One key objective in the MODAL long-term monitoring approach is to identify possible links between groundwater flow through coarse-grained marine sediments and their associated leaching of clays which supposedly weakens the latter and may cause sediment creep and, eventually, failure. The instrument to identify and possibly quantify such groundwater seepage is the Radon (Rn) probe KATARINA, a prototype of which was recently purchased by MARUM. The innovative, one-of-its-kind marine Rn instrument developed by HCMR Athens monitors radioactivity in fluids and will be a powerful means in assessing whether elevated Rn content, a proxy that will unravel effects of transients Var river discharge or non-confined aquifer activity, will positively correlate with elevated pore P transients measured by the IFREMER piezometers.
For test purposes, the acquired KATARINA system was mounted into a frame together with a battery housing and data logger during the recent Fluid3D campaign by the MODAL PI group (see photo). An autonomous CTD was monitoring salinity, temperature and depth simultaneously during this deployment
Three locations were monitored for a period of several hours, spanning a reference site on the sedimentary plateau near the 1979 landslide scar, the formerly very active Seamonice site where pore pressure transients were strong in past monitoring campaigns, and the northern headscar where earlier cruises always found freshened pore fluids in sediment cores.
The diagram shows exemplarily the results from three radioisotope systems, Thorium, Uranium and Potassium. Regardless of any details, it is seen that the levels for these elements are highest in the northern scar, a little bit lower for Seamonice, but significantly lower on the plateau where no sediment failure has been taken place and seawater compositions are prevailing. These initial tests are in line with the salinity variations measured by the CTD. Results attest that the KATARINA system is performing reliably. The next steps include the incorporation of the autonomous units into one measuring system that is then hooked to the EMSO Ligurian node as part of the EMSO ERIC transnational access (TNA) project in August 2019.