How do you find the residence time of carbon in the ocean?

Question

How do you find the residence time of carbon in the ocean?

Answer 1

[Reservoir Size] / [Flux] = Residence Time

Flux is volume in - volume out

Answer 2

I suppose you could measure the amount of radioactive C-14 found in it.  There was a sudden spike in atmospheric C-14 in the mid-1950s caused by atomic bomb blasts, so nearly every year subsequently has had a unique amount of C-14 as it gradually is sequestered by the ocean & living things.  Since the C14 halflife is 5700 years, most of 1950's-era C14 has not yet decayed, thus can be measured directly and correlated to the known content of atmospheric C14 since the 1950s.