How did you end up focused on Lake Superior?

About 15 years ago, the the University of Minnesota Duluth's Large Lakes Observatory (LLO) was looking for two faculty members; specifically, a physicist and a chemist. My wife’s background is in chemical oceanography, and mine is physical oceanography – we both did our PhDs at MIT and the Woods Hole Oceanographic Institution. LLO has a strong reputation, even in the oceanographic community- we applied, and we got the jobs. While the bulk of my work is on Superior, I’ve also participated in work on many other large lakes – Tahoe, Crater, Michigan, even Lake Malawi, a deep rift lake in eastern Africa. Superior is a great base of operations because it is one of the world’s most recognizable lakes, but remarkably little is known about it, at least in proportion to its size and importance.

 

What’s special about the lake to you?

The lake fits in a really interesting niche between small lakes and oceans. A fair amount of effort goes into studying smaller lakes – they’re a lot more approachable. And tremendous amounts of resources go into studying the world oceans- as they should, given their importance to commerce, as a source of food, and as an important part of the climate system. Superior provides a wide range of interesting behaviors – it’s really a small sea, rather than a large lake- but on a somewhat more manageable scale.

 

How can lakes give us a window into the past, and how far back can you look?

There are a couple ways of looking at this. One of the long-term specialties at LLO is a field called paleolimnology, basically using chemical signals in sediment cores brought up from the bottom of the lake to learn things about past climate. Lake sediments (the “floor” of the lake) act as recorders of climate, allowing us to look back tens or even hundreds of thousands of years. A few years ago, a group from LLO collected a core from Lake Tanganyika in East Africa that goes back something like 600 thousand years. Analysis of the sediment provides insight into various climate processes the same way we might use tree rings. One thing I’ve done in my lab is to identify long-term datasets that are collected for some unrelated reason and use them to learn about the past of the lake. Several years ago, I did an analysis of water temperature records kept at a power plant in Sault Ste Marie- daily water temperatures since 1906! It’s one of the longest continuous records of water temperature anywhere in the world. We used it to describe the warming of the lake over the last century.

How has this illuminated how we think about climate change?

I think the important thing that any long-term data provides (whether by proxy, like sediment cores or tree rings, or through direct measurement) is context and perspective. If you only had data from the last 30 years or so, it would be difficult to know whether the rapid changes we’re seeing in climate are unusual, or just par for the course. With thousands of years of pre-industrial data, we know that what we’re experiencing right now is unprecedented. Of course, we know this from other methods, such as computer modeling of the climate system. By placing our modern climate into a broader context, we have a better sense of the fact that we really are causing change right now.

 

What’s unique about studying climate change through Lake Superior?

I’ll broaden the question to large lakes in general. Lakes are great integrators of climate, and they are fixed on the landscape. They provide a clear picture of what is happening at a fixed point. The oceans are also responding to climate change, of course, but they’re far more complicated systems. Right now, one of the big focuses of research in the limnology community is developing a better understanding of the relationship between changes in the earth climate and the subsequent response of lakes. A recent study (I was one of something like 75 authors) showed that lakes across the globe are warming, but warming at different rates. Part of this is that the world atmosphere is not warming at a uniform rates- mid to high latitude and inland sites are warming faster than equatorial or coastal sites. But it also reflects that lakes are all different – different sizes, different depths. Maybe the wind blows more at one site than another. We’re trying to disentangle all of that now.

 

What is it about the lake that amplifies the effects of climate change?

In Lake Superior, winter conditions play a big role in determining what happens the following summer. We often refer to this as the lake having a “memory” of what’s happened in the past. If you have a warm winter with very little ice, the lake is preconditioned at the beginning of the summer and tends to be warmer. How warm the lake is in any given summer is a reflection, almost equally, of how warm of a summer you’re having and how warm of a winter you just experienced. That’s not necessarily true for smaller lakes, but for deep lakes like Superior it’s important.

 

With ice levels dropping we are seeing the intensity of storms increase and have direct impacts on Duluth with flooding and erosion on the south shore. What other kind of physical manifestations of the change can we expect to see?

There are lots of things going on all at the same time, which can make developing a solid understanding of what is going on difficult. Right now, the primary reason we’ve seen so much damage in Duluth the last three years is that water levels are so high – at near-record to record levels, depending on how you look at it. This is simply a reflection of the fact that the last few years have been rainier/snowier than usual. The extra several inches in the lake make the difference between a big storm and a big, damaging storm. The storms that have blown in the last three years (October 2017, 2018, and 2019) have been big storms, but not unprecedented. What made them particularly damaging was the water levels.

 

We know the lake is warming much faster than the air – why?

Our understanding of this is largely due to the “memory” effect I mentioned earlier. Winter conditions play an important role in preconditioning the lake for the subsequent summer. The exact details of the mechanism are still being hashed out – is it changes in ice cover, or changes in the heat stored in the lake in the winter that lead to this effect? Both appear to play some role.

 

Who do you think will be impacted the most as the lake changes?

There are a number of different levels on which to look at this. Loss of ice certainly has significant cultural and recreational impacts – ice fishing, tourism, etc. I think one of the big long-term effects of warmer conditions is going to be a large-scale restructuring of the ecosystem. Temperature is this master-control-knob for the lake ecosystem, effecting metabolisms, uptake rates, spawning, and a lot of other things outside my area of expertise. We are in the process of conducting a big experiment out there, whether we like it or not. It also makes the lake more hospitable to invasive species.

 

What do you wish everyone understood?

Climate change is real. It has effects globally but also locally. It can be difficult to communicate this, because the natural, year-to-year variability tends to be large compared to the climate change signal. How do you convince somebody that the fact that it's going to be a couple degrees warmer by mid-century is important when it’s 10F warmer today than yesterday, or after the harsh winter of 2014? My answer would be that Superior, for instance, is extremely sensitive to these long-term changes, and we are heading, within our lifetimes, towards an era where ice on the lake will be considered unusual.

 

How can people who love the lake help to take care of it?

Become educated and continue to educate yourself about the lake.

Stay in touch with Austin and his work on Facebook and Twitter @UMDbuoys.