Climate models predict that the Atlantic Ocean’s overturning circulation should slow down over the next few decades.1 If they’re right, northern Europe could experience colder winters, and the global cycling of nutrients that feeds biological systems may be disrupted. The regularly functioning meridional overturning circulation (MOC) moves warm surface water from the tropical Atlantic to higher latitudes where it loses heat to the atmosphere. Once the cold, salty, and consequently dense water reaches the northern Atlantic and Arctic, it sinks, or overturns, to a depth of 1–5 kilometers and becomes what’s known as deep water. It then travels southward back to the tropics as part of a global ocean circulation (see the article by J. Robert Toggweiler, Physics Today, November 1994, page 45).
Simulations are the only way to evaluate the future state of the MOC, and direct measurements are needed to test and evaluate models. For...
