| Summary: | 2nd Meeting of the Iberian Ecological Society (SIBECOL), 3-8 July 2022, Aveiro, Portugal Microbes are a fundamental part of the Antarctic marine ecosystem, and their study is essential for understanding the functioning of carbon, nutrient and pollutant biogeochemical cycles. However, there is a dearth of high-resolution data sets of their temporal and spatial abundance, size, distribution and phenotypic diversity. Here we present flow-cytometry data on total bacteria and small phytoplankton collected from surface waters during the ANTOM2 cruise, which sailed through the Bransfield Strait and Bellingshausen Sea during austral summer 2022. The cruise consisted in a north-south transect along the Antarctic peninsula coast and a second south-north transect along the edge of the continental shelf. Sea-water was taken by a faucet linked to a continuum pump (5 m depth) with an automatic sampler connected to a flowcytometer that was sampling every 15 minutes during two weeks yielding a total of 2500 sampling points. Quality assurance and control of the data set was performed by contrasting approaches, including the comparison of microbial data with boat movement along its axis (pitch and roll) as well weather conditions, indicating these did not affect the measurements. Total small phytoplankton abundance ranged between 102 and 104 cells·ml-1; with higher values along the coast. Total bacteria abundance ranged between 105 and 106 cells·ml- 1; abundance values tended to increase in the Bellingshausen Sea at latitudes between 68° and 71° S. In the Bransfield Strait, there was a maximum in bacterial abundance at Deception Island, probably due to several factors including stable human and animal presence, volcano emissions, and the limited water exchange with the open ocean. For each data point, we collected the mean of the forward light scatter emission which are surrogates of the relative size of the cells. Larger sized cells were observed in Marguerite Bay and at the edge of the shelf after crossing 65° South. Finally, ...
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