The tube is 1.50 metres long and nine centimetres in diameter. It contains millennia-old deposits and sediments. Analysing them will reveal new knowledge about tropical forests, a natural heritage still shrouded in mystery. Researchers working on the TROPICOL project took the core samples near São Paulo inside the Colônia crater, in Brazil’s Atlantic rain forest, which is home to 6,000 endemic species, including 450 trees.
These natural archives lie in a 3.6-kilometre crater, probably from a meteorite impact, whose inner lake filled up with sediment during the Ice Age and Inter-Ice Age. “For 15 years,” IRD(1) research director and TROPICOL project manager Marie-Pierre Ledru said during the 7 June Climate Initiative conference, “this material has been studied to find out more about the history of the environment and the tropical forest. The first samples were taken seven metres deep in 2000.” Since TROPICOL started in 2017, scientists have managed to take two 50-metre core samples, and what they found prompted them to revise their working hypotheses.
“At first,” says Ms. Ledru, “we estimated the sediments to be 800,000 years old. Now we think they’re 1.5 million years old.”
For 15 years this material has been studied to find out more about the history of the environment and the tropical forest. The first samples were taken seven metres deep in 2000.
Dating technology has improved. Radiocarbon or carbon-14 dating is no longer enough for those time scales; processes such as luminescence on grains of quartz, paleomagnetism(2) and, especially, analysis of geochemical and biological indicators (pollen, micro-coal, algae and micro-algae) shed light on how the flora and fauna adapted to changes during the Ice Age and Inter-Ice Age in this particular area. “Our knowledge of temperate forests does not apply to tropical forests,” says Ms. Ledru. “Unlike the former, the latter have always been tropical, even during the Ice Ages; only the trees have changed, which might explain its extreme biodiversity.”
Political will can save the forest
That biodiversity is under threat from global warming and the expansion of intensive single-crop farming. How will Brazil’s tropical forest, nurtured by South American monsoons and polar fronts, cope with shrinking ice caps and the changes in the hydrological cycle that will be caused? Just 7% of Brazil’s original Atlantic forest is left, whose sediments, preserved by humidity, are a veritable scientific mine.
If the temperature rises by 4°C, 80% of the species in tropical forests will vanish.
It will take 70 to 100 years for the forest to grow back, depending on the area. Fragmentation due to rampant urbanisation makes that impossible for now. “If the temperature rises by 4°C,” warns Ms. Ledru, “80% of the species in tropical forests will vanish. But even without climate change, they’re doomed by deforestation. Tropical agro-business fragments and destroys the forest without allowing it to regenerate itself in the future.”
But a scientific, ecological and political effort could save the ecosystem. The famous Brazilian photographer Sebastião Salgado has shown it is possible by reforesting the areas around his parents’ property in only around 10 years. Ms. Ledru advises creating corridors between forest fragments that could help to rebuild the entire ecosystem. “The forest can be saved,” says the scientist, who is already campaigning to protect the Colônia site. “It’s survived 10,000 years of human intervention.” But political will, awareness raising and planning are vital. Otherwise, a scientific treasure and a natural heritage will be lost at the same time.
(1) – Institute of Research for Development
(2) – The study of records of the Earth’s magnetic field
Photos © Moises Saman | Magnum Photos