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Radium isotopes as indicators of submarine groundwater discharge to coastal waters

le 06-10-2009 à 10:45

Salle Stendhal, DGO, Bâtiment B18

J. Kirk Cochran, Marine Science Research Center, School of Marine and Atmospheric Sciences, Stony Brook University, NY

In recent decades, submarine groundwater discharge (SGD) has gained increasing attention as a major component in the global budgets of many chemical constituents, and as a source of essential nutrients and trace metals to coastal ecosystems. Ultimately, these inputs may affect biogeochemical cycles in sensitive coastal environments and influence ecological effects, such as eutrophication.
The SGD fluxes usually present high spatial and temporal variability, a characteristic which has historically hindered their assessment. Radium isotopes have been proven to be very useful to estimate submarine groundwater discharge fluxes. The method is based on the four naturallyoccurring Ra isotopes (223Ra, 224Ra, 226Ra and 228Ra), the so-called “radium quartet”, which are enriched in SGD and behave conservatively once introduced to coastal regions. These isotopes have been used singly or in concert to elucidate different characteristics of the SGD phenomenon. Their range of half-lives (226Ra: 1600 yr; 228Ra: 5.75 yr; 223Ra: 11.4 d and 224Ra: 3.66 d) allows the examination of processes that occur during mixing and transport. This method will be introduced and illustrated through examples of recent investigations in two coastal systems in New York (USA) that have been heavily impacted by human activities.
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