Ocean conveyor belt · AMOC · Deep water formation · Climate sensitivity
A planet-scale heat engine driven by tiny density differences. Warm salty water flows poleward, cools, sinks, and returns as cold deep current — redistributing heat and regulating Earth's climate.
Ocean density depends on both temperature (cold = denser) and salinity (salty = denser): ρ = ρ₀[1 − α(T − T₀) + β(S − S₀)]. In the North Atlantic, the Gulf Stream delivers warm salty water from the tropics. As it cools near Greenland it becomes dense enough to sink — this is North Atlantic Deep Water (NADW) formation. The sinking drives a return flow of cold bottom water through the deep ocean, completing the Atlantic Meridional Overturning Circulation (AMOC) with a strength of ~18 Sverdrups (1 Sv = 10⁶ m³/s).
Drag the Global Temperature slider to warm the planet. As Arctic temperatures rise, Greenland ice melts, adding fresh (low-density) water to the North Atlantic surface — this freshwater "cap" prevents deep water formation and weakens the AMOC. Watch the AMOC strength gauge and circulation arrows slow down. The Freshwater Flux slider lets you simulate a catastrophic glacial melt event. At very high freshwater input the model approaches AMOC collapse — a scenario studied by climate scientists as a potential tipping point.
The Gulf Stream carries ~100 times more water than all the world's rivers combined. Without thermohaline circulation, Northern Europe would be 5–10°C colder — similar to Labrador in Canada at the same latitude. Recent studies (2023) suggest AMOC could collapse between 2025 and 2095 under high emissions scenarios — which would cause rapid cooling in Europe even as the global average warms. The last AMOC collapse, ~12 900 years ago during the Younger Dryas, triggered a 1 000-year cold snap in the Northern Hemisphere.