New δ18O measurements on ice samples from Barnes Ice Cap show a relatively large shift from about −23‰ in the blue ice that makes up the bulk of the ice cap to −38‰ in a basal layer of clean white ice. This strongly suggests that the latter is of Pleistocene age, thus confirming an earlier interpretation based on less comprehensive data. The shift between the Pleistocene and Holocene ice is attributed in part to the change in climate at the end of the Pleistocene, and in part to a decrease in elevation of the accumulation area of ∼ 700 m. Beneath the clean white ice, there is a layer of dirty white ice with less negative δ18O values. This ice is believed to have been deposited during a climatically warm period in early to middle Wisconsin time. In addition, however, the less negative δ18O values in it are, in part, attributed to fractionation at a time in the past when the basal ice was at the melting point, and some of the water produced by pressure melting was lost through a permeable bed.