Futures for Arctic lakes, inferred from eight thousand years of mud
November 16, 2025
The Arctic region is warming four times faster than the global average, raising questions about how sensitive Arctic ecosystems will respond. Lake sediment cores are geological archives that preserve histories of how past climates have driven changes in the Arctic and beyond. By reconstructing how ecosystems may have responded to past warm periods, paleolimnologists provide crucial insight to assessing future consequences of climate warming.
But entire ecosystems are hard to reconstruct. For instance, sedimentary sub-fossils from single organisms are not generalizable to entire ecosystems, and thus do not capture the full picture of diverse, multi-directional, ecological changes. Furthermore, very few paleolimnological proxies can capture the dynamics of Earth’s smallest photosynthesizers—cyanobacteria, which pose modern-day risks to some drinking water supplies in the Arctic.
Ph.D. candidate Mia Tuccillo has addressed the need to reconstruct diverse primary producers by developing a novel method at Northwestern University: to extract and quantify photosynthetic pigments from lake sediments. Sedimentary pigments, such as chlorophyll, are diverse molecules, and their different structures provide clues about the relative presence of different organisms during past climate shifts. With guidance from research technicians at IMSERC (Northwestern’s Integrated Molecular Structure Education and Research Center), Tuccillo has a developed a high-resolution liquid chromatography-mass spectrometry method to quantify sedimentary pigments—the first of its kind at Northwestern.
In a paper first-authored by Tuccillo published this month in Quaternary Science Reviews, the group of Northwestern scientists reported how ecosystems in a South Greenland lake responded to large climate and environmental shifts over the past 8,000 years. Most importantly, the team discovered a nearly 2,000-year period of anoxia (a lack of oxygen) in the deepest lake waters. During this time, cyanobacteria dominated, and previously dominant algae and zooplankton disappeared. Using independent paleoclimate evidence, Tuccillo and her team ascribed this period to a time where Greenland was warmer to today—warm summers thermally stratified the lake, preventing deeper waters from coming into contact with the atmosphere.
The paper draws several important connections. For instance, warming drives the mixing of lake waters, which in turn is connected to lake water oxygen. Both the amount of oxygen and warming appear related to ecological transformations—in this case, the decline of algae and zooplankton, and rise of cyanobacteria. All of this raises questions about the futures for Arctic lakes in this time of unprecedented warming: Will warm summers push lakes into new chemical states? Will these drastic changes lead to the rise of cyanobacteria, and could this threaten drinking water supplies or pre-existing ecosystems?
This project was financially supported by the National Science Foundation and Northwestern University, and only possible thanks to wide involvement from Northwestern students (including former-undergraduate alumna Shayna Garla, second-author), the government of Greenland, and multiple Greenland-based organizations.