Methanesulfonic acid in south polar snow layers: A record of strong El Nino?

Abstract

In this paper we present a detailed study of methanesulfonic acid (MSA) and non‐sea‐salt sulfate (nss‐SO4) content in recent south polar precipitation. These two species are major oxidation products of dimethylsulfide (DMS) which is mainly produced by marine biota. The nss‐SO4 content of south polar snow layers deposited over the 1922–1984 time period remained rather stable except short‐term increases after the Mt Agung (1963) and the El Chichon (1982) eruptions. At the opposite, the MSA profile shows over the same time period several sporadic, 0.5 to 2 years, increases (2 to 10 times background level). Taking into account an uncertainty of 1–3 years in the dating of snow layers, all these MSA events seem to be correlated to major ENSO (El Nino‐Southern oscillation) events having occured over the last sixty years (1925–26, 1941, 1957–58, 1972–73 and 1982–83). The relatively high MSA/nssSO4 weight ratios (R) observed in the corresponding snow layers suggest that these events reflect enhanced DMS emissions from the antarctic ocean. This suggested connection between ENSO and high DMS marine emissions at high southern latitudes is discussed in terms of atmospheric and oceanic circulation.