Weather and climate related spatial variability of high turbidity areas in the North Sea and the English Channel

• Main Authors: Fettweis, M., Monbaliu, J., Nechad, B., Baeye, M., Van den Eynde, D.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2012
• Subjects: North Atlantic; North Atlantic oscillation
• Online Access: http://www.vliz.be/nl/open-marien-archief?module=ref&refid=217348

The present research focuses on large scale geographical variability of high turbidity zones in the North Sea and the English Channel using meteorological and remote sensing data. The remote sensing data consist of surface suspended particulate matter (SPM) concentration maps retrieved from the marine reflectance in the visible band centred at 667nm of the MODIS sensor onboard the satellite AQUA, using the SPM algorithm calibrated for turbid waters [Nechad et al., 2010]. Meteorological data are from the UK Met Office and consist of 6 hourly wind and pressure fields. In order to investigate the weather related influence on SPM concentration in a larger area weather classification has been used to summarize the atmospheric circulation. We have used 11 weather types (WT), which are described using the locations of high and low-pressure centres, geostrophic winds and vorticity indices [Demuzere et al., 2009]. This classification is based on a simplification of the original 27 WT of Lamb’s classification [Jenkinson and Collison, 1977]. The SPM concentration derived from MODIS satellite is assembled according to these weather types and statistically treated to investigate the influence of large scale meteorological patterns on the spatial variability of SPM concentration in the southern North Sea and the English Channel. Further the influence of climatology, as expressed by the North Atlantic Oscillation (NAO) index, has been investigated.The results show a correlation of geographical distribution of SPM concentration and weather types in the North Sea. Typically an alternation of higher SPM concentration areas between the Southern and the German Bight during different weather types was observed. Climatological influences are clearly identified when comparing the SPM distribution during a winter with a positive and a negative NAO index. During a winter with negative NAO, the SPM concentration is on average higher in the southern Bight, whereas during a winter with positive NAO index an on average higher SPM concentration occurs in the German Bight. The results also show that satellite images should be used with care, as they are biased to certain weather types and not all types are proportionally represented in satellite images. The method proposed is different from previous work on SPM concentration distribution, which was mainly based on oceanographic data (wave, currents, tides, wind, temperature) and seasonal and neap/spring variations [e.g. Dobrynin et al., 2010, Pietrzak et al., 2011). It offers new research perspectives, such as the possibility of investigating how climate change scenarios will affect the SPM concentration distribution. The latter is important in order to predict changes in habitat types.