Analysis of the quasi-two-year variation of the Zapiola Anticyclone based on the reanalysis data and drifter trajectories

Zapiola anticyclone (ZA) is an anticyclonic circulation trapped by a seamount about 1200 m in height named Zapiola Rise (ZR). The ZA is adjacent to energetic flows of the South Atlantic Ocean, such as the Brazil/Malvinas Confluence (BMC) and the Antarctic Circumpolar Circulation (ACC). The interplay among the circulations makes the dynamic processes of the ZA complex and variable. Based on the reanalysis data and drifter observations, this study mainly aims to investigate the influence of a strong flow field outside of the seamount on variations of the ZA. Results show that the vorticity of the ZA has a significant quasi-two-year variation, which is an independent eigenmode in the basin. The advection of the potential vorticity over the bottom topography from the southern boundary plays the most significant role in controlling the vorticity variations of the ZA. Drifter trajectories also confirm the importance of the flow field in the south of the seamount. The statistical results of the drifter trajectories show that the transport process of the southern boundary flow field has the most significant effect on the dynamic processes of the ZA. It is worth mentioning that the results obtained using the dataset of the reanalysis are limited by its validity in the region. •The Zapiola anticyclone (ZA) shows a quasi-two-year variation, which is an independent eigenmode in the basin.•The advection of the potential vorticity from the southern boundary plays the most significant role.•Drifter trajectories confirm the importance of the flow field in the south of the ZA.•A dynamic process of ACC affecting the nearby basin-scale circulation is revealed.