Samples were obtained during the Schmidt Ocean Institute cruise "Exploring Fronts With Mutiple Robots" to the Pacific Ocean in 2018 (https://schmidtocean.org/cruise/exploring_fronts_with_multiple_aerial-surface-underwater-vehicles/). Water samples for microplankton analysis were collected using a multi water sampler (rosette) from the research vessel "Falkor" and concentrated on board in a 0.2 µm Sterivex filter. This expedition target the Subtropical Front, located approximately 1,000 nautical miles off the coast of Southern California. The study includes samples from: (i) amplicon sequencing after 18S amplification by PCR using TAReuk454FWD1/ TAReukREV3_modified primer set and (ii) amplicon sequencing after 16S amplification by PCR using 515F/926R primer set. Libraries were constructed according to Illumina Library protocol.