The overlapping years indicate clear differences in the magnitude of chlorophyll concentrations between both sensors with a tendency for MODIS to retrieve higher values in regions of high summer concentrations Baltic Proper, Gulf of Finland , and lower or similar values in regions of lower summer concentrations Bothnian Bay, Bothnian Sea, Sounds. The overall spatial distribution remains however stable over the 9-years time series with maximum summer values in the central eastern and southeastern regions, whereas the lowest summer concentrations are observed in the Bothnian Bay and Bothnian Sea, with values equivalent to those recorded in the Skagerrak and Kattegat areas.
Mean summer chlorophyll values for the whole basin reach 2. Click to enlarge. Time series plots are showing the evolution of the summer chlorophyll over 9 years of satellite data in 13 different provinces of the Baltic Sea. In each of the provinces listed below, a mean chlorophyll concentration is estimated for identified polygons fig. MODIS low sampling contributes to a clear difference in chlorophyll values between both sensors and makes the use of these data very difficult. Up to , SeaWiFS data show a rather stable evolution of the chlorophyll around a mean value of 2.
The evolution of summer chlorophyll is stable well within the basin average in the case of SeaWiFS. Bothnian Sea South: the inter-annual variability is relatively low, with a slight increase in chlorophyll value in A most striking feature, however, is an increasing trend of chlorophyll in the MODIS period, going from less than 2. The inter-annual variability is high, with maxima in , and possibly in Inner Gulf of Finland : mean chlorophyll concentration slightly higher than in the outer Gulf, but the inter-annual variability is slightly reduced during the SeaWiFS period.
In contrast, MODIS data vary considerably over time with peaks of summer chlorophyll in and possibly in As for the outer part of the Gulf, the differences between both sensors are at a maximum, ca. The inter-annual variability remains detectable with maxima shifted in , , when compared with Gulf of Finland. A large maximum is also observed in with a chlorophyll concentration almost double relative to mean background values. Gulf of Riga : Chlorophyll values well above basin average ca.
The inter-annual variability is significant during the first years of SeaWiFS period with maximum summer chlorophyll in The progression of this variable after remains rather stable with a tendency to slowly increase during MODIS period. Such positive trend is however not apparent on SeaWiFS overlapping years. Central Baltic Proper: mean chlorophyll concentrations above basin average. A large inter-annual variability is observed with maxima in , and Southern Baltic Proper: Chlorophyll concentrations above basin average.
The inter-annual variability is significant, although not as apparent as in the Central Baltic Proper, with maximum summer chlorophyll in , and Outer Gulf of Gdansk : chlorophyll concentrations above basin average. The inert-annual variability is high with maxima in , and Bornholm Sea : mean concentration of chlorophyll close to basin average.
The inter-annual variability is not so important with a slight increase in and , as well a maximum in Both sensors seem to concur over the three overlapping years. Arkona Sea : mean concentration of chlorophyll equivalent to basin average. The time evolution of summer chlorophyll in this region remains stable, except for MODIS period during which a minimum concentration is observed in , opposite to a situation of maximum usually observed in other regions. Sounds: mean concentrations of chlorophyll below basin average, oscillating around 2.
The inter-annual variability remains low with reasonable agreement between both sensors during the overlapping years.
To reduce potential bias due to the combination of data sets from multiple instruments, a linear trend was calculated using SeaWiFS time series only Over the 9-years period, no significant trend is observed in summer chlorophyll over the entire basin slope of the linear fit averaging 0. On the regional basis, the rate of changes span from The algorithms for both sensors uses a maximum band ratio formulation O'Reilly et al.
The capacity for SeaWiFS to use an additional band at nm could explain the differences in chlorophyll values observed between both sensors in regions of high concentrations. The algorithms are designed for open oceanic waters so-called case 1 waters. Consequently, it can lead to large uncertainties in the Baltic Sea and in river influenced areas due to the presence of dissolved organic matter and suspended particulate matter other than chlorophyll-containing organisms. Accordingly, the absolute values should be interpreted with caution.
The use of 'standard' open-ocean algorithms follows the conclusions from a comprehensive evaluation of different formulations HELCOM, In this process, it was shown on the basis of a restricted match-up database and uncertainties due to atmospheric correction schemes that none of the tested algorithms including regional algorithms could be considered to provide better quality chlorophyll products for the Baltic. For reference purposes, please cite this Baltic Sea environment fact sheet as follows:. You may be trying to access this site from a secured browser on the server.
Please enable scripts and reload this page. Optical Remote Sensing of Intertidal Flats. Pozdnyakov, A. Korosov, L. Microwave Radiometry and Radiometers for Ocean Applications. Sea Ice Parameters from Microwave Radiometry. Kern, L. Kaleschke, G. Spreen, R. Ezraty, F. Girard-Ardhuin, G. Heygster et al. Scatterometer Applications in the European Seas.
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Shaw, A. Pascual, M. Marcos, M. Pasaric, L. Ferraro, B. Bulgarelli, S. Meyer-Roux, O. Muellenhoff, D. Tarchi, K. Hessner, J. Nieto-Borge, P.
Lavrova, M. Mityagina, T. Bocharova, Martin Gade. Back Matter Pages About this book Introduction The enclosed and marginal seas surrounding the European continent exhibit a wide spectrum of environmental traits, ranging from sub-polar to sub-tropical climates, from shallow continental shelves to deep oceanic basins, from pristine marine reserves to regions impacted by countless economic and recreational activities.