September 22, 2021
Senior Research Scientist
National Oceanic and Atmospheric Administration,
Great Lakes Environmental Research Laboratory
Title: Shifting Lake Michigan: Shifting “Deep Water” Ecology Corroborates the Warming Trend of Future Climate Change
Introducer: Dennis Powers
Climate change is reaching all the way down to the depths of one of Earth’s largest lakes.
Water hundreds of feet below the surface of Lake Michigan is warming, especially in winter, according to a report published in mid-March by the National Oceanic and Atmospheric Administration. The warming could change the seasonal patterns of the lake – and alter a way of life for ecosystems and industry alike.
It’s been known that Lake Michigan surface temperatures are increasing and ice cover is lessening as human activity spurs climate change.
“These changes may seem very small, a couple tenths of a degree per decade, but this has been going on for several decades now, perhaps longer than is reflected in our monitoring,” says Craig Stow, the author of the study. The lakes have been changing, ever since they were formed, “but when they change fast it means humans have to adapt to the changes that occur. And if we don’t monitor for them, we run the risk of being caught by surprise.”
The first-of-its-kind look at deep water warming fills in another gap in climate change research, revealing what’s happening below Lake Michigan’s surface. The overall warming, ice loss and shrinking winters could lead to long-term shifts, altering the lake’s food web and sending fisheries toward uncharted territory. Some of the surfaces of the world’s largest lakes are warming faster than ocean and air temperatures. “We’ve known for a while now based on surface temperatures – not just in Lake Michigan but smaller lakes and large lakes worldwide – that the surface temperatures seem to be increasing,” Stow said. Lake Michigan surface temperatures are estimated to be warming at a rate of as much as a third to a fourth of a degree Celsius per decade.
But the story of what’s going on as far as 460 feet below the surface is sparse. Deep water understandings had previously relied on translating surface data or limited observations. So, starting in 1990, researchers turned to a string of thermometers floating vertically in southern Lake Michigan to gather measurements. NOAA Great Lakes Environmental Research Laboratory scientists looked at 30 years of measurements, some hourly, to track seasonal patterns far below the surface. The study, published in the peer-reviewed journal Nature Communications, notes that Lake Michigan is “likely the world’s only large lake with this type of long-term observations of water temperatures at depth.”
In deeper water, warming is estimated to be as much as .06 degrees Celsius per decade.
“This is a big lake,” Stow said. “That’s a lot of water. That’s a lot of change.” Warming so far below the surface wasn’t necessarily a surprise, but it’s hard to know what’s happening without data. “It could have been that we’d only see an effect down in the first 30 or 40 meters,” Stow notes. “But we saw it down really far.” Lakes can serve as “climate change sentinels;” deep water measurements can be particularly important because they provide a “climate memory.”
“What we can see from this data is a reflection of larger scale and longer-term processes,” Stow believes. “They’re not obscured by the noise that might occur from a couple very warm or a couple very cold years.” The water’s warming winters reflect rising surface temperatures and prolonged summers. Some of the most pronounced jumps in winter temperatures are occurring near the Great Lakes. Records dating back to 1973 show maximum ice coverage across the Great Lakes is declining 5% per decade; Lake Michigan’s ice coverage decline is about 3.6%.
Lake Michigan is dimictic, meaning there’s a top-to-bottom mix of the water column twice a year. With warmer surface temperatures, the fall mixing cycle is starting later, leading to a shortened cooling period for deep waters and a longer summer period without mixing.
“The organisms that live there, the plankton and the fish, are used to the lake the way it was,” Stow said. “They evolved over thousands of years to take advantage of those systems that mixed twice a year.”
If the lake changes to warm monomictic, mixing once a year, Stow said it would signal fundamental change.
“And the other thing you have to remember is this is not the only thing going on,” Stow said, noting changes spurred by invasive zebra and quagga mussels. “All of that’s happening at the same time.”
The report lays out some examples of what’s happened in other large lakes. Thermal change can mix up the food web and lead to the proliferation of invasive species. Longer periods when the lake is not mixing can exacerbate low-oxygen conditions. In Lake Erie, for example, low oxygen has contributed to fish die-offs.
Researchers hope to add more censors to gain a better overall picture of how the lakes are responding. “In all, the consequences of changes in subsurface water temperatures will result in a profound shift in lake ecology,” the report says. “Without high-frequency long-term monitoring of subsurface waters, we will be blind to the impacts of climate change on most of Earth’s fresh surface water.”
Ph.D. December 1992 -School of the Environment, Duke University, Durham, NC Faculty Advisor: Dr. Kenneth H. Reckhow Dissertation: The Effect of Errors-in-Variables on Parameter Estimation in a Lake Phosphorus Model.
M.S. May 1981 -Wetland Biogeochemistry Institute, Louisiana State University, Baton Rouge, LA Faculty Advisor: Dr. William H. Patrick, Jr. Major: Marine Sciences Masters Thesis: Seasonal nutrient dynamics in a shallow sub-tropical hypereutrophic lake in south Louisiana.
B.S. May 1977Cornell University, Ithaca, NY. Major: Environmental Technology
senior Research Scientist, NOAA Great Lakes Environmental Research Laboratory Ann Arbor, MI. July 2006-present.
Associate Professor, University of South Carolina, Arnold School of Public Health, Department of Environmental Health Sciences, Columbia, SC. August 2003-June 2006.Courses Taught –Applied Aquatic Sciences (Fall 03, 04, 05), Ecological Modeling and Environmental Planning (Spring 05, 06)
Visiting Assistant Professor, Aquatic Sciences, Duke University, Nicholas School of the Environment and Earth Sciences, Durham, NC. August 1996 –July 2003.Courses Taught -Water Quality Management (Fall 96-02), Water Quality Field and Laboratory Skills (Spring 97-03), Seminar on “The Ecological Detective” by Hilborn and Mangel (Fall 98), Advanced Readings (Spring 01). Teacher of the Year–2002-03 academic year. Teacher of the Year–2001-02 academic year. Administrative Responsibilities -Chair, Water and Air Resources Program, 1997-2003.
Post-Doctoral Researcher, University of Wisconsin, Center for Limnology, Madison, WI. July1992 -August 1996.
Graduate Research and Teaching Assistant, Duke University, School of the Environment, Durham, NC. August 1986 -July 1992.
Environmental Program Specialist, Louisiana Department of Environmental Quality, Baton Rouge, LA. NPDES permit writer. February 1982 -July 1986.
Research Associate, Laboratory for Wetland Soils and Sediments, Louisiana State University, Baton Rouge, LA. November 1981 -January 1982.
Analytical Chemist, Analytical and Environmental Testing, Baton Rouge, LA. January 1981 –November 1981.