Evolution of Chaka Salt Lake in NW China in response to climatic change during the Latest Pleistocene–Holocene

Abstract

The Late Pleistocene and Holocene hydrologic balance of Chaka Salt Lake in the eastern Qaidam Basin of NW China was studied based on the analysis of lithostratigraphy, mineralogy, total organic carbon, and total nitrogen from a 9.0-m long sediment core. An age–depth model for the lake sediments is based on eight accelerator mass spectrometry (AMS) 14C measurements of organic matter and a 1700-year radiocarbon reservoir correction. The Pitzer model was used to calculate the sequence of minerals precipitated as a function of salinity assuming that the initial lake water was recharged from adjacent rivers and springs. Lake salinity values were derived from a good match between the calculated and observed mineral sequences. Our multi-proxy based hydrologic reconstruction of Chaka Lake indicates that it was a clastic-dominated, freshwater lake between 17.2 and 11.4 cal ka BP, which may have resulted from the input of glacial water into the lake at that time. During the Lateglacial and Holocene, a warm climatic regime predominated between 13.9 and 12.7 cal ka BP and then a cold climatic regime prevailed between 12.7 and 11.4 cal ka BP. These warm and cold periods correlate with the Bølling–Allerød and Younger Dryas events in the region. Beginning at 11.4 cal ka BP, a saline or hypersaline lake developed, which may have resulted from increased summer insolation and temperatures. These conditions persisted throughout the Holocene. Modeling indicates that lake salinity fluctuated between 66 and 223 ppt from 11.4 to 7.2 cal ka BP and then increased to 223–322 ppt between 7.2 and 6.0 cal ka BP, when most regions of China recorded high moisture availability (i.e. the so-called “mid-Holocene Climatic Optimum”). Lake salinity decreased to 66–223 ppt during a short time period between 6.0 and 5.3 cal ka BP, possibly caused by reduced evaporation. Subsequently, salinity values rapidly increased to 223–322 ppt between 5.3 and 5.2 cal ka BP and a hypersaline lake with a salinity higher than 324 ppt, similar to modern Chaka Salt Lake, became established around 5.2 cal ka BP. This establishment may have been related to the weakening of Asian monsoon. Regional comparisons of paleoclimatic records indicate that large temporal and spatial variations exist in the occurrence and intensity of drought over Western China since the Lateglacial.

Full text

Quaternary Science Reviews 27 (2008) 867–879
Evolution of Chaka Salt Lake in NW China in response to climatic
change during the Latest Pleistocene–Holocene
Liu Xingqi
a,
, Hailiang Dong
b
, Jason A. Rech
b
, Ryo Matsumoto
c
, Yang Bo
d
, Wang Yongbo
a
a
State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology,
Chinese Academy of Sciences, Nanjing 210008, China
b
Department of Geology, Miami University, Oxford, OH 45056, USA
c
Department of Earth and Planetary Science, University of Tokyo, Tokyo 113-0033, Japan
d
Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, China
Received 23 May 2007; received in revised form 21 November 2007; accepted 4 December 2007
Abstract
The Late Pleistocene and Holocene hydrologic balance of Chaka Salt Lake in the eastern Qaidam Basin of NW China was studied
based on the analysis of lithostratigraphy, mineralogy, total organic carbon, and total nitrogen from a 9.0-m long sediment core. An
age–depth model for the lake sediments is based on eight accelerator mass spectrometry (AMS)
14
C measurements of organic matter and
a 1700-year radiocarbon reservoir correction. The Pitzer model was used to calculate the sequence of minerals precipitated as a function
of salinity assuming that the initial lake water was recharged from adjacent rivers and springs. Lake salinity values were derived from a
good match between the calculated and observed mineral sequences. Our multi-proxy based hydrologic reconstruction of Chaka Lake
indicates that it was a clastic-dominated, freshwater lake between 17.2 and 11.4 cal ka BP, which may have resulted from the input of
glacial water into the lake at that time. During the Lateglacial and Holocene, a warm climatic regime predominated between 13.9 and
12.7 cal ka BP and then a cold climatic regime prevailed between 12.7 and 11.4 cal ka BP. These warm and cold periods correlate with the
Bølling–Allerød and Younger Dryas events in the region. Beginning at 11.4 cal ka BP, a saline or hypersaline lake developed, which may
have resulted from increased summer insolation and temperatures. These conditions persisted throughout the Holocene. Modeling
indicates that lake salinity fluctuated between 66 and 223 ppt from 11.4 to 7.2 cal ka BP and then increased to 223–322 ppt between 7.2
and 6.0 cal ka BP, when most regions of China recorded high moisture availability (i.e. the so-called ‘‘mid-Holocene Climatic
Optimum’’). Lake salinity decreased to 66–223 ppt during a short time period between 6.0 and 5.3 cal ka BP, possibly caused by reduced
evaporation. Subsequently, salinity values rapidly increased to 223–322 ppt between 5.3 and 5.2 cal kaBP and a hypersaline lake with a
salinity higher than 324 ppt, similar to modern Chaka Salt Lake, became established around 5.2 calka BP. This establishment may have
been related to the weakening of Asian monsoon. Regional comparisons of paleoclimatic records indicate that large temporal and spatial
variations exist in the occurrence and intensity of drought over Western China since the Lateglacial.
r2008 Elsevier Ltd. All rights reserved.
1. Introduction
The Asian summer monsoon is thought to play a key
role in atmospheric circulation over Asia and globally.
Paleoclimatic proxies from northeastern Tibet and the
Qaidam Basin, a region influenced by precipitation from
both the Asian summer monsoon and moist air masses
entrained in the Westerlies, are essential for determining
the interplay between these components of the climate
system over East Asia (Gao, 1962;Lehmkuhl and Haselein,
2000). Here, we present a record of the Latest Pleistocene
and Holocene hydrologic changes of Chaka Salt Lake in
the Qaidam Basin of northeast Tibet to determine the
potential role of insolation forcing on climate in a region
that is located at the boundary between Westerly and Asian
summer monsoon summer precipitation.
The Qaidam Basin, bounded by the Kunlun, Aljun, and
Qilian Mountains on the north and the Kunlun Mountains
on the south, is a large intermontane depression on the
northern margin of the Qinghai–Xizang Plateau (Fig. 1).
The basin covers an area of 120,000 km
2
with a catchment
ARTICLE IN PRESS
0277-3791/$ - see front matter r2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.quascirev.2007.12.006

Corresponding author. Tel.: +86 25 8688 2142; fax: +86 25 5771 3063.
E-mail addresses: xingqiliu@yahoo.com,
xqliu@niglas.ac.cn (L. Xingqi).

area of about 250,000 km
2
(Chen and Bowler, 1986;Zhang,
1987). Within this vast basin, there are many salt lakes and
playas containing alternating clastic–evaporite sedimentary
sequences. These sequences are potentially important
archives of hydrologic and paleoclimatic changes in
Western China. Wang et al. (1986) established the
preliminary magnetostratigraphy of Dabusan Lake in
the Qaidam Basin. A research project sponsored jointly
by the Chinese Academy of Sciences and Australian
National University in the 1980s focused on the climatic
evolution history of salt lakes in the Qaidam Basin, from
Late Pleistocene to today (Bowler et al., 1986;Chen and
Bowler, 1986). These authors determined the timing of
major climatic events for Kunteyi, Xiao Chaidan, and
Qarhan salt lakes in the Qaidam Basin (Fig. 1). Their
results indicate that expansion of these lakes occurred from
at least 40 to 15
14
C ka BP, large evaporate deposits
formed after 15
14
C ka BP, and dry conditions prevailed
throughout the Holocene (Bowler et al., 1986). Dry
conditions since the Lateglacial were also indicated by a
high content of gypsum in Barkol Lake of Xinjiang (Gu
et al., 1998), 750 km northwest of the Qaidam Basin. No
further paleoclimatic studies have been carried out in the
Qaidam Basin using clastic–evaporite sequences. A recent
study, based on total organic and inorganic carbon, total
sulfur, and carbon and oxygen stable isotopes of Zabuye
Lake sediments (Wang et al., 2002), reconstructed the Late
Pleistocene/Holocene climate conditions of Qinghai–Xi-
zang Plateau. The authors showed that the Zabuye Lake
overflowed during ca 16.2–10.6
14
C ka BP, closed its surface
outflow during ca 10.6–5.0
14
C ka BP, and a hypersaline
environment formed after 5
14
C ka BP.
Previous research suggests that significant temporal and
spatial variations of wet or dry phases reconstructed from
salt lakes or playas most likely existed in Western China
since the Lateglacial. For example, Lehmkuhl and Haselein
(2000) indicated that higher lake levels in the deserts of
Central Asia and on the Qinghai–Xizang Plateau are dated
to 40–25 ka (OIS 3) and to the Lateglacial/Early to mid-
Holocene periods. This is probably due to various local
hydrological or topographic factors that may have
different responses to two different climate systems
(Westerlies and Asian monsoons). However, well-dated
paleoclimatic records from salt lakes or playas in Western
China are rather limited. Thus, in order to fully understand
the mechanism of the observed temporal and spatial
variations, more paleoclimatic proxy records are highly
desirable. Our objective was to study the hydrologic
evolution of Chaka Salt Lake and to infer its response to
climatic changes that have occurred since the Lateglacial.
We employed mineralogical, lithostratigraphic, total or-
ganic carbon (TOC), and total nitrogen (TN) record from a
ARTICLE IN PRESS
Fig. 1. Map of the Qaidam Basin in China showing the location of Chaka Salt Lake. Also shown are other salt lakes, playas, and fresh or saline lakes in
the Basin. The inset map in the upper right corner shows the location of the coring site (CKL-2004). Numbers are locations of other lake records cited in
Fig. 6 (1, Zabuye Salt Lake; 2, Qinghai Lake; 3, Qarhan Salt Lake).
L. Xingqi et al. / Quaternary Science Reviews 27 (2008) 867–879868

9.0-m long continuous sediment core to achieve our
objective.
2. Study area
Chaka Salt Lake (361380–361450N, 991020–991120E;
3200 m above sea level, m a.s.l.) is located on the eastern
edge of the Qaidam Basin about 150 km west of Qinghai
Lake (Fig. 1). The Chaka Salt Lake region, isolated from
oceanic air masses, is characterized by a highly continental
climate. The mean annual temperature is 3.5 1C, with a low
mean monthly temperature of 12.4 1C in January and a
high mean monthly temperature of 14.4 1C in July. The
mean annual precipitation (197.6 mm) is far less than the
mean annual evaporation (2074.1 mm).
The lake has no outlet but is fed by fresh water from the
Mo River at its northwestern margin, the Hei River at its
southeastern margin, and springs on its northeastern and
southwestern bank (Fig. 1;Table 1). Some glaciers are
distributed in the north and northwest of Chaka Salt Lake
(inset of Fig. 1). It covers an area of 105 km
2
with a
catchment area of 11,600 km
2
. The depth of lake-water
varies greatly from 50–60 cm in the rainy season (June/
July) to just 1 cm in the dry season (January–March).
Similar to many other salt lakes in the Qaidam Basin, the
salinity of the Chaka Salt Lake water at present is between
317 and 347 ppt (about 10 times that of sea water). The
lake water chemistry is dominated with ions Na
+
,Mg
2+
,
Cl

, and SO
4
2
, but also contains smaller amounts of Ca
2+
,
K
+
,CO
3
2
, and HCO
3

(Table 1). The present-day lake
water is saturated with respect to halite, and halite
crystallization occurs during the dry season.
3. Materials and methods
In October 2004, a 9.0-m long sediment core (CKL-
2004) was drilled from the southeastern part of the lake at a
water depth of 2 cm using a strengthened corer made in
China (chamber length 1 m, inner diameter 7 cm). The
stratigraphic sequences recovered from core CKL-2004
generally consist of halite from 0 to 565 cm, a mixture of
soluble and sparingly soluble sulfate salts with dark
siliciclastics from 565 to 693 cm, and dark siliciclastic
layers from 693 to 900 cm. The core was subsampled at a
depth interval of 1 or 2 cm with a total of 590 subsamples.
Subsamples from CKL-2004 were analyzed for TOC, TN,
and mineralogy. A small subset was used for
14
C dating.
Samples for analyses of TOC and TN were treated with
1 N HCl to remove carbonates, rinsed repeatedly with
deionized water to remove soluble salt minerals, and dried.
TOC and TN contents were determined using a CE Model
440 Elemental Analyzer at the Nanjing Institute of
Geography and Limnology, Chinese Academy of Sciences
(CAS).
All samples analyzed for mineralogy were air-dried at
room temperature, disaggregated in a mortar and pestle,
and passed through a 62.5-mm sieve. Mineralogy was
determined at the Institute of Salt Lakes, CAS, using a
Phillips X-pert Pro X-ray diffraction with Cu Karadiation
(l¼1.5406 A
˚) at a scanning rate of 21min
1
for 2yranging
from 101to 801. Mineral identification and concentration
were estimated from the bulk mineral diffractograms using
the intensity of the strongest peak for each mineral
(Schultz, 1964;Chung, 1974;Last, 2001) aided by the use
of an automated search-match computer program X’Pert
HighScore Plus. Duplicate analyses of mineralogy for 15
samples in different lithostratigraphic units indicated that
precision of the mineralogical data is approximately 75%.
To understand the paleohydrological conditions of the
lake during different time periods and to explain the origin
of the evaporite mineral sequence observed in the core, a
computer simulation was carried out. The computer
program PHRQPITZ (Plummer et al., 1988), based on
the Pitzer virial-coefficient approach for activity-coefficient
corrections (Pitzer, 1973), was used to calculate the mineral
sequences through evaporation of initial lake water. This
ARTICLE IN PRESS
Table 1
Chemical composition of Chaka Salt Lake water, river water, and spring (concentration in mg/l)
Water body Sampling date Ca
2+
Mg
2+
Na
+
K
+
HCO
3

+CO
3
2
SO
4
2
Cl

TDS (ppt) Specific gravity pH
Lake water 1986
a
124 26,506 80,231 4473 199 23,625 187,700 322 1.22 6.8
7/1994 210 21,100 86,520 3620 600 22,320 182,710 317 1.21 6.9
11/1994 120 46,170 54,670 7560 1310 45,390 192,020 347 1.25 7.1
10/2004 125 45,160 56,120 6500 1200 44,400 191,230 344 1.23 7.0
Mo River 7/1994 71 84 378 4 192 445 517 1.70 1.00 6.9
11/1994 132 116 438 6 310 450 671 2.10 1.00 7.1
Hei River 7/1994 58. 104 296 15 409 384 113 1.38 1.00 6.8
11/1994 35 73 260 9 259 201 392 1.22 1.00 6.7
Spring 7/1994 52 29 153 4 243 109 193 0.78 1.00 7.1
11/1994 52 23 137 3 212 116 183 0.73 0.99 7.2
Initial water
b
1994 80 69 333 8 279 318 376 1.46
a
Data from Zhang (1987).
b
Data from Liu et al. (2004).
L. Xingqi et al. / Quaternary Science Reviews 27 (2008) 867–879 869

type of thermodynamic-based model is used commonly for
this purpose (Harvie and Weare, 1980;Harvie et al., 1980,
1982). Because presence or absence of a given mineral
assemblage is controlled not only by lake water composi-
tion and hydrological conditions but also by water
temperature, we studied homogenization temperatures of
205 fluid inclusions in halite crystals above 546 cm of the
900-cm core formed in the last 5180 years and 11 fluid
inclusions in halite formed in modern Chaka Salt Lake
(Liu et al., 2007a). Our study suggests that homogenization
temperatures range from 18 to 25 1C with an average of
23.7 1C(Liu et al., 2007a). These temperatures are very
similar to the water temperatures that were measured in the
lake in August 2005, which was the main season for halite
precipitation. Based on the Pitzer virial-coefficient ap-
proach for highly concentrated electrolyte solutions, we
thus calculated the mineral sequence produced from
evaporation of the initial water at 23.7 1C. The initial lake
water was assumed to have the same composition as that
formed by mixing river and spring waters according to
their present-day influxes to the lake.
4. Results and interpretation
4.1. Chronology
Ten samples of bulk organic material were processed for
accelerated mass spectrometry (AMS)
14
C dating to
construct an age model for the Chaka Salt Lake core. Six
samples were chemically pretreated, combusted, and
cryogenically purified at Miami University and then
analyzed at the University of Arizona NSF-AMS Labora-
tory, the United States, and four samples from a parallel
core to CKL-2004 were analyzed at the University of
Tokyo Radiocarbon Laboratory, Japan (Table 2). During
base treatment with 2% NaOH, all samples except for CK-
568 remained clear, indicating that no humic acids were
present. Sample CK-568, however, turned opaque during
base treatment due to high concentrations of humic acids.
The base treatment was repeated three times to remove all
humic acids; however, the
14
C age for CK-568 is 2000
14
C
years younger than sample CK-480 which was located from
1 m above (Table 2). We therefore exclude sample CK-568
from our age model because of the likelihood of secondary
contamination by humic acids. Sample CK-519 also shows
an age reversal of 1000
14
C years. We do not include this
sample in our age model, but we also have no reason to
suspect contamination by secondary humic acids. There is
a good linear relationship between depth and
14
C age for
the remainder of the radiocarbon samples (Fig. 2A). AMS
14
C ages could not be obtained above the depth of 450 cm
because the sediments contain very low TOC content.
The radiocarbon dating of lacustrine sediments in the
arid–semiarid regions of Western China is generally
affected by
14
C reservoir effects (Ren, 1998;Shen et al.,
2005;Morrill et al., 2006). This is especially true for saline
lakes on the Tibetan Plateau (Shen et al., 2005;Herzschuh
et al., 2006b). In an analysis of lake sediments from
Qinghai Lake, Shen et al. (2005) fit a linear regression line
to organic
14
C ages with depth to infer a radiocarbon
reservoir effect of 1039 years. These authors then assumed
a constant
14
C reservoir effect over their 18,000-year lake
record and subtracted 1039 years from all
14
C ages prior to
calibration. Herzschuh et al. (2006b) determined a modern
14
C reservoir effect of 2010
14
C years for Lake Zigetang, by
AMS
14
C dating of organic sediments from the surface
sample of the core. Herzschuh et al. (2006b) also assume a
constant
14
C reservoir effect over their lake record and
ARTICLE IN PRESS
Table 2
AMS
14
C ages and calendar age in CKL-2004 and its parallel core
Sample
no.
Lab I.D. Depth
(cm)
Sample description Dated
material
14
C age
(a BP)
14
C age corrected by 1700
years
Calendar age (cal a BP)
CKL326
a
Tka-
14017
447–453 Middle—grained halite with dark
clayey silt
TOC 4395730 2695730 2754–2851 (2802)
CKL340
a
TKa-
14018
508–511 Coarse halite with dark clayey silt TOC 5070735 3370735 3554–3694 (3624)
CK-308
b
AA67512 546–548 Coarse halite with dark clayey silt TOC 5705745 4005745 4401–4586 (4493)
CKL378
a
TKa-
14019
577–579 Dark clayey silt with gypsum. TOC 6815735 5115735 5749–5830 (5789)
CK-395
b
AA67514 642–643 Dark clayey silt with gypsum. TOC 9035750 7335750 8021–8208 (8114)
CK-435
b
AA67515 695–696 Dark clayey silt with gypsum. TOC 11,740765 10,040765 11,270–11,824 (11,547)
CKL577
a
Tka-
14020
705–706 Dark clayey silt TOC 11,840750 10,140750 11,601–12,041 (11,820)
CK-480
b
AA67516 749–750 Dark clayey silt TOC 12,995785 11,295785 12,997–13,321 (13,159)
CK-
519
b,c
AA67517 798–799 Dark clayey silt TOC 12,054765 10,354765 11,979–12,401 (12,190)
CK-
568
b,c
AA67518 867–868 Dark clayey silt TOC 10,9007120 92007120 10,168–10,707 (10,437)
a
Samples from a parallel core to CKL-2004.
b
Samples from CKL-2004.
c
Rejected ages.
L. Xingqi et al. / Quaternary Science Reviews 27 (2008) 867–879870

subtracted 2010 years from all radiocarbon samples prior
to calibration. In a study of Lake Zabuye, which is a
shallow (o1 m) saline (200–460 g/l) lake similar to Chaka,
Wang et al. (2002) did not determine if a
14
C reservoir
effect was present and therefore did not correct radio-
carbon ages.
In Chaka Salt Lake, we suggest that there is a
14
C
reservoir effect of organic lake sediments similar to other
salt lakes on the Qinghai–Xizang Plateau. However, we
cannot determine the modern reservoir effect due to the
extremely low TOC content of the surface sample from the
core. Moreover, we suggest that it is quite likely that
the
14
C reservoir effect has changed over time, decreasing
in magnitude when there is a more positive hydrologic
budget. We account for the
14
C reservoir effect at Chaka
Lake by correlating a major decrease in the TOC and TN
of Chaka Lake sediments, indicative of colder and drier
conditions, with the globally recognized Younger Dryas
event (Stuiver et al., 1995). TOC and TN contents distinctly
decrease at the depth interval between 693 and 732 cm,
and gypsum begins to precipitate largely at the depth
of 693 cm (Fig. 3). Based on the sedimentation rate
calculated from CK-395 (9035750
14
C a BP, 642 cm)
to CK-480 (12,995785
14
C a BP, 749 cm), the time char-
acterized by decreased TOC and TN content spans from
12.6 to 11.7
14
C ka BP. Gypsum begins to precipitate at
11.7
14
C ka BP. The Younger Dryas event (12.8–11.5 cal k-
a BP), reflected as a cold event in Greenland, has been
recorded throughout most of China, such as Guliya core
(Thompson et al., 1997;Yao et al., 1998) and Qinghai Lake
(Shen et al., 2005) in Qinghai–Xizang Plateau, on the Loess
Plateau (An et al., 1993;Chen et al., 1997;Wang et al.,
1999), salt lakes in Inner Mongolia (Chen et al., 1996), and
even in East China (Wang et al., 2001;Yuan et al., 2004;
DyKoski et al., 2005). The periods at which TOC and TN
contents increase again and gypsum precipitation initiates
ARTICLE IN PRESS
Fig. 2. Plot of
14
C and calendar age versus depth in the core CKL-2004. Circles indicate
14
C ages, squares are
14
C ages that have been corrected for
14
C
reservoir effects by subtracting 1700
14
C years, and triangles are calendar ages.
Fig. 3. Variations in content of gypsum, total organic carbon (TOC), and
total nitrogen (TN) in core CKL-2004.
L. Xingqi et al. / Quaternary Science Reviews 27 (2008) 867–879 871

are thought to correspond with the end of the Younger
Dryas cold event (Stuiver et al., 1995). Thus, it appears that
the end of the Younger Dryas cold event recorded in
Chaka Salt Lake is earlier than the global average by
1700
14
C years. We therefore assume a
14
C reservoir
correction of 1700 years for Chaka Lake. This magnitude
of a
14
C reservoir effect is comparable to the 1000–2000
year range measured or inferred from other salt lakes on
the Qinghai–Xizang Plateau. We then subtracted 1700
years from all measured radiocarbon ages prior to
calibration using Calib 4.4 (Stuiver et al., 1998)(Table 2).
The age of sample CK-519, which was not corrected by the
reservoir effect, falls well into the line of reservoir-corrected
14
C age and depth (Fig. 2A), probably implying that this
section of the lake record, which records a positive
hydrologic balance, has a minimal reservoir effect. Our
age model was then calculated by applying a 1700-year
correction to all radiocarbon samples above CK-519
and then inferring constant sedimentation rates between
radiocarbon samples or the surface in the age–depth model
(Fig. 2).
4.2. TOC and TN
Total organic carbon values are generally low, below
0.4%, but increase to values between 0.8% and 1.2%
between 7.5 and 5.5 m depth in the core (Fig. 3). TN
values are also generally low, below 0.1%, but also show
higher concentrations below 5.5 m depth in the core. TOC
and TN values are both especially low in the halite layer
and in the dark clastic layers. The dark color in clastic
layers is probably due to anoxic conditions, not necessarily
due to organic matter.
Total organic carbon and total nitrogen in lacustrine
sediment, which are closely related to organic matter
signals of biological productivity (Wang and Ji, 1995;
Sifeddine et al., 1996;Nara et al., 2005), are a good
indicator of primary productivity, especially in arid and
semi-arid region (Chen et al., 2001;Zhu et al., 2002;Shen
et al., 2005). Many studies have shown that high TOC and
TN contents indicate enhanced primary productivity due
to warm and/or wet climate, whereas their low contents
imply decreased productivity due to cold and/or dry
climate (Chen et al., 2001;Zhu et al., 2002;Shen et al.,
2005). An increase in TOC and TN contents can also
indicate an increase in the intensity of the summer
monsoon circulation in the monsoonal region (Chen et
al., 2001;Xiao et al., 2002;Shen et al., 2005).
4.3. Detrital minerals
Quartz, clay minerals, and feldspars are the dominant
siliciclastic minerals in Core CKL-2004. These detrital
minerals are allogenic and were derived from outcrops
within the drainage basin of the lake through processes of
weathering and erosion and transported into the lake by
river runoff. Because Chaka Salt Lake is located in a closed
basin, river discharge, controlled by climatic changes, plays
an important role in sediment input to the lake. Humid
conditions, closely related to increased precipitation or
melting glacial water caused by warm temperature, can
increase river runoff and the supply of detrital materials to
the lake.
4.4. Carbonates and evaporite minerals
Calcite and dolomite are the predominant carbonate
minerals in Core CKL-2004. Evaporite minerals include
halite (NaCl), the only halide mineral identified, and sulfate
minerals such as gypsum (CaSO
4
2H
2
O), glauberite
(Na
2
SO
4
CaSO
4
), mirabilite (Na
2
SO
4
10H
2
O), bloedite
[Na
2
Mg(SO
4
)
2
4H
2
O)], polyhalite [K
2
MgCa
2
(-
SO
4
)
4
2H
2
O] and small amounts (o5%) of epsomite
(MgSO
4
7H
2
O). No carbonate or evaporite minerals exist
within the drainage basin, indicating that they formed by
direct precipitation from lake water (i.e. endogenic) or by
post-depositional authigenic/diagenetic precipitation pro-
cesses. The precipitation of evaporite minerals is governed
mostly by lake salinity and the chemical composition of the
lake water, i.e. the balance between precipitation and
evaporation (Kinsman, 1976;Shang and Last, 1999). Our
simulation results show that the calculated mineral
sequence is in good agreement with that determined from
Core CKL-2004 (Figs. 4 and 5), which suggests that (1) no
dramatic changes in water sources or significant variations
in hydrology has occurred since the lake formed; (2) that
ARTICLE IN PRESS
Fig. 4. Calculated mineral sequence based on Pitzer model through
progressive evaporation of initial water (starting with 1000 g) at 23.7 1C
and 1 atm pressure. Minerals precipitated at different salinities are shown,
mass H
2
O is the amount of water remaining and salinity is the total
dissolved salts in water.
L. Xingqi et al. / Quaternary Science Reviews 27 (2008) 867–879872

the evaporatic mineral sequence in Chaka Salt Lake can be
explained by evaporation of present-day river and spring
waters as a major recharge.
4.5. Reconstruction of the lake evolution
Based on lithostratigraphy, mineralogical composition,
and TOC and TN contents, the hydrologic evolution of
Chaka Salt Lake during past 17,000 years is classified into
the following five stages (Fig. 5).
4.5.1. Stage I: 900–693 cm (17.2–11.4 cal ka BP)
The lowest lithostratigraphic unit is characterized by a
firm and dark, laminated, clayey silt. This unit is
predominately detrital siliciclastics, consisting of quartz
(35%), clay minerals (25%), and feldspars (25%). Carbo-
nates are composed of calcite (o10%) with minor amounts
of dolomite (o5%). No evaporite minerals are present in
this unit. TOC and TN content averages 0.43% and 0.11%,
respectively.
The mineral composition of this unit implies a deep lake
with a low salinity between 17.2 and 11.4 cal ka BP.
Relatively low TOC and TN contents indicate low primary
productivity and thus likely low temperatures. However, a
short warm phase and a subsequent cold phase are thought
to have occurred during this time period, as characterized
by a distinct increase then decrease in both TOC and TN
content between 776 and 732 cm (13.9–12.7 cal ka BP) and
between 732 and 693 cm (12.7–11.4 cal ka BP), respectively.
The warm and cold periods are thought to correspond to
the Bølling–Allerød warm event and Younger Dryas cold
event, respectively, which are mirrored in many records
from China (Thompson et al., 1997;Yao et al., 1998;Wang
et al., 2001;Yuan et al., 2004;DyKoski et al., 2005;Shen
et al., 2005;Herzschuh, 2006).
4.5.2. Stage II: 693–582 cm (11.4–6.0 cal ka BP)
Stage II consists of sulfate minerals and faintly bedded
dark clayey silt. This stage is characterized by an abrupt
and simultaneous increase in TOC, TN, and sulfate and a
decrease in detrital mineral content. TOC and TN contents
increase dramatically and almost reach their highest values
at this stage, suggesting that lake primary productivity was
high, possibly due to warmer/wetter temperatures. The
rapid appearance of gypsum at the beginning of this stage
indicates a dramatic transition of the lake from a
freshwater to a saline/hypersaline environment. Computer
modeling suggests that lake salinity probably fluctuated
between 66 and 232 ppt from 11.4 to 7.2 cal ka BP because
evaporitic salt minerals were mostly gypsum with a small
amount of halite (o5%) (Figs. 4 and 5). A short interval
marked by a distinct decrease in gypsum and an increase in
detrital minerals between 670 and 616 cm suggests that lake
salinity decreased at the period from10.0 to 7.2 cal ka BP.
Beginning at the depth of 616 cm (7.2 cal ka BP), gypsum
content increases to about 50%, glauberite appears with an
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Fig. 5. Stratigraphic variation in total organic carbon, total nitrogen, and mineralogy in the core CKL-2004.
L. Xingqi et al. / Quaternary Science Reviews 27 (2008) 867–879 873

average abundance of 21%, and the detrital mineral
content decreases to 34%. All these changes indicate a
decrease in the hydrologic budget of the lake. The salinity
of Chaka Lake is modeled to have been between 232 and
324 ppt between 7.2 and 6.0 cal ka BP (Figs. 4 and 5).
4.5.3. Stage III: 582–567 cm (6.0–5.3 cal ka BP)
This lithostratigraphic unit is characterized by a thin
(15 cm) layer of massive to faintly bedded dark clayey silt
with small amounts of evaporite minerals. Evaporite
concentration decreases to 10%, whereas contents of
detrital minerals increase drastically to 80%. Carbonates
dominated by calcite with a small amount of dolomite also
show a slight increase. TOC and TN still maintain
relatively high values. The increase of detrital mineral
content in this period could be caused by two opposing
conditions: a humid condition (and thus enhanced weath-
ering and transport) or a dry condition (and thus enhanced
eolian deposition). However, the high TOC and TN
contents imply wetter conditions. During this stage, the
lake experienced a short and distinct wet period, but its
salinity was not lower than 66 ppt (Fig. 4), as inferred from
the concentration of gypsum (10%) at this time (Fig. 5).
4.5.4. Stage IV: 567–270 cm (5.3–1.7 cal ka BP)
Glauberite and gypsum are abundant (30% and 40%,
respectively) at the base of this unit, suggesting that lake
salinity rapidly increased to 324 ppt (from 66 ppt) between
5.3 and 5.2 cal ka BP (Figs. 4 and 5). Evaporite minerals
account for 98% of material in this section of the core
with halite being the dominant mineral with smaller
proportions of sulfate minerals, such as gypsum (5%),
mirabilite (1–7%) between 554 and 465 cm, bloedite
(3–21%) between 565 and 465 cm, and polyhalite (o5%)
between 549 and 513 cm. These mineral assemblages
indicate that lake salinity was 325 ppt (Figs. 4 and 5),
which is similar to the salinity of modern Chaka Salt Lake.
Biological activity and primary productivity are very low
during these hypersaline conditions, which is characterized
by very low TOC and TN content (0.2% and 0.03%,
respectively).
4.5.5. Stage V: 270–0 cm (1.7 cal ka BP–modern)
This uppermost lithostratigraphic unit is characterized
by almost a pure bedded halite. Halite content increases to
498% and no other evaporite minerals occur. Carbonate
and detrital minerals (o2%) are nearly absent. All data
suggest that the lake salinity was 4326 ppt (Figs. 4 and 5).
TOC and TN contents further decrease to 0.06% and
0.02%, respectively.
5. Discussion
5.1. Paleoclimate
In order to better understand Chaka Salt Lake evolution
and its response to regional and global climatic changes, we
made a comparison between the Chaka Salt Lake record
and other lakes in the Qinghai–Xizang Plateau, as well as
regional and global climate changes (Fig. 6).
5.1.1. Lateglacial
Studies on air trapped in polar ice show that the last
glacial period was terminated by an abrupt warming event
15.0 ka ago (Severinghaus and Brook, 1999). Similarly,
tropical climate became warmer or wetter (or both) 20 to
80 years after the onset of the Greenland warming event
(Severinghaus and Brook, 1999). Abrupt warming in the
North Atlantic may also have led to slightly greater
warming over the Qinghai–Xizang Plateau, resulting in
melting of glacial ice and the onset of Asian summer
monsoon circulation after the LGM (Prell and Kutzbach,
1992;Meehl and Washington, 1993;Overpeck et al., 1996).
Evidence of a high lake level between 17.2 and 11.4 cal k-
a BP in Chaka Salt Lake is probably attributed to increased
moisture availability in response to warmer temperatures,
melting glacial ice, and the onset of Asian summer
monsoon during the Lateglacial. A wet climate during this
time is consistent with other records from the Qinghai–
Xizang Plateau, such as the lake overflow in Zabuye Salt
Lake between ca 16.2 and 10.6
14
CkaBP (Wang et al.,
2002), the climate amelioration in Qinghai Lake between
16.9, especially 14.1, and 10.8 cal ka BP (Shen et al., 2005),
and higher effective moisture conditions in Western China
during the Lateglacial (Herzschuh, 2006)(Fig. 6). How-
ever, very arid conditions characterized by evaporite
sequences occurred in other salt lakes of the Qaidam Basin
since the Lateglacial, such as Qarhan, Kunteyi, Xiao
Chaidan (Bowler et al., 1986). A possible interpretation for
this discrepancy is that evaporation caused by warmer
temperature in Chaka Salt Lake may have not been
sufficient to balance the quantity of melting glacial water
and the precipitation, but it may have been sufficient in
other lakes (Qarhan, Kunteyi, and Xiao Chaidan). These
lakes are further west and north of Chaka Salt Lake, and
thus are less influenced by the Asian monsoon.
Frequent climatic fluctuations are evident in Chaka Salt
Lake during the transitional period from the Lateglacial to
Holocene. Warm and cold phases are indicated by
variations of TOC and TN contents between 14 and
12.7 cal ka BP and from 12.7 to 11.4 cal ka BP, respectively.
These periods are likely correlated with the Bølling/Allerød
warm event between 14.8 and 12.8 cal ka BP, and the
Younger Dryas cold event between 12.8 and 11.5 cal ka BP
recorded in the GISP2 ice core (Stuiver et al., 1995). These
short climatic oscillations are also reflected in Qinghai lake
sediments (Liu et al., 2002;Shen et al., 2005), the Chinese
loess sequence (An et al., 1993;Chen et al., 1997;Wang et
al., 1999), and Guliya ice core (Thompson et al., 1997;Yao
et al., 1998).
5.1.2. Early Holocene to Early mid-Holocene
The Asian summer monsoon was intensified between 12
and 6 ka ago due to enhanced summer insolation in the
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Northern Hemisphere and a stronger thermal contrast
between land and sea (COHMAP Members, 1988). The
intensified Asian Monsoon caused a much wetter climate
during the early to mid-Holocene than during the
Lateglacial and today in arid regions such as the Sahara
Desert (Ritchie and Haynes, 1987;Kutzbach et al., 1996;
de Menocal et al., 2000), the Arabian Peninsula (Hoelz-
mann et al., 1998), and the Thar Desert, India (Enzel et al.,
1999). Similarly, this wet period was also recorded in the
monsoon areas in Western China such as from Qinghai
Lake (Lister et al., 1991;Liu et al., 2002;Shen et al., 2005;
Liu et al., 2007b), Bangong Lake (Gasse et al., 1991, 1996),
and the Chinese Loess Plateau (Kukla et al., 1988;Feng
et al., 2005). Furthermore, most lakes in northern
Mongolia experienced higher levels during the middle
Holocene (Harrison et al., 1996;Tarasov, 1996;Tarasov
and Harrison, 1998;Grunert et al., 2000), which is
attributed to the expansion of the Asian monsoon to
Mongolia. However, our data from Chaka Salt Lake show
that an abrupt transition of the lake from fresh to saline or
hypersaline water occurred at the beginning of the
Holocene. Likewise, Zabuye Salt Lake closed its surface
outflow at ca 10.6
14
CkaBP (Wang et al., 2002). Pollen
data from two of the closest records to Chaka Salt Lake,
Zigetang Lake on the Central Qinghai–Xizang Plateau
(Herzschuh et al., 2006b) and Luanhaizi Lake on northeast
Qinghai–Xizang Plateau (Herzschuh et al., 2006a), indicate
warm conditions during the first half of the Holocene.
Similar early Holocene transitions from fresh to saline and/
or from hydrologically open to closed, evaporitic condi-
tions have been documented in large arid and semiarid
areas throughout the world including Lake Frome in
Australia (Bowler et al., 1986), Lake Van in Turkey
(Degens et al., 1984), and lakes in Canada such as
Ingebright Lake, Clearwater Lake, Lake Manitoba, Kill-
arney Lake, Moore Lake (Alberta), and lakes in United
States such as Pickerel Lake, Moon Lake, Medicine Lake,
Devils Lake, and Coldwater Lake (Vance and Last, 1994;
Valero-Garce
´s and Kelts, 1995;Laird et al., 1996;Valero-
Garce
´s et al., 1997;Last et al., 1998;Aitken et al., 1999;
Shang and Last, 1999;Dean and Schwalb, 2000;Last and
Vance, 2002). This widespread appearance of evaporite
minerals or the formation of a closed lake under warmer
but drier conditions at the beginning of the Holocene is
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Fig. 6. Comparison between the Chaka Salt Lake record and other regional salt lakes, as well as regional and global climate summaries and forcings: (A)
Chaka Salt Lakes, dashed line is TOC content. (B) Insolation at 301N(Berger and Loutre, 1991). (C) The GRIP d
18
O record from Greenland (Johnsen et
al., 2001). (D) The mean effective moisture inferred from many records of lakes located in the Asian monsoonal region (Herzschuh, 2006). (E) Qinghai
Lake (Shen et al., 2005;Liu et al., 2007b). Solid and broken lines are pollen concentration and d
18
O of ostracode shells, respectively. (F) Zabuye Lake
(Wang et al., 2002). Solid line with circle, broken line with square, and dot line with solid circle are d
18
O and d
13
C of carbonate, and TOC content,
respectively. (G) Qarhan Salt Lake (Chen and Bowler, 1986).
L. Xingqi et al. / Quaternary Science Reviews 27 (2008) 867–879 875

almost synchronous with the increased summer insolation
(Fig. 6). Thereby, increased summer insolation may have
acted as a trigger to increase summer temperatures and
evaporation. Subsequent to this increased summer insola-
tion, the salinity of Chaka Salt Lake decreased slightly
between 10 and 7.2 cal ka BP, centered at 8.3 cal ka BP,
probably responding to the intensified summer monsoon
which lagged behind peak June insolation by about
2–3 cal ka (Fig. 6). However, the salinity of Chaka Salt
Lake increased significantly again at 7.2 cal ka BP, which
coincides with the so-called ‘‘mid-Holocene Climatic
Optimum’’ when both megathermal and megahumid
climate occurred in the period from 7.2 to 6
14
CkaBP
(Shi et al., 1993), further demonstrating that evaporation at
high temperatures exceeds precipitation.
5.1.3. Later mid-Holocene to Late Holocene
The weakening of the Asian summer monsoon appears
to have been linked more directly to decreased insolational
forcing since ca 6 ka BP, which caused a cooler and drier
climate in the Asian Monsoon region (COHMAP Mem-
bers, 1988;Gasse et al., 1991, 1996;Overpeck et al., 1996;
Shen et al., 2005;Herzschuh, 2006;Liu et al., 2007b).
A decreased but still high salinity occurred in Chaka Salt
Lake between 6 and 5.3 cal ka BP, which may have been
related to less evaporation caused by cooler temperatures.
Subsequently, the salinity of the lake increased and a more
hypersaline lake environment dominated by halite pre-
cipitation finally formed in Chaka Salt Lake between
5.3 cal ka BP and present day. Similarly, the sediments in
Zabuye Lake on the Qinghai–Xizang Plateau are pre-
dominantly mirabilite and halite (Wang et al., 2002). Since
5.0
14
C ka BP, a dry playa environment of Frome in
Australia fully formed after 4
14
CkaBP (Bowler et al.,
1986), and Van Lake in Turkey experienced a period with
stable but slightly low lake-levels between 6
14
C ka BP and
present day (Degens et al., 1984). Simultaneously, the
climatic deterioration characterized by dry or cold condi-
tions was widely documented in most lakes from Western
China (Lister et al., 1991;Gasse et al., 1991, 1996;
Kashiwaya et al., 1995;Liu et al., 2002;Shen et al., 2005;
Herzschuh, 2006;Liu et al., 2007b), although they all
recorded a warm and humid phase in the early and middle
Holocene. Therefore, the further desiccation of Chaka Salt
Lake after the middle Holocene may have been related to
the weakening of the Asian summer monsoon.
5.2. Some implications
Some salt lakes in the Qaidam Basin, such as Qarhan,
Kunteyi, Xiaocaidan, formed at the beginning of the
Lateglacial when temperature increased. Chaka Salt Lake
and many other saline or salt lakes in Australia (Bowler
et al., 1986), Turkey (Degens et al., 1984), Canada, and
United States discussed above (Vance and Last, 1994;
Valero-Garce
´s and Kelts, 1995;Laird et al., 1996;Valero-
Garce
´s et al., 1997;Last et al., 1998;Aitken et al., 1999;
Shang and Last, 1999;Dean and Schwalb, 2000;Last and
Vance, 2002), formed at the beginning of the Holocene
when temperature was higher than that during the
Lateglacial. Halite formed in lake water after the late
mid-Holocene, with a very high salinity in both Chaka Salt
Lake and Zabuye Salt Lake (Wang et al., 2002), when
temperature decreased but was still higher than Lateglacial
temperatures. Low monsoon precipitation due to decreased
insolation forcing may have accelerated the increase of
salinity in the two lakes. Therefore, it appears that warm
temperature plays an important role in the formation of the
salt lake. According to this model, we can assume that the
drought will be severe and lakes are threatened to shrink
further, at least in part of the Western China, if
temperatures continue to increase in the future.
6. Conclusions
Lithostratigraphy, mineralogy, TOC, and TN contents,
along with 10 AMS
14
C ages, of a 9.0-m long continuous
lake sediment sequence from Chaka Salt Lake were used to
reconstruct the history of lake evolution since the
Lateglacial, and thus to discuss its response to regional
and global climatic changes. Our main conclusions are as
follows.
(1) It was a freshwater lake during the Lateglacial. The
climate fluctuated frequently during the transitional
period from the Lateglacial to the Early Holocene.
Short-term climatic oscillations such as the Bølling–Al-
lerød warm event and Younger Dryas cold event
appear to be recorded in the lake sediments. Beginning
at 11.4 ka BP, a saline or hypersaline lake formed. The
salinity of Chaka Salt Lake further increased at
7.2 cal ka BP, which corresponds to the middle Holo-
cene Climatic Optimum when most regions of China
recorded availability of high moisture content. During
the Late–middle to Late Holocene, the lake salinity
progressively increased and a hypersaline environment
similar to modern conditions finally established around
5.3 cal ka BP.
(2) Evidence of a high lake level during the Lateglacial is
probably attributed to increased moisture availability
in response to warmer temperatures, melting glacial ice,
and the onset of Asian summer monsoon during the
Lateglacial. Warmer temperatures caused by increased
summer insolation during the early Holocene may have
triggered the formation of a saline or hypersaline lake
at the beginning of the Holocene. Decreased precipita-
tion due to the weakening of Asian monsoon after the
middle Holocene, probably accelerated the formation
of a more hypersaline lake during the middle-Holocene
to Late Holocene. Generally, the hypersaline environ-
ment at Chaka Lake was formed at the beginning of the
Holocene when temperatures were higher than during
the Lateglacial. This suggests that higher temperature
plays an important factor in the formation of salt lakes.
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L. Xingqi et al. / Quaternary Science Reviews 27 (2008) 867–879876

(3) The evolutionary history of Chaka Salt Lake and its
response to climatic changes are characterized by
multiple stages with similarities and differences to
other salt lakes in the region. Chaka and Zabuye Salt
Lake experienced similar evolution and climatic re-
sponse since the Lateglacial. Chaka Salt Lake and
Qarhan, Kunteyi, and Xiaocaidan experienced a similar
history only during the Holocene. Chaka Salt Lake and
other lakes in Western China evolved and responded to
climatic changes in a different way, only with some
broad similarities during the Lateglacial and during the
late mid-Holocene to Late Holocene. Clearly, there
remain many discrepancies among lake sediment
records from the region. In order to determine if these
discrepancies are the result of local differences in past
climate, or are due to problems with chronology or
interpretation, more well-dated paleoclimatic records
from salt lakes in Western China are needed.
Acknowledgments
We thank Prof. Colin Murray-Wallace and two anon-
ymous reviewers for their helpful comments. This research
was supported by the National Natural Science Founda-
tion of China (Grant nos. 40772108, 40373016, 40472064,
and 40672079) and the National Basic Research Program
of China (Grant nos. 2004CB720200 and 2005CB422002).
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