A paradox of warming in a deep peri-Alpine lake (Lake Lugano,Switzerland and Italy)

Coccolithophore were collected and analyzed at 10 stations during summer 2010, from coastal and offshore areas off the eastern Libyan coast (southern Mediterranean Sea). The results were compared with oceanographic data. Total coccosphere concentrations, associated with nutrient-depleted stratified waters, show good correlation with the summer data from the central and eastern Mediterranean sites. K-strategist taxa dominate the surface/intermediate water, while Florisphaera profunda is more abundant in the deep photic zone. The canonical correlation analysis reveals that the distribution of coccolithophore taxa is influenced by environmental parameters: K-strategist taxa are related to nutrient-depleted surface/intermediate waters, whereas lower photic zone taxa are influenced by the development of a deep chlorophyll maximum and high salinity values, well below the thermocline. Finally, the occurrence of three clusters above 50 m, between 50 and 100 m, and below 100 m depth can be detected. These results confirm that a vertical species zonation, as a typical feature of low-middle latitude, characterizes the eastern Libyan coast, where the holococcolithophores represent one of the most important features of coccolithophore production during summer. The distribution of F. profunda matches the depth of the DCM layer, once again confirming its use as a proxy of DCM development and paleoproductivity estimates.