Natural sea surface slicks from the Baltic Sea investigated for cell and virus-like particle abundance, surfactants and dissolved organic carbon in May 2021

Flow cytometry samples for the measurement of virus-like particles and prokaryotic abundance were sampled from the sea-surface microlayer inside and outside a natural surface slick and respective underlying water samples at three sites in the Kalmar Sound, near Rockneby, Sweden, using a boat. A glass plate sampler and a Ruttner sampler were used to sample the sea-surface microlayer and underlying water from 70 cm depth, respectively. For site 1, dissolved organic carbon and surfactants were additionally measured in all four sample types. Samples for flow cytometry were fixed with glutardialdehyde (0.5% final concentration). Some metadata for wind speed, temperature and salinity were collected. These data complement metagenomic analysis of viral communities in the sea-surface microlayer of a natural surface slick (Rahlff et al., unpublished).