Radiocarbon chronology of Holocene glacial and climatic events in southeastern Altai (Central Asia)

Abstract

The geomorphological studies and radiocarbon dating of moraine complexes and the tree line within the North Chuya Ridge, along with active slope processes, soil formation, and peat formation in southeastern Gorny Altai, constrain the age of the main glacial and climatic events in this area at 7 ka to the first half of the 19th century. It is for the first time in the history of Altai studies that 57 absolute dates were obtained for glaciation in a vast but climatically and neotectonically homogeneous area. The new data refute the conventional idea that the Holocene glaciation in this mountain land comprised eight stages of the gradual retreat of the Late Würm (Sartan) glaciation. Also, they evidence that glaciation in the upper parts of the troughs retreated almost completely no later than 7 ka and valley glaciers in southeastern Altai were activated many times in the second half of the Holocene. Data are given on the morphology and age of three moraine generations reflected in the topography. A combination of temperature minima and humidity maxima led to a catastrophically rapid and the largest (up to 5–6 km) ice advance at the Akkem Stage (4.9–4.2 ka). In addition to the radiocarbon data, the time limits of the Historical stage (2.3–1.7 ka) were defined more precisely using dendrochronological and archaeological data from Scythian burials of Pazyryk culture in SE Altai. The moraines closest to the present-day glaciers formed at the Aktru Stage (late 13th–middle 19th century). During warm interglacials, the glaciers waned considerably or retreated completely and the zone of recent glaciation was reforested. As a result of progressive aridization in the Holocene, the glaciers in southeastern Altai waned at each successive stage, and their mass balance was not positive during the greatest temperature minimum of the last millennium (middle 19th century).

Holocene Vegetation and Climate Dynamics in the Altai Mountains and Surrounding Areas

“…Subsequently, the region was occupied by the Mongols until the present day who practice the same pastoral lifestyle. On the other hand, with the decreasing summer insolation (Figure 3d), a large-scale decrease in mean annual temperature in the Northern Hemisphere occurred from around 7 ka (Marcott et al, 2013; Figure 3b), and neoglaciations commenced in the western Mongolian Altai Mountains (Agatova, Nazarov, Nepop, & Orlova, 2012;Herren et al, 2013) and on the northern and central Tibetan Plateau (Thompson et al, 2005), also indicating a cooling climate and more precipitation in winter. After~7-8 ka, a more negative Arctic Oscillation (Figure 3c; Rimbu et al, 2003) and North Atlantic Oscillation would have caused lower temperatures and higher regional precipitation in ACA (Chen et al, 2016).…”

“…In the middle Holocene, summer insolation decreased and glacial advances occurred at many high mountainous areas of the Northern Hemisphere, including the Altai Mountains (Agatova, Nazarov, Nepop, & Orlova, 2012;Chernykh et al, 2013;Clague et al, 2009;Herren et al, 2013). A colder climate (likely a cold winter) prevailed during the middle Holocene (X.…”

“…The quantitatively reconstructed Pann suggested that the annual precipitation did not decrease significantly in the late Holocene (Figure 3h). The forest recession was caused by occasional cold climatic events from around 4 ka and by heavy winter snowfall, as indicated by a simulated increase in regional winter precipitation (Chen et al, 2016) and glacial advances (Agatova, Nazarov, Nepop, & Orlova, 2012;Agatova, Nazarov, Nepop, & Rodnight, 2012;Chernykh et al, 2013;Lehmkuhl, 2012;J. Zhao et al, 2013).…”

“…The lower reconstructed precipitation values during circa 10.5-8.5 ka were most likely contributed to by the following: (i) relatively lower pollen percentages of trees and shrubs, (ii) higher representation of Juniperus and Ephedra (Ephedra's optima Pann is13 mm), and (iii) the reduced representation of Betula, which has an optimum Pann of 625 mm. On the other hand, with the decreasing summer insolation (Figure 3d), a large-scale decrease in mean annual temperature in the Northern Hemisphere occurred from around 7 ka (Marcott et al, 2013; Figure 3b), and neoglaciations commenced in the western Mongolian Altai Mountains (Agatova, Nazarov, Nepop, & Orlova, 2012;Herren et al, 2013) and on the northern and central Tibetan Plateau (Thompson et al, 2005), also indicating a cooling climate and more precipitation in winter. The cooling climate may have resulted in intensified eolian activity (Qiang et al, 2014).…”

The origin of sand deposits in the South Minusa basin

“…Analysis of the previous studies of geologic and geomorphologic processes in the Altai-Sayan mountainous region (Agatova et al, 2012;Deev et al, 2013;Gillespie et al, 2008;Komatsu et al, 2009; and others) reveals a relationship between the formation of these sand massifs and some Late Quaternary events. According to (Grosval'd, 1987(Grosval'd, , 1999Komatsu et al, 2009), the geomorphologic and sedimentologic characteristics of the drainage basin of the upper reaches of the Yenisei River show that the valley experienced catastrophic floods.…”