| Summary: | ASLO Aquatic Sciences Meeting, Resilience and Recovery in Aquatic Systems, 4-9 June 2023, Palma de Mallorca, Spain Small phytoplankton is a fundamental part of the Antarctic marine ecosystem, in particular for its role in carbon fixation and the trophic web. Despite its importance in the carbon cycle, there is a lack of high-resolution datasets of its temporal and spatial abundance, size and phenotypic diversity. Here we present high-frequency flow-cytometry data of total small phytoplankton collected from surface waters during the ANTOM2 cruise, which sailed through the Bransfield Strait and Bellingshausen Sea during austral summer 2021-2022. The cruise consisted on a north-south transect along the Antarctic peninsula coast and a second south-north transect along the edge of the continental shelf. Seawater was taken by a faucet linked to a continuum seawater pump (5 m depth) with an automatic sampler connected to a flow-cytometer that sampled every 15 minutes during two weeks yielding a total of 1250 samples. Total phytoplankton abundance ranged between 102 and 104 cells·ml-1; with higher values along the coast. The optical properties of each single cell (light scatter and pigment fluorescence), which are considered phenotypic attributes, were used to estimate phenotypic diversity using computational cytometry bioinformatic tools. Phenotypic alpha diversity varied throughout the entire cruise and peaked at port Foster (Deception Island), the site with the lowest abundances of small phytoplankton. Similarity among stations (beta-diversity) was well explained by salinity. As far as we know, this is the first study using this spatial and temporal resolution in the maritime Antarctica
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