The breaking up of sea ice in McMurdo Sound means the sea is now within a kilometre of Scott Base, providing easier shipping access.
At nearby McMurdo Station, the seafront is ice-free.
"The last time we saw open sea in front of Scott Base was 1998," Antarctica New Zealand chief executive Lou Sanson said.
"In the ensuing time, we have had these massive icebergs break off the Ross ice shelf that led to these unusual sea ice conditions in McMurdo Sound, and some of the 'bergs were the 'bergs that floated up the coast of Dunedin."
The icebergs, some of which were half the size of Stewart Island, blocked the entrance to McMurdo Sound and led to "massive multi-year sea ice", some of which took ships 160km of icebreaking to get through.
"The United States and New Zealand are both delighted to see the extent of the sea ice breakout this year because it does mean that we are dealing with much cleaner ice, much shallower ice in terms of ice-breaking channels, and new sea ice that freezes for the runways," Mr Sanson said.
He said the break-up of the sea ice could not be put down to climate change.
"We've had a cooling trend in the Ross Sea region related to the ozone hole, so no, we wouldn't relate this to global warming."
