HPLC accessory pigment dataset for the North Sea in 2010 and 2011 accompanying publication of Ford et al. 2017

The International Bottom Trawl Survey (IBTS) is a multinationalecological research effort established by the InternationalCouncil for the Exploration of the Sea (ICES)in the early 1970s. Surveys using fisheries research vesselscurrently take place in the first and third quarter of30 the year and cover the entire North Sea, using standardizedsampling gears and protocols. With cruise lengths oftypically 6–8 weeks, each vessel undertakes a gridded surveyof the North Sea, repeated each year, in which stationsare sampled for groundfish (the primary target of35 the survey), but also secondary targets such as benthos,seabed litter, and hydrographic parameters. Individual stationsampling is often accompanied by visual seabird andcetacean estimates, underway acoustics, and online monitoringof near-surface water quality using FerryBox-type in40struments (Petersen et al., 2008). The IBTS thus fits theneeds of a multi-disciplinary survey capable of collectingdata on human pressures and ecosystem responses forlegislation such as the MSFD (http://www.jpi-oceans.eu/multi-use-infrastructure-monitoring). The open data policy45 of ICES has resulted in many significant publications infisheries research (Jennings et al., 2002; Daan et al., 2005)and fisheries policy (Rombouts et al., 2013; Shephard et al.,2015).Prior to 2010, phytoplankton had not been systematically50 sampled on the UK IBTS. Advances in the autonomous samplingand detection of particles in the water column (e.g.online flow cytometry, Thyssen et al., 2015), and also theneed for high-quality in situ data for validation of satelliteremote-sensing data, indicated that the addition of phytoplanktonto the survey would be beneficial. Hence, sam- 55pling of PFTs using high-pressure liquid chromatography(HPLC – pigment fingerprinting), and analytical flow cytometry(results reported elsewhere) were initiated on the thirdquarter IBTS cruise of the RV Cefas Endeavour in August–September 2010 and subsequent years. 60Seawater samples from depths of 4m (“surface”) were collectedusing 10 L Niskin bottles when weather conditionspermitted, or from the ship’s bow-intake flow-through cleanseawater supply during adverse weather conditions. A knownamount of water, typically 1000 mL, was passed through a 65200 μm gauze to remove larger zooplankton and debris, thenfiltered within 1 h on 47mm GFF filters, which were foldedin half, wrapped in aluminium foil and snap frozen in liquidnitrogen dry shippers. On return to shore, samples weretransferred to a 􀀀80 C freezer for a storage period of 1– 702 months before shipping of samples on dry ice to an accreditedHPLC laboratory (DHIWater Quality Institute; Horsholm,Denmark) for chlorophyll a (Chl a) quantificationand full accessory pigment analysis (Schlüter et al., 2011).Pigment data from the surface stations were quality data 75controlled in several steps: first, with an initial comparisonof HPLC Chl a against independent measures of chlorophyllfluorescence from the fluorometers on the ship’s FerryBoxand CTD system. This step corrected a small number ofmislabelled samples. In a second step, anomalies within a 80sample were detected using methods described by Aiken etal. (2009), e.g. regression of total accessory pigments againstChl a concentration and search for outliers.Diagnostic pigment analysis was then used on the qualitycontrolleddata set to relate the composition of specific ac- 85cessory pigments to the relative contribution of differentsize classes to the total phytoplankton biomass. The designationof specific accessory pigments to algal taxonomicgroups of different size, e.g. fucoxanthin and peridinin forlarge-cell diatoms and dinoflagellates, has been widely es- 90tablished in the biological oceanographic literature (Uitz etal., 2006, 2008). The equations used to estimate the contributionof pico-phytoplankton (0–2 μm), nano-phytoplankton(2–20 μm) and micro- or net phytoplankton (>20 μm) werelater modified by Hirata et al. (2008, 2011) and Brewin 95et al. (2010). The various methods differ in the degree towhich the marker pigments chlorophyll b (Chl b) and 19-hexfucoxanthin(19-hex) are attributed to the three size classes.Here, Chl b and 19-hex were assigned equally to the picophytoplanktonand nano-phytoplankton size classes. Pico- 100phytoplankton are therefore represented by zeaxanthin, Chlb, and 19-hex; nano-phytoplankton are represented by 19-hex, 19-but, alloxanthin, and Chl b; and micro-phytoplanktonare represented by fucoxanthin and peridinin. Results are expressedas a proportion of the total Chl a concentration for 105each station.