Here we present the dissolved organic matter (DOM) data of the sea surface microlayer (SML) and underlying water (ULW) during a multidisciplinary mesocosm study at the Sea sURface Facility (SURF) of the Institute for Chemistry and Biology of the Marine Environment (ICBM) in Wilhelmshaven, Germany (53.5148 °N, 8.1463 °E). The study was conducted from 18 May to 16 June 2023. Water samples were collected using a glass plate for the SML and a tube at a depth of 40 cm. DOM was extracted and desalinated by solid-phase extraction as described by Dittmar et al. (2008). The extracts were stored frozen in methanol until analysis. Aliquots were mixed with 50% ultrapure water (50:50 v/v) and diluted to a final carbon concentration of 2.5 ppm. DOM composition was analysed using a SolariX XR FT-ICR-MS (Bruker Daltonik GmbH, Bremen, Germany) with a 15 Tesla superconducting magnet and an electrospray ionisation source (ESI; Bruker Apollo II ion source) in negative ion mode. Data processing and molecular formula assignment were performed in ICBM-OCEAN, as described by Merder et al. (2020).