Browsing by Subject "KOLA-PENINSULA"

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  • Helama, Samuli; Arppe, Laura; Timonen, Mauri; Mielikäinen, Kari; Oinonen, Markku (2018)
    Tree-ring stable isotope chronologies provide very high-resolution palaeoclimatic data, and the number of records is increasing rapidly worldwide. To extend the chronologies back in time, before the period covered by the old living trees, the use of subfossil wood samples is required. Typically, the longest continuous subfossil chronologies consist of regionally collected tree-ring materials, rather than tree rings from a single site, and are likely more sensitive to data heterogeneity. Yet, the characteristics of such datasets remain hitherto unexplored. Here we produce a continuous, decadally resolved chronology of C-13/C-12 ratio (delta C-13) from Finnish Lapland over the past 7.5 ka (5500 BCE to 2010 CE) for which there is replication of at least five Pinus sylvestris trees. Less negative delta C-13 values were observed as trees age and for western sites (higher in elevation and further from the cold oceanic air flow). The age -related trends in living tree delta C-13 data were expressed mainly over the first fifty years mimicking the "juvenile effect" whereas the subfossil data showed trend over the trees' lifespan. These findings demonstrated the need to detrend the individual delta C-13 series before averaging them into the mean chronology. The corresponding biases were removed from the isotopic data using the methods frequently applied for tree-ring width and density proxies, the Regional Curve Standardization (RCS) combined with signal-free approach. While the RCS procedures commonly preserve the long-term variations in the resulting chronology, not all types of them did so as demonstrated for chronologies produced using separate RCS models for the delta C-13 series with relatively high and low isotopic level (offset from the grand mean). It was shown that these delta C-13 levels (i.e. the relative isotopic enrichment) result both from the low-frequency climate signal and biogeographical aspects (the site longitude/altitudes). The non-climatic biases were removed from the delta C-13 series by using separate RCS models for the subsets (western and eastern) of isotopic series. Similar to previous investigations using annually resolved delta C-13 data from Lapland, our chronology had strong negative correlations to variations in cloud cover. Here, a bootstrapping experiment was used to verify this dendroclimatic association. The resulting palaeo-cloud reconstruction portrayed decadal to multi-millennial variations with centennial anomalies coinciding with the mid and late Holocene events of climate transitions, highlighting the value of subfossil isotope chronologies from tree rings in synthesising climate dynamics from several proxy sources over the present interglacial.
  • Nieminen, Pentti; Panychev, Dmitry; Lyalyushkin, Sergei; Komarov, German; Nikanov, Alexander; Borisenko, Mark; Kinnula, Vuokko L.; Toljamo, Tuula (2013)
  • Chayka, Ivan F.; Zhitova, Liudmila M.; Antsiferova, Tatiana N.; Abersteiner, Adam; Shevko, Artem Ya; Izokh, Andrey E.; Tolstykh, Nadezhda D.; Gora, Marina P.; Chubarov, Valery M.; Kamenetsky, Vadim S. (2020)
    Layers rich in chromian spinel (Cr-spinel) occur in numerous differentiated and layered intrusions. These layers are often characterized by elevated and even economic concentrations of platinum-group-elements (PGEs), but only scarce sulfide mineralization. One particular type of such lithology occurs in the roof parts of the Norilsk-type differentiated intrusions (Russia) and is referred to as the "sulfide-poor PGE ores". We investigated rocks containing variable enrichments in Cr-spinel, sulfides, and platinum-group minerals (PGMs) from two sections of the upper zone of the Norilsk-1 intrusion, with a focus on Cr-spinel. The rocks are dominated by two lithological types: (1) leucogabbro/troctolitic and (2) olivine-gabbro. Fine-grained (5-100 mu m) disperse disseminations with varying modal abundances of Cr-spinel are characteristic for the rocks studied. Those abundances range from scarce mineralization through to very dense (up to 30 vol. % Cr-spinel) cloud-like accumulations. However, compact-grained accumulations and cumulate-like textures, which are typical for chromitites of layered intrusions, are not characteristic for the studied rocks. Instead, the disseminations exhibit chain- and trail-like alignments of Cr-spinel grains, which cross the boundaries between enclosing silicates, and sub-circular arrangements. The study revealed millimeter-scaled patchy distribution of Cr-spinel compositions within a given dissemination with Cr-spinel chemistry being strongly correlated with a kind of the enclosing silicate. (1) In unaltered rocks, plagioclase hosts more magnesian Cr-spinel (Mg# 30-60), while Cr-spinel in mafic minerals is less magnesian (Mg# 18-35). (2) In altered rocks, more magnesian Cr-spinel is hosted by less altered silicates, while strongly altered silicates mainly host less magnesian Cr-spinel. Systematics of trivalent cations exhibits divergent trends, even on a scale of a thin section, and depends on a kind of hosting lithology. Leucogabbro/troctolite lithologies contain Cr-spinel with anomalously low Fe(3+)and extremely high Ti contents, whereas Cr-spinel from olivine-gabbro lithologies have moderate Fe(3+)and moderately-high Ti contents. It is envisaged that crystallization of Cr-spinel and their host rocks occurred from viscous mingled magmas, which had different compositions and redox state. Subsequent processes involved (1) high-temperature re-equilibration of Cr-spinel with enclosing silicates and (2) post-magmatic alteration and partial recrystallization of Cr-spinel. During these processes, Cr-spinel was losing Mg and Al and gaining Fe and Ti. These chemical trends are generally coincident with those established for other intrusions worldwide, but the upper zone of the Norilsk-1 intrusion seems to possess an exceptional variety of Cr-spinel compositions, not recorded elsewhere.
  • Holtta, Pentti; Kivisaari, Tiia; Huhma, Hannu; Rollinson, Gavyn; Kurhila, Matti; Butcher, Alan R. (2020)
    The Tuntsa Suite is a polymetamorphic Archean complex mainly consisting of metasedimentary gneisses. At least two strong metamorphic events can be distinguished in the area. The first took place at high temperatures in the Neoarchean at around 2.70-2.64 Ga, indicated by migmatisation and U-Pb ages of metamorphic zircon. During the Paleoproterozoic, metasedimentary gneisses were penetratively deformed and recrystallized under medium pressures producing staurolite, kyanite and garnet-bearing mineral assemblages. The suggested Paleoproterozoic PT path was clockwise where the temperature and pressure first increased to 540-550 degrees C and 6 kbar, crystallizing high Ca/low Mg garnet cores. The mineral compositions show that commonly garnet core was not in chemical equilibrium with staurolite but crystallized earlier, although garnet-staurolite-kyanite assemblages are common. The temperature and pressure increased to c. 650 degrees C and 8 kbars where staurolite and kyanite coexist. This was followed by decompression down to c. 550-600 degrees C and 3-4 kbars, shown by andalusite crystallization and cordierite formed in the breakdown of staurolite and biotite + kyanite. The observed garnet zoning where Mg increases and Ca decreases from the core to the rim was developed with both increasing and decreasing pressure, depending on the effective bulk composition. The U-Pb and Sm-Nd age determinations for monazite and garnet show that the Paleoproterozoic metamorphic cycle took place at 1.84-1.79 Ga, related with thrusting of the Lapland granulites onto the adjacent terranes and subsequent exhumation.
  • Luoto, Tomi P.; Leppänen, Jaakko Johannes; Weckström, Jan (2019)
    The Talvivaara/Terrafame multi-metal mining company is Europe’s largest nickel open cast mine, it is also known for the largest wastewater leakage in the Finnish mining history and a series of other accidents. In this paleolimnological study, influences of a recently constructed treated waste water discharge pipeline into Lake Nuasjärvi were investigated by analyzing past (pre-disturbance) and present community compositions of key aquatic organism groups, including diatoms, Cladocera and Chironomidae, along spatial (distance, water depth) gradients. In addition to defining ecological changes and impacts of saline mine waters in the lake, chironomids were used to quantitatively reconstruct bottom water oxygen conditions before and after the pipe installation (in 2015). The diatom and cladoceran communities, which reflect more the open-water habitat, showed only relatively minor changes throughout the lake, but a general decrease in diversity was observed within both groups. Chironomids, which live on substrates, showed more significant changes, including complete faunal turnovers and deteriorated benthic quality, especially at the sites close to the pipe outlet, where also chironomid diversity was almost completely lost. Furthermore, the reconstructed hypolimnetic oxygen values indicated a major oxygen decline and even anoxia at the sites near the pipe outlet. The limnoecological influence of the pipe decreased at sites located counter-flow or behind underwater barriers suggesting that the waste waters currently have location-specific impacts. Our study clearly demonstrates that whereas the upper water layers appear to have generally maintained their previous state, the deep-water layers close to the pipe outlet have lost their ecological integrity. Furthermore, the current hypolimnetic anoxia close to the pipe indicates enhanced lake stratification caused by the salinated mine waters. This study clearly exhibits the need to investigate different water bodies at several trophic levels in a spatiotemporal context to be able to reliably assess limnoecological impacts of mining.