It turns out you can learn a lot from lake mud. John Smol, one of Canada’s preeminent climate scientists, has, by and large, built his career on the stuff.

“Lake sediment is an archive of environmental change,” he says from his office at Queen’s University in Kingston, Ontario, where he serves as a biology professor and co-head of the Paleoecological Environmental Assessment and Research Laboratory, or PEARL. “It’s kind of surprising what’s preserved and how well it’s preserved and what we can actually do with lake sediments. Basically, the deeper you go the older it is, and we can go back thousands of years.”

Much of Smol’s work has touched on the Arctic – a region that he’s regularly visited for the past three decades. Beyond the Canadian Arctic, his research has also taken him to Alaska, Greenland, Iceland, northern Russia and Finland.

Some of the Arctic lakes that Smol has studied no longer exist. These shallow lakes have dried up in recent years as the region warms. Other Arctic lakes have grown in size as the permafrost surrounding them thaws, while still others have drained, as disappearing permafrost creates an effect “like pulling a plug in a bathtub,” Smol said. Elsewhere, Arctic fish are dying as lakes stratify, depriving the lake bottoms of oxygen.

Smol has received a long list of accolades for his research. He’s received the Order of Canada, the country’s highest civilian honor. The Royal Canadian Geographical Society named him one of Canada’s greatest explorers. And he’s the first scientist to receive three medals from the Royal Society of Canada.

Arctic Deeply recently spoke with Smol about some takeaways from his Arctic research.

Arctic Deeply: What can you learn from lake mud?

John Smol: We’re biologists, and virtually everything living in that lake is leaving some sort of record in the lake sediments, and this is primarily what we call morphological fossils. It’s like archaeology, except through a microscope.

Or things like blue-green algae, for example, don’t leave good fossils typically morphological, but they leave fossil pigments that are quite specific to that group. And now there’s this whole field of ancient DNA as well in sediments. So it’s quite surprising, you can actually reconstruct a lot of what lived in the lake. And if you know what lived in the lake, you know a lot about the lake.

One of the main things we look at are algae called diatoms. There are thousands of species but some only live in acidic water, some only live in alkaline waters, some only live in circumneutral waters. We basically make paleo pH meters. … If you’ve got 10 percent of this and 5 percent that and 6 percent of this and 20 percent of this, then the pH was about 6.2.

You can show how a lake acidified. But you can do that with nutrients, you can do that with salinity, you can do that with lots of things.

Arctic Deeply: What are some of the big changes underway in Arctic lakes?

Smol: A big thing is ice cover, which greatly influences the amount of light entering the lake. Also, it influences how much of the lake mixes with wind and affects nutrients and all sorts of things. Remember, diatoms are photosynthetic, they need light. When it’s cold you have extensive ice, so the only thing that can live well are things that can only live in very shallow water, because the lakes open with this moat [around the ice].

When it gets really warm the whole lake is available and it’s a totally different lake if there’s no ice than if it’s full of ice. Diatoms have a life-cycle that’s always 24 hours, so species change very quickly. You almost have a paleo ice meter.

Also, if global warming continues, these shallow lakes are going to dry up. Before, they were frozen for a large part of the year; now they’re open weeks longer, and even though we can show with the paleo data they’ve been permanent water bodies for thousands of years, they’ve dried up now.

Arctic Deeply: That’s a great example of how lakes are changing because of climate change in the North. Are there other examples that we should be highlighting?

Smol: Some Arctic lakes, that before we’d say are never warm enough to stratify, now are stratifying, and that changes a lot of things. One of the reasons we went to one of these lakes [south of Hudson Bay] is they’ve had big fish kills. The main thing is they’re getting thermal stress now with the changes in temperature. Of course the native peoples depend on some of these fish for protein and food.

Arctic Deeply: Why should people who live in southern climates be concerned about these changes?

Smol: Because what happens in the Arctic affects us all, that’s the simple answer.

Let’s start off by Canadian perspective. We should care because depending how you define it, about half of Canada’s land mass and two-thirds of its coastline is Arctic, so we have stewardship over a massive piece of real estate that we’re responsible for. And people do live up there; they’re on the front line of climate change and other things like contaminate transport. That’s a moral issue, let’s say, or that’s an issue we have stewardship over a very large part of the Arctic.

But what happens in the Arctic affects us all, and what happens in the Arctic – well, let’s just talk about melting ice caps and stuff, even changing sea ice coverage affects weather patterns – it affects everyone.

And it’s also a bellwether of what’s about to happen in the south. One of the reasons we go to the Arctic is because it’s the most sensitive to environmental change and the first to show signs of environmental change. What happens there is kind of a harbinger of what’s going to be happening down south.