A new study led by UCL researchers has found that pollutants from burning fossil fuels have been detected in corals, giving scientists a potential new tool to track pollution history for the first time.

A study published in the journal Total Environmental Sciencedetected carbon particles released by fossil fuel burning embedded in corals in Illa Grossa Bay, near the Columbretes Islands in the Mediterranean. The discovery of this type of pollution, known as fly ash or spherical carbon particles (SCP), contaminating natural sediments, is seen as an indicator of the existence of human impact on the environment and a historical sign of the beginning of the so-called Anthropocene epoch.

Corals are a natural archive widely used to study paleoclimate because their growth rates can be measured. Like tree rings, their long lifespan and slow, steady growth can provide scientists with annual, monthly, and even weekly ecological data for many years.

So far they have mostly been used to measure past climate conditions such as water temperature and chemical composition, but this is the first time contaminant particles other than microplastics have been extracted from corals.

Lead author Dr Lucy Roberts (UCL Geography) said: “The discovery of these contaminants embedded in coral skeletons takes decades and paints a clear picture of just how huge the human impact is on the environment. This is the first time we have seen this type of contamination in corals and its occurrence in sediments.” “consistent with the historical burning rate of fossil fuels in the region.”

Corals, small invertebrates that typically live in large colonies, absorb SCP pollutants from surrounding waters, including when they grow calcium carbonate skeletons. Researchers from the Instituto de Acuicultura de Torre de la Sal (IATS-CSIC) collected coral samples from several locations along the reef off the coast of Castello, Spain. Cladocora caespitosa, a species of coral, has been studied and observed here for two decades, and the site is considered a global observatory of change.

The corals are located almost 60 kilometers from shore and within a protected marine reserve, minimizing the possibility of local pollution. This species is the only Mediterranean coral capable of forming large reefs and is known to grow at an average rate of 0.3 centimeters per year.

On arrival at the UCL laboratory, the corals were dissolved in acid and all contaminant particles remained within the skeleton. The team first counted all the SCPs in the remains under a microscope. The samples were then examined under an electron microscope and analyzed using X-rays to look for chemical traces of SCP contamination indicative of coal- or oil-fired power plants.

The team found that corals showed a significant increase in SCP contamination between 1969 and 1992. This coincides with a period when Europe was rapidly industrializing and coal consumption in the country increased significantly.

These results are consistent with other SCP pollution measurements from mountain lakes in Spain, supporting the idea that corals can serve as natural archives for measuring changing pollution levels over many years. The findings come as scientists seek tools to mark the beginning of the Anthropocene epoch, a unit of geological time used to describe the final period in Earth history in which human activity became the dominant influence on the planet’s climate and environment. .

Some scientists advocate the use of SCPs as a marker for the beginning of the Anthropocene, and their discoveries in coral skeletons support this argument. They have already been found in lake and sea sediments, ice cores and peat layers.

Dr Roberts said: “As it becomes clear that humans are altering the natural environment at unprecedented levels, these pollutants act as indelible markers marking the beginning of the Anthropocene era. This is important for researchers seeking to better understand the history of human life and its impact on the natural world and the magnitude of human impact on the environment.” It serves as a powerful reminder.”

This research was carried out by UCL in collaboration with the Instituto de Acuicultura de Torre de la Sal, Spain and the University of Leicester.