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Scientists have found evidence to suggest giant icebergs, like those currently south of New Zealand, once drifted by the east coast.
National Institute of Water and Atmospheric Research (Niwa) staff have identified what they believe are ancient iceberg scours on the seabed about 725km east of Christchurch.
The large scours showed up on seabed maps produced from surveys of the Chatham Rise in August as part of the Government's Ocean Survey 20/20 research programme.
Niwa marine geologist Scott Nodder said grooves measuring about 2m to 2.5km long, 200m across and 10m deep could be seen in the seabed on the eastern Chatham Rise at a depth of between 450m and 470m.
"They were probably caused by an iceberg that calved off the Antarctic icesheet during the last Ice Age, 18,000 to 20,000 years ago," Dr Nodder said. Sea levels were 100m lower then, so the iceberg would have sat in about 350m to 450m of water.
The curved grooves were likely to have been caused by the iceberg grounding on the seabed and moving around in the currents.
"Three gouge marks to the north of the grooves may have been where the keel of the iceberg hit the seafloor," Dr Nodder said.
Similar scours were found further west on the Chatham Rise in 2001.
Niwa oceanographer Mike Williams said the iceberg that made these grooves would have been similar in size to the largest berg now off southern New Zealand.
- NZPA
