Weak monsoon event at 4.2 ka recorded in sediment from Lake Rara, Himalayas

Quaternary International xxx (2015) 1e11

Contents lists available at ScienceDirect

Quaternary International journal homepage: www.elsevier.com/locate/quaint

Weak monsoon event at 4.2 ka recorded in sediment from Lake Rara, Himalayas Atsunori Nakamura a, Yusuke Yokoyama a, b, c, *, Hideaki Maemoku d, Hiroshi Yagi e, Makoto Okamura f, Hiromi Matsuoka f, Nao Miyake f, Toshiki Osada g, Danda Pani Adhikari h, Vishnu Dangol h, Minoru Ikehara i, Yosuke Miyairi a, Hiroyuki Matsuzaki j a

Atmosphere and Ocean Research Institute, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8564, Japan Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan c Department of Biogeoscience, Japan Agency of Marine Science and Technology (JAMSTEC), 2-15 Natsushima-cho, Yokosuka, Kanagawa 237-0061, Japan d Department of Geography, Faculty of Letters, Hosei University, 2-17-1 Fujimi, Chiyoda-ku, Tokyo 102-8160, Japan e Department of Information, Environmental and Food Sciences, Faculty of Education, Art and Science, Yamagata University, 1-4-12, Kojirakawa-machi, Yamagata 990-8560, Japan f Research and Education Faculty, Natural Sciences Cluster, Sciences Unit, Kochi University, 2-5-1 Akebono-cho, Kochi-shi, Kochi 780-8520, Japan g Research Institute for Humanity and Nature, National Institutes for the Humanities, Inter-University Research Institute Corporation, 457-4 Motoyama, Kamigamo, Kita-ku, Kyoto, 603-8047, Japan h Department of Geology, Tri-Chandra Campus, Tribhuvan University, Ghantaghar, Kathmandu, Nepal i Center for Advanced Marine Core Research, Kochi University, B200 Monobe, Nankoku, Kochi 783-8502, Japan j The University Museum, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan b

a r t i c l e i n f o

a b s t r a c t

Article history: Available online xxx

The strength of the Indian summer monsoon varied significantly on centennial- to millennial timescales during the Holocene. Among these variations, a weak summer monsoon event occurred approximately at 4 ka, the so called “4.2 ka event”. This event is considered to have been a relatively sustained and widespread phenomenon at regional scales across southern Asia to eastern Africa. However, little is known about the impact of such variations in the Himalayas, a key location for understanding the monsoon system. Here we present a record of changes in summer monsoon strength during the Holocene from Lake Rara, western Nepal, using redox sensitive elements (Mn/Ti and Mn/Fe) measured by Xray fluorescence (XRF) core-scanner. In addition, organic matter properties (TOC, d13C, and C/N) and changes in the 14C age offset between bulk organic matter and leaf matter e namely the old carbon offset e are used to augment the environmental reconstruction. Collectively, the data indicate a period of prolonged weak monsoon interval at around 4 ka. The timing of onset and recovery from the event observed at Lake Rara exhibits particular similarity with changes in the Indus River discharge. This is the first record of the “4.2 ka event” from the Himalayas based on a relatively well-constructed age model using 14C dates that are not influenced by reservoir effects. These findings provide an important step towards better understanding the spatial and temporal variability in the Holocene Indian Monsoon. © 2015 Elsevier Ltd and INQUA. All rights reserved.

Keywords: Indian monsoon 4.2 ka event Himalayas X-ray fluorescence (XRF) Manganese 14 C age offset

1. Introduction The Himalayas play an important role in the Indian monsoon system, contributing to the thermal gradient between the

* Corresponding author. Atmosphere and Ocean Research Institute, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8564, Japan. E-mail address: [email protected] (Y. Yokoyama).

continent and the ocean. The large Himalayan land mass absorbs the heat efficiently in summer due to its elevation, causing low atmospheric pressure and intense convection. Rising air is replaced by moist air from the Indian Ocean, which creates heavy precipitation in front of the Himalayas (Kump et al., 1999). Previous studies report centennial- to millennial-scale changes in the Indian summer monsoon during the Holocene from the Arabian Sea (e.g. Staubwasser et al., 2003; Gupta et al., 2005), the Arabian Peninsula (e.g. Fleitmann et al., 2003; Fleitmann et al., 2007), and India (e.g.

http://dx.doi.org/10.1016/j.quaint.2015.05.053 1040-6182/© 2015 Elsevier Ltd and INQUA. All rights reserved.

Please cite this article in press as: Nakamura, A., et al., Weak monsoon event at 4.2 ka recorded in sediment from Lake Rara, Himalayas, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.05.053

2

A. Nakamura et al. / Quaternary International xxx (2015) 1e11

Berkelhammer et al., 2012; Anoop et al., 2013; Menzel et al., 2014; Prasad et al., 2014). Among the variations reported in these studies, a weak summer monsoon event occurred approximately at 4 ka, the so called “4.2 ka event”. This event is considered to have been a relatively sustained and widespread phenomenon at regional scales (Walker et al., 2012). For example, a 4.2 ka event is reported as a weak monsoon interval in India (Berkelhammer et al., 2012; Anoop et al., 2013; Menzel et al., 2014; Prasad et al., 2014), the Gulf of Oman (Staubwasser et al., 2003), the Middle East (Cullen et al., 2000; Arz et al., 2006), and eastern Africa (Thompson et al., 2002; Tierney et al., 2011), suggesting that the event is interregional. However, little is known about equivalent variations in the Himalayas, a key location for understanding the monsoon system. Here we present data highlighting changes in the summer monsoon strength during the Holocene from Lake Rara, the largest lake in Nepal, using Mn/Ti as an indicator of monsoonal wind strength, which indicate that a weak summer monsoon event also occurred in the Himalayas at ~4 ka. This is the first record of the 4.2 ka event from the Himalayas based on a relatively wellconstrained age model using 14C dates free of reservoir effects. Sea surface temperature (SST) in the Indian Ocean is thought to have an important effect upon the intensity of the Indian monsoon (Webster et al., 1998). Based on data spanning 1945 to 1994, Clark et al. (2000) showed a positive correlation between SST throughout the Indian Ocean and the amount of monsoon rainfall. The relationship between SST in the Indian Ocean and monsoon rainfall is also supported by modeling studies (Kucharski et al., 2006; Cherchi et al., 2007). Given that the 4.2 ka event is mainly reported from low to mid latitude regions, it has been questioned as to whether it is linked to internal variability in the oceaneatmosphere system (Booth et al., 2005). By contrast, no significant changes at 4 ka have been observed in the Greenland ice cores (Vinther et al., 2006), implying that the Northern Hemisphere high latitudes were not the source of the forcing (Walker et al., 2012). In the Southern Hemisphere, Antarctic melting continued to 4 ka (Yokoyama et al., 2012, 2015), yet a connection between Antarctic melting and the 4.2 ka event is unknown. One possible source of ~ o Southern Oscillainternal variability forcing would be the El Nin tion (ENSO) and its influence on the Indian monsoon. It is widely ~ a events correspond with weakening of the accepted that La Nin Indian monsoon (Ashok et al., 2003; Gadgil et al., 2004; Meyers et al., 2007). Although a growing number of studies report changes in ENSO during the Holocene (Moy et al., 2002; Cobb et al.,  et al., 2014), its association with 2013; McGregor et al., 2013; Carre the 4.2 ka event is still under debate. Another important mode of variability that influences the Indian monsoon is the Indian Ocean Dipole (IOD) (Saji et al., 1999). Based on coral records, the negative phase of IOD is associated with a weak Indian monsoon (Abram et al., 2008). Better understanding the spatio-temporal patterns of climate variability is key to illustrate the mechanism of the 4.2 ka event. Thus, having data from the Himalayan region is an important contribution to reconstruct interactions between the monsoon, ENSO, and IOD. Recently, a continuous lake sediment record has become available from Lake Rara in the Lesser Himalayas. Nakamura et al. (2012) measured sedimentary Mn/Ti in these sediments using conventional X-Ray fluorescence (XRF) upon discrete samples, revealing millennial-scale variability in monsoonal strength through the last 4500 years. Manganese in the sedimentary record has been used to track redox conditions in lake bottom water (Davison, 1993; Schaller et al., 1997; Friedl et al., 1997; Koinig et al., 2003), which in turn relates to wind-induced mixing (Brown et al., 2000; Katsuta et al., 2006, 2007; Yancheva et al., 2007). Mn generally exists as a reduced species (Mn2þ) in anoxic bottom waters during periods of lake stratification. Seasonal intensification of vertical lake water

mixing, associated with strong summer monsoonal winds, causes hypolimnetic oxygenation and the precipitation of oxidized Mn2þ as (MnO2) (Schaller et al., 1997). Lake Rara is located at an altitude of 3000 m and is not surrounded by high mountains that could act as wind barriers (Fig. 1c). Vertical mixing of the lake is sensitive to changes of monsoonal wind due to its unique topographic and geographic setting. Hence the lake is well suited to reconstruct past wind strength (Nakamura et al., 2012). In this paper, XRF analyses were performed with an XRF core-scanner using a longer core RARA09-4 obtained from Lake Rara in order to extend the record of Nakamura et al. (2012), validated against published XRF data based on conventional glass bead analyses (Nakamura et al., 2012). The XRF scanner allows us to conduct high-resolution measurements with a resolution of 10.7 years. First, we compare previously reported Mn/Ti with newly obtained TOC, d13C, and C/N in order to strengthen the use of Mn/Ti as a proxy for summer monsoon intensity. We then consider the cause of fluctuations in the oldcarbon offsets reported by Nakamura et al. (2012) using C/N ratios and d13C values of bulk organic matter, which in turn are related to summer monsoon strength. The old-carbon offsets are the age differences between bulk organic matter and leaf samples. Although it is well known that using 14C ages of bulk organic matter overestimates the sedimentation age (Bjorck et al., 1998; Wang et al., 2002; Xu and Zheng, 2003; Fallu et al., 2004; Bertrand et al., 2012; Hou et al., 2012; Yamane et al., 2014), studies discussing the cause of down core variability in old-carbon offsets are scarce (Blaauw et al., 2011; Gaglioti et al., 2014). Here, we propose that 14C offsets are causally linked to surface processes and soil dynamics in the catchment, driven by hydroclimate variability. Finally, we discuss the Indian summer monsoon variation particularly focusing on the 4.2 ka event. 2. Study area and sampling Lake Rara (29 320 N, 82 050 E) is situated near the local summit in the Lesser Himalayas in western Nepal at an altitude of 3000 m (Fig. 1aee). The lake has an area of 9.8 km2, catchment area of ~30 km2, and maximum water depth of 168 m. The bathymetry of the western half of the lake exhibits 90 corners, whereas the eastern half is comprised of a V-shaped submerged valley (Yagi et al., 2010; Fig. 1b). The morphology of the Lake Rara catchment is characteristic of a pull-apart basin caused by the active fault system along the main Central Thrust Belt (Yagi et al., 2010) and the only existing lake outlet flows down to the Ganges. Based on monthly precipitation data from 1991 to 2000, annual precipitation is 1100 mm with a peak in August (Beck et al., 2005). The bedrock is composed of quartzite interbedded with phyllite. Cores RARA09-1 and RARA09-4 were obtained in September 2009 from the locations depicted in Fig. 1b, using a raft-mounted piston corer. The lengths of the cores are 267.5 cm and 420 cm, respectively. 3. Methods 3.1.

14

C dating

RARA09-1 and its associated age model are described by Nakamura et al. (2012; Fig. 2a). The age-depth model was constructed based on linear interpolation of dated leaf samples which were calibrated to calendar years using the calibration software Oxcal v3.10 (Bronk Ramsey, 2001) with the Intcal09 dataset (Reimer et al., 2009). The uncertainties of the age model were generated using the program Clam ver. 2.2 for R, based on linear interpolation between dated horizons (Blaauw, 2010). These uncertainties were propagated to the nominal age model considering the consistency with the one reported by Nakamura et al. (2012). Age offsets were

Please cite this article in press as: Nakamura, A., et al., Weak monsoon event at 4.2 ka recorded in sediment from Lake Rara, Himalayas, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.05.053

A. Nakamura et al. / Quaternary International xxx (2015) 1e11

3

Fig. 1. Location of Lake Rara and coring points. a: Location of (1) Lake Rara and additional records including (2) d18O in G. ruber off the Indus Delta (Staubwasser et al., 2003), (3) speleothem d18O from Maumluh cave, northeast India (Berkelhammer et al., 2012), (4) geochemical analysis from Lonar lake, (5) abundance of G. bulloides within Arabian Sea sediments (Gupta et al., 2005), (6) dolomite record from Gulf of Oman (Cullen et al., 2000), (7) d18O in G. ruber from the Red Sea (Arz et al., 2006), (8) Kilimanjaro dust record (Thompson et al., 2002), (9) dDwax from Lake Challa (Tierney et al., 2011) are shown. b: Bathometry map of Lake Rara (Yagi et al., 2010). c: Photograph of Lake Rara taken from the eastern summit. d: Photograph of Lake Rara taken from the western summit. e: Digital elevation map of Lake Rara. The data is obtained from ASTER GDEM (http://gdem.ersdac. jspacesystems.or.jp/). The black dots show the photographing pints.

then calculated by subtracting the ages of the bulk organic matter and corresponding depositional ages derived from the age model. The age uncertainties for the bulk organic matter samples and the uncertainties of the age model are propagated to the errors of the old-carbon age offsets. 14 C dating for RARA09-4 was performed on 14 leaf samples that were picked from the split core sections. After performing acidealkalieacid pretreatment, the samples were converted to graphite following the procedure of Yokoyama et al. (2007). The graphite was analyzed by accelerator mass spectrometry (AMS) at the University of Tokyo (Yokoyama et al., 2010) and Paleo Labo co., Ltd. The 14 C dates were calibrated to calendar years using the calibration software Oxcal v3.10 (Bronk Ramsey, 2001) with the Intcal09 dataset (Reimer et al., 2009).

3.2. Geochemical analyses from RARA09-1 Bulk sediment samples from RARA09-1 were analysed for total organic carbon (TOC), C/N ratios, and d13C. Samples were pretreated with 3 M HCl for 48 h to remove inorganic carbonate. TOC and total nitrogen (TN) contents and d13C isotopic composition were determined using EA-IRMS (Flash EA 1112 and Delta plus Advantage). The analytical uncertainties of the measurements were 1% RSD (relative standard deviation) for TOC, 2% RSD for TN, and 0.2‰ for d13C.

3.3. XRF core-scanning measurements XRF core-scanning measurements were performed on U-channels from RARA09-4 using the TATSCAN-F2 at Kochi Core Repository (Sakamoto et al., 2006). Samples wrapped in thin prolene film were scanned with a scanning diameter of 1 cm and a scanning interval of 5 mm. Ten major elements (Mg, Al, Si, P, S, K, Ca, Ti, Mn, and Fe) were analyzed. 4. Results 4.1. RARA09-4 core description Core RARA09-4 mainly consists of light olive gray to olive gray silt with interbeded white silt layers (Fig. 2b). Mica rich white sand beds are observed at depth 18.7e21.8 cm and 247.3e251.5 cm. The color changes light olive gray to olive gray at depth ~40 cm. At depth ~170 cm, the color changes lighter. The interval 170e260 cm is visually the lightest part in the core. Below this, the color is olive gray silt, gradually transitional to light olive gray at the bottom part. 4.2. Age-depth model 14 C ages of the leaf samples from core RARA09-4 (Table 1) are shown in Fig. 2b. The core has a relatively constant sedimentation rate of ~60 cm/ky, justifying the use of linear interpolation to

Please cite this article in press as: Nakamura, A., et al., Weak monsoon event at 4.2 ka recorded in sediment from Lake Rara, Himalayas, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.05.053

4

A. Nakamura et al. / Quaternary International xxx (2015) 1e11

Fig. 2. Age depth model for core RARA09-1 and RARA09-4. The solid line is the age model based on linear interpolation of the ages of leaf samples, assuming turbidite layers represent instantaneous sediment accumulation. Old-carbon age offsets are the time lag of the age of bulk organic matter and the age of sedimentation which are based on linear interpolation of the dates of the leaf samples.

construct the age-depth model. We regard mica rich white silt layers and sand beds as event deposits caused by high energy currents such as turbidity flows, and interpret these layers to represent instantaneous sediment accumulation for these layers and beds.

susceptibility to degradation (Fig. 3a). We rejected the 14C ages of bulk organic matter at depth 31.4 cm and 232.2 cm because these samples were taken from the horizon just above the turbidites and shows anomalously old ages.

Table 1 AMS radiocarbon data for core RARA09-4. Sample name

Depth (cm)

b

RARA09-4-om1 RARA09-4-o4a RARA09-4-om7b RARA09-4-o11a RARA09-4-o16a RARA09-4A-p8b RARA09-4A-p9b RARA-4-b-224-1b RARA09-4-o19a RARA09-4-o20a RARA09-4A-p13b RARA09-4-om25b RARA09-4-o26a RARA09-4-om29b a b

2.0 47.2 91.5 116.5 169.0 171.5 185.0 224.0 247.0 270.5 291.0 365.0 383.3 414.8

14

C age (yr BP)

237 1201 1820 2122 2880 2904 2964 3467 3874 4312 4416 5197 5433 5757

± ± ± ± ± ± ± ± ± ± ± ± ± ±

18 30 20 32 32 23 20 23 34 35 21 23 38 27

Calendar age

Calendar age

With 1 s error (cal yr BP)

With 2 s error (cal yr BP)

230 1125 1765 2095 3015 3035 3140 3760 4325 4895 5005 5955 6245 6555

± ± ± ± ± ± ± ± ± ± ± ± ± ±

80 55 55 55 55 45 70 70 85 65 45 35 45 65

230 1125 1765 2145 3015 3050 3140 3735 4285 4900 5045 5955 6220 6560

± ± ± ± ± ± ± ± ± ± ± ± ± ±

80 115 60 155 135 100 80 95 135 70 175 45 90 80

Samples measured at MALT, The University of Tokyo. Samples measured at Paleo Labo co., Ltd.

Ages of bulk organic matter often overestimate the age of deposition, because the sediments consist of a mixture of modern, authochthonous organic matter, and relict terrestrial organic matter (Bertrand et al., 2012). This age offset may vary through time due to changes in the mixing of the two components. In addition, the age of terrestrial organic matter itself have various ages (Blaauw et al., 2011). We estimated the old-carbon age offsets using the age of the bulk organic matter and ages obtained from leaves that can be assumed to reflect true depositional ages due to their

4.3. Bulk organic geochemistry and XRF core-scanning Sediment TOC content varies between 0.5 and 3.5 wt% with variations similar to those of C/N ratios and d13C values (Fig. 3bee). Sedimentary C/N changes between 8 and 15, while d13C varies between 30 and 24‰. XRF core-scanning data from RARA09-4 and conventional XRF data from RARA09-1 show good agreement, except for Si (Fig. 4). This may be due to the fact that light elements are difficult to

Please cite this article in press as: Nakamura, A., et al., Weak monsoon event at 4.2 ka recorded in sediment from Lake Rara, Himalayas, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.05.053

A. Nakamura et al. / Quaternary International xxx (2015) 1e11

5

measure by XRF core-scanner (Sakamoto et al., 2006). It is well known that water content, grain size, porosity, and TOC content biases the intensity of lighter elements because of their higher xray absorption rates (Kido et al., 2006; Tjallingii et al., 2007; Lowemark et al., 2011; Hennekam and Lange, 2012). Estimates of Si concentration differ in particular for the sediments aged 3 to 4 ka, which may be explained by low water content and/or low TOC, as indicated by the lighter colour of these sediments. Time-series variations of the 10 elements (Mg, Al, Si, P, S, K, Ca, Ti, Mn, and Fe) are shown in Fig. 4. Elements Mg, Al, Si, and K exhibit a similar pattern as Ti, suggesting these are of a terrigenous origin. Correlation coefficients, described as r-values of these elements vs Ti, are consistently higher than 0.5 (p < 0.01), indicating moderate correlation (Table 2). These elements show a gradual decrease in concentration between 7 and 5 ka, followed by a broad peak between 5 and 3 ka which corresponds well with the down core changes in color (260e170 cm depth in core). Between 3 and 0 ka, the terriginous elements show relatively stable concentrations. Variations in P, Mn and Fe exhibit negligible correlation with Ti, indicating these elements are likely not terrigenous in origin (Table 2). Table 2 Correlation matrix between elements measured by XRF core-scanner. Mg Mg e Al 0.98* Si 0.96* P 0.04 S 0.41* K 0.86* Ca 0.01 Ti 0.65* Mn 0.00 Fe 0.46*

Al

Si

P

S

K

Ca

Ti

Mn

Fe

e

0.98* e 0.05 0.04 0.37* 0.40* 0.90* 0.86* 0.05 0.04 0.64* 0.70* 0.03 0.06 0.47* 0.49*

e 0.16* e 0.16* 0.20* e 0.00 0.48* 0.18* e 0.04 0.59* 0.52* 0.46* e 0.08 0.21* 0.06 0.10 0.13* e 0.03 0.35* 0.40* 0.05 0.20* 0.23* e

r-values are shown for the elements from core RARA09-4 measured by XRF corescanner. Elements which have p-values less than 0.01.

*

Elemental data are generally normalized to changes in terrigenous input, as indicated by Al or Ti concentrations. However, the intensity of Al (lighter than Si) is less reliable compared to heavier elements as discussed above. Therefore, normalization was carried out against Ti counts in this study. Mn/Ti from RARA09-1 and Mn/ Ti, Mn, and Ti from RARA09-4 with 14C dates are shown in

Fig. 3. Comparison of data from core RARA09-1. a: old-carbon age offset, b: TOC, c: C/ N, d: d13C, and e: Mn/Ti.

offset correspond with decreased TOC content, low C/N, negative

d13C, and low Mn/Ti intervals. There are distinct peaks in oldcarbon age offset, TOC, C/N, d13C, and Mn/Ti at 2.7 ka and 3.3 ka (Fig. 3aee). Table 3 shows a correlation matrix for the proxies. The most noticeable correlations (moderately correlated) are between Mn and TOC (r ¼ 0.57, p < 0.001), Mn and d13C (r ¼ 0.50, p < 0.001), TOC and C/N (r ¼ 0.62, p < 0.001), TOC and d13C (r ¼ 0.62, p < 0.001), and C/N and old-carbon age offset (r ¼ 0.46, p ¼ 0.047). Weak correlations were observed between Mn and C/N, Mn and old-carbon age offset, TOC and old-carbon age offset, C/N and d13C, and d13C and old-carbon age offset (Table 3).

Table 3 Correlation matrix for the proxies from core RARA09-1.

Mn/Ti TOC C/N d13C Old-carbon age offset

Mn/Ti

TOC

C/N

d13C

Old-carbon age offset

e 0.57 (p < 0.001) 0.35 (p < 0.001) 0.50 (p < 0.001) 0.31 (p ¼ 0.20)

e 0.62 (p < 0.001) 0.62 (p < 0.001) 0.32 (p ¼ 0.18)

e 0.24 (p ¼ 0.21) 0.46 (p ¼ 0.047)

e 0.39 (p ¼ 0.10)

e

r-values are shown for the the proxies from core RARA09-1.

Fig. 5aed. Changes in Mn/Ti is primarily drive by changes in Mn, which exhibits higher variability than Ti throughout the core. It should be noted that the age model for RARA09-1 shown in Fig. 4 is aligned to RARA09-4 using 3 tie-points (Fig. 5a and b). 13

4.4. Comparisons between old-carbon age offset, TOC, C/N, d C and Mn/Ti Variations in old-carbon age offset, TOC, C/N, and d13C, are similar to those seen in Mn/Ti (Fig. 3aee). Increased old-carbon age

5. Discussion 5.1. Mechanisms of organic matter deposition in Lake Rara Sedimentary C/N ratios and d13C values have been widely used to distinguish the dominant source of organic matter in lake sediments (e.g. Meyers and Lallier-Verges, 1999; Tyler et al., 2010). Lacustrine algae typically have C/N ratios less than 10, whereas land plans have C/N ratios of 20 and greater (Meyers, 1994, 1997). Lacustrine algae and terrestrial C3 plants have lower d13C values (ca.

Please cite this article in press as: Nakamura, A., et al., Weak monsoon event at 4.2 ka recorded in sediment from Lake Rara, Himalayas, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.05.053

6

A. Nakamura et al. / Quaternary International xxx (2015) 1e11

Fig. 4. Comparison of XRF core-scanning data from core RARA09-4 (thin line) and XRF data from core RARA09-1 (thick line) measured by conventional glass bead method (Nakamura et al., 2012).

27‰), whereas terrestrial C4 plans have heavier values (ca. 14‰) (Meyers, 1997; Leng and Marshall, 2004). Sedimentary C/N and d13C from Lake Rara indicate that organic matter in the sediment consists of a mixture of lacustrine algae and terrestrial C3 plant material (Fig. 3c and d). Therefore, increases in TOC at Lake Rara are explained by both increases in lake productivity and terrestrial organic matter influx. Given that increases in TOC are associated with larger C/N and lighter d13C, input of terrestrial matter has a larger contribution of the two components. In general, changes in TOC concentration is interpreted as a proxy for precipitation, via increases in soil erosion and fluvial transport of organic matter to the lake sediments (Xiao et al., 2006). As Mn/Ti exhibits moderate correlation with TOC, C/N, and d13C, this strengthens the use of Mn/ Ti as a proxy for summer monsoonal wind intensity. Together, the data suggest that stronger monsoonal winds were accompanied by more intense precipitation. The strong monsoon wind intensified vertical mixing of the lake, oxygenating bottom water and inducing precipitation of Mn2þ as the oxidized species MnO2. In the mean time, intense precipitation increased input of terrestrial organic

matter to the lake, leading to increase in TOC content, increase in C/ N, and decrease in d13C. Intensified input of terrestrial soil organic matter is likely to cause larger old-carbon age offsets because terrestrial organic matter is much older than lacustrine algae. The 14C reservoir effect for lacustrine algae is also reported from lakes surrounded by ancient carbonate that allow input of 14C-depleted dissolved inorganic carbon (Hou et al., 2012). However this effect might not be significant at Lake Rara where the entire catchment is composed of quartzite and phyllite. Contrary to expectation, periods of larger old-carbon age offset at Lake Rara are associated with periods of weak monsoon intervals, as inferred from the other proxies (Fig. 3). This suggests that the age of the organic matter transported to the lake fluctuates with monsoon intensity, delivering older organic matter to the lake during periods of weak monsoon intensity. C/N ratios and d13C values indicate that at least several-thousand-year fluctuations are required for the age of terrestrial organic matter to explain the variation of old-carbon age offset (Supplementary data, Fig. S1). Such a change in old-carbon age offset is also

Please cite this article in press as: Nakamura, A., et al., Weak monsoon event at 4.2 ka recorded in sediment from Lake Rara, Himalayas, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.05.053

A. Nakamura et al. / Quaternary International xxx (2015) 1e11

7

Fig. 5. Comparison of Mn/Ti from core RARA09-1 and RARA09-4. a: Mn/Ti from core RARA09-1. b: Mn/Ti from core RARA09-4. c: Mn from core RARA09-4. d: Ti from core RARA09-4.

reported from Lake Challa, East Africa (Blaauw et al., 2011), who reported variation in old-carbon age offsets of ~450 y to ~200 y from the last glacial to the Holocene. Blaauw et al. (2011) attributed this pattern to variable contributions of old terrestrial organic matter eroded from soil and observed increases in the contribution of younger terrestrial organic matter during periods of wetter climate, a pattern similar to that observed at Lake Rara. A simple explanation for the changes in old-carbon age offset relates to variation in the type of terrestrial organic matter flux in response to climate. A greater flux from newly grown vegetation would be expected during wetter periods compared to drier periods. In addition, old-carbon age offset may be related to soil carbon dynamics. The old-carbon age offset observed from Lake Rara is comparable to the previously reported age of terrestrial soil (200e1200 y; Trumbore, 2000). Because the old-carbon offset in Lake Rara shows centennial- to millennial-scale changes, the cause of the fluctuation is not likely due to the changes in mean soil residence time, which might need more time to respond. Given that carbon gets older with depth in most soils (Trumbore, 2009), increased contribution of younger terrestrial organic matter during wet periods could be explained by intensified surface wash. Another possible explanation is variation of the dominant source area of terrestrial organic matter. Some studies report spatial variations in soil carbon along ridge top to hillslope (Harden et al., 2002; Yoo et al., 2006). Considering the difference in erosion rates within a watershed (Heimsath et al., 1999, 2001; Nakamura et al., 2014a), monsoon-induced fluctuations in the spatial pattern of soil erosion could change the oldcarbon offset. Consequently, further research into understanding the mechanism of the old-carbon offset is not only important for sediment geochronology, but also strongly related to vegetation and soil carbon dynamics.

5.2. High-resolution monsoon records based on Mn/Ti and comparison between other paleoclimate archives Sedimentary profiles of Mn are often used as an indicator of bottom water redox conditions, which in turn is controlled by wind-induced mixing (Brown et al., 2000; Katsuta et al., 2006, 2007; Yancheva et al., 2007). A relationship between wind strength and Mn precipitation is supported by modern observations of wind speed and dissolved Mn2þ within the water column of Lake Taihu, China (Zhang et al., 2006). Other general factors which can influence bottom water redox condition relate to either (1) lake surface ice cover and (2) lake level changes. However, it is unlikely that either of these cases effected Lake Rara, which does not freeze today, even in the winter, and whose lake level is stable due to the local topography. Water level of Lake Rara cannot increase beyond the modern level because of the geometry of the lake, whereby the western part of Lake Rara is surrounded by low elevation hills and which allow lake water to drain (Fig. 1cee). In addition, paleo-shorelines are not observed from the bathymetric survey data (Fig. 1b). The depth of Lake Rara (168 m) should make bottom water redox conditions relatively insensitive to slight changes in lake level. Significant lake level drop is unlikely because of continuous supply of precipitation by monsoon. Consequently, change in wind-induced mixing is considered to be the most robust means of interpreting Mn/Ti variability in the sediments of Lake Rara. This is supported by modeling studies that suggest that deep mixing in excess of the maximum water depth of Lake Rara is achieved with a wind velocity of only 10 m/s (Ravens et al., 2000; Botte and Kay, 2002). Direct measurement of dissolved oxygen in Lake Rara on 20 May 1983 shows that the surface and bottom of the lake was 7.50 and 4.48 mg/L, respectively (Okino and Satoh,

Please cite this article in press as: Nakamura, A., et al., Weak monsoon event at 4.2 ka recorded in sediment from Lake Rara, Himalayas, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.05.053

8

A. Nakamura et al. / Quaternary International xxx (2015) 1e11

1986). This indicates that dissolved oxygen was 58% saturated at the sedimentewater interface. The comparison of Mn/Ti from Lake Rara and other paleoclimate archives is shown in Fig. 6. In addition to Mn/Ti, Mn/Fe is also shown (Fig. 6a and b), which have been commonly used to reconstruct changing redox condition in lakes (Loizeau et al.,

Fig. 6. Lake Rara Mn/Ti and Mn/Fe and comparison between other paleoclimate archives. a: Lake Rara Mn/Ti. 14C dates of leaves are shown with 1s errors. b: Lake Rara Mn/Fe. c: d18O in G. ruber off the Indus Delta (Staubwasser et al., 2003). d: speleothem d18O from Maumluh cave, northeast India (Berkelhammer et al., 2012). e: abundance of G. bulloides from Arabian Sea (Gupta et al., 2005). f: dolomite record from Gulf of Oman (Cullen et al., 2000). g: d18O in G. ruber from the Red Sea (Arz et al., 2006). h: Kilimanjaro dust record (Thompson et al., 2002). i: dDwax from Lake Challa (Tierney et al., 2011).

2001; Koinig et al., 2003; Melles et al., 2012; Naeher et al., 2013). Higher Mn/Fe indicates deep convection since Fe oxidizes faster than Mn and thus high Mn/Fe only occurs under oxic conditions. Among the centennial- to millennial-scale variations during the Mid to Late Holocene, the most prominent change observed from Lake Rara is a marked decrease in Mn/Ti at around 4 ka. These Mn/Ti values are interpreted to reflect an increase in monsoonal wind intensity prior to 5 ka followed by a gradual decline to 4.2 ka. A prolonged weak monsoon interval, reflected by low Mn/Ti values, continued to 3.7 ka before increasing toward 3 ka, with a further brief decline at 3.1 ka. Previous research has documented the existence of a weak monsoon interval at around 4 ka in the Himalayas, albeit with poorly resolved age models. Yasuda and Tabata (1988) reported slightly drier conditions (weaker monsoon) from 4.5 to 4 ka based on pollen data from Lake Rara sediments. Phadtare (2000) also found a cold monsoon event from 4 to 3.5 ka using pollen data from alpine peat in the Higher Himalayas. Furthermore, a monsoon record from Tso Kar lake basin in the northwestern Himalayas shows a decrease in moisture supply at around 4 ka (Wunnemann et al., 2010). Collectively, these records may point to a regional decline in precipitation at around 4 ka. A weak summer monsoon interval at around 4 ka also correlates well with the 4.2 ka event, which is a relatively sustained and widespread phenomenon at regional scales across southern Asia to eastern Africa. d18O in G. ruber off the Indus delta (Staubwasser et al., 2003; Fig. 6c) shows good agreement with the record from Lake Rara from 5 to 3 ka, both for onset timing and recovery trend, indicating synchronous monsoon change between wind intensity in the western Himalayas and Indus river discharge. A decrease in precipitation at 4 ka is also reported from the Maumluh Cave speleothem, northeast India (Berkelhammer et al., 2012; Fig. 6d) and Lonar Lake (Anoop et al., 2013; Menzel et al., 2014; Prasad et al., 2014), which was formed by a meteor impact during the last glacial (Nakamura et al., 2014b). In the Arabian Sea, Gupta et al. (2005) reconstructed wind variability using the abundance of G. bulloides, which is therefore related to wind-induced upwelling (Fig. 6e). Although the weakening trend in monsoon from ca. 5 ka is similar between Lake Rara and Arabian Sea (Gupta et al., 2005), the event in the Arabian Sea ended earlier than that is observed in Lake Rara. It is currently uncertain as to whether the differences between these records relates to chronological uncertainty for the Arabian Sea sediments, which are likely subject to variable reservoir age effects. In the Middle East, dry events at 4.2 ka are reported from the Gulf of Oman (Cullen et al., 2000; Fig. 6f) and the Red Sea (Arz et al., 2006; Fig. 6g). They are nearly synchronous with a dust peak found in the ice core from Kilimanjaro (Thompson et al., 2002; Fig. 6h) and a dry interval reported from Lake Challa, eastern Africa (Tierney et al., 2011; Fig. 6i). The spatial pattern of the climate at around 4.2 ka compiled in this study (Figs. 1a and 6) is consistent with a negative phase of IOD across the tropical Indian Ocean during this period (Berkelhammer et al., 2012; Prasad et al., 2014), which in turn accompanies weak Indian summer monsoon and droughts in the Middle East and in eastern Africa (Abram et al., 2008, 2009). Thus, prolonged negative phase of IOD-like condition is one of the possible causes of the weak monsoon event at around 4.2 ka in the Himalayas. In addition to IOD, ENSO would have influenced the strength of the Indian monsoon. A growing number of studies report changes in ENSO during the mid- to late Holocene (Moy  et al., et al., 2002; Cobb et al., 2013; McGregor et al., 2013; Carre 2014), but its association with the 4.2 ka event needs to be carefully considered. The duration of the event is relatively longer at Lake Rara compared to the other records except for Indus delta and Lake

Please cite this article in press as: Nakamura, A., et al., Weak monsoon event at 4.2 ka recorded in sediment from Lake Rara, Himalayas, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.05.053

A. Nakamura et al. / Quaternary International xxx (2015) 1e11

Challa (Fig. 6). While the results from Lake Rara suggest that the 4.2 ka event was a prolonged ~500 year event, the records from Mawmluh Cave, Gulf of Oman, Red Sea, Kilimanjaro suggest the event was very brief. Further, a stalagmite record from Qunf Cave in Oman (Fleitmann et al., 2003) does not show a signature of this event (Staubwasser and Weiss, 2006; Berkelhammer et al., 2012). In East Asia, a stalagmite record from Dongge Cave (Wang et al., 2005) shows weak monsoon period at 4 ka. While this is consistent with the penetration of the Indian monsoon to southwestern part of China (Maher, 2008; Dong et al., 2010; Pausata et al., 2011; Nakamura et al., 2012; Wang and Chen, 2012), the event is not evident from Sanbao Cave and Jiuxian Cave (Wang et al., 2008; Cai et al., 2010), indicating a spatially complex monsoonal response. Further studies are needed to explore the cause of the differences among the regions. The 4.2 ka event is also reported from more distant locations. Booth et al. (2005) report a severe drought at 4.2 ka in the midcontinent of North America, suggesting a synchronous 4.2 ka event occurred in the Northern Hemisphere. Similar to our results, a North Atlantic drift ice record (Bond et al., 2001) exhibits increased values over the interval for ~4.2e3.7 ka. However, there appears to be no consistent relationship between our data and North Atlantic ice rafted debris for the duration of the full sequence (Supplementary data, Fig. S2). Consequently, the weak summer monsoon event at 4 ka reported here is the first record of the 4.2 ka event from the Himalayas based on a well-resolved age model. Given that the number of the records that report the 4.2 ka event from monsoon-sensitive locations is recently increasing (Berkelhammer et al., 2012; Anoop et al., 2013; Menzel et al., 2014; Prasad et al., 2014), evidence from the Himalayas helps to clarify the spatial behavior of this event. 6. Conclusions High-resolution analyses of Mn/Ti within the sediments of Lake Rara, western Nepal, record variability in the strength of monsoonal winds throughout the period 6.5e0 ka. Mn/Ti variation from core RARA09-1 exhibits a moderate correlation with TOC, d13C, and C/N, which support the use of Mn/Ti as a proxy of monsoon intensity, implying that increases in wind strength were accompanied by increases in precipitation, which in turn delivered terrestrial organic matter to the lake. 14C age offsets between bulk organic matter and leaf samples indicate that the age of the organic matter transported to the lake also fluctuates with monsoon intensity. A period of consistently low Mn/Ti and Mn/Fe suggest an interval of weak summer monsoon intensity between 4.2 and 3.7 ka which is consistent with an emerging picture of regionally weakened monsoon at this time. The weak summer monsoon interval at around 4 ka correlates well with the 4.2 ka event which is a relatively sustained and widespread phenomenon at regional scales in southern Asia to eastern Africa (Walker et al., 2012). This is the first evidence of the 4.2 ka event from the Himalayas based on a relatively well-constrained age model. Acknowledgements We thank S.P. Obrochta and T. Ishiwa for their assistance. This study was supported by JSPS KAKENHI Grant number 26247085, JSPS Grant-in-Aid for JSPS fellows, the research project ‘Environmental Change and the Indus Civilization’ managed by Research Institute for Human and Nature, and the program for young researchers managed by Paleo Labo co., Ltd.

9

Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.quaint.2015.05.053.

References Abram, N.J., Gagan, M.K., Cole, J.E., Hantoro, W.S., Mudelsee, M., 2008. Recent intensification of tropical climate variability in the Indian Ocean. Nature Geoscience 1, 849e853. Abram, N.J., McGregor, H.V., Gagan, M.K., Hantoro, W.S., Suwargadi, B.W., 2009. Oscillations in the southern extent of the Indo-Pacific Warm Pool during the mid-Holocene. Quaternary Science Reviews 28, 2794e2803. Anoop, A., Prasad, S., Plessen, B., Basavaiah, N., Gaye, B., Naumann, R., Menzel, P., Weise, S., Brauer, A., 2013. Palaeoenvironmental implications of evaporative gaylussite crystals from Lonar Lake, central India. Journal of Quaternary Science 28, 349e359. Arz, H.W., Lamy, F., Patzold, J., 2006. A pronounced dry event recorded around 4.2 ka in brine sediments from the northern Red Sea. Quaternary Research 66, 432e441. Ashok, K., Guan, Z.Y., Yamagata, T., 2003. Influence of the Indian Ocean Dipole on the Australian winter rainfall. Geophysical Research Letters 30, 1821. Beck, C., Grieser, J., Rudolf, B., 2005. A new monthly precipitation Climatology for the global land areas for the period 1951 to 2000. Klimastatusbericht 2004, Deutsch Wetterdienst, Offenbach. Germany 181e190. Berkelhammer, M., Sinha, A., Stott, L., Cheng, H., Pausata, F.S.R., Yoshimura, K., 2012. An abrupt shift in the Indian monsoon 4000 years ago. American Geophysical Union Geophysical Monograph 198, 75e87. Bertrand, S., Araneda, A., Vargas, P., Jana, P., Fagel, N., Urrutia, R., 2012. Using the N/C ratio to correct bulk 14C ages from lake sediments: insights from Chilean Patagonia. Quaternary Geochronology 12, 23e29. Bjorck, S., Bennike, O., Possnert, G., Wohlfarth, B., Digerfeldt, G., 1998. A high resolution C-14 dated sediment sequence from southwest Sweden: age comparisons between different components of the sediment. Journal of Quaternary Science 13, 85e89. Blaauw, M., 2010. Methods and code for ‘classical’ age-modelling of 14C sequences. Quaternary Geochronology 5, 512e518. Blaauw, M., van Geel, B., Kristen, I., Plessen, B., Lyaruu, A., Engstrom, D.R., van der Plicht, J., Verschuren, D., 2011. High-resolution C-14 dating of a 25,000-year lake-sediment record from equatorial East Africa. Quaternary Science Reviews 30, 3043e3059. Bond, G., Kromer, B., Beer, J., Muscheler, R., Evans, M.N., Showers, W., Hoffmann, S., Lotti-Bond, R., Hajdas, I., Bonani, G., 2001. Persistent solar influence on north Atlantic climate during the Holocene. Science 294, 2130e2136. Booth, R.K., Jackson, S.T., Forman, S.L., Kutzbach, J.E., Bettis, E.A., Kreig, J., Wright, D.K., 2005. A severe centennial-scale drought in mid-continental North America 4200 years ago and apparent global linkages. The Holocene 15, 321e328. Botte, V., Kay, A., 2002. A model of the wind-driven circulation in Lake Baikal. Dynamics of Atmospheres and Oceans 35, 131e152. Bronk Ramsey, C., 2001. Development of the 14C calibration program. Radiocarbon 43, 355e363. Brown, E.T., Le Callonnec, L., German, C.R., 2000. Geochemical cycling of redoxsensitive metals in sediments from Lake Malawi: a diagnostic paleotracer for episodic changes in mixing depth. Geochimica et Cosmochimica Acta 64, 3515e3523. Cai, Y.J., Tan, L.C., Cheng, H., An, Z.S., Edwards, R.L., Kelly, M.J., Kong, X.G., Wang, X.F., 2010. The variation of summer monsoon precipitation in central China since the last deglaciation. Earth and Planetary Science Letters 291, 21e31. , M., Sachs, J.P., Purca, S., Schauer, A.J., Braconnot, P., Falco  n, R.A., Julien, M., Carre e, D., 2014. Holocene history of ENSO variance and asymmetry in the Lavalle eastern tropical Pacific. Science 345, 1045e1048. Cherchi, A., Gualdi, S., Behera, S., Luo, J.J., Masson, S., Yamagata, T., Navarra, A., 2007. The influence of Tropical Indian Ocean SST on the Indian Summer Monsoon. Journal of Climate 20, 3083e3105. Clark, C.O., Cole, J.E., Webster, P.J., 2000. Indian Ocean SST and Indian summer rainfall: predictive relationships and their decadal variability. Journal of Climate 13, 2503e2519. Cobb, K.M., Westphal, N., Sayani, H.R., Watson, J.T., Di Lorenzo, E., Cheng, H., Edwards, R.L., Charles, C.D., 2013. Highly variable El Nino-Southern Oscillation Throughout the Holocene. Science 339, 67e70. Cullen, H.M., deMenocal, P.B., Hemming, S., Hemming, G., Brown, F.H., Guilderson, T., Sirocko, F., 2000. Climate change and the collapse of the Akkadian empire: evidence from the deep sea. Geology 28, 379e382. Davison, W., 1993. Iron and manganese in lakes. Earth-Science Reviews 34, 119e163. Dong, J.G., Wang, Y.J., Cheng, H., Hardt, B., Edwards, R.L., Kong, X.G., Wu, J.Y., Chen, S.T., Liu, D.B., Jiang, X.Y., Zhao, K., 2010. A high-resolution stalagmite record of the Holocene East Asian monsoon from Mt Shennongjia, central China. The Holocene 20, 257e264. Fallu, M.A., Pienitz, R., Walker, I.R., Overpeck, J., 2004. AMS C-14 dating of tundra lake sediments using chironomid head capsules. Journal of Paleolimnology 31, 11e22.

Please cite this article in press as: Nakamura, A., et al., Weak monsoon event at 4.2 ka recorded in sediment from Lake Rara, Himalayas, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.05.053

10

A. Nakamura et al. / Quaternary International xxx (2015) 1e11

Fleitmann, D., Burns, S.J., Mangini, A., Mudelsee, M., Kramers, J., Villa, I., Neff, U., AlSubbary, A.A., Buettner, A., Hippler, D., Matter, A., 2007. Holocene ITCZ and Indian monsoon dynamics recorded in stalagmites from Oman and Yemen (Socotra). Quaternary Science Reviews 26, 170e188. Fleitmann, D., Burns, S.J., Mudelsee, M., Neff, U., Kramers, J., Mangini, A., Matter, A., 2003. Holocene forcing of the Indian monsoon recorded in a stalagmite from Southern Oman. Science 300, 1737e1739. Friedl, G., Wehrli, B., Manceau, A., 1997. Solid phases in the cycling of manganese in eutrophic lakes: new insights from EXAFS spectroscopy. Geochimica et Cosmochimica Acta 61, 3277. Gadgil, S., Vinayachandran, P.N., Francis, P.A., Gadgil, S., 2004. Extremes of the Indian summer monsoon rainfall, ENSO and equatorial Indian Ocean oscillation. Geophysical Research Letters 31, L12213. Gaglioti, B.V., Mann, D.H., Jones, B.M., Pohlman, J.W., Kunz, M.L., Wooller, M.J.J., 2014. 14C age-offsets in an arctic lake reveal the long-term response of permafrost carbon to climate change. Journal of Geophysical Research: Biogeosciences 119, 1630e1651. Gupta, A.K., Das, M., Anderson, D.M., 2005. Solar influence on the Indian summer monsoon during the Holocene. Geophysical Research Letters 32, L17703. Harden, J.W., Fries, T.L., Pavich, M.J., 2002. Cycling of beryllium and carbon through hillslope soils in Iowa. Biogeochemistry 60, 317e335. Heimsath, A.M., Dietrich, W.E., Nishiizumi, K., Finkel, R.C., 1999. Cosmogenic nuclides, topography, and the spatial variation of soil depth. Geomorphology 27, 151e172. Heimsath, A.M., Dietrich, W.E., Nishiizumi, K., Finkel, R.C., 2001. Stochastic processes of soil production and transport: erosion rates, topographic variation and cosmogenic nuclides in the Oregon Coast Range. Earth Surface Processes and Landforms 26, 531e552. Hennekam, R., de Lange, G., 2012. X-ray fluorescence core scanning of wet marine sediments: methods to improve quality and reproducibility of high-resolution paleoenvironmental records. Limnology and Oceanography e Methods 10, 991e1003. Hou, J.Z., D'Andrea, W.J., Liu, Z.H., 2012. The influence of C-14 reservoir age on interpretation of paleolimnological records from the Tibetan Plateau. Quaternary Science Reviews 48, 67e79. Katsuta, N., Takano, M., Kawakami, S., Togami, S., Fukusawa, H., Kumazawa, M., Yasuda, Y., 2006. Climate system transition from glacial to interglacial state around the beginning of the last termination: evidence from a centennial- to millennial-scale climate rhythm. Geochemistry Geophysics Geosystems 7, Q12006. Katsuta, N., Takano, M., Kawakami, S.I., Togami, S., Fukusawa, H., Kumazawa, M., Yasuda, Y., 2007. Advanced Micro-XRF method to separate sedimentary rhythms and event layers in sediments: its application to lacustrine sediment from Lake Suigetsu, Japan. Journal of Paleolimnology 37, 259e271. Kido, Y., Koshikawa, T., Tada, R., 2006. Rapid and quantitative major element analysis method for wet fine-grained sediments using an XRF microscanner. Marine Geology 229, 209e225. Koinig, K.A., Shotyk, W., Lotter, A.F., Ohlendorf, C., Sturm, M., 2003. 9000 years of geochemical evolution of lithogenic major and trace elements in the sediment of an alpine lake e the role of climate, vegetation, and land-use history. Journal of Paleolimnology 30, 307e320. Kucharski, F., Molteni, F., Yoo, H., 2006. SST forcing of decadal Indian Monsoon rainfall variability. Geophysical Research Letters 33, L03709. Kump, L.R., Kasting, J.F., Grane, R.G., 1999. The Earth System. Pearson Education, Inc., Upper Saddle River, New Jersey. Leng, M.J., Marshall, J.D., 2004. Palaeoclimate interpretation of stable isotope data from lake sediment archives. Quaternary Science Reviews 23, 811e831. Loizeau, J.L., Span, D., Coppee, V., Dominik, J., 2001. Evolution of the trophic state of Lake Annecy (eastern France) since the last glaciation as indicated by iron, manganese and phosphorus speciation. Journal of Paleolimnology 25, 205e214. Lowemark, L., Chen, H.F., Yang, T.N., Kylander, M., Yu, E.F., Hsu, Y.W., Lee, T.Q., Song, S.R., Jarvis, S., 2011. Normalizing XRF-scanner data: a cautionary note on the interpretation of high-resolution records from organic-rich lakes. Journal of Asian Earth Sciences 40, 1250e1256. Maher, B.A., 2008. Holocene variability of the East Asian summer monsoon from Chinese cave records: a re-assessment. The Holocene 18, 861e866. McGregor, H.V., Fischer, M.J., Gagan, M.K., Fink, D., Phipps, S.J., Wong, H., Woodroffe, C.D., 2013. A weak El Nino/Southern Oscillation with delayed seasonal growth around 4,300 years ago. Nature Geoscience 6, 949e953. Melles, M., Brigham-Grette, J., Minyuk, P.S., Nowaczyk, N.R., Wennrich, V., DeConto, R.M., Anderson, P.M., Andreev, A.A., Coletti, A., Cook, T.L., HaltiaHovi, E., Kukkonen, M., Lozhkin, A.V., Rosen, P., Tarasov, P., Vogel, H., Wagner, B., 2012. 2.8 Million years of Arctic Climate Change from Lake El'gygytgyn, NE Russia. Science 337, 315e320. Menzel, P., Gaye, B., PMishra, P.K., Anoop, A., Basavaia, N., Marwan, N., Plessen, B., Prasad, S., Riedel, N., Stebich, M., Wiesner, M.G., 2014. Linking Holocene drying trends from Lonar Lake in monsoonal central India to North Atlantic cooling events. Palaeogeography, Palaeoclimatology, Palaeoecology 410, 164e178. Meyers, P.A., 1994. Preservation of Elemental and Isotopic Source Identification of sedimentary organic-matter. Chemical Geology 114, 289e302. Meyers, P.A., 1997. Organic geochemical proxies of paleoceanographic, paleolimnologic, and paleoclimatic processes. Organic Geochemistry 27, 213e250. Meyers, P.A., Lallier-Verges, E., 1999. Lacustrine sedimentary organic matter records of Late Quaternary paleoclimates. Journal of Paleolimnology 21, 345e372.

Meyers, G., McIntosh, P., Pigot, L., Pook, M., 2007. The years of El Nino, La Nina, and interactions with the tropical Indian ocean. Journal of Climate 20, 2872e2880. Moy, C.M., Seltzer, G.O., Rodbell, D.T., Anderson, D.M., 2002. Variability of El Nino/ Southern Oscillation activity at millennial timescales during the Holocene epoch. Nature 420, 162e165. Naeher, S., Gilli, A., North, R.P., Hamann, Y., Schubert, C.J., 2013. Tracing bottom water oxygenation with sedimentary Mn/Fe ratios in Lake Zurich, Switzerland. Chemical Geology 352, 125e133. Nakamura, A., Yokoyama, Y., Maemoku, H., Yagi, H., Okamura, M., Matsuoka, H., Miyake, N., Osada, T., Teramura, H., Adhikari, D.P., Dangol, V., Miyairi, Y., Obrochta, S., Matsuzaki, H., 2012. Late Holocene Asian monsoon variations recorded in Lake Rara sediment, western Nepal. Journal of Quaternary Science 27, 125e128. Nakamura, A., Yokoyama, Y., Shiroya, K., Miyairi, Y., Matsuzaki, H., 2014a. Direct comparison of site-specific and basin-scale denudation rate estimation by in situ cosmogenic nuclides: an example from the Abukuma Mountains, Japan. Progress in Earth and Planetary Science 1, 9. http://dx.doi.org/10.1186/21974284-1-9. Nakamura, A., Yokoyama, Y., Sekine, Y., Goto, K., Komatsu, G., Kumar, P.S., Matsuzaki, H., Kaneoka, I., Matsui, T., 2014b. Formation and geomorphologic history of the Lonar impact crater deduced from in situ cosmogenic 10Be and 26 Al. Geochemistry, Geophysics, Geosystems 15, 3190e3197. Okino, T., Satoh, Y., 1986. Morphology, physics, chemistry and biology of Lake Rara in West Nepal. Hydrobiologia 140, 125e133. Pausata, F.S.R., Battisti, D.S., Nisancioglu, K.H., Bitz, C.M., 2011. Chinese stalagmite delta O-18 controlled by changes in the Indian monsoon during a simulated Heinrich event. Nature Geoscience 4, 474e480. Phadtare, N.R., 2000. Sharp decrease in summer monsoon strength 4000e3500 cal yr BP in the central higher Himalaya of India based on pollen evidence from alpine peat. Quaternary Research 53, 122e129. Prasad, S., Anoop, A., Riedel, N., Sarkar, S., Menzel, P., Basavaiah, N., Krishnan, R., Fuller, D., Plessen, B., Gaye, B., Rohl, U., Wilkes, H., Sachse, D., Sawant, R., Wiesner, M.G., Stebich, M., 2014. Prolonged monsoon droughts and links to Indo-Pacific warm pool: a Holocene record from Lonar Lake, central India. Earth and Planetary Science Letters 391, 171e182. Ravens, T.M., Kocsis, O., Wuest, A., Granin, N., 2000. Small-scale turbulence and vertical mixing in Lake Baikal. Limnology and Oceanography 45, 159e173. Reimer, P.J., Baillie, M.G.L., Bard, E., Bayliss, A., Beck, J.W., Blackwell, P.G., Ramsey, C.B., Buck, C.E., Burr, G.S., Edwards, R.L., Friedrich, M., Grootes, P.M., Guilderson, T.P., Hajdas, I., Heaton, T.J., Hogg, A.G., Hughen, K.A., Kaiser, K.F., Kromer, B., McCormac, F.G., Manning, S.W., Reimer, R.W., Richards, D.A., Southon, J.R., Talamo, S., Turney, C.S.M., van der Plicht, J., Weyhenmeye, C.E., 2009. Intcal09 and Marine09 14C age calibration Curves, 0e50,000 Years Cal BP. Radiocarbon 51, 1111e1150. Saji, N.H., Goswami, B.N., Vinayachandran, P.N., Yamagata, T., 1999. A dipole mode in the tropical Indian Ocean. Nature 401, 360e363. Sakamoto, T., Kuroki, K., Sugawara, T., Aoike, K., Iijima, K., Sugisaki, S., 2006. Nondestructive X-ray fluorescence (XRF) core-imaging scanner, TATSCAN-F2. Scientific Drilling 2, 37e39. Schaller, T., Moor, H.C., Wehrli, B., 1997. Sedimentary profiles of Fe, Mn, V, Cr, As and Mo as indicators of benthic redox conditions in Baldeggersee. Aquatic Sciences 59, 345e361. Staubwasser, M., Sirocko, F., Grootes, P.M., Segl, M., 2003. Climate change at the 4.2 ka BP termination of the Indus valley civilization and Holocene south Asian monsoon variability. Geophysical Research Letters 30. Staubwasser, M., Weiss, H., 2006. Holocene climate and cultural evolution in lateprehistoriceearly historic West Asia. Quaternary Research 66, 372e387. Thompson, L.G., Mosley-Thompson, E., Davis, M.E., Henderson, K.A., Brecher, H.H., Zagorodnov, V.S., Mashiotta, T.A., Lin, P.N., Mikhalenko, V.N., Hardy, D.R., Beer, J., 2002. Kilimanjaro ice core records: evidence of Holocene climate change in tropical Africa. Science 298, 589e593. Tierney, J.E., Russell, J.M., Damste, J.S.S., Huang, Y.S., Verschuren, D., 2011. Late Quaternary behavior of the East African monsoon and the importance of the Congo Air Boundary. Quaternary Science Reviews 30, 798e807. Tjallingii, R., Rohl, U., Kolling, M., Bickert, T., 2007. Influence of the water content on X-ray fluorescence core-scanning measurements in soft marine sediments. Geochemistry Geophysics Geosystems 8. Trumbore, S., 2000. Age of soil organic matter and soil respiration: 14C constraints on belowground C dynamics. Ecological Applications 10, 399e411. Trumbore, S., 2009. 14C and soil carbon dynamics. Annual Review of Earth and Planetary Sciences 37, 47e66. Tyler, J., Kashiyama, Y., Ohkouchi, N., Ogawa, N., Yokoyama, Y., Chikaraishi, Y., Staff, R.A., Ikehara, M., Bronk Ramsey, C., Bryant, C., Brock, F., Gotanda, K., Haraguchi, T., Yonenobu, H., Nakagawa, T., 2010. Chlorin specific carbon and nitrogen isotopes track aquatic change over the last deglaciation in Lake Suigetsu, Japan. Geochemistry, Geophysics, Geosystems 11, 1e19. Vinther, B.M., Clausen, H.B., Johnsen, S.J., Rasmussen, S.O., Andersen, K.K., Buchardt, S.L., Dahl-Jensen, D., Seierstad, I.K., Siggaard-Andersen, M.L., Steffensen, J.P., Svensson, A., Olsen, J., Heinemeier, J., 2006. A synchronized dating of three Greenland ice cores throughout the Holocene. Journal of Geophysical Research e Atmospheres 111, D13102. Walker, M.J.C., Berkelhammer, M., Bjorck, S., Cwynar, L.C., Fisher, D.A., Long, A.J., Lowe, J.J., Newnham, R.M., Rasmussen, S.O., Weiss, H., 2012. Formal subdivision of the Holocene Series/Epoch: a Discussion Paper by a Working Group of INTIMATE (Integration of ice-core, marine and terrestrial records) and the

Please cite this article in press as: Nakamura, A., et al., Weak monsoon event at 4.2 ka recorded in sediment from Lake Rara, Himalayas, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.05.053

A. Nakamura et al. / Quaternary International xxx (2015) 1e11 Subcommission on Quaternary Stratigraphy (International Commission on Stratigraphy). Journal of Quaternary Science 27, 649e659. Wang, H.J., Chen, H.P., 2012. Climate control for southeastern China moisture and precipitation: Indian or East Asian monsoon? Journal of Geophysical Research e Atmospheres 117, D12109. Wang, R.L., Scarpitta, S.C., Zhang, S.C., Zheng, M.P., 2002. Later Pleistocene/Holocene climate conditions of Qinghai-Xizhang Plateau (Tibet) based on carbon and oxygen stable isotopes of Zabuye Lake sediments. Earth and Planetary Science Letters 203, 461e477. Wang, Y.J., Cheng, H., Edwards, R.L., He, Y.Q., Kong, X.G., An, Z.S., Wu, J.Y., Kelly, M.J., Dykoski, C.A., Li, X.D., 2005. The Holocene Asian monsoon: links to solar changes and North Atlantic climate. Science 308, 854e857. Wang, Y.J., Cheng, H., Edwards, R.L., Kong, X.G., Shao, X.H., Chen, S.T., Wu, J.Y., Jiang, X.Y., Wang, X.F., An, Z.S., 2008. Millennial- and orbital-scale changes in the East Asian monsoon over the past 224,000 years. Nature 451, 1090e1093. Webster, P.J., Magana, V.O., Palmer, T.N., Shukla, J., Tomas, R.A., Yanai, M., Yasunari, T., 1998. Monsoons: processes, predictability, and the prospects for prediction. Journal of Geophysical Research 103, 14451e14510. Wunnemann, B., Demske, D., Tarasov, P., Kotlia, B.S., Reinhardt, C., Bloemendal, J., Diekmann, B., Hartmann, K., Krois, J., Riedel, F., Arya, N., 2010. Hydrological evolution during the last 15 kyr in the Tso Kar lake basin (Ladakh, India), derived from geomorphological, sedimentological and palynological records. Quaternary Science Reviews 29, 1138e1155. Xiao, J., Wu, J., Si, B., Liang, W., Nakamura, T., Liu, B., Inouchi, Y., 2006. Holocene climate changes in the monsoon/arid transition reflected by carbon concentration in Daihai Lake of Inner Mongolia. The Holocene 16, 551e560. Xu, S., Zheng, G.D., 2003. Variations in 14C ages of various organic fractions in core sediments from Erhai Lake, SW China. Geochemical Journal 37, 135e144. Yagi, H., Maemoku, H., Okamura, M., Matsuoka, H., Osada, T., Teramura, H., Adhikari, D.P., Dangol, V., 2010. Rara Lake, its bathymetric feature and origin, Jumla District, western Nepal Himalayas. In: Project, Indus (Ed.), Annual Report of Environmental Change and the Indus Civilization 2009. Research Institute for Humanity and Nature, Kyoto, pp. 59e62.

11

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, 74e77. Yamane, M., Yokoyama, Y., Miyairi, Y., Suga, H., Matsuzaki, H., Dunbar, R.B., Ohkouchi, N., 2014. Compound-specific 14C dating of IODP Expedition 318 core U1357A obtained off the Wilkes Land coast, Antarctica. Radiocarbon 56, 1009e1017. Yasuda, Y., Tabata, H., 1988. Vegetation and climatic changes in Nepal Himalayas. A preliminary study of the Holocene vegetational history in the Lake Rara national park area, west Nepal. Proceedings of Indian National Science Academy 54, 538e548. Yokoyama, Y., Miyairi, Y., Matsuzaki, H., Tsunomori, F., 2007. Relation between acid dissolution time in the vacuum test tube and time required for graphitization for AMS target preparation. Nuclear Instruments & Methods in Physics Research Section B e Beam Interactions with Materials and Atoms 259, 330e334. Yokoyama, Y., Koizumi, M., Matsuzaki, H., Miyairi, Y., Ohkouchi, N., 2010. Developing ultra small-scale 14C sample measurement at the University of Tokyo. Radiocarbon 52, 310e318. Yokoyama, Y., Okuno, J., Miyairi, Y., Obrochta, S., Demboya, N., Makino, Y., Kawahata, H., 2012. Holocene sea-level change and Antarctic melting history derived from geological observations and geophysical modeling along the Shimokita Peninsula, northern Japan. Geophysical Research Letters 39, L13502. Yokoyama, Y., Maeda, Y., Okuno, J., Miyairi, Y., Kosuge, T., 2015. Holocene Antarctic melting and lithospheric uplift history of the southern Okinawa trough inferred from mid- to late- Holocene sea level in Iriomote Island, Ryukyu, Japan. Quaternary International. http://dx.doi.org/10.1016/j.quaint.2015.03.030. Yoo, K., Amundson, R., Heimsath, A.M., Dietrich, W.E., 2006. Spatial patterns of soil organic carbon on hillslopes: Integrating geomorphic processes and the biological C cycle. Geoderma 130, 47e65. Zhang, L., Zhu, G., Luo, L., Gao, G., Zhang, Y., Qin, B., Fan, C., 2006. Wind-wave affected phosphate loading variations and their relationship to redox condition in Lake Taihu. Science in China Series D 49, 154e161.

Please cite this article in press as: Nakamura, A., et al., Weak monsoon event at 4.2 ka recorded in sediment from Lake Rara, Himalayas, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.05.053