A¹⁰Be Moraine Chronology of the Last Glaciation and Termination at 49°N in the Mongolian Altai of Central Asia

Abstract

Determining what caused the global Last Glaciation and last glacial termination, despite opposing orbital summer insolation signatures between the polar hemispheres, remains a puzzle of paleoclimatology. This problem can be addressed by comparing chronologies of glaciation from different latitudes and different climatic regimes in both hemispheres. Here, we present a 10Be surface‐exposure chronology of glacial landforms constructed during and since the local Last Glaciation in the continental environment of Central Asia in the high Mongolian Altai (49°N, 88°E). Four belts of lateral moraines document maximal phases of the former Khoton glacier at 35,440 ± 980 years ago, 23,430 ± 850 years ago, 20,780 ± 610 years ago, and 19,520 ± 550 years ago. Our chronology indicates that deglaciation from these maximal positions began as early as 18,810 ± 510 years ago, was well underway by 17,680 ± 510 years ago, and was nearly completed by 16,040 ± 490 years ago. Overall, our chronology shows that glaciation in western Mongolia overlapped with the global Last Glacial Maximum and that extensive recession from glacial‐to‐interglacial limits took place early in the last glacial termination during Heinrich Stadial 1. Khoton Nuur deglaciation led the demise of large Northern Hemisphere ice sheets and increases in radiative forcing agents by several millennia. We suggest that this rapid switch in the mode of glaciation implies the involvement of an additional climatic factor that could have produced locally rapid warming and deglaciation ∼18,800–16,000 years ago.

Timing and extent of glaciation since the Last Glacial Maximum in the upper Kalguty basin, Russian Altai Mountains

“…in the Altai Mountains during MIS 2 (29–14 ka; Martinson et al, 1987), related to temperature change in Tibet (Guliya Ice Cap). (a) this study (grey dots: outliers); (b) Reuther et al, 2006; Agatova et al, 2020; Herget et al, 2020; (c) Gribenski et al, 2016; (d) Gribenski et al, 2018; (e) Radue, 2018; (f) Strand et al, 2022 [arithmetic mean (three to nine samples) for five moraines and three erratic sets]; (g) Blomdin et al, 2018; (h) Ganyuskin et al, 2018a; (i) Dong et al, 2020 (outside the location map); (j) Thompson et al, 2005. Ages of the moraines and erratic boulders are mostly from SED, while GLOF ages resulted from different dating methods: SED on flood‐associated boulders, OSL dating on flood and lacustrine deposits and radiocarbon dating on subaerial deposits.…”

“…While a re‐evaluation of glacial chronologies in the Central Asia concluded that there was no significant ice expansion during MIS 3 (59–29 ka; Gribenski et al, 2018, and references therein), as already suggest by Lehmkuhl et al (2016) for the Mongolian Altai, few studies document a major glacier advance during MIS 3 in the Altai Mountains: a Turgen‐Asgat moraine in drier Ikh Turgen Mountains is dated to c . 45 ka (Blomdin et al, 2018), the outermost one of the Khoton Nuur complex is dated to 35.4 ka (Strand et al, 2022), while Dong et al (2020) propose a local LGM at 34.1 ka in the Xiaokelanhe River basin.…”

“…Other studies place the local LGM earlier than MIS 2, due to wetter conditions (Herget et al, 2020, and references therein), generally during MIS 4 − for example 69-63 ka in the nearby Kanas valley (Gribenski et al, 2018), or as hypothesized by Ganyuskin et al (2018a) for the Mongun-Taiga massif. While a re-evaluation of glacial chronologies in the Central Asia concluded that there was no significant ice expansion during MIS 3 (59-29 ka; Gribenski et al, 2018, and references therein), as already suggest by Lehmkuhl et al (2016) for the Mongolian Altai, few studies document a major glacier advance during MIS 3 in the Altai Mountains: a Turgen-Asgat moraine in drier Ikh Turgen Mountains is dated to c. 45 ka (Blomdin et al, 2018), the outermost one of the Khoton Nuur complex is dated to 35.4 ka (Strand et al, 2022), while Dong et al (2020) propose a local LGM at 34.1 ka in the Xiaokelanhe River basin.…”

“…Surrounding the Khoton Nuur (Mongolia), a 21-km-long lake, a wide morainic complex is composed of four sets of moraines attributed to the last glacial cycle (Figure 10). While the outermost Khoton Moraine IV is attributed to MIS 3 (35.4 ± 1.0 ka), arithmetic mean ages of Khoton Moraines III, II and I are 23.4 ± 0.8, 20.8 ± 0.6 and 19.5 ± 0.5 ka, respectively; erratic boulders were then deposited until 18.1 ± 0.5 ka during the Khoton Glacier recession, before its re-advance at 17.7 ± 0.5 ka (Figure 10; Strand et al, 2022).…”

“…By analogy with these Altai Lateglacial stages, Lg1 and Lg2 stillstands in the upper Kalguty basin could have taken place: (i) around 17.5 and 16 ka, like the Khoton Glacier which had lost at that time 50 and 90% of its MIS 2 maximal length, respectively (Strand et al, 2022), the Potanin Glacier at 17.5 ka (Radue, 2018) or a Kuray GLOF at 16.0 ka (Herget et al, 2020); (ii) immediately after the termination of MIS 2, between c. 14 and 12 ka, in correspondence with 'MIS 2 stages 3, 4 and 5' defined by Ganyuskin et al (2018a) for the Mongun-Taiga massif − with close ELAs (cf. section 4.3).…”