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Stable Isotope Studies at West Antarctic ITASE Sites
Investigators:Eric J. Steig, University of Pennsylvania
Christopher A. Shuman, NASA Goddard Space Flight Center
James W.C. White, INSTAAR--University of Colorado
Snow and ice are both forms of water which contain different oxygen and hydrogen atoms called isotopes. Isotopes differ from atoms in the number of neutrons contained in the atomic nucleus. The oxygen and hydrogen isotopes used in polar studies include:
- oxygen16 (O16),
- oxygen18 (O18),
- hydrogen (H), and
- deuterium (D).
The concentration of these isotopes in the water molecules of polar snow and ice depends largely on the temperature of the snow when it fell. For example, the lower the temperature the less O18 there is in the snow, and consequently there is relatively more O16. This leads to a seasonal variation in the isotopes, depending on when the snow accumulates at a site, which has distinct similarities to the area's temperature cycle.
By measuring the concentration of these pairs of isotopes (O16 to O18 and H to D), it is usually possible to determine if the snow fell in the summer or winter season so that annual layers can be detected. Identification of this seasonal variation is one of the simplest ways to date an ice core. The air temperature history for a polar site can also be interpreted from the isotope profile through a snow pit or ice core.
As the layers in the core are dated by identifying the highs and lows of the isotopic ratios, atmospheric temperature at times in the past can be inferred.
Automatic Weather Station Location Map Click to Enlarge |
Both meteorological observations and results from climate models suggest that global atmospheric circulation is very sensitive to changes in the temperature of the Antarctic atmosphere. Yet spatial and temporal knowledge of temperature variations in the Antarctic is extremely limited. The chief objective of our research is to fill in this gap in the global database by obtaining long-term stable isotope records from snow pits and ice cores along each of the U.S. ITASE corridors. Each of these records will be supplemented by high-resolution (sub-seasonal) analyses from snow pits, including determination of accumulation rates and measurements of firn stratigraphy. Snow pit and ice core isotope records will be calibrated against temperature using a combination of automatic weather stations and satellite passive microwave observations that cover the last two decades. Together, these data will permit us to extend our knowledge of West Antarctic temperatures back over the last 200+ years. Data will be shared with our international colleagues to produce temperature anomaly maps covering the entire Antarctic continent. Such maps should prove valuable both in the interpretation of existing ice core paleoclimate records, and also in the realm of climate-change detection.
