Northwest European shelf seas - Phytoplankton pigments - 2010 to 2019

annually

2 litre water samples were collected on board the RV Cefas Endeavour from the continuous flow ferrybox water supply (4m depth), or from Niskin bottles on a rosette fired at particular depths. Water samples were filtered through a Whatman GFF filter, and immediately frozen in liquid nitrogen (2010-2012) or in a -80°C freezer on board (other years). Pigments were stored at -80°C for 1-4 months, before being selected for analysis, then transferred to the analysis laboratory (DHI; Horsholm, Denmark) using dry ice. Pigments were extracted adding 6 ml of 95% acetone (and an internal standard, vitamin E) to each filter. The samples were sonicated in an ice-cold sonication bath for 10 min and extracted at 4 °C for 20 hours. The samples were then filtered through 0.2 µm Teflon syringe filter into HPLC vials. Buffer and samples were injected on HPLC (Shimadzu LC-10A HPLC system with LC Solution software) in the ratio 5:2 using a pre-treatment program and mixing in the loop before injection (Schlüter et al 2016). The HPLC method used was the Van Heukelem & Thomas (2005) method where the gradient was adjusted to optimise the resolution of the pigments. The raw data were stored in an MS Access database. Quality control was performed after Aiken et al 2009. Samples were removed if they had insufficient chlorophyll (<0.04ug/L), a ratio of above 0.5 of degradation pigments (chlorophyllide + pheophorbide + pheophytin) to chlorophyll a, or if there was a difference between total chlorophyll a (TChla) and accessory pigments (AP) of more than 40% of the total pigments. Additionally, where at least 5 samples were collected for a survey, total chlorophyll a was regressed against total accessory pigments, and the data from the survey was rejected if the regression was poor (r2<0.75, slope <0.65 or <1.4).