Vladimir S. Myglan

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.

Revising midlatitude summer temperatures back to A.D. 600 based on a wood density network

Annually resolved and millennium-long reconstructions of large-scale temperature variability are primarily composed of tree ring width (TRW) chronologies. Changes in ring width, however, have recently been shown to bias the ratio between low- and high-frequency signals. To overcome limitations in capturing the full spectrum of past temperature variability, we present a network of 15 maximum latewood density (MXD) chronologies distributed across the Northern Hemisphere extratropics. Independent subsets of continental-scale records consistently reveal high MXD before 1580 and after 1910, with below average values between these periods. Reconstructed extratropical summer temperatures reflect not only these long-term trends but also distinct cooling pulses after large volcanic eruptions. In contrast to TRW-dominated reconstructions, this MXD-based record indicates a delayed onset of the Little Ice Age by almost two centuries. The reduced memory inherent in MXD is likely responsible for the rapid recovery from volcanic-induced cooling in the fourteenth century and the continuation of warmer temperatures until ~1600.

Temperature-induced responses of xylem structure of Larix sibirica (Pinaceae) from the Russian Altay

PREMISE OF THE STUDY Xylem structure determines the hydraulic and mechanical properties of a stem, and its plasticity is fundamental for maintaining tree performance under changing conditions. Unveiling the mechanism and the range of xylem adjustment is thus necessary to anticipate climate change impacts on vegetation. METHODS To understand the mechanistic process and the functional impact of xylem responses to warming in a cold-limited environment, we investigated the relationship between temperature and tracheid anatomy along a 312-yr tree-ring chronology of Larix sibirica trees from the Altay Mountains in Russia. KEY RESULTS Climate-growth analyses indicated that warming favors wider earlywood cell lumen, thicker latewood walls, denser maximum latewood, and wider rings. The temperature signal of the latewood was stronger (r > 0.7) and covered a longer and more stable period (from June to August) than that of earlywood and tree-ring width. Long-term analyses indicated a diverging trend between lumen and cell wall of early- and latewood. CONCLUSIONS Xylem anatomy appears to respond to warming temperatures. A warmer early-growing season raises water conduction capacity by increasing the number and size of earlywood tracheids. The higher-performing earlywood tracheids promote more carbon fixation of the latewood cells by incrementing the rate of assimilation when summer conditions are favorable for growth. The diverging long-term variation of lumen and cell wall in earlywood vs. latewood suggests that xylem adjustments in latewood increase mechanical integrity and support increasing tree size under the ameliorated growing conditions.

A multi-proxy approach for revealing recent climatic changes in the Russian Altai

For the first time we present a multi-proxy data set for the Russian Altai, consisting of Siberian larch tree-ring width (TRW), latewood density (MXD), δ13C and δ18O in cellulose chronologies obtained for the period 1779–2007 and cell wall thickness (CWT) for 1900–2008. All of these parameters agree well between each other in the high-frequency variability, while the low-frequency climate information shows systematic differences. The correlation analysis with temperature and precipitation data from the closest weather station and gridded data revealed that annual TRW, MXD, CWT, and δ13C data contain a strong summer temperature signal, while δ18O in cellulose represents a mixed summer and winter temperature and precipitation signal. The temperature and precipitation reconstructions from the Belukha ice core and Teletskoe lake sediments were used to investigate the correspondence of different independent proxies. Low frequency patterns in TRW and δ13C chronologies are consistent with temperature reconstructions from nearby Belukha ice core and Teletskoe lake sediments showing a pronounced warming trend in the last century. Their combination could be used for the regional temperature reconstruction. The long-term δ18O trend agrees with the precipitation reconstruction from the Teletskoe lake sediment indicating more humid conditions during the twentieth century. Therefore, these two proxies could be combined for the precipitation reconstruction.

Diverse growth trends and climate responses across Eurasia’s boreal forest

The area covered by boreal forests accounts for similar to 16% of the global and 22% of the Northern Hemisphere landmass. Changes in the productivity and functioning of this circumpolar biome not o ...

Timber Logging in Central Siberia is the Main Source for Recent Arctic Driftwood

Abstract Recent findings indicated spruce from North America and larch from eastern Siberia to be the dominating tree species of Arctic driftwood throughout the Holocene. However, changes in source region forest and river characteristics, as well as ocean current dynamics and sea ice extent likely influence its spatiotemporal composition. Here, we present 2556 driftwood samples from Greenland, Iceland, Svalbard, and the Faroe Islands. A total of 498 out of 969 Pinus sylvestris ring width series were cross-dated at the catchment level against a network of Eurasian boreal reference chronologies. The central Siberian Yenisei and Angara Rivers account for 91% of all dated pines, with their outermost rings dating between 1804 and 1999. Intensified logging and timber rafting along the Yenisei and Angara in the mid-20th century, together with high discharge rates, explain the vast quantity of material from this region and its temporal peak ca. 1960. Based on the combined application of wood-anatomical and dendrochronological techniques on a well-replicated data set, our results question the assumption that Arctic driftwood mainly consists of millennial-old larch and spruce. Nevertheless, data from other species and regions, together with longer boreal reference chronologies, are needed for generating reliable proxy archives at the interface of marine and terrestrial environments.

Constructing the tree-ring chronology and reconstructing summertime air temperatures in southern Altai for the last 1500 years

We have constructed and analyzed the 1896-year-long tree-ring chronology for the territory of the Altai Republic. The chronology was based on wood of live trees and remains of trunks of Siberian larch (Larix sibirica Ledeb.) from the upper timberline (2300 m) of the Dzhelo river valley. The chronology agrees well with palaeoclimatic data and reflects the main climatic changes in the northern hemisphere for the last two millennia: an extraordinary decrease in increment after the year 536, “mean secular warming”, the “Little Ice Age”, and current warming. By calculating the response function between the tree-ring chronology for the Dzhelo and data from weather stations, it was possible to reconstruct the series of June–July air temperature variability for the last 1500 years. The chronology can be used in dating archaeological wood, i.e. in determining the calendar time at which archaeological monuments were constructed.

Variations of the tree line and glaciers in the Central and Eastern Altai regions in the Holocene

Variations in the tree line position and glacier activity in the Central and Eastern Altai regions in the Holocene were reconstructed on the basis of analysis of sixty radiocarbon and eighteen dendrochronological dates. The tree line was higher than now in the Early and Middle Holocene, and the climate was warmer and, likely, more humid. Glaciers advanced in the forests 300, 1400, and 3000–6000 years ago. In the last millennium the forest decline at the upper tree limit occurred in 1206–1256, 1445–1501, and 1642–1736.

Wood transformation in dead-standing trees in the forest-tundra of Central Siberia

Changes in the composition of wood organic matter in dead-standing spruce and larch trees depending on the period after their death have been studied in the north of Central Siberia. The period after tree death has been estimated by means of cross-dating. The results show that changes in the composition of wood organic matter in 63% of cases are contingent on tree species. Wood decomposition in dead-standing trees is accompanied by an increase in the contents of alkali-soluble organic compounds. Lignin oxidation in larch begins approximately 80 years after tree death, whereas its transformation in spruce begins not earlier than after 100 years. In the forest-tundra of Central Siberia, the rate of wood organic matter transformation in dead-standing trees is one to two orders of magnitude lower than in fallen wood, which accounts for their role as a long-term store of carbon and mineral elements in these ecosystems.

Using Dendrochronological Analysis for Dating Earthquake-Triggered Landslides (By the Example of SE Altai, Russia)

Paleoseismogeological investigations of the high mountain, seismically active southeastern part of the Russian Altai reveal a previously unknown complex of earthquake induced landslides. Using dendrochronological analysis of the wood penetrating injuries of trees (both dead and living ones) caused by seismically induced rockfalls allowed establishing the date of previously unknown strong medieval earthquake. This date was also confirmed by radiocarbon dating of seismically cut fossil soil overlapped by undistorted one. The specified recurrence interval of strong (М > 7) earthquakes for the SE Altai (about 400 years during the last 3,000 years) argues the high regional seismicity.