Divergent changes in particulate and mineral-associated organic carbon upon permafrost thaw

Acknowledgements This work was supported by the National Natural Science Foundation of China (31988102, 31825006, 91837312, and 32101332), the Second Tibetan Plateau Scientific Expedition and Research (STEP) program (2019QZKK0106 and 2019QZKK0302), and the Fundamental Research Foundation of Chinese Academy of Forestry (CAFYBB2020MA008).Peer reviewedPublisher PD

Patterns and drivers of prokaryotic communities in thermokarst lake water across Northern Hemisphere

13 páginas.- 5 figuras.- 81referencias.Aim: The formation of thermokarst lakes could make a large amount of carbon accessible to microbial degradation, potentially intensifying the permafrost carbon-climate feedback via carbon dioxide/methane emissions. Because of their diverse functional roles, prokaryotes could strongly mediate biogeochemical cycles in thermokarst lakes. However, little is known about the large-scale patterns and drivers of these communities. Location: Permafrost regions in the Northern Hemisphere. Time period: Present day. Major taxa studied: Prokaryotes. Methods: Based on a combination of large-scale measurements on the Tibetan Plateau and data syntheses in pan-Arctic regions, we constructed a comprehensive dataset of 16S rRNA sequences from 258 thermokarst lakes across Northern Hemisphere permafrost regions. We also used the local contributions to beta diversity (LCBD) to characterize the variance of prokaryotic species composition and screened underlying drivers by conducting a random forest modelling analysis. Results: Prokaryotes in thermokarst lake water were dominated by the orders Burkholderiales, Micrococcales, Flavobacteriales and Frankiales. The relative abundance of dominant taxa was positively associated with dissolved organic matter (DOM) properties, especially for the chromophoric/aromatic compounds. Microbial structure differed between high-altitude and high-latitude thermokarst lakes, with the dominance of Flavobacterium in high-altitude lakes, and the enrichment of Polynucleobacter in high-latitude lakes. More importantly, climatic variables were among the main drivers shaping the large-scale variation of prokaryotic communities. Specifically, mean annual precipitation was the best predictor for prokaryotic beta diversity across the Northern Hemisphere, as well as in the high-altitude permafrost regions, while mean annual air temperature played a key role in the high-latitude thermokarst lakes. Main conclusions: Our findings demonstrate significant associations between dominant taxa and DOM properties, as well as the important role of climatic factors in affecting prokaryotic communities. These findings suggest that climatic change may alter DOM conditions and induce dynamics in prokaryotic communities of thermokarst lake water in the Northern Hemisphere. © 2023 John Wiley & Sons Ltd.This work was supported by the National Key Research and Development Program of China (2022YFF0801903), National Natural Science Foundation of China (31988102, and 31825006), and Tencent Foundation through the XPLORER PRIZE. M.D‐B. acknowledges support from TED2021‐130908B‐C41/AEI/10.13039/501100011033/Unión Europea NextGenerationEU/PRTR and from the Spanish Ministry of Science and Innovation for the I + D + i project PID2020‐115813RA‐I00 funded by MCIN/AEI/10.13039/501100011033.Peer reviewe

Stream dissolved organic matter in permafrost regions shows surprising compositional similarities but negative priming and nutrient effects

Permafrost degradation is delivering bioavailable dissolved organic matter (DOM) and inorganic nutrients to surface water networks. While these permafrost subsidies represent a small portion of total fluvial DOM and nutrient fluxes, they could influence food webs and net ecosystem carbon balance via priming or nutrient effects that destabilize background DOM. We investigated how addition of biolabile carbon (acetate) and inorganic nutrients (nitrogen and phosphorus) affected DOM decomposition with 28-day incubations. We incubated late-summer stream water from 23 locations nested in seven northern or high-altitude regions in Asia, Europe, and North America. DOM loss ranged from 3% to 52%, showing a variety of longitudinal patterns within stream networks. DOM optical properties varied widely, but DOM showed compositional similarity based on Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis. Addition of acetate and nutrients decreased bulk DOM mineralization (i.e., negative priming), with more negative effects on biodegradable DOM but neutral or positive effects on stable DOM. Unexpectedly, acetate and nutrients triggered breakdown of colored DOM (CDOM), with median decreases of 1.6% in the control and 22% in the amended treatment. Additionally, the uptake of added acetate was strongly limited by nutrient availability across sites. These findings suggest that biolabile DOM and nutrients released from degrading permafrost may decrease background DOM mineralization but alter stoichiometry and light conditions in receiving waterbodies. We conclude that priming and nutrient effects are coupled in northern aquatic ecosystems and that quantifying two-way interactions between DOM properties and environmental conditions could resolve conflicting observations about the drivers of DOM in permafrost zone waterways

Combined Acceleration Methods for Solid Rocket Motor Grain Burnback Simulation Based on the Level Set Method

A detailed study of a set of combined acceleration methods is presented with the objective of accelerating the solid rocket motor grain burnback simulation based on the level set method. Relevant methods were improved by making use of unique characteristics of the grains, and graphical processing unit (GPU) parallelization is utilized to perform the computationally intensive operations. The presented flow traced the expansion of burning surfaces, and then Boolean operations were applied on the resulting surfaces to extract various geometric metrics. The initial signed distance field was built by an improved distance field generating method, and a highly optimized GPU kernel was used for estimating the gradient required by the level set method. An innovative Boolean operation method, thousands of times faster than ordinary ones, was ultimately proposed. Performance tests show that the overall speedup was close to 15 on desktop-class hardware, simulation results were proven to converge to analytical results, and the error boundary was 0.25%

efficient simulation of grain burning surface regression

The computation of grain burning surface regression plays a very important role in the internal ballistic performance evaluation of solid rocket motor, however, the traditional methods such as geometry-based one could not handle the self-intersection and characteristic geometric element disappearing problems. This paper presents an effective and efficient framework to simulate 3D grain burning surface regression with level set method which is combined with Fast Marching technique to constrain the calculation area only around the burning surface. At last, a typical grain example is given by our framework to verify our method's effectiveness and efficiency. © (2012) Trans Tech Publications.The computation of grain burning surface regression plays a very important role in the internal ballistic performance evaluation of solid rocket motor, however, the traditional methods such as geometry-based one could not handle the self-intersection and characteristic geometric element disappearing problems. This paper presents an effective and efficient framework to simulate 3D grain burning surface regression with level set method which is combined with Fast Marching technique to constrain the calculation area only around the burning surface. At last, a typical grain example is given by our framework to verify our method's effectiveness and efficiency. © (2012) Trans Tech Publications

Precise Design of Solid Rocket Motor Heat Insulation Layer Thickness under Nonuniform Dynamic Burning Rate

With the purpose of obtaining optimal designs of the heat insulating layers in solid rocket motors, we have proposed a numerical approach to compute the ideal thickness of the heat insulating layer. The proposed method is compatible with solid rocket motors that have any shape and any manner of erosion. The nonuniform dynamic burning rate is taken into consideration to achieve higher accuracy. A high-performance code is developed that uses triangular geometry as an input to allow exchanging data from any CAD platform. An improved geometric intersection algorithm is developed to generate the required sampling points, saving 35% computation time compared to its open source equivalent. Parallel computing technology is utilized to further improve the performance. All operations of the proposed approach can be executed automatically by programs, eliminating the manual work of gathering data from CAD software in the traditional approach. Validation data shows that the proposed approach saves 3.85% of the mass compared to the ordinary design approach. Performance profiling shows that the implemented code operates within 5 seconds, which is much faster than the unoptimized open source version

Robust Three-Dimensional Level-Set Method for Evolving Fronts on Complex Unstructured Meshes

With a purpose to evolve the surfaces of complex geometries in their normal direction at arbitrarily defined velocities, we have developed a robust level-set approach which runs on three-dimensional unstructured meshes. The approach is built on the basis of an innovative spatial discretization and corresponding gradient-estimating approach. The numerical consistency of the estimating method is mathematically proven. A correction technology is utilized to improve accuracy near sharp geometric features. Validation tests show that the proposed approach is able to accurately handle geometries containing sharp features, computation regions having irregular shapes, discontinuous speed fields, and topological changes. Results of the test problems fit well with the reference results produced by analytical or other numerical methods and converge to reference results as the meshes refine. Compared to level-set method implementations on Cartesian meshes, the proposed approach makes it easier to describe jump boundary conditions and to perform coupling simulations