength parameter P*. These show that higher values of P* generally lead to lower sea ice deformation and lower sea ice thickness, and that no single value of P* is the best option for reproducing the observed drift speed and thickness. The methodology proposed in this analysis provides a benchmark for a further model intercomparison related to the relationships between sea ice drift speed and strength, which is especially relevant in the context of the upcoming Coupled Model Intercomparison Project 6 (CMIP6).

Future projections of Arctic sea ice remain poorly constrained, due in large part to the significant inter-model spread across the CMIP6 archive. Various recent studies have explored novel calibration methods to better constrain future sea ice conditions, especially the timing of an ice-free Arctic, but can come to different conclusions based on the calibration approach taken. Some approaches exclude outlier models, while others seek to exploit sensitivities of sea ice area/extent to global warming (e.g., Northern Hemisphere temperatures) to better constrain the multi-model ensemble. As long-term and reliable observations of sea ice thickness are lacking, calibration efforts have primarily relied on sea ice concentration/area data from the passive microwave satellite record.&amp;#160;We are leading a new NASA-funded effort to utilize the multi-year record of observed sea ice freeboard and derived sea ice thickness from ICESat-2, together with similar data from the original ICESat and ESA&amp;#8217;s CryoSat-2 missions, to reduce inter-model uncertainty in future sea ice projections. Although the sea ice altimetry data record is more limited in space and time than the longer-term passive microwave concentration record, it can offer significant advantages; for example, freeboard is measured very accurately by modern laser altimetry satellites, providing more information within the consolidated ice pack, and is now output by some of the CMIP6 models, enabling direct comparisons between the model and the satellite measurements. Only a small fraction of CMIP6 models provide the direct output of derived freeboard so assumptions (mainly related to the bulk ice and snow density) need to be made when estimating freeboard with the core model output. Initial results suggest this can have an important impact on the comparisons. Converting the observations of freeboard to sea ice thickness introduces significantly more uncertainty to the observed data but can radically simplify the model comparison effort.&amp;#160;In this presentation we will showcase our initial efforts to better utilize the satellite altimetry record for calibrating CMIP6 simulations of future sea ice conditions across both poles, but with a primary focus on projections of the timing of an ice-free Arctic. We discuss some of the nuances of using freeboard as a more direct observational constraint compared to thickness, providing motivation for more modeling groups to provide the direct ice density and freeboard outputs in the lead-up to CMIP7.&amp;#160;Finally, our analysis has all been carried out within the NASA-supported CryoCloud compute environment using the cloud-based (AWS) CMIP6 data archive, so we include additional insight into the benefits of this analysis approach and the small but important impact from differences in model output availability (compared to the recent IPCC analysis).&amp;#160;

In this paper, the effects of weathering on durability and deformability properties for three different types of granitoid rocks were investigated. Five weathering grades ranging from fresh to completely weathered rocks were considered for each rock type. Deformability has been evaluated based on failure strain, tangent and secant modulus. For measuring these parameters, at least five uniaxial compressive strength tests with axial strain recorded were conducted on each weathering grade. To assess the weathering effect on the durability behavior of these rocks, a slake durability test was performed up to 40 cycles. The obtained results indicated that uniaxial compressive strength and elastic modulus dramatically decrease with increasing weathering grade. After moderately weathering grade, remarkable damage was observed in the structure and fabric of considered rocks. The results from slake durability tests showed that the slake durability index for each weathering grade has a certain changes trend which can be used in determination of the weathering grade and the long-term durability assessment. Moreover, the results showed that for evaluation of the long-term durability of the mentioned rock types, at least eight cycles should be considered, while two cycles were sufficient for estimation of weathering grade.

The NEMO sea ice model, SI3, includes the simple formulation of Hibler (1979; H79) to parameterise the compressive strength of sea ice. This assumes that thick and compact sea ice has more strength than thin and low concentration sea ice. However, the H79 strength scheme does not consider physical assumptions around energy conservation. The strength scheme of Rothrock (1975; R75) is based on the amount of potential energy gained and frictional energy dissipated during ridging, and has been introduced to SI3. Additionally, the option for a negative exponential redistribution of ridged ice among thickness categories, to better approximate observations and improve stability compared to the existing uniform redistribution when using R75, has been included. The R75 strength formulation is stable and works well in SI3 at version 4.2 with an EVP rheology, under a Met Office forced NEMO/SI3 model configuration. Sea ice strength is generally reduced for the R75 scheme compared to H79. The most notable effect on the model output is a greater number of, and sharper, features in the resulting modelled ice field when using the R75 scheme compared to the H79 scheme, which are particularly apparent in the ice thickness field. An increase in the model effective resolution is therefore demonstrated.

A narrow He1ium:Neon (633nm) laser was used to measure transmission loss and spreading in thin samples of sea ice and snow collected from the Beaufort Sea during LEADEX ’91 and from sites in the high Arctic during March 1987. The sea ice types sampled include first year, multiyear, melt pond, and various stages of young sea ice in the thickness range of 2 to 20 centimeters. Snow samples include old snow from multiyear floes as well as fresher snow from first year ice types. These data were analyzed to characterize intrinsic beam transmission and small angle scattering optical properties. In sea ice the latter scattering properties are highly dependent on the intricate structure of air bubbles, brine channels, and internal platelet boundaries and considered important to the estimation of the volume scattering function and visible radiative transfer through the Arctic sea ice cover. In this technique beam spreading is first used to derive the modulation transfer function (MTF) using a Fourier-Bessel transform. The spatial frequency decay function derived from the MTF can be used to estimate the volume scattering function for small angles. For thin snow and many sea ice samples the beam spread functions could be characterized as having Gaussian shape and therefore easily parameterized for the numerical transforms. Beam transmission measurements derived from snow and sea ice samples compared favorably with previously derived extinction estimates.