Speleothem based 1,000-year high resolution record of Indian monsoon variability during the last deglaciation

   Speleothem based 1,000-year high resolution record of Indian monsoon variability during the last deglaciation Mahjoor Ahmad Lone, Syed Masood Ahmad, Nguyen Chi Dung, Chuan-Chou Shen, Waseem Raza, Anil Kumar PII: DOI: Reference: S0031-0182(13)00540-3 doi: 10.1016/j.palaeo.2013.12.010 PALAEO 6690 To appear in: Palaeogeography, Palaeoclimatology, Palaeoecology Received date: Revised date: Accepted date: 11 June 2013 30 November 2013 8 December 2013 Please cite this article as: Lone, Mahjoor Ahmad, Ahmad, Syed Masood, Dung, Nguyen Chi, Shen, Chuan-Chou, Raza, Waseem, Kumar, Anil, Speleothem based 1,000-year high resolution record of Indian monsoon variability during the last deglaciation, Palaeogeography, Palaeoclimatology, Palaeoecology (2013), doi: 10.1016/j.palaeo.2013.12.010 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. ACCEPTED MANUSCRIPT Speleothem based 1,000-year high resolution record of Indian monsoon variability during NU SC RI PT the last deglaciation Mahjoor Ahmad Lonea, Syed Masood Ahmada*, Nguyen Chi Dungb, Chuan-Chou Shenb, Waseem Razaa and Anil Kumara a CSIR – National Geophysical Research Institute, Hyderabad – 500007, India. (lonemahjoor@gmail.com, * smasoodahmad@rediffmail.com, waseem_naqvi@rediffmail.com, b MA anilkumar@ngri.res.in) High-Precision Mass Spectrometry and Environment Change Laboratory (HISPEC), ED Department of Geosciences, National Taiwan University, Taipei 10617, Taiwan ROC (r96224219@ntu.edu.tw, river@ntu.edu.tw) PT * Abstract CE Corresponding author: Tel. No. +91 40 23434685 AC A high resolution record of the Indian summer monsoon (ISM) is generated using a δ18O time series from a stalagmite collected from the Valmiki cave in southern India. This record covers a time span of ~1,000 years from 15,700 to 14,700 yr BP (before 1950 AD) with an average sampling resolution of ~5 years. High amplitude δ18O variation in this record reflects abrupt changes in ISM activity during the last deglaciation and suggest an age for the onset of Termination 1a (T1a) at ~14,800 yr BP in the Indian sub-continent. This record shows evidence for strong changes in tropical climate during the last deglaciation. Coincident variability in VSPM4 δ18O with speleothems from southern China during Termination 1a suggests that these caves reflect fluctuations in ISM activity. The variance in δ18O amplitude reveals significant 1 ACCEPTED MANUSCRIPT multidecadal variability in ISM activity. Our record reveals intervals of strong monsoon activity during the later phase of Heinrich event 1 (H1) and shows synchronous multidecadal variability NU SC RI PT between ISM and East Asian monsoon (EAM). Spectral analysis of δ18O time series in VSPM4 reveals solar forcing and strong ocean-atmospheric circulation control on ISM dynamics during the studied time interval. Keywords: Speleothem, δ18O, Southern India, Indian summer monsoon, Deglaciation, Termination 1a. MA 1. Introduction ED Indian summer monsoon (ISM) variability is critical in understanding regional and global climate because it is the primary source of rainfall for the densely populated areas in South Asia PT (Fleitmann et al., 2003). Abrupt changes in ISM activity have been cited as a dominant factor in CE the rise and fall of ancient civilizations in south Asia, for example the Harappan cultures - a Bronze Age urban civilization (Giosan et al., 2012). An understanding of past ISM variability at AC high spatiotemporal resolution and its relationship to regional climate change is of paramount importance for accurate model simulations to predict future climate / monsoon changes (Shakun et al., 2007). Records pertaining to ISM intensity during the last deglaciation provide valuable information on monsoon behavior during a period marked by major global climate transitions. Most of these studies are based on marine sediments (Overpeck et al., 1996; Rashid et al., 2007; Govil and Naidu, 2010; Raza and Ahmad, 2013). These records, however, are somewhat limited by their spatiotemporal resolution and chronological uncertainties. Therefore there is a need to generate high resolution ISM variability records, particularly from continental archives, to test our concepts of past climatic changes in the Indian sub-continent and aid projections of future 2 ACCEPTED MANUSCRIPT change. This has led to a rapidly increasing focus on the study of speleothems from the Indian sub-continent. NU SC RI PT During the past few decades, δ18O records from speleothem carbonate have provided compelling evidence for decadal to multidecadal variation in Asian monsoon systems and the relationship of this variability to solar insolation (Wang et al., 2001; Fleitman et al., 2003; Dykoski et al., 2005; Shakun et al., 2007; Cai et al., 2012). The available marine and lacustrine records in and around the Indian subcontinent are prone to low temporal resolution and MA significant chronological discrepancies, thereby impeding the precise identification of the timing of abrupt climatic / monsoonal changes. A few high resolution (annual to sub-decadal) δ18O ED records using speleothems from Asia have aided our understanding of the nature and cause of abrupt change in ancient monsoon systems (Sinha et al., 2005; Shakun et al., 2007; Shen et al., PT 2010; Laskar et al., 2013). Records of δ18O in speleothems reveal the detailed structure of these CE abrupt events. Moreover it is important to study abrupt climatic fluctuations across varying latitudes in order to identify and understand the possible leads or lags between the low and high AC latitudes and to determine the possible epicenter of these changes (Shakun et al., 2007). Debate continues over whether speleothem records from southern China are tied to ISM or EAM activity or whether they respond to both (Dykoski et al., 2005; Yang et al., 2010). In tropical regions like India, speleothem δ18O is a reliable proxy for the past variability in δ18O value of meteoric water and is related to the amount effect (Neff et al., 2001; Wang et al., 2001, 2008; Burns et al., 2002; Yadava et al., 2004). Cave δ18O records provide high resolution data ranging from annual to centennial time scales, making them an ideal proxy for understanding past monsoon variability and especially abrupt change. Speleothems from India, as archives of past monsoon variation for different time intervals, have been studied by several 3 ACCEPTED MANUSCRIPT workers (Yadava and Ramesh, 2001, 2005, 2006; Yadava et al., 2004; Sinha et al., 2005, 2007, 2011a, 2011b; Laskar et al., 2011, 2013; Kotlia et al., 2012; Sanwal et al., 2013). Likewise, NU SC RI PT speleothem based ISM reconstructions have also been attempted from other countries like Nepal (Denniston, et al., 2000); Oman and Yemen (Neff et al., 2001; Burns et al., 2002; Fleitmann et al., 2003, 2007; Shakun et al., 2007) and China (Cai et al., 2006, 2012). However, most of the existing δ18O records for the last deglacial period are from the margins of the ISM region (Neff et al., 2001; Burns et al., 2002; Fleitmann et al., 2003; Sinha et al., 2005; Shakun et al., 2007). To the best of our knowledge there is only one published speleothem record for the last deglacial MA period from Himalayan region (Timta cave) in India (Sinha et al., 2005) and no record from the peninsular region, which would represent the central zone of ISM activity. Our high resolution ED VSPM4 record is an attempt to fills this gap. In this study we present a new high resolution, PT absolutely dated, speleothem δ18O record from Valmiki cave to reconstruct the last deglacial ISM variability in southern India. The present work addresses the factors affecting the ISM AC ISM and EAM. CE activity on decadal to multidecadal timescales and examines the relationship, if any, between 2. Cave location and climate Valmiki cave (Kuruva Bali Guha) is located in Boylavadlapalle, Dhone Taluk, in the Kurnool district of Andhra Pradesh (15° 09′N: 77° 49′E). This cave lies at an elevation of 420 m above sea level (asl) with a narrow entrance (1 m high and 2m wide) and high humidity (>95%) (Figure 1). Valmiki cave is one of the deepest known caves in India with a length of 318 m and depth of -77 m below the surface. The cave is located in the Paleoproterozoic Vempalle dolomite (Chakrabarti et al., 2011), in the western part of the Cuddapah basin. Vegetation in the area is mostly open scrub with rain-fed and irrigated crops (Dar et al., 2011). The regional 4 ACCEPTED MANUSCRIPT climate is semi-arid with mean annual rainfall of ~670 mm (mean annual precipitation δ18OVSMOW = -4‰; 95% CI = 0.3‰; Bowen and Revenaugh, 2003) and mean annual temperature NU SC RI PT of 28 °C. About 70 – 90% of annual precipitation occurs during the summer monsoon season (June to September) with overall constant temperature (Figure S1, supplementary material). 3. Material and methods A stalagmite sample (VSPM4), measuring ~185 mm in length, (Figure 2) was collected from Valmiki cave in June 2009. The sample was cut along the growth axis and polished. Three MA distinctive layers from the top, center and bottom portions of the sample were identified for Hendy test (Figure 3). The mineralogy of the stalagmite was determined by chemical staining on ED a thin (4 mm) slab of VSPM4 using Feigl’s solution (Kato et al., 2003). Two samples (1 g each) PT were drilled using micro-driller (MANIX - 180) with a 1 mm drill bit at the top and bottom of VSPM4 (Figure 2) for X-ray diffraction (XRD). XRD analysis was carried out on a Philips X-ray CE diffractometer using nickel filtered CuKα radiation at the CSIR-National Institute of 230 AC Oceanography (NIO), Goa, India (Kessarkar et al., 2010). Th dating also referred to as U-Th dating or 238 U–234U–230Th dating, was used to determine stalagmite ages. Nine distinct layers were identified from VSPM4 and drilled for 230 Th dating on a Thermo Fisher NEPTUNE multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS) at the High-Precision Mass Spectrometry and Environment Change Laboratory (HISPEC), National Taiwan University, Taiwan (Shen et al., 2012). Details of the chemical procedures followed are described in Shen et al. (2003). Instrumental methods and offline data reduction are described in Shen et al. (2002; 2012). Estimated 230 Th dates (relative to 1950 AD) with a 2error from ±44 to ±98 years are in correct stratigraphic order (Table 1). The 5 ACCEPTED MANUSCRIPT speleothem age model was constructed using StalAge model (Scholz and Hoffmann, 2011) (Figure 4). The model uses U- series ages along with their associated age uncertainties and NU SC RI PT stratigraphic information to improve the age model. It provides modeled ages with 95% confidence limits using a Monte-Carlo simulation. To construct a δ18O time series, continuous drilling was carried out along the growth axis using a micro-driller (MANIX - 180) with a 0.8 mm drill bit. Subsamples were reacted with saturated orthophosphoric acid (100% H3PO4) at ~70ºC in a vacuum system and the evolved CO2 MA was analyzed for δ18O by mass spectrometry (Ahmad et al., 2012). The oxygen isotope ratio measurements were carried out at the CSIR-National Geophysical Research Institute, Hyderabad, ED India, using a DeltaPlus Advantage Isotope Ratio Mass Spectrometer (IRMS) coupled with a Kiel IV automatic carbonate device. Standards were run every 8 samples and duplicates were PT measured every 12-16 samples to check the reproducibility. All the results of δ18O are reported CE relative to Vienna Pee Dee Belemnite (VPDB) standard. Calibration to the VPDB standard was achieved by repeated measurements of NBS-18 and NBS-19 standards. The analytical (external) AC precision was better than 0.10‰ for δ18O. The millennial-length VSPM4 record contains 222 δ18O measurements with temporal resolution ranging from 1 to 7 yrs (Average resolution = 4.5 yr.) and an average growth rate of 0.19 mm/yr. Spectral analysis of the δ18O dataset was used to investigate periodicities in the time series. In order to decipher the periodic components in the δ18O time series (unevenly spaced in time), we used REDFIT v. 3.8 in Matlab (Schulz and Mudelsee, 2002). Most paleoclimate time series contain unevenly distributed data, impeding an accurate estimate of their temporal spectrum. The REDFIT program used in this study is based on Lomb-Scargle Fourier transform 6 ACCEPTED MANUSCRIPT (Lomb, 1976; Scargle, 1982, 1989) and has been specifically developed to address unevenly spaced paleoclimate time series. NU SC RI PT 4. Results and discussion Mineralogy of the sample was determined by using Feigl’s solution and XRD analysis. A 4 mm thin slab of VSPM4 was stained black by Feigl’s solution, revealing a pure aragonite sample. The two sub-samples taken from top and bottom portions of VSPM4 reveal that the sample is 100% aragonite. The XRD results are shown in Figure S2 of the supplementary 230 Th ages are presented in Table 1. All the nine absolute dates are in correct ED The MA material. stratigraphic order ranging from 15,677 to 14,698 yr BP (Figure 4). Ages exhibit 2analytical PT error from ±44 to ±98 years. The high U content (~5500 to ~11000 ppb) and low 232 Th content CE (100s-1000s ppt) indicates that the detrital Th level is very low in VSPM4 thereby indicating the robustness of our 230Th chronology. Nine 230Th ages are plotted against their sampling depths in AC Figure 4. Because the speleothem growth rate is uneven, a linear interpolation was avoided for age modeling. The StalAge model based on a Monte-Carlo simulation (Scholz and Hoffmann, 2011) was used to infer ages for each δ18O sub-sample. The growth rate of VSPM4 varies from 0.1 to 0.9 mm/yr, with an average of 0.19 mm/yr (Figure S3, supplementary material). During the later phase of H1 from ~15,700 to ~14,850, the VSPM4 growth rate was mostly less than 0.15 mm/yr. At the start of Termination 1a (~14,835 - 14,700 yr BP), the growth rate increased significantly with greater availability of drip water due to the increased intensity of ISM precipitation. The average growth rate during T1a was 0.45 mm/yr, ranging between 0.25 and 0.9 mm/yr. Visual examination suggests that VSPM4 contains few hiatuses, caused by either 7 ACCEPTED MANUSCRIPT precipitation hiatuses or fast drip rate events marked by clay deposition. A hiatus affects the age calibration by adding to the uncertainty of modeled ages. While we observed a few hiatuses in NU SC RI PT VSPM4, it is assumed that these events were of very short (few years) duration. High amplitude δ18O variation in the speleothem aragonite suggests significant changes in ISM precipitation during the last deglaciation. A total of 222 δ18O values are plotted against their interpolated ages in Figure 5. The δ18O values in VSPM4 range from -0.31 to -2.81 ‰ with a mean value of -1.31‰ (relative to VPDB). The temporal resolution of the δ18O data ranges MA from 1 to 7 years with a mean of ~5 years. Our high resolution δ18O record contains four distinct features. First, rapid intensification in ISM precipitation is observed in sharp decreases in δ18O ED (1.1 – 1.9 ‰) during four major time intervals: 15,330 – 15,290, 15,135 – 15,105, 14,835 – 14,795, and 14,755 – 14,725 yr BP. Second, abrupt declines in ISM precipitation are represented PT by sudden increases in δ18O (1.3 – 1.7 ‰) during three intervals: 15,595 – 15,535, 15,105 – CE 15,075, and 14,940 – 14,890 yr BP. Third, a major increase in ISM activity occurred during Termination 1a, between ~14,835 and ~14,700 yr BP marked by a decrease of ~2.5‰ in δ18O. AC Fourth, the older portion of the record, representing the later phase of Heinrich event 1 (H1), can be divided into two phases of intermittently dry and wet climates: 15,570 – 15,130 (avg. δ18O = ~-1.0‰) and 15,130 – 14,870 yr BP (avg. δ18O = -1.5‰). Based on the average amplitude of δ18O variations during these two phases, we infer that 15,570 – 15,130 yr BP was a relatively dry period, punctuated by two wet events at 15,430 and 15,290 yr BP. The climate in the interval from 15,130 to 14,870 yr BP was mostly wet. Large fluctuations in the δ18O value of VSPM4 aragonite are due to temporal changes in the δ18O value and amount of monsoon precipitation, reflecting varying ISM activity during the last deglaciation. The impact of amount effect in the δ18O signature of Indian speleothems has 8 ACCEPTED MANUSCRIPT been very well demonstrated in previous studies (Yadava et al., 2004; Yadava and Ramesh, 2005; Sinha et al., 2005, 2007, 2011b; Berkelhammer et al., 2010), implying that the temperature NU SC RI PT effect on δ18O of Indian speleothems are insignificant, particularly in the peninsular region. Data from the Global Network of Isotopes in Precipitation (GNIP) demonstrate that the amount effect is the main cause of δ18O variability during the monsoon season in the Indian region (Bhattacharya et al., 2003). Vuille et al., (2005) demonstrated a negative correlation between δ18O of precipitation and monsoon activity (amount effect) across the Asian monsoon region. The amount effect in southern India during summer monsoon has also been established by MA Kumar et al. (2010) while studying the isotopic characteristics of Indian precipitation. On the basis of these studies, we interpret the δ18O changes in VSPM4 as a reflection of fluctuations in ED the amount / intensity of ISM precipitation. PT A test for isotopic equilibrium deposition of speleothem carbonate was proposed by CE Hendy, (1971). This entails measurement of δ18O at different portions of individual growth layers within a speleothem sample. If a speleothem is formed under isotopic equilibrium AC conditions, it should display almost identical δ18O values along a single growth layer. We performed Hendy test on three distinct growth layers of VSPM4 (Figure 2). No significant variation in δ18O or any correlative trend between δ18O and δ13C was observed in these layers (Figure 3). Therefore, we conclude that the deposition of VSPM4 occurred under the isotopic equilibrium conditions. Although some researchers have attributed aragonitic speleothem deposition to evaporation instead of degassing, the precipitation of aragonite is favored in dolomite host rocks (McDermott, 2004; Alonso-Zarza and Martín-Pérez, 2008) due to high aqueous Mg content (Gussone et al., 2005). Because the Valmiki cave is hosted by Vempalle dolomite and is at approximately 100% humidity and near constant temperature, we attribute the 9 ACCEPTED MANUSCRIPT aragonitic nature of VSPM4 to the high Mg content of the host rock. This suggests that evaporation is insignificant and the slow degassing of CO2 preserves isotopic equilibrium NU SC RI PT conditions in the speleothem deposits. The equilibrium test also involves replication of isotopic records from the same cave or from different caves (Dykoski et al., 2005; Cai et al., 2012). Interestingly our δ18O record correlates well with the speleothem records from China (e.g. Dongge cave, Dykoski et al., 2005; Yamen cave, Yang et al., 2010) indicating that the climate signal from VSPM4 is of wide regional significance. MA Oxygen isotope trends move in parallel in Indian and southern China speleothem records during the last deglacial period, providing evidence of synchronous variability in monsoon ED regimes (Figure 5). Atmospheric water vapor over southern China during the summer period is primarily transported from the Indian Ocean (Wang and Chen, 2012). In a simulated Heinrich PT event 1 (H1), Pausata et al., (2011) proposed that the ISM has a strong influence on Chinese CE stalagmite δ18O values. Simultaneous strengthening of rainfall intensity, shown in a comparison of the VSPM4 record with Dongge and Yamen caves (Dykoski et al., 2005; Yang et al., 2010) AC located in southern China support the idea that the Chinese speleothem isotope excursions actually reflect distant changes in ISM activity during the last deglaciation. This is consistent with the inferences drawn by Pausata et al., (2011) and Wang and Chen (2012). Comparison of VSPM4 record with those of Hulu cave (east China; Wang et al., 2001), Maboroshi cave (Japan; Shen et al., 2010) and NGRIP ice core (Greenland; GICC05 timescale; NGRIP, 2006) records reveal absence of one-to-one relationship between ISM and EAM. However, some synchronous changes are seen on multidecadal timescales during certain time intervals (Figure 6). Our high-resolution record provides insight into both the onset and evolution of a rapid climate shift during the last deglaciation. The δ18O record from VSPM4 demonstrates that strong 10 ACCEPTED MANUSCRIPT monsoon events during late Heinrich 1 (H1) preceded the inception of Termination 1a (T1a). Tropical warming induced a northward shift of the Intertropical Convergence Zone (ITCZ) NU SC RI PT resulting in an abrupt intensification of the Indian monsoon. A lag of ~100 years between T1a in VSPM4 and NGRIP (GICC05 timescale (NGRIP, 2006)) and Maboroshi Cave (Shen et al., 2010) record could be attributed to the reorganization of the tropical atmospheric circulation followed by changes in the mid to high latitude atmospheric circulation patterns (Steffensen et al., 2008). While this lag is clearly evident during T1a, it appears to be fading during reported interval of H1. We speculate that such a lag may be more prominent during major climatic MA events like T1a via some unknown mechanism. However, the time lag may also be ascribed to ED age errors in these records. The abrupt δ18O changes revealed in our record correspond to multidecadal variability in PT ISM activity and the sub-decadal resolution of the VSPM4 record reveals the fine structure of CE these sudden changes. Previous studies have provided sufficient evidence indicating abrupt changes in ISM strength (Overpeck et al., 1996; Sinha et al., 2005; Shakun et al., 2007), with AC multidecadal power (Yadava and Ramesh, 2007; Berkelhammer et al., 2010). These variations are revealed by drastic changes in δ18O (>1‰) of our VSPM4 record, with transitions from extremely wet to dry conditions and vice versa occurring within a few decades. Because Valmiki cave is nearer to the Indian Ocean than Himalayan and Chinese caves (Figure 1), VSPM4 is expected to have higher speleothem δ18O values. Therefore a variation of even 1‰ represents a large change in precipitation amount. The present day average annual δ18O values of precipitation at Valmiki cave are high due to close proximity to the northern Indian Ocean (Figure 1) (Bowen and Revenaugh, 2003). Therefore, we suggest that the abrupt shifts in ISM activity during the later phase of Heinrich event 1 (H1) may be responsible for inducing a 11 ACCEPTED MANUSCRIPT triggering mechanism for Termination 1a via solar forcing in association with ocean-atmospheric circulation. This eventually led to the warmer Bølling-Allerød. NU SC RI PT A spectral analysis of δ18O time series in VSPM4 reveals two strong peaks at approximately 0.030 and 0.081 cycles per year at the 99% confidence level (Figure 7), possibly indicating a solar and / or ocean-atmospheric circulation controls on ISM variability. The peak centered on 0.081 cycles per year (~12 year periodicity) in our record may be linked to the solar sunspot cycle (decadal variability). While the average resolution of our record is ~5 years, nearly MA half of the data points were sampled at ~2 year resolution, which makes this cycle close to the cutoff frequency. The peak at 0.030 cycles per year (~33 year periodicity) is assumed to be ED related to solar and / or ocean-atmospheric circulation changes. This cycle may also be a multiple of the sun spot cycle. A 33 – 38 year cycle reported by Stocker, (1994) has been attributed to PT natural fluctuations of thermohaline circulation in the North Atlantic. A 32 year solar cycle has CE been reported by Tiwari et al., (2012), from a tree ring record of the western Himalaya. Moreover a 33 year cycle has been reported from various Chinese speleothem records (Ku and AC Li, 1998; Paulsen et al., 2003; Zhang et al., 2013) and a 36 year cycle was reported by Cai et al. (2012). Although the nature of 33 year cycle is still unclear, in light of the available literature we attribute this cycle in VSPM4 to solar forcing and / or ocean-atmospheric control on ISM dynamics. Some paleoclimatic records suggest a direct link between solar activity and ISM variability (Kodera, 2004; Gupta et al., 2005), on both centennial and decadal scales (Neff et al., 2001; Agnihotri et al., 2002; Fleitmann et al., 2003). The Indian monsoon tends to strengthen during peaks in the 11 year solar cycle (van Loon and Meehl, 2012). We suggest that solar variability in conjunction with ocean-atmospheric circulation and other related feedback processes may have resulted in abrupt changes in ISM activity during the last deglaciation. 12 ACCEPTED MANUSCRIPT Through some triggering mechanism, solar variability seems to have induced large changes leading to major climate system transitions, such as Termination 1a. NU SC RI PT 5. Conclusions Stalagmite VSPM4 from Valmiki Cave in southern India provides the first highresolution, absolutely dated 1,000-year ISM precipitation record for the last deglacial period. The record shows large amplitude δ18O variations corresponding to abrupt fluctuations in ISM intensity with decadal to multidecadal phases. The data reveals the probable timing of MA Termination 1a in the Indian peninsula and demonstrates the importance of this tropical region in a major abrupt climate change in the northern hemisphere. The correlation of the VSPM4 record ED with southern Chinese speleothems suggests a significant teleconnection with south China by PT demonstrating ISM influence on these caves. Synchronous variability on multidecadal timescales is found between ISM and EAM during the recorded period. Spectral analysis reveals ~12 and 33 CE year cycles which suggest a possible solar and / or ocean-atmospheric control on ISM dynamics AC during the studied period. Acknowledgements The authors are grateful to Prof. Mrinal K. Sen, Director, CSIR-NGRI, Hyderabad and thank Dr. Jerome Perrin, Dr. V. Purnachandra Rao, Prof. Ashish Sinha and colleagues at paleoclimate lab, NGRI for their support. Thanks are due to Dr. J. Kedariswari and Mr. Vijay Kumar, Dept. of Archaeology and Museums, for permission to collect the sample. Constructive reviews by Dr. Silviu Constantin and two anonymous reviewers significantly improved this paper. Prof. David Dettman and Prof. Joyanto Routh are acknowledged for thorough review and improving the language of the manuscript. The first author is thankful to the Council of 13 ACCEPTED MANUSCRIPT Scientific and Industrial Research (CSIR) for a Senior Research Fellowship. Financial support provided by the CSIR-National Geophysical Research Institute through INDEX and SHORE NU SC RI PT projects, is thankfully acknowledged. 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Yang, Y., Yuan, D.X., Cheng, H., Zhang, M.L., Qin, J.M., Lin, Y.S., Zhu, X.Y., Edwards, R.L., AC 2010. Precise dating of abrupt shifts in the Asian Monsoon during the last deglaciation based on stalagmite data from Yamen Cave, Guizhou Province, China. Sci China Earth Sci. 53(5), 633641, doi: 10.1007/s11430-010-0025-z. Zhang, H.-L., Yu, K.-F., Zhao, J.-X., Feng, Y.X., Lin, Y.-S., Zhou, W., Liu, G.-H., 2013. East Asian Summer Monsoon variations in the past 12.5 ka: High-resolution δ18O record from a precisely dated aragonite stalagmite in central China. Journal of Asian Earth Sciences 73, 162175, doi:10.1016/j.jseaes.2013.04.015. 23 ACCEPTED MANUSCRIPT List of Captions Figure 1. Map showing location of Valmiki cave and other cave sites discussed in this study. The NU SC RI PT map displays modern weighted mean annual precipitation δ18O over the Asian region (modified from Bowen and Revenaugh (2003). The δ18O of precipitation at Valmiki cave site is higher than Himalayan and other Chinese cave sites due to its proximity to the source of atmospheric water vapor (the northern Indian Ocean). Figure 2. VSPM4 stalagmite. Black line represents the drilling sites for δ18O measurements. Red 230 Th dating samples. Blue lines show Hendy test layers and green lines MA lines represent nine ED mark XRD analysis. Figure 3. Hendy test results. Blue, green and red lines represent three different test layers. (a) PT δ18O values, (b) δ13C values, (c) compares δ18O and δ13C. R2 in (c) suggests that the sample CE formed under equilibrium conditions. AC Figure 4. The age model (green line) with 95% confidence limits (red lines) based on StalAge algorithm. The black dots with vertical error bars represent nine error. 230 Th samples with standard Figure 5. Low VSPM4 δ18O values (blue) reflects intense precipitation events at 15,640, 15,595, 15,290, 15,105, 15,005, 14,940, 14,885, 14,795, 14,725 and 14,700 yr BP and high δ18O values at 15,535, 15,135 and 14,835 yr BP, suggest extremely dry episodes. Comparison between the δ18O time series of VSPM4, with southern China cave records Yamen (red; Yang et al., 2010) and Dongge (purple; Dykoski et al., 2005). The vertical grey bar represents Termination 1a. 24 ACCEPTED MANUSCRIPT Horizontal error bars correspond to age error (2in the records of the same color (before 1950 NU SC RI PT AD). Figure 6. In-phase relationship between VSPM4 (blue), Hulu YT (dark green; Wang et al., 2001), Maboroshi (brown; Shen et al., 2010) and NGRIP (black; (GICC05 timescale) NGRIP, 2006). GICC05 b2k time series is corrected to years before 1950 AD. Black arrows indicate periods of synchronous changes between ISM and EAM. Figure 7. Power spectrum of the VSPM4 time series data using REDFIT 3.8 with 90, 95 and ED ocean atmospheric control on ISM. MA 99% significance level. Data reveals ~12 and 33 year cycles probably connected to solar and Figure S1. Monthly average climate data from Kurnool, 1901 to 2002. Red line represents PT temperature (°C), and Blue vertical bars represent rainfall (mm). The green line shows monthly CE δ18OVSMOW of precipitation at the cave site derived from the Online Isotopes in Precipitation Calculator (OIPC 2.2), Bowen (2012), available at http://www.waterisotopes.org. Note the AC amount effect during monsoon months when temperature is near annual average. Figure S2. X-ray diffraction (XRD) results referring to complete aragonitic mineralogy of VSPM4. Figure S3. Growth rate curve showing variable growth rate during VSPM4 formation. Note the abrupt increase in growth rate at ~6 cm referring to the start of Termination 1a with increased monsoon activity. 25 ACCEPTED MANUSCRIPT List of Tables Table 1. Uranium and thorium isotopic compositions and 230 Th ages (before 1950 AD) for AC CE PT ED MA NU SC RI PT subsamples of stalagmite VSPM4 from Valmiki cave, southern India, by MC-ICP-MS. 26 AC Fig 1 CE PT ED MA NU SC RI PT ACCEPTED MANUSCRIPT 27 AC CE PT ED MA NU SC RI PT ACCEPTED MANUSCRIPT Fig 2 28 AC CE PT ED MA NU SC RI PT ACCEPTED MANUSCRIPT Fig 3 29 Fig 4 AC CE PT ED MA NU SC RI PT ACCEPTED MANUSCRIPT 30 ED MA NU SC RI PT ACCEPTED MANUSCRIPT AC CE PT Fig 5 31 AC CE PT ED MA NU SC RI PT ACCEPTED MANUSCRIPT Fig 6 32 PT ED MA NU SC RI PT ACCEPTED MANUSCRIPT AC CE Fig 7 33 ACCEPTED MANUSCRIPT AC CE PT ED MA NU SC RI PT Table 1 34 ACCEPTED MANUSCRIPT Research Highlights:   First high resolution last deglacial ISM record from a south Indian speleothem  Strong solar and ocean-atmospheric control on Indian Summer Monsoon variability  South China caves influenced by Indian summer monsoon (ISM) NU SC RI PT  Decadal to multidecadal variability with abrupt changes in ISM activity AC CE PT ED MA Timing of Termination 1a in Indian region and ISM relation with East Asian Monsoon 35