Dynamic, Chemical and Biological Features of the Southern Ocean Fronts in Austral Autumn 2024

This study provides a multidisciplinary analysis of the fronts and frontal zones along a 6,000 km transect in the Southern Ocean. Observations were carried out aboard the research vessel “Akademik Tryoshnikov” from April 2 to 13, 2024 on the way from Cape Town to Mirny wintering station and cover the waters of the Atlantic and Indian sectors of the Southern Ocean. Using satellite altimetry and shipboard data, we mapped the Antarctic Circumpolar Current (ACC) and its multi-branch structure, including the Subantarctic Front (SAF), Polar Front (PF), and Southern ACC Front (SACCF). Observations revealed dynamic interactions within the ACC, with the convergence of the PF branches producing strong southeastward flows, reaching 53 cm/s at the surface levels and decreasing to 26 cm/s at a depth of 550 m. Alongside physical measurements, nutrient and phytoplankton distributions were analyzed, highlighting sharp gradients in silica, phosphorus, and chlorophyll-a concentrations across fronts. In nutrient-rich zones such as the Polar Front and south of the ACC, diverse and abundant phytoplankton communities were observed, particularly diatoms such as Fragilariopsis kerguelensis and Rhizosolenia simplex. These findings show how combined use of biochemical and hydrodynamic data can contribute to better understanding of the complex structure of the ACC and surrounding waters.