LAUSR

Abstract The analysis of chlorophyll-a (chl-a) variability on a long-term basis could allow detecting possible issues in the whole marine ecosystem functioning. The Gulf of Taranto (Southern Italy), in the North-western Ionian Sea (Mediterranean Sea), has been affected by several environmental threats in the last decade, thus deserving the implementation of an adequate monitoring system able to provide accurate indications about the variability of the most relevant bio-optical parameters. In this context, the main objectives of this study are to investigate the long-term chl-a variability in the Gulf of Taranto and identify the occurrence of any past spatiotemporal anomalies by implementing the multi-temporal Robust Satellite Technique (RST) on a 12-year (2003–2015) period of MODIS/AQUA Level 3/Level 2 chlorophyll-a data. The achieved results show well-clustered near-surface positive chl-a anomalies during the January–February 2011 period. This detected offshore phytoplankton bloom may be related to sub-basin processes, such as the inflow of the Western Adriatic Coastal Current (WACC), probably fostered by the cyclonic reversal of the Bimodal Oscillating System (BiOS) mechanism. Therefore, the RST approach proved successful in detecting chl-a anomalous variations with a high level of confidence regardless of the absolute value measured, thus suggesting its exportability in other areas with different site-setting conditions.