Oxygen-Isotope Variations in the Malaspina and Saskatchewan Glaciers

Abstract

Oxygen-isotope analyses of ice and firn from the Saskatchewan Glacier, Canada, and the Malaspina Glacier, Alaska, show that variations in $$O^{18}/O^{16}$$ ratios are likely to be of considerable value in glaciological research. The general trend of $$O^{18}/O^{16}$$ ratios in ice along the center flow line of Saskatchewan Glacier is a decrease from firn limit to terminus. This is interpreted as indicating that ice at successively lower points in the glacier tongue originated at progressively higher positions in the accumulation area, thus confirming Reid's early deductions concerning flow lines in a valley glacier. Ice in the glacier tongue has a higher average $$O^{18}/O^{16}$$ ratio than the 1953-1954 layer of firn in the accumulation area. This may be due to the fact that meltwater relatively rich in $$O^{18}$$ percolating down from the surface has refrozen in the deeper firn, or it may possibly indicate a change to cooler climatic conditions within the last few hundred years. Ice samples from a transverse profile across Saskatchewan Glacier have higher $$O^{18}/O^{16}$$ ratios near the center than near the margins. This occurs because the marginal ice comes from a higher altitude in the accumulation area. Separate strata within Saskatchewan firn display large differences in oxygen-isotope ratios which are preserved to some degree in the ice tongue and may be useful in the identification of vestigial sedimentary layering. However, a high degree of homogenization can occur by the time the ice reaches the lower part of the glacier, as shown by a series of closely spaced samples of well-foliated ice with remarkably consistent oxygen-isotope ratios. In Malaspina Glacier, the oxygen-isotope ratios confirm a deduction made earlier as to the principal units composing this piedmont sheet. Ice that originates in the upper Seward Basin has a higher $$O^{18}/O^{16}$$ ratio than material supplied from higher mountain slopes bounding that basin. Oxygen-isotope data also confirm an earlier interpretation to the effect that the intensely deformed and greatly thinned bands of ice in the outer part of Malaspina Glacier represent individual valley glaciers separated by medial moraines.