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Picture, Jenny Sjöström

Jenny Sjöström

Doktorand

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Arbetar vid Institutionen för geologiska vetenskaper
E-post jenny.sjostrom@geo.su.se
Besöksadress Svante Arrheniusväg 8 C, Geohuset
Rum R 210
Postadress Institutionen för geologiska vetenskaper 106 91 Stockholm

Om mig

Jag är doktorand vid Institutionen för Geologiska vetenskaper. Inom min forskning arbetar jag med att rekonstruera deposition av mineraldamm i högmossar under de senaste 8000 åren. Mitt studieområde ligger i sydsvenska höglandet, Småland. 

Publikationer

I urval från Stockholms universitets publikationsdatabas
  • 2018. Jenny Sjöström (et al.).

    Atmospheric mineral dust plays a dynamic role in the climate system acting both as a forcing and a feedback mechanism. To date, the majority of paleodust studies have been conducted on marine sediments or polar ice cores, while terrestrial deposition has been less studied. As such, it is important to produce new terrestrial Holocene paleo–dust records and fill existing regional gaps. Ombrotrophic (atmospherically–fed) peat bogs can be used to reconstruct dust deposition through elemental chemistry analysis. Multi–elemental data sets are commonly used infer net dust deposition rates, source changes, grain size, and mineral composition. Mineralogical identification of dust particles is particularly important because it allows both provenance tracing and increased understanding in climate and ecosystem feedbacks. Establishing mineralogy from elemental data of mixed mineral matrixes can however be challenging. X–ray diffraction analysis (XRD) is a standard technique for mineral identification which ideally requires removal of organic matter (OM). Therefore, a test procedure was undertaken where common OM removal methods were evaluated on bulk peat samples was therefore undertaken. The results showed that combustion at 500°C was most efficient in removing OM, while leaving the majority of minerals intact, but not all. In this Licenciate thesis, early result of a paleodust study from Draftinge Mosse, southern Sweden, are also outlined. Here, the method development mentioned above was applied, enabling a combination of elemental data with mineralogy. Future work includes minor and trace element analysis by ICP–AES and ICP–MS, evaluation of the reproducibility of single core reconstructions, tests of some of the methodological assumptions used in previous paleodust studies, source tracing and paleodust reconstruction from a second site (Gällsered Mosse). 

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

    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.

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

    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.

  • 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. 

Visa alla publikationer av Jenny Sjöström vid Stockholms universitet

Senast uppdaterad: 10 november 2018

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