Mukhtar M. Naurzbaev

Variation of early summer and annual temperature in east Taymir and Putoran (Siberia) over the last two millennia inferred from tree rings

Regional tree ring chronology with extension 2209 years (from 212 B.C. till 1996 A.D.) was built for east Taymir and Putoran according to wood of living trees, well-preserved remains of dead trees, and subfossil wood from alluvial bank deposits by the cross-dating method. In addition, the “floating” tree ring width chronology for the period of Holocene optimum (3300–2600 B.C.) was built with extention 685 years and supported by several radiocarbon dates. High values of synchrony and correlation of individual tree ring series show a prevailing effect of one external factor on radial tree growth change in the studied region of the Siberian subarctic. It was established that the main factors of growth variability are the early summer and annual temperature, which explain up to 70% of tree growth rate variability. Cyclic components stable for two millennia were revealed at analysis of the tree ring chronology: double secular (∼180 years), secular (78–90 years), and intrasecular (44, 28, 11, and 6.7–6.9 years) variations. Models for reconstruction of the early summer and annual air temperature were obtained according to tree ring variability. Temperature dynamics in the eastern part of Taymir for the last two millenia agree well with temperature variations in the Northern Hemisphere obtained according to other indirect sources. The warming of the middle of the twentieth century is not extraordinary. The warming at the end of the first and beginning of the second millennia (“Medieval Warm Period”) was longer in time and closer in amplitude.

Forest-tundra larch forests and climatic trends

Climate-related changes that occurred in the Ary-Mas larch forests (the world’s northernmost forest range) in the last three decades of the 20th century have been analyzed. An analysis of remote-sensing images made by Landsat satellites in 1973 and 2000 has provided evidence for an increase in the closeness of larch forest canopy (by 65%) and the expansion of larch to the tundra (for 3–10 m per year) and to areas relatively poorly protected from wind due to topographic features (elevation, azimuth, and slope). It has also been shown that the radial tree increment correlates with summer temperatures (r = 0.65, τ = 0.39) and the amounts of precipitation in summer (r = −0.51, τ = 0–41) and winter (r = −0.70, τ = −0.48), decreases with an increase in the closeness of forest canopy (r = −0.52, p > 0.8; τ = −0.48, p > 0.95), and increases with an increase in the depth of soil thawing (r = 0.63, p > 0.9; τ = 0.46, p > 0.9). The density of undergrowth depends on temperatures in winter (τ = 0.53, p > 0.8) and summer (r = 0.98, p > 0.99, τ = 0.9, p > 0.99) and the date of the onset of the growing period (r = −0.60, p > 0.99; τ = −0.4, p > 0.99) and negatively correlates with the amount of precipitation in summer (r = −0.56, p > 0.99, τ = −0.38, p > 0.99).

Regional features of the radial growth of larch in north central Siberia according to millennial tree-ring chronologies

A 1138-year tree-ring chronology has been constructed for the region of the Bol’shoi Avam River (the Putoran Plateau). Its comparison with millennial chronologies for the Taimyr Peninsula and Mangazeya has shown that all these chronologies are fairly synchronous with respect to both high-frequency (annual) and low-frequency (long-term) components, although each has its specific regional features. The results of dendroclimatic analysis provide evidence for the prevailing influence of air temperature in July (compared to that in June) on the radial growth of larch in the middle reaches of the Bol’shoi Avam. Consistent long-term changes in radial tree increment (and in summer air temperature) in a large sector of the Subarctic over the past 1000 years have been revealed.

Characterization and Monitoring of Tundra-Taiga Transition Zone with Multi-sensor Satellite Data

Monitoring the dynamics of the circumpolar boreal forest (taiga) and Arctic tundra boundary is important for understanding the causes and consequences of changes observed in these areas. Because of the inaccessibility and large extent of this zone, remote sensing data can play an important role for the purposes. In this study, climate-related changes that occurred in the Ary-Mas larch forests (the world’s northernmost forest range) in the last three decades of the twentieth century were analyzed. An analysis of Landsat images in 1973 and 2000 has provided evidence for an increase in the closeness of larch forest canopy by 65% and the expansion of larch to the tundra for 3–10 m per year and to areas relatively poorly protected from wind due to topographic features (elevation, azimuth, and slope). It was found that a tundra-taiga transitional area can be characterized using multi-spectral Landsat ETM+ summer images, multi-angle MISR red band reflectance images, RADARSAT images with larger incidence angle, or multi-temporal and multi-spectral MODIS data. Because of different resolutions and spectral regions covered, the transition zone maps derived from different data types were not identical, but the general patterns were consistent.