In a Sinkhole In a Lake

Tall “blip” on purple microbial mat in Middle Island Sinkhole, Lake Huron, June 2019 (Credit: Phil Hartmeyer, NOAA Thunder Bay National Marine Sanctuary)

11 February 2021

When I found this photo I had to find out more.

Though it looks something from outer space this unearthly pink blip is rising from a microbial mat inside the Middle Island Sinkhole (45.192515,-83.327195) in Lake Huron, about 12 miles from Alpena, Michigan.

Approximate location of the Middle Island Sinkhole (map from Wikimedia Commons, annotated)

Great Lakes sinkholes were found by accident in 2001 while looking for shipwrecks and have been studied for only 20 years.

Some, including the Middle Island Sinkhole, have vents that add water to the lake. This water is warmer than the nearby lake, has lower oxygen, 10 times the chloride, 100 times the sulfide, and a higher concentration of bacteria. The water looks very green.

This is the “perfect habitat for microorganisms known as cyanobacteria that form the somewhat eerie purple, white and green carpets on the lake floor.” Underneath the mats, methane and hydrogen sulfide bubble to the surface. The mat expands upward like wax in a lava lamp.

See what it’s like to scuba dive in the sinkhole at Diving with Ric: An underwater view of the Lake Huron Middle Island Sinkhole.

p.s. Fish live in some parts of the sinkhole. The photo below shows a burbot resting on a rock. If you don’t see the fish, click on the photo for a hint.

Burbot resting on rocks covered in purple and white microbial mats, Middle Island Sinkhole (Credit: Phil Hartmeyer, NOAA Thunder Bay National Marine Sanctuary)

(map from Wikimedia Commons, photos from NOAA Great Lakes Environmental Research Lab on Flickr)

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