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Browsing by study line "Paleontologia ja globaali muutos"

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  • Redmond Roche, Benjamin Heikki (2019)
    Significant changes in sea-ice variability have occurred in the northern North Atlantic since the last deglaciation, resulting in global scale shifts in climate. By inferring the dynamic changes of palaeo seaice to past changes in climate, it is possible to predict future changes in response to anthropogenic climate change. Diatoms allow for detailed reconstructions of palaeoceanographic and sea-ice conditions, both qualitatively, using information of species ecologies and quantitatively, via a transfer function based upon diatom species optima and tolerances of the variable to be reconstructed. Three diatom species comprising a large portion of the training set are proxies for the presence of sea ice: Fragilariopsis oceanica, Fragilariopsis reginae-jahniae and Fossula arctica, have currently been grouped into one species – F. oceanica – in the large diatom training set of the northern North Atlantic region. The clustering of the species may result in an imprecise reconstruction of sea ice that does not take into account all the available ecological information. The proportions of the three species were recounted from the original surface sediment slides alongside the additional chrysophyte cyst Archaeomonas sp. and statistically analysed using Canoco and the R software package eHOF. A core from Kangerlussuaq Trough comprising the Late Holocene (~690–1498 Common Era) was also recounted and analysed using C2. The separated diatom species and chrysophyte cyst Archaeomonas sp. exhibited different relationships to both sea-ice concentration (aSIC) and sea surface temperature (aSST). The separated F. oceanica is a ‘cold-mixed’ water species occurring at cold aSST and both low and high aSIC. High abundances occur in the marginal ice zone (MIZ) where surficial meltwater is high during the spring bloom, with additional inputs from glacial meltwaters nearshore. F. reginae-jahniae is a sea-ice associated species related to cold aSST and high aSIC. High abundances occur in the low salinity Arctic Water dominated MIZ which experiences significant aSIC. F. arctica is a sea-ice associated species related to cold aSST and high aSIC. High abundances occur in the low salinity Arctic Water dominated MIZ which experiences high aSIC, particularly in polynya conditions. F. arctica can be considered a characteristic polynya species at high abundances. Archaeomonas sp. is a ‘cold-mixed’ water species related to both cold and relatively warm aSST and low and high aSIC. High abundances occur in both relatively warm ice-free Atlantic Water and also in cold high aSIC Arctic Water conditions rendering it a more complex indicator for aSST or aSIC proxy. However, the aversion to MIZ conditions indicates that Archaeomonas sp. is associated with a relatively saline unstratified water column. This is the first time that the distribution and ecology of Archaeomonas sp. has been presented. As such, the ecology described here can be used in future studies. The separation of the three diatom species is crucial for the ecological interpretation of downcore assemblage changes. It is also crucial for the application of transfer functions in order to have greater precision in reconstructing aSIC and assessing the influence of Arctic Water or Atlantic Water, even at low abundances.
  • Stark, Piritta (2022)
    In this study, single-grain rutile techniques (rutile U-Pb geochronology, Zr-in rutile thermometry, rutile Nb-Cr systematics and trace element composition) are applied on Red Clay samples from Lingtai, central-southern Chinese Loess Plateau (CLP), to reveal more detailed information on provenance of the Red Clay and wind regimes responsible for transporting the particles from source to sink between 7 Ma and 2.6 Ma. The new rutile data are combined with previous zircon U-Pb data from Lingtai and nearby Chaona to strengthen the interpretations with multi-proxy approach. The results suggest that from 7.05 Ma to 6.23 Ma the westerlies and the East Asian Winter Monsoon (EAWM) were relatively equally responsible for the sediment transportation to the CLP. At 5.55 Ma, the Red Clay was mostly derived from the westerly sources. At 3.88 Ma, contribution from northeastern Tibetan Plateau was most dominant suggesting enhanced East Asian Summer Monsoon (EASM) and surficial drainage from the source regions. At 3.20 Ma, the Red Clay was mainly sourced from proximal areas and fluctuation between EAWM and EASM had begun. This study demonstrates that single-grain rutile techniques have strong potential to aid a more precise distinction between individual primary and secondary sources for aeolian dust in the CLP region, especially when combined with zircon geochronology or other single-grain techniques. However, at present the applicability of rutile in provenance studies is hindered by scarcity of rutile data from the potential primary as well as secondary source regions, and lack of truly homogenous rutile standards for the analysis.
  • Laakkonen, Aliisa (2022)
    Peatlands are complex ecosystems that not only respond to external changes but also influence their environment. Permafrost peatlands have an important role in the global carbon (C) cycle as they store about 200 Pg of C. As permafrost thaws this C can be released either as methane (CH4) or carbon dioxide (CO2). In addition to these peatlands also emit nitrous oxide (N2O). Climate warming may change this sink-source balance of peatlands. Hydrological conditions are an important factor in peatland C dynamics. As permafrost thaws it can shift these ecosystems towards wetter or dryer conditions. Peat decomposition under dry conditions can have a strong positive feedback to climate change due CO2 emissions. Though wetter conditions can increase CH4 emissions. Through topography and hydrology, permafrost also affects vegetation dynamics. In this thesis I am examining peat profiles collected from two subarctic permafrost peatlands located in Kevo, Finland and Karlebotn, Norway. The profiles included an un-frozen active layer profile and a permafrost sample collected from inside a palsa mound. These samples were analysed for vegetation composition and peat properties (C and N content, C/N ratio and bulk density), they were also 14C dated and incubated. The purpose was to simulate a warmer climate to which these ecosystems will be exposed to in the future and observe how they will respond. The observations focused on the three most common GHGs of peatlands, CH4, CO2 and N2O. The permafrost samples showed potential for CH4 and CO2 emissions, whereas the active layer only emitted CO2. The CH4 emissions were interpreted to represent old CH4, whereas the CO2 was interpreted to be produced by the peat.