Saturday, May 18, 2024

Milton’s Crawford Lake chosen to define start of proposed Anthropocene epoch

An international group of researchers has selected Conservation Halton’s Crawford Lake in Milton, Ontario, as the site that could formally define the start of the Anthropocene, a proposed new epoch shaped by the significant global impacts of recent human activity.

On July 11, 2023, the Anthropocene Working Group (AWG) announced that out of 12 sites in consideration worldwide, Crawford Lake was voted to be the most suitable location for the proposed ‘golden spike,’ a global reference point in the Earth’s stratigraphic record indicating the start of a new geological unit of time.

Under the leadership of project Principal Investigators, Brock University Professors of Earth Sciences Francine McCarthy and Martin Head, and Earth Sciences Professor Tim Patterson from Carleton University, a multi-institutional team of experts, based mainly in Canada, has been studying well-preserved annually laminated sediment found on the bottom of this deep lake to uncover clear evidence of the ‘Great Acceleration,’ a period of intense resource use, population growth and environmental impact in the mid-20th century.

The AWG, which falls under the International Commission on Stratigraphy, has identified evidence of a tipping point in Earth systems at this period in history, with conditions very different from the Holocene Epoch that began nearly 12,000 years ago, at the end of the last ice age.

The AWG will present its proposal to the Subcommission on Quaternary Stratigraphy followed by the International Commission on Stratigraphy, suggesting that the Holocene Epoch has come to an end, and proposing the Crawfordian as the first age of the Anthropocene epoch. If the proposal receives a supermajority in votes by both bodies, and by the International Union for Geological Sciences, the Anthropocene will be ratified as the latest epoch and Crawford Lake will become one of more than 70 ‘golden spike’ sites recognized around the world to define boundary points in geological time.

McCarthy and Patterson, along with an interdisciplinary team of researchers from Queen’s University, the Canadian Museum of Nature, the Royal Ontario Museum, and other university and government institutions, led three sediment sampling projects at Crawford Lake between 2019 and 2023.

“Crawford Lake is a storyteller,” said Brad Howie, Indigenous Education Coordinator, Conservation Halton. “She collects information from our atmosphere, telling local and global stories of our past. What we know about the teaching village at Crawford Lake and the proposed Anthropocene comes directly from our special little lake, and we are so thankful for her.”

With well-preserved layers in the bottom of the lake that can be read like tree rings, laboratory analysis of the lake’s sediment cores revealed a mid-20th century “plutonium fallout signal” related to nuclear weapons testing that occurred in the Pacific Ocean from the 1950s through 1963, consistent with other samples collected worldwide. This plutonium signature coincides with the ‘Great Acceleration’ and is the primary marker proposed to identify the start of the Anthropocene epoch.

Additional biological and environmental indicators found in the cores, including microscopic diatoms and chrysophytes as well as chemical markers, show evidence of large-scale changes in Earth’s atmosphere and other systems since 1950, supporting the lake as the candidate site to define the start of the proposed Anthropocene. The scientific results were published in The Anthropocene Review (Volume 10, Issue 1, 2023).

“Crawford Lake is an exceptional site for scientific research,” said McCarthy. “The lake’s rare meromictic qualities prevent layers of water from mixing. In turn, the deep, cool, undisturbed waters above the lakebed help to preserve annually resolvable sediment deposits that we can carefully extract, using freeze-core methods, and analyze to pinpoint geological changes in time and history.”

Whether or not the Anthropocene is ratified as the official current epoch, sediment cores and research collections from Crawford Lake will be curated for scientific research in the permanent collections of the Canadian Museum of Nature and the Royal Ontario Museum to preserve this significant natural record of human impact and planetary change.

“If museum objects are stories, then the Crawford Lake sediment cores are epics — hundreds of years of geological change, written in earth and frozen in time. But they are also, more simply, a poignant reminder of humanity’s profound impact on our planet,” added Josh Basseches, Director and CEO, Royal Ontario Museum.

Conservation Halton acquired Crawford Lake in the 1960s, and the site has been contributing to local and international research efforts ever since then.


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