A firn core from within the polar vortex in the Weddell Sea sector of Antarctica shows nitrate peaks that occur in the spring or early summer. They are far less prominent in two other cores from sites that are further north. Although other data are needed, circumstantial evidence suggests that the peak may be due to sedimentation of polar stratospheric clouds from the stratosphere during winter and spring. No change in the form of the peak is seen over the last three decades. It may be possible to observe pass stratospheric conditions over longer time scales from ice cores, but other sources may obliterate the signal in ice from the glacial periods.