Jack describes the ancient climate shift known as the Younger Dryas. He states that, as the world was coming out of the last glacial period, melting ice sheets added so much freshwater to the Atlantic Ocean that certain ocean circulation patterns shut down. Since thermohaline circulation is a major source of heat for the surfaces of continents, the globe was plunged back into an ice age.
This clip illustrates ocean currents and the factors that affect them. It mentions that there are both surface currents and deep sea currents, which make up 90% of the ocean's water. It also explains how the Earth's rotation causes phenomena such as the Coriolis Effect.