1. First high-resolution, century-scale ice-core records of hydrogen peroxide from West Antarctica: Contribution of accumulation variability
Markus M. Freya, Joseph R. McConnellb , Edward Hannac, Roger C. Balesd
aDepartment of Hydrology and Water Resources, University of Arizona, 1133 E.North Campus Drive, Tucson AZ 85721, USA.
bDesert Research Institute , Divison of Hydrologic Sciences, 2215 Raggio Parkway, Reno, NV 89512, USA.
cDepartment of Geography, University of Sheffield, Sheffield, UK.
dUniversity of California, Merced, 4225 N. Hospital Road, Atwater, CA 95301, USA.
1. Introduction
Hydrogen peroxide (H2O2) is a major atmospheric oxidant that is closely linked to chemical feedback mechanisms controlling the composition of the atmosphere. H2O2 is highly soluble & so is deposited in snow on the large ice sheets & preserved over time. Ice core records of H2O2 offer the potential to reconstruct past changes in the oxidation capacity of the atmosphere if the processes controlling deposition and long-term preservation are quantitatively understood. The seasonal timing & rate of snow accumulation, as well as the site temperature largely determine the amount of H2O2 preserved in an ice core.
5. Hydrogen peroxide concentrations
2. Core locations
Map of the West Antarctic Ice Sheet (WAIS) showing ice core locations on the U.S. ITASE traverse during & cores drilled in 1995 at RIDS-A,B & C & the South Pole.
The continuous H2O2 record (resampled at a uniform rate of 48 samples yr-1, shaded in pink) shows preservation of the seasonal cycle along the entire core at 00-2, 00-3, all 2001 sites & Also reported are the 5-yr running mean (thick red line) & the mean concentration for to illustrate both temporal and spatial variability of mean H2O2 in firn & ice. Comparison of the time periods vs shows on average, a 43% higher mean H2O2 at all sites during the latter half of the 20th century.
3. Site characteristics
Mean annual air temperatures at each site are based on either AWS data(a), 10-m borehole temperatures(b) or linearly extrapolated values using the dry-adiabatic lapse rate. Mean accumulation rates are reported for the entire core length. At low accumulation sites the vulcanic eruption of Tambora (1815) provided an absolute time horizon(*). Depth-age scales published previously were used at the RIDS sites & South Pole (Kreutz et al., 2000(i), Meyerson et al., 2002(ii)).
6. Accumulation rates
4. Analysis & dating
Trace chemical measurements on the cores were done using continuous flow analysis (CFA) (Röthlisberger et al., 2000) linked with an Inductively Coupled Plasma (ICP). Dating was based on H2O2, NO3-, Cl-, electric conductivity, Na+, Ca2+ & Mg2+. Records of multiple chemical species coregistered at 1-2 cm depth resolution were dated (sub)annually using seasonal maxima & minima of H2O2, NO3- & sea salts (a./b. low & c./d. high accumulation sites). Vertical lines represent annual picks
Annual (shaded light blue) & 5-yr running mean (thick blue line) accumulation rates in meters of snow water equivalent (SWE) are shown. Comparison of the same 50-yr periods yields no uniform result across the ice sheet with some negative trends (mean -7.9% at 7 sites), some positive (mean 10.2% at 8 sites) & no trend at all (3 sites). There was a good correlation between core-derived net accumulation & ERA-40 meteorological model simulations (data not shown).
7. Variability of H2O2 & accumulation
The records of H2O2 (thick red line) & accumulation (shaded blue) from high accumulation sites are compared by plotting 5-yr means normalized to the common time period Mean H2O2 (period ) preserved varies up to a factor 8 between sites & correlates well with mean accumulation averaged over the same time (r2=0.61), but accumulation versus H2O2 patterns at a single site do not correlate well. No significant correlation was found between mean H2O2 & mean annual site temperature.
References
Kreutz, K. J., P. A. Mayewski, L. D. Meeker, M. S. Twickler, and S. I. Whitlow. The effect of spatial and temporal accumulation rate variability in West Antarctica on soluble ion deposition, Geophysical Research Letters 27, , 2000.
Meyerson, E. A., P. A. Mayewski, K. J. Kreutz, L. D. Meeker, S. I. Whitlow, and M. S. Twickler. The polar expression of ENSO and sea-ice variability as recorded in a South Pole ice core, Annals of Glaciology 35, , 2002.
Röthlisberger, R., M. Bigler, M. A. Hutterli, S. Sommer, and B. Stauffer. Technique for continuous high-resolution analysis of trace substances in firn and ice cores, Environmental Science & Technology 34, , 2000
Acknowledgements
This work was supported by NSF grants OPP & OPP We thank the U.S. ITASE team for core retrieval and processing in the field. D. Belle-Oudry, D. Friel, R.Banta & D. Solter-Goss provided invaluable help with core analysis at the UofA (Tucson/AZ) and at DRI (Reno/NV).