A stark warning: remnants of corals in Seychelles help sea level rise scientists predict the future
Andrea Dutton, a geochemist from the University of Florida and her team look for coral fossils in a promising limestone outcrop between imposing granite boulders (Andrea Dutton, University of Florida)
(Seychelles News Agency) - Forty out of the 115 islands of the Seychelles archipelago, located in the western part of the Indian Ocean, are formed from hard, reddish-grey granite rocks.
Indeed, these granitic islands in the Seychelles are believed to be the oldest ocean islands in the world, the crumbs left behind from the continental breakfast breakup of what was once the supercontinent of Gondwana before the Indian subcontinent was pushed away from the Mascarene plateau by the expanding ocean floor 66 million years ago.
The rock formation similar to an ascending flight of stairs, at Port Launay in the north-west of the archipelago’s main island of Mahé known among local inhabitants as ‘ros leskalye’ (rock steps), might lead an idle mind to wonder if the stairs were designed by the forces of Nature to lure an absent-minded observer directly into the abyss of the ocean.
Other fascinating granite formations of the Seychelles includes a majestic giant granite boulder at l’Union Estate, La Digue, the third most populated island of the Seychelles.
Having been formed millions of years ago, these massive boulders are edifices scarred by a diverse number of geological events including, according to a geochemist from the University of Florida in the United States, the evidence of the last time the earth experienced an interglacial period.
|Geochemist Andrea Dutton stands on a beach in the Seychelles - according to her research, sea levels here were almost twice the height of her survey stick in the last interglacial period over 125,000 years ago. (Andrea Dutton, University of Florida) Photo license: CC-BY|
Andrea Dutton’s research has caused a sensation among the scientific community and in the media – her evidence suggests that 125,000 the earth’s sea levels suddenly rose to a massive 7.5 metres above current levels after a glacial ice sheet in Antarctica collapsed. And she warns that history could repeat itself sooner than we might think.
“At present our data suggests that [at that time] the sea level rose from somewhere below present to nearly 6 metres above [current] sea level in less than one thousand years, but then rose slowly to its peak of 7.5 metres over several thousand years,” says Dutton in an e-mail to SNA.
Dutton’s came to this conclusion after studying fossil corals or white outcrops of limestone, found in protected overhangs of the granite boulders located between 0 to 9 meters above the present sea level. If not covered with algae, fossilised corals are often easily recognized for their white colour.
“The Seychelles is one of the best places on the planet to conduct such a study because the sea-level change in the Seychelles is almost the same as the global average sea level position, which is what we are trying to reconstruct,” says Dutton.
“Most people do not realize that sea-level change, both today as well as in the past, is geographically variable. What this means is that even if the global average sea level is rising, in some places the sea level will rise faster than in others and in some places sea level will even be falling, so we need to be careful to choose a site that will give us a sea level record that is very close to the global average sea level signal.”
|Dutton's colleague, Dan Zwartz of the Victoria University of Wellington, examines a huge limestone outcrop containing fossil corals in Seychelles (Andrea Dutton, University of Florida) Photo license: CC-BY|
Using the past to predict the future
The findings of the research which has been published in the Quaternary Science Reviews are expected to shed light on what to expect should the ice sheets trapped in the Greenland and Antarctic starts to melt, which is usually at regular cycles of around 10,000 years between ice ages.
The last time such an event occurs Dutton says the temperature at the poles was only ‘slightly warmer’ than they are at present.
So just how much would the temperature have to rise before it is likely that a large ice sheet collapses?
“We do not know at this stage how gradual or sudden that initial rise in sea level was,” said the researcher, adding that they expect however, “some lag time for the ice sheets to respond”.
It is predicted that a domino effect of an ice meltdown will be a rise in sea level which will subsequently cause many low-lying areas to be submerged under water.
According to the 2014 assessment report by the United Nations' Intergovernmental Panel on Climate Change (IPCC), the world’s sea levels are predicted to rise 30 to 90 centimetres by 2100.
In Seychelles’ case, should the seas rise to these levels once again, this may result in the loss of up to 70 percent of land masses - especially in coastal areas where many of the 90,000 people reside and on coralline islands, which are barely a metre or two above sea level.
Hunting precious relics
Often mistaken by locals during their research for treasure hunters, searching for the fabled remnants of ancient pirate gold, Dutton and her team had to crawl though gaps between huge boulders to find their own version of gold - information-rich coral fossil samples.
Using the samples collected in the sunny archipelago, her research determined the speed at which coastlines became submerged during the last ice melt incident.
“We are using a combination of evidence, including looking at the combination of coral species and other fossils to determine the pale depth at which they grew, as well as the carbonate cements that fill the pore spaces in the reef limestone, and also a technique to date the time at which the corals grew. This dating technique is how we are able to 'tell time' in the past,” explained Dutton.
But for this American researcher, it wasn’t only the stunning scenery that she enjoyed about her time in the Seychelles.
“The best thing about being there was to meet all the people who were so welcoming and willing to help us with our expedition and also very eager to learn about these wonderful fossil corals that can tell us so much about how Earth responds to climate change through time,” she said, adding a special vote of thanks to PetroSeychelles, the Seychelles National Parks Authority, the Ministry of Environment and Energy, and the Seychelles Bureau of Standards for facilitating the fieldwork.
“We would love to come back and do more research there. Our work has raised a lot of new questions for us that we hope to return to study and answer one day,” she concluded.