SPATIAL & SEASONAL PATTERNS IN SNOWPACK SULPHATE IN THE CANADIAN ARCTIC

Sulphate stable isotopes (d³⁴S and d¹⁸O) offer new tools to apportion snowpack aerosol sulphate among biogeochemical sources. The sulphate ion is chemically inert under snowpack conditions, and its isotope ratios are preserved. In the context of global change, there is major interest in the biogeochemical cycle of atmospheric sulphur as it is complex, poorly understood, and has a significant role in radiative forcing. Of particular interest in the Arctic is the role of sulphate derived from oceanic phytoplankton emitted gases (dimethylsulphide (DMS) and its oxidation products), potential negative climatic feedbacks through the formation of cloud condensation nuclei, and relationships to sea ice extent. This study evaluates the methodology and logistics associated with using DMS sulphate in Arctic snow as a proxy for sea ice versus open water, and contributes to the calibration phase of a deep ice-core project.

High-resolution snow sampling along two transects on The Prince of Wales Icefield, Ellesmere Island (POW) from sea level to 1450 m.a.s.l was used to explore differences in transport and deposition of primary sea-salt sulphate and DMS sulphate.  Snow pits every 1500 meters in elevation gain were sampled at 10 cm depth intervals for sulphate isotopes (d³⁴S, d¹⁸O), water isotopes (d¹⁸O, d²H), MSA, and major ions. At the 1700 m.a.s.l. proposed drill site, a 2.5 year profile was sampled. Preliminary sulphur isotopic analyses (d³⁴S = +9‰ to +22‰) show definite seasonal cycles and variation with distance from coast and with elevation. SO₄^2-and Cl^- are well correlated on the Jewell Glacier (R² = 0.85). This relationship is less apparent on the gentler sloped Lower Leffert Glacier (R²= 0.81) and is weakest at the Summit (R²=.66).  These and other results will be discussed in the context of aerosol transport and its relationship with isotope composition.