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Article

A Highly Resolved Speleothem δ13C Record from Central China and Its Manifestation on Multiple Time Scales during the Last Glacial

by
Qingmin Chen
1,*,†,
Xing Cheng
1,2,*,†,
Li Deng
1,†,
Kaikai He
1,
Wenshuo Zhang
1,
Gang Xue
2,3,
Zeke Zhang
2,
Le Ma
2,
Gaohong Wang
1,
Hai Cheng
4,5 and
R. Lawrence Edwards
5
1
Shaanxi Experimental Center of Geological Survey, Shaanxi Institute of Geological Survey, Xi’an 710065, China
2
State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China
3
State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi’an 710069, China
4
Institute of Global Environmental Change, Xi’an Jiaotong University, Xi’an 710049, China
5
Department of Earth Sciences, University of Minnesota, Minneapolis, MN 55455, USA
*
Authors to whom correspondence should be addressed.
†
These authors contribute equally to this work.
Minerals 2024, 14(5), 450; https://doi.org/10.3390/min14050450
Submission received: 14 January 2024 / Revised: 3 April 2024 / Accepted: 21 April 2024 / Published: 25 April 2024
(This article belongs to the Special Issue Stalagmite Geochemistry and Its Paleoenvironmental Implication)
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Abstract

:
Speleothem δ13C in monsoonal China differs from speleothem δ18O, which is widely used as a climatic proxy for several complex control reasons. Nevertheless, δ13C records have the potential to reveal the implications of hydroclimatic changes. This study reports a speleothem δ13C record from Didonghe (DDH) Cave in central China spanning 34 to 13 kyr BP. After we investigated the factors that influence speleothem δ13C, we found that the δ13C record showed that DDH Cave can prompt directional shifts via local hydroclimatic changes, such as in vegetation types, biomass, and rock–water interaction processes, suggesting that δ13C is mainly controlled by the local hydroclimate. Ensemble empirical mode decomposition (EEMD) results revealed a coupling relationship between δ18O and δ13C on multiple timescales, which suggested that changes in precipitation caused by large-scale monsoonal circulation are controlled by regional hydrological conditions to a great extent. However, the hydrological conditions of the cave were relatively mild and humid during the last glacial maximum (LGM), which revealed the impact of evaporation on changes in the region’s hydrological conditions. We also found that the δ18O and δ13C profiles decoupled when δ13C changed with a shift in the location of the westerly during HS1. The δ13C record correlates well with other paleoclimate records, suggesting that regional hydrological conditions are also modulated by the Earth’s internal and external driving factors.

1. Introduction

Hydroclimate conditions are vital to ecosystem variations in the Qinba Mountains, which are located in an important water source area [1]. Changes in regional precipitation and hydrological conditions have significant effects on the flood disasters in the Qinba Mountains and potentially influenced ancient human settlements. Therefore, clarifying hydroclimatic changes in the Qinba Mountains is of great significance for water-using strategies. Particularly, identifying hydroclimate variations before the Anthropocene is the key to understanding the driving forces behind it. However, since this region (the Qinba area, located in central China) is subject to the Indian Monsoon (IM) and the East Asian Monsoon (EAM), its complexity has led to a poor state of research regarding the dynamic evolution of the long sequences of hydrological conditions [2].
Speleothems are one of the most important types of archives in reconstructing paleoclimate change because of their high resolution, wide distribution, and accurate dating [3,4,5]. Based on accurate U-series-dated chronology, a few studies have reconstructed regional hydroclimate changes using variable speleothem proxies. A previous study proposed that the difference in oxygen isotopes between two stalagmites can reflect local precipitation [6]. Later, the relative fluctuation of the local hydrology was reconstructed based on the ratio of speleothem anhysteretic remanent magnetism (ARM) to saturation isothermal remanent magnetism (SIRM) [7]. Recently, stalagmite δ13C has been proposed as a potential way to reconstruct local ecological environments and hydrological climates [8,9].
Generally, speleothem δ13C is controlled by vegetation and soil processes in overlying systems, percolating characteristics in seepage systems, and some cave factors [10,11]. Speleothem carbon can originate from atmospheric CO2, biogenic CO2 from autotrophic and heterotrophic soil respiration, and carbonate bedrock [12]. Recently, deep underground reservoirs of carbon [13] and deeply rooted vegetation [14] were recognized as crucial influence factors in the karst carbon cycle. The relative contribution degree of these different sources to stalagmite δ13C is modulated by the hydroclimate and temperature. Nevertheless, by comparing other proxies, including speleothem δ18O, an increasing number of studies have shown that hydroclimate conditions are significant in speleothem δ13C changes. For example, Novello et al. [15] determined the relationship between local hydroclimate and atmospheric convective processes related to the South American Monsoon System through a comparative study of speleothems δ13C and δ18O. With further studies of speleothem δ13C, more research has suggested that δ13C records can be employed to reflect hydroclimate variation by excluding the isotope kinetic fractionation process [16,17,18,19,20,21].
In some cases, stalagmite δ13C may respond to millennial climate changes more sensitively than stalagmite δ18O. The oxygen and carbon isotope records of stalagmites in China show millennial-time-scale oscillations, for instance, some records from Hulu Cave [20,22]. Other records from stalagmites in southern China show that the amplitude of millennial-time-scale events recorded by δ13C is twice as large as that of the δ18O record during the last two glacial cycles [22,23]. The structural characteristics of D-O (Dansgaard–Oeschger) events documented in stalagmite δ13C are more similar to the record of the NGRIP (North GRIP) ice core than the δ18O stalagmite record [18,24].
This study presents a highly resolved speleothem δ13C record spanning the period 34 to 13 kyr BP from Didonghe (DDH) Cave in Shaanxi Province, exploring the variations in stalagmite δ13C and their implications for the local hydroclimate and related driving mechanisms.

2. Cave Setting and Study Sample

Didonghe (DDH) Cave (32°44′14″ N, 106°24′26″ E, 1262 m a.s.l.) is located in Ningqiang County, Shaanxi Province, China (Figure 1). This cave developed in the Permian Wujiaping strata with a length of 1200 m and a maximum depth of 340 m [25]. The overlying section is covered by yellow-brown soil, and the vegetation is mainly composed of evergreens, a deciduous broad-leaf mixed forest belt (Quercus, Acer), and erect shrubs (Indigofera pseudotinctoria Matsum, Lespedeza). Our previous work [25] showed that the hydrology of this cave site is mainly controlled by the ISM (Indian Summer Monsoon) and the EASM (East Asian Summer Monsoon) (Figure 1a). Data from 1957 to 2007 taken from Ningqiang Meteorological Station (Figure 1c) indicate that the mean annual temperature and the mean annual rainfall are 13 ℃ and 1104 mm, respectively, and the precipitation mainly falls during the summer season (from May to August) [25]. Stalagmite DDH-B15 was collected from the Yulong chamber at the deepest part of Cave B in the DDH Cave system, 2 km from the cave entrance. The length of DDH-B15 is 158 mm, and the diameter varies between 64 mm and 30 mm. After cutting a stalagmite with a diamond wire saw, the center of the stalagmite was observed to be yellowish-brown, and the two sides were yellowish-white, with some cracks. Other detailed information about the cave setting and sample description can be found in Chen and Cheng et al. [25].

3. Methods

DDH-B15 was cut along the growth axis using a diamond wire saw and polished, and a total of 322 subsamples were drilled along the axis for stable isotope analysis at 0.5 mm intervals using a dental drill. Stable isotope analysis was performed at the Institute of Earth Environment, Chinese Academy of Sciences, using an Isoprime100 gas source stable isotope ratio mass spectrometer equipped with a MultiPrep system. To monitor the stability, laboratory internal standard samples, TB1, were measured for every 10–20 subsamples. The δ13C and δ18O results are relative to the Vienna Pee Dee Belemnite (VPDB) standard. We have analyzed the variability of oxygen isotopes in detail before [25]; this paper focuses on analyzing carbon isotopes.
Based on the results of a previous study [25], we drilled another 7 samples from DDH-B15 for a more accurate chronological scale and performed U-Th dating using a multi-collection inductively coupled plasma mass spectrometer (MC-ICP-MS) at the Isotope Laboratory of Xi’an Jiaotong University. The chemical procedures used to separate the uranium and thorium for 230Th dating are similar to those described in Edwards et al. (1987) [27], and the measuring protocol is the same as the one used by Cheng et al. (2013) [28]. A 230Th/232Th atomic ratio of 4.4 ± 2.2 × 10−6 was used to correct for the initial 230Th.

4. Results

4.1. Age Model and Growth Rate

By combining our newly obtained dating results (Table 1) with previous U-Th dating ages [25], a new age model of DDH-B15 was established (Figure 2). The growth period of DDH-B15 spans 33.97 to 13.12 kyr BP, and the growth rate ranges from 2.3 to 14.6 mm/kyr, with a mean growth rate of 8.03 mm/kyr. Overall, the growth rate of DDH-B15 was relatively high during 34~29 kyr BP and 22~16 kyr BP, but it was low during 29~16 kyr BP.

4.2. The δ13C and δ18O Records

A total of 322 sets of δ13C and δ18O data were obtained from stalagmite DDH-B15, with an average resolution of ~64.8 years. The δ18O record varies between −5.60‰ and −11.00‰, with a mean value of −8.29‰ [25] (Figure 3a). The δ13C ranges from −1.16‰ to −7.73‰, with a mean value of −3.801‰, and its oscillation (6.57‰) exhibits a larger amplitude compared with δ18O. In accordance with oscillation amplitude, the δ13C record is divided into three parts. During 34.0~26.0 kyr BP, the amplitude of δ13C is relatively large, with a negative carbon isotope mean. Subsequently, the DDH-B15 δ13C values gradually decrease and then oscillate around −3.08‰ until 15.0 kyr BP. After that, speleothem δ13C is interrupted by a positive excursion from 15.0 to 13.12 kyr BP and followed by a decreasing trend.

4.3. 238U, δ234Uinitial, and 232Th

The values of 238U, δ234Uinitial, and 232Th were acquired using a table of 230Th dating results derived from DDH-B15. The value of 238U ranges from 757.4 to 1245.8 ppb, with a mean value of 1007.8 ppb, while 232Th fluctuates greatly and varies between 3917 ppt and 68 ppt. Most 232Th values are less than 1000 ppt, except for samples collected from 2 mm and 7 mm, reflecting that most samples are barely contaminated. The δ234Uinitial data show a pattern similar to the δ13C record. Generally, δ234Uinitial increases slightly over the period from 13.12 kyr BP to 19 kyr BP, with a significant decrease from 14.72 kyr BP to 16.17 kyr BP. This is followed by a rapid decrease to a steady low value at 22.81 kyr BP and a subsequent rise during 16.18~26.67 kyr BP. Then, δ234Uinitial maintains a downward trend until 33.41 kyr BP.

5. Discussion

5.1. Interpretation of Stalagmite δ13C at DDH Cave

The Hendy test is an important way to verify whether a speleothem has formed under an isotopic equilibrium condition. If so, there should be no correlation between δ13C and δ18O from the same layer [30]. However, speleothems δ13C and δ18O can also change in the same direction if they are controlled by the same driving forces. Carbon in stalagmites mainly originates from soil CO2 controlled by an overlying system involving soil CO2 and organic matter degradation (80%–95%), parent rock (10%–15%), and atmospheric CO2 (the concentration is only about 0.03%) [17,31]. Therefore, speleothem δ13C is affected by the carbon source and can largely record information on vegetation variations. Nevertheless, during the percolating process, the dynamic processes in the seepage system should also be considered. Thus, we argue that the “Hendy test” cannot determine whether a dynamic fractionation exists because these factors are more or less influenced by climate.
The δ13C value of C3 plants is more negative than that of C4 plants since C3 plants mainly incorporate carbon using the C3 Calvin pathway [32,33], although previous work has suggested that the relative abundance of the C3/C4 types has the greatest impact on stalagmite δ13C [30]. The values of δ13C under the control of C3 vegetation are more negative (−14‰~−6‰) than when they are under the control of C4 vegetation (−6‰~−2‰) [33]. Spore pollen reconstruction results have shown that ancient vegetation in central China was dominated by mixed broadleaf evergreen and deciduous forests during the last glacial maximum [34], and this kind of forest is mainly composed of C3 plants. DDH-B15 δ13C ranges from −1.16‰ to −7.73‰, with a mean value of −3.80‰, which is largely consistent with the speleothem δ13C range expected at a site overlain with C4 vegetation (−6 to −2‰), contradicting the spore pollen reconstruction results. Hence, the change in DDH-B15 δ13Cdoes not support the explanation of C3/C4-type vegetation changes. The densities of vegetative cover and biomass are the main controlling factors for δ13C in regions dominated by C3-type vegetation [35]. As kinetic fractionation in biological processes favors 12C, organically derived CO2 is released into the soil through root respiration, and the microbial decomposition of organic matter is relatively depleted in 13C [21].
Cave system conditions can also govern speleothem δ13C. Soil CO2 makes a more significant contribution to speleothem carbon under an open system with relatively negative δ13C, and vice versa [36]. However, studies have shown that variations in the open/closed ratio are often small between speleothems from the same cave [19,37,38,39].
Furthermore, seasonal temperature changes can alter air pCO2 and, hence, result in a variable gas pressure gradient between the inside and outside of a cave [21]. A higher pCO2 gradient likely causes higher δ13C values in drip water because of degassing enhancement [40,41]. The DDH-B15 δ13C we collected came from deep in the cave, where the environment is relatively stable, which may show that the effect of ventilation on δ13C is relatively small.
An increasing number of studies show that the regional hydroclimate is very important to variations in speleothem δ13C; that is, an increase in precipitation may lead to a decrease in the residence time of seepage water in epikarst, hence resulting in a lower stalagmite δ13C value due to weakened bedrock dissolution and degassing [42,43].
Given the above, vegetation changes, cave system conditions, and kinetic fractionation in caves can be ruled out as the dominant influencing factors. The regional hydroclimate is likely the main driver, and although it is difficult to pinpoint one or more factors that affect speleothem δ13C, we can be sure that they affect it in the same direction [21,44].

5.2. The Phase Relationship between DDH-B15 δ13C and δ18O on Multiple Timescales

The phase relationship between speleothem δ18O and δ13C is still an open question. To clarify the coupling relationship between δ18O and δ13C, we used the EEMD method to decompose DDH-B15 δ13C and δ18O records [45] and obtained seven intrinsic mode functions (imfs) and one residual function (res), respectively. These intrinsic mode functions were reconstructed as three signals according to different timescales (Figure 4).
On the centennial time scale, our decomposed data derived from the EEMD method showed that the major periods of DDH-B15 δ13C (0.22 kyr, 0.41 kyr, and 0.87 kyr) are consistent with those of δ18O (0.19 kyr, 0.37 kyr, 0.81 kyr). A correlation analysis showed a positive correlation, and the correlation coefficient between the imf1 + imf2 + imf3 values of δ13C and δ18O is 0.59 (p < 0.01). A stalagmite from Yunnan province showed that changes in temperature and precipitation due to monsoon circulation lead δ13C and δ18O to change in the same direction on a centennial scale [46]. A similar change mode has also been demonstrated in stalagmites in Europe, North America, and Arabia [47,48,49]. δ13C and δ18O consistencies may be attributable to hydroclimatic changes. This is because EASM dominates precipitation at our study site; it further influences the regional hydroclimate and, hence, has the same rhythm [32,50,51,52].
On the millennial time scale, the decomposed δ13C results significantly correlated with the δ18O results, with a high correlation coefficient (r = 0.53, p < 0.01). The covariations of speleothems δ13C and δ18O on the millennial scale have been confirmed with stalagmite records from southern China [21,23,53]. This strong coupling relationship may be due to a spate of weak monsoons, resulting in periodic changes in the intensity of Asian monsoon rainfall and ultimately causing variations in cave seepage water flow. Millennial-scale climatic changes, perhaps induced by Henrich events, led to a cold climate in the high latitude of the Northern Hemisphere and changed the intensity of low-latitude monsoons [54].
Significantly, the HS3 and HS2 events recorded in δ18O almost match the δ13C record (Figure 4). However, the δ13C record does not exhibit a positive trend during 16~15 kyr BP and shows an opposite structure to the δ18O record (Figure 4b); in other words, the hydroclimate in DDH Cave was wet (or at least not dry) during this period. Similar phenomena appear in other stalagmite records in central China (Figure 5d,e) [55,56]. By studying trace elements, Zhang et al. [57] found that central China experienced a humid hydrological climate (Figure 5b). The decoupling of δ13C and δ18O over this period may be attributable to the anticorrelation between the intensity of monsoons and the precipitation of central China may be linked to the movement of the westerly [57]. A weak AMOC (Figure 5d) led to the westerly’s delayed northward migration, resulting in a prolonged Meiyu stage in central China. However, this weak AMOC in 27~25 kyr BP did not cause a moist climate in the research area. In considering this phenomenon, we assumed that its responses to climate change vary during different climate boundary conditions, especially during different HS events. The transition period from MIS3 to MIS2, a period with a decrease in summer solar insolation in the North Hemisphere [58], presents significant climatic instability.
On the orbital time scale, the variance in δ18O and δ13C records is dominated by processional and half-precessional cycles (10.5 kyr; 21 kyr), but these two cycles are not statistically significant because the DDH Cave record is only 20,500 years long. Generally, the cycles represented by the DDH Cave δ13C record’s imfs are consistent with a millennial-to-centennial scale, and this relationship has important implications for the environmental significance of δ13C stalagmite. The refs of stalagmite δ13C and δ18O on a centennial scale have cycles (0.22 kyr; 0.19 kyr) similar to the Suess cycle [62], implying the δ13C and δ18O stalagmites may be affected by solar activity on a centennial scale. However, the amplitude of δ13C is almost twice that of δ18O, suggesting that δ13C variance may be amplified by hydrological signals and more sensitive to climate change. On a millennial scale, the δ18O and δ13C records both have a 2.1 kyr cycle, which reflects climate change at high latitudes in the Northern Hemisphere. Aside from the 2.1 kyr cycle, a corresponding 5.2 kyr cycle due to oxygen isotopes might result from a one-quarter resonance oscillation with respect to precession. The correlation coefficient between δ13C and δ18O on the centennial time scale is larger than that of the millennial time scale because hydroclimatic sensitivities are different on multiple time scales.

5.3. Variation in Local Hydroclimate and Its Driving Forces

The hydroclimatic changes in DDH Cave may be roughly divided into three stages based on the above analysis of its δ13C variation (Figure 6a). From 34.0 to 25.0 kyr BP, the δ13C values were relatively negative, with several abrupt fluctuations, indicating more precipitation and wet climate conditions. Subsequently, δ13C increased slightly and kept a relatively stable level, suggesting that precipitation decreased mildly, but the local climate condition was still relatively humid and persisted up to 15.5 kyr BP. This change is also supported by pollen records. The pollen sequence from the western part of Hubei Province suggested an evolution into dark coniferous forests dominated by Abies over the LGM period, which reflects wet climate conditions [62,63].
DDH Cave stalagmite records are comparable to speleothem records from other caves during HS1 (Figure 5), and all of these records are characterized by a period with a relative increase in humidity. Therefore, at the beginning of the HS1 event, the hydrological conditions in the region deteriorated, and the climate shifted from wet to dry. However, the hydrological conditions in the region gradually improved, and the climate was humid up until 16 kyr BP, a period that lasted for about 1 kyr. The hydrological conditions in the region deteriorated again at the end of HS1. The average δ13C rose to −2.7‰ from 15 to 14.5 kyr BP, implying that precipitation depletion continued and the climate condition started to dry. At the end of the last glacial, the global temperature rose, the ASM strengthened, and δ13C gradually decreased, indicating humid hydrological conditions.
The changes in the hydrological environment of central China are related to internal and external driving factors. The changes driven by solar activity on the millennial-to-centennial time scale have had significant impacts on the climate and environment and can lead to global climate changes via feedback from the Earth’s internal systems [64,65,66,67]. The most intuitive conclusion is that changes in solar activities drive the uneven distribution of energy on the Earth’s surface, resulting in increased surface temperature gradients and changes in atmospheric circulation [68].
DDH-B15 δ13C is consistent with the 10Be record of Greenlandic ice cores, which are regarded as proxies of solar activity (Figure 6b). Previous spectrum analysis results have also shown that solar activity and the DDH δ13C record have similar cycles on a millennial time scale (Figure 6d,e). Furthermore, 330 and 310 years correspond to variable oscillation mode cycles caused by the solar convective zone. Therefore, we conclude that enhanced/attenuated solar irradiance was triggered by variations in the strength of solar activity during the glacial periods, which led to an intensified/weakened thermodynamic gradient between the Asian continent and the North Pacific and contributed to increases/decreases in monsoon-related precipitation in central China [69]. Notably, the reduction in solar irradiance may have reduced regional evaporation and thus led to a reverse hydrological evolution pattern [55,70]. Lower evaporation in the glacial period instead of decreased monsoonal-driven precipitation would have played a predominant role in regional effective moisture changes [71]. This assumption provides a plausible explanation for the humid climate conditions documented in DDH Cave and other records during the LGM period.
Internal factors driven by the Earth, including the movement of the intertropical convergence zone (ITCZ), also play a crucial role in climate change [72,73]. The southward/northward shift in the ITCZ caused by changes in solar activity leads to variations in atmospheric circulation and affects the regional hydroclimate [74,75]. During 34~13 kyr BP, the DDH δ13C record positively correlated with the Cariaco Basin reflectance—which was used to reflect the southward/northward shift in the ITCZ [76]—and characterized by an enhanced δ13C trend corresponding to an increased reflectance value. Thus, when the ITCZ moves southward, the intensity of ASM decreases and leads to depleted precipitation, which is consistent with previous studies [73,77,78].
Minerals 14 00450 g006
Figure 6. Comparison of the δ13C stalagmite in DDH Cave with other records reflecting regional or global climate change: (a) δ13C in this study; (b) 10Be record of Greenlandic ice core [72]; (c) Cariaco Basin reflectance record [73]; (d) spectrum analysis of DDH δ13C record; (e) spectrum analysis of 10Be record; (f) spectrum analysis of Cariaco Basin reflectance record.
Figure 6. Comparison of the δ13C stalagmite in DDH Cave with other records reflecting regional or global climate change: (a) δ13C in this study; (b) 10Be record of Greenlandic ice core [72]; (c) Cariaco Basin reflectance record [73]; (d) spectrum analysis of DDH δ13C record; (e) spectrum analysis of 10Be record; (f) spectrum analysis of Cariaco Basin reflectance record.
Minerals 14 00450 g006

6. Conclusions

This study utilized highly resolved and precisely dated δ13C and δ18O records of the DDH-B15 stalagmite, taken from Didonghe Cave, that formed 34~13 kyr BP. We discussed the hydrological changes in central China and the relationship between carbon and oxygen isotope records. Based on the similarity between DDH-B15 δ13C and other hydroclimatic indicators in the monsoonal region, we concluded that DDH-B15 δ13C reflects regional hydroclimatic changes. By decomposing the data using the EEMD method, we showed that there is a coupling relationship between δ18O and δ13C stalagmites on multiple timescales, indicating that the Asian summer monsoon controls hydroclimatic changes in the Qinba Area. However, the δ18O and δ13C profiles decoupled during HS1 because the hydroclimate is susceptible to the westerly location. Our comparative analysis demonstrated that changes in regional hydrological conditions on a millennial-to-centennial scale are subject to changes caused by solar activity and superimposed by the ITCZ, which implies that the internal and external driving factors of the Earth jointly participate in regulating changes in the hydrological environment in central China in different forms.

Author Contributions

Conceptualization, X.C. and Q.C.; methodology, X.C., L.D., L.M., H.C. and R.L.E.; software, X.C. and L.D.; validation, X.C., Q.C., G.X. and Z.Z.; formal analysis, X.C., L.D., K.H. and W.Z.; investigation, X.C., L.D., K.H. and G.W.; resources, X.C., K.H. and G.W.; data curation, X.C.; writing—original draft preparation, X.C. and L.D.; writing—review and editing, X.C., L.D., Q.C., G.X. and Z.Z.; visualization, X.C. and Q.C.; supervision, X.C. and Q.C.; project administration, X.C. and Q.C.; funding acquisition, X.C. and Q.C. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Commonweal Geological Survey Project of Shaanxi Province (202310 to Q.C.), the Shaanxi Province Natural Science Basic Research Program—Youth Project (2023-JC-QN-0298 to X.C.), the Opening Fund of State Key Laboratory of Loess and Quaternary Geology (SKLLQG2209 to X.C.), the Shaanxi Science and Technology Association Youth Talent Lifting Program (20230538 to X.C.), and the US National Science Foundation (NSF 2202913 to R.L.E.).

Data Availability Statement

Data are contained within the article. Specific data on carbon and oxygen isotopes are also available by contacting corresponding author xing-cheng529@outlook.com (X.C.).

Acknowledgments

We acknowledge Yanbin Lu and Yanjun Cai for helping with the article’s framework and Yingying Wei and Jinhu Ren for their fieldwork.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. (a) Overview of the research area: the red star is DDH Cave, and the blue triangles are the other caves. (b) Location of Didonghe Cave. (c) Annual mean precipitation and temperature of Ningqiang County from 1957 to 2007 [26].
Figure 1. (a) Overview of the research area: the red star is DDH Cave, and the blue triangles are the other caves. (b) Location of Didonghe Cave. (c) Annual mean precipitation and temperature of Ningqiang County from 1957 to 2007 [26].
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Figure 2. DDH-B15 stalagmite and age model (the white and red bars are the previous sampling positions and newly taken sampling positions, respectively).
Figure 2. DDH-B15 stalagmite and age model (the white and red bars are the previous sampling positions and newly taken sampling positions, respectively).
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Figure 3. Time series of (a) original DDH δ18O record; (b) original DDH δ13C record; (c,d) detrended record of δ18O and δ13C; (e) δ234Uinitial. The three yellow bars are HS1, HS2, and HS3 cold events, and the blue area is the LGM period.
Figure 3. Time series of (a) original DDH δ18O record; (b) original DDH δ13C record; (c,d) detrended record of δ18O and δ13C; (e) δ234Uinitial. The three yellow bars are HS1, HS2, and HS3 cold events, and the blue area is the LGM period.
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Figure 4. (a,b) Speleothems δ18O (pink) and δ13C (green) in DDH Cave; (c) imf 1–3 components of speleothems δ18O and δ13C; (d) imf 4 + 5 components of speleothems δ18O and δ13C; (e) imf 6 + 7 components of speleothems δ18O and δ13C; (f) res components of speleothems δ18O and δ13C.
Figure 4. (a,b) Speleothems δ18O (pink) and δ13C (green) in DDH Cave; (c) imf 1–3 components of speleothems δ18O and δ13C; (d) imf 4 + 5 components of speleothems δ18O and δ13C; (e) imf 6 + 7 components of speleothems δ18O and δ13C; (f) res components of speleothems δ18O and δ13C.
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Figure 5. Comparison of DDH record (this study) to other stalagmite records: (a) original DDH δ13C record; (b) stalagmite Sr/Ca in Haozhu Cave, Hubei Province [56]; (c) 231Pa/230Th record of the Atlantic core [59,60]; (d) Qingtian Cave δ13C record, Hubei Province [56]; (e) Longfugong Cave δ13C record, Hubei Province [61]; (f) Yangzi Cave δ13C record, Chongqing City [55].
Figure 5. Comparison of DDH record (this study) to other stalagmite records: (a) original DDH δ13C record; (b) stalagmite Sr/Ca in Haozhu Cave, Hubei Province [56]; (c) 231Pa/230Th record of the Atlantic core [59,60]; (d) Qingtian Cave δ13C record, Hubei Province [56]; (e) Longfugong Cave δ13C record, Hubei Province [61]; (f) Yangzi Cave δ13C record, Chongqing City [55].
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Table 1. 230Th supplemental dating results for DDH-B15.
Table 1. 230Th supplemental dating results for DDH-B15.
Sample Depth238U232Th230Th/232Thδ234U *230Th/238U230Th Age (yr)230Th Age (yr)δ234Uinitial **230Th Age (yr BP) ***
Numbermm(ppb)(ppt)(Atomic × 10−6)(Measured)(Activity)(Uncorrected)(Corrected)(Corrected)(Corrected)
DDH-B1530956.2±3.6516±1124425±5454436.4±10.80.7999±0.003816997±9416995±944654±1116922±94
DDH-B15-7070898.4±3.3157±590503±30304200.3±11.90.9563±0.004321579±11821578±1184464±1321505±118
DDH-B15-8080990.8±4.4537±1232583±7274357.9±12.41.0703±0.005423594±14223591±1424658±1323518±142
DDH-B15-8383985.2±4.9220±783260±25094414.1±15.61.1286±0.006424713±17124712±1714733±1724639±171
DDH-B15-115115858.5±3.5117±4156823±55524162.2±12.11.2937±0.006230273±18030272±1804533±1330199±180
DDH-B15-1301301036.4±4.4139±5162628±60464088.0±11.21.3188±0.006931436±19931435±1994467±1231362±199
DDH-B15-145145875.4±2.0216±688101±26003952.9±6.21.3209±0.003832462±11432461±1144332±732388±114
U decay constants: λ238 = 1.55125 × 10−10 [29] and λ234 = 2.82206 × 10−6 [28]. Th decay constant: λ230 = 9.1705 × 10−6 [28] * δ234U = ([234U/238U]activity − 1) × 1000. ** δ234Uinitial was calculated based on 230Th age (T), i.e., δ234Uinitial = δ234Umeasured × eλ234 × T. Corrected 230Th ages assume an initial 230Th/232Th atomic ratio of 4.4 ± 2.2 × 10−6. These are the values for a material at secular equilibrium, with a bulk earth 232Th/238U value of 3.8. The errors are arbitrarily assumed to be 50%. *** B.P. stands for “before present”, where the “present” is defined as the year A.D. 1950.
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Chen, Q.; Cheng, X.; Deng, L.; He, K.; Zhang, W.; Xue, G.; Zhang, Z.; Ma, L.; Wang, G.; Cheng, H.; et al. A Highly Resolved Speleothem δ13C Record from Central China and Its Manifestation on Multiple Time Scales during the Last Glacial. Minerals 2024, 14, 450. https://doi.org/10.3390/min14050450

AMA Style

Chen Q, Cheng X, Deng L, He K, Zhang W, Xue G, Zhang Z, Ma L, Wang G, Cheng H, et al. A Highly Resolved Speleothem δ13C Record from Central China and Its Manifestation on Multiple Time Scales during the Last Glacial. Minerals. 2024; 14(5):450. https://doi.org/10.3390/min14050450

Chicago/Turabian Style

Chen, Qingmin, Xing Cheng, Li Deng, Kaikai He, Wenshuo Zhang, Gang Xue, Zeke Zhang, Le Ma, Gaohong Wang, Hai Cheng, and et al. 2024. "A Highly Resolved Speleothem δ13C Record from Central China and Its Manifestation on Multiple Time Scales during the Last Glacial" Minerals 14, no. 5: 450. https://doi.org/10.3390/min14050450

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