Late Quaternary Vegetation History And Climate Change In The Gobi Desert, South Mongolia

Abstract

Southern Mongolia is a part of the arid to semiarid region of Central Asia and represents a transitional zone between the circulation systems of westerlies and associated North Atlantic Oscillation (NAO), the Asian summer monsoon and the Mongolian High Pressure System (MHPS). The sedimentary records from this geographically important region are a central key to understand past vegetation and climate changes, owing to variations in the intensity of the interacting climate systems. It is imperative to understand the palaeoclimate dynamics and landscape development of arid Central Asia based on past vegetation history and to get a notion about the future environmental conditions under the ongoing Global change. The available palaeo-vegetation and palaeo-climate data from arid Central Asia are mainly conducted in Northwestern Mongolia and Northwestern China. The present research work focus on palaeo-ecological analyses of two lake archives of southern Mongolia (Bayan Tohomiin Nuur and Orog Nuur). The multidisciplinary analyses of these two sediment cores were carried out to reconstruct lake level changes, palaeo-vegetation and palaeo-climate dynamics and to expose the associated influencing biotic or abiotic factors during the last 50 kilo calibrated years before present (50 ka cal BP). Palynological and geochemical analyses of the Bayan Tohomiin Nuur revealed a detailed history of vegetation and landscape dynamics in continental Central Asia from 15 to 4 ka cal BP. The reconstructed arid climate phases between 12.3- 11.1 and 8.6- 7.6 ka cal BP can be correlated to the Younger Dryas and the 8.2 ka event respectively. Stable and relatively moist conditions occurred in the mid-Holocene from 6.3 to 4.9 ka cal BP. A mid-Holocene climate moisture maximum is attributed to the strengthening of the westerlies. However, the combined influence of the westerlies and summer monsoon caused a quite humid phase just before the Holocene climate optimum, while bordering areas in north and south of the investigation area were dry. The aridity in southern Mongolia increased after 3.8 ka cal BP as inferred from the geochemical record of the lake archive. The palynological study from the sediments of Orog Nuur show reconstructed vegetation and climate history during the last 50 ka. Generally semi humid conditions prevailed between 49.5 and 44.7 ka cal BP, correlating to Marine Oxygen Isotope stage 3 (MIS 3). It is followed by relatively a dry and cool climate from 44.7 to 23.2 ka cal BP corresponding to Marine Oxygen Isotope stage 2 (MIS 2). The increase in the concentration of green algae Pediastrum and Botryococcus indicate increase in semi arid conditions between 23.2 and 22.7 ka cal BP. The aridity of the climate increases since 18.9 kacal BP till the onset of early Holocene. Our findings indicate continuous climate oscillations during the documented period of about 50 ka. Generally desert or desert steppe vegetation is prevailing as indicated by Artemisia, Chenopodiaceae and Ephedra. Our findings show a general consistence to the palaeoclimate data with the surrounding regions of Central Asia. However, further multidisciplinary studies of palaeo-vegetation and palaeo-climate archives from the continental southern Mongolia are emphasized to gain a deeper understanding of the past environmental changes and to decode the complex spatial pattern of climate history of arid Central Asia during the late Quaternary. Such multidisciplinary approach will provide a base to understand the predictions for future environmental changes and will contribute information for nature conservation.