WHY PROPOSE A GSSP FOR THE ANTHROPOCENE IN A FREEZE CORE FROM CRAWFORD LAKE, CANADA? (Invited Presentation)

In 2009, the International Subcommission on Quaternary Stratigraphy commissioned a working group to investigate whether the “Anthropocene” as introduced by Crutzen had geologic merit. Anthropocene Working Group (AWG) members scoured the literature and debated the existence of, and merits of various potential bases for, this possible new epoch. They recognized substantial transition driven by multiple factors including anthropogenic emissions of CO₂, an altered state likely to persist for at least 50,000 years. In May 2019, they voted in favor of working toward a GSSP to define an epoch with a mid-20^thC base, with the main shift in trajectory of the Earth System attributed to the Great Acceleration. With support from the Haus der Kulturen der Welt, twelve widely geographically distributed geological successions from various depositional settings were investigated as potential candidates to define an Anthropocene epoch/ series. All sites record a substantial globally synchronous shift during the 1950s, but in April 2023, a supermajority of AWG members selected the varved sediments of Crawford Lake as best representing the departure of conditions from Holocene norms, with the coincident rise in plutonium fallout from nuclear weapons testing as the primary chronostratigraphic marker. Key factors in that choice are the ease of correlation of ‘Anthropocene markers’ of atmospheric, hydrologic, and biologic change at annual resolution across the karstic basin and radionuclide activity clearly reflecting the Cold War in a meter-long succession with evidence of earlier local/ regional anthropogenic impact (including Indigenous agriculture). Other important considerations include ease of access to the lake in a protected conservation area and curation of the freeze core proposed as GSSP in a secure cryogenic facility at the Canadian Museum of Nature and its well-understood hydrologic/ depositional setting. Given the broad significance of the AWG findings for society, another attractive feature is the opportunity to communicate the evidence for a permanent planetary shift attributable to human agency via interpretive and educational programs in the conservation area and at museums. Irrespective of the final decision of the stratigraphic commissions, Crawford Lake stands as a key site to engage discourse, debate and evaluation of the effects of humans on our planet.