C04_01

Analysis of solar minima by using radiocarbon in tree-rings

Brehm N¹, Christl M¹, Synal H¹, Bayliss A², Nicolussi K³, Pearson C⁴, Bleicher N⁵, Brown D⁶, Wacker L¹

¹Eth Zürich, Zürich, Switzerland, ²Historic England, London, UK, ³Universität Innsbruck, Innsbruck, Austria, ⁴University of Arizona, Tucson, USA, ⁵Underwater archaeology and Dendroarchaeology, Zürich, Switzerland, ⁶ The Queen’s University, Belfast, UK

The Sun provides virtually all the principal energy input to the Earth’s climate system and solar variability is a significant external climate forcing. While direct observations of the sun’s activity via sunspots only cover the last about 400 years, cosmogenic radionuclides such as ¹⁴C, 10Be and 36Cl stored in tree-rings and ice cores serve as  solar activity proxies extending back thousands of years.

¹⁴C is produced continuously in the Earth’s atmosphere by highly energetic cosmic rays. The rate of production depends on solar activity and geomagnetic field strength. Dendrochronologically dated trees represent the most reliable archive for reconstruction of the past atmospheric ¹⁴C concentration over the past 14 000 yr, because of the absolute dating of a tree ring and the tree’s capability to record the atmospheric ¹⁴C concentrations at annual resolution.

Here we present two annually resolved records of atmospheric ¹⁴C covering two different solar minima and the following solar maxima. The new data, which covers the time periods from 5450-5000 and 1950-2400 years BP, is analyzed by using a carbon cycle box model to reconstruct past solar activity. The reconstructed high-resolution solar activity records are compared with the solar activity recontructed from the Spörer and Maunder minima which occurred during the last millennium. The data gives more high resolution insight on two of the most extreme solar minima during the past 6000 years.

C04_02

The effect of altitude and latitude on growing season and radiocarbon content in tree rings

Svarva H¹, Grootes P¹, Seiler M¹, Nadeau M¹

¹The National Laboratory for Age Determination, NTNU University Museum, Trondheim, Norway

The construction of high-precision, single-year calibration curves for radiocarbon dating needs to take into account the tree physiological, seasonal, and regional differences in the radiocarbon content of tree rings. ¹⁴C variations can be caused by e.g. carbon stored from previous years and by growing season differences. 

Previous studies have shown that the stored photosynthate component is less important for evergreen conifers. However, the timing of growing season can have a significant impact on the radiocarbon content of tree rings, especially during periods of large atmospheric ¹⁴C fluctuations such as the 1960s bomb spike. The calibration of results from trees that grew during different periods of the year than the trees used for the calibration curve will also be impacted. Cellulose in sub-annual sections of tree rings can be used to trace changes in atmospheric radiocarbon content at a biweekly to monthly resolution.

We present the sub-annual radiocarbon contents of three Scots pines from Norway from 1953 to 1965. One tree grew at a low elevation near Trondheim in central Norway. The others grew nearby at a high elevation and at a low elevation in northern Norway, thus having a generally shorter growing season. Analyses of the differences between the radiocarbon content in the trees through time and comparison with climate records allows us to untangle the differences caused by growing season from inaccuracies in the timing of each increment and potential latitudinal differences in atmospheric ¹⁴C content.

C04_03

Interfacing Radiocarbon Production Events from Cosmic-ray Bursts with Other Fields of Research

Kuitems M¹, Dee M¹

¹University Of Groningen, Groningen, Netherlands

Since Miyake et al. (2012) published the spike in radiocarbon production caused by a cosmic-ray strike in the year 774 CE, numerous other distinct yet ephemeral features in the radiocarbon record have been discovered. The cosmic-ray events that occurred in 774 and 993 CE have proven especially effective for dating wooden items, and their associated historical or geological contexts, to the exact year. As part of the ECHOES project, other avenues of research centring on the utilisation of these events are now being explored. The new applications vary in nature and scope. One aspect involves the use of high-precision radiocarbon measurements on individual tree-rings to overcome long-standing barriers in dendrochronology. In other applications, radiocarbon data from disparate periods and geographical regions are being combined with new proxies, such as stable isotope records and even genetic data, to maximise the potential of these versatile time markers.

C04_04

European Glacial tree-ring chronologies - New high-resolution ¹⁴C-series

Friedrich M¹, Kromer B², Cercatillo S³, Wacker L⁴, Toniello V⁵, Bicho N⁶, Horta P⁶, Adolphi F⁷, Muscheler R⁸, Talamo S³

¹Hohenheim Gardens (772), University of Hohenheim, D-70599 Stuttgart, Germany, ²Institute of Environmental Physics, Heidelberg University, Heidelberg, Germany, ³Department of Chemistry G. Ciamician, Alma Mater Studiorum, University of Bologna, Bologna, Italy, ⁴Laboratory of Ion Beam Physics, ETH Zurich, Zurich, Switzerland, ⁵Gruppo Speleologico C.A.I. di Vittorio Veneto (TV), Vittorio Veneto, Italy, ⁶Interdisciplinary Centre for Archaeology and the Evolution of Human Behavior, University of Algarve, Faro, Portugal, ⁷Helmholtz Centre for Polar and Marine Research, Alfred Wegener Institute, Bremerhaven, Germany, ⁸Department of Geology, Quaternary Sciences, Lund University, Lund, Sweden

The ¹⁴C-calibration curve IntCal is a key-record in paleosciences that provides a chronological framework for a wide range of disciplines studying environmental and cultural changes during the late Pleistocene and the Holocene. Tree-rings directly record atmospheric ¹⁴C/¹²C relationship at their time of growth and are thus the ideal natural archive to construct a terrestrial calibration curve - if they can be well dated. However, they are continuously available only back to 14.226 years BP.  Before this time, the resolution of the calibration curve drops substantially, or relies on ¹⁴C data that do not directly reflect atmospheric ¹⁴C.

In the Late Pleistocene, a number of floating tree-ring ¹⁴C-series from subfossil trees exist, that can provide snapshots of past ¹⁴C-variability and have a tremendous potential. The challenge here is to establish their absolute chronology by providing high-resolution ¹⁴C-dates with tight error ranges, because that is the prerequisite e.g. for successful comparisons of the solar induced decadal to sub-centennial ¹⁴C-variability to the ¹⁰Be-record of the ice cores.

In this contribution, we present newly constructed Glacial tree-ring chronologies of subfossil trees from northern Italy and Portugal at 18ka resp. 32ka BP, and respective high precision, sub-decadal ¹⁴C-series achieved by the ERC-project ‘RESOLUTION’. We discuss their absolute chronological dating by comparisons with terrestrial calibration series and the possibility to infer links to the Greenland ice core timescale.

The new tree-ring based ¹⁴C-series will contribute to characterize past atmospheric ¹⁴C variability and will improve the radiocarbon calibration towards achieving a precise high-resolution chronology of human evolution.

C04_05

Towards a continuous, annually resolved tree-ring record spanning the past 6000 years

Wacker L¹,  Brehm N¹, Christl M¹, Synal H¹, Bayliss A², Nicolussi K³, Pearson C⁴, Bleicher N⁵, Brown D⁶, Bollhalder S¹, Alter M¹

¹Laboratory of Ion Beam Physics, ETH Zurich, Zürich, Switzerland, ²Historic England, London, Great Britain, ³Universität Innsbruck, Innsbruck, Austria, ⁴University of Arizona, Tucson, USA, ⁵Underwater archaeology and Dendroarchaeology Zurich, Zürich, Switzerland, ⁶The Queen's University, Belfast, Great Britain

As a consequence of the instrumental progresses combined with more efficient sample preparation, IntCal20 contains now 5 000 new AMS measurements in addition to 1 000 decay measurements on annually resolved tree-rings of the previous IntCal iteration (IntCal13). It is primarily this new annually resolved data, that nearly doubled the dataset, on which IntCal20 is  based today. Still, the significantly increased resolution of IntCal20 can be considered just as the start for a more detailed (spatio-) temporal mapping of past atmospheric radiocarbon concentrations. Only 20% of the last 14 000 years available at annual resolution are yet measured, while the rest is only available at decadal or lower resolution.

We will present an update on our efforts to measure the hole tree-ring based part of IntCal  annual resolution. We present more than 3 000 new annually resolved ¹⁴C measurements performed on tree-ring samples covering the last 6 000 years. A thorough analysis of reproducibility will be presented and  possible reginal offsets will be discussed. The new data represents a significant progress  towards  an enhanced high-resolution calibration curve.

C04_06

Establishing prehistoric tree-ring chronologies for the southern Balkans: first results from lakeshore settlements of the 6th to 1st millennium BC

Maczkowski A^1,2, Bolliger M^1,2,3, Francuz  J¹, Reich  J^1,3, Hostettler M^1,2,5, Szidat  S^4,2, Hafner A^1,2,6

¹Institute of Archaeological Sciences, University of Bern, Bern, Switzerland, ²Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland, ³Archaeological Service of the Canton of Bern, Bern, Switzerland, ⁴Department of Chemistry, Biochemistry and Pharmacy, University of Bern, Bern, Switzerland, ⁵Department of Archaeology and Ancient History, University of Uppsala, Uppsala, Sweden, ⁶MacMillan Center for International and Area Studies, Yale University, New Haven, USA

During several archaeological campaigns on wetland prehistoric sites in North Macedonia, Greece and Albania almost 2000 subfossil wood samples have been collected. The fieldwork campaigns were conducted within the framework of the ERC Synergy Project EXPLO. The wood has been sampled from building and structural remains on lakeside and underwater archaeological sites and is thus unambiguously linked to the human occupation of these sites. Through dendrochronological measurement of wood from various tree species, multicentennial floating tree-ring (TR) chronologies have been constructed. Radiocarbon dating was used to position the floating chronologies on the calendar age frame, but also to confirm dendrochronological findings. The new TR chronologies open the possibility for refining the cultural chronology in the region, during various periods in the 6th through 1st millennia BC. Possible off-sets between species on non-annual radiocarbon will also be discussed. Additionally, newly discovered Miyake events enable the absolute dating of floating prehistoric chronologies much sooner than it seemed possible only a decade ago.

C04_07

Tree species in Central Amazon basin show uniform levels of ¹⁴C bomb-peak as well as fossil-CO₂ contributions from mining operations

Santos G¹, Albuquerque R², Barros C², Ancapichun S^3,4, Oelkers  R⁵, Andreu-Hayles L⁵, de Faria S⁶, De Pol-Holz R³, Brandes A⁷

¹University of California, Irvine, Irvine,, United States, ²Escola Nacional de Botânica Tropical, Rio de Janeiro, , Brazil, ³Universidad de Magallanes, Punta Arenas, Chile, ⁴Universidad de Concepción, Concepción, Chile, ⁵Columbia University, Palisades, , USA, ⁶Empresa Brasileira de Pesquisa Agropecuária, Seropédica, , Brazil, ⁷Universidade Federal Fluminense, Niterói, , Brazil

Tree rings has been widely used for atmospheric radiocarbon (¹⁴C) calibration purposes, but such records have been limited along tropical latitudes. Here we report precisely measured ¹⁴C dates in tree rings (1937 to 2007) of the parenchyma-rich Hymenolobium petraeum tree species from the Central Brazilian Amazon (Porto Trombetas, 1°S, 56°W). Bomb-peak tree-ring ¹⁴C reconstruction coincides with the broader changes associated with reported values of the Southern Hemisphere ¹⁴C curve (Hua et al. 2021), suggesting that inter-hemispheric air-mass transport of excess-¹⁴C injected into the stratosphere during aboveground nuclear tests is relatively uniform across distinct longitudinal regions. From the early 1970s onwards, H. petraeum had lower ¹⁴C values than recently developed pantropical ¹⁴C records (e.g., Camanducaia; Santos et al. 2015, and Altiplano; Ancapichún et al. 2021). Through ¹⁴C-based estimation, we found a strong influence of local fossil-fuel CO₂ contributions. While the Oriximiná district’s population density (0.5/km²) cannot be considered as its main cause, mining operations and waterway shipping traffic are potentially responsible for the local dilution of atmospheric ¹⁴CO₂. In addition, air parcels reaching Porto Trombetas during the growing season follow the Amazon River path, which handles most of export shipments of country’s ore, soybean and corn by transnational business giants. Our findings invite further ¹⁴C analyses using tree rings of tropical tree species as a potential tracer for a wide range of environmental sources of atmospheric ¹⁴C-variability.

Hua et al. 2021. Radiocarbon, 1-23. DOI: https://doi.org/10.1017/RDC.2021.95

Santos et al. 2015. QUAGEO 25, 96-103

Ancapichún et al. 2021. STOTEN 774, 145126

C04_08

Single-year radiocarbon dating applied to Viking Age towns and trade connections

Philippsen B^1,2,3, Feveile C⁴, Olsen J^2,3, Sindbæk S²

¹Museum Lolland-Falster, Nykøbing F, Denmark, ²Centre for Urban Network Evolutions, School of Culture and Society, Aarhus University, Højbjerg, Denmark, ³Aarhus AMS Centre, Department of Physics and Astronomy, Aarhus University, Aarhus, Denmark, ⁴Museum of Southwest Jutland, Ribe, Denmark

Radiocarbon calibration curves have improved significantly after the discovery of solar particle events and the addition of annual data to calibration datasets. In this study, we apply IntCal20 with additional annual measurements to 140 radiocarbon dates from the Viking Age emporium Ribe in Denmark. We combine the radiocarbon dates with dendrochronological dates and the site's detailed stratigraphy, built up of clay floors and activity layers, in a Bayesian age model. We show that maritime trade began already around AD 750, as evidenced by artefacts imported from Norway. The expansion of trade, especially towards the Middle East, and other aspects of the beginning of the Viking Age occur in layers dated here to AD 790 ± 10. We also identify the clay floor that was in use when the AD 775 solar particle event took place.

Finally, we apply the same techniques to radiocarbon dates of other Viking Age sites from the literature. We explore the potential of re-calibrating and modelling legacy dates to improve the chronology of individual sites and their relations with other sites.

C04_09

A Simulation Approach to Quantify the Parameters and Limits of the Radiocarbon Wiggle Match Dating Technique

McDonald L¹, Manning S¹

¹Cornell Tree-ring Laboratory, Ithaca, United States

Worldwide, radiocarbon (¹⁴C) wiggle-match dating is increasingly used to produce high-resolution, ‘near-absolute’, chronologies in a range of different contexts, yet the exact properties and limitations of the technique are not well understood. Here we present the results of extensive and systematic simulations that allow the precision limits of wiggle-match dating to be quantified for different time periods. In this presentation we use the periods 4000-3600 BCE and 1000-1800 CE as case studies. We have also been able to quantify the effect of modeling decisions on precision possible in terms of how many measurements to make, how far apart to space them, and which calibration curve to employ. We find that while recent trends towards large numbers of annually spaced measurements can improve precision, the effect is generally small, except when the dated sequence falls on a plateau in the calibration curve. Finally, we demonstrate that wiggle matching against an unsmoothed record of atmospheric ¹⁴C can provide better precision than wiggle matching against the smoothed IntCal20 or SHCal20 curves. We argue, however, that until intra-hemispheric variation in ¹⁴C is better understood, the hemispheric averages provided by IntCal20 and SHCal20 will be the more appropriate datasets for the majority of wiggle-match applications.

C04_P01

δ¹³C and intrinsic water use efficiency (iWUE) for trees in various health conditions – case study for Świerklaniec Forest District

Benisiewicz B¹,  Pawełczyk S², Kłusek M³

¹Silesian University Of Technology, Gliwice, Poland, ²Silesian University Of Technology, Gliwice, Poland, ³Silesian University Of Technology, Gliwice, Poland

The research was carried out for two pines growing side by side in the Świerklaniec Forest District. One tree was in good health condition, the other pine had damaged crown and was destined to be cut down. Tree cores were subjected to dendrochronological analysis. Based on these studies, cores were divided into annual increments and subjected to chemical preparation. Carbon isotopic composition of α-cellulose samples was determined using mass spectrometer coupled to the elemental analyzer. Additionally, based on the δ¹³C  values, the iWUE values were calculated, and trees sensitivity to change of  temperature and sum of precipitation was checked.  Isotopic studies covered the years 1967-2020.

              Until the end of the 1990s, the record of  δ¹³C had significantly lower values for a healthy tree than for a damaged tree. The isotope record of a healthy tree since 1980 is characterized by a horizontal trend, in the case of a damaged tree there is a clear downward trend from 1985 to 2000. Correlation coefficients between isotopic and climatic data indicate different sensitivity of trees to climatic factors. Apart from climatic factors, pollutant emissions could have had an impact on tree growth and δ¹³C values, especially since there is a zinc smelter near the sampling site. The characteristics of the trend can be justified by the number of pollutants emitted by industrial plants (especially SO₂), which were the highest in the 1970s and 1980s, and significantly decreased in the 1990s. Differences in iWUE, calculated from data sets, representing two trees are signifficant.

C04_P02

New high RESOLUTION project ¹⁴C data from a Glacial sub-fossil pine forest in Furadouro, Portugal

Cercatillo S¹, Friedrich M², Kromer B³, Palecek D¹, Wacker L⁴, Talamo S¹

¹Department of Chemistry G. Ciamician, Alma Mater Studiorum, University of Bologna, Via Selmi 2, 40126, Bologna, Italy, ²Hohenheim Gardens, University of Hohenheim, Ottilie-Zeller-Weg 8, D-70599, Stuttgart, Germany, ³Institute of Environmental Physics, Heidelberg University, D-69120 , Heidelberg, Germany, ⁴Laboratory of Ion Beam Physics, ETH Zurich, 8093 , Zurich, Switzerland

The year 14,226 BP marks an important border in the actual radiocarbon (¹⁴C) calibration curve: the high resolution and precision characterising the first part of the curve thanks to the potential of tree-rings, systematically decrease going back in time, where only a few floating tree-ring chronologies alternate to other low-resolution records.

The lack of resolution in the dating procedure before 14,200 years BP leads to significant issues in the interpretation and untangling of tricky facts of our past.

The research for sub-fossil trees, within the RESOLUTION project, which directly recorded atmospheric carbon (¹²C, ¹³C and ¹⁴C), and the construction of new Glacial tree-ring chronologies can improve the radiocarbon dating and therefore, to resolve puzzles in the Human Evolution history.

The sub-fossil pine trees found in situ under the current coast sediments of Furadouro, Portugal, are remnants of a Glacial lagoonal forest and represent a significant example of the huge potential given by the rare findings of trees grown during the Glacial in refugia areas, where the environmental conditions and climate allowed growth of pine trees.

Here we report of a new 220-year long pine tree-ring chronology, grown during GI 5: we describe the carefully sampling, the dendrochronological analysis and cross-dating of the trees, and the high resolution, highly reliable radiocarbon age-series with tight error ranges that we have achieved by applying the most suitable cellulose extraction protocol for sub-fossil Glacial trees, and the most advanced technologies of the MICADAS system at ETH-Zurich.

C04_P03

Radiocarbon ages of annual tree rings collected in Korea (AD 900 - 2021, 81 - 168, 131 - 211)

Hong W¹, Park Y¹, Sung K¹, Park G¹, Sakamoto M², Hakozaki M², Park J¹

¹Korea Institute of Geoscience and Mineral Resources (KIGAM), Daejeon, South Korea, ²National Museum of Japanese History, Sakura City, Japan

Radiocarbon ages of annual tree rings collected in Korean Peninsula were measured using KIGAM 1MV AMS. All samples were treated by alpha cellulose extraction methods at KIGAM and NMJH. Reduction process of CO₂ to graphite was done using 24-line automatic reduction system at KIGAM. The radiocarbon ages from AD 1250 to 1850 were reported in 2013 (Hong et al.1, 2013 and Hong et al.2, 2013) with dendrochronological ages. After the reports, radiocarbon ages of tree rings from AD 1093 to 1162, AD 1188 to 1249, and AD 1851 to 1950 have been measured. The calendric ages of these samples were determined by dendrochronology or oxygen isotope patters. And recently, additional tree rings from AD 81 to 168 and from AD 131 to 211 collected from an archaeological site, Gochon-ri, were measured. The calendric ages of the samples were determined by oxygen isotope dendrochronology. Modern tree rings after AD 1950 collected from a mountain called Sogri-san, which is located in the center of South Korea, were also measured up to 2021. Those ages will be reported in this presentation and compared with IntCal13 and IntCal20 curves. Chronological variation of regional offsets in the radiocarbon ages of tree rings grown in East Asia from IntCal13 and IntCal20 will be discussed.

C04_P04

A growth rate variability of Ziziphus spina christi in North-central Oman determined by a series of radiocarbon measurements

Kitagawa H¹, Miki T², Kuronuma T³, Kondo Y³

¹Institute for Space‐Earth Environmental Research, Nagoya University, Nagoya, Japan, ²The University Museum, The University of Tokyo, Tokyo, Japan, ³Research Institute for Humanity and Nature, Kyoto, Japan

Ziziphus spina christi, known as Christ's Thorn Jujube, is a thermophilic tree grown in arid and semi-arid areas. It was already in use as a medical plant in Ancient Egypt and is currently used for multipurpose such as food, fodder, fodder fuel, drink, timber, and medicine. The ecological and chemical properties of the multipurpose plant have been intensively studied, but there is a missing knowledge about the growth rate of Ziziphus spin christi that the annual ring is unclear. We conducted a series of radiocarbon measurements of a 23 cm-long core of Ziziphus spina christi collected from Wādī Tanūf, Northcentral Oman. The secular change of growth rate was estimated by a wiggle matching method incorporating dynamic time wrapping (DTW) algorism for measuring similarity between two temporal sequences: radiocarbon calibration (IntCal20) and dataset from the Ziziphus spina christi（this study). Based on the growth rate estimated, we discussed the climatic influence on the growth rate. Our result supports the hypothesis that an increase in winter temperature may be beneficial for growth and the recent widespread of Ziziphus spina christi in the eastern Mediterranean is presumably related to a gradual increase in winter temperatures.

C04_P05

Single-year ¹⁴C dating of the lake-fortress at Āraiši, Latvia

Meadows J^1,2, Zunde M³, Lēģere L⁴, Dee M⁵, Hamann C²

¹ZBSA (Centre for Baltic and Scandinavian Archaeology), Schleswig, Germany, ²Leibniz-Laboratory for AMS Dating and Stable Isotope Research, Christian-Albrechts-University Ki, Kiel, Germany, ³Institute of Latvian History, University of Latvia, Riga, Latvia, ⁴Āraiši lake-fortress archaeological park, Cēsis, Latvia, ⁵Centre for Isotope Research, University of Groningen, Groningen, Netherlands

A timber lake-fortress on a flooded island in Lake Āraiši, central Latvia, was excavated in 1965-69 and 1975-79 by the pioneering underwater archaeologist Jānis Apals, who recognised five construction phases. Dendrochronological analysis originally produced a mixed-species conifer site chronology, which was tentatively cross-matched to a reference chronology from Novgorod, Russia, indicating a felling date of c.AD 930 for timbers from the earliest phase. A more rigorous analysis produced a 95-year floating chronology for the best-preserved Norway spruce (Picea abies (L.) Karst.) timbers from the earliest phase, which was dated by ¹⁴C wiggle-matching with the IntCal13 calibration curve, suggesting a felling date of cal AD 775–784 (Meadows and Zunde 2014, Geochronometria 41(3):223-33). If this range was accurate, it should have been possible to locate the AD 775 Miyake event (Miyake et al. 2012, Nature 486(7402):240-2) in single-year cellulose samples from the final decade of the Āraiši spruce chronology. However, repeated attempts, with replication of the final decade between the Kiel and Groningen laboratories, were unsuccessful. Additional sampling in 2020-21 unambiguously located the AD 775 event 60 years before the spruce felling date, dating the first phase of construction to AD 835. The new results raise questions both about the treatment of ¹⁴C outliers in the original (2014) wiggle-match, and about the IntCal20 data set; like Philippsen et al. (2021, Nature 601(7893):392-6), we suspect that IntCal20 is too low in the 830s AD.

C04_P06

AMS radiocarbon investigation of the African baobabs from the semi-arid cloud forest of Wadi Hinna, Dhofar, Oman

Patrut A^1,2, Molnar M³, Patrut R¹, Rakosy L⁴, Brown J⁵, Varga T⁶, Ratiu I^1,2

¹Babes-Bolyai University, Faculty of Chemistry and Chemical Engineering, Cluj-Napoca, Romania, ²Babes-Bolyai University, Raluca Ripan Institute for Research in Chemistry, Cluj-Napoca, Romania, ³Interact Centre,Institute for Nuclear Research, Debrecen, Hungary, ⁴Babes-Bolyai University, Faculty of Biology and Geology, , Cluj-Napoca, Romania, ⁵Qatar University, College of Arts and Sciences, Doha, Qatar, ⁶University of Debrecen, Doctoral School of Physics, , Debrecen, Hungary

Wadi Hinna is a small semi-arid valley (3 km2) at the edge of the Dhofar Mountains (17º03' N, 54º36' E, altitude 300-360 m) and at 20 km from the coastal plain, in southern Oman. Wadi Hinna hosts a unique water-limited cloud forest of African baobabs (Adansonia digitata).

The precipitation (annual rainfall 130 mm) falls during the rainy season (mid-June to mid-September), when moist air from the Indian Ocean, i.e., the southwest monsoon, encounters the mountains, leading to clouds and dense fog. The rainfall is significantly supplemented by horizontal precipitation, namely cloud water interception within the canopy of trees.

Over 120 baobabs grow on a slope among huge stones of sedimentary rocks. We dated by AMS radiocarbon wood samples from the largest baobabs. We found that they exhibit, with one exception, ages of several hundreds of years. The exception is the Big tree of Wadi Hinna, which is by far the biggest and oldest baobab. The oldest part of the Big tree started growing more than 1000 years ago.

The African baobab typically exhibits well-defined growth rings, which correspond in many cases to one rainy season. Nevertheless, age modeling of baobab rings demonstrated that ring-growth anomalies occur more frequent than for other tree species. For the old baobabs of Wadi Hinna, we found that the ring frequency varies between 0.43 and 0.78 rings/year. The large number of missing rings is due to the semi-arid climate.

The research was funded by the Romanian Ministry of Research CNCS-UEFISCDI under grant PN-III-P4-ID-PCE-201620-2567, No. 145/2021.

C04_P07

Improved calibration method for dating multiple tree-rings and its implication on the Santorini debate

Raj H¹, Regev L¹, Boaretto E¹

¹Dangoor Research Accelerator Mass Spectromerty (D-REAMS) Laboratory, Weizmann Institute of Science, Rehovot, Israel

The Minoan eruption of Santorini, Greece, is an important and probably most debated chronological marker in contexts of the Eastern Mediterranean region. Among various age estimates of this event, one based on wiggle-matching of ¹⁴C dates from an olive branch found in Santorini by Friedrich et al. (2006) has been widely discussed. Four ¹⁴C ages were reported from this olive branch, each corresponding to a group of rings identified by X-ray tomography. Calibrated age estimates based on wiggle-matching of these ¹⁴C ages have been changing with improvements in the radiocarbon calibration curve. Such changes are important as the debate on the timing of the Minoan eruption is still not settled. It is understood that the calibration curve plays a crucial role in defining the calendar age range corresponding to ¹⁴C age(s). Interannual ¹⁴C levels can change significantly in the calibration curve, and the average ¹⁴C age of multiple rings dated together cannot always be calibrated to the middle year. Therefore, a different approach should be taken to calibrate the average ¹⁴C age of the multiple tree rings. We propose that calibration using the moving average calibration curve is more appropriate in such a case. Here, we recalibrated the four ¹⁴C  ages reported for the above olive section on the moving average calibration curves. Considering the ring counts of the above olive section accurate, the resulting calendar age for the last ring ranges between 1608-1589 BCE (68.3% confidence) and 1616-1576 BCE (95.4% confidence) with a peak at ca. 1600 BCE.

C04_P08

High precision dating of a Neolithic wooden trackway from Lower Saxony, Germany, using radiocarbon wiggle matching

Rose H¹, Brozio J², Shindo L³, Meadows J^1,4, Feeser I², Dörfler W², Heumüller M⁵

¹Zentrum für Baltische und Skandinavische Archäologie (ZBSA), Schleswig, Germany, ²Institute of Pre- and Protohistoric Archaeology, University of Kiel, Kiel, Germany, ³ROOTS Cluster of Excellence , University of Kiel, Kiel, Germany, ⁴Leibniz-Laboratory for Radiometric Dating and Stable Isotope Research, University of Kiel, Kiel, Germany, ⁵Lower Saxony State Office for Heritage, Hannover, Germany

Wooden trackways dating from the Neolithic to the medieval period are well-documented in Europe. The earliest finds date to the middle of the 5th millennium BC and are linked to the invention of wheeled wagons, which are known in northern Germany from 3400 BC. We present new results from a wooden trackway found east of Aschener Moor in Lower Saxony, Germany. It was discovered in the 1890s and a 100-meter-long section was excavated in the 1980s. We returned to the site in 2021 and excavated a smaller section left untouched by the earlier campaign. The trackway is wide enough to allow passage of a wagon, but it is unclear where it led; across the marshy area of the Aschener Moor would be an obvious possibility, but previous attempts to prove this have been unsuccessful. The trackway is constructed of wooden trunks placed diagonally in two layers, consisting primarily of alder (Alnus sp.), but with a smaller number of birch (Betula sp.). This excludes traditional dendrochronological dating, but using radiocarbon wiggle matching, we have dated the felling date of one alder trunk to a 20-year-window in the mid-25th century BC. Such a precise date is rare for the Neolithic period, but it is supported by chronological modelling of dates on branch wood found between the trackway logs. On-site palaeoenvironmental analyses relate the trackway construction to its local environment and periods of increasing precipitation. We will also compare our findings to the chronology of other wooden trackways in northern Europe.

C04_P09

Origin and age of carbon in cellulose of mid-latitude tree rings

Kromer B¹, Wacker L², Friedrich M³, Lindauer S⁴, Friedrich R⁴, Treydte K⁵, Fonti P⁵, Martinez E⁵

¹Institute of Environmental Physics, Heidelberg, Germany, ²Laboratory of Ion Beam Physics, ETH Zurich, Zurich, Switzerland, ³University of Hohenheim, Stuttgart, Germany, ⁴Curt-Engelhorn-Centre Archaeometry, Mannheim, Germany, ⁵WSL Birmensdorf, Birmensdorf, Switzerland

Annual rings of most trees in the middle and high latitudes are composed of the earlywood (EW), formed at the beginning of the growing season, and the latewood (LW), formed from summer onwards. A substantial part of EW in ring-porous deciduous tree species is formed before budburst, i.e. before leaves or needles have unfolded, which is a prerequisite for uptake of atmospheric CO₂. Hence, an essential share of carbon for the construction of EW must come from non-structural, mobile carbon sources (NSC), i.e. from reserve materials formed in the previous year or years. This naturally raises the question to what extent the carbon of an annual ring reflects the atmospheric carbon of the current year.

Here, ¹⁴C measurements on EW and LW tree-ring cellulose from deciduous tree species as well as non-deciduous species in selected years around the ¹⁴C bomb spike in the 1960s are presented. The measured ¹⁴C concentrations of the EW and to a lesser extend of the LW show significant deviations from the atmospheric ¹⁴C values at the time xylem cell wall deposition. With a simple model the fraction of NSC from reserves in addition to carbohydrates photosynthesized in the year of formation is quantified.

C04_P10

Using rapid atmospheric ¹⁴C changes to precise dating part of the floating chronology for pine tree from Józefowo (north Poland)

Wiktorowski D¹, Krąpiec M¹, Barniak J¹

¹AGH University of Science and Technology, Kraków, Poland

Miyake was the first to describe rapid and short-lasting increases of radiocarbon (¹⁴C) concentration in the annual tree rings between AD 774 and 775 and AD 993 and 994. This sudden increase of radiocarbon has been confirmed also by other scientists. Similar study has been conducted in Poland at the AGH University of Science and Technology. The results clearly show a rapid increase of ¹⁴C concentration in these years. Results of last studies confirmed that the abrupt increase in ¹⁴C concentration is also visible between 663 and 662 BC. In this period is also located the floating pine chronology for north Poland. Due to the characteristic of the sharp increase in radiocarbon concentration that occurs in this phenomena, and due to the global character of this effect, it is possible to use it for accurate dating of annual tree rings, using radiocarbon method. In practice, linking the relative dendrochronological dating and radiocarbon analysis of annual growth rings is possible to use “Wiggle matching” technique to precise determination of the calendar age. Samples from Grabie, a village near Krakow (south-easter Poland) were control series, of known calendar age and known changes of radiocarbon concentration around 660 BC. The values of these changes were compared with the values noted in samples of pine tree from Józefowo (floating pine chronology) to its precise dating (with an accuracy of up to one year). This allowed the absolute dating of tree rings from floating pine chronology, which has been so far unattainable using radiocarbon method.