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Sökning: WFRF:(Kylander malin)

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1.
  • Ampel, Linda, et al. (författare)
  • Abrupt climate change and early lake development - the Lateglacial diatom flora at Hasseldala Port, southeastern Sweden
  • 2015
  • Ingår i: Boreas. - : Wiley. - 0300-9483 .- 1502-3885. ; 44:1, s. 94-102
  • 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)
  • Late Holocene high precipitation events recorded in lake sediments and catchment geomorphology, Lake Vuoksjavratje, NW Sweden
  • 2015
  • Ingår i: Boreas. - : Wiley. - 0300-9483 .- 1502-3885. ; 44:4, s. 676-692
  • 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)
  • Late Holocene high precipitation events recorded in lake sediments and catchment geomorphology, Lake Vuoksjávrátje, NW Sweden
  • 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)
  • Inorganic geochemistry of lake sediments : a review of analytical techniques and guidelines for data interpretation
  • 2024
  • Ingår i: Earth-Science Reviews. - : Elsevier. - 0012-8252 .- 1872-6828. ; 249
  • 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)
  • A South Atlantic island record uncovers shifts in westerlies and hydroclimate during the last glacial
  • 2019
  • Ingår i: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 15:6, s. 1939-1958
  • 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)
  • Nordlaguna – A unique lake basin at the foot of the Beerenberg volcano, Jan Mayen, containing partially enigmatic sediments
  • 2022
  • Ingår i: Quaternary Science Advances. - : Elsevier BV. - 2666-0334. ; 7
  • 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)
  • Experimental assessment of a large sample cell for laser ablation-ICP-MS, and its application to sediment core micro-analysis
  • 2010
  • Ingår i: Mikrochimica Acta. - : Springer Science and Business Media LLC. - 1436-5073 .- 0026-3672. ; 170:1-2, s. 39-45
  • 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)
  • Lake Kumphawapi - an archive of Holocene palaeoenvironmental and palaeoclimatic changes in northeast Thailand
  • 2013
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 68, s. 59-75
  • 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)
  • Testing commonly used XRF core scanning based proxies for organic rich lake sediments and peat
  • 2016
  • Ingår i: Boreas. - : Wiley. - 0300-9483 .- 1502-3885. ; 45:1, s. 180-189
  • 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)
  • Stable Lead Isotope Compositions In Selected Coals From Around The World And Implications For Present Day Aerosol Source Tracing
  • 2009
  • Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 43:4, s. 1078-1085
  • 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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11.
  • Emmanouilidis, Alexandros, et al. (författare)
  • Middle to late Holocene palaeoenvironmental study of Gialova Lagoon, SW Peloponnese, Greece
  • 2018
  • Ingår i: Quaternary International. - : Elsevier BV. - 1040-6182 .- 1873-4553. ; 476, s. 46-62
  • Tidskriftsartikel (refereegranskat)abstract
    • The coastal areas of Eastern Mediterranean have long been the subject of research, due to their rapid geomorphological changes, but also because of their archaeological interest. Our study is focused on a shallow coastal lagoon of Peloponnese, Gialova Lagoon, which for several years has attracted the scientific interest of archaeologists, geomorphologists as well as sedimentologists. Gialova lagoon is located near the ancient city of Pylos, the kingdom of king Nestor during the Mycenaean period (1600-1100 BC). The objectives of this study are: (a) to reconstruct the middle to late Holocene depositional environments of the lagoon and (b) to correlate our data to already existing publications, in order to shed new light on the Holocene evolution of the lagoon and the associated coastal palaeoenvironmental changes. An 8m deep vibracore was drilled and a multi proxy analysis was carried out on the sediment sequence, including sedimentological (grain size analysis and moment measures, total organic carbon - TOC, total nitrogen e TN and total phosphorus - TP), high resolution geochemical (XRF-scanning) and palaeontological (micro-and macro faunal) analysis. The chronological framework is based on five C-14 datings forming the basis for an age depth model, calculated using the OxCal software. The radiocarbon dates from previous studies (6 cores, similar to 20 dates) were also taken into account. The data synthesis and interpretation provided robust and coherent indications regarding the palaeoenvironment, shoreline changes and the rate of geomorphological changes of the coastal area of Gialova Lagoon, as well as useful information about the palaeonvironmental and palaeoclimatic conditions that prevailed during the Mycenaean period. The interpretation, reveal a transition from a shallow marine environment (65005800 yr B.P.) to a brackish/lagoonal (5800-3300 yr B.P.), followed by a shift towards a freshwater/marsh environment (3300 yr B.P. to present).
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12.
  • Finné, Martin, et al. (författare)
  • Can XRF scanning of speleothems be used as a non-destructive method to identify paleoflood events in caves?
  • 2015
  • Ingår i: International Journal of Speleology. - 0392-6672 .- 1827-806X. ; 44:1, s. 17-23
  • Tidskriftsartikel (refereegranskat)abstract
    • We have developed a novel, quick and non-destructive method for tracing flood events in caves through the analysis of a stalagmite thick section with an XRF core scanner. The analyzed stalagmite has multiple horizons of fine sediments from past flood events intercalated with areas of cleaner calcite. Flood events detected from the elemental XRF core scanning data show good agreement with the position of flood horizons identified in petrographic thin sections. The geochemical composition of the individual flood layers shows that in certain cases the clay horizons had a distinct geochemical fingerprint suggesting that it may be possible to distinguish individual flood layers based on their geochemistry. This presents the possibility for using flood events as marker horizons to chronologically tie different speleothems in a cave to each other.
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13.
  • Gallagher, K, et al. (författare)
  • Inference of abrupt changes in noisy geochemical records using transdimensional changepoint models
  • 2011
  • Ingår i: Earth and Planetary Science Letters. - : Elsevier BV. - 0012-821X .- 1385-013X. ; 311:1-2, s. 182-194
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a method to quantify abrupt changes (or changepoints) in data series, represented as a function of depth or time. These changes are often the result of climatic or environmental variations and can be manifested in multiple datasets as different responses, but all datasets can have the same changepoint locations/timings. The method we present uses transdimensional Markov chain Monte Carlo to infer probability distributions on the number and locations (in depth or time) of changepoints, the mean values between changepoints and, if required, the noise variance associated with each dataset being considered. This latter point is important as we generally will have limited information on the noise, such as estimates only of measurement uncertainty, and in most cases it is not practical to make repeat sampling/measurement to assess other contributions to the variation in the data. We describe the main features of the approach (and describe the mathematical formulation in supplementary material), and demonstrate its validity using synthetic datasets, with known changepoint structure (number and locations of changepoints) and distribution of noise variance for each dataset. We show that when using multiple data, we expect to achieve better resolution of the changepoint structure than when we use each dataset individually. This is conditional on the validity of the assumption of common changepoints between different datasets. We then apply the method to two sets of real geochemical data, both from peat cores, taken from NE Australia and eastern Tibet. Under the assumption that changes occur at the same time for all datasets, we recover solutions consistent with those previously inferred qualitatively from independent data and interpretations. However, our approach provides a quantitative estimate of the relative probability of the inferred changepoints, allowing an objective assessment of the significance of each change.
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14.
  • Hansson, Sophia V., et al. (författare)
  • Evaluating paleoproxies for peat decomposition and their relationship to peat geochemistry
  • 2013
  • Ingår i: The Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 23:12, s. 1666-1671
  • Tidskriftsartikel (refereegranskat)abstract
    • The past decade has seen a rapid increase in interest in the biogeochemical record preserved in peat, particularly as it relates to carbon dynamics and environmental change. Importantly, recent studies show that carbon dynamics, that is, organic matter decomposition, can influence the record of atmospherically derived elements such as halogens and mercury. Most commonly, bulk density, light transmission, or carbon/nitrogen (C/N) ratios are used as a proxy to qualitatively infer the degree of decomposition in peat, but do these three proxies reflect the same patterns? Furthermore, how do each of these proxies relate to other geochemical data? To address these questions, we analyzed bulk density, light transmission, and C/N ratios, as well as multielement geochemistry (wavelength-dispersive x-ray fluorescence (WD-XRF)), in three hummock cores (70 cm in length, c. 500 years) from an ombrotrophic Swedish bog. To compare the proxies, we applied principal component analysis (PCA) to identify how the proxies relate to and interact with the geochemical matrix. This was coupled with changepoint modeling to identify and compare statistically significant changes for each proxy. Our results show differences between the proxies within and between cores, indicating each responds to a different part of the decomposition process. This is supported by the PCA, where the three proxies fall on different principal components. Changepoint analysis also showed that the inferred number of changepoints and their depths vary for each proxy and core. This suggests that decomposition is not fully captured by any one of these commonly used proxies, and thus, more than one proxy should be included.
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15.
  • Helmens, Karin F., et al. (författare)
  • Major cooling intersecting peak Eemian Interglacial warmth in northern Europe
  • 2015
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 122, s. 293-299
  • Tidskriftsartikel (refereegranskat)abstract
    • The degree of climate instability on the continent during the warmer-than-present Eemian Interglacial (around ca. 123 kyr ago) remains unsolved. Recently published high-resolution proxy data from the North Atlantic Ocean suggest that the Eemian was punctuated by abrupt events with reductions in North Atlantic Deep Water formation accompanied by sea-surface temperature cooling. Here we present multiproxy data at an unprecedented resolution that reveals a major cooling event intersecting peak Eemian warmth on the North European continent. Two independent temperature reconstructions based on terrestrial plants and chironomids indicate a summer cooling of the order of 2-4 degrees C. The cooling event started abruptly, had a step-wise recovery, and lasted 500-1000 yr. Our results demonstrate that the common view of relatively stable interglacial climate conditions on the continent should be revised, and that perturbations in the North Atlantic oceanic circulation under warmer-than-present interglacial conditions may also lead to abrupt and dramatic changes on the adjacent continent.
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16.
  • Hällberg, Lars Petter, PhD student, 1988- (författare)
  • Paleoclimate and seasonality on Sumatra during the Late Glacial and Holocene : Insights from biomarkers and climate model simulations
  • 2024
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Deep atmospheric convection in the Indo-Pacific Warm Pool (IPWP) is a key driver of the Hadley and Walker Circulations that modulate the Asian-Australian monsoons and the El Niño Southern Oscillation (ENSO). Temperature and rainfall seasonality, i.e., the amount and timing of precipitation, impacts ecosystems, carbon content in soils and peats, and human livelihoods. Yet, past climate variability in the IPWP is poorly constrained. The Maritime Continent, located in the center of the IPWP remains a “quantification desert”, with a scarcity of terrestrial paleoenvironmental reconstructions.This thesis investigates the evolution of temperature, precipitation amount and seasonality over the Late Glacial (14.7-11.7 ka BP) and the Holocene (last 11.7 ka). This is achieved by combining climate model simulations and lipid biomarker analyses of terrestrial peat archives from Sumatra. Temperature and seasonality were explored by analysis of climate model simulations for the Late Glacial and Holocene. Microbial membrane-derived glycerol dialkyl glycerol tetraethers (GDGTs) were investigated as temperature and hydro-environmental proxies. Using n-alkane distributions, the abundance of algae, aquatic and terrestrial plants was reconstructed and linked to past hydroclimate variability. The hydrogen isotopic composition (dD) of the n-alkanes was then used to disentangle seasonal and annual precipitation signals.The analysis of Sumatran GDGTs revealed that bacterial community shifts of the GDGT producers had a strong impact on reconstructed temperatures, and that H-shaped branched GDGT isomers are good tracers of such community shifts. The branched GDGT temperature reconstruction indicates gradual warming over the Holocene, consistent with models and nearby marine records.Rainfall seasonality has shifted drastically over the studied time frame, in particular during the end of the Late Glacial, and between 6-4.2 ka BP. The Late Glacial climate was characterized by a much stronger seasonality, with a cold and dry Asian winter monsoon suppressing atmospheric deep convection in the region. The resulting mean state conditions resembled the atmospheric circulation and sea surface temperature patterns during extreme El Niño events in the modern climate. The Mid-Holocene (6-4.2 ka BP) was characterized by increased seasonality, with alternating droughts and heavy rains due to strong monsoon precipitation and longer dry season.The Early Holocene was relatively dry. Wetter conditions started around 7-6 ka BP, and peaked at 4.5-3 ka BP. This is consistent with a dD reconstruction on Sulawesi, but 1.5-2 ka later than indicated by speleothem oxygen isotopic (d18O) records on Sumatra and Sulawesi. However, the speleothem records closely follow algal dD values, interpreted here as a seasonal monsoon signal, suggesting that speleothems in the region reflect monsoonal precipitation rather than an annual signal. Rapid drying was reconstructed for the Late Holocene, starting at 3 ka BP, co-occurring with the onset of strengthened ENSO variability. The Late Holocene drying caused drying out and decomposition of peat in one of the studied cores which resulted in a hiatus of 1700 years, highlighting the importance of hydroclimate for peat and carbon accumulation in tropical wetlands.In conclusion, this dissertation enhances our understanding of past climatic conditions in the Maritime Continent and contributes toward constraining the evolution of temperature, precipitation, and monsoon-driven seasonality over the Late Glacial and Holocene in a region that has a scarce coverage of paleoclimate proxy information. Additionally, the methodological aspects of this thesis advance terrestrial paleoclimatological reconstructions by constraining source shifts of GDGTs and proposing a novel approach to disentangle seasonal and annual precipitation signals from dD.
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17.
  • Hällberg, Petter, 1988-, et al. (författare)
  • Disentangling seasonal and annual precipitation signals in the tropics over the Holocene: insights from δD, alkanes and GDGTs
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • Rainfall seasonality in the tropics has a substantial impact on both ecosystems and human livelihoods. Yet, reconstructions of past rainfall variability have so far generally been unable to differentiate between annual and seasonal precipitation changes. Past variations in seasonality are therefore largely unknown. Here, we disentangle hydrogen isotopic (dD) signals from terrestrial leaf waxes and algae in an 8000-year peat core from Sumatra, which reflect annually integrated versus wet season signals, respectively. We validate these results using lipid biomarkers by reconstructing vegetation dynamics via n-alkane distributions and peatland hydrological conditions using glycerol dialkyl glycerol tetraethers (GDGTs). Finally, we reconstruct biomass burning using levoglucosan concentrations in the core. Algal dD indicate stronger winter (~DJF) monsoon precipitation in the Mid-Holocene, between 8-4.2 ka BP. A period of alternating flooding, droughts and wildfires is reconstructed between 6-4.2 ka BP, implicating very strong monsoonal precipitation and drying out and burning during a longer and intensified dry season. We attribute this strong rainfall seasonality in the Mid-Holocene mainly to orbitally forced insolation seasonality, and a strenghtened Indonesian-Australian summer monsoon. In terms of annually integrated conditions, terrestrial plant dD, vegetation composition and GDGTs all indicate wetter conditions peaking between 3-4.5 ka BP, preceded by drier conditions, and followed by drastic and rapid drying in the late Holocene from around 2.8 ka BP. Our multiproxy annual precipitation reconstruction thereby indicates the wettest overall conditions approximately 1500-2000 years later than a nearby speleothem d18O record, which instead follows the dD recorded by algae in our record. We therefore hypothesize that speleothem reconstructions predominantly record the wet season isotopic signal, due to cave groundwater recharge occurring mainly after heavy precipitation. These results resolve the seasonal versus annual components of past rainfall variability in the Indo Pacific Warm Pool region, and highlight the importance of considering seasonality in rainfall reconstructions.
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18.
  • Johnson, Mark D., et al. (författare)
  • Varved glaciomarine clay in central Sweden before and after the Baltic Ice Lake drainage : a further clue to the drainage events at Mt Billingen
  • 2013
  • Ingår i: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 135:3-4, s. 293-307
  • Tidskriftsartikel (refereegranskat)abstract
    • Glaciomarine clay found west of Mt Billingen, central Sweden, contains two distinct varve units separated by a sand layer that we interpret to be sediment deposited in the North Sea during the catastrophic drainage of the Baltic Ice Lake (BIL). The lower varve series was deposited proximal to the retreating ice margin and consists of varves that grade upward from gray to red. The upper varve series was deposited after the drainage event when fresh water within the Baltic basin flowed westward north of Billingen; the upper varves grade from red to gray. Grain size, elemental composition (determined by X-ray fluorescence (XRF)), iron and organic-carbon content vary within each varve, with values that grade upward through each varve, but with a sharp contact with the overlying varve. The two varve units differ from each other, with the lower sequence being coarser and the upper containing a higher iron and organic-carbon content. We attribute the differences between pre- and post-drainage varves to reflect changes in distance to the ice margin and provenance. The stratigraphy at the site suggests that the BIL drainage lasted <1 year. Lithostratigraphic correlations to the Lake Langen basin west of Mt Billingen support the idea of glacier ice in the Langen basin during the drainage and a retreat and advance of the ice sheet during Allerod and Younger Dryas, including the possibility of an earlier, Allerod drainage.
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19.
  • Johnson, Mark D., 1954, et al. (författare)
  • Varved glaciomarine clay in central Sweden before and the Baltic Ice Lake drainage: a further clue to the drainage event at Mt. Bilingen
  • 2013
  • Ingår i: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 135:3-4, s. 293-307
  • Tidskriftsartikel (refereegranskat)abstract
    • Glaciomarine clay found west of Mt Billingen, central Sweden, contains two distinct varve units separated by a sand layer that we interpret to be sediment deposited in the North Sea during the catastrophic drainage of the Baltic Ice Lake (BIL). The lower varve series was deposited proximal to the retreating ice margin and consists of varves that grade upward from gray to red. The upper varve series was deposited after the drainage event when fresh water within the Baltic basin flowed westward north of Billingen; the upper varves grade from red to gray. Grain size, elemental composition (determined by X-ray fluorescence (XRF)), iron and organic-carbon content vary within each varve, with values that grade upward through each varve, but with a sharp contact with the overlying varve. The two varve units differ from each other, with the lower sequence being coarser and the upper containing a higher iron and organic-carbon content. We attribute the differences between pre- and post-drainage varves to reflect changes in distance to the ice margin and provenance. The stratigraphy at the site suggests that the BIL drainage lasted ,1 year. Lithostratigraphic correlations to the Lake La°ngen basin west of Mt Billingen support the idea of glacier ice in the La°ngen basin during the drainage and a retreat and advance of the ice sheet during Allero¨d and Younger Dryas, including the possibility of an earlier, Allero¨d drainage.
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20.
  • Katrantsiotis, Christos, et al. (författare)
  • Eastern Mediterranean hydroclimate reconstruction over the last 3600 years based on sedimentary n-alkanes, their carbon and hydrogen isotope composition and XRF data from the Gialova Lagoon, SW Greece
  • 2018
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 194, s. 77-93
  • Tidskriftsartikel (refereegranskat)abstract
    • Understanding past hydroclimate variability and related drivers is essential to improve climate forecasting capabilities especially in areas with high climatic sensitivity, such as the Mediterranean. This can be achieved by using a broad spectrum of high resolution, multiple proxy records which can also allow us to assess linkages between regional hydroclimate variability and shifts in the large-scale atmospheric patterns. Here, we present a multiproxy reconstruction of the central-eastern Mediterranean hydro climate changes over the last 3600 years based on a sediment core from the Gialova Lagoon, a shallow coastal ecosystem in SW Peloponnese, Greece. Our combined dataset consists of the distribution and compound-specific carbon and hydrogen isotope (delta C-13 and 8D) composition of n-alkanes, bulk organic matter properties and X-ray fluorescence (XRF) core scanning data. This approach was complemented with a semi-quantitative analysis of plant remains in the core. The results indicate a high contribution of local aquatic vegetation to organic matter. Large delta C-13 variations in predominantly aquatic plant-derived mid-chain alkanes (C23-23) mainly reflect changes in the aquatic plant abundance and their carbon source. Our data suggest that higher delta C-13(23-25) values (up to 19 parts per thousand) largely correspond to expansion of aquatic vegetation during wet and/or cold periods causing carbon-limiting conditions in the water and assimilation of isotopically-enriched bicarbonate by the plants. The 8D records of the individual n-alkanes (C-17 to C-31) exhibit a nearly identical pattern to each other, which implies that they all reflect changes in the source water isotope composition, driven by hydroclimate variability. In addition, the 8D profiles are consistent with the XRF data with both proxies being driven by a common hydroclimate signal. We observe two major shifts from dry and/or warm periods at ca 3600-3000 cal BP and ca 17001300 cal BP to wet and/or cold episodes at ca 3000-2700 cal BP and ca 1300-900 cal BP. The period ca 700-200 cal BP is the wettest and/or coldest in our record and coeval with the Little Ice Age. The climatic fluctuation reported in this study can be explained by the relative dominance of high-latitude (e.g. North Atlantic Oscillation during winters) and the low-latitude atmospheric patterns (Intertropical convergence zone, Subtropical High and the effects of Asian monsoons during summers) which suggests an Atlantic-Mediterranean-Monsoon climate link in this area for the late Holocene.
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21.
  • Kylander, Malin, et al. (författare)
  • A New Micro-Analytical Technique for the Identification of Tephra Layers in Sediments
  • 2008
  • Konferensbidrag (populärvet., debatt m.m.)abstract
    • Tephrochronology uses material emitted during volcanic eruptions as isochronous markers for linking paleoclimatic records. Cryptotephra (i.e., those tephra not visible to the naked eye) layers can be as little as one to two shards thick while the shards themselves can be smaller than 10 m. The methods used to locate cryptotephra are often time consuming and laborious (e.g., sieving and point counting, density separation techniques) and in some cases may not be applicable (e.g., magnetic susceptibility of tephra may not differ from the sediment). XRF is a well-established analytical tool that has recently taken a new direction with the introduction of core scanning systems. The ITRAX XRF core scanning system is non-destructive, can acquire continuous data for a broad range of elements in situ in both marine and lacustrine sediments as well as take radiographic images. We test the possibility of screening sediment cores to flag the potential location of cryptotephra layers thereby eliminating lengthy laboratory work and saving on often precious sample. The method was tested by seeding a sediment core with tephra shards in layers of increasing thickness and then scanning the core with the ITRAX. The method was then further tested on sequences from two different sites: Hässeldala Port in Southern Sweden where up to 5 different cryptotephra have been detected and Lake Pechora from Russia which has several visible tephra layers. We show that using the ITRAX it is possible to locate most tephra layers without using any sample and within a minimal amount of time (a 1 m core can be analyzed reasonably in 12 hours and it requires essentially no sample preparation).
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22.
  • Kylander, Malin, 1977-, et al. (författare)
  • A novel geochemical approach to paleorecords of dust deposition and effective humidity: 8500 years of peat accumulation at Store Mosse (the "Great Bog") , Sweden )
  • 2013
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 69, s. 69-82
  • Tidskriftsartikel (refereegranskat)abstract
    • Both bog surface wetness and atmospheric dust deposition are intricately linked to changes in the hydrological cycle and pairing these types of records at the same site provides complementary information. Here a peat core from Store Mosse in southern Sweden covering the last 8500 years was used to make a high-resolution paleoclimate reconstruction based on a combination of bog development, colourimetric humification and inorganic geochemistry data. The coupling of Principal Component Analysis with changepoint modelling allowed for precise linking of changes in bog surface wetness and dust deposition records.A long-term trend towards warm (and possibly wet) conditions starts ca 8150 cal yr BP and culminates with the most pronounced conditions from 6900 to 6600 cal yr BP. The most significant arid period at Store Mosse occurred between 6500 and 5600 cal yr BP during which dust deposition was significantly higher. Wetter conditions dominate from 5500 to 4980 cal yr BP as the transition from the Hypsithermal and into the Neoglacial is made. After a shift to drier conditions, humification enters a more stable period that lasts from 4525 until 3200 cal yr BP. It is during this time that the first possible anthropogenic dust signals occur at ca 4200 cal yr BP. From 3200 cal yr BP to present humification generally shows a long-term decline moving towards wetter conditions. The main exceptions are during the transition from the Neoglacial to Roman Warm Period which is registered as a significantly wetter period and two dry periods recorded 2365 to 2155 cal yr BP and 1275–1105 cal yr BP. In general, the observed changes agree well with regional records of effective humidity and temperature. The high temporal resolution of the Store Mosse record reveals that palaeoclimatic change over the last 8500 years in southern Sweden has had a complex and variable structure.
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23.
  • Kylander, Malin E., et al. (författare)
  • A rapid and reliable method for Pb isotopic analysis of peat and lichens by laser ablation-quadrupole-inductively coupled plasma-mass spectrometry for biomonitoring and sample screening
  • 2007
  • Ingår i: Analytica Chimica Acta. - : Elsevier BV. - 0003-2670. ; 582:1, s. 116-124
  • Tidskriftsartikel (populärvet., debatt m.m.)abstract
    • An analytical protocol for rapid and reliable laser ablation-quadrupole (LA-Q)- and multi-collector (MC-) inductively coupled plasma-mass spectrometry (ICP-MS) analysis of Pb isotope ratios (207Pb/206Pb and 208Pb/206Pb) in peats and lichens is developed. This technique is applicable to source tracing atmospheric Pb deposition in biomonitoring studies and sample screening. Reference materials and environmental samples were dry ashed and pressed into pellets for introduction by laser ablation. No binder was used to reduce contamination. LA-MC-ICP-MS internal and external precisions were <1.1% and <0.3%, respectively, on both 207Pb/206Pb and 208Pb/206Pb ratios. LA-Q-ICP-MS internal precisions on 207Pb/206Pb and 208Pb/206Pb ratios were lower with values for the different sample sets <14.3% while external precisions were <2.9%. The level of external precision acquired in this study is high enough to distinguish between most modern Pb sources. LA-MC-ICP-MS measurements differed from thermal ionisation mass spectrometry (TIMS) values by 1% or less while the accuracy obtained using LA-Q-ICP-MS compared to solution MC-ICP-MS was 3.1% or better using a run bracketing (RB) mass bias correction method. Sample heterogeneity and detector switching when measuring 208Pb by Q-ICP-MS are identified as sources of reduced analytical performance.
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24.
  • Kylander, Malin E., et al. (författare)
  • Inorganic Geochemistry in Paleoclimate : Tools and Trends in the Analysis of Peat and Lake Sediments
  • 2008
  • Ingår i: Climate Change Research Progress. - : Nova Publishers. - 9781600219986 ; , s. 161-186
  • Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
    • This chapter presents an overview of inorganic geochemistry as it is used in paleoclimate studies using peat and lake sediments. A brief look at the important dynamics occurring in lakes and mires highlights the fact that we are examining small scale processes to deduce large scale changes. Analytical techniques including sample preparation and instrumentation are summarized and important statistical and interpretive tools are explored. Specific examples from recent publications demonstrate the practical application of these tools and the kind of paleoclimatic interpretations that can be drawn from them.
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25.
  • Kylander, Malin E., et al. (författare)
  • It's in your glass : a history of sea level and storminess from the Laphroaig bog, Islay (southwestern Scotland)
  • 2020
  • Ingår i: Boreas. - : Wiley. - 0300-9483 .- 1502-3885. ; 49:1, s. 152-167
  • Tidskriftsartikel (refereegranskat)abstract
    • Severe winter windstorms have become an increasingly common occurrence over recent decades in northwestern Europe. Although there exists considerable uncertainty, storminess is projected to increase in the future. On centennial to millennial time scales in particular, the mechanisms forcing storminess remain unsettled. We contribute to available palaeostorm records by reconstructing changes over the last 6670 years using a coastal peat sequence retrieved from the ombrotrophic Laphroaig bog on Islay, southwestern Scotland. We use a combination of ash content, grain size and elemental chemistry to identify periods of greater storminess, which are dated to 6605, 6290-6225, 5315-5085, 4505, 3900-3635, 3310-3130, 2920-2380, 2275-2190, 2005-1860, 1305-1090, 805-435 and 275 cal. a BP. Storm signals in the first half of the record up to similar to 3000 cal. a BP are mainly apparent in the grain-size changes. Samples from this time period also have a different elemental signature than those later in the record. We speculate that this is due to receding sea levels and the consequent establishment of a new sand source in the form of dunes, which are still present today. The most significant events and strongest winds are found during the Iron Ages Cold Epoch (2645 cal. a BP), the transition into, and in the middle of, the Roman Ages Warm Period (2235 and 1965 cal. a BP) and early in the Little Ice Age (545 cal. a BP). The Laphroaig record generally agrees with regionally relevant peat palaeostorm records from Wales and the Outer Hebrides, although the relative importance of the different storm periods is not the same. In general, stormier periods are coeval with cold periods in the region as evidenced by parallels with increased ice-rafted debris in the North Atlantic, highlighting that sea-ice conditions could impact future storminess and storm track position.
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26.
  • Kylander, Malin E., et al. (författare)
  • Late glacial (17,060-13,400 cal yr BP) sedimentary and paleoenvironmental evolution of the Sekhokong Range (Drakensberg), southern Africa
  • 2021
  • Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 16:3
  • Tidskriftsartikel (refereegranskat)abstract
    • Southern Africa sits at the junction of tropical and temperate systems, leading to the formation of seasonal precipitation zones. Understanding late Quaternary paleoclimatic change in this vulnerable region is hampered by a lack of available, reliably-dated records. Here we present a sequence from a well-stratified sedimentary infill occupying a lower slope basin which covers 17,060 to 13,400 cal yr BP with the aim to reconstruct paleoclimatic variability in the high Drakensberg during the Late Glacial. We use a combination of pollen, total organic carbon and nitrogen, delta C-13, Fourier transform infrared spectroscopy attenuated total reflectance (FTIR-ATR) spectral and elemental data on contiguous samples with high temporal resolution (10 to 80 years per sample). Our data support a relatively humid environment with considerable cold season precipitation during what might have been the final stage of niche-glaciation on the adjoining southern aspects around 17,000 cal yr BP. Then, after an initial warmer and drier period starting similar to 15,600 cal yr BP, we identify a return to colder and drier conditions with more winter precipitation starting similar to 14,380 cal yr BP, which represents the first local evidence for the Antarctic Cold Reversal (ACR) in this region. On decadal to centennial timescales, the Late Glacial period was one marked by considerable climatic fluctuation and bi-directional environmental change, which has not been identified in previous studies for this region. Our study shows complex changes in both moisture and thermal conditions providing a more nuanced picture of the Late Glacial for the high Drakensburg.
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27.
  • Kylander, Malin E., et al. (författare)
  • Lead Penetration and Leaching in a Complex Temperate Soil Profile
  • 2008
  • Ingår i: Environmental Science and Technology. ; 42, s. 3177-3184
  • Tidskriftsartikel (refereegranskat)abstract
    • The documented loss of anthropogenic Pb from soil organic horizons and its migration into the mineral soil below has raised several environmental concerns, especially over the leaching of Pb into groundwater aquifers and subsequently into other environmental compartments of the ecosystem. Here, a complex colluvial soil formed over the last 10,000 years in NW Spain is studied. The objective is to evaluate the behavior of Pb in soils, including its migration rates and the potential use of complex soils as archives of atmospheric Pb pollution. To this end, Pb concentrations and Pb isotope ratios for total soil, and for acid-extractable (0.5 M HNO3) and residual fractions were determined. We show that the acid-extractable fraction is more radiogenic than the residual one in most of the soil profile and that this relationship is reversed in the surface layers (<15 cm) where pollution is greatest. Radiogenic Pb seems to have been leached out during rock weathering and pedogenesis of the soil. Comparison with a nearby peat record of atmospheric Pb deposition over the last 8 kyears demonstrates that though signals from pollution are detected in the soil record, the soil itself does not provide an accurate reconstruction of Pb deposition. On the basis of the history of soil formation the most likely Pb migration rate is estimated at approximately 0.01 cm year−1. At this migration rate Pb would be retained in the soil column for ~20 kyear. In other words, there is no evidence for the relatively rapid movement of Pb into the soil.
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28.
  • Kylander, Malin E., et al. (författare)
  • Mineral dust as a driver of carbon accumulation in northern latitudes
  • 2018
  • Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 8:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Peatlands in northern latitudes sequester one third of the world's soil organic carbon. Mineral dusts can affect the primary productivity of terrestrial systems through nutrient transport but this process has not yet been documented in these peat-rich regions. Here we analysed organic and inorganic fractions of an 8900-year-old sequence from Store Mosse (the "Great Bog") in southern Sweden. Between 5420 and 4550 cal yr BP, we observe a seven-fold increase in net peat-accumulation rates corresponding to a maximum carbon-burial rate of 150 g C m(-2) yr(-1) -more than six times the global average. This high peat accumulation event occurs in parallel with a distinct change in the character of the dust deposited on the bog, which moves from being dominated by clay minerals to less weathered, phosphate and feldspar minerals. We hypothesize that this shift boosted nutrient input to the bog and stimulated ecosystem productivity. This study shows that diffuse sources and dust dynamics in northern temperate latitudes, often overlooked by the dust community in favour of arid and semi-arid regions, can be important drivers of peatland carbon accumulation and by extension, global climate, warranting further consideration in predictions of future climate variability.
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29.
  • Kylander, Malin E., et al. (författare)
  • New insights from XRF core scanning data into boreal lake ontogeny during the Eemian (Marine Isotope Stage 5e) at Sokli, northeast Finland
  • 2018
  • Ingår i: Quaternary Research. - : Cambridge University Press (CUP). - 0033-5894 .- 1096-0287. ; 89:1, s. 352-364
  • 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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30.
  • Kylander, Malin E., et al. (författare)
  • Potentials and problems of building detailed dust records using peat archives : An example from Store Mosse (the "Great Bog"), Sweden
  • 2016
  • Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier BV. - 0016-7037 .- 1872-9533 .- 0046-564X. ; 190, s. 156-174
  • Tidskriftsartikel (refereegranskat)abstract
    • Mineral dust deposition is a process often overlooked in northern mid-latitudes, despite its potential effects on ecosystems. These areas are often peat-rich, providing ample material for the reconstruction of past changes in atmospheric deposition. The highly organic (up to 99% in some cases) matrix of atmospherically fed mires, however, makes studying the actual dust particles (grain size, mineralogy) challenging. Here we explore some of the potentials and problems of using geochemical data from conservative, lithogenic elements (Al, Ga, Rb, Sc, Y, Zr, Th, Ti and REE) to build detailed dust records by using an example from the 8900-yr peat sequence from Store Mosse (the "Great Bog"), which is the largest mire complex in the boreo-nemoral region of southern Sweden. The four dust events recorded at this site were elementally distinct, suggesting different dominant mineral hosts. The oldest and longest event (6385-5300 cal yr BP) sees a clear signal of clay input but with increasing contributions of mica, feldspar and middle-REE- rich phosphate minerals over time. These clays are likely transported from a long-distance source (< 100 km). While dust deposition was reduced during the second event (5300-4370 cal yr BP), this is the most distinct in terms of its source character with [Eu/Eu*] UCC revealing the input of plagioclase feldspar from a local source, possibly active during this stormier period. The third (2380- 2200 cal yr BP) and fourth (1275-1080 cal yr BP) events are much shorter in duration and the presence of clays and heavy minerals is inferred. Elemental mass accumulation rates reflect these changes in mineralogy where the relative importance of the four dust events varies by element. The broad changes in major mineral hosts, grain size, source location and approximated net dust deposition rates observed in the earlier dust events of longer duration agree well with paleoclimatic changes observed in northern Europe. The two most recent dust events are much shorter in duration, which in combination with evidence of their local and regional character, may explain why they have not been seen elsewhere. 
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31.
  • Kylander, Malin E., et al. (författare)
  • Rare earth element and Pb isotope variations in a 52 kyr peat core from Lynch’s Crater (NE Queensland, Australia): Proxy development and application to paleoclimate in the Southern Hemisphere
  • 2007
  • Ingår i: Geochemica et Cosmochimica Acta. ; 71:4, s. 942-960
  • Tidskriftsartikel (refereegranskat)abstract
    • Accurate prediction of future climate scenarios is contingent on our understanding of past and present climate mechanisms. This is done in part through the reconstruction of historical climate changes using proxy records from terrestrial and marine archives. Terrestrial archives covering the Holocene and late Pleistocene are limited, most acutely in the Southern Hemisphere. Here, Rare earth elements (REE) and Pb isotopes are developed as inorganic geochemical proxies of mineral dust source changes and, by extension, climate change. Using a peat core from Lynch’s Crater in NE Queensland, Australia, we present the first long-term (c. 52 kyr) terrestrial record of atmospheric REE and Pb deposition (with the exception of four wet events which represent periods of erosion from the crater itself) in the Southern Hemisphere covering both glacial and interglacial times. Based on a combination of correlation analyses, Al and Ti normalised profiles and elemental patterns, we establish REE are immobile within the peat deposit and not subject to significant post depositional diagenetic changes (important particularly for Ce). This is vital as REE can be mobile under acid and organic rich conditions like those that can occur during the development of a peat deposit. The volcanic provinces of eastern Australia have characteristic Eu anomaly signatures, which allowed their use in a novel way to detect changes in dust source to Lynch’s Crater. Between 41,095 and 52,505 BP the deposit was under the influence of dust carried by long distance transport (>1500 km) from SE Australia. From 8525 to 40,815 BP regional sources (100–1500 km) dominated the deposited signals while between 1740 and 8390 BP the dust signal was controlled by local sources (<100 km). These findings were also confirmed by Pb isotope data. Changepoint modelling refined the timing of these changes in dust source, recognizing concurrent shifts in our tracing tools ((Eu/Eu*)PAAS and 206Pb/207Pb). These changepoints were then compared to other palaeoenvironmental records (pollen, lake levels and dune building) from eastern Australia and found to be similar. Our results demonstrate that REE and Pb isotopes are effective tools for tracing past changes in atmospheric dust sources and to the study of climate change using minerotrophic peat deposits.
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32.
  • Kylander, Malin E., 1977-, et al. (författare)
  • Storm chasing : Tracking Holocene storminess in southern Sweden using mineral proxies from inland and coastal peat bogs
  • 2023
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 299, s. 107854-
  • Tidskriftsartikel (refereegranskat)abstract
    • Severe extratropical winter storms are a recurrent feature of the European climate and cause widespread socioeconomic losses. Due to insufficient long-term data, it remains unclear whether storminess has shown a notable response to changes in external forcing over the past millennia, which impacts our ability to project future storminess in a changing climate. Reconstructing past storm variability is essential to improving our understanding of storms on these longer, missing timescales. Peat sequences from coastal ombrotrophic bogs are increasingly used for this purpose, where greater quantities of coarser grained beach sand are deposited by strong winds during storm events. Moving inland however, storm intensity decreases, as does sand availability, muting potential paleostorm signals in bogs. We circumvent these issues by taking the innovative approach of using mid-infrared (MIR) spectral data, supported by elemental information, from the inorganic fraction of Store Mosse Dune South (SMDS), a 5000-year-old sequence from a large peatland located in southern Sweden. We infer past changes in mineral composition and thereby, the grain size of the deposited material. The record is dominated by quartz, whose coarse nature was confirmed through analyses of potential local source sediments. This was supported by further mineralogical and elemental proxies of atmospheric input. Comparison of SMDS with within-bog and regionally relevant records showed that there is a difference in proxy and site response to what should be similar timing in shifts in storminess over the-100 km transect considered. We suggest the construction of regional storm stacks, built here by applying changepoint modelling to four transect sites jointly. This modelling approach has the effect of reinforcing signals in common while reducing the influence of random noise. The resulting Southern Sweden-Storm Stack dates stormier periods to 4495-4290, 3880-3790, 2885-2855, 2300-2005, 1175-1065 and 715-425 cal yr BP. By comparing with a newly constructed Western Scotland-Storm Stack and proximal dune records, we argue that regional storm stacks allow us to better compare past storminess over wider areas, gauge storm track movements and by extension, increase our understanding of the drivers of storminess on centennial to millennial timescales.
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33.
  • Kylander, Malin, 1977-, et al. (författare)
  • High‐Resolution XRF Core Scanning Analysis of Les Echets (France) Sedimentary Sequence: New Insights from Chemical Proxies
  • 2011
  • Ingår i: Journal of Quaternary Science. - : Wiley. - 1099-1417 .- 0267-8179. ; 26:1, s. 109-117
  • Tidskriftsartikel (refereegranskat)abstract
    • The Les Echets sediment sequence has recently been the subject of a high-resolution, multi-proxy study which revealed shifts in lake productivity linked to Greenland stadials and interstadials over the last 40 kyr (Wohlfarth et al., 2008. Rapid ecosystem response to abrupt climate changes during the last glacial period in western Europe, 40-16 ka. Geology 36:407-410). Here we present new elemental data for this sequence as acquired using an XRF core scanning system which provides in situ high-resolution, continuous, multi-element analyses. It was found that the strength of associations between the studied elements (Ti, Rb, K, Zr, Si, Ca, Sr, Mn and Fe) varied over time with changes in lake status which are ultimately driven by changes in climate. Increases in fine grained, detrital input (as indicated by Ti, Rb, K and Zr/Rb) overlap with independently established periods of lower lake productivity and are interpreted to represent more arid conditions. Several of these arid periods are coincident with low diatom concentrations and the timing of Heinrich events H4, H3 and H2. The duration of the environmental impacts linked to the H events varied based on the proxy used with the elemental data (Ti and Zr/Rb) estimating shorter events than the diatom data. Periods of lower detrital input and coarser grain sizes agreed in time with periods of higher lake productivity. The elemental data provides new insight into hydrological changes and related sediment processes within the catchment, and highlights the need for multi-element and multi-proxy approaches when reconstructing climate change using lacustrine sediment sequences. 
  •  
34.
  • Kylander, malin, et al. (författare)
  • Impact of automobile emissions on the levels of platinum and lead in Accra, Ghana
  • 2003
  • Ingår i: Journal of Environmental Monitoring. - : Royal Society of Chemistry (RSC). - 1464-0333 .- 1464-0325. ; 5:1, s. 91-95
  • Tidskriftsartikel (refereegranskat)abstract
    • Examination of car fleet records in Accra demonstrates an increasing proportion of catalytic converter-equipped cars in the relatively old car fleet (average age 13 years) due to their import from developed countries. However, only leaded petrol is sold in Ghana. Lead anti-knocking additives, which are known to affect catalyst activity and promote thermal sintering and mechanical abrasion, may increase Pt emissions. This possible synergism prompted the concomitant determination of Pb and Pt levels in road dust and roadside soils in Ghana. Both metals followed traffic density with higher concentrations in urban areas compared to remote sites. In urban areas, the range for Pb (365 ± 93 µg g1 for dust and 291 ± 76 µg g1 for soil) reflects pre-catalyst levels in Europe and the US, while the range for Pt (39 ± 24 ng g1 for dust and 15 ± 5.3 ng g1 for soil) is typical for the same countries. The elevated Pt concentrations were unexpected due to recent introduction of catalysts to Ghana compared to the prolonged use of catalysts in Europe and the US.
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35.
  • Kylander, malin, et al. (författare)
  • Lead Penetration and Leaching in a Complex Temperate Soil Profile
  • 2008
  • Ingår i: Environmental Science & Technology. ; 42:9, s. 3177-3184
  • Tidskriftsartikel (refereegranskat)abstract
    • The documented loss of anthropogenic Pb from soil organic horizons and its migration into the mineral soil below has raised several environmental concerns, especially over the leaching of Pb into groundwater aquifers and subsequently into other environmental compartments of the ecosystem. Here, a complex colluvial soil formed over the last 10,000 years in NW Spain is studied. The objective is to evaluate the behavior of Pb in soils, including its migration rates and the potential use of complex soils as archives of atmospheric Pb pollution. To this end, Pb concentrations and Pb isotope ratios for total soil, and for acid-extractable (0.5 M HNO3) and residual fractions were determined. We show that the acid-extractable fraction is more radiogenic than the residual one in most of the soil profile and that this relationship is reversed in the surface layers (
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36.
  • Kylander, Malin M, et al. (författare)
  • Geochemical responses to paleoclimatic changes in southern Sweden since the late glacial : the Hasseldala Port lake sediment record
  • 2013
  • Ingår i: Journal of Paleolimnology. - : Springer Science and Business Media LLC. - 0921-2728 .- 1573-0417. ; 50:1, s. 57-70
  • Tidskriftsartikel (refereegranskat)abstract
    • There is a relatively good understanding of the paleoenvironmental changes that have occurred in southern Sweden since the Late Glacial. A main exception, however, is the sedimentary response of lacustrine systems during this period of rapid climate shifts. To address this, high-resolution X-ray fluorescence core scanning, Total Organic Carbon (TOC), C/N and delta C-13 analyses were made on a core from Hasseldala Port, a paleolake in the region. Site-specific geochemical analyses documented variations in silicate inputs (Zr/Ti, Si/Ti, K/Ti and K/Rb), productivity (TOC, Ca/Ti and Sr/Ti), as well as redox conditions in the sediment (delta C-13, Mn/Ti and Fe/Ti), which were then linked to the regional climatic framework. During the Bolling/Older Dryas sediment accumulation was at its highest, particularly prior to colonization by terrestrial vegetation, and hydrological transport dominated. No clear signal of the Older Dryas was detected in the elemental chemistry. The Allerod was a period of relatively constant sediment accumulation, with the exception of during the Gerzensee oscillation when rates increased. There is evidence for increased within-lake and -catchment productivity and a change in silicate source during parts of the Allerod. As opposed to other records from the region, constant sediment accumulation rates were found during the Younger Dryas. Other proxies also suggest that this was a rather static period at Hasseldala Port. A gradual change in productivity and hydrological activity was observed from 12,000 cal year BP. The Preboreal section is rather short but the geochemical response was similar to that seen during other periods with milder climate conditions. The geochemical record archived in the sediments at Hasseldala Port was found to be the integrated result of physical erosion, landscape and soil development, vegetation changes, basin hydrology and moisture and temperature variations and it fills an important information gap in our understanding of the geochemical response of lake sediments to past climate change.
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37.
  • Kylander, Malin M, et al. (författare)
  • Recommendations for using XRF core scanning as a tool in tephrochronology
  • 2012
  • Ingår i: The Holocene. - : Sage. - 0959-6836 .- 1477-0911. ; 22:3, s. 371-375
  • Tidskriftsartikel (refereegranskat)abstract
    • X-ray fluorescence (XRF) core scanning is a relatively new arrangement of a classic analytical technique which allows for non-destructive, in situ XRF analysis of sediment cores from submillimetre resolution upwards. In this contribution we explore the use of XRF core scanning for tephrochronology based on the analysis of three gyttja-rich sediment cores from the Faroe Islands. Using a combination of optical and radiographic images, analytical parameters and elemental profiles (Si, K, Ca, Ti, Mn, Fe, Sr and Zr), higher concentration basaltic tephra layers (>1000 shards/cm3) were positively identified. The XRF core scanning did not capture the lower concentration (<850 shards/cm3) rhyolitic layers found in the core. The elemental data generated for the detected tephra layers using XRF core scanning was not comparable to individual shard analysis by electron microprobe. We recommend using XRF core scanning for tephra screening in order to localize depths for high-resolution subsampling and to avoid depths where sediment mixing has caused tailing/mixing of the tephra signal. At the studied site the basaltic Saksunarvatn ash as well as a tephra belonging to the Askja-S/10 ka eruption were identified.
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38.
  • Kylander, Malin, 1977-, et al. (författare)
  • Natural lead isotope variations in the atmosphere
  • 2010
  • Ingår i: Earth and Planetary Science Letters. - : Elsevier BV. - 0012-821X .- 1385-013X. ; 290:1-2, s. 44-53
  • Tidskriftsartikel (refereegranskat)abstract
    • Stable lead (Pb) isotope data from pre-contamination peat sections has the potential to contribute to our understanding of earth system processes (e.g., atmospheric circulation, erosion, volcanic activity) in the past. Key questions arise however. Can the Pb isotopes archived in peat records be used for assessing aerosol dynamics on a hemispheric scale or do they mainly reflect inputs from local soils? What natural Pb sources are important and do contributions vary over time? In order to answer these questions we have synthesized all available Pb isotope data from pre-contamination peat sections in Europe, Australia, North America and South America. We specifically examine the spatial and temporal variability of the Pb isotope records and identify regionally important trends and Pb sources. A pooling of all available pre-contamination peat data generated an average natural 206Pb/207Pb background ratio of 1.21±0.05 (2σ, n=300)(206Pb/204Pb= 18.90±0.86, 207Pb/204Pb= 15.66±0.10 and 208Pb/204Pb= 38.74±0.57, n=207). The majority of the records showed limited temporal and compositional agreement, suggesting that the peat record receives mainly inputs from local (<10 km) and/or regional (10-500 km) sources. Three-isotope plots also support local and regional control and evidence a wide natural spread at some sites, particularly those located in radiogenic geological settings. A temporally synchronous isotope excursion to values between 1.16-1.18 at sites across Europe ca 4000-3000 B.C. was detected, however. While usually associated with anthropogenic sources, there are indeed natural aerosols having 206Pb/207Pb signatures as low as 1.16 as evidenced in several peat and ice core records globally. Three-isotope plots suggest that this unlikely to be a signal of mineral dust contributions, which tend to have 206Pb/207Pb ratios ≥1.19, but rather sourced to volcanic emissions. These results stress caution when using estimates of the upper continental crust to constrain natural Pb sources in, e.g., mixing equations. Considering the strong influence from local and regional sources on Pb-containing aerosols in the peat record, the assessment of aerosol dynamics at lower latitudes is likely best achieved using a compliment of archives rather than just polar ice cores, for example. 
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39.
  • Kylander, Malin, 1977-, et al. (författare)
  • The Itrax and organic rich sediments: Tephrochronologyand humification
  • 2010
  • Konferensbidrag (refereegranskat)abstract
    • Holocene records of climate change can be derived from organic rich sediments such as peats (with organic contents >99%) and gyttja rich lake sediments. While the performance of the Itrax is generally negatively affected by higher organic matter contents, we are currently developing two separate Itrax applications for such sediments. Tephras are an important part of establishing good chronologies for Holocene sequences. Tephras can vary in thickness from a few centimeters to a few shards thick. Finding crypotephra (i.e., those tephra not visible to the naked eye) is a time consuming process involving tedious sub-sampling and density separations. In order to improve the efficiency of tephra extraction we are developing a method to ‘screen’ sediment cores for tephra. Using small step sizes (<1 mm), we identify areas where changes in the sample matrix (signaled through changes in the mean standard error) and elemental chemistry suggest the possible presence of tephra. These ‘target depths’ are then sub-sampled at a higher resolution (1 cm vs. 5 cm) for tephra extraction. To date we have tested three different sites and shard counts made at target depths shows that the Itrax can successfully locate both rhyolitic and basaltic tephra layers. In those cores with visible tephra, we are also testing the possibility of using major element concentrations from Itrax scans to make preliminary identifications of tephra layers through their elemental fingerprints. The Itrax generated plots are tested for accuracy by comparing them against conventional electron microprobe analyses of traditionally extracted tephra shards. Humification analyses reflect the level of decomposition of an organic deposit which in itself signals changes in evaporation/precipitation and temperature regimes, and by extension, paleo-climate. At present humification is measured through leaching of samples and the use of a colorimeter. We are developing the use of the Itrax to capture major changes in humification by using the ratio of coherent to incoherent scattering.
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40.
  • Kylander, Malin, et al. (författare)
  • Two high resolution terrestrial records of atmospheric Pb deposition from New Brunswick, Canada, and Loch Laxford, Scotland
  • 2009
  • Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 407:5, s. 1644-1657
  • Tidskriftsartikel (refereegranskat)abstract
    • Environmental archives like peat deposits allow for the reconstruction of both naturally and anthropogenically forced changes in the biogeochemical cycle of Pb and the quantification of past and present atmospheric Pb pollution. Records of atmospheric Pb deposition from pre-industrial times however, are lacking.                 In a publication by Weiss et al. (2002) Pb isotope data measured by Q-ICP-MS and TIMS, concentration and enrichment data was presented for sites in eastern Canada (PeW1) and northwestern Scotland (LL7c), dating to 1586 A.D and 715 A.D., respectively. Here we re-analyse these same cores for Pb isotopes by MC-ICP-MS thereby acquiring 204Pb data and improving on the original data in terms of resolution and temporal coverage. Significant differences were found between the Q-ICP-MS/TIMS and MC-ICP-MS measurements, particularly at PeW1. These discrepancies are attributed to the problematic presence of organic matter during sample preparation and analysis compounded by the heterogeneity of the organic compounds that survived sample preparation steps. The precision and accuracy of Pb isotopes in complex matrices like peat is not always well estimated by industrial standards like NIST-SRM 981 Pb.                 Lead pollution histories at each site were constructed using the MC-ICP-MS data. The entire LL7c record is likely subject to some amount of anthropogenic pollution. Contributions from local mining were detected in Medieval times. Later, coal use and mining in Scotland, Wales and England became important. After industrialization (ca. 1885 A.D.) contributions from Broken Hill type ores and hence, leaded petrol, dominate atmospheric Pb signatures right up to modern times. At PeW1 anthropogenic impacts are first distinguishable in the late 17th century with the mining and use of local coal. After industrialization (ca. 1810 A.D.), coal and petrol are the main Pb sources. A comprehensive estimate of the natural atmospheric background 206Pb/207Pb signature in eastern Canadian aerosols is made with a value of ~1.19.
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41.
  • Kylander, Malin, et al. (författare)
  • Using Peatlands as Archives of Dust Deposition : A Preliminary Record from Southern Sweden
  • 2010
  • Ingår i: European Geosciences Union. ; , s. 2677-
  • Konferensbidrag (refereegranskat)abstract
    • Our understanding of the complex role that mineral dust and its feedbacks play in the Earth's climate system is limited by its highly variable nature in space and time and a lack of data reflecting this variability. Paleorecords of dust provide a means by which we can examine the response of dust over time under very different climatic conditions. These records also supply the data (dust deposition rates, grain size, mineralogy and provenance) necessary to validate models of the dust cycle. Ombrotrophic peat is hydrologically isolated and therefore, like ice, records atmospheric deposition alone. Peatlands have a wide distribution globally, particularly in formerly glaciated regions, and are established environmental archives which provide continuous, high-resolution, datable records of atmospheric deposition and climate change. The use of peat for reconstructing dust deposition has been demonstrated, but as yet, not systematically examined. Their use as an archive of dust deposition must be further tested before they can be used to improve on the relatively poor spatial coverage of current terrestrial dust records (e.g., loess, lake sediments, dune building records). We present here a first focussed effort to reconstruct past changes in dust deposition through loss on ignition (LOI), bulk density, humification and inorganic geochemistry data using a peat sequence from Store Mosse in southern Sweden. This deposit has been studied previously and reveals a record that extends back some 5000 years. LOI data, in combination with elemental chemistry of the samples, aids in identifying those depths where the observed signal is atmospheric in source only. Humification analyses and bulk density are used as a proxy for surface wetness and allows for the linking of broader climatic changes (precipitation, evaporation, temperature) with fluctuations in dust deposition rates and changes in grain character (grain size, surface roughness). The inorganic geochemistry provides a means to quantify dust deposition as well as make a first attempt at source tracing of the deposited materials; this is important in terms of reconstructing changes in paleo wind regimes. Past variations in aeolian activity in Scandinavia are relatively unknown. Dune building records from Denmark and elsewhere around Europe show several periods of inland sand invasion and dune building during the Holocene. These are linked to cooler and stormier climates caused by shifts in the North Atlantic Oscillation and/or movement of the polar front. We compare the dust deposition record from Store Mosse with available dune building records and records of storminess from the region in order to make a preliminary assessment of the use of peatlands as paleo records of dust deposition.
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42.
  • Large, DJ, et al. (författare)
  • The influence of climate, hydrology and permafrost on Holocene peat accumulation at 3500 m on the eastern Qinghai-Tibetan plateau
  • 2009
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 28:27-28, s. 3303-3314
  • Tidskriftsartikel (refereegranskat)abstract
    • Peatland of the eastern Qinghai–Tibetan Plateau lies at the convergence of the East Asian and Indian monsoon systems in eastern Asia. To understand the evolution of this peatland and its potential to provide new insights into the Holocene evolution of the East Asian monsoon a 6 m peat core was collected from the undisturbed central part of a peat deposit near Hongyuan. The age-depth profile was determined using 16 14C-AMS age dates, the peat analysed for a range of environmental variables including carbon, nitrogen and hydrogen concentration, bulk density, δ13C and the associated spring water analysed for hydrogen and oxygen isotopes. The age-depth profile of the recovered peat sequence covers the period from 9.6 to 0.3 kyr BP and is linear indicating that the conditions governing productivity and decay varied little over the Holocene. Using changes in carbon density, organic carbon content and its δ13C, cold dry periods of permafrost characterised by low density and impeded surface drainage were identified. The low δ18O and δD values of the spring water emanating around the peat deposit, down to −13.8 and −102‰ (VSMOW), respectively, with an inverse relationship between electrical conductivity and isotopic composition indicate precipitation under colder and drier conditions relative to the present day. In view of the current annual mean air temperature of 1 °C this suggests conditions in the past have been conducive to permafrost. Inferred periods of permafrost correspond to independently recognised cold periods in other Holocene records from across China at 8.6, 8.2–7.8, 5.6–4.2, 3.1 and 1.8–1.5 kyr BP. The transition to a cold dry climate appears to be more rapid than the subsequent recovery and cold dry periods at Hongyuan are of longer duration than equivalent cold dry periods over central and eastern China. Light–dark banding peat on a scale of 15–30 years from 9.6 to 5.5 kyr BP may indicate a strong influence of decadal oscillations possibly the Pacific Decadal Oscillation and a potential link between near simultaneous climatic changes in the northwest Pacific, ENSO, movement of the Intertropical Convergence Zone and the East Asian Monsoon.
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43.
  • Larsson, Simon A., 1990-, et al. (författare)
  • Synchronous or Not? The Timing of the Younger Dryas and Greenland Stadial-1 Reviewed Using Tephrochronology
  • 2022
  • Ingår i: Quaternary. - : MDPI AG. - 2571-550X. ; 5:2
  • Tidskriftsartikel (refereegranskat)abstract
    • The exact spatial and temporal behaviour of rapid climate shifts during the Last Glacial– Interglacial Transition are still not entirely understood. In order to investigate these events, it is necessary to have detailed palaeoenvironmental reconstructions at geographically spread study sites combined with reliable correlations between them. Tephrochronology, i.e., using volcanic ash deposits in geological archives as a dating and correlation tool, offers opportunities to examine the timing of events across wider regional scales. This study aims to review the posited asynchrony of the Younger Dryas stadial in comparison with Greenland Stadial-1 by correlating new proxy data from southernmost Sweden to previous palaeoclimate reconstructions in Europe based on the presence of the Hässeldalen Tephra, the Vedde Ash, and the Laacher See Tephra. µ-XRF core-scanning data were projected using a recently published age–depth model based on these tephras and several radiocarbon dates, and compared to previous findings, including by adapting previous chronologies to the recently proposed earlier date of the Laacher See Tephra (13,006 ± 9 cal. a BP). Although the results to some extent support the idea of a more synchronous Younger Dryas event than previously assumed, this issue requires further high-resolution proxy studies to overcome limitations of temporal precision.
  •  
44.
  • Larsson, Simon, et al. (författare)
  • Synchronous or not? The timing of the Younger Dryas and Greenland Stadial-1 reviewed by tephrochronology
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • The exact spatial and temporal behaviour of rapid climate shifts during the Last Glacial–Interglacial Transition are still not entirely understood. In order to investigate these events, it is necessary to have detailed palaeoenvironmental reconstructions at geographically spread study sites combined with reliable correlations between them. Tephrochronology, i.e. using volcanic ash deposits in geological archives as a dating and correlation tool, offers opportunities to examine the timing of events across wider-regional scales. This study aims to review the posited asynchrony of the Younger Dryas stadial in comparison to Greenland Stadial-1 by correlating new proxy data from southernmost Sweden to previous palaeoclimate reconstructions in Europe based on the presence of the Hässeldalen Tephra, the Vedde Ash, and the Laacher See Tephra. μ-XRF core-scanning data were projected using a recently published age–depth model based on these tephras and several radiocarbon dates, and compared to previous findings, including by adapting previous chronologies to the recently proposed earlier date of the Laacher See Tephra (13,006 ± 9 cal. a BP). Although the results to some extent support the idea of a more synchronous Younger Dryas event than previously assumed, this issue requires further high-resolution proxy studies to overcome limitations of temporal precision.
  •  
45.
  • Lind, Ewa, 1968-, et al. (författare)
  • Lacustrine response to short rapid climate shifts during Late Younger Dryas-Early Holocene in Central Norway, registred by XRF and stable isotopes
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • There is relatively good knowledge about the climate and the deglaciation pattern during the Late Glacial-Early Holocene transitionin Norway. The origin and mechanisms behind the short, rapid climate shifts that occurred during this period are however notwell known. In this context climate studies in this region can contribute to our understanding of climate patterns. Our specificobjectives in this study were to compare the geochemical response of lake sediments during Late Younger Dryas-Early Holoceneto the general picture of deglaciation in Central Norway and also to evaluate if the Preboreal oscillation (PBO), the Erdalen events,the 9.3 and 8.2 ka cal BP could be detected, superimposed on the general Late Glacial-Early Holocene climate. To address this; highresolutionXRF fluorescence core-scanning, Total organic carbon (TOC), carbon/nitrogen (C/N), stable isotopes of carbon andnitrogen (δ13C, δ15N) and total nitrogen (TN) were made on a palaeolake core from Grønlia fen situated on the Fosen peninsula,Central Norway. The reconstructed Late Younger Dryas-Early Holocene climate from the Grønlia record was noteworthily similarto other reconstructions from the region. The Younger Dryas-Preboreal transition was dated to c. 11 420 cal a BP and five climateshifts were identified in the Early Holocene; c. 11 190 cal a BP, 10 500 cal a BP, 10 200 cal a BP, 9900 cal a BP and 9250 cal a BP.
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46.
  • Lind Mettävainio, Ewa, 1968-, et al. (författare)
  • New Early Holocene tephra horizons from the Faroe Islands
  • 2010
  • Ingår i: International Field Conference and Workshop on Tephrochronology, Volcanism and Human Activity.. ; , s. 60-
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • The early Holocene climate in the North Atlantic region was rather unstable and three cold events superimposed upon a general warming took place during the earliest part of the Holocene: the Preboreal oscillation (11.3-11.1 ka BP), the Erdalen event (10.3-10.2 ka BP) and the 9.3 ka BP event (e.g. Dahl et al., 2002; Rasmussen et al. 2007). There is relatively little known about early Holocene tephrochronology in comparison to the Last Glacial/Interglacial transition and the mid to late Holocene, although there is no reason to believe that Icelandic eruptions were less frequent during the early Holocene. The main focus of the present study is improve the dating and geochemical identification of early Holocene tephras on the Faroe Islands, using wiggle-match or Bayesian techniques for age-depth modelling and EMPA analyses for geochemical fingerprinting of tephras. Identification of tephras is also aided by XRF core scanning. While this method is still in its infancy, some promising results have been reported recently regarding the identification of cryptotephra in marine and lacustrine sediments. The Faroe Islands is an ideal area to test the method, since tephras ranging from basaltic to rhyolitic are abundant but usually not visible to the naked eye (Wastegård, 2002). We have investigated new cores taken in 2009 from previously studied sites and new sites with high sediment accumulation rates during the early Holocene. Results from the first analyzed peat and lake sediment cores from the Faroe Islands show that several previously unreported tephra horizons occur below the visible Saksunarvatn tephra dated to c. 10 300 cal. yr BP (Rasmussen et al. 2007). Two layers are rhyolitic, one dacitic and one basaltic. The XRF core-scanner data has been especially useful for identifying basaltic cryptotephra horizons.
  •  
47.
  • Ljung, Karl, et al. (författare)
  • The last termination in the central South Atlantic
  • 2015
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 123, s. 193-214
  • Tidskriftsartikel (refereegranskat)abstract
    • Lake sediments and peat deposits from two basins on Nightingale Island (37 degrees S), in the Tristan da Cunha archipelago, South Atlantic, have been analyzed. The studies were focused on the time period 16.2-10.0 cal ka BP, determined by 36 C-14 dates from the two sequences. A wide variety of proxies were used, including pollen and diatom analyzes, biogenic silica content, C and N analyzes, stable isotopes (C-13 and N-15), elemental concentrations and magnetic susceptibility measurements, to detect environmental changes that can be related to shifts of the circulation belts of the Southern Ocean. In addition, climate model simulations were carried out. We find that the sediments are underlain by a >2 cal ka BP long hiatus, possibly representing a dried-out lake bed. The climate simulations corroborate that the area might have been exposed to arid conditions as a consequence of the Heinrich I event in the north and a southward displacement of the ITCZ. The development on the island after 16.2 cal ka BP is determined by the position of the Subtropical Front (STF) and the Southern Hemisphere Westerlies (SHW). The period 16.2-14.75 cal ka BP was characterized by varying influence from SHW and with STF situated south of Tristan da Cunha, ending with a humidity peak and cooler conditions. The stable conditions 14.7-14.1 cal ka BP with cool and fairly arid conditions imply that STF and SHW were both north of the islands during the first part of the Antarctic Cold Reversal. The most unstable period, 14.1-12.7 cal ka BP, indicates incessant latitudinal shifts of the zonal circulation, perhaps related to climate variability in the Northern Hemisphere and bipolar seesaw mechanisms as the strength of the Atlantic Meridional Overturning Circulation (AMOC) varied. At 12.7 cal ka BP the Holocene warming began with a gradually drier and warmer climate as a result of a dampened AMOC during the Younger Dryas cooling in the north with ITCZ, STF and SHW being displaced southwards. Peak warming seems to have occurred in the earliest part of the Holocene, but this period was also characterized by humidity shifts, possibly an effect of retraction and expansion phases of SHW during AMOC variations in the north. (C) 2015 Elsevier Ltd. All rights reserved.
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48.
  • Lopez-Costas, Olalla, et al. (författare)
  • Human bones tell the story of atmospheric mercury and lead exposure at the edge of Roman World
  • 2020
  • Ingår i: Science of the Total Environment. - : Elsevier. - 0048-9697 .- 1879-1026. ; 710
  • Tidskriftsartikel (refereegranskat)abstract
    • Atmospheric metal pollution is a major health concern whose roots pre-date industrialization. This study pertains the analyses of ancient human skeletons and compares them with natural archives to trace historical environmental exposure at the edge of the Roman Empire in NW Iberia The novelty of our approach relies on the combination of mercury, lead and lead isotopes. We found over a 700-year period that rural Romans incorporated two times more mercury and lead into their bones than post-Romans inhabiting the same site, independent of sex or age. Atmospheric pollution sources contributed on average 57% (peaking at 85%) of the total lead incorporated into the bones in Roman times, which decreased to 24% after the decline of Rome. These values and accompanying changes in lead isotopic composition mirror changes in atmospheric Pb deposition recorded in local peatlands. Thus, skeletons are a time-transgressive archive reflecting contaminant exposure.
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49.
  •  
50.
  • Löwemark, Ludvig, et al. (författare)
  • Normalizing XRF-scanner data : A cautionary note on the interpretation of high-resolution records from organic-rich lakes
  • 2011
  • Ingår i: Journal of Asian Earth Sciences. - : Elsevier BV. - 1367-9120 .- 1878-5786. ; 40:6, s. 1250-1256
  • Tidskriftsartikel (refereegranskat)abstract
    • X-ray fluorescence (XRF) scanning of unlithified, untreated sediment cores is becoming an increasingly common method used to obtain paleoproxy data from lake records. XRF-scanning is fast and delivers high-resolution records of relative variations in the elemental composition of the sediment. However, lake sediments display extreme variations in their organic matter content, which can vary from just a few percent to well over 50%. As XRF scanners are largely insensitive to organic material in the sediment, increasing levels of organic material effectively dilute those components that can be measured, such as the lithogenic material (the closed-sum effect). Consequently, in sediments with large variations in organic material, the measured variations in an element will to a large extent mirror the changes in organic material. It is therefore necessary to normalize the elements in the lithogenic component of the sediment against a conservative element to allow changes in the input of the elements to be addressed. In this study we show that Al, which is the lightest element that can be measured using the Wax XRF-scanner, can be used to effectively normalize the elements of the lithogenic fraction of the sediment against variations in organic content. We also show that care must be taken when choosing resolution and exposure time to ensure optimal output from the measurements.
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