| 1. |
- Kylander, Malin E., et al.
(författare)
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New insights from XRF core scanning data into boreal lake ontogeny during the Eemian (Marine Isotope Stage 5e) at Sokli, northeast Finland
- 2018
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Ingår i: Quaternary Research. - : Cambridge University Press (CUP). - 0033-5894 .- 1096-0287. ; 89:1, s. 352-364
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Tidskriftsartikel (refereegranskat)abstract
- Biological proxies from the Sokli Eemian (Marine Isotope Stage 5e) paleolake sequence from northeast Finland have previously shown that, unlike many postglacial records from boreal sites, the lake becomes increasingly eutrophic over time. Here, principal components (PC) were extracted from a high resolution multi-element XRF core scanning dataset to describe minerogenic input from the wider catchment (PC1), the input of S, Fe, Mn, and Ca-rich detrital material from the surrounding Sokli Carbonatite Massif (PC2), and chemical weathering (PC3). Minerogenic inputs to the lake were elevated early in the record and during two abrupt cooling events when soils and vegetation in the catchment were poor. Chemical weathering in the catchment generally increased over time, coinciding with higher air temperatures, catchment productivity, and the presence of acidic conifer species. Abiotic edaphic processes play a key role in lake ontogeny at this site stemming from the base cation- and nutrient-rich bedrock, which supports lake alkalinity and productivity. The climate history at this site, and its integrated effects on the lake system, appear to override development processes and alters its long-term trajectory.
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| 2. |
- Plikk, Anna, 1982-, et al.
(författare)
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Chironomid-based temperature reconstruction for the Eemian Interglacial (MIS 5e) at Sokli, northeast Finland
- 2019
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Ingår i: Journal of Paleolimnology. - : Springer Science and Business Media LLC. - 0921-2728 .- 1573-0417. ; 61:3, s. 355-371
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Tidskriftsartikel (refereegranskat)abstract
- The Last Interglacial (Eemian, MIS 5e) can be considered a test-bed for climate dynamics under a warmer-than-present climate. In this study we present a chironomid record from the high latitude Sokli site (N Finland), where a long continuous sediment sequence from the Last Interglacial has been preserved from glacial erosion. The chironomid-analysis shows a diverse fauna, with dominance of warm-water indicators and shifts in assemblage composition that can be attributed to temperature, lake depth, productivity and habitat availability. Quantitative mean July paleotemperature estimates based on the chironomid data indicate overall mean July temperatures up to 1°C warmer than present. Two cooling events can be discerned, the Tunturi event, dated to about 127 ka BP, in the lower part of the sequence, and the Värriö event, dated to about 119 ka BP, associated with the beginning of a cooling trend in the upper part of the record. Warm conditions already at the onset of the interglacial contrast with a recent chironomid-based Last Interglacial temperature reconstruction from Denmark which suggests a late onset of Eemian warming. The relatively small increase in inferred temperatures compared to present day temperatures differs from other high latitude Eemian sites, and likely reflects the influence of the Atlantic Meridional Overturning Circulation in maintaining already elevated temperatures in Fennoscandia during interglacials.
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| 3. |
- Plikk, Anna, 1982-, et al.
(författare)
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Diatom assemblages from an Eemian palaeolake in northern Europe with morphological observations of rare Aulacoseira sp. resting spores
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- An overview of the diatom flora of the last interglacial (Eemian) lacustrine gyttja deposit at Sokli, northeastern Finland is presented together with detailed descriptions including photomicrographs of resting spores similar to the Aulacoseira islandica-skvortzowii group, not found in recent material from Europe. Comparisons are made with literature data on similar taxa. The morphology of the resting spores (e.g. the number of striae and areolae in 10 µm) attributes them to the A. islandica-skvortzowii group but the lack of vegetative cells in the Sokli record makes declaration of true synonymy difficult. The presence of spores similar/related to the A. islandica-skvortzowii group in the Sokli Eemian palaeolake may reflect a more widespread distribution of this group in the past.
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| 4. |
- Plikk, Anna, 1982-, et al.
(författare)
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Diatom assemblages from an Eemian palaeolake in Northern Europe with morphological observations of rare Aulacoseira sp. resting spores
- 2021
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Ingår i: Diatom Research. - 0269-249X .- 2159-8347. ; 36:4, s. 313-321
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Tidskriftsartikel (refereegranskat)abstract
- An overview of the diatom flora of the last interglacial (Eemian) lacustrine gyttja deposit at Sokli, northeastern Finland is presented together with descriptions including photomicrographs of resting spores similar to the Aulacoseira islandica-skvortzowii group, not found in recent material from Europe. Comparisons are made with literature data on similar taxa. The morphology of the resting spores (e.g., the number of striae and areolae in 10 mu m) links them to the A. islandica-skvortzowii group, but the lack of vegetative cells in the Sokli record makes the determination of true synonymy difficult. The presence of spores similar/related to the A. islandica-skvortzowii group in the Sokli Eemian palaeolake may reflect a more widespread distribution of this group in the past.
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| 5. |
- Plikk, Anna, 1982-
(författare)
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The Eemian Interglacial at Sokli, northern Finland : A multi-proxy environmental and climatic reconstruction based on a 9 m long lacustrine sediment sequence
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Understanding the fundamentals of the Earth’s climate system during the Quaternary Period (the past ca 2.6 million years) is of imminent interest in light of the reported recent climatic changes. The Eemian Interglacial (ca 129,000-116,000 years ago) is the last period before the present interglacial (the Holocene, the last ca 11,700 years) when temperatures were as warm as or warmer than today and may serve as an analogue to future climatic warming. The Eemian is a relatively well-studied period, but many aspects of the interglacial climatic dynamics still remain unresolved. One reason for this is the chronological uncertainties of many records from this time period; another is the relatively uneven distribution of palaeoarchives. Especially from high latitude areas, terrestrial records from the Eemian are few due to the impact of glacial erosion during the Weichselian Glacial (ca 116,000-11,700 years ago).This thesis is based on data from Sokli, N Finland, where cold-based conditions of the Weichselian ice sheets and non-typical bedrock conditions have allowed preservation of an unusually thick Eemian lacustrine deposit in stratigraphic sequence with overlying Weichselian and Holocene deposits. The main purpose of this thesis is to contribute to the knowledge of climate variability in Fennoscandia and the North Atlantic region during the Eemian, and it involves a qualitative multi-proxy reconstruction of the Eemian lake and its development as well as a quantitative reconstruction of the regional Eemian July temperature evolution using subfossil chironomids. Attention is paid also to the identification and characterization of short-term climatic events in the Sokli record.The main contribution of this study is to increase the spatial coverage of Eemian palaeoclimatological data. Specific results include the description of the lake development, identifying phases where non-climatic variables likely affect the quantitative chironomid-based temperature reconstruction, as well as qualitative and quantitative reconstructions of climatic features such as changes in seasonality and temperature. Five major lake phases are distinguished. A glaciolacustrine phase is followed by an early Eemian lake phase characterized by short mixing periods and rising nutrient levels. The following early mid-Eemian lake phase is characterized by a prolonged open water season and high productivity and possibly corresponds to the Eemian climatic optimum. The late mid-Eemian lake phase is characterized by infilling and eutrophic conditions while the late Eemian lake phase reflects shallow, dynamic and cooling conditions.The qualitative study suggests a shift from a higher seasonality in the early Eemian towards more oceanic conditions during the mid-Eemian, while chironomid-inferred July temperatures indicate that near present-day temperatures prevailed at Sokli already from the beginning of the interglacial and that optimum temperatures were only moderately (ca + 1°C) higher than at present. These results suggest that the climatic development at Sokli followed that of central Europe during the Eemian. Two events characterized by colder and more arid conditions are identified, and can be tentatively correlated to meltwater events registered in marine records from the Nordic seas and subpolar north Atlantic, possibly reflecting the effect that meltwater pulses and related disruptions in the thermohaline circulation had on adjacent continental areas.
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