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This data set includes 15N, 18O/2, O2/N2/4, 40Ar/4, 38Ar/2, 84Kr/48, and 132Xe/96 values for air drawn from the top 15 to 50 m of firn at two sites on Siple Dome (summers 1996 and 1998) and at the South Pole (summer and winter 1998). Data also include related firn temperature measurements.
The objective of this research was to better understand thermal fractionation processes affecting records of atmospheric history from firn and ice core gases. Recent work (e.g., Severinghaus and Brook, 1999) has exploited trapped air in ice and deep firn as a record of past atmospheric composition and climate change. Interpretation of these paleoclimate archives is complicated by artifacts of thermal diffusion, a process in which heavier gases migrate down temperature gradients toward colder regions in the firn. Seasonal temperature change at the snow surface creates strong temperature gradients in the top few meters of the firn, which cause isotopic fractionation of firn gases. A specific goal of this research is to identify any long-term effects of seasonal temperature fluctuations on firn air isotopic anomalies.
Investigators obtained samples using tubes inserted into boreholes. (The 18 December 1996 samples, acquired using the "bladder method" are an exception.) They extended tubes into the boreholes until their stainless steel intake screens were positioned at the desired depth. Snow and slush used to backfill the hole impeded downward movement of surface air. They pumped samples at 4 L per minute for 16 minutes to flush the tubing and sample flasks. A phosphorous pentoxide column dried the air before it was stored in 2-L flow-through glass flasks. Gas ratios were later measured by mass spectrometry at the University of Rhode Island and Scripps Institution of Oceanography (University of California, San Diego).
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The ASCII file "firn_air_isotopes.txt" contains gas isotope data (also available in Microsoft Excel format) and is formatted as follows:
Flask ID "depth, m" d15N d18O/2 dO2/N2/4 d40Ar/4 d38Ar/2 d84Kr/48 d132Xe/96 sdf02 0 0.0205 0.0101 0.0212 0.0133 0.0075 0.0009 0.0009 sdf03 1.55 0.0524 0.0459 0.0499 0.0279 0.0235 0.0042 0.0034 sdf05 1.55 0.0509 0.0465 0.0534 0.0283 0.023 0.0064 0.0014 sdf06 3.42 0.1216 0.1057 0.1222 0.0845 0.0728 0.0405 0.0274
An additional column header provides the estimated analytical precision of each isotopic measurement. Data are subdivided by sampling location and date. The South Pole site is located at 89.997 degrees south latitude, 102.0 degrees west longitude. The Siple Dome site is located at 81.667 degrees south latitude, 148.767 degrees west longitude. The "shallow" and "deep" holes referred to in the table are separated by 46 m horizontally.
The ASCII file "firn_temps.txt" contains firn temperature data (also available in Microsoft Excel format) and is formatted as follows:
"Depth, m" "Firn temperature, C" 0.1 -9.61 1.43 -19.5 2.43 -24.22 3.31 -25.78
Estimated accuracy of temperature measurements is ±0.05 C. Data are subdivided by sampling location and date.
Severinghaus, J. P., and E. J. Brook. 1999. Abrupt climate change at the end of the last glacial period inferred from trapped air in polar ice. Science 286: 930-934.