| 1. |
- Ampel, Linda, 1979-, et al.
(författare)
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Diatom assemblage dynamics during abrupt climate change : The response oflacustrine diatoms to Dansgaard-Oeschger cycles during the last glacialperiod
- 2010
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Ingår i: Journal of Paleolimnology. - : Springer Science and Business Media LLC. - 0921-2728 .- 1573-0417. ; 44:2, s. 397-404
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Tidskriftsartikel (refereegranskat)abstract
- The sedimentary record from the paleolake at Les Echets in eastern France allowed a reconstruction of the lacustrine response to several abrupt climate shifts during the last glacial period referred to as Dansgaard-Oeschger (DO) cycles. The high-resolution diatom stratigraphy has revealed distinct species turnover events and large fluctuations in stable oxygen isotope values in diatom frustules, as a response to DO climate variability. More or less identical species compositions became re-established during each DO stadial and interstadial phases, respectively. However, the relative abundance of the most dominant species within these assemblages varies and might indicate differences in climatic conditions. Interstadial phases are characterized by identical species successions. Transitions from stadial to interstadial conditions show a distinct Fragilaria-Cyclotella succession, which resembles the diatom regime shifts that have been recognized in some lakes in the Northern Hemisphere since the mid-nineteenth century.
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| 2. |
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| 3. |
- Augustsson, Anna, et al.
(författare)
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Trace metal and geochemical variability during 5,500 years in the sediment of Lake Lehmilampi, Finland
- 2010
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Ingår i: Journal of Paleolimnology. - : Springer Science and Business Media LLC. - 0921-2728 .- 1573-0417. ; 44:4, s. 1025-1038
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Tidskriftsartikel (refereegranskat)abstract
- A high-resolution geochemical profilefrom a 5,500-year-old sediment core of Lake Lehmilampiin eastern Finland was analyzed to study longtermtrends and variability in element concentrationsand accumulation rates. The accumulation rates of allstudied elements followed the same trend, respondingto changes in the total sedimentation rate. Concentrationprofiles differed among elements and showedconsiderable variation over time. Principal componentsanalysis (PCA) was used on the concentrationdata to identify groups of elements that have similargeochemical controls. The first principal componentwas influenced by changes in mineral matter accumulation,and it incorporated elements that areassociated with stable allochthonous minerals (suchas Mg, K, Cs, Rb, Li, Ti and Ga), as well as elementsin forms that become diluted when mineral matterincreases (e.g., S, Fe and Mn). The second and thirdprincipal components showed that a large proportionof the variance was accounted for by elements withcontinuously increasing or decreasing concentrationsrelated to pedogenetical development of the catchmentsoil. In the case of Hg, Pb and Cd, however,accumulation rates increased faster at the surface thanis simply accounted for by changes in total sedimentationrates. For Cu, Cr, Ni and Zn, concentrationsincreased over the past 150 years, but there were noindications of a significant addition due to atmosphericdeposition. These elements had more variableconcentrations before the mid nineteenth century thanafter, as did elements that are often used fornormalization. These findings suggest that lakesediments may not properly reflect the history of atmospheric metal deposition in remote areas.
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| 4. |
- Belle, Simon
(författare)
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Holocene shifts in the primary producer community of large, shallow European Lake Peipsi, inferred from sediment pigment analysis
- 2019
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Ingår i: Journal of Paleolimnology. - : Springer Science and Business Media LLC. - 0921-2728 .- 1573-0417. ; 61, s. 403-417
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Tidskriftsartikel (refereegranskat)abstract
- We used HPLC to identify and quantify pigments in a Holocene sediment record from large, shallow Lake Peipsi, Estonia. The aim of our study was to track the influence of long-term climate change (i.e. temperature fluctuations) on past dynamics of aquatic primary producers. Sedimentary pigments were separated and quantified in 182 samples that span the last ca. 10,000 years. There was an increasing trend in sedimentary pigment concentrations from basal to upper sediment layers, suggesting a gradual increase in lake trophic status through time. Using additive models, our results suggested that primary producer dynamics in Lake Peipsi were closely related to temperature fluctuations. We, however, identified two periods (early Holocene and after ca. 2.5 cal ka BP) when the relationship between primary producer composition and temperature was weak, suggesting the influence of additional drivers on the primary producer community. We postulate that: (a) the increase of primary producer biomass in the early Holocene could have been caused by input of allochthonous organic matter and nutrients from the flooded areas when water level in Lake Peipsi was increasing, and (b) changes in the abundance and structure of primary producer assemblages since ca. 2.5 cal ka BP was related to widespread agricultural activities in the Lake Peipsi catchment. These results suggest that human activities can disrupt the relationship between the primary producer community and temperature in large, shallow lakes.
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| 5. |
- Belle, Simon, et al.
(författare)
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Use of sedimentary algal pigment analyses to infer past lake-water total phosphorus concentrations
- 2022
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Ingår i: Journal of Paleolimnology. - : Springer Science and Business Media LLC. - 0921-2728 .- 1573-0417. ; 68, s. 415-426
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Tidskriftsartikel (refereegranskat)abstract
- We tested the feasibility of using sedimentary algal pigment analyses by spectral deconvolution to infer past lake-water total phosphorus concentrations. We established equations that link lake-water nutrient concentrations and sediment pigment concentrations, using a combination of calibration in both space and time, with a training set of 31 Swedish lakes. The calibration dataset yielded a significant positive relationship between total carotenoid concentrations and lake-water total phosphorus concentrations. We also compared sediment-pigment-based nutrient inferences with time series of water column monitoring data to evaluate whether temporal changes in total phosphorus concentrations are well captured by analysis of sedimentary pigments. We found that changes in pigment preservation through time can alter the relationship between concentrations of lake-water nutrients and sedimentary pigments, thus limiting the reliability of historical ecological conditions inferred from pigments in the sediment. Our data suggested that ratios of Chlorophyll derivatives to total carotenoids (CD/TC ratio) and Chlorophyll a to Chlorophyll derivatives (CPI) can be used as proxies for pigment preservation. Using our approach, inferred temporal changes in water-column total phosphorus concentrations in lakes are promising, but require further development, specifically with respect to the influence of pigment degradation in both the water column and sediments, as well as the factors that control such degradation.
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| 6. |
- Bengtsson, Lars, et al.
(författare)
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Using rainfall-runoff modeling to interpret lake level data
- 1997
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Ingår i: Journal of Paleolimnology. - 0921-2728. ; 18:3, s. 235-248
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Tidskriftsartikel (refereegranskat)abstract
- Using water balance computations, the behavior of different kinds of lakes is discussed. Simple analytical expressions relating water level to hydrological conditions and lake bathymetry are given. The importance of knowing the river basin area when analyzing lake levels is stressed. A conceptual rainfall-runoff model including lake routing is used to simulate runoff and lake levels and to compute quasi-steady state conditions and long-term transient situations. It is suggested that models can be used to construct curves relating lake levels to precipitation and lake evaporation. By comparing with paleo-lake levels, the annual precipitation related to these levels can be found, provided information is available about the seasonal distribution of the precipitation.
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| 7. |
- Berggren, Ann-Marie, 1969-, et al.
(författare)
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10Be and solar activity cycles in varved lake sediments, AD 1900–2006
- 2010
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Ingår i: Journal of Paleolimnology. - : Springer Science and Business Media LLC. - 0921-2728 .- 1573-0417. ; 44:2, s. 559-569
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Tidskriftsartikel (refereegranskat)abstract
- Annually resolved terrestrial 10Be archives other than those in polar ice sheets are heretofore unexplored sources of information about past solar activity and climate. Until now, it has proven difficult to find natural archives that have captured and retained a 10Be production signal, and that allow for annual sampling and contain sufficient 10Be for AMS measurement. We report the first annually resolved record of 10Be in varved lake sediments. The record comes from Lake Lehmilampi, eastern Finland, which lies at 63°37′N, 29°06′E, 95.8 m a. s. l. The focus on the last 100 years provided an unprecedented opportunity to compare sediment 10Be data with annual ice core, neutron monitor and sunspot number data. Results indicate successful recovery of 10Be atoms from as little as 20 mg sediment. Sediment 10Be accumulation rates suggest control by solar activity, manifested as a reflection of the 11-year Schwabe solar cycle and its amplitude variations throughout the investigated period. These results open the possibility of using varved lake sediment 10Be records as a new proxy for solar activity, thus providing a new approach for synchronization of paleoclimate events worldwide.
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| 8. |
- Bigler, Christian, et al.
(författare)
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Diatoms as indicators of climatic and limnological change in Swedish Lapland: A 100-lake calibration set and its validation for paleoecological reconstructions
- 2002
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Ingår i: Journal of Paleolimnology. - 0921-2728 .- 1573-0417. ; 27:1, s. 97-115
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Tidskriftsartikel (refereegranskat)abstract
- This study investigated the distribution of subfossil diatom assemblages in surficial sediments of 100 lakes along steep ecological and climatic gradients in northernmost Sweden (Abisko region, 67.07degrees N to 68.48degrees N latitude, 17.67degrees E to 23.52degrees E longitude) to develop and cross-validate transfer functions for paleoenvironmental reconstruction. Of 19 environmental variables determined for each site, 15 were included in the statistical analysis. Lake-water pH (8.0%), sedimentary loss-on-ignition (LOI, 5.9%) and estimated mean July air temperature (July T, 4.8%) explained the greatest amounts of variation in the distribution of diatom taxa among the 100 lakes. Temperature and pH optima and tolerances were calculated for abundant taxa. Transfer functions, based on WA-PLS (weighted averaging partial least squares), were developed for pH (r(2) = 0.77, root-mean-square-error of prediction (RMSEP) = 0.19 pH units, maximum bias = 0.31, as assessed by leave-one-out cross-validation) based on 99 lakes and for July T (r(2) = 0.75, RMSEP = 0.96 degreesC, max. bias = 1.37 degreesC) based on the full 100 lake set. We subsequently assessed the ability of the diatom transfer functions to estimate lake-water pH and July T using a form of independent cross-validation. To do this, the 100-lake set was divided in two subsets. An 85-lake training-set (based on single limnological measurements) was used to develop transfer functions with similar performance as those based on the full 100 lakes, and a 15-lake test-set (with 2 years of monthly limnological measurements throughout the ice-free seasons) was used to test the transfer functions developed from the 85-lake training-set. Results from the intra-set cross-validation exercise demonstrated that lake-specific prediction errors (RMSEP) for the 15-lake test-set corresponded closely with the median measured values (pH) and the estimations based on spatial interpolations of data from weather stations (July T). The prediction errors associated with diatom inferences were usually within the range of seasonal and interannual variability. Overall, our results confirm that diatoms can provide reliable and robust estimates of lake-water pH and July T, that WA-PLS is a robust calibration method and that long-term environmental data are needed for further improvement of paleolimnological transfer functions.
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| 9. |
- Bigler, Christian, et al.
(författare)
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Holocene environmental change at Lake Njulla (999 m asl), northern Sweden : a comparison with four small nearby lakes along an altitudinal gradient
- 2003
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Ingår i: Journal of Paleolimnology. - 0921-2728 .- 1573-0417. ; 29:1, s. 13-29
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 10. |
- Bindler, Richard, et al.
(författare)
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Bridging the gap between ancient metal pollution and contemporary biogeochemistry
- 2008
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Ingår i: Journal of Paleolimnology. - : Springer. - 0921-2728 .- 1573-0417. ; 40:3, s. 755-770
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Tidskriftsartikel (refereegranskat)abstract
- Paleolimnology provides long-term data that are often essential for understanding the current state of the environment. Even though there is great potential, paleolimnology is rarely used together with process-related studies to solve issues regarding cycling of elements in the environment. Clearly, this is a drawback because the cycling of many elements, which cause great concern in the present-day environment, was altered long before the advent of monitoring programs. The pioneering work of C.C. Patterson and his colleagues emphasized the importance of a long-term perspective for understanding the current cycling of metals, with a focus on lead, and in particular for estimating background concentrations and human-related impacts in the environment. In Sweden the first traces of atmospheric lead pollution are found in lake sediments dated to about 3500 years ago. The long-term changes in the pollution lead record in lake sediments led us to consider how lead biogeochemistry has changed over time in response to this historical deposition‹where has this lead gone, and how much does this lead contribute to the present-day biogeochemical cycling of lead? How was lead distributed in Œpre-industrial¹ soils or more properly in natural soils not impacted by atmospheric pollution? There are many studies that have examined the effects of increased metal concentrations on soil biota, but what are the appropriate background conditions for comparison? Using lake sediments as our foundation we have analyzed lead, including its stable isotopes, in other environmental compartments, including peat, soil, and a range of boreal forest plant species, to develop a better understanding of the fate of lead derived from long-term pollution. Three important conclusions from our studies in Sweden are: (1) atmospheric lead deposition rates during the 20th century were 100 to as much as 1000 times higher than natural deposition rates a few thousand years ago. Even with stricter emission standards during the past three decades and the resultant reductions in deposition, lead deposition rates today are still 10100 times greater than natural rates. This increase in deposition rates modeled from sediment and peat records is of a similar scale to estimated changes in body burdens of lead in modern versus ancient humans. (2) In Europe about half of the cumulative burden of atmospherically deposited lead was deposited before industrialization. In southern Sweden the cumulative burden of pollution lead during the past 3500 years is 25 g Pb m-2 and in the Œpristine¹ northern parts of the country there is about 1 g Pb m-2. (3) Predicted recovery rates for soils are slow; in the cold climate of Scandinavia, we find that the soil surface (O horizon), where most soil biota reside, retains lead deposited over the past 150500 years. Therefore, although lead deposition rates in Europe, as well as N. America, are only 10% of those a few decades ago, it will take several decades or longer for lead concentrations in soils to respond appreciably. The slow turnover rates for lead in the environment and gradual immobilization of lead in deeper soil mineral horizons also inhibits a loss of lead to surface waters in areas removed from point sources.
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