Sulphur-Derived Species in Polar Ice: A Review

Abstract

Sulphate, which is one the major ions present in polar ice, has been extensively studied in ice cores since about fifteen years. More recently, a few studies of sulphate concentrations in polar ice have been achieved along with determinations of CH3SO3H (MSA), another important sulphur species trapped in snow layers. Such studies have been conducted along both Greenland and Antarctic ice cores spanning the last decades as well as the last great climate change which occurred some 18,000 years ago. Sulphate trapped in polar ice is associated with several chemical compounds including sea salt, Na2SO4, CaSO4, NH4HSO4, (NH4)2SO4, and H2SO4 which are present in variable proportions depending on the location and on the considered time period. While sulphuric acid dominates the sulphate budget of ice of present-day climatic conditions, the contribution of sulphate associated with sea salt and soil dust increased in ice deposited during past colder climate. NH4HSO4, the concentration of which is insignificant in Antarctic ice, is believed to be present in significant amounts in Greenland ice. Sulphate depth-profiles show that fossil fuel combustion has enhanced sulphate concentrations in Greenland snow by a factor of 2 to 4 since the beginning of this century and that no similar trend occurred in Antarctica. Numerous studies have demonstrated that sulphate concentrations of Greenland and Antarctic ice increased very often, bet for short-time periods (a few months to two years), after large volcanic eruptions. Ice core data also suggest that the non-volcanic natural sulphate background level is mainly marine and biogenic (DMS emissions) in origin in Antarctica under present climatic conditions as well as during the last two ice ages. It is also suggested that the rate of these DMS emissions have changed in the past in response to short and long-term climatic variations. The interpretation of the composition of Greenland ice is more complex and the possible contribution of other non-biogenic sources of sulphate like terrestrial emissions and continuous volcanic degassing will be here discussed.