Abyssal Circulation

Physics: Thermohaline circulation is driven by density differences from cooling and salinity. NADW (North Atlantic Deep Water) forms at ~60°N: surface cooling + evaporation increases density; water sinks to 2–4 km depth. AABW (Antarctic Bottom Water) is the world's densest water (ρ ≈ 1028 kg/m³), filling ocean basins below 4 km. Transport ~15 Sv (1 Sverdrup = 10⁶ m³/s = 100× Amazon river). Deep water residence time ~1000 years; diapycnal mixing by tides/waves returns water upward. 1 Sv = 10⁶ m³/s.