New TIMS constraints on the uranium-238 and uranium-234 in seawaters from the main ocean basins and the Mediterranean Sea 1 1Throughout the paper we use the δ234U notation which represents the deviation of the measured 234U/238U atomic ratio from the 234U/238U atomic ratio at secular equilibrium: δ234U=1000×[(234U/238U)/(234U/238U)eq−1], where (234U/238U)eq is the ratio of the two decay constants: λ238=1.5513×10−10 year−1 (Jaffey et al., 1971) and λ234=2.826×10−6 year−1 recently revised by Cheng et al. (2000). Therefore, an activity ratio of 1 equals (234U/238U)eq=λ238/λ234=54.89×10−6 in atomic ratio. This latter value is ∼3‰ different than the one previously used and thus data from the literature have been recalculated accordingly. All U concentrations are expressed in pmol/g (to be multiplied by 0.2380274 for comparison with some previous works which used ng/g; e.g. Chen et al., 1986).