Abstract
Sea surface and atmospheric measurements of dimethylsulphide (DMS) were performed during the TransBrom cruise in the West Pacific Ocean between Japan and Australia in October 2009. Air-sea DMS fluxes were computed between 0 and 30 μmol m−2 d−1, which are in agreement with those computed by the current climatology, and peak emissions of marine DMS into the atmosphere were found during the occurrence of tropical storm systems. Atmospheric variability in DMS, however, did not follow that of the computed fluxes and was more related to atmospheric transport processes. The computed emissions were used as input fields for the Langrangian dispersion model FLEXPART, which was set up with actual meteorological fields from ERA-interim data and different chemical lifetimes of DMS. A comparison with aircraft in-situ data from the adjacent HIPPO2 campaign revealed an overall good agreement between modeled versus observed DMS profiles over the tropical West Pacific ocean. Based on observed DMS emissions and the meteorological fields over the cruise track region, the model projected that up to 30 g S per month in the form of DMS can be transported above 17 km in this region. This surprisingly large DMS entrainment into the stratosphere is disproportionate to the regional extent of the cruise track area and mainly due to the high convective activity in this region as simulated by the transport model. Thus, we conclude that the considerably larger area of the tropical West Pacific Ocean can be an important source of sulphur to the stratospheric persistent sulphur layer, which has not been considered as yet.