CRYSYS - CRYosphere SYStem in Canada

LEARN MORE ABOUT LAKE ICE!

Surface-atmosphere interactions are altered by the presence of ice on a lake and the formation of lake ice has important ecological and economic implications. The dates of ice freeze-up and break-up have been shown to be good indicators for climate monitoring in data sparse areas. Knowledge of the timing of complete freeze-over and break-up of the ice is essential to understanding the nature of surface/atmosphere energy budget and water exchanges in a lake region.

Ice cover on a lake also impacts greatly on the chemical characteristics of the underlying water, for ice cuts the lake water off from direct atmospheric influences and it reduces significantly the amount of shortwave radiation (sunlight) that penetrates to the water below. The amount of this reduction depends upon ice type and the properties of any overlying snow. For example, bubble-free black ice is essentially transparent to sunlight, but white ice and snow reflect much of the incoming radiation, and limit its penetration. Radiation that does penetrate the ice can cause a rise in water temperature. Ice cover restricts the movement of gases between water and air. This commonly results in a depletion of dissolved oxygen in the lake, but a buildup of carbon dioxide, methane, hydrogen sulphide, and other reduced gases.

Sometimes, however, the freezeout of oxygen during ice formation can compensate for oxygen loss from other processes. An increase in other constituents (e.g. potassium, sodium, calcium) also occurs as ice forms, but is reversed as ice melts. Such changes in energy and chemistry have implications for the biota and whole productivity of a lake. Other consequences associated with ice formation can include a loss in volume of water, decline in the amount of unfrozen lake bottom, a decrease in turbidity, and reduction in the amount of water moving through the lake when ice formation reduces (or even stops) the amount of water entering or leaving the lake.

LAKE ICE AND SSM/I

A major component of current CRYSYS lake ice research is determining the potential usefulness of passive microwave satellite data for extracting information related to lake ice processes. CRYSYS data analysis has focussed on Great Slave Lake in northern Canada and results have confirmed that it is possible to discriminate between areas of ice cover and open water using SSM/I (Special Sensor Microwave Imagery) 85 GHz data, hence indicating a potential to monitor the progression of ice formation and decay over the lake until complete freeze-over or ice-free conditions exist.

Figure 1: SSM/I 85 GHz horizontal polarization brightness temperature data mapped over Great Slave Lake from an orbit pass on June 10, 1992 (source: Anne Walker, MSC, Climate Research Branch).

Figure 1 above depicts SSM/I 85 GHz horizontal polarization brightness temperature data mapped over Great Slave Lake from an orbit pass on June 10, 1992. An area of contrasting low brightness temperatures in the lower right portion of the lake indicates the presence of open water. This was confirmed from a NOAA AVHRR visible image obtained on the same day, and from aircraft visual observations. The variability observed during the period preceding freeze-up is related to weather conditions over the lake (e.g. cloud, rain) and roughness of the water surface. During the winter season, the brightness temperature trends are influenced by the accumulation of a snow cover over the ice surface. The variability observed during the spring season before ice break-up occurs may be related to changes occurring on the ice surface (e.g. snow melt, flooding) or meteorological conditions (e.g. rain).

• Lake Ice Terminology
• SOCC - Current and past lake ice conditions in Canada
• CRYSYS Photo Gallery for Lake Ice

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