Site1: NorthSea English Channel etc.
North Sea, English Channel, Bay of Biscay, Celtic Sea, Irish Sea, Southern Brittany
The North Sea is a large sea with a diverse set of optical properties and influences. In the south it is permanently mixed with high SPM concentrations; in deeper northern waters it is seasonally stratified with noticeable highly scattering coccolithophore blooms between May and early August. Along the Dutch and Belgian coasts there are high chlorophyll blooms which may cause coastal scum and in the east there have been massive blooms of harmful algae such as Chattonella spp. that can threaten fish farms in Norway. Along the coast of Norway the surface outflow from the Baltic containing higher CDOM concentrations can give erroneous chl-a estimates in relatively deep waters. Hence, waters range from case 1 to case 2 with the latter dominated by SPM and/or CDOM.
The Eastern English Channel joins the southern North Sea and the western end joins the Celtic Sea. In the east the water is well mixed with re-suspended particulate material; the west is seasonally stratified along the English coast with chl-a ranging from 0.25 up to ~4 mgm-3. During the Summer extensive blooms of the red tide dinoflagellate Karenia mikimotoi can form (Miller et al, 2006) and coccolithophore blooms also occur. Along the French Brittany coast the waters are well mixed.
PML operates a long-term optical sampling site where weekly measurements are taken on IOP, AOP, phytoplankton pigments by HPLC, phytoplankton composition by microscope, together with a variety of physical and chemical measurements including vertical CTD profiles (Groom et al., 2009). Since 2009 a permanent mooring has been in place providing hourly physical and biological measurements. The PML station is ideally suited to investigating CoastColour algorithms since it is in case 2 waters near to the coast with measurements taken throughout the lifetime of MERIS.
The Celtic Sea is a broad continental shelf with depths between 100 and 200m. It is stratified during Spring-Autumn with stratification starting off the south coast of Ireland and developing towards the south. In winter it is mixed with re-suspended particulates causing enhanced scattering. During the Spring-Summer the edge of the continental shelf exhibits a higher standing stock of phytoplankton caused by internal wave generated at the steep continental shelf mixing the water column. This higher chl-a (1-2 mg m-3) concentration is seen as a distinct band separating the lower chl-a regions (~0.25 mg m-3) in oceanic and shelf waters. During May high scattering coccolithophore blooms occur just inshore of the shelf edge and have been widely studied through UK and Belgian experiments but in situ optical data are relatively limited. The Irish Sea is restricted exchange environment between the UK and Ireland. It is well mixed throughout the year with water dominated by suspended particulate matter. The exception is a region to the NW of the Isle of Man which is seasonally stratified.
The Irish Sea is very well studied with extensive in situ measurements, especially around Anglesey, with regular ferrybox transects across the sea and much work has been done on satellite remote sensing (e.g. Bowers et al., 2007). There are highly turbid regions and in Liverpool bay an area of higher CDOM.
The Bay of Biscay comprises an open ocean case 1 environment together with continental shelf waters off the coast of France and Spain. The shelf off Spain is relatively narrow but broader towards the North off France. Coccolithophore blooms occur in April – early May inshore of the shelf break and can sometimes occur in the oceanic waters.