Dr Stevens, who works for the National Institute of Water and Atmospheric Research and the University of Auckland, says more icebergs are likely, but that a repeat of 2006’s spectacular flotilla off the coast of Otago is "a lottery".
"Over the next decade or so, it is highly likely we’ll see more icebergs in the Southern Ocean,’’ Dr Stevens said.‘‘This probability will increase if melting of ice-shelves continues to accelerate.
"As to whether they’ll appear off Otago, that’s a bit of a lottery."
In November, 2006, two large icebergs — one measuring 500m by 50m — and about 18 smaller ones were sighted 90km off the Otago coast, prompting international interest.
Three years later, an iceberg of similar size was seen about 8km northwest of Macquarie Island, between Australia and the Antarctic. It failed to make its way to New Zealand.
The Antarctic is in its annual "melt season".
Dr Stevens will be there later this month, with a team led by University of Otago professor Christina Hulbe, researching ice melt. He says researchers already on the ice have reported a long, thin iceberg grounded on the McMurdo Sound coast. Another iceberg, created when a section of the Nansen Shelf broke away, in April, has probably damaged United States research equipment and may have affected New Zealand equipment.
But what is happening in the Antarctic right now, has little bearing on the possibility of icebergs off New Zealand’s coast this spring, Dr Stevens says.
Typically, fresh icebergs "slosh around the Antarctic coast" for several years, travelling slowly in an anticlockwise direction, before being caught in the Antarctic Circumpolar Current (ACC), which is fast-flowing in a clockwise direction.
"We don’t really know where a berg will spin out of that," he said.
"But the ACC will consistently flow past New Zealand. So, if we see more bergs getting out, we will see them off New Zealand, for sure."
The icebergs that were sighted off Otago a decade ago had probably broken free five or six years before that.
In 2013, a massive iceberg, known as B31, broke off the Pine Island Glacier, south of South America, thousands of kilometres from New Zealand’s main Antarctic research area, Scott Base, Ross Island.
"[This] is a normal phenomenon. But in a melting world we are likely to see more of this happen."
At present, B31 is a few hundred kilometres from where it "calved".
"It’s very difficult to know where these things will end up,’’ Dr Stevens said.
If it did float north off the east coast of New Zealand, it is unlikely it would be seen any further north than the Chatham Rise, where a shallow, warm band of water flows east from Banks Peninsula. Ice melt is accelerating in some parts of the Antarctic.
Nasa’s Operation IceBridge has planes flying 12-hour research missions using radar to measure Antarctic ice melt south of South America. Those researchers are observing what they say is the speediest ongoing Western Antarctic glacial retreat rates yet observed.
They say that particular ice sheet may be in a state of irreversible decline, directly contributing to rising sea levels.
