Exercise 3 solution

The deep North Pacific water should have the older radiocarbon age.

Carbon-14 is taken up from the atmosphere only when water is at the surface. Once the water sinks, the carbon-14 decays with a half-life of about 5,700 years and is not replaced, so the longer the water has been out of contact with the air, the less carbon-14 it contains and the older it appears. Deep Atlantic water has sunk recently (in the north) and has had little time to age; deep Pacific water is at the far end of the deep flow, after travelling through the Atlantic, Southern and Indian Oceans, and has had centuries more to age (of the order of 1,000 years since the surface).

This implies that the deep water flows from the Atlantic and Antarctic regions toward the Pacific, and gets older along the way.