| 11. |
- Pirk, Norbert
(författare)
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Tundra meets atmosphere : Seasonal dynamics of trace gas exchange in the High Arctic
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Arctic environments have experienced strong warming in recent decades, which is affecting the carbon cycle of tundra ecosystems.Degrading permafrost, diminishing snow cover, and changing hydrology are examples of ongoing processes that affect the land-atmosphere interactions and seasonal ecosystem dynamics.Since a number of the affected processes involve the exchange of atmospheric greenhouse gases, such as the trace gases methane (CH4) and carbon dioxide (CO2), there is a potential for these interactions to lead to climate feedbacks.The impact this feedback could have on the global climate is currently not well known due to gaps in our knowledge about the involved processes.One reason for this mismatch is the scarcity of direct, continuous and comparable measurements of CH4 and CO2 fluxes in the high Arctic tundra.The relatively remote, harsh, and low-flux conditions dominating these environments for most of the year pose challenges for flux measurement techniques that have proven to work well at lower latitudes.The present study is, therefore, not only aiming to advance our understanding of trace gas exchanges in the Arctic tundra, but also trying to improve commonly-used flux measurement techniques to yield new insights.The two main study sites of this work are located in permafrost-underlain wetlands in Adventdalen, Svalbard and Zackenberg, NE Greenland.These sites show distinctly different processes that govern the trace gas exchange throughout the different seasons:The snow-free season is characterized by high CH4 emissions, which seem to follow predictable spatial and temporal patterns. Large CO2 uptake by photosynthesis and release by respiration give rise to a large amplitude of net ecosystem exchange during the growing season.The autumnal freeze-in period can feature the highest gas emissions, most likely due to physical mechanisms connected to the soil freezing that release a part of the soil gas reservoir.During winter and spring a low level of microbial activity is sustained but the gas transport capability of the frozen soil is relatively low. Still, snowpack gas concentrations indicate consistent emissions of CH4 and CO2 from the soil.Around the snowmelt period, emissions of stored gases in the snowpack and soil are superimposed on the fast increase of biological activity. The flooded and heterogeneous conditions make the representative flux estimation extremely challenging around this time of year.The diverse range of processes governing the seasonal flux dynamics at these two study sites exemplifies the complexity and possibilities of predicting the resilience and vulnerability of Arctic tundra ecosystems to climate change.
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| 12. |
- Qiu, Chunjing, et al.
(författare)
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ORCHIDEE-PEAT (revision 4596), a model for northern peatland CO2, water, and energy fluxes on daily to annual scales
- 2018
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Ingår i: Geoscientific Model Development. - : Copernicus GmbH. - 1991-959X .- 1991-9603. ; 11:2, s. 497-519
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Tidskriftsartikel (refereegranskat)abstract
- Peatlands store substantial amounts of carbon and are vulnerable to climate change. We present a modified version of the Organising Carbon and Hydrology In Dynamic Ecosystems (ORCHIDEE) land surface model for simulating the hydrology, surface energy, and CO2 fluxes of peatlands on daily to annual timescales. The model includes a separate soil tile in each 0.5° grid cell, defined from a global peatland map and identified with peat-specific soil hydraulic properties. Runoff from non-peat vegetation within a grid cell containing a fraction of peat is routed to this peat soil tile, which maintains shallow water tables. The water table position separates oxic from anoxic decomposition. The model was evaluated against eddy-covariance (EC) observations from 30 northern peatland sites, with the maximum rate of carboxylation (Vcmax) being optimized at each site. Regarding short-term day-to-day variations, the model performance was good for gross primary production (GPP) (r2 Combining double low line 0.76; Nash-Sutcliffe modeling efficiency, MEF Combining double low line 0.76) and ecosystem respiration (ER, r2 Combining double low line 0.78, MEF Combining double low line 0.75), with lesser accuracy for latent heat fluxes (LE, r2 Combining double low line 0.42, MEF Combining double low line 0.14) and and net ecosystem CO2 exchange (NEE, r2 Combining double low line 0.38, MEF Combining double low line 0.26). Seasonal variations in GPP, ER, NEE, and energy fluxes on monthly scales showed moderate to high r2 values (0.57-0.86). For spatial across-site gradients of annual mean GPP, ER, NEE, and LE, r2 values of 0.93, 0.89, 0.27, and 0.71 were achieved, respectively. Water table (WT) variation was not well predicted (r2<0.1), likely due to the uncertain water input to the peat from surrounding areas. However, the poor performance of WT simulation did not greatly affect predictions of ER and NEE. We found a significant relationship between optimized Vcmax and latitude (temperature), which better reflects the spatial gradients of annual NEE than using an average Vcmax value.
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| 13. |
- Seco, Roger, et al.
(författare)
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Strong isoprene emission response to temperature in tundra vegetation
- 2022
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 1091-6490. ; 119:38, s. 2118014119-2118014119
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Tidskriftsartikel (refereegranskat)abstract
- Emissions of biogenic volatile organic compounds (BVOCs) are a crucial component of biosphere-atmosphere interactions. In northern latitudes, climate change is amplified by feedback processes in which BVOCs have a recognized, yet poorly quantified role, mainly due to a lack of measurements and concomitant modeling gaps. Hence, current Earth system models mostly rely on temperature responses measured on vegetation from lower latitudes, rendering their predictions highly uncertain. Here, we show how tundra isoprene emissions respond vigorously to temperature increases, compared to model results. Our unique dataset of direct eddy covariance ecosystem-level isoprene measurements in two contrasting ecosystems exhibited Q10 (the factor by which the emission rate increases with a 10 °C rise in temperature) temperature coefficients of up to 20.8, that is, 3.5 times the Q10 of 5.9 derived from the equivalent model calculations. Crude estimates using the observed temperature responses indicate that tundra vegetation could enhance their isoprene emissions by up to 41% (87%)-that is, 46% (55%) more than estimated by models-with a 2 °C (4 °C) warming. Our results demonstrate that tundra vegetation possesses the potential to substantially boost its isoprene emissions in response to future rising temperatures, at rates that exceed the current Earth system model predictions.
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| 14. |
- Tømmervik, Hans, et al.
(författare)
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The northernmost hyperspectral FLoX sensor dataset for monitoring of high-Arctic tundra vegetation phenology and Sun-Induced Fluorescence (SIF)
- 2023
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Ingår i: Data in Brief. - 2352-3409. ; 50
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Tidskriftsartikel (refereegranskat)abstract
- A hyperspectral field sensor (FloX) was installed in Adventdalen (Svalbard, Norway) in 2019 as part of the Svalbard Integrated Arctic Earth Observing System (SIOS) for monitoring vegetation phenology and Sun-Induced Chlorophyll Fluorescence (SIF) of high-Arctic tundra. This northernmost hyperspectral sensor is located within the footprint of a tower for long-term eddy covariance flux measurements and is an integral part of an automatic environmental monitoring system on Svalbard (AsMovEn), which is also a part of SIOS. One of the measurements that this hyperspectral instrument can capture is SIF, which serves as a proxy of gross primary production (GPP) and carbon flux rates. This paper presents an overview of the data collection and processing, and the 4-year (2019–2021) datasets in processed format are available at: https://thredds.met.no/thredds/catalog/arcticdata/infranor/NINA-FLOX/raw/catalog.html associated with https://doi.org/10.21343/ZDM7-JD72 under a CC-BY-4.0 license. Results obtained from the first three years in operation showed interannual variation in SIF and other spectral vegetation indices including MERIS Terrestrial Chlorophyll Index (MTCI), EVI and NDVI. Synergistic uses of the measurements from this northernmost hyperspectral FLoX sensor, in conjunction with other monitoring systems, will advance our understanding of how tundra vegetation responds to changing climate and the resulting implications on carbon and energy balance.
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