PI: Roger Bales, Dept. Hydrology and Water Resources, Univ. Arizona, Tucson, AZ 85721 (ph: 520-621-7113; email: roger@hwr.arizona.edu)
Co-I's: Joseph McConnell, Univ. Arizona; Anne Thompson and Richard Stewart, NASA

Title: Analysis of Ice Cores for Estimating Accumulation Patterns and Past Atmospheric Chemistry in Greenland

The primary aim of our proposed research is to develop an accurate estimate of the annual accumulation at several sites on the Greenland ice sheet, both in recent years and over the past few hundred years. To accomplish this we propose to recover and analyze four cores that cover the past few hundred years (in the range of 100-200 m in depth), and several shallower cores covering the past 20-50 years (in the range of 20-30 m depth). The work will be carried out over a period of three years. It is expected that drilling will be done by the Polar Ice Coring Office, University of Nebraska, Lincoln; with core processing and analyses done in cooperation with Ellen Mosley-Thompson, Ohio State University (OSU). The methods and analyses proposed are the same as those in use on our current project. The chemical trace species hydrogen peroxide, calcium, nitrate, ammonium, chloride and electrical conductivity will be analyzed with a continuous flow analysis system. Each of these species exhibits a distinct annual cycle in part or all of similar Greenland shallow cores, and will be used together with dust and oxygen isotope analyses (by OSU) in a multi-parameter approach to estimating annual accumulation at a site. The aim is to develop an annual accumulation record with essentially no error in dating, or as little error as possible. Spatial variability will be evaluated using multiple 20 meter deep cores in the vicinity of each deeper core. These annual accumulation estimates from different sectors of the ice sheet are a key part of NASA's Program for Arctic Regional Climate Assessment (PARCA), which has as its main goal gaining a better understanding of the mass balance of the Greenland ice sheet. As part of PARCA we are currently analyzing 100-150 meter cores from 4 locations, several 20-m cores in the vicinity of thee cores, and 20-meter cores from 9 other sites. These cores were collected over the 1995-97 field seasons. The first results were presented in two AGU meeting talks, in PARCA internal reports, and in a manuscript to be submitted in July, 1997. \footnote{M. Anklin, R. Bales, E. Mosley-Thompson and K. Steffen. Annual Accumulation at Two Sites in Northwest Greenland During Recent Centuries, in preparation for Journal of Geophysical Research} Besides providing annual accumulation information, these high-resolution, spatially distributed records will also provide an excellent data set for understanding subannual accumulation patterns and past atmospheric chemistry. A second aim of our research is to develop high-resolution, spatially distributed ice-core chemical data for estimating changes in intra-annual snow accumulation. We also propose to analyze MSA and sulfate on the cores from the higher accumulation sites using ion chromatography. The full suite of species will help us to develop estimates of intra-annual accumulation patterns, which influence the concentrations of seasonally varying species in ice cores. Atmospheric photochemical modeling will be used to help us develop these unique intro-annual estimates, which will then allow examination of several questions about changes in past atmospheric chemistry. Our assessment will focus on hydrogen peroxide, nitrate and ammonium, and will involve integrated modeling of atmospheric snow/firn processes.