Ocean colour satellite remote sensing of phytoplankton standing stock, surface hydrography processes as well as spatial and temporal variability of primary production in the western Black Sea
The following cumulative study investigates the phytoplankton standing stock, its advection and variability by means of satellite remote sensing of ocean colour in the western Black Sea between 1997 and 2006. One of the main aims of this study is to estimate the quality of the ocean colour data from the different seasons and different regions of the western Black Sea area. Furthermore, the performance of the atmospheric correction algorithms as well as the bio-optical algorithms for the retrieval of chlorophyll-a in the western Black Sea area are assessed. The spatial and temporal variability of the chlorophyll-a concentration in the surface layer of the western Black Sea and an estimation of the controlling mechanisms are described. The potential of the use of optical remote sensing data for studying geophysical interactions in near-coastal areas of the Black Sea is demonstrated in Chapter I. The results in Chapter II show that in spite of some limitations, the existing atmospheric correction and bio-optical algorithms can determine and monitor the phytoplankton standing stock in the surface layer of the western Black Sea quite well. The description of the spatial distribution of chlorophyll-a concentration and its temporal variability in the western Black Sea by ocean colour remote sensing in Chapter III suggests a separation of the sea into four regions with characteristic patterns. The analysis of the spatial pattern of satellite-derived chlorophyll-a shows that a considerable part of the western Black Sea is covered by eutrophied waters throughout the year. The results show that there are differences in the variability of the satellite-derived chlorophyll-a concentration in the different regions, which at relatively constant seasonal forcing possibly reflect the different mechanisms of nutrient supply. Furthermore, the results demonstrate on the one hand the potential of the statistical analysis of time series in the western Black Sea and on the other hand the complexity of the investigated processes. Also the net primary production calculated with the Behrenfeld-Falkowski vertically generalized production model from the satellite remote sensing data appears to resolve the spatial and temporal variability in the western Black Sea well despite neglecting the nutrient limitation by this approach. However, it remains unclear whether the observed general reduction in the satellite-derived chlorophyll-a concentration for the period 1997-2006 is part of a long-term trend rather than a minimum and thus a turning point of oscillation. The results in Chapter IV show that the model simulated chlorophyll-a patterns present good agreement compared to the satellite-derived chlorophyll-a images. The most noticeable differences are observed in the open sea area, consisting of an overestimation during spring and an underestimation during autumn periods. However, good agreement exists between the model and the observations in the coastal areas that are the focus of this study.
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