THE DISTRIBUTION OF NITRATE CONTENT IN THE SURFACE SNOW OF THE ANTARCTIC ICE-SHEET ALONG THE ROUTE OF THE 1990 INTERNATIONAL TRANS-ANTARCTICA EXPEDITION

Previous work showed that nitrate measured at very high resolution (1.5 cm) in snow depositional sequences in Antarctica could be correlated with short-term phenomena such as solar proton events (Dreschhoff and Zeller, 1990). It was clear that deposition of the ionization products in the snow is strongly dependent upon precipitation and atmospheric conditions during and immediately after the event. Information about the geographic distribution of the nitrate fallout over Antarctica was limited to only a few sites, however. A unique opportunity to examine this aspect of the nitrate distribution and to test more fully the hypothesis that atmospheric ionization from solar-charged particles is responsible for a significant portion of nitrate was presented to us by a set of surface snow samples collected by the International Trans-Antarctica Expedition foot traverse. The set of 95 samples of the upper 25 cm was collected by one of us (Qin) at roughly equal distances along the 5736-km route from July 27, 1989, to March 3, 1990. Samples are distributed along a track from 65-degrees-05'S, 59-degrees-35'W, through 90-degrees-S, to 66-degrees-33'S, 95-degrees-39'E, which represents geomagnetic latitudes 50-degrees-S, west longitude, to 77-degrees-S, east longitude. The profiles of nitrate concentration and flux along the route were plotted and indicate that (especially at the higher elevation of the polar plateau) the distribution may be affected by electron precipitation.