Molecular Fossils Offer Universal Way to Track Climate Change

Lurking beneath the surface of Inner Mongolia’s striking saline lakes are a potential Rosetta stone of paleoclimate.

Jingjing Li and her colleagues from the Nanjing Institute of Geology and Limnology and the University of Bristol studied the lakes and characterized the bacteria that produced branched GDGTs, a fatty record of Earth’s climate history.

So far, scientists have used branched GDGTs to create temperature records for temperate, arctic, and tropical environments. Branched GDGTs are what scientists call temperature proxies—data drawn from them can be used to calculate historical air temperatures. But that hasn’t been quite possible in saline environments until now.

With a record spanning thousands of years, long dead bacteria—from lakes such as this one in Mongolia—may help scientists predict future climate trends around the world.

While some molecular fossils allow researchers to create climate records only in lakes, oceans, or soils, GDGTs are so prevalent, in fact, that you’d probably find them in a handful of dirt from your neighborhood park. Branched GDGTs found in Mongolia could generate a climate record similarly to the way they would elsewhere on Earth. This allows scientists to draw accurate comparisons of how the temperature changed in different regions over time.

“In order to understand future climate change, scientists look at past climate change to understand the climate system,” said David Naafs, an organic biogeochemist involved in the study. He looks at branched GDGTs and uses molecular fossils to construct past environmental conditions. Li applied his refined mathematical formula to turn data drawn from the branched GDGTs samples into temperature values.

“One of the main challenges is that we do not know [which bacteria are] producing [branched] GDGTs” Naafs said. “This is really a key step that the community needs to make, but it has been very difficult so far.”

Li’s study revealed something that may help elevate efforts to identify the bacteria that produce branched GDGTs.

Previous studies of lakes in different environments showed that branched GDGTs were produced by bacteria that lived in the lake waters. That’s not quite the case in Inner Mongolia, according to the study.

Li and her colleagues found that the branched GDGTs in saline lakes came from bacteria that lived in the soils around the lake. Instead of being produced in the lake waters themselves, most branched GDGTs were deposited into lakes when the surrounding soils were blown, kicked, or washed into the lake.

That sort of information can help researchers interpret the historical temperatures and how they changed over time. This could mean that the salt content of the waters affects how the bacteria grow and produce GDGTs. Even further, it may help climate scientists decide where to sample for branched GDGTs in future efforts involving the previously understudied region.

“When we generate temperature reconstructions, sometimes, [records] look beautiful, [or] sometimes nonsensical. Right now, we don’t know why,” said Jim Russell, a paleoclimatologist at Brown University.

Understanding where the GDGTs were produced may help explain. It also may help scientists predict future temperature trends.

As climate researchers model Earth’s future climate outlook, the pressure is on geoscientists to create reliable climate records that can be used in climate models. The more accurate and plentiful the data available, the more reliable the model.