Large amounts of methane are stored in the bottom of Arctic lakes. If released, it could accelerate global warming even further. American researchers found this out by studying fossils of ancient aquatic plants.
More precisely, they looked at the waxy coating of mosses, which are stored as organic molecules in the lake sediments and date back to the early to mid-Holocene. This was a period of massive warming due to slow changes in the Earth’s orbit about 11,700 to 4,200 years ago. These biomarkers – once part of common brown water mosses – were found in sediments at the bottom of four lakes in Greenland.
Wipe sign
The first conclusion: the Greenland lakes did indeed release large amounts of methane during that period of warming. A bad sign for the future, since methane is thirty times more powerful than CO2.
It is not yet clear exactly how much methane the Arctic lakes produce and how warming affects this. But the new study shows that rising temperatures could potentially lead to previously underestimated emissions of methane from the lakes.
Last Ice Age
“The last time Greenland’s lakes experienced major warming, we were coming out of the last ice age. And it took a while before the methane cycle in the lakes also increased,” says lead researcher Jamie McFarlin of Northwestern University. “But once that happened, the lakes released more methane for thousands of years, until natural cooling started at the end of the Holocene. This shows that the methane cycle in some Arctic lakes is dependent on the climate.”
The data show that more methane is released during warm periods. “Living on a warming planet, we can look at these signals from the past to help predict our future,” adds researcher Magdalena Osburn. “We suspect that this process will become increasingly important in the future of these lakes.”
Methane traces
The Arctic lakes are an important natural source of methane, but exactly how much methane production changes due to warming of the lakes has not been fully mapped out. But because the Arctic is among the fastest warming regions on Earth, it is important to better understand the dynamics between rising temperatures and methane production in these lakes.
Some of the sediment from Wax Lips Lake in northern Greenland. Photo: Jamie McFarlin
Therefore, the researchers collected new data in two lakes, Wax Lips Lake and Trifna Sø, and analyzed already known data from two other lakes, Lake N3 and Pluto Lake. They compared the isotopic composition of hydrogen of aquatic plant wax in the sediment with biomarkers of other plants on land. The isotopic composition of aquatic plant biomarkers revealed methane traces during the Early to Middle Holocene at most sites.
Methane-eating bacteria
Because these plants also absorb methane, they may be blocking some of the methane before it ends up in the atmosphere. “In the lakes in our study, some of the methane was taken up by the mosses growing in the lakes, likely through a symbiotic relationship with a bacterium that eats methane,” McFarlin explains. “We don’t yet know how much methane was produced and how much was consumed during that time, so how much ends up in the atmosphere on balance remains unclear. However, there are probably only a small number of moss species that absorb methane, so not all lakes will have the same dynamics.”
Researcher Yarrow Axford also agrees. “Huge areas of the Arctic are covered in lakes. Not every lake has mosses that absorb methane, but our study also shows that large parts of Arctic lakes are vulnerable to climate change in terms of the methane cycle, whether there are mosses or not. This is therefore yet another way in which rapid Arctic warming could impact global climate.”
2023-10-02 09:03:56
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