Highlights of Ongoing Project
Relationships Between Air and Snow Chemistry in Winter at Summit, Greenland

Cooperative Research involving
University of Arizona, University of New Hampshire,
U.S. Army Cold Regions Research and Engineering Laboratory
Carnegie Mellon University, University of Wisconsin, Milwaukee
and University of California, Irvine.

Brent Matson Photo A new modular building, named the Greenhouse, has been constructed at the Summit site. Designed by Winston Yan of the University of Nebraska, the Greenhouse is a modular building that can be disassembled and transported in an LC-130H aircraft. Although small, it boasts four bedrooms, a kitchen, a bathroom with shower, a living area, a communications room, and three laboratories, and a large walk-in freezer dug under the floor. The Greenhouse serves as the hub of winter-over activity.

Brent Matson Photo Over the course of the winter, the science team will dig shallow pits to collect snow samples. This image shows such a pit after samples have been collected. Slices of snow 1 cm thick are scraped into clean bags from a continuous column, leaving the indentation at the end of the wall. The ruler is used to measure the 1 cm intervals as samples are collected. Samples will be shipped frozen to many institutions for analysis.

The first year-round investigation of air-snow relations in the Summit region of the Greenland ice sheet began in summer, 1997. Year-round data on key meteorological and chemical parameters (in the atmosphere and in surface and near-surface snow) and microstructural characteristics of the snowpack will greatly increase our understanding of exchange of energy and mass (water and chemical species) between the atmosphere and polar snow. Chemical records from polar ice cores represent one of the finest archives of information on the past composition of the atmosphere available to researchers interested in climate change issues. However, ice chemistry is only a proxy for atmospheric chemistry. Full use of ice core chemistry records requires a quantitative, process-based, understanding of the transfer functions relating atmospheric and ice chemistry. The investigators on the present collaborative project are all part of an ongoing international effort focusing on these questions in the Summit region of the Greenland ice sheet, where the GISP2 and GRIP ice cores have recently been recovered and analyzed in unprecedented detail for a wide range of chemical constituents. Through a combination of laboratory experiments, model development and collection of field data for several summer seasons, we have gained considerable insight into air-snow relationships. For some chemical species we can now use concentrations measured in the summer layer of the snowpack to estimate mean atmospheric concentrations that agree with those measured during the summer season to better than a factor of two.

Brent Matson Photo A primary goal of the winter-over program is to collect and analyze air samples during the winter months for many chemical species. University of Arizona scientists installed a detector to measure hydrogen peroxide levels, and NOAA scientists sent an ozone monitor to the site. Air is drawn in from outside into the detectors, where it is analyzed immediately. Twice daily the data are downloaded from the detector to the computers shown in the photo.

Brent Matson Photo Although located in an extremely remote environment, human activity at Summit produces enough air pollution to affect our chemical analysis of hydrogen peroxide in the air. Locating the air intake line well up a tower helps insure more pristine air is collected and analyzed. The line is wrapped in black foam and heated with resistor wire to prevent condensation of moisture in the tubing. Such condensation results in significant signal loss. The end of the line is protected from blowing snow with a plastic shield.

However, so far all field experiments to develop and verify such models have been restricted to the summer months of May through August. A small team of researchers, making similar measurements through the winter of 1996-1997 at the GISP2 camp, is addressing many of our current knowledge gaps regarding air-snow exchange processes at Summit through the greater portion of the year. The records from the GISP2 and GRIP cores have already been proven to contain evidence of unexpectedly rapid and dramatic shifts of climate, with changes in the composition of the ice signaling, or at least accompanying, most such climate shifts. Being able to infer variations in atmospheric chemical processes from these changes in ice composition will provide a powerful tool for examining the role of atmospherically-based forcing in the climate system, as well as the response of the atmosphere to climate change.

At the end of June, 1997, four winter-over staff were left at Summit to collect atmospheric and snow samples for chemical analyses, make detailed observations of local meteorological and micrometeorological conditions, document the interaction between snowfall events and subsequent reworking of surface snow by wind and sublimation that determine the relationship between depth in the accumulating snow pack and the passage of time, and document the evolution of the microphysical characteristics of snow grains and layers of snow that control the exchange of energy and material between the snow pack and overlying air. These experiments share the primary objective of quantifying air-snow exchange processes in order to allow more quantitative reconstruction of climate states and the composition of the atmosphere at past times from the extraordinary glaciochemical records recently recovered at Summit by the Greenland Ice Sheet Project 2 and the Greenland Icecore Program deep drilling efforts. The 1997-1998 winter-over campaign also represents a logistical "experiment", in that new modular structures have been deployed at Summit, the crew size is considerably smaller than those that used in other recent deployments. Resupply flights are being conducted throughout the winter.