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  • 1.
    Berntsson, Annika
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Rosqvist, Gunhild C.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Velle, Gaute
    Late-Holocene temperature and precipitation changes in Vindelfjallen, mid-western Swedish Lapland, inferred from chironomid and geochemical data2014In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 24, no 1, p. 78-92Article in journal (Refereed)
    Abstract [en]

    In this article, we present results from a palaeolimnological study from Lake Vuoksjavratje in the mountain tundra region in the Vindelfjallen Mountains, northwest Sweden. We suggest that the influence of precipitation may be one of the factors causing discrepancies between chironomid-based late-Holocene July temperature (JulyT) reconstructions from Fennoscandia. We combine quantitative temperature reconstruction using chironomids for the last 5100 years with qualitative analysis of chironomid composition and geochemical analyses, such as x-ray fluorescence (XRF), total organic carbon (TOC) and C/N analysis. The studied sequence is dated by Pb-210, Cs-137 and 11 C-14 datings from terrestrial macrofossils. The aim of the study was to use chironomids to reconstruct late-Holocene summer temperature variation on a multi-centennial to centennial timescale and to use geochemical data to identify periods during which the changes in chironomid composition might have been forced by environmental variables other than temperature, such as within lake processes or precipitation. Based on ordination techniques, and a comparison between chironomid-inferred JulyTs and changes in minerogenic sedimentation with regional temperature and wetness records, it is concluded that the JulyT signal was modulated by precipitation. The proxies indicate that both JulyT and annual precipitation have influenced the chironomid communities in Lake Vuoksjavratje, and that catchment-related processes caused by enhanced precipitation have overridden the summer temperature signal between 3000 and 2200 cal. yr BP, and between 1050 and 100 cal. yr BP.

  • 2. Björklund, Jesper
    et al.
    Gunnarson, Björn E.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Seftigen, Kristina
    Zhang, Peng
    Linderholm, Hans W.
    Using adjusted Blue Intensity data to attain high-quality summer temperature information: A case study from Central Scandinavia2015In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 25, no 3, p. 547-556Article in journal (Refereed)
    Abstract [en]

    The inexpensive Blue Intensity proxy has been considered a complement or surrogate to maximum latewood density (MXD), but is associated with biases from differential staining between sapwood and heartwood and also between deadwood samples and living-wood samples that compromise centennial-scale information. Here, we show that, with some minor adjustments, Blue Intensity (BI) is comparable with MXD or Density (=the difference or contrast between latewood and earlywood density) in dendroclimatological reconstructions of summer temperatures in the Central Scandinavian region, using Pinus sylvestris L. (Scots pine), on annual and multi-centennial timescales. By using BI, this bias is significantly reduced, but the contrast between earlywood and latewood in BI is altered with degree of staining, while for density it is not. Darker deadwood samples have a reduced contrast compared with the lighter living-wood samples that make BI and Density chronologies diverge. Here, we quantify this behaviour in BI and offer an adjustment that can reduce this bias. The adjustment can be derived on independent samples, so in future work on BI, parallel density measurements are not necessary. We apply this methodology to two Central Scandinavian Scots pine chronologies that averaged into a composite is able to reconstruct summer temperatures with an explained variance in excess of 60% in each verification period using a split sample calibration verification procedure. Although the amount of data used to derive this contrast adjustment produces desirable results, more tests are needed to confirm its performance, and we suggest that future work on the BI proxy should aim for a small subset of parallel BI and density measurements while the bulk of the data is only measured with the BI technique. This is to ensure that the adjustment is continuously updated with new data and that the conclusions derived here are robust.

  • 3.
    Chawchai, Sakonvan
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Chulalongkorn University, Thailand.
    Yamoah, Kweku Afrifa
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Smittenberg, Rienk H.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kurkela, Janita
    Väliranta, Minna
    Chabangborn, Akkaneewut
    Stockholm University, Faculty of Science, Department of Geological Sciences. Chulalongkorn University, Thailand.
    Blaauw, Marten
    Fritz, Sherilyn C.
    Reimer, Paula J.
    Wohlfarth, Barbara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Lake Kumphawapi revisited – a synthesis of Holocene environmental and climatic changes for NE Thailand2016In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 26, no 4, p. 614-626Article in journal (Refereed)
    Abstract [en]

    Kumphawapi, which is Thailand’s largest natural freshwater lake, contains a >10,000-year-long climatic and environmental archive. New data sets (stratigraphy, chronology, hydrogen isotopes, plant macrofossil and charcoal records) for two sedimentary sequences are here combined with earlier multi-proxy studies to provide a comprehensive reconstruction of past climatic and environmental changes for Northeast Thailand. Gradually higher moisture availability due to a strengthening of the summer monsoon led to the formation of a large shallow lake in the Kumphawapi basin between >10,700 and c. 7000 cal. BP. The marked increase in moisture availability and lower evaporation between c. 7000 and 6400 cal. BP favoured the growth and expansion of vegetation in and around the shallow lake. The increase in biomass led to gradual overgrowing and infilling, to an apparent lake level lowering and to the development of a wetland. Multiple hiatuses are apparent in all investigated sequences between c. 6500 and 1400 cal. BP and are explained by periodic desiccation events of the wetland and erosion due to the subsequent lake level rise. The rise in lake level, which started c. 2000 cal. BP and reached shallower parts c. 1400 cal. BP, is attributed to an increase in effective moisture availability. The timing of hydroclimatic conditions during the past 2000 years cannot be resolved because of chronological limitations.

  • 4. Cunningham, Laura K.
    et al.
    Austin, William E. N.
    Knudsen, Karen Luise
    Eiriksson, Jon
    Scourse, James D.
    Wanamaker, Alan D., Jr.
    Butler, Paul G.
    Cage, Alix G.
    Richter, Thomas
    Husum, Katrine
    Hald, Morten
    Andersson, Carin
    Zorita, Eduardo
    Linderholm, Hans W.
    Gunnarson, Björn E.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Swedish University of Agricultural Sciences, Sweden.
    Sicre, Marie-Alexandrine
    Sejrup, Hans Petter
    Jiang, Hui
    Wilson, Rob J. S.
    Reconstructions of surface ocean conditions from the northeast Atlantic and Nordic seas during the last millennium2013In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 23, no 7, p. 921-935Article in journal (Refereed)
    Abstract [en]

    We undertake the first comprehensive effort to integrate North Atlantic marine climate records for the last millennium, highlighting some key components common within this system at a range of temporal and spatial scales. In such an approach, careful consideration needs to be given to the complexities inherent to the marine system. Composites therefore need to be hydrographically constrained and sensitive to both surface water mass variability and three-dimensional ocean dynamics. This study focuses on the northeast (NE) North Atlantic Ocean, particularly sites influenced by the North Atlantic Current. A composite plus regression approach is used to create an inter-regional NE North Atlantic reconstruction of sea surface temperature (SST) for the last 1000 years. We highlight the loss of spatial information associated with large-scale composite reconstructions of the marine environment. Regional reconstructions of SSTs off the Norwegian and Icelandic margins are presented, along with a larger-scale reconstruction spanning the NE North Atlantic. The latter indicates that the Medieval Climate Anomaly' warming was most pronounced before ad 1200, with a long-term cooling trend apparent after ad 1250. This trend persisted until the early 20th century, while in recent decades temperatures have been similar to those inferred for the Medieval Climate Anomaly'. The reconstructions are consistent with other independent records of sea-surface and surface air temperatures from the region, indicating that they are adequately capturing the climate dynamics of the last millennium. Consequently, this method could potentially be used to develop large-scale reconstructions of SSTs for other hydrographically constrained regions.

  • 5. Delmonte, Barbara
    et al.
    Winton, Holly
    Baroni, Melanie
    Baccolo, Giovanni
    Hansson, Margareta
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Andersson, Per
    Baroni, Carlo
    Salvatore, Maria Cristina
    Lanci, Luca
    Maggi, Valter
    Holocene dust in East Antarctica: Provenance and variability in time and space2019In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, article id UNSP 0959683619875188Article in journal (Refereed)
    Abstract [en]

    In this paper, we provide a comprehensive overview of the state-of-knowledge of dust flux and variability in time and space in different sectors of East Antarctica during the Holocene. By integrating the literature data with new evidences, we discuss the dust flux and grain-size variability during the current interglacial and its provenance in the innermost part of the East Antarctic plateau as well as in peripheral regions located close to the Transantarctic Mountains. The local importance of aeolian mineral dust aerosol deflated from low-elevation areas of peripheral East Antarctica is also discussed in the light of new data from several coastal, low-elevation sites.

  • 6. Ekblom, Anneli
    et al.
    Risberg, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Coastal forest and Miombo woodland history of the Vilankulo region, Mozambique2014In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 24, no 3, p. 284-294Article in journal (Refereed)
    Abstract [en]

    The present day distribution of Miombo savanna-woodland in Mozambique has been attributed to an expansion due to the clearing of original coastal forests through agriculture and use of fire. Here, we test this hypothesis using palaeoecological data from Lake Nhauhache, situated in the Vilankulo region. Our analysis shows that Brachystegia, one of the main constituents of the Miombo, has varied over time, and its variability seems to be driven by hydrological changes related to climatic variability rather than by land-use changes. The analyses show that Brachystegia was most common during ad 200-700 when a marshy forest/shrub community was dominant. After ad 700, this community changes to a dominance of Syzygium and Fagara linked to gradually rising water levels. Brachystegia remains in low abundance and fluctuating over time. From ad 1000, a general decline in trees/shrubs in favour of grasses concurs with an increase in grass pollen (possibly cereal) and charcoal, most probably as a result of farming activities. The decline in tree taxa was probably exacerbated by periodic droughts after c. ad 1200 as indicated by the diatom assemblage. In the period ad 1700 to late 1800, arboreal pollen is well represented, and this is concurrent with the diatom record suggesting high lake levels.

  • 7. Erbs-Hansen, Dorthe Reng
    et al.
    Knudsen, Karen Luise
    Gary, Anthony Cavedo
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jansen, Eystein
    Holocene climatic development in Skagerrak, eastern North Atlantic: Foraminiferal and stable isotopic evidence2012In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 22, no 3, p. 301-312Article in journal (Refereed)
    Abstract [en]

    A high-resolution multiproxy study of core MD99-2286 reveals a highly variable hydrographic environment in the Skagerrak from 9300 cal. yr BP to the present. The study includes foraminiferal faunas, stable isotopes and sedimentary parameters, as well as temperature and salinity reconstructions of a c. 29 m long radiocarbon-dated core record. The multivariate technique fuzzy c-means was applied to the foraminiferal counts, and it was extremely valuable in defining subtle heterogeneities in the foraminiferal faunal data corresponding to hydrographic changes. The major early-/mid-Holocene (Littorina) transgression led to flooding of large former land areas in the North Sea, the opening of the English Channel and Danish straits, and initiation of the modern circulation system. This is reflected by fluctuating C/N values and an explosive bloom of Hyalinea balthica. A slight indication of ameliorated conditions between 8000 and 5750 cal. yr BP is related to the Holocene Thermal Maximum. A subsequent increase in freshwater/Baltic water influence between 5750 and 4350 cal. yr BP is reflected by dominance of Bulimina marginata and depleted delta O-18 values. The Neoglacial cooling (after 4350 cal. yr BP) is seen in the Skagerrak as enhanced turbidity, increasing TOC values and short-term changes in an overall Cassidulina laevigata-dominated fauna suggesting a prevailing influence of Atlantic waters. This is in agreement with increased strength of westerly winds, as recorded for this period. The last 2000 years were also dominated by Atlantic Water conditions with generally abundant nutrient supply. However, during warm periods, particularly the 'Medieval Warm Period'and the modern warming, the area was subject to a restriction in the supply of nutrients and/or the nutrient supply had a more refractory character.

  • 8.
    Feurdean, Angelica
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Holocene forest dynamics in north-western Romania2005In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 15, no 3, p. 435-446Article in journal (Refereed)
    Abstract [en]

    Pollen analyses and AMS radiocarbon measurements were carried out on peat deposits from the former crater lake Preluca Tiganului, located in a mid-altitude area of the Gutaiului Mountains (NW Romania), in order to reconstruct the postglacial vegetation history. At the Lateglacial/Holocene transition the open vegetation was replaced by forest, suggesting a fast response to climatic warming. The rapid expansion of Pinus, Betula and later Picea may be due to their existence in the area during the Lateglacial. At approximately 11 250 cal. yr BP, the dense forest was composed primarily of Ulmus and some Picea, Betula and Pinus. A small population of Ulmus might also have survived in the area during the Lateglacial. At 10 750 cal. yr BP, Quercus, Tilia and Fraxinus, followed by Corylus at c. 10 200 cal. yr BP, expanded significantly in the forest. The delay of approximately 550 years in their establishment, as compared to the expansion of Ulmus, was probably due to their immigration from more distant localities. Between 9300 and 5750 cal. yr BP, the forest became denser and was composed of Corylus (dominating), Ulmus, Quercus, Tilia, Fraxinus and Picea. At 5750 cal. yr BP Carpinus became established and expanded, possibly as a response to higher temperatures. At 5200 cal. yr BP, Fagus became locally established, and expanded from about 4800 cal. yr BP, possibly as a result of moist climatic conditions, although human activities cannot be excluded. From 4000 cal. yr BP to the present, Fagus dominated the woodlands, and all other deciduous trees (except for Carpinus and Quercus) became greatly reduced. Evidence of human influence on the local vegetation is low for this time period, but becomes more evident in the pollen stratigraphy around 2300 cal. yr BP. This is reflected by a decrease in forest diversity and an increase in pasture and forest grazing.

  • 9.
    Finné, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Norström, Elin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Risberg, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Siliceous microfossils as Late Quaternary paleo-environmental indicators at Braamhoek wetland, South Africa2010In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 20, no 5, p. 747-760Article in journal (Refereed)
    Abstract [en]

    A peat-sequence covering the last 16 ka (16 000 cal. yr BP) from Braamhoek wetland, eastern South Africa, was analysed in terms of phytolith and diatom composition. The fossil peat was rich in phytoliths, while diatoms were less prominent, probably as a result of degradation during wetland plant growth associated with silica uptake. With this study we present the first continuous phytolith and diatom record from South Africa covering the Late Pleistocene and Holocene period. The phytolith assemblages indicate a clear dominance of C

    3-grasses within the wetland throughout the sequence. The fossil diatom record infer changes in past moisture conditions. Unlike the modern wetland, which is dominated by benthic and aerophilic diatoms, the Late Pleistocene– early Holocene wetland favoured growth of planktonic species. Abundance of planktonic diatoms suggests three main phases when water depth was deeper than today; at c.13.6 ka, 11.3 ka and 10.4–10.0 ka. These indications of past fluctuations in humidity mostly provide confirmation of previously published indications of pollen, charcoal fragments and isotopes in the same core, but the siliceous microfossil data also help to refine the paleo-environmental interpretation of the sequence.

  • 10. Fuentes, Mauricio
    et al.
    Salo, Riikka
    Björklund, Jesper
    Seftigen, Kristina
    Zhang, Peng
    Gunnarson, Björn E.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Aravena, Juan-Carlos
    Linderholm, Hans W.
    A 970-year-long summer temperature reconstruction from Rogen, west-central Sweden, based on blue intensity from tree rings2018In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 28, no 2, p. 254-266Article in journal (Refereed)
    Abstract [en]

    To assess past climate variability in west-central Scandinavia, a new 972-year-long temperature reconstruction, based on adjusted delta blue intensity (ΔBIadj), was created. Presently, it is the longest blue intensity chronology in Fennoscandia and the third longest in the northern hemisphere. Measurements were obtained from 119 tree line Scots pine (Pinus sylvestris L.) samples from Rogen, in the central Scandinavian Mountains, Sweden. Early and latewood blue intensity absorption data were used to create ΔBIadj. The data were detrended using a signal-free regional curve standardization method (RSFi) to minimize biological noise and maximize low-frequency climate information. The Rogen ΔBIadj chronology has a substantially stronger temperature signal at inter-annual timescales than the corresponding tree-ring width (RW) chronology, and it displays good spatial representation for the south-central parts of Scandinavia. The ΔBIadj summer (June through August) temperature reconstruction, extending back to 1038 CE, exhibits three warm periods in 1040–1190 CE, 1370–1570 CE and the 20th century and one extended cold period between 1570 and 1920 CE. Regional summer temperature anomalies are associated with a Scandinavian–Greenland dipole sea-level pressure pattern, which has been stable for the past several centuries. Major volcanic eruptions produce distinct anomalies of ΔBIadj indices indicating cooling of summer temperatures in the subsequent years. Our results show that ΔBIadj from Pinus sylvestris in Scandinavia is a suitable proxy providing opportunities to explore past temperature variability at various frequencies, atmospheric dynamics and variability in external forcing. Nevertheless, long-term trend differences with RW imply that further research is needed to fully understand the application of this technique in dendroclimatology.

  • 11. Gliganic, Luke A.
    et al.
    Cohen, Timothy J.
    May, Jan-Hendrik
    Jansen, John D.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. University of Wollongong.
    Nanson, Gerald C.
    Dosseto, Anthony
    Larsen, Josh R.
    Aubert, Maxime
    Late-Holocene climatic variability indicated by three natural archives in arid southern Australia2014In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 24, no 1, p. 104-117Article in journal (Refereed)
    Abstract [en]

    Three terrestrial climate proxies are used to investigate the evolution of Holocene palaeoenvironments in southern central Australia, all of which present a coherent record of palaeohydrology. Single-grain optically stimulated luminescence from sediments supplemented by C-14 from charcoal and lacustrine shells was obtained to date shoreline deposits (Lake Callabonna) and the adjacent Mt Chambers Creek alluvial fan. Our findings are complemented by a U/Th-based record of speleothem growth in the Mt Chambers Creek catchment, which we interpret to reflect increased precipitation. Together, these archives shed light on the timing of, and possible sources of water for, Holocene pluvial intervals. We identified several phases of elevated lake levels dated at similar to 5.8-5.2, 4.5, 3.5-2.7 and 1 kyr, most of which correspond to fluvial activity resulting from increased precipitation in the adjacent ranges. The enhanced hydrology during phases of the late Holocene likely increased the reliability of resources for regional human populations during a time of reduced winter rainfall. When considered within the framework of the current understanding of Holocene palaeoclimate in central Australia, our data suggest that the pattern of landscape response was broadly synchronous with larger scale climatic variability and punctuated by pluvial periods greater than today.

  • 12.
    Grudd, Håkan
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Briffa, KR
    Karlén, W
    Bartholin, TS
    Jones, PD
    Kromer, B
    A 7400-year tree-ring chronology in northern Swedish Lapland: Natural climatic variability expressed on annual to millennial timescales2002In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 12, no 6, p. 657-665Article in journal (Refereed)
    Abstract [en]

    Tree-ring widths from 880 living, dry dead, and subfossil northern Swedish pines (Pinus sylvestris L.) have been assembled into a continuous and precisely dated chronology (the Tornetrask chronology) covering the period 5407 BC to AD 1997. Biological trends in the data were removed with autoregressive standardization (ARS) to emphasize year-to-year variability, and with regional curve standardization (RCS) to emphasize variability on timescales from decades to centuries. The strong association with summer mean temperature (June-August) has enabled the production of a temperature reconstruction for the last 7400 years, providing information on natural summer-temperature variability on timescales from years to centuries. Numerous cold episodes, comparable in severity and duration to the severe summers of the seventeenth century, are shown throughout the last seven millennia. Particularly severe conditions suggested between 600 and 1 BC correspond to a known period of glacier expansion, The relatively warm conditions of the late twentieth century do not exceed those reconstructed for several earlier time intervals, although replication is relatively poor and confidence in the reconstructions is correspondingly reduced in the pre-Christian period, particularly around 3000, 1600 and 330 BC. Despite the use of the RCS approach in chronology construction, the 7400-year chronology does not express the full range of millennial-timescale temperature change in northern Sweden.

  • 13.
    Gyllencreutz, Richard
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mahiques, M. M.
    Alves, D. V. P.
    Wainer, I. K. C.
    Mid- to late-Holocene paleoceanographic changes on the southeastern Brazilian shelf based on grain size records2010In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 20, no 6, p. 863-875Article in journal (Refereed)
    Abstract [en]

    ; High-resolution grain size analyses of three AMS C-14-dated cores from the Southeastern Brazilian shelf provide a detailed record of mid- to late-Holocene environmental changes in the Southwestern Atlantic Margin. The cores exhibit millennial variability that we associate with the previously described southward shift of the Inter Tropical Convergence Zone (ITCZ) average latitudinal position over the South American continent during the Holocene climatic maximum. This generated changes in the wind-driven current system of the SW Atlantic margin and modified the grain size characteristics of the sediments deposited there. Centennial variations in the grain size are associated with a previously described late-Holocene enhancement of the El Nino-Southern Oscillation (ENSO) amplitude, which led to stronger NNE trade winds off eastern Brazil, favouring SW transport of sediments from the Paraiba do Sul River. This is recorded in a core from off Cabo Frio as a coarsening trend from 3000 cal. BP onwards. The ENSO enhancement also caused changes in precipitation and wind pattern in southern Brazil, allowing high discharge events and northward extensions of the low-saline water plume from Rio de la Plata. We propose that this resulted in a net increase in northward alongshore transport of fine sediments, seen as a prominent fine-shift at 2000 cal. BP in a core from similar to 24 degrees S on the Brazilian shelf. Wavelet-and spectral analysis of the sortable silt records show a significant similar to 1000-yr periodicity, which we attribute to solar forcing. If correct, this is one of the first indications of solar forcing of this timescale on the Southwestern Atlantic margin.

  • 14. Hansson, Sophia V.
    et al.
    Rydberg, Johan
    Kylander, Malin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gallagher, Kerry
    Bindler, Richard
    Evaluating paleoproxies for peat decomposition and their relationship to peat geochemistry2013In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 23, no 12, p. 1666-1671Article in journal (Refereed)
    Abstract [en]

    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.

  • 15. Hebbeln, Dierk
    et al.
    Knudsen, Karen-Luise
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Kristensen, Peter
    Klitgaard-Kristensen, Dorthe
    Backman, Jan
    Scheurle, Carolyn
    Jiang, Hui
    Gil, Isabelle
    Smelror, Morten
    Jones, Phil
    Sejrup, Hans-Petter
    Late Holocene coastal hydrographic and climate changes in the eastern North Sea2006In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 16, no 7, p. 987-1001Article in journal (Refereed)
    Abstract [en]

    We present a high-resolution palaeoenvironmental reconstruction covering the late Holocene from the Skagerrak and other sites in the North Sea area. The data, which are based on the analyses of marine sediment cores, reveal a marked environmental shift that took place between AD 700 and AD 1100, with the most pronounced changes occurring at AD 900. Both surface and bottom waters in the Skagerrak were subject to major circulation and productivity changes at this time due to an enhanced advection of Atlantic waters to the North Sea marking the beginning of the 'Mediaeval Warm Period' (MWP). The observed increase in bottom current strength is especially remarkable as there is hardly any comparable signal in the older part of the record going back to 1000 BC. At the transition to the 'Little Ice Age' (LIA) the bottom current strength remains at a high level, now probably forced by atmospheric circulation. Thus, despite opposite temperature forcing, these two consecutive climate scenarios are apparently able to generate distinctly stronger bottom currents in the Skagerrak than observed in the preceding 2000 years, and demonstrate the significance of climatic forcing in shaping the marine environment. Indeed, both the MWP and the LIA are reported as strong climatic signals in northwest Europe, being the warmest (except the late twentieth century) and coldest periods, respectively, during at least the last 2000 years.

  • 16. Holmes, Naomi
    et al.
    Langdon, Peter G.
    Caseldine, Chris J.
    Wastegård, Stefan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Leng, Melanie J.
    Croudace, Ian W.
    Davies, Siwan M.
    Climatic variability during the last millennium in Western Iceland from lake sediment records2016In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 26, no 5, p. 756-771Article in journal (Refereed)
    Abstract [en]

    The aim of this research was to create a decadal-scale terrestrial quantitative palaeoclimate record for NW Iceland from lake sediments for the last millennium. Geochemical, stable isotope and chironomid reconstructions were obtained from a lake sequence constrained by tephra deposits on the Snaefellsnes peninsula, western Iceland. Obtaining a quantitative record proved problematic, but the qualitative chironomid record showed clear trends associated with past summer temperatures, and the sedimentological records provided evidence for past changes in precipitation, mediated through catchment soil in-wash. When the full range of chronological uncertainty is considered, four clear phases of climatic conditions were identified: (1) a relatively warm phase between AD 1020 and 1310; (2) a relatively stable period between AD 1310 and 1510, cooler than the preceding period but still notably warmer than the second half of the millennium; (3) a consistent reduction of temperatures between AD 1560 and 1810, with the coolest period between AD 1680 and 1810; and (4) AD 1840-2000 has temperatures mainly warmer than in the preceding two centuries, with a rising trend and increased variability from c. AD 1900 onwards. The reconstructions show clearly that the first half of the millennium experienced warmer climatic conditions than the second half, with a return to the warmer climate only occurring in the last c. 100 years. Much of the variability of the chironomid record can be linked to changes in the North Atlantic Oscillation (NAO). The reconstructions presented can track low-frequency and long-term trends effectively and consistently but high-resolution and calibrated quantitative records remain more of a challenge - not just in finding optimal sedimentary deposits but also in finding the most reliable proxy. It is this that presents the real challenge for Holocene climate reconstruction from this key area of the North Atlantic.

  • 17.
    Kaislahti Tillman, Päivi
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Holzkämper, Steffen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Joest Andersen, Thorbjörn
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Oksanen, Pirita
    Stable isotopes in Sphagnum fuscum peat as late-Holocene climate proxies in northeastern European Russia2013In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 23, no 10, p. 1381-1390Article in journal (Refereed)
    Abstract [en]

    The environment of the northern taiga to tundra transition is highly sensitive to climate fluctuations. In this study from northeastern European Russia, stable carbon and oxygen isotope ratios (δ13C, δ18O) in α-cellulose of Sphagnum fuscum stems subsampled from hummocks and peat plateau profiles have been used as climate proxies. The entire isotope time series, dated by lead (210Pb), caesium (137Cs) and AMS-radiocarbon (14C) dating, spans the past 2500 years. Plant macrofossil analyses were used as an aid in single species selection, but are also helpful in identifying past surface moisture conditions. The most significant relationships were found between the recent δ13C record and summer (July–August) temperatures (R 2 = 0.58, p < 0.01), and the recent δ18O record and winter (October–May) precipitation anomalies in the tundra region (R 2 = 0.36, p < 0.01). The study demonstrates that stable isotopes preserved in northern peat deposits are useful indicators for summer temperature and winter precipitation at decadal to millennial timescales.

  • 18.
    Katrantsiotis, Christos
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Norström, Elin
    Stockholm University, Faculty of Science, Department of Physical Geography. Stockholm University, Faculty of Science, Department of Geological Sciences.
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Risberg, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Skelton, Alasdair
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    High-resolution environmental reconstruction in SW Peloponnese, Greece, covering the last c. 6000years: Evidence from Agios Floros fen, Messenian plain2016In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 26, no 2, p. 188-204Article in journal (Refereed)
    Abstract [en]

    A paleolimnological record from the central Messenian plain (southwestern Peloponnese, southern Greece) indicates rapid changes in the water level and chemistry of a transient lake on the flanks of the Taygetos Mountains during the last c. 6000years. The analyses are based on diatoms as well as carbon and nitrogen isotopes from bulk sediments in a 7.5-m-long sediment core retrieved from the drained fen of Agios Floros, at the northern banks of the ancient River Pamisos. The sequence consists of fen peat in the uppermost section underlain by lacustrine sediments, which are punctuated by two layers of clay with diatomaceous silt bands. High accumulation rate is recorded in the oldest part of the section (up to 23mm/yr), particularly during two decadal-long periods centered at c. 5700 and c. 5300 cal. BP. The diatom record reveals pronounced peaks in the planktonic taxon Cyclotella distinguenda, which correspond to the laminated sequences, reflecting the rapid development of a deep lake with an open water environment during these two time periods. Another two events with intermediate water levels are inferred at c. 5200 and c. 4600 cal. BP. These short-lived phases were probably, to a large extent, caused by local tectonic processes and the consequent hydrological anomalies of the nearby karst springs, although abrupt climatic changes with enhanced precipitation might have also played a role. At c. 4500 cal. BP, our data suggest the development of terrestrial conditions in this area, which can be attributed to the decreasing activity/dry up of springs, probably associated with more arid climate. After c. 2500 cal. BP, the diatom record infers a return to wetter conditions, probably as a response to more humid climate with marked seasonality and human activities, developing the present-day environment with cultivated and seasonally semi-flooded fields.

  • 19.
    Kjellman, Sofia E.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography. UiT The Arctic University of Norway, Norway.
    Axelsson, Pia E.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Etzelmüller, Bernd
    Westermann, Sebastian
    Sannel, A. Britta K.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Holocene development of subarctic permafrost peatlands in Finnmark, northern Norway2018In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 28, no 12, p. 1855-1869Article in journal (Refereed)
    Abstract [en]

    Subarctic permafrost peatlands are important soil organic carbon pools, and improved knowledge about peat properties and peatland sensitivity to past climate change is essential when predicting future response to a warmer climate and associated feedback mechanisms. In this study, Holocene peatland development and permafrost dynamics of four subarctic peat plateaus in Finnmark, northern Norway have been investigated through detailed analyses of plant macrofossils and geochemical properties. Peatland inception occurred around 9800 cal. yr BP and 9200 cal. yr BP at the two continental sites Suossjavri and Iskoras. Younger basal peat ages were found at the two coastal locations Lakselv and Karlebotn, at least partly caused by the time lag between deglaciation and emergence of land by isostatic uplift. Here, peatland development started around 6150 cal. yr BP and 5150 cal. yr BP, respectively. All four peatlands developed as wet fens throughout most of the Holocene. Permafrost aggradation, causing frost heave and a shift in the vegetation assemblage from wet fen to dry bog species, probably did not occur until during the last millennium, ca. 950 cal. yr BP in Karlebotn and ca. 800 cal. yr BP in Iskoras, and before ca. 150 cal. yr BP in Lakselv and ca. 100 cal. yr BP in Suossjavri. In Karlebotn, there are indications of a possible earlier permafrost phase around 2200 cal. yr BP due to climatic cooling at the late Subboreal to early Subatlantic transition. The mean long-term Holocene carbon accumulation rate at all four sites was 12.3 +/- 4.1 gC m(-2) yr(-1) (+/- SD) and the mean soil organic carbon storage was 97 +/- 46 kgC m(-2).

  • 20.
    Kylander, Malin M
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Lind, Ewa M
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Wastegård, Stefan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Löwemark, Ludvig
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Recommendations for using XRF core scanning as a tool in tephrochronology2012In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 22, no 3, p. 371-375Article in journal (Refereed)
    Abstract [en]

    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.

  • 21.
    Leijonhufvud, Lotta
    et al.
    Stockholm University, Faculty of Social Sciences, Department of Economic History.
    Wilson, Rob
    Moberg, Anders
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Documentary data provide evidence of Stockholm average winter to spring temperatures in the eighteenth and nineteenth centuries2008In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 18, no 2, p. 333-343Article in journal (Refereed)
    Abstract [en]

    Swedish archives provide several types of documentary sources relating to port activities in Stockholm for the eighteenth and nineteenth centuries. These documentary sources reflect sea ice conditions in the harbour inlet and correlate well with late-winter to early-spring temperatures. Instrumental measurements of temperature in Stockholm began in 1756, which allow for careful empirical assessment of the proxies from that date. After combining proxy series from several sources to derive a mean time series, calibration and verification trials are made and a preliminary January–April temperature reconstruction is developed from 1692 to 1892. This series, which explains 67% of the temperature variance, is further verified against independent temperature data from Uppsala, which go back to 1722. This additional verification of the reconstruction also assesses the quality of the early instrumental data from Uppsala, which has potential homogeneity problems before 1739 as a result of the thermometer being located indoors. Our analysis suggests that before this date, the instrumental data may be ‘too warm’ and need correction. Together, the documentary and instrumental data identify the post-1990 period as the warmest in three centuries. Continuing assessment of the historical archives should result in some of the documentary records being extended back into the early sixteenth century, allowing the future development of a southern Swedish winter temperature reconstruction for the last ~500 years.

  • 22. Loisel, Julie
    et al.
    Yu, Zicheng
    Beilman, David W.
    Camill, Philip
    Alm, Jukka
    Amesbury, Matthew J.
    Anderson, David
    Andersson, Sofia
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Bochicchio, Christopher
    Barber, Keith
    Belyea, Lisa R.
    Bunbury, Joan
    Chambers, Frank M.
    Charman, Daniel J.
    De Vleeschouwer, Francois
    Fialkiewicz-Koziel, Barbara
    Finkelstein, Sarah A.
    Galka, Mariusz
    Garneau, Michelle
    Hammarlund, Dan
    Hinchcliffe, William
    Holmquist, James
    Hughes, Paul
    Jones, Miriam C.
    Klein, Eric S.
    Kokfelt, Ulla
    Korhola, Atte
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Lamarre, Alexandre
    Lamentowicz, Mariusz
    Large, David
    Lavoie, Martin
    MacDonald, Glen
    Magnan, Gabriel
    Makila, Markku
    Mallon, Gunnar
    Mathijssen, Paul
    Mauquoy, Dmitri
    McCarroll, Julia
    Moore, Tim R.
    Nichols, Jonathan
    O'Reilly, Benjamin
    Oksanen, Pirita
    Packalen, Maara
    Peteet, Dorothy
    Richard, Pierre J. H.
    Robinson, Stephen
    Ronkainen, Tiina
    Rundgren, Mats
    Sannel, A. Britta K.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Tarnocai, Charles
    Thom, Tim
    Tuittila, Eeva-Stiina
    Turetsky, Merritt
    Valiranta, Minna
    van der Linden, Marjolein
    van Geel, Bas
    van Bellen, Simon
    Vitt, Dale
    Zhao, Yan
    Zhou, Weijian
    A database and synthesis of northern peatland soil properties and Holocene carbon and nitrogen accumulation2014In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 24, no 9, p. 1028-1042Article in journal (Refereed)
    Abstract [en]

    Here, we present results from the most comprehensive compilation of Holocene peat soil properties with associated carbon and nitrogen accumulation rates for northern peatlands. Our database consists of 268 peat cores from 215 sites located north of 45 degrees N. It encompasses regions within which peat carbon data have only recently become available, such as the West Siberia Lowlands, the Hudson Bay Lowlands, Kamchatka in Far East Russia, and the Tibetan Plateau. For all northern peatlands, carbon content in organic matter was estimated at 42 +/- 3% (standard deviation) for Sphagnum peat, 51 +/- 2% for non-Sphagnum peat, and at 49 +/- 2% overall. Dry bulk density averaged 0.12 +/- 0.07 g/cm(3), organic matter bulk density averaged 0.11 +/- 0.05 g/cm(3), and total carbon content in peat averaged 47 +/- 6%. In general, large differences were found between Sphagnum and non-Sphagnum peat types in terms of peat properties. Time-weighted peat carbon accumulation rates averaged 23 +/- 2 (standard error of mean) g C/m(2)/yr during the Holocene on the basis of 151 peat cores from 127 sites, with the highest rates of carbon accumulation (25-28 g C/m(2)/yr) recorded during the early Holocene when the climate was warmer than the present. Furthermore, we estimate the northern peatland carbon and nitrogen pools at 436 and 10 gigatons, respectively. The database is publicly available at https://peatlands.lehigh.edu.

  • 23. Luoto, Tomi P.
    et al.
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Holzkämper, Steffen
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Solovieva, Nadia
    Self, Angela E.
    A 2000-year record of lake ontogeny and climate variability from the north-eastern European Russian Arctic2017In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 27, no 3, p. 339-348Article in journal (Refereed)
    Abstract [en]

    A lake sediment record from the north-eastern European Russian Arctic was examined using palaeolimnological methods, including subfossil chironomid and diatom analysis. The objective of this study is to disentangle environmental history of the lake and climate variability during the past 2000 years. The sediment profile was divided into two main sections following changes in the lithology, separating the limno-telmatic phase between similar to 2000 and 1200 cal. yr BP and the lacustrine phase between similar to 1200 cal. yr BP and the present. Owing to the large proportion of semi-terrestrial chironomids and poor modern analogues, a reliable chironomid-based temperature reconstruction for the limno-telmatic phase was not possible. However, the lacustrine phase showed gradually cooling climate conditions from similar to 1200 cal. yr BP until similar to 700 cal. yr BP. The increase in stream chironomids within this sediment section indicates that this period may also have had increased precipitation that caused the adjacent river to overflow, subsequently transporting chironomids to the lacustrine basin. After a short-lived warm phase at similar to 700 cal. yr BP, the climate again cooled, and a progressive climate warming trend was evident from the most recent sediment samples, where the biological assemblages seem to have experienced an eutrophication-like response to climate warming. The temperature reconstruction showed more similarities with the climate development in the Siberian side of the Urals than with northern Europe. This study provides a characteristic archive of arctic lake ontogeny and a valuable temperature record from a remote climate-sensitive area of northern Russia.

  • 24. Martinez Cortizas, Antonio
    et al.
    Lopez-Costas, Olalla
    Orme, Lisa
    Mighall, Tim
    Kylander, Malin E.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Bindler, Richard
    Gallego Sala, Angela
    Holocene atmospheric dust deposition in NW Spain2019In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, article id UNSP 0959683619875193Article in journal (Refereed)
    Abstract [en]

    Atmospheric dust plays an important role in terrestrial and marine ecosystems, particularly those that are nutrient limited. Despite that most dust originates from arid and semi-arid regions, recent research has shown that past dust events may have been involved in boosting productivity in nutrient-poor peatlands. We investigated dust deposition in a mid-latitude, raised bog, which is surrounded by a complex geology (paragneiss/schist, granite, quartzite and granodiorite). As proxies for dust fluxes, we used accumulation rates of trace (Ti, Zr, Rb, Sr and Y) as well as major (K and Ca) lithogenic elements. The oldest, largest dust deposition event occurred between similar to 8.6 and similar to 7.4 ka BP, peaking at similar to 8.1 ka BP (most probably the 8.2 ka BP event). The event had a large impact on the evolution of the mire, which subsequently transitioned from a fen into a raised bog in similar to 1500 years. From similar to 6.7 to similar to 4.0 ka BP, fluxes were very low, coeval with mid-Holocene forest stability and maximum extent. In the late Holocene, after similar to 4.0 ka BP, dust events became more prevalent with relatively major deposition at similar to 3.2-2.5, similar to 1.4 ka BP and similar to 0.35-0.05 ka BP, and minor peaks at similar to 4.0-3.7, similar to 1.7, similar to 1.10-0.95 ka BP and similar to 0.74-0.58 ka BP. Strontium fluxes display a similar pattern between similar to 11 and similar to 6.7 ka BP but then became decoupled from the other elements from the mid Holocene onwards. This seems to be a specific signal of the granodiorite batholith, which has an Sr anomaly. The reconstructed variations in dust fluxes bear a strong climatic imprint, probably related to storminess controlled by North Atlantic Oscillation conditions. Complex interactions also arise because of increased pressure from human activities.

  • 25. McCarroll, Danny
    et al.
    Loader, Neil J.
    Jalkanen, Risto
    Gagen, Mary H.
    Grudd, Håkan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Gunnarson, Björn E.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kirchhefer, Andreas J.
    Friedrich, Michael
    Linderholm, Hans W.
    Lindholm, Markus
    Boettger, Tatjana
    Los, Sietse O.
    Remmele, Sabine
    Kononov, Yuri M.
    Yamazaki, Yasuhiro H.
    Young, Giles H. F.
    Zorita, Eduardo
    A 1200-year multiproxy record of tree growth and summer temperature at the northern pine forest limit of Europe2013In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 23, no 4, p. 471-484Article in journal (Refereed)
    Abstract [en]

    Combining nine tree growth proxies from four sites, from the west coast of Norway to the Kola Peninsula of NW Russia, provides a well replicated (> 100 annual measurements per year) mean index of tree growth over the last 1200 years that represents the growth of much of the northern pine timberline forests of northern Fennoscandia. The simple mean of the nine series, z-scored over their common period, correlates strongly with mean June to August temperature averaged over this region (r = 0.81), allowing reconstructions of summer temperature based on regression and variance scaling. The reconstructions correlate significantly with gridded summer temperatures across the whole of Fennoscandia, extending north across Svalbard and south into Denmark. Uncertainty in the reconstructions is estimated by combining the uncertainty in mean tree growth with the uncertainty in the regression models. Over the last seven centuries the uncertainty is < 4.5% higher than in the 20th century, and reaches a maximum of 12% above recent levels during the 10th century. The results suggest that the 20th century was the warmest of the last 1200 years, but that it was not significantly different from the 11th century. The coldest century was the 17th. The impact of volcanic eruptions is clear, and a delayed recovery from pairs or multiple eruptions suggests the presence of some positive feedback mechanism. There is no clear and consistent link between northern Fennoscandian summer temperatures and solar forcing.

  • 26. Melvin, Thomas M.
    et al.
    Grudd, Håkan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Briffa, Keith R.
    Potential bias in 'updating' tree-ring chronologies using regional curve standardisation: Re-processing 1500 years of Tornetrask density and ring-width data2013In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 23, no 3, p. 364-373Article in journal (Refereed)
    Abstract [en]

    We describe the analysis of existing and new maximum-latewood-density (MXD) and tree-ring width (TRW) data from the Tornetrask region of northern Sweden and the construction of 1500 year chronologies. Some previous work found that MXD and TRW chronologies from Tornetrask were inconsistent over the most recent 200 years, even though they both reflect predominantly summer temperature influences on tree growth. We show that this was partly a result of systematic bias in MXD data measurements and partly a result of inhomogeneous sample selection from living trees (modern sample bias). We use refinements of the simple Regional Curve Standardisation (RCS) method of chronology construction to identify and mitigate these biases. The new MXD and TRW chronologies now present a largely consistent picture of long-timescale changes in past summer temperature in this region over their full length, indicating similar levels of summer warmth in the medieval period (MWP, c. CE 900-1100) and the latter half of the 20th century. Future work involving the updating of MXD chronologies using differently sourced measurements may require similar analysis and appropriate adjustment to that described here to make the data suitable for the production of un-biased RCS chronologies. The use of 'growth-rate' based multiple RCS curves is recommended to identify and mitigate the problem of 'modern sample bias'.

  • 27. Nirgi, Triine
    et al.
    Rosentau, Alar
    Habicht, Hando-Laur
    Hang, Tiit
    Jonuks, Tõnno
    Jõeleht, Argo
    Kihno, Kersti
    Kriiska, Aivar
    Mustasaar, Mario
    Risberg, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Suuroja, Sten
    Talviste, Peeter
    Tõnisson, Hannes
    Holocene relative shore-level changes and Stone Age palaeogeography of the Pärnu Bay area, eastern Baltic Sea2019In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911Article in journal (Refereed)
    Abstract [en]

    The shore displacement and palaeogeography of the Pärnu Bay area, eastern Baltic Sea, during the Stone Age, were reconstructed using sedimentological and archaeological proxies and GIS-based landscape modelling. We discovered and studied buried palaeochannel sediments on the coastal lowland and in the shallow offshore of the Pärnu Bay and interpreted these data together with previously published shore displacement evidence. The reconstructed relative shore-level (RSL) curve is based on 78 radiocarbon dates from sediment sequences and archaeological sites in the Pärnu Bay area and reported here using the HOLSEA sea-level database format. The new RSL curve displays regressive water levels at -5.5 and -4 m a.s.l. before the Ancylus Lake and Litorina Sea transgressions, respectively. According to the curve, the total water-level rise during the Ancylus Lake transgression (10.7-10.2 cal. ka BP) was around 18 m, with the average rate of rise about 35 mm per annum, while during the Litorina Sea transgression (8.5-7.3 cal. ka BP), the water level rose around 14 m, with average rate of 12 mm per annum. During the short period around 7.8-7.6 cal. ka BP, the RSL rose in Pärnu, but probably also in Samsø (Denmark), Blekinge (Sweden) and Narva-Luga (NE Estonia-NW Russia), faster than the concurrent eustatic sea level calculated from the far-field sites. The palaeogeographic reconstructions show the settlement patterns of the coastal landscape since the Mesolithic and provide new perspective for looking Mesolithic hunter-fisher-gatherer settlement sites on the banks of the submerged ca. 9000 years old river channel in the bottom of the present-day Pärnu Bay.

  • 28.
    Norström, Elin
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Bringensparr, Caroline
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Fitchett, Jennifer M.
    Grab, Stefan W.
    Rydberg, Johan
    Kylander, Malin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Late-Holocene climate and vegetation dynamics in eastern Lesotho highlands2018In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 28, no 9, p. 1483-1494Article in journal (Refereed)
    Abstract [en]

    The eastern Lesotho highlands are of considerable hydrological importance to southern Africa as a so-called water tower' for the surrounding region. Here, we contribute proxy-data inferring climate and vegetation changes over the past 1600 years, assessing in parallel inorganic and organic chemical analyses on a sediment core from Ladybird wetland, eastern Lesotho. Several proxies were used to determine changes in local vegetation dynamics, productivity, hydrology ((13) C, (15) N, C/N, TOC) and the input and source of the detrital components (Ca/Ti, CIA). The first part of the multi-proxy record (AD 400-800) shows stable terrestrial conditions and low detrital input, followed by higher variability in almost all proxies between ca. AD 900 and 1200. The (13) C record infers a higher proportion of C-4 vegetation, tentatively associated with higher temperatures during this phase, coeval with the Medieval Climate Anomaly (MCA). After AD 1200, local conditions change gradually from purely terrestrial, towards the typical wetland environment prevailing today. A higher proportion of C-3 plants and possibly an increase in aquatic organisms within the organic matrix corresponds with decreasing detrital input, suggesting locally high available moisture in this part of Lesotho during the Little Ice Age (LIA). Although age-model constraints impedes a robust regional comparison, the inferred climate variability is discussed as a tentative response to enhanced mid-latitude cyclonic activity during LIA, and the variable MCA climate conditions as indirectly dictated by changes in solar activity.

  • 29.
    Norström, Elin
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Stockholm University, Faculty of Science, Department of Physical Geography.
    Öberg, Helena
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Sitoe, Sandra R.
    Stockholm University, Faculty of Science, Department of Physical Geography. University of Eduardo Mondlane, Mozambique.
    Ekblom, Anneli
    Westerberg, Lars-Ove
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Risberg, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Vegetation dynamics within the savanna biome in southern Mozambique during the late Holocene2018In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 28, no 2, p. 277-292Article in journal (Refereed)
    Abstract [en]

    This study explores temporal dynamics within grassland and Miombo woodland ecosystems in southern Mozambique and their potential coupling to hydro-climate change during the late-Holocene period. Palaeo-reconstructions are based on phytolith and diatom assemblages and mineral magnetic properties in fossil sediments from Lake Chilau, southern Mozambique. Phytolith interpretation was aided by previous ecological studies on modern plants and soils. The Lake Chilau record suggests high abundance of Panicoideae and other mesophytic grasses during the AD 1200s and 1300s, followed by an increase in Chloridoideae and grasses of more xerophytic affinity between ca. AD 1400 and 1550. This vegetation transition takes place during the early phase of the so-called ‘Little Ice Age’ (LIA), when regional palaeoclimate records report a shift from warmer and wetter towards drier and cooler conditions in southern Africa. Concurrent to these shifts within the grassland biome, the Chilau record reports an increase in phytoliths associated with arboreal vegetation (ca. AD 1400–1550), probably associated with the woody component of the Miombo savanna ecosystem. This supports previous studies hypothesizing that the forest component of the Miombo savanna was favoured by LIA dryness, although at Chilau, this expansion may have been amplified by a decline in fire disturbance. These tentative responses in the woody components of the savanna biome to shifts in moisture availability in the past have implications for future management and sustainability of the Miombo ecosystem in southern Mozambique under a changing climate.

  • 30. Olchev, Alexander
    et al.
    Novenko, Elena
    Popov, Viktor
    Pampura, Tatiana
    Meili, Markus
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Evidence of temperature and precipitation change over the past 100years in a high-resolution pollen record from the boreal forest of Central European Russia2017In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 27, no 5, p. 740-751Article in journal (Refereed)
    Abstract [en]

    Near-annual pollen records for the last 100years were obtained from a 65-cm peat monolith from a raised peat bog in the Central Forest State Natural Biosphere Reserve (southern part of the Valdai Hills, European Russia) and compared with the available long-term meteorological observations. An age-depth model for the peat monolith was constructed by Pb-210 and Cs-137 dating. Cross-correlation and the Granger causality analysis indicated a broad range of statistically significant correlations between the pollen accumulation rate (PAR) of the main forest-forming trees and shrubs (Picea, Pinus, Betula, Tilia, Quercus, Ulmus, Alnus, and Corylus) and the air temperature and precipitation during the previous 3years. Results showed that high air temperatures during the growing season (May-September) in the year prior to the flowering led to an increase in pollen productivity of the main tree species. The statistically significant correlation between the PAR of trees and shrubs and winter precipitation of the current and previous years could reflect the influence of winter precipitation on soil water availability and as a result on tree growth and functioning in the spring.

  • 31.
    Pluchon, Nathalie
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Swedish University of Agricultural Sciences, Sweden.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kuusinen, Nea
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Recent paludification rates and effects on total ecosystem carbon storage in two boreal peatlands of Northeast European Russia2014In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 24, no 9, p. 1126-1136Article in journal (Refereed)
    Abstract [en]

    Forest and peatland ecosystems constitute the two major carbon pools in the boreal region. We assess the evolution in total storage and partitioning of ecosystem carbon following recent paludification of forest into peatland at two sites in Northeast European Russia. Based on radiocarbon dating of basal peat and quantification of total ecosystem carbon storage, our results show that paludification rates and its consequences for carbon storage vary significantly between sites. A peatland expanding on ground with steeper slopes has experienced a slow lateral advance in recent times, about 2.6 m on average per century, whereas a peatland in flatter terrain has expanded much more rapidly, about 35 m on average per century. The total ecosystem carbon storage (sum of phytomass, top soil organics or peat, and 30 cm of underlying mineral soil) showed a long-term trend toward increased ecosystem C storage following the replacement of forest (mean value = 20.8 kg C/m(2), range = 13.0-43.4 kg C/m(2)) by peatland (>100 kg C/m(2) in the deepest peat deposits). However, the transitional stage in which the forest is replaced by the margin of the peatland results in a short-term decrease of carbon stored in the ecosystem with a mean loss of 7.5 kg C/m(2). After the initiation of a peatland through paludification, a period of decades to centuries of peat accumulation is needed to compensate for the initial loss of carbon. In the short term, an intensification of the paludification process could lead to a loss of carbon stored in the boreal region.

  • 32.
    Rosqvist, G. C.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Leng, M. J.
    Jonsson, C.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    North Atlantic region atmospheric circulation dynamics inferred from a late-Holocene lacustrine carbonate isotope record, northern Swedish Lapland2007In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 17, no 7, p. 867–873-Article in journal (Refereed)
    Abstract [en]

    The first high-resolution record of climate variation based on the oxygen and carbon isotope composition of authigenic carbonate for northern Scandinavia is presented. Modern lake-water isotope data indicate that controls on its oxygen and hydrogen (δ18O<sub>w</sub> and δD<sub>w</sub>) composition are unlikely to be evaporation or temperature, and its variations must therefore reflect changes in, or at the source of, precipitation. Substantial and persistent changes of the isotopic composition of the precipitation are required to change the mean annual isotope composition of lake surface water. For this reason we argue that the recorded changes were significant and that the recurrence of such changes would greatly affect future regional climate conditions in the North Atlantic region. Oxygen isotope (δ<sup>18</sup>O) minima occurring at ~ 200, 500, 1300, 1600 and at 2900 cal. yr BP all coincide with major peaks in North Atlantic ice rafted debris deposition. We suggest that the depletion events in δ<sup>18</sup>O cycles recorded in several lakes in northern Swedish Lapland are caused by the same climatic shifts as those noted in the North Atlantic marine records. This is because changes of atmospheric circulation pattern and the lower ocean and atmospheric temperatures associated with the IRD events help to explain why 18O depletion of precipitation occurred during these events. Our findings indicate that the recorded changes in North Atlantic ice drift and surface hydrography are coupled to changes in atmospheric circulation. 

  • 33. Rubensdotter, Lena
    et al.
    Rosqvist, Gunhild
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Influence of geomorphological setting, fluvial-, glaciofluvial- and mass-movement processes on sedimentation in alpine lakes2009In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 19, no 4, p. 665-678Article in journal (Refereed)
    Abstract [en]

    Lacustrine sediments are often used for paleoclimate reconstructions as continuous archives of several physical and biological proxies. The relation between autochthonous and allochthonous sedimentation in alpine lakes is a complex system that may cause difficulties when interpreting biological and physical parameters. Results from previous studies of alpine lakes in northern Sweden have demonstrated that non-glacial processes produce minerogenic lake deposits with similar physical characteristics (density, LOI, magnetic susceptibility, grain-size) as those that have been associated with glacier fluctuations in proglacial lakes. In this study of two consecutive proglacial alpine lakes we show that fluvial redeposition of alluvial fan deposits significantly affects the Holocene lake sedimentation. Depending on the geomorphological setting, such fluvial redeposition signals may actually overprint a glaciofluvial signal. We also show that minerogenic laminations of fluvial origin are impossible to separate from the type of laminations usually used to infer glacier activity using the most common lithological sediment parameters. This emphasizes the complexity of sediment transport system in proglacial (paraglacial) settings where redeposition of older glacial sediment is of major importance. Our results highlight the need for thorough understanding of the geomorphological setting before inferences are made about climate variations from sedimentation in alpine lakes. moth lakes in this study contain sediment sequences with both episodic (turbidites) and continuously deposited sediments. Unfortunately we have too few radiocarbon dates to exactly date the turbidites but it is clear that turbidite layers in any case should be excluded from age model constructions since episodic sedimentation significantly influences the sediment age-depth relationship. In our age-model turbidites cause a potential dating error of several hundred, up to a thousand, years.

  • 34.
    Salonen, J. Sakari
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Univ Helsinki, FIN-00014 Helsinki, Finland.
    Seppä, Heikki
    Birks, H. John B.
    The effect of calibration data set selection on quantitative palaeoclimatic reconstructions2013In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 23, no 11, p. 1650-1654Article in journal (Refereed)
    Abstract [en]

    Quantitative palaeoclimatic reconstructions based on biological fossils are a major source of information on long-term climatic variability. Such reconstructions typically use some kind of a modern calibration data set describing the variation of the studied biological group in present-day climate space. Here, we explore the effect of calibration data set selection on palaeoclimatic reconstructions, by creating alternate calibration data sets via stratified random sampling to reconstruct mean July temperature (T-jul) for four fossil pollen sequences from northern Europe. We show that palaeoclimatic reconstructions using methods based on taxon-response models can be highly sensitive to the calibration data set used. In particular, the absolute reconstructed temperatures show great sensitivity to calibration data selection, which suggests that the absolute values of palaeoclimatic reconstructions may not be robust. By contrast, we find the relative shapes of the reconstructed curves to be more robust to calibration data selection because taxa tend to occupy similar relative locations along the sampled gradient regardless of calibration data set location. Based on this robustness of relative palaeoclimate curves, we suggest a debiasing procedure in which palaeoclimate values are estimated by fixing the relative curve with the modern observed value, thus correcting biases resulting from calibration data selection.

  • 35.
    Sannel, Britta
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Long-term stability of permafrost in subarctic peat plateaus, west-central Canada2008In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 18, no 4, p. 589-601Article in journal (Refereed)
    Abstract [en]

    Long-term vegetation succession and permafrost dynamics in subarctic peat plateaus of west-central Canada have been studied through detailed plant macrofossil analysis and extensive AMS radiocarbon dating of two peat profiles. Peatland inception at these sites occurred around 5800-5100 yr BP (6600-5900 cal. BP) as a result of paludification of upland forests. At the northern peat plateau site, located in the continuous permafrost zone, palaeobotanical evidence suggests that permafrost was already present under the forested upland prior to peatland development. Paludification was initiated by permafrost collapse, but re-aggradation of permafrost occurred soon after peatland inception. At the southern site, located in the discontinuous permafrost zone, the aggradation of permafrost occurred soon after peatland inception. In the peat plateaus, permafrost conditions have remained very stable until present. Sphagnum fuscum-dominated stages have alternated with more xerophytic communities characterized by ericaceous shrubs. Local peat fires have occurred, but most of these did not cause degradation of the permafrost. Starting from 2800-1100 yr BP (2900-1000 cal. BP) consistently dry surface conditions have prevailed, possibly related to continued frost heave or nearby polygon crack formation.

  • 36.
    Shala, Shyhrete
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Helmens, Karin F.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Luoto, Tomi P.
    Salonen, J. Sakari
    Väliranta, Minna
    Weckström, Jan
    Comparison of quantitative Holocene temperature reconstructions using multiple proxies from a northern boreal lake2017In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 27, no 11, p. 1745-1755Article in journal (Refereed)
    Abstract [en]

    Four biotic proxies (plant macrofossils, pollen, chironomids and diatoms) are employed to quantitatively reconstruct variations in mean July air temperatures (T-jul) at Lake Loitsana (northern Finland) during the Holocene. The aim is to evaluate the robustness and biases in these temperature reconstructions and to compare the timing of highest T-jul in the individual reconstructions. The reconstructed T-jul values are evaluated in relation to local-scale/site-specific processes associated with the Holocene lake development at Loitsana as these factors have been shown to significantly influence the fossil assemblages found in the Lake Loitsana sediments. While pollen-based temperatures follow the classical trend of gradually increasing early-Holocene T-jul with a mid-Holocene maximum, the aquatic/wetland assemblages reconstruct higher-than-present T-jul already during the early Holocene, that is, at the peak of summer insolation. The relatively low early-Holocene July temperatures recorded by the pollen are the result of site-specific factors possibly combined with a delayed response of the terrestrial ecosystem compared with the aquatic ecosystem. Our study shows that all reconstructions are influenced at least to some extent by local factors. This finding stresses the need to evaluate quantitatively reconstructed climate values against local lake development and highlights the benefit of using multi-proxy data in Holocene climate reconstructions.

  • 37. Sheldon, Christina M.
    et al.
    Seidenkrantz, Marit-Solveig
    Pearce, Christof
    Stockholm University, Faculty of Science, Department of Geological Sciences. Aarhus University, Denmark .
    Kuijpers, Antoon
    Hansen, Mette J.
    Christensen, Eva Zilmer
    Holocene oceanographic changes in SW Labrador Sea, off Newfoundland2016In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 26, no 2, p. 274-289Article in journal (Refereed)
    Abstract [en]

    Benthic foraminiferal assemblages supported by selected geochemical data from three marine sediment cores collected in Placentia Bay, SE Newfoundland, are used to construct an ~13,000-year-long record of regional oceanographic changes in the SW Labrador Sea. The area is located in the boundary zone between the cold, ice-loaded Labrador Current (LC) in the north and the warm Gulf Stream (GS) waters to the south. After the Younger Dryas termination, the influence of GS-derived water increased and was further strengthened at 10.7 cal. kyr BP through enhanced northward flow of Atlantic water via the Slopewater Current. A short-term event of increased terrestrial input and water column stratification at 8.4 cal. kyr BP was likely linked to the distal drainage of glacial Lake Agassiz. After 7.3 cal. kyr BP, a stronger LC weakened the inflow of warmer subsurface waters from the GS. This may be explained by extensive meltwater release from ice sheets in Arctic Canada and is concurrent with a general shift in oceanographic conditions in the Labrador Sea region. Around 4.0 cal. kyr BP, conditions became more stable with a slight increase in salinity, indicating a decrease in meltwater transported via the LC. The Northern Hemisphere neoglacial cooling around 2.8 cal. kyr BP was characterized off SE Newfoundland by a further stabilization of the current system, dominated by the LC with some continued influx of GS water.

  • 38. Thorn, Colin E.
    et al.
    Darmody, Robert D.
    Holmqvist, Johan
    Jull, A. J. Timothy
    Dixon, John C.
    Schlyter, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Comparison of radiocarbon dating of buried paleosols using arbuscular mycorrhizae spores and bulk soil samples2009In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 19, no 7, p. 1031-1037Article in journal (Refereed)
    Abstract [en]

    Ten paleosols from four separate soil pits located in Karkevagge, a glaciated trough in Swedish Lapland, were dated using radiocarbon. Each soil was dated using both conventional bulk soil organic material (SOM) and a pure sample of arbuscular mycorrhizae (AM) fungal spores. The latter are produced by ubiquitous mycorrhizal fungi associated with the roots of many plant genera and may be viewed as a fossil material that has not interacted with any soil constituent subsequent to its emplacement in the soil - at a time presumed to mark the cessation of a favorable soil-forming environment. Regional deglaciation is presumed to have been about 10 000 BP, while a cosmogenic exposure date obtained from the valley floor in Karkevagge dated at 13 100 +/- 1638 BP. The youngest paleosol, buried at similar to 6 cm in soil pit M3, produced a spore date of 0-281 cal. yr BP (1 sigma). However, bulk SOM dates of the same paleosol A horizon gave widely divergent dates and varied with the sample pretreatment, ie, the combustion temperature and the acid-base treatment. For example, the bulk SOM dates for that paleosol ranged from a post-bomb date of 0-314 cal. yr BP (1 sigma) to 2366-2710 cal. yr BP (1 sigma) when subjected to different pretreatments (acid only, acid-base-acid) and the ignition temperatures (400, 800, or 900 degrees C). The oldest paleosol in the set, buried at similar to 61 cm in soil pit M6, dated at 5479-5698 cal. yr BP (1 sigma) using spores, but beyond calibration using bulk SOM. The spore dates were all within the range to be expected of postglacial paleosols, but the bulk SOM dates were frequently beyond the generally accepted time of deglaciation. In addition, all of the spore dates followed a conventional age/depth pattern while the bulk SOM dates did not. There are known possible sources of geogenic carbon contamination in Karkevagge which may well account for the obviously invalid older bulk SOM dates. An additional complication is that the spore dates vary somewhat with their density and diameter. However, where other types of fossil or charcoal are unavailable it appears that the enormously broad distribution of spores and their lack of interaction within the soil and persistence may well offer the prospect of an unusually useful radiocarbon dating medium within paleosols.

  • 39. Totten Minzoni, Rebecca
    et al.
    Majewski, Wojciech
    Anderson, John B.
    Yokoyama, Yusuke
    Fernandez, Rodrigo
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Oceanographic influences on the stability of the Cosgrove Ice Shelf, Antarctica2017In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 27, no 11, p. 1645-1658Article in journal (Refereed)
    Abstract [en]

    Ferrero Bay, located in eastern Pine Island Bay (PIB) of the Amundsen Sea Embayment, is one of the largest and southernmost fjords yet studied in Antarctica. High-resolution multibeam swath bathymetric data, chirp sonar sub-bottom profiles, and three Kasten cores were collected in Ferrero Bay during the IB Oden Southern Ocean 2009-2010 cruise (OSO0910). Core KC-15 from the inner bay yielded two carbonate ages providing a minimum age for ice sheet recession from this sector of PIB by similar to 11 cal. kyr BP. In total, seven additional acid insoluble organic (AIO) fraction radiocarbon ages provide a linear age model with an R-2 of 0.99. Variations in magnetic susceptibility, grain size, total organic carbon (TOC) and nitrogen, diatom abundance, and foraminiferal assemblage and abundance are used to interpret glacial history and paleoceanographic conditions. Grounding line retreat was characterized by advection of planktic foraminifera beneath an ice shelf that may have extended across the middle continental shelf. Following initial deglaciation, the Cosgrove Ice Shelf covered Ferrero Bay, and productivity was virtually absent during the mid-Holocene, while benthic foraminifera indicate periodic incursion of warm Circumpolar Deep Water. The ice shelf persisted until 2.3 cal. kyr BP, when TOC and diatom abundance increased as the bay opened and coastal areas deglaciated. Abundant diatoms demonstrate open marine conditions and seasonal sea ice during the recent open water phase, while high benthic foraminiferal abundance indicates active benthos. The retreat of the Cosgrove Ice Shelf was out of phase with Antarctic Peninsula ice shelves and ice-core proxy temperatures, implying that it did not respond to Holocene climate events but rather to the influence of Circumpolar Deep Water and possibly to internal glacial dynamics.

  • 40. Ukkonen, Pirkko
    et al.
    Aaris-Sorensen, Kim
    Arppe, Laura
    Daugnora, Linas
    Halkka, Antti
    Lougas, Lembi
    Oinonen, Markku Juhani
    Pilot, Malgorzata
    Storå, Jan
    Stockholm University, Faculty of Humanities, Department of Archaeology and Classical Studies, Osteoarchaeological Research Laboratory.
    An Arctic seal in temperate waters: History of the ringed seal (Pusa hispida) in the Baltic Sea and its adaptation to the changing environment2014In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 24, no 12, p. 1694-1706Article in journal (Refereed)
    Abstract [en]

    The ringed seal (Pusa hispida) is an early immigrant in the Baltic Basin and has since its arrival experienced substantial changes in the climate, salinity and productivity of the Basin. In this paper, we discuss the dispersal and distribution of the ringed seal during different stages of the Baltic Sea in relation to past and ongoing environmental changes. Subfossil ringed seal remains around the Baltic Sea and the Danish Straits were radiocarbon dated in order to map the distribution of the species in different time periods. The delta C-13 data were used in evaluating the changes in the marine character of the Baltic Basin. The sequence of the dates indicates a continuous presence of the species in the Baltic Basin. The earliest ringed seal finds come from the Skagerrak/Kattegat area (Denmark, Swedish west coast) and date to the full glacial period and Baltic Ice Lake. In the Baltic Basin, the species appears in the subfossil record during the Ancylus period, but the main part of the remains date to the Littorina stage. During the Littorina stage, the distribution of the species was at least periodically wider than today, covering also southern parts of the Baltic. The presence of breeding populations in southern parts of the Baltic during the Holocene Thermal Maximum (HTM) indicates that the winters were at least periodically cold enough for winter ice. The changes in the marine influence in the Baltic Basin can be seen in the seal collagen delta C-13 values, which serve as a proxy for qualitative changes in water mass salinity.

  • 41. Wilson, R.
    et al.
    Anchukaitis, K.
    Andreu-Hayles, L.
    Cook, E.
    D'Arrigo, R.
    Davi, N.
    Haberbauer, L.
    Krusic, Paul
    Stockholm University, Faculty of Science, Department of Physical Geography. University of Cambridge, UK.
    Luckman, B.
    Morimoto, D.
    Oelkers, R.
    Wiles, G.
    Wood, C.
    Improved dendroclimatic calibration using blue intensity in the southern Yukon2019In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 29, no 11, p. 1817-1830Article in journal (Refereed)
    Abstract [en]

    In north-western North America, the so-called divergence problem (DP) is expressed in tree ring width (RW) as an unstable temperature signal in recent decades. Maximum latewood density (MXD), from the same region, shows minimal evidence of DP. While MXD is a superior proxy for summer temperatures, there are very few long MXD records from North America. Latewood blue intensity (LWB) measures similar wood properties as MXD, expresses a similar climate response, is much cheaper to generate and thereby could provide the means to profoundly expand the extant network of temperature sensitive tree-ring (TR) chronologies in North America. In this study, LWB is measured from 17 white spruce sites (Picea glauca) in south-western Yukon to test whether LWB is immune to the temporal calibration instabilities observed in RW. A number of detrending methodologies are examined. The strongest calibration results for both RW and LWB are consistently returned using age-dependent spline (ADS) detrending within the signal-free (SF) framework. RW data calibrate best with June-July maximum temperatures (Tmax), explaining up to 28% variance, but all models fail validation and residual analysis. In comparison, LWB calibrates strongly (explaining 43-51% of May-August Tmax) and validates well. The reconstruction extends to 1337 CE, but uncertainties increase substantially before the early 17th century because of low replication. RW-, MXD- and LWB-based summer temperature reconstructions from the Gulf of Alaska, the Wrangell Mountains and Northern Alaska display good agreement at multi-decadal and higher frequencies, but the Yukon LWB reconstruction appears potentially limited in its expression of centennial-scale variation. While LWB improves dendroclimatic calibration, future work must focus on suitably preserved sub-fossil material to increase replication prior to 1650 CE.

  • 42. Wilson, R.
    et al.
    Loader, N. J.
    Rydval, M.
    Patton, H.
    Frith, A.
    Mills, C. M.
    Crone, A.
    Edwards, C.
    Larsson, L.
    Gunnarson, Björn E.
    Stockholm University, Faculty of Science, Department of Physical Geography. Swedish University of Agricultural Sciences, Sweden.
    Reconstructing Holocene climate from tree rings: The potential for a long chronology from the Scottish Highlands2012In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 22, no 1, p. 3-11Article in journal (Refereed)
    Abstract [en]

    Despite promising research in the 1980s showing the potential of Scots pine (Pinus sylvestris L.) for the reconstruction of past summer temperatures in the Scottish Highlands, little dendroclimatic work has been attempted in this region since. This reflects, in part, the limited number of sparsely distributed remnant natural/ semi-natural pine woodlands in the Scottish Highlands and the lack of old growth forest therein. On average, most of the pine trees dated in this region are around 225 years in age. Here, we present the first results of an ongoing interdisciplinary initiative to develop a long Scottish chronology through the acquisition of modern, historical and subfossil pine material from the native pinewoods, historic structures and lakes of the Scottish Highlands. Radiocarbon dating of 25 subfossil pine timbers recovered from lake sediments identified the presence of preserved material covering the last 8000 years with initial clusters focused on the last two millennia and early-mid Holocene. Although developing a well-replicated 8000 year pine chronology will take many years, this preliminary study indicates that a millennial length pine chronology from the northwest Cairngorm region is a feasible and realistic objective in the near future. The importance of such a record in this climatically important sector of northwest Europe cannot be underestimated.

  • 43.
    Wohlfarth, Barbara
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Higham, Charles
    Yamoah, Kweku Afrifa
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Chabangborn, Akkaneewut
    Chawchai, Sakonvan
    Smittenberg, Rienk H.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Human adaptation to mid- to late-Holocene climate change in Northeast Thailand2016In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 26, no 11, p. 1875-1886Article, review/survey (Refereed)
    Abstract [en]

    This article integrates palaeoenvironmental and archaeological sequences covering the mid- to late-Holocene in Northeast Thailand. The former reveal the fluctuating intensity of the Asian summer monsoon, leading to periods of higher moisture availability with intervals of relative aridity. The latter are founded on a series of new radiocarbon determinations that provide a basic chronological framework, from the initial Neolithic settlements by rice farmers (c. 3700 cal. BP) to the end of the prehistoric Iron Age around 1300 cal. BP. By dovetailing the two, we find that periods of relative aridity occurred during the later Iron Age as an agricultural revolution witnessed water control measures, plough and irrigated rice cultivation and a marked rise in social elites. The correlation between climatic and cultural changes is found to continue into the period of the Angkorian state. Rather than cause a decline and/or abandonment of late Iron Age settlements, we find that the environmental stress caused by a weaker summer monsoon was met by a strong social response and by adaptations that generated a transition into early socially hierarchic polities.

  • 44.
    Yamoah, Kweku Afrifa
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Higham, Charles F. W.
    Wohlfarth, Barbara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Chabangborn, Akkaneewut
    Chawchai, Sakonvan
    Schenk, Frederik
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Smittenberg, Rienk H.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Societal response to monsoonal fluctuations in NE Thailand during the demise of Angkor Civilisation2017In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 27, no 10, p. 1455-1464Article in journal (Refereed)
    Abstract [en]

    This paper investigates the possible social responses to changes in the strength of the southwest monsoon in northeastern Thailand during the currency of the Angkor civilisation. These assessments are based on hydrogen and carbon isotope records of leaf waxes (delta D-wax and delta 13C(wax)) from a 2000-year-long wetland sequence of Pa Kho in northeastern Thailand, a region that formed the northern boundary of the Angkor Kingdom. Our data indicate anthropogenic flooding of the Pa Kho wetland through the control of water through dam construction from c. AD 1300 in response to the fluctuating strength of monsoon rains. delta D-wax, a proxy for regional hydroclimate variability, corroborates pre-existing evidence that increased summer monsoon rains, which supported the expansion of the agrarian economy, aided the rise of the Angkorian Empire whereas extreme drought contributed to its demise. Interestingly, our delta D-wax record shows already a gradual decreasing monsoon intensity from c. AD 1000 onwards, although Angkor's prosperity reached its peak at c. AD 1200. We suggest that the complex hydrological system established under royal patronage at Angkor provided a resilient buffer against short-term monsoon fluctuations. The long-term decline in monsoon rains over a similar to 300-year period, combined with ongoing urbanisation, may have stretched the hydrological systems to their limit. We suggest that this was a major factor that contributed to the demise of Angkor in the mid-15th century.

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