They did not get much further north. Waters around the Chatham Rise near the Chatham Islands are warmed by subtropical currents, meaning that Cook Strait was probably the furthest north the icebergs ever reached.
Some would have been dirty and grey from rocks and sediment in the ice but others would have been brilliant white and deep blue.
"There are records in the literature from sailing ships around New Zealand seeing these things," said Niwa oceanographer Dr Lionel Carter. "They described them as large white mountains. I guess they would have been very impressive."
He said past iceberg invasions that flowed in pulses from Antarctica were indirect responses to ocean and climate changes and provided insights into what might happen to Antarctica under global warming.
In 100 years, it is thought that Earth will look like it did during warm periods over the past 200,000 years.
"There were certain periods within that 200,000 years when Earth was two, three, four degrees warmer, which is what they are projecting for global warming in the next two centuries.
"We are concentrating on that period to see how Earth behaved during those very warm periods as a sort of example of what will happen in the future."
Dr Carter said the Antarctic circumpolar current carried the icebergs to NZ waters, where they melted over the Chatham Rise and the Campbell Plateau south of Stewart Island.
"The amount of debris found on the seafloor from Antarctica gives us an idea of past iceberg activity. Periods of high iceberg activity are associated with the rapidly warming conditions that immediately follow ice ages."
During those times the ice shelves were at their largest but the combination of a rising sea level and increased temperatures caused them to break up.
Samples from the South Atlantic Ocean seabed also showed evidence of iceberg activity at about the same time that icebergs were melting in NZ waters.
"This suggests that the break-up of ice shelves were major events and that the currents shifted large numbers of icebergs over much of the Southern Ocean."
Dr Carter said scientists were unsure of what the driving force was behind the break-up of Antarctic ice shelves but it was possible there was a link between temperature changes in the climate and oceans in the Northern Hemisphere.
"The presence of icebergs in the Southern Hemisphere coincides with warm periods in the North Atlantic Ocean where evaporation of the ocean surface produced saltier than normal water.
"The density of this salty and warm water, known as North Atlantic deep water, causes it to sink and flow south. It eventually reached Antarctica and might have contributed to the melting and breaking up of the ice shelves.
"If this is right then it shows a strong link between the oceans and climates of both hemispheres."
Dr Carter said that iceberg formation was not restricted to warm periods immediately after the ice ages.
The institute had also found evidence of strong iceberg activity in the last warm period which has persisted for 10,000 years to the present.
Sampling has shown that a big flotilla of icebergs reached New Zealand 5000 years ago.
One of the last sightings of icebergs in New Zealand was in 1948 when they were seen southeast of the Antipodes Island in subantarctic waters.
www.nzherald.co.nz/climate
Intergovernmental Panel on Climate Change
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Summary: Climate Change 2001
United Nations Environment Program
World Meteorological Organisation
Framework Convention on Climate Change
