Oceanic tracer and proxy time scales revisited

Quantifying time-responses of the ocean to passive and active tracers is critical for the interpretation of paleodata from sediment cores because surface-injected tracers do not instantaneously spread throughout the ocean. To obtain insights into the time response, a computationally efficient state transition matrix method is demonstrated and used to compute successive states of passive tracer concentrations in the global ocean. Times to equilibrium exceed a thousand years for any one region of the global ocean outside of the injection and convective regions and concentration gradients give time-lags from hundreds to thousands of years between the Atlantic and Pacific abyss, depending on the injection region and the nature of the boundary conditions employed. Equilibrium times can be much longer than radiocarbon ages as the latter are strongly biased towards the youngest fraction of fluid captured in a sample. Pulse-like inputs can produce very different transient approaches to equilibrium in different parts of the ocean generating event identification problems.