In a major step towards formal recognition of the Anthropocene as a new stage in Earth System history, scientists have identified a small lake near Toronto as the best marker of epochal change. The announcement was made at news conferences in Germany and Italy on July 11.
Tiny Crawford Lake covers just 2.4 hectares (6 acres) in a legally protected conservation area close to the city of Milton. Unusually, it is meromictic — composed of layers of water that do not intermix. As a result, centuries of sinking materials have formed sharply defined layers of sediment — comparable to tree rings — a precise, year-by-year record of local, regional and global environment change.
Previous studies of Crawford sediments obtained detailed information about Indigenous communities that farmed maize (corn) near the lake 600 years ago, and about the environmental impacts of later land clearing and logging by European colonists.
Frozen cores pulled from the lake bottom since 2019 (see video below) also show distinct layers that have formed since the middle of the 20th century. A multidisciplinary scientific team that calls itself “Team Crawford” has found carbon particles from high energy power production, plutonium-239 from nuclear bomb tests, nitrates from massive application of chemical fertilisers, and other recent pollutants including indicators of decades of acid rain. None of that existed until well after World War II: the layers mark a clear division between the end of the Holocene epoch and the beginning of the Anthropocene.
Interviewed by The Washington Post, British geologist Colin N Waters, chair of the Anthropocene Working Group (AWG), called the division is “a very precise geochemical boundary that is present across the planet, across all environments”. To ensure that future scientists can study the evidence, a frozen sediment core from Crawford Lake is stored in the Canadian Museum of Nature’s National Biodiversity Cryobank.
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Crawford Lake was one of 12 locations submitted by Earth System scientists around the world for consideration by the Anthropocene Working Group as a possible Global boundary Stratotype Section and Point (GSSP), colloquially known as a “golden spike”. As AWG Chair Colin Waters and colleagues wrote recently, the sites were not only all strong GSSP candidates, they clearly showed that a new global epoch began in the mid-20th century.
“All sites examined, from widely varying and globally distributed environments, include or delimit an interval that may be clearly referred to the Anthropocene … usually on the basis of multiple stratigraphic signals. This analytical exercise has hence emphasised the stratigraphic reality of the Anthropocene, as well as providing the factual basis for formal definition.
Most of the site teams identified the presence of plutonium as the primary indicator of the beginning of the Anthropocene.
It took three rounds of voting, which shows how closely matched the candidates were, but the AWG finally selected Crawford Lake as the location that best represents the start of the Anthropocene epoch.
Francine McCarthy, a geologist at nearby Brock University and member of the AWG told The Guardian that there is now “compelling evidence globally of a massive shift, a tipping point, in the Earth’s system. Crawford Lake is so special because it allows us to see at annual resolution the changes in Earth history”.
Despite the strong evidence collected by the AWG, official acceptance of the Anthropocene as a new epoch in the Geological Time Scale is far from certain. It must obtain 60% approval from two other geological committees, and then be approved by the large and conservative International Union of Geological Sciences (IUGS), which will probably vote on it at the next International Geological Congress, in South Korea in August 2024.
Some prominent IUGS members argue that it is too soon to formalise a new epoch — alternative suggestions include defining the Anthropocene as an Age in the ongoing Holocene epoch, or just labelling it as a loosely-defined geological event.
Stay tuned for more debate.
[Reprinted from climateandcapitalism.com. Ian Angus is the editor of Climate & Capitalism and the author of Facing the Anthropocene: Fossil Capitalism and the Crisis of the Earth System.]