Wind drags the ocean surface into basin-scale gyres, while cold, salty polar water becomes dense enough to sink, driving the deep thermohaline "conveyor belt" that slowly returns water to the surface at lower latitudes — a cycle that redistributes heat around the planet.
ρ = ρ₀ [1 − α(T − T₀) + β(S − S₀)] (seawater density, simplified)
v_surface ∝ wind_stress
v_deep ∝ Δρ (polar sinking) — density-driven, much slower than wind-driven flow
- Surface wind — drives the fast surface gyre current visible near the top of the basin.
- Pole-equator ΔT — bigger temperature contrast increases polar water density and conveyor strength.
- Polar salinity boost — extra salt (from sea-ice formation) makes polar water denser, accelerating sinking.
- Particle count — number of tracer particles shown following the currents; more particles reveal the flow pattern more clearly.
Real-world: this global conveyor (thermohaline circulation) moves heat from the tropics toward Europe via the Gulf Stream/North Atlantic Drift — its slowdown from melting polar ice is a major climate-tipping-point concern.