Capuozzo, Barbara (2013) Particulate trace metals chemistry: new constraints for the Si budget in the Mediterranean Sea. [Tesi di dottorato]

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Abstract

Silicon plays a key role in the ocean biogeochemical cycles by its direct link with the carbon cycle through the chemical weathering of silicate minerals and transfer of carbon dioxide from the atmosphere to the lithosphere and the massive transfer of carbon from the surface to the deep seawater through sinking of marine siliceous phytoplankton such as diatoms. Despite the great importance of silicon in biogeochemical cycles budgets of this element at the scale of marginal seas, as Mediterranean sea, which are among the main contributors to the global ocean, are scarce. On the other hand Mediterranean sea is well suited to monitor elemental fluxes towards the open ocean because of the narrow connection with it. Recent observations evidence that the silica cycle in the Mediterranean sea is characterized by a net deficit of silicon. Observed fluxes are only partially able to compensate net losses, and suggest a net accumulation in the western basin and a deficit in the eastern basin. This research presents a review of the mass balance of the silicon through the exploration of the potential role played by the atmospheric dust and particulate forms from river inputs, taking into account also of the dynamic biogeochemical of the basin. In addition, analysis of trace elements chemistry in seawater particulate, provides a good tool to investigate on natural and anthropogenic sources influencing different area of the Mediterranean basin. The resulting contribution to dissolved Si contribution from atmospheric and river particulates, shows a relatively low impact, in relation to the strongly variability of the system, meant as a variation of atmospheric flows and river flows. There are considerable difficulties associated with the assessment of the role of the particulate in the budget of the silicon, therefore further investigations are needed to better constraint the silicon budget by more specific data collection of particulate in seawater associated to estimates of atmospheric deposition from satellite observations. However the revisited budget based on an updated mass fluxes, specifically of deep waters, at the Sicily strait , allows us to formulate a new hypothesis concerning biogeochemical behavior of silicon in marine systems.

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