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Answer: Thermohaline circulation is the deep-ocean current system driven by differences in water density, which is controlled by temperature (thermo) and salinity (haline). Winds drive currents only in the upper 100 meters of the ocean; these density-driven currents flow thousands of meters below the surface.

How it starts

Thermohaline circulation begins in the Earth's polar regions. When ocean water there gets very cold, sea ice forms. The salt is left behind, so the surrounding seawater gets saltier, increases in density, and sinks. Surface water is pulled in to replace the sinking water, which in turn eventually becomes cold and salty enough to sink. This initiates the deep-ocean currents driving the global conveyor belt.

The conveyor belt's path

• Cold, salty, dense water sinks at the Earth's northern polar region and heads south along the western Atlantic basin.
• The current is "recharged" as it travels along the coast of Antarctica and picks up more cold, salty, dense water.
• The main current splits into two sections, one traveling northward into the Indian Ocean, while the other heads up into the western Pacific.
• The two branches warm and rise as they travel northward, then loop back around southward and westward.

How slow

It is estimated that it can take 1,000 years for a "parcel" of water to complete the journey along the global conveyor belt.

Claims

• id: C1 claim: Thermohaline circulation begins in the Earth's polar regions. source: S1 evidence: "Thermohaline circulation begins in the Earth's polar regions."
• id: C2 claim: Winds drive currents in the upper 100 meters of the ocean. source: S1 evidence: "Winds drive ocean currents in the upper 100 meters of the ocean's surface."
• id: C3 claim: The conveyor belt's main current splits into two sections. source: S2 evidence: "The main current splits into two sections"

Sources

• [S1] Thermohaline Circulation - Currents: NOAA's National Ocean Service Education. NOAA. https://oceanservice.noaa.gov/education/tutorial_currents/05conveyor1.html . License: US government work, public domain. Accessed 2026-11-04.
• [S2] The Global Conveyor Belt - Currents: NOAA's National Ocean Service Education. NOAA. https://oceanservice.noaa.gov/education/tutorial_currents/05conveyor2.html . License: US government work, public domain. Accessed 2026-11-04.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).

@misc{iil_note_jxj994yj,
  author = {{iinventedlight}},
  title = {{Thermohaline circulation and the global conveyor belt}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-04},
  url = {https://iinventedlight.com/library/notes/thermohaline-circulation/},
  note = {Permanent ID iil:note:jxj994yj. License: CC-BY-4.0.},
}

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