Dünyanın 7. Kıtası: ZELANDİYA

31 Ocak 2019

Earlier this year, Zealandia was confirmed as Earth’s seventh continent, but little is known about it because it’s 94% submerged under water. After a two-month voyage to study the sunken land, a multinational team of researchers affiliated with the International Ocean Discovery Program (IODP) has just arrived in Hobart, Tasmania, aboard the research vessel JOIDES Resolution.

Based on various lines of geological and geophysical evidence, particularly those accumulated in the last two decades, Nick Mortimer et al argue that Zealandia is not a collection of partly submerged continental fragments but is a coherent 4.9 million km2 continent. NC – New Caledonia; WTP – West Torres Plateau; CT – Cato Trough; Cf – Chesterfield Islands; L – Lord Howe Island; N – Norfolk Island; K – Kermadec Islands; Ch – Chatham Islands; B – Bounty Islands; An – Antipodes Islands; Au – Auckland Islands; Ca – Campbell Island. Image credit: Nick Mortimer et al, doi: 10.1130/GSATG321A.1.

Zealandia has 4.9 million km2 (1.9 million miles2) of landmass and once made up approximately 5% of the area of the supercontinent Gondwana.

“Zealandia, a sunken continent long lost beneath the oceans, is giving up its 60 million-year-old secrets through scientific ocean drilling,” said Dr. Jamie Allan, Program Director in the U.S. National Science Foundation’s Division of Ocean Sciences, which supports IODP.

“This expedition offered insights into Earth’s history, ranging from mountain-building in New Zealand to the shifting movements of the planet’s tectonic plates to changes in ocean circulation and global climate.

The researchers drilled deep into the seabed at six sites in water depths of more than 4,101 feet (1.25 km).

They collected 8,202 feet (2.5 km) of sediment cores from layers that record how the geography, volcanism and climate of Zealandia have changed over the last 70 million years.

“The new fossil discoveries prove that Zealandia was not always as deep beneath the waves as it is today,” said expedition co-chief scientist Dr. Gerald Dickens, of Rice University.

“More than 8,000 specimens were studied, and several hundred fossil species were identified.”

“The discovery of microscopic shells of organisms that lived in warm shallow seas, and of spores and pollen from land plants, reveal that the geography and climate of Zealandia were dramatically different in the past.”

The new discoveries show that the formation 40 to 50 million years ago of the ‘Pacific Ring of Fire,’ an active seafloor zone along the perimeter of the Pacific Ocean, caused dramatic changes in ocean depth and volcanic activity and buckled the seabed of Zealandia.

“Scientists had believed that Zealandia was submerged when it separated from Australia and Antarctica about 80 million years ago,” said expedition co-chief scientist Dr. Rupert Sutherland, from Victoria University of Wellington.

“That is still probably accurate, but it is now clear that dramatic later events shaped the continent we explored on this voyage.”

“Big geographic changes across northern Zealandia have implications for understanding questions such as how plants and animals dispersed and evolved in the South Pacific.”

“The discovery of past land and shallow seas now provides an explanation. There were pathways for animals and plants to move along.”

“Studies of the sediment cores obtained during the expedition will focus on understanding how Earth’s tectonic plates move and how the global climate system works. Records of Zealandia’s history will provide a sensitive test for computer models used to predict future changes in climate,” the scientists said.

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