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  • 1. Balouet, J-C
    et al.
    Oudijk, G
    Smith, K.T.
    Petrisor, I
    Grudd, H
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stocklassa, B
    Applied Dendroecology and Environmental Forensics. Characterizing and Age Dating Environmental Releases:: Fundamentals and Case Studies.2007In: Environmental Forensics, ISSN 1527–5922, Vol. 8, no 1-2, p. 1-17Article in journal (Refereed)
    Abstract [en]

    Dendroecology, or the use of ring patterns to assess the age of trees and environmental factors controlling their growth, is a well-developed method in climatologic studies. This method holds great potential as a forensic tool for age dating, contamination assessment, and characterization of releases. Moreover, the method is independent of the physical presence of contamination at the time of sampling because it is focused on the effect rather than the cause. This review is one of the very few articles published to date exploring the forensic applicability of dendroecology. This article is organized in two parts: Part I describes the method principles and proposes a practical procedure for forensic applications; Part II exemplifies and validates the method through six case studies of successful forensic application (related to petroleum products and chlorinated solvent spills).

  • 2. Balouet, Jean Christophe
    et al.
    Burken, Joel G.
    Karg, Frank
    Vroblesky, Don
    Smith, Kevin T.
    Grudd, Håkan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Rindby, Anders
    Beaujard, Francois
    Chalot, Michel
    Dendrochemistry of Multiple Releases of Chlorinated Solvents at a Former Industrial Site2012In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 46, no 17, p. 9541-9547Article in journal (Refereed)
    Abstract [en]

    Trees can take up and assimilate contaminants from the soil, subsurface, and groundwater. Contaminants in the transpiration stream can become bound or incorporated into the annual rings formed in trees of the temperate zones. The chemical analysis of precisely dated tree rings, called dendrochemistry, can be used to interpret past plant interactions with contaminants. This investigation demonstrates that dendrochemistry can be used to generate historical scenarios of past contamination of groundwater by chlorinated solvents at a site in Verl, Germany. Increment cores from trees at the Verl site were collected and analyzed by energy-dispersive X-ray fluorescence (EDXRF) line scanning. The EDXRF profiles showed four to six time periods where tree rings had anomalously high concentrations of chlorine (Cl) as an indicator of potential contamination by chlorinated solvents.

  • 3. Björklund, Jesper A.
    et al.
    Gunnarson, Björn E.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Swedish University of Agricultural Sciences, Sweden.
    Krusic, Paul J.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Grudd, Håkan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Josefsson, Torbjörn
    Östlund, Lars
    Linderholm, Hans W.
    Advances towards improved low-frequency tree-ring reconstructions, using an updated Pinus sylvestris L. MXD network from the Scandinavian Mountains2013In: Journal of Theoretical and Applied Climatology, ISSN 0177-798X, E-ISSN 1434-4483, Vol. 113, no 3-4, p. 697-710Article in journal (Refereed)
    Abstract [en]

    The dendrochronological use of the parameter maximum density (MXD) in Pinus Sylvestris L., at high latitudes, has provided valuable insights into past summer temperature variations. Few long MXD chronologies, from climatically coherent regions, exist today, with the exception being in northern Europe. Five, 500-year-long, Fennoscandian, MXD chronologies were compared with regard to their common variability and climate sensitivity. They were used to test Signal-free standardization techniques, to improve inferences of low-frequency temperature variations. Climate analysis showed that, in accordance with previous studies on MXD in Fennoscandia, the summer temperature signal is robust (R (2) > 50 %) and reliable over this climatically coherent region. A combination of Individual standardization and regional curve standardization is recommended to refine long-term variability from these MXD chronologies and relieve problems arising from low replication and standardization end-effects.

  • 4. Briffa, KR
    et al.
    Shishov, VV
    Melvin, TM
    Vaganov, EA
    Grudd, H
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hantemirov, RM
    Eronen, Matti
    Naurzbaev, MM
    Trends in recent temperature and radial tree growth spanning 2000 years across northwest Eurasia.2008In: Philos Trans R Soc Lond B Biol Sci, ISSN 0962-8436, Vol. 363, p. 2271-2284Article in journal (Refereed)
    Abstract [en]

    This paper describes variability in trends of annual tree growth at several locations in the high latitudes of Eurasia, providing a wide regional comparison over a 2000-year period. The study focuses on the nature of local and widespread tree-growth responses to recent warming seen in instrumental observations, available in northern regions for periods ranging from decades to a century. Instrumental temperature data demonstrate differences in seasonal scale of Eurasian warming and the complexity and spatial diversity of tree-growing-season trends in recent decades. A set of long tree-ring chronologies provides empirical evidence of association between inter-annual tree growth and local, primarily summer, temperature variability at each location. These data show no evidence of a recent breakdown in this association as has been found at other high-latitude Northern Hemisphere locations. Using Kendall's concordance, we quantify the time-dependent relationship between growth trends of the long chronologies as a group. This provides strong evidence that the extent of recent widespread warming across northwest Eurasia, with respect to 100- to 200-year trends, is unprecedented in the last 2000 years. An equivalent analysis of simulated temperatures using the HadCM3 model fails to show a similar increase in concordance expected as a consequence of anthropogenic forcing.

  • 5. Büntgen, U
    et al.
    Frank, DC.
    Grudd, H
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Esper, J
    Eight centuries of Pyrenees summer temperatures from tree-ring density2008In: Climate Dynamics, ISSN 0930-7575, Vol. 31, p. 615-631Article in journal (Refereed)
    Abstract [en]

    Two hundred and sixty one newly measured tree-ring width and density series from living and dry-dead conifers from two timberline sites in the Spanish Pyrenees were compiled. Application of the regional curve standardization method for tree-ring detrending allowed the preservation of inter-annual to multi-centennial scale variability. The new density record correlates at 0.53 (0.68 in the higher frequency domain) with May–September maximum temperatures over the 1944–2005 period. Reconstructed warmth in the fourteenth to fifteenth and twentieth century is separated by a prolonged cooling from ∼1450 to 1850. Six of the ten warmest decades fall into the twentieth century, whereas the remaining four are reconstructed for the 1360–1440 interval. Comparison with novel density-based summer temperature reconstructions from the Swiss Alps and northern Sweden indicates decadal to longer-term similarity between the Pyrenees and Alps, but disagreement with northern Sweden. Spatial field correlations with instrumental data support the regional differentiation of the proxy records. While twentieth century warmth is evident in the Alps and Pyrenees, recent temperatures in Scandinavia are relatively cold in comparison to earlier warmth centered around medieval times, ∼1450, and the late eighteenth century. While coldest summers in the Alps and Pyrenees were in-phase with the Maunder and Dalton solar minima, lowest temperatures in Scandinavia occurred later at the onset of the twentieth century. However, fairly cold summers at the end of the fifteenth century, between ∼1600–1700, and ∼1820 were synchronized over Europe, and larger areas of the Northern Hemisphere.

  • 6. Campbell, R
    et al.
    McCarroll, D
    Loader, NJ
    Grudd, H
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Robertson, I
    Jalkanen, R
    Blue intensity in Pinus sylvestris tree-rings: developing a new palaeoclimate proxy2007In: The Holocene, Vol. 17, no 6, p. 821-828Article in journal (Refereed)
    Abstract [en]

    Minimum blue intensity measurements of resin-extracted Pinus sylvestris (L.) samples, conducted using a flat-bed scanner and commercially available software, are shown to provide a robust and reliable surrogate for maximum latewood density. Blue intensity data from 15 trees, from three stands, are reported relative to a standard blue-scale in a manner similar to grey-scale calibration in x-ray densitometry. The resulting time series are highly correlated with x-ray densitometry data generated from the same samples and preserve the same high level of signal strength. Sensitivity to summer climate variables is similar to that identified in the relative density record, demonstrating that minimum blue intensity can also be used for the study of climate change. While not a replacement for the powerful range of x-ray densitometry techniques, blue intensity provides an inexpensive and accessible alternative for accessing palaeoclimatic information.

  • 7. Campell, R
    et al.
    Robertson, I
    McCarrol, D
    Loader, NJ
    Grudd, H
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Gunnarson, B
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Calibration proxy-climate relationshis in central Sweden using stable isotopes in tree rings.2008Conference paper (Other academic)
  • 8.
    Charpentier Ljungqvist, Fredrik
    et al.
    Stockholm University, Faculty of Humanities, Department of History.
    Grudd, Håkan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Arctic summer temperature variability since AD 8002009In: European climate of the last millennium: Millennium milestone meeting 3: Book of abstract, 2009, p. 8-9Conference paper (Other academic)
  • 9. Diego Galvan, J.
    et al.
    Buentgen, Ulf
    Ginzler, Christian
    Grudd, Håkan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Gutierrez, Emilia
    Labuhn, Inga
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Julio Camarero, J.
    Drought-induced weakening of growth-temperature associations in high-elevation Iberian pines2015In: Global and Planetary Change, ISSN 0921-8181, E-ISSN 1872-6364, Vol. 124, p. 95-106Article in journal (Refereed)
    Abstract [en]

    The growth/climate relationship of theoretically temperature-controlled high-elevation forests has been demonstrated to weaken over recent decades. This is likely due to new tree growth limiting factors, such as an increasing drought risk for ecosystem functioning and productivity across the Mediterranean Basin. In addition, declining tree growth sensitivity to spring temperature may emerge in response to increasing drought stress. Here, we evaluate these ideas by assessing the growth/climate sensitivity of 1500 tree-ring width (TRW) and 102 maximum density (MXD) measurement series from 711 and 74 Pinus uncinata trees, respectively, sampled at 28 high-elevation forest sites across the Pyrenees and two relict populations of the Iberian System. Different dendroclimatological standardization and split period approaches were used to assess the high- to low-frequency behavior of 20th century tree growth in response to temperature means, precipitation totals and drought indices. Long-term variations in TRW track summer temperatures until about 1970 but diverge afterwards, whereas MXD captures the recent temperature increase in the low-frequency domain fairly well. On the other hand summer drought has increasingly driven TRW along the 20th century. Our results suggest fading temperature sensitivity of Iberian high-elevation P. uncinata forest growth, and reveal the importance of summer drought that is becoming the emergent limiting factor of tree ring width formation in many parts of the Mediterranean Basin.

  • 10. Fors, Yvonne
    et al.
    Grudd, Håkan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Rindby, Anders
    Jalilehvand, Farideh
    Sandström, Magnus
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Cato, Ingemar
    Bornmalm, Lennart
    Sulfur and iron accumulation in three marine-archaeological shipwrecks in the Baltic Sea: The Ghost, the Crown and the Sword2014In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 4, p. 4222-Article in journal (Refereed)
    Abstract [en]

    Sulfur and iron concentrations in wood from three 17th century shipwrecks in the Baltic Sea, the Ghost wreck, the Crown and the Sword, were obtained by X-ray fluorescence (XRF) scanning. In near anaerobic environments symbiotic microorganisms degrade waterlogged wood, reduce sulfate and promote accumulation of low-valent sulfur compounds, as previously found for the famous wrecks of the Vasa and Mary Rose. Sulfur K-edge X-ray absorption near-edge structure (XANES) analyses of Ghost wreck wood show that organic thiols and disulfides dominate, together with elemental sulfur probably generated by sulfur-oxidizing Beggiatoa bacteria. Iron sulfides were not detected, consistent with the relatively low iron concentration in the wood. In a museum climate with high atmospheric humidity oxidation processes, especially of iron sulfides formed in the presence of corroding iron, may induce post-conservation wood degradation. Subject to more general confirmation by further analyses no severe conservation concerns are expected for the Ghost wreck wood.

  • 11. Gagen, Mary
    et al.
    Zorita, Eduardo
    McCarroll, Danny
    Young, Giles H. F.
    Grudd, Håkan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jalkanen, Risto
    Loader, Neil J.
    Robertson, Iain
    Kirchhefer, Andreas
    Cloud response to summer temperatures in Fennoscandia over the last thousand years2011In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 38, p. L05701-Article in journal (Refereed)
    Abstract [en]

    Cloud cover is one of the most important factors controlling the radiation balance of the Earth. The response of cloud cover to increasing global temperatures represents the largest uncertainty in model estimates of future climate because the cloud response to temperature is not well-constrained. Here we present the first regional reconstruction of summer sunshine over the past millennium, based on the stable carbon isotope ratios of pine treerings from Fennoscandia. Comparison with the regional temperature evolution reveals the Little Ice Age (LIA) to have been sunny, with cloudy conditions in the warmest periods of the Medieval at this site. A negative shortwave cloud feedback is indicated at high latitude. A millennial climate simulation suggests that regionally low temperatures during the LIA were mostly maintained by a weaker greenhouse effect due to lower humidity. Simulations of future climate that display a negative shortwave cloud feedback for high-latitudes are consistent with our proxy interpretation. Citation: Gagen, M., E. Zorita, D. McCarroll, G. H. F. Young, H. Grudd, R. Jalkanen, N. J. Loader, I. Robertson, and A. Kirchhefer (2011), Cloud response to summer temperatures in Fennoscandia over the last thousand years, Geophys. Res. Lett., 38, L05701, doi:10.1029/2010GL046216.

  • 12.
    Grudd, H
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Torneträsk tree-ring width and density AD 500 – 2004: A test of climatic sensitivity and a new 1500-year reconstruction of north Fennoscandian summers2008In: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 31, p. 843-857Article in journal (Refereed)
    Abstract [en]

    This paper presents updated tree-ring width(TRW) and maximum density (MXD) from Tornetra¨sk innorthern Sweden, now covering the period AD 500–2004. Byincluding data from relatively young trees for the most recentperiod, a previously noted decline in recent MXD is eliminated.Non-climatological growth trends in the data areremoved using Regional Curve Standardization (RCS), thusproducingTRWandMXDchronologies with preserved lowfrequencyvariability. The chronologies are calibrated usinglocal and regional instrumental climate records. A bootstrappedresponse function analysis using regional climatedata shows that tree growth is forced by April–August temperaturesand that the regression weights for MXD are muchstronger than for TRW. The robustness of the reconstructionequation is verified by independent temperature data andshows that 63–64% of the instrumental inter-annual variationis captured by the tree-ring data. This is a significantimprovement compared to previously published reconstructionsbased on tree-ring data from Tornetra¨sk. Adivergence phenomenon around AD 1800, expressed as anincrease in TRW that is not paralleled by temperature andMXD, is most likely an effect of major changes in the densityof the pine population at this northern tree-line site. The biasintroduced by this TRW phenomenon is assessed by producinga summer temperature reconstruction based onMXDexclusively. The new data show generally higher temperatureestimates than previous reconstructions based onTornetra¨sk tree-ring data. The late-twentieth century, however,is not exceptionally warm in the new record: Ondecadal-to-centennial timescales, periods around AD 750,1000, 1400, and 1750 were equally warm, or warmer. The200-year long warm period centered on AD 1000 was significantlywarmer than the late-twentieth century (p\0.05)and is supported by other local and regional paleoclimatedata. The new tree-ring evidence from Tornetra¨sk suggeststhat this ‘‘Medieval WarmPeriod’’ in northern Fennoscandiawas much warmer than previously recognized.

  • 13.
    Grudd, H
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Briffa, KR
    Gunnarson, BE
    Linderholm, HW
    Swedish tree rings provide new evidence in support of a major, widespread environmental disruption in 1628 BC2000In: Geophysical Research Letters, Vol. 27, no 18, p. 2957-2960Article in journal (Refereed)
  • 14.
    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.

  • 15. Larsen, LB
    et al.
    Vinther, BM
    Briffa, KR
    Melvin, TM
    Clausen, HB
    Jones, PD
    Siggaard-Andersen, M-L
    Hammer, CU
    Eronen, M
    Grudd, H
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Gunnarson, BE
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hantemirov, RM
    Naurzbaev, MM
    New ice core evidence for a volcanic cause of the A.D. 536 dust veil2008In: Geophysical Research Letters, Vol. 35, no L04708Article in journal (Refereed)
    Abstract [en]

    New and well-dated evidence of sulphate deposits in Greenland and Antarctic ice cores indicate a substantial and extensive atmospheric acidic dust veil at A.D. 533–534 ± 2 years. This was likely produced by a large explosive, near equatorial volcanic eruption, causing widespread dimming and contributing to the abrupt cooling across much of the Northern Hemisphere known from historical records and tree-ring data to have occurred in A.D. 536. Tree-ring data suggest that this was the most severe and protracted short-term cold episode across the Northern Hemisphere in the last two millennia, even surpassing the severity of the cold period following the Tambora eruption in 1815.

  • 16. Levanic, T
    et al.
    Gricar, J
    Grudd, H
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Gunnarson, B
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Climate sensitivity of European larch (Larix deciduas Mill.) in the southeasternpart of the Alps2008Conference paper (Other academic)
  • 17. Linderholm, H. W.
    et al.
    Björklund, J. A.
    Seftigen, K.
    Gunnarson, B. E.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Grudd, Håkan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Jeong, J. -H
    Drobyshev, I.
    Liu, Y.
    Dendroclimatology in Fennoscandia - from past accomplishments to future potential2010In: Climate of the past, ISSN 1814-9324, Vol. 6, no 1, p. 93-114Article in journal (Refereed)
    Abstract [en]

    Fennoscandia has a strong tradition in dendrochronology, and its large tracts of boreal forest make the region well suited for the development of tree-ring chronologies that extend back several thousands of years. Two of the world's longest continuous (most tree-ring chronologies are annually resolved) tree-ring width chronologies are found in northern Fennoscandia, with records from Tornetrask and Finnish Lapland covering the last ca. 7500 yr. In addition, several chronologies between coastal Norway and the interior of Finland extend back several centuries. Tree-ring data from Fennoscandia have provided important information on regional climate variability during the mid to late Holocene and have played major roles in the reconstruction of hemispheric and global temperatures. Tree-ring data from the region have also been used to reconstruct large-scale atmospheric circulation patterns, regional precipitation and drought. Such information is imperative when trying to reach better understanding of natural climate change and variability and its forcing mechanisms, and placing recent climate change within a long-term context.

  • 18. Linderholm, HW
    et al.
    Moberg, A
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Grudd, H
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Peatland pines as climate indicators? A regional comparison of the climatic influence on Scots pine growth in Sweden2002In: Canadian Journal of Forest Research, Vol. 32, no 8, p. 1400-1410Article in journal (Refereed)
  • 19. Lindholm, M.
    et al.
    Aalto, T.
    Grudd, Håkan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    McCarroll, D.
    Ogurtsov, M.
    Jalkanen, R.
    Common temperature signal in four well-replicated tree growth series from northern Fennoscandia2012In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 27, no 8, p. 828-834Article in journal (Refereed)
    Abstract [en]

    Four Nordic temperature proxies based on tree growth at the northern timberline ring-width from Sweden and Finland, maximum latewood density from Sweden, and height increment from Finland were compared. Three indexing methods were used to enhance the low (centennial and above), medium (decadal-to-multidecadal) and high (decadal-to-interannual) frequencies. The proxies are shown to have a strong temperature signal (common variance) at the interannual-to-multidecadal scale, while the multidecadal-to-centennial trends are less coherent, perhaps reflecting intra-regional differences in growing conditions but more likely due to the more noisy regional curve standardization method used to retain the longest trends. Various methods of combining the four proxy series were explored and tested by comparison with four long temperature records from northern Fennoscandia. Only relatively high-frequency, spline-indexed series produced consistently positive verification statistics as a reconstruction model for summer temperature using all four proxies.

  • 20. Loader, N. J.
    et al.
    Young, G. H. F.
    Grudd, Håkan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    McCarroll, D.
    Stable carbon isotopes from Tornetrask, northern Sweden provide a millennial length reconstruction of summer sunshine and its relationship to Arctic circulation2013In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 62, p. 97-113Article in journal (Refereed)
    Abstract [en]

    This paper presents results from the first 1100 years of a long stable carbon isotope chronology currently in development from Scots Pine (Pinus sylvestris L.) trees growing in the Tornetrask region of northern Sweden. The isotope record currently comprises a total of 74 trees with a mean annual replication of >12, thereby enabling it to be compared directly with other tree-ring based palaeoclimate reconstructions from this region. In developing the reconstruction, several key topics in isotope dendroclimatology (chronology construction, replication, CO2 adjustment and age trends) were addressed. The resulting carbon isotope series is calibrated against instrumental data from the closest meteorological station at Abisko (AD1913-2008) to provide a record of June August sunshine for northern Fennoscandia. This parameter is closely linked to the direct control of assimilation rate; Photosynthetically Active Radiation (PAR) and the indirect measures; mean July August temperature and percent cloud cover. The coupled response of summer sunshine and temperature in this region permits a multiparameter comparison with a local reconstruction of past temperature variability based upon tree growth proxies to explore the stability of this coupling through time. Several periods are identified where the temperature (X-ray density) and sunshine (stable carbon isotope ratio) records diverge. The most significant and sustained of these occur between c AD1200-1380 and c AD1550-1780, providing evidence for a cool, sunny, two-phase Little Ice Age. Whilst summer sunshine reconstructed for the 20th century is significantly different from the mean of the last 1100 years (P < 0.01), conditions during the early medival period are similar to those experienced in northern Fennoscandia during the 20th century (P > 0.01), so it is the 17th-18th, and to a lesser extent, the 13th centuries rather than the early medival period that appear anomalous when viewed within the context of the last 1100 years. The observed departures between temperature and sunshine are interpreted as indicating a change in large-scale circulation associated with a southward migration of the Polar Front. Such a change, affecting the Northern Annular Mode (Arctic Oscillation) would result in more stable anticyclonic conditions (cool, bright, summers) over northern Fennoscandia, thus providing a testable mechanism for the development of a multi-phase, time-transgressive Little Ice Age across Europe.

  • 21. 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.

  • 22. Mccarroll, Danny
    et al.
    Tuovinen, Mervi
    Campbell, Rochelle
    Gagen, Mary
    Grudd, Håkan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jalkanen, Risto
    Loader, Neil J.
    Robertson, Iain
    A critical evaluation of multi-proxy dendroclimatology in northern Finland2011In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 26, no 1, p. 7-14Article in journal (Refereed)
    Abstract [en]

    Twentieth-century summer (July-August) temperatures in northern Finland are reconstructed using ring widths, maximum density and stable carbon isotope ratios (delta(13)C) of Scots pine tree rings, and using combinations of these proxies. Verification is based on the coefficient of determination (r(2)), reduction of error (RE) and coefficient of efficiency (CE) statistics. Of the individual proxies, delta(13)C performs best, followed by maximum density. Combining delta(13)C and maximum density strengthens the climate signal but adding ring widths leads to little improvement. Blue intensity, an inexpensive alternative to X-ray densitometry, is shown to perform similarly. Multi-proxy reconstruction of summer temperatures from a single site produces strong correlations with gridded climate data over most of northern Fennoscandia. Since relatively few trees are required (<15) the approach could be applied to long sub-fossil chronologies where replication may be episodically low.

  • 23. 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'.

  • 24.
    Moberg, Anders
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Sundberg, Rolf
    Stockholm University, Faculty of Science, Department of Mathematics.
    Grudd, Håkan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Hind, Alistair
    Stockholm University, Faculty of Science, Department of Physical Geography. Stockholm University, Faculty of Science, Department of Mathematics.
    Statistical framework for evaluation of climate model simulations by use of climate proxy data from the last millennium - Part 3: Practical considerations, relaxed assumptions, and using tree-ring data to address the amplitude of solar forcing2015In: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 11, no 3, p. 425-448Article in journal (Refereed)
    Abstract [en]

    A statistical framework for evaluation of climate model simulations by comparison with climate observations from instrumental and proxy data (part 1 in this series) is improved by the relaxation of two assumptions. This allows autocorrelation in the statistical model for simulated internal climate variability and enables direct comparison of two alternative forced simulations to test whether one fits the observations significantly better than the other. The extended framework is applied to a set of simulations driven with forcings for the pre-industrial period 1000-1849 CE and 15 tree-ring-based temperature proxy series. Simulations run with only one external forcing (land use, volcanic, small-amplitude solar, or large-amplitude solar) do not significantly capture the variability in the tree-ring data - although the simulation with volcanic forcing does so for some experiment settings. When all forcings are combined (using either the small- or large-amplitude solar forcing), including also orbital, greenhouse-gas and non-volcanic aerosol forcing, and additionally used to produce small simulation ensembles starting from slightly different initial ocean conditions, the resulting simulations are highly capable of capturing some observed variability. Nevertheless, for some choices in the experiment design, they are not significantly closer to the observations than when unforced simulations are used, due to highly variable results between regions. It is also not possible to tell whether the small-amplitude or large-amplitude solar forcing causes the multiple-forcing simulations to be closer to the reconstructed temperature variability. Proxy data from more regions and of more types, or representing larger regions and complementary seasons, are apparently needed for more conclusive results from model-data comparisons in the last millennium.

  • 25. Pritzkow, C.
    et al.
    Heinrich, I.
    Grudd, Håkan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Helle, G.
    Relationship between wood anatomy, tree-ring widths and wood density of Pinus sylvestris L. and climate at high latitudes in northern Sweden2014In: Dendrochronologia, ISSN 1125-7865, E-ISSN 1612-0051, Vol. 32, no 4, p. 295-302Article in journal (Refereed)
    Abstract [en]

    In this study, wood anatomy, tree-ring width and wood density of Pinus sylvestris at the northern timberline in Fennoscandia were used to identify relationships among the parameters and to screen them for their climatic signals. Furthermore we investigated the influence of the juvenile wood section for all parameters developed. The measurements of wood anatomy were conducted with confocal laser scanning microscopy (CLSM) while the density profiles were produced using an Itrax MultiScanner. We developed chronologies of ring width, wood density and anatomy for a period between 1940 and 2010. Correlations between wood density and wood anatomy were strong in the latewood part. For some wood anatomy and density chronologies youth trends were found in the juvenile part. Wood density decreased from the pith up to the 9th ring and stabilized afterwards, while cell lumen diameter and lumen area increased simultaneously up to the 15th ring. All chronologies contained strong summer temperature signals. The wood anatomical variables provided additional information about seasonal precipitation which could not be found in wood density and tree-ring widths. Our study confirmed previous results stating that the parameter maximum density contains the strongest climate signal, that is, summer temperatures at the northern timberline. Nevertheless, the intra-annual data on tracheid dimensions showed good potential to supply seasonal climatic information and improve our understanding of climatic effects on tree growth and wood formation.

  • 26. Roig, FA
    et al.
    Le-Quesne, C
    Boninsegna, JA
    Briffa, KR
    Lara, A
    Grudd, H
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Jones, PD
    Villagran, C
    Climate variability 50,000 years ago in midlatitude Chile as reconstructed from tree rings2001In: Nature, Vol. 410, p. 567-570Article in journal (Refereed)
  • 27. Saurer, Matthias
    et al.
    Spahni, Renato
    Frank, David C.
    Joos, Fortunat
    Leuenberger, Markus
    Loader, Neil J.
    McCarroll, Danny
    Gagen, Mary
    Poulter, Ben
    Siegwolf, Rolf T. W.
    Andreu-Hayles, Laia
    Boettger, Tatjana
    Dorado Linan, Isabel
    Fairchild, Ian J.
    Friedrich, Michael
    Gutierrez, Emilia
    Haupt, Marika
    Hilasvuori, Emmi
    Heinrich, Ingo
    Helle, Gerd
    Grudd, Håkan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jalkanen, Risto
    Levanic, Tom
    Linderholm, Hans W.
    Robertson, Iain
    Sonninen, Eloni
    Treydte, Kerstin
    Waterhouse, John S.
    Woodley, Ewan J.
    Wynn, Peter M.
    Young, Giles H. F.
    Spatial variability and temporal trends in water-use efficiency of European forests2014In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 20, no 12, p. 3700-3712Article in journal (Refereed)
    Abstract [en]

    The increasing carbon dioxide (CO2) concentration in the atmosphere in combination with climatic changes throughout the last century are likely to have had a profound effect on the physiology of trees: altering the carbon and water fluxes passing through the stomatal pores. However, the magnitude and spatial patterns of such changes in natural forests remain highly uncertain. Here, stable carbon isotope ratios from a network of 35 tree-ring sites located across Europe are investigated to determine the intrinsic water-use efficiency (iWUE), the ratio of photosynthesis to stomatal conductance from 1901 to 2000. The results were compared with simulations of a dynamic vegetation model (LPX-Bern 1.0) that integrates numerous ecosystem and land-atmosphere exchange processes in a theoretical framework. The spatial pattern of tree-ring derived iWUE of the investigated coniferous and deciduous species and the model results agreed significantly with a clear south-to-north gradient, as well as a general increase in iWUE over the 20th century. The magnitude of the iWUE increase was not spatially uniform, with the strongest increase observed and modelled for temperate forests in Central Europe, a region where summer soil-water availability decreased over the last century. We were able to demonstrate that the combined effects of increasing CO2 and climate change leading to soil drying have resulted in an accelerated increase in iWUE. These findings will help to reduce uncertainties in the land surface schemes of global climate models, where vegetation-climate feedbacks are currently still poorly constrained by observational data.

  • 28. Smith, Kevin T.
    et al.
    Balouet, Jean Christophe
    Shortle, Walter C.
    Chalot, Michel
    Beaujard, Francois
    Grudd, Håkan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Vroblesky, Don A.
    Burken, Joel G.
    Dendrochemical patterns of calcium, zinc, and potassium related to internal factors detected by energy dispersive X-ray fluorescence (EDXRF)2014In: Chemosphere, ISSN 0045-6535, E-ISSN 1879-1298, Vol. 95, p. 58-62Article in journal (Refereed)
    Abstract [en]

    Energy dispersive X-ray fluorescence (EDXRF) provides highly sensitive and precise spatial resolution of cation content in individual annual growth rings in trees. The sensitivity and precision have prompted successful applications to forensic dendrochemistry and the timing of environmental releases of contaminants. These applications have highlighted the need to distinguish dendrochemical effects of internal processes from environmental contamination. Calcium, potassium, and zinc are three marker cations that illustrate the influence of these processes. We found changes in cation chemistry in tree rings potentially due to biomineralization, development of cracks or checks, heartwood/sapwood differentiation, intraannual p'rocesses, and compartmentalization of infection. Distinguishing internal from external processes that affect dendrochemistry will enhance the value of EDXRF for both physiological and forensic investigations.

  • 29. Tuovinen, M
    et al.
    McCarroll, D
    Grudd, H
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jalkanen, R
    Los, S
    Spatial and temporal stability of the climatic signal in northern Fennoscandian pine tree ring width and maximum density2009In: Boreas, Vol. 38, p. 1-12Article in journal (Refereed)
  • 30. Tuovinen, M
    et al.
    McCarroll, D
    Grudd, H
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jalkanen, R
    Los, S
    Spatial and temporal stability of the climatic signal in northern Fennoscandian pine tree ring width and maximum density2008Conference paper (Other academic)
1 - 30 of 30
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