The autonomous perennial acoustic observatory in the Antarctic Ocean (PALAOA) constitutes a powerful tool to monitor the acoustic presence of marine mammals at a pristine location in the Southern Ocean. For a limited period of time, these recordings are dominated by vocalizations of the Ross seal (Ommatophoca rossii) a species considered to be the rarest and the least known of all Antarctic seals. PALAOAs acoustic data provides new information on the presence of Ross seals at the location of Atka Bay. Ross seal calls are shown to comprise of four distinct call types, which are explicitly described for the first time. Their seasonal as well as their diurnal calling patterns are presented and placed into a behavioural context. The number of vocalizing seals is estimated by using time-delays between the two recorded channels of the hydrophone array. The results provide information required for the development of automated pattern recognition for acoustic censusing, particularly when faced with analysing the PALAOA multi-year recordings.