Shorefast Sea Ice Research Articles

A Field Study of Rough Shore-Fast Sea Ice

AbstractDuring December 1973 the initial smooth ice cover on the Chukchi Sea near Barrow, Alaska, broke away from the shore during a period of strong wind and was replaced by a cover of broken, rafted ice which remained for the rest of the winter. Cores pulled from this cover were examined visually, and the salinity and density of sections of the cores were measured. Temperatures at several depths in the ice were recorded continuously, and these are presented near the date when the temperature gradient changed sign. Despite large deviations probably due to the irregularity of the ice cover, thickness and salinity followed the patterns seen by other observers.

A Field Study of Rough Shore-Fast Sea Ice

AbstractDuring December 1973 the initial smooth ice cover on the Chukchi Sea near Barrow, Alaska, broke away from the shore during a period of strong wind and was replaced by a cover of broken, rafted ice which remained for the rest of the winter. Cores pulled from this cover were examined visually, and the salinity and density of sections of the cores were measured. Temperatures at several depths in the ice were recorded continuously, and these are presented near the date when the temperature gradient changed sign. Despite large deviations probably due to the irregularity of the ice cover, thickness and salinity followed the patterns seen by other observers.

Quantitative Composition, Distribution, Community Structure and Standing Stock of Sea Ice Microalgae in the Canadian Arctic

One hundred and ninety-six (196) species of microalgae were identified from the annual shore-fast sea ice samples collected from the Canadian Arctic between November and June in the years 1971 to 1978. The diatoms were represented by 189 species (21 centric and 168 pennate), the flagellates by three species, the dinoflagellates and chrysophytes by two species each. There were no blue-green algae. Species composition and distribution are tabulated. The dominant species of the microalgal communities in the bottom of the ice different from those found elsewhere in the ice. The sea ice microalgal communities and standing stock started to develop in late fall at the time of ice formation. They grew very slowly through the winter months, exponentially increased in early spring, reached a peak just prior to the thaw period in late spring or early summer, and declined rapidly in summer as ice melting occurred. Standing stock was greatest at the bottom of the sea ice, where it was one to two orders of magnitude larger than in other parts of the ice column, and 50 to 500 times greater than in the phytoplankton in the underlying waters. The ice communities consisted mainly of diatoms with a great majority of pennate forms. Large numbers of species and cells of diatoms were found at the bottom of the sea ice. Dinoflagellates, flagellates and chrysophytes occurred in relatively low numbers except in a few cases when ice blooms were observed. During May most of the sea ice microalgal blooms occurred in the bottom of the ice except for Phaeocystis pouchetii, which occurred elsewhere in the ice. Environmental factors controlling standing stock, growth and distribution of sea ice microalgae are discussed.

Surface-Based Scatterometer Results of Arctic Sea Ice

Radar backscatter measurements were made of shorefast sea ice near Point Barrow, AK, in May 1977, with a surface-based FM-CW scatterometer that swept from 1-2 GHz and from 8.5-17.5 GHz. The 1-2 GHz measurements showed that thick first-year and multiyear ice cannot be distinguished at 10-70° incidence angles, but that undeformed sea ice can be discriminated from pressure ridges and lake ice. Results also indicate that frequencies between 8-18 GHz have the ability to discriminate between thick first-year, multiyear, and lake ice. Cross polarization was found to be a better discriminator than like polarization. In addition, at these latter frequencies the differential scattering cross section σ° was found to have an approximately linearly increasing frequency response.

Beaufort Sea ice zones as delineated by microwave imagery

Microwave and infrared data were obtained from a research aircraft over the Beaufort Sea ice from the shoreline of Harrison Bay northward to a latitude of almost 81 deg N. The data acquired were compared with microwave data obtained on the surface at an approximate position of 75 deg N, 150 deg W. Over this north-south transect of the polar ice canopy it was discovered that the sea ice could be divided into five distinct zones. The shorefast sea ice was found to consist uniformly of first-year sea ice. The second zone was found to be a mixture of first-year sea ice, medium size multiyear floes, and many recently refrozen leads, polynyas, and open water; considerable shearing activity was evident in this zone. The third zone was a mixture of first-year and multiyear sea ice which had a uniform microwave signature. The fourth zone was found to be a mixture of first-year sea ice and medium-to-large size multiyear floes which was similar in composition to the second zone. The fifth zone was almost exclusively multiyear ice extending to the North Pole.

Ambient Noise under Sea Ice and Further Measurements of Wind and Temperature Dependence

Measurements of underwater-pressure spectral density from M'Clure Strait (2–5 May 1966), the Beaufort Sea (31 July and 16 August 1965),and the Canada Deep (14 April 1965) are presented. The M'Clure Strait measurements, made under shore-fast sea ice, exhibited a variability related to air-temperature and wind-speed changes of a similar nature to those reported previously for midwinter under-ice noise. The great differences in the magnitude and variation with frequency, of the ambient noise observed under sea ice is again illustrated with three sets of measurements obtained during 1965–1966. The noise observed under the shore-fast ice of M'Clure Strait in the springtime appeared to be governed by air-temperature and wind-speed changes in a similar manner to noise observed previously in the midwinter [J. H. Ganton and A. R. Milne, J. Acoust. Soc. Am. 38, 406–411 (1965)]. On the other hand, measurements made under the moving ice cover of the Canada Deep in the springtime and of the Beaufort Sea in the summer appeared to be less amenable to description in terms of easily observable physical variables.

Statistical Description of Noise under Shore-Fast Sea Ice in Winter

Ambient noise under short-fast sea ice in midwinter is generated at the surface of the ice by wind action as well as by mechanical cracking caused by declining air temperatures. An attempt has been made to relate field measurements of underwater noise to the sources of the noise by means of a geometrical model of the environment. The statistical properties and the spectra of the under ice noise can be related to the surface density and the waveform of the source pressure pulses by means of the model.