Biogeochemical modelling of upper ocean sulfur dynamics and its impact on cloud forming aerosols

• Autores: Sergio Manuel Vallina Fernandez
• Directores de la Tesis: Rafel Simó Martorell (dir. tes.)
• Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2006
• Idioma: español
• Tribunal Calificador de la Tesis: Carles Pedrós-Alió (presid.), José Luis Pelegrí Llopart (secret.), Roger Cropp (voc.), Jaime Piera Fernández (voc.), Jordi Dachs Marginet (voc.)
• Materias:
  • Ciencias de la tierra y del espacio
    • Oceanografía
      • Interacciones mar-aire
• Enlaces
  • Tesis en acceso abierto en: Digital CSIC
• Resumen

  • The CLAW hypothesis postulates that an increase in solar irradiance or in the heat flux to the ocean can trigger a biogeochemical response to counteract the associated increase in temperature and available sunlight. This natural (negative) feedback mechanism would be based on a multi-step response: first, an increase in seawater dimethylsulfide concentrations (DMSw) and then its fluxes to the atmosphere (DMSflux); second, an increase in the atmospheric cloud condensation nuclei (CCN) burden as a consequence of DMS oxidation to form biogenic CCN (CCNbio); third, an increase in cloud albedo due to higher CCN numbers. Therefore, DMS is suggested to exert a cooling effect on the Earth radiative budget through its involvement in the formation and optical properties of tropospheric clouds over the ocean. Such a feedback has been regarded as a potential natural mechanism that might partly counteract anthropogenic Global Warming. This hypothesis, although suggestive, is highly speculative and some of its main postulates remain unproved. In this study we sought to contribute to the current knowledge of the oceanic biogenic sulfur cycle and its potential impact on climate by addressing some relevant open questions regarding the CLAW hypothesis. The climatic factor that drives oceanic DMS production, the impact of DMS oxidation on atmospheric CCN, and the potentiality of DMS to counteract Global Warming are investigated in detail based on modeling and data analyses. A new one-dimensional (1D) model of DMS dynamics (DMOS) is developed and coupled to a pre-existing ecological model that explicitly simulates the microbial-loop. The model is applied to the Sargasso Sea in order to explain what drives DMS seasonality. We have conducted a series of modeling experiments where some of the DMOS sulfur paths are turned 'off' or 'on', and the results on chlorophyll-a, dimethylsulfoniopropionate (DMSP; the DMS precursor) and DMS concentrations have been compared with the vertical profile.