Time concepts in hydrodynamic systems with an application to 7Be in the Gironde estuary

The main definitions involving time concepts in dynamic systems are reviewed and extended. It is shown that a better understanding of aquatic systems can be achieved taking into consideration their mean age. The relationships between residence time and mean age and the behaviour of chemical components in dynamic systems is studied; the importance of radionuclides whose decay is perfectly known is demonstrated. Finally, an application to the Gironde estuary (France) is attempted using a cosmic ray-produced radionuclide, 7Be, whose half-life is especially relevant to macrotidal estuarine dynamics. (Auth.)