“The smaller diatoms tend to like warmer conditions,” says Dr. Bramburger.

Brandon Michaels reports for KBJR6, in Duluth, MN, that a scientist with the Natural Resources Research Institute in Duluth has had a paper published that suggests a warming climate’s potential impact on the Great Lakes.

Andy Bramburger and his team have probed core samples through a depth of the lakebed representing 250 years worth of sediment, looking for one thing: diatoms – small, shelled species of algae.

“Each of those layers correspond to a period in time where that sediment rained down out of the water column and settled on the bottom of the lake. So as we go further and further down through the core, down through the sediment we go further back in time, and at the bottom of these cores we’re probably looking at 250 years before the present,” he said.

Specifically the team is looking into how the diatoms have changed over time. “Each diatom has a set of environmental conditions in which it likes to grow, so by looking at the diatoms that were present at different time intervals, we can reconstruct what the environmental conditions were like,” he said.

This allows Dr. Bramburger and his team to make inferences about the climate at any given point in the core sample.

In more recent sediments, the team has found an increase in smaller diatoms. “The smaller diatoms tend to like warmer conditions, but also longer growing periods where there’s not ice on the lake,” he said.

The findings show that the climate has been warming over the past century, which correlates well with what scientists from other fields have found. “Climate scientists have been studying changes in the atmosphere and changes in temperature from thousands and thousands of years ago, and it points to: yes, there is global warming and the climate is changing as a result,” said Carol Christenson of the National Weather Service.