Exploring the world's 8th continent, Zealandia

Fig 1: The continent of Zealandia. 

by Nick Herold

On June 30, 2016 the RV Investigator set sail from Fiji on a course almost directly west, to the northern tip of the Lord Howe Rise, a large undersea plateau that runs roughly parallel to the east coast of Australia. This plateau makes up most of the northern half of Zealandia, the world’s 8th and least well-known continent.

Why haven’t you heard of an 8th continent before? Largely because over 90% of Zealandia is underwater and so hasn’t been officially recognised until recently. Pretty much the only part of Zealandia that’s above water is New Zealand.

So, what makes it a continent if it’s over 90% submerged you say? Well, the answer lies in the crust, Zealandia is pretty much made up of the same kind of continental crust that makes up other continents. Typically, continental crust is less dense than oceanic crust, which is what makes the ocean floors sink while the continents ‘float’ on top. However, in the case of Zealandia, an odd geological history has led to most of it being underwater today.

As a side note, all continents do have some portion that is underwater, often called the continental shelf, unfortunately in Zealandia’s case the continental shelf could be said to be largest part of the continent. About 80 Myrs ago all of Zealandia was in fact above sea-level, but since then stretching has caused it to thin and sink until all that remains to be seen are its highest peaks, New Zealand.

The aim of this 15-day cruise from Fiji to Hobart 15 was to dredge rocks from the ocean floor that would help reconcile the age of the northern margin of Zealandia. Joining us on this cruise were a motley bunch of oceanographers, remote sensing specialists and geophysicists, all aiming to conduct their own science on our way to Hobart. 

Fig 2/3: The hard work of being on the geology team.
 

When we reached our dredging sites we let out our more than 2km’s worth of cable with dredging buckets on the end to try and scoop up precious samples. Being officially part of the geology team I was involved in lots of rock smashing and rock sawing.

 

Fig 4/5: Conductivity-Temperature-Depth (CTD) measuring devices and (right) ARGO floats.

However, after collecting samples there is not much for a geologist to do on a boat (as all analysis has to be conducted on land)! Thus we had plenty of time to help the oceanographers deploy their instruments, like Conductivity-Temperature-Depth (CTD) measuring devices and ARGO floats.

 

Fig 6: A rough ride across Bass Strait.

Most people suffered some degree of sea-sickness (yours truly was no exception), which peaked when crossing the Bass Strait in characteristic rough conditions. The trip offered a fascinating insight into field work (I spend most of my time at a computer), tremendous views of the ocean, surprisingly great food, a chance to catch up on my table-tennis skills and the opportunity to meet some truly fascinating and dedicated people in completely different fields of research.

 

Fig 7: My fellow researchers.

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