Winter upper ocean stability and ice-ocean feedbacks in the sea-ice-covered Southern Ocean

AbstractIn this study, under-ice ocean data from profiling floats, instrumented seals, and shipboard casts are used to assess wintertime upper ocean stability and heat availability in the sea-ice-covered Southern Ocean. This analysis reveals that the southern Weddell region, which features a weak upper ocean stratification and relatively strong thermocline, is preconditioned for exceptionally high rates of winter ventilation. This preconditioning also facilitates a strong negative feedback to winter ice growth. Idealized experiments with a 1D ice-ocean model show that the entrainment of heat into the mixed layer of this region can maintain a near-constant ice thickness over much of winter. However, this quasi-equilibrium is attained when the pycnocline is thin and supports a large temperature gradient. We find that the surface stress imparted by a powerful storm may upset this balance and lead to substantial ice melt. This response can be greatly amplified when coincident with anomalous thermocline shoali...