Evidence for a stratigraphic record of supernovae in polar ice

The presence of photon induced ionization from supernovae at detectable levels in the polar ice sheets has been an interesting issue for some time. Evidence for such a signal is reported in 1200-year time sequences from the Antarctic continent at South Pole and Vostok, respectively. The supernova candidate events all appear as nitrate concentration spikes apparently caused by ionization from high energy radiation interacting with the upper atmosphere of the Earth. Further support for this interpretation has been obtained from an ice core drilled in Greenland covering 430 years. These ultrahigh resolution measurements (averaging 18 data points/year) have revealed nitrate anomalies at the times of the Tycho and Kepler Supernovae. In addition, the possibility is being suggested that the supernova Cassiopeia A appears in the record, thus pinpointing its year of occurrence. Other, less understood phenomena such as γ-ray bursts also occasionally may produce anomalies in the nitrate record.