#	Pagina
attuale pagina	/open-h2020/projects/204873/results.html

Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - CC-TOP (Cryosphere-Carbon on Top of the Earth (CC-Top):Decreasing Uncertainties of Thawing Permafrost and Collapsing Methane Hydrates in the Arctic)

Teaser

Summary

\"The ERC-AdG project CC-TOP is addressing one of the Grand Challenges in Earth System Science: â€œRe-awakeningâ€ (remobilization) of carbon from the huge frozen surface reservoirs contained in terrestrial and subsea permafrost in the Eurasian Arctic. Thawing permafrost is one of the few processes that can cause a large net repartitioning of carbon as greenhouse gases to the atmosphere on decade-century timescales. CC-TOP aims reduce the uncertainties for this to aid societal mitigation to combat climate change.

To address the overall objective, to enable decreasing uncertainties in our understanding of Arctic thawing permafrost and its effects, the work is broadly structured into four core domains: Terrestrial Cryosphere Carbon (\"\"Terra\"\"), Shelf/Subsea Cryosphere Carbon (\"\"Shelf\"\"), Slope Hydrate Cryosphere Carbon (\"\"Slope\"\"), and Atmospheric constraints on CH4 sources (\"\"Atmos\"\").\"

Work performed

Objective Terra-1
There is already one break-through in this area. Our 2019 PNAS paper (Wild et al., 2019) presents a first quantitative estimate of how much of the river organic carbon that comes from permafrost and peat deposits across the Eurasian Arctic. While there had been many Arctic river studies earlier, these long-term 14C results are the first one to pinpoint that only a small portion of DOC was from peat and permafrost (PP), whereas about half of the POC is released from PP. This is an essential component for meaningful predictions of the Arctic permafrost/peat carbon-climate feedbacks.

Objective Terra-2
The project has produced about ten strong papers on the sources, transport and degradation of terrestrial carbon to and in the wide Siberian-Arctic shelf seas. Among other results, our 2018 Nature Comm. paper provided breakthrough on a long-standing challenge in the ocean carbon cycle: what is the time for cross-shelf transport, allowing unique constraint on ambient degradation rates and fluxes of different compound classes of translocated permafrost carbon (BrÃ¶der et al., 2018, 2019).

Objective Terra-3
Permafrost carbon remobilization during earlier rapid warming periods may give clues to what is in store with current climate warming. Here we have started a whole new line of investigation by deciphering the historical record of changing permafrost-C input to the Arctic Ocean recipients in the Laptev Sea (Tesi et al., 2016, Nature Comm), The East Siberian Sea (Keskitalo et al., 2017, Climate of the Past) and Chukchi Sea (Martens et al., 2019, Global Biogeochemical Cycles). Using advanced molecular and isotopic techniques, these CC-TOP studies document that there were massive remobilization of permafrost-C during the Younger Dryas â€“ Preboreal warm spell some 11500 years ago, which is synchronous to a sudden increase in global atmospheric CO2.

Objective Shelf-1
The CC-TOP investigates 20-60 m drill cores of subsea permafrost from Laptev Sea. Our first major publication (Shakhova et al., 2017, Nature Comm.) provided true breakthrough: The thermal state of the subsea permafrost is now near 0degC, which is about 10degC warmer than neighboring permafrost cores on land â€“ this is likely due to the warming of overlying seawater. Comparison with the thermal state of cores recovered by the Soviets in the 1970s at same location, we documented that the thaw horizon of the subsea permafrost was lowered by 4-5 m, corresponding to an average thaw-out of 14Â±3 cm/yr; this is an order of magnitude more rapid thawing than for more-studied land-based permafrost.

Objective Shelf-2
There is a large void of data on the composition of the subsea permafrost system. Our 2017 Nature Comm. study provided some first data on physical properties. We have another paper soon to be submitted on the organic matter content and molecular composition across the thaw horizons, investigating the degradation status of the organic matter. There is also more work underway including incubations of subsea permafrost to explore the potential for GHG generation in thawing subsea permafrost.

Objective Shelf-3
Samples for triple-isotope analysis of methane (dD, d13C, D14C) have been obtained from the East Siberian Arctic Sea for 2018 and 2019. Advances have been made for improved sample processing in our laboratories. The first study from methane hotspots in Laptev Sea using the triple-isotope approach is nearly ready for submission and publication.

Objective Slope-1
The Arctic shelf slopes are believed to hold extensive marine hydrates, which may be vulnerable to destabilization through warming by the intermediate Atlantic Water mass - yet there are to date no published observations on this. We have processed data from earlier expeditions and find evidence for methane releases from slope hydrates at some 3-4 transects (ms in prep.)

Objective Atmos-1
The 2018-2019 period has seen intensive work on preparing and testing systems for on-line isotope

Final results

There has already been massive progress on most objectives of CC-TOP. Some of the key breakthroughs to date have been:
â€¢ The first quantitative estimate for the fluvial remobilization of organic carbon specifically from permafrost and peat deposits across the Eurasian Arctic (Wild et al., PNAS 2019): The long-term 14C results are the first ones to pinpoint how large a fraction of the total river carbon is really coming from peat/permafrost; surprisingly, only a small portion of DOC was from permafrost and peat, whereas about half of the POC originated from these sources with clear spatial trends across the Eurasian-Arctic climosequence. This is an essential component for meaningful predictions of the Arctic permafrost/peat carbon-climate feedbacks.

â€¢ The first quantitative constraint on cross-shelf transport (and degradation) time: This allows deriving the expected degradation flux in this receptor 1000s of km away from the original point of permafrost thaw.

â€¢ The first observation-based estimate on the rate of thawing of subsea permafrost: The studies of the 20-60 m subsea permafrost drill cores revealed that this elusive Arctic cryosphere has recently reached a thermal state near or at the point of thawing. The thermal state in the top tens of meters is about 10 degC warmer than nearby land-based permafrost. The rate of lowering of the permafrost table (the interface between still frozen and thawed matter) is at least ten times faster than for surface permafrost on land. This CC-TOP finding has large repercussions on predictions of how methane may be released from vulnerable subsea permafrost.

In line with the DoA and according to plan, there is now an increasing emphasis on methane: the generation mechanisms and sources, including isotope-based source fingerprinting in the Eurasian Arctic margin.