Surrounding New Zealand is a mass of Earth's crust about half the size of Australia, the continent Zealandia. What makes Zealandia different from other continents is that more than 90 percent of it is submerged.
Increasingly detailed seafloor maps have attracted attention to Zealandia. Now scientists are asking: What secrets does it hold?
To find out, 30 researchers will set sail July 27 on a two-month ocean drilling expedition to search for clues to Zealandia's history.
Participants in International Ocean Discovery Program (IODP) Expedition 371, sponsored by the National Science Foundation (NSF) and its international partners in IODP, will sail from Townsville, Australia, aboard the JOIDES Resolution, one of the world's most sophisticated scientific drillships.
IODP is an international research collaboration that coordinates seagoing expeditions to study the history of Earth recorded in sediments and rocks beneath the ocean floor.
Expedition 371 scientists will join more than 20 crew members in drilling at six Tasman Sea sites at water depths ranging from 1,000 to 5,000 meters.
At each site, the scientists will drill from 300 to 800 meters into the seafloor to collect cores — complete samples of sediments deposited over millions of years. The cores hold fossil evidence the scientists will use to assemble a detailed record of Zealandia's past.
"If you go way back, about 100 million years ago, Antarctica, Australia and Zealandia were all one continent," said expedition co-chief scientist Gerald Dickens, a geoscientist at Rice University. "Around 85 million years ago, Zealandia split off on its own, and for a time, the seafloor between it and Australia was spreading on either side of an ocean ridge that separated the two."
The relative movements of Zealandia and Australia are due to plate tectonics, the constant movement of interlocking sections of Earth's surface.
Some 25 tectonic plates fit together like puzzle pieces to form Earth's crust. The plates are in constant motion. They can crash together to form mountain ranges or slide past one another in earthquake zones.
Oceanic plates form on either side of ocean ridges and slide beneath lighter, more buoyant continental plates in a process known as subduction.
Expedition 371 will examine such a shift, which occurred about 50 million years ago in the direction of the enormous Pacific Plate northeast of Zealandia.
"Some 50 million years ago, a massive shift in plate movement happened in the Pacific Ocean," said Jamie Allan, a program director in NSF's Division of Ocean Sciences, which supports IODP. "It resulted in the diving of the Pacific Plate under New Zealand, the uplift of New Zealand above the waterline, and the development of a new arc of volcanoes. This IODP expedition will look at the timing and causes of these changes as well as at related changes in ocean circulation patterns and ultimately Earth's climate."
In the expedition's scientific prospectus, researchers refer to this shift as "the most profound subduction initiation event and global plate-motion change" in the past 80 million years.
"We're looking at the best place in the world to understand how plate subduction initiates," said Dickens. "This expedition will answer a lot of questions about Zealandia."
Prior to the shift, Australia and New Zealand were spreading apart. After the shift, the area that separated them was under compression for millions of years.
Then, in the final stage, the Pacific Plate dove beneath Zealandia, forming a new subduction zone.
"What we want to understand is why and when the various stages from extension to relaxation occurred," Dickens said. "The cores will help tell us that. They'll be analyzed for sediment composition, microfossil components, mineral and water chemistry, and physical properties."
He said the research may also answer questions about the way Earth's climate has evolved in the last 60 million years.
Zealandia has been left out of many climate models, Dickens said. That could be one explanation for the difficulty scientists have had in developing accurate models of the greenhouse climates of around 50 million years ago.
"When the community does climate modeling for the Eocene Epoch [56 to 33.9 million years ago], this is the area that causes consternation, and we're not sure why," said Dickens. "It may be because we had continents that were much shallower than we thought. Or we could have the continents right but at the wrong latitude. The cores will help us figure that out."
Answers to Zealandia's mysteries may soon be revealed.
Note: Video from IODP Expedition 371 will be available post-expedition.