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  • 1.
    Bigler, Christian
    et al.
    Umeå universitet, Ekologi och geovetenskap.
    Grahn, E.
    Larocque, I.
    Jeziorski, A.
    Hall, Roland
    Umeå universitet, Ekologi och geovetenskap.
    Holocene environmental change at Lake Njulla (999 m asl), northern Sweden: a comparison with four small nearby lakes along an altitudinal gradient2003In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 29, no 1, p. 13-29Article in journal (Refereed)
    Abstract [en]

    We assess Holocene environmental change at alpine Lake Njulla (68degrees22'N, 18degrees42'E, 999 m a.s.l.) in northernmost Sweden using sedimentary remains of chironomid head capsules and diatoms. We apply regional calibration sets to quantitatively reconstruct mean July air temperature (using chironomids and diatoms) and lake-water pH (using diatoms). Both chironomids and diatoms infer highest temperatures (1.7-2.3degreesC above present-day estimates, including, a correction for glacio-isostatic land up-lift by 0.6degreesC) during the early Holocene (c. 9,500-8,500 cal. yrs BP). Diatoms suggest a decreasing lake-water pH trend (c. 0.6 pH units) since the early Holocene. Using detrended canonical correspondence analysis (DCCA), we compare the Holocene development of diatom communities in Lake Njulla with four other nearby lakes (Lake 850, Lake Tibetanus, Vuoskkujavri, Vuolep Njakajaure) located along an altitudinal gradient. All five lakes show similar initial DCCA scores after deglaciation, suggesting that similar environmental processes such as high erosion rates and low light availability associated with high summer temperature appear to have regulated the diatom community, favouring high abundances of Fragilaria species. Subsequently, the diatom assemblages develop in a directional manner, but timing and scale of development differ substantially between lakes. This is attributed primarily to differences in the local geology, which is controlling the lake-water pH. Imposed on the basic geological setting, site-specific processes such as vegetation development, climate, hydrological setting and in-lake processes appear to control lake development in northern Sweden.

  • 2. Cunningham, Laura
    et al.
    Bishop, Kevin
    Mettävainio, Eva
    Rosén, Peter
    Paleoecological evidence of major declines in total organic carbon concentrations since the nineteenth century in four nemoboreal lakes2011In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 45, no 4, p. 507-518Article in journal (Refereed)
    Abstract [en]

    A decade of widespread increases in surface water concentrations of total organic carbon (TOC) in some regions has raised questions about longer term patterns in this important constituent of water chemistry. This study uses near-infrared spectroscopy (NIRS) to infer lake water TOC far beyond the decade or two of observational data generally available. An expanded calibration dataset of 140 lakes across Sweden covering a TOC gradient from 0.7 to 24.7 mg L−1 was used to establish a relationship between the NIRS signal from surface sediments (0–0.5 cm) and the TOC concentration of the water mass. Internal cross-validation of the model resulted in an R 2 of 0.72 with a root mean squared error of calibration (RMSECV) of 2.6 mg L−1. The TOC concentrations reconstructed from surface sediments in four Swedish lakes were typically within the range of concentrations observed in the monitoring data during the period represented by each sediment layer. TOC reconstructions from the full sediment cores of four lakes indicated that TOC concentrations were approximately twice as high a century ago.

  • 3.
    Fernandez, Marilen
    et al.
    CADIC CONICET, Lab Geomorfol & Cuaternario, RA-9410 Ushuaia, Tierra Del Fueg, Argentina..
    Björck, Svante
    Lund Univ, Dept Geol, S-22362 Lund, Sweden..
    Wohlfarth, Barbara
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Maidana, Nora I.
    Univ Buenos Aires, CONICET, Fac Ciencias Exactas & Nat, Dept Biodiversidad & Biol Expt,Lab Diatomeas Cont, Buenos Aires, DF, Argentina..
    Unkel, Ingmar
    Univ Kiel, Inst Ecosyst Res, D-24118 Kiel, Germany..
    Van der Putten, Nathalie
    Lund Univ, Dept Geol, S-22362 Lund, Sweden..
    Diatom assemblage changes in lacustrine sediments from Isla de los Estados, southernmost South America, in response to shifts in the southwesterly wind belt during the last deglaciation2013In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 50, no 4, p. 433-446Article in journal (Refereed)
    Abstract [en]

    Isla de los Estados (54A degrees 45'S, 63A degrees 10'aEuro"64A degrees 46'W) lies east of the main island of Tierra del Fuego and is the southeastern-most point in Argentina. Because of its geographic position near the latitudes of the Southern Hemisphere Westerlies and the strong influence of the Antarctic Circumpolar Current (ACC), the area is suitable for paleoecological and paleoclimate research. The island is not far north of the Subantarctic Front, which limits the northern boundary of the ACC. Paleoenvironmental study in this geographic location can shed light on past changes in atmospheric and marine circulation patterns. Diatom analysis of the lower part of a sediment sequence from Laguna Cascada (54A degrees 45' 51.3''S, 64A degrees 20' 20.07''W) enabled inference of changing lake conditions between 16 and 11.1 cal ka BP. Between 16 and 14.4 cal ka BP fragilarioid diatom species, often a pioneer group, dominated the record. Their presence shows seasonally open-water conditions from the onset of sedimentation. In zone II (14.4-12.8 cal ka BP), the dominance of planktonic/tychoplanktonic Aulacoseira spp. might represent longer ice-free periods and windier conditions, which would have kept this heavy species suspended in the water column. This period corresponds to the Antarctic Cold Reversal, when the Southern Hemisphere Westerlies were possibly centered on the latitudes of Tierra del Fuego, resulting in windy and wet conditions. Zone III (12.8-11.1 cal ka BP) is dominated by benthic diatom taxa that are mainly associated with peat and wetland vegetation. This suggests that climate conditions had become milder and less windy, favoring aquatic productivity and terrestrial vegetation development. This change in environmental conditions may have been a consequence of the southward movement of the Southern Hemisphere Westerlies at the start of the Antarctic Holocene thermal optimum.

  • 4. Kokfelt, Ulla
    et al.
    Reuss, Nina
    Struyf, Eric
    Sonesson, Mats
    Rundgren, Mats
    Skog, Göran
    Rosén, Peter
    Hammarlund, Dan
    Wetland development, permafrost history and nutrient cycling inferred from late Holocene peat and lake sediment records in subarctic Sweden2010In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 44, no 1, p. 327-342Article in journal (Refereed)
    Abstract [en]

    Permafrost in peatlands of subarctic Sweden is presently thawing at accelerated rates, which raises questions about the destiny of stored carbon and nutrients and impacts on adjacent freshwater ecosystems. In this study we use peat and lake sediment records from the Stordalen palsa mire in northern Sweden to address the late Holocene (5,000 cal BP-present) development of the mire as well as related changes in carbon and nutrient cycling. Formation, sediment accumulation and biogeochemistry of two studied lakes are suggested to be largely controlled by the development of the mire and its permafrost dynamics. Peat inception took place at ca. 4,700 cal BP as a result of terrestrialisation. Onset of organic sedimentation in the adjacent lakes occurred at ca. 3,400 and 2,650 cal BP in response to mire expansion and permafrost aggradation, respectively. Mire erosion, possibly due to permafrost decay, led to re-deposition of peat into one of the lakes after ca. 2,100 cal BP, and stimulated primary productivity in the other lake at ca. 1,900–1,800 cal BP. Carbonate precipitation appears to have been suppressed when acidic poor fen and bog (palsa) communities dominated the catchment mire, and permafrost-induced changes in hydrology may further have affected the inflow of alkaline water from the catchment. Elevated contents of biogenic silica and diatom pigments in lake sediments during periods of poor fen and bog expansion further indicate that terrestrial vegetation influenced the amount of nutrients entering the lake. Increased productivity in the lake likely caused bottom-water anoxia in the downstream lake and led to recycling of sediment phosphorous, bringing the lake into a state of self-sustained eutrophication during two centuries preceding the onset of twentieth century permafrost thaw. Our results give insight into nutrient and permafrost dynamics in a subarctic wetland and imply that continued permafrost decay and related vegetation changes towards minerotrophy may increase carbon and nutrient storage of mire deposits and reduce nutrient fluxes in runoff. Rapid permafrost degradation may on the other hand lead to widespread mire erosion and to relatively short periods of significantly increased nutrient loading in adjacent lakes.

  • 5. Larocque, I.
    et al.
    Hall, R. I.
    Grahn, E.
    Chironomids as indicators of climate change: a 100‐lake training set from a subarctic region of northern Sweden (Lapland)2001In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 26, no 3, p. 307-322Article in journal (Refereed)
    Abstract [en]

    Multivariate numerical analyses (DCA, CCA) were used to study the distribution of chironomids from surface sediments of 100 lakes spanning broad eco‐climatic conditions in northern Swedish Lapland. The study sites range from boreal forest to alpine tundra and are located in a region of relatively low human impact. Of the 19 environmental variables measured, ordination by CCA identified mean July air temperature as one of the most significant variables explaining the distribution and the abundance of chironomids. Loss‐on‐ignition (LOI), maximum lake depth and mean January air temperature also accounted for significant variation in chironomid assemblages. A quantitative transfer function was created to estimate mean July air temperature from sedimentary chironomid assemblages using weighted‐averaging partial least squares regression (WA‐PLS). The coefficient of determination was relatively high (r2 = 0.65) with root mean squared error of prediction (RMSEP, based on jack-knifing) of 1.13 °C and maximum bias of 2.1 °C, indicating that chironomids can provide useful quantitative estimates of past changes in mean July air temperature. The paper focuses mainly on the relationship between chironomid composition and July air temperature, but the relationship to LOI and depth are also discussed.

  • 6. Reuss, Nina
    et al.
    Leavitt, Peter R.
    Hall, Roland I.
    Bigler, Christian
    Hammarlund, Dan
    Development and application of sedimentary pigments for assessing effects of climatic and environmental changes on subarctic lakes in northern Sweden2010In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 43, no 1, p. 149-169Article in journal (Refereed)
    Abstract [en]

    A surface-sediment survey of pigments in 100 lakes in the Scandes Mountains, northern Sweden, was combined with a reconstruction of Holocene sedimentary pigments from Lake Seukokjaure to assess the major factors regulating phototrophic communities, and how these controls may have changed during the period from the deglaciation (~9700 cal. years BP) to the present. The study area covers a pronounced gradient of temperature and precipitation, and encompasses the subarctic tree line, an important ecotonal boundary in this region. Lake Seukokjaure is located in a presently treeless basin close to the modern tree line. The spatial survey of sedimentary pigments was analyzed using principle components analysis (PCA) and redundancy analysis (RDA). PCA explained 73–83% of variance in pigment abundance and composition, whereas RDA explained 22–32% of variation in fossil assemblages. Dissolved organic carbon (DOC) content of lake water, sediment δ13C, maximum lake depth, elevation and lake-water conductivity were all identified as environmental variables with significant association with pigment abundances in the spatial survey, although phototrophic communities of lakes situated in different vegetation zones (alpine, birch, conifer/birch) were incompletely distinguished by the ordinations. In the RDAs, the primary pigment variability occurred along a production gradient that was correlated negatively to water-column DOC content and δ13C signature of sediments. This pattern suggested that the important controls of primary production were light regime and terrestrial supplies of 13C-depleted carbon. In contrast, depth, elevation and conductivity were found to be more important for the differentiation of the phototrophic community composition. Application of these spatial survey results to the Holocene sediment record of Lake Seukokjaure demonstrated the importance of DOC for the temporal development of the lake, from an early state of high production to a period of slight oligotrophication. In general, the algal changes were regulated by the interaction of DOC and conductivity, although transitions in the phototrophic community during the late Holocene were less easily interpreted. Terrestrial vegetation development thus appears to be of utmost importance for the regulation of primary production in oligotrophic alpine and subarctic lakes and climate impacts on lakes, whereas other basin-specific factors may control the ontogeny of algal community composition.

  • 7. Rosén, Peter
    et al.
    Vogel, Hendrik
    Cunningham, Laura
    Reuss, Nina
    Conley, Daniel J.
    Persson, Per
    Fourier transform infrared spectroscopy, a new method for rapid determination of total organic and inorganic carbon and biogenic silica concentration in lake sediments2010In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 43, no 2, p. 247-259Article in journal (Refereed)
    Abstract [en]

    We demonstrate the use of Fourier transform infrared spectroscopy (FTIRS) to make quantitative measures of total organic carbon (TOC), total inorganic carbon (TIC) and biogenic silica (BSi) concentrations in sediment. FTIRS is a fast and cost-effective technique and only small sediment samples are needed (0.01 g). Statistically significant models were developed using sediment samples from northern Sweden and were applied to sediment records from Sweden, northeast Siberia and Macedonia. The correlation between FTIRS-inferred values and amounts of biogeochemical constituents assessed conventionally varied between r = 0.84–0.99 for TOC, r = 0.85–0.99 for TIC, and r = 0.68–0.94 for BSi. Because FTIR spectra contain information on a large number of both inorganic and organic components, there is great potential for FTIRS to become an important tool in paleolimnology.

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