Warm water near the equator rises towards the surface, creating a current. what would you expect to happen to this current if the temperature at the equator decreased?

The Earth is a giant heat engine. The warm less dense tropical waters flow away from the equator and help moderate the climate of coastal areas. Eventually the heat is lost and the cooler denser water sinks and flows back toward the equator where the cycle is repeated. 
A change in the pattern would be very serious. Areas used to warmer waters could have colder weather, snow and ice. Trees, plants and animals used to warmer weather may die out. 
A breakdown of this circulating system is one possibility that some scientists think caused the ice age.