William D'Andrea spends a lot of time worrying over fat.
It's not the same kind of fat that invades arteries or makes it difficult to put on a pair of skinny jeans. For D'Andrea, fat is a major scientific breakthrough -- when it's buried in the depths of a lake.
Photo courtesy of pennstatelive
The paleoclimatologist at Columbia University in New York is the first in his field to quantify temperature changes in the Arctic using fat measurements taken from algae at the bottom of Lake Kongressvatnet.
"My objective is to reconstruct how climates have changed in the past using geological archives, things that have naturally recorded changes in climate," he said.
Whereas health officials lecture the American public about their intake of unsaturated and saturated fats, D'Andrea has spent the past several years of his life collecting the lipids. According to his study published in the journal Geology, for the past 20 years, Lake Kongressvatnet has been the hottest it's been during the summer in a 1,800-year sample.
This potentially dispels an old theory that the medieval period, an interval from about A.D. 950 to 1250, was the warmest on record. If D'Andrea is right, this anomalous period was not as hot as scientists thought -- and his fat proves it.
The medieval period "seems to have a unique spatial pattern of temperature change," he said, "but it wasn't a time period that shows the type of warming that we're seeing in the past 40 years or so."
A microscopic clock
Haptophyte algae congregate in many -- but not all -- lakes throughout the world. The scientific community is not sure why haptophytes choose one region over another, but when they decide to settle, they can colonize an area for thousands of years. The microscopic life-forms contain polyunsaturated fats.
Fats that are more polyunsaturated are analogous to vegetable oil, and fats that have less polyunsaturation are more like lard. The algae must keep their fats at a specific consistency in order to survive. If it gets too cold, the fats lower in polyunsaturation could congeal, and if it gets too warm, the fats with higher polyunsaturation levels could become too thin. So haptophytes compensate by increasing their output of specific fats depending on the temperature.
According to D'Andrea, the haptophytes he studied made a lot more lard -- or, rather, fats that are less polyunsaturated, which means it got warmer, an average of 2 to 2.5 degrees Celsius warmer since 1987.
D'Andrea and his team tied the fat-specific temperature data to a timeline by looking at volcanic ash embedded in the lake bed. Each eruption has a specific chemical signature. By matching the molecules in the sediment to the specific geological event, D'Andrea was able to construct a data set.
"You can fingerprint the eruptions based on the geochemistry," he said. "We measured the different oxides that are present in the volcanic ash."
More puzzles to solve
The approach is unique. Scientists have historically used ice cores -- not algae and volcanoes -- to determine temperature fluctuations. But those can only quantify wintertime temperatures, leaving the scientific community with a missing piece of the puzzle. Carbon-dating pollen grains and bivalve shells can also do the job, but they are less reliable and often have greater margins of error.
"I chose these molecules that are produced by this specific type of algae because they allow us to quantify how lake water temperature has changed," D'Andrea said.
And that is a big deal for climatologists trying to map the climate change of a particular area. However, the question of how climate change has affected the northern latitudes is far from answered.Lake Kongressvatnet is not indicative of the Arctic. In fact, D'Andrea's research isn't necessarily indicative of Lake Kongressvatnet. There are several confounding factors that could have skewed results.
For example, the algae could have evolved with temperature changes over the millennium, meaning the comparison of fats 1,000 years ago to those deposited 20 years ago is a bit like comparing apples to oranges. Large shifts in wind patterns or water levels could also affect temperatures without a notable tie to climate change.
It is unlikely that these elements would significantly affect the results, but it can't be ruled out, D'Andrea said. The Geology study has a margin of error of plus or minus 1 degree Celsius.
So far, D'Andrea has analyzed a 50-centimeter sample of sediment. His next step is to return to Kongressvatnet and lakes like it around the world to gather more information about the world's climate.
"These algae do something amazing with their fat," he said. "They allow us to look at what temperatures were back in time."
Reprinted from ClimateWire with permission from Environment & Energy Publishing, LLC. 202-628-6500. E&E Publishing is the leading source for comprehensive, daily coverage of environmental and energy issues. Click here to start a free trial to E&E's information services.