Realtime Jetty Observations

Realtime Jetty Observations

Temperature & Salinity

Responsible person: Hendrik M. van Aken Introduction: The Marsdiep is the tidal inlet which connects the western Wadden Sea with the North Sea. It separates the Island of Texel from the mainland. On average it is an outflow channel for the Wadden Sea. On the southern shore of the Marsdiep the town of Den Helder is situated, with the main Dutch naval base and an important offshore port. The Royal Netherlands Institute for Sea Research (NIOZ) is presently situated at 't Horntje on Texel on the northern shore of the Marsdiep, opposite Den Helder.
Daily observations: From July 1860 until 1962 daily water samples were taken at the Den Helder side of the Marsdiep, and temperature and salinity of the samples were determined. Before 1904 the samples were taken at high-and low water during the day, from 1904 onwards at 08:00 hours local time. In 1947 the State Institute for Fisheries Research (RIVO) started daily observations of salinity and temperature in ''t Horntje, on the opposite side of the Marsdiep, which from 1982 onwards were taken over by NIOZ. So there is an overlap of 16 years of both time series. From the daily observations of both time series monthly mean values for salinity and temperature were determined. From the 16 years overlap of both series the monthly mean systematic differences between 't Horntje and Den Helder was determined. This systematic difference was used to extend the Den Helder series to present, based on the observations from 't Horntje. Because of interference of observations of a fixed time of the day and the main semi-diural M2 tide beats with a period of about 14 days will develop in the daily time series. Therefore the daily data were reduced to monthly mean values from which annual mean values of temperature and salinity have been derived.


Literature: The data and data processing until 1981 have been described by P.C.T. van der Hoeven from the Royal Dutch Meteorological Institute (KNMI) in de Bilt in the following technical report (in Dutch with English summary): P.C.T. van der Hoeven Watertemperatuur en zoutgehaltewaarnemingen van het Rijksinstituut voor Visserij Onderzoek (RIVO): 1860-1981, Koninklijk Nederlands Meteorologisch Instituut, Wetenschappelijk Rapport W.R. 82-8, De Bilt, 1982. More recent descriptions of the data can be found in: van Aken, H.M. (2003) 140 years of daily observations in a tidal inlet (Marsdiep). ICES Marine Science Symposia, 219: Hydrobiological Variability in the ICES Area, 1990 - 1999, pp. 359-361 (download as PDF-file for personal use). van Aken, H.M. (2008) Variability of the salinity in the western Wadden Sea on tidal to centennial time scales. Journal of Sea Research, 59, 121-132, doi:10.1016/j.seares.2007.11.001 (download as PDF-file for personal use). van Aken, H.M. (2008) Variability of the water temperature in the western Wadden Sea on tidal to centennial time scales. Journal of Sea Research, 60, 227-234, doi: 10.1016/j.seares.2008.09.001 (download as PDF-file for personal use). van Aken, H.M. Meteorological forcing of long-term temperature variations of the Dutch coastal waters. Journal of Sea Research, doi:10.1016/ j.seares.2009.11.005.� (download as PDF-file for personal use). Data availability: The monthly mean temperature and salinity data are available for scientific research on the condition that in any scientific publication the source of the data is mentioned. Please refer to one of the JSR publications mentioned above. Tables of the monthly mean temperature and salinity data can be found in the MS Excel file ts_marsdiep.xls. For further questions with regard to the Marsdiep Time Series you can contact Hendrik van Aken. Continuous recording: In March 2000 electronic sensors were mounted on the jetty near 't Horntje from where the daily observations were carried out. At regular times water samples were taken for the calibration of the conductivity sensor. The continuously recorded data were reduced to one data cycle every 30 minutes. With these data the daily time series was extended by sub-sampling all 08:00 UTC data records.