The first Greenland ice core record of methanesulfonate and sulfate over a full glacial cycle

Abstract

Methanesulfonate (MSA) in ice cores has attracted attention as a possible tracer of past oceanic emissions of dimethylsulfide (DMS). After sulfate MSA is the second most prevalent aerosol oxidation product of DMS, but in contrast to sulfate, DMS oxidation is the only known source of MSA. The hypothesis by Charlson et al., [1987] of a climate feedback mechanism with sulfur emissions from marine phytoplankton influencing the cloud albedo adds to the interest in establishing long records of MSA and non‐seasalt sulfate spanning large climatic changes. Records of MSA and non‐seasalt sulfate covering time periods from a few years to thousands of year have been extracted from antarctic ice cores [Ivey et al., 1986; Saigne and Legrand, 1987; Legrand and Feniet‐Saigne, 1991; Mulvaney et al., 1992] but only the record from the Vostok ice core [Legrand et al., 1991] covers a full glacial cycle. The concentrations of MSA and non‐seasalt sulfate in Antarctica have been found to increase under glacial conditions. Here we present the first Northern Hemisphere record of MSA, and the first continuous record of non‐seasalt sulfate, both extracted from the Renland ice core, East Greenland. The records are extending from the Holocene to the Eem interglacial 130,000 years B.P. The contrast to the Southern Hemisphere records is striking, with a decreasing concentration of MSA with the advance of glaciation but an increasing concentration of non‐seasalt sulfate. A strong linear relationship is found in the Renland ice core between the ratio of MSA to non‐seasalt sulfate and the temperature, with higher ratios associated with warmer climatic stages, while the opposite relationship to temperature is found in the Vostok ice core. A more complicated picture is emerging of the use of MSA in ice cores as a quantitative tracer which suggests that previous interpretations can have been overly simplistic.