U.S.Dept of Commerce / NOAA / PMEL / Atmospheric Chemistry 

Oceanic Dimethylsulfide (DMS) and Climate

 

Timothy Bates & Patricia Quinn,
Derek Coffman, Drew Hamilton, 
James Johnson, & Theresa Miller

Goal: Assess the importance of oceanic DMS emissions to the tropospheric sulfur burden and the formation and growth of atmospheric aerosol particles.

 

Accomplishments:  Oceanic dimethylsulfide (DMS) is the major natural source of sulfur to the atmosphere and contributes both to the tropospheric sulfur burden and to particle formation and growth in the atmosphere.  The atmospheric sulfate aerosol particles that evolve from biogenically-derived DMS emissions play a role in the global radiation balance directly through the upward scatter of solar radiation and indirectly as cloud condensation nuclei (CCN).


 
 

Results from PMEL research cruises are being used to assess the magnitude of the flux ofoceanic DMS to the atmosphere. 

 

Oceanic DMS emissions account for 15% of the total global sulfur emissons of 3.2 Tg S/year.  Although anthropogenic emissions dominate the global sulfur budget, natural sulfur emissions are still a significant fraction (30-100%) of the total sulfur emissions in the tropical latitudes of the northern hemisphere and in all latitude belts of the southern hemisphere (Bates et al., J. Atmos. Chem., 14:315-337, 1992).


 
 

Charlson et al. (Nature, 326:655-661, 1987) hypothesized a climate feedback link where changes in cloud albedo and subsequent changes in surface temperature and/or solar radiation below clouds could affect the production of DMS by marine phytoplankton. Evidence for the climatic significance of DMS emissions continues to grow, linking regions (periods) of high DMS emissions with regions (periods) of high particle concentration and enhanced cloud albedo.  However, the hypothesized feedback link, whereby climate affects the level of DMS emissions, has remained elusive.

 
 

The large interannual variations in oceanic (SST, mixed layer depths, and upwelling rates) and atmospheric (cloud cover and precipitation) properties in the equatorial Pacific Ocean, associated with the El Nino-Southern Oscillation (ENSO), would appear to be an ideal natural environment to search for DMS-climate feedbacks.  However, measurements from 11 cruises between 1982 and 1996 show that the mean surface seawater DMS concentration in this region (15°N to 15°S) is relatively constant both seasonally and interannually (2.7 ± 0.7 nM). The large interannual variations in oceanic and atmospheric properties, associated with ENSO events appear to have little effect on the concentration of DMS in surface ocean waters.  The hypothesized DMS-climate feedback link thus remains elusive (Bates and Quinn, Geophys. Res. Lett., 24:861-864, 1997).

 

Future Directions:  We will continue to measure DMS on Atmospheric Chemistry cruises to refine estimates of the ocean to atmosphere flux and to assess seasonal, inter-annual and decadal trends in seawater DMS concentrations.

Funding support provided by the NOAA RITS Program and NOAA Office of Global Programs.

Atmospheric Chemistry Group,  http://saga.pmel.noaa.gov