17:15 〜 18:30
[MIS01-P03] The Lacustrine Sediment Analysis to Understand the Past Environmental Changes and the Effect of Ongoing Global Warming in Valley of The Gobi Lakes, Mongolia: Analyses of Tsagaan Lake Sediment
キーワード：Lacustrine sediment, Short-time series, Environmental changes, Tsagaan lake
Environmental change causes a large influence on a significant part of the world's population in the fragile ecological systems of arid central Asia concerning livestock husbandry, nomadic migration, irrigation farming, and stability of political societies (Pederson et al., 2014; Yu et al., 2017). For instance, a portion of the population depends on the nomadic husbandry in Mongolia. This lifestyle is under the direct impact on the natural disasters and vulnerable to environmental changes. One of the severe environmental issue is desertification, that is observed in 67% of the total area in Mongolia (Mongolian Environment, 2017).
The most parts of Mongolia are in arid and semi-arid region with extreme climate conditions. The air temperature fluctuates approximately between -40OC /winter/ and 40OC /summer/. The climate of Mongolia is controlled by Westerlies, East Asian Summer Monsoon (EASM), and Siberian anticyclone. Therefore, Mongolia is the suitable region to understand the past climate system in long or short-time series to predict future trends.
There are few studies conducted in this region. Komatsu et al., (2001) identified paleoshorelines on the east edge of the Tsagaan lake basin and other sites. For late Quaternary, the expanded lake had covered the greater part of the arid region including “The Valley of the Gobi Lakes” and “Great Valley of the lakes” in Mongolia (Lehmkuhl & Lang, 2001). However, the current condition has drastically altered and become drier for hydrology and climatic comparing to that time. However, the large lakes (e.g., Buuntsagaan and Orog lakes) are extant until nowadays fed by rivers originated in the Mountain area. For this study, Tsagaan lake (45O33'N, 100O2'E) in “Valley of the Gobi lakes”, a small ephemeral lake in the arid region is studied.
Lacustrine sediment of the short core was taken at Tsagaan lake by a Russian peat sampler in order to reconstruct environmental changes of short time series of last 100-150 years in the drainage basin or region. The short core samples were divided into 3 parts that is being the upper part /0-50 cm/, the middle part /50-90 cm/, and the lower part /90-130 cm/. The upper part was predominantly greyish silt, interrupted 5 cm thick brownish sand layer between 38-45 cm. The middle part is dominated by whitish clay with intercalated sand spots at ~ 67 cm, ~75 cm, and ~82 cm. The lower part was dominated by greyish silt and sand layer with the spotted distribution. We cut the sample every 1 cm the multiproxy analysis including water content, organic matter, carbonate, amorphous silica, and grain size to reconstruct sedimentation and climatic process in the study area. The water content was measured by desiccating a given amount of the sediment at 105°C. The samples of 50±3 mg were dried at 77°C for 24 hours followed by the treatment with 10% hydrogen peroxides (H2O2) for 24 hours to estimate organic matter concentration. Carbonate in the sediment was dissolved by 1-N hydrochloric acid (HCl) to calculate the concentration. The amorphous silica content was estimated by 0.1 ml solution taken after NA2CO3 treatment using the ICP-OES instrument. Mineral and Whole grain size were measured by SALD2200 laser diffraction particle size analyzer. The age dating of sediments was carried out by the RI method (210 Lead) due to the short time series of the sediment.
The accumulated sediment proxies can reconstruct the changes in regional climatic and hydrological conditions. For example, the whole and mineral grains size fraction can indicate the sedimentation process (river discharge changes, wind accumulation activity, and other factors), the change in carbonate deposit may associate with water level changes, the organic matter accumulation reflects organic productivity in the catchment area. Consequently, we’re identifying the effect of ongoing global warming and future trend of climate changes in the arid region from the lacustrine sediment sequences in a short time scale.
The most parts of Mongolia are in arid and semi-arid region with extreme climate conditions. The air temperature fluctuates approximately between -40OC /winter/ and 40OC /summer/. The climate of Mongolia is controlled by Westerlies, East Asian Summer Monsoon (EASM), and Siberian anticyclone. Therefore, Mongolia is the suitable region to understand the past climate system in long or short-time series to predict future trends.
There are few studies conducted in this region. Komatsu et al., (2001) identified paleoshorelines on the east edge of the Tsagaan lake basin and other sites. For late Quaternary, the expanded lake had covered the greater part of the arid region including “The Valley of the Gobi Lakes” and “Great Valley of the lakes” in Mongolia (Lehmkuhl & Lang, 2001). However, the current condition has drastically altered and become drier for hydrology and climatic comparing to that time. However, the large lakes (e.g., Buuntsagaan and Orog lakes) are extant until nowadays fed by rivers originated in the Mountain area. For this study, Tsagaan lake (45O33'N, 100O2'E) in “Valley of the Gobi lakes”, a small ephemeral lake in the arid region is studied.
Lacustrine sediment of the short core was taken at Tsagaan lake by a Russian peat sampler in order to reconstruct environmental changes of short time series of last 100-150 years in the drainage basin or region. The short core samples were divided into 3 parts that is being the upper part /0-50 cm/, the middle part /50-90 cm/, and the lower part /90-130 cm/. The upper part was predominantly greyish silt, interrupted 5 cm thick brownish sand layer between 38-45 cm. The middle part is dominated by whitish clay with intercalated sand spots at ~ 67 cm, ~75 cm, and ~82 cm. The lower part was dominated by greyish silt and sand layer with the spotted distribution. We cut the sample every 1 cm the multiproxy analysis including water content, organic matter, carbonate, amorphous silica, and grain size to reconstruct sedimentation and climatic process in the study area. The water content was measured by desiccating a given amount of the sediment at 105°C. The samples of 50±3 mg were dried at 77°C for 24 hours followed by the treatment with 10% hydrogen peroxides (H2O2) for 24 hours to estimate organic matter concentration. Carbonate in the sediment was dissolved by 1-N hydrochloric acid (HCl) to calculate the concentration. The amorphous silica content was estimated by 0.1 ml solution taken after NA2CO3 treatment using the ICP-OES instrument. Mineral and Whole grain size were measured by SALD2200 laser diffraction particle size analyzer. The age dating of sediments was carried out by the RI method (210 Lead) due to the short time series of the sediment.
The accumulated sediment proxies can reconstruct the changes in regional climatic and hydrological conditions. For example, the whole and mineral grains size fraction can indicate the sedimentation process (river discharge changes, wind accumulation activity, and other factors), the change in carbonate deposit may associate with water level changes, the organic matter accumulation reflects organic productivity in the catchment area. Consequently, we’re identifying the effect of ongoing global warming and future trend of climate changes in the arid region from the lacustrine sediment sequences in a short time scale.