DRAFT NEWS ITEM FOR Eos
Year-Around Science on the Summit of the Greenland Ice Sheet
The 3200-m summit of the Greenland ice sheet is the proposed location for a year-around environmental observatory that would enable researchers from multiple disciplines to make continuous scientific measurements at a unique, high-elevation northern-hemisphere location. From August 1997 through April 1998 a pilot winter-over program of atmospheric and snow measurements was carried out, in part to test the feasibility of a longer-term year-round facility. Here we report highlights from the successful 1997-98 winter-over experiment, and outline opportunities for future programs. Year-round measurements are expected to resume in summer 2000.
In August 1997 a crew of four watched as the final ski-equipped LC130 transport plane for the year left Summit with the summer crew. All four had previous polar experience, and were well equipped to both make scientific measurements and carry out the varied tasks of maintaining a remote camp through nine months of limited sunlight (72oN) and cold temperatures (daily lows of -20 to -60oC). As they departed they shared a sense of pride over the role they had played in proving that a small crew could be safe, reasonably comfortable and highly productive in a somewhat modest facility at the top of Greenland.
The 1997-98 pilot project evolved from a summer atmospheric sampling program that began in parallel with the 1989-93 GISP2 and GRIP deep ice core drilling programs at Summit. One main motivation for making the atmospheric and near-surface snow measurements was to aid in ice core interpretation. For many chemical species the relation between concentration in an ice core and atmospheric concentration at the time of deposition (i.e. transfer function) is non-linear, and depends on accumulation, temperature and other meteorological conditions. A second motivation was to better understand polar tropospheric chemistry.
The timing of snowfall through the year exerts first-order control on the temporal resolution with which the snowpack can record variations in the composition of the overlying air. Redistribution and sublimation of snow tend to mix signals from individual events, thereby degrading the preserved record. Two arrays of accumulation stakes demonstrated that there were no extended periods without accumulation, but that the summer and fall seasons had greater accumulation than at other times. One array was a dense network of 100 stakes in an 80-m square grid was set near the camp to allow weekly measurements. An additional 122 stakes at 100-m separation, established along a line heading away from camp, were measured monthly.
Continuous monitoring of atmospheric O3 and Rn helped track the oxidative state of the polar troposphere and indicate transport from continental regions, respectively. Whole air (canister) samples for hydrocarbon, halocarbon and alkyl nitrate determination will provide indications of the extent of photochemical processing of air masses reaching Summit. Temporal patterns of atmospheric particles showed short spikes of high concentration due to specific episodes of transport, with some species (e.g., MSA and NH4+) also showing clear seasonal variations. Radionuclide tracers (7Be and 210Pb) showed no sign of the broad winter maximum characteristic of sea-level sites in the Arctic, consistent with the assumption that arctic haze does not extend to this elevation. Transport climatologies are being examined to better understand seasonal patterns. H2O2 concentrations in surface snow confirm the very low winter-time levels inferred from previous pit studies. Analysis of aerosol carbon in snow indicate clear seasonal patterns in volatile organic species, with strong concentration peaks in spring and summer.
Physical measurements show that the snow surface becomes covered with much larger sastrugi and dunes during the winter than summer season. Enhanced surface roughness creates larger pressure gradients that could force greater advective flow of air through the firn.
Financial support came from the National Science Foundation (NSF), Office of Polar Programs. The Polar Ice Coring Office (University of Nebraska) was responsible for logistics.
In 1997 NSF, in cooperation with the Danish Commission for Scientific Research in Greenland, initiated planning for the new environmental observatory at Summit, which would offer the opportunity for an expanded group of European and U.S. scientists to make observations throughout the year. The highest elevation north of the Arctic Circle, Summit clearly provides unique opportunities for making year-round measurements of the Earth's atmosphere. The relatively cold temperatures and low atmospheric water vapor associated with this location make it the clear site of choice for a number of measurements.
Based on scientific input from two workshops and many individual scientists, five priority areas have been identified where a high-elevation site on the Greenland ice sheet is required for year-around measurements: i) ice-core interpretation, ii) tropospheric chemistry, iii) radiation, energy balance and boundary layer, iv) stratospheric observations, and v) atmospheric electricity. For these areas of research, the Summit site will provide unique data that cannot be developed at coastal Greenland or other arctic sites. In addition, two areas have been identified where year-around measurements at Summit would help complete an arctic network of measurement sites, and thus greatly enhance existing data: i) polar aeronomy and space sciences, and ii) seismic and geodetic measurements.
A white paper and draft science plan has been circulated (www.hwr.arizona.edu/Alpine/Summit/observatory.html), which calls for the facility to be in place and support an expanded science program by summer 2000. For U.S. scientists, NSF's office of polar programs has a February 1999 deadline for proposals involving field work in Greenland beginning in 2000 (Contact: Tom Pyle, tpyle@nsf.gov). Deadlines in other programs may differ.
Roger C. Bales, University of Arizona
Jack E. Dibb, University of New Hampshire