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

Periodic Reporting for period 3 - THAWSOME (THAWing permafrost: the fate of Soil Organic Matter in the aquatic Environment)

Reporting period: 2019-12-01 to 2021-05-31

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.
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.
For the first time, this project measured degradation rates of particulate organic carbon in large Arctic rivers. A recent publication (one team member and PI involved) showed that POC in large Arctic rivers is tracing permafrost thaw very effectively, but we do not know yet where this permafrost POC will end up. The results of our field and laboratory experiments will provide quantitative numbers for this missing pathway. Additionally, we have gathered data on the fate of this permafrost POC in the nearshore zone, just after its coastal release. This zone is severely understudied because ice breakers cannot access these shallow waters, and terrestrial researchers do not travel far on boats. At the same time, this zone experiences increasing impact from storms and waves due to more pronounced open water conditions on the Arctic Ocean. When laboratory analyses are finalized, we will be able to say more about the dynamics of permafrost POC in the dynamic nearshore zone.
Permafrost thaw slump on the Peel Plateau, image by Lisa Bröder