| 1. |
- 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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| 2. |
- 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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| 3. |
- Berggren, Ann-Marie, et al.
(författare)
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Linking ice sheet and lake sediment archives of Be-10, 1468-1980 CE
- 2013
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Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier BV. - 0168-583X .- 1872-9584. ; 294, s. 524-529
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Tidskriftsartikel (refereegranskat)abstract
- As part of understanding and reconstructing our climate history it is important to investigate the link between climate and solar activity. Ice cores and ocean sediments have provided information on a range of timescales on atmospheric Be-10 production, which is a proxy for past solar activity due to its cosmogenic nature of production. We here present results from the first, to our knowledge, multi-centennial and annual resolution study of Be-10 in varved lake sediments. Varves were sampled over an interval covering the period 1468-2006 CE in sediment cored from Lake Lehmilampi in eastern Finland. The measured concentrations were converted into annual Be-10 deposition rates by using the weights of dried samples as an estimation of sedimentation rates and scaling the result from sampling to catchment area size. We compare the lake catchment Be-10 deposition rates to those derived from the Greenlandic ice cores NGRIP and Dye-3 along with past solar activity. Sediment Be-10 concentrations range 2.1-17.6 x 10(8) atoms g(-1). The high end of this range is represented by a limited number of samples, and the average is near the lower end at 4.1 x 10(8) atoms g(-1). The deposition rates range 0.5-3.9 x 10(6) atoms cm(-2) year(-1), with an average of 1.8 x 10(6) atoms cm(-2) year (0.057 atoms cm(-2) s(-1)). We note higher Be-10 deposition during the Sporer (similar to 1415-1535 CE) and Maunder (similar to 1645-1715 CE) solar minima, and also at the onset of the Dalton (similar to 1790-1830 CE) minimum. Equally high Be-10 values in the 1840s and lower deposition during the Dalton minimum are not consistent with contemporaneous solar activity. Although this may in part be a result of incomplete measurements in the 19th century, it also shows the complexity of deposition and the intricacy of reconstructing past solar activity from sediment Be-10 data. A comparison with ice core data reveals particularly good agreement between sediment and Dye-3 Be-10 flux around 1500-1750 CE.
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| 4. |
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| 5. |
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| 6. |
- Englund, Edvard, et al.
(författare)
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Modeling fallout of anthropogenic I-129
- 2008
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 42:24, s. 9225-9230
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Tidskriftsartikel (refereegranskat)abstract
- Despite the relatively well-recognized emission rates of the anthropogenic 128I, there is little knowledge about the temporal fallout patterns and magnitude of fluxes since the start of the atomic era at the early 1940s.We here present measurements of annual 129I concentrations in sediment archives from Sweden and Finland covering the period 1942-2006. The results revealed impression of 129I emissions from the nuclear reprocessing facility at Sellafield and La Hague and a clear Chernobyl fallout enhancement during 1986. In order to estimate relative contributions from the different sources, a numerical model approach was used taking into accountthe emission rates/ estimated fallout, transport pathways, and the sediment system. The model outcomes suggest a relatively dominating marine source of 129I to north Europe compared to direct gaseous releases. A transfer rate of 129I from sea to atmosphere is derived for pertinent sea areas (English Channel, Irish Sea, and North Sea), which is estimated at 0.04 to 0.21 y-1.
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| 7. |
- Melles, Martin, et al.
(författare)
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2.8 million years of arctic climate change from Lake El'gygytgyn, NE Russia
- 2012
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 337:6092, s. 315-320
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Tidskriftsartikel (refereegranskat)abstract
- The reliability of Arctic climate predictions is currently hampered by insufficient knowledge of natural climate variability in the past. A sediment core from Lake El'gygytgyn in northeastern (NE) Russia provides a continuous, high-resolution record from the Arctic, spanning the past 2.8 million years. This core reveals numerous "super interglacials" during the Quaternary; for marine benthic isotope stages (MIS) 11c and 31, maximum summer temperatures and annual precipitation values are similar to 4 degrees to 5 degrees C and similar to 300 millimeters higher than those of MIS 1 and 5e. Climate simulations show that these extreme warm conditions are difficult to explain with greenhouse gas and astronomical forcing alone, implying the importance of amplifying feedbacks and far field influences. The timing of Arctic warming relative to West Antarctic Ice Sheet retreats implies strong interhemispheric climate connectivity.
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| 8. |
- Mellström, Anette, et al.
(författare)
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Radiocarbon wiggle-matching of bulk sediments - how accurate can it be?
- 2013
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Ingår i: Radiocarbon. - : Cambridge University Press (CUP). - 0033-8222 .- 1945-5755. ; 55:2-3, s. 1173-1186
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Tidskriftsartikel (refereegranskat)abstract
- We used the radiocarbon wiggle-match dating technique to date the varved sediments of Lake Gyltigesjön in southern Sweden with the main aim to construct an accurate chronology covering the period between about 3000 and 2000 cal BP. Wiggle-match dating was applied to bulk sediments to evaluate the possibility of constructing accurate chronologies in the absence of terrestrial plant macrofossils and when the amount of old carbon in the sediments is unknown. Facilitated by a floating varve chronology and relatively stable 14C reservoir ages, the results show the possibility to assess the contribution of old carbon solely based on the 14C wiggle-matching of bulk sediments. We confirm the wiggle-matched chronology and the 14C reservoir age of approximately 260 yr by cross-checking the results with 14C dating of macrofossils. The obtained calibrated ages based on bulk sediments have an uncertainty range of about 60–65 yr (95.4% confidence interval). This study confirms that 14C wiggle-match dating of bulk sediments is a viable tool when constructing high-resolution chronologies. The method is especially useful in Sun-climate studies since the timing between solar activity variations (expressed as 14C variations) and climate changes can be accurately determined.
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| 9. |
- Snowball, Ian, et al.
(författare)
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An estimate of post-depositional remanent magnetization lock-in depth in organic rich varved lake sediments
- 2013
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Ingår i: Global and Planetary Change. - : Elsevier BV. - 1872-6364 .- 0921-8181. ; 110, s. 264-277
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Tidskriftsartikel (refereegranskat)abstract
- We studied the paleomagnetic properties of relatively organic rich, annually laminated (varved) sediments of Holocene age in Gyltigesjon, which is a lake in southern Sweden. An age-depth model was based on a regional lead pollution isochron and Bayesian modelling of radiocarbon ages of bulk sediments and terrestrial macrofossils, which included a radiocarbon wiggle-matched series of 873 varves that accumulated between 3000 and 2000 Cal a BP (Mellstrom et al., 2013). Mineral magnetic data and first order reversal curves suggest that the natural remanent magnetization is carried by stable single-domain grains of magnetite, probably of magnetosomal origin. Discrete samples taken from overlapping piston cores were used to produce smoothed paleomagnetic secular variation (inclination and declination) and relative paleointensity data sets. Alternative temporal trends in the paleomagnetic data were obtained by correcting for paleomagnetic lock-in depths between 0 and 70 cm and taking into account changes in sediment accumulation rate. These temporal trends were regressed against reference curves for the same region (FENNOSTACK and FENNORPIS; Snowball et al., 2007). The best statistical matches to the reference curves are obtained when we apply lock-in depths of 21-34 cm to the Gyltigesjon paleomagnetic data, although these are most likely minimum estimates. Our study suggests that a significant paleomagnetic lock-in depth can affect the acquisition of post-depositional remanent magnetization even where bioturbation is absent and no mixed sediment surface layer exists. (C) 2013 The Authors. Published by Elsevier B.V. All rights reserved.
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| 10. |
- Tarasov, P. E., et al.
(författare)
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A pollen-based biome reconstruction over the last 3.562 million years in the Far East Russian Arctic - new insights into climate-vegetation relationships at the regional scale
- 2013
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Ingår i: Climate of the Past. - : Copernicus GmbH. - 1814-9332. ; 9:6, s. 2759-2775
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Tidskriftsartikel (refereegranskat)abstract
- The recent and fossil pollen data obtained under the frame of the multi-disciplinary international El'gygytgyn Drilling Project represent a unique archive, which allows the testing of a range of pollen-based reconstruction approaches and the deciphering of changes in the regional vegetation and climate. In the current study we provide details of the biome reconstruction method applied to the late Pliocene and Quaternary pollen records from Lake El'gygytgyn. All terrestrial pollen taxa identified in the spectra from Lake El'gygytgyn were assigned to major vegetation types (biomes), which today occur near the lake and in the broader region of eastern and northern Asia and, thus, could be potentially present in this region during the past. When applied to the pollen spectra from the middle Pleistocene to present, the method suggests (1) a predominance of tundra during the Holocene, (2) a short interval during the marine isotope stage (MIS) 5.5 interglacial distinguished by cold deciduous forest, and (3) long phases of taiga dominance during MIS 31 and, particularly, MIS 11.3. These two latter interglacials seem to be some of the longest and warmest intervals in the study region within the past million years. During the late Pliocene-early Pleistocene interval (i.e., similar to 3.562-2.200 Ma), there is good correspondence between the millennial-scale vegetation changes documented in the Lake El'gygytgyn record and the alternation of cold and warm marine isotope stages, which reflect changes in the global ice volume and sea level. The biome reconstruction demonstrates changes in the regional vegetation from generally warmer/wetter environments of the earlier (i. e., Pliocene) interval towards colder/drier environments of the Pleistocene. The reconstruction indicates that the taxon-rich cool mixed and cool conifer forest biomes are mostly characteristic of the time prior to MIS G16, whereas the tundra biome becomes a prominent feature starting from MIS G6. These results consistently indicate that the study region supported significant tree populations during most of the interval prior to similar to 2.730 Ma. The cold-and drought-tolerant steppe biome first appears in the reconstruction similar to 3.298 Ma during the tundra-dominated MIS M2, whereas the tundra biome initially occurs between similar to 3.379 and similar to 3.378 Ma within MIS MG4. Prior to similar to 2.800 Ma, several other cold stages during this generally warm Pliocene interval were characterized by the tundra biome.
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