A comparison of FerryBox data vs. monitoring data from research vessels for near surface waters of the Baltic Sea and the Kattegat

Abstract The variability of near surface properties of the Baltic Sea and the Kattegat was investigated using data from research vessel sampling and data from a FerryBox system during the years 2010–2013. The FerryBox system was mounted on a cargo vessel with a route covering the Gulf of Bothnia, the Baltic proper and the Kattegat twice a week. Water samples from the FerryBox system were analysed from 2011 to 2013 to investigate the quality of the FerryBox-underway data. Salinity from water samples and underway measurements showed a strong correlation. Chlorophyll a samples collected in the Belt Sea and the Kattegat and corresponding in vivo fluorescence underway data showed a correlation (R 2  = 0.75, p  a data from water samples collected using research vessels in general had a weak consistency with the chlorophyll fluorescence data from the FerryBox system. The use of FerryBox systems for observations related to descriptors in the EU Marine Strategy Framework Directive is discussed.