Waxy Coatings of Plant Fossils Reveal the Effect of Global Warming on Methane Produced in Arctic Lakes

By analyzing fossils from prehistoric aquatic plants, researchers gained better insight into the production of methane in Arctic lakes and how they were probably affected by climate change.

Production of Methane in Arctic Lakes

Lakes act as important natural sources of methane, but the changes in methane production is still not fully understood. Researchers currently lack knowledge on the amount of methane produced in Arctic lakes, and how the ongoing global warming could affect methane production.

The last time lakes in Greenland experienced major warming was when the planet was coming out of the last ice age. From then, it took some time for the required conditions to develop and enable increase in lake methane cycling. Once it developed, the lakes maintained an intensified methane cycle for thousands of years until the start of late Holocene cooling. This supports the idea that climate depends on lake methane cycling in some Arctic lakes.

Revelations From Ancient Plant Wax

A team of researchers from Northwestern University and University of Wyoming studied the waxy coatings of leaves which were preserved as organic molecules within sediments buried beneath four lakes in Greenland. These ancient plant wax, which were once a part of common aquatic brown mosses, were assumed to be buried from early-to-middle Holocene, a period in history characterized by intense warming brought by slow changes in Earth's orbit.

Scientists recognize the importance of understanding methane production since methane is a more potent greenhouse gas than carbon dioxide. Since Arctic and boreal landscapes are among the fastest warming regions on the planet, it is important for researchers to understand the dynamics between warming temperatures and methane production in these bodies of water.

Led by Jamie McFarlin, the experts studied the biomarkers and discovered that a prehistoric global warming occurred during the middle Holocene, causing lakes across Greenland to produce methane. To explore these dynamics, they generated new data at Wax Lips Lake and Trifna Sø Lake.

The team investigated the hydrogen isotopic composition of aquatic plant waxes within the sediment and compared it to biomarkers from terrestrial plants and other sources. Data from aquatic plants revealed a signature from methane at most sites during the early-middle Holocene. Since aquatic plants absorb methane, they could reduce some of the methane produced in lakes before it is released into the atmosphere. This means that there are increased periods of methane cycling during the prehistoric warm periods.

The findings of the study suggests that global warming could potentially lead to a previous under-appreciated flux in methane emissions from lakes. As the Earth continues to get warm, scientists can look to these signs from the past in predicting the future of our planet. They suspect that this process will become more important in understanding the future of these lakes.

A huge area of the Arctic region is covered in lakes, but not every lake has mosses that will record methane dynamics. According to study co-author Yarrow Axford, their study shows the vulnerability of vast swaths of Arctic lakes to climate-driven changes in methane cycling, whether mosses are present on site or not.