| 1. |
- Anchukaitis, Kevin, et al.
(författare)
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Last millennium Northern Hemisphere summer temperatures from tree rings: Part II, spatially resolved reconstructions
- 2017
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 163, s. 1-22
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Tidskriftsartikel (refereegranskat)abstract
- Climate field reconstructions from networks of tree-ring proxy data can be used to characterize regionalscale climate changes, reveal spatial anomaly patterns associated with atmospheric circulation changes, radiative forcing, and large-scale modes of ocean-atmosphere variability, and provide spatiotemporal targets for climate model comparison and evaluation. Here we use a multiproxy network of tree-ring chronologies to reconstruct spatially resolved warm season (MayeAugust) mean temperatures across the extratropical Northern Hemisphere (40-90N) using Point-by-Point Regression (PPR). The resulting annual maps of temperature anomalies (750e1988 CE) reveal a consistent imprint of volcanism, with 96% of reconstructed grid points experiencing colder conditions following eruptions. Solar influences are detected at the bicentennial (de Vries) frequency, although at other time scales the influence of insolation variability is weak. Approximately 90% of reconstructed grid points show warmer temperatures during the Medieval Climate Anomaly when compared to the Little Ice Age, although the magnitude varies spatially across the hemisphere. Estimates of field reconstruction skill through time and over space can guide future temporal extension and spatial expansion of the proxy network.
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| 2. |
- Björklund, Jesper, 1979, et al.
(författare)
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Advances towards improved low-frequency tree-ring reconstructions, using an updated Pinus sylvestris L. MXD network from the Scandinavian Mountains
- 2013
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Ingår i: Journal of Theoretical and Applied Climatology. - : Springer Science and Business Media LLC. - 0177-798X .- 1434-4483. ; 113:3-4, s. 697-710
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Björklund, Jesper, 1979, et al.
(författare)
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Blue intensity and density from Northern Fennoscandian tree rings, exploring the potential to improve summer temperature reconstructions with earlywood information
- 2014
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Ingår i: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 10, s. 877-885
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Tidskriftsartikel (refereegranskat)abstract
- Here we explore two new tree-ring parameters, derived from measurements of wood density and blue intensity (BI). The new proxies show an increase in the interannual summer temperature signal compared to established proxies, and present the potential to improve long-term performance. At high latitudes, where tree growth is mainly limited by low temperatures, radiodensitometric measurements of wood density, specifically maximum latewood density (MXD), provides a temperature proxy that is superior to that of tree-ring widths. The high cost of developing MXD has led to experimentation with a less expensive method using optical flatbed scanners to produce a new proxy, herein referred to as maximum latewood blue absorption intensity (abbreviated MXBI). MXBI is shown to be very similar to MXD on annual timescales but less accurate on centennial timescales. This is due to the fact that extractives, such as resin, stain the wood differentially from tree to tree and from heartwood to sapwood. To overcome this problem, and to address similar potential problems in radiodensitometric measurements, the new parameters 1blue intensity (1BI) and 1density are designed by subtracting the ambient BI/density in the earlywood, as a background value, from the latewood measurements. As a case-study, based on Scots pine trees from Northern Sweden, we show that 1density can be used as a quality control of MXD values and that the reconstructive performance of warm-season mean temperatures is more focused towards the summer months (JJA – June, July, August), with an increase by roughly 20% when also utilising the interannual information from the earlywood. However, even though the new parameter 1BI experiences an improvement as well, there are still puzzling dissimilarities between 1density and 1BI on multicentennial timescales. As a consequence, temperature reconstructions based on 1BI will presently only be able to resolve information on decadalto- centennial timescales. The possibility of trying to calibrate BI into a measure of lignin content or density, similarly to how radiographic measurements are calibrated into density, could be a solution. If this works, only then can 1BI be used as a reliable proxy in multicentennial-scale climate reconstructions.
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| 4. |
- Björklund, Jesper, et al.
(författare)
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Fennoscandian tree-ring anatomy shows a warmer modern than medieval climate.
- 2023
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Ingår i: Nature. - 1476-4687 .- 0028-0836. ; 620:7972, s. 97-103
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Tidskriftsartikel (refereegranskat)abstract
- Earth system models and various climate proxy sources indicate global warming is unprecedented during at least the Common Era1. However, tree-ring proxies often estimate temperatures during the Medieval Climate Anomaly (950-1250CE) that are similar to, or exceed, those recorded for the past century2,3, in contrast tosimulation experiments at regional scales4. This not only calls into question the reliability of models and proxies but also contributes to uncertainty in future climate projections5. Here we show that the current climate of the Fennoscandian Peninsula is substantially warmer than that of the medieval period. This highlights the dominant role of anthropogenic forcing in climate warming even at the regional scale, thereby reconciling inconsistencies between reconstructions and model simulations. We used an annually resolved 1,170-year-long tree-ring record that relies exclusively on tracheid anatomical measurements from Pinus sylvestris trees, providing high-fidelity measurements of instrumental temperature variability during the warm season. We therefore call for the construction of more such millennia-long records to further improve our understanding and reduce uncertainties around historical and future climate change at inter-regional and eventually global scales.
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| 5. |
- Björklund, J., et al.
(författare)
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Scientific Merits and Analytical Challenges of Tree-Ring Densitometry
- 2019
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Ingår i: Reviews of geophysics. - 8755-1209 .- 1944-9208. ; 57:4, s. 1224-1264
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Forskningsöversikt (refereegranskat)abstract
- X-ray microdensitometry on annually resolved tree-ring samples has gained an exceptional position in last-millennium paleoclimatology through the maximum latewood density (MXD) parameter, but also increasingly through other density parameters. For 50 years, X-ray based measurement techniques have been the de facto standard. However, studies report offsets in the mean levels for MXD measurements derived from different laboratories, indicating challenges of accuracy and precision. Moreover, reflected visible light-based techniques are becoming increasingly popular, and wood anatomical techniques are emerging as a potentially powerful pathway to extract density information at the highest resolution. Here we review the current understanding and merits of wood density for tree-ring research, associated microdensitometric techniques, and analytical measurement challenges. The review is further complemented with a careful comparison of new measurements derived at 17 laboratories, using several different techniques. The new experiment allowed us to corroborate and refresh long-standing wisdom but also provide new insights. Key outcomes include (i) a demonstration of the need for mass/volume-based recalibration to accurately estimate average ring density; (ii) a substantiation of systematic differences in MXD measurements that cautions for great care when combining density data sets for climate reconstructions; and (iii) insights into the relevance of analytical measurement resolution in signals derived from tree-ring density data. Finally, we provide recommendations expected to facilitate futureinter-comparability and interpretations for global change research.
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| 6. |
- Björklund, Jesper, 1979, et al.
(författare)
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Using adjusted Blue Intensity data to attain high-quality summer temperature information : A case study from Central Scandinavia
- 2015
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Ingår i: The Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 25:3, s. 547-556
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
- Büntgen, Ulf, et al.
(författare)
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The influence of decision-making in tree ring-based climate reconstructions
- 2021
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- Tree-ring chronologies underpin the majority of annually-resolved reconstructions of Common Era climate. However, they are derived using different datasets and techniques, the ramifications of which have hitherto been little explored. Here, we report the results of a double-blind experiment that yielded 15 Northern Hemisphere summer temperature reconstructions from a common network of regional tree-ring width datasets. Taken together as an ensemble, the Common Era reconstruction mean correlates with instrumental temperatures from 1794–2016 CE at 0.79 (p < 0.001), reveals summer cooling in the years following large volcanic eruptions, and exhibits strong warming since the 1980s. Differing in their mean, variance, amplitude, sensitivity, and persistence, the ensemble members demonstrate the influence of subjectivity in the reconstruction process. We therefore recommend the routine use of ensemble reconstruction approaches to provide a moreconsensual picture of past climate variability.
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| 8. |
- Buntgen, U., et al.
(författare)
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Tree rings reveal globally coherent signature of cosmogenic radiocarbon events in 774 and 993 CE
- 2018
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Though tree-ring chronologies are annually resolved, their dating has never been independently validated at the global scale. Moreover, it is unknown if atmospheric radiocarbon enrichment events of cosmogenic origin leave spatiotemporally consistent fingerprints. Here we measure the 14C content in 484 individual tree rings formed in the periods 770–780 and 990–1000 CE. Distinct 14C excursions starting in the boreal summer of 774 and the boreal spring of 993 ensure the precise dating of 44 tree-ring records from five continents. We also identify a meridional decline of 11-year mean atmospheric radiocarbon concentrations across both hemispheres. Corroborated by historical eye-witness accounts of red auroras, our results suggest a global exposure to strong solar proton radiation. To improve understanding of the return frequency and intensity of past cosmic events, which is particularly important for assessing the potential threat of space weather on our society, further annually resolved 14C measurements are needed.
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| 9. |
- Campbell, Rochelle, et al.
(författare)
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BLUE INTENSITY IN PINUS SYLVESTRIS TREE RINGS : A MANUAL FOR A NEW PALAEOCLIMATE PROXY
- 2011
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Ingår i: TREE-RING RESEARCH. - : Tree-Ring Society. - 1536-1098. ; 67:2, s. 127-134
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Tidskriftsartikel (refereegranskat)abstract
- Minimum blue intensity is a reflected light imaging technique that provides an inexpensive, robust and reliable surrogate for maximum latewood density. In this application it was found that temperature reconstructions from resin-extracted samples of Pious sylvestris (L.) from Fennoscandia provide results equivalent to conventional x-ray densitometry. This paper describes the implementation of the blue intensity method using commercially available software and a flat-bed scanner. A calibration procedure is presented that permits results obtained by different laboratories, or using different scanners, to be compared. In addition, the use of carefully prepared and chemically treated 10-mm-diameter cores are explored; suggesting that it may not be necessary to produce thin laths with the rings aligned exactly perpendicular to the measurement surface.
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| 10. |
- Cerrato, Riccardo, et al.
(författare)
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A Pinus cembra L. tree-ring record for late spring to late summer temperature in the Rhaetian Alps, Italy
- 2019
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Ingår i: Dendrochronologia. - : Elsevier BV. - 1125-7865 .- 1612-0051. ; 53, s. 22-31
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Tidskriftsartikel (refereegranskat)abstract
- Ongoing climate change strongly affects high-elevation environments in the European Alps, influencing the cryosphere and the biosphere and causing widespread retreat of glaciers and changes in biomes. Nevertheless, high-elevation areas often lack long meteorological series, and global datasets cannot represent local variations well. Thus, proxy data, such as tree rings, provide information on past climatic variations from these remote sites. Although maximum latewood density (MXD) chronologies provide better temperature information than those based on tree-ring width (TRW), MXD series from the European Alps are lacking. To derive high-quality temperature information for the Rhaetian Alps, Pinus cembra L. trees sampled at approximately 2000 m a.s.l. were used to build one MXD chronology spanning from 1647 to 2015. The MXD data were significantly and highly correlated with seasonal May-September mean temperatures. The MXD chronology showed a generally positive trend since the middle of the 19th century, interrupted by short phases of climatic deterioration in the beginning of the 20th century and in the 1970s, conforming with the temperature trends. Our results underline the potential for using Pinus cembra L. MXD to reconstruct mean temperature variations, especially during the onset and latter part of the growing season, providing additional information on parts of the growing season not inferred from TRW. Future studies on MXD for this species will increase the availability of temporal and spatial data, allowing detailed climate reconstructions.
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| 11. |
- Cerrato, Riccardo, et al.
(författare)
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Pinus cembra L. tree-ring data as a proxy for summer mass-balance variability of the Careser Glacier (Italian Rhaetian Alps)
- 2020
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Ingår i: Journal of Glaciology. - : Cambridge University Press (CUP). - 0022-1430 .- 1727-5652. ; 66:259, s. 714-726
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Tidskriftsartikel (refereegranskat)abstract
- Copyright © The Author(s), 2020. Published by Cambridge University Press. Glacial extent and mass balance are sensitive climate proxies providing solid information on past climatic conditions. However, series of annual mass-balance measurements of more than 60 years are scarce. To our knowledge, this is the first time the latewood density data (MXD) of the Swiss stone pine (Pinus cembra L.) have been used to reconstruct the summer mass balance (Bs) of an Alpine glacier. The MXD-based Bs well correlates with a Bs reconstruction based on the May to September temperature. Winter precipitation has been used as an independent proxy to infer the winter mass balance and to obtain an annual mass-balance (Bn) estimate dating back to the glaciological year 1811/12. The reconstructed MXD/precipitation-based Bn well correlates with the data both of the Careser and of other Alpine glaciers measured by the glaciological method. A number of critical issues should be considered in both proxies, including non-linear response of glacial mass balance to temperature, bedrock topography, ice thinning and fragmentation, MXD acquisition and standardization methods, and finally the 'divergence problem' responsible for the recently reduced sensitivity of the dendrochronological data. Nevertheless, our results highlight the possibility of performing MXD-based dendroglaciological reconstructions using this stable and reliable proxy.
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| 12. |
- Charpentier Ljungqvist, Fredrik, et al.
(författare)
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Assessing non-linearity in European temperature-sensitive tree-ring data
- 2020
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Ingår i: Dendrochronologia. - : Elsevier BV. - 1125-7865 .- 1612-0051. ; 59
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Tidskriftsartikel (refereegranskat)abstract
- © 2019 The Authors We test the application of parametric, non-parametric, and semi-parametric calibration models for reconstructing summer (June–August) temperature from a set of tree-ring width and density data on the same dendro samples from 40 sites across Europe. By comparing the performance of the three calibration models on öpairs” of tree-ring width (TRW) and maximum density (MXD) or maximum blue intensity (MXBI), we test whether a non-linear temperature response is more prevalent in TRW or MXD (MXBI) data, and whether it is associated with the temperature sensitivity and/or autocorrelation structure of the dendro parameters. We note that MXD (MXBI) data have a significantly stronger temperature response than TRW data as well as a lower autocorrelation that is more similar to that of the instrumental temperature data, whereas TRW exhibits a öredder” variability continuum. This study shows that the use of non-parametric calibration models is more suitable for TRW data, while parametric calibration is sufficient for both MXD and MXBI data – that is, we show that TRW is by far the more non-linear proxy.
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| 13. |
- Cook, ER, et al.
(författare)
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Old World megadroughts and pluvials during the Common Era
- 2015
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Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 1:10
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Tidskriftsartikel (refereegranskat)abstract
- Climate model projections suggest widespread drying in the Mediterranean Basin and wetting in Fennoscandia in the coming decades largely as a consequence of greenhouse gas forcing of climate. To place these and other “Old World” climate projections into historical perspective based on more complete estimates of natural hydroclimatic variability, we have developed the “Old World Drought Atlas” (OWDA), a set of year-to-year maps of tree-ring reconstructed summer wetness and dryness over Europe and the Mediterranean Basin during the Common Era. TheOWDAmatches historical accounts of severe drought and wetness with a spatial completeness not previously available. In addition, megadroughts reconstructed over north-central Europe in the 11th and mid-15th centuries reinforce other evidence from North America and Asia that droughts were more severe, extensive, and prolonged over Northern Hemisphere land areas before the 20th century, with an inadequate understanding of their causes. The OWDA provides new data to determine the causes of Old World drought and wetness and attribute past climate variability to forced and/or internal variability.
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| 14. |
- Cunningham, LK, et al.
(författare)
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Reconstructions of surface ocean conditions from the North East Atlantic and Nordic Seas during the last Millennium
- 2013
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Ingår i: The Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 23:7, s. 921-935
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 15. |
- Edvardsson, Johannes, et al.
(författare)
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Old wood in a new light : an online dendrochronological database
- 2023
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Ingår i: International Journal of Wood Culture. - : Brill Academic Publishers. - 2772-3194 .- 2772-3186. ; 3:1-3, s. 442-463
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Tidskriftsartikel (refereegranskat)abstract
- The Old Wood in a New Light database project focuses on the digitization and accessibility of the results of dendrochronological samples analyzed and archived at four Swedish university-based tree-ring laboratories at Lund University, Stockholm University, University of Gothenburg, and the Swedish University of Agricultural Sciences. Collaboration with the Environmental Archaeology Laboratory and Humlab at Umeå University enables long-term open access to data, raw data, and metadata. In this project, we (1) systematically undertake large-scale entry and open access publication of results from wood samples scientifically analyzed and archived by Swedish laboratories and the associated metadata, into the Strategic Environmental Archaeology Database (SEAD; www.sead.se) research data infrastructure, and (2) actively promote the database as a resource for new and ongoing interdisciplinary research initiatives. Including dendrochronological data in SEAD infrastructure allows interdisciplinary studies that combine major scientific and societal questions. Building on a pilot study of construction timber from southern Sweden and adaptation of SEAD digitization workflows, more than 70 000 samples archived at the four dendrochronological laboratories are now being handled in the project. The broad coverage of research networks, stakeholder interaction, and strategic support from the cultural heritage community is guaranteed owing to the ongoing collaboration between laboratories and an established international and multidisciplinary reference group.
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| 16. |
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| 17. |
- Edwards, J., et al.
(författare)
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The Origin of Tree-Ring Reconstructed Summer Cooling in Northern Europe During the 18th Century Eruption of Laki
- 2022
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Ingår i: Paleoceanography and Paleoclimatology. - 2572-4517 .- 2572-4525. ; 37:2
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Tidskriftsartikel (refereegranskat)abstract
- Basaltic fissure eruptions, which are characteristic of Icelandic volcanism, are extremely hazardous due to the large quantities of gases and aerosols they release into the atmosphere. The 1783–1784 CE Laki eruption was one of the most significant high-latitude eruptions in the last millennium and had substantial environmental and climatic impacts. Contemporary observations recorded the presence of a sulfuric haze over Iceland and Europe, which caused famine from vegetation damage and resulted in a high occurrence of respiratory illnesses and related mortality. Historical records in northern Europe show that the summer of 1783 was anomalously warm, but regional tree-ring maximum latewood density (MXD) data from that year are low and lead to erroneously colder reconstructed summer temperatures. Here, we measure wood anatomical characteristics of Scots pine (Pinus sylvestris) from Jämtland, Sweden in order to identify the cause of this discrepancy. We show that the presence of intraannual density fluctuations in the majority of 1783 growth rings, a sudden reduction in lumen and cell wall area, and the measurement resolution of traditional X-ray densitometry led to the observed reduced annual MXD value. Multiple independent lines of evidence suggest these anatomical anomalies were most likely the result of direct acidic damage to trees in Northern Europe and that the normal relationship between summer temperature and MXD can be disrupted by this damage. Our study also demonstrates that quantitative wood anatomy offers a high-resolution approach to identifying anomalous years and extreme events in the tree-ring record. © 2022. American Geophysical Union. All Rights Reserved.
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| 18. |
- Farahat, Emad, et al.
(författare)
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Are standing dead trees (snags) suitable as climate proxies? A case study from the central Scandinavian Mountains
- 2018
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Ingår i: Scandinavian Journal of Forest Research. - : Informa UK Limited. - 0282-7581 .- 1651-1891. ; 33:2, s. 114-124
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Tidskriftsartikel (refereegranskat)abstract
- © 2017 Informa UK Limited, trading as Taylor & Francis Group Standing dead trees (snags) play important roles in forest ecology by storing carbon as well as providing habitats for many species. Moreover, snags preserved for hundreds of years can provide useful data to extend tree-ring chronologies used for climatological and ecological studies beyond the lifespans of living trees. Here we examined the growth patterns of Scots pine snags from the central Scandinavian Mountains, in relation to still living trees. Using changes point analyses, we showed that a majority (74%) of the snags displayed significant negative growth changes prior (on average 17 years) to death. Change points around the same years were also seen in living trees, but they recovered their growth. The average growth reduction of snags showing negative growth changes before death was 46%. In most cases the final growth change points coincided with very cold summers, or to a lesser degree to period of cool summers. It was suggested that pines ending up as snags were less resilient than the trees which continued living, and thus not able to recover after cold summer events. Since the snag growth reductions prior to death were partly unrelated to climate, care should be taken when using such data in dendroclimatological studies.
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| 19. |
- Fuentes, Mauricio, et al.
(författare)
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A 970-year-long summer temperature reconstruction from Rogen, west-central Sweden, based on blue intensity from tree rings
- 2018
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Ingår i: The Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 28:2, s. 254-266
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 20. |
- Fuentes, Mauricio, et al.
(författare)
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A comparison between Tree-Ring Width and Blue Intensity high and low frequency signals from Pinus sylvestris L. from the Central and Northern Scandinavian Mountains
- 2016
-
Ingår i: TRACE - Tree Rings in Archaeology, Climatolog y and Ecology, Volume 14. Scien tific Technical Report 16/04, GFZ German Research Centre for Geosciences, p. 38-43. doi: 10.2312/GFZ.b103-16042.. ; 14, s. 38-43
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- During the last decades, dendroclimatological methods have been used to produce several climate reconstructions, where chronologies based on maximum latewood d ensity (MXD) data (e.g.,Briffa et al. 2002, Gunnarson et al. 2011, Esper et al. 2012) have pro vided estimates of past temperature variability. Despite an often superior signal strength of the M XD parameter compared to tree ring width (RW) (e.g., Briffa et al. 2002), very few laboratories in the world use this technique, mainly because this proxy is expensive and labour intensive to produce . As an alternative, blue intensity (BI) utilizing reflected/absorbed blue light from scanned sampl e-images of tree rings, is explored as a surrogate to radio densitometry (McCarroll et al. 2002, Campb ell et al. 2011, Björklund et al. 2014, Rydval et al. 2014). However, BI seems more susceptible t o biases caused by the transition between the heartwood and the sapwood, but also by the mixing o f modern wood and deadwood (Björklund et al. 2014). This has according to Rydval et al. (2 014) and Wilson et al. (2014) restricted the application of the, to the MXD analogue, MXBI pa rameter (Björklund et al. 2014) to frequencies higher than 20 years. To overcome this bias, Björkl und et al. (2014, 2015) suggested the use of a new variant of BI parameter: the adjusted Δblue in tensity (ΔBI adj ), which is derived by subtracting the BI in the earlywood from the MXBI, after sample s have been contrast adjusted, based on their general level of staining (Björklund et al. 2015 ). Few comparisons between RW and MXD have been made (e.g., Briffa et al. 2002, Franke et al. 201 3), and even fewer comparisons between MXBI and RW have been made (Wilson et al. 2014). The ai m of this study is to assess the similarities and differences in temperature sensitive Pinus sylvestris L. RW and ΔBI adj j chronologies sampled across three sites in Sweden, by exploring 1) the climate correlation and spectral characteristics of the different parameters, 2) the in ter correlation and frequency association between them.
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| 21. |
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| 22. |
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| 23. |
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| 24. |
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| 25. |
- Gunnarson, Björn E., et al.
(författare)
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Legacies of pre-industrial land use can bias modern tree-ring climate calibrations
- 2012
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Ingår i: Climate Research (CR). - : Inter-Research Science Center. - 0936-577X .- 1616-1572. ; 53:1, s. 63-76
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Tidskriftsartikel (refereegranskat)abstract
- In Scandinavia, dendrochronological reconstructions of past climate have mostly been based on tree-ring data from forests in which there has been, supposedly, very little or no human impact. However, human land use in sub-alpine forests has a substantially longer history and more profound effects on the forest ecosystems than previously acknowledged. Therefore, to assess human influence on tree-ring patterns over the last 500 yr, we have analyzed tree-ring patterns using trees from 2 abandoned Sami settlements and a reference site with no human impact-all situated in the Tjeggelvas Nature Reserve in north-west Sweden. The hypothesis was that land use legacies have affected tree-ring patterns, and in turn, the resulting palaeoclimate inferences that have been made from these patterns. Our results show that climate signals are strongest at the reference site and weakest at one of the settlement sites. From the 1940s to the present, tree growth at this settlement site has been significantly lower than at the reference site. Lower tree growth at old settlements may have resulted from rapid changes in the traditional land use, or following the abrupt change when the settlements were abandoned. Without site-specific know ledge of past land use, there is a high risk of accidently sampling trees that have been affected by human-induced disturbances in the past. This may create bias in the climate signals inferred from such trees, and hence bias the outcome of climate reconstructions. We therefore recommend sampling several separate sites in study areas to improve the robustness of inferences.
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| 26. |
- Gunnarson, Björn Erik
(författare)
-
Temporal distribution pattern of subfossil pines in central Sweden: perspective on Holocene humidity fluctuations
- 2008
-
Ingår i: The Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 35:4, s. 569-577
-
Tidskriftsartikel (refereegranskat)abstract
- The temporal variations in distribution pattern of Scots pines (Pinus sylvestris L.) have been used as an annual resolution record of past lake-level changes. Logs, preserved for thousands of years in bog and lakes (subfossil wood), were sampled from small lakes of the Scandinavian Mountains in west-central Sweden to construct a tree-ring chronology from an area where pines are sensitive to growth season (ie, summer) temperature. The chronology spans from AD 2006 to 4868 BC, with two minor gaps at 1600 BC and AD 900 and one larger gap at 2900 BC. The dendrochronological approach can provide a high quality long-term perspective on lake level fluctuations, which possibly can be coupled to changes in humidity. Submerged trunks were found in situ, embedded in sediments, and because trees from the earliest periods were not necessarily found at the deepest levels, this shows clearly that lake levels must have been lower than present at the time of tree-growth. The lake levels must have fluctuated, creating alternating conditions of pine regeneration and mortality. The fluctuating lake levels recorded are suggested to be a result of regional humidity increases and decreases, mainly governed by precipitation changes. Periods of lower lake levels were inferred at 4900-4800 BC, 3800-3600 BC, 3400-3250 BC, 2400-2200 BC, 2100-1800 BC, 1500-1100 BC, 900-800 BC, 400-100 BC, AD 50-300, AD 400-600, AD 900-1100, AD 1350-1500 and AD 1700-1800. Periods of higher lake levels are tentatively encountered at 3600-3400 BC, 3200-2900 BC, 2200-2100 BC, 1700-1500 BC, 1100-900 BC, 800-400 BC, 100 BC-AD 50, AD 300-400, AD 750-900, AD 1100-1250 and AD 1550-1700.
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| 27. |
- Gunnarson, Björn, et al.
(författare)
-
Improving a tree-ring reconstruction from west-central Scandinavia : 900 years of warm-season temperatures
- 2011
-
Ingår i: Climate Dynamics. - : Springer Science and Business Media LLC. - 0930-7575 .- 1432-0894. ; 36:1-2, s. 97-108:36, s. 97-108
-
Tidskriftsartikel (refereegranskat)abstract
- Dendroclimatological sampling of Scots pine (Pinus sylvestris L.) has been made in the province of Jamtland, in the west-central Scandinavian mountains, since the 1970s. The tree-ring width (TRW) chronology spans several thousand years and has been used to reconstruct June August temperatures back to 1632 BC. A maximum latewood density (MXD) dataset, covering the period AD 1107-1827 (with gap 1292-1315) was presented in the 1980s by Fritz Schweingruber. Here we combine these historical MXD data with recently collected MXD data covering AD 1292-2006 into a single reconstruction of April September temperatures for the period AD 1107 2006. Regional curve standardization (RCS) provides more low-frequency variability than non-RCS and stronger correlation with local seasonal temperatures (51% variance explained). The MXD chronology shows a stronger relationship with temperatures than the TRW data, but the two chronologies show similar multi-decadal variations back to AD 1500. According to the MXD chronology, the period since AD 1930 and around AD 1150-1200 were the warmest during the last 900 years. Due to large uncertainties in the early part of the combined MXD chronology, it is not possible to conclude which period was the warmest. More sampling of trees growing near the tree-line is needed to further improve the MXD chronology.
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| 28. |
- Gunnarson, Björn, et al.
(författare)
-
Jakten på drivved i Arktis
- 2019
-
Ingår i: Geografiska Notiser. - 0016-724X. ; 77:4, s. 129-137
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 29. |
- Gunnarson, Björn, 1967-
(författare)
-
Nycklar till kunskap - om människan bruk av naturen
- 2010
-
Ingår i: <em>Nycklar till kunskap - om människan bruk av naturen</em>. - Stockholm : Kungl. Skogs- och Lantbruksakademin. ; , s. 357-360
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 30. |
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| 31. |
- Helama, Samuli, et al.
(författare)
-
Disentangling the Evidence of Milankovitch Forcing From Tree-Ring and Sedimentary Records
- 2022
-
Ingår i: Frontiers in Earth Science. - : Frontiers Media SA. - 2296-6463. ; 10
-
Tidskriftsartikel (refereegranskat)abstract
- Tree-ring records constitute excellent high-resolution data and provide valuable information for climate science and paleoclimatology. Tree-ring reconstructions of past temperature variations agree to show evidence for annual-to-centennial anomalies in past climate and place the industrial-era warming in the context of the late Holocene climate patterns and regimes. Despite their wide use in paleoclimate research, however, tree rings have also been deemed unsuitable as low-frequency indicators of past climate. The arising debate concerns whether the millennia-long tree-ring records show signals of orbital forcing due to the Milankovitch cycles. Here, we produce a summer-temperature reconstruction from tree-ring chronology running through mid- and late-Holocene times (since 5486 BCE) comprising minimum blue channel light intensity (BI). The BI reconstruction correlates with existing and new tree-ring chronologies built from maximum latewood density (MXD) and, unlike the MXD data, shows temperature trends on Milankovitch scales comparable to various types of sedimentary proxy across the circumpolar Arctic. Our results demonstrate an unrevealed potential of novel, unconventional tree-ring variables to contribute to geoscience and climate research by their capability to provide paleoclimate estimates from inter-annual scales up to those relevant to orbital forcing.
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| 32. |
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| 33. |
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| 34. |
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| 35. |
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| 36. |
- Linderholm, Hans W., 1968, et al.
(författare)
-
Arctic hydroclimate variability during the last 2000 years – current understanding and research challenges
- 2018
-
Ingår i: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 14, s. 473-514
-
Forskningsöversikt (refereegranskat)abstract
- Reanalysis data show an increasing trend in Arctic precipitation over the 20th century, but changes are not homogenous across seasons or space. The observed hydroclimate changes are expected to continue and possibly accelerate in the coming century, not only affecting pan-Arctic natural ecosystems and human activities, but also lower latitudes through the atmospheric and ocean circulations. However, a lack of spatiotemporal observational data makes reliable quantification of Arctic hydroclimate change difficult, especially in a long-term context. To understand Arctic hydroclimate and its variability prior to the instrumental record, climate proxy records are needed. The purpose of this review is to summarise the current understanding of Arctic hydroclimate during the past 2000 years. First, the paper reviews the main natural archives and proxies used to infer past hydroclimate variations in this remote region and outlines the difficulty of disentangling the moisture from the temperature signal in these records. Second, a comparison of two sets of hydroclimate records covering the Common Era from two data-rich regions, North America and Fennoscan-dia, reveals inter- and intra-regional differences. Third, building on earlier work, this paper shows the potential for providing a high-resolution hydroclimate reconstruction for the Arctic and a comparison with last-millennium simulations from fully coupled climate models. In general, hydroclimate proxies and simulations indicate that the Medieval Climate Anomaly tends to have been wetter than the Little Ice Age (LIA), but there are large regional differences. However, the regional coverage of the proxy data is inadequate, with distinct data gaps in most of Eurasia and parts of North America, making robust assessments for the whole Arctic impossible at present. To fully assess pan-Arctic hydroclimate variability for the last 2 millennia, additional proxy records are required.
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| 37. |
- Linderholm, Hans W., et al.
(författare)
-
Comparing Scots pine tree-ring proxies and detrending methods among sites in Jamtland, west-central Scandinavia
- 2010
-
Ingår i: Dendrochronologia. - : Elsevier BV. - 1125-7865 .- 1612-0051. ; 28:4, s. 239-249
-
Tidskriftsartikel (refereegranskat)abstract
- Scots pine tree-ring width (TRW) data from Jamtland in the Central Scandinavian Mountains has been used to reconstruct summer temperatures back to 1630 BC. However, it was recently shown that this reconstruction was of limited spatial importance. In this paper, we aim to explain this limitation in the TRW data as a temperature proxy, as well as assess the temperature information from new maximum latewood density (MXD) data. Furthermore, the effect of two standardization methods is evaluated: regional curve standardization (RCS) and a more traditional standardization, termed "non-RCS" standardization. Three TRW and two MXD sites were analyzed. Our results showed that despite the proximity to the Norwegian Sea, the MXD data is a powerful temperature proxy. Difference among sites in TRW data, especially on decadal timescales, together with a lower temperature association, suggests that other factors, such as changes in the local climate regimes, weakens the temperature signal. In general the RCS method overestimates pine growth trends in the latter half of the twentieth century, a feature not seen when using "non-RCS" standardization. This is likely due to an age-bias of older trees in most recent parts of the tree-ring chronologies. This effect will have consequences when reconstructing climate with tree-ring data. To overcome this problem, all age-classes should be represented throughout a chronology. If this is not possible, the use of "non-RCS" standardization is recommended, although this method results in a loss of low-frequency variability. (C) 2010 Istituto ltaliano di Dendrocronologia.
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| 38. |
- Linderholm, Hans W., 1968, et al.
(författare)
-
Comparing Scots pine tree-ring proxies and detrending methods among sites in Jämtland, west-central Scandinavia
- 2010
-
Ingår i: Dendrochronologia. - 1125-7865. ; 28:4, s. 239-249
-
Tidskriftsartikel (refereegranskat)abstract
- Scots pine tree-ring width (TRW) data from Jämtland in the Central Scandinavian Mountains has been used to reconstruct summer temperatures back to 1630 BC. However, it was recently shown that this reconstructionwas of limited spatial importance. In this paper, we aim to explain this limitation in the TRW data as a temperature proxy, as well as assess the temperature information from new maximum latewood density (MXD) data. Furthermore, the effect of two standardization methods is evaluated: regional curve standardization (RCS) and a more traditional standardization, termed “non-RCS” standardization. Three TRW and two MXD sites were analyzed. Our results showed that despite the proximity to the Norwegian Sea, the MXD data is a powerful temperature proxy. Difference among sites in TRW data, especially on decadal timescales, together with a lower temperature association, suggests that other factors, such as changes in the local climate regimes, weakens the temperature signal. In general the RCS method overestimates pine growth trends in the latter half of the twentieth century, a feature not seen when using “non-RCS” standardization. This is likely due to an age-bias of older trees in most recent parts of the tree-ring chronologies. This effect will have consequences when reconstructing climate with tree-ring data. To overcome this problem, all age-classes should be represented throughout a chronology. If this is not possible, the use of “non-RCS” standardization is recommended, although this method results in a loss of low-frequency variability.
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| 39. |
- Linderholm, Hans W., 1968, et al.
(författare)
-
Dendroclimatology in Fennoscandia – from past accomplishments to future potential
- 2010
-
Ingår i: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 6
-
Tidskriftsartikel (refereegranskat)abstract
- 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 Tornetr¨ask 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.
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| 40. |
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| 41. |
- Linderholm, Hans W., 1968, et al.
(författare)
-
Fennoscandia revisited : a spatially improved tree-ring reconstruction of summer temperatures for the last 900 years
- 2015
-
Ingår i: Climate Dynamics. - : Springer Science and Business Media LLC. - 0930-7575 .- 1432-0894. ; 45:3-4, s. 933-947
-
Tidskriftsartikel (refereegranskat)abstract
- Despite the spatially homogenous summer temperature pattern in Fennoscandia, there are large spreads among the many existing reconstructions, resulting in an uncertainty in the timing and amplitude of past changes. Also, there has been a general bias towards northernmost Fennoscandia. In an attempt to provide a more spatially coherent view of summer (June-August, JJA) temperature variability within the last millennium, we utilized seven density and three blue intensity Scots pine (Pinus sylvestris L.) chronologies collected from the altitudinal (Scandinavian Mountains) and latitudinal (northernmost part) treeline. To attain a JJA temperature signal as strong as possible, as well as preserving multicentury-scale variability, we used a new tree-ring parameter, where the earlywood information is removed from the maximum density and blue intensity, and a modified signal-free standardization method. Two skilful reconstructions for the period 11002006 CE were made, one regional reconstruction based on an average of the chronologies, and one field (gridded) reconstruction. The new reconstructions were shown to have much improved spatial representations compared to those based on data from only northern sites, thus making it more valid for the whole region. An examination of some of the forcings of JJA mean temperatures in the region shows an association with sea-surface temperature over the eastern North Atlantic, but also the subpolar and subtropical gyres. Moreover, using Superposed Epoch Analysis, a significant cooling in the year following a volcanic eruption was noted, and for the largest explosive eruptions, the effect could remain for up to 4 years. This new improved reconstruction provides a mean to reinforce our understanding of forcings on summer temperatures in the North European sector.
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| 42. |
- Linderholm, Hans W., 1968, et al.
(författare)
-
Growth dynamics of tree-line and lake-shore Scots pine (Pinus sylvestris L.) in the central Scandinavian Mountains during the Medieval Climate Anomaly and the early Little Ice Age
- 2014
-
Ingår i: Frontiers in Ecology and Evolution. - : Frontiers Media SA. - 2296-701X. ; 2
-
Tidskriftsartikel (refereegranskat)abstract
- Trees growing at their altitudinal or latitudinal distribution in Fennoscandia have been widely used to reconstruct warm season temperatures, and the region hosts some of the world’s longest tree-ring chronologies. These multi-millennial long chronologies have mainly been built from tree remains found in lakes (subfossil wood from lake-shore trees). We used a unique dataset of Scots pine tree-ring data collected from wood remains found on a mountain slope in the central Scandinavian Mountains, yielding a chronology spanning over much of the last 1200 years. This data was compared with a local subfossil wood chronology with the aim to 1) describe growth variability in two environments during the Medieval Climate Anomaly (MCA) and the early Little Ice Age (LIA), and 2) investigate differences in growth characteristics during these contrasting periods. It was shown that the local tree-line during both the MCA and early LIA was almost 150 m higher that at present. Based on living pines from the two environments, tree-line pine growth was strongly associated with mid-summer temperatures, while the lake-shore trees showed an additional response to summer precipitation. During the MCA, regarded to be a period of favourable climate in the region, the tree-ring data from both environments showed strong coherency and moderate growth variability. In the early LIA, the two chronologies were less coherent, with the tree-line chronology showing more variability, suggesting different growth responses in the two environments during this period of less favourable growing conditions. Our results indicate that tree-ring width chronologies mainly based on lake-shore trees may need to be reevaluated.
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| 43. |
- Linderholm, Hans W., 1968, et al.
(författare)
-
Summer temperature variability in central Scandinavia during the last 3600 years
- 2005
-
Ingår i: Geografiska Annaler Series a-Physical Geography. - 0435-3676. ; 87A:1, s. 231-241
-
Tidskriftsartikel (refereegranskat)abstract
- A Scots pine (Pinus sylvestris L.) treering width chronology from Jamtland, in the central Scandinavian Mountains, built from living and sub-fossil wood, covering the period 1632 BC to AD 2002, with a minor gap during AD 887-907, is presented. This is the first multi-millennial tree-ring chronology from the central parts of Fennoscandia. Pine growth in this tree line environment is mainly limited by summer temperatures, and hence the record can be viewed as a temperature proxy. Using the regional curve standardization (RCS) technique, pine-growth variability on short and long time scales was retained and subsequently summer (June-August) temperatures were reconstructed yielding information on temperature variability during the last 3600 years. Several periods with anomalously warm or cold summers were found: 450-550 BC (warm), AD 300-400 (cold), AD 900-1000 (the Medieval Warm Period, warm) and AD 1550-1900 (Little Ice Age, cold). The coldest period was encountered in the fourth century AD and the warmest period 450 to 550 BC. However, the magnitude of these anomalies is uncertain since the replication of trees in the Jamtland record is low during those periods. The twentieth century warming does not stand out as an anomalous feature in the last 3600 years. Two multi-millennial tree-ring chronologies from Swedish and Finnish Lapland, which have previously been used as summer temperature proxies, agree well with the Jamtland record, indicating that the latter is a good proxy of local, but also regional, summer temperature variability.
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| 44. |
- Linderholm, Hans W., 1968, et al.
(författare)
-
The origin of driftwood on eastern and south-western Svalbard
- 2021
-
Ingår i: Polar Science. - : Elsevier BV. - 1873-9652 .- 1876-4428. ; 29
-
Tidskriftsartikel (refereegranskat)abstract
- The Arctic is one of the regions where the effect of global change is most evident. Associated with warming are changes in snow, sea ice and hydroclimate, all which have significant impacts on environments and society. However, due to short observational records, it is difficult to set the current climate in a long-term context. Arctic driftwood (DW), available throughout the Holocene, is a paleoclimate resource that may shed information on past sea-ice, ocean current and atmospheric conditions because it is transported by sea ice across the Arctic. Moreover, DW tree-ring data can be used to interpret climate in the boreal forests where the trees grew. Here we present a study of 380 DW samples collected on eastern and south-western Svalbard. Combining species identification and dendrochronology, it was found that the DW mainly consisted of Pinus sylvestris, Picea sp. and Larix sp. (87% of all samples), mainly originating from northern Russia. In total, 60% of the DW could be dated and their provenance determined, and four tree-ring width chronologies representing Yenisei and Dvina-Pechora were constructed, facilitating extension and improvement of the existing chronologies representing those regions. Moreover, DW from relict beaches that can be subjected to dendrochronological analyses, provides possibilities to extend pan-Arctic tree-ring data even further back in time. Because there are several processes governing the temporal patterns of wood deposition in the Arctic, using DW as an indicator of sea-ice variations needs further investigation. © 2021 The Author(s)
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| 45. |
- Linderholm, Hans W., 1968, et al.
(författare)
-
Were medieval warm-season temperatures in Jamtland, central Scandinavian Mountains, lower than previously estimated?
- 2019
-
Ingår i: Dendrochronologia. - : Elsevier BV. - 1125-7865 .- 1612-0051. ; 57:October
-
Tidskriftsartikel (refereegranskat)abstract
- Today few high-quality tree-ring based temperature reconstructions extending over the past millennium exist, and those have, in general, low replication in their early parts. Here we present a new and updated maximum latewood density (MXD) chronology extending over the last 1200 years, built from local Scots pine wood sources (living trees, drywood preserved the ground, and subfossil wood extracted from lakes) all collected within 20 km in the Scandinavian Mountains in Jamtland. The MXD data was used to reconstruct April-September mean temperatures, where 60% of the variance in observed temperatures could be explained. The reconstruction exhibited distinct multidecadal variability, with the coldest periods centred on ca. 900, 1450, 1600 and 1900 CE, and the warmest periods on ca. 1160, 1250, 1500, 1660 CE. The last part of the 20th - early part of 21st century was the warmest period throughout the whole record, and the reconstruction suggests that, on average, the Medieval Climate Anomaly (MCA, 950-1250 CE) was only slightly warmer than the Little Ice Age (LIA, 1450-1900 CE). In fact, compared to earlier reconstructions from the region, the new reconstruction suggested lower MCA warm-season temperatures. However, despite sufficient replication during that period, high inhomogeneity among the MXD series makes this period slightly uncertain. The unique drywood on which the chronology was built, displayed a distinct regeneration pattern, where changes in Scots pine establishment was interpreted as responses to changes in forest fire activity and climate throughout the past millennium.
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| 46. |
- Löwemark, Ludvig, et al.
(författare)
-
The Tienchi Pond on Lanyu Island (Western Pacific) : Lake formation and potential as environmental archive
- 2015
-
Ingår i: Journal of Asian Earth Sciences. - : Elsevier BV. - 1367-9120 .- 1878-5786. ; 114, s. 435-446
-
Tidskriftsartikel (refereegranskat)abstract
- The formation, evolution, and potential as a climate archive of Tienchi Pond was evaluated using geomor-phology, sedimentology, geochemistry, and AMS radiocarbon measurements of tree ring cores. Tienchi Pond is a small ephemeral lake situated on the subtropical Lanyu Island in the Western Pacific Ocean about 90 km east of southern Taiwan. The lake is situated on a mountain ridge and is today characterized by numerous dead trees and stumps. The position at the boundary between the two main components of the SE Asian monsoon system, the Asian landmass and the Western Pacific, makes this lake particularly interesting as a potential natural climate archive. Since previous studies have shown that the bedrock underlying the lake formed over 2 my ago, a volcanic crater origin was ruled out. Rather, element ratios of K/Ti and Ca/Fe together with Pb-210 dating suggest a recent origin for the lake, probably as the result of a natural damming event in the southern, narrower, part of the lake basin, or as a result of increased precipitation at the end of the Little Ice Age (or a combination of both). Radiocarbon measurements on a dead tree near the lake perimeter show C-14 levels of more than 1.7% modern radiocarbon near the bark, suggesting that the tree died in the early 1970s. In contrast, by correlating a large number of radiocarbon measurements to a northern hemisphere reference curve, it was shown that trees closer to the center of the lake died in the early 20th century. This agrees with a scenario where a small lake formed by initial damming, and gradually grew larger through erosion of the surrounding shore lines caused by rapid lake level oscillations.
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| 47. |
- Martin, Peter, et al.
(författare)
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Climatic controls on the survival and loss of ancient types of barley on North Atlantic Islands
- 2023
-
Ingår i: Climatic Change. - : Springer Science and Business Media LLC. - 0165-0009 .- 1573-1480. ; 176:2
-
Tidskriftsartikel (refereegranskat)abstract
- For ancient types of barley at sites in the Scottish Isles, Faroes, and Iceland, we calculated minimum temperature requirements for grain production (grain production threshold, GPT) as accumulated degree days over the cropping season. Site suitability for barley from AD 1200 to 2000 was investigated by comparing these thresholds with reconstructions of annual cropping season degree days (CSDD) using temperature and tree-ring data. In Iceland, between AD 1200 and 1500, reconstructed CSDD were more favorable in the southwest (Reykjavik), with fewer years below the GPT, than in the North, East and West, but there were two periods (1340–1389 and 1426–1475) with low average CSDD and several years below the GPT which possibly influenced the abandonment of barley cultivation around this time. Reconstructed CSDD for the Faroes (Tórshavn) had only one year below the GPT, but 15 periods of four or more consecutive years with low CSDD which would have challenged barley cultivation, especially in the thirteenth century. Reconstructed CSDD were highest for the Scottish Isles, allowing a more prominent role of barley in the farming system and economy. Nevertheless, years with poor harvests or famines were common and about half were associated with low CSDD, resulting in a significant temperature link but also demonstrating the important contribution of other factors. Despite frequent unfavorable years in both the Faroes and Scottish Isles, resilient production systems, well-adapted barley strains and socio-economic factors allowed barley cultivation to continue, and some ancient types to survive to the present day.
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| 48. |
- McCarroll, D., et al.
(författare)
-
A 1200-year multiproxy record of tree growth and summer temperature at the northern pine forest limit of Europe
- 2013
-
Ingår i: Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 23:4, s. 471-484
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 49. |
- Mjærum, Axel, et al.
(författare)
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Middelalderfiske, fellefangst og fraflytting : en dendrokronologisk undersøkelse av et 1300-talls stasjonært fiskeanlegg i Nord-Mesna, Sørøst-Norge
- 2024
-
Ingår i: Fornvännen. - Stockholm : Kungl. Vitterhets Historie och Antikvitets Akademien. - 0015-7813 .- 1404-9430. ; 119:1, s. 25-44
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Tidskriftsartikel (refereegranskat)abstract
- Fishing in rivers and lakes has traditionally been a longstanding and dependable means of sustenance for the people of inland Scandinavia. However, our understanding of pre-modern fishing traditions has been hampered by a lack of written sources, as well as a scarcity of archaeological data. However, a recent excavation and comprehensive dendrochronological analysis of a fish trapping enclosure system in Lake Nord-Mesna (520 masl.), in the boreal forests of inland Norway, has provided unique insight into freshwater fishing traditions, techniques and organization. The excavated structure, believed to be a fish weir with lath screen traps set into shallow water, was established in the late 1200s. In the following years it was regularly maintained in the spring/early summer. The last documented repair was in 1343. Its abandonment is interpreted as resulting from a recession likely induced by factors such as plague and climatic deterioration, that affected inland areas of Scandinavia in the 1300s. These results provide archaeological evidence of medieval utilization of effective enclosure traps in the region. This contradicts the prevailing notion that this form of fishing was later introduced by Forest Finns who migrated to the area in the 17th century. In addition, the findings give new and significant information about the organization and practice of medieval fishing in inland Scandinavia.
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| 50. |
- Pan, Y. Y., et al.
(författare)
-
The 20-million-year old lair of an ambush-predatory worm preserved in northeast Taiwan
- 2021
-
Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- The feeding behavior of the giant ambush-predator "Bobbit worm" (Eunice aphroditois) is spectacular. They hide in their burrows until they explode upwards grabbing unsuspecting prey with a snap of their powerful jaws. The still living prey are then pulled into the sediment for consumption. Although predatory polychaetes have existed since the early Paleozoic, their bodies comprise mainly soft tissue, resulting in a very incomplete fossil record, and virtually nothing is known about their burrows and behavior beneath the seafloor. Here we use morphological, sedimentological, and geochemical data from Miocene strata in northeast Taiwan to erect a new ichnogenus, Pennichnus. This trace fossil consists of an up to 2 m long, 2-3 cm in diameter, L-shaped burrow with distinct feather-like structures around the upper shaft. A comparison of Pennichnus to biological analogs strongly suggests that this new ichnogenus is associated with ambush-predatory worms that lived about 20 million years ago.
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