ollivier, p. r., university of delaware, newark, USA, ollivier@udel.edu
claude, c. ., Universite Paul Cezanne - CEREGE, Aix-en-Provence, France, cclaude@cerege.fr
radakovitch, o. ., Universite Paul Cezanne - CEREGE, Aix-en-Provence, France, radakovitch@cerege.fr
hamelin, b. ., Universite Paul Cezanne - CEREGE, Aix-en-Provence, France, hamelin@cerege.fr

SUBMARINE GROUNDWATER INPUTS TO GULF OF LION (FRANCE) REVEALED BY 226RA AND 228RA ENRICHMENTS.

Here we propose to use 226Ra and 228Ra as tracers of submarine groundwater (SGW) inputs to the Gulf of Lion. We measured the radium isotopes activities by thermal ionization mass spectrometry (TIMS) in coastal waters and in the aquifer waters of the Rhone deltaic plain after pre-concentration of radium by MnO2. Compared to conventional counting techniques, TIMS requires lower quantities of water (0.25-2 L) for the analyses, and leads to higher analytical precision (equal to 2%). The high precision radium measurements display a small but significant 226Ra and 228Ra enrichment within a strip of circa 30km from the coast, that cannot be accounted for by the river nor by the early diagenesis. Using a mass-balance model, we estimated the advective fluxes of 226Ra and 228Ra through SGW to be 5.2 x 1010 and 21 x 1010 dpm/d respectively. Taking radium activities from the Rhone deltaic plain aquifer waters as typical of the SGW end-member, a minimum volume of 0.24-4.5 x 1010 l/d is required to support the excess radium isotopes on the inner shelf (i.e, 1.6 to 29% of the river flow).

Oral presentation

Presentation is given by student: No
Session #:089
Date: 03-03-2008
Time: 16:45