Change search
Refine search result
1 - 11 of 11
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Berntsson, Annika
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Velle, Gaute
    University of Bergen.
    Rosqvist, Gunhild
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Bergman, Jonas
    Holzkämper, Steffen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Eriksson, Lars
    Sveriges Landbruksuniversitet.
    An evaluation of a chironomid-based summer temperature reconstruction from west 1 central Sweden covering the last millenniumManuscript (preprint) (Other (popular science, discussion, etc.))
    Abstract [en]

    Here we present a lake sediment study from west central Sweden that covers the last thousand years. The study site Lake Spåime is a shallow, hydrologically open lake situated above the present tree line. We applied chironomid analysis with the aim to reconstruct mean July air temperature at a high temporal resolution and we evaluated our reconstruction with significance tests and comparison with observed meteorological data. We examined the relationship between changes in chironomid-inferred July temperature, isotope hydrology and minerogenic detrital input. We also assessed the influence of running water and semi-terrestrial/terrestrial chironomids. The inferred July air temperatures ranged from 8.5˚C to 11.6˚C (mean 9.6˚C) over the past millennium. The temperatures inferred with running water- and terrestrial taxa removed was similar, but with a 0.6 ˚C higher amplitude. The results of significance testing were inconclusive. Comparison with meteorological data showed that the chironomid-based July air temperatures were similar during the last 110 years. Individual years when chironomid-inferred July air temperatures were lower than the instrumental data were characterized by low June air temperatures and high amounts of winter precipitation. From this, we assume that late snowmelt led to cool melt water input in July which in turn caused a decoupling between water and air temperatures causing too low inferred temperatures. Inferred July temperatures show similarities and discrepancies with reconstructions derived from other proxies in the region, such as tree-ring and sea surface temperature records, and fail to reconstruct the cold summer conditions characteristic of the years between AD 1650 and 1750. We conclude that the Spåime July temperature reconstruction was partly biased, possibly because of major changes in the Spåime catchment system that influenced the chironomids. For example, changes in hydrology caused by shifts in seasonality and amount of precipitation may have triggered changes in sediment erosion and deposition rates, affecting the chironomid composition to a larger extent than mean July air temperatures. Future challenges include examination of the temperature sensitivity of chironomid taxa and continued critical assessment of individual chironomid inferred temperature reconstructions, not only against other temperature proxies but also against proxies for variations in hydrology.

  • 2. Duethorn, Elisabeth
    et al.
    Holzkämper, Steffen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Timonen, Mauri
    Esper, Jan
    Influence of micro-site conditions on tree-ring climate signals and trends in central and northern Sweden2013In: Trees, ISSN 0931-1890, E-ISSN 1432-2285, Vol. 27, no 5, p. 1395-1404Article in journal (Refereed)
    Abstract [en]

    Tree-ring chronologies are important indicators of pre-instrumental, natural climate variability. Some of the longest chronologies are from northern Fennoscandia, where ring width measurement series from living trees are combined with series from sub-fossil trees, preserved in shallow lakes, to form millennial-length records. We here assess the recent ends of such timeseries by comparing climate signals and growth characteristics in central and northern Sweden, of (1) trees growing at lakeshore micro-sites (representing the source of sub-fossil material of supra-long chronologies), with (2) trees collected in dryer micro-sites several meters inland. Calibration trials reveal a predominating June-September temperature signal in N-Sweden and a weaker but significant May-September precipitation signal in C-Sweden. At the micro-site level, the temperature signal in N-Sweden is stronger in the lakeshore trees compared to the inland trees, whereas the precipitation signal in C-Sweden remains unchanged among the lakeshore and inland trees. Tree-rings at cambial ages > 40 years are also substantially wider in the lakeshore micro-site in C-Sweden, and juvenile rings are more variable (and wider) in the dryer micro-site in N-Sweden (compared to the adjacent micro-sites). By combining the data of the various micro-sites with relict samples spanning the past 1,000 years, we demonstrate that growth rate differences at the micro-site scale can affect the low frequency trends of millennial-length chronologies. For the supra-long chronologies from northern Fennoscandia, that are derived from sub-fossil lake material, it is recommended to combine these data with measurement series from only lakeshore trees.

  • 3. Esper, Jan
    et al.
    Holzkämper, Steffen
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Büntgen, Ulf
    Schöne, Bernd
    Keppler, Frank
    Hartl, Claudia
    St. George, Scott
    Riechelmann, Dana F. C.
    Treydte, Kerstin
    Site-specific climatic signals in stable isotope records from Swedish pine forests2018In: Trees, ISSN 0931-1890, E-ISSN 1432-2285, Vol. 32, no 3, p. 855-869Article in journal (Refereed)
    Abstract [en]

    Pinus sylvestris tree-ring delta C-13 and delta O-18 records from locally moist sites in central and northern Sweden contain consistently stronger climate signals than their dry site counterparts. We produced twentieth century stable isotope data from Pinus sylvestris trees near lakeshores and inland sites in northern Sweden (near Kiruna) and central Sweden (near Stockholm) to evaluate the influence of changing microsite conditions on the climate sensitivity of tree-ring delta C-13 and delta O-18. The data reveal a latitudinal trend towards lower C and O isotope values near the Arctic tree line (-0.8 parts per thousand for delta C-13 and - 2.4 parts per thousand for delta O-18 relative to central Sweden) reflecting widely recognized atmospheric changes. At the microsite scale, delta C-13 decreases from the dry inland to the moist lakeshore sites (- 0.7 parts per thousand in Kiruna and - 1.2 parts per thousand in Stockholm), evidence of the importance of groundwater access to this proxy. While all isotope records from northern and central Sweden correlate significantly against temperature, precipitation, cloud cover and/or drought data, climate signals in the records from moist microsites are consistently stronger, which emphasizes the importance of site selection when producing stable isotope chronologies. Overall strongest correlations are found with summer temperature, except for delta O-18 from Stockholm correlating best with instrumental drought indices. These findings are complemented by significant positive correlations with temperature-sensitive ring width data in Kiruna, and inverse (or absent) correlations with precipitation-sensitive ring width data in Stockholm. A conclusive differentiation between leading and co-varying forcings is challenging based on only the calibration against often defective instrumental climate data, and would require an improved understanding of the physiological processes that control isotope fractionation at varying microsites and joined application of forward modelling.

  • 4. Esper, Jan
    et al.
    Konter, Oliver
    Krusic, Paul J.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Saurer, Matthias
    Holzkämper, Steffen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Buentgen, Ulf
    LONG-TERM SUMMER TEMPERATURE VARIATIONS IN THE PYRENEES FROM DETRENDED STABLE CARBON ISOTOPES2015In: Geochronometria, ISSN 1733-8387, E-ISSN 1897-1695, Vol. 42, no 1, p. 53-59Article in journal (Refereed)
    Abstract [en]

    Substantial effort has recently been put into the development of climate reconstructions from tree-ring stable carbon isotopes, though the interpretation of long-term trends retained in such timeseries remains challenging. Here we use detrended delta C-13 measurements in Pinus uncinata tree-rings, from the Spanish Pyrenees, to reconstruct decadal variations in summer temperature back to the 13th century. The June-August temperature signal of this reconstruction is attributed using decadally as well as annually resolved, 20th century delta C-13 data. Results indicate that late 20th century warming has not been unique within the context of the past 750 years. Our reconstruction contains greater amplitude than previous reconstructions derived from traditional tree-ring density data, and describes particularly cool conditions during the late 19th century. Some of these differences, including early warm periods in the 14th and 17th centuries, have been retained via d13C timeseries detrending - a novel approach in tree-ring stable isotope chronology development. The overall reduced variance in earlier studies points to an underestimation of pre-instrumental summer temperature variability derived from traditional tree-ring parameters.

  • 5.
    Holzkämper, Steffen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stable isotopes in tree rings as proxies for winter precipitation changes in the Russian Arctic over the past 150 years2008In: Geochronometria, ISSN 1897-1695, Vol. 32, p. 37-46Article in journal (Refereed)
    Abstract [en]

    We present results from an analysis of tree ring width and stable carbon and oxygen isotopes

    in tree ring cellulose of Siberian Spruce collected from remote forest islands in the northwestern

    Russian tundra. Ring width is often considered a proxy for summer temperatures. The aim of this pilot

    study was to test whether stable isotopes can provide additional information about climate during

    the growth of trees in this extreme environment. Comparison of ä13C and ä18O with observed meteorological

    data shows that there is a link between stable isotopes and winter precipitation. This may

    be explained by the strong influence that snow exerts on the isotopic composition of soil moisture

    during spring and early summer, when the new cellulose is formed. Our results show that winter precipitation

    in the study area was increasing from 1865-1900, and thereafter decreasing until ~1930.

    The 1960-1980 period was again rather humid, followed by a drying trend until 1990. The study highlights

    the potential of stable carbon and oxygen isotopes in tree rings as proxies for winter precipitation.

     

     

     

     

     

     

  • 6.
    Holzkämper, Steffen
    et al.
    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.
    Lee-Thorp, Julia
    Geographical and Environmental Sciences, University of Bradford, UK.
    Talma, Siep
    Natural Resources and the Environment, CSIR, Pretoria, South Africa.
    Mangini, Augusto
    Heidelberger Akademie der Wissenschaften, Heidelberg, Germany.
    Partridge, Tim
    School of Geography, University of Witwatersrand, Johannesburg, South Africa.
    Late Pleistocene stalagmite growth in Wolkberg Cave, South Africa2009In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 282, p. 212-221Article in journal (Refereed)
    Abstract [en]

    Little is known about the sequence of climate and environmental change in southern Africa during the last glacial period, in spite of the intimations from records, such as Antarctic ice cores and archaeological sites, that very marked changes took place which would have had profound effects on vegetation and animal distributions across the sub-continent. High-resolution, (semi-) continuous climate and environmental records can be extracted from suitable cave speleothems. Speleothems are reasonably abundant in southern Africa, but their occurrence is patchy in time and space and the records can be difficult to interpret. Here we report our assessment of the stalagmite W5 from Wolkberg Cave in the northeastern part of South Africa, as an archive for glacial-period climatic and environmental shifts. The cave is located at 1450 m asl, in the dolomitic limestones of the Transvaal System in an area currently dominated by C4 grass vegetation. Nine U/Th dates show growth from 58 to 46 ka, and a second brief phase ca. 40 ka, indicating that the available moisture was sufficient to allow speleothems to form. The δ18O and δ13C values along the growth axis show variability in the order of 2‰ for the former, while variability in the latter is characterized by a shift from values near − 2‰ in the older section to + 2‰ or more in the younger part. These high δ13C values are probably the combined result of CO2 degassing of the percolating soil water prior to the carbonate precipitation in the cave chamber, the increasing dominance of C4 over C3 vegetation, and the high percentage of aragonite towards the stalagmite's top. The retrieved data point towards increasingly drier and colder conditions during the growth period of the stalagmite. Furthermore, the high-frequency variations of δ18O values indicate the presence of short term climate oscillations that are probably linked to shifts of the Intertropical Convergence Zone.

  • 7.
    Holzkämper, Steffen
    et al.
    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. Stockholm University.
    Stable isotopes in tree rings from the Russian Arctic - a proxy for winter precipitation?2009In: PAGES Newsletter, Vol. 17, no 1, p. 14-15Article, review/survey (Other academic)
  • 8.
    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.

  • 9.
    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.
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Sannel, A. Britta K.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Loader, Neil J.
    Robertson, Iain
    Stable carbon and oxygen isotopes in Sphagnum fuscum peat from subarctic Canada: implications for palaeoclimate studies2010In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 270, no 1-4, p. 216-226Article in journal (Refereed)
    Abstract [en]

    Stable carbon and oxygen isotope ratios in single plant components in Sphagnum peat have a good potential to reveal environmental changes in peat archives. Two peat profiles, covering the past ~6000 years, and a Sphagnum hummock from a discontinuous permafrost area in west central Canada were studied in order to evaluate the effect of decomposition rate on isotope records and to assess which plant components are most suitable for climate reconstructions. The stable isotope values from the most recently forming Sphagnum tissues were compared with observational climate data to study the impact of variations in temperature and precipitation on the peat isotopes. Our results show that there is high correlation between δ13C values in α-cellulose isolated from Sphagnum fuscum stems and summer temperatures, whereas δ18O in the plant tissues is controlled by several factors, such as summer precipitation, summer temperature and evaporation. According to our results, decomposition as derived from C/N values and colorimetry does not seem to affect the oxygen and carbon isotope values of α-cellulose from Sphagnum fuscum peat significantly. There is, however, a (quasi-) constant offset between the isotope values of branches and stems and between whole plant material and  α-cellulose, which makes it crucial to select single moss-fractions when past climate and environmental changes are to be derived from the isotope record.

  • 10. Konter, Oliver
    et al.
    Holzkämper, Steffen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Johannes Gutenberg University of Mainz, Germany.
    Helle, Gerhard
    Buentgen, Ulf
    Saurer, Matthias
    Esper, Jan
    Climate sensitivity and parameter coherency in annually resolved delta C-13 and delta O-18 from Pinus uncinata tree-ring data in the Spanish Pyrenees2014In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 377, p. 12-19Article in journal (Refereed)
    Abstract [en]

    We explore the 20th century climate sensitivity of annually resolved carbon and oxygen isotope ratios in five Pinus uncinata individuals from the upper treeline in similar to 2400 m asl of the Spanish Pyrenees. Time series of delta C-13 and delta O-18 are calibrated against temperature, precipitation, and drought indices over the period 1901-2009. Negative correlations of delta C-13 with summer precipitation and drought indices, as well as positive correlations with summer temperatures, confirm previous evidence from similar habitats in the Pyrenees. In contrast to this summer climate signal in the carbon isotopes, the delta O-18 record reveals mainly negative correlations with spring precipitation and drought. We explore the coherence between delta C-13 and delta O-18 time series derived from individual trees and assess the influence of widely applied delta C-13 correction procedures on the climate signal strength. Spatial correlation patterns and decomposition of the time series into high-and low-frequency components are used to develop a calibration setup for carbon and oxygen isotope ratios, which will improve long-term climate reconstructions in a region, where classical tree-ring width and density data are limited.

  • 11. 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.

1 - 11 of 11
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf