The sleeping giants of the global carbon cycle
The melting of Arctic ice will pour more than just fresh water into our oceans. Greenhouse gases such as methane trapped in permafrost will also break free, a fact that complicates global warming predictions. We still don’t know how much of these gases will evaporate into the atmosphere, when, and how this will affect the current climate. That’s where CC-TOP (Cryosphere-Carbon on Top of the Earth (CC-Top): Decreasing Uncertainties of Thawing Permafrost and Collapsing Methane Hydrates in the Arctic) can make a difference. After 5 years of intensive European Research Council funded research, Örjan Gustafsson has managed to uncover precious information on what he calls the “sleeping giants in the global carbon cycle.” “We are now closer to scientifically sound predictions for future releases of methane over the coming decades and centuries,” says Gustafsson, a professor at the Department of Environmental Science at Stockholm University. “CC-TOP tells us more about carbon-climate coupling and methane hydrates, specifically for permafrost on land, along the coastline and in the subsea.” Gustafsson and his team pursued these giants in the distant East Siberian Arctic Ocean. They could do so thanks to advanced molecular and isotopic fingerprinting of the sources and fluxes of organic matter, as well as of the methane released from thawing permafrost. “We notably developed triple-isotope source forensics for massive releases of methane over the East Siberian Arctic Shelf – the world’s largest coastal sea. With these, we can provide high-precision measurements of the stable isotopes of carbon, hydrogen and natural abundance radiocarbon,” explains Gustafsson. This method helped Gustafsson’s team ascertain what proportion of the escaping methane comes from biogenic near-surface sources, thawing subsea permafrost, and deep reservoirs of thermogenic methane penetrating up through the thawing permafrost.
New knowledge of subsea permafrost
The project resulted in well over 30 papers, eight of which were published in high-impact journals such as ‘Science’, ‘PNAS’ and ‘Nature’. Moreover, it compiled the first open-science database dedicated to the distribution and sources of carbon in all Arctic Ocean sediments. Project studies on past rapid warming periods have found a correlation between massive permafrost carbon releases and rapid increases in atmospheric CO2. As Gustafsson points out: “This suggests that the existing paradigm of ocean venting carbon may need to be complemented by a remobilisation of terrestrial carbon/methane. This may be a sneak peek of what is in store for current climate change.” It also provides new knowledge on subsea permafrost. “Our studies show that the permafrost that’s currently underneath the shallow shelf ocean has recently reached the thaw point. Over the past decades, it has been thawing at a rate 10 times faster than land-based permafrost,” adds Gustafsson. He continues: “Observations of methane emissions hotspots in the Laptev Sea also revealed that the dominant source of methane there is a deep thermogenic pool. This suggests that there can be rapid release of such preformed methane.” Thanks to isotope source apportionment of black carbon aerosol particles around the Arctic rim, which estimates the contribution of pollution sources such as diesel engines and wood burning, the team even provided a scientific underpinning for targeting dominant emissions sources in mitigation measures. CC-TOP’s international network remains very active. Several major international expeditions on both Russian and Swedish research vessels and icebreakers are planned, and Gustafsson hopes to put together another ERC proposal soon. As he underlines: “The project’s findings inspire us to step up and bend the curves on climate change. The current decade will be critical if we are to win this fight.”
Keywords
CC-TOP, Arctic, permafrost, methane, carbon cycle, pollution, ice, isotope, climate change
