We study a large and long-lived earthquakes swarm occurring in 2020-2021 in the Bransfield Basin, south of the South Shetland islands, Antarctica. We make use of local seismological stations to detect and characterize more than 36000 small earthquakes, occurring from the end of August 2020 to June 2021. Together with the occurrence of the ~36000 earthquakes, we observe a significant (up to 8cm) geodetic deformation at nearby GPS stations. By joint interpretation of b-value, spatiotemporal evolution of seismicity and geodetic deformation, we infer a volcanic origin for this swarm, which takes place close to the ridge axis. Our study suggest that a significant amount of extension observed at the Bransfield Basin ridge is occurring in rapid deformation episodes (e.g., 1 year), and is most likely driven by volcanic activity localized at the ridge axial volcanic structure, rather than at the rifting bounding border faults.