Exercise 2 solution (model answer; other choices are fine)

Tool chosen: Argo floats. They are best suited to questions about the layered structure of the ocean, such as the depth and strength of the thermocline (Chapter 3) and how much heat the upper 2,000 m is storing (Chapter 8), because they measure temperature and salinity against depth, all over the world, for years.

Less suited: satellites see only the surface, so they cannot show the thermocline; a research ship gives a detailed section but only along its track and only once; a glider covers a regional section well but not the globe; and an ROV is for close-up work on the bottom, not for large-scale structure. For the age of a deep water mass, none of these alone is enough: it needs water samples from a ship for radiocarbon analysis (Chapter 7).