Monitoring of multi-year algal bloom dynamics in the North Sea using MERIS and MODIS
Van Der Zande, D.; Ruddick, K. (2012). Monitoring of multi-year algal bloom dynamics in the North Sea using MERIS and MODIS, in: 44th international Liège colloquium on ocean dynamics "Remote sensing of colour, temperature and salinity – new challenges and opportunities" - May 7-11, 2012. pp. 1
In: (2012). 44th international Liège colloquium on ocean dynamics "Remote sensing of colour, temperature and salinity – new challenges and opportunities" - May 7-11, 2012. GHER, Université de Liège: Liège. 126 pp., meer
Algal blooms (AB) are generally defined as a rapid increase in the biomass of algae in an aquatic system. Satellite chlorophyll a concentrations (CHL) data are a suitable proxy for phytoplankton biomass and provide a unique means to monitor AB dynamics over a large area such as the North Sea and over many years. MUMM provides an operational daily AB detection service in European waters using MERIS and MODIS data within the framework of the MarCoast project. The basic product of this service is a daily map of AB detected using an algorithm which compares the instantaneous CHL map with a threshold CHL map. The threshold map used is a 90 percentile map of CHL for the growing season (March-November incl.) of the studied year. Such a threshold map is able to capture the high spatial variability in typical CHL concentrations throughout the European seas and hence relativise the concept of AB.In this study, AB detection maps were created using a historical dataset of MERIS and MODIS CHL data for the years 2003 to 2010. The daily AB detection maps were subsequently used to generate yearly AB timing maps providing pixel by pixel information of the date at which a first AB was detected. With these AB timing maps representing AB dynamics both in space and time, the impact of factors such as euphotic depth (KdPAR, TSM), total water depth, water column stratification, and nutrient availability could be investigated. In European waters at the large scale a general link between the AB timing and latitude can be observed where the AB occur later in the growing season from South to North due to light availability. The situation in the North Sea is more complex since other factors such as bathymetry, turbidity and human induced eutrophication play a more significant role. Results will be presented for the spatial and interannual variability of AB timing in the North Sea as detected by satellite data, and will be explained in terms of the relevant factors.
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