Large transient concentrations of nitrates in polar ice cores have been ide
ntified as the signature of some major solar proton fluence events between
1940 and 1991. We review this solar proton proxy identification technique u
sing nitrate concentration measurements in ice cores from the Arctic and An
tarctic. Using this identification technique we go back in time in an attem
pt to identify major solar proton events during the past several centuries.
There is a very large nitrate increase corresponding to the Carrington fla
re of 1859 evident in the Arctic ice core. Other significant nitrate increa
ses may indicate that major solar proton events occurred toward the end of
the last century. The problems associated with this new technique of using
nitrates as proxies to identify solar proton events are discussed. (C) 1999
Elsevier Science Ltd. All rights reserved.