Profiling Float Observations of the Upper Ocean under Sea Ice off the Wilkes Land Coast of Antarctica

Abstract

Abstract Multiyear under-ice temperature and salinity data collected by profiling floats are used to study the upper ocean near the Wilkes Land coast of Antarctica. The study region is in the seasonal sea ice zone near the southern terminus of the Antarctic Circumpolar Current. The profiling floats were equipped with an ice-avoidance algorithm and had a survival rate of 74% after 2.5 yr in the ocean. The data show that, in this part of Antarctica, the rate of sea ice decay exceeds the rate of sea ice growth. During the sea ice growth period, the water column is weakly stratified because of brine rejection and is only marginally stable. The average winter mixed layer temperature is about 0.12°C above the surface freezing point, providing evidence of entrainment of warmer water from the permanent pycnocline. The average mixed layer salinity increases by 0.127 from June to October. A one-dimensional model is used to quantify evolution of the winter mixed layer under a sea ice cover. The local winter entrainment rate is estimated to be 49 ± 11 m over 5 months, supplying a heat flux of 34 ± 8 W m−2 to the base of the mixed layer in winter. Model output gives a thermodynamic sea ice growth of 28 ± 15 cm over the same period. The winter ocean–atmosphere heat loss through leads and sea ice is estimated to be 14–25 W m−2 in this area, which is broadly in line with other winter observations from the East Antarctic region.