THAWing permafrost: the fate of Soil Organic Matter in the aquatic Environment

Project Information

THAWSOME

Grant agreement ID: 676982

DOI

10.3030/676982

Project closed

EC signature date 18 May 2016

Start date 1 December 2016

End date 30 September 2022

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 500 000,00

EU contribution

€ 1 500 000,00

Coordinated by

STICHTING VU
Netherlands

Periodic Reporting for period 4 - THAWSOME (THAWing permafrost: the fate of Soil Organic Matter in the aquatic Environment)

Reporting period: 2021-06-01 to 2022-09-30

Summary of the context and overall objectives of the project

As the Arctic permafrost region warms, its large organic carbon (OC) pool becomes vulnerable to decomposition. This generates greenhouse gases (GHG) that in turn fuel increased surface warming: the permafrost carbon feedback. Higher temperatures will jump-start the coupling between the carbon and hydrological cycle, allowing for the introduction of previously frozen OC pools in aquatic systems. This lateral, or horizontal, aquatic flux remains largely unknown in contrast to the relatively well-studied vertical flux, GHG emission on land.
Horizontal OC release either occurs via gradual thaw, slowly leaching OC into aquatic systems, or via abrupt thaw, where ground-ice melt causes destructive surface collapse and slumping of OC into aquatic systems. Both types of thaw facilitate decomposition of OC (generating GHG) but also re-bury OC into sediments (sequestering OC). The relative importance of decomposition versus burial is unknown.
In THAWSOME, we will combine a multi-scale approach combining detailed process-based field studies with up-scaling techniques on multiple levels: (i) observational, using large Arctic rivers as natural integrators, (ii) numerical, using a coupled hydrological-biogeochemical model, and (iii) spatial, using GIS-based analysis. Our objectives are to quantify, for the first time, decomposition of particulate OC from permafrost and to assess the fate of permafrost OC in the nearshore zone and the continental shelf.
THAWSOME will generate critically needed quantitative data on the amount of decomposition versus burial of permafrost OC, as well as qualitative insights into the processes that control this.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Three successful field campaigns have been planned and executed to the Canadian and Siberian Arctic, one field campaign is currently ongoing. We are working on data and results from the incubation experiments in the field, as well as the geochemical laboratory analyses on the large set of samples that we managed to transport back home.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

After several intensive field campaigns in the Siberian and Canadian Arctic, we performed a range of experiments and laboratory analyses to answer the main questions posed in the research objectives. We assessed the quality and quantity of thawing permafrost organic matter, and assessed its fate in arctic aquatic environments, in which we distinguished between abrupt and gradual thaw. Publications by Jong et al. (2020) showed that particulate matter in nearshore zones close to eroding permafrost coasts (abrupt thaw) settles rapidly implying that its further route is predominantly at the water-sediment interface and degradation may be limited. Keskitalo et al. (2021) and Bröder et al (2021) showed that particulate matter from inland permafrost thaw slumps (abrupt thaw) is degraded to some extent, but likely mostly limited to sites close to the thaw slump. This suggests that temporary storage in large debris tongues is temporarily removing this carbon from the active carbon cycle. Keskitalo et al. (2022) and Jong et al (2022, accepted) showed that particulate matter in fluvial systems (dominated by gradual thaw) is mostly derived from autochthonous sources (i.e. plankton), and not from permafrost.

Our publication record is strengthening the realisation that in the scientific studies focusing on thawing and degrading permafrost, it is absolutely needed to include particulate matter. The research communities that study permafrost thaw are frequently NOT considering (aquatic) lateral transport, and the research community that does focus on lateral transport is frequently only focusing on dissolved matter. Our research has changed this.We also have highlighted the strong spatial heterogeneity of particulate matter degradation. In some systems, overwhelmed by abrupt and local thaw features, particulate matter may be a fairly conservative transport mode moving thawing organic matter from soils into debris tongues. In these systems, degradation and greenhouse gas release may be low. In other systems, where gradual but wide-scale thaw occurs, particulate matter is not so abundant but does degrade more quickly. Including particulate matter dynamics in aquatic systems surrounded by permafrost thaw can therefore either be an attenuating or a strengthening component in the generation of greenhouse gases.

Permafrost thaw slump on the Peel Plateau, image by Lisa Bröder