Under-sea study will help India

Prattipati Shivshankar Rao is the first Indian scientist to sail the seabed of the mid-Atlantic ridge. His search for hydrothermal fields and vents -- also known as deep-sea geysers -- took him on an unusual voyage aboard a former us Navy submersible, Atlantis. Rao spoke to Frederick Noronha about his thrilling experience

Published: Wednesday 31 December 1997

On the process of being selected to the mission:
Peter Rona of the department of geology and geophysics at the Rutgers Institute of Coastal and Marine Science, usa , came to the National Institute of Oceanography (nio), Goa, in October 1996, for an international symposium on the Indian Ocean. He made a presentation on the hydro-thermal mineralisation of global oceans, and specifically of the Indian Ocean. On that occasion, we presented some of our findings on the Andamans basin, where we had started work two years earlier. He visited our geological oceanography department and held discussions with the staff. Some of my colleagues were working on a programme on the Karlberg ridge, in the North Indian Ocean, located in the middle of the Arabian Sea.Rona, who had been conducting scientific explorations in the mid-Atlantic ridge and the back-arc basins of the Pacific, proposed that we could compare our results to see whether these ridges are similar. That was the beginning of the collaboration.

On the preparations for the exploration:
I thought it was a great opportunity for Indian oceanographers who had never been on submersibles to explore the sea-bed. Until now, they have been only sampling or undertaking remote-sensing. As such, there was no special training to undertake this voyage. I was only briefed by the pilot for about two hours a week before the dive. The brie-fing was mainly on how to handle the equipment. In such dives, observers are expected to assist the pilot, if needed. All scientific operations to be executed during the dive were finalised before the dive. Our scientific contingent came from nine countries including the us , the uk , Portugal, Russia, Italy, Panama, Colombia and India. I was covering the geology aspect of the cruise.

On the journey to the seabed:
The cruise began on July 5 from Ponta Delgada in the Azores Islands off Portugal and ended at Barbados, West Indies, on July 30. We travelled about 2,000 kilometres on the mid-Atlantic ridge - where there are eight hydrothermal fields - and collected various samples. The main contingent was from the Rutgers University, usa , which planned the cruise with the support of the National Science Foundation of the us. In all, we undertook about 18 dives during the cruise.

On temperatures under sea:
We were in the middle-latitudes, mainly the tropical areas. On surface waters, it's about 20 c. But deep into the sea and close to the sea-bed, the ambient temperature is about two degrees. In spite of the temperature-control mechanism in the submersible, temperatures do drop.

On touching the ocean floor:
'Atlantis' was the mother-ship. Deep Submergence Vehicle Alvin, which went all the way down to the sea-bed, is about seven metres long and has a two metre titanium sphere inside - the pressure chamber, where scientists and the pilot sit. The pressure chamber is an air and water-tight sphere. There is place for only three persons - a pilot and two scientific observers. Our mission there was to go down to the bottom of the sea-bed and work for about nine to 10 hours. Only the chief scientists participate in most of the dives. When the submersible was going down, we were in pitch darkness in the water column. When we were close to the sea-bed, the pilot switched on the lights. Slowly we saw a very hazy image of the sea-bed. And all of a sudden, we were there.

At that moment one gets the feeling that the sea-bed is rising, and not that the submersible is going down. It was really a thrilling experience. The sea-bed's depth varied between 3640-3680 metres. The pressures would have been about 400 bars - which is about four hundred times the atmospheric pressure. One could see solutions coming out of the hydrothermal vents. Solutions, which were black in colour, were coming out from the ocean vents. That's why they are called black-smokers. In some places, there are also white smokers.

On whether there were any difficulties while undertaking this mission:
There were no major difficulties. On the contrary in one hydrothermal field, there was a French vessel, and a European Commission-sponsored cruise. Our chief scientist invited them to come on board and we exchanged notes about under-sea exploration.

On the scientific relevance of these explorations to India:
Hydro-thermal systems contribute to ocean chemistry in a significant way. Solutions coming out of these hydro-thermal vents contain a great deal of metal elements. They are very hot. These solutions have a significant control over the ocean chemistry and thermal budget - the heat budget of the ocean. Secondly, we are also studying the process of how the ore minerals are formed.

Even in central India there are some ancient sulphide deposits. But we can study these only by indirect means. These explorations help us to understand as to how they have been formed. One also sees the lithology and entire geology of the region and find out the scientific activity there. But on the sea-bed one is studying the minerals formation itself - just as it is forming. By understanding this, we can know how these ancient deposits - which are being mined on land - were formed. One also gets insights as to where to look for them.

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