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Subsea permafrost carbon stocks and climate change sensitivity estimated by expert assessment

Environmental Research Letters

Sayedi, Sayedeh S.; Abbott, Benjamin W.; Thornton, Brett F.; Frederick, Jennifer M.; Vonk, Jorien E.; Overduin, Paul; Schadel, Christina; Schuur, Edward A.G.; Bourbonnais, Annie; Demidov, Nikita; Gavrilov, Anatoly; He, Shengping; Hugelius, Gustaf; Jakobsson, Martin; Jones, Miriam C.; Joung, Dongjoo; Kraev, Gleb; Macdonald, Robie W.; David Mcguire, A.; Mu, Cuicui; O'Reagon, M.; Schreiner, K.M.; Stranne, C.; Pizhankova, E.; Vasiliev, A.; Westermann, S.; Zarnetske, J.P.; Zhang, T.; Ghandehari, M.; Baeumler, S.; Brown, B.C.E.; Frei, R.J.

The continental shelves of the Arctic Ocean and surrounding seas contain large stocks of organic matter (OM) and methane (CH4), representing a potential ecosystem feedback to climate change not included in international climate agreements. We performed a structured expert assessment with 25 permafrost researchers to combine quantitative estimates of the stocks and sensitivity of organic carbon in the subsea permafrost domain (i.e. unglaciated portions of the continental shelves exposed during the last glacial period). Experts estimated that the subsea permafrost domain contains ~560 gigatons carbon (GtC; 170–740, 90% confidence interval) in OM and 45 GtC (10–110) in CH4. Current fluxes of CH4 and carbon dioxide (CO2) to the water column were estimated at 18 (2–34) and 38 (13–110) megatons C yr–1, respectively. Under Representative Concentration Pathway (RCP) RCP8.5, the subsea permafrost domain could release 43 Gt CO2–equivalent (CO2e) by 2100 (14–110) and 190 Gt CO2e by 2300 (45–590), with ~30% fewer emissions under RCP2.6. The range of uncertainty demonstrates a serious knowledge gap but provides initial estimates of the magnitude and timing of the subsea permafrost climate feedback.

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TYPE Journal Article YEAR 2020
DOIOSTI

Arctic Coastal Erosion: Modeling and Experimentation

Bull, Diana L.; Bristol, Emily M.; Brown, Eloise; Choens, Robert C.; Connolly, Craig T.; Flanary, Christopher; Frederick, Jennifer M.; Jones, Benjamin M.; Jones, Craig A.; Ward Jones, Melissa; Mcclelland, James W.; Mota, Alejandro M.; Kalashnikova, Irina

Increasing Arctic coastal erosion rates have put critical infrastructure and native communities at risk while also mobilizing ancient organic carbon into modern carbon cycles. Although the Arctic comprises one-third of the global coastline and has some of the fastest eroding coasts, current tools for quantifying permafrost erosion are unable to explain the episodic, storm-driven erosion events. Our approach, mechanistically coupling oceanographic predictions with a terrestrial model to capture the thermo-mechanical dynamics of erosion, enables this much needed treatment of transient erosion events. The Arctic Coastal Erosion Model consists of oceanographic and atmospheric boundary conditions that force a coastal terrestrial permafrost environment in Albany (a multi-physics based finite element model). An oceanographic modeling suite (consisting of WAVEWATCH III, Delft3D-FLOW, and Delft3D-WAVE) produced time-dependent surge and run-up boundary conditions for the terrestrial model. In the terrestrial model, a coupling framework unites the mechanical and thermal aspects of erosion. 3D stress/strain fields develop in response to a plasticity model of the permafrost that is controlled by the frozen water content determined by modeling 3D heat conduction and solid-liquid phase change. This modeling approach enables failure from any allowable deformation (block failure, slumping, etc.). Extensive experimental work has underpinned the ACE Model development including field campaigns to measure in situ ocean and erosion processes, strength properties derived from thermally driven geomechanical experiments, as well as extensive physical composition and geochemical analyses. Combined, this work offers the most comprehensive and physically grounded treatment of Arctic coastal erosion available in the literature. The ACE model and experimental results can be used to inform scientific understanding of coastal erosion processes, contribute to estimates of geochemical and sediment land-to-ocean fluxes, and facilitate infrastructure susceptibility assessments.

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TYPE SAND Report YEAR 2020
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Geometric and Material Variability Influences Stress States Relevant to Coastal Permafrost Bluff Failure

Frontiers in Earth Science

Thomas, Matthew A.; Mota, Alejandro M.; Jones, Benjamin M.; Choens, Robert C.; Frederick, Jennifer M.; Bull, Diana L.

Scientific knowledge and engineering tools for predicting coastal erosion are largely confined to temperate climate zones that are dominated by non-cohesive sediments. The pattern of erosion exhibited by the ice-bonded permafrost bluffs in Arctic Alaska, however, is not well-explained by these tools. Investigation of the oceanographic, thermal, and mechanical processes that are relevant to permafrost bluff failure along Arctic coastlines is needed. We conducted physics-based numerical simulations of mechanical response that focus on the impact of geometric and material variability on permafrost bluff stress states for a coastal setting in Arctic Alaska that is prone to toppling mode block failure. Our three-dimensional geomechanical boundary-value problems output static realizations of compressive and tensile stresses. We use these results to quantify variability in the loci of potential instability. We observe that niche dimension affects the location and magnitude of the simulated maximum tensile stress more strongly than the bluff height, ice wedge polygon size, ice wedge geometry, bulk density, Young's Modulus, and Poisson's Ratio. Our simulations indicate that variations in niche dimension can produce radically different potential failure areas and that even relatively shallow vertical cracks can concentrate displacement within ice-bonded permafrost bluffs. These findings suggest that stability assessment approaches, for which the geometry of the failure plane is delineated a priori, may not be ideal for coastlines similar to our study area and could hamper predictions of erosion rates and nearshore sediment/biogeochemical loading.

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TYPE Journal Article YEAR 2020
DOIOSTIScopus
Results 26–50 of 132
Results 26–50 of 132