The potential of perennial cave ice in isotope palaeoclimatology

Perennial ice from caves on and to the east of the Canadian Great Divide yi eld delta(18)O and delta D values, which are unusually high measurements wh en compared with the average precipitation for the region. Furthermore, the se ice data fall below and along lines of lower slope than the Global Meteo ric Water Line. To explain the observed relationships, we propose the follo wing process. A vapour-ice isotopic fractionation mechanism operates on war m-season vapour when it precipitates as boar ice on entering the caves. The subsequent fall of boar to the cave floor through mechanical overloading, along with ice derived from ground-water seepage (with a mean annual isotop ic composition), results in massive ice formation of a mixed composition. T his mixed composition is what is observed in the characteristic relationshi ps found here. Such findings suggest that a warm versus cold climate interp retation for ancient cave ice may be the opposite of that found in the more familiar polar and glacial ice cores.