The evolution of N$^2$[s$^−1$] and the SIC [%] on top. The mixed layer depth (MLD) is shown in white and the depth of the permanent pycnocline (PP) is in yellow, for SOSE (a), 590538 Argo float for 2019 (b) and 5904471 Argo float for 2016 (c).
Abstract
Understanding the seasonal dynamics of the permanent pycnocline is crucial for explaining the physical processes governing oceanic stratification and its implications for ocean dynamics. This study investigates the seasonal evolution of the permanent pycnocline at Maud Rise, a key region in the Southern Ocean characterised by sea-ice variability and the occurrence of polynyas. Utilising data from two Argo floats, one during a polynya year and another one during a non-polynya year, to analyse the temporal variability of the permanent pycnocline’s depth and strength. The results reveal strong seasonal variability in the characteristics of the permanent pycnocline at Maud Rise, driven by the interplay between freshwater and temperature forcing, as well as wind stress. At the beginning of the year, the permanent pycnocline shoals until it merges with the seasonal pycnocline and its strength increases. In winter, cooling and sea-ice formation deepen and weaken the pycnocline, destabilising the upper ocean. Additionally, the polynya year and inter-annual variability in upper ocean freshwater content show the influence of a strong gradient between the upper ocean and warmer, saltier, deeper water masses. Overall, this study provides valuable insights into the seasonal evolution of the permanent pycnocline in a key region of the Southern Ocean, advancing our understanding of the underlying mechanisms.
