Scientists have uncovered a submerged landmass two-thirds the size of Australia, which has implications for climate science, biology and how Zealandia could be designated a continent.
If you could drain the Pacific Ocean, you’d be staring at the lost continent of Zealandia, which is 18 times larger than New Zealand. Although 94 percent submerged, Zealandia, a large region in the southwest Pacific Ocean underlain by continental crust, is gaining momentum to be dubbed a continent, thanks to new research published in GSA Today.
Zealandia offers a wealth of insight due to its age: it began separating from the combined Australia-Antarctica portion of Gondwana in the late Cretaceous period around 80 million years ago, according to Jerry Dickens, a professor of Earth sciences at Rice University and co-chief scientist of an upcoming drilling expedition to learn more about Zealandia.
What Makes a Continent?
“We want to learn how the continental crust got so thin there,” says Dickens. “Continents like Europe and North America broke apart easily, but Zealandia didn’t. Zealandia doesn’t sit easily with current models.”
Dickens goes on to say, “How can a continent become so thin during rifting that it remains mostly submerged? That’s a real challenge for the community that studies plate tectonics.”
Zealandia is being dubbed the thinnest, most submerged and smallest continent, but there should be an asterisk above the word “continent.” The study authors say they want to give the region a full designation of continent, but there isn’t an organizing body to do so.
“If we add Zealandia as a continent, it forces us to think about what makes a continent, the type of Earth crust it has,” says Dickens. “These days we don’t really think about what makes a continent a continent.”
Unlike an organization responsible for naming new planets and stars, no group exists to dub a region a continent. But if other scientists use Zealandia in their work and cite the GSA paper, then that will be a validation of the work by Dickens et al. But it will take time.
“Being more than one million square kilometers in area, and bounded by well-defined geologic and geographic limits, Zealandia is, by our definition, large enough to be termed a continent,” says lead author Dr. Nick Mortimer.
Dr. Mortimer goes on to say that scientists in biology and marine science who didn’t “consider this part of the world would say, ‘Hang on a sec. This leads me down a certain path and gives new context to various strands of scientific work.’”
Diving into Climate Science
Dickens says Zealandia may offer insight into climate research. He notes in a reddit AMA that one of the great challenges in current Earth science literature is the Early Eocene period, particularly 50 to 53 million years ago. Earth surface temperatures were nominally 10-12°C greater than they are today and exceptionally warm at high latitudes.
All explanations to date relate to elevated atmospheric pCO2 (partial pressure of carbon dioxide), but the extreme high latitude temperatures remain an issue, even after considering differences in albedo (little or no “white”-reflective ice at the poles during the early Eocene), Dickens notes. The scientific community has not been able to replicate such temperatures using climate models.
There is also the issue of why pCO2 was so high, Dickens says. The most difficult early Eocene temperature records to account for are those generated from within and around New Zealand. “Not only does the submerged portion of Zealandia have many early Eocene sediment sequences, but the past location and water depth of Zealandia may explain much of the data-model issues,” he adds.
Dr. Mortimer notes, “It all comes down to getting better context and appreciation for what’s out there.”
Expedition to Zealandia
And what’s out there will be explored in a drilling expedition scheduled to run from late July to late September 2017. On a 473-foot-long ship, the 100-plus crew will seek to uncover the history of Zealandia and when and how it became such a submerged region.
According to the expedition’s prospectus, “Zealandia is an ideal location for generating detailed paleoceanographic records from the Miocene through the Pleistocene that can be linked to previous ocean drilling expeditions in the region (Deep Sea Drilling Project Legs 21, 29, and 90; Ocean Drilling Program Leg 189) and elsewhere in the Pacific Ocean.”
The supercontinent Gondwana’s vestiges have long interested researchers, and recent finds show encouraging signs that interest won’t wane. Earlier this year, South African scientists say they discovered evidence of a “lost continent,” left from the breakup of Gondwana which began around 200 million years ago. It’s located under the popular island destination of Mauritius, and its remains may be dispersed widely across the Indian Ocean basin.
For those neck-deep in marine science, Zealandia is not a new concept, especially to many New Zealanders. Earth scientists have been discussing Zealandia for more than 20 years, since California scientist Bruce Luyendyk first named the landmass Zealandia in 1995.
In an interview, Luyendyk, now retired, says the biggest takeaway he’d like to see from Zealandia’s newfound publicity is that “we think of continents as places where people live above sea level. Sure, that’s how everyday life sees it, but geologists don’t see it that way, since sea level is relative. It goes up and down across centuries and millennia.”