Description: During cruise MSM103 (12.9. 15.11.2021), carried out as part of the SOURCE project, multidisci-plinary investigations were carried out in the Gulf of St. Lawrence Gulf north of Prince EdwardIsland (PEI) to identify and quantify offshore aquifers in the region. For this purpose, seismic, elec-tromagnetic and hydroacoustic measurements were carried out and sediment samples were obtainedwith the gravity corer. The structure of the seabed and the seafloor were explored using acousticmethods. A large number of channel structures could be detected in sections, which are interpretedas parts of glacial or postglacial drainage systems. It is not yet possible to say whether these are con-nected to any existing deeper groundwater systems. In the hydroacoustic data, no escapes of freshwater or gas could be observed in the water column during the cruise. In several places, however, ablanking was evident in the seafloor, which indicates the occurrence of gases and could hint atpotential pathways for gas and / or freshwater in the seafloor. Here, an extended evaluation of thehydroacoustic data after the cruise will provide further insight. In sediment samples taken at a loca-tion north of PEI, a significant drop in salinity and resistivity could be detected in the upper 3m ofthe sediment, which provided a first direct indication of the presence of fresher groundwater. Fromthe electromagnetic measurements carried out in seven working areas, we hope to be able to con-tinue this punctual information over larger areas in order to obtain an extended insight into the pres-ence and distribution of freshwater deposits by the detection of anomalies of the electricalconductivity.