How do oceanographers use carbon-14 to estimate the age and mixing of deep water masses?

Oceanographers utilize carbon-14 as a radioactive tracer to function as a "time clock" for studying the deep ocean. Because carbon-14 is incorporated into the carbon cycle and enters marine waters as a dissolved component, its concentration helps researchers determine the age of water masses and calculate the absolute rates of oceanic mixing and transport.12

The methodology relies on measuring the abundance of carbon-14 within oceanic dissolved carbon. Historically, this required large water samples, but modern oceanographic laboratories now employ a linear accelerator as a highly sensitive mass spectrometer. This advanced technique allows for high-accuracy measurements using significantly smaller sample volumes.1

When interpreting these measurements, scientists must account for the fact that the distribution of these isotopes is influenced by both physical and biological processes. Furthermore, because the upwelling of deep ocean water can introduce carbon-14-depleted carbon into the surface, these influences must be carefully disentangled to accurately read the "clocks" and understand the movement and origin of deep water masses.12