I called Atlas today at 844-442-8527 (44ATLAS). For Feb 15 Antarctic Circle:
Flybondi departs EZE domestic terminal C at 2:30 pm on 2/15
Aerolinas Argentinas departs Ushuaia at 4:05 pm on 2/27
Personal item must fit under the seat.
Carry-on weight limit is 16 lbs Dimensions: 21 X 13 X 10
Checked bag weight limit is 50 lbs.
There does not appear to be a planned activity for departure day. My brother and I are going to find a private transfer that will include a tour of some things around Ushuaia with drop off at the airport.