Deep ocean currents are mainly driven by differences in water density caused by temperature and salinity, a process known as thermohaline circulation. Earth’s rotation and the global pattern of surface winds help shape and steer these deep flows into a slow-moving “global conveyor belt” that redistributes heat, oxygen, and nutrients around the planet.

Core driver: density differences

  • Cold water is denser than warm water, so very cold water near the poles sinks toward the deep ocean. This sinking helps initiate deep currents.
  • When sea ice forms, the salt is left behind in the surrounding water, increasing salinity and therefore density; this extra-dense water also sinks and feeds deep currents.
  • Together, low temperature and high salinity create heavy water masses that slide down into the depths and spread out, forming the backbone of deep ocean circulation.

Thermohaline circulation “conveyor belt”

  • The global thermohaline circulation is often described as a giant oceanic conveyor belt that takes about a thousand years to complete a full loop.
  • Dense water that sinks in the North Atlantic and around Antarctica slowly flows along the seafloor toward other basins, eventually upwelling elsewhere and returning toward the surface.
  • This conveyor moves heat from low to high latitudes and transports dissolved gases and nutrients, strongly influencing climate and marine life patterns.

Supporting roles: winds and Earth’s rotation

  • Energy from the Sun drives atmospheric circulation and surface winds, which in turn help set up the large-scale surface currents connected to deep circulation.
  • The Coriolis effect, caused by Earth’s rotation, deflects moving water to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, guiding both surface and deep currents along basin boundaries.
  • The arrangement of continents and underwater topography further channels these flows, steering deep currents along particular paths on the seafloor.

TL;DR: Deep ocean currents are driven mostly by cold, salty, dense water sinking in polar regions (thermohaline circulation), then slowly flowing through the deep ocean as part of a global conveyor belt shaped by winds, Earth’s rotation, and seafloor features.

Information gathered from public forums or data available on the internet and portrayed here.