Move over Australia: little brother Zealandia is a continent too

By Ewan McDonald

Zealandia - it's bigger than you thought
Zealandia - it's bigger than you thought
New Zealand isn't just a few small islands: it's a continent, called Zealandia, mostly under water

Turns out New Zealand isn’t a few small islands at the bottom of the world. Just like Australia, it’s actually a continent.

Most of it just happens to be under the sea, which is probably in keeping with Kiwis’ self-effacing national personality. After all, we don’t like to make waves.

The case for the continent of “Zealandia” is made in a paper with considerable input from New Zealand’s GNS Science, the government body for earth, geoscience and isotope research sciences. It is published in GSA Today, the journal of the Geological Society of America.

According to the authors, Zealandia and Australia come remarkably close to each other across the Cato Trough, off the coast of Queensland. At that point, the continental crusts of the two continents are just 25km apart.

In total, Zealandia covers about 4.9 million sq km, of which 94% is underwater.

It would be revealed “if you pulled the plug on the world’s oceans”, says the paper’s principal author, GNS geologist Nick Mortimer.

Zealandia includes the Chatham Islands and sub-Antarctic islands to the south of New Zealand, and New Caledonia. Fiji and Tonga are not included.

But there are no territorial implications, with maritime boundaries long agreed upon.

“It’s mainly a better and more accurate description of what’s there in this corner of the planet,” Mortimer says.

Water in the ocean around Zealandia is about 4000m deep, while the shelves around the Chathams, sub-Antarctic islands and New Caledonia are about 1000m. The highest point on the continent is Aoraki-Mt Cook.

“This is not a sudden discovery but a gradual realisation. As recently as 10 years ago, we would not have had the accumulated data or confidence in interpretation to write this paper,” the authors say.

“Being more than 1m sq km in area, and bounded by well-defined geologic and geographic limits, Zealandia is, by our definition, large enough to be termed a continent.”

It is 12 times bigger than Mauritia, a continent that broke up when India and Madagascar separated some 60m years ago. It is six times bigger than Madagascar and about the same area as greater India.

It is not unique among continents in being mostly submerged: “An ice-free, isostatically corrected West Antarctica would also largely be submerged.”

Zealandia once made up about 5% of the area of the great continent of Gondwana, the ancient super-continent that included most of the land masses in today’s Southern Hemisphere, including Antarctica, South America, Africa, Madagascar, Australia, the Arabian Peninsula and the Indian sub-continent.

“It’s been pretty panelbeaten on its journey,” Mortimer says. “It’s had 100m years of stretching and moving.”

The continent of Zealandia provided a useful context for looking at a few things. One was New Zealand’s offshore resources; another was native plants and animals.

Mortimer says there is no body that can declare Zealandia a continent but it is increasingly being used in scientific literature by geologists and biologists.

“We’ve taken the time here to write a formal scientific paper on it.”

In 2014, Mortimer and GNS geologist and palaeontologist Hamish Campbell wrote a book, now out of print, about Zealandia.

The name was first proposed by geophysicist Bruce Luyendyk in 1995 as a collective name for New Zealand, the Chatham Rise, Campbell Plateau and Lord Howe Rise.

As well as GNS staff who contributed to the paper, other authors come from Victoria University (Wellington), the University of Sydney and the Service Geologique de Nouvelle Caledonie.

Now, on the grounds (well, waters) that we’re equals, please can we have Phar Lap, pavlova, Crowded House, Anzac biscuits, the flat white, Russell Crowe and Keith Urban back? Okay, you can keep Russell Crowe.



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