The formation of platelet ice is well known to occur under Antarctic sea ice, where subice platelet layers form from supercooled ice shelf water. In the Arctic, however, platelet ice formation has not been extensively observed, and its formation and morphology currently remain enigmatic. Here, we present the first comprehensive, long‐term in situ observations of a decimeter thick subice platelet layer under free‐drifting pack ice of the Central Arctic in winter. Observations carried out with a remotely operated underwater vehicle (ROV) during the midwinter leg of the MOSAiC drift expedition provide clear evidence of the growth of platelet ice layers from supercooled water present in the ocean mixed layer. This platelet formation takes place under all ice types present during the surveys. Oceanographic data from autonomous observing platforms lead us to the conclusion that platelet ice formation is a widespread but yet overlooked feature of Arctic winter sea ice growth.
Abstract. The motion of an individual ice floe in the ArcticOcean was monitored at the Russian research station North Pole 35 established on the ice pack in 2008. The ice floe speed (V ) was found to be correlated with wind speed (v) in main features, such as the positions of maxima and minima of V and v. However, the fine structure of the V -variation cannot be explained by the wind forcing alone. There were periods of time when the floe drift was affected by the interactions of ice floes between each other or by the periodical forcing due to either the Coriolis inertia effect or the tidal activity. These data were compared with the "waiting times" statistics that are the distributions of time intervals between subsequent, sufficiently strong changes in the kinetic energy of drifting ice floe. These distributions were measured in several time windows differing in the average wind speed and wind direction, and/or in the mechanical state of the ice pack. The distribution functions N(t > τ ), where N is the number of successive events of energy change separated by the time interval t that exceeds τ , constructed in different time windows demonstrate fractal or a multifractal nature of the time series during motion in the consolidated ice pack but were truly random when the ice floe drifted in the highly fragmented sea ice. The latter result shows the existence of a relationship between the long-range mechanical interactions in the pack and long-term memory (time scaling behaviour) of the sea-ice motion.
The formation of platelet ice is well known to occur under Antarctic sea ice, where subice platelet layers form from supercooled ice shelf water. In the Arctic, however, platelet ice formation has not been extensively observed, and its formation and morphology currently remain enigmatic. Here, we present the first comprehensive, long-term in situ observations of a decimeter thick subice platelet layer under free-drifting pack ice of the Central Arctic in winter. Observations carried out with a remotely operated underwater vehicle (ROV) during the midwinter leg of the MOSAiC drift expedition provide clear evidence of the growth of platelet ice layers from supercooled water present in the ocean mixed layer. This platelet formation takes place under all ice types present during the surveys. Oceanographic data from autonomous observing platforms lead us to the conclusion that platelet ice formation is a widespread but yet overlooked feature of Arctic winter sea ice growth. Plain Language Summary Platelet ice is a particular type of ice that consists of decimeter sized thin ice plates that grow and collect on the underside of sea ice. It is most often related to Antarctic ice shelves and forms from supercooled water with a temperature below the local freezing point. Here we present the first comprehensive observation of platelet ice formation in freely drifting pack ice in the Arctic in winter during the international drift expedition MOSAiC. We investigate its occurrence under the ice with a remotely controlled underice diving robot. Measurements of water temperature from automatic measurement devices distributed around the central MOSAiC ice floe show that supercooled water and thus platelet ice occur widely in the winter Arctic. This way of ice formation in the Arctic has been overlooked during the last century, as direct observations under winter sea ice were not available and contrary to typical Antarctic observations; manifestation of platelet ice in Arctic ice core stratigraphy has been more challenging to identify.
<p>During the melt season, sea ice melts from the surface and bottom. The melt rates substantially vary for sea ice ridges and undeformed first- and second-year ice. Ridges generally melt faster than undeformed ice, while the melt of ridge keels is often accompanied by further summer growth of their consolidated layer. This summer consolidation is related to refreezing of less saline meltwater, originating from snowmelt and ridge keel melt. We examine the spatial variability of ice melt for different types of ice from <em>in situ</em> drilling, coring, and from multibeam sonar scans of remotely operated underwater vehicle (ROV). Seven ROV scans, performed from 24 June 2020 to 28 July 2020 during the Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC) expedition were analyzed. The area investigated by the ROV (400 by 200 m) consisted of several ice ridges, surrounded by first- and second-year ice. Seven ice drilling transects were additionally performed to validate ROV measurements. The maximum keel depth of the ridge investigated by ice drilling was 6.5 m. We show a substantial difference in melt rates of first-year ice, second-year ice, and sea ice ridge keels. We also show how ridge keels decay depending on keel depth, width, steepness, and orientation relative to the ice drift direction. These results are important for quantifying ocean heat fluxes for different types of ice during advanced melt, and for estimation of the ridge contribution to the total ice mass and summer meltwater balances of the Arctic Ocean.</p>
The Arctic Coring Expedition or ACEX was conducted as a special project under the Integrated Ocean Drilling Project. A review of the operational and ice management aspects of this project is provided in Keinonen et al (2006). This current paper reviews the ice observations and forecasting in more detail. Six scientists and naval architects were on board the IB Oden and Sovetskiy Soyuz to collect relevant ice data and forecast ice movement. The work involved the collection of ice data during transit and ice management, interpreting satellite imagery, ice forecasting, and providing the information to the vessels. The purpose of the project was to obtain a core from the seafloor to bed rock (420 m) on the Lomonosov Ridge, to study the paleo history of the polar cap region. This was achieved. The optimum transit route was determined using the Fengyun and Envisat satellite data which were showed the region of most leads. Once at the drill site at 88º north, Radarsat satellite data were used to identify regions of lighter ice. Ice thickness was generally 2.5 to 3.5 m, with mainly second year and old ice. Ice forecasting, using a very simple model, allowed the identification of any heavy ice expected to pass over the site and the regions where more information on ice severity was required. During the first two weeks at the drill site, the inertial oscillations of the ice were very small and not noticeable. Later the oscillations became much larger and the ice went through several complete loops, which created a minor problem for the drilling operation. Ice drift was measured by means of GPS buoys placed onto the ice and recovered by helicopter. This method worked well as the ice moved very slowly so that the buoys were within range for 2 to 3 days. A recent publication indicates that tropical conditions existed at the pole about 55 million years ago. Preliminary. Results indicated that the Polar Cap region was a shallow fresh water sea until about 15 million years ago. At that time, the region between Greenland and Norway opened, allowing the water from the Atlantic Ocean to flow north, with the result that the upper 15 million years of sediments are saline.
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