Calendar-dated tree-ring sequences offer an unparalleled resource for high-resolution paleoenvironmental reconstruction. Where such records exist for a few limited geographic regions over the last ...8,000 to 12,000 years, they have proved invaluable for creating precise and accurate timelines for past human and environmental interactions. To expand such records across new geographic territory or extend data for certain regions further backward in time, new applications must be developed to secure “floating” (not yet absolutely dated) tree-ring sequences, which cannot be assigned single-calendar year dates by standard dendrochronological techniques. This study develops two approaches to this problem for a critical floating tree-ring chronology from the East Mediterranean Bronze–Iron Age. The chronology is more closely fixed in time using annually resolved patterns of 14C, modulated by cosmic radiation, between 1700 and 1480 BC. This placement is then tested using an anticorrelation between calendardated tree-ring growth responses to climatically effective volcanism in North American bristlecone pine and the Mediterranean trees. Examination of the newly dated Mediterranean tree-ring sequence between 1630 and 1500 BC using X-ray fluorescence revealed an unusual calcium anomaly around 1560 BC. While requiring further replication and analysis, this anomaly merits exploration as a potential marker for the eruption of Thera.
The rate and magnitude of temperature variability at the transition from the Last Glacial Maximum into the early Holocene represents a natural analog to current and predicted climate change. A ...limited number of high-resolution proxy archives, however, challenges our understanding of environmental conditions during this period. Here, we present combined dendrochronological and radiocarbon evidence from 253 newly discovered subfossil pine stumps from Zurich, Switzerland. The individual trees reveal ages of 41–506 years and were growing between the Allerød and Preboreal (∼13′900–11′300 cal BP). Together with previously collected pines from this region, this world's best preserved Late Glacial forest substantially improves the earliest part of the absolutely dated European tree-ring width chronology between 11′300 and 11′900 cal BP. Radiocarbon measurements from 65 Zurich pines between ∼12′320 and 13′950 cal BP provide a perspective to prolong the continuous European tree-ring record by another ∼2000 years into the Late Glacial era. These data will also be relevant for pinpointing the Laacher See volcanic eruption (∼12′900 cal BP) and two major Alpine earthquakes (∼13′770 and ∼11′600 cal BP). In summary, this study emphasizes the importance of dating precision and multi-proxy comparison to disentangle environmental signals from methodological noise, particularly during periods of high climate variability but low data availability, such as the Younger Dryas cold spell (∼11′700 and 12′900 cal BP).
•A total of 253 subfossil pine stumps were discovered in Zurich, CH.•Trees were growing between the Allerød and Preboreal ∼13′900–11′300 cal BP.•The Swiss Late Glacial pines improve the longest EU tree-ring chronology.•Combined dendro and radiocarbon dating provides insight into the Younger Dryas.
Advances in accelerator mass spectrometry have resulted in an unprecedented amount of new high-precision radiocarbon (14C) -dates, some of which will redefine the international 14C calibration curves ...(IntCal and SHCal). Often these datasets are unaccompanied by detailed quality insurances in place at the laboratory, questioning whether the 14C structure is real, a result of a laboratory variation or measurement-scatter. A handful of intercomparison studies attempt to elucidate laboratory offsets but may fail to identify measurement-scatter and are often financially constrained. Here we introduce a protocol, called Quality Dating, implemented at ETH-Zürich to ensure reproducible and accurate high-precision 14C-dates. The protocol highlights the importance of the continuous measurements and evaluation of blanks, standards, references and replicates. This protocol is tested on an absolutely dated German Late Glacial tree-ring chronology, part of which is intercompared with the Curt Engelhorn-Center for Archaeometry, Mannheim, Germany (CEZA). The combined dataset contains 170 highly resolved, highly precise 14C-dates that supplement three decadal dates spanning 280 cal. years in IntCal, and provides detailed 14C structure for this interval.
As the worldwide standard for radiocarbon (14C) dating over the past ca. 50,000 years, the International Calibration Curve (IntCal) is continuously improving towards higher resolution and ...replication. Tree-ring-based 14C measurements provide absolute dating throughout most of the Holocene, although high-precision data are limited for the Younger Dryas interval and farther back in time. Here, we describe the dendrochronological characteristics of 1448 new 14C dates, between ~11,950 and 13,160 cal BP, from 13 pines that were growing in Switzerland. Significantly enhancing the ongoing IntCal update (IntCal20), this Late Glacial (LG) compilation contains more annually precise 14C dates than any other contribution during any other period of time. Thus, our results now provide unique geochronological dating into the Younger Dryas, a pivotal period of climate and environmental change at the transition from LG into Early Holocene conditions.
The Laacher See eruption (LSE) in Germany ranks among Europe's largest volcanic events of the Upper Pleistocene
. Although tephra deposits of the LSE represent an important isochron for the ...synchronization of proxy archives at the Late Glacial to Early Holocene transition
, uncertainty in the age of the eruption has prevailed
. Here we present dendrochronological and radiocarbon measurements of subfossil trees that were buried by pyroclastic deposits that firmly date the LSE to 13,006 ± 9 calibrated years before present (BP; taken as AD 1950), which is more than a century earlier than previously accepted. The revised age of the LSE necessarily shifts the chronology of European varved lakes
relative to the Greenland ice core record, thereby dating the onset of the Younger Dryas to 12,807 ± 12 calibrated years BP, which is around 130 years earlier than thought. Our results synchronize the onset of the Younger Dryas across the North Atlantic-European sector, preclude a direct link between the LSE and Greenland Stadial-1 cooling
, and suggest a large-scale common mechanism of a weakened Atlantic Meridional Overturning Circulation under warming conditions
.
REPLY TO MANNING Pearson, Charlotte; Salzer, Matthew; Wacker, Lukas ...
Proceedings of the National Academy of Sciences,
08/2020, Letnik:
117, Številka:
31
Journal Article
Reinig et al.1 briefly explored magmatic CO2 incorporation as the reason for an age offset in one of their carbonized wood samples, but ultimately did not correct for it. Because the subfossil trees ...were sampled at localities near vents, it seems probable that all of the samples were affected by magmatic CO2 to variable extents. Studies from the USA, New Zealand and Italy have demonstrated that magmatic CO2 incorporation rates into trees are spatiotemporally variable4,6-8 (Fig. 1). ...temporally variable magmatic CO2 fluxes7,8 preceding the LSE may have not only made the radiocarbon dates of the wood samples seem generally older, but also affected the shape of the radiocarbon curve produced by Reinig et al.1 (Fig. 1), thus yielding a spurious correlation when wiggle-matched with the Swiss Late Glacial Master Radiocarbon dataset9,10. ...the observed increase in radiocarbon values immediately before the LSE is surprising. ...we disagree that our radiocarbon (14C) measurements from three subfossil trees killed and buried at different locations by the pyroclastic deposits of the Laacher See eruption (LSE)2 are possibly affected by outgassing magmatic carbon dioxide (CO2).
Previous studies have suggested that the Late Glacial period (LG; ∼14 600–11 700 cal BP) was characterised by abrupt and extreme climate variability over the European sector of the North Atlantic. ...The limited number of precisely dated, high-resolution proxy records, however, restricts our understanding of climate dynamics through the LG. Here, we present the first annually-resolved tree-cellulose stable oxygen and carbon isotope chronology (δ18Otree, δ13Ctree) covering the LG between ∼14 050 and 12 795 cal BP, generated from a Swiss pine trees (P. sylvestris; 27 trees, 1255 years).
Comparisons of δ18Otree with regional lake and ice core δ18O records reveal that LG climatic changes over the North Atlantic (as recorded by Greenland Stadials and Inter-Stadials) were not all experienced to the same degree in the Swiss trees. Possible explanations include: (1) LG climate oscillations may be less extreme during the summer in Switzerland, (2) tree-ring δ18O may capture local precipitation and humidity changes and/or (3) decayed cellulose and various micro-site conditions may overprint large-scale temperature trends found in other δ18O records. Despite these challenges, our study emphasises the potential to investigate hydroclimate conditions using subfossil pine stable isotopes.
•Millennial stable isotope chronologies of δ13C and δ18O from 27 Swiss subfossil pine trees, covering the Late Glacial (∼14 050–12 795 cal BP).•Two extreme δ18Otree depletions parallel North Atlantic ‘cool periods’ (GI-1c, GS-1), another LG event (GI-1b) is not expressed in δ18Otree.•Trees with less extensive decay have significantly higher inter-isotope (δ18Otree: δ13Ctree) correlations.
The measurement of rare radioactive lead isotopes (205Pb or 210Pb) by AMS requires the production of strong Pb negative molecular anion beams from the ion source. This paper summarizes the results of ...tests of different target composition on the strength and stability of 208PbF3− currents and 210Pb counts. In an 834 SIMS-type Cs+ sputter source, the superhalogen, PbF3− had the largest current or ionization efficiency from a survey of Pb molecular anions. The target matrix that produced the largest current of PbF3− was composed of PbF2, AgF2 and CsF. The ratio of AgF2 and CsF does not affect the ionization efficiency of PbF3−. Chemically refluxed targets of PbF2, AgF2 and CsF increased the ionization efficiency of PbF3−. The count rate of the rare isotope, 210Pb, was increased with the addition of microgram quantities of stable PbF2 to the targets. In an SO-110 type Cs+ sputter source the ionization efficiency of PbF3− was increased with lower rather than higher Cs+ fluence.
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