Ice-Core Records of Atmospheric Sulphur

Sulphate and methanesulphonate (MSA), the two major sulphur species trapped in polar ice, have been extensively studied in Antarctic and Greenland ice cores spanning the last centuries as well as the entire last climatic cycle. Data from the cores are used to investigate the past contribution of volcanic and biogenic emissions to the natural sulphur budget in high latitude regions of both Hemispheres. Sulphate concentrations in polar ice very often increased during one or two years after large volcanic eruptions. Sulphate records show that fossil fuel combustion has enhanced sulphate concentrations in Greenland snow by a factor of four since the beginning of this century, and that no similar trend has occurred in Antarctica. At present, sulphate in Antarctic snow is mainly marine and biogenic in origin and the rate of dimethyl sulphide (DMS) emissions may have been enhanced during past developments of El Nino Southern Oscillations (ENSO). Marine biota and non-eruptive volcanic emissions represent the two main contributors to the natural high northern latitude sulphur budget. While these two sources have contributed equally to the natural sulphate budget of Greenland ice over the last 9000 years B.P., non-eruptive volcanic emissions largely dominated the budget at the beginning of the Holocene. A general negative correlation is observed between surface air temperatures of the Northern Hemisphere and Greenland snow MSA concentrations over the last two centuries. Positive sea-ice anomalies also seem to strengthen DMS emissions. A steady decrease of MSA is observed in Greenland snow layers deposited since 1945, which may either be related to decreasing DMS emissions from marine biota at high northern latitudes or a changing yield of MSA from DMS oxidation driven by modification of the oxidative capacity of the atmosphere in these regions. Slightly reduced MSA concentrations are observed in Greenland glacial ice with respect to interglacial levels. In contrast, sulphate and calcium levels are strongly enhanced during the ice age compared to the present day. These long-term variations in Greenland cores are opposite in sign to those revealed by Antarctic ice cores. Such a difference suggests that climate changes led to a quite different sulphur cycle response in the two Hemispheres.