(University of Sydney) In the remote waters of the Indian Ocean, west of Perth, scientists have just discovered two sunken islands, almost the size of Tasmania, which were once part of the supercontinent Gondwana.
“The data collected on the voyage could significantly change our understanding of the way in which India, Australia and Antarctica broke off from Gondwana,” said Dr Joanne Whittaker, a postdoctoral fellow at the University of Sydney’s School of Geosciences.
Researchers from the University of Sydney, Macquarie University and the University of Tasmania led an international team of scientists on the voyage to map the seafloor of the Perth Abyssal Plain. The expedition returned to Perth last week after a three-week cruise.
Traveling on the CSIRO vessel Southern Surveyor the scientists discovered the islands through detailed seafloor mapping and by dredging rock samples from the steep slopes of the two islands, now in water depths of over 1.5km.
“The sunken islands charted during the expedition have flat tops, which indicates they were once at sea level before being gradually submerged,” said Dr Whittaker.
Collecting rocks from the abyss more than 1.5km below the surface was not easy, but the geologists managed to retrieve hundreds of kilograms and unexpectedly found rocks that showed the islands had not always been underwater.
The University of Sydney’s Dr Simon Williams, the chief scientist on the expedition said: “We expected to see common oceanic rocks such as basalt in the dredge, but were surprised to see continental rocks such as granite, gneiss and sandstone containing fossils.”
In the Cretaceous period when dinosaurs roamed the Earth (more than 130 million years ago), India was adjacent to Western Australia. When India began to break away from Australia, the islands formed part of the last link between the two continents.
Eventually these islands, referred to as ‘micro-continents’ by scientists, were separated from both landmasses and stranded in the Indian Ocean, thousands of kilometres from the Australian and Indian coasts.
Dr Williams commented: “A detailed analysis of the rocks dredged up during the voyage will tell us about their age and how they fit into the Gondwana jigsaw.”
Sophisticated instruments were put to use…
Helping the scientists to acquire this data was the suite of Kongsberg Maritime hydroacoustic sensors and systems aboard the RV Southern Surveyor, which included:
- Simrad EK60 scientific echo sounder
- Simrad EK500 scientific echo sounder
- KONGSBERG EA 500 hydrographic echo sounder
- KONGSBERG EM 300 multibeam hydrographic echo sounder
- KONGSBERG PS 018 Sub-bottom profiler
Travelling on RV Southern Surveyor the scientists discovered the islands through detailed seafloor mapping using the EM 300 multibeam system and by the challenging collection of rocks from the abyss more than 1.5 km below the surface.
What is a multibeam hydrographic echo sounder you ask? Check out this video from Kongsberg…