BASS HARBOR, Maine — An ancient freshwater lake, now submerged under salt water off the coast of Mount Desert Island, offers insights into how Maine’s coastline was formed and how those areas that are now under water became habitable for the state’s earliest settlers.
A team of researchers from the University of Maine and the University of New Hampshire discovered the lake during a study of an area off the coast of Mount Desert Island near where fishermen had found prehistoric stone tools more than a decade ago.
During a 3,000-year interval when the sea level rose slowly, the earliest humans inhabited coastal areas that now are under 65 to 100 feet of water. The discovery of the now submerged lake provides a glimpse into the early life of the Indian tribes that inhabited lands that are now submerged.
“Archaeological deposits of life along the Maine coast really date back only about 5,000 years; everything older than 5,000 years of Indian life has been submerged under the seas,” said Arthur Spiess, senior archaeologist with the Maine Historic Preservation Commission. “We have virtually no idea how people lived along the Maine coast from the end of the ice age to 5,000 years ago.”
The study provides a “little, teeny glimpse” into what those lives were like, he said.
The “drowned” lake is located off Bass Harbor on the southern shores of MDI near where scallop draggers in the 1990s dragged up stone tools dating back about 8,000 years.
“The fishermen knew about where they were when they found the tools,” said Joseph Kelley, chairman of the department of earth sciences at UMaine. “We wanted to see what the bottom looked like where they were recovered. It ended up being extremely interesting.”
The history of the lake is tied to the end of the last glacial period, according to Kelley, who, with Daniel Belknap, also a professor in the UM earth sciences department, and Stefan Claesson of the University of New Hampshire, conducted a study of the site in 2008 funded by a grant from the National Oceanic and Atmospheric Administration.
An article about the study, written by Kelley, Belknap and Claesson, appears in this month’s issue of the scientific journal Geology.
During the last ice age, Maine and much of North America were covered by a glacier, which began melting about 15,000 years ago, exposing the land that is now Maine, according to the researchers. Sea level rose, but at an unsteady pace. There were periods of rapid rise, but there also were periods when there was little or no in-crease in sea level.
According to Kelley, between 11,500 and 7,500 years ago, the sea level off the coast of Maine barely rose at all, a period scientists call “slowstand.” It was during that slowstand that coastal lands were exposed long enough for freshwater environments to develop there, including freshwater marshes and lakes similar to the one in the study.
The researchers used a variety of underwater imaging equipment to survey the site, including sonar and other mapping technology that developed a picture of the underwater lake, which, despite being under water, looked very much like a beach, Kelley said recently.
They also took core samples at several locations around the site that included saltwater materials, such as shellfish fragments and eelgrass, according to Kelley. But the samples also contained deposits of freshwater peat, evidence that at some point in its history the area had supported a freshwater wetland, he said.
Evidence of the drowned lake offers information about the geologic history of the Maine coastline, about how coastal environments change, and how they might change in the future as sea levels rise. It also provides researchers with an indication of where additional archaeological artifacts might be found.
“We have a time interval and a depth, and we haven’t had that before,” Kelley said.
The slowstand period was the important factor, he said.
“We recognized that was the key element in preserving things,” he said. “With sea level in the same place, there was the opportunity for glacial materials to erode and for the construction of coastal land forms.”
Knowing that this site was formed during a slowstand period, Kelley said, researchers can use the characteristics of this site to locate similar sites all around the Gulf of Maine.
“In other areas, if there were intervals like this, that is likely where you’ll find archaeological materials,” he said.
The information gathered from the site will benefit state archaeologists in a number of ways, according to Spiess. For one, it gives them some idea about how the prehistoric peoples lived.
“We know that these people collected shellfish and created shell heaps, that they have been eating clams and oysters for many thousands of years,” he said. “We can look back and make some assumptions about life on this land that is now under water.”
On a broader scale, he said, the date range and depth range established for the specific site may provide direction in finding other prehistoric sites that are now under water.
“We may find more preserved archaeological sites that survived the rise of sea level at that depth,” he said.
That will be important for the Maine Historic Preservation Commission, which works with other state and federal agencies to ensure that environmental surveys are conducted for any construction projects that might disturb archaeological sites, even those under water. Those types of projects include siting power cables and set-ting anchors for offshore wind power generators.
Spiess said the preservation commission would want to keep an eye on any project that proposed doing work in the identified “slowstand” depths along the coast.
It is unlikely that archaeologists will mount a study of those areas unless they are related to a construction project, Spiess said. Kelley, however, said he is eager to conduct further studies at the Bass Harbor site. This initial study allowed for limited core samples at the site, and Kelley said he hopes to attract additional funding to take more core samples there.