As a non-expert in oceanography, its my understanding that ocean currents are driven by a number of forces, including:

--wind shear across surface of ocean

--coriolos force due to rotation of the spherical earth

--density differences between different parcels of water, due mainly to (1) differences in temperature (2) differences in salinity. Differences in temperature are driven mainly by areal differences in sunlight energy absorbed in shallow water (near & above thermocline); IR exchange at the ocean surface, and sensible and latent heat transfer at the oceans surface. Differences in salinity result from areal differences in evaporation and rainfall at the surface of the open ocean; as well as fresh water inflow from rivers and streams near continents and islands (secondary players include contributions of water flowing into the ocean, across a large range of salinity, from oceanic springs including thermal springs. Also, deposition & dissolution of soluble minerals such as carbonate minerals affect the salinity and thus also the density of ocean water)

Deep ocean currents are density-driven and differ from surface currents in scale, speed, and energy. Water density is affected by the temperature, salinity (saltiness), and depth of the water. The colder and saltier the ocean water, the denser it is. Winds drive ocean currents in the upper 100 meters of the ocean's surface. However, ocean currents also flow thousands of meters below the surface. These deep-ocean currents are driven by differences in the water's density, which is controlled by temperature (thermo) and salinity (haline). Large-scale surface ocean currents are driven by global wind systems that are fueled by energy from the sun. These currents transfer heat from the tropics to the Polar Regions, influencing local and global climate. In contrast to wind-driven surface currents, deep-ocean currents are caused by differences in water density. The process that creates deep currents is thermohaline circulation “thermo” referring to temperature and “haline” to saltiness. The global ocean conveyor belt is a constantly moving system of deep-ocean circulation driven by temperature and salinity. Deep ocean currents are driven by density and temperature gradients. This thermohaline circulation is also known as the ocean's conveyor belt. These currents, sometimes called submarine rivers, flow deep below the surface of the ocean and are hidden from immediate detection.These deep-ocean currents are driven by differences in the water's density, which is controlled by temperature (thermo) and salinity (haline). This process is known as thermohaline circulation. The sun provides what almost everything on Earth needs to go energy, or heat. Heat causes liquid and frozen water to evaporate into water vapor gas, which rises high in the sky to form clouds and clouds that move over the globe and drop rain and snow. This process is a large part of the water cycle. When water moves through the water cycle it changes between these states of matter over and over again. The water cycle is the process that water moves through between the air and Earth's surface. The water cycle is powered by heat energy from the Sun. When water moves through the water cycle it changes between these states of matter over and over again. The water cycle is the process that water moves through between the air and Earth's surface. The water cycle is powered by heat energy from the Sun. The Sun causes evaporation, which is the process of heat turning water from a liquid to a gas called water vapor. Water vapor eventually condenses and forms clouds that produce rain and return water back to Earth's surface.