Temperature Gradient above the Deep-Sea Floor

Abstract

AT sufficient ocean depths (several km) there is an increase of temperature with depth corresponding to the adiabatic lapse rate Γ ≈ 10⁻⁶ °C/cm. Toward the bottom, the gradient becomes increasingly superadiabatic, because the water is heated from below by a geothermal heat flux H. Because H is small (∼10⁻⁶ calories cm⁻² s⁻¹), only a slight superadiabatic effect is expected: |dT/dz| < 2Γ at elevation z > 1 m. Measurements of hyperadiabatic gradients (|dT/dz| = 10–1,000 Γ) several metres, or even tens of metres, above the bottom have been reported^1–4, though it seems inconceivable that a strongly unstable layer several metres thick can persist. The experiment described here indicates that |dT/dz| = 1.3 Γ at z ∼ 1 m.