Scientist study area lakeOn the surface, Lake George looks like any other North Dakota lake, glistening in the summer sun. But beneath those placid waters may lie critical clues about the region’s climate history. Known by locals as “Salt Lake,” Lake George is considered to be the deepest natural lake in North Dakota.
By: Kari Lucin, The Jamestown Sun
On the surface, Lake George looks like any other North Dakota lake, glistening in the summer sun. But beneath those placid waters may lie critical clues about the region’s climate history.
Known by locals as “Salt Lake,” Lake George is considered to be the deepest natural lake in North Dakota.
Its depth, combined with its high concentrations of sodium and sulfate, make it unique — and uniquely useful to a group of scientists who want to reconstruct the climate history of the region.
“There are plenty of salt lakes throughout North Dakota, but most of the other ones I know about are relatively shallow,” said Sherilyn Fritz, a professor of earth and atmospheric sciences at the University of Nebraska, Lincoln. “There are a lot of salt lakes that are extremely shallow — a couple of feet deep, for example.”
Fritz is part of a multi-university, multi-disciplinary team of researchers hoping to better understand the natural variability of climate over time.
That data may offer a long-term perspective on the natural variability of precipitation, droughts and floods in the region, and assist officials in water management.
Fritz’s team includes geochemists Paul Baker of Duke University, Durham, N.C., Yong Song Huang of Brown University, Providence, R.I., and plant ecologist Eric Grimm of the Illinois State Museum.
Fritz and Baker visited Lake George in mid-August to conduct a seismic survey and complete a chemical profile of the lake. They were assisted by Rick Bohn, a range technician with the North Dakota State Central Grasslands Research Center, who drove the boat.
The group started work at 7 a.m. and went north and south several times and then crossed the lake east and west several times, very slowly. Their position constantly recorded via GPS, they used a seismic system to shoot sound waves into the lake.
“You basically put a speaker into the lake, and you tow it alongside a boat,” Fritz said. “The speaker is sending out, at regular intervals, these sound waves. They’re reflected back depending on how dense the mud is, and you record that signal — and that signal is translated into an image.”
It took about five hours to complete the survey, Bohn said.
The salinity in Lake George is caused by salts in the groundwater, and the specific level of salinity depends on how much the salt is diluted by rain or strengthened by evaporation.
“During dry periods, Lake George gets saltier, and in wet periods — such as now, when you have more precipitation — the lake gets wetter,” Fritz explained.
Lake George is too salty for most fish, but it does contain rooted plants, invertebrates and microscopic organisms.
It also contains algae, including several species of an unusual type of algae that grows only in saltwater — haptophytes. These haptophytes make a fatty acid that records temperature changes, Fritz explained.
Because of the lake’s salinity, haptophytes thrive there, and because of the lake’s 150-foot depth, its sediment has never been disturbed, allowing scientists to determine the region’s historical temperatures and precipitation.
“We want a sequence of mud that hasn’t been disturbed by the drying-out of the lake and mixing,” Fritz said.
The research at Lake George was part of a four-year project funded by a grant from the National Science Foundation. Originally, the group had been working in western North Dakota, along the Montana border.
Fritz has been working in the region for 20 years, and first visited Lake George in the mid-1980s. Earlier studies have included taking 30-foot sediment cores from the lake, and the seismic images will offer a more complete context for those cores.
“They’ll help tell us where there’s evidence for lake level change or lake level lowering, and what depth that occurs,” Fritz said.
The sediment cores can be radio-carbon-dated and the dead haptophytes, whose chemical remains are preserved in the mud, will help reconstruct temperature variations. The seismic images will allow scientists to see if the cores are really representative of the whole lake.
Down in the icy depths
Lake George is believed to be an ice-push basin, meaning it was scoured out by a moving glacier, Fritz said.
It is so deep the lake stratifies in the warm summer months, with its top layer warming significantly into the 70s, and its bottom layer remaining barely above freezing.
To get a chemical profile of the lake, the scientists used a probe on a cable and lowered it down meter by meter, getting a complete image of temperature, pH levels and salinity in different parts of the lake.
Combined with the seismic survey and the cores, the chemical profile will help the group of scientists get a complete picture of regional climate changes over time.
Though some scientific papers about the coring process are already in the draft stage, it will likely be a year before the group begins writing up the complete results for publication.
Having an accurate account of climate on a more geological time-scale — one that goes back thousands of years — should help scientists understand what’s happening now.
“Arguably, in the 20th century human actions have had influence on climate. And also, the 20th century is a pretty short period of time in the world of climate variability,” Fritz said.
When the complete study is published, Fritz hopes the data and analysis will hold critical insights for modern problems.
“Here we have this very unusual flood, for example. Is what happened now unprecedented?” Fritz said. “Do things like this really occur once every 500 years?”
Sun reporter Kari Lucin can be reached at 701-952-8453 or by email at email@example.com