This dataset comprises the phytoplankton abundance and biovolume estimates as part of a broader sampling program carried out at the Southern Ocean Time Series, a facility within the Integrated Marine Observing System (IMOS). The primary focus is sustained observing of ocean properties and processes important to climate, carbon cycling, and ocean productivity. Regular phytoplankton samples are collected at approximately 14 day intervals (exact intervals and seasonal coverage dependent on deployment length). The moorings are serviced annually, at which time the existing moorings are recovered and new moorings are deployed. Water samples from within the surface mixed-layer are collected at pre-programmed intervals using a Remote Access Sampler, in pairs about 1 hour apart. One sample in each pair is preserved for phytoplankton community composition by microscopy, and the other sample is preserved and used for accompanying chemical analysis of nutrients, total dissolved inorganic carbon (DIC) and alkalinity. Each sample is collected from within the surface mixed-layer at 32 m depth (2010 - 2017) or 5 m depth (2018-current) depending on the design of the mooring surface assembly and instrumentation. Typically a maximum of 24 samples are collected over an annual deployment cycle. The samples collected are analysed for: 1. Community composition / abundance (cells/L) 2. calculated biovolume (um3/L). Protocols for the phytoplankton time-series are described in Eriksen et al (2018), and the annual sample reports for each deployment. Data storage and access is planned to be interoperable with other national and international programs through the IMOS Infrastructure. Station metadata can be found through this resource. Data is available freely via the AODN portal: https://portal.aodn.org.au. As the taxonomic resolution of the data has changed over time, due to continual training, it is important that users refer to the change log tables included in your data download. These will provide information on the validity of the taxa, from what date we have been identifying certain taxa etc. Classification fields may be blank depending on the level to which that taxa has been identified, i.e. if only identified to family, genus and species will be blank.