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Article

Characteristics of Lake Sediment from Southwestern Mongolia and Comparison with Meteorological Data

by
Uyangaa Udaanjargal
1,*,
Noriko Hasebe
2,*,
Davaadorj Davaasuren
3,
Keisuke Fukushi
2,
Yukiya Tanaka
4,
Baasansuren Gankhurel
1,
Nagayoshi Katsuta
5,
Shinya Ochiai
2,
Yoshiki Miyata
2,6 and
Tuvshin Gerelmaa
3
1
Department of Earth Sciences, Kanazawa University, Kakuma, Kanazawa 920-1192, Japan
2
Institute of Nature and Environmental Technology, Kanazawa University, Kakuma, Kanazawa 920-1192, Japan
3
Department of Geography, School of Art & Science, National University of Mongolia, Ulaanbaatar 210646, Mongolia
4
Department of Geography, College of Sciences, Kyung Hee University, 26 Kyunghee-daero, Dongdaemun-gu, Seoul 02447, Korea
5
Faculty of Education, Gifu University, Gifu 501-1193, Japan
6
The University Museum, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
*
Authors to whom correspondence should be addressed.
Geosciences 2022, 12(1), 7; https://doi.org/10.3390/geosciences12010007
Submission received: 18 November 2021 / Revised: 16 December 2021 / Accepted: 21 December 2021 / Published: 24 December 2021
(This article belongs to the Section Climate)
Browse Figures
Review Reports Versions Notes

Abstract

:
To understand how the climate system works in the continental interior, sediment cores that are approximately 30-cm long were taken from Olgoy, Boontsagaan, and Orog lakes, Mongolia. These cores were analyzed and compared with meteorological data (air temperature, precipitation, and wind) from climate stations in the study area. Comparison of metrological data from four stations shows similar climate fluctuations. When the temperature was high, less precipitation occurred in general. The sedimentary features measured in this study were water content, organic matter, carbonate, amorphous silica contents, whole and mineral grain size, and grain density. Excess 210Pb measurements were used to estimate sedimentary ages. According to principal component analysis (PCA), temperature correlates well to sediment characteristics in Olgoy Lake. Whole and mineral grain sizes are coarser when the temperature is high, while the amorphous-silica concentration is lower. A coarse grain size is interpreted to reflect low lake levels due to evaporation under high temperature with less precipitation. Amorphous silica may be from surrounding plants and reflects less vegetation when the temperature is high. However, in the recent 30 years, after the social system changed and overgrazing became a problem, the amount of amorphous silica has positively correlated with temperature on a short time scale. In the past 30 years, with less vegetation, amorphous silica has mainly come from weathered mineral particles. High temperature caused a thick, weathered mantle for each mineral particle, resulting in high amorphous-silica concentration. In Boontsagaan Lake, whole and mineral grain sizes are coarser when the wind speed is increased. Low precipitation correlates with a decrease in organic matter and an increase in carbonate and amorphous silica. In Orog Lake, it is difficult to establish an age model due to dried-up events. Some fluctuations in sedimentary characteristics may correspond to extreme events, such as earthquakes, and natural hazards, such as dzuds (harsh winters).

1. Introduction

Southwestern Mongolia spans the arid and semiarid regions of Asia. It is a geographically important region for understanding the environmental and climatic changes in the continental interior under ongoing global climate change. Over the last 40 years, Mongolia’s mean annual temperature has increased by 1.8 °C. This is significantly more than the global average, which has experienced an increase of 0.7 °C per year over the last 100 years [1]. The climate is getting warmer and drier in the high mountainous areas and their valleys, but this trend is less significant in southern districts [1]. The rising temperature and precipitation changes associated with global warming are likely to increase climate variability and the frequency of extreme events [2]. For instance, natural hazards, such as dzuds (severe winter) and droughts, caused enormous damages to livestock and the national economy. According to [3], there were 24 dzuds in Mongolia between 1944 and 1993. The highest livestock mortality rates were 32% and 24% in 1962 and 1983, respectively, which were caused by dzuds combined with drought in previous years [4]. In Mongolia, 90% of the country is regarded as an area that is vulnerable to desertification [5]. Overgrazing is an additional environmental issue, especially after the 1990s, when Mongolia’s social system changed [6]. Extreme temperature drops with large amounts of snow severely affected the livestock mortality rate during the 2009–2010 dzud (23.4% in the country), combined with overgrazing due to livestock overpopulation [7].
To predict future environmental issues and take countermeasures for their unpleasant consequences, it is important to understand, through paleoenvironmental studies, how the environmental system works under the known climatic conditions. In Mongolia, studies on climatic and environmental changes during the Holocene are limited and regionally scattered [8]. Lake sediments are archives of past terrestrial environmental changes. We can extract information from the sediments by analyzing appropriate proxy data [9,10,11,12]. Terminal lakes record climatic conditions in catchments, and lake-level changes are representative indicators of climatic changes [13].
This study aimed to enhance understanding of how the lake catchment system works under certain local and global climatic conditions, specifically in the semiarid southwestern region of Mongolia, where numerous lakes fill endorheic basins. The southern lakes had the highest lake levels throughout the Middle Holocene, which may be attributed to various moisture-bearing atmospheric systems [8]. We analyzed multiple sediment characteristics, namely water content, grain density, grain size, organic matter, carbonate, and amorphous-silica concentrations from Olgoy (sometimes spelled Olgoi), Boontsagaan (Boon Tsagaan), and Orog lakes. Sediment characteristics were compared with meteorological data, such as air temperature, precipitation, and wind strength, to understand which sediment data represent the most appropriate proxy for climate change. This helps us reconstruct past meteorological conditions from lake sediments, assuming that their relationship is similar for both past and present.

2. Site Description

Olgoy, Boontsagaan, and Orog lakes are saline lakes located in the Gobi–Altai transition zone called the Valley of Gobi Lakes, which stretches from central to western Mongolia (Figure 1). It is a steppe and a semi-desert zone. The Valley of Gobi Lakes is an elongated mountain depression formed between the Siberian Craton and the Tarim and Sino-Korean Cratons [14] and a tectonically active foreland basin in Gobi-Altai and Khangai strike-slip regimes [8,15]. The Gobi-Altai ranges were formed by transpressional Cenozoic movements of Palaeozoic volcanic and sedimentary rocks [16]. The Gobi-Altai range consists of lateral alternates of basins filled by Quaternary alluvial fans [17] and lakes [8,18], all affected by aeolian morphodynamics [19]. The Valley of Gobi Lakes is 500-km long and 150-km wide, with an average elevation between 1000 and 1400 m above sea level. Quaternary lake sediments fill the flat basin between the lakes [20].
The primary catchment area spreads north of the lakes and includes the base of the Khangai Mountain range, which consist of mainly Precambrian and Palaeozoic sedimentary rocks and Mesozoic granitic intrusions and metamorphic rocks [20,22]. The Gobi-Altai mountains, mostly composed of Paleozoic volcanic and plutonic rocks, are an additional sediment source through the flash flows on the mountain slope [23]. According to [8], semi-active dunes exist in the Valley of Gobi Lakes, and active barchan dunes are locally formed by strong west–northwest winds. Swamps and salt crusts surround the western and eastern sides of Orog Lake around dynamic and sparsely vegetated dunes. Sand containing gravel and carbonate-rich silt exists to the north of the lake, and perennial and periodically flowing streams from the Khangai Mountains run through it. Several more intensive paleoenvironmental studies were conducted in the Orog Lake basin than in other lake basins in southern Mongolia [18,19,24,25,26,27,28]. Geomorphological and geochronological observations imply that the aggradation of alluvial fans occurred from mid-MIS2 and extensively during preceding glacial periods in the south of the Valley of Gobi lakes (e.g., Orog lake). Increased moisture enhanced runoff and sediment storage in the Khangai mountains. Tectonic activities did not affect the level of Orog Lake, based on the constant altitudes of mapped beach ridge [28].
Major ruptures and faults can be found in fanglomerates and alluvial fans around the lakes [14]. In 1905 and 1957, magnitude-8 earthquakes occurred in western Mongolia and the adjacent region in China [29] along >100-km strike-slip faults (i.e., Tsetserleg, Bulnai, Fuyun, and Bogd faults) in the northernmost deformation zone related to the India–Asia continental collision. Furthermore, numerous fault scarps crosscut Quaternary deposits in the Valley of Gobi Lakes, despite the lack of recorded earthquakes [27]. Paleoseismological investigations along the Gurvan Bogd fault, which ruptured in 1957 during the Gobi–Altai earthquake, have demonstrated recurrence intervals of 3–5 kyr for large earthquakes [30].
There are six major vegetation zones in Mongolia based on differences in altitude, temperature, rainfall distribution, and soils [31]. The Valley of Gobi Lakes belongs to the desert–steppe and steppe regions (Figure 1A). Due to the salinity of the soil, vegetation is scarce and is mainly characterized by sparse shrubs up to 0.5-m tall and some grasses. The primary species are Stipa gobica, Stipa glareosa, Allium polyrhizum, Cleistogenes soongorica, Anabasis brevifolia, Ajania achilleoides, and Caragana pygmaea [32,33].
The hydrological status of the lakes largely depends on the water supply from the surrounding mountain area [34]. An extensive hydrographic river net exists in the valley, but numerous river beds are only filled with water during periods of heavy rainfall in the summer [33]. Therefore, the lakes are mainly fed by precipitation and surface runoff.
Olgoy Lake lies in the northernmost part of the Valley of the Gobi Lakes on the southern foothills of the Khangai Mountains, where the main water source is relatively high levels of precipitation. Its surface area is 1.55 km2, with a depth of 1 m. There are no inflow or outflow rivers. For Boontsagaan Lake, the main source of water is the Baidrag River (310-km long). The surface area of Boontsagaan Lake is 252 km2, with a maximum depth of 10 m. Olgoy Lake is located in the catchment area of Boontsagaan Lake (Figure 1). The surface area of Orog Lake is 140 km2, with a maximum depth of 2 m. It is fed by the Tuin River, which is 243-km long. Flooding in the Baidrag River, Tuin River, and other minor streams in the study area occurs primarily during the summer due to the high levels of precipitation from July to August. Secondary floods usually occur during the spring due to snowmelt. Both rivers originate in the Khangai Mountains, where continuous and discontinuous permafrost occurs (Figure 1B).
These lakes have experienced lake-level changes in the past, leaving terraces (paleoshoreline) in nearby localities [18,35]. In the Valley of Gobi Lakes, the high lake level was reconstructed for the periods of 10–6 and 1.5–1.4 ka [19]. An integrated discussion of past environmental changes, land-surface processes, and provenance signals in the Orog Lake catchment over the last 45 kyr is provided by [25], based on chemical analysis. Walther [33] analyzed pollen profiles from sediment samples obtained from Orog Lake and concluded that the lake existed during the Holocene and that the environment is becoming drier over time. The recent relationship between climatic factors and lake-surface fluctuations in Orog and Boontsagaan lakes was discussed by [24]. In some years, the level of Orog Lake has fluctuated more than usual, disappearing entirely in 2005–2007, 2009, and 2011 [24,36]. Geochemical and hydrometeorological processes influence the water chemistry in the river–lake systems of central Mongolia [37].

3. Materials and Methods

In 2014, lake-sediment cores were obtained by a gravity corer at points closest to the deepest part of each lake (Figure 1 and Table 1) from Olgoy Lake (OL02—43-cm length), Boontsagaan Lake (BTS01—31-cm length and BTS02—31-cm length), and Orog Lake (OR02—43-cm length). All cores were sliced into 1-cm-thick segments at the National University of Mongolia.

3.1. Laboratory Analysis

The sediment characteristics analyzed in this study are water content (%), organic-matter content (%), carbonate content (%), amorphous-silica content (%), bulk specific density (g/cm3) of the dried sample, whole grain size (φ), mineral grain size (φ), and mineral assemblages. In paleoenvironmental reconstructions, grain size is often a good proxy of climatic changes [9] that can provide evidence of dust storms in closed lakes, especially in the arid area [38]. Amorphous silica, which is sometimes called biogenic silica, often indicates an abundance of diatoms in freshwater sediment [39,40,41]. However, highly saline lakes are not suitable to support or preserve diatoms [42]. Amorphous silica in saline lakes could originate from some types of grass (e.g., Poaceae) or the weathered outer rim of silicate minerals [43].
To overcome the effect of compaction, mass depth (accumulated weight per unit area, g/cm2) is estimated by the bulk density and porosity calculated from water content, and all data are plotted against mass depth. The water content was directly measured by drying a specified amount of sediment. The samples were placed in an oven at 110 °C for 24 h, and the weight difference of the wet and dry samples was measured to calculate the water content. The amount of organic matter was estimated by the weight change in the samples after a 10% hydrogen peroxide treatment. After 1 mL of the solution was added to 50 mg of dried sediment, the samples were placed in a water bath with shaking (130 rpm) at 60 °C (Yamato shaking bath, Model BW200) for 1 h. Then, the samples were left at room temperature for 24 h. After the samples were cleaned with distilled water and an ultrasonic treatment, each sample tube was centrifuged for approximately 20 min (KUBOTA 5220, Model IE61010-2-020 rotor at 3000 rpm), and the liquid was disposed of. Then, the samples were placed in an oven to dry overnight at 77 °C. The amount of carbonate in the sediment was estimated by the weight change after 1N hydrochloric acid (HCl) treatment. After the addition of 1 mL of 1N HCl solution, the sample was treated with an ultrasonic cleaner for ~20 min at room temperature. Subsequently, the sample was washed, centrifuged, and dried. Analysis of amorphous silica was conducted following the method described by Mortlock and Froelich [44]. After HCl treatment, 8 mL of a 2-mol/Na2CO3 solution was added to each sample and mixed well. Then, the samples were placed in a water bath preheated to 85 °C. After 7 h of heating to dissolve the amorphous silica, 0.1 mL of the sample liquid was subsampled to a newly prepared tube. The amount of dissolved amorphous silica was estimated via molybdenum blue spectrophotometry (Shimazu UV1200) [44].
The specific density was measured from the dried bulk samples using the AccuPyc 1330 Pycnometer. Helium gas was used to fill the gaps in the samples and measure the volume. The weight of the samples was measured using a balance. The specific density was calculated from the volume and weight of the samples. Mass depth (g/cm3) is calculated based on the specific density and water content. Grain size was measured for the whole sediment, and the mineral fraction remained after amorphous silica treatment (mentioned above). Dispersant sodium hexametaphosphate was added to the samples and mixed well using an ultrasonicator for 5 min. Then, the particle-size distribution was measured using a laser diffraction particle-size analyzer (Shimadzu SALD-2200), and mean particle size was calculated.
Mineral assemblages of selected samples were observed via X-ray diffraction (XRD). XRD pat-terns were scanned from 2° to 65° for four powdered samples from each core after being dried at room temperature using an XRD instrument (Ultima IV) with a Cu target (40 kV/30 mA).

3.2. Sediment Dating

Unsupported 210Pb concentrations were measured to estimate the sedimentation rate via gamma counting (Table 2) using a high-purity germanium detector (ORTEC, GLP-16195) at the Radioisotope Laboratory for Natural Science and Technology, Kanazawa University. A total of 12 samples from Orog Lake (OR02) were measured at a resolution of 3 cm. For the Olgoy Lake samples (OL02), nine samples were processed at a resolution of 5 cm. An additional core (BTS02) collected from Boontsagaan Lake was sliced into 0.5-cm-thick segments for excess 210Pb measurement, and 13 samples were measured at the Low-Level Radioactivity Laboratory, Institute of Nature and Environmental Technology, Kanazawa University (ORTEC, GEM-FX5825-HJ).
Every sample remained in the detector for approximately five days, and concentrations were determined by counting emissions at 46.5 keV. The activity of supported 210Pb was estimated by measuring the activity of 214Pb. The activity of 210Pbexc was calculated by the difference between the total and supported 210Pb [45]. Concentrations of 137Cs were also measured to pinpoint 1963, when the concentration of 137Cs should be high due to atomic-bomb tests [46]. However, probably due to the mobility of 137Cs in alkaline lakes, we were unable to obtain reliable 137Cs concentrations.

3.3. Meteorological Data

Several meteorological stations are present in the catchment area of the studied lakes, although some of them have a short-term record with limited data. In this study, air-temperature, wind, and precipitation data from stations with relatively long-term records and stable data acquisition were utilized. These stations include Bayankhongor (1963–2014), Jinst (1973–2014), Galuut (1957–2014), and Baidrag (1994–2014) (data from the National Agency for Meteorology and Environmental Monitoring, Mongolia) (Figure 2). The Bayankhongor and Jinst stations are in the catchment area of Orog Lake (Figure 1). The Bayankhongor station is located in the Bayankhongor prefecture center and is close to the head tributaries of the Tuin River. The Jinst station is the nearest to Orog Lake and close (approximately 1 km) to the Tuin River. Multiple stations exist in the northern part of the watershed area. The Baidrag and Galuut stations are located on the slopes of the Khangai Mountains. They are in the catchment area of Boontsagaan Lake (Figure 1). The Baidrag station is located in a higher elevation than other stations, and it is next to the head tributaries of the Baidrag River in the Khangai Mountains. The Galuut station is the closest to Olgoy Lake and in its catchment area.

3.4. Principal Component Analysis

Principal component analysis (PCA) was employed to determine the similarities among the four stations and to reveal the main latent factors among sediment characteristics and climate factors. PCA reveals the relationship among proxies and is used to interpret the differences in their features. Based on the age model of each core, 9, 12, and 12 samples for Olgoy, Boontsagaan, and Orog lakes, respectively, were considered in the PCA, as they were deposited within the observation periods of the meteorological stations. One analyzed sample with a thickness of 1 cm corresponds to a few years. Therefore, an average of the meteorological data for the corresponding years was calculated and compared with sediment characteristics. PCA was performed using “FactoMineR” package [47] under the standard R installation in the RStudio software. Proxies with high positive and negative loadings (≥0.5) are indicated by bold letters in Table 3.

4. Results

4.1. Meteorological Data

At the Bayankhongor station, the mean annual air temperature ranged between 0.5 °C (1978) and 1.5 °C (2006), with an average of 0.1 °C. The average annual precipitation is 216 mm. The maximum precipitation occurred in 1976 (339 mm) and 2003 (318 mm), whereas the minimum precipitation occurred in 2001 (107 mm). The average of annual mean wind speed is 3.1 m/s.
At the Jinst station, the average temperature is 0.6 °C, and the annual mean temperature ranged between −1.5 °C (1984) and 1.9 °C (2007). The average annual precipitation is 110.2 mm. The maximum precipitation occurred in 2003 (182 mm), whereas the minimum precipitation occurred in 2009 (42 mm). The average wind speed is 3.6 m/s.
At the Galuut station, the mean annual air temperature ranged between −7.8 °C (1984) and −2.0 °C (2007), with an average of −4.3 °C. The average annual precipitation is 216 mm. The maximum precipitation occurred in 1964 (450 mm) and 1960 (390 mm), whereas the minimum precipitation occurred in 2008 (84 mm). The annual mean wind speed amounts to 3.0 m/s, with an average of 1.4 m/s. Wind strength has increased by nearly 1.5 m/s in the past 10 years.
At the Baidrag station, the mean annual air temperature ranged between −6.9 °C (1994) and −2.2 °C (2007), with an average of −4.2 °C over the past two decades. The average annual precipitation is 184 mm. The maximum precipitation occurred in 1995 (270 mm) and 1999 (259 mm), whereas the minimum precipitation occurred in 2009 (130 mm). The annual mean wind speed amounts to 2.9 m/s, with an average of 2.2 m/s.
When the meteorological data from the four stations are compared, colder and more stable wind conditions are found in northern area (the Galuut and Baidrag stations). On the other hand, the southern Bayankhongor and Jinst stations experienced a warmer climate with stronger winds. However, they exhibit similar fluctuations in all records. When the temperature was high, less precipitation occurred in the records of all stations (Figure 2). The annual mean wind speed exhibits a slightly different fluctuation for the Jinst station, most likely because the location is in close proximity to the Tuin River, at a different elevation, and in a different natural zone (Figure 1 and Figure 3). When PCA is applied to the meteorological data from all stations, the result clearly indicates that the main trends are similar throughout the watershed area (Figure 3A).

4.2. Radioactive Concentration and Sedimentation Rate

The fraction of unsupported 210Pb was calculated for 9, 13, and 12 samples from the Olgoy, Boontsagaan, and Orog Lake core sediments, respectively (Table 2). In Figure 4, the unsupported 210Pb concentration is plotted against mass depth, except for some samples plotted off the trend. For those samples, the assumption of constant initial concentration would be inappropriate. The apparent ages in Table 2 were calculated using a continuous initial-concentration model. Initial concentration was estimated from the intercept value at zero mass depth. For Orog Lake, in which the top sample is off the trend, we used the value of the top sample as the initial concentration.
The average sedimentation rate was estimated using the regression lines in Figure 4, and the sedimentation year of each analyzed sample was calculated. In Olgoy and Boontsagaan lakes, the sedimentation rate was estimated to be approximately 0.2 g/cm2 per year (Figure 4A,B). In Orog Lake, the uppermost sample is plotted off the trend line of the seven samples (Figure 4C, Table 2). As Orog Lake fully evaporated in 1890, 1934–1936, 1952–1953, 1986–1987 [33], 2005–2007, 2009, and 2011 [36], the sedimentation is not continuous. The most recent drying event was longer than the previous events, as recorded in the satellite images from 2005 to 2010 [48], and left evidence in the variation of organic matter (see discussion below in Section 4.4). Therefore, the sedimentation rate was estimated based on the amount of excess 210Pb from seven samples, and it is about 0.5 g/cm2 per year (Table 2 and Figure 4C). We used this value from a mass depth of 2.7 g/cm2 (3.5-cm core depth) to 43.4 g/cm2 (35.5-cm core depth) to convert the mass-depth profile into an age profile. The upper two samples were deposited after the drying event of 2005–2010, and the year of sedimentation was estimated accordingly.

4.3. Mineral Assemblages (XRD)

Quartz, feldspar, plagioclase, calcite, and clays (illite and chlorite) were found in the sediment cores from the three lakes (Figure 5). Monohydrocalcite is only found in the sediment core from Olgoy Lake and the upper part of the sediment core (mass depths of 1 and 3 g/cm2) from Boontsagaan Lake. Monohydrocalcite is an uncommon mineral that is typically found in recently deposited sediments from alkaline lakes [49]. It is a metastable mineral and transforms into an aragonite or calcite after a significant time interval [49]. The abundance of monohydrocalcite in Olgoy Lake indicates higher authigenic productivity during the last 100 years. The samples from Boontsagaan Lake contain large calcite peaks in the bottom part of the sediment core (mass depth of 12 g/cm2), whereas the upper part shows small peaks but with monohydrocalcite. This large calcite peak may be the result of the alternation of monohydrocalcite into calcite. In Boontsagaan Lake (Figure 5B), monohydrocalcite can survive for approximately 20 years, which is less than in Olgoy Lake (Figure 5A), where monohydrocalcite may remain for more than 100 years.
Amphibole is found in Orog Lake (Figure 5C), but it is not evident in Olgoy nor Boontsagaan Lakes. Olgoy and Boontsagaan Lakes belong to the same catchment area, which is different from that of Orog Lake. The existence of amphibole may reflect the geology of the catchment area, although detailed geological information on amphibole-bearing formations is not available in this area.

4.4. Physical and Chemical Properties of Sediment

Figure 6 presents the physical properties of the samples from the three lakes. The sedimentation year is given based on the estimated sedimentation rates (see Section 4.2).
Water content increases upward in all three lakes, mainly due to less compaction in the upper sediments. Grain density ranges between 2.3 and 2.8 g/cm3 in all lakes, with the lowest density in Olgoy Lake. Amounts of organic matter and calcium carbonate range between 0.5% and 40% in the three lakes. Whole and mineral grain sizes range between 8 φ and 4 φ and fluctuate similarly in all lakes. For Olgoy Lake, organic matter and carbonate concentrations negatively fluctuate, whereas amorphous silica shows positive fluctuations to carbonate in the lower part but not in the upper part (Figure 6A). In Boontsagaan Lake, amorphous silica and carbonate fluctuate similarly (Figure 6B). Grain density exhibits a decreasing tendency after the 1990s, combined with increases in carbonate and organic matter (Figure 6B). Orog Lake demonstrated large spikes in sediment characteristics compared with the other two lakes, possibly due to the evaporation events that occurred in the last decade (Figure 6C). The greatest fluctuation in organic matter is observed at the upper part of the core, and it corresponds to the evaporation event in 2005–2010 [48]. Conversely, there is less variation in the amorphous silica content in Orog Lake (1.3–2.3%). An increase in whole grain size occurred in the upper part of the sediment cores of Olgoy and Boontsagaan lakes after ~1980. Greater fluctuations in grain density between 1955 and the 1960s are observed in Olgoy and Boontsagaan lakes (Figure 6B). In a similar times interval in the Orog Lake sediment, a downward spike in grain density is observed (Figure 6C, around 1960).

4.5. Comparison between Sediment Characteristics and Meteorological Data by Principal Component Analysis

Based on the examination of meteorological data from the four stations within the catchment area, meteorological fluctuation is similar in the area. Therefore, data from one or two representative stations are considered for statistical analyses to be compared with sediment characteristics. The sediment characteristics of Boontsagaan Lake are analyzed with the meteorological data of Galuut and Baidrag stations. The Orog Lake sediment characteristics are compared with the meteorological data from the Bayankhongor and Jinst stations (Figure 3). The sediment data from Olgoy Lake is compared with the meteorological data from the Galuut station, as it is the only station in the catchment area of Olgoy Lake.
The result of the PCA is presented in Table 3, and the comparisons among representative data are shown in Figure 7 and Figure 8. The correlation between the Galuut station and sediment data from Olgoy Lake, PC1, with the highest proportion of 0.3, indicates that temperature is one of the dominant factors. Temperature is positively correlated with whole and mineral grain sizes (0.9 and 0.8 in PC1) (note: the smaller the phi scale, the larger the grain size). The similarity in temperature and whole grain size fluctuations has been evident since around 2000 (Figure 7B). In 1984, when a sharp temperature drop was observed, this area experienced a dzud (harsh winter). During this period (dashed line in Figure 7) and for several subsequent years, the relationship trend between temperature and whole grain size is reversed. Temperature and amorphous silica (0.7 in PC1) are negatively correlated. Amorphous silica exhibits an opposing trend to temperature, especially before the mid-1980s (Figure 7A). After the 1990s, the trend of amorphous silica on a short time scale is positively correlated with temperature, which is different from the general negative trend. In PC2, organic matter and calcium carbonate are negatively correlated (0.9 and −0.8, Table 3).
Climate data from the Galuut and Baidrag stations were analyzed with the Boontsagaan Lake sediment proxies. The PCA suggests that wind strength has a dominant impact on the sediment as PC1, with the highest proportion of 0.3. It reveals that whole and mineral grain sizes (loading of −1.0 and −0.6) are positively correlated and grain density (−0.7) is negatively correlated with wind strength (Figure 3C and Table 3). When the wind is strong, large particles with lower density are delivered to Boontsagaan Lake. Temperature and precipitation are factors in PC2, and they are negatively correlated; this is the general trend observed in the catchment area (see Section 4.1), as is shown for PC3.
With a proportion of 0.2, precipitation from the Baidrag station is negatively correlated with carbonate and amorphous silica (−0.9 and −0.7, respectively) and positively correlated with organic matter (0.9) (Table 3).
In Orog Lake, the dominant proportion (0.32) of PC1 includes grain size, calcium carbonate, and amorphous silica. Wind strength and temperature are correlated with water content in PC2. Precipitation at both stations and wind strength at only the Jinst station are in PC3 and correlated with grain density (Table 3 and Figure 3D). Strong wind near the lake (Jinst station) causes less grain density, which is similar to the findings in Boontsagaan Lake. However, Orog Lake disappeared in 2005–2007, 2009, and 2011 [24,36]. Due to multiple evaporation events, the age model of the Orog sediment core under the assumption of a constant sedimentation rate would be inappropriate, and this would make the PCA results more unreliable. Therefore, in the following discussion, only the results from Olgoy and Boontsagaan lakes are considered.

5. Discussions

5.1. Authegenic Mineral Formation

The relative abundance of minerals, mainly of allogeneic origin, provides useful information about past lake-basin hydrology, source areas, transport mechanisms, weathering processes, and erosion characteristics [50]. Moreover, carbonate minerals provide information on the chemical and temperature conditions of the lake water and precipitation [51]. As indicated by the XRD results, carbonate minerals, such as calcite, were found in all three lakes. Monohydrocalcite is a rare mineral in geological settings. It has been occasionally found in sediments from modern saline lakes, precipitated from lake waters [52]. Precipitation of monohydrocalcite occurs when the pH of the lake water is higher than 8, provided that the Mg/Ca ratio is higher than 4, as indicated by the synthesis conditions of monohydrocalcite in a laboratory setting [49]. Monohydrocalcite was found in the Boontsagaan and Olgoy lake sediments, and it stayed for a longer time in Olgoy Lake than in Boontsagaan Lake. Water temperature appears to be a factor in the preservation of monohydrocalcite, especially in Olgoy Lake. Owing to differences in elevation and natural zone, the Olgoy Lake area is much colder than the other two lake areas (Boontsagaan and Orog). Chemistry of the lake water is also a factor in the transformation of monohydrocalcite. Phosphate is known to prevent the transformation of monohydrocalcite to calcite [53]. Olgoy Lake is shallow and greenish and contains a significant amount of organic matter, most likely phosphate [54]. The water chemistry at the time of deposition also contributes to the long life of monohydrocalcite in Olgoy Lake. The sediments in Orog Lake did not preserve enough monohydrocalcite to be identified via XRD, most likely because the water temperature at the deepest depth is easily increased due to its smaller lake size than that of Boontsagaan under a similar climate. This facilitates the transformation of monohydrocalcite to calcite. Evaporation events may also contribute to the decay of monohydrocalcite.

5.2. Impact of Climate Factors on the Lake-Level Fluctuation

The influence of several environmental factors on the sedimentation processes is evident in the analyzed samples. Temperature correlates well to grain size and amount of amorphous silica in the northern catchment area, where the altitude is relatively high (Olgoy Lake). The temperature has increased over the last few decades, which was initiated by the shifting in climatic conditions since the 1980s. Kang and Hong [36] revealed that the surface area of Boontsagaan Lake has exhibited a decreasing trend over the past 20 years. An increasing trend in temperature from at the Galuut station suggests a fluctuating lake surface in Olgoy Lake, though no such observation had yet been conducted in Olgoy Lake. In general, coarse grain size is observed at the site closer to the inlet [55]. When the lake level is low, the distance between the sampling site and inlet becomes shorter, which results in the deposition of coarse sediments. In Olgoy Lake, coarse grain size under high temperature provides evidence of the decrease in the lake level, most likely due to evaporation and less precipitation. The coarse sediment exposed along the shoreline due to lower lake level may also be transported to the lake by slop flow. The behavior of amorphous silica against temperature changed after 1990. The social system changes in 1990 led to a massive increase in the number of livestock [56]. The increase in livestock caused overgrazing, land degradation, and vegetation changes, which would affect the sediment supply to the lake and water chemistry. This change in the social system may be the cause of the different behaviors of amorphous silica against temperature. Before 1990, amorphous silica originated from plants in the catchment or lake-surrounding area. Afterwards, overgrazing caused less vegetation and would have caused a lesser supply of amorphous silica from plants. Instead, amorphous silica most likely would have originated from the weathered part of minerals. After the 1990s, amorphous silica was positively correlated with temperature, indicating more input of weathered minerals under high temperature. Before that, amorphous silica increased when temperature was low. Increased precipitation under low temperature may have contributed to more vegetation and higher inputs of amorphous silica from plants to the sediment.
For Boontsagaan Lake, increased precipitation is correlated with increased organic-matter concentrations and decreased carbonate and amorphous-silica concentrations (Table 3). The Boontsagaan Lake surface was smaller during 2003–2005 and 2007–2010 [24], probably due to the increase in temperature and decrease in precipitation since 1995; moreover, the organic-matter content decreased when the lake shrank. In the southern part of the Valley, where the temperature is generally higher than in the northern area (Figure 2), high precipitation accompanied by low temperature would have increased the lake level and decreased the water salinity [57,58], which would cause increased biological activity in and around the lake. The high and often variable salinity of salt lakes results in decreased biodiversity; the higher the salinity, the fewer the species of plankton, with a decline in both the diversity index and total number of species [59,60]. Meanwhile, authigenic mineral formation under high salinity is active, resulting in high carbonate concentrations when the lake level is low as a result of lower levels of precipitation.

5.3. Wind-Blown Input

In the Valley of Gobi Lakes, wind strength is the main factor affecting the sediment characteristics. For example, grain size is larger when the wind is strong in Boontsagaan Lake (Figure 8). Density is lower when the wind is strong for all three lakes (Table 3, Figure 3). Boontsagaan Lake is large and deep. Here, aeolian input can be a significant sediment source in its central part, where the sediment core was collected. In the Valley of Gobi Lakes, active barchans formed due to the local existence of strong west–northwest winds [26]. Aeolian input could have originated from these active dunes. In arid and dry conditions, a wind-eroded material is directly supplied to the lakes, and it is a crucial source of particulate material due to strong winds and sparse vegetation cover [61,62]. The importance of aeolian activity is also evident in the studies on lake sediment or surface deposition in cold and dry regions [63].

5.4. Event Fingerprint

Dzud and earthquake events left their signature in sediment characteristics. They disrupt the typical correlation between climate and sediment. The higher fluctuations observed in the grain density between 1955 and the 1960s in Olgoy and Boontsagaan lakes (Figure 5A,B) could be the result of the earthquake in 1957, which was caused by left-lateral strike-slip movement of the Bogd fault [30] (Figure 1). Evidence of the 1905 earthquake is indicated by a spike in organic carbon and amorphous silica fluctuations in Olgoy Lake.
The disturbed correlation between grain size and temperature observed in the Olgoy Lake data (Figure 7B) could be indicative of extreme climate events. The combination of drought and white dzud (harsh winter with heavy snow) in 1983 may have impacted sediment supply processes and changed the relationship between sedimentation and climate (Figure 7 and Figure 8). The drought would have decreased grass cover, and the rich snow-meltwater would have easily eroded the resulting bare land after the white dzud.
Therefore, coarse material was supplied (Olgoy, Figure 7), even under the high lake level, when the average temperature was low. Conversely, during the white dzud years in 2000–2002 and 2009–2010 (Figure 7 and Figure 8, highlighted in gray), the correlation was not disturbed, most likely because the scale of the dzuds could have been smaller than that of the event in 1984, as indicated by the moderate temperature drop in the meteorological data. So far, it may be too speculative to detect a dzud from sediment characteristics.

5.5. Summary: Proxy of Climate

When the temperature was high, less precipitation occurred in general in the Valley of Gobi Lakes. In northern Valley of Gobi Lakes (Olgoy Lake), grain size and amorphous silica from small-scale lakes is a proxy of temperature (therefore, also related to precipitation). In southern Valley of Gobi Lakes (Boontsagaan Lake), grain size from large-scale lakes is a proxy of wind strength. Organic matter, carbonate, and amorphous-silica concentrations are the proxy of precipitation (therefore, also related to temperature). When fluctuation among proxies is disturbed, it may be caused by disasters (e.g., earthquake and dzud) or human impact.

5.6. Reconstruction of Past Climate beyond the Observation Era

Based on the temperature impact on grain size and amorphous-silica concentrations found in the Olgoy Lake sediment, we can reconstruct past temperature changes, even for the time range with no meteorological data. Regardless of less sensitivity to anomalous climatic events, such as dzuds, the long-term trend was reconstructed.
When grain size and amorphous-silica concentrations are considered as a proxy of temperature, they indicate gradually increasing temperature trends between the 1880s and 1930s, followed by a decreasing trend until the 1980s (Figure 6A). Regardless of less sensitivity to anomalous climatic events, such as dzuds, the long-term trend was reconstructed. Since then, it has increased correspondingly. This reconstruction is similar to the temperature changes in Greenland reconstructed from ice-core-oxygen isotope data [64]. On the other hand, the global climate trend decreased between 1880 and 1940 and then gradually increased (based on the NOAA data). When meteorological data from the Galuut station (near Olgoy Lake) is compared with the global temperature average, some peaks fit well, but the overall trend is different. The temperature trends in the northern valley of the study area must have been affected by local geographical and climatic conditions.
In Boontsagaan Lake, grain size is a proxy of wind strength. Furthermore, organic matter, carbonate, and amorphous-silica concentrations in Boontsagaan Lake are correlated with precipitation. Based on the data from Boontsagaan Lake, if we obtain a long core and analyses, then a record of precipitation and wind strength beyond the observation era could be reconstructed.

6. Conclusions

Comparison of metrological data from four stations shows similar climate fluctuations across the Valley of Gobi Lakes. When the temperature was high, less precipitation occurred in general. Based on the comparison between sediment characteristics and climatic conditions over the past 60 years, temperature is the most dominant factor that contributes to sediment characteristics in the northern Valley of Gobi Lakes (Olgoy Lake). Increases in temperature combined with decreases in precipitation may lower the lake level in the arid area and make the grain size at the sample site coarser by changing the distance from the inlet. Social-system changes caused changes in vegetation and material supply to the lake, affecting the proxy data. The concentration of amorphous silica in Olgoy Lake could be a proxy of vegetation, which is rich when temperature is low and precipitation levels are high, but since 1990, amorphous silica may be coming from weathered mineral mantle, owing to overgrazing and decreased sparse vegetation, and is a proxy of temperature.
High wind speed results in large grain size in Boontsagaan Lake and lower grain density in all three lakes. In the much drier area in southern part of the Valley of Gobi Lakes, grain size is a proxy of wind speed, together with grain density. According to PCA results, in Boontsagaan Lake, the higher levels of organic matter and lower carbonate and amorphous-silica levels are proxies of the higher lake level under wet periods with more precipitation. In Orog Lake, due to a less precise age model, the relationship between climate and sediment characteristics is unclear in this study.
In some sediment samples, we observed disturbed fluctuations different from the general correlation trend. Some of these fluctuations may indicate events such as earthquakes or white dzuds combined with drought.

Author Contributions

Conceptualization, N.H. and D.D.; methodology, N.H., S.O. and N.K.; validation, N.H. and K.F.; formal analysis, U.U., S.O. and Y.M.; investigation, U.U., N.H., D.D., K.F., Y.T., B.G. and T.G.; resources, N.H.; data curation, U.U.; writing—original draft preparation, U.U. and N.H.; writing—review and editing, N.H.; visualization, U.U. and T.G.; supervision, N.H.; project administration, N.H.; funding acquisition, U.U. and N.H. All authors have read and agreed to the published version of the manuscript.

Funding

This study is supported by the Japan Society for the Promotion of Science (KAKENHI Grant 16H05643), a cooperative research program of the Institute of Nature and Environmental Technology at Kanazawa University (No. 7, 2015; No. 30, 2016) and the Mongolian-Japanese Engineering Education Development Project (No. J11A15).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Acknowledgments

We would like to express our gratitude to the editor and anonymous reviewers for their comments to improve our manuscript. We also thank students from National University of Mongolia and Kanazawa University for their supports during the field work.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Location of the research area: (A) natural zone map; (B) permafrost map; (C) Boontsagaan and Orog watershed area; and (D) bathymetric maps of Olgoy Lake; (E) Orog Lake; and (F) Boontsagaan Lake (modified from [21]).
Figure 1. Location of the research area: (A) natural zone map; (B) permafrost map; (C) Boontsagaan and Orog watershed area; and (D) bathymetric maps of Olgoy Lake; (E) Orog Lake; and (F) Boontsagaan Lake (modified from [21]).
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Figure 2. Meteorological data from the Jinst station (1973–2014), Bayankhongor (BKH) station (1963–2014), Galuut station (1956–2014), and Baidrag station (1994–2014). (A) Mean annual temperature; (B) annual precipitation; (C) mean annual wind speed (data from the National Agency for Meteorology and the Environmental Monitoring, Mongolia). Numbers in bracket are the averaged values.
Figure 2. Meteorological data from the Jinst station (1973–2014), Bayankhongor (BKH) station (1963–2014), Galuut station (1956–2014), and Baidrag station (1994–2014). (A) Mean annual temperature; (B) annual precipitation; (C) mean annual wind speed (data from the National Agency for Meteorology and the Environmental Monitoring, Mongolia). Numbers in bracket are the averaged values.
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Figure 3. PCA variable graph. (A) All meteorological stations; (B) Olgoy Lake sediment proxies with the Galuut station; (C) Boontsagaan Lake sediment proxies with the Galuut and Baidrag stations; and (D) Orog Lake sediment proxies with the Bayankhongor (BKH) and Jinst stations. T stands for temperature, w stands for wind, and p stands for precipitation.
Figure 3. PCA variable graph. (A) All meteorological stations; (B) Olgoy Lake sediment proxies with the Galuut station; (C) Boontsagaan Lake sediment proxies with the Galuut and Baidrag stations; and (D) Orog Lake sediment proxies with the Bayankhongor (BKH) and Jinst stations. T stands for temperature, w stands for wind, and p stands for precipitation.
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Figure 4. Profile of excess 210Pb concentration against mass depth of (A) Olgoy, (B) Boontsagaan, and (C) Orog lakes. Shaded data in Table 2 are plotted.
Figure 4. Profile of excess 210Pb concentration against mass depth of (A) Olgoy, (B) Boontsagaan, and (C) Orog lakes. Shaded data in Table 2 are plotted.
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Figure 5. XRD results of the sediment from (A) Olgoy, (B) Boontsagaan, and (C) Orog lakes.
Figure 5. XRD results of the sediment from (A) Olgoy, (B) Boontsagaan, and (C) Orog lakes.
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Figure 6. Sediment characteristics of (A) Olgoy, (B) Boontsagaan, and (C) Orog lakes (water content % (water), grain density g/cm3, organic matter % (organic), carbonate %, amorphous silica %, whole grain size φ (whole G.S), and mineral grain size φ (mineral G.S)). Earthquake events are indicated in brown. The dried event is indicated in gray.
Figure 6. Sediment characteristics of (A) Olgoy, (B) Boontsagaan, and (C) Orog lakes (water content % (water), grain density g/cm3, organic matter % (organic), carbonate %, amorphous silica %, whole grain size φ (whole G.S), and mineral grain size φ (mineral G.S)). Earthquake events are indicated in brown. The dried event is indicated in gray.
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Figure 7. Comparison between meteorological data and sediment characteristics of Olgoy lake. (A) Temperature versus amorphous silica content and (B) temperature versus whole grain size. The drought combined with the dzud record is covered with a dashed line, and the white dzud is highlighted in gray.
Figure 7. Comparison between meteorological data and sediment characteristics of Olgoy lake. (A) Temperature versus amorphous silica content and (B) temperature versus whole grain size. The drought combined with the dzud record is covered with a dashed line, and the white dzud is highlighted in gray.
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Figure 8. Comparison between meteorological data and sediment characteristics of Boontsagaan Lake. (A) Wind versus mineral grain size and (B) precipitation versus carbonate. The drought combined with the dzud record is covered with a dashed line, and the white dzud is highlighted in gray.
Figure 8. Comparison between meteorological data and sediment characteristics of Boontsagaan Lake. (A) Wind versus mineral grain size and (B) precipitation versus carbonate. The drought combined with the dzud record is covered with a dashed line, and the white dzud is highlighted in gray.
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Table
Table 1. Sediment-core information.
Table 1. Sediment-core information.
Lake NameCore NameCore LengthWater DepthLatitudeLongitude
OlgoyOL0243 cm1 m46°33′07.72″ N100°05′38.88″ E
OrogOR0243 cm1 m45°03′17.60″ N100°37′40.87″ E
BoontsagaanBTS0131 cm9.7 m45°36′17.20″ N099°13′11.80″ E
BoontsagaanBTS0231 cm10 m45°36′19.50″ N099°12′28.90″ E
Table
Table 2. Excess 210Pb results from Olgoy, Boontsagaan, and Orog Lakes. (Ages are calculated under the assumption of constant initial radioactivity). Shaded data are utilized to calculate the sedimentation rate.
Table 2. Excess 210Pb results from Olgoy, Boontsagaan, and Orog Lakes. (Ages are calculated under the assumption of constant initial radioactivity). Shaded data are utilized to calculate the sedimentation rate.
Sample IDCore Depth (cm)Mass Depth (g/cm2)210Pbex (Bq/kg)Apparent Age (a)210Pbex Error (%)
Olgoy 010.50.11500.510.6
Olgoy 054.51.31139.514.2
Olgoy 109.54.68917.114.8
Olgoy 1514.57.0185-12
Olgoy 2019.511.33745.110.8
Olgoy 2524.515.21672.316.6
Olgoy 3029.518.71379.616.6
Olgoy 3534.523.7--13
Olgoy 4039.526.72459.417
BT02 010.50.22222.511.41
BT02 031.50.72084.69.43
BT02 052.51.12035.49.5
BT02 073.51.41956.79.03
BT02 094.51.716811.510.5
BT02 115.52.117011.110.54
BT02136.52.413817.812.86
BT02 178.53.213219.214.12
BT02 2110.54.012720.515.45
BT02 3517.56.88035.320.31
BT02 4120.58.36343.028.72
BT02 4522.59.66044.626.81
BT02 5527.516.02968.079.56
Orog 010.50.31280.015.5
Orog 033.52.75825.420.2
Orog 055.53.55228.813
Orog 1010.59.83541.716.1
Orog 1313.513.83740.123.3
Orog 1515.517.71177.623.5
Orog 1818.521.52059.924.3
Orog 2020.524.23046.922.8
Orog 2323.528.51765.923.8
Orog 2525.531.35101.624.5
Orog 3030.536.9--24.6
Orog 3535.543.4889.117.7
Table
Table 3. PCA of meteorological data and sediment characteristics for Olgoy Boontsagaan and Orog lakes (highest (≥0.5). Coefficients for climatic factors are marked in bold, and temp stands for temperature, prec stands for precipitation, and var stands for variance).
Table 3. PCA of meteorological data and sediment characteristics for Olgoy Boontsagaan and Orog lakes (highest (≥0.5). Coefficients for climatic factors are marked in bold, and temp stands for temperature, prec stands for precipitation, and var stands for variance).
ProxiesOLGOYProxiesBOONTSAGAANProxiesOROG
PC1PC2PC3ComPC1PC2PC3ComPC1PC2PC3Com
Water content−0.40.7−0.32.0Water content0.80.20.41.5Water content0.40.9−0.11.4
Grain density-0.20.51.3Grain density−0.7-0.31.3Grain density−0.1−0.20.61.3
Organic−0.10.90.11.0Organic−0.20.10.91.1Organic0.30.1−0.11.3
Carbonate0.4−0.8−0.11.5Carbonate−0.2−0.1−0.91.1Carbonate0.9-0.21.1
Amorphous silica0.7−0.40.21.7Amorphous silica−0.30.2−0.71.5Amorphous silica0.90.30.11.2
Whole grain size0.9−0.10.11.0Whole grain size−0.60.4−0.32.3Whole grain size0.9−0.1−0.11.1
Mineral grain size0.8−0.1-1.0Mineral grain size−1.0−0.1-1.0Mineral grain size0.8−0.2-1.1
Galuut temp−0.80.2−0.11.2Galuut temp0.1−0.90.21.2BKH temp−0.30.9-1.2
Galuut wind0.10.3−0.81.4Galuut wind0.9−0.10.21.1BKH wind0.20.8−0.11.2
Galuut prec0.3-0.71.4Galuut prec0.30.9-1.2BKH prec0.3−0.10.81.2
Baidrag temp0.2−0.9−0.11.1Jinst temp−0.10.9−0.31.3
Baidrag wind0.8--1.0Jinst wind0.40.3−0.72.1
Baidrag prec0.00.70.61.9Jinst prec0.1−0.10.91.0
SS loadings3.12.41.5 SS loadings4.23.12.7 SS loadings3.63.22.6
Proportion var0.30.20.2 Proportion var0.30.20.2 Proportion var0.30.30.2
Cumulative var0.30.60.7 Cumulative var0.30.60.8 Cumulative var0.30.50.7
Proportion explain0.50.30.2 Proportion explain0.40.30.3 Proportion explain0.40.30.3
Cumulative proportions0.50.81.0 Cumulative proportions0.40.71.0 Cumulative proportions0.40.71.0
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Udaanjargal, U.; Hasebe, N.; Davaasuren, D.; Fukushi, K.; Tanaka, Y.; Gankhurel, B.; Katsuta, N.; Ochiai, S.; Miyata, Y.; Gerelmaa, T. Characteristics of Lake Sediment from Southwestern Mongolia and Comparison with Meteorological Data. Geosciences 2022, 12, 7. https://doi.org/10.3390/geosciences12010007

AMA Style

Udaanjargal U, Hasebe N, Davaasuren D, Fukushi K, Tanaka Y, Gankhurel B, Katsuta N, Ochiai S, Miyata Y, Gerelmaa T. Characteristics of Lake Sediment from Southwestern Mongolia and Comparison with Meteorological Data. Geosciences. 2022; 12(1):7. https://doi.org/10.3390/geosciences12010007

Chicago/Turabian Style

Udaanjargal, Uyangaa, Noriko Hasebe, Davaadorj Davaasuren, Keisuke Fukushi, Yukiya Tanaka, Baasansuren Gankhurel, Nagayoshi Katsuta, Shinya Ochiai, Yoshiki Miyata, and Tuvshin Gerelmaa. 2022. "Characteristics of Lake Sediment from Southwestern Mongolia and Comparison with Meteorological Data" Geosciences 12, no. 1: 7. https://doi.org/10.3390/geosciences12010007

APA Style

Udaanjargal, U., Hasebe, N., Davaasuren, D., Fukushi, K., Tanaka, Y., Gankhurel, B., Katsuta, N., Ochiai, S., Miyata, Y., & Gerelmaa, T. (2022). Characteristics of Lake Sediment from Southwestern Mongolia and Comparison with Meteorological Data. Geosciences, 12(1), 7. https://doi.org/10.3390/geosciences12010007

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