The area is not a major shipping lane and few sailors are out in November - spring in the southern hemisphere - but ships that traverse the area have little hull protection and could be significantly damaged by a collision with an iceberg, which typically has 90 per cent of its mass under water.
"It's an alert to shipping to be aware these potential hazards are around and to be on the lookout for them," Maritime New Zealand spokeswoman Sophie Hazelhurst said of an official navigation warning issued for the area south of the country.
Large numbers of icebergs last floated close to New Zealand in 2006, when some were visible from the coastline - the first such sighting since 1931.
The current flotilla of icebergs that split off Antarctic ice shelves are slowly drifting in the direction of New Zealand. The nearest one, measuring about 330 to 660 feet long, was 160 miles southeast of New Zealand's Stewart Island on Tuesday, Australian glaciologist Neal Young said. He said it was impossible to tell from the satellite image how tall the iceberg is.
He couldn't say how many icebergs in total were roaming the Pacific, but he counted 130 in one satellite image alone and 100 in another.
New Zealand oceanographer Mike Williams said the icebergs are drifting at a speed of about 16 miles a day and he expects most won't reach New Zealand, similar to the 2006 flotilla, of which many were directed eastward away from the country by ocean currents and wind.
Williams, a scientist with the National Institute of Water and Atmospheric Research, said he was "pretty sure these icebergs came from the break-up of the Ross Sea Ice Shelf in 2000" - an ice shelf the size of France and the origin of the 2006 flotilla of icebergs.
Icebergs are routinely sloughed off as part of the natural development of ice shelves. As temperatures have risen in the Antarctic Peninsula area near South America by as much as 5 degrees Fahrenheit (3 degrees Celsius) in the past 60 years, "whole ice shelves have broken up," Young said.
But Young said the iceberg flotilla south of New Zealand came from the Ross Sea, a completely different area of Antarctica, and is unrelated to climate change.
The appearance of the bergs in waters south of New Zealand depends as much on weather patterns and ocean currents as on the rate at which icebergs are calving off Antarctic ice shelves.
In the current case, a cold snap around southern New Zealand and favorable ocean currents conspired to push the towering visitors, which have drifted around Antarctica for the past nine years, into the region's ocean.
"Icebergs this far north (near New Zealand) are not that unusual," said New Zealand glaciologist Dr. Wendy Lawson, noting that an iceberg's reach was determined by its size.
(Left: A satellite image of a flotilla of icebergs off New Zealand's Macquarie Island. The largest iceberg sighted is approximately 1¼ miles long, more than 500 yards across, and rises over 50 meters above sea level.)
On Monday, Rodney Russ, expedition leader on the tourist ship Spirit of Enderby, spotted an iceberg about 60 miles northeast of Macquarie Island and heading north - about 500 miles south of New Zealand. Australian scientists reported another mass of 20 icebergs drifting north past Macquarie Island two weeks ago.
Maritime New Zealand safety services general manager Nigel Clifford said as the icebergs drift closer, "the more the potential risks grow of them posing a hazard to shipping" as they break up and float lower in - or just under - the ocean surface.
The agency was "keeping a close eye on the increasing risk ... it's tracking iceberg positions and has begun initial planning for any incident," he told the AP.
He noted the area is not a major shipping lane, with commercial fishing vessels and a limited number of passenger cruise ships passing through and reporting positions for the drifting ice.
Young said satellite images showed the group of icebergs, spread over a sea area of 600 miles by 440 miles, moving on ocean currents away from Antarctica.
Icebergs are formed as ice shelves develop. Snow falls on the ice sheet and forms more ice, which flows to the edges of the floating ice shelves. Eventually, pieces around the edge break off.
For more info:
News: Southern Ocean Icebergs - Australian Antarctic Division (11.25.09)
By Associated Press Writer Ray Lilley