CPR data for OSPAR PH1 FW5 PH2 PH3 FW2 QSR2023

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The Continuous Plankton Recorder (CPR) is a marine sampler that is towed behind volunteer ships of opportunity at speeds of up to ∼20 knots and samples at a depth of ∼7 m below the surface. Plankton have been sampled on routes crossing the North Atlantic and NW European shelf seas using a consistent methodology since 1958. Plankton species abundance counts are included here from 1960-2019. The CPR unit is a metal casing in the shape of a ∼1 m torpedo that houses a roll of silk which automatically rotates using a geared propeller system. The seawater enters the front aperture where plankton and small particles are captured onto the rotating silk, which has a mesh size of 270 µm. This silk is stored in 4 % buffered formalin to preserve the sample until microscopic analysis at the laboratory in Plymouth. The silk is cut into pre-defined sections that represent one sample and equate to 10 nautical miles of tow. Phytoplankton and zooplankton are identified and counted at different stages of the microscopic analysis: semi-quantitative count of phytoplankton across 20 fields of view per sample, quantitative count of all zooplankton >= 2 mm (these are picked off the silk for identification), and semi-quantitative traverse count of all zooplankton 2 mm. For a more in-depth description of the sampling methodology please refer to Richardson et al. (2006). Ostle, C., et al. The Plankton Lifeform Extraction Tool: A digital tool to increase the discoverability and usability of plankton time-series data, Earth Syst. Sci. Data Discuss. https://doi.org/10.5194/essd-2021-171, 2021. The Phytoplankton Colour Index is a record of the colour gradient of the mesh as one of 4 colour categories (0,1,2,6.5) and has been shown to relate to the chlorophyll content of the water, including organisms not visible in the sample (Raitsos et al., 2013, Raitsos, D.E., Walne, A., Lavender, S.J., Licandro, P., Reid, P.C., and Edwards, M. 2013. A 60-year ocean colour data set from the Continuous Plankton Recorder. Journal of Plankton Research, 35(1): 158–164).