Annual evolution of the ice–ocean interaction beneath landfast ice in Prydz Bay, East Antarctica

Abstract

High-frequency observations of the ice–ocean interaction and high-precision estimation of the ice–ocean heat exchange are critical to understanding the thermodynamics of the landfast ice mass balance in Antarctica. To investigate the oceanic contribution to the evolution of the landfast ice, an integrated ocean observation system, including an acoustic Doppler velocimeter (ADV), conductivity–temperature–depth (CTD) sensors, and a sea ice mass balance array (SIMBA), was deployed on the landfast ice near Chinese Zhongshan Station in Prydz Bay, East Antarctica from April to November 2021. The CTD sensors recorded the ocean temperature and salinity. The ocean temperature experienced a rapid increase in late April, from −1.62°C to the maximum of −1.30°C, and then, it gradually decreased to −1.75°C in May and remained at this temperature until November. The seawater salinity and density exhibited similar increasing trends during April and May, with mean rates of 0.04 psu day−1 and 0.03 kg m−3 day−1, respectively, which was related to the strong salt rejection caused by freezing of the landfast ice. The ocean current observed by the ADV had mean horizontal and vertical velocities of 9.5±3.9 cm s−1 and 0.2±0.8 cm s−1, respectively. The domain current direction was ESE (120°)–WSW (240°), and the domain velocity (79%) was 5–15 cm s−1. The oceanic heat flux (Fw) estimated using the residual method reached a peak of 41.3±9.8 W m−2 in April, and then, it gradually decreased to a stable level of 7.8±2.9 W m−2 from June to October. The Fw values calculated using three different bulk parameterizations exhibited similar trends with different magnitudes due to the uncertainties of the empirical friction velocity. The spectral analysis results suggest that all of the observed ocean variables exhibited a typical half-day period, indicating the strong diurnal influence of the local tidal oscillations. The large-scale sea ice distribution and ocean circulation contributed to the seasonal variations in the ocean variables, revealing the important relationship between the large-scale and local phenomena. The high frequency and cross-seasonal observations of oceanic variables obtained in this study allow us to deeply investigate their diurnal and seasonal variations and to evaluate their influences on the landfast ice evolution.