Climate Detectives

More than 11,000 years of southwest Yukon’s climate history is preserved in a slender column of layered sand, clay, mud and organic debris that resides in a walk-in fridge in the university’s geography building on St. George Street.

The 2.8-metre-long core’s original home was beneath the bottom of Kusawa Lake, which stretches north and south for more than 70 kilometres southwest of Whitehorse. The size of the drainage basin (4,300 square kilometres) and maximum depth (135 metres) of the lake’s southern half make it an outstanding natural lab for reconstructing the past climate from the lake-bottom sediments.

Nicole Chow, 24, and Krish Chakraborty, 23, are the paleodetectives decoding the clues from the 2.8-metre core. It is one of 11 cores that Chow (BSc 2007 St. Mike’s) helped extract from Kusawa in 2006. Chakraborty (BSc 2007 Woodsworth, MSc 2008) has recorded the populations of diatoms – microscopic algae that leave behind distinctive glassy skeletons – in the core’s many layers. The relative abundance of diatoms is a tipoff to whether the ambient conditions were warm or cool.

Using all 11 cores, Chow, who is working on her MSc in geography, is investigating the quantity and composition of sediment. The sand layers deposited by fl ood waters can signal the melting of a warmer period. Already the two researchers have discovered that the climate in the southwest Yukon underwent swings spanning several thousand years starting 11,000 years ago. They don’t know exact temperatures, but can surmise the lake’s conditions. “[Our research] says more about the biology of the lake as opposed to exact temperature reconstruction,” notes Chakraborty.

The two researchers hope that by showing how the physical and biological nature of a big northern lake changed during large natural climate swings, they will help scientists get a better handle on the effects of human-induced climate change in the coming decades.