W. F. Weeks

The Growth, Structure, and Properties of Sea Ice

On the geophysical scale sea ice is a thin, fragile, dynamic, solid layer that forms under the thermodynamic conditions that occur near the Poles. There it serves as a boundary between two much larger fluid bodies — the ocean and the atmosphere. Typical scales of interest would be 103 to 106 m. In the present paper we take a more detailed view, focusing on the ice itself at scales ranging between 100 and 10−3 m, with an occasional glimpse at a scale of 10−10 m. It is our purpose to help the reader understand the internal structure of sea ice, how this structure develops, and how it affects the bulk properties of the ice. Although this is a subject that has received little attention in comparison to similar studies of metals and ceramics, it is, in our view, very important, as many details in the behavior of sea ice are structurally controlled. The variations in structure are, in turn, determined by the environmental conditions under which the ice has formed.

The potential transport of pollutants by Arctic sea ice

Abstract Drifting sea ice in the Arctic may transport contaminants from coastal areas across the pole and release them during melting far from the source areas. Arctic sea ice often contains sediments entrained on the Siberian shelves and receives atmospheric deposition from Arctic haze. Elevated levels of some heavy metals (e.g. lead, iron, copper and cadmium) and organochlorines (e.g. PCBs and DDTs) have been observed in ice sampled in the Siberian seas, north of Svalbard, and in Baffin Bay. In order to determine the relative importance of sea ice transport in comparison with air/sea and oceanic processes, more data is required on pollutant entrainment and distribution in the Arctic ice pack.

The effect of sea ice on the solar energy budget in the atmosphere-sea ice-ocean system: A model study

A coupled one-dimensional multilayer and multistream radiative transfer model has been developed and applied to the study of radiative interactions in the atmosphere, sea ice, and ocean system. The consistent solution of the radiative transfer equation in this coupled system automatically takes into account the refraction and reflection at the air-ice interface and allows flexibility in choice of stream numbers. The solar radiation spectrum (0.25 pm-4.0 pm) is divided into 24 spectral bands to account adequately for gaseous absorption in the atmosphere. The effects of ice property changes, including salinity and density variations, as well as of melt ponds and snow cover variations over the ice on the solar energy distribution in the entire system have been studied quantitatively. The results show that for bare ice it is the scattering, determined by air bubbles and brine pockets, in just a few centimeters of the top layer of the ice that plays the most important role in the solar energy absorption and partitioning in the entire system. Ice thickness is important to the energy distribution only when the ice is thin, while the absorption in the atmosphere is not sensitive to ice thickness variations, nor is the total absorption in the entire system once the ice thickness exceeds about 70 cm. The presence of clouds moderates all the sensitivities of the absorptive amounts in each layer to the variations in the ice properties and ice thickness. Comparisons with observational spectral albedo values for two simple ice types are also presented.

Changes in the salinity and porosity of sea-ice samples during shipping and storage

A theoreti cal examination of salinity and porosity changes introduced in sea-ice samples by brine expulsion and gas entrapment caused by thermal cycling during shipping and storage shows that in extreme cases such effects can be significant, resulting in 15 % reductions in porosity (1/). More representative scenarios give porosity changes of less than 2% which, assuming that ice-property variations scale with n 1 / 2 , result in property variations of less than 1%.

Transport of photosynthetically active radiation in sea ice and the ocean

A recently developed radiative transfer model is applied to study the transport of photosynthetically active radiation (PAR) in the whole coupled atmosphere, sea ice and ocean system. This model rigorously accounts for the multiple scattering and absorption by the atmospheric molecules, clouds, snow and sea water, as well as the brine pockets and air bubbles trapped in sea ice. Both the spectral distribution and the seasonal variation of PAR at various levels in the ice and ocean have been investigated for different conditions. Results show that clouds, snow and ice algae all have important effects on the PAR availability to the microbial community under ice. The algae in the ice also significantly alters the spectral distribution of PAR transmitted to the ocean. Compared with the effects of clouds, snow and ice algae, the effect of changes in the amount of ozone in the atmosphere, the main absorptive gas in the PAR spectrum, on the amount of PAR entering the ice and ocean is negligible.