Biogenic sulfur emissions from the Subantarctic and Antarctic Oceans

Abstract

Measurements of the atmospheric distributions of dimethylsulfide (DMS), sulfur dioxide (SO2), methanesulfonate (MSA), non‐seasalt sulfate (nss‐SO42−), and methylmercaptan (MeSH) were made over the Drake Passage and the coastal and inshore waters west of the Antarctic Peninsula during the 1986 austral fall season. DMS concentrations were also measured in the surface ocean, and vertical profiles were obtained at several locations in the inshore water areas. Surface seawater concentrations of DMS were on the order of 2 nmol L−1, similar to values observed in temperate latitudes. The vertical profiles showed maximum values at depths between 5–40 m. DMS concentrations in the atmosphere were near 4 nmol m−3 (96 parts per trillion by volume, (pptv)), close to the global average for remote oceanic regions. The sea‐to‐air flux of DMS ranged between 1–5 μmol m−2 d−1, with the highest values found in the open ocean areas. The total sea‐to‐air flux of DMS from the Southern Ocean is estimated to be 0.2 Tmol yr −1. MeSH was detected occasionally at concentrations up to 0.15 nmol m−3 (3.6 pptv). The average aerosol MSA concentration (0.27 nmol m−3) was surprisingly high relative to the level of nss‐SO42− (0.31 nmol m−3). Both compounds were found predominantly in fine particles. The nss‐SO42− values were extremely low, comparable to winter values reported for the South Pole. SO2 concentrations were also very low (0.45 nmol m−3 (11 pptv)), consistent with the low levels of nss‐SO42−. The residence time of DMS in the Antarctic marine atmosphere is estimated to be about 2–3 days during clear weather and about 6–7 days during overcast conditions. Photooxidation of DMS in the Southern Ocean atmosphere may lead to a higher yield of MSA and a lower yield of SO2 compared to other world ocean areas.