The mechanisms controlling the distribution of radiocarbon over the deep Pacific are examined using, firstly, a simplified one-and-a-half-layer model and, secondly, an isopycnic circulation model with parameterized radiocarbon sources and sinks. Two mechanisms control the radiocarbon at depth: relatively fast, lateral transport of bottom waters determining the horizontal distribution and a slower balance between advection-diffusion and radio decay in the vertical. In the isopycnic model, there is a strong topographic control of the bottom water spreading, which is more complex than in the idealized model. Sensitivity studies reveal that altering the bottom intensified diapycnic mixing leads to significant changes in the radiocarbon distribution through both the direct diapycnic transfer and, indirectly, by modifying the bottom water transport and northward penetration of young radiocarbon waters.