Abstract
Abstract. Sea surface and atmospheric measurements of dimethylsulphide (DMS) were performed during the TransBrom cruise in the western 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 Lagrangian 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 modelled versus observed DMS profiles over the tropical western Pacific Ocean. Based on observed DMS emissions and meteorological fields along the cruise track, the model projected that up to 30 g S per month in the form of DMS, emitted from an area of 6 × 104 m2, can be transported above 17 km. This surprisingly large DMS entrainment into the stratosphere is disproportionate to the regional extent of the area of emissions and mainly due to the high convective activity in this region as simulated by the transport model. Thus, if DMS can cross the tropical tropopause layer (TTL), we suggest that the considerably larger area of the tropical western Pacific Ocean can be a source of sulphur to the stratosphere, which has not been considered as yet.
Highlights
Radiative In addiof the computed fluxes and was more related to atmospheric tion, because DMS is rapidly oxidised when emitted to the transport processes
The computed emissions were used as atmosphere, studies input fields for the Lagrangian dispersion model FLEXPART, which was set up with actual meteorological fields from ERA-Interim data and different chemical lifetimes of have been conducted showGinegothsact iceenrtatiinficDMS oxidation products tribute to can the pbeeMrstriosatndesnpetoslrttrDeadteoasvbpoheveleroictphseumltproehpunorptlaauyseer, and conor Junge
If DMS can cross the tropical tropopause atmosphere have a distinct global footprint with regard to the layer (TTL), we suggest that the considerably larger area of Junge layer (Bruhl et al, 2012, Bourassa et al, 2012; Vernier the tropical western Pacific Ocean can be a source of sulphur et al, 2011b)
Summary
Underway surface water samples for DMS and air samples for DMS were collected aboard the R/V Sonne from 9 to 24 October 2009 during a transit from Tomakomai (Japan) to Townsville (Australia). The DMS oceanic and atmospheric data were used for the flux calculation. Sea surface temperature and wind speed data from ship sensors at one-minute resolution were selected dependent on time and latitude of the DMS samples (Fig. 2). Flux calculations were performed by applying three different gas transfer coefficient parameterisations at a Schmidt number of 720, that of DMS in seawater at 25 ◦C according to Saltzman et al (1993): Marandino et al (2007) – UCI; Wanninkhof (1992) – W92; Liss and Merlivat (1986) – LM. The parameterisations were chosen to reflect the different theories of wind speed dependence and measurement techniques for k, where UCI is linear and derived from eddy covariance measurements, W92 is quadratic and derived from the 14C ocean inventory, and LM contains three different linear parameterisations based on tracer studies and wind/wave tank measurements
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