Navigation – Plan du site

Middle to late Holocene sedimentation dynamics and paleoclimatic conditions in the Lake Ulaan basin, southern Mongolia

Dynamique de la sédimentation à l'Holocène moyen et final et ses implications paléoclimatiques dans le bassin du lac Ulaan, sud de la Mongolie
Alexander Orkhonselenge, Goro Komatsu et Munkhjargal Uuganzaya
p. 351-363

Résumés

Cette étude propose une reconstruction de la dynamique de la sédimentation à l'Holocène moyen et final et de ses implications paléoclimatiques dans le lac Ulaan, au sud de la Mongolie. Cette dynamique est reliée à l'intensité des intempéries, à l'estimation de taux de sédimentation et est calée temporellement par datation au radiocarbone (AMS). Les résultats montrent qu'un fort taux de sédimentation équivalant à 4,6 cm/1000 ans, entre 2,7 et 6,0 années cal BP, et un taux de sédimentation très bas d’environ 1,6-1,8 cm/1000 ans après 2,7‑3,2 années cal BP, sont associés à un changement climatique évoluant d'une ambiance humide au milieu de l'Holocène à une ambiance aride à la fin de l'Holocène dans le bassin du lac Ulaan. Ce résultat est corrélé avec les relevés climatiques de l'Holocène moyen et final reconstitués à partir d'autres lacs en Mongolie et en Asie centrale. Une étude plus approfondie des séquences sédimentaires lacustres et des données temporelles sont encore nécessaires pour mieux contraindre l'histoire de la sédimentation holocène dans le sud de la Mongolie et en Asie centrale.

Haut de page

Notes de la rédaction

Article soumis le 07 juin 2017, reçu sous sa forme révisée le 21 mai 2018 et définitivement accepté le 24 septembre 2018.

Texte intégral

We appreciate the constructive comments from anonymous reviewers. The manuscript has been greatly improved. We would like to thank the Asian Research Center of National University of Mongolia for encouraging the Basic Science and for supporting the research grant ARC2016‑1253. We thank N. Altansukh and D. Batzorig for helping our fieldwork.

1. Introduction

1Mongolia has an extremely dry continental climate developing under the interaction of the Siberian high- and Asian low-pressure cells, and the westerlies (Hilbig, 1995; Gong and Ho, 2002; Panagiotopoulos et al., 2005), which is modulated by the North Atlantic Oscillation (NAO) (Visbeck, 2002). Because of its geographical position at the junction of these three large-scale climatic systems (i.e., the westerlies, NAO and the East Asian summer monsoon: EASM), Mongolia is considered to play an important role in the climatic system of Central Asia. Southern Mongolia is climatologically important because variations in the intensity of the Mongolian High Pressure System (MHPS) have had a strong control on the regional climate of Central Asia during the Quaternary Period (Owen et al., 1997). However, despite the importance of environmental changes in Mongolia for understanding of large-scale regional climate changes, the temporal and spatial environmental sequences within Mongolia itself have not been well established (An et al., 2008).

2Climate change is the major driving force resulting in the environmental changes in lake basins (Andrén et al., 2015; Komatsu et al., 2007, 2016). For reconstructing paleoclimate and paleoenvironment in lake basins, lake-level fluctuation data in a closed lake system are important (Lee et al., 2011). Lacustrine sedimentation also provides important information for understanding climate change and landscape evolution in lake basins. A number of studies on lake sedimentation have reconstructed climate and environmental changes in northern (Fedotov et al., 2004; Gillespie et al., 2008; Narantsetseg et al., 2013), central (Peck et al., 2002; Fowell et al., 2003; Davaagatan et al., 2014) and western Mongolia (Grunert et al., 2000; Rudaya and Li, 2013). Instead, the paleoclimate in southern Mongolia has rarely been reconstructed from its lake systems (Komatsu et al., 2001, 2007; Felauer et al., 2012; Lee et al., 2011, 2013; Lehmkuhl et al., 2018). In southern Mongolia, the lacustrine sediments have revealed Pleistocene and Holocene climates to some extent, but it still remains poorly understood due to the lack of sufficient sediment coring and dating.

3In southern Mongolia, the Valley of Lakes is characterized by numerous remnant lakes of once much larger paleolakes. In the Valley of Lakes, Lehmkuhl and Lang (2001) reconstructed evidence for the late Quaternary glaciations, lake-level fluctuations with a larger extent of the remnant lakes at about 8.5 kyr BP and a slightly more humid period around 1.5 kyr BP. The larger paleolake was fed by thawed snow derived from mountain glaciers in the Khangai and Govi Altai Mountain Ranges (Komatsu et al., 2001; Sevastyanov and Dorofeyuk, 2005). The earlier expansions of the remnant lakes in the Valley of Lakes may have occurred during periods of more humid and warmer climates such as during the Marine Isotope Stage (MIS) 3 and Holocene, and/or during the terminal Late Glacial period if low temperature somehow favored lake expansion (Komatsu et al., 2001). For instance, the lake level of Lake Buun Tsagaan rose from 15 to 20 m high in the Late Glacial time and Holocene (Lehmkuhl and Lang, 2001). Furthermore, beach ridges (~1,326 and 1,331 m a.s.l.) along the shore of Lake Adgiin Tsagaan (1,283 and 1,299 m a.s.l.), providing evidence for higher lake stands and a paleolake of about 1,923 km² are hypothesized to indicate that during the late Pleistocene, and likely the Holocene, the Lake Adgiin Tsagaan formed a huge paleolake encompassing also Lake Buun Tsagaan (Lehmkuhl and Lang, 2001; Komatsu et al., 2001). Optically stimulated luminescence (OSL) ages of about 70 to 80 kyr BP recorded from sediments of Lake Orog provide evidence for high lake levels at the beginning of the Last Glacial period (Lehmkuhl and Lang, 2001). The remnant lakes of such paleolakes are facing shrinkage due to the present global warming (Orkhonselenge et al., 2018).

4In this study at the eastern end of the Valley of Lakes, we investigate Lake Ulaan in southern Mongolia to reconstruct sedimentation dynamics during the middle to late Holocene. Here, Sternberg and Paillou (2015) identified geomorphological evidence for a paleolake, paleochannels and paleoshorelines using the Shuttle Radar Topography Mission (SRTM) and the Phased Array type L-band Synthetic Aperture Radar (PALSAR) data. Holguin and Sternberg (2016) hypothesized a paleohydrological system using the Geographic Information System (GIS) hydrology modelling. Furthermore, Lee et al. (2011, 2013) applied both radiocarbon and OSL dating methods in lake sediments and reconstructed the paleoclimate changes in the Lake Ulaan area during the last 17,000 years. Lehmkuhl et al. (2018) reconstructed a paleo-Lake Ulaan approximately 500 km² in area at the middle Holocene based on 14C-dating (4414 ± 153 cal BP) and OSL-dating (7.8 ± 1.0 kyr) at an upstream location of the lake basin. The present study reconstructs the lacustrine sedimentation of Lake Ulaan influenced by the middle to late Holocene climatic shift in southern Mongolia. The climatic record from Lake Ulaan is compared with the existing climatic data in Mongolia, southern Siberia and northern China. We also estimated lake area change in the very latest period of the Holocene (1970-2014) based on a topographic map and a satellite image in order to evaluate if the latest trend reflects the long-term climate change of the middle to late Holocene.

2. Site description

5Lake Ulaan is located in the eastern end of the Valley of Lakes between the Khangai and Govi Altai Mountain Ranges (fig. 1). Its modern elevation is 1,008 m a.s.l. and the lake extends 45 km long and 40 km wide (Tsegmid, 1969; Tserensodnom, 1971).

Fig. 1 – Geographical location of Lake Ulaan in southern Mongolia.
Fig. 1 – Localisation du lac Ulaan dans le sud de la Mongolie.

Fig. 1 – Geographical location of Lake Ulaan in southern Mongolia.   Fig. 1 – Localisation du lac Ulaan dans le sud de la Mongolie.

6Lake Ulaan is tectono-stratigraphically included in the island arc terrain consisting mainly of middle to late Paleozoic oceanic ophiolites, tholeitic to calc-alkaline volcanic and volcano-clastic rocks overlain by the non-marine sedimentary rocks (Badarch and Tumurtogoo, 2001; Badarch et al., 2002). Hills to the west and south of Lake Ulaan are composed mainly of Silurian limestone and dolomite and Cretaceous basalt and clastic sedimentary rocks, while to the east and north the bedrock is dominated by Archaean and Paleoproterozoic metamorphic complexes and Paleozoic and Mesozoic sedimentary rocks (Academy of Sciences of Mongolia and Academy of Sciences of USSR, 1990). Because diverse sediments of the Govi (Gobi) filled in the lake depression radiate red ray from the lake surface, the lake has been called “Ulaan” meaning “red” (Tsegmid, 1969; Tserensodnom, 1971). The Govi desert is dominantly of reg type comprising alluvial fans and deeply weathered Paleozoic, Mesozoic and early Tertiary bedrocks (Owen et al., 1997).

7The modern topography of the Lake Ulaan basin formed in a late Mesozoic rift, especially with terrigenic red deposits of the upper Cretaceous Baruun Bayan Formation (Narantsetseg et al., 2011). The late Mesozoic rift is a graben-synclinal structure surrounded by the Paleozoic linear uplifts extended along the latitude (Narantsetseg et al., 2011). Therefore, Lake Ulaan is a tectonic-graben lake (Tserensodnom, 2000) and is bounded by the Mt. Bor Khairkhan (1,233 m a.s.l.) in the northwest, Mt. Ikh Khongor (1,202 m a.s.l.) and Mt. Maikhan Tolgoi (1,232 m a.s.l.) in the south (Academy of Sciences of Mongolia and Academy of Sciences of USSR, 1990). Generally, the Lake Ulaan basin is marshy and it is located between relatively low hills at 1,050-1,110 m a.s.l. (fig. 2A). The marshy areas (fig. 2A) with scattered reeds and sedges (fig. 2C) are widely distributed in the lake basin.

8Lake Ulaan is a potential water resource in southern Mongolia (Sternberg and Paillou, 2015). The lake is fed by the Ongi River (fig. 2). Because the Ongi River draining the Khangai Mountain Range flows into Lake Ulaan temporarily (fig. 2), depth and area of the lake often vary and lake level is unstable. The Ongi River has shrunk and has not supplied water to the lake continuously since the mid- 1990s (Lee et al., 2011), i.e., the river cannot permanently feed the lake today (fig. 3A). The lake level is strongly dependent on precipitation, i.e., the lake water covers a large area from more than ten to over a hundred square kilometers during heavy rainfall (fig. 2-3B-C) and is almost dried out during low precipitation (fig. 2B). This phenomenon implies the shallowness and flat bottom of the lake (Tsegmid, 1969; Tserensodnom, 1971). In other words, the level of Lake Ulaan can temporarily fluctuate due to seasonal and annual rainfalls in the lake basin and the discharge of the Ongi River. Although Lake Ulaan has no any outflow, the lake water is very fresh compared to other lakes. In the case of the highly evaporative Govi desert, the freshness of lake water implies that a large part of lake water is absorbed and drains through the surrounding hills’ soils (Tsegmid, 1969) and infiltration to the subsurface (Sternberg and Paillou, 2015; Holguin and Sternberg, 2016).

9The Lake Ulaan basin was filled with an amount of 3,150 km³ of fresh water in the past and a recent lake reconstructed from SRTM data occupied an area of 1,700 km² as one stage before the present-day drying (Sternberg and Paillou, 2015). During high rainfall, the lake covers an area of 175 km² (Tserensodnom, 2000) (fig. 2A). Under such conditions, average and maximum depths of the lake are 0.9 m and 1.6 m, respectively (Tserensodnom, 2000). There is a record noting that the lake was almost completely dried out in 1952-1953, exposing the lake bottom (Tsegmid, 1969; Tserensodnom, 1971). In the 1960s Lake Ulaan occupied about 65 km² (Lee et al., 2011), but at present, the lake bottom is generally exposed (fig. 2C-D).

10Because the Lake Ulaan basin is situated in the lowest elevation within the Valley of Lakes, thick alluvial and lacustrine sediments have been deposited in the lake basin (Tsegmid, 1969; Tserensodnom, 1971). The recent lake sediments consist of fine silts and clays (see Section 3.2). However, during torrential rains, flash floods transport the sands and gravels from the surrounding hills into the lake along the Ongi River (fig. 2A). The bottom of the river valley is lled with slope sediments in the upper reaches (fig. 2A) and by oodplain sediments in the lower reaches (fig. 2B). Lake Ulaan is fed not only by the Ongi River draining the Khangai Mountain Range in the north, but also by freshwater Sukhait, Leg and Tsagaan Rivers ephemerally draining the Govi Altai Mountain Range in the west (Tsegmid, 1969). As indicated by Sternberg and Paillou, (2015) and Holguin and Sternberg (2016), these rivers transport alluvial sands and gravels into the lake. However these rivers do not feed the lake continuously (fig. 2-3A).

Fig. 2 – The Lake Ulaan basin and sampling sites.
Fig. 2 – Le bassin versant du lac Ulaan et les sites d'échantillonage.

Fig. 2 – The Lake Ulaan basin and sampling sites.   Fig. 2 – Le bassin versant du lac Ulaan et les sites d'échantillonage.

A. Changes in lake areas in 1970 and 2014 for Lake Ulaan are overlain over a topographic map of the Lake Ulaan basin. B. Sampling sites within the lake area. Insets: views of exposed lake floors facing the northwest at sampling site 1 (C) and the east at sampling site 2 (D).
A. Évolution de la surface du lac entre 1970 et 2014, sur un fond de carte topographique. B. Les sites échantillonnés dans le lac. Vignettes : vues du plancher lacustre émergé regardant vers le nord-ouest, site 1 (C), et vers l'est, site 2 (D).

11The climate of the Lake Ulaan basin is extremely arid and/or desert-like today. The westerly and southwesterly winds are dominant in the Govi region including the Lake Ulaan basin. In the winter, the Govi region is influenced by the MHPS, which drives strong westerly wind systems and produces snow (Owen et al., 1997). The intermittent meltwater inflow that feeds Lake Ulaan (fig. 3B-C) was indicated by fluctuation of mean grain size (Lee et al., 2011). According to the Mandal-Ovoo meteorological station located 23.1 km northeast of the lake, the annual average temperature between 1975 and 2015 (fig. 4A) and precipitation between 1973 and 2015 (fig. 4B) are 5.4oC and 69.1 mm, respectively. Most of the total annual precipitation occurs between June and August.

Fig. 3 – Ground photos around the Lake Ulaan basin.
Fig. 3 – Photographies dans le bassin du Lake Ulaan.

Fig. 3 – Ground photos around the Lake Ulaan basin.   Fig. 3 – Photographies dans le bassin du Lake Ulaan.

A. Northeast-facing view of a channel of the Ongi River entering Lake Ulaan. The arrow indicates the river flow direction. Photo by A. Orkhonselenge, October 25th, 2015. B. East-facing view of Lake Ulaan. Photo by D. Adiya, September, 2013. C. North-facing view of Lake Ulaan. Photo by “Ongi River Movement” Non-Governmental Organization (NGO), November 5th, 2014.
A. Vue de regard Nord-Ouest du cours de la rivière Ongi se jetant dans le lac Ulaan. La flèche indique le sens de l'écoulement. Photo A. Orkhonselenge, 25 octobre 2015. B. Vue du lac Ulaan, regard Est. Photo D. Adiya, Septembre 2013. C. Vue du lac Ulaan, regard Nord. Photo “Ongi River Movement” Non-Governmental Organization (NGO), 5 novembre 2014.

3. Method

3.1. Estimation of lake area change between 1970 and 2014

12In order to define lake areas, the 1:100 000 topographical map (1970) showing the lake extent of the year and a Landsat 8 image acquired on June 6th, 2014 (path of 133 and row of 29) are used as the primary data source (fig. 2) for compiling on-screen digitizing of lake areas (fig. 2A). A layer of the satellite imagery (fig. 2B) was draped over the topographic data to estimate the change in lake area during the past 44 years.

3.2. Field sampling

13During a fieldwork at the end of October 2015, four bulk samples were collected from two sites at the exposed bottom of Lake Ulaan (fig. 2B). The first site (fig. 2C) is located at 1,024 m a.s.l. (44o3311N, 103o3646E) where samples UN15-1a and UN15-1b were obtained from depths of 5 cm and 20 cm, respectively (fig. 2B, 5). The second site (fig. 2D) is located at 1,025 m a.s.l. (44o3329N, 103o3725E) where samples UN15-2a and UN15-2b were collected from the depths of 5 cm and 20 cm, respectively (fig. 2B, 5). The elevations for these sites were measured using a handheld Garmin Etrex 30 GPS. Although as shown in Figure 2B the first and second sites are located toward margin and center of the lake, respectively, the site 1 is situated on a point which is temporarily inundated during rainfall and site 2 is situated on a small island of the lake under the modern condition. Lake water is visible in the Landsat 8 image in 2014 (fig. 2B), however it disappeared during the field sampling in 2015 (fig. 2C-D). For the site 1, the sample UN15-1a is yellowish red (5YR 4/6) fine silt, while the sample UN15-1b is dark reddish brown (2.5YR 3/3) clay. For the site 2, the sample UN15-2a is brown (7.5YR 4/4) very fine silt, while the sample UN15-2b is dark reddish brown (5YR 3/3) clay. These samples are analyzed for major element compositions (tab. 1), weathering intensity (tab. 2) and radiocarbon dating (tab. 3).

Tab. 1 – Major element compositions of the Lake Ulaan sediments.
Tab. 1 – Nature des éléments majeurs caractérisant les sédiments du lac Ulaan.

Tab. 1 – Major element compositions of the Lake Ulaan sediments.   Tab. 1 – Nature des éléments majeurs caractérisant les sédiments du lac Ulaan.

Tab. 2 – Chemical Index of Alteration (CIA) and Weathering Product Index (WPI) values of the Lake Ulaan sediments.
Tab. 2 – Valeurs de l'index chimique d'altération (CIA) et de l'index d'altération potentielle (WPI) des sédiments du lac Ulaan.

Tab. 2 – Chemical Index of Alteration (CIA) and Weathering Product Index (WPI) values of the Lake Ulaan sediments.   Tab. 2 – Valeurs de l'index chimique d'altération (CIA) et de l'index d'altération potentielle (WPI) des sédiments du lac Ulaan.

Tab. 3 – Radiocarbon ages without δ13C correction and calibrated ages.
Tab. 3 – Âges radiocarbone sans la correction du δ13C et âges calibrés.

Tab. 3 – Radiocarbon ages without δ13C correction and calibrated ages.   Tab. 3 – Âges radiocarbone sans la correction du δ13C et âges calibrés.

3.3. Chemical analyses

14Major element compositions of the lake sediments were analyzed at the Division of Radionuclide Analysis, the Central Geological Laboratory in Mongolia using the Axios Max X-ray fluorescence (XRF) spectrophotometer. The major element compositions are presented in Table 1.

15In arid regions, where available climatic proxies are limited, a geochemical weathering index can provide useful information about climatic changes (Lee et al., 2013), i.e., the degree of chemical weathering of Lake Ulaan sediments can be used as a proxy for climatic conditions in the Govi region. In this study, we calculated the chemical index of alteration (CIA; Eq. 1) and weathering potential index (WPI; Eq. 2). The results of the CIA and WPI are shown in Table 2. A high value of CIA indicates dominance of intensive weathering (Harnois, 1988), while a low value of WPI implies presence of extreme weathering process (Vogel, 1975).

CIA = [Al2O3 / (Al2O3 + Na2O + K2O + CaO)] x 100     [1]

WPI = [((Na2O + K2O + CaO + MgO) – (LIO)) /
                   (SiO
2 + Al2O3 + Na2O + K2O + CaO + MgO + Fe2O3)] x 100     [2]

3.4. Measurement of radiocarbon

16The ages of the collected lake sediments were constrained by four 14C dates obtained by the Accelerated Mass Spectrometry (AMS) at the Institute of Accelerator Analysis Ltd., in Japan. Analytic materials for the dating procedure are bulk samples for sediments UN15-1a, UN15-1b and UN15-2b, and organic matter for sediment UN15-2a. The graphite samples were measured against a standard of Oxalic acid (HOxII) provided by the National Institute of Standards and Technology (USA) using a 14C-AMS system based on the Tandem accelerator. For the calculation of 14C age the Libby half-life of 5568 years (Stuiver and Polach, 1977) was used. The calibration in this study (tab. 3) was conducted by OxCal v.4.2 (Bronk Ramsey, 2009) based on IntCal13 database (Reimer et al., 2013).

4. Results

4.1. Change in lake area in recent years

17For Lake Ulaan, the lake area has been reduced by 18.2 km² from 62.38 km² in 1970 to 44.16 km² in 2014 (fig. 1-2A). The decrease in lake area for Lake Ulaan during the past 44 years may have been related to local climate change of rising temperature since 1995 (fig. 4A) and decreasing precipitation since 1987 (fig. 4B). Lake Ulaan was identified in 1991 but did not appear in Landsat images for a period since 2000 (Kang et al., 2015) and during the field sampling in 2015 (fig. 2B-C), Lake Ulaan briefly reappeared and it was described in the Landsat 8 image in 2014 (fig. 2B). The most recent condition of the lake seems to indicate that the Lake Ulaan basin is transiting to a playa (dry lake) environment (Komatsu et al., 2007). Climatologically, the decrease in lake area shows that Lake Ulaan responded more directly and significantly to the temperature rise since 1995 (fig. 4A) probably resulting in intense evaporation and the consequent lake shrinkage. The reduction in lake area for Lake Ulaan following the rising temperature is in agreement with those for other lakes in the Valley of Lakes (Orkhonselenge et al., 2018). However, Lake Ulaan in the eastern end of the Valley of Lakes may be more sensitive to the rising temperature and dropping precipitation than the other lakes in the Valley of Lakes, especially Lakes Orog and Buun Tsagaan (fig. 1). Topographically, Lake Ulaan is surrounded by lowlands, hills and mountains elevated at 1,050‑1,600 m a.s.l. (fig. 2A), while the other lakes in the Valley of Lakes are surrounded by high mountains elevated at 1,400‑3,800 m a.s.l. (fig. 1) possibly providing more meltwater in spring. This reduction in lake area coincides with the reported trend of that Lake Ulaan occupied a large paleolake covering an area more than 19,500 km², the medium-sized lake covering a surface area of about 6,900 km² and a small-sized lake covering an area close to 1,700 km² (Sternberg and Paillou, 2015). However the ages of these different-sized lakes are unknown.

Fig. 4 – Climate anomalies.
Fig. 4 – Anomalies de variables climatiques.

Fig. 4 – Climate anomalies.   Fig. 4 – Anomalies de variables climatiques.

A. Anomalies of annual mean air temperature between 1975 and 2015; B. Anomalies of annual mean precipitation between 1973 and 2015 observed at the Mandal-Ovoo meteorological station.
A. Anomalies de la température moyenne annuelle de l'air entre 1975 et 2015 ; B. Anomalies des précipitations moyennes annuelles entre 1973 et 2015, enregistrées à la station météorologique de Mandal-Ovoo.

4.2. Major element compositions

18Major element compositions of Lake Ulaan sediments are presented in Table 1. Abundance of the major elements in Lake Ulaan sediments shows that although four sediments largely contain oxides of semimetal and transition metals, UN15-1a and UN15-2a surface sediments in marginal and central parts of Lake Ulaan are dominated by the presence of oxides of alkali and alkaline earth metals, respectively (tab. 1). This coincides with the report (Badarch et al., 2002) noting the middle to late Paleozoic oceanic ophiolites, tholeitic to calc-alkaline volcanic and volcanoclastic rocks distributed in the Lake Ulaan area. Furthermore, Lee et al. (2013) stated that the upper part for the Lake Ulaan sediments with higher contents of TiO2, Fe2O3, MgO and Al2O3 is derived from rocks in an oceanic-arc setting with a mafic igneous provenance. According to Dashzeveg et al. (2005), the upper Cretaceous Djadokhta Formation consisting of medium- to fine-grained sands and sandstones containing subordinate layers of calcareous concretions and silty clay may be related to the Lake Ulaan sediments. Our results suggest that the dominant trace oxides are linked to erosional and depositional processes in the marginal and central parts of the lake, respectively.

4.3. Weathering intensity

19CIA and WPI of the surface sediments indicate higher weathering intensity in the marginal part than those in the central part of Lake Ulaan. The higher value of CIA in sediment UN15-1a than that in sediment UN15-2a (tab. 2) shows that the erosion is intensive in the margin-side than the center of the lake. The lower values of WPI in sediments UN15-1a and UN15-1b than that in sediments UN15-2a and UN15-2b (tab. 2) imply the weathering is intensive on the margin of the lake. In Lake Ulaan CIA values have decreased since ca. 3 kyr BP when the climatic conditions became drier (Lee et al., 2013), i.e., the CIA values may indicate moisture availability in the source areas of Lake Ulaan sediments. The weathering intensity and oxide distributions contain valuable information indicative of climate-induced erosional and depositional processes in the lake basin.

4.4. Radiocarbon dating

20The radiocarbon dating of the collected Lake Ulaan sediments indicates the middle to late Holocene ages (tab. 3). The calibrated 2σ ages of the 14C dating allow us to infer that the near-surface sediments (at 5 cm depth) of Lake Ulaan deposited at 2.7 and 3.2 cal kyr BP in the marginal and central parts of the lake, while deeper sediments (at 20 cm depth) deposited at 6.0 and 3.4 cal kyr BP (tab. 3, fig. 5). The 14C ages show that the near-surface sediment UN15-1a at the margin is 0.5 kyr younger than the surface sediment UN15-2a at the center, while the deeper sediment UN15-1b at the margin is 2.6 kyr older than the deeper sediment UN15-2b at the center of Lake Ulaan (tab. 3, fig. 5).

Fig. 5 – A synthesized view of the collected samples revealing middle to late Holocene sedimentary deposition rates in Lake Ulaan.
Fig. 5 – Schéma synthétique des taux d'accumulation sédimentaire de l'Holocène moyen à final dans le lac Ulaan.

Fig. 5 – A synthesized view of the collected samples revealing middle to late Holocene sedimentary deposition rates in Lake Ulaan.   Fig. 5 – Schéma synthétique des taux d'accumulation sédimentaire de l'Holocène moyen à final dans le lac Ulaan.

1. Fine silt; 2. Clay; 3. Very fine silt; 4. Clay; 5. Site 1: UN 15-1; 6. Site 2: UN 15-2. The lithology is recorded from the field observation along the sampling pits.
1. Limon fin ; 2. Argile ; 3. Limon très fin ; 4. Argile. 5. Site 1 : UN 15-1 ; 6. Site 2 : UN 15-2.

21For age corrections, the dates obtained from plant macrofossils are considered to be more reliable than those obtained from bulk organics (e.g., McGeehin et al., 2001). For instance, in Lake Khuvsgul, 14C ages of bulk organic are 0.4-4.0 kyr older than those of wood fragments (Watanabe et al., 2009). However these materials of plant macrofossils and wood fragments for precise dating are applicable if they are only found in deep sediments. It is common for that plants recently deposited in surface sediment are dated as modern. Although in further study the same materials of lake sediments are required for obtaining precise dating and for reconstructing depositional environments in the past, the bulk sediment and organic materials dated in the present study are available for age corrections as the well-preserved sediments of the shallow Lake Ulaan. It is known for deep lakes that terrestrial organic materials are redeposited by streams (Orkhonselenge et al., 2013). For example, in Lake Khuvsgul the ages of surface sediments average at ca. 0.5 kyr (Prokopenko et al., 2005), while in Lake Baikal the ages of surface sediments range from 0.47 to 1.22 kyr (Colman et al., 1996). The older ages of surface sediments in Lakes Baikal and Khuvsgul were attributed to the input of terrestrial organics and to the resuspension of previously deposited algal carbon (Colman et al., 1996), and were considered as a lake reservoir effect (Prokopenko et al., 2005). If so, the dates obtained from deeper layers of sediments in both lakes also require reservoir effect correction (Orkhonselenge et al., 2013).

22The reservoir effect correction for the shallow Lake Ulaan is estimated to be negligible at 0.2 kyr (tab. 3). The older ages of surface sediments in Lake Ulaan corresponding to UN15-1a and UN15-2a (tab. 3) can be implied due to the lake reservoir effect because of that the input of terrestrial organics after removal of the surface sediments by aeolian processes during the intensive drought in the late Holocene (fig. 6A). Moreover, in the Lake Ulaan basin the reservoir effect reects variation in the water balance of Lake Ulaan in the middle to late Holocene, which was shifting in times of climate-induced environmental changes (fig. 6B). Therefore, shrinkage of the shallow Lake Ulaan in the late Holocene (since 2.7‑3.2 cal kyr BP) provides overestimation of the age of the surface sediments (tab. 3) due to no-water supplies in the lake and usage of bulk organic materials in surface sediments instead of plant tissue in deep sediments. The age data calibrated in Table 3 are used for discussing sedimentation dynamics in southern Mongolia.

Fig. 6 – Holocene climate and sedimentation rate in Lake Ulaan.
Fig. 6 – Climat et sédimentation holocènes dans le lac Ulaan.

Fig. 6 – Holocene climate and sedimentation rate in Lake Ulaan.   Fig. 6 – Climat et sédimentation holocènes dans le lac Ulaan.

A. The local climate-induced environmental conditions during the sedimentation in Lake Ulaan; B. The difference in sedimentation rate between marginal and central parts of Lake Ulaan in the middle to late Holocene.
A. Tendances climatiques et sédimentation dans le lac ; B. Différences des taux de sédimentation entre les parties marginale et centrale du lac, de l'Holocène moyen à final.

4.5. Sedimentation rate

23Our results show that sedimentation rates of Lake Ulaan down to 20 cm from the surface average about 3.3 and 5.8 cm.kyr¹ in the marginal and central parts, respectively (tab. 4). Based on the ages of the collected samples, the sedimentation rates in the marginal and central parts indicate lacustrine records from the middle and late Holocene to the present, respectively. The high sedimentation rate of 4.6 cm.kyr¹ in the marginal part of the lake (tab. 4, fig. 5-6B) implies that the Lake Ulaan basin may have experienced a humid climate supporting delivery of sediments in the lake during the middle Holocene to the early period of the late Holocene between 6.0 and 2.7 cal kyr BP (fig. 5-7). The low sedimentation rate of 1.6‑1.8 cm.kyr¹ during the late Holocene (tab. 4, fig. 5-6B) marks that in the Lake Ulaan basin aridification strengthened since about 2.7‑3.2 ca. kyr BP (fig. 6A-7) and it may have caused shrinkage of the shallow lake, which seems to be continuing up to the modern time (fig. 2A). The high sedimentation rate of 6.4 cm.kyr¹ in the central part of the lake between 3.4 and 3.2 cal kyr BP (tab. 4, fig. 5-6B) may have been related to intensive erosion and redeposition, probably influenced by its local condition (the sampling site 2 is on a small island today), during the short-term heavy rainfall event(s) occurring sometimes near the small island of the lake in the early period of the late Holocene. We note that the concept of “sedimentation rate” considered at both sites UN15-1 and UN15-2 represents a net effect of plus (i.e., deposition) and minus (i.e., deflation) (fig. 5-6B).

Tab. 4 – Calibrated age and sedimentation rate.
Tab. 4 – Ages calibrés et taux de sédimentation.

Tab. 4 – Calibrated age and sedimentation rate.   Tab. 4 – Ages calibrés et taux de sédimentation.

4.6. Synthesized results of sample analyses

24The intensive weathering in Lake Ulaan indicated with CIA and WPI (tab. 2) in UN15-1b and UN15-2b is coincided with the higher sedimentation rates of 4.6 and 6.4 cm.kyr¹ during the middle Holocene to the early period of the late Holocene (tab. 4, fig. 5-6). It implies that the Lake Ulaan basin may have experienced a humid climate resulting in higher erosion and rigorous oxidation between 6.0 and 2.7 cal kyr BP (fig. 7). In contrast, the superficial weathering in UN15-1a and UN15-2a is in agreement with the lower sedimentation rates of 1.6-1.8 cm.kyr¹ in the late Holocene (tab. 4). It shows that in the Lake Ulaan basin climate shifted to arid since about 2.7-3.2 cal kyr BP (fig. 7) and the dry climate resulted in the shrinkage of the shallow lake.

25The measured sedimentation rates seem to reveal their dependency on the local conditions such as position within the lake area, elevation and topography. For instance, the average sedimentation rate of 5.8 cm.kyr¹ in the central part of the lake since 3.4 cal kyr BP to the present (the rate is increased to 6.4 cm.kyr¹ if only the period between 3.4 and 3.2 cm.kyr¹ is considered) is higher than the average sedimentation rate of 3.3 cm.kyr¹ in the marginal part since 6.0 cal kyr BP to the present (tab. 4). It may be due to intensive erosion and redeposition caused by short-term heavy rainfall event(s), possibly on a small island existed at or near the sampling site.

Fig. 7 – Climatic trends.
Fig. 7 – Tendances climatiques.

Fig. 7 – Climatic trends.   Fig. 7 – Tendances climatiques.

The derived climatic trends from the sedimentation rates are compared with trends in other lakes in southern Mongolia (S.MGL), southern Russia (S. Russia) and northern China (N. China).
Comparaison des tendances climatiques dérivées des taux de sédimentation aux tendances observées dans d'autres lacs du sud de la Mongolie (S.MGL), du sud de la Russie (S. Russia) et du nord de la Chine (N. China).

5. Discussion

26The middle to late Holocene sedimentation dynamics in Lake Ulaan are interpreted in the context of the humid to arid climate transition in southern Mongolia. Our findings of paleoclimatic conditions in the Lake Ulaan basin in southern Mongolia are consistent with other paleoclimatic records from southern Siberia and northern China.

5.1. Middle Holocene: humid climatic condition

27In the middle Holocene the marginal part of Lake Ulaan is represented with a high sedimentation rate of 4.6 cm.kyr¹ (fig. 5‑6B) and it may have been induced by a humid climate prevailed in southern Mongolia between 6.0 and 2.7 cal kyr BP (fig. 7). It is concordant with the wet climate identified between 8.6 and 4.7 kyr BP in the Lake Ulaan area (Lee et al., 2013). The humid conditions which contributed to a large network of paleohydrological complex in southern Mongolia including the Lake Ulaan area were reconstructed by Holguin and Sternberg (2016). The Lake Ulaan level was found to be high at the middle Holocene (Lehmkuhl et al., 2018). Furthermore, in Lake Bayan Tohom located 110 km south of Lake Ulaan, Felauer et al. (2012) reconstructed that wet conditions prevailing from 11.0 to 4.0 cal kyr BP (fig. 7).

28The humid middle Holocene revealed at Lake Ulaan coincided with the evidence of relatively higher lake levels during the middle Holocene recorded at Lakes Dood, Khuvsgul and Gun (Dorofeyuk and Tarasov, 1998) in northern Mongolia and Lakes Uvs and Bayan (Grunert et al., 2000) in western Mongolia. For example, in northern Mongolia, a wet and warm climate was reconstructed in the Lake Gun basin at 7.7‑2.2 cal kyr BP based on lake fluctuations (Feng et al., 2005), where Feng et al. (2013) noted the wet and warm climate with high‑amplitude fluctuations since the ~6.0 cal kyr BP. The onset of the Holocene climatic optimum (the most humid and warm stage) was recorded in the paleolake Darkhad basin between 7.8 and 5.8 cal kyr BP (Narantsetseg et al., 2013).

29The record of the humid phase in the middle Holocene is observed not only throughout Mongolia and but also in regional data from northern China and southern Siberia. For example, a wet climate at 7.3‑6.2 kyr BP with a deep lake and increased plants were reconstructed from the Tere‑Khol basin at the southwestern edge of the Baikal Rift Zone (Panin et al., 2012; fig. 7). Numerous records from China depicted the middle Holocene as a Holocene Optimum (i.e., effective moisture maximum; Shi et al., 1993). Wulungu Lake in northern Xinjiang (Xiao et al., 2006; Liu et al., 2008) had experienced a general wet trend since 6.7 cal kyr BP when an increasing of Artemisia/Chenopodiaceae (A/C) ratio and a decreasing of pollen‑based desert biome scores. Moreover, Herzschuh et al. (2004) reconstructed most favorable conditions of a rather wet climate on the basis of relative increase in abundance of Artemisia pollen between 5400 and 3900 cal year B.P. using relationships between the pollen spectra and modern vegetation and precipitation patterns in the Alashan Plateau and the Qilian Mountains, northwestern China (fig. 7). The high lake levels throughout most of arid Central Asia recorded at 8.5 and 6.0 cal kyr BP (Li and Morril, 2010) may have been related to the high precipitation associated with the mid‑latitude westerlies increased from the early to middle Holocene.

5.2. Late Holocene: arid climatic condition

30In the late Holocene the slow sedimentation rate of 1.6‑1.8 cm.kyr¹ is induced by the arid conditions dominated in the Lake Ulaan basin. The dry climate since 2.7‑3.2 cal kyr BP in the Lake Ulaan basin may have strengthened the recent shrinkage of the shallow lake, a phenomenon seems to be continuing up to the modern time. Although the current study is incomplete due to a lack of sedimentary sequences and age data to directly respond to the question of when the aridity in the Lake Ulaan basin started, we can infer that the Lake Ulaan basin has been influenced by the drought since 3.2 cal kyr BP (fig. 7) when the precipitation decreased and the temperature increased. The aridity since 3.2 cal kyr BP recorded in the Lake Ulaan basin is in agreement with the dry climate since 3.0 kyr BP reconstructed by Lee et al. (2013). Sternberg and Paillou (2015) also showed the progressive drying phase in the late Holocene. Moreover, in Lake Bayan Tohom, Felauer et al. (2012) revealed that aridity increased after 3.5 cal kyr BP in the late Holocene when a clear trend towards lake desiccation and a strengthening of the aeolian activity were prevailed (fig. 7). Hülle et al. (2010) noted the dune reactivation in the Khongoriin Els dune field of the Govi region during the late Holocene representing the ongoing aridity, i.e., a dune accumulated during the late Holocene when arid conditions were prevailing in the region. According to Lehmkuhl and Lang (2001) it was drier in southern Mongolia before and after the high‑standing lakes in the Valley of Lakes at 1.5‑1.4 kyr BP, and the last enhanced humidity phase occurred several hundred years ago (Komatsu et al., 2001).

31The continuous drying trend in the Lake Ulaan basin since 2.7‑3.2 cal kyr BP is clearly described by the reduction in lake area and rapid shrinkage of the shallow lake in recent years (see Section 4.1). The lake area has been reduced by 18.2 km² between 1970 and 2014 and the decrease in lake area during the past 44 years may have been related to local climate change of rising temperature and decreasing precipitation. The decrease in lake area shows that Lake Ulaan responded directly and significantly to the temperature rise since 1995 (fig. 4A) probably resulting in intense evaporation and the consequent lake shrinkage.

32Records from paleolakes in Mongolia indicate that climate in the late Holocene was somewhat more humid or arid depending on each region (Orkhonselenge et al., 2018). In addition to the weakening of both the summer monsoon (Morrill et al., 2003) and solar radiation (Berger and Loutre, 1991) during the late Holocene, evaporation decreased in response to dropping temperatures in some regions of Mongolia (An et al., 2008). Throughout Mongolia, that the humidity and aridity prevailed in the first (~3.0‑~1.5 kyr BP) and second (~1.5 kyr BP to present) half of the late Holocene, respectively, is commonly recorded. The lake level began to increase around 3.0 cal kyr BP because of decreased evaporation in Central Asia when temperatures dropped and it is a result of reinforced cyclonic westerlies from the North Atlantic, which pushed farther south and east in response to a stronger thermal gradient between high and low latitudes (An et al., 2012). The first phase in Mongolia is in good agreement with a general temporal trend in the late Holocene climate in southern Siberia including the Lake Baikal region. For instance, moist conditions prevailed in the Lake Baikal region between ca. 3.3 and 2.0 cal kyr BP (Mackay et al., 2011). The second phase in Mongolia is in agreement with the Chinese records. For instance, a dry period from 2900 14C age BP to the present was reconstructed from two lakes in the southeastern Inner Mongolian Plateau in northern China. Fossil pollen data recorded in the Juyan paleolake in northwestern China also show a rather dry climate at about 3.9 cal kyr BP (Herzschuh et al., 2004; fig. 7).

Conclusion

33In this study the middle to late Holocene sedimentation dynamics in southern Mongolia were reconstructed based on the weathering intensity, radiocarbon dating and estimated sedimentation rates of the Lake Ulaan sediment. The intensive weathering and rapid sedimentation rate of 4.6 cm.kyr¹ between 2.7 and 6.0 cal kyr BP may imply the presence of a humid climatic condition in the middle Holocene. The superficial weathering and slow sedimentation rate of 1.6‑1.8 cm.kyr¹ infer the dominance of an arid climate in the late Holocene. The arid climate may have accelerated the reduction in lake area resulting in the aerial exposure of sediments deposited after 2.7‑3.2 cal kyr BP. The middle and late Holocene climatic conditions recorded in the Lake Ulaan basin in southern Mongolia well correspond to the results from other parts of Mongolia, and southern Siberia and northern China in Central Asia. Further investigations with sedimentary sequences and their ages from the lake are required to constrain more precisely the Holocene sedimentation dynamics in southern Mongolia and Central Asia.

Haut de page

Bibliographie

Academy of Sciences of Mongolia, Academy of Sciences of USSR (1990) – National Atlas of the Peoples Republic of Mongolia. Ulaanbaatar, Moscow (Russian), 156 p.

An C.B., Chen F.H., Barton L. (2008) – Holocene environmental changes in Mongolia: A review. Global and Planetary Change, 63, 283‑289.
DOI : 
10.1016/j.gloplacha.2008.03.007

An C.B., Lu Y., Zhao J., Tao S., Dong W., Li H., Jin M., Wang Z. (2012) – A high-resolution record of Holocene environmental and climatic changes from Lake Balikun (Xinjiang, China): Implications for Central Asia. The Holocene, 22, 43‑52.
DOI : 
10.1177/0959683611405244 hol.sagepub.com

Andrén E., Klimaschewski A., Self A.E., Amour N.St., Andreev A.A., Bennett K.D., Conley D.J., Edwards T.W.D., Solovieva N., Hammarlund D. (2015) – Holocene climate and environmental change in north-eastern Kamchatka (Russian Far East), inferred from a multi-proxy study of lake sediments. Global and Planetary Change, 134, 41‑54.
DOI : 
10.1016/j.gloplacha.2015.02.013

Badarch G., Cunningham W.D., Windley B.F. (2002) – A new terrane subdivision for Mongolia: implications for the Phanerozoic crustal growth of Central Asia. Journal of Asian Earth Sciences, 21, 87‑110.
DOI : 
10.1016/S1367-9120(02)00017-2

Badarch G., Tumurtogoo O. (2001) – Tectonostratigraphic Terranes of Mongolia. Gondwana Research 4 (2), 143‑144.
DOI : 
10.1016/S1342-937X(05)70667-5

Berger A., Loutre M.F. (1991) – Insolation values for the climate of the last 10,000,000 years. Quaternary Science Reviews, 10, 297‑317.
DOI : 
10.1016/0277-3791(91)90033-Q

Bronk Ramsey C. (2009) – Bayesian analysis of radiocarbon dates, Radiocarbon, 51(1), 337‑360.

Colman S.M., Jones G.A., Rubin M., King J.W., Peck J.A., Orem W.H. (1996) – AMS radiocarbon analyses from Lake Baikal, Siberia: challenges of dating sediments from a large, oligotrophic lake. Quaternary Science Reviews, 15, 669‑684.
DOI : 
10.1017/S0033822200033865

Dashzeveg D., Dingus L., Loope D.B., Swisher C.C., Dulam T., Sweeney M.R. (2005) – New stratigraphic subdivision, epositional environment, and age estimate for the upper cretaceous Djadokhta formation, southern Ulan Nur basin, Mongolia. American Museum Novitates, 3498, 1‑31.
DOI : 
10.1206/0003-0082(2005)498[0001:NSSDEA]2.0.CO;2

Davaagatan T., Orkhonselenge A., Fukushi K., Yabe M. (2014) – Sedimentary records in intermontane and prairie lakes in central Mongolia: Preliminary results from Lake Terkhiin Tsagaan and Lake Ugii. Journal of Geographical Issues, 14 (408), 19‑26.

Dorofeyuk N.I., Tarasov P.E. (1998) – Vegetation and lake levels of northern Mongolia since 12,500 yr B.P. based on the pollen and diatom records. Stratigraphy and Geological Correlation, 6 (1), 70‑83.

Fedotov A.P., Chebykin E.P., Semenov M.Y., Vorobyova S.S., Osipov E.Y., Golobokova L.P., Pogodaeva T.V., Zheleznyakova T.O., Grachev M.A., Tumurhuu D., Oyunchimeg Ts., Narantsetseg Ts., Tumurtogoo O., Dolgikh P.T., Arsenyuk M.I., Batist M.De. (2004) – Changes in the volume and salinity of Lake Khubsugul (Mongolia) in response to global climate changes in the upper Pleistocene and the Holocene. Paleogeography, Paleoclimatology, Paleoecology, 209, 245257.
DOI : 
10.1016/j.palaeo.2003.12.022

Felauer T., Schultz F., Murad W., Mischke S., Lehmkuhl F. (2012) – Late Quaternary climate and landscape evolution in arid Central Asia: A multiproxy study of lake archive Bayan Tohomin Nuur, Gobi desert, southern Mongolia. Journal of Asian Earth Sciences, 48,125‑135.
DOI : 
10.1016/j.jseaes.2011.12.002

Feng Z.D., Ma Y.Z., Zhang H.C., Narantsetseg Ts., Zhang X.S. (2013) – Holocene climate variations retrieved from Gun Nuur lake-sediment core in the northern Mongolian Plateau. The Holocene, 23 (12), 1721‑1730.
DOI : 
10.1177/0959683613505337hol.sagepub.com

Feng Z.D., Wang W.G., Guo L.L., Khosbayar P., Narantsetseg T., Jull A.J.T., An C.B., Li X.Q., Zhang H.C., Ma Y.Z. (2005) – Lacustrine and eolian records of Holocene climate changes in the Mongolian Plateau: preliminary results. Quaternary International, 136, 25‑32.
DOI : 
10.1016/j.quaint.2004.11.005

Fowell S.J., Hansen B.C., Peck J.A., Khosbayar P., Ganbold E. (2003) – Mid to late Holocene climate evolution of the Lake Telmen basin, north central Mongolia, based on palynological data. Quaternary Research, 59 (3), 353‑363.
DOI : 
10.1016/S0033-5894(02)00020-0

Gillespie A.R., Burke R.M., Komatsu G., Bayasgalan A. (2008) – Late Pleistocene glaciers in Darhad Basin, northern Mongolia. Quaternary Research, 69 (2), 169‑187.
DOI : 
10.1016/j.yqres.2008.01.001

Gong D.Y., Ho C.H. (2002) – The Siberian High and climate change over middle to high latitude Asia. Theoretical and Applied Climatology, 72, 1‑9.
DOI : 
10.1007/s007040200

Grunert J., Lehmkuhl F., Walther M. (2000) – Paleoclimatic evolution of the Uvs Nuur basin and adjacent areas (Western Mongolia). Quaternary International, 65‑66, 171‑192.
DOI : 
10.1016/S1040-6182(99)00043-9

Harnois L. (1988) – The CIW index: A new chemical index of weathering. Sedimentary Geology 55 (3‑4), 319‑322.
DOI : 
10.1016/0037-0738(88)90137-6

Herzschuh U., Tarasov P., Wünnemann B., Hartmann K. (2004) – Holocene vegetation and climate of the Alashan Plateau, NW China, reconstructed from pollen data. Palaeogeography, Palaeoclimatology, Palaeoecology, 211, 1‑17.
DOI : 
10.1016/j.palaeo.2004.04.001

Hilbig W. (1995) – The Vegetation of Mongolia. SPB Academic Publishing, Amsterdam, 260 p.

Holguin L.R., Sternberg T. (2016) – A GIS based approach to Holocene hydrology and social connectivity in the Gobi Desert, Mongolia. Archaeological Research in Asia, 39, 1‑9.
DOI : 
10.1016/j.ara.2016.12.001

Hülle D., Hilgers A., Radtke U. Stolz C., Hempelmann N., Grunert J., Felauer T., Lehmkuhl F. (2010) – OSL dating of sediments from the Gobi Desert, Southern Mongolia. Quaternary Geochronology, 5, 107‑113.
DOI : 
10.1016/j.quageo.2009.06.002

Kang S., Lee G., Togtock C., Jang K. (2015) – Characterizing regional precipitation-driven lake area change in Mongolia. Journal of Arid Land, 7 (2), 146‑158.
DOI : 
10.1007/s40333-014-0081-x jal.xjegi.com

Komatsu G., Brantingham P.J., Olsen J.W., Baker V.R. (2001) – Paleoshoreline geomorphology of Boon Tsagaan Nuur, Tsagaan Nuur and Orog Nuur: the Valley of Lakes, Mongolia. Geomorphology, 39 (3‑4), 83‑98.
DOI : 
10.1016/S0169-555X(00)00095-7

Komatsu G., Baker V.R., Arzhannikov S., Gallagher R., Arzhannikova A.V., Murana A., Oguchi T. (2016) – Catastrophic flooding, palaeolakes and late Quaternary drainage reorganization in northern Eurasia. International Geology Review, 58, 1693‑1722.
DOI : 
10.1080/00206814.2015.1048314

Komatsu G., Ori G., Marinangeli L., Moersch J.E. (2007) – Playa environments on Earth: Possible analogues for Mars, In: Chapman M.G. (Ed.), The Geology of Mars: Evidence from Earth-based analogs. Cambridge University Press, Cambridge, 322‑348.

Lee M.K., Lee Y.I., Lim H.S., Lee J.I., Choi J.H., Yoon H.I. (2011) – Comparison of radiocarbon and OSL dating methods for a Late Quaternary sediment core from Lake Ulaan, Mongolia. Journal of Paleolimnology, 45, 127‑135.
DOI : 
10.1007/s10933-010-9484-7

Lee M.K., Lee Y.I., Lim H.S., Lee J.I., Yoon H.I. (2013) – Late Pleistocene–Holocene records from Lake Ulaan, southern Mongolia: implications for east Asian palaeomonsoonal climate changes. Journal of Quaternary Science, 28 (4), 370‑378.
DOI : 
10.1002/jqs.2626

Lehmkuhl F., Lang A. (2001) – Geomorphological investigations and luminescence dating in the southern part of the Khangay and the Valley of the Gobi Lakes (Central Mongolia). Journal of Quaternary Science, 16 (1), 69‑87.
DOI : 
10.1002/1099-1417(200101)16:1<69::AID-JQS583>3.0.CO;2-O

Lehmkuhl F., Grunert J., Hülle D., Batkhishig O., Stauch G. (2018) – Paleolakes in the Gobi region of southern Mongolia. Quaternary Science Reviews, 179, 1‑23.
DOI : 
10.1016/j.quascirev.2017.10.035

Li Y., Morrill C. (2010) – Multiple factors causing Holocene lake-level change in monsoonal and arid central Asia as identified by model experiments. Climate Dynamics, 35, 1119‑1132.
DOI : 
10.1007/s00382-010-0861-8

Liu X.Q., Herzschuh U., Shen J., Jiang Q.F., Xiao X.Y. (2008) – Holocene environmental and climatic changes inferred from Wulungu Lake in northern Xinjiang, China. Quaternary Research, 70 (3), 412‑425.
DOI : 
10.1016/j.yqres.2008.06.005

Mackay A.W., Swann G.E.A., Brewer T.S., Leng M.J., Morley D.W., Piotrowska N., Rioqual P., White D. (2011) – A reassessment of late glacial – Holocene diatom oxygen isotope record from Lake Baikal using a geochemical mass-balance approach. Journal of Quaternary Science, 26 (6), 627‑634.
DOI : 
10.1002/jqs.1484

McGeehin J., Burr G.S., Jull A.J.T., Reines D., Gosse J., Davis P.T., Muhs D., Southon J.R. (2001) – Stepped-combustion 14C dating of sediment: a comparison with established techniques. Radiocarbon, 43 (2A), 255‑261.
DOI : 
10.1017/S003382220003808X

Morrill C., Overpeck J.T., Cole J.E. (2003) – A synthesis of abrupt changes in the Asian summer monsoon since the last deglaciation. The Holocene, 13, 465‑476.
DOI : 
10.1191/0959683603hl639ft

Narantsetseg Ts., Badamgarav J., Ariunbileg S., Badamgarav D., Oyunchimeg Ts., Idermunkh T., Uugantsetseg B., Tuvshinjargal B., Dolgorsuren Kh. (2011) – Geology of the Meso-Cenozoic depressions. Institute of Geology and Mineral Resources, Ulaanbaatar, 146 p.

Narantsetseg Ts., Krivonogov S.K., Oyunchimeg Ts., Uugantsetseg B., Burr G.S., Tomurhuu D., Dolgorsuren Kh. (2013) – Late Glacial to Middle Holocene climate and environmental changes as recorded in Lake Dood sediments, Darhad Basin, northern Mongolia. Quaternary International, 311, 12‑24.
DOI : 
10.1016/j.quaint.2013.08.043

Orkhonselenge A., Komatsu G., Uuganzaya M. (2018) – Climate-driven changes in lake areas for the last half century in the Valley of Lakes, Govi Region, Southern Mongolia. Natural Science, 10 (7), 263‑277.
DOI : 
10.4236/ns.2018.107027

Orkhonselenge A., Krivonogov S.K., Mino K., Kashiwaya K., Safonova I.Y., Yamamoto M., Kashima K., Nakamura T., Kim J.Y. (2013) – Holocene sedimentary records from Lake Borsog, eastern shore of Lake Khuvsgul, Mongolia, and their paleoenvironmental implications. Quaternary International, 290‑291, 95‑109.
DOI : 
10.1016/j.quaint.2012.03.041

Owen L.A., Windley B.F., Cunningham W.D., Badamgarav J., Dorjnamjaa D. (1997) – Quaternary alluvial fans in the Gobi of southern Mongolia: evidence for neotectonics and climate change. Journal of Quaternary Science, 12 (3), 239‑252.
DOI : 
10.1002/(SICI)1099-1417(199705/06)12:3<239:AID-JQS293>3.0.CO;2-P

Panagiotopoulos F., Shahgedanova M., Hannachi A., Stephenson D.B. (2005) – Observed Trends and Teleconnections of the Siberian High: A Recently Declining Center of Action. Journal of Climate, 18, 1411‑1422.
DOI : 
10.1175/JCLI3352.1

Panin A.V., Bronnikova M.A., Uspenskaya O.N., Arzhantseva I.A., Konstantinov E.A., Koshurnikov E.A., Selezneva V.V., Fuzeina Y.N., Yu. N., Sheremetskaya E.D. (2012) – Evolution of Tere-Khol Lake and the Holocene Dynamics of the Environment in the Southeastern Part of the Sayan-Tuva Highland. Earth Sciences, 446 (2), 1204‑1210.
DOI : 
10.1134/S1028334X12100108

Peck J.A., Khosbayar P., Fowell S.J., Pearce R.B., Ariunbileg S., Hansen B.C.S., Soninkhishig N. (2002) – Mid to Late Holocene climate change in north central Mongolia as recorded in the sediments of Lake Telmen. Palaeogeography, Palaeoclimatology, Palaeoecology, 183, 135‑153.
DOI : 
10.1016/S0031-0182(01)00465-5

Prokopenko A.A., Kuzmin M.I., Williams D.F., Gelety V.F., Kalmychkov,G.V., Gvozdkov A.N., Solotchin P.A. (2005) – Basin-wide sedimentation changes and deglacial lake-level rise in Lake Hovsgol basin, NW Mongolia. Quaternary International, 136, 59‑69.
DOI : 
10.1016/j.quaint.2004.11.008

Reimer P.J., Bard E., Bayliss A., Beck J.W., Blackwell P.G., Ramsey C.B., Buck C.E., Cheng H., Edwards R.L., Friedrich M., Grootes P.M., Guilderson T.P., Haflidason H., Hajdas I., Hatte C., Heaton T.J., Hoffmann D.L., Hogg A.G., Hughen K.A., Kaiser K.F., Kromer B., Manning S.W., Niu M., Reimer R.W., Richards D.A., Scott E.M., Southon J.R., Staff R.A., Turney C.S.M., van der Plicht J. (2013) – IntCal13 and Marine13 radiocarbon age calibration curves, 0–50 000 years cal BP. Radiocarbon, 55 (4), 1869‑1887.
DOI : 
10.2458/azu_js_rc.55.16947

Rudaya N., Li H. (2013) – A new approach for reconstruction of the Holocene climate in the Mongolian Altai: The high-resolution 13C records of TOC and pollen complexes in Hoton-Nur Lake sediments. Journal of Asian Earth Sciences, 69, 185‑195.
DOI : 
10.1016/j.jseaes.2012.12.002

Sevastyanov D.V., Dorofeyuk N.I. (2005) – A short review: limnological and paleolimnological researches in Mongolia carried out by joint Russian-Mongolian expeditions. Journal of Mountain Science, 2 (1), 86‑90.
DOI : 
10.1007/s11629-005-0086-1

Shi Y.F., Kong Z.C., Wang S.M. (1993) – Mid-Holocene climates and environments in China. Global and Planetary Change, 7 (1‑3), 219‑233.
DOI : 
10.1016/0921-8181(93)90052-P

Sternberg T., Paillou P. (2015) – Mapping potential shallow groundwater in the Gobi Desert using remote sensing: Lake Ulaan Nuur. Journal of Arid Environments, 118, 21‑27.
DOI : 
10.1016/j.jaridenv.2015.02.020

Stuiver M., Polach H.A. (1977) – Discussion: Reporting of 14C data. Radiocarbon, 19 (3), 355‑363.
DOI : 
10.1017/S0033822200003672

Tsegmid Sh. (1969) – Physical Geography of Mongolia. State Press, Ulaanbaatar (Mongolian), 405 p.

Tserensodnom J. (1971) – Lakes of Mongolia. State Publishing, Ulaanbaatar (Mongolian), 192 p.

Tserensodnom J. (2000) – A catalog of lakes in Mongolia. Shuvuun Saaral Publishing, Ulaanbaatar (Mongolian), 141 p.

Visbeck M. (2002) – The ocean’s role in Atlantic climate variability. Science, 297, 2223‑2224.
DOI : 
10.1126/science.1074029

Vogel D.E. (1975) – Precambrian Weathering in Acid Metavolcanic Rocks from the Superior Province, Villebon Township, South-Central Québec. Canadian Journal of Earth Sciences, 12 (12), 2080‑2085.
DOI : 
10.1139/e75-183

Watanabe T., Nakamura T., Nara F.W., Kakegawa T., Horiuchi K., Senda R., Oda T., Nishimura M., Matsumoto G.I. (2009) – High-time resolution AMS 14C data sets for Lake Baikal and Lake Hovsgol sediment cores: changes in radiocarbon age and sedimentation rates during the transition from the last glacial to the Holocene. Quaternary International, 205, 12‑20.
DOI : 
10.1016/j.quaint.2009.02.002

Xiao X.Y., Jiang Q.F., Liu X.Q., Xiao H.F., Shen J. (2006) – High resolution sporopollen record and environmental change since Holocene in the Wulungu Lake, Xinjiang. Acta Micropalaeontologica Sinica, 23 (1), 77‑86.

Haut de page

Annexe

Version française abrégée

Cette étude propose une reconstruction de la dynamique de la sédimentation à l'Holocène moyen et final et de ses implications paléoclimatiques dans le lac Ulaan, au sud de la Mongolie. Cette dynamique est reliée à l'intensité des intempéries, à l'estimation de taux de sédimentation et est calée temporellement par datation au radiocarbone (AMS). La superficie du lac Ulaan s'est réduite de 18,2 km² à la fin du 20e siècle, passant de 62,38 km² en 1970 à 44,16 km² en 2014 (fig. 1- 2A). La diminution de la superficie du lac Ulaan au cours des 44 dernières années peut être liée à un changement climatique local, marqué par une hausse des températures depuis 1995 (fig. 4A) et une diminution des précipitations depuis 1987 (fig. 4B). La correction de l'effet réservoir pour le lac Ulaan, peu profond, est considérée comme négligeable à 0,2 kyr (tab. 3). Les âges plus anciens des sédiments de surface du lac (UN15-1a et UN15-2a) peuvent s'expliquer par l'effet réservoir lacustre, dû à l'apport de matières organiques terrestres après la remobilisation des sédiments de surface par les processus éoliens durant l'intense sécheresse de l'Holocène final (fig. 6).

L'altération intense affectant le lac Ulaan, approchée à l'aide de deux indicateurs de l'altération chimique, l'index chimique d'altération (CIA) et l'index d'altération de Parker WPI (Weathering Product Index) (tab. 2) appliqués aux échantillons UN15-1b et UN15-2b, coïncide avec les taux de sédimentation les plus élevés de 4,6 et 6,4 cm/1000 ans de l'Holocène moyen et du début de l'Holocène final (tab. 4, fig. 5-6). Cela implique que le bassin du lac Ulaan a pu connaître un climat humide entraînant une érosion plus élevée et une oxydation marquée entre 6,0 et 2,7 kyr cal BP (fig. 7). Au contraire, l'altération superficielle identifiée dans les échantillons UN15-1a et UN15-2a est en phase avec les taux de sédimentation les plus faibles, de 1,6-1,8 cm/1000 ans à la fin de l'Holocène (tab. 4). Ce constat laisse penser que le climat est devenu aride depuis environ 2,7-3,2 kyr cal BP (fig. 7) et que cette sécheresse a entraîné un rétrécissement de ce lac peu profond. Le taux de sédimentation élevé de 4,6 cm/1000 ans observé dans une partie marginale du lac (tab. 4, fig. 5-6) implique que le bassin du lac Ulaan ait connu un climat humide favorisant un apport de sédiments dans le lac au cours de l'Holocène moyen et le début de l'Holocène final, soit entre 6,0 et 2,7 kyr cal BP (fig. 5,7).

Le faible taux de sédimentation de 1,6-1,8 cm/1000 ans durant l'Holocène final (tab. 4, fig. 5-6) indique que dans le bassin du lac Ulaan, l'aridification s'est renforcée depuis environ 2,7-3,2 cal kyr BP (fig. 6-7), ce qui a pu provoquer la réduction du plan d'eau, phénomène qui semble se prolonger jusqu'à l'époque moderne (fig. 2A). La forte altération et le taux de sédimentation important, 4,6 cm/1000 ans, entre 2,7 et 6,0 cal kyr BP, peut impliquer des conditions climatiques humides durant l'Holocène moyen. L'altération superficielle et le faible taux de sédimentation, 1,6-1,8 cm/1000 ans, induisent la prédominance d'un climat aride à la fin de l'Holocène. L'aridité du climat a peut-être été confortée par la réduction de la superficie des lacs, ce qui a entraîné l'émersion de sédiments déposés après 2,7 à 3,2 kyr cal BP. Les conditions climatiques de l'Holocène moyen et tardif enregistrées dans le bassin du lac Ulaan, dans le sud de la Mongolie, correspondent bien aux résultats obtenus dans d'autres parties de la Mongolie, dans le sud de la Sibérie et le nord de la Chine en Asie centrale. Des études plus poussées sur les séquences sédimentaires et l'apport de plus de données permettant de caractériser l'évolution temporelle du lac Ulaan sont nécessaires pour contraindre plus précisément la dynamique de la sédimentation holocène dans le sud de la Mongolie et en Asie centrale.

Haut de page

Table des illustrations

Titre Fig. 1 – Geographical location of Lake Ulaan in southern Mongolia. Fig. 1 – Localisation du lac Ulaan dans le sud de la Mongolie.
URL http://journals.openedition.org/geomorphologie/docannexe/image/12219/img-1.jpg
Fichier image/jpeg, 1,8M
Titre Fig. 2 – The Lake Ulaan basin and sampling sites. Fig. 2 – Le bassin versant du lac Ulaan et les sites d'échantillonage.
Légende A. Changes in lake areas in 1970 and 2014 for Lake Ulaan are overlain over a topographic map of the Lake Ulaan basin. B. Sampling sites within the lake area. Insets: views of exposed lake floors facing the northwest at sampling site 1 (C) and the east at sampling site 2 (D). A. Évolution de la surface du lac entre 1970 et 2014, sur un fond de carte topographique. B. Les sites échantillonnés dans le lac. Vignettes : vues du plancher lacustre émergé regardant vers le nord-ouest, site 1 (C), et vers l'est, site 2 (D).
URL http://journals.openedition.org/geomorphologie/docannexe/image/12219/img-2.jpg
Fichier image/jpeg, 2,3M
Titre Fig. 3 – Ground photos around the Lake Ulaan basin. Fig. 3 – Photographies dans le bassin du Lake Ulaan.
Légende A. Northeast-facing view of a channel of the Ongi River entering Lake Ulaan. The arrow indicates the river flow direction. Photo by A. Orkhonselenge, October 25th, 2015. B. East-facing view of Lake Ulaan. Photo by D. Adiya, September, 2013. C. North-facing view of Lake Ulaan. Photo by “Ongi River Movement” Non-Governmental Organization (NGO), November 5th, 2014. A. Vue de regard Nord-Ouest du cours de la rivière Ongi se jetant dans le lac Ulaan. La flèche indique le sens de l'écoulement. Photo A. Orkhonselenge, 25 octobre 2015. B. Vue du lac Ulaan, regard Est. Photo D. Adiya, Septembre 2013. C. Vue du lac Ulaan, regard Nord. Photo “Ongi River Movement” Non-Governmental Organization (NGO), 5 novembre 2014.
URL http://journals.openedition.org/geomorphologie/docannexe/image/12219/img-3.jpg
Fichier image/jpeg, 880k
Titre Tab. 1 – Major element compositions of the Lake Ulaan sediments. Tab. 1 – Nature des éléments majeurs caractérisant les sédiments du lac Ulaan.
URL http://journals.openedition.org/geomorphologie/docannexe/image/12219/img-4.png
Fichier image/png, 23k
Titre Tab. 2 – Chemical Index of Alteration (CIA) and Weathering Product Index (WPI) values of the Lake Ulaan sediments. Tab. 2 – Valeurs de l'index chimique d'altération (CIA) et de l'index d'altération potentielle (WPI) des sédiments du lac Ulaan.
URL http://journals.openedition.org/geomorphologie/docannexe/image/12219/img-5.png
Fichier image/png, 10k
Titre Tab. 3 – Radiocarbon ages without δ13C correction and calibrated ages. Tab. 3 – Âges radiocarbone sans la correction du δ13C et âges calibrés.
URL http://journals.openedition.org/geomorphologie/docannexe/image/12219/img-6.png
Fichier image/png, 49k
Titre Fig. 4 – Climate anomalies. Fig. 4 – Anomalies de variables climatiques.
Légende A. Anomalies of annual mean air temperature between 1975 and 2015; B. Anomalies of annual mean precipitation between 1973 and 2015 observed at the Mandal-Ovoo meteorological station. A. Anomalies de la température moyenne annuelle de l'air entre 1975 et 2015 ; B. Anomalies des précipitations moyennes annuelles entre 1973 et 2015, enregistrées à la station météorologique de Mandal-Ovoo.
URL http://journals.openedition.org/geomorphologie/docannexe/image/12219/img-7.jpg
Fichier image/jpeg, 452k
Titre Fig. 5 – A synthesized view of the collected samples revealing middle to late Holocene sedimentary deposition rates in Lake Ulaan. Fig. 5 – Schéma synthétique des taux d'accumulation sédimentaire de l'Holocène moyen à final dans le lac Ulaan.
Légende 1. Fine silt; 2. Clay; 3. Very fine silt; 4. Clay; 5. Site 1: UN 15-1; 6. Site 2: UN 15-2. The lithology is recorded from the field observation along the sampling pits. 1. Limon fin ; 2. Argile ; 3. Limon très fin ; 4. Argile. 5. Site 1 : UN 15-1 ; 6. Site 2 : UN 15-2.
URL http://journals.openedition.org/geomorphologie/docannexe/image/12219/img-8.jpg
Fichier image/jpeg, 428k
Titre Fig. 6 – Holocene climate and sedimentation rate in Lake Ulaan. Fig. 6 – Climat et sédimentation holocènes dans le lac Ulaan.
Légende A. The local climate-induced environmental conditions during the sedimentation in Lake Ulaan; B. The difference in sedimentation rate between marginal and central parts of Lake Ulaan in the middle to late Holocene. A. Tendances climatiques et sédimentation dans le lac ; B. Différences des taux de sédimentation entre les parties marginale et centrale du lac, de l'Holocène moyen à final.
URL http://journals.openedition.org/geomorphologie/docannexe/image/12219/img-9.jpg
Fichier image/jpeg, 324k
Titre Tab. 4 – Calibrated age and sedimentation rate. Tab. 4 – Ages calibrés et taux de sédimentation.
URL http://journals.openedition.org/geomorphologie/docannexe/image/12219/img-10.png
Fichier image/png, 21k
Titre Fig. 7 – Climatic trends. Fig. 7 – Tendances climatiques.
Légende The derived climatic trends from the sedimentation rates are compared with trends in other lakes in southern Mongolia (S.MGL), southern Russia (S. Russia) and northern China (N. China). Comparaison des tendances climatiques dérivées des taux de sédimentation aux tendances observées dans d'autres lacs du sud de la Mongolie (S.MGL), du sud de la Russie (S. Russia) et du nord de la Chine (N. China).
URL http://journals.openedition.org/geomorphologie/docannexe/image/12219/img-11.jpg
Fichier image/jpeg, 228k
Haut de page

Pour citer cet article

Référence papier

Alexander Orkhonselenge, Goro Komatsu et Munkhjargal Uuganzaya, « Middle to late Holocene sedimentation dynamics and paleoclimatic conditions in the Lake Ulaan basin, southern Mongolia  », Géomorphologie : relief, processus, environnement, vol. 24 - n° 4 | 2018, 351-363.

Référence électronique

Alexander Orkhonselenge, Goro Komatsu et Munkhjargal Uuganzaya, « Middle to late Holocene sedimentation dynamics and paleoclimatic conditions in the Lake Ulaan basin, southern Mongolia  », Géomorphologie : relief, processus, environnement [En ligne], vol. 24 - n° 4 | 2018, mis en ligne le 01 octobre 2018, consulté le 16 février 2019. URL : http://journals.openedition.org/geomorphologie/12219 ; DOI : 10.4000/geomorphologie.12219

Haut de page

Auteurs

Alexander Orkhonselenge

Laboratory of Geochemistry & Geomorphology, School of Arts & Sciences – National University of Mongolia – Ulaanbaatar 15160, Mongolia (rkhnslng@num.edu.mn). Phone: +976 75754400 2453; Fax: +976 11 320159.

Articles du même auteur

Goro Komatsu

International Research School of Planetary Sciences – Università d'Annunzio – Viale Pindaro 42, 65127, Pescara, Italy (goro@irsps.unich.it).

Munkhjargal Uuganzaya

Laboratory of Geochemistry & Geomorphology, School of Arts & Sciences – National University of Mongolia – Ulaanbaatar 15160, Mongolia (m.uuganzayaaa@gmail.com).

Haut de page

Droits d’auteur

© Groupe français de géomorphologie

Haut de page
  • Logo CNRS - Institut des sciences humaines et sociales
  • Logo Groupe français de géomorphologie
  • OpenEdition Journals