Absolute and relative age of moraines of the Aktru and Historical stages of glaciers of Central Altai based on lichenometry and dendrochronology

Abstract

Dendrochronology, and lichenometry were used to determine the relative and absolute age of the Late Holocene moraines of the glaciers of the Aktru, Maashei and Shavla valleys (North Chuya ridge, Central Altai). An array of 86dendrochronological dates, related to moraine deposits, is analyzed, 30 of which are published for the first time. Also, for the first time, data on the relative (lichenometric) age of the young deposits of the Aktru Valley, and data on the lichenometry of the moraines of the Maashey glacier and one of the glaciers of the Shavly valley were obtained. We used the capabilities of each method and the expediency of their combined use in the study area. It was confirmed that the growth rates of lichens on the moraines of the Aktru stage (XVIII–XIX centuries) are generally consistent with the previously published estimates. The moraines of the Historical stage, which date earlier than 1700–2300 years ago, supports the lichens as large as 120–160 mm, but the scattering of their diameters is too large and the assessment of the lichenometric ages of these moraines seems to be problematic, but not completely excluded. The Akkem stage of glacier advance according to the recent publications dates back to the Late Glacial or Early Holocene time; the lichenometry is obviously not applicably at such ancient surfaces. According to dendrochronological dating, the glaciers of the North Chuisky Ridge in the last millennium advanced at least twice up to their maximum extent in the XVII– early XIX and XII centuries. In the 8th century, the sizes of the glaciers possibly, approached modern ones. Aſter the XVII century, the cedar (Pinus Sibirica) in Central Altai significantly reduced its distribution area due to the climate cooling, retreating from the periglacial territories, where it was distributed earlier. All trees that grew near the glaciers, above 2300 m, died. The comparison of the dates of glacier advances in the past millennia with the tree-ring, ice-core, and palynological reconstructions of summer temperature and precipitation show a good correspondence.

Keywords

• altai
• glacier fluctuations
• moraines
• tree rings
• lichenometry
• dendrochronology
• little ice age
• late holocene