MAPPING SUBMARINE GROUNDWATER INPUTS WITH SHORT-LIVED RADIONUCLIDES ALONG THE FRENCH MEDITERRANEAN COAST
Along the French Mediterranean coast, few SGD spots are known when they are related to karstic areas while SGD from coastal aquifers within quaternary sediments are less easy to map. Two cruises of 8 days were conducted in 2013 and 2014 with the objective of measuring 222Rn and 223,224Ra in surface waters, as close as possible to the 500 km-long coastline, in order to locate SGD inputs. 222Rn activities were measured using a continuous monitoring system (RAD-7) with a 10 mn running time, providing one measurement each 1-1.5 km. About 60 points only were sampled for 223,224Ra, analyzed with Radecc system from 30-60L of surface seawater passed through Mn-fiber.
The 222Rn sampling especially allows to locate precisely unknown karstic springs, while the SGD signal from quaternary aquifers is overwhelmed by the river inputs already enriched in 222Rn. However, the 222Rn signal can be modified by wind events, and coupling these values with 223,224Ra surveys provides a good comparison, even if the sampling resolution is lower in this case. We will present and discuss here these first short-lived Ra-Rn maps along the French Mediterranean coast.