Coral reefs growing along the Lakshadweep islands and Maldives could offer some key answers to the Indian summer monsoon variabilities that occurred in the recent centuries.
As like tree rings used commonly to determine the information on the past climate, bands growing on the coral surface reveal about the paleoclimatic conditions, rainfall, ambient water temperatures and similar aspects from the past.
A recent study from Pune-based Indian Institute of Tropical Meteorology (IITM) has stated that corals found in the North Indian Ocean had potential to provide new insights into the onset and withdrawal of the Indian monsoon until a few hundred years ago.
Sea Surface Temperature (SST) is one of the many vital factors that governs the Indian monsoon. In this sense, SST regulates the moisture production in the sea and affects the wind circulation pattern causing rainfall during the monsoon season.
Scientists say that in most oceans around the world, the salinity of the sea water increases with an increase in SST. That is, warmer conditions lead to a higher rate of evaporation of seawater, thus leaving behind larger concentrations of salt in the sea. This is commonly observed during summers. But, in case of waters over the North Indian Ocean, especially in the Lakshadweep Sea, there was a departure in this trend.
“Soon after the monsoon onset in June, the sea begins to automatically cool. This cooling was a coupled effect of the monsoon circulation and the supply of low saline water flowing from the Bay of Bengal into the southeastern regions of the Arabian Sea,” said Supriyo Chakraborty, senior IITM scientist whose work was recently published in Current Science.
Due to these characteristic features, corals growing in the Lakshadweep regions enjoy favourable conditions in order to record the sea surface conditions better than their counterparts growing in the Andaman islands region, he said.
Researchers also made use of oxygen isotope measurements, which indicate the extent of bleaching experienced by corals due to environmental stress.
Normally, corals live anywhere between 300 to 400 years, and the bands growing on their surface suggest their lifespan.
Some earlier studies on the coral band width had traced links to the rainfall recorded over the Western Ghats.
Climate change is posing a serious threat to the survival of corals, which are now considered endangered species.
“Without any corrective measures, acidification of the ocean surface could push the corals to eventually get dissolved in the seawater over a period of time,” Chakraborty said.