Year-round observations of the physical snow and ice properties and processes that govern the ice pack evolution and its interaction with the atmosphere and the ocean were conducted during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition of the research vessel Polarstern in the Arctic Ocean from October 2019 to September 2020. This work was embedded into the interdisciplinary design of the 5 MOSAiC teams, studying the atmosphere, the sea ice, the ocean, the ecosystem, and biogeochemical processes. The overall aim of the snow and sea ice observations during MOSAiC was to characterize the physical properties of the snow and ice cover comprehensively in the central Arctic over an entire annual cycle. This objective was achieved by detailed observations of physical properties and of energy and mass balance of snow and ice. By studying snow and sea ice dynamics over nested spatial scales from centimeters to tens of kilometers, the variability across scales can be considered. On-ice observations of in situ and remote sensing properties of the different surface types over all seasons will help to improve numerical process and climate models and to establish and validate novel satellite remote sensing methods; the linkages to accompanying airborne measurements, satellite observations, and results of numerical models are discussed. We found large spatial variabilities of snow metamorphism and thermal regimes impacting sea ice growth. We conclude that the highly variable snow cover needs to be considered in more detail (in observations, remote sensing, and models) to better understand snow-related feedback processes. The ice pack revealed rapid transformations and motions along the drift in all seasons. The number of coupled ice–ocean interface processes observed in detail are expected to guide upcoming research with respect to the changing Arctic sea ice.
[1] 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.INDEX TERMS: 4540 Oceanography: Physical: Ice mechanics and air/sea/ice exchange processes;
The signature and occurrence of frequency lock-in (FLI) vibrations of full-scale offshore structures are not well understood. Although several structures have experienced FLI, limited amounts of time histories of the responses alongside measured met-ocean data are available in the literature. This paper presents an analysis of 61 measured events of resonant vibrations of the Norströmsgrund lighthouse from 2001 until 2003. Most of these events did not reach a steady-state response; thus, they violate an often-quoted criterion for frequency lock-in vibrations and remain outside any modes of ice-induced vibrations suggested in standards.
This paper describes measurements of ice conditions in the fjord Van Mijenfjorden, Spitsbergen, in the Svalbard Archipelago, between 1998 and 2006. Ice thickness, ice temperatures and ice properties were measured, and simple simulations of oceanic flux were performed. The maximum annual peak ice thickness was measured in 2004: 1.3 m in the inner basin and 1.2 m in the outer basin. The minimum annual peak thickness was 0.72 m in the inner basin and no fast ice in the outer basin, in 2006. The estimated oceanic flux was about 2-5 W m -2 in the outer basin, and was close to zero in the inner basin. Flooding and brine drainage may have caused an overestimation of the oceanic flux. The measurements demonstrate different ice growth mechanisms, and the simplest model (Stefan's Law with air temperatures and a correction factor) fails to predict the ice growth. Finally, there is reason to believe that the ice conditions were heavier in the 1980s.
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 (N 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 m 2 .
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