Late Quaternary climate in southern China deduced from Sr–Nd isotopes of Huguangyan Maar sediments

Earth and Planetary Science Letters 496 (2018) 10–19

Contents lists available at ScienceDirect

Earth and Planetary Science Letters www.elsevier.com/locate/epsl

Late Quaternary climate in southern China deduced from Sr–Nd isotopes of Huguangyan Maar sediments Shikma Zaarur a,∗ , Mordechai Stein a,b , Ori Adam a , Jens Mingram e , Guoqiang Chu c , Jiaqi Liu c,d , Jing Wu c , Yigal Erel a a

Institute of Earth Sciences, The Hebrew University of Jerusalem, Givat Ram, 91904, Israel Geological Survey of Israel, 30 Malkhe Israel St., Jerusalem, 95501, Israel c Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China d College of Earth and Planetary Sciences, Chinese Academy of Sciences, Beijing, China e GFZ German Research Centre for Geosciences, Potsdam, Germany b

a r t i c l e

i n f o

Article history: Received 7 December 2017 Received in revised form 13 May 2018 Accepted 16 May 2018 Available online xxxx Editor: D. Vance Keywords: paleo-climate East Asian monsoon Huguangyan Maar Sr–Nd

a b s t r a c t The hydro-climatic conditions that prevailed during the last Glacial and early to mid-Holocene periods in South China are inferred from chemical compositions and Sr–Nd isotope ratios of sediments from lake Huguangyan Maar and its vicinity. The lake sediments are comprised of organic matter, volcanic materials and aeolian input from nearby granitoid-derived soils. Variations in 87 Sr/86 Sr ratios in the lake sediments indicate two modes of climate conditions: wet intervals during which the lake sediments are mainly derived from the volcanic-lake rim materials, expressed in low 87 Sr/86 Sr ratios, and dry intervals during which fine particles from the nearby granitic soils are windblown to the lake and supply local dust expressed in high 87 Sr/86 Sr ratios in the sediments. These wet and dry intervals generally correspond to regional climate records (e.g., speleothem δ18 O profiles in southeast China) and correlate with global climate events (e.g., Heinrich events). While δ18 O records of speleothems from southeast China caves are dominated by the precession signal, the Huguangyan Maar Sr record mainly correlates with obliquity. This most likely reflects masking of the precession signal due to regional climate variability, accentuating the obliquity signal. These local effects may also account for some of the differences that have been observed between the various East Asian monsoon records. More importantly, the masking of the precession signal reveals the direct influence of obliquity on the hydro-climate regime in South China. © 2018 Published by Elsevier B.V.

1. Introduction The East Asian monsoon is an important climate system, impacting the lives and livelihood of billions of people. Understanding the dynamics of the system and its sensitivity to climate forcings are instrumental in predicting its future response to global and regional climate changes. The history of the East Asian monsoon has been inferred from cave deposits (e.g., Cheng et al., 2016; Wang et al., 2001; Yuan et al., 2004), loess-based proxies (e.g., Li et al., 2017; Maher, 2016; Porter, 2001; Sun et al., 2006), lacustrine (An et al., 2011; Ao et al., 2012) and marine sediments (e.g., Ao et al., 2011), as well as numerical paleo-climate simulations (e.g., Mohtadi et al., 2016). Millennial-scale North Atlantic climate events have been shown to have dramatic effects on the climate

*

Corresponding author. E-mail address: [email protected] (S. Zaarur).

https://doi.org/10.1016/j.epsl.2018.05.025 0012-821X/© 2018 Published by Elsevier B.V.

in East Asia. For example, Heinrich Event 1 (H1) at ∼17.4–16 ka, is thought to have invoked a catastrophic drought (Zhou et al., 2016); similarly, the mid-Holocene north Atlantic cooling is associated with an intensification of the East Asian winter monsoon (Hao et al., 2017). Long-term variability in the various paleo-monsoon records is related to eccentricity (∼100 ka), obliquity (∼41 ka) and precession (∼23 ka) orbital cycles. Glacial–interglacial rhythms (obliquity and eccentricity) dominate aeolian deposits in the Chinese loess (Sun et al., 2006) and lacustrine deposits (An et al., 2011; Ao et al., 2012), while changes in the δ18 O cave deposits are dominated by precession (e.g., Cheng et al., 2016). These differences raise questions regarding the primary drivers and controls on monsoon variability over time and the role of local versus global climate variability and proxy sensitivity. Here, using chemical compositions and Sr–Nd isotope ratios in sediments from Huguangyan Maar lake (Fig. 1), we examine the prevailing hydro-climatic conditions related to the East Asia monsoon systems in southern China, during the past ∼70 ka. The

S. Zaarur et al. / Earth and Planetary Science Letters 496 (2018) 10–19

11

Fig. 1. Study area. (a) Map of East Asia depicting the location of Lake Huguangyan Maar. Red and blue arrows point to the general directions of the summer and winter monsoon systems, respectively. (b) Geological map (Lifang et al., 2004) of Lake Huguangyan Maar (red circle) basalt in volcanic field (bright green), surrounding Quaternary fluvial and alluvial sediments (light yellow), and granitic units (pink). (c) Huguangyan Maar lake after Mingram et al. (2004). (For interpretation of the colors in the figure(s), the reader is referred to the web version of this article.)

occurrence and sources of aeolian input to Huguangyan Maar sediment are at the core of a scientific debate, with far reaching consequences regarding our understanding of the East Asian monsoon system. Yancheva et al. (2007) assumed that relative changes in Ti concentrations in Huguangyan Maar sediments over the past 16 ka reflect variations in dust influx to the lake from remote or local sources in response to changes in the intertropical convergence zone (ITCZ) and strengthening of the winter monsoon winds. This argument was later challenged by the inconsistencies between the chemical and isotopic compositions of the lake sediments and the Chinese loess deposits (Wang et al., 2016; Zhou et al., 2009). We re-examine this question by expanding the information on the chemical and Sr–Nd isotopes of the lake sediments and nearby deposits, and extend the study to the last glacial cycle. Our analyses and results point to the importance of regional climate variability in interpreting the monsoon climate records. 2. Geological and climatic background Huguangyan Maar lake (21◦ 9 N, 110◦ 17 E) is located in a volcanic crater in the Leiqiong Volcanic Field, on the Leizhou Peninsula (Fig. 1). The lake is 23 m above sea level, and is surrounded by a tephra rim, reaching 88 m above sea level with a steep inner slope. The lake is ∼1.7 km in diameter, 20 m deep

and has a surface area of 2.25 km2 . The catchment area comprises only the inner slopes of the crater rim, with no surface in- or out-flows (Mingram et al., 2004). The hydrochemistry of the lake is influenced by surface flow in the catchment area, regional groundwater flow, aeolian deposits, sea-spray, and authigenic precipitation–dissolution processes (Mingram et al., 2004; Yancheva et al., 2007). The Leiqiong Volcanic Field is located in an extensional basin at the granitic-passive continental margins of South China (Fig. 1; Ma and Wu, 1987). Volcanic activity began in the Oligocene and lasted through the Holocene. Early volcanism was dominated by quartz tholeiites and olivine tholeiites, and late volcanism was dominated by alkali olivine basalts and basanites (Huang et al., 2007); ilmenite and titanomagnetite are the main Fe-oxides (Ho et al., 2000). The basalts intruded the South China Precambrian Basement (e.g., the Neoproterozoic Cathaysia Granitoids, Chen and Jahn, 1998; Jahn et al., 1976, 1990) whose granitoid terrains are exposed about 50 km north of the maar (Fig. 1). The volcanic field is overlain by Quaternary fluvial and alluvial deposits (Lifang et al., 2004), likely derived from the exposed granitoid terrains. The mean annual temperature and precipitation in the area are 23.1 ◦ C and 1440 mm/yr, respectively (Mingram et al., 2004). The region is strongly affected the East Asian summer monsoon and to a lesser degree by the Indian monsoon, and northern cold fronts

12

S. Zaarur et al. / Earth and Planetary Science Letters 496 (2018) 10–19

Table 1 Samples collected from Huguangyan Maar rim and vicinity and their mineralogical composition.

HUM HUM HUM HUM HUM HUM HUM HUM HUM HUM

1 2 3 4 5 6 7 10 11 12

Material

Phyllosilicate/Clays

Quartz

Plagioclase

K-Feldspar

paleosol paleosol paleosol paleosol tuff tuff pyroclastic material soil soil soil

10–20% 20–30% 30–40% 20–30% 25–35% 20–30% 5–15% 20–30% 30–40% 20–30%

25–35% 45–55% 30–40% 50–60% 20–30% 35–45% 55–65% 65–75% 55–65% 60–70%

35–45% 5–15% 20–30% 5–15% 20–30% 15–25% 15–25%

5–15% 10–20% 5–15% 5–15% 20–25% 5–15% 1–10%

originating from the Siberian anti-cyclone (Mingram et al., 2004; Yancheva et al., 2007). Today, strong winter (November–March) winds blow from the north and northeast. During the summer, southwest and southeast Asian summer monsoons bring large amounts of precipitation to the region (Zhang and Crowley, 1989). Unless otherwise stated in the text “summer” and “winter” monsoon refer to the East Asian monsoon systems. Huguangyan Maar sediments have been previously used to study East Asian climate history. The glacial period paleo-environmental record of the lake, based on pollen and organic compound analyses could not, however, be correlated directly and consistently to global climate patterns (Mingram et al., 2004). Late and post-glacial climate history relating to global climate events, has been inferred from pollen, magnetic susceptibility and chemical data (e.g., Chu et al., 2017; Jia et al., 2015; Sheng et al., 2017; Wang et al., 2016; Wu et al., 2012; Yancheva et al., 2007). 3. Materials and methods 3.1. General Core sediment samples from Huguangyan Maar, extending to

∼70 ka were collected from the sediment core archives at GeoForchungszentrum (GFZ) Potsdam, Germany (core F, Mingram et al., 2004). Lake cores were obtained by the German–Chinese drilling project and were previously described and dated by Mingram et al. (2004). In brief, seven cores were recovered from three sites in the lake, the longest of which reaches 57.8 m. The chronostratigraphy is based on 14 C dating and linear extrapolation. The correlation between cores is based on magnetic susceptibility and water content (Mingram et al., 2004). Using a multi-proxy approach, the core was divided into seven lithological zones (LZ) described in brief below: LZ 1 (present to 4 ka) is comprised of homogeneous algal gyttja and is characterized by high sedimentation rates and high frequency of changes in dry-sediment density, water content and magnetic susceptibility. Since pollen data in this lithozone is indicative of anthropogenic activities, it is not included in our analysis. LZ 2 (4 to 15 ka) is comprised of macroscopically homogeneous algal gyttja and occasionally siderite, and is characterized by low sedimentation rates. LZ 3 (15 to 40.5 ka) is comprised of macroscopically homogeneous algal gyttja with high values of dry-sediment density, low values of magnetic susceptibility and an elevated level of inorganic carbon. LZ 4 (40.5 to 48 ka) is comprised of macroscopically homogeneous algal gyttja with frequently occurring reworked plant macro-remains. LZ 5 (48 to 58 ka) is similar to LZ 3, with high biogenic silica content and high magnetic susceptibility values. LZ 6 (58 to ∼73.5 ka) is comprised of algal gyttja, similar to LZ 4 but with frequent siderite, and exhibits some lamination with diatom-rich layers. LZ 7 (∼73.5 to 78.5 ka, not included in this study) is partly laminated and is comprised of biogenic silica rich algal gyttja with scattered plant remains.

1–10%

≥1%

Goethite

≥1% ≥1% ∼5%

In addition to the core materials, we collected several samples from the lake inner rim (local basalt, pyroclastic materials and paleosols) and from the vicinity of the lake (2 km NE of the lake) outside the catchment area (three nearby soils; Table 1). The mineralogical, chemical and isotopic compositions of the samples were analyzed as follows. 3.2. Grain size analysis The grainsize distribution of unconsolidated samples was measured by Mastersizer2000, at the Institute of Chemistry, the Hebrew University of Jerusalem. Following Crouvi et al. (2008), roughly 30 mg of sample material was suspended in 20 ml of distilled water for at least 5 min on a magnetic stirrer. A few drops of an anti-coagulant (Calgon) were added to enhance aggregate dispersion. Once suspended, samples were transferred to the Mastersizer2000 and measured three times. To ensure homogeneous and random sampling, three separate aliquots from each sample were measured independently. Results enabled definitive graphical determination of modality (uni, bi or tri modal distribution) and the different grainsize fractions were separated accordingly by a combination of automated sieving (GilSonic AutoSiever GA 1A), manual sieving and water. 3.3. Mineralogy Powdered samples were side-loaded into a standard aluminum holder and were scanned by a PANALYTICAL X’Pert3 Powder diffractometer equipped with a PIXcel detector using Data Collector, at the Geological Survey of Israel. Scanning range was 3◦ –70◦ 2θ , step size was 0.013◦ , and the speed was set to 70.1 s per step. Mineral identification was mostly done manually and with some minerals identified by the Highscore+ software. 3.4. Chemical compositions Roughly 100 mg of homogenized powdered samples were dissolved for the purpose of chemical and isotopic analyses. Materials were dissolved in Teflon beakers at 185 ◦ C on a hot-plate with concentrated HNO3 , HF and HCl until complete dissolution. Once dissolved, the acid was evaporated and the sample was re-dissolved and stored in 10 ml of 1N HNO3 . The dissolved samples were used for major and trace element analyses by an ICP-MS (Agilent 7500cx), in the Institute of Earth Sciences, the Hebrew University of Jerusalem. Each run included a set of internal and international (T-207 and T-209) standards. Measurement uncertainty was 10% relative to the standard materials. Silica and Ti oxides concentrations were determined by X-ray fluorescence (Tracer III-V Bruker instrument and S1PXRF software), using an array of international standards for calibration. Each sample was measured three times. Measurement uncertainty was 10%.

S. Zaarur et al. / Earth and Planetary Science Letters 496 (2018) 10–19

Table 2 Mineralogical composition of select samples from Huguangyan Maar core sediments.

HUG HUG HUG HUG HUG HUG HUG HUG HUG HUG

7 15 21 29 31 35 36 37 42 45

Age (ka BP)

Phyllosilicate/Clays

Quartz

Plagioclase

Siderite

7.5 12.1 14.2 25.0 30.0 35.9 39.5 40.1 53.5 62.9

55–65% 60–70% 40–50% 65–75% 60–70% 65–75% 60–70% 55–65% 65–75% 60–70%

25–35% 5–15% 40–50% 10–20% 10–20% 10–10% 15–25% 15–25% 10–20% 10–20%

5–15% 1–10% 1–10% 5–15% 1–10% 1–10% 5–15% 5–15% 1–10% 15–25%

≥1% 15–25% ≥1% ≥1% 5–15% ≥1% 1–10% 1–10% 5–15%

3.5. Sr and Nd isotopes analyses We used Sr-spec 50–100 mesh columns to separate Sr for Sr isotopic analysis. Dissolved samples (described above) were evaporated and re-dissolved in 3.5 M HNO3 and introduced to a preconditioned column, rinsed with 3.5 M HNO3 . Sr was released from the resin and collected by washing the column with 0.5 M HNO3 following Stein et al. (1997). Nd separation for isotopic analysis was done in two steps following Palchan et al. (2013). First, REEs were separated using Eicrom TRU-spec resin. Samples were introduced to the columns dissolved in 1N HNO3 , and REEs we released and collected with 1N HCl. To separate Nd from the REEs, samples were re-dissolved in 0.22N HNO3 and passed through a second column filled with Eichrom LN-spec resin. Isotope analyses were conducted on a Neptune Plus multi-collector, inductively coupled plasma mass spectrometer in the Institute of Earth Sciences, the Hebrew University of Jerusalem. SRM 987 Sr standard was measured every 5–10 samples yielding an average ratio of 87 Sr/86 Sr = 0.71025 ± 1 (2σ , n = 32). One batch of analyses (bulk HUM 1–12) yielded an average SRM 987 value of 0.71036 ± 1 (2σ , n = 8); these samples were corrected to the commonly accepted SRM 987 value of 0.71024. Nd isotope analyses were normalized to JNdi standard of 143 Nd/144 Nd = 0.512115 ± 7 (Tanaka et al., 2000), with multiple analyses yielding an average of 143 Nd/144 Nd of 0.512061 ± 6 (2σ , n = 12) for the HUM samples, and 143 Nd/144 Nd of 0.512099 ± 8 (2σ , n = 6) for the HUG samples. Rock standard BCR-1A yielded 143 Nd/144 Nd = 0.512636 ± 6 (2σ , n = 14, corrected using the JNdi standard). This value agrees with the value of BCR-2 of 143 Nd/144 Nd = 0.512637 ± 13 (Jweda et al., 2016). The Nd isotopic ratios are expressed as εNd = [[143 Nd/144 Nd(meas.)/143 Nd/144 Nd(CHUR)]−1] × 104 ; CHUR 143 Nd/144 Nd ratio = 0.512638 (Wasserburg et al., 1981).

13

4.2. Mineralogy Rough estimates of relative mineral amounts are listed in Tables 1 and 2. Paleosols are dominated by quartz (25–60%), phyllosilicates (including clays) (10–40%), plagioclase (5–45%), and K-feldspar (5–20%). Given the nature of the volcanic materials, we suspect that the large quantities of quartz (20–65%) in the tuffs and pyroclastic samples are from an external source. The nearby soils (HUM 10–12) are dominated by quartz (55–75%), and phyllosilicates (including clays) (20–40%); they contain up to 4% goethite and only up to 5% and 2% plagioclase and K-feldspar, respectively. The lake sediments contain ∼30% organic matter; the inorganic sediment fraction is dominated by phyllosilicate minerals (including clays) (40–75%), quartz (5–50%), plagioclase (0–25%), and siderite (0–20%). The baselines of the X-ray diffraction patterns of the lake-sediment samples indicate varying amounts of amorphous material (mostly likely diatoms). 4.3. Chemical composition Major and trace element compositions of lake-rim materials and nearby soils, and lake-core sediments are listed in SI Tables 1 and 2. Both the lake-rim materials and nearby soils are dominated by Si, Al and Fe. The nearby soils are poor (<1%) in the soluble elements (Na, Mg, K and Ca). On the other hand, in the lake-rim materials, Na and K oxides comprise ∼1%, each; MgO and CaO concentrations in the paleosols are ∼3% and 2.5% respectively, and in the tuffs and pyroclastic materials are ∼4.5% and 4%, respectively (SI Table 1). The inorganic fraction of the lake sediments is dominated by Si, Al and Fe and is poor (<1%) in the soluble elements. The sediments are enriched in Ti relative to the lake-rim materials and nearby soils (SI Table 2 and Fig. 2). The chondrite-normalized REE of the bulk lake-rim materials exhibit enriched LREE patterns ((La)n = 62 to 108) with no Eu anomaly, resembling patterns of alkali basalts (Fig. 3 and SI Table 1). The nearby soils show enriched LREE patterns ((La)n = 55 to 135), with negative Eu anomalies, resembling patterns of loess and calc-alkaline granites. A close examination of the fine fractions of different samples suggests there is mixing between particles derived from basaltic and granitic type sources. For example, the bulk material (that includes grains >1 mm) of the pyroclastic sample (HUM 7) has an REE pattern that resembles the basalt, whereas the fine fraction has a granitic pattern (Fig. 3a). In contrast, the bulk and largest fraction (∼800 μm) of the nearby soil HUM 10 have granitic REE patterns while the finer fractions have basaltic patterns (Fig. 3b). The REE concentrations of the lake-core sediments vary between samples, but they all have basaltic patterns (Fig. 4).

4. Results 4.4. Sr and Nd isotopes 4.1. Grain-size distribution Paleosols, soils and pyroclastic samples contain both coarse grains (larger than 1 mm) and fine particles (smaller than 1 mm) (SI Table 1). The fine fraction of the paleosols (HUM 2–4) and the pyroclastic sample (HUM 7) have unimodal normal distributions and average grain diameter of ∼30–40 μm, and ∼70 μm, respectively. The three nearby soil samples (HUM 10–12) have a tri-modal distribution with ∼750–850, 20, and 0.2 μm average particle diameter (Table 1). Chemical and isotopic analyses were conducted on both bulk and the separated fractions of these samples. Grainsize distributions of the lake sediment samples are unimodal (with mean grainsizes between ∼30–60 μm) and were therefore analyzed as bulk materials. Consolidated (e.g., basalt and tuff) samples were analyzed as bulk materials.

Sr and Nd isotopic ratios of the lake-rim materials, nearby soils and lake-core sediments are listed in SI Tables 1 and 2. The 87 Sr/86 Sr isotope ratios of the lake-rim materials and nearby soils span a wide range, from 0.70409 to 0.71754. The lowest ratios are found in the basalt and other lake-rim samples, while the most radiogenic values were measured in the three nearby soils (HUM 10–12). The range of Sr isotope ratios of lake-core sediments is smaller (0.70522 to 0.70962), with ratios clustering closer to those of the volcanic samples. εNd values of the lakerim materials and nearby soils also span a wide range of values, from +5.4 of the basalt to −9.1 and −6.6 for the paleosol materials and nearby soils, respectively. εNd of the lake-core sediments cover a narrower range of values, between +0.9 to −2.5. The εNd–87 Sr/86 Sr diagram (Fig. 5) reveals that the nearby soils

14

S. Zaarur et al. / Earth and Planetary Science Letters 496 (2018) 10–19

Fig. 2. Chemical composition of lake sediments (black circles), local basalt (sample HUM 9 SI Table 1; red diamond), lake-rim volcanic materials and paleosols (orange diamonds) and nearby soils (blue diamonds). The Cathaysia granitoids and Chinese loess chemical compositions are marked by the blue and green fields, respectively (Huang et al., 2017; Jahn et al., 2001).

have a distinctively different origin than the local volcanic materials and lake-rim paleosols, and suggests that these soils are a mixture of the local basalt and an external granitic source (see section 5.1.2 in the discussion). Similarly to the nearby soils, the lake-rim volcanic materials and paleosols form a Sr–Nd array that is suggestive of a mixing with an additional material that has low εNd values and radiogenic 87 Sr/86 Sr, relative to local basalt. The nature of this material is not clear and is a matter of future study. The εNd–87 Sr/86 Sr values of the core sediments fluctuate between those of the lake-rim volcanic materials and the fine fractions of the nearby soils (Fig. 5). 4.5. Summary of the results

Fig. 3. Chondrite-normalized REE patterns of bulk and finer fractions of (a) pyroclastic sample HUM 7 from the lake rim and (b) nearby soil (HUM 10) in reference to local basalt (red line) and Cathaysia Granitoids (dark blue line) (Huang et al., 2017) and loess (Jahn et al., 2001). Bulk pyroclastic material has basaltic composition, while the fine fraction has granite composition. In the nearby soil, the bulk and largest fraction have granitic compositions while the finer fractions have basaltic compositions.

The grainsize distribution, lithology and mineralogy provide a general framework for deciphering the sources of the different samples. The chemical and isotopic compositions of the-lake rim samples and nearby soils clearly indicate contributions of two distinct sources: basaltic and granitic. The chemical compositions, particularly the REE patterns of the lake-core sediments, are consistent with contribution of mainly the local basaltic material. Nevertheless, the variations in the 87 Sr/86 Sr isotopic ratios throughout the sediment core indicate an additional, likely granitic, sediment source to the lake, as discussed below. 5. Discussion In the following sections we use the grainsize distribution, mineralogy, chemical and isotopic compositions of Huguangyan Maar

S. Zaarur et al. / Earth and Planetary Science Letters 496 (2018) 10–19

15

Fig. 4. Chondrite-normalized REE patterns of lake core sediments, compared to local basalt (black line), Cathaysia Granitoids (dashed line) (Huang et al., 2017), and loess (dotted line) (Jahn et al., 2001). Samples are separated by age to groups according to the lithozones described by Mingram et al. (2004). All core samples have basaltic REE patterns.

Fig. 5. εNd–Sr isotopic fields of Huguangyan Maar lake core sediments (black lines), lake-rim paleosols (diamonds), lake-rim volcanic materials (triangles) and soils from nearby the lake, outside the lake drainage area (blue circles). The different shades (e.g., shades of blue and green) of the different samples in each group (e.g., soils and paleosols) represent an individual sample within the group, and the different sizes represent the separated size fractions of each sample. For example, the three shades of blue of the nearby soils represent the three soil samples, and the largest circle for each sample represents the bulk material and the smallest symbol represents the smallest separated fraction (see SI Table 1 for size fractions). Core samples vary between the volcanic material from the lake rim and fine fractions of the nearby soils. Isotopic compositions fields of the Cathaysia granitoids (Chen and Jahn, 1998) and loess (Zhou et al., 2009) are marked in blue and green respectively.

sediments and the local materials to understand the processes and mechanisms of sediment transport to the lake as a means to deduce the prevailing climatic conditions throughout their deposition between ∼70 and 4 ka. 5.1. Sediment sources 5.1.1. Nearby soils The nearby soils (HUM 10–12) are distinctly different in their mineralogical, chemical and isotopic compositions from the local

volcanic materials and have a clear granitic origin (Figs. 3 and 5). The different grain-size fractions of the nearby soils vary in their chemical, and more strongly, in their isotopic compositions; the bulk and coarse fractions are isotopically more radiogenic, signifying their granitic origin while the fine particles are isotopically less radiogenic and indicate mixing with local volcanic particles (Fig. 5). The isotopic concordance of the Cathaysia granitoids with the nearby soils (Fig. 5; Chen and Jahn, 1998), along with their geographical proximity to the volcanic field make the Cathaysia granitoids the most likely parent material of the soils. Further-

16

S. Zaarur et al. / Earth and Planetary Science Letters 496 (2018) 10–19

more, it is suggestive of an important regional weathering and a fluvial-sediment-transport system (indicated by the transport of large grains) that was likely active during wet periods. 5.1.2. Lake-rim and core sediments To determine the occurrence of aeolian material in the lake sediments and trace its sources, we examine the chemical and isotopic compositions of the sediments in the hydrological and geological contexts of the lake and the potential sediment sources. The small catchment area of the lake dictates that sediment particles can only enter and accumulate in the lake from the inner slopes of the crater rim or as aeolian influx. Considering that the lake receives large amounts of rainfall, and is located far from major dust sources, it is expected that the bulk of the sediment would originate from the lake rim and that remote dust contribution would be smaller. The lithology, chemical and isotopic compositions of the lakerim materials (HUM 1–9) reflect their volcanic origin. The major elements chemical composition of the lake sediments is characteristic of highly weathered materials, indicated by high (84 to 97) CIA weathering index values; CIA = [Al2 O3 /(Al2 O3 + CaO + MgO + K2 O)] × 100 (Price and Velbel, 2003). These high CIA values result from the removal of the soluble elements, likely by groundwater, and thus the relative enrichment of the insoluble Al in the sediment. Similarly to Al, Ti is also highly insoluble and accumulates in residual weathered material. Ti concentrations in the sediments are higher than the volcanic-rim samples, which are themselves Ti-rich (Fig. 2), suggesting that the sediments contain rim-derived weathered material. This is supported by the correlation between Ti and Al and Ti and CIA in the sediments (Fig. 2), as well as by REE patterns (discussed below). In addition, the general correlation between Ti and organic content (Fig. 2), suggests that the Ti record might be complicated by biochemical processes or trapping in the sediment. Hence, in contrast to the assumption of Yancheva et al. (2007) that Ti enrichment in the sediment results from aeolian input, likely from arid areas in northern China, we conclude that Ti in Huguangyan Maar sediments does not reflect aeolian contribution to the lake and cannot be used as a sediment-provenance proxy in this case. In concordance, however, to the findings of Zhou et al. (2009) and Wang et al. (2016), the REE patterns of the core sediments are similar to the local basalt (Fig. 4) and strongly support the assertion that the lake sediment is dominated by weathering products of the local volcanic materials. Nevertheless, there is also clear evidence for contribution of external material, particularly from Sr–Nd isotopes. Sr and Nd isotopes have been widely used as tracers of the origin of detritus particles (e.g., Cole et al., 2009; Grousset and Biscaye, 2005). We argue that the Sr and Nd concentrations and isotopic compositions in the lake sediment are governed by particle input to the lake, as Nd is highly insoluble and Sr, which is soluble, is unlikely derived from sea spray or groundwater because the sediment is depleted in soluble elements, including Sr (SI Table 2). Similarly, Zhou et al. (2009) used Sr and Nd isotopes to show that Huguangyan Maar surface sediments are dominated by local volcanic materials, and estimated that aeolian input from the Chinese Loess Plateau could attribute up to 20% of the isotopic variance. In our study, the Sr and Nd isotope ratios of the core sediments range between values of the volcanic materials from the lake rim (tuffs and pyroclastic materials) and values of the fine fractions of the nearby soils (Fig. 5). The contribution of only the fine fractions, rather than bulk soils suggests that the transport of the soils to the lake is aeolian. The isotopic composition of Chinese loess is comparable to the Cathaysia granitoids and its weathering products and thus, it cannot be isotopically excluded as a sediment source to the lake. However, the proximity of the nearby granitic derived soils to

Huguangyan Maar makes them a more likely source of radiogenic Sr and Nd to the lake sediments. The exposed continental shelf could have been an additional sediment source to Huguangyan Maar during time periods of low sea levels, whilst the composition of this potential source is unknown. However, 87 Sr/86 Sr and εNd values of a sediment core from the northern South China Sea (ODP site 1145) range from 0.71137 to 0.72281 and −8.8 to −11.7 for 87 Sr/86 Sr and εNd, respectively and reflect in part, sediment contribution from the Pearl River (that cuts through the Cathaysia granitoids; Boulay et al., 2005). If this site represents the isotopic composition of the continentalshelf sediments, it might suggest that during low sea levels, an exposed shelf could have been an additional granitoid source to Huguangyan Maar. εNd and 87 Sr/86 Sr co-vary in the lake sediment but the variations in εNd are smaller. Hence, we continue our discussion of aeolian input to the lake through the changes of 87 Sr/86 Sr ratios in the core sediments. 5.2. The Sr record and climate Having established the framework for Huguangyan Maar sediment sources (lake-rim volcanic materials and nearby granitic soils) and the likely aeolian pathway of the nearby soils to the lake, we examine the temporal changes in the relative contribution of these sources in a climatic context. The formation and accumulation of the granitoid-derived soils in the vicinity of the lake require wet conditions, however, the primary requirement for the soil particles to be carried by wind and transported to the lake is that the soils are exposed and sufficiently dry (Tsoar and Pye, 1987). Hence, we hypothesize that an increase in 87 Sr/86 Sr isotopic ratios in the sediment indicates a transition to drier conditions. We test our hypothesis through a comparison of the 87 Sr/86 Sr isotopic record of the lake to other proxies in Huguangyan Maar, as well as regional and global climate records. We first compare 87 Sr/86 Sr ratios to paleo-environmental conditions in Huguangyan Maar deduced from pollen analysis of the lake sediments (Mingram et al., 2004). The 87 Sr/86 Sr ratios are the highest in lithozone 3, described by Mingram et al. (2004) as the driest in the sediment sequence. Lithozone 4 has lower 87 Sr/86 Sr ratios, and is described by Mingram et al. (2004) as a warmer and wetter period. The post-glacial period (lithozone 2) has relatively lower and fluctuating 87 Sr/86 Sr ratios, and is described as a transition to wetter yet, unstable climatic period (Mingram et al., 2004). In a global context, our hypothesis is strengthened through a strong correspondence between ages of 87 Sr/86 Sr peaks in the Huguangyan Maar sediments and the timing of the Heinrich events in the northern Atlantic Ocean and the Younger Dryas period, events that were reported as dry episodes in various places over the globe including East Asia (Stager et al., 2011; Wang et al., 2001; Yuan et al., 2004; Zhou et al., 2016) (Fig. 6). The 87 Sr/86 Sr peaks are observed most clearly in the younger part of the record, where our sample resolution is higher (e.g., H1, H2 and Younger Dryas). We suspect that the less pronounced signals deeper in the core (e.g. H4 and H5), reflect the low sample resolution or sediment reworking (Mingram et al., 2004). Low 87 Sr/86 Sr ratios during the wet Bølling–Allerød interstadial (e.g., Yuan et al., 2004) further supports our hypothesis. In a regional context, the pattern of temporal changes in 87 Sr/86 Sr ratios in Huguangyan Maar is overall similar to the δ18 O records of the Hulu and Dongge caves speleothems (Wang et al., 2001; Yuan et al., 2004), with high ratios corresponding to high δ18 O values. Both records exhibit the millennial-scale peaks during the Heinrich events and Younger Dryas, as well as a general increase in values towards the glacial maximum. Variations in the speleothem δ18 O records are mainly attributed to changes in

S. Zaarur et al. / Earth and Planetary Science Letters 496 (2018) 10–19

17

Fig. 6. 87 Sr/86 Sr ratios and εNd values of lake-core sediments varying over time (a), compared to obliquity (c), precession (b), sea level (d) (Spratt and Lisiecki, 2016), δ18 O values of cave deposits (e) (Wang et al., 2001; Yuan et al., 2004) and magnetic susceptibility in Chinese loess deposits (f) (Li et al., 2017). Orange bars mark Heinrich events (1–6) and the blue bar marks the Younger Dryas.

the relative contribution of summer (low δ18 O values) and winter (high δ18 O values) monsoons (Wang et al., 2001); thus we can indirectly link the changes in Huguangyan Maar 87 Sr/86 Sr record to the monsoon system. Compared to magnetic susceptibility of the Chinese loess, high 87 Sr/86 Sr ratios in Huguangyan Maar (dry conditions) correspond to low magnetic susceptibility values (Fig. 6; Li et al., 2017) that are associated with weakening of the summer monsoon (Porter, 2001). All three proxies reflect a transition towards drier conditions throughout the Glacial period, and thus weakening of the summer and possibly strengthening of the winter monsoons, particularly leading up to the LGM, and a Post-LGM transition to wetter conditions. The 87 Sr/86 Sr ratios during the Holocene indicate a transition to a relatively wet period punctuated by two episodes of dry conditions, at 10–9 ka and a more extreme one at 6.5–5.5 ka. Both peaks are also evident in Huguangyan paleo-botany records (Jia et al., 2015; Mingram et al., 2004; Sheng et al., 2017). While these episodes are not clearly seen in the speleothems (Yuan et al., 2004), the mid-Holocene peak coincides with a major drop in water level of Lake Dali in Northeast China (Goldsmith et al., 2017) and with dry conditions in Chinese loess records indicated by paleo-botany (Lu et al., 2007). Hence, we conclude that changes in 87 Sr/86 Sr ratios in Huguangyan Maar reliably record climate changes related to the summer monsoon. 5.3. Climate forcing and the Huguangyan Maar Sr record The leading short and long-term drivers of regional monsoon dynamics are not well understood. Paleoclimate evidence shows

that local temperature and the position of the ITCZ, which are key to monsoon dynamics, are sensitive to both regional and global climate drivers (see Mohtadi et al., 2016 for a review). Due to the tendency of the ITCZ to shift towards the differentially heated hemisphere, and due to the increase in atmospheric moisture with temperature, precession is generally considered a major control on changes in summer monsoon extent and intensity, most strongly affecting the low latitudes through its impact on seasonal incoming radiation. Obliquity, on the other hand, affects the seasonality of incoming solar radiation more strongly at high latitudes (Mohtadi et al., 2016). Therefore, it is expected that precession will dominate the long-term climate record of Huguangyan Maar with a possible small contribution from obliquity. Keeping in mind that Huguangyan Maar record only covers roughly two obliquity cycles and a time period of relatively weak precession, we compare the 87 Sr/86 Sr record to these orbital cycles. Our statistical analysis indicates that the long-term 87 Sr/86 Sr record correlates more strongly with obliquity (R 2 = 0.33, p-value < 0.05, n = 34) than precession (R 2 = 0, p-value = 0.77, n = 34; millennial scale events are excluded, Fig. 6). The relatively weak precession during this time period could explain the low correlation between precession and the long-term 87 Sr/86 Sr record relative to obliquity, as is observed in other records (e.g., Cheng et al., 2016). Additionally, or alternatively, Huguangyan Maar is located in a climate-transition zone with large climate variability that exhibits weak climatic response to precession (e.g., Fig. 9 in Clement et al., 2004; and Fig. 3 in Mohtadi et al., 2016). It is possible that this created a natural filter of the precession signal from Huguangyan Maar Sr record, similar to the computational filtering of the Hulu cave deposits that

18

S. Zaarur et al. / Earth and Planetary Science Letters 496 (2018) 10–19

revealed the otherwise obscured obliquity signal (Clemens et al., 2010). The correspondence of Huguangyan Maar climate record shows similarity to global sea level changes (Fig. 6; R 2 = 0.26, n = 34, p-value < 0.05; Spratt and Lisiecki, 2016). This could result from the contribution of granitic derived sediments from the exposed continental shelf during low sea levels (section 5.1.2). It also likely results from the strong correlation of both records to obliquity, which accounts for nearly half of the variance in the sealevel record (R 2 = 0.45, p-value < 0.05). However, it is not clear whether the pronounced obliquity signal in Huguangyan Maar results from physical mechanisms which reinforces the regional response to obliquity variations or from the weakened precession signal. More importantly, the masking of the precession signal reveals the direct influence of obliquity on the hydro-climate regime in South China.

late from materials washed in from the lake rim with low 87 Sr/86 Sr ratios. During dry intervals, fine particles from the nearby graniticderived soils are windblown to the lake, supplying sediments with higher 87 Sr/86 Sr ratios. The strong correlation between 87 Sr/86 Sr peaks in the Huguangyan Maar sediment record and Heinrich events, points to the importance of the North Atlantic on global climate systems, and the East Asian monsoon in particular. Furthermore, despite its location at low latitude, Huguangyan Maar climate record exhibits no precession signal, most likely as a result of regional climate variability that locally masks the influence of precession. Instead, the role of obliquity at low latitudes is accentuated. Our results point to the importance of regional and local parameters that might overwrite global climate drivers; these may account for some of the differences that have been observed between the various monsoon records in the region.

5.4. Huguangyan Maar and other regional monsoon records Acknowledgements Huguangyan Maar sediments, the various Chinese loess records and cave deposits differ in how they reflect changes in the East Asian monsoons and the orbital drivers. Loess (Sun et al., 2006) and lacustrine (An et al., 2011; Ao et al., 2012) deposits in the Chinese Loess Plateau are dominated by glacial cyclicity, i.e., obliquity in the early Pleistocene and eccentricity during the past ∼900 ka. The periodicity of cave deposits (Cheng et al., 2016) and records from the South China Sea (Ao et al., 2011) are generally dominated by precession. These differences can be attributed to proxy sensitivities, for these archives are comprised of different materials and record the monsoons through different pathways, as well as their location. Ao et al. (2012) for example, suggest that during glacial periods a southwards migration of the winter and summer monsoons could result in placing the plateau beyond the reach of the summer monsoon, leaving only the lower latitudes within the limits of the precession-driven summer monsoon. While geographical location might generally dictate the dominance of precession versus obliquity, Ma et al. (2017) recently identified the precession signal in Chinese loess archives and Clemens et al. (2010) and Caley et al. (2013) highlighted the role of obliquity in the cave deposits. Furthermore, contrary to previous studies, Li et al. (2017) identified obliquity (rather than eccentricity) in the late Pleistocene Chinese loess deposits, using a new geochemical proxy. These studies demonstrate the complexity of the monsoon system and its affects and preservation in the geological record, and suggest that it cannot be reduced to one variable that explains all the records. In this emerging complex picture, the absence of the precession signal in the Huguangyan Maar Sr record reveals the contribution of obliquity to the climate in southern China. This could be an indirect influence through the effects of obliquity on high latitudes or through the direct influence of obliquity on low latitudes (Bosmans et al., 2015). 6. Summary Using chemical and Sr–Nd isotopic compositions of sediments near and from Huguangyan Maar, Leizhou Peninsula in South China, we identified the sources of the sediments and the prevailing climatic conditions during their deposition. The graniticderived soils that developed in the vicinity of the lake reflect weathering of the nearby Cathaysia granitoids and a regional fluvial transport system likely during wet periods. In Huguangyan Maar, local volcanic materials dominate the sediment throughout the past ∼70 kyr, with changing amounts of aeolian input from the nearby granitic-derived soils, most clearly observed in the fluctuating 87 Sr/86 Sr ratios of the lake sediments. The 87 Sr/86 Sr record of the lake sediments reflects two climatic modes. During wet intervals, the lake sediments mainly accumu-

We thank Ari Matmon, Daniel Palchan, Assaf Zipori, Ronit Kessel and Tzvi Garfunkel for fruitful discussions. We thank Ofir Tirosh, Ward Said-Ahmad, Elad Boiangiu, Elyahu Veldman, and Zachary Rand for their assistance in sample processing and analysis. We thank Amir Sandler from the Geological Survey of Israel for his assistance in XRD analysis and interpretation, and Suheir OmarZarour and Onn Crouvi for their assistance in grain size analysis. This study was funded by the CAS-ISF 2236/15 grant and National Natural Science Foundation of China 41561144010. Appendix A. Supplementary material Supplementary material related to this article can be found online at https://doi.org/10.1016/j.epsl.2018.05.025. References An, Z.S., Clemens, S.C., Shen, J., Qiang, X.K., Jin, Z.D., Sun, Y.B., Prell, W.L., Luo, J.J., Wang, S.M., Xu, H., Cai, Y.J., Zhou, W.J., Liu, X.D., Liu, W.G., Shi, Z.G., Yan, L.B., Xiao, X.Y., Chang, H., Wu, F., Ai, L., Lu, F.Y., 2011. Glacial–interglacial Indian summer monsoon dynamics. Science 333, 719–723. Ao, H., Dekkers, M.J., Qin, L., Xiao, G.Q., 2011. An updated astronomical timescale for the Plio–Pleistocene deposits from South China Sea and new insights into Asian monsoon evolution. Quat. Sci. Rev. 30, 1560–1575. Ao, H., Dekkers, M.J., Xiao, G.Q., Yang, X.Q., Qin, L., Liu, X.D., Qiang, X.K., Chang, H., Zhao, H., 2012. Different orbital rhythms in the Asian summer monsoon records from North and South China during the Pleistocene. Glob. Planet. Change 80–81, 51–60. Bosmans, J.H.C., Hilgen, F.J., Tuenter, E., Lourens, L.J., 2015. Obliquity forcing of lowlatitude climate. Clim. Past 11, 1335–1346. Boulay, S., Colin, C., Trentesaux, A., Frank, N., Liu, Z., 2005. Sediment sources and East Asian monsoon intensity over the last 450 ky. Mineralogical and geochemical investigations on South China Sea sediments. Palaeogeogr. Palaeoclimatol. Palaeoecol. 228, 260–277. Caley, T., Malaize, B., Kageyama, M., Landais, A., Masson-Delmotte, V., 2013. Bihemispheric forcing for Indo-Asian monsoon during glacial terminations. Quat. Sci. Rev. 59, 1–4. Chen, J.F., Jahn, B.M., 1998. Crustal evolution of southeastern China: Nd and Sr isotopic evidence. Tectonophysics 284, 101–133. Cheng, H., Edwards, R.L., Sinha, A., Spotl, C., Yi, L., Chen, S.T., Kelly, M., Kathayat, G., Wang, X.F., Li, X.L., Kong, X.G., Wang, Y.J., Ning, Y.F., Zhang, H.W., 2016. The Asian monsoon over the past 640,000 years and ice age terminations. Nature 534, 640. Chu, G., Sun, Q., Zhu, Q., Shan, Y., Shang, W., Ling, Y., Su, Y., Xie, M., Wang, X., Liu, J., 2017. The role of the Asian winter monsoon in the rapid propagation of abrupt climate changes during the last deglaciation. Quat. Sci. Rev. 177, 120–129. Clemens, S.C., Prell, W.L., Sun, Y.B., 2010. Orbital-scale timing and mechanisms driving Late Pleistocene Indo-Asian summer monsoons: reinterpreting cave speleothem delta O-18. Paleoceanography 25. Clement, A.C., Hall, A., Broccoli, A.J., 2004. The importance of precessional signals in the tropical climate. Clim. Dyn. 22, 327–341. Cole, J.M., Goldstein, S.L., deMenocal, P.B., Hemming, S.R., Grousset, F.E., 2009. Contrasting compositions of Saharan dust in the eastern Atlantic Ocean during the last deglaciation and African Humid Period. Earth Planet. Sci. Lett. 278, 257–266.

S. Zaarur et al. / Earth and Planetary Science Letters 496 (2018) 10–19

Crouvi, O., Amit, R., Enzel, Y., Porat, N., Sandler, A., 2008. Sand dunes as a major proximal dust source for late Pleistocene loess in the Negev Desert, Israel. Quat. Res. 70, 275–282. Goldsmith, Y., Broecker, W.S., Xu, H., Polissar, P.J., Demenocal, P.B., Porat, N., Lan, J., Cheng, P., Zhou, W., An, Z., 2017. Northward extent of East Asian monsoon covaries with intensity on orbital and millennial timescales. Proc. Natl. Acad. Sci. USA 114, 1817–1821. Grousset, F.E., Biscaye, P.E., 2005. Tracing dust sources and transport patterns using Sr, Nd and Pb isotopes. Chem. Geol. 222, 149–167. Hao, T., Lium, Xiaojie, Ogg, J., Liang, Z., Xiang, R., Zhang, X., Zhang, D., Zhang, C., Liu, Q., Li, X., 2017. Intensified episodes of East Asian Winter Monsoon during the middle through late Holocene driven by North Atlantic cooling events: highresolution lignin records from the South Yellow Sea, China. Earth Planet. Sci. Lett. 479, 144–155. Ho, K.S., Chen, J.C., Juang, W.S., 2000. Geochronology and geochemistry of late Cenozoic basalts from the Leiqiong area, southern China. J. Asian Earth Sci. 18, 307–324. Huang, W.T., Wu, J., Zhang, J., Liang, H.Y., Qiu, X.L., 2017. Geochemistry and Hf–Nd isotope characteristics and forming processes of the Yuntoujie granites associated with W–Mo deposit, Guangxi, South China. Ore Geol. Rev. 81, 953–964. Huang, X.L., Xu, Y.G., Lo, C.H., Wang, R.C., Lin, C.Y., 2007. Exsolution lamellae in a clinopyroxene megacryst aggregate from Cenozoic basalt, Leizhou Peninsula, South China: petrography and chemical evolution. Contrib. Mineral. Petrol. 154, 691–705. Jahn, B.M., Chen, P.Y., Yen, T.P., 1976. Rb–Sr ages of granitic rocks in southeastern China and their tectonic significance. Geol. Soc. Am. Bull. 87, 763–776. Jahn, B.M., Gallet, S., Han, J.M., 2001. Geochemistry of the Xining, Xifeng and Jixian sections, Loess Plateau of China: eolian dust provenance and paleosol evolution during the last 140 ka. Chem. Geol. 178, 71–94. Jahn, B.M., Zhou, X.H., Li, J.L., 1990. Formation and tectonic evolution of southeastern China and Taiwan—isotopic and geochemical constraints. Tectonophysics 183, 145–160. Jia, G.D., Bai, Y., Yang, X.Q., Xie, L.H., Wei, G.J., Ouyang, T.P., Chu, G.Q., Liu, Z.H., Peng, P.A., 2015. Biogeochemical evidence of Holocene East Asian summer and winter monsoon variability from a tropical maar lake in southern China. Quat. Sci. Rev. 111, 51–61. Jweda, J., Bolge, L., Class, C., Goldstein, S.L., 2016. High Precision Sr–Nd–Hf–Pb isotopic compositions of USGS reference material BCR-2. Geostand. Geoanal. Res. 40, 101–115. Li, T., Liu, F., Abels, H.A., You, C.F., Zhang, Z.K., Chen, J., Ji, J.F., Li, L.F., Li, L., Liu, H.C., Ren, C., Xia, R.Y., Zhao, L., Zhang, W.F., Li, G.J., 2017. Continued obliquity pacing of East Asian summer precipitation after the mid-Pleistocene transition. Earth Planet. Sci. Lett. 457, 181–190. Lifang, M., Weisheng, D., Xiaozhong, D., Xiong, L., Zhenyang, W., Xilin, X., Kunying, H., 2004. Geological map of China. Xianglei, Q., Hanzhang, T. (Eds.). Geological Publishing House, Beijing, China. Lu, H.Y., Wu, N.Q., Liu, K.B., Jiang, H., Liu, T.S., 2007. Phytoliths as quantitative indicators for the reconstruction of past environmental conditions in China II: palaeoenvironmental reconstruction in the Loess Plateau. Quat. Sci. Rev. 26, 759–772. Ma, L., Li, Y., Liu, X.X., Sun, Y.B., 2017. Registration of precession signal in the last interglacial paleosol (S-1) on the Chinese Loess Plateau. Geochem. Geophys. Geosyst. 18, 3964–3975. Ma, X.Y., Wu, D.N., 1987. Cenozoic extensional tectonics in China. Tectonophysics 133, 243–255. Maher, B.A., 2016. Palaeoclimatic records of the loess/palaeosol sequences of the Chinese Loess Plateau. Quat. Sci. Rev. 154, 23–84. Mingram, J., Schettler, G., Nowaczyk, N., Luo, X.J., Lu, H.Y., Liu, J.Q., Negendank, J.F.W., 2004. The Huguang maar lake – a high-resolution record of palaeoenvironmental and palaeoclimatic changes over the last 78,000 years from South China. Quat. Int. 122, 85–107.

19

Mohtadi, M., Prange, M., Steinke, S., 2016. Palaeoclimatic insights into forcing and response of monsoon rainfall. Nature 533, 191–199. Palchan, D., Stein, M., Almogi-Labin, A., Erel, Y., Goldstein, S.L., 2013. Dust transport and synoptic conditions over the Sahara–Arabia deserts during the MIS6/5 and 2/1 transitions from grain-size, chemical and isotopic properties of Red Sea cores. Earth Planet. Sci. Lett. 382, 125–139. Porter, S.C., 2001. Chinese loess record of monsoon climate during the last glacial– interglacial cycle. Earth-Sci. Rev. 54, 115–128. Price, J.R., Velbel, M.A., 2003. Chemical weathering indices applied to weathering profiles developed on heterogeneous felsic metamorphic parent rocks. Chem. Geol. 202, 397–416. Sheng, M., Wang, X.S., Zhang, S.Q., Chu, G.Q., Su, Y.L., Yang, Z.Y., 2017. A 20,000-year high-resolution pollen record from Huguangyan Maar Lake in tropical–subtropical South China. Palaeogeogr. Palaeoclimatol. Palaeoecol. 472, 83–92. Spratt, R.M., Lisiecki, L.E., 2016. A Late Pleistocene sea level stack. Clim. Past 12, 1079–1092. Stager, J.C., Ryves, D.B., Chase, B.M., Pausata, F.S.R., 2011. Catastrophic drought in the Afro-Asian monsoon region during Heinrich event 1. Science 331, 1299–1302. Stein, M., Starinsky, A., Katz, A., Goldstein, S.L., Machlus, M., Schramm, A., 1997. Strontium isotopic, chemical, and sedimentological evidence for the evolution of Lake Lisan and the Dead Sea. Geochim. Cosmochim. Acta 61, 3975–3992. Sun, Y.B., Clemens, S.C., An, Z.S., Yu, Z.W., 2006. Astronomical timescale and palaeoclimatic implication of stacked 3.6-Myr monsoon records from the Chinese Loess Plateau. Quat. Sci. Rev. 25, 33–48. Tanaka, T., Togashi, S., Kamioka, H., Amakawa, H., Kagami, H., Hamamoto, T., Yuhara, M., Orihashi, Y., Yoneda, S., Shimizu, H., Kunimaru, T., Takahashi, K., Yanagi, T., Nakano, T., Fujimaki, H., Shinjo, R., Asahara, Y., Tanimizu, M., Dragusanu, C., 2000. JNdi-1: a neodymium isotopic reference in consistency with LaJolla neodymium. Chem. Geol. 168, 279–281. Tsoar, H., Pye, K., 1987. Dust transport and the question of desert loess formation. Sedimentology 34, 139–153. Wang, X.S., Chu, G.Q., Sheng, M., Zhang, S.Q., Li, J.H., Chen, Y., Tang, L., Su, Y.L., Pei, J.L., Yang, Z.Y., 2016. Millennial-scale Asian summer monsoon variations in South China since the last deglaciation. Earth Planet. Sci. Lett. 451, 22–30. Wang, Y.J., Cheng, H., Edwards, R.L., An, Z.S., Wu, J.Y., Shen, C.C., Dorale, J.A., 2001. A high-resolution absolute-dated Late Pleistocene monsoon record from Hulu Cave, China. Science 294, 2345–2348. Wasserburg, G.J., Jacobsen, S.B., Depaolo, D.J., McCulloch, M.T., Wen, T., 1981. Precise determination of Sm/Nd ratios, Sm and Nd isotopic abundances in standard solutions. Geochim. Cosmochim. Acta 45, 2311–2323. Wu, X.D., Zhang, Z.H., Xu, X.M., Shen, J., 2012. Asian summer monsoonal variations during the Holocene revealed by Huguangyan maar lake sediment record. Palaeogeogr. Palaeoclimatol. Palaeoecol. 323, 13–21. Yancheva, G., Nowaczyk, N.R., Mingram, J., Dulski, P., Schettler, G., Negendank, J.F.W., Liu, J.Q., Sigman, D.M., Peterson, L.C., Haug, G.H., 2007. Influence of the intertropical convergence zone on the East Asian monsoon. Nature 445, 74–77. Yuan, D.X., Cheng, H., Edwards, R.L., Dykoski, C.A., Kelly, M.J., Zhang, M.L., Qing, J.M., Lin, Y.S., Wang, Y.J., Wu, J.Y., Dorale, J.A., An, Z.S., Cai, Y.J., 2004. Timing, duration, and transitions of the Last Interglacial Asian Monsoon. Science 304, 575–578. Zhang, J., Crowley, T.J., 1989. Historical climate records in China and reconstruction of past climates. J. Climate 2, 833–849. Zhou, H., Wang, B.-S., Guan, H., Lai, Y.-J., You, C.-F., Wang, J., Yang, H.-J., 2009. Constraints from strontium and neodymium isotopic ratios and trace elements on the sources of the sediments in Lake Huguang Maar. Quat. Res. 72, 289–300. Zhou, X., Sun, L.G., Chu, Y.X., Xia, Z.H., Zhou, X.Y., Li, X.Z., Chu, Z.D., Liu, X.J., Shao, D., Wang, Y.H., 2016. Catastrophic drought in East Asian monsoon region during Heinrich event 1. Quat. Sci. Rev. 141, 1–8.