The National Oceanic and Atmospheric Administration’s (NOAA) Great Lakes Environmental Research Laboratory (GLERL) has identified nearly 40 circular formations on the lakebed of Lake Michigan, according to a report by Live Science.
Discovery of the Circular Depressions
In 2022, NOAA researchers began surveying the Great Lakes using sonar and detected strange circular depressions on the floor of Lake Michigan. These depressions, which range between 91 meters (300 feet) and 183 meters (600 feet) in diameter, were first brought to attention by a shipwreck hunter. However, it wasn’t until recently that scientists were able to take a closer look.
In an August expedition, around 40 of these formations were discovered, and they are believed to be sinkholes. The features are located about 22.5 kilometers (14 miles) southeast of Sheboygan, Wisconsin, arranged in a line that stretches toward Port Washington.
Brendon Baillod, the shipwreck hunter who first spotted them in 2022, shared his thoughts with Live Science: “There were dozens of them in our search grid. Most ranged between 500 and 1,000 feet [152 to 309 meters] in diameter and were irregular in shape.”
What Are Sinkholes?
These sinkholes are thought to have formed through natural geological processes. According to the US Geological Survey, sinkholes are most commonly found in areas with “karst terrain,” where certain types of rocks, such as limestone, gypsum, or salt beds, dissolve due to groundwater. In the case of Lake Michigan, the limestone bedrock under the lake helps explain the development of these sinkholes.
Connection to Lake Huron Sinkholes
While the geological process behind these sinkholes is understood, they are not typical formations. Similar sinkholes in Lake Huron host unique microbial communities that thrive in environments with low oxygen and high sulfur levels, mimicking conditions on Earth around 2.5 billion years ago.
A study on the Lake Huron sinkholes explains how microorganisms dominate this environment: “Much like early Earth, microorganisms dominate the Middle Island Sinkhole in Lake Huron. Scientists recognize three major domains of life: Bacteria, Archaea, and Eukarya.”
Microbial Life in Sinkholes
One fascinating aspect of these sinkholes is the microbial life that exists within them. On the lake floor, bacteria form a distinctive purple mat. DNA analysis has shown that a significant part of this mat consists of Phormidium autumnale, a type of cyanobacterium. These filamentous organisms use sunlight to convert dissolved carbon dioxide into organic carbon. Additionally, methane-producing Archaea and various Eukaryotic species have been identified within the mat. Some of the DNA sequences point to previously unknown microbial life forms.
Future Research in Lake Michigan
Although further research is needed, scientists believe that the sinkholes in Lake Michigan could harbor similar life forms to those found in Lake Huron. These findings may provide valuable insights into the conditions on Earth billions of years ago. GLERL researchers have indicated that the sinkholes in Lake Michigan likely share similarities with those in Lake Huron and may offer clues to understanding the planet’s early history.
