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On the results of studying ice ridges in the Shokal'skogo Strait, part III: New data
Abstract
The paper presents information on the studies of the first-year ice ridges conducted by the AARI experts in April–May 2018 in the fast ice of the Shokal'skogo Strait (Severnaya Zemlya Archipelago) using hot water drilling with computer recording of the penetration rate. Boreholes were drilled along the cross-section of the ridge crest at 0.25 m intervals mainly. One of the ice ridges had an unusual configuration: the sail crest was on the edge of the perpendicular extended keel crest. Cross-sectional profiles of ice ridges are illustrated. The records of thermodrilling rate revealed the presence of residual ice fragments in the keel of the ice ridges. The sail height varied from 2.9 up to 3.2 m, the keel depth varied from 8.5 up to 9.6 m. The average keel depth to sail height ratio varied from 2.8 to 3.3, and the thickness of the consolidated layer was 2.5–3.5 m. The porosity of the unconsolidated part of the keel was about 23–27%. The distributions of porosity versus depth for all ice ridges are presented and discussed.
... Äàí íîå èñ ñëå äî âà íèå ïðî äîë aeà åò ñå ðèþ ðà áîò, ïðî âî äèâ øèõ ñÿ â âå ñåííèå ñå çî íû 2016 è 2018 ãã. â ïðè ïàå ïðî ëè âà Øî êà ëüñêî ãî àð õè ïå ëà ãà Ñåâåð íàÿ Çåì ëÿ [6,17]. Ïðåä ñòàâ ëå íà èí ôîð ìà öèÿ î ìîð ôî ìåò ðè ÷åñ êèõ õàðàê òå ðèñ òè êàõ è âíóò ðåí íåì ñòðî å íèè òðåõ òî ðî ñîâ, èñ ñëå äî âàí íûõ ñ ïîìîùüþ âî äÿ íî ãî áó ðå íèÿ âåñ íîé 2019 ã. ...
Morphological characteristics of three first-year ice ridges were investigated in the Shokalsky Strait in April and May 2019 by hot-water ther mal drill ing with the recording of penetration rate. Boreholes were drilled along the ice ridge cross-section with an interval of 0.25 m. The ice ridge cross-sectional profiles are presented. The sail height for the investigated ridges varied within 1.8–2.7 m, and the keel draft varied from 7.0 to 9.1 m. The ratio of the keel draft to the sail height was equal to 2.7–5.2, the thickness of the consolidated layer was 2.4–2.7 m. The mean porosity of the unconsolidated part of the keel in the ice ridges made up 28–36%. The porosity distributions for the unconsolidated part of the keel along the drilling profile are given for the analyzed ice ridges. The main feature of one of the ridges was an almost rectilinear slope of the keel, which laterally extended for 16 m.
The paper presents information on the studies of the first-year ice ridges conducted by the AARI experts in April–May 2016 in the Shokal'skogo Strait (Severnaya Zemlya Archipelago) using hot water drilling with computer recording of the penetration rate. Boreholes were drilled along the cross-section of the ridge crest at 0.25 m intervals mainly. The results of a detailed study of one of the ice ridges are presented. The sail height varied from 2.5 up to 3.4 m, the keel depth varied from 8.3 up to 10.3 m. The average thickness of the consolidated layer was 2.2–2.4 m. Cross-sectional profiles of the ice ridge are illustrated. Ratio of the mean CL thickness of ice ridge to the mean thickness of level ice was equal 1.7. The distribution of salinity in the upper part of the CL is Z-shaped, and on the scale of the entire ice column, C-shaped. The CL growth rate is approximately twice as high as the growth rate of level ice. It was detected that the ridged ice was slightly stronger than the level ice. The porosity of the ice ridges is investigated in Part II.
The paper describes the morphometric characteristics of three first-year ice ridges investigated in April and May 2016 in the Shokal'skogo Strait (Severnaya Zemlya Archipelago). These studies were conducted using hot water thermal drilling with computer recording of the penetration rate. Boreholes were drilled along the cross-section of the ridge crest mainly at 0.25 m intervals. The main results of the ice ridges studies are given in Part I. Cross-sectional profiles of ice ridges are illustrated. In each borehole, porosity of an ice ridge was calculated as the ratio of the length of all voids to total length of the borehole. Processing of the results showed that when studying ice ridges for obtaining the porosity values close to the true ones, the boreholes should be drilled with a spacing not exceeding two meters. Away from the point where the keel has the maximum draft, the average porosity of the unconsolidated part of the keel tends to increase. This feature is a consequence of the effect of the Archimedes force and agrees with the model of porosity changes from the theory of granular media.
The results from 3 years of comprehensive field investigations on first-year ice ridges in the Arctic are presented in this paper. The scopes of these investigations were to fill existing knowledge gaps on ice ridges, gain understanding on ridge characteristics and study internal properties of ice. The ability of developing reliable simulations and load predictions for ridge-structure interactions is the final principal purpose, but beyond the scope of this paper. The presented data comprise ridge geometry, ice block dimensions from ridge sails, ice structure in the ridge and values on the ridge porosity and the degree of consolidation. The total ridge thickness conformed to other ridges studied in the same regions. The consolidated layer thickness was on average 2–3 times the level ice thickness. Minimum 33% and in average 90% of the ridge keel area was consolidated. The distribution of ice block sizes and block shapes within a ridge appears to be predictable. A new approach for deriving a possible ridging scenario and ridge age is presented. Different steps of the ridge building process were identified, which are in good agreement with earlier simulated ridging events. After formation of very thin lead ice between two floes deformation occurs through rafting and ridging until closure of the lead. Subsequently the adjacent level ice floe fractures proceeding ridge formation until ridging forces exceed driving forces. A time span of 10 days could be assessed for a possible ridge formation date, estimating the ridge age of the studied ridge located east of Edgeøya at 78° N to be 7 to 8 weeks.
From the 1970s to the present time, a great deal of field work and analysis has been done on the physical and mechanical properties of sea ice ridges. Despite numerous measurements made on hundreds of ridges, knowledge gaps still remain. Ridge properties have been summarized in terms of their relevance to shipping and offshore structures. An emphasis is placed on the degree of consolidation within the ridge, which is a key factor in the determination of the exerted ice load. The amount of data published on each ridge parameter is discussed, along with the variability in measurements for various parameters, and the measurement techniques used. Geographic location is also considered; ridge properties vary with location, and some regions have few published data.
Ice ridge keel geometry was studied by analyzing one year of upward looking sonar data collected in the Transpolar drift stream at 79°N, 6.5°W in 2008/2009. Ridges were identified using the Rayleigh criterion with a threshold value of 2.5 m and a minimum draft of 5 m. The keel shape was studied after the identification of ridges from temporal data. On average ridge keels were symmetric both with respect to the centroid of the keel and the keel crest location. By quantifying the ratio between observed keel area and the keel area of an assumed triangular keel shape (often assumed for first year ridges) we observed that in 79% of the cases the ridge cross sectional area would be underestimated by a triangular keel shape. Because keel loads on ships and structures increase with keel draft and keel area it is important that an assumed keel shape maintains the observed keel area. Thus we suggest that a better generalization of the shape of first year ridges is a trapezoidal keel shape rather than triangular. Based on the observations the mean trapezoidal keel, representing both first year ridges and old ridges, has a keel bottom-width which on average is 17% of the keel width. For the deepest keels (> 15 m) the mean keel bottom width was 12% of the keel width. The mean keel draft was 7.3 m and the deepest ridge was 25 m. The temporal data was converted to spatial data based on an ice drift speed estimate which assumed free drift. From the spatial data we found that the mean keel width was 28 m and the mean keel cross sectional area was 164 m2.
Sakhalin Oil and Gas Institute Okha, Russia iNTR ODI 5C TI()N Several oil and gas fields have been discovered on the northern Sakhalin offshore most of which are planned to operate by fixed plat*brms. Ice loads are the basic environmental loads to be considered in designing offshore platforms. Considerable contribution to such loads is made by hulnmock formations: hummocks, hummock ridges, grounded hummocks. The load exerted by hulmnock formations on a structure depends on external parameters (ice feature geometry, ice drift, etc.) and internal parameters (internal structure and lnechanical characteristics of ice blocks, etc.) Internal structure of hummocks is determined by ice blocks, which make up the ice massiE Ice blocks frozen together in the hummocks have various sizes and configurations as well as random space orientation. As a result of ice block fi-eezing together, ice skeleton of hummock formations is fonned which has an extremely intricate spatial structure of a random pattern. To analyze the internal structure of hummocks, general characteristics are usually applied such as porosity, filling of voids, etc. obtained by drilling. However, general characteristics do not describe the required details of internal structure of humnmck tbrmations. For example, hummock features with similar general characteristics may be made up of ice blocks both large and small in size. Cohesion and internal friction mlgles for ice blocks in a hummock are known to depend considerably on ice block sizes.
Some features of external and internal structures of one-year hummocks formed as a result of multiple interaction of ice fields in various time intervals are considered. Using the concrete results of field researches of ice hummocks as examples, both the main differences in their structure as compared with the single hummocks and common features arisen under certain hydrometeorological and ice conditions are demonstrated.
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, hs, and the maximum keel depth, hk, for all ridges is best described by the power equation hk = 5.11hs0.69. The correlation differs depending on the region. For Arctic ridges a linear relationship was found to be the best fit (hk = 3.84hs), while for the Subarctic ridges a power relationship (hk = 6.14hs0.53) 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.
Compared with freshwater ice, whose physical properties are well known, sea ice is a relatively complex substance whose transition to a completely solid mixture of pure ice and solid salts is completed only at extremely low temperatures rarely encountered in nature. The physical properties of sea ice are thus strongly dependent on salinity, temperature and time. Many of these properties are still not fully understood or accurately known, particularly those important for the understanding of a natural ice cover. The specific heat for example is an important term in the calculation of the heat energy content of a cover. However, Malmgren (1927), whose calculated values of the specific heat of sea ice are in general use, neglected the direct contribution of the brine present in inclusions. Re-examination of the question of specific and latent heats of sea ice has led to distinguishing between the freezing and melting points and enabled significant observations in this range. Similarly, because the thermal conductivity is a necessary parameter in the description of the thermal behaviour of ice. the sea-ice model suggested by Anderson (1958) has been modified and extended in the present work to the case of saline ice containing air bubbles. This enabled the completion of calculations of density and conductivity. In order to illustrate the theoretically calculated values. measurements were made on sea-ice samples to determine the specific heat, density and thermal conductivity.
Measurements of spatial and temporal temperature development, geometry morphology, and physical properties in three first-year sea ice ridges at Spitsbergen and in the Gulf of Bothnia have been performed. The corresponding thickness and the physical properties of the surrounding level ice were also measured. The thickness of the consolidated layer was examined through drilling and temperature measurements: the temperatures gave a ratio of the thickness of the consolidated layer to the level ice thickness from 1.39 to 1.61, whereas the drillings indicated a ratio of 1.68-1.85. The measured consolidated layer appeared to be 28% thicker when based on drillings in comparison to temperature. Thus the result depended on the method of investigation; the drillings included a partly consolidated layer. However, the measured growth of the consolidated layer did not depend on the method of investigation. The scatter of the physical properties in the consolidated layer was higher than that of the level ice. The consistency of the unconsolidated rubble differed markedly at the two sites. It was soft and slushy at Spitsbergen and harder in the Gulf of Bothnia. Three possible explanations for these differences are discussed: surrounding currents, different keel shapes, and difference in salinity.
During the resent years (1996–2005) the Arctic and Antarctic Research Institute performed expeditionary research in marginal seas. One of the tasks consisted in the determination of morphometric characteristics of ice ridges and stamukhas with the help of thermodrilling, with recording of the rate using a computer. The record of the penetration rate of the thermodrill and the water column pressure in the borehole as a function of depth, as well as processing of the recorded data, enabled to get information about the boundaries of consolidated layer. Principles of interpretation of the records of penetration rate of the thermodrill are discussed. Depth-wise distribution of volume content of solid phase of ice is presented for ice ridges and stamukhas in the various regions. Methodological grounds are discussed, of the determination of this distribution, based on the results of averaging of the data obtained through thermodrilling. Internal structure of ice ridges and stamukhas is discussed, for the Pechora Sea, the Sea of Okhotsk, the Caspian Sea, the Sea of Azov and near-polar district of Arctic basin, as well as its consideration with respect to other literary sources. Based on the accomplished analysis of the internal structure of ice ridges and stamukhas of the shelf of the Sakhalin Island and the Pechora Sea, a conclusion was made, that the thickness of consolidated layer determined based on the rate of drilling, according to subjective perception of the operator, frequently proves to be overestimated. The ratio between average thickness of consolidated layer of ice ridges and average thickness of level ice which surrounds the same in the regions in question varies within the range of 0.83…1.63, about 1.2 on the average. For stamukhas this ratio varies within the range of 1.3…2.1, about 1.7 on the average. Average porosity of the investigated ice ridges varies within the range of 12–28%, of the stamukhas — 7–20%.
The mechanical deformation of a sea ice cover takes place through ridging and rafting. These processes have been studied in an ice basin by pushing two identical ice sheets together. Nonuniform ice sheets consisting of floes of thickness t1 and thin ice of thickness t2 connecting the floes were used. The major thickness t1 and the thickness ratio t2/t1 were varied. Ice sheets of uniform thickness (t2/t1 = 1) never formed ridges; they only rafted. However, when ice sheets of nonuniform thickness were used, initial rafting transformed into ridging. In general, high values of t1 and low values for t2/t1 favored ridging, while low values of t1 and high values for t2/t1 favored rafting. The forces during the tests were measured. During the initial rafting stage the force increased linearly with displacement. The experiments also suggest that the ridging force has a maximum value. This limit can be related to horizontal growth of the ridge or onset of ridging in another site. The relation between force and ice sheet thickness has also been analyzed. Further, from the force and the measured ridge profiles it was possible to estimate the ratio of work to change in potential energy. This ratio was about 15 for ridging and about 35 for rafting.
Four medium to large first-year ridges have been examined with respect to geometry, porosity, morphology, and physico-mechanical properties in the Barents Sea close to the island Hopen in May 2002 to 2005. The geometry and morphology of the ridges compares well with the acknowledged literature, and ridges in the Barents Sea are expected to be similar to other Arctic ridges. The size of the pores increased with depth until about 1/3 to 1/2 of the keel depth, and decreased after about 2/3–3/4 of the keel depth. The porosity throughout the keels increased with depth. The salinity of the level ice and the consolidated layer was about 4 to 5 ppt and no systematic differences were found. Altogether 494 samples were tested in uniaxial compression for ε˙nom = 10− 3 s− 1. Salinity, density and temperature was measured for each individual sample and the porosity (η) calculated. The strength (f) for different parts of the ridge and the level ice is presented and discussed as a function of η. The mean value and the coefficient of variation of f both decreased with increasing η. The strength dropped for relative air volumes (ηa) above 10% and fmax(ηa > 10%) = 2.60 MPa. The ratio of the vertical and horizontal strength of the consolidated layer (fclV / fclH) was about 1.1, and fcl was between the vertical and horizontal strength of level ice (fliV > fcl > fliH). This strength characteristics is due to the different ice texture in level ice and consolidated layer. The strength of the sail and the consolidated layer was comparable and higher than that of the rubble blocks. Brittle samples were (except for η < 5%) stronger than the ductile ones and the porosity seemed to be important for the brittle-to-ductile transition.
Field data are described and analyzed from all-winter monitoring of the structure and temperature of one sea ice ridge in the northern Baltic Sea in the winter of 1991. The ridge aged to 3.5 months and experienced substantial structural evolution: the consolidated layer grew to 1 m, average porosity decreased from 0.28 to 0.18, keel thickness decreased by 1 m, and the ridge geometry became smoother. The porosity decreased due to freezing and showed a persistent minimum of 0.20–0.23 in the midkeel region; the void distribution changed due to packing rearrangements of ice blocks. Ice volume changed due to thermodynamic growth and decay. Within the sail and consolidated layer the heat flow was mainly vertical varying with time according to the surface forcing; the corresponding total ice production estimated from the temperature data would be 0.14 m, a bit more than the measured ice production 0.10 m. Predictions of the consolidated layer growth, based on (a) ice surface temperature or (b) air temperature or (c) local undeformed ice growth, gave good results. In spring the ice blocks throughout the keel beneath the consolidated layer melted uniformly.
Copyright (c) 1996 Elsevier Science B.V. All rights reserved. An analysis has been made of the salient features of 112 first-year and 64 multi-year sea ice ridges. Based on this information, the important characteristics of the ridges have been related through simple equations. In particular, the ratio of the keel-depth to sail-height was found to be 4.4 for first-year ridges, and 3.3 for multi-year ridges; the ratio of the keel-area to sail-area was 8.0 for first-year ridges and 8.8 for multi-year ridges. Also, for first-year ridges, the ratio of the keel-width to sail-height was approximately 15, and the ratio of the keel-width to keel-depth was 3.9. An analysis of the sail and keel angles indicates a distribution of values with an average sail angle of 21° for temperate ridges, and 33° for ridges in the Beaufort Sea. In this paper, the results of this analysis are described, and the important ridge characteristics are discussed.
Statistical model of ice ridge morphometry in the southwestern part of the Kara Sea
- Mironov
Thickness of the consolidated layer in first-year hummocks
- Surkov
Formation and consolidation of hummocks on the Arctic seas (laboratory experiments and natural investigations)
- Tyshko
Consolidated layer of hummocks on the North Sakhalin Offshore
- Surkov