Drivers of carbon dioxide fluxes in high-Arctic tundra: data-driven models

Arctic regions are extreme environments where ecosystems are undergoing significant changes induced by the temperature rise, that is progressing about twice faster than in the rest of the world. In the high-Arctic, the Critical Zone (CZ) has a thin above-ground component, consisting of tundra vegetation, and a highly seasonal below-ground component, with varying extension and chemical-physical characteristics. The complexity of this system makes future projections of the Arctic CZ a challenging goal. In particular, it is still unclear whether the system will turn from a carbon sink to a carbon source. On the one hand, the uptake of carbon dioxide (CO2) by vegetation is expected to increase in future years owing to the widening growing season and the shift in community composition but, on the other, increasing soil temperatures are fostering carbon release by thawing permafrost and degradation of organic matter through heterotrophic respiration in deglaciated soils. In this work, we identified the main biotic and abiotic drivers of CO2 emissions (Ecosystem Respiration, ER), and CO2 uptake (Gross Primary Production, GPP), in the Arctic tundra biome. During summer 2019 we extensively measured CO2 fluxes at the soil-vegetation-atmosphere interface, basic meteoclimatic variables and ecological descriptors at the Critical Zone Observatory of Bayelva river basin (CZO@Bayelva), Spitzbergen, in the Svalbard Archipelago (NO). Flux measurements were obtained by a portable accumulation chamber, allowing for the statistical analysis of fluxes variability at small scale. Together with flux measurements, we sampled soil temperature and humidity at the chamber base and local air temperature, pressure and humidity. In addition, the vegetation cover was obtained from digital RGB pictures of the sampled surfaces. By means of multi regression models, we related flux data to environmental parameters, vegetation cover extent and vegetation type, thus obtaining empirical data-driven models that describe the coupled dynamics of soil, vegetation, water and atmosphere that contribute to the present budgeting of the carbon cycle in the arctic CZ. This work may help in assessing the possible future evolution of high-Arctic environment under projected changes in vegetation community composition and abiotic parameters.

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Microscale drivers of summer CO2 fluxes in the Svalbard High Arctic tundra

Scientific Reports ◽

10.1038/s41598-021-04728-0 ◽

2022 ◽

Vol 12 (1) ◽

Author(s):

Marta Magnani ◽

Ilaria Baneschi ◽

Mariasilvia Giamberini ◽

Brunella Raco ◽

Antonello Provenzale

Keyword(s):

Ecosystem Respiration ◽

Vegetation Type ◽

Gross Primary Production ◽

Arctic Tundra ◽

High Arctic ◽

The Arctic ◽

Small Scale ◽

Arctic Ecosystems ◽

Additional Source ◽

And Storage

AbstractHigh-Arctic ecosystems are strongly affected by climate change, and it is still unclear whether they will become a carbon source or sink in the next few decades. In turn, such knowledge gaps on the drivers and the processes controlling CO2 fluxes and storage make future projections of the Arctic carbon budget a challenging goal. During summer 2019, we extensively measured CO2 fluxes at the soil–vegetation–atmosphere interface, together with basic meteoclimatic variables and ecological characteristics in the Bayelva river basin near Ny Ålesund, Spitzbergen, Svalbard (NO). By means of multi-regression models, we identified the main small-scale drivers of CO2 emission (Ecosystem Respiration, ER), and uptake (Gross Primary Production, GPP) in this tundra biome, showing that (i) at point scale, the temporal variability of fluxes is controlled by the classical drivers, i.e. air temperature and solar irradiance respectively for ER and GPP, (ii) at site scale, the heterogeneity of fractional vegetation cover, soil moisture and vegetation type acted as additional source of variability for both CO2 emissions and uptake. The assessment of the relative importance of such drivers in the multi-regression model contributes to a better understanding of the terrestrial carbon dioxide exchanges and of Critical Zone processes in the Arctic tundra.

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Plant community composition and species richness in the High Arctic tundra: From the present to the future

Ecology and Evolution ◽

10.1002/ece3.3496 ◽

2017 ◽

Vol 7 (23) ◽

pp. 10233-10242 ◽

Cited By ~ 12

Author(s):

Jacob Nabe-Nielsen ◽

Signe Normand ◽

Francis K. C. Hui ◽

Laerke Stewart ◽

Christian Bay ◽

...

Keyword(s):

Species Richness ◽

Community Composition ◽

Plant Community ◽

Arctic Tundra ◽

High Arctic ◽

Plant Community Composition ◽

The Future

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Eddy covariance flux measurements of momentum, heat and carbon dioxide in Hudson Bay at the onset of sea ice melt

10.5194/egusphere-egu21-15711 ◽

2021 ◽

Author(s):

Richard Sims ◽

Brian Butterworth ◽

Tim Papakyriakou ◽

Mohamed Ahmed ◽

Brent Else

Keyword(s):

Carbon Dioxide ◽

Gas Exchange ◽

Sea Ice ◽

Eddy Covariance ◽

Open Water ◽

The Arctic ◽

Gas Transfer ◽

Hudson Bay ◽

Flux Measurements ◽

Ice Fraction

Remoteness and tough conditions have made the Arctic Ocean historically difficult to access; until recently this has resulted in an undersampling of trace gas and gas exchange measurements. The seasonal cycle of sea ice completely transforms the air sea interface and the dynamics of gas exchange. To make estimates of gas exchange in the presence of sea ice, sea ice fraction is frequently used to scale open water gas transfer parametrisations. It remains unclear whether this scaling is appropriate for all sea ice regions. Ship based eddy covariance measurements were made in Hudson Bay during the summer of 2018 from the icebreaker CCGS Amundsen. We will present fluxes of carbon dioxide (CO2), heat and momentum and will show how they change around the Hudson Bay polynya under varying sea ice conditions. We will explore how these fluxes change with wind speed and sea ice fraction. As freshwater stratification was encountered during the cruise, we will compare our measurements with other recent eddy covariance flux measurements made from icebreakers and also will compare our turbulent CO2&#160;fluxes with bulk fluxes calculated using underway and surface bottle pCO2&#160;data.&#160;&#160;

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Environmental controls on ecosystem-scale cold-season methane and carbon dioxide fluxes in an Arctic tundra ecosystem

Biogeosciences ◽

10.5194/bg-17-4025-2020 ◽

2020 ◽

Vol 17 (15) ◽

pp. 4025-4042

Author(s):

Dean Howard ◽

Yannick Agnan ◽

Detlev Helmig ◽

Yu Yang ◽

Daniel Obrist

Keyword(s):

Carbon Dioxide ◽

Methane Emission ◽

Arctic Tundra ◽

Cold Season ◽

The Arctic ◽

Future Climate Change ◽

Climate Change Scenarios ◽

Carbon Dioxide Fluxes ◽

Soil Temperatures ◽

Annual Total

Abstract. Understanding the processes that influence and control carbon cycling in Arctic tundra ecosystems is essential for making accurate predictions about what role these ecosystems will play in potential future climate change scenarios. Particularly, air–surface fluxes of methane and carbon dioxide are of interest as recent observations suggest that the vast stores of soil carbon found in the Arctic tundra are becoming more available to release to the atmosphere in the form of these greenhouse gases. Further, harsh wintertime conditions and complex logistics have limited the number of year-round and cold-season studies and hence too our understanding of carbon cycle processes during these periods. We present here a two-year micrometeorological data set of methane and carbon dioxide fluxes, along with supporting soil pore gas profiles, that provide near-continuous data throughout the active summer and cold winter seasons. Net emission of methane and carbon dioxide in one of the study years totalled 3.7 and 89 g C m−2 a−1 respectively, with cold-season methane emission representing 54 % of the annual total. In the other year, net emission totals of methane and carbon dioxide were 4.9 and 485 g C m−2 a−1 respectively, with cold-season methane emission here representing 82 % of the annual total – a larger proportion than has been previously reported in the Arctic tundra. Regression tree analysis suggests that, due to relatively warmer air temperatures and deeper snow depths, deeper soil horizons – where most microbial methanogenic activity takes place – remained warm enough to maintain efficient methane production whilst surface soil temperatures were simultaneously cold enough to limit microbial methanotrophic activity. These results provide valuable insight into how a changing Arctic climate may impact methane emission, and highlight a need to focus on soil temperatures throughout the entire active soil profile, rather than rely on air temperature as a proxy for modelling temperature–methane flux dynamics.

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Insights from mercury stable isotopes on terrestrial–atmosphere exchange of Hg(0) in the Arctic tundra

Biogeosciences ◽

10.5194/bg-16-4051-2019 ◽

2019 ◽

Vol 16 (20) ◽

pp. 4051-4064 ◽

Cited By ~ 11

Author(s):

Martin Jiskra ◽

Jeroen E. Sonke ◽

Yannick Agnan ◽

Detlev Helmig ◽

Daniel Obrist

Keyword(s):

Stable Isotope ◽

Dominant Role ◽

Arctic Tundra ◽

Atmospheric Mercury ◽

The Arctic ◽

Night Time ◽

Field Station ◽

Terrestrial Atmosphere ◽

Tundra Ecosystem ◽

Flux Measurements

Abstract. The tundra plays a pivotal role in the Arctic mercury (Hg) cycle by storing atmospheric Hg deposition and shuttling it to the Arctic Ocean. A recent study revealed that 70 % of the atmospheric Hg deposition to the tundra occurs through gaseous elemental mercury (GEM or Hg(0)) uptake by vegetation and soils. Processes controlling land–atmosphere exchange of Hg(0) in the Arctic tundra are central, but remain understudied. Here, we combine Hg stable isotope analysis of Hg(0) in the atmosphere, interstitial snow air, and soil pore air, with Hg(0) flux measurements in a tundra ecosystem at Toolik Field Station in northern Alaska (USA). In the dark winter months, planetary boundary layer (PBL) conditions and Hg(0) concentrations were generally stable throughout the day and small Hg(0) net deposition occurred. In spring, halogen-induced atmospheric mercury depletion events (AMDEs) occurred, with the fast re-emission of Hg(0) after AMDEs resulting in net emission fluxes of Hg(0). During the short snow-free growing season in summer, vegetation uptake of atmospheric Hg(0) enhanced atmospheric Hg(0) net deposition to the Arctic tundra. At night, when PBL conditions were stable, ecosystem uptake of atmospheric Hg(0) led to a depletion of atmospheric Hg(0). The night-time decline of atmospheric Hg(0) was concomitant with a depletion of lighter Hg(0) isotopes in the atmospheric Hg pool. The enrichment factor, ε202Hgvegetationuptake=-4.2 ‰ (±1.0 ‰) was consistent with the preferential uptake of light Hg(0) isotopes by vegetation. Hg(0) flux measurements indicated a partial re-emission of Hg(0) during daytime, when solar radiation was strongest. Hg(0) concentrations in soil pore air were depleted relative to atmospheric Hg(0) concentrations, concomitant with an enrichment of lighter Hg(0) isotopes in the soil pore air, ε202Hgsoilair-atmosphere=-1.00 ‰ (±0.25 ‰) and E199Hgsoilair-atmosphere=0.07 ‰ (±0.04 ‰). These first Hg stable isotope measurements of Hg(0) in soil pore air are consistent with the fractionation previously observed during Hg(0) oxidation by natural humic acids, suggesting abiotic oxidation as a cause for observed soil Hg(0) uptake. The combination of Hg stable isotope fingerprints with Hg(0) flux measurements and PBL stability assessment confirmed a dominant role of Hg(0) uptake by vegetation in the terrestrial–atmosphere exchange of Hg(0) in the Arctic tundra.

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Dried, closed-path eddy covariance method for measuring carbon dioxide flux over sea ice

Atmospheric Measurement Techniques ◽

10.5194/amt-11-6075-2018 ◽

2018 ◽

Vol 11 (11) ◽

pp. 6075-6090 ◽

Cited By ~ 4

Author(s):

Brian J. Butterworth ◽

Brent G. T. Else

Keyword(s):

Carbon Dioxide ◽

Sea Ice ◽

Eddy Covariance ◽

Co2 Flux ◽

Carbon Dioxide Flux ◽

The Arctic ◽

Closed Path ◽

Eddy Covariance Method ◽

Open Path ◽

Flux Measurements

Abstract. The Arctic marine environment plays an important role in the global carbon cycle. However, there remain large uncertainties in how sea ice affects air–sea fluxes of carbon dioxide (CO2), partially due to disagreement between the two main methods (enclosure and eddy covariance) for measuring CO2 flux (FCO2). The enclosure method has appeared to produce more credible FCO2 than eddy covariance (EC), but is not suited for collecting long-term, ecosystem-scale flux datasets in such remote regions. Here we describe the design and performance of an EC system to measure FCO2 over landfast sea ice that addresses the shortcomings of previous EC systems. The system was installed on a 10 m tower on Qikirtaarjuk Island – a small rock outcrop in Dease Strait located roughly 35 km west of Cambridge Bay, Nunavut, in the Canadian Arctic Archipelago. The system incorporates recent developments in the field of air–sea gas exchange by measuring atmospheric CO2 using a closed-path infrared gas analyzer (IRGA) with a dried sample airstream, thus avoiding the known water vapor issues associated with using open-path IRGAs in low-flux environments. A description of the methods and the results from 4 months of continuous flux measurements from May through August 2017 are presented, highlighting the winter to summer transition from ice cover to open water. We show that the dried, closed-path EC system greatly reduces the magnitude of measured FCO2 compared to simultaneous open-path EC measurements, and for the first time reconciles EC and enclosure flux measurements over sea ice. This novel EC installation is capable of operating year-round on solar and wind power, and therefore promises to deliver new insights into the magnitude of CO2 fluxes and their driving processes through the annual sea ice cycle.

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Nitrogen fixation beyond leguminous plants: characterising overlooked plant-bacteria associations in the light of climate change

10.5194/egusphere-egu2020-103 ◽

2020 ◽

Author(s):

Kathrin Rousk

Keyword(s):

Climate Change ◽

Nitrogen Fixation ◽

Community Composition ◽

Abiotic Factors ◽

Arctic Tundra ◽

The Arctic ◽

Mean Annual Precipitation ◽

Precipitation Gradient ◽

Cyanobacterial Community ◽

Moss Species

Nitrogen (N2) fixation performed by moss-associated cyanobacteria is one of the main sources of new N in pristine, high latitude ecosystems like boreal forests and arctic tundra. Here, mosses and associated cyanobacteria can contribute more than 50% to total ecosystem N input. However, N2 fixation in mosses is strongly influenced by abiotic factors, in particular moisture and temperature. Hence, climate change will significantly affect this key ecosystem process in pristine ecosystems. Here,&#160;I will present a synthesis of several field and laboratory assessments of moss-associated N2 fixation in response to climate change by manipulating moisture and temperature in subarctic and arctic tundra.Both in a long-term climate warming experiment in the arctic, and along a continental climate gradient, spanning arctic, subarctic and temperate ecosystems, increased temperatures (up to 30 &#176;C) lead to either no effect or decreased N2 fixation rates in different moss species. Yet, N2 fixation rates were strongly dependent on moss-moisture, which seems to be a more important driver of N2 fixation in mosses than temperature.In another set of studies, two dominant moss species (Hylocomium splendens, Pleurozium schreberi) were collected from a steep precipitation gradient (400-1200 mm mean annual precipitation, MAP) in the Subarctic close to Abisko, Northern Sweden, and were incubated at different moisture and temperature levels in the laboratory. Nitrogen fixation, cyanobacterial abundance (via qPCR) and cyanobacterial community composition (via sequencing) on the mosses were assessed. Moisture and temperature interacted strongly to control moss-associated N2 fixation rates, and the highest activity was found at the wet end of the precipitation gradient. Although cyanobacterial abundance was higher in one of the investigated mosses (H. splendens), translating into higher N2 fixation rates, cyanobacterial community composition did not differ between the two moss species. Nostoc was the most common cyanobacterial genera on both mosses, and hardly any methanotrophic N2 fixing bacteria were found on the mosses along the precipitation gradient. Increased temperatures lead to increased abundances of certain cyanobacterial genera (Cylindrospermum and Nostoc), while others declined in response to warming. Hence, cyanobacterial communities colonizing mosses will be dominated by a few cyanobacteria species in a warmer climate, and temperature and moisture interact strongly to affect their activity. Thus, these two major climate change factors should be considered in unison when estimating climate change effects on key ecosystem processes such as N2 fixation. Further, host identity determines cyanobacterial abundance, and thereby, N2 fixation rates.&#160;&#160;&#160;

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Environmental controls on ecosystem-scale cold season methane and carbon dioxide fluxes in an Arctic tundra ecosystem

10.5194/bg-2019-437 ◽

2019 ◽

Author(s):

Dean Howard ◽

Yannick Agnan ◽

Detlev Helmig ◽

Yu Yang ◽

Daniel Obrist

Keyword(s):

Carbon Dioxide ◽

Methane Emission ◽

Arctic Tundra ◽

Cold Season ◽

The Arctic ◽

Future Climate Change ◽

Climate Change Scenarios ◽

Carbon Dioxide Fluxes ◽

Soil Temperatures ◽

Annual Total

Abstract. Understanding the processes that influence and control carbon cycling in Arctic tundra ecosystems is essential for making accurate predictions about what role these ecosystems will play in potential future climate change scenarios. Particularly, air–surface fluxes of methane and carbon dioxide are of interest as recent observations suggest that the vast stores of soil carbon found in the Arctic tundra are becoming more available to release to the atmosphere in the form of these greenhouse gases. Further, harsh wintertime conditions and complex logistics have limited the number of year-round and cold season studies and hence too our understanding of carbon cycle processes during these periods. We present here a two-year micrometeorological data set of methane and carbon dioxide fluxes that provides near-continuous data throughout the active summer and cold winter seasons. Net emission of methane and carbon dioxide in one of the study years totalled 3.7 and 89 g C m−2 a−1 respectively, with cold season methane emission representing 54% of the annual total. In the other year, net emission totals of methane and carbon dioxide were 4.9 and 485 g C m−2 a−1 respectively, with cold season methane emission here representing 82 % of the annual total – a larger proportion than has been previously reported in the Arctic tundra. Regression tree analysis suggests that, due to relatively warmer air temperatures and deeper snow depths, deeper soil horizons – where most microbial methanogenic activity takes place – remained warm enough to maintain efficient methane production whilst surface soil temperatures were simultaneously cold enough to limit microbial methanotrophic activity. These results provide valuable insight into how a changing Arctic climate may impact methane emission, and highlight a need to focus on soil temperatures throughout the entire active soil profile, rather than rely on air temperature as a proxy for modelling temperature–methane flux dynamics.

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Snowpack fluxes of methane and carbon dioxide from high Arctic tundra

Journal of Geophysical Research Biogeosciences ◽

10.1002/2016jg003486 ◽

2016 ◽

Vol 121 (11) ◽

pp. 2886-2900 ◽

Cited By ~ 9

Author(s):

Norbert Pirk ◽

Mikkel P. Tamstorf ◽

Magnus Lund ◽

Mikhail Mastepanov ◽

Stine H. Pedersen ◽

...

Keyword(s):

Carbon Dioxide ◽

Arctic Tundra ◽

High Arctic

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Dried, closed-path eddy covariance method for measuring carbon dioxide flux over sea ice

10.5194/amt-2018-158 ◽

2018 ◽

Author(s):

Brian J. Butterworth ◽

Brent G. T. Else

Keyword(s):

Carbon Dioxide ◽

Sea Ice ◽

Eddy Covariance ◽

Co2 Flux ◽

Carbon Dioxide Flux ◽

The Arctic ◽

Closed Path ◽

Eddy Covariance Method ◽

Open Path ◽

Flux Measurements

Abstract. The Arctic marine environment plays an important role in the global carbon cycle. However, there remain large uncertainties in how sea ice affects air–sea fluxes of carbon dioxide (CO2), partially due to disagreement between the two main methods (enclosure and eddy covariance) for measuring CO2 flux (FCO2). The enclosure method has appeared to produce more credible FCO2 than eddy covariance (EC), but is not suited for collecting long-term, ecosystem-scale flux datasets in such remote regions. Here we describe the design and performance of an EC system to measure FCO2 over landfast sea ice that addresses the shortcomings of previous EC systems. The system was installed on a 10-m tower on Qikirtaarjuk Island – a small rock outcrop in Dease Strait located roughly 35 km west of Cambridge Bay, Nunavut in the Canadian Arctic Archipelago. The system incorporates recent developments in the field of air–sea gas exchange by measuring atmospheric CO2 using a closed-path infrared gas analyzer (IRGA) with a dried sample airstream, thus avoiding the known water vapor issues associated with using open-path IRGAs in low-flux environments. A description of the methods and the results from four months of continuous flux measurements from May through August 2017 are presented, highlighting the winter to summer transition from ice cover to open water. We show that the dried, closed-path EC system greatly reduces the magnitude of measured FCO2 compared to simultaneous open-path EC measurements, and for the first time reconciles EC and enclosure flux measurements over sea ice. This novel EC installation is capable of operating year-round on solar/wind power, and therefore promises to deliver new insights into the magnitude of CO2 fluxes and their driving processes through the annual sea ice cycle.

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