A satellite ocean colour spectral library for the analysis and classification of extreme optical conditions in European seas

In a context of climate change, extreme conditions may be becoming more frequent. For instance, ecologically disruptive or harmful algal blooms in the marine environment show signs of increased frequencies. Some of these blooms are also optical extremes with intense manifestations in the satellite ocean colour record but often without correct derived metrics related to their occurrence, in some cases they are even omitted completely due to failures in atmospheric correction or cloud masking. Considering the ecological importance of these conditions on marine ecosystems and even human activities, they should be described quantitatively by remote sensing to be properly integrated into the statistical treatment of extreme events. Therefore, a spectral library was created containing the two main types of extreme blooms in European waters, namely intense cyanobacteria blooms in the Baltic Sea and coccolithophore blooms in the North-East Atlantic and Black Sea, including data previously excluded by operational satellite ocean colour processing. This library is a unique resource that can facilitate the use of novel spectral analysis and classification techniques for extreme marine optical events. Demonstration applications of such techniques gave results indicating single spectral classes may be sufficient to describe each case and that this kind of spectral library, analysis and classification could serve as important tools in the monitoring of these extreme events in terms of their occurrence, size, extent and evolution.