Date of Award

2006

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Earth Sciences

Advisor

Karl J. Kreutz

Second Committee Member

Paul A. Mayewski

Third Committee Member

Stephen A. Norton

Abstract

Samples of snow and firn from accumulation zones on the Victoria Upper Glacier, the Clark Glacier, the Commonwealth Glacier and the Blue Glacier in the McMurdo Dry Valleys (~77 to 78º S and 161 to 164º E), Antarctica, are evaluated chemically and isotopically to determine the relative importance of local (site-specific) factors versus regional-scale climatic influences in defining regional glaciochemistry. Two approaches for distinguishing these controls are examined: comparing chemical concentrations using multivariate statistical analysis, and examining the effect of physical filtration (capturing particulate material largely originating in close proximity to each site) on sample values. These techniques provide constraints for interpretation of connections between Dry Valleys climate and the broader Ross Sea and East Antarctic Ice Sheet climate systems. Spatial variation in snow and firn chemistry confirms documented trends within individual valleys regarding ion deposition relative to elevation and to distance from the coast. The results here, however, demonstrate that intra-valley trends break down when chemistry is compared among valleys. Temporally, major ions (with the exception of methane sulfonate and to a lesser extent calcium ion) yield common seasonal signals at each site for the time period 1989 - 2002. Trace metals have concentration peaks offset from ion peaks; using Empirical Orthogonal Function (EOF) analysis to clarify this distinction, a secondary climate pattern accounting for ~13% to 33% of dataset variability contains opposing deposition patterns for 10-cm averages of major ions compared to corresponding 10-cm samples of trace metals. Differing resolutions between these data sets, however, dictate caution in this assessment. Site-specific exposure to marine and local chemical sources plays a dominant role over trends in elevation or in distance from the coast in defining snow and firn chemistry along the coastal axis of the Dry Valleys. Physical filtration of samples from the Victoria Upper Glacier (77.3005º S, 161.0419º E, 1350 m.a.s.l.) yields variability of ~25% for trace metals. Samples analyzed for Al, Cd, Co, Cr, Mn, and S have variability – within 95% confidence – larger than the range of the 16 samples analyzed. Acidification of unfiltered samples provides more consistent results, with sample variability <15% for all elements. For future chemical analysis of snow and ice at sites with significant particulate deposition, combined filtration and HF acidification is recommended. Trace metals are associated to varying degrees with particulate (>0.4 µm) and non-particulate (< 0.4µm) input. The elements Al, Co, Cs, Fe, Mn, Ti, U, V and the rare earth elements (REE) are linked to particulate deposition, with an average 82% occurring in particles >0.4 µm. Ca, Cd, S and Sr, on the other hand, are either completely or dominantly (average 65% - 85%) present in dissolved or soluble particulate form. Statistical analysis and physical filtration together demonstrate that in areas where glaciochemical signals are influenced by locally derived particulates, interpreting regional trends requires caution. Differences in local effects between two locations may overwhelm broader climate signals. In areas of complex topography and terrain, the influence of these local factors must be understood before climate inferences can be drawn.

Download

Included in

Glaciology Commons

Share