Phytoplankton taxonomic abundance and biomass time-series at Plymouth Station L4 in the Western English Channel, 1992-2020.

The Station L4 phytoplankton time-series (Widdicombe <em>et al</em> 2010) contains taxa-specific and total functional group abundance (cells mL^-1) and biomass (mgC m^-3) data collected from the Western Channel Observatory's Station L4 monitoring site (50°15.0'N; 4°13.0'W), situated off the south-west coast of England, United Kingdom. Samples have been collected weekly (weather permitting) from the 10m depth since October 1992. Note the time of collection is estimated (local time) where CTD data are not available, and a gap in sampling occurred between October 1994-June 1995. Paired 200 mL water samples are collected using a 10 L Niskin bottle attached to a CTD and are fixed in acid Lugol's iodine (Throndsen, 1978) for enumerating all phytoplankton cells &gt;2 µm and neutral formaldehyde for enumerating coccolithophores. Samples are analysed at Plymouth Marine Laboratory according to the Utermöhl counting technique (Utermöhl, 1958) and since 2016, these methods follow the British and European standard document "Water quality - Guidance standard for routine microscopic surveys of phytoplankton using inverted microscopy (Utermöhl technique)" (BS EN 15204:2006). Individual taxa are grouped into Diatoms, Dinoflagellates, Coccolithophores, Flagellates, Phaeocytis and Ciliates and these pooled data precede the individual taxa-specific data. Abundance of each taxa (cells mL^-1) are calculated according to the number of individuals per unit volume of sub-sample analysed. Mean cell dimensions (µm) of each taxa have been estimated using digital measurements, calibrated against an ocular micrometer and converted to biovolume assuming appropriate geometric shapes (e.g. Olenina <em>et al</em> 2006). Cell biovolumes are converted to carbon (pgC cell^-1) using the formulae of Menden-Deuer and Lessard (2000). Two analysts have generated the data since 1992 and in 2005 more ciliates were identified to species level hence the increase in the number of taxa. Please read the taxa-specific metadata file for information on individual biovolume and carbon values, identification consistency and data quality issues.<br>It is encouraged that users of these data should please quote the DOI and maintain contact with the data originators to prevent misuse or misunderstanding of this complex data set. Informing originators of use of the data will also help justify value for money to funders. If the data form a major part of a study, the originators would also appreciate more involvement to ensure that the source data and their caveats are interpreted correctly.