...and yet the Polar star experienced more / thicker ice than usual:http://gcaptain.com/ship-photos-u-s-icebreaker-polar-star-reaches-mcmurdo-station-antarctica/
The Coast Guard says that in previous years Polar Star typically worked through approximately 12 to 13 miles of ice to reach McMurdo Station. This year, however, there was more than 60 miles of ice to break with thickness ranging from two feet to more than 10 feet.
“We experienced a significantly larger ice field this year compared to the last several years,” said Capt. Michael Davanzo, commanding officer of the Polar Star. “In several areas, the ice was under considerable pressure and covered with several inches of snow, slowing our progress. Despite these challenges, the crew worked around the clock to prepare the resupply channel before the arrival of the first ship.”
Looking in NSIDC Chartic this seems odd as it shows next to no ice in the area
Photo caption: The Coast Guard Cutter Polar Star (WAGB-10) and crew create a navigable channel through the frozen Ross Sea off of Antarctica, Jan. 16, 2017. U.S. Coast Guard Photo