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Article

Holocene Paleoclimate Changes around Qinghai Lake in the Northeastern Qinghai-Tibet Plateau: Insights from Isotope Geochemistry of Aeolian Sediment

by
Qiang Peng
1,2,
Chongyi E
1,2,3,*,
Xiangzhong Li
3,4,
Yongjuan Sun
1,2,3,
Jing Zhang
1,2,3,
Shuaiqi Zhang
1,2,
Yunkun Shi
1,2,
Xianba Ji
1,2 and
Zhaokang Zhang
1,2
1
Qinghai Provincial Key Laboratory of Physical Geography and Environmental Process, College of Geographical Sciences, Qinghai Normal University, Xining 810008, China
2
Key Laboratory of Tibetan Plateau Land Surface Processes and Ecological Conservation (Ministry of Education), Qinghai Normal University, Xining 810008, China
3
Academy of Plateau Science and Sustainability, People’s Government of Qinghai Province and Beijing Normal University, Xining 810008, China
4
Yunnan Key Laboratory of Earth System Science, Yunnan University, Kunming 650500, China
*
Author to whom correspondence should be addressed.
Atmosphere 2024, 15(7), 833; https://doi.org/10.3390/atmos15070833
Submission received: 21 April 2024 / Revised: 4 July 2024 / Accepted: 11 July 2024 / Published: 12 July 2024
(This article belongs to the Special Issue Paleoclimate Changes and Dust Cycle Recorded by Eolian Sediments)
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Abstract

:
The stable carbon isotope composition of total organic matter (δ13Corg) has been utilized in aeolian sediments, serving as an indicator for reconstructing terrestrial paleoenvironments. The Qinghai Lake (QHL) Basin is a climate-sensitive region of significant importance in paleoclimatic reconstruction. However, the reconstructed climatic variations based on δ13Corg in aeolian sediments in the QHL Basin in the northeastern Qinghai-Tibet Plateau (QTP) are lacking, and their paleoclimatic significance remains poorly understood. By conducting δ13Corg measurements on the Niaodao (ND) aeolian profile near QHL, we reconstructed the paleoclimate changes of 11 ka–present. The variation range of the δ13Corg values in the ND profile indicated the terrestrial ecosystems were not the sole contributor to lacustrine organic matter. The δ13Corg values are an indicator of historical temperature changes in the study area, exhibiting similar trends with the reconstruction of Chinese summer temperatures, East Asian air temperature, global temperature, and Northern Hemisphere summer insolation at 37° N. The temperature increased with high frequency and amplitude oscillations, with strong aeolian activity and low total organic carbon accumulation during the Early Holocene. The temperature was maintained at a high and stable level, with the weakest aeolian activity and intensified pedogenesis during the Middle Holocene. The temperature decreased at a high rate, with renewed aeolian activity and weak pedogenesis during the Late Holocene.

1. Introduction

The Qinghai-Tibet Plateau (QTP) is situated at a climatic crossroads where the westerly system, Indian Summer Monsoon (ISM), and East Asian Summer Monsoon (EASM) strongly interact. The Qinghai Lake (QHL) Basin is located in the northeastern part of the QTP and is one of the most climate-sensitive regions on the plateau. This is of significant importance for paleoclimatic reconstruction [1]. Lacustrine sediments are important carriers for climate reconstruction. A spectrum of environmental and climatological reconstructions has been executed in the QHL, predicated on a diversity of climatological proxies [2,3,4,5,6,7]. Numerous studies have employed a variety of biogeochemical examinations of QHL sediments to reconstruct the regional environmental evolution [2,4,8]. However, there researchers disagree on the interpretation of their environmental significance. The stable carbon isotope composition of total organic matter (δ13Corg) is frequently used to trace paleoenvironmental changes in lakes [4,9]. This research suggests a gradual trend from the warm and wet Early Holocene to the cool and dry Late Holocene. High-resolution and continuous climatic records were obtained from lacustrine sediments. However, radiocarbon dating of sediment cores from the QHL faces challenges owing to the lake reservoir effect [10,11]. This refers to the discrepancy between the calendar age and that of the organisms or materials found within the lake sediment owing to the mixing of water with varying residence times and the incorporation of older carbon from the catchment area [11,12]. Additionally, conflicting proxies within lacustrine sediments contribute to the controversy regarding the Holocene climatic fluctuations observed in the QHL [1,2,10,11]. The climate of the QHL area has been suggested to have been dry in the Middle Holocene, compared with the wettest Early Holocene, as inferred from carbonate and ostracod shell δ18O values [1]. However, based on pollen assemblage and redness, other studies have suggested a wet climate in the Middle Holocene from the Early Holocene [2].
δ13Corg has been widely used in terrestrial sediment as a significant indicator for reconstructing the terrestrial paleoenvironment worldwide [13,14,15,16]. In the peat bogs of the QHL Basin, plant δ13Corg is regarded as a crucial indicator of summer precipitation. δ13Corg is used to trace precipitation variation in the study area in the past 8.4 ka [17]. Holocene aeolian profiles are widely distributed throughout this region [18]. Several studies have been conducted on the δ13Corg in aeolian sediments from the QHL Basin and infer that the organic constituents present in the QHL sediments during the Holocene were predominantly derived from the aquatic biota inhabiting the lake [19]. However, owing to the low deposition rate and discontinuity in aeolian sediment, the systematic reconstructed climatic variations based on δ13Corg in aeolian sediments in the QHL Basin remain lacking. In this study, the Niaodao (ND) aeolian sediment profile, with a high resolution and continuity on millennium scales [20], around QHL was selected to analyze the variation of the δ13Corg and total organic carbon (TOC). There is increasing evidence that temperature has played a crucial role in influencing the soil δ13Corg during the Holocene [16,21]. This opens up the possibility of using the δ13Corg indicator to quantify Holocene temperatures [21,22]. The δ13Corg of the ND profile was used as a proxy of temperature change. In conjunction with the high-resolution chronological framework, TOC, low-frequency magnetic susceptibility (χlf), and median grain size (Mz), environmental records on the QHL Basin were reconstructed to further understand climate change on the northeastern QTP during the Holocene. This study further extends the applicability of the δ13Corg indicator in paleoclimate reconstruction.

2. Materials and Methods

2.1. Study Area

QHL (36.53–37.25° N, 99.61–100.78° E, 3198 m), nestled in the northeastern region of the QTP, holds the distinction of being the largest inland lake in China. Early to Middle Pleistocene lakes began to form in the Qinghai Basin as tectonism topographically separated it from the Yellow River drainage [18]. As of 2019, the water surface area of the QHL had reached 45,190.2 km2 [23] (Figure 1). The climate in the QHL Basin is influenced by both the Asian monsoon (EASM and ISM) and westerly system (Figure 1). The winters are dry and cold, whereas the summers are wet and warm. The temperature in this area varies significantly with altitude, with an annual average temperature ranging from −4.5 to 4.0 °C. The average annual precipitation is 350–450 mm, with a decreasing trend from southeast to northwest [24]. The Gangcha meteorological station, positioned 10 km north of QHL, recorded a total precipitation of 370 mm and an average temperature of −0.6 °C between 1975 and 2011. The maximum wind speed, registered at 18 m s−1, predominantly occurs during spring [20]. The predominant vegetation types in the region are temperate steppes, deserts, and alpine meadows.

2.2. Samples and Analytical Methods

In this study, we specifically targeted the ND profile (37.04° N, 99.74° E, 3215 m) (Figure 1). The surface vegetation in this area is dominated by arid and semi-arid vegetation, including Potentilla fruticose L., Achnatherum splendens, and Stipa krylovii. With a substantial thickness of approximately 600 cm, the ND profile was located on the second terrace of the Buha River. The uppermost 30 cm of this profile consisted of modern soil enriched with plant roots. At greater depths, that is, strata at 165–240 cm and 310–350 cm, we encountered two comparatively dark, compacted, erosion-defying sandy ancient paleosols [20] (Figure 2). We meticulously collected 95 bulk samples and 22 optically stimulated luminescence (OSL) samples within a height range of 0–475 cm. The OSL samples were used for age testing, whereas the bulk samples were analyzed for TOC. Additionally, we selected 53 bulk samples at intervals of 5–15 cm for δ13Corg testing.
Pretreatment and test analyses of the δ13Corg sample were conducted at the Stable Isotope Laboratory at the Institute of Earth Environment, Chinese Academy of Sciences. The organic carbon samples were dried in an oven at 50 °C, and visible animal and plant residues were removed before grinding the samples to a 100 μm mesh size. To eliminate carbonates, approximately 3 g of the sample was reacted with excess (2 mol/L) hydrochloric acid at ambient temperature for one day. To achieve neutrality, the specimen was exhaustively rinsed with deionized water, subsequently dried at 40 °C, and further pulverized. The desiccated samples were incinerated within vacuum-sealed quartz tubes at 850 °C for a duration of 4 h, with 1 g each of CuO, Cu, and Pt foil. The resultant carbon dioxide was isolated via cryogenic purification. The isotopic ratios of the purified CO2 were quantified using a Finnigan MAT 251 gas source mass spectrometer. These isotopic ratios are documented in δ-notation and articulated as per mil (‰) variances relative to the V-PDB benchmark for carbon [25]. Replicate analyses of the 53 samples showed an average standard deviation of 0.2‰. The experimental procedure is shown in Figure 3.
The pretreatment and analysis of TOC samples were conducted at the Qinghai Provincial Key Laboratory of Physical Geography and Environmental Processes, Qinghai Normal University. The samples were dried in an oven at 50 °C, and visible animal and plant residues were meticulously removed and ground to a 200 μm mesh. Approximately 0.3 g of samples was treated with 10% HCl at an ambient temperature. After completion of the reaction, the samples were washed repeatedly with deionized water until the pH exceeded 6. The samples were then dried at 40 °C and analyzed using a Vario TOC cube Analyzer [26]. The overall precision of the TOC analysis was less than 0.5%.
Analysis of χlf and Mz, along with OSL dating, was conducted at the Qinghai Provincial Key Laboratory of Physical Geography and Environmental Processes, Qinghai Normal University. Detailed information regarding the specific experimental process can be found in the relevant literature [20].

3. Results

In accordance with the results of the OSL dating [20], the profile predominantly documents the compositional features of the δ13Corg and TOC in the aeolian sediment during the Holocene.
The ND profile suggested that the regional environmental changes from 11 ka to the present. During this period, the δ13Corg values exhibited a range spanning from −25.24‰ to −22.72‰, with an average of −23.58‰. During the Early Holocene (11–9 ka), the δ13Corg values ranged from −23.93‰ to −22.93‰, averaging −23.30‰. The Middle Holocene (9–4 ka) witnessed the δ13Corg values varying between −23.43‰ and −22.72‰, with an average of −23.19‰. During the Late Holocene (4–0 ka), the δ13Corg values spanned from −25.24‰ to −22.99‰, with an average of −23.91‰. From the overall trend of the curve, the δ13Corg values exhibit significant fluctuations during the Early Holocene, gradually shifting towards positive values. Throughout the Middle Holocene, a predominantly positive trend persisted. However, beginning in the Late Holocene, a pronounced negative trend emerged (Figure 4a).
From 11 ka to the present, the TOC values exhibited a range spanning from 0.32 to 1.66 wt%, with an average of 0.85 wt%. During the Early Holocene (11–9 ka), the TOC values ranged from 0.32 to 0.73 wt%, with an average of 0.52 wt%. During the Middle Holocene (9–4 ka), the TOC values ranged from 0.52 to 1.47 wt%, with an average of 1.00 wt%. The TOC values ranged from 0.59 to 1.66 wt%, with an average of 0.92 wt% during the Late Holocene (4–0 ka). Analyzing the overall trend throughout the Early Holocene, the TOC values were comparatively subdued, exhibiting a gradual ascent to reach a plateau of elevated levels throughout the Middle Holocene. The overall fluctuation range expanded significantly, the trend gradually decreased during the Late Holocene, and the TOC reached its peak at approximately 2 ka (Figure 4b).

4. Discussion

4.1. Terrestrial Ecosystem Is Not a Major Contributor to the Lake Organic Matter

The δ13Corg values of the ND profile spanned from −25.24‰ to −22.72‰, exhibiting a fluctuation amplitude of 2.52‰. The Zhongyangchang (ZYC) aeolian profile is located at the southeastern margin of the QHL [19]. This profile is similar to the ND profile and can be divided stratigraphically from top to bottom into modern soil, loess containing a paleosol, and aeolian sand. The δ13Corg values range from −25.8‰ to −24.8‰, with an amplitude of 1‰ [19]. The δ13Corg values of the two profiles had a small change. However, the variation range of the δ13Corg in the sediment of QHL is between −30‰ and −20‰, with an amplitude of 10‰ [2]. The aquatic plants are primarily dominated by Cladophora in modern QHL, and the δ13Corg values ranged from −33.6‰ to −28.6‰ [4]. Genggahai Lake is a diminutive and superficial aquatic entity located in the Gonghe Basin in the northeastern QTP. The oscillation magnitude of δ13Corg within the lacustrine sediment was approximately 12‰ [27] (Figure 5A). The δ13Corg values of terrestrial ecosystems have changed slightly, whereas those of lacustrine ecosystems have significantly changed during the Holocene. Studies of the δ13Corg, δ15Ntot, and atomic Corg/Ntot ratio of sediments from Lake Ximencuo in the eastern QTP show that the bulk organic matter in these lake sediments originates from a mixed source comprising autochthonous algae and aquatic and terrestrial plant inputs [28]. As inferred from the preceding analysis, irrespective of the lacustrine spatial extent, the content and variation of the δ13Corg diverge from terrestrial ecosystem deposits. Terrestrial ecosystems were not the principal contributors to lacustrine organic matter during the Holocene.
Research has shown that TOC around the QHL undergoes little degradation in arid and cold climates [19,29]. The TOC values of the ND profile spanned from 0.32 to 1.66 wt%, whereas that of the ZYC profile range from 0.12 to 3.19 wt% [19]. TOC values were lower in the Early Holocene and higher in the Late Holocene. During the Early Holocene, the TOC values were low, whereas they were considerably elevated during the Middle and Late Holocene. However, the TOC values in lacustrine sediments of the QHL are higher than that in terrestrial sediments, ranging from 0.4 to 9.0 wt%. Its trend was higher at 10.5–4 ka, and its content decreased after 4 ka [2]. The TOC values of the Genggahai Lake sediments were significantly higher than those of the terrestrial sediments [27] (Figure 5B). The TOC content and its variations in the terrestrial aeolian and lacustrine sediments indicate that the organic matter sources of the sediments from Genggahai and QHL were not primarily derived from terrestrial ecosystems during the Holocene. In the Early Holocene, the lake water level was low [4], the summer monsoon was enhanced, the summer sunshine duration was long [1,4], and the algae (mainly Cladophora) in the lake increased. In the Middle and Late Holocene, the water level was several meters higher than it is now [30], and algae (mainly Cladophora) became the dominant contributor to lacustrine organic matter [31], resulting in more negative δ13Corg values in lacustrine sediments. Therefore, the organic matter in the lacustrine sediments of the QHL may have been derived from aquatic organisms.

4.2. The Impact of Temperature on the δ13Corg Values

In the study of the relationship between modern vegetation and δ13Corg values, the soil δ13Corg values have been observed to be ≤−24‰ when the prevalence of the C3 vegetation is at its maximum (100%), and the soil δ13Corg values are ≥−14‰ when the dominance of the C4 vegetation is absolute (100%) [32]. The δ13Corg values of the ND profile ranged from −25.24‰ to −22.72‰, with an average of −23.58‰. Researchers have found that the isotopic fractionation occurring during the metamorphosis of vegetal remnants into organic matter after deposition may lead to a δ13Corg matter change of approximately 1‰ [33]. Therefore, the δ13Corg values of vegetation in the ND profile should be between −26.24‰ and −23.72‰, with an average of −24.58‰. The vegetation composition of the ND profile was predominantly C3 species, with the influence of C4 species largely overlooked during the Holocene. The fluctuation in the δ13Corg values of the ND profile primarily reflects the reaction of the C3 vegetation to the climatic conditions, rather than the change in the relative abundance of the C3 and C4 vegetation.
Numerous elements can potentially impact the composition of the δ13Corg values of vegetation with the most important being atmospheric CO2 concentration, precipitation, and temperature [17,21,34]. Research shows that for every 100 ppmv increase in atmospheric CO2 concentration, the δ13Corg of vegetations decreases by 2‰ [35]. During the Holocene, the overall change range is 20 ppmv, indicating that the influence of atmospheric CO2 concentration changes on the composition of δ13Corg is approximately 0.4‰ [36]. The variation range of the δ13Corg values recorded by aeolian sediment in the ND profile is approximately 2.5‰. The change in CO2 concentration is not primarily influencing the δ13Corg values of δ13Corg plants. Numerous studies have shown that the relative humidity, as well as the amount of precipitation, is negatively relative to the δ13Corg of terrestrial plants [37,38]. Based on the quantitative study of the carbon isotope composition of C3 plants and precipitation in Northern China, the average carbon isotope composition of C3 plants decreased by approximately 0.49 ‰ for every 100 mm increase in precipitation [38]. During the late Holocene, the δ13Corg value of the ND section decreased by 1.25‰, and the precipitation increased by about 255 mm, which was inconsistent with the gradual decrease in precipitation in the Late Holocene [39] (Figure 6b). Therefore, precipitation is not a climatic factor affecting the δ13Corg values of the aeolian sediments in the QHL Basin since the Holocene.
Through extensive research on modern surface soil δ13Corg across the QTP, the δ13Corg values have been observed to be predominantly influenced by temperature and precipitation [21,40,41]. In Northern China, the study of C3 plants in the 400 mm annual average precipitation isoline has discovered a significant positive correlation between the δ13Corg values of C3 plants and the annual average temperature [21]. The Gangcha weather station, situated 50 km from the ND profile, recorded a mean annual precipitation of 370 mm between 1975 and 2011 [20]. The ND profile was located near the QHL, and the climatic conditions were similar to those at Gangcha station. The δ13Corg values in aeolian sediments may be influenced by petrogenic carbon [42]. In the study of δ13Corg in loess since the Last Glacial Period in Northwest China, the δ13Corg of loess falls into roughly the same value range as that of parent rocks in the dust source area [43]. The ND profile is also in this study area, and therefore the δ13Corg of parent rocks has less influence on the isotopes of sediments.
The significance of δ13Corg in soils is consistent with the plant. Research shows that the δ13Corg composition of C3 plants is more strongly influenced by temperature in arid and semi-arid regions [44,45,46]. Thus, temperature may be the principal factor influencing the soils’ δ13Corg values in the studied region. The researchers have found that the δ13Corg and δ15Ntot proxies of the lacustrine sediment record air temperature variations in the growing season in the Ximencuo Lake area [28]. Other researchers have found that the variation of δ13Corg values in a Holocene loess profile, located in the eastern Hunshandake Sandy Land, showed significant positive correlations with accumulated temperatures above 10 and 0 °C [16]. The δ13Corg variability within the ND profile exhibits limited amplitude, suggesting that vegetation composition in this region has undergone minimal alterations, and the ecosystem remains relatively stable during the Holocene. The modern ecosystem near the ND profile is a temperate steppe and desert. Therefore, we used δ13Corg analysis of the ND profile as a proxy of temperature change in the QHL Basin.
In this study, the δ13Corg of the ND profile was compared with the summer temperature of the QHL alkenone record during the Holocene [47]. We found that the δ13Corg is different from the above temperature reconstruction, but the general trend is consistent. However, the comparison of the δ13Corg and East Asian temperatures inferred from brGDGTs in loess [48]; the summer temperatures in Northern China reconstructed by integrating instrumental data, proxy records, and model simulations [49]; and the global temperature anomaly from 73 globally distributed records [50] reveal a substantial degree of similarity (Figure 5). This may be due to the lake reservoir effect, which has been noted across numerous lacustrine sediments, particularly in the cold and dry lakes in the northeast of QTP [2,12]. Aeolian sediments have certain limitations, such as low temporal resolution and discontinuous deposition. During the Middle Holocene, sedimentation rates were low, resulting in challenges in representing the finer details of the ND profile [20].
Atmosphere 15 00833 g006
Figure 6. Comparison of the δ13Corg in the ND profile of QHL with other indicators during the Holocene. (a) The δ13Corg of the ND profile, (b) the quantitative precipitation reconstruction of QHL [39], (c) the summer temperature of QHL [47], (d) the reconstruction of summer temperature of China [49], (e) the East Asian air temperature [48], and (f) the global temperature [50].
Figure 6. Comparison of the δ13Corg in the ND profile of QHL with other indicators during the Holocene. (a) The δ13Corg of the ND profile, (b) the quantitative precipitation reconstruction of QHL [39], (c) the summer temperature of QHL [47], (d) the reconstruction of summer temperature of China [49], (e) the East Asian air temperature [48], and (f) the global temperature [50].
Atmosphere 15 00833 g006

4.3. Temperature Changes in QHL Basin during the Holocene Recorded in the ND Profile

In many studies in Northern China, the δ13Corg values of C3 plants have been found to exhibit a significant positive correlation with temperature [21,51]. When the temperature decreases, the loss of water evaporation decreases and the fractionation of carbon isotopes increases; thus, the carbon isotopes of plants decrease [37]. This study reconstructed the temperature record in the area by employing a comprehensive analysis of the δ13Corg and TOC analysis, in conjunction with a high-resolution chronological framework, the χlf and the Mz [20]. These conventional proxy indices were compared with the Northern Hemisphere summer insolation at 37° N [52] during the Holocene (Figure 7). The δ13Corg values observed in the ND profile exhibited a strong concordance with the Northern Hemisphere summer insolation at 37° N. The impact of summer insolation on temperature subsequently influences the δ13Corg of vegetations. Additionally, the δ13Corg values in the soils are influenced by the δ13Corg values of the local vegetation [32]. The effect of temperature variation on the fractionation processes of different plant species is accurately recorded within the plant body, resulting in changes in both plant and soil δ13Corg values [16]. Therefore, the temperature changes during the Holocene around the QHL Basin have been reconstructed through analyzing the δ13Corg in the ND profile.
During the Early Holocene, the χlf was at its lowest, indicating reduced pedogenesis, and the Mz was substantial and exhibited pronounced fluctuations, indicating the wind conditions were characterized by their strong, unstable, and recurrent nature (Figure 7). Dry climate conditions are suggested by the low χlf and high Mz [20]. Several studies have been conducted on different environmental proxy indicators in aeolian sediments from this period and have inferred that evaporation was intense, the moisture required for vegetation was insufficient, and aeolian activity was pronounced [12,53]. The temperature in the QHL Basin was higher, albeit with notable fluctuations. Therefore, the initial TOC diminished, and the soil TOC value decreased. During the Middle Holocene, the χlf was at its finest, it was primarily composed of silt, and the rate of sand deposition was at a minimum, suggesting a transition to stable warm and wet conditions (Figure 7). An examination of the salinity proxies from the paleo-shoreline and waters of the QHL revealed climatic conditions characterized by warmth and humidity during this period [30], which agrees with the conclusions drawn from the research presented in this study. During this stage, the temperature remains consistently high and stable. Aeolian activity was subdued, whereas pedogenesis intensity increased [20,54], resulting in a substantial accumulation of TOC. During the Late Holocene, indications of an unstable climate were evidenced by a marked decrease in χlf and roughening of Mz (Figure 7). These signs indicated an intensification of aeolian activity and a shift towards a climate that is both colder and more arid. There was a rapid decline in temperature accompanied by intensified aeolian activity [20,55]. There was a significant decline in temperature during this period [53,54], coinciding with an increase in aeolian activity. The χlf and Mz indicate the partial development of paleosol at approximately 2 ka, leading to an increase in TOC. Subsequent to approximately 2 ka, there was a noted reduction in χlf, coupled with a coarsening of Mz. These changes signal an intensification of aeolian activity, indicating a shift towards increasingly arid and cold climatic conditions. The research findings indicate that the climatic conditions became colder and drier, further intensifying aeolian activity [53,54]. Based on the above analysis, during the Early Holocene, the temperature increased with high frequency and amplitude oscillations, strong aeolian activity, and low TOC accumulation. During the Middle Holocene, the temperature remained high and stable with the weakest aeolian activity and intensified pedogenesis. During the Late Holocene, the temperature decreased at a high rate, with renewed aeolian activity and weak pedogenesis. The climatic system exhibits greater complexity in the QHL Basin of the QPT, situated at the periphery of the EASM and ISM influences, compared to other sectors of the QPT. This is probably due to the complicated interaction between the EASM and ISM.
In the study of the relationship between the temperature and δ13Corg of surface soil, the δ13Corg values have been observed to elucidate the relationship between these two variables, providing insights into paleoenvironmental reconstruction [16]. Therefore, surface soil δ13Corg will be collected in subsequent research. We attempt to quantitatively reconstruct Holocene seasonal and accumulated temperatures in the QHL Basin based on δ13Corg changes in an aeolian profile using the surface soil δ13Corg dataset and high-resolution modern climate reanalysis data.

5. Conclusions

Based on the study of the TOC and δ13Corg in the Niaodao (ND) profile, this study further extends the applicability of the δ13Corg indicator in paleoclimate reconstruction. The variation trend and amplitude of the TOC and δ13Corg in aeolian and lacustrine sediments are found to be different. The terrestrial ecosystem was not a principal contributor to lacustrine organic matter within the northeastern QTP during the Holocene.
The change in δ13Corg values in the ND profile primarily reflects the response of C3 plants to environmental factors. The δ13Corg values of C3 plants are primarily influenced by temperature. During the Holocene, variations in the δ13Corg values in the ND profile serve as an indicator of temperature fluctuations in the QHL Basin.
During the Early Holocene, the temperature increased with relatively high frequency and amplitude oscillations, strong aeolian activity, and low TOC accumulation. During the Middle Holocene, the temperature remained relatively high and stable with the weakest aeolian activity and intensified pedogenesis. During the Late Holocene, the temperature decreased at a relatively high rate, with renewed aeolian activity and weak pedogenesis.

Author Contributions

Conceptualization, C.E.; methodology, X.L.; software, Z.Z.; validation, X.J.; formal analysis, J.Z.; investigation, Q.P. and Y.S. (Yunkun Shi); data curation, S.Z.; writing—original draft preparation, Q.P.; writing—review and editing, C.E.; supervision, Y.S. (Yongjuan Sun). All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China (grant no. 42171011) and the Natural Science Foundation of the Qinghai Provincial Science and Technology Department (grant no. 2021-ZJ-918).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available on request from the corresponding author. The data are not publicly available due to privacy.

Acknowledgments

We would like to thank Yongxin Zeng, Qi Zhang, Jie Zhang, and Xianyu Cao for their help with field and laboratory work. We would also like to thank Manping Sun for his valuable suggestions. Special thanks go to the anonymous reviewers and editors, whose constructive suggestions and useful comments helped clarify and improve the quality of the paper.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Map of the study area. The Qinghai-Tibet Plateau (QTP) is located in Central Asia, and the Qinghai Lake (QHL) Basin is located in the northeastern QTP, as indicated by the inset map. The red pentagon on the map denotes the location of the Niaodao (ND) profile examined in this study.
Figure 1. Map of the study area. The Qinghai-Tibet Plateau (QTP) is located in Central Asia, and the Qinghai Lake (QHL) Basin is located in the northeastern QTP, as indicated by the inset map. The red pentagon on the map denotes the location of the Niaodao (ND) profile examined in this study.
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Figure 2. Stratigraphy and dating of the ND profile, with the age scale of the profile referenced to [20]; the ND profile is located along the Buha River.
Figure 2. Stratigraphy and dating of the ND profile, with the age scale of the profile referenced to [20]; the ND profile is located along the Buha River.
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Figure 3. Experimental procedures for the δ13Corg sample.
Figure 3. Experimental procedures for the δ13Corg sample.
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Figure 4. Data results are correlated with the age of the ND profile. (a) δ13Corg and (b) total organic carbon (TOC).
Figure 4. Data results are correlated with the age of the ND profile. (a) δ13Corg and (b) total organic carbon (TOC).
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Figure 5. Numerical comparison of the δ13Corg (A) and TOC (B) in terrestrial (ND profile and ZYC profile) and lacustrine sediments (Genggahai Lake and QHL).
Figure 5. Numerical comparison of the δ13Corg (A) and TOC (B) in terrestrial (ND profile and ZYC profile) and lacustrine sediments (Genggahai Lake and QHL).
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Figure 7. Comparison of the δ13Corg in the ND profile of QHL with other indicators since the Holocene. (a) The δ13Corg of the ND profile, (b) the Northern Hemisphere summer insolation at 37° N [52], (c) the TOC, (d) low-frequency magnetic susceptibility (χlf), and (e) median grain size (Mz) of the ND profile. (d,e) Have been published in detail in the literature [20].
Figure 7. Comparison of the δ13Corg in the ND profile of QHL with other indicators since the Holocene. (a) The δ13Corg of the ND profile, (b) the Northern Hemisphere summer insolation at 37° N [52], (c) the TOC, (d) low-frequency magnetic susceptibility (χlf), and (e) median grain size (Mz) of the ND profile. (d,e) Have been published in detail in the literature [20].
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MDPI and ACS Style

Peng, Q.; E, C.; Li, X.; Sun, Y.; Zhang, J.; Zhang, S.; Shi, Y.; Ji, X.; Zhang, Z. Holocene Paleoclimate Changes around Qinghai Lake in the Northeastern Qinghai-Tibet Plateau: Insights from Isotope Geochemistry of Aeolian Sediment. Atmosphere 2024, 15, 833. https://doi.org/10.3390/atmos15070833

AMA Style

Peng Q, E C, Li X, Sun Y, Zhang J, Zhang S, Shi Y, Ji X, Zhang Z. Holocene Paleoclimate Changes around Qinghai Lake in the Northeastern Qinghai-Tibet Plateau: Insights from Isotope Geochemistry of Aeolian Sediment. Atmosphere. 2024; 15(7):833. https://doi.org/10.3390/atmos15070833

Chicago/Turabian Style

Peng, Qiang, Chongyi E, Xiangzhong Li, Yongjuan Sun, Jing Zhang, Shuaiqi Zhang, Yunkun Shi, Xianba Ji, and Zhaokang Zhang. 2024. "Holocene Paleoclimate Changes around Qinghai Lake in the Northeastern Qinghai-Tibet Plateau: Insights from Isotope Geochemistry of Aeolian Sediment" Atmosphere 15, no. 7: 833. https://doi.org/10.3390/atmos15070833

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