ALBERT

Description: Two marine geophysical methods are tested over a shallowly buried and hydrothermally inactive massive sulfide occurrence at the Palinuro Seamount in the Tyrrhenian Sea. A novel EM configuration consisting of a ship-towed loop transmitter and remote dipole receivers was deployed over the seamount, and electric field transients were successfully recorded by the remote receivers. An SP system consisting of two perpendicular pairs of electrodes towed close to the seafloor was also deployed. Anomalously high electric field strengths were recorded over the zone of known massive sulfide mineralization, demonstrating that the SP method is effective at detecting inactive, buried massive sulfide sites.

Description: We present the first results of an electromagnetic survey for gas hydrates offshore Taiwan using a novel marine controlled-source electromagnetic system. Seismic evidence suggests the presence of gas hydrates and free gas in both accretionary (Four-Way-Closure) and erosional (Formose Ridge) settings to the southwest of the island, but complementary geophysical techniques are required to further quantify the distribution and concentration of the deposits. Electromagnetic experiments were conducted along profiles in both regions and show an increase in apparent resistivity at depth, which may be associated with the presence of methane hydrates. However, both profiles are characterized by severe bathymetric relief, in some cases having slope angles greater than 30 degrees, such that the apparent resistivity section may be biased by tilts of the instruments. We therefore derive a first-order bathymetric correction which can be applied to apparent resistivities and tested the correction procedure on data collected at Four-Way-Closure. Results show that increased apparent resistivities persist and reach up to 7Ωm, which suggests the presence of significant concentrations of hydrate or free gas at this location.

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.