Pancake Ice Research Articles

Field observations of slush ice generated during freeze-up in arctic coastal waters

In some years, large volumes of slush ice charged with sediment are generated from frazil crystals in the shallow Beaufort Sea during strong storms at the time of freeze-up. Such events terminate the navigation season, and because of accompanying hostile conditions, little is known about the processes acting. The water-saturated slush ice, which may reach a thickness of 4 m, exists for only a few days before freezing from the surface downward arrests further wave motion or pancake ice forms. Movements of small vessels and divers in the slush ice occurs only in phase with passing waves, producing compression and rarefaction, and internal pressure pulses. Where in contact with the seafloor, the agitated slush ice moves cobble-size material, generates large sediment ripples, and may possibly produce a flat rampart observed on the arctic shoreface in some years. Processes charging the slush ice with as much as 1000 m 3 km −2 of sediment remain uncertain, but our field observations rule out previously proposed filtration from turbid waters as a likely mechanism. Sedimentary particles apparently are only trapped in the interstices of the slush ice rather than being held by adhesion, since wave-related internal pressure oscillations result in downward particle movement and cleansing of the slush ice. This loss of sediment explains the typical downward increase in sediment concentration in that part of the fast-ice canopy composed largely of frazil ice. The congealing slush ice in coastal water does not become fast ice until grounded ridges are formed in the stamukhi zone, one to two months after freeze-up begins. During this period of new-ice mobility, long-range sediment transport occurs. The sediment load held by the fast-ice canopy in the area between the Colville and Sagavanirktok River deltas in the winter of 1978–1979 was 16 times larger than the yearly river input to the same area. This sediment most likely was rafted from Canada, more than 400 km to the east, during a brief time period in the previous fall. Ocean turbulence is greatly reduced while the congealing slush ice drifts about. Therefore, new ice then forming in intervening open-water areas is clean. These events explain the patchy appearance of the fast ice after the summer snowmelt. More work on the important phenomena reported here is needed to close a major gap in the knowledge of the arctic marine environment.

A physical mechanism for establishing algal populations in frazil ice

In polar regions ice algal communities are not only conspicuous but may also be important production sites and sources of seed populations for pelagic communities1–3. Except for some studies near land-based stations1,4–7, there are few long-term observations of ice algal populations, and few studies have considered how they form and develop. Most researchers suggest that ice algae are derived from sparse water column assemblages that become trapped during ice formation; ice algal populations then develop through in situ growth1. Some previous observations have suggested that ice crystals forming in the water column concentrate algal cells6–8. Dense algal populations in young sea ice may have been recognized as early as the mid-nineteenth century, since Hooker (cited by Alexander2) described discoloured brash and pancake ice (“ …a pale ochreous colour”). But until now, neither the mechanism for this harvesting nor the effects on the composition of the ice community has been clearly demonstrated. In the Weddell Sea, we have sampled young sea ice discoloured by algae, and we present evidence that the algae were concentrated by a physical mechanism. We explain how such a process may accumulate planktonic forms in ice communities.

Spectral Reflectances of Snow and Fresh-Water Ice from 340 Through 1 100 nm

AbstractMeasured spectral reflectances of new and moderately metamorphosed snow were generally >80% from 340–950 nm. From 950–1 100 nm a characteristic dip and rise of spectral reflectances occurred. One spectroradiometer scan over a deteriorated snow patch showed much lower spectral reflectances than fresh snow, but the shape of the curve remained similar to that of fresher snow. Spectral reflectances for clear ice contrasted sharply with those for snow. In general, values were <10% and the curves lacked distinctive shape. Higher spectral reflectances, due to “lighter”-appearing ice in the measurement area, were measured at some sites. Refrozen slush, pancake, brash, and slush curd ice revealed spectral reflectance curves similar in form to each other, but which varied significantly in the range of spectral reflectances for each ice type. Generally, reflectances rose slowly from 340 nm to a peak near 550 nm. From 550–775 nm reflectances decreased slowly but significantly. A slight dip and rise in reflectances occured from 775–850 nm after which values again dipped significantly (850–900 nm). From 950–1 100 nm, a dip and rise in reflectances similar to that for snow was observed. The amount of slush included seems to control the reflectances of these ice types. All measurements were acquired with a pair of scanning spectroradiometers having picowatt accuracy, adapted to obtain, automatically, simultaneous readings of incident and reflected radiation from 340–1 100 nm. The spectroradiometers were field-calibrated using Sun-plus-sky radiation as a calibration source.

Spectral Reflectances of Snow and Fresh-Water Ice from 340 Through 1 100 nm

AbstractMeasured spectral reflectances of new and moderately metamorphosed snow were generally >80% from 340–950 nm. From 950–1 100 nm a characteristic dip and rise of spectral reflectances occurred. One spectroradiometer scan over a deteriorated snow patch showed much lower spectral reflectances than fresh snow, but the shape of the curve remained similar to that of fresher snow. Spectral reflectances for clear ice contrasted sharply with those for snow. In general, values were <10% and the curves lacked distinctive shape. Higher spectral reflectances, due to “lighter”-appearing ice in the measurement area, were measured at some sites. Refrozen slush, pancake, brash, and slush curd ice revealed spectral reflectance curves similar in form to each other, but which varied significantly in the range of spectral reflectances for each ice type. Generally, reflectances rose slowly from 340 nm to a peak near 550 nm. From 550–775 nm reflectances decreased slowly but significantly. A slight dip and rise in reflectances occured from 775–850 nm after which values again dipped significantly (850–900 nm). From 950–1 100 nm, a dip and rise in reflectances similar to that for snow was observed. The amount of slush included seems to control the reflectances of these ice types. All measurements were acquired with a pair of scanning spectroradiometers having picowatt accuracy, adapted to obtain, automatically, simultaneous readings of incident and reflected radiation from 340–1 100 nm. The spectroradiometers were field-calibrated using Sun-plus-sky radiation as a calibration source.

The Study of Fresh-Water Lake Ice using Multiplexed Imaging Radar

The study of ice in the upper Great Lakes, both from the operational and the scientific points of view, is receiving continued attention. Both quantitative and qualitative field work is being conducted to provide the needed background for accurate interpretation of remotely sensed data. The sensor data under discussion in this paper were obtained by a side-looking multiplexed airborne radar (SLAR). These were supplemented with ground-truth data. Radar, due to its ability to penetrate adverse weather, is an especially important instrument for monitoring ice in the upper Great Lakes. It has been previously shown that imaging radars can provide maps of ice cover in these areas. However, questions concerning both the nature of the surfaces reflecting radar energy and the interpretation of the radar imagery continually arise. Our analysis office in Whitefish Bay (Lake Superior) indicated that the combination of the ice/water interface with the ice/air interface is the major contributor to the radar backscatter as seen on the imagery. The ice has a very low dielectric constant (<3.0) and a low loss tangent. Thus, this ice is somewhat transparent to the energy used by the imaging SLAR system. The ice types studied include newly formed black ice, pancake ice, and frozen and consolidated pack and brash ice. Although ice thickness cannot be measured directly from the received signals, it is suspected that by combining the radar backscatter information with both meteorological and sea-state history of the area and with some basic ground truth, better estimates of the ice thickness may be provided. In addition, certain ice features (e.g. ridges, ice foots, areas of brash ice) may be identified with reasonable confidence. There is a continued need for additional ground work to verify the validity of imaging radars for these types of interpretations. This paper is being published in full in another issue of the Journal of Glaciology.

The Study of Fresh-Water Lake Ice using Multiplexed Imaging Radar

The study of ice in the upper Great Lakes, both from the operational and the scientific points of view, is receiving continued attention. Both quantitative and qualitative field work is being conducted to provide the needed background for accurate interpretation of remotely sensed data. The sensor data under discussion in this paper were obtained by a side-looking multiplexed airborne radar (SLAR). These were supplemented with ground-truth data.Radar, due to its ability to penetrate adverse weather, is an especially important instrument for monitoring ice in the upper Great Lakes. It has been previously shown that imaging radars can provide maps of ice cover in these areas. However, questions concerning both the nature of the surfaces reflecting radar energy and the interpretation of the radar imagery continually arise.Our analysis office in Whitefish Bay (Lake Superior) indicated that the combination of the ice/water interface with the ice/air interface is the major contributor to the radar backscatter as seen on the imagery. The ice has a very low dielectric constant (<3.0) and a low loss tangent. Thus, this ice is somewhat transparent to the energy used by the imaging SLAR system. The ice types studied include newly formed black ice, pancake ice, and frozen and consolidated pack and brash ice.Although ice thickness cannot be measured directly from the received signals, it is suspected that by combining the radar backscatter information with both meteorological and sea-state history of the area and with some basic ground truth, better estimates of the ice thickness may be provided. In addition, certain ice features (e.g. ridges, ice foots, areas of brash ice) may be identified with reasonable confidence. There is a continued need for additional ground work to verify the validity of imaging radars for these types of interpretations.This paper is being published in full in another issue of the Journal of Glaciology.

The Study of Fresh-Water Lake Ice Using Multiplexed Imaging Radar

The study of ice in the upper Great Lakes, both from the operational and the scientific points of view, is receiving continued attention. Quantitative and qualitative field work is being conducted to provide the needed background for accurate interpretation of remotely sensed data. The data under discussion in this paper were obtained by a side-looking multiplexed airborne radar (SLAR) supplemented with ground-truth data.Because of its ability to penetrate adverse weather, radar is an especially important instrument for monitoring ice in the upper Great Lakes. It has previously been shown that imaging radars can provide maps of ice cover in these areas. However, questions concerning both the nature of the surfaces reflecting radar energy and the interpretation of the radar imagery continually arise.Our analysis of ice in Whitefish Bay (Lake Superior) indicates that the combination of the ice/water interlace and the ice/air interface is the major contributor to the radar backscatter as seen on the imagery. At these frequencies the ice has a very low relative dielectric permittivity (< 3.0) and a low loss tangent. Thus, this ice is somewhat transparent to the energy used by the imaging SLAR system. The ice types studied include newly formed black ice, pancake ice, and frozen and consolidated pack and brash ice.Although ice thickness cannot be measured directly from the received signals, it is suspected that by combining the information pertaining to radar backscatter with data on the meteorological and sea-state history of the area, together with some basic ground truth, better estimates of the ice thickness may be provided. In addition, certain ice features (e.g. ridges, ice-foot formation, areas of brash ice) may be identified with reasonable confidence. There is a continued need for additional ground work to verify the validity of imaging radars for these types of interpretations.

The Study of Fresh-Water Lake Ice Using Multiplexed Imaging Radar

The study of ice in the upper Great Lakes, both from the operational and the scientific points of view, is receiving continued attention. Quantitative and qualitative field work is being conducted to provide the needed background for accurate interpretation of remotely sensed data. The data under discussion in this paper were obtained by a side-looking multiplexed airborne radar (SLAR) supplemented with ground-truth data. Because of its ability to penetrate adverse weather, radar is an especially important instrument for monitoring ice in the upper Great Lakes. It has previously been shown that imaging radars can provide maps of ice cover in these areas. However, questions concerning both the nature of the surfaces reflecting radar energy and the interpretation of the radar imagery continually arise. Our analysis of ice in Whitefish Bay (Lake Superior) indicates that the combination of the ice/water interlace and the ice/air interface is the major contributor to the radar backscatter as seen on the imagery. At these frequencies the ice has a very low relative dielectric permittivity (< 3.0) and a low loss tangent. Thus, this ice is somewhat transparent to the energy used by the imaging SLAR system. The ice types studied include newly formed black ice, pancake ice, and frozen and consolidated pack and brash ice. Although ice thickness cannot be measured directly from the received signals, it is suspected that by combining the information pertaining to radar backscatter with data on the meteorological and sea-state history of the area, together with some basic ground truth, better estimates of the ice thickness may be provided. In addition, certain ice features (e.g. ridges, ice-foot formation, areas of brash ice) may be identified with reasonable confidence. There is a continued need for additional ground work to verify the validity of imaging radars for these types of interpretations.

Total albedo of Great Lakes ice

The total (0.3‐3.0μ) albedo of various types of ice common to the Great Lakes ranged from 10% for clear ice to 46% for snow ice at solar altitudes ranging from 32 to 40 degrees. Explanations are given for similarities between the albedo of pancake (31%) and slush curd ice (32%), and slush (41%) and brash ice (41%).

The Arctic wintering of HMS Hecla and Fury in Prince Regent Inlet, 1824–25

Sept. 18th [1824]. The young bay ice was found this morning to have formed over Barrows Straits, in which we were firmly fixed until next morning, when a smart breeze from the north broke it all up again and let us free to work up to the head of the bay; passing several whales and sea urchins en route. The young bay ice which had formed in sheltered places had, by the strong wind, been converted into (what is known here as) Pan-cake ice. The ships bored their way through with difficulty.

The Salinity Distribution in Young Sea-Ice

When undertaking a study of the lateral variation of the salinity of sea-ice it is necessary to select an area of ice with a known history. The field measurements reported here were made in North Star Bay, Thule, northwestern Greenland .... The sampling for the sheet ice grid was started at 1100 on November 6 and by 2100 the 2-, 4-, 8- and 16-foot grids were completed. The 32-, 64- and 128-foot grids were completed the following morning. ... Sampling of the pancake ice was started at 0900 on November 9 and completed by the evening of the same day. ... the standard deviation of the salinity values from closely spaced cored samples in sheet ice is always equal to or greater than ±0.3 per mil. In pancake ice, the standard deviation is usually ±1.0 per mil. ... this uncertainty will produce a standard deviation of approx. ±4 to 6 per cent of the total brine volume in the sheet ice and ±11 to 19 per cent of the total brine volume in pancake ice. This then accounts for a considerable proportion of the scatter observed in studying the strength properties of sea-ice.