To most of us, water is water... and if we are being really technical we call it H₂O. But for a groundwater hydrologist, water can be divided into much more precise classifications. It can also be used to look into the past and the future, and even determine the temperature of the air at other times.

Ian Clark, a professor at the University of Ottawa, has studied the ebbs and flows of groundwater at several sites in the North. In arctic regions, the state of groundwater is closely tied to that of permafrost; and when frozen soil starts to melt, the groundwater is also affected.

Clark is looking at groundwater as yet another indicator of climate change. Along with another colleague, Professor Bernard Lauriol, he has been looking at what happened to groundwater 7,000 years ago during a time called the Holocene hypsithermal.

They have been investigating the paleohydrology of several sites in the Ogilvie Mountains as well as one near Inuvik. "We're looking at water systems as they flowed in the past. Then we can learn what the climate was like in the past and use that information as an analogue for the impacts of climate change in the future," says Clark.

As is often the case, learning about the distant past can help to predict the future. "During the hypsithermal it was about five to six degrees warmer than it is now, and that is about the temperature increase that is being predicted for the Arctic with climate change," says Clark.

How, one might well wonder, does one figure out ancient annual air temperatures from ancient water? The researchers have found one clue in delicate fingers of carbonate rock called calcretes, which Lauriol discovered in cracks within the permafrost.

The calcretes, which can be as thin as a hair or thicker than a finger, form in an environment that is saturated with water. Their growth is controlled by a type of bacteria that does not require light to survive, and the rate of growth rate is directly linked to temperature.

A rare isotope of oxygen, oxygen-18, provides the clue to the temperature. Rain falling in a warm climate holds more oxygen-18 than rain falling in cold regions, and this temperature difference can be tracked by measuring the isotope in the groundwater.

Clark describes this isotope as an analytical tool that can be used to trace the origins of water. It can even be used to determine from which elevation the water originally flowed.

By measuring the amount of oxygen-18 in the calcretes, scientists can determine how much of this isotope would have been present in the groundwater when the calcretes were formed. Taking it to the next step, they can figure out what the mean annual air temperature would have been at the time.

So what was the Arctic like when it was a much warmer place? The permafrost was buried much deeper in the ground, as much as several metres lower than it is today. That means more unfrozen soil near the surface, and more run-off from groundwater.

Research in the Mackenzie Delta has already established that the permafrost there is starting to thaw. Clark says that he and Lauriol have seen huge scars from melting permafrost when flying over the western Arctic.

Near Aklavik, on the eastern side of the Richardson Mountains, he describes seeing "rivers of mud coming out of the landscape as the permafrost melts back. It is impressive to see these landslides in permafrost terrain, and one cannot help but think that it is a consequence of modern global warming," he says.

Clark says that elders in Aklavik think that they can even taste the difference in the water of one creek that flows out of the Richardson Mountains. They say that the water of Big Fish Creek is not as salty as it was in the past.

Clark says this change in the water is the sort of effect that one would expect to see if the climate is warming. The melting permafrost would allow more groundwater to flow during the winter, which would help to dilute the salty water in the creek.

These changes in the water could also affect areas where char spawn and overwinter. "The groundwater is important for char habitat. It feeds into pools in the river that provide overwintering habitat. They also spawn in zones of groundwater discharge," he says.

Clark has been studying groundwater in the north for three to four years, and can track seasonal variations in the chemistry of the water. But he thinks that he needs up to a decade worth of data to track long-term trends, and help determine how Arctic warming will affect the flow of water in the North.

Ian Clark can be contacted at idclark@uottawa.ca.