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Reconstruction of hydrological fluctuations in arid regions has proven challenging due to a lack of reliable chronologic constraints on sparse geological archives. The aim of this study was to establish an independent record of hydrologic changes in the hyper-arid Tarim Basin (TB; northwest China) with high spatiotemporal resolution. We present comprehensive radiocarbon and tree-ring data sets of subfossilized plant remains in the TB compiled from geomorphological investigations of the paleochannels of the Tarim River (TR), the longest endorheic river in China, crossing the world’s second-largest shifting sand desert. Results show that the late medieval configuration of the TR basin was characterized by enhanced hydrological connectivity, as indicated by the formation of significant riparian forests in the desert regions at ca. 1170 CE. A distinct low-flow interval (ca. 1500−1650 CE) is identified for the first time, refining the period of a wetter-than-present TB. The present-day organization of streams in the lower TR was proto-formed after the dry period, possibly led by episodic flood-induced diversion. Our study describes the centennial-scale dynamics in the TR flow over the past millennium, offering a robust long-term context for hydrological assessment in the extensive drylands of the Asian interior.
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Manuscript received 9 December 2023
Revised manuscript received 25 January 2024
Manuscript accepted 1 February 2024
https://doi.org/10.1130/G51962.1
© 2024 Geological Society of America. For permission to copy, contact editing@geosociety.org.
Hydrological uctuations in the Tarim Basin, northwest
China,over the past millennium
Kangkang Li1,2,*, Xiaoguang Qin1, Gill Plunkett2, David Brown2, Bing Xu1, Lei Zhang3, Zhaoyan Gu1, Guijin Mu4,
Hongjuan Jia5, Zhiqiang Yin6, and Jiaqi Liu1
1 Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences,
Beijing 100029, China
2 Archaeology and Palaeoecology, School of Natural and Built Environment, Queen’s University Belfast, Belfast BT7 1NN,
NorthernIreland, UK
3 Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China
4 Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China
5 Experiment and Practice Teaching Centre, Hebei GEO University, Shijiazhuang 050031, China
6 China Institute of Geo-environment Monitoring, Beijing 100081, China
ABSTRACT
Reconstruction of hydrological uctuations in arid regions has proven challenging due
to a lack of reliable chronologic constraints on sparse geological archives. The aim of this
study was to establish an independent record of hydrologic changes in the hyper-arid Tarim
Basin (TB; northwest China) with high spatiotemporal resolution. We present comprehensive
radiocarbon and tree-ring data sets of subfossilized plant remains in the TB compiled from
geomorphological investigations of the paleochannels of the Tarim River (TR), the longest
endorheic river in China, crossing the world’s second-largest shifting sand desert. Results
show that the late medieval conguration of the TR basin was characterized by enhanced
hydrological connectivity, as indicated by the formation of signicant riparian forests in the
desert regions at ca. 1170 CE. A distinct low-ow interval (ca. 1500–1650 CE) is identied for
the rst time, rening the period of a wetter-than-present TB. The present-day organization
of streams in the lower TR was proto-formed after the dry period, possibly led by episodic
ood-induced diversion. Our study describes the centennial-scale dynamics in the TR ow
over the past millennium, offering a robust long-term context for hydrological assessment
in the extensive drylands of the Asian interior.
INTRODUCTION
River systems have played a signicant role
in the emergence and decline of human cultures
and subsistence practices in desert oasis regions,
such as the extremely arid Tarim Basin (TB) in
northwest China, and random shifts of stream
organization (diversions and changes in ow) can
present major natural disasters for riverine societ-
ies (Macklin etal., 2013). However, the history of
stream organization and ow dynamics continues
to be challenging to reconstruct reliably due to a
lack of high-resolution geological archives.
The TB contains the longest endorheic river
in China, the Tarim River (TR), owing along
the margins of the world’s second-largest shift-
ing sand desert (Taklamakan Desert; Figs.1A
and 1B). Numerous oasis settlements were
established along the river and its tributaries,
comprising a critical segment of the ancient Silk
Road (Li etal., 2019). Although the dynamics
of the TR can be traced back to the early Com-
mon Era with the aid of descriptions in Chinese
historic documents (Zhang etal., 2016), inde-
pendent geological evidence is sparse because of
the inaccessible, harsh environment and the dif-
culty of dating sediments (Zhang etal., 2023a).
The hyper-arid climate across the TB con-
tributes to the preservation of plant remains
along river paleochannels, which are the most
direct evidence of catchment-scale hydrologi-
cal uctuations (Putnam etal., 2016; Li etal.,
2018), allowing us to investigate changes in the
TR organization and ow with high spatiotem-
poral resolution. Because of the TB’s location
at the center of the Asian desert zone, recon-
structed TR hydrological uctuations can inform
water resources alteration in the extensive Asian
drylands and ll the signicant knowledge gap
in river-related global assessments by contex-
tualizing modern river-climate (Putnam etal.,
2016; Gudmundsson et al., 2021; Macklin
etal., 2023). The objective of this study is to
provide a robustly dated geological history of
TR dynamics over the past millennium, using
ground-based eld investigations, radiocarbon
(
14
C) dates, and dendrochronological data of
subfossilized plant remains.
STUDY AREA AND METHODS
The TR catchment covers 1,020,000 km2
nourished by ice/snow melt and orographic
precipitation from the neighboring mountains
(Y.Chen etal., 2019). The river presently ows
eastward to merge with Taitema Lake, but pre-
viously its terminal was the dried-up Lake Lop
Nur (LN) (Fig.1B; Xia etal., 2007). We inves-
tigated and mapped the well-preserved system
of paleochannels in the easternmost LN region
(Figs.1B and 1C), supplemented by satellite
images where channels were covered by sand
dunes.
Major paleochannel systems in the LN region
run eastward or southeastward and indicate a
river-dominated paleodelta on the western bank
of LN (Figs.1B and 1C). The width of some dry
channels is >100 m, slightly enlarged from their
origin extent by wind erosion (Figs.2A and 2C).
CITATION: Li, K., etal., 2024, Hydrological uctuations in the Tarim Basin, northwest China, over the past millennium: Geology, v. XX, p. XXX–XXX, https://
doi .org /10 .1130 /G51962 .1
Kangkang Li https://orcid.org/0000-0001
-6041-7041
*kangkangli@mail .iggcas .ac .cn
Published online 14 February 2024
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Eolian landforms composed of shifting dunes
in the delta plain and yardangs (wind-eroded,
mound-like terrains) in the delta front are wide-
spread (Li etal., 2018). Deation depressions
are developed across the delta front (Geng etal.,
2019). The large LN playa is currently covered
by an extensive salt crust.
A subfossilized woodland in the paleodelta is
the TB’s best-preserved late medieval forest (Li
etal., 2018), mainly consisting of poplar trees
(Populus euphratica), tamarisk shrubs (Tama
-
rix sp.), and reeds (Phragmites sp.) (Fig.2). In
situ tree, shrub, and reed remains are densely
rooted on channel banks (Figs.2B, 2E, and
2F). Many poplar trunks with or without roots
have drifted a short distance to the middle of
the dry riverbed (Fig.2C), notably gathered on
bends or relatively wide segments of the chan-
nel. Some poplar trunks lie on the ground sur-
face of yardangs dozens of meters away from
a paleochannel (Fig.2D). Most of the standing
poplars have smaller trunk diameters than those
that fell (Li etal., 2018). The medieval ground
surface, marked by reed meadows and tamarisk
cones on top of yardangs (Fig.2F), is at least
1 m higher than the current surface.
We collected the outermost wood (youngest
growth) of collapsed and drifted poplars, bark
or twigs of standing poplars and tamarisks, and
stems of reeds for
14
C dating. Cross sections of
local drifted poplars (n = 10) in the middle of dry
riverbeds and of in situ tamarisks (n = 11) rooted
on riverbanks were collected for tree-ring analy-
sis. 14C dates were calibrated and modeled using
OxCal v. 4.4.4 (Bronk Ramsey, 2017; https://
c14 .arch .ox .ac .uk /oxcal .html) and the IntCal20
(Northern Hemisphere Radiocarbon Age Calibra-
tion Curve) data set (Reimer etal., 2020). Kernel
density (KDE_Model) and wiggle-match models
were used to summarize the
14
C data set and rene
the age of tree growth. The locations of plant
samples and their corresponding
14
C dates can be
found in the Supplementary Material.
RESULTS
Radiocarbon Dates
Calibrated dates of all subfossilized plant
remains (I = 134, of which 51 are rst reported
AC
B
Figure 1. (A) Geographical overview of the Tarim Basin in northwest China. Dots represent the sites of two δ18O paleoclimatic reconstructions:
Kesang cave (Tianshan mountains; Cai etal., 2017) and Chongce ice core (Kunlun mountains; Pang etal., 2020). (B) Map of the Tarim River catch-
ment. Black squares show sites of modern poplar dendrochronology (Li, 1989; Ye etal., 2023). Blue lines show perennial channels, and black
lines show seasonal channels. (C) Channel networks of the lower Tarim River. Black lines show paleochannels terminated with dried-up lakes.
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here; Table S1 in the Supplemental Material
1
)
suggest the medieval riparian forests can be
traced back to ca. 1171 CE (median age [MA],
σ = 52; Fig.2G). Bayesian modeled dates show
that the forest developed between the thirteenth
and sixteenth centuries (Fig.3A). A few dates fall
between the late seventeenth and the middle nine-
teenth centuries in the upper to middle reaches
of the TR (Fig.3A), and between the late seven-
teenth and the early nineteenth centuries in the
LN region (Figs.2H and 3B). There are no appar-
ent chronological differences among the poplar,
tamarisk, and reed remains (Figs.2G and 2H).
Tree-Ring Analysis
Tree-ring counts of the poplar cross sections
indicate that the sampled trees have 25–53 rings
(Figs. S1 and S2; Table S1). Wiggle-match dat-
ing of a 47-ring poplar using a series of ve 14C
dates (rings 2, 10, 20, 30, and 39) indicates that
the tree grew between 1307 CE and 1340 CE
(MA of the outermost ring, σ = 22) (Fig. S3).
The ring-width data suggest a recurrent pop-
lar growth pattern (Fig. S1), characterized by a
juvenile growth (10 yr) followed by 15 yr
of slow growth (narrow rings) before a growth
spurt lasting 10–15 yr (Figs. S1 and S2).
Six tamarisks have 45–85 rings (Figs. S4 and
S5; Table S1).
14
C dating constrains the dates
of these trees to ca. 1406 CE (MA of ring 30,
σ = 31), 1398 CE (MA of ring 30, σ = 36) and
1465 CE (MA of ring 65, σ = 40). One sample
has >200 rings, of which ring 7 was dated to
1171 CE (MA, σ = 52; Fig. S6). The ring-width
data of tamarisks suggest slightly wider rings
interrupt a generally narrow-ring pattern after
a juvenile stage (Figs. S4–S6).
DISCUSSION
The vegetational landscape of the TB is com-
posed of riparian forests (Thevs etal., 2008).
The growth rate of the TB poplar, for example, is
rapidly enhanced in river belts as soon as a sus-
tained hydrological regime allows for ooding
of the river oodplain (Chu etal., 2002; Thevs
etal., 2008), and the forest declines sharply
when ooding ceases (Zhou etal., 2019; Xu
etal., 2023). Our
14
C data set of in situ sub-
fossilized plant remains therefore indicates the
changes in TR channel regime and ow (when
channels owed and dried up).
The kernel density–modeled
14
C cluster
suggests a sustained hydrological connectiv-
ity across the entire TR catchment from the
upper reaches of the river to the terminal LN
area (>1200 km), indicating a high-ow period
between the late twelfth and middle sixteenth
centuries (Figs. 3Dc and 4A). The earliest
recruitment age of living poplars (n = 254)
across the modern TR has been shown (through
dendrochronological analysis of trees found in
the lower reaches of the river) to be ca. 1674 CE
(Fig.3C; Li, 1989; Putnam etal., 2016; Ye etal.,
2023). Integration of
14
C and dendrochronologi-
cal data therefore shows a distinct low-ow
interval of the TR from ca. 1500 CE to ca. 1650
CE (Figs.3Dc and 4B), which was overlooked
in a previous study (Putnam etal., 2016). From
a broader perspective, tree-ring–based recon-
structions from the upper catchment of Bosten
Lake (Fig.1B) suggest a depleted streamow
during the sixteenth century (Liu etal., 2023).
The central Tianshan area also experienced a
dry hydroclimate (1550–1700 CE) or a distinct
low streamow (1500–1560 CE and 1625–1690
CE) during that time (Chen etal., 2015, 2022).
1
Supplemental Material. Figures S1–S9 and chrono-
logical data. Please visit https://doi .org /10 .1130 /GEOL
.S.25193237 to access the supplemental material; con-
tact editing@geosociety .org with any questions.
A
CD
E
G
H
B
F
Figure 2. (A) A typical paleochannel in the Lop Nur region of the Tarim Basin. (B) The Tarim Basin late medieval forest, consisting of in situ
plant remains (poplars, tamarisk, and reeds). (C) Poplars drifted into the middle of a paleochannel bed. (D) Poplar remains in a yardang cluster.
(E) A tamarisk cone rooted on the dry channel bank. (F) Reed meadow rooted on top of yardangs. (G, H) Spatially plotted, calibrated 14C dates
(G: the entire Tarim Basin; H: the Lop Nur region). Circles are poplar dates; squares are tamarisk dates; triangles are reed dates).
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Notably, subfossilized plants dating to
between the late seventeenth century and
the nineteenth century were recovered from
paleochannels of the upper to middle TR
(Fig.2G) and at the northern and southern mar-
gins of the delta (Fig.2H). After the low-ow
period, therefore, the channels of the lower TR
were detached from the Kongque River and
diverted from an eastward ow to a southward
ow (Fig.4C), implying that a proto-pattern of
the modern TR network formed at that time. The
timing of these paleochannels overlaps with the
chronology of living poplars in those reaches
from the late eighteenth to early nineteenth cen-
turies, suggesting that channels avulsed to the
north and the south over distances of >100 km
(Fig.4C; Fig. S8).
Many of the ancient settlements along the
TR catchment had declined substantially before
the late medieval period (Zhang etal., 2021;
Ding etal., 2023), implying that human activ-
ity did not play a signicant role in the channel
diversion. Although the life spans of the trees in
the medieval TB forest are short, tree-ring pat-
terns of both poplar and tamarisk suggest poten-
tially rapid uctuations of both in-channel and
groundwater levels, which are major factors for
the radial growth of these riparian trees within
the context of an extremely dry environment
(Chu etal., 2002; Zhou etal., 2019). Periods of
wide rings in the wood samples imply a good
level of water availability in successive years
(the period of high ow) while the medieval
forests were growing (Figs. S1 and S2). Growth
spurts indicate ow abundances (ooding), sug-
gesting episodic increases in the streamow of
the medieval channels. The large-scale drainage
channel shifts of the lower TR may therefore be
a result of episodic high ow that changed the
geomorphology and vegetational distribution
of the avulsional areas. Since the mid-twentieth
century, changes in the TR course have been
mainly caused by human activities (Zhou etal.,
2019).
Since the late nineteenth century, geographi
-
cal investigations of the LN region suggest there
were west-to-east channels at the southern mar-
gin of the delta, forming a shallow lake (Karako-
shun; Fig.1C). Subsequently, the lake migrated
to the northern margin of the delta in 1921 CE,
partially lling the dried-up LN (Hörner and
Chen, 1935). The “wandering” and “alternative”
lake hypotheses were proposed to describe these
surface processes, triggering a long-standing
conundrum about the so-called LN displacement
(Hedin, 1903; Hörner and Chen, 1935). The ter-
minal LN was formed in the easternmost, lowest
depression (Geng etal., 2019), acting as a persis-
tent depositional center of the TR catchment. We
argue that the connectivity of the entire TR basin
is a decisive factor in locating the terminal lake;
i.e., temporary lakes formed in front of the LN
depression were mistaken for the end-lake (LN)
during the low-ow period of the TR.
Warm-season ice/snow melt and orographic
precipitation from surrounding mountains are
A
B
CD
Figure 3. (A, B) Kernel density–modeled (KDE_Model; Bronk Ramsey, 2017) 14C dates with the calibration curve. Red crosses show the central
values of the simulated
14
C dates. (A) Dates for the entire Tarim Basin. (B) Dates for the Lop Nur region. (C) Statistic distributions of recruitment
dates for modern poplars from sites in Figure1B (columns are relative frequency; curves are kernel smooth). Orange shows the lower Tarim
River (TR) samples (n = 50); green shows the middle TR samples (n = 128); purple shows the upper TR samples (n = 76). (D) a: A δ18O-based
precipitation reconstruction from a stalagmite in the central Tianshan (Cai etal., 2017). b: A δ18O-based temperature reconstruction from an ice
core in the western Kunlun (Pang etal., 2020). Gray dotted plot represents reconstructed temperature anomalies. c: Probability distribution of
14C dates (black—entire Tarim Basin; gray—the Lop Nur region) and recruitment dates (dashed line) of modern trees in C.
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the main sources of runoff supply to the TB inte-
rior. However, the causes of decadal- and centen-
nial-scale hydrological uctuations are ambigu-
ous because of a lack of conclusive geological
archives. Our study offers a direct reconstruction
(a high-low-high pattern) of the TR ow over
the past 1000 yr, providing a unique window to
investigate those causes (Fig. 3Dc). δ
18
O records
from ice cores from the western Kunlun and
central Tianshan mountains suggest a warming
trend in regional temperature over the past mil-
lennium (Fig. 3Db; Takeuchi etal., 2014; Pang
etal., 2020). A δ18O reconstruction from a late
Holocene stalagmite from the central Tianshan
shows distinct centennial-scale variation, and to
some extent reects high-elevation precipitation
uctuations (Fig.3Da; Cai etal., 2017). Integra-
tion of these reconstructions from the headwa-
ter catchments of the TR implies that the ow
pattern of the TR over the past millennium was
closely related to precipitation in high-elevation
areas of arid central Asia. The instability of the
intertropical convergence zone and/or of the
westerly jet may modulate the hydrodynamics
in the Tarim region due to the TB’s location (Fig.
S9; Schneider etal., 2014; F. Chen etal., 2019;
Liu etal., 2022).
Recent warming has affected the TR ow.
Based on our inferred TR ow pattern over the
past millennium, the last high-ow period termi-
nated before the mid-twentieth century, followed
by a centennial-scale low-ow period. However,
instrumental data show an increasing trend in
the annual ow of the TR tributaries from 1952
to 2008 CE (Tao etal., 2011), which should
lead to a high-ow mainstem. This discrepancy
can be explained by recent rapid warming in the
region, increasing deglaciation in the surround-
ing mountains. Water of the warming-induced,
high-ow TR catchment was largely consumed
by human activities (agricultural irrigation).
Therefore, the present-day condition of the TR
is dictated by a rapidly warming climate and
human consumption. As a major cryosphere-fed
catchment of Asia’s dryland rivers, the future
hydrological variability of the TR requires us to
consider the relative importance of regional tem-
perature and mountain precipitation in determin-
ing the streamow (Ombadi etal., 2023; Zhang
etal., 2023b) and in promoting proper manage-
ment of water resources.
CONCLUSIONS
Our independent, precisely dated geological
data allow reconstruction of the TR dynamics
over the past millennium. The late-medieval
riparian forests of the TR developed as early as
ca. 1170 CE, suggesting enhanced hydrological
connectivity across entire catchments. Bayesian
modeled 14C dates of in situ plant remains iden-
Figure 4. A conceptual diagram of the Tarim River drainage regime in the Tarim Basin. Arrows
show the ow regimes of the Tarim River catchment with inferred good (green) or poor (yellow)
connectivity of channel networks. Question marks denote that no age data of plant remains
in this study are from these segments.
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tify a low-ow interval between 1500 CE and
1650 CE. We argue that the present-day stream
organization in the lower TR began to form at ca.
1650 CE, possibly triggered by episodic oods.
Our study describes centennial-scale uctua-
tions in the TR ow, contributing to desert oasis
ecosystem assessment by contextualizing the
current state of major dryland rivers.
ACKNOWLEDGMENTS
This work was nancially supported by grants
from the National Natural Science Foundation of
China (42207508 and 42072215), the Chinese Acad-
emy of Sciences (XDB26020301), the Ministry of
Science and Technology (China) (2022xjkk0300,
2021xjkk1104, and 2014FY210500), and the China
Scholarship Council. We thank all members who par-
ticipated in the Lop Nur eldwork. We are grateful to
the 14CHRONO Centre of Queen’s University Belfast
(Northern Ireland) for radiocarbon dating. We thank
the reviewers and editor for their constructive com-
ments on our manuscript.
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... It is probable that these may have occurred during periods when trees are physiologically inactive or in soils with a low water-holding capacity or low infiltration rate. When developing an annual streamflow reconstruction, tree growth is limited during the winter season, making it difficult to capture the entire streamflow behavior in the reconstruction [42,43]. However, our results showed that specific sites had the ability to detect extreme positive flow peaks, as well as reflect years of low runoff. ...
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