Thermohaline Circulation — AMOC
Density-driven deep water formation with salinity-temperature feedbacks and potential collapse
AMOC state: ON — Active (20 Sv)
Stommel (1961) box model: two boxes (tropical T vs North Atlantic N) exchange heat and salt.
Density ρ ∝ -αT + βS drives overturning. Freshwater input dilutes salinity, reducing sinking.
The system has a bifurcation: above critical freshwater forcing, AMOC collapses irreversibly (saddle-node).
Current AMOC ~17 Sv; paleo collapses (Younger Dryas) took decades.