Subfossil Wood Research Articles

Were medieval warm-season temperatures in Jämtland, central Scandinavian Mountains, lower than previously estimated?

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 Jämtland. 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.

An 1800-year stable carbon isotope chronology based on sub-fossil wood from Lake Schwarzensee, Austria

An 1800-year stable carbon isotope chronology based on sub-fossil wood from Lake Schwarzensee, Austria

Introducing anatomical techniques to subfossil wood

Successful cross-dating of subfossil wood, ideally in combination with precise information on germination and dieback, requires the accurate detection of tree-ring width (TRW) boundaries along continuous measurement tracks from pith to bark. However, wood decay and the mechanical deformation of cells often challenge the dendrochronological analysis and subsequent paleoclimatic and environmental interpretations. Here, we show that wood anatomical techniques can improve the assessment of heavily degraded and/or deformed material. We apply state-of-the-art sample preparation, thin sectioning and double-staining to a unique collection of Late Glacial pines that were growing ∼13,000 years ago in the vicinity of Zurich, Switzerland. Highly resolved anatomical observations not only reveal detailed insights into the quality of each cell, but also allow the extent of wood deformation to be identified. By improving the detection and cross-dating of particularly narrow rings, TRW series might be extended towards the pith and bark, where decomposition and distortion is usually most severe, thus adding to a better understanding of possible germination and dieback processes, respectively. Moreover, thin sectioning has the potential to manually reconstruct original TRWs by correcting for post-mortem deformed ring structures. Our results suggest that anatomical techniques should be routinely applied in the assessment of historical, archaeological and subfossil wood.

A 7.5 ka chronology of stable carbon isotopes from tree rings with implications for their use in palaeo-cloud reconstruction

Abstract Tree-ring stable isotope chronologies provide very high-resolution palaeoclimatic data, and the number of records is increasing rapidly worldwide. To extend the chronologies back in time, before the period covered by the old living trees, the use of subfossil wood samples is required. Typically, the longest continuous subfossil chronologies consist of regionally collected tree-ring materials, rather than tree rings from a single site, and are likely more sensitive to data heterogeneity. Yet, the characteristics of such datasets remain hitherto unexplored. Here we produce a continuous, decadally resolved chronology of 13C/12C ratio (δ13C) from Finnish Lapland over the past 7.5 ka (5500 BCE to 2010 CE) for which there is replication of at least five Pinus sylvestris trees. Less negative δ13C values were observed as trees age and for western sites (higher in elevation and further from the cold oceanic air flow). The age-related trends in living tree δ13C data were expressed mainly over the first fifty years mimicking the “juvenile effect” whereas the subfossil data showed trend over the trees' lifespan. These findings demonstrated the need to detrend the individual δ13C series before averaging them into the mean chronology. The corresponding biases were removed from the isotopic data using the methods frequently applied for tree-ring width and density proxies, the Regional Curve Standardization (RCS) combined with signal-free approach. While the RCS procedures commonly preserve the long-term variations in the resulting chronology, not all types of them did so as demonstrated for chronologies produced using separate RCS models for the δ13C series with relatively high and low isotopic level (offset from the grand mean). It was shown that these δ13C levels (i.e. the relative isotopic enrichment) result both from the low-frequency climate signal and biogeographical aspects (the site longitude/altitudes). The non-climatic biases were removed from the δ13C series by using separate RCS models for the subsets (western and eastern) of isotopic series. Similar to previous investigations using annually resolved δ13C data from Lapland, our chronology had strong negative correlations to variations in cloud cover. Here, a bootstrapping experiment was used to verify this dendroclimatic association. The resulting palaeo-cloud reconstruction portrayed decadal to multi-millennial variations with centennial anomalies coinciding with the mid and late Holocene events of climate transitions, highlighting the value of subfossil isotope chronologies from tree rings in synthesising climate dynamics from several proxy sources over the present interglacial.

A New Graphitization System for Radiocarbon Dating with AMS in the Dendrochronological Laboratory at AGH-UST Kraków

AbstractA new vacuum system for the preparation of graphite samples for radiocarbon (14C) measurement using an accelerator mass spectrometer (AMS) was constructed at the Dendrochronological Laboratory in AGH-UST Kraków. The central part of the system is a manual vacuum line for the production of graphite from carbon dioxide for subsequent AMS measurements. The graphitization system can handle up to five samples simultaneously, and the process lasts for approximately 1 hour. The graphitization line was built to support the preparation of wood samples for a project dedicated to dating a subfossil tree from the Younger Dryas period. For this purpose, the chemical preparation procedure for wood samples was optimized to obtain more reliable results. This includes the extraction of α-cellulose to increase the precision of the age determination. The performance of the system was tested with NIST OxII, IAEA standards (IAEA C3, C5, C6, and C8), and background samples. The results of the 13 samples of subfossil wood were tested and are presented. The methodology gives good reproducibility of results obtained for the samples prepared using this system.

Aerial decay influence on the stable oxygen and carbon isotope ratios in tree ring cellulose

Sub-fossil wood is often affected by the decaying process that introduces uncertainties in the measurement of oxygen and carbon stable isotope composition in cellulose. Although the cellulose stable isotopes are widely used as climatic proxies, our understanding of processes controlling their behavior is very limited. We present here a comparative study of stable oxygen and carbon isotope ratios in tree ring cellulose in decayed and non-decayed wood samples of Swiss stone pine (Pinus cembra) trees. The intra-ring stable isotope variability (around the circumference of a single ring) was between 0.1 and 0.5‰ for δ18O values and between 0.5 and 1.6‰ for δ13C values for both decayed and non-decayed wood. Observed intra-tree δ18O variability is less than that reported in the literature (0.5–1.5‰), however, for δ13C it is larger than the reported values (0.7–1.2‰). The inter-tree variability for non-decayed wood ranges between 1.1 and 2.3‰ for δ18O values, and between 2 and 4.7‰ for δ13C values. The inter-tree differences for δ18O values are similar to those reported in the literature (1–2‰ for oxygen and 1–3‰ for carbon) but are larger for δ13C values. We have found that the differences for δ18O and δ13C values between decayed and non-decayed wood are smaller than the variation among different trees from the same site, suggesting that the decayed wood can be used for isotopic paleoclimate research.

A Dráva durvaszemcsés folyóvízi üledékéből előkerült szubfosszilis uszadékfák dendrokronológiai és faanatómiai vizsgálata

This paper presents preliminary results of dendro-chronological analyses of the first occurrence of subfossil tree trunks from drava alluvial sediments. Driftwood logs were found at an outer bend of the Drava river near the village of Babócsa. The site is covered by >6 m fluvial sand and gravel. Trunks are arranged horizontally, roughly in the same bed, between massive gravel and sand layers.. Fourteen samples had been collected within a hundred metre long outcrop, ar-ranged in three distinct sets.. half of the samples are oak (Quercus roburl., n=7), fewer samples belonged to beech (Fagus sylvatica, n=2), wych elm (Ulmus scabra, n=1), eu-ropean white elm (Ulmus laevis, n=2) and finally a there are one sample each of poplar (Populus spp.) and larch (Larix decidua). the samples were processed following the stan-dard dendrochronological protocol. ring width was measured to the nearest 0.01mm. despite the most likely origin of the samples is the riverbank; the oak trunks had narrow tree-ring sequences. an oak trunk of a diameter not more 20 cm con-tains more than 240 rings and two other oak samples have about 200 rings. These three long series could be crossdat-ed, forming a 249 year long chronology. The chronology built from the three synchronized records (sample codes bab002, bab003, bab007) was tested with surrounding oak master chronologies, without success. The first subfossil wood re-mains from the drava river and their loating chronology will be of help to understand changes in river dynamics and the former composition of the tree species on the floodplain.

Drying quality and colour of subfossil oak from central Serbia

The subject of this paper is the analysis of the quality of natural and conventional drying of subfossil oak wood. In addition to the drying quality, the colour of this material, as well as the effect of the drying process on colour change have been tested. The subfossil oak logs that were used in this experiment originate from the Morava River in Central Serbia. After sawing, timber was air-dried to about 20% moisture content (MC) followed by kiln-drying to 9.5% MC. By examining the quality of air-drying of the subfossil oak wood, a high presence of cracks was found, as well as the inaccuracy of humidity measurement using electric moisture meters. The stack for kiln-drying consisted of 24 boards, of which 4 were used for the monitoring of MC and MC distribution across the thickness of plank during drying. Drying quality was evaluated after the kiln-drying process. Although mild drying conditions during kiln-drying were applied, the gap as a measure of case-hardening had a value greater than usual for oak of same thickness. It was found that the drying process has no significant effect on the change in the colour of subfossil wood. The colour of the subfossil oak wood was significantly darker than the usual oak wood, and the colour difference between the central and the outer parts of the trunk of the subfossil oak was determined.

Improved recovery of ancient DNA from subfossil wood - application to the world's oldest Late Glacial pine forest.

Ancient DNA from historical and subfossil wood has a great potential to provide new insights into the history of tree populations. However, its extraction and analysis have not become routine, mainly because contamination of the wood with modern plant material can complicate the verification of genetic information. Here, we used sapwood tissue from 22 subfossil pines that were growing c. 13000yr bp in Zurich, Switzerland. We developed and evaluated protocols to eliminate surface contamination, and we tested ancient DNA authenticity based on plastid DNA metabarcoding and the assessment of post-mortem DNA damage. A novel approach using laser irradiation coupled with bleaching and surface removal was most efficient in eliminating contaminating DNA. DNA metabarcoding confirmed which ancient DNA samples repeatedly amplified pine DNA and were free of exogenous plant taxa. Pine DNA sequences of these samples showed a high degree of cytosine to thymine mismatches, typical of post-mortem damage. Stringent decontamination of wood surfaces combined with DNA metabarcoding and assessment of post-mortem DNA damage allowed us to authenticate ancient DNA retrieved from the oldest Late Glacial pine forest. These techniques can be applied to any subfossil wood and are likely to improve the accessibility of relict wood for genome-scale ancient DNA studies.

Neoglacial history of Robson Glacier, British Columbia

As glaciers in the Canadian Rockies recede, glacier forefields continue to yield subfossil wood from sites overridden by these glaciers during the Holocene. Robson Glacier in British Columbia formerly extended below tree line, and recession over the last century has progressively revealed a number of buried forest sites that are providing one of the more complete records of glacier history in the Canadian Rockies during the latter half of the Holocene. The glacier was advancing ca. 5.5 km upvalley of the Little Ice Age terminus ca. 5.26 cal ka BP, at sites ca. 2 km upvalley ca. 4.02 cal ka BP and ca. 3.55 cal ka BP, and 0.5–1 km upvalley between 1140 and 1350 A.D. There is also limited evidence based on detrital wood of an additional period of glacier advance ca. 3.24 cal ka BP. This record is more similar to glacier histories further west in British Columbia than elsewhere in the Rockies and provides the first evidence for a post-Hypsithermal glacier advance at ca. 5.26 cal ka BP in the Rockies. The utilization of the wiggle-matching approach using multiple 14C dates from sample locations determined by dendrochronological analyses enabled the recognition of 14C outliers and an increase in the precision and accuracy of the dating of glacier advances.

Wood14C Dating with AixMICADAS: Methods and Application to Tree-Ring Sequences from the Younger Dryas Event in the Southern French Alps

AbstractThe AixMICADAS facility is in part dedicated to research on radiocarbon (14C) calibration by means of various archives. For this purpose, we are improving upon the capacity to accurately date subfossil wood. In the current study, nine chemical pretreatment protocols are tested on six wood samples of known ages. The optimization based on14C ages,13C/12C ratios, carbon % and overall mass yield % leads us to favor the acid-base-acid-bleaching pretreatment (ABA-B). This efficient method is shown to provide a residue of holocellulose with optimal blanks equivalent to an age of 51,30014C BP with a standard deviation of 1500 yr based on 25 analyses. The seven wood samples from the Sixth International Radiocarbon Intercomparison (SIRI) are then analyzed as a further verification of the accuracy of our method. As a first scientific contribution, we studied two tree-ring sequences from subfossil pines (Barb12 and Barb17) collected in the southern French Alps. New14C analyses were performed at high resolution (every third year) and are shown to agree well with results obtained previously by high precision β-counting on CO2from large samples at lower resolution for Barb17 and accelerator mass spectrometry (AMS) data for Barb12. The new14C series are then matched to the Kauri and YDB chronologies: the new sequence of Barb12-17 tentatively corresponds to the interval between 12,836 and 12,594 cal BP within the Younger Dryas cold period. The14C comparison between the Barb12-17 sequence from France and the Kauri sequence from New Zealand allows calculating the14C Inter-Hemispheric Gradient (IHG), with an average value of ca. 57 yr. The IHG stayed relatively high throughout the studied period. Interestingly, the IHG exhibits a transient maximum value (ca. 100 yr) during the period of rapid Δ14C rise (12,750–12,720 cal BP), a behavior that could be due to a delayed response of the Southern Hemisphere.

A 1400-Year Bølling-Allerød Tree-Ring Record from the U.S. Great Lakes Region

Abstract Since the late 19th Century, geologists and naturalists working in the US Midwest have reported an abundance of tree macrofossils embedded in glacial and lacustrine deposits formed after the Last Glacial Maximum. The most widely-known of these sites is the Two Creeks type locality in Wisconsin. We report progress on development of a long tree-ring record from this subfossil wood in the US Great Lakes region, employing samples collected during a decade-long series of field campaigns at recently eroded lake shorelines, construction projects, and excavations, along with acquisition of archived samples collected from the 1950s to the 1980s during past lake erosion events. A previously-reported tree-ring chronology from the Two Creeks type locality reached ca. 250 years in length; here we used radiocarbon dates and tree-ring crossdating to develop a 1408-year tree-ring chronology (mainly spruce [Picea spp.] with some tamarack [Larix]) comprising a total of 135 overlapped tree-ring width series in thre...

Last Glacial pollen–climate reconstructions from Northland, New Zealand

ABSTRACTDespite wide‐ranging interest in the vegetation and climate of Northland, New Zealand, during the last glacial cycle, the region and timeframe lack quantitative climate reconstructions while land‐based pollen records have tended to be poorly dated and fragmentary. The region is also important for geochronology due to the co‐occurrence of the Rotoehu tephra, a widely dispersed isochron near the current limits of radiocarbon dating, and extensive subfossil wood remains of Agathis australis, with strong dendrochronological and dendroclimatological potential. We present new pollen records and temperature reconstructions from three sites set in coastal dune belts from western mid‐Northland (∼35°S), all containing Rotoehu tephra, that collectively span the last 70 ka. The phases and amplitude of temperature changes broadly align with those reported from elsewhere in New Zealand and with marine isotope climate–stratigraphic records, including maximum temperature depression of 6–8 °C during the last glacial maximum. We argue that these climatic patterns are intimately linked to shifts in the southern westerly wind belt, the northern margins of which extend to the region today. Correspondence between the Northland temperature shifts and atmospheric CO2 supports the model of ocean–atmosphere CO2 flux modulated by latitudinal migration of the southern westerlies. Copyright © 2017 John Wiley & Sons, Ltd.

Effects of microstructural orientation on the abrasive wear resistance of subfossil elm wood in three orthogonal planes

The research is part of a more extensive project in wood science, and its aim was to identify the effects of microstructural orientation on the two-body abrasive wear of sub-fossil wood. Samples to be tested were prepared from an approximately 670 year-old sub-fossil elm trunk retrieved from the Sava River bed in the northern part of Bosnia and Herzegovina. The samples were mounted to present three orthogonal planes (transverse, radial, and tangential) to a rotating disk of sandpaper. The effects of three average grit sizes (35, 82, and 201µm) were also investigated. The rate of abrasive wear for each microstructural orientation grew linearly with the number of grinding cycles. The lowest wear rate was observed on the transverse cross-section and the highest on the radial cross-section. As the sandpaper grit size was decreased, the wear rate values decreased for all cross-sections and became similar to one another. The wear resistance appears to be less affected by the heterogeneity of the wood microstructure than it is by a decrease in diameter of the abrasive grains. It was therefore concluded that the abrasion response of subfossil elm wood exhibits the same characteristics as the hitherto researched, more recent wood samples.

LATE PLEISTOCENE FUEL MANAGEMENT AND HUMAN COLONIZATION OF THE ATACAMA DESERT, NORTHERN CHILE

Hunter-gatherers collected and used various woody species depending on the landscape, availability of plant communities, and sociocultural considerations. With extensive paleo-wetlands and groundwater-fed oases, the Atacama Desert was interspersed with riparian woodlands that provided vital resources (fuel, water, and game) at the end of the Pleistocene in areas such as the Pampa del Tamarugal (PdT) basin. We use anthracological analyses to determine the fuel management strategies of hunter-gatherer societies in this hyperarid environment and explore whether the “Principle of Least Effort” applies. First, we present the combustion qualities and characteristics of woody taxa from the Atacama and analyze possible exploitation strategies. Second, we use anthracological analyses from Quebrada Maní 12 (QM12), a late Pleistocene archaeological site (dated from 12,750 to 11,530 cal B.P.) located in the PdT basin, to show the prevalence of two woody species that were either freshly collected or gathered (very likely on purpose) from subfossil wood. Our results suggest that fuel selection strategies were based on prior knowledge of the qualities of these woody taxa and how they burned. Thus we conclude that fuel management was part of a number of social and economic decisions that allowed for effective colonization of this region. Furthermore, we stress the need for caution when using charcoal to exclusively date archaeological sites located in desert environments.

Annual ring orientation effect on bending strength of subfossil elm wood

The effect of annual rings’ orientation on bending strength was examined on subfossil elm wood. Elm is extremely rarely found as subfossil wood, and during the last 50–60 years it has almost disappeared from natural forest stands of south-eastern Europe, due to the Elm Dutch disease. The samples were cut from approximately 670 years old subfossil elm trunk retrieved from the bed of the river Sava in the area between the villages Grebnice and Domaljevac in north Bosnia. The wood was identified to the genus level based on optical microscopy analysis of three wood sections—transverse, tangential and radial. Bending strength was determined by the three-point bending test. The load was applied to the longitudinal–tangential surface (LT) and to the longitudinal–radial surface (LR). The bending strength values of subfossil elm do not differ from the values of recent elm, despite the 700-year resting in anoxic river conditions. Bending strength in LT direction was slightly higher than bending strength in LR direction. The coefficient of variation and the standard deviation of the arithmetical mean were higher for LT direction. It was found that the measured bending strength for both directions follows Weibull distribution. Coefficient of determination of Weibull functions was close to 1 for both directions. The Weibull shape parameter was higher for LR direction.

Subfossil bog-pine chronologies from The Puścizna Wielka raised bog, Orawa Basin, southern Poland

Subfossil wood of the Scots pine (Pinus sylvestris L.) appearing in the peat sediments in southern Poland presents material for the construction of long tree-ring chronologies that are of potential utility in palaeoclimatic reconstructions. Over 600 subfossil pine samples, in form of discs, were taken for dendrochronological analyses from the Puścizna Wielka peat bog, the only economically exploited bog in the Carpathians. Based on these samples, five floating chronologies covering ca. 1700 years were constructed. They were dated with the wiggle-matching technique to the years: 3485–3295 (±25), 3205–2575 (±25), 2445–2200 (±50), 2210–1990 (±40), 1100–610 (±10) cal BC. These results indicate that the trees grew on the valley bog during the initial phase of its development. The vast majority of the trees analysed grew on the peat bog between ca. 3500 and ca. 2000 cal BC, with breaks in the record dated to ca. 3290–3200 cal BC, ca. 2570–2450 cal BC. Pines invaded the peat bog in drier periods, whereas a high groundwater level, presumably related to increased precipitation, was a factor determining mortality of the trees. This study therefore fills a geographical gap in the coverage by subfossil pine records as there are no studies on subfossil pine trees from peat bogs in Central-Eastern Europe.

X-RAY DENSITOMETRY OF NORWAY SPRUCE SUBFOSSIL WOOD FROM THE AUSTRIAN ALPS.

The processing of subfossil wood poses some difficulties in densitometric research. Problems arise because of the physio-chemical changes of wood occurring in the sedimentation environment. Subfossil wood modification can result from the uptake of mineral and organic substances into the wood tissue. It can also occur as the effect of microbiological degradation of wood. The goal of this study was to identify the appropriate method of subfossil wood preparation for the densitometric research. For this purpose the wood of Norway spruce from Lake Schwarzensee was subjected to extraction in deionized water, acetone and diluted acetic acid. The application of acetic acid did not significantly influence the density of the wood and acetone seemed to be too aggressive. The best result was obtained by rinsing the samples in cold de-ionized water. This extraction procedure allowed removal of unwanted water-soluble, organic and inorganic compounds from wood and simultaneously did not lead to the degradation of subfossil samples.

Patterns of moisture source and climate variability in the southeastern United States: a four-century seasonally resolved tree-ring oxygen-isotope record

This study presents a climate reconstruction utilizing a seasonally resolved 417-year oxygen-isotope record of tree rings from southern Georgia, United States (1580–1997 CE). Oxygen isotopes within the cellulose predominately reflect moisture source observed on a seasonal scale between earlywood and latewood growth. Signatures of large climate oscillations were captured in modern and subfossil wood. Spectral and wavelet transform analyses of seasonally resolved oxygen isotopes showed distinct periodicities coinciding with the Atlantic multidecadal oscillation and other major climate oscillation phenomena. Oxygen-isotope values in latewood growth revealed a significant correlation with North Atlantic sea surface temperature anomalies. This correlation suggests that the precipitation source was strongly influenced by fluctuations in the Atlantic multidecadal oscillation and teleconnections with other major climate phenomena such as the North Atlantic subtropical high-pressure system, El Nino Southern Oscillation, and Pacific Decadal Oscillation. These results emphasize the utility of oxygen isotopes in tree rings for revealing seasonal influences associated with major climate drivers over centuries and enhance our understanding of long-term climate behavior on a detailed scale.

A long-term context (931–2005 C.E.) for rapid warming over Central Asia

Warming over Mongolia and Central Asia has been unusually rapid over the past few decades, particularly in the summer, with surface temperature anomalies higher than for much of the globe. With few temperature station records available in this remote region prior to the 1950s, paleoclimatic data must be used to understand annual-to-centennial scale climate variability, local response to large-scale forcing mechanisms, and the significance of major features of the past millennium such as the Medieval Climate Anomaly (MCA) and Little Ice Age (LIA) both of which can vary globally. Here we use an extensive collection of living and subfossil wood samples from temperature-sensitive trees to produce a millennial-length, validated reconstruction of summer temperatures for Mongolia and Central Asia from 931 to 2005 CE. This tree-ring reconstruction shows general agreement with the MCA (warming) and LIA (cooling) trends, a significant volcanic signature, and warming in the 20th and 21st Century. Recent warming (2000–2005) exceeds that from any other time and is concurrent with, and likely exacerbated, the impact of extreme drought (1999–2002) that resulted in massive livestock loss across Mongolia.