The radium (Ra) quartet ( 228 Ra, 226 Ra, 224 Ra, and 223 Ra) has been investigated in Loch Etive, a Scottish fjord, to provide new constraints on water mixing rates and on the inputs of Ra from sediments. Maximum water transport rates for the inflowing estuarine layer at 5 m depth, determined from the excess 223 Ra ( 223 Ra ex ), indicate that this water travels at no more than 2.4 6 0.2 cm s 21 net and that it takes 17 6 2 d for waters to travel from the mouth to the head of the loch if no horizontal mixing is taken into account. Alternatively, neglecting advection, the short-lived Ra distribution could be explained by horizontal mixing rates of 6.1 3 10 6 cm 2 s 21 ( 223 Ra ex ) or 9.1 3 10 6 cm 2 s 21 ( 224 Ra ex ). Periodic overturning circulation plays an important role in resetting chemical cycles in the isolated deep basin of the inner loch. Sediment in this deep basin provides the major input of 228 Ra to the isolated deep water, and the accumulation of 228 Ra in deep waters allows an assessment of sedimentary fluxes of 228 Ra, a poorly constrained aspect of the 228 Ra input to the global ocean. The calculated sedimentary 228 Ra flux of 2.1 6 0.2 (3 10 9 ) atoms m 22 yr 21 in the inner deep basin is comparable with previous measurements of sedimentary 228 Ra inputs from shelf sediments, supporting existing global 228 Ra budgets, which are used to assess global rates of groundwater discharge to the ocean.