Background  

Lake Ice Science

The duration of the ice cover on lakes and rivers in the Northern Hemisphere has decreased by 20 days since 1845. This is equivalent to a temperature change of -1.2°C per 100 years (Magnuson et al., 2000). Changes in the duration of the ice cover have significant ecological consequences. For example, at Experimental Lakes, western Ontario, Canada, as the ice duration decreased by 20 days over the course of 18 years, the water temperature, and phytoplankton biomass and diversity increased, but trout and shrimp populations declined because they could not tolerate the water temperature change (Schindler et al., 1990).

The Magnuson et al. study did not include any Alaska data, but it is known that break-up on the Tanana River, Nenana, AK, is now 5.5 days earlier than when records began in 1917 (Sagarin and Michaeli, 2001). Who would have predicted that gambling, i.e., the Nenana Ice Classic, would benefit science?

We believe that it is not sufficient to know only the duration of the ice cover. We also need to know about other lake ice and snow variables, e.g., ice thickness and growth processes, and snow depth and density, because they too affect the duration of the ice cover, the flow of heat from the water through the ice and snow to the atmosphere in winter, and light transmission and heat transfer into the water in spring.

As ice grows, latent heat is released and conducted through the ice and snow to the atmosphere. The conductive heat flow is an important climate variable as it is the major source of heat transfer from a water body to the atmosphere in winter and a significant component of the energy balance of the ice and snow cover. The magnitude of the conductive heat flow through sea ice and snow in the Arctic and Antarctic has been well documented (Sturm and others, 1997, 1998, 2001). The same can not be said for freshwater ice and snow.

The need for a better knowledge and understanding of lake ice growth and decay processes, and their role in heat transfer, has provided the impetus for Martin's lake ice studies at Poker Flat. The objectives of the research are to determine (1) how lake ice thickness, growth processes and duration vary and under what circumstances, (2) whether these variables and their response to climate change can be simulated well on the computer, and (3) the magnitude of the conductive heat flow through freshwater ice and snow.

Located in Alaska's interior, Poker Flat represents only one Alaska climate zone and its effect on lake ice growth and decay. ALISON provides an opportunity for teachers to participate in a genuine research experience and contribute to the development of an Alaska-wide database on lake ice growth and decay, and conductive heat flow that can be used to assess the performance of computer models and understanding of lake ice and its response to climate variability and change throughout Alaska.

References

Magnuson, J. J. and ten others. 2000. Historical trends in lake and river ice cover in the Northern Hemisphere. Science, 289(5485), 1743-1746.

Sagarin, R. and F. Micheli. 2001. Climate change in nontraditional data sets. Science, 294(5543), 811.

Schindler, D. W. and nine others. 1990. Effects of climatic warming on the lakes of the central boreal forest. Science, 250(4983), 967-970.

Sturm, M., J. Holmgren, M. König and K. Morris. 1997. The thermal conductivity of snow. Journal of Glaciology, 43(143), 26-41.

Sturm, M., K. Morris and R. A. Massom. 1998. The winter snow cover of the West Antarctic pack ice: Its spatial and temporal variability. In, M. O. Jeffries (editor), Antarctic Sea Ice: Physical Processes, Interactions and Variability, Washington D.C., American Geophysical Union, 1-18. (Antarctic Research Series 74.).

Sturm., M., J. Holmgren and D. Perovich. 2001. Spatial variations in the winter heat flux at SHEBA: Estimates from snow-ice interface temperatures. Annals of Glaciology, 33, 213-220.