Identification of major proton fluence events from nitrates in polar ice cores

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.