The Chemistry of Antarctic Lakes
A new study, led by SAEF researcher Dr Liza McDonough from ANSTO, has sought to understand the organic molecules in five lakes around Casey Station in Antarctica.
When you go swimming in a lake in Australia, you’ll encounter a range of water conditions. Some lakes have water that is crystal clear and luxurious, while others have water that is slightly brown and earthy, offering a more back-to-nature type bathing experience. These varying conditions are due to the mix of tiny organic molecules floating around in the water that are typically made up of carbon, hydrogen, oxygen, nitrogen and sulphur. They’re influenced by the amount of debris, from things like leaves and branches, that naturally end up in the water.
Now, if you were to consider taking a dip in an Antarctic lake, what type of water conditions would you expect? Since there are no trees and great expanses of fresh snow, you might expect that it would be one of the most pure (and icy) swimming experiences you could find. Especially since humans are generally not allowed to swim in these lakes and therefore haven’t had the chance to soil them.
Well, I’m sorry but the penguins have.
What’s in the water?
A new study, led by SAEF researcher Dr Liza McDonough from ANSTO, has sought to understand the organic molecules in five lakes around Casey Station in Antarctica.
Known as dissolved organic matter, she and her team from across SAEF wanted to know where these molecules come from and how they are changing over time.
“We know that Antarctica is warming quickly, and changes in snowmelt, moss cover, microbial communities and penguin populations could change what’s in this mix of molecules, which in turn could change how much carbon these lakes store or release into the atmosphere,” Dr McDonough said.
So, in 2022 SAEF scientists, completing fieldwork as part of the Australian Antarctic Program, collected water from five lakes near Casey Station in East Antarctica. These samples were tested at ANSTO and some were sent to Florida State University and the National High Magnetic Field Laboratory in Tallahassee, USA, for analysis with the strongest mass spectrometer in the world.
This allowed the team to identify the exact chemical composition of thousands of different types of organic molecules and match them with likely sources. They then used statistical analyses to find patterns and identify the main sources…which included penguins.
Traces of poo, dust and moss molecules
Just to be clear. The penguins have done nothing wrong.
The team found that the organic molecules in the lakes were coming from a range of completely natural sources (and bodily processes).
“Some lake samples had a lot of organic molecules that matched molecules from penguin poo, and these were richer in nitrogen and certain metals coming from the penguins’ diet,” Dr McDonough said.
“Some lakes, especially at lower elevations, had organic molecules that came mainly from dust deposited on snow which then melted into the lakes, including material that had been altered by sunlight before it entered the lake. Other lakes near moss beds had organic molecules that were likely derived from the mosses.”
One of the most surprising findings was in relation to how the organic molecules in these Antarctic lakes were being transformed. In most lakes around the world, especially those in warmer climates, living organisms such as microbes, plants and animals control how organic molecules are transformed. For example, microbes in the water might “eat” the penguin poo. In Antarctic lakes, these microbial processes are slowed down due to the cold temperatures, and the majority of the changes are instead caused by sunlight. This is probably a result of the high UV exposure in the warmer months when the ozone hole forms directly above Antarctica.
What’s next?
The team now hopes to study more lakes across Antarctica and the sub-Antarctic, and track how the organic molecules change across seasons and years. They’d also like to collaborate with members of the SAEF microbiology team to link which microbes are active in processing different types of organic molecules.
As Dr McDonough highlights, these lakes are part of the carbon cycle, which affects the global climate.
“If penguin numbers, moss cover, or snowmelt patterns change with warming, the mix of molecules in these lakes will also change, possibly shifting how much carbon they store or release. Knowing the current sources of organic molecules and processes gives us a baseline to predict and detect future changes.”
Read more
McDonough, L. K., Holt, A. D., Hamilton, E., Randall, K., Saunders, K. M., Robinson, S. A., Spencer, R. G. M., McKenna, A. M., Linnenlucke, L., & Meredith, K. T. (2025) Shaping DOM signatures in East Antarctic lakes: Penguins, mosses, meltwater, and processing mechanisms. JGR Biogeosciences, 130(9), e2025JG008931. https://doi.org/10.1029/2025JG008931
