15 research outputs found
Cloud Cover Feedback Moderates Fennoscandian Summer Temperature Changes Over the Past 1,000Â Years
Northern Fennoscandia has experienced little summer warming over recent decades, in 24 contrast to the hemispheric trend, which is strongly linked to greenhouse gas emissions. A likely25 explanation is the feedback between cloud cover and temperature. We establish the long- and26 short-term relationship between summer cloud cover and temperature over Northern27 Fennoscandia, by analysing meteorological and proxy climate data. We identify opposing28 feedbacks operating at different timescales. At short timescales, dominated by internal29 variability, the cloud cover-temperature feedback is negative; summers with increased cloud30 cover are cooler and sunny summers are warmer. However, over longer timescales, at which31 forced climate changes operate, this feedback is positive, rising temperatures causing increased32 regional cloud cover and vice versa. This has occurred both during warm (Medieval Climate33 Anomaly and at present) and cool (Little Ice Age) periods. This two-way feedback relationship34 therefore moderates Northern Fennoscandian temperatures during both warm and cool35 hemispheric periods
Oxygen isotope dendrochronology of Llwyn Celyn; One of the oldest houses in Wales
We report the application of oxygen isotope dendrochronology to date a high-status and remarkably unaltered late medieval hall house on the eastern border of South Wales. The oak timbers have either short and complacent ring series, or very strong growth disturbance, and none were suitable for ring-width dendrochronology. By using stable oxygen isotopes from the latewood cellulose, rather than ring widths, it was possible to cross-match and date all 14 timber samples and to provide felling dates related to several phases of building. The hall and solar cross-wing were constructed shortly after 1420CE, which is remarkably early. The house was upgraded using timbers felled in the winter of 1695/6CE by ceiling over of the hall and inserting a chimney. A separate small domestic building was added at the same time and the addition of the kitchen is likely to be contemporaneous. A substantial beast house was added a few years before the house was refurbished, emphasising the importance of cattle as the main source of wealth. A small barn with timbers felled in spring 1843 CE was added later. Llwyn Celyn is one of the most important domestic buildings in Wales, but without the new approach none of the phases of its evolution could have been dated precisely. Oxygen isotope dendrochronology has enormous potential for dating timbers that have small numbers of rings and/or show severe growth disturbance and it works well in regions where tree growth is not strongly constrained by climate. The research was generously supported by the Leverhulme Trust, Natural Environment Research Council, Landmark Trust and the UK National Lottery Heritage Fund
Interrogating glacier mass balance response to climatic change since the Little Ice Age: reconstructions for the Jotunheimen region, southern Norway
202
Developing tree ring chronologies from New Zealand matai (Prumnopitys taxifolia (D.Don) Laub.) for archaeological dating: Stable isotope dendrochronology
202
Blue intensity for dendroclimatology:should we have the blues? Experiments from Scotland
Abstract Blue intensity (BI) has the potential to provide information on past summer temperatures of a similar quality to maximum latewood density (MXD), but at a substantially reduced cost. This paper provides a methodological guide to the generation of BI data using a new and affordable BI measurement system; CooRecorder. Focussing on four sites in the Scottish Highlands from a wider network of 42 sites developed for the Scottish Pine Project, BI and MXD data from Scots pine (Pinus sylvestris L.) were used to facilitate a direct comparison between these parameters. A series of experiments aimed at identifying and addressing the limitations of BI suggest that while some potential limitations exist, these can be minimised by adhering to appropriate BI generation protocols. The comparison of BI data produced using different resin-extraction methods (acetone vs. ethanol) and measurement systems (CooRecorder vs. WinDendro) indicates that comparable results can be achieved. Using samples from the same trees, a comparison of both BI and MXD with instrumental climate data revealed that overall, BI performs as well as, if not better than, MXD in reconstructing past summer temperatures (BI r2 = 0.38â0.46; MXD r2 = 0.34â0.35). Although reconstructions developed using BI and MXD data appeared equally robust, BI chronologies were more sensitive to the choice of detrending method due to differences in the relative trends of non-detrended raw BI and MXD data. This observation suggests that the heartwoodâsapwood colour difference is not entirely removed using either acetone or ethanol chemical treatment, which may ultimately pose a potential limitation for extracting centennial and longer timescale information when using BI data from tree species that exhibit a distinct heartwoodâsapwood colour difference. Additional research is required in order to develop new methods to overcome this potential limitation. However, the ease with which BI data can be produced should help justify and recognise the role of this parameter as a potential alternative to MXD, particularly when MXD generation may be impractical or unfeasible for financial or other reasons
Blue intensity for dendroclimatology:should we have the blues? Experiments from Scotland
Abstract Blue intensity (BI) has the potential to provide information on past summer temperatures of a similar quality to maximum latewood density (MXD), but at a substantially reduced cost. This paper provides a methodological guide to the generation of BI data using a new and affordable BI measurement system; CooRecorder. Focussing on four sites in the Scottish Highlands from a wider network of 42 sites developed for the Scottish Pine Project, BI and MXD data from Scots pine (Pinus sylvestris L.) were used to facilitate a direct comparison between these parameters. A series of experiments aimed at identifying and addressing the limitations of BI suggest that while some potential limitations exist, these can be minimised by adhering to appropriate BI generation protocols. The comparison of BI data produced using different resin-extraction methods (acetone vs. ethanol) and measurement systems (CooRecorder vs. WinDendro) indicates that comparable results can be achieved. Using samples from the same trees, a comparison of both BI and MXD with instrumental climate data revealed that overall, BI performs as well as, if not better than, MXD in reconstructing past summer temperatures (BI r2 = 0.38â0.46; MXD r2 = 0.34â0.35). Although reconstructions developed using BI and MXD data appeared equally robust, BI chronologies were more sensitive to the choice of detrending method due to differences in the relative trends of non-detrended raw BI and MXD data. This observation suggests that the heartwoodâsapwood colour difference is not entirely removed using either acetone or ethanol chemical treatment, which may ultimately pose a potential limitation for extracting centennial and longer timescale information when using BI data from tree species that exhibit a distinct heartwoodâsapwood colour difference. Additional research is required in order to develop new methods to overcome this potential limitation. However, the ease with which BI data can be produced should help justify and recognise the role of this parameter as a potential alternative to MXD, particularly when MXD generation may be impractical or unfeasible for financial or other reasons
Reply to Comment by S. Helama and V. V. Matskovsky onâAbsence of AgeâRelated Trends in Stable Oxygen Isotope Ratios From Oak Tree Ringsâ
202
Dating of non-oak species in the United Kingdom historical buildings archive using stable oxygen isotopes
202
A 500-year record of summer near-ground solar radiation from tree-ring stable carbon isotopes
Tree-ring stable carbon isotope ratios (d(13)C) in environments of low moisture stress are likely to be controlled primarily by photosynthetic rate. Therefore, sunshine, rather than temperature, represents the more direct controlling factor. Temperature reconstructions based on tree-ring d(13)C results thus rest on the assumption that temperature and sunshine are strongly coupled. This assumption is tested using a d(13)C series from pine trees in NW Norway, where there are long (>100 yr) records of both summer temperature and cloud cover. It is demonstrated that when summer temperature and d(13)C diverge, summer temperature and cloud cover also diverge, and that cloud cover/sunshine may provide a stronger and more consistent parameter with which to calibrate tree-ring d(13)C series in this area. When a 500-year reconstruction of summer cloudiness is compared with a published reconstruction of summer temperatures in northern Sweden based on tree-ring maximum densities, the two time-series are largely parallel, with high levels of annual-decadal coherence. We identify, however, three distinct periods of lower frequency divergence: two (AD 1600-1650 and ad 1900-1927) when we propose summers were cool but sunny and one during the first half of the sixteenth century when summers were warm but cloudy. These episodes where temperature and sunshine decouple may represent large-scale changes in circulation as recorded in the Arctic Oscillation (AO) index. Strongly negative values of the summer AO index, as occurred during the early twentieth century, are associated with persistent high pressure over northern Norway and Fennoscandia, bringing cool summers with clear skies. Long reconstructions of cloudiness (near-ground radiation), based on tree-ring d(13)C series from suitable sites, would be extremely valuable for testing General Circulation Models (GCMs), because the generation of cloud is a strong control on temperature evolution, but remains a major source of uncertainty
High-temperature pyrolysis/gas chromatography/isotope ratio mass spectrometry : simultaneous measurement of the stable isotopes of oxygen and carbon in cellulose
Stable isotope analysis of cellulose is an increasingly important aspect of ecological and palaeoenvironmental research. Since these techniques are very costly, any methodological development which can provide simultaneous measurement of stable carbon and oxygen isotope ratios in cellulose deserves further exploration. A large number (3074) of tree-ring α-cellulose samples are used to compare the stable carbon isotope ratios (Ύ13C) produced by high-temperature (1400°C) pyrolysis/gas chromatography (GC)/isotope ratio mass spectrometry (IRMS) with those produced by combustion GC/IRMS. Although the two data sets are very strongly correlated, the pyrolysis results display reduced variance and are strongly biased towards the mean. The low carbon isotope ratios of tree-ring cellulose during the last century, reflecting anthropogenic disturbance of atmospheric carbon dioxide, are thus overestimated. The likely explanation is that a proportion of the oxygen atoms are bonding with residual carbon in the reaction chamber to form carbon monoxide. The 'pyrolysis adjustment', proposed here, is based on combusting a stratified sub-sample of the pyrolysis results, across the full range of carbon isotope ratios, and using the paired results to define a regression equation that can be used to adjust all the pyrolysis measurements. In this study, subsamples of 30 combustion measurements produced adjusted chronologies statistically indistinguishable from those produced by combusting every sample. This methodology allows simultaneous measurement of the stable isotopes of carbon and oxygen using high-temperature pyrolysis, reducing the amount of sample required and the analytical costs of measuring them separately