Next month, if the ice is thick enough, Carleton University environmental geologist Tim Patterson plans to return to Crawford Lake with his research team to extract another “freeze core” from the lakebed.
The lower reaches of this small, steep-sided, deep lake — located in a conservation area just west of Toronto — are chemically distinct and permanently isolated from the waters above, making it inhospitable to most organisms. The sediments at the bottom thus remain undisturbed, with distinct layers deposited annually.
So when Patterson pushes a flat-faced metal rod filled with a slurry of dry ice and alcohol into the lakebed, the sediment that freezes to it provides a perfectly preserved tree-ring-like record of industrial emissions, radioactive elements and other chemical signals released into the atmosphere over the years.
Carleton University environmental geologist Tim Patterson (Photo: Luther Caverly)
After being winched out of the lake, these core samples, up to two metres tall and 15 centimetres wide, are analyzed by Patterson and his students in their lab at Carleton, as well as by a large team of national and international collaborators, including Indigenous partners.
The data they come up with is a key part of the campaign to have Crawford Lake declared the “golden spike” for the Anthropocene — ground zero for the start of a new geological epoch, circa 1950, in which unprecedented human activity has had a significant impact on the planet’s climate and biosphere.
“This is a tremendous opportunity to show people how sensitive our world is to human activity,” says Patterson, who also does freeze core field work to help monitor and safeguard the environmental health of lakes in northern Canada.
“As environmental earth scientists, we’re mostly interested in things that leave a permanent geological record. Crawford Lake archives the key indicators proposed to mark the beginning of the Anthropocene: plutonium isotope peaks associated with nuclear weapons testing, fly ash produced by high-temperature combustion of fossil fuels, and major ecological changes.
“The concept of the Anthropocene has captured the imagination of both the general public and the scientific community. It would be a great honour to have the golden spike here in Canada.”