Netherlands Journal of Sea Research 12 (3/4): 338-344 (1978) URANIUM BEHAVIOUR IN THE ZAIRE ESTUARY by J.-M. MARTIN, M. MEYBECK and M. PUSSET ( Laboratoire de G~ologie, F, cole Normale Sup¢rieure, Paris, France) CONTENTS I. Introduction .......................... 338 II. Sampling and analytical procedures ................. 338 III. Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 339 1. Uranium-238 . . . . . . . . . . . . . . . . . . . . . . . 339 2. 234U-z3sU activity ratio ................... 341 IV. Conclusion .......................... 342 V. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . 342 VI. References ........................... 343 I. INTRODUCTION Uranium geochemistry in the oceanic system is still poorly known. Past studies to establish uranium mass balances have used highly variable uranium river input concentrations ranging ti~om 0.04 to 1 ~g-1 -t (KoczY, 1954; MOORE, 1967; VEEH, 1967; TUREKIAN & CHAN, 1971) resulting in a residence time variation of more than one order of magnitude. Moreover it is usually considered that the uranium removal rate by authigenic material is much lower than the input by rivers (KoczY, TOMIC & HECHT, 1957; VEEm 1967). Finally the magnitude of isotopic desequilibrium in the world ocean is striking- ly constant, the 234U-23sU activity ratio equaling 1.14 i 0.03 (KoIDE & GOLDBERG, 1965; Ku, 1966; BHAT, 1970). Any attempt to solve these problems requires a better knowledge of average input by rivers and of nature and intensity ofcstuarine geochemical processes. Acknowledgements. -We are grateful to Dr rl'. L. Ku and L. Labeyrie for reading the manuscript and for their constructiw' remarks. Financial support by C.N.R.S. through A.T.P. contract no 2003 is gratefully acknowledged. II. SAMPLING AND ANALYTICAL PROCEDURES Large volume water samples (30 to 50 litres) were taken in river, estua- ry and plume of the Zaire. For the location of the stations and the general hydrography see EISMA & VAN BENNEKOM (1978). The samples