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Late Holocene temperature and precipitation variations in an alpine region of the northeastern Tibetan Plateau and their response to global climate change



Knowledge of temperature and precipitation variations on the northeastern Tibetan Plateau (NETP) during the recent past can improve our understanding of late Holocene regional climate change and its response to global climate change, in the past and potentially the future. Based on records of multiple geochemical indicators and branched glycerol dialkyl glycerol tetraethers from the sediments of alpine Lake Bihu on the NETP, we reconstructed high-resolution precipitation sequences and quantified the variation of the mean air temperature of months above freezing (MAF, between May and October) over the past ~3500 years. The MAF reconstruction shows obvious fluctuations on decadal to centennial timescales, and the absolute values of the reconstructed temperature range from 0.70 to 3.98 °C, with an average of 2.19 °C. The precipitation record reflects the high-frequency variability of the East Asian summer monsoon (EASM). The maximum precipitation and temperature on the NETP occurred during the Medieval Warm Period (MWP, ~800–1400 CE), rather than during the Current Warm Period (CWP, the last 150 years). We also observed broadly similar patterns of warm–wet and cold–dry climatic variations over the NETP and the broader EASM region; moreover, the decadal to centennial temperature fluctuations were consistent on a large spatial scale. Our results indicate that temperature variability during the late Holocene was primarily controlled by solar radiation, interrupted by multiple decades of successive volcanic eruptions. In addition, anomalous and rapid warming during the CWP may also be related to the unprecedented increase in atmospheric greenhouse gases. Precipitation variability in this region, driven by changes in the EASM, may have been primarily a response to changes in total solar irradiance and associated changes in atmospheric–oceanic modes (e.g., the El Niño–Southern Oscillation, Intertropical Convergence Zone, and Western Pacific Subtropical High). Overall, our results provide robust evidence for global climate teleconnections between different regions, especially in high mountains, in the past, present, and potentially in the future.
Palaeogeography, Palaeoclimatology, Palaeoecology 615 (2023) 111442
Available online 9 February 2023
0031-0182/© 2023 Elsevier B.V. All rights reserved.
Late Holocene temperature and precipitation variations in an alpine region
of the northeastern Tibetan Plateau and their response to global
climate change
Youmo Li
, Duo Wu
, Tao Wang
, Lin Chen
, Chenbin Zhang
, Shilong Guo
Key Laboratory of Western China's Environmental Systems (Ministry of Education), College of Earth and Environmental Sciences, Lanzhou University, Lanzhou
730000, China
Alpine Paleoecology and Human Adaptation Group (ALPHA), Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China
Editor: Dr. Howard Falcon-Lang
Northeastern Tibetan Plateau
Alpine lake
Temperatureprecipitation reconstruction
Late Holocene
Climatic forcing
Global climate teleconnection
Knowledge of temperature and precipitation variations on the northeastern Tibetan Plateau (NETP) during the
recent past can improve our understanding of late Holocene regional climate change and its response to global
climate change, in the past and potentially the future. Based on records of multiple geochemical indicators and
branched glycerol dialkyl glycerol tetraethers from the sediments of alpine Lake Bihu on the NETP, we recon-
structed high-resolution precipitation sequences and quantied the variation of the mean air temperature of
months above freezing (MAF, between May and October) over the past ~3500 years. The MAF reconstruction
shows obvious uctuations on decadal to centennial timescales, and the absolute values of the reconstructed
temperature range from 0.70 to 3.98 C, with an average of 2.19 C. The precipitation record reects the high-
frequency variability of the East Asian summer monsoon (EASM). The maximum precipitation and temperature
on the NETP occurred during the Medieval Warm Period (MWP, ~8001400 CE), rather than during the Current
Warm Period (CWP, the last 150 years). We also observed broadly similar patterns of warmwet and colddry
climatic variations over the NETP and the broader EASM region; moreover, the decadal to centennial temper-
ature uctuations were consistent on a large spatial scale. Our results indicate that temperature variability during
the late Holocene was primarily controlled by solar radiation, interrupted by multiple decades of successive
volcanic eruptions. In addition, anomalous and rapid warming during the CWP may also be related to the un-
precedented increase in atmospheric greenhouse gases. Precipitation variability in this region, driven by changes
in the EASM, may have been primarily a response to changes in total solar irradiance and associated changes in
atmosphericoceanic modes (e.g., the El Ni˜
noSouthern Oscillation, Intertropical Convergence Zone, and
Western Pacic Subtropical High). Overall, our results provide robust evidence for global climate teleconnections
between different regions, especially in high mountains, in the past, present, and potentially in the future.
1. Introduction
Global warming is expected to amplify a hydrological imbalance on
the Tibetan Plateau, also known as the Asian water tower, caused by
the accelerated transformation of ice and snow into liquid water
(Immerzeel et al., 2010; Yao et al., 2022). The Tibetan Plateau has
experienced substantial recent warming, evidenced by observation data
from meteorological stations beginning in the mid-1950s (Liu and Chen,
2000). In recent decades the annual temperature over the Tibetan
Plateau has increased twice as fast as the global average (Chylek et al.,
2009; Chen et al., 2015a), and this regional warming rate since the
1980s is unparalleled over the past two millennia (Chylek et al., 2009;
Yao et al., 2019; Yan et al., 2020; Zhang et al., 2020; You et al., 2021).
The northeastern Tibetan Plateau (NETP) is especially sensitive to
climate change, given its location on the edge of the subtropical Asia
monsoon circulations, and it may act as a link between high- and low-
latitude climatic processes in the Northern Hemisphere (Ding and
Wang., 2005; Chen et al., 2010).
During the past few decades numerous studies have been conducted
involving modern climate observations and paleoclimate reconstruction
on increasingly long timescales, especially for the late Holocene, with
the aim of predicting future climatic changes across the ecologically
* Corresponding author.
E-mail address: (D. Wu).
Contents lists available at ScienceDirect
Palaeogeography, Palaeoclimatology, Palaeoecology
journal homepage:
Received 4 November 2022; Received in revised form 4 February 2023; Accepted 6 February 2023
Palaeogeography, Palaeoclimatology, Palaeoecology 615 (2023) 111442
fragile NETP. It has been found that several periods of distinct temper-
ature uctuations have occurred on a centennial timescale, with a series
of abrupt climatic events occurring during the late Holocene; they
include the Roman Warm Period (RWP, ~250450 CE, Common Era),
Dark Ages Cold Period (DACP, ~450800 CE), Medieval Warm Period
(MWP, ~8001400 CE), Little Ice Age (LIA, ~14001800 CE), and
Current Warm Period (CWP; since ~1850 CE) (Moberg et al., 2005;
Ljungqvist, 2010; Ge et al., 2010, 2013; Diaz et al., 2011; Chen et al.,
2015b; PAGES 2k Consortium, 2017; Feng et al., 2019; Lan et al., 2020).
The climate of the MWP was like that during the CWP, and thus it
provides a reference frame for evaluating the possible future precipita-
tion response to ongoing climatic warming (Diaz et al., 2011).
Temperature is generally spatially consistent on a large spatial scale.
However, recent studies have revealed signicant contradictions be-
tween temperatures reconstructed using paleoclimatic records and
climate simulations during the Holocene (Marcott et al., 2013; Liu et al.,
2014; Brierley et al., 2020). Therefore, the long-term trend of temper-
ature uctuations during the late Holocene is still debated. In contrast to
temperature records, there is notable spatial heterogeneity in recon-
structed hydroclimatic records across the NETP and its surrounding
areas, over the last ~3500 years (Yang et al., 2003; Zhang et al., 2003a;
Chen et al., 2006; Liu et al., 2006; He et al., 2013a; Yang et al., 2014; An
et al., 2018; Wu et al., 2020, 2022). Moreover, numerous paleoclimatic
studies have revealed signicant differences in regional climatic pat-
terns across the NETP, where the climate was inuenced by interactions
between the westerlies and the East Asian summer monsoon (EASM)
during the late Holocene (Tian et al., 2001; Yang et al., 2003, 2014,
2021; Zhang et al., 2003b; Chen et al., 2006, 2010; Liu et al., 2006;
Zhang et al., 2008; He et al., 2013a). For example, the Sugan Lake and
Gahai Lake areas on the NETP were affected by the interaction between
the mid-latitude westerlies circulation and the EASM, and they experi-
enced a warmdry MWP and coldhumid LIA (He et al., 2013a; Yao
et al., 2013; Chen et al., 2016; Lan et al., 2020). In contrast, the Dunde,
Delingha and Dulan areas, in the southeastern Qilian Mountains, and the
Lake Qinghai basin, were inuenced solely by the EASM and experi-
enced a warmhumid MWP and colddry LIA (Yang et al., 2003; Zhang
et al., 2003b; Liu et al., 2006; Yang et al., 2014, 2021).
Although a series of relevant paleoclimatic studies have been un-
dertaken in recent decades, the contradictions in the hydrothermal
conguration on the NETP during the climatic periods mentioned above,
and the driving forces behind the natural variability, remain poorly
understood (Yang et al., 2003, 2014; Zhang et al., 2003b; Liu et al.,
2006). In addition, there is a lack of high-resolution hydroclimatic and
quantitative temperature reconstructions with an independent chro-
nology obtained from the same core, resulting in a heavy reliance on the
accuracy of sedimentary age models; hence, the various late Holocene
paleoclimate studies of the Tibetan Plateau cannot directly be compared
without taking chronological uncertainties into account. Therefore,
additional and reliable paleotemperature and hydroclimatic re-
constructions are needed to improve our understanding of the mecha-
nisms of climate change across the NETP during the late Holocene.
Previous studies have shown that the distribution of branched
glycerol dialkyl glycerol tetraethers (brGDGTs) is related to environ-
mental factors, including mean annual air temperature (MAAT) and soil
pH (Weijers et al., 2007; Peterse et al., 2012; De Jonge et al., 2014; Dang
et al., 2018; Russell et al., 2018). This is the result of bacteria producing
more/less methyl branches to adjust to colder/warmer conditions, and
thus quantitative functions based on the methylation of branched tet-
raether (MBT) index between brGDGT distributions and temperature
have been proposed as a novel proxy for using in terrestrial settings (e.g.,
in soils and lakes) across the Tibetan Plateau (Wu et al., 2013; Günther
et al., 2014; Ding et al., 2015; Wang et al., 2015a, 2016a, 2021; Li et al.,
2017, 2019; Feng et al., 2019, 2022; He et al., 2020; Zhao et al., 2021;
Sun et al., 2021; Zhang et al., 2022a) and other regions (De Jonge et al.,
2014; Dang et al., 2018; Russell et al., 2018). Additionally, Lake Bihu, an
alpine lake with continuous and high-resolution sedimentary strata,
contains abundant lipids, and thus it is regarded as an ideal archive for
investigating temperature changes on the NETP during the late Holo-
cene. However, in high-altitude regions, lake water temperature
reconstructed from sedimentary brGDGTs may not reect the true at-
mospheric temperature during the freezing season, because the water in
alpine lakes cannot fully exchange heat with the atmosphere when the
lake surface is frozen. Which hinders brGDGTs-based air temperature
reconstruction. During the ice-free season, the mean air temperature of
the months above freezing (MAF, between May and October) of lake
water is close to that of the atmosphere; moreover, there is the abundant
production of brGDGTs from bacteria in the lake during this period, and
thus the temperature reconstructed by brGDGTs can reliably represent
the local atmospheric temperature (Sun et al., 2021; Raberg et al., 2021;
Zhang et al., 2021, 2022a).
Consequently, the aims of the present study are as follows. 1) To
quantitatively reconstruct the MAF during the late Holocene (the last
3500 years), and to compare it with the instrumental temperature record
from a high-elevation site on the NETP, based on the brGDGTs data from
a sediment core from Lake Bihu. 2) To reconstruct high-resolution
summer monsoon precipitation changes from the same core spanning
the same interval, using multiple geochemical proxies, including X-ray
uorescence (XRF)-based elements, grain size, loss-on-ignition (LOI),
and sedimentary mineralogy. 3) To elucidate the climatic patterns over
the NETP and their possible forcing mechanisms on decadal to centen-
nial timescales during the late Holocene, based on a comparison of our
results with previously published paleoclimatic records, as well with
climate forcing factors.
2. Regional setting
Lake Bihu (353028.61′′ 353029.10′′ N, 1024052.84′′
1024054.06′′ E; 4360 m a.s.l.) is located within the southwestern
Dalijia Mountains, a transitional region between the NETP and the
Chinese Loess Plateau (Fig. 1a, b). The average elevation of the Dalijia
Mountains is ~3600 m a.s.l., with Dalijia Peak reaching 4636 m a.s.l.
Lake Bihu is located on a planation surface between 4000 and 4400 m a.
s.l., at higher levels in the Dalijia Mountains (Wang et al., 2013). The
topography of this region is complex and there are valleys to both the
west (Qitai valley) and east (Deheisui valley), which intersect and
converge to the south. There are no glaciers in this area at the present-
day, but during the Quaternary the area was intensively and repeatedly
glaciated, and numerous well-preserved moraines were formed (Li and
Pan, 1989; Shen et al., 1989; Pan, 1993; Wang et al., 2013). The bedrock
around the lake consists mainly of intensely folded and faulted Pre-
cambrian crystalline complexes of granite and schist (Wang et al.,
2015b). The geological structure is characterized by deformation, which
is mainly the result of late Neogene orogenic events (Mahaney and
Rutter, 1992). Field surveys and remote sensing images show that the
surrounding landscape is alpine meadow and alpine grassland. The re-
gion has a temperate semi-arid continental climate, with dry and cold
conditions during winter and spring, and wet and warm conditions
during summer and autumn. Moisture in this region is derived mainly
from the EASM in summer, and transported by the westerlies in winter,
on both seasonal and interdecadal timescales (Yao et al., 2012, 2013; Ma
et al., 2022). At Linxia Station (3534N, 10311E; 1917 m a.s.l.), ~40
km from the eastern slopes of Dalijia Shan Peak, a MAAT of 7.23 C, MAF
of 14.59 C, and mean annual precipitation (MAP) of 418 mm were
reported during 19512020 CE, and precipitation between May and
October accounts for >85% of the annual total (Fig. 1c).
Lake Bihu and its surroundings were occupied by an ice cap during
the middle of Marine Oxygen Isotope Stage 3, the oldest glacial advance
event; subsequently, the range of glaciers retreated below 4300 m, and a
small, closed lake was formed following glacial retreat and erosion (Li
and Pan, 1989; Pan, 1993; Wang et al., 2013). Today, Lake Bihu is a
small, semi-open lake and its water is primarily supplied by precipita-
tion during the rainy summers. The water overows from the outlet
Y. Li et al.
Palaeogeography, Palaeoclimatology, Palaeoecology 615 (2023) 111442
when the maximum water depth exceeds 5.7 m, while the lake surface is
ice-covered from November to April. The lake covers an area of
~13,000 m
, and its catchment area is ~0.02 km
The ecosystem of this piedmont basin has been inuenced by human
activity, including agricultural practices, beginning with settlement in
the 11
century (Zhang et al., 2022b), and intensied grazing (mainly
by yaks and sheep) has occurred in the catchment of Lake Bihu and the
surrounding areas during the last few decades. Additionally, several
ancient settlements were built on the at and gentle slopes of the Ganjia
Basin (Xia et al., 2020).
3. Materials and methods
3.1. Materials
In September 2020, a 218-cm-long core (BH20) was obtained from
the center of Lake Bihu (water depth of 5.7 m; see Fig. 1b for the site
location), using a Livingstone corer. The core was collected in half-
section polyethylene tubes and transported to the laboratory, where it
was stored at 4 C prior to analysis. Core BH20 core was split vertically
and one half was used for XRF analysis. The other half was sub-sampled
at 0.5 cm intervals and the samples were freeze-dried for various other
laboratory analyses. One surface soil sample was obtained from the lake
catchment and two loess samples were collected from the Ganjia Basin
(the piedmont basin in the study area).
3.2. Methods
3.2.1. Dating
The ages of selected samples from core BH20 were determined by
accelerator mass spectrometry (AMS)
C dating. Six samples of bulk
organic matter from different depths (Table 1) were treated with stan-
dard acidbaseacid preparational procedures following (Olsson, 1986),
C analysis was conducted by Beta Analytic (Florida, USA). The
‘intercept method based on least-squares tting was used to evaluate
the possible inuence of the old carbon effect on the sediments of Lake
Bihu. Subsequently, the radiocarbon ages (after calibration for the car-
bon reservoir effect) were calibrated to calendar years before present (yr
BP, where the present is dened as the year 1950 CE) using the CALIB
8.0.1 program. Finally, an agedepth model, including the age uncer-
tainty, was developed using R software, implemented by the Clam li-
brary (Blaauw, 2010) with the IntCal 20 calibration curve (Reimer et al.,
3.2.2. Geochemistry and grain-size analyses
After covering its surface with Ultralene lm (4
m), one half of core
BH20 was imaged and analyzed using a Core Scanner (Avaatech, NL).
The elements Al, Si, Ca, Ti, Mn, and Fe were scanned at 1 mA, 10 s, and
with a tube voltage of 10 kV; Cu, Zn, Rb, Sr, and Zr were scanned at 2
mA, 20 s, and 30 kV. The core was scanned at a resolution of 2 mm, and
the results are expressed as counts per second (cps).
Fig. 1. Map showing the location and climate of
the study area. (a) Locations of Lake Bihu and the
cited paleoclimatic records on the Tibetan
Plateau and the surrounding region (1: Lake
Bihu, 2: Lake Qinghai, 3: Lake Gahai, 4: Lake
Sugan, 5: Linggo Co, 6: Lake Cuoqia, 7: Lake
Tiancai, 8: Lake Heihai, 9: Lake Lugu, 10:
Wangxiang Cave, 11: Dongge Cave). Filled circles
and triangles denote lake and stalagmite records,
respectively. Black arrows show the regional at-
mospheric circulation (Westerlies, Indian sum-
mer monsoon (ISM), and East Asian summer
monsoon (EASM)) (Yao et al., 2013). The red
dotted line shows the modern limit of the Asian
summer monsoon (ASM; modied from Chen
et al. (2010)). (b) Lake surface extent and sam-
pling site. (c) Monthly mean precipitation and
temperature recorded at Linxia Meteorological
Station (19512020) ( (For
interpretation of the references to colour in this
gure legend, the reader is referred to the web
version of this article.)
Y. Li et al.
Palaeogeography, Palaeoclimatology, Palaeoecology 615 (2023) 111442
Pretreatment for grain-size analysis included immersing ~0.3 g
subsamples in 10 mL 10% H
and 0.5 mol/L HCl at ~200 C to
remove organic matter and carbonate, respectively. Deionized water
was then added to the decarbonized samples and they were left to settle
for 24 h. Next, (Na
(10 mL, 10%) was added to each sample after
siphoning off the supernatant, followed by ultrasonic dispersal for ~5
min. The samples were measured using a Mastersizer 2000 (Malvern,
UK) laser grain-size analyzer (0.022000
m), with 700 r/min agitator
speed, 80 Hz ultrasonic intensity, and 1750 r/min pump speed. Each
sample was measured three times to ensure repeatability. Forty-six
samples were homogenized and analyzed by X-ray diffraction (XRD)
using an X'PERT Pro MPD (PANalytical, NL).
The percentage water content was obtained by subtracting the
weight of the freeze-dried subsamples from that of the wet subsamples.
The weight LOI was measured at 1-cm intervals by combusting the
samples in a mufe furnace. The weight loss after combustion at 550 C
represents the organic matter content, and that at 950 C represents the
carbonate content (Dean, 1974; Heiri et al., 2001). After subtracting the
organic matter and carbonate contents the residue is regarded as silicate
clastic material.
All pretreatments and geochemical experiments were conducted at
the Key Laboratory of Western China's Environmental Systems (Ministry
of Education), Lanzhou University, China.
3.2.3. Extraction, analysis, and proxy calculation of GDGTs
All freeze-dried and homogenized samples (~3 g) were ultrasoni-
cally agitated in a dichloromethane: methanol (v:v =9:1) solution four
times (15 min each) and then concentrated to dryness using N
gas. The
total lipid extract was separated over a silica gel chromatography col-
umn using hexane, dichloromethane, and methanol as eluents to isolate
the neutral and polar fractions (containing GDGTs), respectively (Chen
et al., 2021). The polar fractions were redissolved and ltered through a
m polytetrauoroethylene (PTFE) lter prior to liquid chroma-
tographymass spectrometry (LCMS) analysis. The GDGT analyses
were performed using an Agilent 1290 series ultra-performance liquid
chromatographyatmospheric pressure chemical ionization6465B tri-
ple quadruple mass spectrometer (UPLCAPCIMS/MS). The ow rate
was 0.3 mL/min, an aliquot of 10
L was injected and separated on two
Hypersil Gold Silica columns in sequence (each 150 mm ×2.1 mm, 1.9
m, Thermo Fisher Scientic; USA), maintained at 40 C. The GDGTs
were isocratically eluted with 84% A and 16% B for the rst 5 min,
where A =n-hexane and B =EtOA, followed by a linear gradient change
to 82% A and 18% B from 5 to 65 min, and then a linear change to 100%
B for 10 min to separate OH-GDGTs; elution with 100% B was continued
for a further 5 min, before changing to 84% A and 16% B to equilibrate
the pressure. Analyses were performed using the selective ion moni-
toring (SIM) mode to track m/z 1302, 1300, 1298, 1296, 1292, 1050,
1048, 1046, 1036, 1034, 1032, 1022, 1020, 1018, and 744 (C
). All
lipid extract analyses were conducted at the Key Laboratory of Western
China's Environmental Systems (Ministry of Education), Lanzhou Uni-
versity, China.
The revised MBT (MBT) and cyclisation of branched tetraether
(CBT) indices of brGDGTs were calculated using [Eq. (1)] and [Eq. (4)]
(see Table S1). The roman numerals denote the abundance of the
corresponding brGDGT structures, and they refer to Weijers et al.
(2007), Peterse et al. (2012), and Schouten et al. (2013). MBT
were based solely on either 5- or 6-methyl brGDGTs (De Jonge
et al., 2014; Ding et al., 2015) calculated using [Eq. (2)] and [Eq. (3)].
This is because Hopmans et al. (2016) improved the chromatographic
procedure for analysis of brGDGTs and achieved the separation of 5- and
6-methyl brGDGTs in their studied sediments. The relative amounts of 6-
vs. 5-methyl brGDGTs (dened as IR
) were calculated according to
De Jonge et al. (2015a) as [Eq. (5)]. The Branched and Isoprenoid Tet-
raether (BIT) index, based on the relative abundance of brGDGTs versus
Crenarchaeol, was calculated using [Eq. (6)] (Hopmans et al., 2004).
4. Results
4.1. Lithology and chronology of core BH20
The sediments of core BH20 has a very low organic matter content,
ranging from 7.32% to 16.25%, with an average of 13.35%, which is
consistent with the water content that varied from 33.41% to 78.75%.
The silicate content is substantially higher than the organic content,
ranging from 79.39% to 90.75%, with the average of 82.89%. Core
BH20 consists of lacustrine sediments with alternating thin (24 cm)
grayish-white layers within the 4884-cm depth range (Fig. 2a). These
thin layers are characterized by rapid changes in lithology and they had
an anomalously low water and organic matter content, and a high sili-
cate content, and a relatively high sedimentation rate.
The chronology of core BH20 core is based six AMS
C dates after
correction for an 880-year reservoir effect (Fig. 2b, c). The age model
indicates that the base of the 218-cm-long core is ~3500 cal yr BP,
giving an average sedimentation rate of ~0.63 mm/yr.
4.2. Variations in geochemical indices
The results of XRF scanning, grain-size, and LOI measurements are
shown in Fig. 3. The variations in Al, Si, Ca, Ti, Zn, Rb, Sr, and Zr (in cps)
are all positively correlated with each other for the entire core record
(Table S2; Fig. S1). The application of principal component analysis
(PCA) to the elements listed above showed that the rst principal
component (PC1) comprised 45% of the total variance, and it was more
signicant than components PC2 and PC3 (Table S3; Fig. S2).
The sediments of Lake Bihu are composed mainly of clay and silt,
with a minor sand content (sand, silt and clay are here dened as the
m, 464
m, and <4
m fractions, respectively). The proportion of
clay was the largest (average of 54.39%), followed by silt (average of
45.60%), and the average sand content was <1% (Fig. 3a). The median
grain size (d (0.5)) in lake sediments ranges between 6.10 and 10.91
with an average of 7.74
m, whereas the mean of median grain size at
soil sample from catchment and loess samples from the Ganjia Basin is
m and 40
m (Fig. 3b; Fig. 4a). The variations of the silt content,
median grain size, and silicate content are generally consistent and they
are well correlated (p <0.01) (Fig. 3). The results of analyses of the
composition and morphology of the minerals in samples from core
BH20, analyzed by XRD and scanning electron microscopy (SEM),
showed that the mineral composition is dominated by silicate minerals,
Table 1
C dating results for core BH20.
Laboratory no. Depth (cm) Material AMS
C age (yr BP) Reservoir- corrected
C age (yr BP)*
Calibrated age (2
, cal yr BP) δ
C ()
Beta - 571562 0.5 Bulk organic matter 920 ±30 40 ±30 3472 (53) 30.9
Beta - 571563 38.0 Bulk organic matter 1320 ±30 440 ±30 456529 (502) 28.2
Beta - 571564 78.5 Bulk organic matter 2440 ±30 1560 ±30 13771523 (1454) 26.5
Beta - 571565 123.0 Bulk organic matter 2660 ±30 1780 ±30 15981679 (1656) 28.4
Beta - 571566 160.5 Bulk organic matter 3220 ±30 2440 ±30 23572540 (2485) 28.1
Beta - 571567 201.0 Bulk organic matter 3880 ±30 3000 ±30 31023254 (3189) 28.1
The reservoir age correction of 880 yr BP was used.
Y. Li et al.
Palaeogeography, Palaeoclimatology, Palaeoecology 615 (2023) 111442
including quartz and aragonite, and that these minerals had not been
transported over long distances (Fig. 4cf).
4.3. Distribution of brGDGTs and paleotemperature reconstruction
4.3.1. Distribution of brGDGTs
Our results show that brGDGTs-Ia, IIa, IIa', IIIa', and IIIa were the
most abundant compounds (total fractional abundance of 78.98%) in
sediments of Lake Bihu. We found that these acyclic brGDGTs were also
the dominant compounds in globally-distributed soils, including in
China, and in lake surface sediments from East Africa (Fig. 5a). In
contrast, the relative amounts of cyclopentane ring-containing brGDGTs
in the sediment samples from Lake Bihu were generally lower, and
sometimes not even detectable.
The pentamethylated (brGDGTs-II; 45.85%) and hexamethylated
(brGDGTs-III; 27.42%) brGDGTs dominated the total brGDGTs in the
Lake Bihu sediments, followed by tetramethylated (brGDGTs-I; 26.73%)
brGDGTs. The isomer ratio (IR
) varied from 0.26 to 0.38 (Table 2),
revealing that the 5-methyl isomer brGDGTs, rather than 6-methyl
material, are dominant in these sediments, which is in accord with
values for Tibetan Plateau soils and with surface lake sediments from
China and East Africa (Fig. 5b). However, the Lake Bihu sediments had
much higher acyclic moieties, including Ia, IIa, IIIa, IIIa' and the pen-
tamethylated brGDGTs were the most abundant. This differs from the
distribution pattern for soils of the Tibetan Plateau and the surrounding
areas within China, where IIc, IIIb' and IIIc brGDGTs were the most
abundant (Fig. 5a, b). Ternary plots of the relative abundances of tetra-,
penta-, and hexamethylated brGDGTs reveal that the global and Chinese
soils have a tetramethylated dominance, whereas the Tibetan Plateau
soils have a greater proportion of pentamethylated brGDGTs, which is
also the case for both Chinese lakes and Lake Bihu (Fig. 5b). Notably, the
surface lake sediments from the Tibetan Plateau have a different dis-
tribution pattern to that of the plateau soils, whereas the Lake Bihu
sediments have a same distribution pattern to these soils, which in-
dicates that the distribution of brGDGTs in the lake surface sediments
can be regulated by the input of soils, and this distribution pattern is also
manifested on a global basis.
4.3.2. BrGDGT calibrations for paleotemperature reconstruction
, and IR
indices in core BH20 vary
consistently with each other (Fig. S4), and the absolute mean values
were also similar, ranging from 0.27 to 0.41 (Table 2). These indices
uctuated with large amplitudes on multidecadal to centennial time-
scales during the late Holocene. In contrast, the CBT shows the opposite
trend to all the other indices throughout the entire sedimentary
sequence, with an absolute mean value of 0.45.
Previously published brGDGT calibrations for modern temperature
reconstruction based on global (De Jonge et al., 2014) and Tibetan
Plateau (Ding et al., 2015) soils, and surface lake sediments from East
Africa (Russell et al., 2018), China (Dang et al., 2018), and the Tibetan
Plateau (Günther et al., 2014) were applied to our lake sediment dataset
(Table S4; Fig. S3). The brGDGTs-based temperature variations at Lake
Bihu area during the past 3500 years were reconstructed using the
transfer functions based on the modern datasets mentioned above
(Table S4). The temperatures reconstructed from these transfer func-
tions are strongly correlated with the brGDGT indices (MBT, MBT
, and IR
), except for the reconstruction using transfer func-
tions based on surface lake sediments of the Tibetan Plateau, which
shows the opposite trend during the last 3500 years (Fig. S4). Notably,
the reconstructed temperature record based on Günther et al. (2014) for
the surface lake sediments of the Tibetan Plateau ranged from 0.70 to
3.98 C, with an average of 2.19 C (Table 2).
Fig. 2. Lithology and age model for core BH20. (a) Core photograph. (b) Calibration of the carbon reservoir effect (x and y represent depth and age, respectively). (c)
Agedepth model. (d) Sedimentation rate. (e)(g) High-resolution proles of (e) water content, (f) organic matter content, (g) and silicate content, spanning the last
3500 years.
Y. Li et al.
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Fig. 3. Summary of the grain size and geochemical results for core BH20. (a) Percentages of clay and silt. (b) Median grain size. (c) Sample scores on PC1 of the
elements determined by XRF scanning. (d) Silicate content. The sequence during the last 3500 years is divided into the following intervals: 1500900 BCE, 900250
BCE, Roman Warm Period (RWP, 250 BCE450 CE), Dark Ages Cold Period (DACP, 450800 CE), Medieval Warm Period (MWP, 8501400 CE), Little Ice Age (LIA,
14001800 CE), and Current Warm Period (CWP, 1850 CEpresent).
Fig. 4. Establishment of a precipitation proxy for the sediments of Lake Bihu. (a) Measured grain-size distributions of 216 samples from core BH20. (b) Measured
grain-size distributions of samples of the surrounding soils and loess deposits. (c)(f) Mineral species and morphology of the lacustrine sediments of core BH20,
determined by SEM and XRD analysis of representative samples from different depths. A =aragonite, Q =quartz.
Y. Li et al.
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5. Discussion
5.1. Temperature change on the northeastern Tibetan Plateau during the
last 3500 years
5.1.1. brGDGTs-induced temperature variations in Lake Bihu
The correlation of brGDGTs (MBT and CBT indices) with air
temperature and soil pH was initially identied in global soil datasets by
Weijers et al. (2007). Subsequently, in the last decade, it was found that
brGDGTs in different geological archives, including lake sediments
(Günther et al., 2014; Dang et al., 2018; Zhang et al., 2022a), peats
(Naafs et al., 2017), and marine sediments (De Jonge et al., 2015b) are
correlated with water/air temperature. In lake systems, the brGDGTs in
the lake sedimentary pool has mixed sources, because brGDGTs are
Fig. 5. Comparison of the fractional abundances of brGDGTs in the sediments of Lake Bihu with previously published data. (a) Comparison of the fractional
abundances of individual brGDGTs in Lake Bihu sediments with previously published data, including global soils (De Jonge et al., 2014); the Tibetan Plateau and soils
within the China (Günther et al., 2014; Ding et al., 2015; Naafs et al., 2017; Li et al., 2018; Zang et al., 2018; Wang et al., 2018, 2019; Ning et al., 2019; Pei et al.,
2019; Qian et al., 2019; Dearing Crampton-Flood et al., 2020; Cao et al., 2020; Zhao et al., 2020; Wang and Liu, 2021; Wang et al., 2020, 2023); and surface lake
sediments from the Tibetan Plateau (Günther et al., 2014), lakes within China (Dang et al., 2018; Ning et al., 2019; Yao et al., 2019; Qian et al., 2019; Cao et al., 2020;
Zhao et al., 2020; Wu et al., 2021; Wang et al., 2023), and East African lakes (Russell et al., 2018). (b) Fractional abundances of summed tetra-, penta-, and hex-
amethylated brGDGTs in the sediments of Lake Bihu and the previously published dataset shown in (a).
Table 2
brGDGTs indices and temperature reconstruction based on soil and surface lake sediment calibrations.
MAF (Günther et al.,
MAF (Dang et al.,
MAF (Russell et al.,
MAF (Ding et al.,
MAF (De Jonge et al.,
Maximum 0.46 0.55 0.63 0.66 0.38 3.98 16.29 16.77 11.30 8.87
Minimum 0.09 0.13 0.20 0.28 0.26 0.70 11.96 2.86 2.3 4.62
Mean 0.27 0.35 0.41 0.45 0.32 2.19 14.19 10.23 4.47 2.53
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abundant in soils and thus soil inputs can undoubtedly affect brGDGT
distributions in lake sediments. However, a recent study found a strong
similarity between brGDGT fractional abundances (MBT/MBT
) and
temperature, across almost all sample types examined (based on a global
dataset, including soils, peats, groundwater, bone, and suspended/
settling particulate matter in lacustrine, riverine, and marine settings)
(Raberg et al., 2022). This wide distribution of brGDGTs indicates that
there is no vector bias for bacterial communities in the natural envi-
ronment, which is supported by published data from surface lake sedi-
ments and soils on the Tibetan Plateau and elsewhere within China
(Fig. S5). The MBTis signicantly correlated with MAAT and MAF, both
in surface soils and lake sediments, and especially in surface lake sedi-
ments from China and has the lowest degree of dispersion, although the
distribution of brGDGTs in lake sediments may contain a soil-derived
signal. In addition, we used the BIT index, which is an index of lipid
biomarkers correlated with the uvial input of terrestrial organic ma-
terial, to assess the stability of the soils-derived brGDGTs in the lake
system (Hopmans et al., 2004). A survey of globally distributed marine
and lacustrine surface sediments shows that the BIT index in these en-
vironments is correlated with the uvial input of terrestrial organic
material, and the BIT index shows high values in marine and lake en-
vironments with large uvial inputs (Hopmans et al., 2004). Indeed,
previous studies showed that high values of the BIT index in Holocene
lake sediments from Lake Cuoqia (China), Lake Paloma (Chili), Lake Siso
(Spain) and Lake Bihuspanning a large environmental gradient
(Hopmans et al., 2004; Zhang et al., 2022a)indicate a stable microbial
community and the supply of terrigenous brGDGTs to these lacustrine
environment (Sinninghe Damst´
e et al., 2009). Consequently, this ther-
mometer can reasonably be used for paleotemperature reconstruction,
given that the distribution of brGDGTs is signicantly associated with
the atmospheric temperature, whether in lakes or the surrounding soils.
These extensive modern sample datasets have been widely used in
recent decades to produce calibration equations based on multiple linear
regression analysis (see details in Section 4.3.2). However, there is a
warm-season bias of brGDGT-based temperature reconstructions when
using these calibration equations, which is caused by the freezing of lake
water at high elevations and latitudes during the cold season, as re-
ported in previous studies (Shanahan et al., 2013; Deng et al., 2016; Hu
et al., 2016; Cao et al., 2020; Zhang et al., 2021, 2022a). As a high-
altitude water body, Lake Bihu (4360 m a.s.l.) may freeze during the
cold season, likely insulating the lake water from changes in air tem-
perature and maintaining a relatively stable water temperature above
0 C when the air temperature is below 0 C. Thus, the water tempera-
ture of Lake Bihu mainly records changes in air temperature during the
ice-free season (e.g., MAF, between May and October) inferred from the
nearest meteorological station (Linxia) data, after elevation correction.
Additionally, lacustrine sediments were recently shown to correlate with
the MAF warm-season air temperature index, on a global scale (Martí-
nez-Sosa et al., 2021; Raberg et al., 2021). The seasonal bias of tem-
perature reconstructions indicates that there are systematic changes in
the length of the warm season, as well as the seasonal period of brGDGTs
production by different microbial communities, which can result in the
overestimation of brGDGTs-based temperatures (Shanahan et al., 2013;
Deng et al., 2016; Dang et al., 2018; Zhang et al., 2022a).
Given the warm-season temperature bias, we used all the brGDGTs-
temperature calibrations to reconstruct MAF changes of the surface
sediments from core BH20, which were then compared, after elevation
calibration, with instrumental data for the period 19512020 (Table S4).
The results indicate that the brGDGTs-inferred MAF reconstructed from
Günther et al. (2014) (3.09 ±1.10 C) matches well with the instru-
mental MAF (3.01 C), but it is markedly higher than the instrumental
MAAT (5.72 C). This suggests that the MAF reconstructed using the
brGDGTs transfer equation of Günther et al. (2014) from the surface
sediments of core BH20 (and with the deeper sediments) is reliable, and
that the amplitude of MAF variability is more reasonable than those
obtained using other transfer equations (some of which produced the
absolute value of 16 C; Fig. S4). We conclude that careful selection of an
appropriate calibration equation is needed to screen the brGDGTs-based
temperature dataset. For example, the equation based on the group of
lakes from East Africa produced results that often ranged from 1.6 to
26.8 C (Russell et al., 2018), while for the Tibetan Plateau, an alpine
region, the range of temperature variation was from 1.5 to 3.6 C
(Günther et al., 2014), which is consistent with that of observations from
Dalijia Mountain. Moreover, the modern temperature estimated from
surface sediment brGDGTs is supported by a comparison with the
measured temperature, which further validates the applicability of this
equation. There are similar cases in which brGDGTs calibrations using
linear regression of measured temperature and brGDGTs-based proxies
(MBT/MBT, CBT) from Bangong Co (Wang et al., 2016b, 2021), Linggo
Co (He et al., 2020) and Aweng Co (Li et al., 2017), together with those
of Günther et al. (2014), are applicable to Tibetan Plateau lakes,
although these brGDGTs-inferred MAAT records may be biased towards
the most biologically productive season.
Regarding the overall trend, the regional MAF reconstruction based
on surface lake sediments from the Tibetan Plateau shows pronounced
uctuations on decadal to centennial timescales during the warm pe-
riods of 1500900 BCE, and the MWP and CWP, and a distinct cooling
trend during 900250 BCE and the LIA (Fig. 6a). The absolute values of
the reconstructed temperatures range between 0.70 and 3.98 C, with an
average of 2.19 C over the past ~3500 years. Our record shows that the
regional MAF during the MWP optimum exceeded the MAF during the
CWP. Additionally, the reconstructed MAF increased from the beginning
of the 20
century across the NETP, which is consistent with the positive
temperature trend shown in local instrumental observations, and in the
results of climate modeling and analysis (Chen et al., 2015a; Yao et al.,
2019; You et al., 2021). However, it should be noted that the sampling
resolution during the RWP is relatively low.
5.1.2. Paleotemperature variations on the northeastern Tibetan Plateau and
in the surrounding regions
We reviewed various published late Holocene quantitative temper-
ature records to characterize the pattern of temperature changes on the
NETP and in the surrounding regions (although there are a limited
number of high-resolution quantitative temperature records for this
region) (Yang et al., 2003; Liu et al., 2006; Liu et al., 2009; Wu et al.,
2013; He et al., 2013b; Zhao et al., 2013; Feng et al., 2019, 2022).
Comparison of the late Holocene NETP temperature records indicates
that warm intervals can be correlated to the WCP, MWP, RWP, and the
interval of 1500900 BCE; while cold intervals can be correlated to the
LIA, DACP, and the interval of 9002500 BCE (Fig. 6). Specically, the
MAAT reconstructed from tree-ring widths from the central-eastern Ti-
betan Plateau indicates distinct warm intervals during the RWP
(403413 CE), with a temperature 2.89 C higher than that of the mean
for 19702000 CE, and during the MWP (864882 and 965994 CE),
when the temperature was 2.81 C higher. Cold intervals are indicated
during the DACP (686705 CE), with a cooling of ~1.71 C, and during
the LIA (15991702 CE), with a cooling of ~1.77 C (Liu et al., 2009).
Likewise, synthetic data reecting paleotemperature changes from the
NETP show distinct climatic episodes, with warm intervals during
8001100 and 11501400 CE, a cold interval during the LIA between
1400 and 1900 CE, and an earlier cold period between the 4th and 6th
centuries (Yang et al., 2003). We also compared the existing lacustrine
sedimentary records with our reconstruction and found that the
brGDGTs-inferred MAF from Lake Cuoqia (Zhang et al., 2022a) and
MAAT from Lake Lugu (Zhao et al., 2021) and Lake Tiancai (Feng et al.,
2019, 2022), on the southwestern Tibetan Plateau, are consistent,
although these records have a greater temperature variability and more
pronounced centennial-scale uctuations. Likewise, alkenone-inferred
summer/warm-season temperature records from Lake Qinghai (Liu
et al., 2006; Hou et al., 2016), Lake Sugan and Lake Gahai (He et al.,
2013b) on the northeastern Tibetan Plateau, and summer temperatures
inferred from subfossil chironomids from Lake Heihai (Chang et al.,
Y. Li et al.
Palaeogeography, Palaeoclimatology, Palaeoecology 615 (2023) 111442
2017) on the southeastern Tibetan Plateau, are also consistent with our
record. However, some of the temperature records are not well corre-
lated with our MAF record, including the brGDGTs-inferred MAAT re-
constructions from Lake Kusai (Wu et al., 2013) on the northeastern
Tibetan Plateau, and from Linggo Co (He et al., 2020) on the central
Tibetan Plateau, and Bangong Co (Wang et al., 2021) and Aweng Co (Li
et al., 2017), on the western Tibetan Plateau. We hypothesize that fac-
tors like seasonal biases of the proxies, age-model inaccuracies, and
strong regional contrasts (including differences in altitude and topog-
raphy, and lake size and depth, and vegetation cover and associated
climate feedbacks) may affect the consistency of these records.
We also compared the temperature records from the NETP and
Fig. 6. Comparison of the reconstructed temperature
variations at Lake Bihu and other paleotemperature
records from the Tibetan Plateau, China, and the
Northern Hemisphere during the last 3500 years. (a)
brGDGTs-based MAF at Lake Bihu (black line shows
instrumental MAF values during 19512020 CE) (this
study). (b) Alkenone-based temperature record from
Lake Qinghai (Liu et al., 2006) and reconstructed
annual mean temperatures based on tree-ring width
from the central-eastern Tibetan Plateau (Liu et al.,
2009). (c) Alkenone-based temperature record from
Lake Sugan and Lake Gahai (He et al., 2013b). (d)
brGDGTs-inferred MAAT records from Lake Kusai
(Wu et al., 2013) and Linggo Co (He et al., 2020); (e)
brGDGTs-inferred MAAT record from Lake Tiancai
(Feng et al., 2019, 2022), and mean July tempera-
tures inferred from subfossil chironomids from Lake
Heihai (Chang et al., 2017). (f) brGDGTs-inferred
MAAT record from Lake Lugu (Zhao et al., 2021)
and brGDGTs-inferred MAF record from Lake Cuoqia
(Zhang et al., 2022a). (g) Composite temperature re-
cord for the entire Tibetan Plateau (Hou et al., 2013;
Li et al., 2020). (h) Ensemble temperature re-
constructions for China based on principal component
regression (red lines) and partial least squares (blue
lines) methods on the centennial timescale (with 5-
point smoothing using a Fast Fourier Transform l-
ter) (Ge et al., 2013). (i) Composite temperature
anomalies for the Northern Hemisphere (Moberg
et al., 2005; Ljungqvist, 2010). The gray shaded ver-
tical bars indicate cold periods. (For interpretation of
the references to colour in this gure legend, the
reader is referred to the web version of this article.)
Y. Li et al.
Palaeogeography, Palaeoclimatology, Palaeoecology 615 (2023) 111442
nearby regions (Liu et al., 2007; Zhu et al., 2008; Li et al., 2020, 2022a
and therein; Fig. 6bg) with records from other regions in China (Yang
et al., 2002; Ge et al., 2010, 2013; Fig. 6h) and the Northern Hemisphere
(Moberg et al., 2005; Mann et al., 2009; Ljungqvist, 2010; Fig. 6i). This
shows that temperature uctuation during the last 3500 years were
generally consistent on the centennial timescale. In addition, our
reconstruction from Lake Bihu shows a signicant warming trend after
the 1900s, which is consistent with modern observations that show that
the rate of modern warming of the Tibetan Plateau is twice that of the
global average (Chen et al., 2015a), indicating an amplied response of
air temperature variations on the Tibetan Plateau (Pepin et al., 2015).
5.2. Hydroclimatic changes on the northeastern Tibetan Plateau during
the last 3500 years
5.2.1. Hydroclimatic changes at Lake Bihu
Previous studies have shown that detrital elements (including Al, Si,
Ti) can be used to reect the erosional energy in lake catchments, which
is closely linked to the intensity of runoff or precipitation within the
catchment (Yancheva et al., 2007; Kylander et al., 2011; Jin et al.,
2015). Specically, higher sedimentary contents of these detrital con-
tents indicate more intense catchment erosion in response to increased
regional precipitation (Shen et al., 2013; Zhang et al., 2017; Peng et al.,
2019). Additionally, we used the BIT index to eliminate a possible
aeolian source in the Lake Bihu sediments. The generally high and stable
BIT values throughout the core (Fig. S6) demonstrate the consistency of
the level of terrigenous erosion, reecting a stabile precipitation regime,
and corresponding to the geochemical index (Fig. 7a). The high-
resolution record of sample scores on PC1, based on the XRF-scanning
elements, offers the possibility of directly linking the lake sedimentary
record with erosion within the catchment.
The grain-size distributions of lake sediments can reect the trans-
port dynamics and sedimentary environment (Peng et al., 2005; Liu
et al., 2016; Zhang et al., 2017): coarse-grained particles may reect
either strong winds associated with aeolian transport (An et al., 2012;
Qiang et al., 2014; Li et al., 2022b), or heavy precipitation-induced
runoff input and alluvial deposition (Chen et al., 2003; Zhang et al.,
2003a; Liu et al., 2016). A polymodal grain-size distribution of lake
sediments can be caused by various factors, including the source of the
clastic material, specic depositional processes and environments, lake
size and shape, lake level uctuations, and the hydrological dynamics of
the lake water (Sun et al., 2002; Xiao et al., 2013; Liu et al., 2016). The
grain size of the loess samples we collected from the Ganjia Basin is
larger than that of sediments and soils of the Lake Bihu catchment,
which indicates that the loess deposits are unlikely to be wind-
transported to the catchment, and thus we can exclude an aeolian
transport mechanism for the lake sediments (Fig. 4b). The lithology of
the Lake Bihu sediments changed only slightly during the late Holocene,
Fig. 7. Comparison of reconstructed precipitation on
the northeastern Tibetan Plateau with that in the
EASM region during the last 3500 years. (a) Recon-
structed precipitation inferred from normalized
stacked proxy indicators of the sediments of Lake
Bihu. The normalized stacked values are calculated
as: (x
x) /
(where x is the mean and
is the
standard deviation). (b) Alkenone-inferred salinity
record from Lake Qinghai (Liu et al., 2006). (c)(d)
Stalagmite δ
O records from Wanxiang Cave (Zhang
et al., 2008) and Dongge Cave (Wang et al., 2005). (e)
Estimates of annual precipitation on the northeastern
Tibetan Plateau based on an absolutely dated tree-
ring chronology with 50-year smoothing (Yang
et al., 2014). The locations of the sites are shown in
Fig. 1a.
Y. Li et al.
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being dominated by deep-water lake facies, and thus any variations of
the grain-size parameters are not associated with changes in the sedi-
mentary environment. Lake Bihu is small, semi-open, and relatively
shallow, and the water is primarily supplied by runoff during the rainy
summers; also, the catchment is narrow and the detrital materials are
transported only a limited distance (Fig. 4e4f). Moreover, Lake Bihu is
unlikely to be affected by sediment remobilization caused by lake-level
uctuations, and thus the grain size record likely reects changes in
runoff-supplied clastics driven by precipitation variations. Clastic ma-
terials in the catchment area are eroded and transferred to the lake via
runoff; coarse particles are mainly deposited near the lake shore, while
ne particles are transported to the deep water, where the site of core
BH20 is located (Fig. 4b). Thus, we consider the grain size of the Ho-
locene sediments in Lake Bihu is an indicator of precipitation-driven
runoff from the steep slopes of the catchment, and an increased pro-
portion of ne silt reects a decrease in precipitation, and that an
increased proportion of coarse silt reects an increase in precipitation.
The variation of the median grain size is consistent with that of silt
fraction (which dominates the sediments) and it reects the overall
changes in the grain-size composition. The median grain size, sample
scores on PC1 of the XRF-scanned elements, and the silicate content
estimated from the LOI vary consistently on decadal to centennial
timescales (Fig. 3). We produced a normalized index based on the
stacking of these geochemical indices, to eliminate any errors associated
with individual proxies (Fig. 7a). We interpret this index as an indicator
of runoff variations, controlled by the summer monsoon precipitation in
the EASM region, since the summer monsoon precipitation comprises up
to 85% of total annual precipitation.
As shown in Fig. 7, the results reveal several distinct decadal- to
centennial-scale climatic events, including the wet periods of 1500900
BCE, RWP, MWP, and CWP, and the dry periods of 900 BCE250 CE,
DACP, and LIA. Additionally, SEM analysis showed that the degree of
roundness of quartz grains during the MWP was higher than that during
the LIA (Fig. 4), indicating stronger transport and depositional dynamics
during the MWP, which can be attributed to increased runoff or pre-
cipitation within the catchment. Precipitation during the MWP was the
highest during the past 3500 years, and it was also high during the CWP,
with a peak at ~1850 CE, after which it decreased slightly. However,
precipitation was overall relatively stable, except for brief events at the
end of the DACP and in the middle of the MWP. We suggest that several
factors may have affected the hydrology of the lake catchment, as fol-
lows. 1) Lake Bihu, as an alpine lake, is an ideal hydrometer because the
lake water is mainly fed directly by atmospheric precipitation during the
summer; thus, hydrological records from such lakes can reliably repre-
sent precipitation changes. For example, alpine Lake Daye, in the Qin-
ling Mountains, is characterized by synchronous changes in lake level
and atmospheric precipitation (Chen et al., 2021), and this may be one
of the reasons for the relatively stable hydrological uctuations within
such small alpine lakes. 2) Soil erosion induced by precipitation is a
major driver of the inux of clastic sediments, and thus the geochemical
indicators can sensitively reect changes in precipitation. 3) The hy-
drology of lake catchments is also inuenced by the vegetation condi-
tions (Li et al., 2022b). The vegetation around Lake Bihu is dominated by
alpine meadow and the vegetation coverage is high during the warm and
wet season, thus maintaining stable hydrological conditions and
reducing runoff and soil erosion in the catchment.
5.2.2. Hydroclimatic variations across the NETP and EASM region
We used a stacked proxy record based on the geochemical indices
from Lake Bihu to reconstruct the hydrological and climatic history of
the NETP over the last ~3500 years, which we compared with typical
hydrological records from the EASM region (Fig. 7). Several studies have
reported stalagmite δ
O data from the middle to late Holocene for the
EASM region, and they are widely interpreted as a proxy for summer
monsoon intensity, with lower δ
O values representing a strong Asian
summer monsoon, and vice versa (Wang et al., 2005; Zhang et al., 2008).
For example, δ
O records from Wanxiang Cave, located at the junction
of the Tibetan Plateau and Chinese Loess Plateau, ~300 km from Lake
Bihu, showed pronounced δ
O enrichment during the DACP and LIA,
compared with the RWP, MWP, and CWP, suggesting decreased Asian
summer monsoon precipitation during the DACP and LIA (Zhang et al.,
2008; Fig. 7c). Stalagmite records from Dongge Cave in southern China
also show strongly enriched δ
O values during the 900250 BCE and
the DACP, and LIA periods, compared to those during 1500900 BCE,
and the MWP and CWP, indicating decreased and increased Asian
summer monsoon precipitation, respectively (Wang et al., 2005;
Fig. 7d). Additionally, stalagmite δ
O records from Huangye Cave (Tan
et al., 2011) and Sahiya Cave (Sinha et al., 2015), on the Tibetan
Plateau, also show temporal variations like those of the stacked proxy
record from core BH20. Overall, these stalagmite δ
O records and the
precipitation reconstruction from Lake Bihu show almost parallel tem-
poral changes.
The hydroclimatic patterns reconstructed from Lake Bihu during the
last 3500 years are supported by precise tree-ring records from the
adjacent regions of the NETP, where precipitation is controlled by the
EASM (Yang et al., 2014). A high-resolution tree-ring based record from
Dulan on the NETP indicates that the MWP was accompanied by pro-
nounced wet springs during the period 9291031 CE, with the peak
occurring at ~974 CE (Zhang et al., 2003b). Furthermore, a tree-ring
record of annual precipitation from the Qilian Mountains of the NETP
suggests dry periods during the 4th century BCE and the second half of
the 15th century CE; the driest individual year (since 1500 BCE) was
1048 BCE, while the wettest year was 2010 CE (Yang et al., 2014;
Fig. 7e). Similarly, a tree-ring record from the NETP, reecting moisture
conditions at the onset of the growing season, shows two prominent low-
growth periods corresponding to drought events centered on 1480 and
1710 CE, while notable high-growth periods were centered on 590 and
1570 CE, as well as in the last 30 years (Shao et al., 2010).
Hydroclimatic changes inferred from high-resolution lacustrine
sedimentary records across the NETP and EASM region also co-vary on
multidecadal to centennial timescales. For example, long-term trends in
precipitation/salinity at Lake Qinghai, inferred from sedimentary C/N
ratios, grain-size (Xu et al., 2015), and %C
of alkenones (Liu et al.,
2006; Fig. 7b) are like those of the precipitation reconstructions from the
sediments at Lake Gonghai (Liu et al., 2011a) and Lake Dali (Xiao et al.,
2008), in northern China. In summary, the existing high-resolution,
well-dated climate proxy records, representing Asian summer
monsoon precipitation, suggest that the hydroclimate varied synchro-
nously across the NETP and EASM region during the last 3500 years, on
multidecadal to centennial timescales. Overall, wet hydroclimatic con-
ditions occurred during warm periods and relatively dry conditions
during cold periods.
5.3. Driving mechanisms of late Holocene climatic variations on the NETP
Possible forcing mechanisms of the distinct warmwet and colddry
climatic patterns over the NETP and northern China during the last
3500 years include solar irradiance, volcanic eruptions, greenhouse
gases, and atmosphericoceanic modes (e.g., El Ni˜
noSouthern Oscil-
lation (ENSO, closely linked to variations in equatorial sea surface
temperature (SST)), and the Intertropical Convergence Zone (ITCZ), and
Western Pacic Subtropical High (WPSH)). Next, we evaluate these
possible factors.
The quantitative MAF reconstruction from Lake Bihu and total solar
irradiance are highly correlated on decadal and centennial timescales,
suggesting that larger-scale temperature variability (Steinhilber et al.,
2012; Fig. 8a and c) may arise from direct heating of the NETP, mainly
during the summer months, although evidence for this is lacking on the
inter-annual timescale. In addition, the abrupt temperature rise during
the CWP was likely caused by the increase in greenhouse gases during
the industrial period (post-1850 CE) (Crowley, 2000; Fig. 8h), as noted
in numerous other climate studies (IPCC, 2021). It is also well known
Y. Li et al.
Palaeogeography, Palaeoclimatology, Palaeoecology 615 (2023) 111442
that hemispheric to global climatic cooling following strong or contin-
uous volcanic eruptions may last decades, enabling the multi-centennial
to millennial quantication of the climate response to volcanic forcing
(Castellano et al., 2005; Sigl et al., 2015; Toohey et al., 2016). A
reconstruction of global volcanic aerosol forcing suggests that there
were more eruptions during the DACP and LIA, and fewer eruptions
during the MWP; these eruptions can potentially be linked to several of
the extreme cold events in our reconstruction (Sigl et al., 2015; Fig. 8d).
It should be noted that accurately-dated tree-ring records are well-suited
to resolving the climatic response to volcanic eruptions which often
show close relationships with climate variables (Mann et al., 2012; Sigl
et al., 2015). The coldest decade in the past 3500 years, indicated by the
greatest reduction in tree growth during a sustained cooling period, was
associated with several successive volcanic eruptions over the Tibetan
Fig. 8. Possible forcing mechanisms of climate
change on the Tibetan Plateau during the past
3500 years. (a) Reconstructed precipitation
basing on the stacked geochemical index, and
(b) brGDGTs-based MAF (gray line showing
instrumental MAF values during 19512020
CE) for Lake Bihu (this study). (c) Recon-
structed total solar irradiance (Steinhilber et al.,
2012). (d) Global volcanic aerosol forcing (Sigl
et al., 2015). (e) Dinosterol abundance (a mo-
lecular organic geochemical proxy) in ODP
Hole 1228D on the Peru margin, indicating El
no activity (dark cyan; Makou et al., 2010),
and composite stalagmite δ
O record from the
AsianAustralian monsoon region (gray; Zhang
et al., 2022c). (f) Ti concentration in the sedi-
ments of the Cariaco Basin (Haug et al., 2001).
(g) Zonal SST gradient for the tropical Pacic
calculated as the difference between the west-
ern (Stott et al., 2004) and eastern (Rein et al.,
2005) Pacic Ocean (violet line), and SST
reconstruction from El Junco in the eastern
Pacic Ocean (gray line; Conroy et al., 2009).
(h) Greenhouse gas forcing (Crowley, 2000).
The light brown shaded columns indicate
warmwet periods, and the blue shaded col-
umns indicate colddry periods. (For interpre-
tation of the references to colour in this gure
legend, the reader is referred to the web version
of this article.)
Y. Li et al.
Palaeogeography, Palaeoclimatology, Palaeoecology 615 (2023) 111442
Plateau and surrounding regions (Briffa et al., 2013; Salzer et al., 2014;
Zhang et al., 2014).
In addition to temperature records, precipitation variations during
the late Holocene, reconstructed from the numerous proxy indices ob-
tained from the NETP and the wider EASM region, are also potentially
related to external forcing, namely solar activity on decadal to millen-
nial timescales (Wang et al., 2005; Zhang et al., 2008; He et al., 2013a; Li
et al., 2022b; Liu et al., 2022). Increased summer precipitation over
these regions was driven by higher solar irradiance, corresponding to a
greater thermal gradient between the East Asian continent and the
northern Pacic Ocean, and thus a northward migration of the WPSH
(Liu et al., 2011b; Chen et al., 2015b; Shi et al., 2018; Shi and Wang,
2019); and there was also a northward shift of the ITCZ during warm
periods (Haug et al., 2001; Yan et al., 2015; Wang et al., 2017; Asmerom
et al., 2020). Together, these changes in atmosphericoceanic modes
likely resulted in the northward migration of the EASM margin during
warm periods, and vice versa during cold periods (Figs. 7 and 8).
It should be noted that ENSO is closely linked to equatorial Pacic
SSTs, which are also controlled by solar irradiance (caused by the
greater sensitivity of the western equatorial Pacic to radiative forcing
relative to the eastern equatorial Pacic; see Rustic et al., 2015). This
was the dominant modulator of precipitation changes in the EASM re-
gion during the late Holocene, via atmospheric circulation tele-
connections on interannual to longer timescales, as shown by existing
proxy records and climate modeling (e.g., Conroy et al., 2008; Chen
et al., 2015b; Xu et al., 2016; Liu et al., 2019; Lan et al., 2020). For
example, shifts to more or less El Ni˜
nolike conditions (Fig. 8e) spanning
cold to warm periods should lead to a decrease in EASM intensity by
changing the position of the WPSH (Chen et al., 2015b; Lan et al., 2020;
Jiang et al., 2021).
Specically, El Ni˜
no-like conditions could occur during cold periods,
when radiative forcing is weak and a decreased zonal SST gradient in the
ocean occurs owing to decreased SSTs in the western tropical Pacic
(Stott et al., 2004; Rein et al., 2005; Conroy et al., 2009; Jian et al., 2022;
Fig. 8). This would lead to a weakened EASM and reduced moisture
transport from the low-latitude Pacic to northern China and the margin
of the NETP owing to the southward migration of the WPSH (Hou et al.,
2003; Zhang et al., 2008; Li et al., 2010; Tan et al., 2011; Liu et al.,
2019), but increased precipitation in the Yangtze River valley region.
During warm periods, when radiative forcing was strong, this situation
was reversed (Tong et al., 1997; He et al., 2003; Man, 2009). In sum-
mary, we argue that EASM intensity was dramatically enhanced
(diminished) during warm (cold) periods, which may have primarily
been a response to both the external forcing of strong (weak) total solar
irradiance and the associated changes in atmosphericoceanic modes,
including internal forcing factors like the northern (southern) shift of the
ITCZ and WPSH. La Ni˜
na-like (El Ni˜
no-like) conditions linked to an
increased (decreased) tropical Pacic SST gradient resulted in increased
(decreased) precipitation on the margin of the NETP and in northern
China over the past 3500 years.
6. Conclusion
We have produced a reliably-dated quantitative multi-proxy paleo-
climatic reconstructions for the late Holocene sediments of Lake Bihu, an
alpine lake on the NETP. The record spans the last ~3500 years and the
average sedimentation rate of ~0.63 mm/yr is sufcient to resolve
climate variations on decadal to centennial timescales. High-resolution
reconstructions of precipitation and quantitative mean air temperature
are based on XRF-scanning element contents, grain-size, organic and
silicate contents, and brGDGTs. The regional MAF reconstruction values
ranged between 0.70 and 3.98 C, with an average of 2.19 C. Precipi-
tation and temperature optima on the NETP occurred during the MWP,
rather than during the CWP. Comparison of our precipitation and
paleotemperature reconstructions with other local and global climate
records indicate that notable and spatially extensive warmwet climatic
conditions occurred during the periods of 1500900 BCE, RWP (250
BCE450 CE), MWP (8001400 CE), and CWP (1850present); and
relatively colddry climatic conditions during the intervals of 900250
BCE, the DACP (450800 CE), and LIA (14001800 CE), across the NETP
region. The late Holocene temperature uctuations on the NETP were
primarily controlled by total solar irradiance, interrupted by successive
volcanic eruptions, on a multidecadal timescale. The anomalous and
rapid warming during the CWP could also be related to the unprece-
dented increase in atmospheric greenhouse gases during the 20
tury. Precipitation, driven by EASM intensity, decreased substantially
during cold periods, and it increased during warm periods; this may
primarily have been a response to both the external forcing factor of
total solar irradiance and the associated changes in atmosphericoceanic
modes. Specically, when the zonal SST gradient in the tropical Pacic
increases (decreases), owing to an increased (decreased) SST in the
western tropical Pacic, the eastern tropical Pacic becomes dominated
by a La Ni˜
na-like (El Ni˜
no-like) state, triggered by the stronger (weaker)
radiative forcing; this coincides with periods of northward (southward)
migration of both the ITCZ and WPSH, resulting in enhanced (dimin-
ished) precipitation in northern China and on the margin of the NETP
region during historical warm (cold) periods. Overall, the climatic re-
cord from Lake Bihu is a unique dataset that can be used to understand
temperature and precipitation patterns and their potential climate
forcing mechanisms during the late Holocene, and to provide a reference
frame for predicting future climate change over the Tibetan Plateau.
Declaration of Competing Interest
The authors declare that they have no known competing nancial
interests or personal relationships that could have appeared to inuence
the work reported in this paper.
Data availability
Data will be made available on request.
This research was supported by National Natural Science Foundation
of China (42171150), and Second Tibetan Plateau Scientic Expedition
and Research Program (STEP) (2019QZKK0601).
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://doi.
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