Oceanographic and biogeochemical data of time series station Spiekeroog for 2018

The Time Series Station Spiekeroog (TSS) was set up in 2002 in the tidal inlet between the East Frisian islands of Langeoog and Spiekeroog in the southern German Bight at position 53°45′01.0″ N, 007°40′16.3″ E. Goal was to measure physical, biological, chemical and meteorological parameters continuously even in harsh weather situations like storms, ice conditions and storm surges. The TSS was established in the framework of the Deutsche Forschungsgemeinschaft (DFG) research group BioGeoChemistry of Tidal Flats. Here, water temperature, salinity, water pressure, air temperature, air pressure, relative humidity, wind direction, wind speed, nitrite, nitrate, silicate and phosphate were measured in 2018. All raw data were corrected for steps as range, outliers and stationarity checks. Water pressure data obtained in 11.5 m water depth were furthermore converted to sea level data. Water temperature and salinity were measured in five different depths (4m, 5.5m, 7.5 m, 9.5 m, 11.5 m below MSL/NN). Due to fouling at the sensors and accompanying drift of measured data water temperature and salinity were corrected via linear regression by reference values which were obtained by CTD measurements regularly. As the water column in this region is well mixed, data of all five depths were averaged. Smoothing of data and a final manual check was performed for water temperature and salinity in order to exclude inexplicable data, mostly nonlinear drifting caused by growth of marine organisms. As salinity is quite sensitive to fouling a quality flag is given for the correction of this parameter. Wind direction data were corrected for small offsets of several degrees due to technical issues. All meteorological sensors were installed in a height of 12 m above the sea surface. Nutrients were measured in a depth of 4 m with continuous flow analyzers after filtration by photometric method. Data are manually checked afterwards and provided with a quality flag. For validation reference samples were collected during every maintenance visit. Three discrete water samples were taken in 30 cm depth and measured in the lab for NOX (nitrate and nitrite), nitrite, phosphate, silicate and ammonium afterwards by photometric methods using Thermo Fisher Multiskan GO microplate reader. These steps of checking the data do not demand the correctness, but are a first approach of correcting the data and excluding obvious unrealistic data. Post-processing of measured data was done using MATLAB and Excel. Quality indices of salinity and nutrients are given according to SeaDataNet: paragraph 6. Quality flags from https://www.seadatanet.org/content/download/596/file/SeaDataNet_QC_procedures_V2_%28May_2010%29.pdf. A detailed description of the Time Series Station Spiekeroog, its structure and sensor systems can be found in Zielinski et al. (2022) and in Reuter et al. (2009). The set up of the nutrient measurement system and background of the measurement method is presented in Grunwald et al. (2007), Schnetger and Lehners (2014), Miranda et al. (2001), Fanning and Pilson (1973), Benesch and Mangelsdorf (1972), Laskov et al. (2007), Itaya and Ui (1966) and Strickland and Parsons (1972).