Objective Terra-1
One illustrative break-through in this area is represented by our 2019 PNAS paper (Wild et al., 2019). It 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 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 (Bröder 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 the project pioneered 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; Martens et al., Science Advances 2021), 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 – Preboreal warm spell some 11500 years ago, which is synchronous to a sudden increase in global atmospheric CO2.
Objective Shelf-1
The CC-TOP investigated 20-60 m drill cores of subsea permafrost from Laptev Sea. One 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 – 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 14±3 cm/yr; this is an order of magnitude more rapid thawing than for 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. A follow-up study in the ERC project documenting the composition around the subsea permafrost thaw horizon and its propensity to be converted microbially to methane is currently in re-review in a high-impact journal.
Objective Shelf-3
Samples for triple-isotope analysis of methane (dD, d13C, D14C) were obtained from the East Siberian Arctic Sea in 2014, 2018 and 2019. A method was advanced that enbabled high-precision triple isotope measurements of methane in seawater. The first study, from methane hotspots in Laptev Sea, using the triple-isotope approach revealed that a major source was a deep thermogenic pool of methane penetrating up through the subsea permafrost.
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 processed data from earlier expeditions and found evidence for methane releases from slope hydrates at some 3-4 transects (ms in prep.)
