scholarly journals An assessment of the carbon balance of Arctic tundra: comparisons among observations, process models, and atmospheric inversions

2012 ◽  
Vol 9 (8) ◽  
pp. 3185-3204 ◽  
Author(s):  
A. D. McGuire ◽  
T. R. Christensen ◽  
D. Hayes ◽  
A. Heroult ◽  
E. Euskirchen ◽  
...  

Abstract. Although Arctic tundra has been estimated to cover only 8% of the global land surface, the large and potentially labile carbon pools currently stored in tundra soils have the potential for large emissions of carbon (C) under a warming climate. These emissions as radiatively active greenhouse gases in the form of both CO2 and CH4 could amplify global warming. Given the potential sensitivity of these ecosystems to climate change and the expectation that the Arctic will experience appreciable warming over the next century, it is important to assess whether responses of C exchange in tundra regions are likely to enhance or mitigate warming. In this study we compared analyses of C exchange of Arctic tundra between 1990 and 2006 among observations, regional and global applications of process-based terrestrial biosphere models, and atmospheric inversion models. Syntheses of flux observations and inversion models indicate that the annual exchange of CO2 between Arctic tundra and the atmosphere has large uncertainties that cannot be distinguished from neutral balance. The mean estimate from an ensemble of process-based model simulations suggests that Arctic tundra has acted as a sink for atmospheric CO2 in recent decades, but based on the uncertainty estimates it cannot be determined with confidence whether these ecosystems represent a weak or a strong sink. Tundra was 0.6 °C warmer in the 2000s compared to the 1990s. The central estimates of the observations, process-based models, and inversion models each identify stronger sinks in the 2000s compared with the 1990s. Some of the process models indicate that this occurred because net primary production increased more in response to warming than heterotrophic respiration. Similarly, the observations and the applications of regional process-based models suggest that CH4 emissions from Arctic tundra have increased from the 1990s to 2000s because of the sensitivity of CH4 emissions to warmer temperatures. Based on our analyses of the estimates from observations, process-based models, and inversion models, we estimate that Arctic tundra was a sink for atmospheric CO2 of 110 Tg C yr−1 (uncertainty between a sink of 291 Tg C yr−1 and a source of 80 Tg C yr−1) and a source of CH4 to the atmosphere of 19 Tg C yr−1 (uncertainty between sources of 8 and 29 Tg C yr−1). The suite of analyses conducted in this study indicate that it is important to reduce uncertainties in the observations, process-based models, and inversions in order to better understand the degree to which Arctic tundra is influencing atmospheric CO2 and CH4 concentrations. The reduction of uncertainties can be accomplished through (1) the strategic placement of more CO2 and CH4 monitoring stations to reduce uncertainties in inversions, (2) improved observation networks of ground-based measurements of CO2 and CH4 exchange to understand exchange in response to disturbance and across gradients of climatic and hydrological variability, and (3) the effective transfer of information from enhanced observation networks into process-based models to improve the simulation of CO2 and CH4 exchange from Arctic tundra to the atmosphere.

2012 ◽  
Vol 9 (4) ◽  
pp. 4543-4594 ◽  
Author(s):  
A. D. McGuire ◽  
T. R. Christensen ◽  
D. Hayes ◽  
A. Heroult ◽  
E. Euskirchen ◽  
...  

Abstract. Although arctic tundra has been estimated to cover only 8% of the global land surface, the large and potentially labile carbon pools currently stored in tundra soils have the potential for large emissions of carbon (C) under a warming climate. These emissions as radiatively active greenhouse gases in the form of both CO2 and CH4 could amplify global warming. Given the potential sensitivity of these ecosystems to climate change and the expectation that the Arctic will experience appreciable warming over the next century, it is important to assess whether responses of C exchange in tundra regions are likely to enhance or mitigate warming. In this study we compared analyses of C exchange of Arctic tundra between 1990–1999 and 2000–2006 among observations, regional and global applications of process-based terrestrial biosphere models, and atmospheric inversion models. Syntheses of the compilation of flux observations and of inversion model results indicate that the annual exchange of CO2 between arctic tundra and the atmosphere has large uncertainties that cannot be distinguished from neutral balance. The mean estimate from an ensemble of process-based model simulations suggests that arctic tundra acted as a sink for atmospheric CO2 in recent decades, but based on the uncertainty estimates it cannot be determined with confidence whether these ecosystems represent a weak or a strong sink. Tundra was 0.6 °C warmer in the 2000s compared to the 1990s. The central estimates of the observations, process-based models, and inversion models each identify stronger sinks in the 2000s compared with the 1990s. Similarly, the observations and the applications of regional process-based models suggest that CH4 emissions from arctic tundra have increased from the 1990s to 2000s. Based on our analyses of the estimates from observations, process-based models, and inversion models, we estimate that arctic tundra was a sink for atmospheric CO2 of 110 Tg C yr−1 (uncertainty between a sink of 291 Tg C yr−1 and a source of 80 Tg C yr−1) and a source of CH4 to the atmosphere of 19 Tg C yr−1 (uncertainty between sources of 8 and 29 Tg C yr−1). The suite of analyses conducted in this study indicate that it is clearly important to reduce uncertainties in the observations, process-based models, and inversions in order to better understand the degree to which Arctic tundra is influencing atmospheric CO2 and CH4 concentrations. The reduction of uncertainties can be accomplished through (1) the strategic placement of more CO2 and CH4 monitoring stations to reduce uncertainties in inversions, (2) improved observation networks of ground-based measurements of CO2 and CH4 exchange to understand exchange in response to disturbance and across gradients of hydrological variability, and (3) the effective transfer of information from enhanced observation networks into process-based models to improve the simulation of CO2 and CH4 exchange from arctic tundra to the atmosphere.


2020 ◽  
pp. 75-99
Author(s):  
O. I. Sumina

One of the thermokarst relief forms is baidzharakh massif — the group of mounds separated by trenches formed as a result of the underground ice-wedge polygonal networks melting (Fig. 1). Study of baidzharakh vegetation took place on the northeast coast of the Taimyr Peninsula (the Pronchishcheva Bay area) and on the New Siberian Islands (the Kotelny Island) in 1973–1974 (Sumina, 1975, 1976, 1977a, b, 1979 et al.). The aim of this paper is to produce the classification of baidzharakh mound and trenches communities according to the Brown-Blanquet approach (Westhoff, Maarel, 1978) and to compare these data with the community types earlier established on domination principle (Sumina, 1975 et al.). The information obtained in the 1970s could be helpful in a comparative assessment of the thermokarst process dynamics over the past 4 decades, as well as for comparing these processes in other regions of the Arctic. Both studied areas are located in the northern part of the arctic tundra subzone. On the Taimyr Peninsula (and in particular in the Pronchishcheva Bay area) the plakor (zonal) communities belong to the ass. Salici polaris–Hylocomietum alaskani Matveyeva 1998. Our relevés of plakor tundra on the Kotelny Island demonstrate similarity with the zonal communities of the northeast coast of the Taimyr Peninsula (Table 2). Relevés of communities of thermokarst mounds were made within their boundaries, the size of ~ 30 m². In trenches sample plots of the same area had rectangular shape according to trench width. Relevés of plakor tundra were made on 5x6 m plots. There were marked: location in relief, moistening, stand physiognomy, nanorelief, the percent of open ground patches and degree of their overgrowing, total plant cover, that of vascular plants, mosses, and lichens (especially — crustose ons), and cover estimates for each species. The shape of thermokarst mounds depends on the stage of thermodenudation processes. Flat polygons about 0.5 m height with vegetation similar to the plakor tundra are formed at the beginning of ice melting (Fig. 3, a), after which the deformation of the mounds (from eroded flat polygon (Fig. 3, b) to eroded conical mound (Fig. 3, c). Such mounds of maximal height up to 5 m are located on the middle part of steep slopes, where thermodenudation is very active. The last stage of mound destruction is slightly convex mound with a lumpy surface and vegetation, typical to snowbed sites at slope foots (Fig. 3, d, and 5). Both on watersheds and on gentle slopes mounds are not completely destroyed; and on such elongated smooth-conical mounds dense meadow-like vegetation is developed (Fig. 6). On the Kotelny Island thermokarst mounds of all described shapes occur, while in the Pronchishcheva Bay area only flat polygons, eroded flat polygons, and elongated smooth-conical mounds are presented. Under the influence of thermodenudation the plakor (zonal) vegetation is being transformed that allows to consider the most of mound and trench communities as the variants of zonal association. On the base of 63 relevés, made in 14 baidzharakh massifs, 2 variants with 7 subvariants of the ass. Salici polaris–Hylocomietum alaskani Matveyeva 1998 were established, as well as 1 variant of the azonal ass. Poo arcticae– Dupontietum fisheri Matveyeva 1994, which combines the vegetation of wet trenches with dense herbmoss cover. A detailed description of each subvariant is done. All these syntaxa are compared with the types of mound and trenh communities established previously by the domination principle (Sumina, 1975, 1976, 1979 et al.) and with Brown-Blanquet’ syntaxa published by other authors. The Brown-Blanquet approach in compare with domination principle, clearly demonstrates the similarity between zonal and baidzharakh massifs vegetation. Diagnostic species of syntaxa of baidzharakh vegetation by other authors (Matveyeva, 1994; Zanokha, 1995; Kholod, 2007, 2014; Telyatnikov et al., 2017) differ from ours. On the one hand, this is due to the fact that all mentioned researchers worked in another areas, and on the other, with different hierarchial levels of syntaxa, which are subassociations (or vicariants) in cited works or variants and subvariants in the our. Communities of mounds as well as of trenches in different regions have unlike species composition, but similar apearance, which depends on the similarity of the life form composition and community pattern, stage of their transformation and environmental factors. This fact is a base to group communities by physiognomy in order to have an opportunity of comparative analysis of baidzharakh vegetation diversity in different regions of the Arctic. In total, 6 such groups for thermokarst mounds and trenches are proposed: “tundra-like” ― vegetation of flat polygonal mounds (or trenches) is similar to the plakor (zonal) communities; “eroded tundra-like” ― tundra-like vegetation is presented as fragments, open ground occupies the main part of flat polygonal mounds; “eroded mounds with nonassociated vegetation” ― eroded mounds of various shapes up to sharp conical with absent vegetation at the top and slopes, sparse pioneer vascular plants on a bare substrate and crustose lichens and chionophilous grasses at foots; “meadow-like” ― herb stands with a participation of tundra dwarf-shrubs, mosses, and lichens on elongated smooth-conical mounds and in moderately moist trenches; “communities in snowbeds” ― thin plant cover formed by small mosses, liverworts, crustose lichens, and sparse vascular plants in snowbed habitats on destroyed slightly convex mounds with a lumpy surface and in trenches; “communities of cotton grass” or others, depending on the dominant species ― in wet trenches where vegetation is similar to the arctic hypnum bogs with dominant hygrophyte graminoids as Eriophorum scheuchzeri, E. polystachion, Dupontia fischeri et al. This sheme according to physiognomic features of thermokarst mound and trench communities, as a simplier way to assess the current dynamic stage of the baidzharakh massifs, may be useful for monitoring the thermodenudation activity in different areas of the Arctic, particularly in connection with observed climate changes (ACIA, 2004) and a possible dramatic “cascade of their environmental consequences” (Fraser et al., 2018).


The Holocene ◽  
2020 ◽  
Vol 30 (7) ◽  
pp. 1091-1096 ◽  
Author(s):  
Eleanor MB Pereboom ◽  
Richard S Vachula ◽  
Yongsong Huang ◽  
James Russell

Wildfires in the Arctic tundra have become increasingly frequent in recent years and have important implications for tundra ecosystems and for the global carbon cycle. Lake sediment–based records are the primary means of understanding the climatic influences on tundra fires. Sedimentary charcoal has been used to infer climate-driven changes in tundra fire frequency but thus far cannot differentiate characteristics of the vegetation burnt during fire events. In forested ecosystems, charcoal morphologies have been used to distinguish changes in fuel type consumed by wildfires of the past; however, no such approach has been developed for tundra ecosystems. We show experimentally that charcoal morphologies can be used to differentiate graminoid (mean = 6.77; standard deviation (SD) = 0.23) and shrub (mean = 2.42; SD = 1.86) biomass burnt in tundra fire records. This study is a first step needed to construct more nuanced tundra wildfire histories and to understand how wildfire will impact the region as vegetation and fire change in the future.


2014 ◽  
Vol 11 (2) ◽  
pp. 293-308 ◽  
Author(s):  
E. E. Popova ◽  
A. Yool ◽  
Y. Aksenov ◽  
A. C. Coward ◽  
T. R. Anderson

Abstract. The Arctic Ocean is a region that is particularly vulnerable to the impact of ocean acidification driven by rising atmospheric CO2, with potentially negative consequences for calcifying organisms such as coccolithophorids and foraminiferans. In this study, we use an ocean-only general circulation model, with embedded biogeochemistry and a comprehensive description of the ocean carbon cycle, to study the response of pH and saturation states of calcite and aragonite to rising atmospheric pCO2 and changing climate in the Arctic Ocean. Particular attention is paid to the strong regional variability within the Arctic, and, for comparison, simulation results are contrasted with those for the global ocean. Simulations were run to year 2099 using the RCP8.5 (an Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5) scenario with the highest concentrations of atmospheric CO2). The separate impacts of the direct increase in atmospheric CO2 and indirect effects via impact of climate change (changing temperature, stratification, primary production and freshwater fluxes) were examined by undertaking two simulations, one with the full system and the other in which atmospheric CO2 was prevented from increasing beyond its preindustrial level (year 1860). Results indicate that the impact of climate change, and spatial heterogeneity thereof, plays a strong role in the declines in pH and carbonate saturation (Ω) seen in the Arctic. The central Arctic, Canadian Arctic Archipelago and Baffin Bay show greatest rates of acidification and Ω decline as a result of melting sea ice. In contrast, areas affected by Atlantic inflow including the Greenland Sea and outer shelves of the Barents, Kara and Laptev seas, had minimal decreases in pH and Ω because diminishing ice cover led to greater vertical mixing and primary production. As a consequence, the projected onset of undersaturation in respect to aragonite is highly variable regionally within the Arctic, occurring during the decade of 2000–2010 in the Siberian shelves and Canadian Arctic Archipelago, but as late as the 2080s in the Barents and Norwegian seas. We conclude that, for future projections of acidification and carbonate saturation state in the Arctic, regional variability is significant and needs to be adequately resolved, with particular emphasis on reliable projections of the rates of retreat of the sea ice, which are a major source of uncertainty.


2012 ◽  
Vol 9 (4) ◽  
pp. 1423-1440 ◽  
Author(s):  
C. S. Sturtevant ◽  
W. C. Oechel ◽  
D. Zona ◽  
Y. Kim ◽  
C. E. Emerson

Abstract. Accurate estimates of annual budgets of methane (CH4) efflux in arctic regions are severely constrained by the paucity of non-summer measurements. Moreover, the incomplete understanding of the ecosystem-level sensitivity of CH4 emissions to changes in tundra moisture makes prediction of future CH4 release from the Arctic extremely difficult. This study addresses some of these research gaps by presenting an analysis of eddy covariance and chamber measurements of CH4 efflux and supporting environmental variables during the autumn season and associated beginning of soil freeze-up at our large-scale water manipulation site near Barrow, Alaska (the Biocomplexity Experiment). We found that the autumn season CH4 emission is significant (accounting for 21–25% of the average growing season emission), and that this emission is mostly controlled by the fraction of inundated landscape, atmospheric turbulence, and the decline in unfrozen water during the period of soil freezing. Drainage decreased autumn CH4 emission by a factor of 2.4 compared to our flooded treatment. Flooding slowed the soil freezing process which has implications for extending elevated CH4 emissions longer into the winter season.


2021 ◽  
Vol 15 (3) ◽  
pp. 1627-1644
Author(s):  
Andrea J. Pain ◽  
Jonathan B. Martin ◽  
Ellen E. Martin ◽  
Åsa K. Rennermalm ◽  
Shaily Rahman

Abstract. Accelerated melting of the Greenland Ice Sheet has increased freshwater delivery to the Arctic Ocean and amplified the need to understand the impact of Greenland Ice Sheet meltwater on Arctic greenhouse gas budgets. We evaluate subglacial discharge from the Greenland Ice Sheet for carbon dioxide (CO2) and methane (CH4) concentrations and δ13C values and use geochemical models to evaluate subglacial CH4 and CO2 sources and sinks. We compare discharge from southwest (a sub-catchment of the Isunnguata Glacier, sub-Isunnguata, and the Russell Glacier) and southern Greenland (Kiattut Sermiat). Meltwater CH4 concentrations vary by orders of magnitude between sites and are saturated with respect to atmospheric concentrations at Kiattut Sermiat. In contrast, meltwaters from southwest sites are supersaturated, even though oxidation reduces CH4 concentrations by up to 50 % during periods of low discharge. CO2 concentrations range from supersaturated at sub-Isunnguata to undersaturated at Kiattut Sermiat. CO2 is consumed by mineral weathering throughout the melt season at all sites; however, differences in the magnitude of subglacial CO2 sources result in meltwaters that are either sources or sinks of atmospheric CO2. At the sub-Isunnguata site, the predominant source of CO2 is organic matter (OM) remineralization. However, multiple or heterogeneous subglacial CO2 sources maintain atmospheric CO2 concentrations at Russell but not at Kiattut Sermiat, where CO2 is undersaturated. These results highlight a previously unrecognized degree of heterogeneity in greenhouse gas dynamics under the Greenland Ice Sheet. Future work should constrain the extent and controls of heterogeneity to improve our understanding of the impact of Greenland Ice Sheet melt on Arctic greenhouse gas budgets, as well as the role of continental ice sheets in greenhouse gas variations over glacial–interglacial timescales.


2021 ◽  
Author(s):  
Ruby R. Pennell

The climate change phenomenon occurring across the globe is having an increasingly alarming effect on Canada’s Arctic. Warming temperatures can have wide spanning impacts ranging from more rain and storm events, to increasing runoff, thawing permafrost, sea ice decline, melting glaciers, ecosystem disruption, and more. The purpose of this MRP was to assess the climate-induced landscape changes, including glacial loss and vegetation change, in Pond Inlet, Nunavut. A time series analysis was performed using the intervals 1989-1997, 1997-2005, and 2005-2016. The two methods for monitoring change were 1) the Normalized Difference Snow Index (NDSI) to detect glacial change, and 2) the Normalized Difference Vegetation Index (NDVI) to detect vegetation change, both utilizing threshold and masking techniques to increase accuracy. It was found that the percent of glacial loss and vegetation change in Pond Inlet had consistently increased throughout each time period. The area of glacial loss grew through each period to a maximum of 376 km2 of glacial loss in the last decade. Similarly, the area of the Arctic tundra that experienced vegetation change increased in each time period to a maximum of 660 km2 in the last decade. This vegetation change was characterized by overall increasing values of NDVI, revealing that many sections of the Arctic tundra in Pond Inlet were increasing in biomass. However, case study analysis revealed pixel clustering around the lower vegetation class thresholds used to classify change, indicating that shifts between these vegetation classes were likely exaggerated. Shifts between the higher vegetation classes were significant, and were what contributed to the most change in the last decade. The observations of higher glacial melt and increases in biomass are occurring in parallel with the increasing temperatures in Pond Inlet. Relevant literature in the Arctic agrees with the findings of this MRP that there are significant trends of glacial loss and vegetation greening and many studies attribute this directly to climate warming. The results of this study provide the necessary background with regards to landscape changes which could be used in future field studies investigating the climate induced changes in Pond Inlet. This study also demonstrates that significant landscape modifications have occurred in the recent decades and there is a strong need for continued research and monitoring of climate induced changes.


2020 ◽  
Vol 17 (15) ◽  
pp. 4025-4042
Author(s):  
Dean Howard ◽  
Yannick Agnan ◽  
Detlev Helmig ◽  
Yu Yang ◽  
Daniel Obrist

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.


Sign in / Sign up

Export Citation Format

Share Document