| 1. |
- Sim, Thomas G., et al.
(författare)
-
Regional variability in peatland burning at mid-to high-latitudes during the Holocene
- 2023
-
Ingår i: Quaternary Science Reviews. - : Elsevier. - 0277-3791 .- 1873-457X. ; 305
-
Tidskriftsartikel (refereegranskat)abstract
- Northern peatlands store globally-important amounts of carbon in the form of partly decomposed plant detritus. Drying associated with climate and land-use change may lead to increased fire frequency and severity in peatlands and the rapid loss of carbon to the atmosphere. However, our understanding of the patterns and drivers of peatland burning on an appropriate decadal to millennial timescale relies heavily on individual site-based reconstructions. For the first time, we synthesise peatland macrocharcoal re-cords from across North America, Europe, and Patagonia to reveal regional variation in peatland burning during the Holocene. We used an existing database of proximal sedimentary charcoal to represent regional burning trends in the wider landscape for each region. Long-term trends in peatland burning appear to be largely climate driven, with human activities likely having an increasing influence in the late Holocene. Warmer conditions during the Holocene Thermal Maximum (similar to 9e6 cal. ka BP) were associated with greater peatland burning in North America's Atlantic coast, southern Scandinavia and the Baltics, and Patagonia. Since the Little Ice Age, peatland burning has declined across North America and in some areas of Europe. This decline is mirrored by a decrease in wider landscape burning in some, but not all sub-regions, linked to fire-suppression policies, and landscape fragmentation caused by agricultural expansion. Peatlands demonstrate lower susceptibility to burning than the wider landscape in several instances, probably because of autogenic processes that maintain high levels of near-surface wetness even during drought. Nonetheless, widespread drying and degradation of peatlands, particularly in Europe, has likely increased their vulnerability to burning in recent centuries. Consequently, peatland restoration efforts are important to mitigate the risk of peatland fire under a changing climate. Finally, we make recommendations for future research to improve our understanding of the controls on peatland fires.(c) 2023 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
|
|
| 2. |
- Larsson, Simon A., 1990-, et al.
(författare)
-
Synchronous or Not? The Timing of the Younger Dryas and Greenland Stadial-1 Reviewed Using Tephrochronology
- 2022
-
Ingår i: Quaternary. - : MDPI AG. - 2571-550X. ; 5:2
-
Tidskriftsartikel (refereegranskat)abstract
- The exact spatial and temporal behaviour of rapid climate shifts during the Last Glacial– Interglacial Transition are still not entirely understood. In order to investigate these events, it is necessary to have detailed palaeoenvironmental reconstructions at geographically spread study sites combined with reliable correlations between them. Tephrochronology, i.e., using volcanic ash deposits in geological archives as a dating and correlation tool, offers opportunities to examine the timing of events across wider regional scales. This study aims to review the posited asynchrony of the Younger Dryas stadial in comparison with Greenland Stadial-1 by correlating new proxy data from southernmost Sweden to previous palaeoclimate reconstructions in Europe based on the presence of the Hässeldalen Tephra, the Vedde Ash, and the Laacher See Tephra. µ-XRF core-scanning data were projected using a recently published age–depth model based on these tephras and several radiocarbon dates, and compared to previous findings, including by adapting previous chronologies to the recently proposed earlier date of the Laacher See Tephra (13,006 ± 9 cal. a BP). Although the results to some extent support the idea of a more synchronous Younger Dryas event than previously assumed, this issue requires further high-resolution proxy studies to overcome limitations of temporal precision.
|
|
| 3. |
- Piilo, Sanna R., et al.
(författare)
-
Consistent centennial-scale change in European sub-Arctic peatland vegetation toward Sphagnum dominance—Implications for carbon sink capacity
- 2023
-
Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 29:6, s. 1530-1544
-
Tidskriftsartikel (refereegranskat)abstract
- Climate warming is leading to permafrost thaw in northern peatlands, and current predictions suggest that thawing will drive greater surface wetness and an increase in methane emissions. Hydrology largely drives peatland vegetation composition, which is a key element in peatland functioning and thus in carbon dynamics. These processes are expected to change. Peatland carbon accumulation is determined by the balance between plant production and peat decomposition. But both processes are expected to accelerate in northern peatlands due to warming, leading to uncertainty in future peatland carbon budgets. Here, we compile a dataset of vegetation changes and apparent carbon accumulation data reconstructed from 33 peat cores collected from 16 sub-arctic peatlands in Fennoscandia and European Russia. The data cover the past two millennia that has undergone prominent changes in climate and a notable increase in annual temperatures toward present times. We show a pattern where European sub-Arctic peatland microhabitats have undergone a habitat change where currently drier habitats dominated by Sphagnum mosses replaced wetter sedge-dominated vegetation and these new habitats have remained relatively stable over the recent decades. Our results suggest an alternative future pathway where sub-arctic peatlands may at least partly sustain dry vegetation and enhance the carbon sink capacity of northern peatlands.
|
|
| 4. |
- Qiu, Chunjing, et al.
(författare)
-
A strong mitigation scenario maintains climate neutrality of northern peatlands
- 2022
-
Ingår i: One Earth. - : Elsevier BV. - 2590-3330 .- 2590-3322. ; 5:1, s. 86-97
-
Tidskriftsartikel (refereegranskat)abstract
- Northern peatlands store 300–600 Pg C, of which approximately half are underlain by permafrost. Climate warming and, in some regions, soil drying from enhanced evaporation are progressively threatening this large carbon stock. Here, we assess future CO2 and CH4 fluxes from northern peatlands using five land surface models that explicitly include representation of peatland processes. Under Representative Concentration Pathways (RCP) 2.6, northern peatlands are projected to remain a net sink of CO2 and climate neutral for the next three centuries. A shift to a net CO2 source and a substantial increase in CH4 emissions are projected under RCP8.5, which could exacerbate global warming by 0.21°C (range, 0.09–0.49°C) by the year 2300. The true warming impact of peatlands might be higher owing to processes not simulated by the models and direct anthropogenic disturbance. Our study highlights the importance of understanding how future warming might trigger high carbon losses from northern peatlands.
|
|
| 5. |
- Sannel, A. Britta K., 1968-, et al.
(författare)
-
High-resolution remote sensing identification of thermokarst lake dynamics in a subarctic peat plateau complex
- 2010
-
Ingår i: Canadian journal of remote sensing. - : Informa UK Limited. - 0703-8992 .- 1712-7971. ; 36:1, s. S26-S40
-
Tidskriftsartikel (refereegranskat)abstract
- Methods to quantify the dynamics of thermokarst lake margins in subarctic permafrost peatlands have been examined using historical aerial photographs and QuickBird imagery from the Hudson Bay Lowlands in west-central Canada, spanning a time period of 52 years (1954-2006). The goal of this study was to develop a method for detection of metre-scale changes in thermokarst lake extent using a time series of high resolution imagery. The method should be applicable to a variety of lake forms, transferable to other locations and sufficiently robust as to support different data types. Semi-automatic remote sensing techniques such as unsupervised and supervised classification and texture and high-pass filtering were tested, evaluated and rejected. According to an experiment of manual digitalization of shorelines by multiple operators the relative uncertainty for lakes surrounded by peat plateau was ±1.5 m. The uncertainty was reduced to ±0.6 m when binary encoding of transects perpendicular to the shoreline was used to refine the manual delineation. This proved to be the most accurate method to detect small-scale changes in lake extent. An increased understanding and quantification of thermokarst dynamics in permafrost peatlands is important for predicting future scenarios of greenhouse gas emissions from these ecosystems under changing climatic conditions and our method supports such goals.
|
|
| 6. |
- Sannel, A. Britta K., 1968-
(författare)
-
Temporal and spatial dynamics in subarctic peat plateaus and thermokarst lakes
- 2010
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Permafrost peatlands are widespread at high northern latitudes and are important soil organic carbon reservoirs. A future warming in these areas, as suggested by global climate models, can cause thawing and increased ground subsidence (thermokarst), resulting in changes in surface hydrology and ecosystem functioning. The aim of this thesis is to increase our knowledge of temporal and spatial dynamics in subarctic peat plateaus with interspersed thermokarst lakes in order to better understand how these ecosystems respond to climate change. Detailed plant macrofossil and carbon/nitrogen ratio analyses of two peat plateaus located in the continuous and northern discontinuous permafrost zones in west-central Canada show that permafrost conditions have been stable since permafrost developed around 5600–4500 cal yr BP. Peat plateaus act as carbon sinks over time. The lack of wet phases since the plateaus formed, despite several local fires, suggests that this type of peatlands have been negligible as methane sources throughout most of their history, representing a negative net radiative forcing on climate. Thermokarst lakes are common features in peat plateaus across the northern permafrost region. A time-series analysis of aerial photographs and high resolution satellite images in three peat plateau/thermokarst lake complexes along a climatic and permafrost gradient shows that where the mean annual air temperature (MAAT) is below -5ºC and ground temperatures are -2ºC or colder, only minor changes in thermokarst lake extent have occurred from the mid 1970s until the mid 2000s. During the same time interval extensive lake drainage and new lake formation has taken place where the MAAT is ca -3ºC and the ground temperature is close to 0ºC. In a future progressively warmer and wetter climate, permafrost degradation can cause significant impacts on landscape pattern and greenhouse gas exchange also in the vast peat plateaus presently experiencing stable permafrost conditions.
|
|
| 7. |
- Hichens-Bergström, Marit, et al.
(författare)
-
Permafrost development in northern Fennoscandian peatlands since the mid-Holocene
- 2023
-
Ingår i: Arctic, Antarctic and Alpine research. - 1523-0430 .- 1938-4246. ; 55:1
-
Tidskriftsartikel (refereegranskat)abstract
- Increased permafrost temperatures have been reported in the circum-Arctic, and widespread degradation of permafrost peatlands has occurred in recent decades. The timing of permafrost aggradation in these ecosystems could have implications for the soil carbon lability upon thawing, and an increased understanding of the permafrost history is therefore needed to better project future carbon feedbacks. In this study, we have conducted high-resolution plant macrofossil and geochemical analyses and accelerator mass spectrometry radiocarbon dating of active layer cores from four permafrost peatlands in northern Sweden and Norway. In the mid-Holocene, all four sites were wet fens, and at least three of them remained permafrost-free until a shift in vegetation toward bog species was recorded around 800 to 400 cal. BP, suggesting permafrost aggradation during the Little Ice Age. At one site, Karlebotn, the plant macrofossil record also indicated a period of dry bog conditions between 3300 and 2900 cal. BP, followed by a rapid shift toward species growing in waterlogged fens or open pools, suggesting that permafrost possibly was present around 3000 cal. BP but thawed and was replaced by thermokarst.
|
|
| 8. |
- Sannel, A. Britta K., 1968-
(författare)
-
Holocene dynamics in subarctic peat plateaus of west-central Canada : Vegetation succession, peat accumulation and permafrost history
- 2007
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Dynamics in vegetation, permafrost and peat and net carbon accumulation rates throughout the Holocene have been studied in two subarctic peat plateaus of west-central Canada through plant macrofossil analysis, geochemical analyses and AMS radiocarbon dating. Peatland formation at the studied sites began around 6600-5900 cal yr BP as a result of paludification of upland forests. Permafrost aggradation probably occurred 5600-4500 cal yr BP when Sphagnum fuscum became established and rootlet layers started to appear. Alternating layers of Sphagnum fuscum and rootlet peat throughout most of the peat profiles are indicating relatively dry surface conditions, suggesting that permafrost conditions have remained stable since the peat plateau stages were initiated. Local fires have occurred in the peatlands, but most fires did not cause degradation of the permafrost. However, lower peat and net carbon accumulation rates are recorded from rootlet layers containing charcoal. The long-term peat and net carbon accumulation rates for both studied peat profiles are 0,30-0,31 mm/yr and 12,5-12,7 gC/m2yr. Accumulation rates are variable depending on peat plateau stage. Peat accumulation rates are in general 4-5 times higher in S. fuscum than in rootlet stages, and net carbon accumulation rates are 3-4 times higher. Therefore even though Sphagnum peat makes up a majority of the peat profile depth, rootlet peat stages can represent most of the time since the peatland was initiated. The gross stratigraphy and plant macrofossil analyses show that there have been no wet phases, indicating permafrost collapse, since the peat plateau stages were initiated. This suggests that subarctic peat plateaus with alternating Sphagnum fuscum and rootlet peat layers have been acting as long-term net carbon sinks, accumulating carbon which has been incorporated into the permafrost, throughout most of the Holocene. High and stable carbon/nitrogen ratios throughout most of the profiles suggest that decomposition has not occurred in the perennially frozen peat. Since the peat plateaus are characterized by no decay in the permafrost and dry surface conditions, methane emissions are negligible from these ecosystems. In a future warmer climate carbon that has been stored under permafrost conditions can be remobilized. The warming may cause drier surface conditions resulting in increased emissions of carbon dioxide or, alternatively, permafrost collapse resulting in wetter surface conditions and increased methane emissions.
|
|
