Chlorophyll distribution and variability in the Sicily Channel (Mediterranean Sea) as seen by remote sensing data

• Physical processes in modulating the phytoplankton variability in Sicily Channel.
• Analysis of satellite chlorophyll, sea surface temperature and kinetic energy.
• We perform EOF analysis of 9 years of data.
• Modified Atlantic Waters seasonal advection modulates chlorophyll variability.
• Well known Coastal upwelling explains only 0.5% of chlorophyll variability.

Remotely sensed ocean chlorophyll concentration is related to the presence of phytoplankton in the upper ocean layers. Its spatial and temporal variability significantly differs from region to region, originating from both purely ecological factors and local environmental conditions (e.g. species involved, grazing, light and nutrient availability, temperature, etc.). As a result, various physical processes are known to significantly affect chlorophyll distribution especially in coastal areas. Among these, wind-driven upwelling, river discharge, cross-shelf exchanges related to local dynamics and horizontal advection due to larger scale dynamics are often invoked as dominant mechanisms. In this work, we investigate which physical process mostly contributes to the phytoplankton variability in the Channel of Sicily (Mediterranean Sea), based on satellite estimates of surface chlorophyll (CHL) concentration, kinetic energy (KE) and sea surface temperature (SST). An empirical orthogonal function (EOF) analysis is applied to the three time series, spanning the 1998–2006 period. The main patterns of variability of each parameter and the physical processes associated with KE and SST modes are identified. The successive cross-correlation analysis shows that most of the CHL variability (explained variance 78%) is induced by the seasonal advection of the Atlantic Waters (r=0.7), while wind-driven upwelling, generally considered the main process modulating phytoplankton growth in the area, only explains 1.4% of the total CHL variance.