Dimethylsulphide :- The Global Coolant

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This presentation was made by me when I was studying my Masters from TERI. I Chose this topic because everyone was talking about warming and this was little different and interesting.

This presentation was made by me when I was studying my Masters from TERI. I Chose this topic because everyone was talking about warming and this was little different and interesting.

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  • 1. Dimethylsulphide- the global coolant Shilpi Misra Senior Research Fellow IARI- Delhi
  • 2. Introduction
    • Global cooling refers to the overall cooling of the Earth.
    • Dimethyl sulphide (DMS) is the most dominant sulphur gas emanating from the oceans.
    • In the oceans dimethylsulphide is produced by the various biological interactions between the phytoplanktons, microscopic algae and the bacterial population.
    • Various species of algae are involved in the production of high concentrations of DMS in the oceans e.g. Phaeocystis, Emiliania, and Alexandrium .
  • 3. About Dimethylsulphide
    • Dimethyl Sulphide is a naturally produced biogenic gas and plays an important role in the natural sulphur cycle.
    • Dimethyl sulphide is a product of biological processes involving marine phytoplankton and is estimated to account for approximately 60 % of the total natural sulphur gas released to the atmosphere in both hemispheres.
    • Lovelock et al. (1972) showed that the biogenic gas DMS was found in surface ocean waters throughout the Atlantic Ocean.
  • 4. About Dimethylsulphide
    • DMS originates from the enzymatic breakdown of Dimethylsulphoniopropionate (DMSP). DMSP is then cleaved into DMS and acrylic acid.
    • (CH 3 ) 2 S + CH 2 COO - > CH 3 SCH 3 + CH 2 =CH-COO - + H +
    • DMSP DMS Acrylate
    •  
    • Haas first identified DMS emissions from the marine algae Polysiphonia fastigata in 1935.
    • The main function of DMSP in phytoplankton is that it plays a role of an osmolyte and a cryoprotectant.
  • 5. About Dimethylsulphide
    • The concentration of DMSP and DMS released into the atmosphere varies from one phytoplankton species to another in the following order:
    • Coccolithophores > Phaeocystis > Dinoflagellates > Diatoms
    • DMSP is released by the phytoplankton cells when they are damaged by viral lysis, senescence and zooplankton grazing.
    • The breakdown of DMSP, after it is transferred from algal cells into the seawater is mediated my specific enzymes. DMSP lyase activity has been found in algal extracts and has also been associated with marine bacteria.
  • 6. Sea-Air Exchange of DMS
    • The most important factors, which influence gas exchange, are the difference in the concentration of the gas between the air and the water and the speed of the wind. 
    • As the waves break they introduce billions of bubbles into the surface waters.  These bubbles transfer gases from the atmosphere into the water. 
    • When the bubbles rise up through the water and reach the surface, they burst and a jet of seawater enters the air.   As this jet rises, it breaks up into droplets.  The water evaporates and leaves aerosol particles made up of seasalt. 
  • 7. Sea-Air Exchange of DMS
  • 8. A bubble rising through the sea and bursting, releasing sea-salt aerosol into the air.
  • 9. Global Cooling due to Dimethyl Sulphide
    • Phytoplankton don't just simply affect climate by producing the gas dimethyl sulphide (DMS) but actually play a role in regulating the climate of the Earth. (Charlson et al., 1987).
    • The CLAW hypothesis (named after the authors of the paper) says that if a change in the temperature of the Earth occurs, for example due to global warming, phytoplankton respond to reduce this change (Charlson et al., 1987).
    • Once DMS is emitted from the oceans it is oxidized by free radicals, such as OH and NO 3, to form a variety of products including methane sulphonic acid and sulphur dioxide which in turn are oxidized to form non sea salt-sulphate aerosols.
  • 10.  
  • 11. Variations in DMS concentrations
    • Phytoplankton alone is not responsible in controlling the extent of DMS concentrations .
    • Chlorophyll
    • Nitrate
    • Salinity
    • Wind speed
  • 12. Vertical profiles of DMS, DMSP and chlorophyll at 7  N in the Bay of Bengal. (Shenoy et al. 2000)
  • 13. Relationships for DMS with chlorophyll and nitrate in the upper 30 m of the study region. (Shenoy et al. 2000).
  • 14. Relation between differences, horizontally or vertically between two depths or locations, in salinity and DMSP. (Shenoy et al. 2000)  
  • 15. Relationships for salinity with DMSP and chlorophyll in the upper 30 m of the study region. (Shenoy et al. 2000)
  • 16. Dependence of DMS and DMSP concentrations in aerosols on wind speeds. (Kumar et al. 2002)
  • 17. Remarks
    • Measurements of methane sulphonic acid (MSA, which is derived from DMS) in ice core bubbles indicate that there were more phytoplankton in the polar oceans during the ice ages.
    • The production of DMS by plankton only has a small effect on the Earth's temperature.
    • The effects of the DMS production by plankton are particularly noticeable at a regional level.
    • Sulphate aerosols have a lifetime of only five days in the atmosphere compared to 120 days for CO 2 so the net effect of the two compounds would be a warming.
  • 18. References
    •       Bates, T.S., B.K. Lamb, A. Guenther, J. Dignon, and R.E. Stoiber (1992): Sulfur emissions to the atmosphere from natural sources. Journal of Atmospheric Chemistry, 14, 315-337.
    •    Kumar, M. D., Shenoy, D. M., Sarma, V. V. S.S., George, M. D., & Dandekar, M. (2002). Export fluxes of dimethylsulfoniopropionate and its break down gases at the air-sea interface. Geophys. Res. Lett., 29 (10.1029/2001GL013967).
    •     Shenoy, D. M., M.D. Kumar, and V. V. S .S. Sarma, Controls of dimethyl sulphide in the Bay of Bengal during BOBMEX – Pilot cruise 1998, Proc. Indian Acad. Sci. (Earth Planet Sci.), 109, 279-283, 2000.
  • 19. References
    •     Shenoy, D.M., S. Joseph, M. Dileep Kumar, and M.D. George. Control and inter-annual variability of dimethyl sulfide in Indian Ocean., J. Geophys. Res. (Atmosphere), 107 (D19), (10. 1029/ 2001 JD000371).
    •      Shenoy, D.M., Patil, J. S. Temporal variations in Dimethylsulphoniopropionate and dimethylsulphide in the Zuari estuary, Goa (India). Marine Environmental Research, 56 (2003) 387-402.
    •       Shenoy, D.M., Paul, T. J., Gauns, M., Ramaiah, N., and Kumar, M.D. Spatial variations of DMS, DMSP and phytoplankton in the Bay of Bengal during the summer monsoon 2001. Marine Environmental Research , 62 (2006) 83-97.