Fettweis, Michael; Desmit, Xavier; Parmentier, Koen: Biogeochemical monitoring of suspended particulate matter in the Belgian part of the North Sea [dataset bundled publication]. PANGAEA, https://doi.pangaea.de/10.1594/PANGAEA.938674 (dataset in review)

The water sample data were taken in the Belgian part of the North Sea between October 2004 and August 2020. The data set consists of hourly (or 1.5 hourly) water samples and particle size distributions collected during 125 tidal cycles (sometimes half tidal cycles) in 12 stations. The three main stations (MOW1, W05 and W08, Figure 1) are located along a cross-shore section that ranges from the nearshore coastal turbidity maximum (MOW1) to the offshore under complete Channel water influence (W08). W05 is located in between at the outer margin of the coastal turbidity maximum. From 2004 until 2011 the measured parameters were SPM, POC, PON concentrations and salinity. Concentration measurements of chlorophyll-a (Chl-a), phaeophytine-a (Pheo-a), chlorophyll-b (Chl-b), phaeophytine-b (Pheo-b) were added from 2012 onward. All the samples collected until March 2018 were taken at about 3 m above the bed. From March 2018 onward near surface samples were also collected and the turbidity of the samples was measured with a Hach TL2360 LED Turbidimeter. From December 2018 onward, observations also covered TEP, Dissolved Organic Carbon (DOC) and inorganic nutrient concentrations(total phosphate, total nitrogen, nitrogen oxides, nitrite, ammonia, phosphate and silica), the number of stations was reduced to 3 (MOW1, W05, W08) while the frequency increased to monthly samplings. The measured dissolved components were only sampled at the surface, as the water column is well mixed throughout the entire year. At every sampling occasion, three subsamples for SPM concentration were taken and filtered on board using pre-combusted (405°C, 24 hours) , rinsed, dried for 24h at 105°C and pre-weighted 47mm GF/C filters. After sampling the filters were rinsed with ultrapure water (resistivity 18.2 MΩ.cm normalized at 25°C) and immediately stored at -20°C, before being dried during 24 hours at 50°C and weighted to obtain the concentration. The uncertainty of the SPM concentration data has been estimated from the variability of the triplicates and from systematic errors. The RMSE of the triplicates divided by the mean value decreases with increasing concentration from 8.5% (SPM concentration <5 mg/l) to 6.7% (<10 mg/), 3.5% (10–50 mg/l) and 2.1% (>100 mg/l) and represent the random error related to the lack of precision during filtrations. Systematic errors have been estimated based on Röttgers et al. (2014) as 1 mg/l. The samples for POC and PON were filtered on board using 25mm GF/C filters (pretreated as above for SPM), stored immediately at -20°C, before being analyzed using a Thermo Finnigan Flash EA1112 elemental analyzer (for details see Ehrhardt & Koeve, 1999). The analytical uncertainty for POC and PON are 12% and 18%. The method for TEP analysis follows the one described in Nosaka et al. (2017). Three subsamples for TEP concentration were filtered using 25 mm 0.4 µm polycarbonate filters with low under-pressure (<200 hPa). The filters were colored immediately after filtration with Alcian blue and stored at -20°C. The units for TEP are expressed as mg xanthan gum equivalents per liter (mg XG eq./l) and the uncertainty is assumed to be equal to the one of POC. The sample for pigment concentration was filtered on 47mm GF/C filters, stored in liquid nitrogen and determined in the lab using ultra high-performance liquid chromatography with fluorometric detection. The filtrates were collected in sample tubes for DOC and inorganic nutrients and analyzed using standard spectrophotometric methods with a Skalar autoanalyzer, for details see Van Der Zee & Chou (2005). A LISST 100X (type C) was used to measure the size and volume concentrations of the suspended particles. The sensor emits a laser beam and detects the intensities of the light scattered by particles on 32 concentric ring detectors. These intensities were inverted to estimate particle size distributions assuming spherical shapes (Agrawal & Pottsmith, 2000). Agrawal, Y., & Pottsmith, H. (2000). Instruments for particle size and settling velocity observations in sediment transport. Marine Geology, 168, 89–114. doi:10.1016/S0025-3227(00)00044-X Ehrhardt, M., & Koeve, W. (1999). Determination of particulate organic carbon and nitrogen. In: Methods of Seawater Analysis, Third Edition (Eds. Grasshoff, K., Kremling, K., Ehrhardt, M.), Wiley, pp. 437-444. https://doi.org/10.1002/9783527613984.ch17 Nosaka, Y., Yamashita, Y., & Suzuki, K. (2017). Dynamics and origin of Transparent Exopolymer Particles in the Oyashio region of the Western Subarctic Pacific during the spring diatom bloom. Frontiers in Marine Science, 4, 79. doi:10.3389/fmars.2017.00079 Röttgers, R., Heymann, K., & Krasemann, H. (2014). Suspended matter concentrations in coastal waters: methodological improvements to quantify individual measurement uncertainty. Estuarine, Coastal and Shelf Science, 151, 148–155. doi:10.1016/j.ecss.2014.10.010 Van Der Zee, C., & Chou, L. (2005). Seasonal cycling of phosphorus in the Southern Bight of the North Sea. Biogeosciences, 2, 27–42. doi:10.5194/bg-2-27-2005