As the ship travels south we reach the pack ice. Most of the coastline of Antarctica is covered permantly with ice. Fast pack ice nearest to the continent lasts year-round. The extent of pack ice beyond varies with the time of year. Pack ice is measured as fraction of surface coverage, i.e. 3/10 means that 30% of the surface is covered with ice. The icebreaker can continue to proceed even with 10/10 pack ice as long as it isn't too thick. Pack ice thickness of a few 10s of centimeters seemed to have little effect on forward progress. However as the ice depth grew beyond a meter, the ship labored to make good progress. This page
describes the mechanics of ice breaking and includes a video of the Kapitan at work.