More than you expect to use, and several moderate cards rather than one enormous one. Antarctica produces far more photographs than people anticipate once burst shooting, video and RAW files get involved, and a card is effectively impossible to replace mid-voyage. Spreading the trip across several cards means a failure, a loss or an accidental format only costs you part of it.
Test every card before you leave and format them in the camera rather than only on a computer. Confirm each one sustains your camera's burst and video settings.
Work out your storage need properly rather than guessing. Shoot a normal day at home, check the total size, multiply by your expedition days, then add a generous margin. Clear your phone and computer before travelling, and don't count on ship internet or cloud for large backups.
Keep completed cards separate from empty ones in a weather-resistant wallet, with a system clear enough that nothing gets reformatted by accident at the end of a long day.