I don' know anything about Antartica, but I do know that a terrific resource for any question about cruising is the Cruise Critic website -- http://boards.cruisecritic.com/. Their message boards are for cruising what this website is for flying, IMHO! The boards were very helpful for some cruise research and planning we did in recent years.

If you go to the Boards link and select Ports of Call, you will see South America listed: should be able to find some answers there. And if no-one has asked that particular question, you can register and post a question yourself.