Rekonstruktion av stormars mönster de senaste 10.000 åren

I norra Europa har en ökad stormfrekvens rapporteras de senaste decennierna. Det finns dock osäkerheter om hur stormmönster (dvs frekvens och intensitet) kan komma att påverkas av framtida klimatförändringar. Inom detta projekt arbetar vi för att rekonstruera hur stormmönster varierat de senaste 10.000 åren. Våra fältområden återfinns i kustnära områden i Nordatlanten (Irland, Skottland, Färöarna, Norge, Sverige) där vi använder två olika sorter naturliga arkiv: högmossar samt sanddyner, för att rekonstruera förhistoriska stormmönster. Det övergripande målet är att dels förstå hur stormaktvitet registreras i de olika klimatarkiven (dvs högmossar respektive sanddyner), samt att i nå ökad insikt kring vilka klimatfaktorer som orsakar minskad eller ökad stormaktvitet. Målet är att förbättra kunskapsläget kring hur och varför stormmönster varierat förhistoriskt, vilket kan leda till ökad förståelse kring hur stormmönster kan påverkas av pågående, samt framtida, klimatförändringar. Mer att läsa om projektet, och dess medlemmar, finns i projektbeskrivningen (se länk).

I urval från Stockholms universitets publikationsdatabas

• Procedure for organic matter removal from peat samples for XRD mineral analysis

  Jenny Sjöström.

  Ombrotrophic peatlands are recognised archives of atmospheric mineral dust deposition, where mainly elemental data has been used to infer past net dust deposition rates, sources, grain size and mineralogy of the deposited dust. Although geochemical analysis can be data–rich, there are some inherent limitations. X–ray diffraction (XRD) directly determines the mineralogy of environmental samples but few studies have applied this method to peat samples and a well–developed protocol for extracting the inorganic fraction of highly organic samples (>95 %) is lacking. We tested and compared different levels of pre–treatment: no pre–treatment, thermal combustion (300, 350, 400, 450 and 500°C) and chemical oxidation (H₂O₂ and Na₂S₂O₈) using a homogenized high organic content (>98 %) composite peat sample. Subsequently, minerals were identified by XRD. The results show that combustion is preferred to chemical oxidation because it most efficiently removes organic matter (OM), an important pre–requisite in order to identify mineral phases by XRD analysis of a mixed sample matrix, and phase transitions that may occur can be anticipated when temperature is the only factor to take into consideration. Combustion at 500°C is the most efficient temperature for OM removal whereas combustion at lower temperatures left significant OM residues. 

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• Paleodust deposition and peat accumulation rates - Bog size matters

  2020. Jenny K. Sjöström (et al.). Chemical Geology 554

  Artikel

  We present a high-resolution peat paleodust and accumulation rate record spanning the last 8300 years from Draftinge Mosse (400 ha), southern Sweden (57 degrees 06'27.6 '' N 13 degrees 42'54.1 '' E). The record was analysed for peat accumulation rates (PAR), elemental concentrations, mineralogy, and plant macrofossil content. Five periods of increased mineral deposition were recorded. The first event occurred between similar to 6280 and similar to 5570 cal BP, during the fen to bog transition. This is followed by four atmospheric mineral dust events (DE) which were recorded in the ombrotrophic section of the sequence at (cal BP): similar to 2200; similar to 1385-1150; similar to 830-590, and from similar to 420 to the present. Statistical analysis and elemental ratios indicated that both the mineralogy and grain size shifted when the system transitioned from fen into bog, showing that the governing transport process shifted with the peat-land succession stages. This highlights the importance of identifying peatland succession stages within peat paleodust studies. Following all four DE, increases in PAR were observed, implying a coupling to dust deposition. Comparison of DE and PAR with a paleodust record from Store Mosse, a 20 times larger bog located ca 18 km away (Kylander et al. 2016), showed that both PAR and dust deposition are largely represented by single-core reconstructions, indicating that they are driven by a common climate forcing mechanism. However, higher PAR and dust deposition rates were observed in the more moderately sized Draftinge Mosse, suggesting that the size of the bog is important to consider in peat paleodust studies. Furthermore, the smaller bog responded more rapidly to hydrological changes, indicating that the size of the bog affects its' buffering capacity. Authigenic carbonates, observed here during episodes of rapid peat growth, coincide with changes in REE ratios, indicating that authigenic peat processes potentially cause REE fractionation.

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• Mid-Holocene mineral dust deposition in raised bogs in southern Sweden

  2021. Jenny Sjöström (et al.).

  Avhandling (Dok)

  Atmospheric mineral dust is a key component of the climate system, which affects insolation, brings nutrients to marine and terrestrial ecosystems, and acts as a cloud condensation nuclei. To reconstruct past patterns in terrestrial dust deposition natural archives may be utilized, such as loess, dunes, lakes, and peat bogs. Bogs became an established dust archive in the early 2000s, and the number of studies has since increased. However, most studies use single records to represent dust deposition, meaning that we have limited understanding of regional paleodust dynamics or about the representativeness of single bog records. This thesis aims to address these uncertainties by comparing paleodust deposition between bogs located on a 65 km transect. The thesis includes a methodological development for organic matter removal from peat samples for XRD mineral analysis (Paper I) and two peat paleodust reconstruction studies (Paper II, III). 

  The first paleodust reconstruction from Draftinge Mosse (mosse translates to bog in English), Småland, showed that four dust events (DE) were recorded during the ombrotrophic stage (Paper II). These results were compared to a previously conducted study on Store Mosse, 20 km northeast of Draftinge Mosse, which showed similar patterns in DE and peat accumulation rate (PAR), indicating that the events were at least regional in character. However, the magnitude of the DE differed, which was related to differences in the sizes of the two bogs. The second paleodust reconstruction, from (Davidsmosse) located c. 25 km from the west coast, recorded many more DE (14) compared to the more inland sites (Paper III). Two longer periods saw numerous DE, dominated by coarse particles: between 2800 and 2130 cal BP, and from 1000 towards 490 cal BP. These two periods occurred during regionally cold periods. Human activities also intensified during the latter period, possibly amplifying the DE. 

  Most of these episodic events were not recorded at the inland sites, and the Davidsmosse record seemed to be more in line with previously constructed coastal paleostorm records. That the bog located closer to the coast recorded many more events compared to the inland sites suggests that the location of a bog will influence the aeolian events recorded. However, the DE observed at the inland sites were also recorded at Davidsmosse, indicating that the inland events might represent winds that were sustained over longer distance, or alternatively, that regionally dry conditions prevailed during these periods. The paleostorm records from south-western Sweden, including the new results from Davidsmosse presented here, suggest that storm intensities have varied during the last 3000 years, with increased storminess frequency coupled to colder episodes related to extended sea ice and a southward shift of storm tracks. When comparing DE and PAR at both sites studied here, a recurring pattern of increased accumulation rates were observed during a majority of DE, supporting the suggestion of previous studies that dust deposition may affect peat growth, and thus also peat carbon sequestration.

  Combining elemental data with XRD mineral analysis enabled anchoring of elemental inferences with mineral observations, allowed identification of authigenic minerals, and aided in source tracing. Despite the fact that local factors affect mineral deposition and PAR, this work has outlined some of the possible mechanisms behind these observations (e.g. distance to the coast, or bog size difference) which may be important for future peat paleodust studies to consider. For example, future studies should include grain size analysis (down-core, as well as across a bog surface); pollen analysis to further elaborate on human activities and vegetation cover; and further investigate differences in mass accumulation rates between bogs.

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• Late Holocene peat paleodust deposition in south-western Sweden - exploring geochemical properties, local mineral sources and regional aeolian activity

  2022. Jenny K. Sjöström (et al.). Chemical Geology 602

  Artikel

  Atmospheric mineral dust not only interacts with the climate system by scattering incoming solar radiation and affecting atmospheric photochemistry, but also contributes critical nutrients to marine and terrestrial ecosystems. In a high-resolution analysis of paleodust deposition, peat development and soil dust sources, we assess the interplay between dust deposition and bog development of the Davidsmosse bog in south-western Sweden. Analyses of the 5400-year record (458 cm) included radiocarbon dating, bulk density, ash content, chemical and mineralogical composition and carbon stable isotopes, subsequently explored using principal component analysis. Fourteen dust events (DEs) were recorded (cal BP) in the peat sequence: 3580–3490; 3280; 3140; 3010–2840; 2740; 2610; 2480; 2340; 2240–2130; 1690; 1240; 960, 890–760, and 620–360. The majority of the DEs were coupled to increases in peat accumulation rates and increased nutrient content (N, P and K) suggesting that the DEs contributed with nutrients to the bog ecosystem, promoting increased accumulation. We also analyzed the chemical and mineral composition of potential mineral source deposits (separated into 6 grain-size fractions) from sites within a 4 km radius as well as aeolian dunes closer to the coast (25 km). The composition deposited on the present-day bog surface indicates that the bulk of the contemporary minerals have a local origin (<1.5 km), but the DEs may be of a more distant origin. The results also indicate that quartz and plagioclase feldspar content consistently increase with increasing grain-size, both in the source samples as well as in the peat sequence, and that the Si/Al ratio can be used to infer grain size changes in the peat. Two longer phases saw numerous DEs, between 2800 and 2130 cal BP and a stepwise increase from 960 towards 360 cal BP. The episodic character of the events, together with the inferred coarse grain size, suggest that the particles were deposited by (winter) storms. Future studies should include grain size analysis as well as a more in-depth comparison with regional paleo dust and storm records to increase knowledge on both transport processes (creep, saltation, suspension) and the climate processes driving late Holocene dust and storm events in Scandinavia.

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• Phosphorus supply affects long-term carbon accumulation in mid-latitude ombrotrophic peatlands

  2021. Daniel N. Schillereff (et al.). Communications Earth & Environment 2 (1)

  Artikel

  Increased long-term phosphorus accumulation reduces carbon sequestration in mid-latitude peatlands reliant on atmospheric nutrient sources, according to a synthesis of data from Central Europe, North America, Chile, Sweden and the UK. Ombrotrophic peatlands are a globally important carbon store and depend on atmospheric nutrient deposition to balance ecosystem productivity and microbial decomposition. Human activities have increased atmospheric nutrient fluxes, but the impacts of variability in phosphorus supply on carbon sequestration in ombrotrophic peatlands are unclear. Here, we synthesise phosphorus, nitrogen and carbon stoichiometric data in the surface and deeper layers of mid-latitude Sphagnum-dominated peatlands across Europe, North America and Chile. We find that long-term elevated phosphorus deposition and accumulation strongly correlate with increased organic matter decomposition and lower carbon accumulation in the catotelm. This contrasts with literature that finds short-term increases in phosphorus supply stimulates rapid carbon accumulation, suggesting phosphorus deposition imposes a threshold effect on net ecosystem productivity and carbon burial. We suggest phosphorus supply is an important, but overlooked, factor governing long-term carbon storage in ombrotrophic peatlands, raising the prospect that post-industrial phosphorus deposition may degrade this carbon sink.

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• 9000 years of changes in peat organic matter composition in Store Mosse (Sweden) traced using FTIR-ATR

  2021. Antonio Martínez Cortizas (et al.). Boreas 50 (4), 1161-1178

  Artikel

  Store Mosse (the ‘Great Bog’ in Swedish) is one of the most extensive bog complexes in southern Sweden (~77 km²), where pioneering palaeoenvironmental research has been carried out since the early 20th century. This includes, for example, vegetation changes, carbon and nitrogen dynamics, peat decomposition, atmospheric metal pollution, mineral dust deposition, dendrochronology, and tephrochronology. Even though organic matter (OM) represents the bulk of the peat mass and its compositional change has the potential to provide crucial ecological information on bog responses to environmental factors, peat OM molecular composition has not been addressed in detail. Here, a 568-cm-deep peat sequence was studied at high resolution, by attenuated reflectance Fourier-transform infrared spectroscopy (FTIR-ATR) in the mid-infrared region (4000–400 cm^–1). Principal components analysis was performed on selected absorbances and change-point modelling was applied to the records to determine the timing of changes. Four components accounted for peat composition: (i) depletion/accumulation of labile (i.e. carbohydrates) and recalcitrant (i.e. lignin and other aromatics, aliphatics, organic acids and some N compounds) compounds, due to peat decomposition; (ii) variations in N compounds and carbohydrates; (iii) residual variation of lignin and organic acids; and (iv) residual variation of aliphatic structures. Peat decomposition showed two main patterns: a long-term trend highly correlated to peat age (r = 0.87), and a short-term trend, which showed five main phases of increased decomposition (at ~8.4–8.1, ~7.0–5.6, ~3.5–3.1, ~2.7–2.1 and ~1.6–1.3 ka) – mostly corresponding to drier climate and its effect on bog hydrology. The high peat accumulation event (~5.6–3.9 ka), described in earlier studies, is characterized by the lowest degree of peat decomposition of the whole record. Given that FTIR-ATR is a quick, non-destructive, cost-effective technique, our results indicate that it can be applied in a systematic way (including multicore studies) to peat research and provide relevant information on the evolution of peatlands.

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• Mineral dust as a driver of carbon accumulation in northern latitudes

  2018. Malin E. Kylander (et al.). Scientific Reports 8

  Artikel

  Peatlands in northern latitudes sequester one third of the world's soil organic carbon. Mineral dusts can affect the primary productivity of terrestrial systems through nutrient transport but this process has not yet been documented in these peat-rich regions. Here we analysed organic and inorganic fractions of an 8900-year-old sequence from Store Mosse (the Great Bog) in southern Sweden. Between 5420 and 4550 cal yr BP, we observe a seven-fold increase in net peat-accumulation rates corresponding to a maximum carbon-burial rate of 150 g C m(-2) yr(-1) -more than six times the global average. This high peat accumulation event occurs in parallel with a distinct change in the character of the dust deposited on the bog, which moves from being dominated by clay minerals to less weathered, phosphate and feldspar minerals. We hypothesize that this shift boosted nutrient input to the bog and stimulated ecosystem productivity. This study shows that diffuse sources and dust dynamics in northern temperate latitudes, often overlooked by the dust community in favour of arid and semi-arid regions, can be important drivers of peatland carbon accumulation and by extension, global climate, warranting further consideration in predictions of future climate variability.

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• Late Holocene palaeoenvironmental reconstruction from Mpumalanga Province (South Africa) inferred from geochemical and biogenic proxies

  2017. Jenny Sjöström (et al.). Review of Palaeobotany and Palynology 246, 264-277

  Artikel

  Here we present a palaecological reconstruction covering the last 1700 yr from Lydenburg fen, located in the north-eastern grassland biome, Mpumalange, South Africa. A 300 cm peat sequence was analysed for biogenic (grass phytoliths, diatoms) and geochemical proxies (delta C-13, delta N-15, carbon/nitrogen content) to infer past grassland dynamics and hydro-climatic changes. The Lydenburg record reports a C-4 dominated grassland throughout the studied period, with more or less pronounced fluxes between C-4-Chloridoideae and C-4-Panicoideae grass subfamilies. The record reflects moderate to dry conditions from AD 400 to 1000; more mesic conditions until around AD 1250; followed by a significantly drier period between c. AD 1250 and c. AD 1350, when Chloridoideae grasses expand at the expense of Panicoideae grasses. During this phase, the delta C-13-record reports more enriched values indicating higher influx of C-4 grasses. Furthermore, lithological evidence indicates highly erosive conditions, with significant gravel input from the surrounding hills. After AD 1350, proxy indications suggest a shift towards more mesic conditions. During this increasingly mesic but also unstable period, farming communities using specialized agricultural practices (e.g. the people in Bokoni) expanded their settlements into new regions (Delius et al., 2008). This expansion was also coupled to population growth, suggesting these communities applied techniques that enabled improved food production under environmentally challenging conditions. Over the last century, Lydenburg delta C-13-values indicate increased input of C-3 taxa. The phytolith record shows that this increase is not coupled to an increase in Pooideae (C-3) grasses, suggesting that the C-3 input may be related to woody encroachment.

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