Halocline & Double Diffusion

Physics: Seawater density ρ(T,S) ≈ ρ₀(1 - α·ΔT + β·ΔS) where α ≈ 2×10⁻⁴ K⁻¹ (thermal expansion), β ≈ 7.6×10⁻⁴ psu⁻¹ (haline contraction). Salt fingers form when warm salty water overlies cool fresh water — heat diffuses faster than salt (D_T/D_S ≈ 100). Diffusive convection is the reverse: cool fresh over warm salty, leading to thermohaline staircases. Double diffusion drives significant diapycnal mixing in subtropical and Arctic oceans.