The sulfur cycle at high-southern latitudes in the LMD-ZT General Circulation Model
Résumé
This modeling study was motivated by the recent publication of year-round records of
dimethylsulfide (DMS) and dimethylsulfoxide (DMSO) in Antarctica, completing the
available series of sulfate and methanesulfonic acid (MSA). Sulfur chemistry has been
incorporated in the Laboratoire de Me´te´orologie Dynamique-Zoom Tracers (LMD-ZT)
Atmospheric General Circulation Model (AGCM), with high-resolution and improved
physics at high-southern latitudes. The model predicts the concentration of six major sulfur
species through emissions, transport, wet and dry deposition, and chemistry in both gas and
aqueous phases. Model results are broadly realistic when compared with measurements in
air and snow or ice, as well as to results of other modeling studies, at high- and middlesouthern
latitudes. Atmospheric MSA concentrations are underestimated and DMSO
concentrations are overestimated in summer, reflecting the lack of a DMSO heterogeneous
sink leading to MSA. Experiments with various recently published estimates of the rate
of this sink are reported. Although not corrected in this work, other defects are identified
and discussed: DMS concentrations are underestimated in winter, MSA and non-sea-salt
(nss) sulfate concentrations may be underestimated at the South Pole, the deposition
scheme used in the model may not be adapted to polar regions, and the model does not
adequately reproduces interannual variability. Oceanic DMS sources have a major
contribution to the variability of sulfur in these regions. The model results suggest that in a
large part of central Antarctica ground-level atmospheric DMS concentrations are larger in
winter than in summer. At high-southern latitudes, high loads of DMS and DMSO are
found and the main chemical sink of sulfur dioxide (SO2) is aqueous oxidation by ozone
(O3), whereas oxidation by hydrogen peroxide (H2O2) dominates at the global scale. A
comprehensive modeled sulfur budget of Antarctica is provided.
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