The Impact Of Desert Dust Across The Mediterranean PDF Download

The potential capacity of fertilization of surface oceans by atmospheric deposition is of scientific interest. This is especially true in the oligotrophic Mediterranean Sea. Its surface waters are extremely poor in nutrients necessary for plankton growth. At the same time, it borders with the largest and most active desert area in the world and the atmosphere over the basin is subject to frequent injections of mineral dust particles. Moreover, future scenarios foresee increases in the region's aridity, thus increasing the dust load, as well as changes in ocean stratification that will increase the potential impact of dust deposition on surface waters. Thus, it is important to study the links between deposition and plankton stimulation. In this context, the present thesis addresses relationships between desert dust deposition and phytoplankton dynamics in the Mediterranean Sea. It places especial emphasis: (1) on the seasonal and geographical patterns of both dust deposition and chlorophyll variability, (2) on the correlation between dust deposition and chlorophyll concentration, (3) on the analysis of the large deposition events and (4) on the effects on chlorophyll concentration due to very large dust deposition events occurred between 2000 and 2007. Broadly, dust deposition seasonal dynamics shows highest values in late autumn and winter in the Central and Eastern Mediterranean. While, the high dust deposition occurs close to Africa with a decreasing gradient from South to North in the basin. By contrast, the distribution of chlorophyll shows decreasing gradients both from West to East and from North to South. In addition, its broadest variability was found in the Western Mediterranean, coinciding with the highest chlorophyll concentrations on average. Positive correlations between dust deposition and chlorophyll concentration were found in large areas of the Mediterranean Sea, with a clear South to North decreasing gradient in correlation coefficient. This is especially true for the Central and the Eastern Mediterranean, where dust deposition dynamics matches with chlorophyll annual dynamics. Areas with positive correlations can be found during all seasons, although it is in spring when we see the largest correlation coefficients mainly in the Central, Eastern and Southwestern Mediterranean. Finally, 153 large dust deposition events were identified between 2000 and 2007. May of them occurred in the years 2000 and 2004, especially in autumn and winter even if they showed a high variability. The Eastern Mediterranean was more affected by the extensive events especially in winter. About the very large dust deposition events, 31 were identified during this period. They were distributed unequally over seasons and over the Mediterranean sub-basins, occurring mainly in autumn and winter in the Central and eastern Mediterranean. Chlorophyll concentration increases significantly after very large dust deposition events showing peaks in concentration between days 1 and 6 after the event, with chlorophyll increments ranging from 13% to 345% for the different outbreaks. The impact of these large events on chlorophyll shows a decreasing trend from west to east and seems to be related to the eastward increasing importance of heterotrophic bacteria with respect to phytoplankton.