The correct options are
A The movements of ocean currents regulate Earth's climate by transporting heat and carbon.
D Density differences in ocean water contribute to a global-scale circulation system called the global conveyor belt.
Ocean currents, including the ocean conveyor belt, play a key role in regulating and stabilizing climate patterns. They determine the distribution of heat energy throughout the planet. It also affects the regulation of local weather conditions and temperature extremes, cycling of gases, and delivery of nutrients and larva to marine ecosystems. Ocean currents are located at the ocean surface and in deep water as well. Density differences in ocean water contributes to the global-conveyer belt. The global conveyor belt includes both surface and deep ocean currents that circulate the globe.