Mackenzie River no relation impact event
Mainstream explanation
The most widely accepted is that it began because of a significant reduction or shutdown of the North Atlantic "Conveyor" – which circulates warm tropical waters northward – as the consequence of deglaciation in North America. Geological evidence for such an event is not fully secure, but recent work has identified a pathway along the Mackenzie River that would have spilled fresh water from Lake Agassiz into the Arctic and thence into the Atlantic. The global climate would then have become locked into the new state until freezing removed the fresh water "lid" from the North Atlantic.
no relation