ICE-CORE RESEARCH IN A CAVE ENVIRONMENT IN THE SALMON-CHALLIS NATIONAL FOREST, IDAHO

Representatives of the U.S. Forest Service (USFS), the Idaho National Engineering and Environmental Laboratory (INEEL) and U.S. Geological Survey (USGS) are working to protect and investigate a recently discovered cave in the Salmon-Challis National Forest, Idaho. The cave contains a massive deposit of layered ice and snow that may be a valuable record of environmental changes over the last few centuries. Scientists involved in the project sampled the ice during the summers of 2002 and 2003 and the USFS is currently working to develop a plan to protect the cave and resources therein, while permitting limited scientific and exploratory access.

While cave-ice deposits are not uncommon, scientists are excited about this example because it appears to be unique among those discussed in the scientific literature. The cave opening is a large dolomite sinkhole and the main ice block appears to have developed via accumulation of successive layers of annual snowfall through the mouth of the cave. The layers of snow and ice are clearly evident to a depth of about 40 meters, the bottom of the accessible portion of the cave, but may extend even deeper. The layered nature of the ice suggests that it may be a much better archive of environmental changes than is typically found in cave ice which is most often formed by freezing of groundwater seepage rather than direct snowfall.

The value of the paleoclimatic and paleoenvironmental data stored in the ice depends on the time period it represents. The unique means by which the ice forms in this Idaho cave also may simplify the process of dating the ice. A considerable amount of pine needles and other organic debris falls into the cave with each year’s snow accumulation. The abundant organic material increases the number of individual layers that can be reliably dated, via radiocarbon decay, as well as improving the accuracy of dates obtained. To date, carbon-14 dating of organic matter found in the ice in 2002 suggest that a portion of this ice was deposited as snow somewhere between the years 1470 and 1650 AD. An additional sample-collection expedition was conducted in the fall of 2003 to better “date” the ice formation to establish a more complete chronology. Additionally, analyses for the mercury and radionuclide content of the ice are underway. The results of the 2003 sampling campaign conducted in September will be presented.