Fish ear bones help detect sea temperature: IISc

BENGALURU: After undertaking a successful study of estimating seawater temperature of the Atlantic Ocean, researchers from the Indian Institute of Science (IISc) are now keen on stretching their study to the Indian Ocean and the Arabian Sea.

The researchers from Centre for Earth Sciences, IISc, have found a way to estimate ancient seawater temperature and the rise in temperatures by probing the bones in the ears of the fish (otoliths).  Five fish species were assessed for the study, including Atlantic Cord, Black drum and Snapper. These are common fish and are known to stay in temperatures varying from 2-25 degrees Celsius. “With this, we are keen to do the same study in the oceans and seas in the Indian sub-continent with local fish species,” Ramananda Chakrabarthi, Associate Professor, CES, IISc, told TNIE.

“When you go back in time, you do not have any fossilised seawater. Like corals, otoliths are made of calcium carbonate and grow throughout a fish’s lifetime by accumulating minerals from seawater. Similar to tree rings, these otoliths also hold clues to the fish’s age, migration patterns and the type of water that the fish lived in. In the current study, we have discovered fossilised otolith samples dating as far back as the Jurassic period,” he said.

Organisms that live in the ocean are extremely sensitive to temperatures. A two-degrees temperature rise could lead to extinction of several species. In addition, because the atmosphere and the ocean are on talking terms, a lot of carbon dioxide in the atmosphere eventually dissolves into the ocean and this ability is also linked to seawater temperature – the lower the temperature, the more carbon dioxide is trapped.

Just like a carbonated drink that loses its fizz as it warms up, the ocean loses its ability to hold carbon dioxide as it gets warmer, he explained.  With the close correlation of calcium isotope ratios and temperatures, researchers are now confident that their approach can now be used on fossilised samples. Mapping early seawater temperature is important to better understand Earth’s history, they said. “What happened back in time is key to our understanding of what will happen in the future,” Chakrabarti said.