| 1. |
- de Jong, Rixt, et al.
(författare)
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Climate and Peatlands
- 2010
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Ingår i: Changing Climates, Earth Systems and Society. - Dordrecht : Springer Netherlands. - 9789048187157 - 9789048187164 ; , s. 85-121
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Peatlands are an important natural archive for past climatic changes, primarily due to their sensitivity to changes in the water balance and the dating possibilities of peat sediments. In addition, peatlands are an important sink as well as potential source of greenhouse gases. The first part of this chapter discusses a range of well-established and novel proxies studied in peat cores (peat humification, macrofossils, testate amoebae, stomatal records from subfossil leaves, organic biomarkers and stable isotope ratios, aeolian sediment influx and geochemistry) that are used for climatic and environmental reconstructions, as well as recent developments in the dating of these sediments. The second part focuses on the role that peatland ecosystems may play as a source or sink of greenhouse gases. Emphasis is placed on the past and future development of peatlands in the discontinuous permafrost areas of northern Scandinavia, and the role of regenerating mined peatlands in north-western Europe as a carbon sink or source.
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| 2. |
- Gallego-Sala, Angela V., et al.
(författare)
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Latitudinal limits to the predicted increase of the peatland carbon sink with warming
- 2018
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Ingår i: Nature Climate Change. - : Springer Science and Business Media LLC. - 1758-678X .- 1758-6798. ; 8:10, s. 907-
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Tidskriftsartikel (refereegranskat)abstract
- The carbon sink potential of peatlands depends on the balance of carbon uptake by plants and microbial decomposition. The rates of both these processes will increase with warming but it remains unclear which will dominate the global peatland response. Here we examine the global relationship between peatland carbon accumulation rates during the last millennium and planetary-scale climate space. A positive relationship is found between carbon accumulation and cumulative photosynthetically active radiation during the growing season for mid- to high-latitude peatlands in both hemispheres. However, this relationship reverses at lower latitudes, suggesting that carbon accumulation is lower under the warmest climate regimes. Projections under Representative Concentration Pathway (RCP)2.6 and RCP8.5 scenarios indicate that the present-day global sink will increase slightly until around AD 2100 but decline thereafter. Peatlands will remain a carbon sink in the future, but their response to warming switches from a negative to a positive climate feedback (decreased carbon sink with warming) at the end of the twenty-first century.
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| 3. |
- Clemmensen, Lars B., et al.
(författare)
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The evolution of Holocene coastal dunefields, Jutland, Denmark: A record of climate change over the past 5000 years
- 2009
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Ingår i: Geomorphology. - : Elsevier BV. - 0169-555X. ; 105:3-4, s. 303-313
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Tidskriftsartikel (refereegranskat)abstract
- Coastal dunefields have developed on the west coast of Jutland in Denmark over the past 5000 years. The dunefields are situated in a temperate climate zone with frequent high energy wind events. Dunefield development was characterized by repeated periods of transgressive dune formation punctuated by periods of dune stabilization and soil formation. The chronology of dunefield evolution is based on Accelerator Mass Spectrometry (AMS) radiocarbon dating of peaty palaeosols (24 samples) and Optically Stimulated Luminescence (OSL dating of aeolian sand deposits (19 samples). These dates indicate that the completeness of the stratigraphic record varies considerably, but that the timing of aeolian activity events was identical in the dunefields examined here. Initiation of aeolian activity occurred around 2200 BC, 800 BC, AD 100, AD 1050-1200, and between AD 1550 and 1650. Proxy-climate data from bogs in southwestern Sweden suggest that these periods of dunefield activity were initiated during wet/cool summers. Most likely these climatic situations were associated with a more frequent passage of cyclones across Denmark in the summer seasons (increased storminess) causing aeolian sand movement and dune formation. The continued removal of vegetation in Jutland between 4000 BC and AD 1850 allowed the aeolian sand, when first activated, to move more and more easily across the coastal plains; the final phase of aeolian sand movement between AD 1550-1650 and 1900 had catastrophic implications for many coastal inhabitants in the region. (C) 2008 Elsevier B.V. All rights reserved.
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| 4. |
- de Jong, Rixt, et al.
(författare)
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A chrysophyte stomatocyst-based reconstruction of cold-season air temperature from Alpine Lake Silvaplana (AD 1500-2003); methods and concepts for quantitative inferences
- 2013
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Ingår i: Journal of Paleolimnology. - : Springer Netherlands. - 0921-2728 .- 1573-0417. ; 50:4, s. 519-533
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Tidskriftsartikel (refereegranskat)abstract
- Relatively little is known about past cold-season temperature variability in high-Alpine regions because of a lack of natural cold-season temperature proxies as well as under-representation of high-altitude sites in meteorological, early-instrumental and documentary data sources. Recent studies have shown that chrysophyte stomatocysts, or simply cysts (sub-fossil algal remains of Chrysophyceae and Synurophyceae), are among the very few natural proxies that can be used to reconstruct cold-season temperatures. This study presents a quantitative, high-resolution (5-year), cold-season (Oct-May) temperature reconstruction based on sub-fossil chrysophyte stomatocysts in the annually laminated (varved) sediments of high-Alpine Lake Silvaplana, SE Switzerland (1,789 m a.s.l.), since AD 1500. We first explore the method used to translate an ecologically meaningful variable based on a biological proxy into a simple climate variable. A transfer function was applied to reconstruct the 'date of spring mixing' from cyst assemblages. Next, statistical regression models were tested to convert the reconstructed 'dates of spring mixing' into cold-season surface air temperatures with associated errors. The strengths and weaknesses of this approach are thoroughly tested. One much-debated, basic assumption for reconstructions ('stationarity'), which states that only the environmental variable of interest has influenced cyst assemblages and the influence of confounding variables is negligible over time, is addressed in detail. Our inferences show that past cold-season air-temperature fluctuations were substantial and larger than those of other temperature reconstructions for Europe and the Alpine region. Interestingly, in this study, recent cold-season temperatures only just exceed those of previous, multi-decadal warm phases since AD 1500. These findings highlight the importance of local studies to assess natural climate variability at high altitudes.
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| 5. |
- de Jong, Rixt, et al.
(författare)
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Exploring the patterns and causes of land use changes in south-west Sweden
- 2011
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Ingår i: Vegetation History and Archaeobotany. - : Springer Science and Business Media LLC. - 0939-6314 .- 1617-6278. ; 20:1, s. 15-27
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Tidskriftsartikel (refereegranskat)abstract
- To study the causes of agricultural declines in south-west Sweden, a multi-proxy study including pollen analysis, bog surface wetness indicators and aeolian sediment influx reconstructions was carried out on the Store Mosse Bog, situated on the coastal plain of Halland. Patterns of agricultural changes during the past 6,000 years from this study were compared to one additional site on the coastal plain (Undarsmosse Bog) and to four sites in the forested upland region. First, we compared land use activity on the coastal plain and in upland regions of south-west Sweden. Three periods with reduced agricultural activities were observed, primarily in records from the coastal plain. Next, the causes for these declines were studied by comparing land use indicators in the pollen records from the Store Mosse and Undarsmosse peat bogs to independent climatic reconstructions based on the same core material (past storm activity based on aeolian sediment influx onto the peat bogs; bog surface wetness reconstructed from organic bulk density measurements). Since the climatic reconstructions and pollen analysis were carried out on the same peat cores, a direct comparison between the timing of climatic events and land use changes was possible. Results indicate that climatic perturbations prior to ca. 1,000 years ago contributed to or possibly caused agricultural declines. The agricultural expansions near the Store Mosse and Undarsmosse bogs from 3000 to 2600 cal. yrs b.p. ended at the time when climatic proxy indicators recorded climatic instability (from ca 2600 to 2200 cal. yrs b.p.). The same sequence of events was recorded around 1500 cal. yrs b.p. and from 1200 to 1000 cal. yrs b.p., suggesting a climatic cause for these agricultural declines as well. The well-known climatic perturbations associated with the Little Ice Age, however, did not have a visible impact on agricultural activities. By this time, advances in land use knowledge and technology may have drastically diminished society's sensitivity to climatic changes.
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| 6. |
- de Jong, Rixt, et al.
(författare)
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Increased aeolian activity during humidity shifts as recorded in a raised bog in south-west Sweden during the last 1700 years
- 2007
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Ingår i: Climate of the Past. - 1814-9332. ; 3, s. 411-422
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Tidskriftsartikel (refereegranskat)abstract
- Analyses of testate amoebae and aeolian sediment influx (ASI) were used to reconstruct effective humidity changes and aeolian activity in the coastal zone of south-west Sweden. Cores were taken from an ombrotrophic peat sequence from the Undarsmosse bog. Since both types of analysis were carried out on the same core, a direct comparison between humidity fluctuations in the bog and aeolian activity was possible, potentially providing detailed information on atmospheric circulation changes in this region. Relatively wet bog surface conditions occurred from around 1500 to 1230 and 770 to 380 cal. yrs BP, whereas dry conditions dominated from ca. 1630 to 1530, 1160 to 830 and 300 to 50 cal. yrs BP. The transitions between these phases occurred within 60–100 years and are characterised by a major change in the testate amoebae assemblages. A watertable reconstruction was used to study the hydrological changes at the bog surface in more detail. ASI peak events were reconstructed around 1450, 1150, 850 and after 370 cal. yrs BP. Most interestingly, these aeolian activity peaks started during the recorded hydrological transitions, regardless of the direction of these shifts. Our results therefore suggest that humidity shifts in this region were associated with temporary intensifications of atmospheric circulation during the past 1700 years. Several ASI peaks apparently coincide with reduced solar activity, possibly suggesting a solar related cause for some of the observed events.
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| 7. |
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| 8. |
- de Jong, Rixt, et al.
(författare)
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Late Holocene effective precipitation variations in the maritime regions of south-west Scandinavia
- 2009
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 28:1-2, s. 54-64
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Tidskriftsartikel (refereegranskat)abstract
- At present, the climate in south-west Scandinavia is predominantly controlled by westerlies carrying moist Atlantic air, which forms a main source of precipitation in all seasons. Past variations in the ratio between precipitation and evaporation (effective precipitation) from terrestrial sites, however, may indicate changes in the degree of maritime influence. Palaeoclimatic archives in this region are thus ideally situated to study past changes in atmospheric circulation patterns. In this study, multi-proxy comparisons of records from three peat bogs and two lakes are used to reconstruct regional-scale variations of effective precipitation in south-west Sweden during the Late Holocene. The total aeolian sediment influx into two peat bogs is used as a proxy for storm activity. The frequency of storm phases increases strongly after ca 2500 cal yrs BP. Dry conditions occur on a regional scale around 4800-4400, 2000-1700, 1300-1000, 700-500 and 300-100 cal yrs BP. In addition, a comparison to winter precipitation reconstructed from four Norwegian glaciers shows similar variations during the past ca 2000 years. This indicates that the climate in both regions was controlled by large-scale atmospheric circulation dynamics of the North Atlantic region. The strong variability of effective precipitation and storm activity after ca 2500 cal yrs BP indicates a highly variable climate. (C) 2008 Elsevier Ltd. All rights reserved.
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| 9. |
- de Jong, Rixt, et al.
(författare)
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Storminess variation during the last 6500 years as reconstructed from an ombrotrophic peat bog in Halland, southwest Sweden
- 2006
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Ingår i: Journal of Quaternary Science. - : Wiley. - 1099-1417 .- 0267-8179. ; 21:8, s. 905-919
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Tidskriftsartikel (refereegranskat)abstract
- Cores taken from an ombrotrophic peat bog in the coastal zone of Halland, southwest Sweden, were examined for wind transported mineral grains, pollen and humidity indicators. The core covers the period from 6500 cal. yr BP to present. Ombrotrophic conditions existed from ca. 4200 cal. yr BP onwards. Bog surface wetness fluctuated strongly until ca. 3700 cal. yr BP, with an apparent dominance of dry summer conditions from 4800-4500 cal. yr BP. Local wet shifts occurred around 4300, 2800, 2400 and 1500 cal. yr BP, whereas the most recent 600 years of the record show increasingly dry conditions. Mineral grain content, interpreted as aeolian sand influx (ASI), was used as a proxy for (winter) storm frequency and intensity until ca. 1500 cal. yr BP, after which increasing human impact, as reconstructed by pollen analysis, became a second important potential cause for increased sand drift. Strongly increased storminess occurred at 4800, 4200, 2800-2200, 1500, 1100 and 400-50 cal. yr BP, indicating a dominance of cold and stormy winters during these periods. Many of these storm periods apparently coincide with storm events in other sites in southwestern Scandinavia, suggesting that our ASI record reflects a regional scale climatic signal. Furthermore these stormy periods correlate to well-known cold phases in the North Atlantic region, suggesting a link to large-scale fluctuations in atmospheric circulation patterns.
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| 10. |
- de Jong, Rixt
(författare)
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Stormy records from peat bogs in south-west Sweden : implications for regional climatic variability and vegetation changes during the past 6500 years
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis aims to reconstruct and explain variations in storm activity, humidity, vegetation composition and land cover in south-west Sweden during the past 6500 years. Two ombrotrophic bogs, Store Mosse and Undarsmosse, situated on the coastal plain of Halland, were selected for this purpose. The coastal plain of Halland is positioned in the cyclone path and is therefore particularly sensitive to changing cyclone frequencies and associated storms. Cyclones have a strong control on the climate in this region, by moderating summer and winter temperatures and being the main source of precipitation. Aeolian sediment influx (ASl) was used as a proxy for storm activity. Bog surface wetness reconstructions were based on organic bulk density values from both study sites, whereas testate amoebae analysis was applied on cores from Undarsmosse bog only. Pollen analysis was carried out to reconstruct vegetation and land use changes. In addition the hypothetical regional scale vegetation composition around the Store Mosse bog was reconstructed by applying the REVEALS model, which corrects for differences in pollen productivity and dispersal between plant taxa. The land use reconstructions were also used to discriminate between climatic and human induced variations in ASI values, since increased sediment availability resulting from human activity may have affected sand influx into the bogs. The reconstructions of storm activity are similar at both study sites, with peaks of storminess around 4700, 2800-2000, 1500, 1100, 700 and 400-50 cal. yrs BP. These time periods are in good agreement with, for example, dune re-activation phases in Denmark. A comparison to land use in the region shows that ASI values are highest when the indications for cultivated fields are low, which implies that land use cannot explain the occurrence of ASI peaks. These are therefore most likely causally related to regional scale climatic changes. Humidity shifts were recorded around 4800, 2000 and 400 cal. yrs BP at both sites, which concurs with lake chemistry and lake level reconstructions from southern Sweden. These results were used to propose a regional scale reconstruction of climatic change, and may be used to infer variations in past atmospheric circulation patterns. In addition, a detailed comparison between ASI values and testare amoebae based wetness reconstructions has revealed an enigmatic pattern of increased storm activity during shifts in humidity during the past 1700 years.
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