| 其他摘要 | Snow-firn pack links the atmosphere and the ice core in geochemical composi-tions. In order to interpret the records in ice core, the present environmental proc-esses of snow and firn, such as the atmospheric transfer function and the effect of post-depositional processes, need to be known. To investigate the effects of deposi-tional and post-depositional processes on chemical signals recorded in glacier snow and ice, organic acids and inorganic anions were analyzed over the course of one year. The investigation was undertaken as part of the Program for Glacier Processes Investigations (PGPI), which was initiated in July 2002 by the Tianshan Glaciol-ogical Station (TGS).
Snow samples collected during March 2004 to March 2005 field campaign from the accumulation zone of the Glacier No.1 (43°06′N; 86°49′E; 4 130m a.s.l.) at the Ürümqi river head, eastern Tianshan, China, were analyzed for low molecular weight organic acids and inorganic anions by DIONEX ICS-90 Ion Chromatogra-phy with RFC-30 Reagent-Free Controller. The organic acids in the sample include HCOO-, CH3COO-, C2H5COO- and (COO)22-, while the inorganic anions are F-, Cl-, NO2-, NO3-, SO42- and PO43-.
Surface snow sets the benchmark for identifying post-depositional changes of the geochemical constituent in the ice forming processes. For monitoring the varia-tions of chemical composition in the transforms from snow to ice, low molecular weight organic acids and inorganic anions in surface snow (the topmost 5cm snow in the snow pit) were analyzed. Most of the organic acids except for (COO)22- and high-concentration inorganic anions as Cl-, NO3- and SO42- demonstrate seasonal variations from April to September, which we believe are primarily caused by strong local atmospheric circulations and the prevailing west wind in the seasons, while much even concentrations in the winter. All the anions changed considerably from the late spring to early autumn, and revealed both the lowest and highest con-centrations in a year. On the other hand, (COO)22- and low-concentration inorganic anions as F-, NO2- and PO43- showed high variations in the whole year. Our results indicate that the majority of high concentration anions can be preserved in the sur-face snow for a long time (at least half a year) without changes in their concentra-tions if the weather conditions remain relatively stable.
During the post-depositional processes, organic acids and inorganic anions in high-concentrations were analyzed. It is found that the temperature and the percola-tion of meltwater had a definitive impact on the transformation process. These compositions in snowpits during different periods show visible seasonal character-istics and elution processes. When meltwater appeared in snow pit, they assembled the ions and increased the concentrations of the compositions as they moved downward. And at the same time, successive peaks occur at the upper parts of snow-firn pack. As the temperature reaches above zero completely, meltwater per-colated through the snow pit, and leached the ions, however, alteration deeper in the snow-firn pack was slight and the general information was still preserved. When the temperature stayed below zero, the peaks present a stable fluctuation, which can in-dicate the conclusion again, that the majority of high concentration anions can be preserved in the surface snow for a long time (at least half a year) without changes in their concentrations if the weather conditions remain relatively stable; and to some extent, the peaks in the upper parts of snow-firn packs can represent their primary levels in the atmosphere. We also found that during melting season, the peaks move downward rapidly, while during other seasons the peaks move down-ward slowly until merging into ice. Furthermore, both CH3COO- and (COO)22- peaks coincide with dust layers, this implies that dust layers may have an influence on the elution process of CH3COO- and (COO)22-. |
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