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Origin of mysterious giant ‘gravity hole’ in Indian Ocean unravelled

Sea level can be over 100 meters lower than global average in this section of Indian Ocean

Vishwam Sankaran
Friday 30 June 2023 11:48 BST
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A vast section of the Indian Ocean seafloor strangely sinks into a depression as there is less mass under this region on Earth, according to a new study.

While previous research suggested many theories for why this region has a much lower depth than the global average sea level, proving the theories has been difficult, say scientists from the Indian Institute of Science in Bangalore.

A new study, published in the journal Geophysical Research Letters on Thursday, found that this giant “hole” in the Indian Ocean is due to the Earth’s gravity being very low in this region.

In the study, scientists ran computer simulations to trace the origin of the “gravity hole” by reconstructing the last 140 million years of plate tectonic movements.

Since the Earth is not a perfect sphere and is bulged towards the equator, the planet’s gravity is not even across its geographical regions.

In addition, scientists have also found that different regions on Earth exert different gravity depending on the mass of crust, mantle, and core layers beneath them.

The new research assessed the origin of the low gravity anomaly found in a large section of over three million square kilometers in the Indian Ocean seafloor, which is located about 1,200km southwest of India’s southern tip.

In this region, the sea level has been found to be over 106m lower than the global average.

Researchers found in the new study that some sections of tectonic plates have sunk through the mantle under Africa.

Counteracting this depression, they say plumes of lesser dense, and hot mantle are springing up from under the Indian Ocean.

“Here we assimilate plate reconstruction in global mantle convection models starting from 140 Ma and show that sinking Tethyan slabs perturbed the African Large Low Shear Velocity province and generated plumes beneath the Indian Ocean, which led to the formation of this negative geoid anomaly,” the scientists wrote in the study.

The computer simulation could also predict that the tectonic plates below Africa reached the lower mantle nearly 30 million years ago, and the counteracting mantle plume began rising under the Indian Ocean about 20 million years ago, leading to this section of the planet becoming the lightest.

Scientists predict that this anomaly is likely to last for many more millions of years and may stop once the mantle material flows cease.

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