A rich coastal ecosystem dating back 125,000 years discovered beneath the Ariane 6 launch site in French Guiana

[Press Release] - Published on March 26, 2024 in Press Room, Science and Society

An international consortium of paleontologists, geologists, and biologists, coordinated by scientists from the Institute of Evolutionary Sciences in Montpellier (University of Montpellier/CNRS/IRD) and the University of French Guiana/Géosciences Montpellier, describes the discovery of fossil assemblages spanning the last 130,000 years beneath the Ariane 6 rocket launch site in Kourou, French Guiana. These coastal assemblages, rich in more than 270 animal, plant, and microorganism species, are the first to be uncovered in the equatorial Atlantic. They provide insight into the environmental and climatic conditions that prevailed in the region and its biota, both during a very warm period (the last interglacial, from 128,000 to 116,000 years ago) and the cold period that followed (the last glacial stage, from 100,000 to 15,000 years ago).

This finding, published in the Proceedings of the National Academy of Sciences of the United States of America, provides valuable insights into undisturbed tropical coastal ecosystems in the equatorial Atlantic and the potential long-term impact of climate change on species threatened with extinction.

A fossilized oyster dating back approximately 125,000 years, discovered near the Ariane 6 launch pad in Kourou, French Guiana, during the 2019 field campaign. (Credit: P.-O. Antoine)

French Guiana: A Research Hub with a Favorable Environment

Tens of thousands of fossils were unearthed on the grounds of the Guiana Space Center (CSG) between 2017 and 2021, thanks to a permit granted by CNES, the site’s owner. By pooling their expertise, paleontologists, geologists, and biologists were able, for the first time, to accurately reconstruct the past ecosystems of French Guiana. According to the authors, the findings provide a better understanding of the ecology and biogeography of tropical coastal ecosystems in the equatorial Atlantic prior to any human influence, as well as the potential long-term impact of ongoing climate change on current and endangered species. Indeed, climate fluctuations over the past 2.5 million years have led to radical changes in the distribution of organisms across the globe. In particular, the last interglacial period (128,000–116,000 years ago) was characterized by higher sea levels and warmer temperatures than today, making this period a plausible analog for the global conditions projected for 2100. However, nothing was known about the equatorial coastal flora and fauna of that period around the Atlantic until the discovery of fossil-bearing clays during construction work on the Ariane 6 launch site.

Some truly surprising discoveries

First, the scientists were able to characterize a coastal fossil assemblage dating back approximately 130,000 to 115,000 years. According to Pierre-Olivier Antoine (University of Montpellier) and Arnauld Heuret (University of French Guiana), who led this study, “the reconstructed marine and terrestrial fossil communities included more than 270 species, including foraminifera, mollusks, bony fish, bryozoans, decapods, sharks, and numerous plants. All fossil specimens identified at Kourou belong to extant species, some of which are now on the brink of extinction.” The results document a brief period of high sea level during the last interglacial, when the area was home to a mangrove ecosystem and shallow-water habitats, notably featuring highly diverse mollusk assemblages. According to Austin Hendy (Natural History Museum, Los Angeles), “this diversity shows that there were very strong affinities at the time between the coastal waters of the Caribbean and the Guianas, likely with less influence from the Amazonian megacurrents. ” After the ocean retreated approximately 110,000 years ago, linked to the global cooling of the last glacial period, “the plant fossils discovered at the site (pollen, phytoliths, and charcoal) suggest the existence of savannas and drier local conditions, with episodes of natural fires, until about 50,000 years ago,” explains Carina Hoorn (University of Amsterdam). Finally, Pierre-Olivier Antoine hopes “that this work will contribute to a better understanding of the major environmental upheavals the region could experience between now and 2100.”

This work was funded by the French National Research Agency (ANR) as part of the LabEx CEBA (ANR-10-LABX-25-01), through the Source, NeotroPhyl, Timespan, and Emergence, the GAARAnti project (ANR-17-CE31-0009), and a “Investments for the Future” project (ANR-18-MPGA-0006). The team also received funding from the Brazilian Council for Science and Technological Development (CNPq 304693/2021-9), the European Research Council (ERC 2019 StG 853394), the Australian Research Council (ARC DP220100195 and LE200100022). None of these discoveries would have been possible without the authorizations granted by the French National Center for Space Studies (CNES) or the logistical support provided by Eiffage and Sodexo.