Ionic variability in snow and firn along an Antarctic transect

Abstract

In order to interpret the ionic variability in snow and firn from Patriot Hills (80º18’S, 81º21’W) to the South Pole, we determined the major ions concentrations and isotopic ratios of five snow and firn cores (less than 46 m deep) for the 200 first fractions, collected during the 2004–2005 Chilean-Brazilian traverse. After cleaning the samples (in a cold room) and melting it (in a class 100 clean room), we determined the Na⁺ , K⁺ , Mg²⁺, Ca²⁺, MS^- (CH₃ SO₃ ^- ), Cl^- , NO₃ ^- and SO₄ ^2- concentrations by ion chromatography, with detection limits from 0.3 to 1.8 µg L-1 depending on the ion. For deuterium/hydrogen isotopic ratio (δD) the precision is 0.5‰. We dated the samples with annual precision and ±2 years accuracy, by counting the Na⁺ , nssSO₄ ^2- (non-sea-salt sulfate) and δD annual layers. Then we obtained, for the five snow and firn cores sites, the mean net snow accumulation rates. They show a negative correlation (r >0.4, module) with increasing elevation and sea distance, yet responding to local superficial features and katabatic winds occurrence. The snow and firn cores reveal alterations in the sea salt aerosols Na⁺ /Cl^- ratios, but the aerosols produced during sea ice formation appear only on the nearest sites of the coast. The NO₃ ^- , as the MS- record, indicates the occurrence of post-depositional processes connected to volcanic events and photochemical reactions, which intensity increases on glaze surfaces.