Irina P. Panyushkina

Excursions in the 14C record at A.D. 774–775 in tree rings from Russia and America

The calibration of radiocarbon dates by means of a master calibration curve has been invaluable to Earth, environmental and archeological sciences, but the fundamental reason for calibration is that atmospheric radiocarbon content varies because of changes in upper atmosphere production and global carbon cycling. Improved instrumentation has contributed to high-resolution (interannual) radiocarbon activity measurements, which have revealed sudden and anomalous activity shifts previously not observed at the common resolution of 5–10 years of most of the calibration scale. One such spike has been recently reported from tree rings from Japan and then again in Europe at A.D. 774–775, for which we report here our efforts to both replicate its existence and determine its spatial extent using tree rings from larch at high latitude (northern Siberia) and bristlecone pine from lower latitude (the White Mountains of California). Our results confirm an abrupt ~ 15‰ 14C activity increase from A.D. 774 to 776, the size and now the hemispheric extent of which suggest that an extraterrestrial influence on radiocarbon production is most likely responsible.

CLIMATE IN THE GREAT LAKES REGION BETWEEN 14,000 AND 4000 YEARS AGO FROM ISOTOPIC COMPOSITION OF CONIFER WOOD

The isotopic composition of ancient wood has the potential to provide information about past environments. We analyzed the δ13C, δ18O, and δ2H of cellulose of conifer trees from several cross-sections at each of 9 sites around the Great Lakes region ranging from ~4000 to 14,000 cal BP. Isotopic values of Picea, Pinus, and Thuja species seem inter- changeable for δ18O and δ2H comparisons, but Thuja appears distinctly different from the other 2 in its δ13C composition. Iso- topic results suggest that the 2 sites of near-Younger Dryas age experienced the coldest conditions, although the Gribben Basin site near the Laurentide ice sheet was relatively dry, whereas the Liverpool site 500 km south was moister. The spatial isotopic variability of 3 of the 4 sites of Two Creeks age shows evidence of an elevation effect, perhaps related to sites farther inland from the Lake Michigan shoreline experiencing warmer daytime growing season temperatures. Thus, despite floristic similarity across sites (wood samples at 7 of the sites being Picea), the isotopes appear to reflect environmental differences that might not be readily evident from a purely floristic interpretation of macrofossil or pollen identification.

CALENDAR AGE OF LISAKOVSKY TIMBERS ATTRIBUTED TO ANDRONOVO COMMUNITY OF BRONZE AGE IN EURASIA

We measured radiocarbon ages of 22 decadal replications and 1 bulk group from 5 tree-ring specimens using acid-base-acid pretreatment and accelerator mass spectrometry (AMS). The study has the goal of refining the precision and resolution of a segment of the conventional Bronze Age chronology in the Eurasian steppe attributed to the multicultural com- munity known as Andronovo. The archaeological timbers were gathered from 3 cemeteries at the Lisakovsky cluster of sites in Kazakhstan, where there is a prominent Andronovo occurrence that appears to show evidence of overlapping Alakul and Fedorovo cultures in the southern margin of the Eurasian steppe. The new set of Andronovo calendar dates derived from 14C wiggles and a composite floating tree-ring chronology places the cultural overlap from 1780 to 1660 cal BC. Results indicate older ages of artifacts from the Lisakovsky site than were previously determined by the typological chronology, shifting them from the Late Bronze Age to also include the transition between the Middle and Late Bronze Age. The chronological order of the Lisakovsky cemeteries provides strong evidence of contemporaneity of the Alakul and Fedorovo cultures in the Tobol River Valley for a portion of the 120-yr period of occupation. We discuss an application of the dated Alakul-Fedorovo overlap to the relationship and origin of different groups of the Andronovo community in the Ural region. Our results demonstrate the substantial power that tree rings from Bronze Age timbers provide for developing a precise and highly resolved calendar chro- nology of prehistoric human occupation in the Eurasian steppe during the 2nd millennium BC.

Floating Larch Tree-Ring Chronologies from Archaeological Timbers in the Russian Altai Between About 800 BC and AD 800

We obtained over 200 archaeological wood specimens from the southeastern part of the Altai Mountains (Russia) to establish accurate calendar dates of the timbers using both radiocarbon and tree-ring analyses. Most timbers came from small and elite tombs of the Pazyryk culture (Siberian Scythians of the Iron Age period). Timbers from Hun-Sarmatian and Turk times (1st millennium AD) were studied for the first time. Three floating tree-ring width chronologies of larch (Larix sibirica) with lengths of 486 yr to 144 yr were developed from the tree-ring data. Tree rings of the composite 486-yr chronology of the Pazyryk culture represent the regional scale of Altai tree-ring width variability between about 720240 BC. The composite chronology dates the earliest construction of Pazyryk culture tombs to ~320 BC (ordinary tombs) and the latest ones at 240 BC (Pazyryk noble tomb #5). The composite chronology might be used for tree-ring dating wood from Scythian tombs in the region. It will also help confirm the precision of 14C dating of the Scythian tombs around the Hallstatt plateau of 14C calibration curves. We developed a 110-yr decadal 14C sequence from the Kurayka site that dates Kok-Pash culture timbers back to cal AD 240 (Hun-Sarmatian period). 14C dates of wooden poles from 3 sites of Turk stone enclosures suggested wood cutting dates between cal AD 470 and 830. The results demonstrate that crossdating tree rings along with 14C dating of crossdated rings provide the most reliable and highest precision dates for these archaeological sites.

Large 14C excursion in 5480 BC indicates an abnormal sun in the mid-Holocene

Significance Carbon-14 contents in tree rings tell us information of the past cosmic ray intensities because cosmic rays produce 14C in the atmosphere. We found a signature of a quite large increase of incoming cosmic ray intensity in the mid-Holocene (the 5480 BC event) from the measurement of 14C content in North American tree rings. The cause of this event is supposed to be an extremely weak sun, or a combination of successive strong solar bursts and variation of a solar magnetic activity. In any case, 14C variation of the 5480 BC event is extraordinary in the Holocene, and this event indicates the abnormal solar activity compared with other periods. Radiocarbon content in tree rings can be an excellent proxy of the past incoming cosmic ray intensities to Earth. Although such past cosmic ray variations have been studied by measurements of 14C contents in tree rings with ≥10-y time resolution for the Holocene, there are few annual 14C data. There is a little understanding about annual 14C variations in the past, with the exception of a few periods including the AD 774−775 14C excursion where annual measurements have been performed. Here, we report the result of 14C measurements using the bristlecone pine tree rings for the period from 5490 BC to 5411 BC with 1- to 2-y resolution, and a finding of an extraordinarily large 14C increase (20‰) from 5481 BC to 5471 BC (the 5480 BC event). The 14C increase rate of this event is much larger than that of the normal grand solar minima. We propose the possible causes of this event are an unknown phase of grand solar minimum, or a combination of successive solar proton events and a normal grand solar minimum.

Radiocarbon Wiggles in Great Lakes Wood at About 10,000 to 12,000 BP

High-resolution radiocarbon calibration for the last 14,000 cal yr has been developed in large part using European oaks and pines. Recent subfossil wood collections from the Great Lakes region provide an opportunity to measure 14C activity in decadal series of rings in North America prior to the White Mountains bristlecone record. We developed decadal 14C series from wood at the classic Two Creeks site (~11,850 BP) in east-central Wisconsin, the Liverpool East site (~10,250 BP) in northwestern Indiana, and the Gribben Basin site (~10,000 BP) in the Upper Peninsula of Michigan. Initial AMS dates on holocellulose produced younger-than-expected ages for most Two Creeks subsamples and for a few samples from the other sites, prompting a systematic comparison of chemical pretreatment using 2 samples from each site, and employing holocellulose, AAA-treated holocellulose, alpha-cellulose, and AAA-treated whole wood. The testing could not definitively reveal the source of error in the original analyses, but the best original ages together with new AAA-treated holocellulose and a-cellulose ages were visually fitted to the IntCal04 calibration curve at ages of 13,76013,530 cal BP for the Two Creeks wood, 12,10012,020 cal BP for Liverpool East, and 11,30011,170 cal BP for Gribben Basin. The Liverpool East age falls squarely within the Younger Dryas (YD) period, whereas the Gribben Basin age appears to postdate the YD by ~300 yr, although high scatter in the decadal Gribben Basin results could accommodate an older age nearer the end of the YD.

Ancient tree ring archives in the U.S. great lakes region

Rather than being a seamless transition from Late Glacial Maximum to the start of the Holocene between 15,000 and 8000 years ago, the warming during this period was punctuated by abrupt climatic instabilities. These include the Younger Dryas cold event, the Preboreal Oscillation, and an isolated cooling event around 8200 years ago (see Figure 1, bottom right).

137 ancient human genomes from across the Eurasian steppes

For thousands of years the Eurasian steppes have been a centre of human migrations and cultural change. Here we sequence the genomes of 137 ancient humans (about 1× average coverage), covering a period of 4,000 years, to understand the population history of the Eurasian steppes after the Bronze Age migrations. We find that the genetics of the Scythian groups that dominated the Eurasian steppes throughout the Iron Age were highly structured, with diverse origins comprising Late Bronze Age herders, European farmers and southern Siberian hunter-gatherers. Later, Scythians admixed with the eastern steppe nomads who formed the Xiongnu confederations, and moved westward in about the second or third century bc, forming the Hun traditions in the fourth–fifth century ad, and carrying with them plague that was basal to the Justinian plague. These nomads were further admixed with East Asian groups during several short-term khanates in the Medieval period. These historical events transformed the Eurasian steppes from being inhabited by Indo-European speakers of largely West Eurasian ancestry to the mostly Turkic-speaking groups of the present day, who are primarily of East Asian ancestry.Sequences of 137 ancient and 502 modern human genomes illuminate the population history of the Eurasian steppes after the Bronze Age and document the replacement of Indo-European speakers of West Eurasian ancestry by Turkic-speaking groups of East Asian ancestry.

Trends In Elemental Concentrations of Tree Rings From the Siberian Arctic

ABSTRACT The biogeochemistry and ecology of the Arctic environment have been heavily impacted by anthropogenic pollution and climate change. We used ICP-MS to measure concentrations of 26 elements in the AD 1300–2000 tree rings of larch from the Taymyr Peninsula in northern Siberia for studying the interaction between environmental change and wood chemistry. We applied a two-stage data reduction technique to identify trends in the noisy measurement data. Statistical assessment of variance of normalized time series reveals pronounced depletion of xylem Ca, Mg, Cl, Bi and Si concentrations and enrichment of P, K, Mn, Rb, Sr and Ba concentrations after ca. AD 1900. The trends are unprecedented in the 700-year records, but multiple mechanisms may be at work and difficult to attribute with certainty. The declining xylem Ca and Mg may be a response to soil acidification from air pollution, whereas increasing P, K, and Mn concentrations may signal changes in root efficiency and excess water-soluble minerals liberated by the permafrost thaw. The changes seem consistent with mounting stress on Arctic vegetation. This study supports the potential of tree rings for monitoring past and ongoing changes in biogeochemistry of Arctic ecosystems related to pollution and permafrost thaw.

Radiocarbon and Tree-Ring Dates of the Bes-Shatyr #3 Saka Kurgan in the Semirechiye, Kazakhstan

This study employs tree-ring crossdating and radiocarbon measurements to determine the precise calendar age of the Bes-Shatyr Saka necropolis (4347N, 8121E) built for wealthy tribe leaders in the Ili River Valley (Semirechiye), southern Kazakhstan. We developed a 218-yr tree-ring chronology and a highly resolved sequence of 14C from timbers of Bes-Shatyr kurgan #3. A 4-decadal-point 14C wiggle dates the Bes-Shatyr necropolis to 600 cal BC. A 47-yr range of cutting dates adjusted the kurgan date to ~550 BC. This is the first result of high-resolution 14C dating produced for the Saka burials in the Semirechiye. The collective dating of Bes-Shatyr indicates the early appearance of the Saka necropolis in the Semirechiye eastern margins of the Saka dispersal. However, the date is a couple of centuries younger than previously suggested by single 14C dates. It is likely that the Shilbiyr sanctuary (location of the Bes-Shatyr) became a strategic and sacral place for the Saka leadership in the Semirechiye long before 550 BC. Another prominent feature of the Semirechiye burial landscape, the Issyk necropolis enclosing the Golden Warrior tomb, appeared a few centuries later according to 14C dating reported by other investigators. This study contributes to the Iron Age chronology of Inner Asia, demonstrating successful results of 14C calibration within the Hallstatt Plateau of the 14C calibration curve. It appears that the wide range of calibrated dates for the Saka occurrences in Kazakhstan (from 800 BC to AD 350) is the result of the calibration curve constraints around the middle of the 1st millennium BC.