Reference measurements of surface waters were collected during the RV MARIA S Merian cruise MSM97/2 (12.12.2020 - 23.12.2020, Emden, Germany - Emden Germany). Accompanying the underway measurements of the DAM transit cruise water samples were taken from the CTD and the onboard measurement containers (RSWS) for later validation of bio-optical water properties. Turbidity and fluorescent dissolved organic matter (fDOM) were measured directly onboard via handheld instruments (see methods/device) whereas suspended particular matter (SPM) and chlorophyll a (Chl a) were filtered onboard on glas fibre filters (GFF, 47mm, 0,7 µm) and frozen at -25°C and -80°C immediately after sampling. Values were determined in the lab after the cruise within 2 months, for SPM via gravimetric analysis and for Chl a according to EPA Method 445. Water samples for nitrate analysis were taken and frozen at -25°immediately after sampling for later lab analysis according to Grasshoff et al. (1999).