| 1. |
- Ampel, Linda, et al.
(författare)
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Abrupt climate change and early lake development - the Lateglacial diatom flora at Hasseldala Port, southeastern Sweden
- 2015
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Ingår i: Boreas. - : Wiley. - 0300-9483 .- 1502-3885. ; 44:1, s. 94-102
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Tidskriftsartikel (refereegranskat)abstract
- The fossil diatom record from the Hasseldala Port palaeolake, southeastern Sweden, offers an excellent opportunity to investigate how past climatic shifts influenced catchment conditions and early lake development. The record, dating to between 13900 and 11200 cal. a BP, covers a climatically dynamic period, starting with deglaciation followed by oscillations between warmer and colder climate states. The stratigraphical changes in the fossil diatom assemblages show a trend of less open-water taxa and a successively more complex periphytic community as the lake shallows and the aquatic habitat structure develops. A diatom-based reconstruction of lake water pH indicates a natural acidification trend early in the record from 13900 to 12500 cal. a BP. From 12500 cal. a BP, coincident with the start of climate cooling, to 11300 cal. a BP this trend is disrupted and lake waters become more alkaline. A cooler and drier climate most likely resulted in reduced soil organic matter build-up as well as more frozen ground that impeded hydrological flow and decreased the input of dissolved organic matter and organic acids into the lake system. This study demonstrates the importance of the hydrological system as a link between terrestrial and aquatic ecosystems during early lake ontogeny.
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| 2. |
- Berntsson, Annika, et al.
(författare)
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Late Holocene high precipitation events recorded in lake sediments and catchment geomorphology, Lake Vuoksjavratje, NW Sweden
- 2015
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Ingår i: Boreas. - : Wiley. - 0300-9483 .- 1502-3885. ; 44:4, s. 676-692
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we show the potential of combining multi-proxy analysis of lake sediments with catchment geomorphology to better understand palaeoenvironmental changes. Previous studies have suggested that alpine lakes in N Sweden may be highly sensitive to variations in catchment erosion and precipitation, and that this sensitivity may influence ecologically based reconstructions of past temperature changes. We analysed lake sediments covering the last 5100 years from the alpine Lake Vuoksjavratje in NW Sweden in order to identify different erosional regimes in the lake catchment, sediment sources and lake sedimentary processes, which ultimately affect the palaeoecological record. The measured proxies include elemental geochemistry from XRF core scanning, grain size, sediment accumulation rates, fraction of terrestrial organic carbon and geomorphological mapping, supported by previously published chironomid and total organic carbon data. From the integrated results we identified time intervals when increased intensity of precipitation altered sedimentation and lake catchment erosional processes. The most prominent event occurred c. 2900 cal. a BP and is interpreted to be the result of excessive precipitation, possibly related to the climatic shift towards cooler and wetter conditions referred to as the 2.8 ka event.
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| 3. |
- Berntsson, Annika, 1979-, et al.
(författare)
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Late Holocene high precipitation events recorded in lake sediments and catchment geomorphology, Lake Vuoksjávrátje, NW Sweden
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In this paper, we highlight the importance of combining multi-proxy analysis of lake sediments with associated catchment geomorphology to better understand the late Holocene palaeoenvironmental evolution in a high latitude Alpine lake in N Sweden. Previous studies have suggested that such lakes may be highly sensitive to variations in catchment erosion and variations in precipitation, and that this sensitivity may influence ecologically-based reconstructions of past temperature changes. Here we have analysed lake sediments covering the last 5100 years from Lake Vuoksjávrátje in NW Sweden to identify different erosional regimes in the lake catchment and to identify sediment sources and lake sedimentary processes, which ultimately affect the palaeoecological record. Methods that were used include XRF core scanning, grain size analysis and geomorphological mapping, supported by previously published chironomid, total organic carbon and carbon/nitrogen data. From the integrated results we identify time intervals when increased amounts/intensity of precipitation altered sedimentation and lake catchment erosional processes. The most prominent event in our record occurred between 3090 and 2750 cal. a BP and is interpreted to be the result of excessive precipitation in relation to the 2.8 ka event. By combining the multi-proxy analysis of a lake sediment core with a detailed catchment characterisation it is possible to reach a better understanding of the processes active within the lake catchment, the factors governing the erosional regimes and the way these are recorded in lake sediments. For future palaeoclimatological research based on lake sediments we recommend increasing the integration of catchment geomorphology, sedimentology and palaeoecology.
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| 4. |
- Bertrand, Sebastien, et al.
(författare)
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Inorganic geochemistry of lake sediments : a review of analytical techniques and guidelines for data interpretation
- 2024
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Ingår i: Earth-Science Reviews. - : Elsevier. - 0012-8252 .- 1872-6828. ; 249
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Forskningsöversikt (refereegranskat)abstract
- Inorganic geochemistry is a powerful tool in paleolimnology. It has become one of the most commonly used techniques to analyze lake sediments, particularly due to the development and increasing availability of XRF core scanners during the last two decades. It allows for the reconstruction of the continuous processes that occur in lakes and their watersheds, and it is ideally suited to identify event deposits. How earth surface processes and limnological conditions are recorded in the inorganic geochemical composition of lake sediments is, however, relatively complex. Here, we review the main techniques used for the inorganic geochemical analysis of lake sediments and we offer guidance on sample preparation and instrument selection. We then summarize the best practices to process and interpret bulk inorganic geochemical data. In particular, we emphasize that log-ratio transformation is critical for the rigorous statistical analysis of geochemical datasets, whether they are obtained by XRF core scanning or more traditional techniques. In addition, we show that accurately interpreting inorganic geochemical data requires a sound understanding of the main components of the sediment (organic matter, biogenic silica, carbonates, lithogenic particles) and mineral assemblages. Finally, we provide a series of examples illustrating the potential and limits of inorganic geochemistry in paleolimnology. Although the examples presented in this paper focus on lake and fjord sediments, the principles presented here also apply to other sedimentary environments.
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| 5. |
- Björck, Svante, et al.
(författare)
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A South Atlantic island record uncovers shifts in westerlies and hydroclimate during the last glacial
- 2019
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Ingår i: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 15:6, s. 1939-1958
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Tidskriftsartikel (refereegranskat)abstract
- Changes in the latitudinal position and strength of the Southern Hemisphere westerlies (SHW) are thought to be tightly coupled to important climate processes, such as cross-equatorial heat fluxes, Atlantic Meridional Overturning Circulation (AMOC), the bipolar seesaw, Southern Ocean ventilation and atmospheric CO2 levels. However, many uncertainties regarding magnitude, direction, and causes and effects of past SHW shifts still exist due to lack of suitable sites and scarcity of information on SHW dynamics, especially from the last glacial. Here we present a detailed hydroclimate multiproxy record from a 36.4-18.6 kyr old lake sediment sequence on Nightingale Island (NI). It is strategically located at 37ĝF S in the central South Atlantic (SA) within the SHW belt and situated just north of the marine Subtropical Front (SF). This has enabled us to assess hydroclimate changes and their link to the regional climate development as well as to large-scale climate events in polar ice cores. The NI record exhibits a continuous impact of the SHW, recording shifts in both position and strength, and between 36 and 31 ka the westerlies show high latitudinal and strength-wise variability possibly linked to the bipolar seesaw. This was followed by 4 kyr of slightly falling temperatures, decreasing humidity and fairly southerly westerlies. After 27 ka temperatures decreased 3-4 ĝC, marking the largest hydroclimate change with drier conditions and a variable SHW position. We note that periods with more intense and southerly-positioned SHW seem to be related to periods of increased CO2 outgassing from the ocean, while changes in the cross-equatorial gradient during large northern temperature changes appear as the driving mechanism for the SHW shifts. Together with coeval shifts of the South Pacific westerlies, our results show that most of the Southern Hemisphere experienced simultaneous atmospheric circulation changes during the latter part of the last glacial. Finally we can conclude that multiproxy lake records from oceanic islands have the potential to record atmospheric variability coupled to large-scale climate shifts over vast oceanic areas..
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| 6. |
- Björck, Svante, et al.
(författare)
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Nordlaguna – A unique lake basin at the foot of the Beerenberg volcano, Jan Mayen, containing partially enigmatic sediments
- 2022
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Ingår i: Quaternary Science Advances. - : Elsevier BV. - 2666-0334. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- Sediments from the only permanent lake on the island of Jan Mayen (71°N, 08°30′W), Lake Nordlaguna (NL), were investigated. The lake, with an area of ∼1 km2, is situated at the foot of the world's northernmost active subaerial volcano and is separated from the sea by a 150–240 m wide beach barrier, which reaches 4–5 m above sea level. Most of the lake is deeper than 25 m, with the deepest part being 36 m. Altogether five coring sites, evenly spread out, were chosen and the sediment cores were retrieved from the lake ice with Uwitec and Nesje corers. After detailed descriptions of the very organic-poor and silt dominated sediments (of supposedly tephra-dominated origin), three sites were chosen for further analyses: macrofossils for 14C dating, tephra chemistry, C, S, grain-size, and XRF analyses. Based on 14C dates and the occurrence of the so-called Eggøya tephra (AD 1732), age models show variable bottom ages for the three sites: ∼3000, 600 and 400 cal yr BP. Due to the position of the core sites, with different sediment source areas, the elemental signals vary considerably between sites. An interesting feature of the lake is an isolated stock of Arctic char, which shows that the now land-locked lake has once been in contact with the sea. The almost total lack of organic material excluded any advanced paleo-ecologic investigations of the lake, and the study therefore focused on its marine-limnic history by different examinations of the XRF data with focus on the oldest and longest record. This development is based on elemental ratios (Br/Zn), PCA analyses of a center log ratio (clr) transformation of the original XRF data and magnetic susceptibility. It shows that the lake was isolated just before the time of the Eggøya tephra fall-out (∼220 cal yr BP), when the stock of Arctic char was most likely isolated from the sea. This was preceded by a ∼2200 yr long period of marine bay with a more or less open connection with the sea, and thus varying fresh-water impact. Between ∼2400 and 2600 cal yr BP the basin was more or less isolated, preceded by almost full marine conditions for at least the 300–400 preceding years we have data from, a period when relative sea level might have been higher.
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| 7. |
- Carugati, Gabriele, 1980, et al.
(författare)
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Experimental assessment of a large sample cell for laser ablation-ICP-MS, and its application to sediment core micro-analysis
- 2010
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Ingår i: Mikrochimica Acta. - : Springer Science and Business Media LLC. - 1436-5073 .- 0026-3672. ; 170:1-2, s. 39-45
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Tidskriftsartikel (refereegranskat)abstract
- The coupling of laser ablation (LA) to inductively coupled plasma-mass spectrometry (ICP-MS) enables the direct analysis of solid samples with micrometric resolution. Analysis is often restricted to relatively small samples owing to the dimensions of conventional ablation cells. Here, we assess the performance of a large rectangular, commercially-available sample cell which enables analysis over a 10.2 x 5.2 cm(2) area. Comparison with the conventional cell shows a small to moderate performance decrease for the large cell resulting from the dilution of ablated particles in a larger volume with a 4-31% lower signal output and longer signal tailings. The performance of this cell is however sufficient for the determination of both major and trace elements in many kinds of samples. The applicability of the large cell LA-ICP-MS setup was demonstrated by the determination of Al, Si, Mn, Fe, Cu, Zn Pb and U in sediment core sections at a resolution of 0.6 mm. Detection limits for sediment analysis were 7 mg Al kg(-1), 68 mg Si kg(-1), 0.5 mg Mn kg(-1), 20 mg Fe kg(-1), 0.2 mg Cu kg(-1), 0.3 mg Zn kg(-1), 0.08 mg Pb kg(-1) and 0.003 mg U kg(-1). Cyclic patterns, which would have been overlooked by conventional analysis at cm resolution, were observed in analysed sediments. This study demonstrates the potential of LA-ICP-MS in environmental analysis, with the large sample cell setup offering the possibility to analyse a wider range of samples without sectioning.
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| 8. |
- Chawchai, Sakonvan, et al.
(författare)
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Lake Kumphawapi - an archive of Holocene palaeoenvironmental and palaeoclimatic changes in northeast Thailand
- 2013
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 68, s. 59-75
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Tidskriftsartikel (refereegranskat)abstract
- The long-term climatic and environmental history of Southeast Asia, and of Thailand in particular, is still fragmentary. Here we present a new C-14-dated, multi-proxy sediment record (TOC, C/N, CNS isotopes, Si, Zr, K, Ti, Rb, Ca elemental data, biogenic silica) for Lake Kumphawapi, the second largest natural lake in northeast Thailand. The data set provides a reconstruction of changes in lake status, groundwater fluctuations, and catchment run-off during the Holocene. A comparison of multiple sediment sequences and their proxies suggests that the summer monsoon was stronger between c. 9800 and 7000 cal yr BP. Lake status and water level changes around 7000 cal yr BP signify a shift to lower effective moisture. By c. 6500 cal yr BP parts of the lake had been transformed into a peatland, while areas of shallow water still occupied the deeper part of the basin until c. 5400-5200 cal yr BP. The driest interval in Kumphawapi's history occurred between c. 5200 and 3200 cal yr BP, when peat extended over large parts of the basin. After 3200 cal yr BP, the deepest part of the lake again turned into a wetland, which existed until c. 1600 cal yr BP. The observed lake-level rise after 1600 cal yr BP could have been caused by higher moisture availability, although increased human influence in the catchment cannot be ruled out. The present study highlights the use of multiple sediment sequences and proxies to study large lakes, such as Lake Kumphawapi in order to correctly assess the time transgressive response to past changes in hydroclimate conditions. Our new data set from northeast Thailand adds important palaeoclimatic information for a region in Southeast Asia and allows discussing Holocene monsoon variability and ITCZ movement in greater detail.
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| 9. |
- Chawchai, Sakonvan, et al.
(författare)
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Testing commonly used XRF core scanning based proxies for organic rich lake sediments and peat
- 2016
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Ingår i: Boreas. - : Wiley. - 0300-9483 .- 1502-3885. ; 45:1, s. 180-189
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Tidskriftsartikel (refereegranskat)abstract
- X-ray fluorescence (XRF) core scanning has become widely available for geological studies during the last decade. The data obtained from XRF core scanning, however, may be strongly influenced by the amount of organic matter, water content, density and porosity of the sediment matrix. In this study we discuss the usefulness of XRF core scanning to distinguish different kinds of organic-rich sediments and peat based on examples from tropical Lakes Kumphawapi and Nong Leng Sai in Thailand. We examined how sedimentary factors influence XRF core scanning analyses by comparing elemental and scattering ratios to lithological changes and quantitative LOI, TOC, biogenic silica (BSi) and grain-size values. Our comparison suggests that the (inc/coh) scattering ratio is of limited use as an indicator for variations in LOI and TOC in peaty gyttja or peat. In Lake Kumphawapi's sediments, Si/Ti ratios reflect clastic input associated with grain-size variations rather than BSi contents. The Ti-normalized ratios of Si, Zr, Sr, K and Rb are linked to mineral input and associated grain-size variations. We conclude that XRF core scanning of organic-rich tropical lake sediments and peat is useful to infer palaeoenvironmental conditions. However, XRF core scanning data does not stand-alone and needs to be underpinned by additional proxies.
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| 10. |
- Diaz Somoano, Mercedes, et al.
(författare)
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Stable Lead Isotope Compositions In Selected Coals From Around The World And Implications For Present Day Aerosol Source Tracing
- 2009
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 43:4, s. 1078-1085
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Tidskriftsartikel (refereegranskat)abstract
- The phasing out of leaded gasoline in many countries around the world at the end of the last millennium has resulted in a complex mixture of lead sources in the atmosphere. Recent studies suggest that coal combustion has become an important source of Pb in aerosols in urban and remote areas. Here, we report lead concentration and isotopic composition for 59 coal samples representing major coal deposits worldwide in an attempt to characterize this potential source. The average concentration in these coals is 35 μg Pb g−1, with the highest values in coals from Spain and Peru and the lowest in coals from Australia and North America. The 206Pb/207Pb isotope ratios range between 1.15 and 1.24, with less radiogenic Pb in coals from Europe and Asia compared to South and North America. Comparing the Pb isotopic signatures of coals from this and previous studies with those published for Northern and Southern Hemisphere aerosols, we hypothesize that coal combustion might now be an important Pb source in China, the eastern U.S., and to some extent, in Europe but not as yet in other regions including South Africa, South America, and western U.S. This supports the notion that “old Pb pollution” from leaded gasoline reemitted into the atmosphere or long-range transport (i.e., from China to the western U.S.) is important. Comparing the isotope ratios of the coals, the age of the deposits, and Pb isotope evolution models for the major geochemical reservoirs suggests that the PbIC in coals is strongly influenced by the depositional coal forming environment.
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