2013 Dye Test Shows Lake Michigan’s Open Waters Mix Far Faster Than Expected
Researchers released fluorescent dye in Lake Michigan in 2013 and observed rapid dispersion far from shore.
In a 2013 field experiment, Purdue University researchers collaborating with NOAA’s Great Lakes Environmental Research Laboratory released a pink-red Rhodamine WT tracer into the surface layer of Lake Michigan to measure how quickly a water parcel spreads away from the coast. Over roughly 21 hours the plume’s dispersion coefficient increased from roughly 1.5 to 4.2 square metres per second, a speed far greater than expected for open-lake conditions.
The team attributed the rapid spread to near-inertial Poincaré waves that create shear between the warm upper layer and colder water below during summer stratification. A subsequent 24-day deployment of floating drifters confirmed that calm periods produce slow, orderly movement, while stronger winds trigger faster, irregular dispersion. These findings reveal that Lake Michigan’s interior can experience vigorous mixing, influencing predictions of pollutant spills, nutrient transport, and heat redistribution under changing climate.
