Links Between Dimethylated Sulfur and Phytoplankton Photophysiology in the Surface Ocean Geographical Paterns and Short-Term Variability
[eng] Dimethylsulfide (DMS) and its algal metabolite precursor, dimethylsulfoproprionate (DMSP), are major players in the oceanic and atmospheric sulfur cycle. DMS is the most abundant volatile organic sulfur compound in the upper ocean and its global emission accounts ca. 28 Tg S per year, thus rep...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2015 |
| País: | España |
| Institución: | Universidad de Barcelona |
| Repositorio: | Dipòsit Digital de la UB |
| OAI Identifier: | oai:diposit.ub.edu:2445/68863 |
| Acceso en línea: | https://hdl.handle.net/2445/68863 http://tdx.cat/handle/10803/336378 |
| Access Level: | acceso abierto |
| Palabra clave: | Oceanografia química Fitoplàncton marí Biogeoquímica Fisiologia vegetal Compostos de sofre Chemical oceanography Marine phytoplankton Biogeochemistry Plant physiology Sulfur compounds |
| Sumario: | [eng] Dimethylsulfide (DMS) and its algal metabolite precursor, dimethylsulfoproprionate (DMSP), are major players in the oceanic and atmospheric sulfur cycle. DMS is the most abundant volatile organic sulfur compound in the upper ocean and its global emission accounts ca. 28 Tg S per year, thus representing the main natural source of sulfur to the troposphere and about 30% of the global (including anthropogenic) sulfur emissions. DMS cycle has been the subject of hundreds of studies over the last 27 years because of its hypothesized role in climate regulation (CLAW hypothesis), where it has been postulated to regulate the number of cloud condensation nuclei over the oceans and hence reduce the total amount of solar radiation reaching the Earth's surface. However, this simplistic view has not been proven so far as the relationship between oceanic DMS concentrations and solar radiation is complex and involves several different actors. Both DMS and DMSP (hereafter referred together as DMS(P)) concentrations are variable in the surface ocean and physics, chemistry and biology in the photic upper layer all play important roles in their cycling, from DMSP biosynthesis to DMS ventilation, with their relative importance varying amongst the diversity of biomes and pelagic ecosystem settings encountered in the world's oceans. Hence, predicting DMS at a global scale needs an intricate understanding of processes affecting its cycle at all temporal and spatial scales. The premise of the thesis is to contribute to a better understanding of the different physical, chemical and biological drivers that shape the DMS(P) cycle in polar, tropical and sub- tropical oceanic environments from very short to longer term temporal scales. This work combines an extensive database of DMS measured at low and high frequency, in different regions and across environmental gradients, and at temporal scales that span from minutes to seasons. In the short term (minutes to hours) , exposure to UVR seems to play an important role in the physiological response of phytoplankton cells and DMS(P) production. Solar radiation also dictates the pace of variability in DMS concentration over diel (day-night) cycles, where DMS seems to be surprisingly coupled to photobiological clocks. However, while gross biological DMS production generally increases with light exposure, concentration depends on the net effect of production and losses by photolysis, microbial consumption and ventilation. As a result, no single pattern for diel DMS oscillations is valid for the global oceans. Extensive data gathering across many biogeographical provinces in the tropical and subtropical oceans confirmed that DMS distribution is better explained by abiotic factors (solar radiation, vertical mixing, light absorption by organic matter) and phytoplankton physiology (efficiency of photosystem II) than by indicators of plankton abundance and general activity. Our work also shows that inferences about the causes of the variability of DMS depend on the frequency of the data collection. During a circumnavigation cruise, data collected at low frequency translated into relatively low variation factor (5.1) within individual biogeochemical provinces. In contrast, high frequency data revealed much higher variation factor (96) because of the capture of sub-mesoscale variability. Statistical work on high frequency data showed that critical variability distances for DMS average 15 and 50 km for coastal and open ocean marine provinces, respectively. DMS distribution patchiness increases with productivity and latitude, with important implication for designing fieldwork and computational mapping of DMS concentration and emissions. Overall, this thesis sheds light on the complex interplay of physical, chemical and biological variables in the DMS cycle and emphasizes the difficulty of finding simple environmental drivers of quantitative applicability at global scales. |
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