Biofuels Reserve Controlled Wildfire Regimes Since the Last Deglaciation: A Record From Gonghai Lake, North China

Abstract

Wildfire activity is an important activity in evolution of vegetation and carbon cycling. Whether wet weather will suppress wildfire or promote them by increasing fuel reserves during the Holocene is not clear. We obtained a record of black carbon from a sediment core spanning the last 14.8 kyr from Gonghai Lake, in North China. There is a close relationship between the timing of wildfire activity and vegetation development driven by the East Asian summer monsoon intensity. On a millennial timescales, wet climatic conditions provide a sufficient biofuels reserve, in the same period wildfire increase; thus, the regional potential biofuels reserve is shown to be an important controlling of regional wildfire activity in the monsoon region of China, under natural conditions. We infer that with the strengthening of Asian summer monsoon caused by global warming, the wildfire carbon emission in Asian monsoon region may increase in the future.
Get the full text: https://onlinelibrary.wiley.com/share/author/4XFSEB4IX2DA6UN7MGXT?target=10.1029/2021GL094042

Full text

1. Introduction
Wildfire is a common and important natural phenomenon in the biosphere, being a critical link between
vegetation succession on the land surface and the terrestrial carbon cycle (Abatzoglou etal.,2018; Thev-
enon etal.,2010). The occurrence of wildfire results in the transformation of forest and grassland from
a carbon sink to a carbon source, with effects on the carbon dioxide content of the atmosphere and on
the cycling of materials in terrestrial ecosystems (Han etal.,2020; Marlon et al., 2013). The products of
combustion are the most direct evidence of wildfire; for example, black carbon (BC) is a chemically inert,
micron- or submicron-sized spherical material with high thermal stability and a highly condensed aromatic
hydrocarbon structure, which is produced by the incomplete combustion of biomass or fossil fuels (Bond
etal.,2013; Goldberg,1985; Pei etal.,2020; Salvadó etal.,2017; Smith etal.,1973). Because of its stability
and high detectability, BC analysis is widely applied to various sedimentary archives such as ice cores (Chýl-
ek etal.,1995; Osmont etal.,2019), loess (Tan etal.,2015), marine sediments (Dickens etal.,2004; Smith
etal.,1973), and lake sediments (Han etal.,2011; Wang etal.,2019). BC can be used as a proxy indicator
of fire activity and hence it can be used to reconstruct fire histories on different spatial and temporal scales
(Ditas etal.,2018; Han etal.,2020).
Abstract Wildfire activity is an important activity in evolution of vegetation and carbon cycling.
Whether wet weather will suppress wildfire or promote them by increasing fuel reserves during the
Holocene is not clear. We obtained a record of black carbon from a sediment core spanning the last
14.8kyr from Gonghai Lake, in North China. There is a close relationship between the timing of
wildfire activity and vegetation development driven by the East Asian summer monsoon intensity. On
a millennial timescales, wet climatic conditions provide a sufficient biofuels reserve, in the same period
wildfire increase; thus, the regional potential biofuels reserve is shown to be an important controlling of
regional wildfire activity in the monsoon region of China, under natural conditions. We infer that with
the strengthening of Asian summer monsoon caused by global warming, the wildfire carbon emission in
Asian monsoon region may increase in the future.
Plain Language Summary Much attention has been paid to the response of wildfire
activity to climate change. Understanding the past history of wildfires and their triggering factors may
help us to mitigate the effects of future wildfires. Our study of the black carbon record of the sediments
from an alpine lake (Gonghai Lake) in North China indicates that the level of biofuels (mainly woody
vegetation) was the main control on the intensity of wildfire on a millennial timescales over the past
∼14,800yr. When the climate was wetter, more biofuels were available as a result of increased biomass
storage, wildfires were more intense with a relatively stable ignition probability. So, climate trends that
favor vegetation development will lead to a higher intensity of wildfire and carbon emission in the Asian
monsoon region in the future, with the strengthening of Asian summer monsoon caused by global
warming.
JI ET AL.
© 2021. American Geophysical Union.
All Rights Reserved.
Biofuels Reserve Controlled Wildfire Regimes Since the
Last Deglaciation: A Record From Gonghai Lake, North
China
Panpan Ji1 , Jianhui Chen1 , Aifeng Zhou1 , Rui Ma1, Ruijin Chen1, Shengqian Chen1,
Feiya Lv1, Guoqiang Ding1, Yan Liu1 , and Fahu Chen1,2,3
1MOE Key Laboratory of Western China's Environmental System, College of Earth and Environmental Sciences,
Lanzhou University, Lanzhou, China, 2State Key Laboratory of Tibetan Plateau Earth System Science (LATPES),
Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, China, 3CAS Center for Excellence in
Tibetan Plateau Earth Sciences, Chinese Academy of Sciences, Beijing, China
Key Points:
• The variation of wildfire and
summer monsoon is consistent on
the millennial scale, wet climate
drives wildfire enhancing
• Biofuels reserve has controlled
wildfire for the Holocene in Asian
summer monsoon region
• Stronger monsoons caused by global
warming would increase wildfire
carbon emission
Supporting Information:
Supporting Information may be found
in the online version of this article.
Correspondence to:
J. Chen,
jhchen@lzu.edu.cn
Citation:
Ji, P., Chen, J., Zhou, A., Ma, R.,
Chen, R., Chen, S., etal. (2021).
Biofuels reserve controlled wildfire
regimes since the last deglaciation:
A record from Gonghai Lake, North
China. Geophysical Research Letters,
48, e2021GL094042. https://doi.
org/10.1029/2021GL094042
Received 29 APR 2021
Accepted 29 JUL 2021
10.1029/2021GL094042
Special Section:
Fire in the Earth System
RESEARCH LETTER
1 of 11

Geophysical Research Letters
Although the study of paleoclimatic records has provided much information on past climates (Sherwood
etal.,2020; Zalasiewicz & Williams,2016), the recording and analysis of fire history is still at a fairly rudi-
mentary stage, research on the relationship between wildfire and climate change during the Holocene is
increasing. A humid climate, by promoting vegetation growth and enhancing biofuels availability are an
important drivers of wildfire. For example, a multi-proxy sedimentary record from a small lake at Cape
Flats, South Africa, showed that wildfire was more intense under a humid climate and less intense in a dry
climate, and that the supply of biofuels from the vegetation contributed to wildfire occurrence (Cordova
etal.,2019). A BC record from the sediments of Meerfelder Maar Lake in Germany indicated that during
the historical past the intensity of fire activity in the region was strongly correlated with the development
of human society (Lehndorff etal.,2015). So, the intensity of wildfire activity can be controlled by various
factors, and hence it varies between different regions. In the monsoon region of China, there are different
perspective about the relationship between wildfire activity and dry/wet climatic shifts. A study has con-
cluded that an arid climate drives the occurrence of wildfire: a study of Qinghai Lake in Tengchong, south-
west China, reached a similar conclusion, with regional wildfire activity increasing during a relatively dry
period (E. Zhang etal.,2015). However, other studies concluded that wildfire activity was associated with
wet climatic conditions: such as, a study of wildfire in the middle and lower reaches of the Yangtze River of
China found that before 3kyr BP wildfire was mainly controlled by temperature and precipitation and that
subsequently it was promoted by intensified human activities to some extent (Pei etal.,2020). A study of
Daihai Lake indicated that changes in the vegetation community driven by precipitation fluctuations was
an important factor in occurrence of wildfire, and that vegetation development and wildfire activity varied
synchronously (Wang etal.,2013). These studies indicate that the nature of the relationship between wild-
fire and climatic shifts between wetter and drier phases, on the millennial timescale, remains controversial.
Hence, a comparative analysis of reliable environmental records between regions may enable a clarification
of the incidence of wildfire and the driving factors during the Holocene.
Given the uncertainty regarding the relationship between wildfire and climate change, it is important to ob-
tain additional reliable sedimentary records of wildfire and their relationship. The Chinese monsoon region
is an important climatic research area which can reflect the East Asian Summer Monsoon (EASM) and the
climate change of the Northern Hemisphere. Gonghai Lake in the Lvliang Mountains of Shanxi Province
is one of the few alpine lakes in the marginal zone of the EASM region in North China. The sedimentary
environment of the lake is stable and the sedimentary record indicates a sensitive response to past climate
changes and that the effects of human disturbances are limited; therefore, the site is well suited to studies
of regional climatic and environmental change under natural conditions (Chen etal.,2010,2019; F. Chen,
Xu, etal.,2015; J. Chen, Chen, etal.,2015). Previous studies of the sedimentary record of Gonghai Lake
have been conducted in order to inform vegetation restoration programs (Q. Xu etal.,2017), and to provide a
quantitative reconstruction of precipitation (F. Chen, Xu, etal.,2015); a geochemical study of the sediments
has also been conducted (J. Liu etal.,2018). Here we present a study of the variation of BC in the sediments
of Gonghai Lake, which is used to construct a regional wildfire history since the last deglaciation. Our study,
combined with various other environmental proxies and evidence from other wildfire studies and modern
observation data from the region, enable us to determine the evolution and driving mechanisms of wildfire
in the monsoon region of China. It was hoped that the findings would provide an improved understanding
of the interaction between climate change, vegetation, and fire activity, and hence shed light on the princi-
ples underlying wildfire occurrence under natural conditions.
2. Study Site, Materials, and Methods
2.1. Regional Setting
Gonghai Lake is located in the Lvliang Mountains (38° 54′N, 112° 14′E), in southwest Ningwu County,
Shanxi Province, North China (Figure1). The lake surface area is 0.36km2, the maximum water depth is
10m, and the elevation is 1,860m. The average annual temperature is ∼6.2°C, and the average annual pre-
cipitation is ∼468mm, which mainly occurs from June to September, as is typical of the EASM region (Cao
etal.,2017; F. Chen, Xu, etal.,2015; Q. Xu etal.,2017). The regional vegetation type is transitional between
temperate forest and grassland, and it is strongly influenced by changes in regional precipitation. The mod-
ern vegetation consists mainly of Larix principis-rupprechtii, Pinus tabulaeformis, and Populus davidiana
JI ET AL.
10.1029/2021GL094042
2 of 11
19448007, 2021, 16, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021GL094042 by Lanzhou University, Wiley Online Library on [03/07/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License

Geophysical Research Letters
forest, while Hippophae rhamnoides scrub, Bothriochloa ischaemum grassland and Carex spp. are widely
distributed on the plateau (F. Chen, Xu, etal.,2015). The long-term sedimentary environment of Gonghai
Lake was stable and thus the site is well suited for paleoenvironmental research (Chen etal.,2018; F. Chen,
Xu, etal.,2015; J. Chen, Chen, etal.,2015).
2.2. Chronology
Sediment cores were collected with a Livingstone piston corer at 112.2347°E, 38.9079°N in Gonghai Lake.
Coring was carried out in winter from the frozen lake surface. A series of incremental 1-m-long cores were
obtained from the same location, with a total length of 950cm (designated core GH19A). The lithology of
core GH19A is as follows: 9.50–9.23m: coarse-grained sand and gravel; 9.23–7.60m: interbeds of black silty
clay and black-gray silty sand; 7.60–2.55m: interbeds of brown silty clay and black silty clay; 2.55–0.00m:
light-brown silty clay. Twelve plant macrofossil materials samples were obtained from core GH09A for AMS
14C dating, which was conducted by Beta Analytic Inc., USA. The results including calibrated 14C ages are
listed in TableS1. Stratigraphic correlation was conducted between core GH19A (12 dating points) and
core GH09B (with an age model based on 24 dating points) (F. Chen, Xu, etal.,2015). The correlations
were made using the Ca record for core GH19A and the carbonate record for core GH09B, which were
used to determine the equivalent depths of core GH19A in core GH09B (Wu etal.,2018) (see FigureS1a).
JI ET AL.
10.1029/2021GL094042
3 of 11
Figure 1. Location, bathymetry and landscape of Gonghai Lake. (a) Location of Gonghai Lake (red star), and other sites mentioned in the text (Dali lake,
Daihai lake, site LJC in the Chinese Loess Plateau, Mugeco Lake, and core ECMA from the East China Sea [yellow triangle]). (b) Bathymetry of Gonghai Lake
and the location of core GH19A used in this study, and of cores GH09B and GH09C (Chen etal.,2020; F. Chen, Xu, etal.,2015). (c) Panoramic image of the
modern landscape of Gonghai Lake. Dashed line means Asian summer monsoon limit (Chen etal.,2008). Maps were generated using ArcMap 10.2.
19448007, 2021, 16, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021GL094042 by Lanzhou University, Wiley Online Library on [03/07/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License

Geophysical Research Letters
The IntCal20 database within the rbacon (v2.3.9.1) R package was used for calendar year correction, and
Bayesian age depth modeling of GH19A (all 36 dating points, dating results see TableS1, the model see
FigureS1b) (Blaauw & Christen,2011; Ramsey,2008; Reimer etal.,2009).
2.3. Laboratory Methods and Statistical Analyses
A total of 308 samples at a 3-cm interval were measured for BC. The chemothermal oxidation method
(CTO-375) was used to extract BC from freeze-dried sediment samples, and the procedure consisted of
the following steps: (a) 0.2g of homogenized samples was heated in ceramic crucibles at 500°C for 3h (b)
Carbonate was removed with HCl, followed by rinsing to neutral and drying. (c) Samples were heated in an
SG-GL 1100 tube furnace at 375°C for 24h (d). The concentration of BC was measured using an ELTRA CS
800 sulfur carbon analyzer (Gélinas etal.,2001; Gustafsson etal.,2001; Kuhlbusch,1995; X. Xu etal.,2018).
Prior to the analyses, a carbon standard sample (914E stainless steel, Eltra Company, Germany; 0.1860%
carbon) was measured for quality control. Fast Fourier Transform filtering, smoothing, resampling and
regression analysis were conducted on the data, using Origin 9.0.
3. Results
The mass concentration of BC in core GH19A ranges from 0.0150 to 0.9899wt% (see FigureS2). The profile
shows three major peaks in BC content. Beginning with 14.8ka BP, the BC content gradually increases and
reaches the first major peak of 0.4469wt%, at ∼14.0calkyr BP. After ∼12.5kyr BP the BC content rises and
then becomes relatively stable at ∼0.35wt% after ∼11kyr BP. The BC content then increases rapidly after
∼7.8kyr BP and reaches the second major peak of 0.9899wt% at ∼6.5kyr BP; it then decreases and remains
relatively stable at ∼0.33wt% during 5.5–3.3kyr BP, followed by a decrease. At ∼1.2kyr BP, the BC content
increases again and reaches the third major peak of 0.9083wt% at ∼1kyr BP; the BC content then gradually
decreases before increasing again after ∼0.5kyr BP.
The BC time series was resampled at a 50-yr interval to enable regression analysis of the relationship be-
tween BC concentration (y) and a pollen-based precipitation reconstruction from Gonghai Lake (x) (F.
Chen, Xu, etal.,2015). For average annual precipitation <550mm (with the inflection point at 550mm, de-
termined using a cubic polynomial fit - see FigureS3a), a regression model with a moderately strong linear
relationship was obtained: y=9.518×10−4x−0.135 (Adj. R2=0.335, p<0.05; see FigureS3b). However, for
precipitation >550mm, the linear relationship was not significant. Average annual precipitation >550mm
occurred mainly during ∼7.8–5.6kyr BP, corresponding to the interval of most intense wildfire occurrence,
when the relationship between BC content and precipitation exhibits a nonlinear positive relationship.
4. Discussion
4.1. Wildfire History in the Gonghai Lake Region
The variations of the BC content of the sediments of Gonghai Lake suggest a response of wildfire activity to
global climatic events, including the Bølling/Allerød (B/A) interstadial, the Younger Dryas (YD) cold event,
the mid-Holocene EASM maximum (F. Chen, Xu, etal.,2015), the Medieval Warm Period (MWP), and the
Little Ice Age (LIA) (Figure2).Wildfire activity increased during 14.8–14.6kyr BP and there was a peak in
activity during the B/A interstadial (∼14.6–12.9kyr BP) (peak Ⅰ), and a minimum occurred during the sub-
sequent YD cold event (∼12.6–11.6kyr BP). Wildfire activity was relatively uniform in the early Holocene,
during ∼11.6–7.8kyr BP, and it then increased rapidly during ∼7.8–6.6kyr BP (peak Ⅱ). Wildfire activity
decreased rapidly during 6.6–5.6kyr BP, remained stable during 5.6–3.3kyr BP, and then decreased gradually
during ∼3.3–1.5 kyr BP. Wildfire activity then increased during ∼1.5–1.0kyr BP (peak Ⅲ), which was fol-
lowed by a decrease during ∼1.0–0.5kyr BP, and finally by an increasing trend from 0.5kyr BP to the present.
The mean BC content for the entire sequence is 0.344wt%. Periods that exceeded the mean value were
mainly the B/A interstadial (∼14.6–12.9kyr BP), the interval of maximum vegetation coverage (∼10–3.3kyr
BP), as indicated by the pollen record of Gonghai Lake (F. Chen, Xu, etal.,2015), and the MWP (∼1000–
1300 CE). There are three distinct peaks in BC content, corresponding to the B/A interstadial, the middle
Holocene EASM maximum (∼7.8–5.3kyr BP), and the MWP. During the interval of maximum vegetation
JI ET AL.
10.1029/2021GL094042
4 of 11
19448007, 2021, 16, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021GL094042 by Lanzhou University, Wiley Online Library on [03/07/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License

Geophysical Research Letters
coverage at Gonghai Lake, the BC content was generally high (average of 0.438wt%), when wildfire were
the most active.
4.2. Factors Driving the Occurrence of Wildfire
There are two preconditions for wildfire activity: available biofuels for combustion – that is, sufficient sur-
face vegetation biomass reserve; and the fuel temperature reaching the ignition point. Therefore, the factors
that influence these two preconditions need to be considered when interpreting variations in wildfire ac-
tivity. There is a correlation between wildfires recorded at Gonghai Lake and global climatic events on the
millennial timescale, and thus large-scale climate change has had a significant impact on the occurrence of
wildfire in the region. Moreover, there is no interval within the studied record from Gonghai Lake in which
the trend of wildfire deviated from the climatic trajectory of the region. Therefore, it can be inferred that the
regional fire history reflected by the BC record at Gonghai Lake was largely unaffected by human activity
and it can be regarded as a product of natural environmental factors.
The wildfire in the study region is consistent with the trend of reconstructed precipitation (F. Chen, Xu,
etal.,2015) and vegetation development (Li etal.,2015; Q. Xu etal.,2017; P. Zhang etal.,2017) on millen-
nial timescales (Figure3). The BC record from Gonghai Lake shows that wildfire activity was more intense
during the B/A interstadial, when there was the active growth of forest vegetation under favorable precip-
itation conditions. By contrast, degradation of the vegetation and decreased wildfire occurred during the
YD cold period. Subsequently, during ∼11.6–6.6kyr BP, there was an increase in the forest coverage, and
wildfire activity increased accordingly. After ∼6.6kyr BP both forest coverage and wildfire activity gradually
decreased. Thus our results clearly indicate that over much of the studied interval the evolution of wildfire
activity and the status of the regional vegetation were directly related and changed synchronously. Based
on this highly consistent relationship between wildfire and vegetation status, we infer that for most of the
Holocene the probability of wildfire in the region was relatively stable, with the EASM indirectly limiting
the occurrence of wildfire via its control on the amount of biofuels.
The BC record for Gonghai Lake reveals three peaks in wildfire activity since ∼14.8kyr BP, during which
the incidence of wildfire seemingly exceeded the level expected by the status of the vegetation (Figure3).
This suggests that wildfire activity at these intervals may have been enhanced by factors other than the
vegetation status. These intervals of peak BC content correspond to warm periods: the B/A interstadial
(∼14.6–12.9kyr BP), the Holocene warm period (∼7.7–5.9kyr BP) (S. Liu etal.,2015), and the Medieval
Warm Period (∼1000–1300 CE). This suggests that the enhanced probability of wildfire may have been
influenced by high temperatures (Figure3). Modern instrumental observations can help to elucidate the
JI ET AL.
10.1029/2021GL094042
5 of 11
Figure 2. Wildfire history indicated by the black carbon (BC) content of core GH19A from Gonghai Lake. The orange
dots are the measured BC content and the red continuous curve is the result of smoothing with a 1,000-yr moving
window. The blue dotted line corresponds to the mean BC content of 0.344wt% for the entire profile, and the violet
dotted line corresponds to the mean BC content (0.438 wt%) of the period of maximum vegetation coverage (indicated
by the dotted rectangular outlined area [F. Chen, Xu, etal.,2015]). The gray shaded intervals corresponds to climatic
events: the warm Bølling/Allerød interstadial (B/A), the Younger Dryas (YD) cold event, the EASM maximum (F. Chen,
Xu, etal.,2015), the Medieval Warm Period (MWP), and the Little Ice Age (LIA).
19448007, 2021, 16, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021GL094042 by Lanzhou University, Wiley Online Library on [03/07/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License

Geophysical Research Letters
relationship between annual temperature and wildfire activity. We conducted a spatial analysis of modern
observational data and found that there is a positive relationship between wildfire carbon emission (van der
Werf etal., 2017) and annual mean temperature (FigureS4). This demonstrates that wildfire occurrence
in North China responds to regional high temperatures and wildfire is more frequent in the warmer year,
which may explain the correspondence between wildfire activity revealed by the Gonghai Lake record and
the warm climate events. Reanalysis of several decades of Earth observation data indicated that the tropics
are the most active region in terms of wildfire on a global scale, where high biomass and high temperatures
JI ET AL.
10.1029/2021GL094042
6 of 11
Figure 3. Comparison of the black carbon record from Gonghai Lake with selected regional environmental records.
(a) Black carbon (BC) concentration at Gonghai Lake (pink open circles are the raw data and the smoothed red curve
is the result of the application of a 500-years low pass filter [this study]). (b) Relative tree cover index (=∑[tree taxa
pollen%/relative productivity]) for Gonghai Lake, based on tree pollen data and the relative productivity of tree taxa
(Juglans, Ulmus, Quercus, Betula, Pinus, which represent ∼95% of total tree pollen). The pollen productivities of the tree
taxa are relative to Quercus (=1) (Li etal.,2015; Sugita,2007; Q. Xu etal.,2017; P. Zhang etal.,2017). (c) Pollen-based
reconstructed precipitation at Gonghai Lake (F. Chen, Xu, etal.,2015). (d) Holocene temperature anomalies for China
(Fang & Hou,2011). (e) The Holocene Warm Period (HWP, ∼7.7–5.9kyr BP) recorded by a record of the anhysteretic
remanent magnetization (ARM) of the sediments of Dali Lake (S. Liu etal.,2015). The rectangle delimited by the light-
blue broken line corresponds to the interval of maximum vegetation cover revealed by the pollen record of Gonghai
Lake (∼10–3.3kyr BP) (F. Chen, Xu, etal.,2015). The broken lines in (a–c) are the result of the application of a low-
pass filter with a 3,000-yr window. Note the close linkage between BC concentration and the warm B/A interstadial
(∼14.8–12.9kyr BP), the HWP (∼7.7–5.9kyr BP), and the Medieval Warm Period (MWP, 1000–1300 CE), indicated by
the light pink shading.
19448007, 2021, 16, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021GL094042 by Lanzhou University, Wiley Online Library on [03/07/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License

Geophysical Research Letters
combine to favor the increased incidence of wildfire (Chen etal.,2017), and recent study suggests that the
occurrence of heatwaves are known to trigger more wildfire (Ridder etal.,2020).
Overall, we infer that during main of the studied interval, when the regional environmental evolution was
dominated by natural environmental factors, the probability of wildfire was relatively stable, and the biofu-
els reserve controlled the evolution of regional wildfire activity. We also infer that higher ambient tempera-
tures could create favorable conditions for fire ignition in warmer periods, which increased the probability
of wildfire (Fang etal.,2021; Ridder et al.,2020); thus higher temperatures had regulatory effect on the
incidence of wildfire, on a relatively long timescale.
4.3. Role of the Biofuels Reserve as a Control on Wildfire in the Monsoon Region of China
The incidence of wildfire in the Gonghai Lake area is controlled mainly by the biofuels reserve. We now
address the issue of whether the same relationship exists elsewhere in the monsoon region of China. Fuel
is a prerequisite for wildfire, but there are regional differences in the vegetation response to fluctuations
between humid and arid conditions (Zhou etal.,2016) and therefore the control of biofuels on wildfire may
vary between regions. A study of the sedimentary BC record of the Daihai region of northern China showed
that wildfire increased with the Early Holocene. In the middle Holocene (∼8–3kyr BP), wildfire activity was
greater, which was likely a response to the optimum in regional vegetation development. In the late Holo-
cene, the regional climate was more arid, the vegetation coverage decreased, and the incidence of wildfire
also decreased. Thus there was an overall synchrony between the development of forest vegetation and the
sedimentary record of BC (Wang etal.,2013) (Figure4). A similar relationship was found in a study of sed-
imentary BC and pollen assemblages in the Liangjiacun (LJC) loess profile in Shaanxi, China. In this case,
there was a significant correlation between the concentrations of BC and the percentages of Quercus pollen,
both showing synchronous trends with a gradual increase before 4 kyr BP, followed by a gradual decrease
(Tan etal.,2018). A record of BC in the sediments of the East China Sea, which was used to produce a 7-kyr
fire history for the Yangtze River Basin in central China, indicated that before 3kyr BP, wildfire occurrence
was mainly controlled by temperature and precipitation, but that subsequently wildfire may have been en-
hanced by human activity; however, after 7kyr BP both the sedimentary BC content and the vegetation cover
continued to decline (Pei etal.,2020). In the sediments of Mugeco Lake in Sichuan, SW China, there was a
consistency between the BC content and the pollen record. The BC content and the pollen sum of deciduous
and coniferous trees peaked at ∼10kyr BP and then decreased gradually (Sun etal.,2016). From these in-
vestigations we conclude that the correspondence between the incidence of wildfire and vegetation develop-
ment observed at Gonghai Lake is wildly representative of a large area that are widely involved in the EASM
region and the Indian monsoon region. So, in the Asian Summer Monsoon (ASM) region, forest vegetation is
the primary fuel source for wildfire and hence it is major control of regional wildfire under natural condition.
Based on an analysis of the BC content of a well-dated sediment core from the EASM region of China,
together with comparable records from elsewhere in China, we conclude that the biofuels reserve is the
most important factor controlling the incidence of wildfire in the monsoon region of China. On millennial
timescales the intensity of regional wildfire activity varied with regional fuel storage conditions, which was
ultimately controlled by the regional precipitation and thus the intensity of the EASM.
By area-weighted calculations, we found that annual global wildfire carbon emissions were rapidly in-
creased with land temperature anomalies in the recent 5yr, are already close to 40% of anthropogenic
fossil fuel emissions (Friedlingstein etal.,2020) (FigureS5). Given the likely continuation of anthropogenic
greenhouse gas emissions and rising global temperatures and the strengthening of the EASM in the future
(Yang etal.,2015), wildfire carbon emission in the monsoon region of China may increase. In this context
the relatively stable relationship during most of the Holocene between climate and vegetation ecosystems,
and the related fluxes of materials and energy, may be disrupted by the rapid warming process (Brown
etal.,2020; Martin et al., 2020). As the Earth system becomes increasingly destabilized and vegetation
systems become more vulnerable, the positive feedback effects of wildfire will be amplified and the planet's
homeostatic ability may be increasingly endangered (Sherwood etal.,2020). The long-term feedback effect
of wildfire on terrestrial ecosystems remains to be fully assessed, to help us get a comprehensive under-
standing about environmental impact of wildfire in the future.
JI ET AL.
10.1029/2021GL094042
7 of 11
19448007, 2021, 16, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021GL094042 by Lanzhou University, Wiley Online Library on [03/07/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License

Geophysical Research Letters
5. Conclusions
We have used a sedimentary record of BC content from Gonghai Lake on the northern marginal zone of
the EASM region to reconstruct a wildfire history for the last ∼14.8 kyr, with the aim of determining the
relationship between climate change and wildfire in North China, under natural conditions. The principal
conclusions are as follows:
JI ET AL.
10.1029/2021GL094042
8 of 11
Figure 4. Comparison of the Holocene wildfire history at various sites in China with tree pollen records from
the same sites. Blue text indicates statistically significant correlations between the sedimentary black carbon (BC)
content and the pollen data. (a) BC concentration and tree pollen records from Daihai Lake (Wang etal.,2013).
(b) BC concentration (this study) and tree pollen record from Gonghai Lake (F. Chen, Xu, etal.,2015). (c) BC soot
concentration and Quercus pollen percentages in the LJC loess profile (Tan etal.,2018). (d) BC concentration and
Moisture index for the Yangtze River Basin (core EXMZ) (Pei etal.,2020). (e) BC concentration and the sum of
deciduous and coniferous pollen at Mugeco Lake (Sun etal.,2016).
19448007, 2021, 16, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021GL094042 by Lanzhou University, Wiley Online Library on [03/07/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License

Geophysical Research Letters
1. Since the last deglaciation wildfire activity in the monsoon region of North China responded on millen-
nial timescales to variation of EASM intensity, the strength of the monsoon(wet climate) drives wildfire.
2. Biofuels reserve was the most important control on the regional wildfire regime in Asian summer mon-
soon region.
3. Increasing ambient temperatures may have increased the probability of wildfire so that enhanced re-
gional wildfire
4. Wildfire carbon emission would increase with the stronger monsoon caused by Global Warming in the
future.
Conflict of Interest
The authors declare no conflicts of interest relevant to this study.
Data Availability Statement
Dating results of GH09B and paleoclimatic data are available in the study by F. Chen, Xu, et al. (2015);
Holocene temperature anomalies of China are available in the study by Fang and Hou(2011); The anhy-
steretic remanent magnetization (ARM) of the sediments of Dali Lake are available in the study by S. Liu
etal.(2015); BC concentration and tree pollen records of Daihai Lake are available in the study by Wang
etal. (2013); BC soot concentration and Quercus pollen percentages in the LJC loess profile are available
in the study by Tan etal.(2018); BC concentration and Moisture index for the Yangtze River Basin (core
EXMZ) are available in the study by Pei etal.(2020); BC concentration and the sum of deciduous and conif-
erous pollen at Mugeco Lake are available in the study by Sun etal.(2016); Global Fire Emission Database
(GFED v4) are available in the study by van der Werf etal.(2017). Black carbon data of Gonghai Lake are
available from https://doi.org/10.6084/m9.figshare.14439425.
References
Abatzoglou, J. T., Williams, A. P., Boschetti, L., Zubkova, M., & Kolden, C. A. (2018). Global patterns of interannual climate-fire relation-
ships. Global Change Biology, 24(11), 5164–5175. https://doi.org/10.1111/GCB.14405
Blaauw, M., & Christen, J. A. (2011). Flexible paleoclimate age-depth models using an autoregressive gamma process. Bayesian Analysis,
6(3), 457–474. https://doi.org/10.1214/11-BA61810.1214/ba/1339616472
Bond, T. C., Doherty, S. J., Fahey, D. W., Forster, P. M., Berntsen, T., DeAngelo, B. J., etal. (2013). Bounding the role of black carbon in the
climate system: A scientific assessment. Journal of Geophysical Research: Atmospheres, 118(11), 5380–5552. https://doi.org/10.1002/
JGRD.50171
Brown, S. C., Wigley, T. M. L., Otto-Bliesner, B. L., Rahbek, C., & Fordham, D. A. (2020). Persistent Quaternary climate refugia are hospices
for biodiversity in the Anthropocene. Nature Climate Change, 10(3), 244–248. https://doi.org/10.1038/S41558-019-0682-7
Cao, J., Rao, Z., Jia, G., Xu, Q., & Chen, F. (2017). A 15 ka pH record from an alpine lake in north China derived from the cycliza-
tion ratio index of aquatic brGDGTs and its paleoclimatic significance. Organic Geochemistry, 109, 31–46. https://doi.org/10.1016/J.
ORGGEOCHEM.2017.02.005
Chen, F., Chen, J., Holmes, J., Boomer, I., Austin, P., Gates, J. B., etal. (2010). Moisture changes over the last millennium in arid cen-
tral Asia: A review, synthesis and comparison with monsoon region. Quaternary Science Reviews, 29(7–8), 1055–1068. https://doi.
org/10.1016/J.QUASCIREV.2010.01.005
Chen, F., Chen, J., Huang, W., Chen, S., Huang, X., Jin, L., etal. (2019). Westerlies Asia and monsoonal Asia: Spatiotemporal differences
in climate change and possible mechanisms on decadal to sub-orbital timescales. Earth-Science Reviews, 192, 337–354. https://doi.
org/10.1016/J.EARSCIREV.2019.03.005
Chen, F., Chen, S., Zhang, X., Chen, J., Wang, X., Gowan, E. J., etal. (2020). Asian dust-storm activity dominated by Chinese dynasty
changes since 2000 BP. Nature Communications, 11(1), 992. https://doi.org/10.1038/S41467-020-14765-4
Chen, F., Xu, Q., Chen, J., Birks, H. J. B., Liu, J., Zhang, S., etal. (2015). East Asian summer monsoon precipitation variability since the last
deglaciation. Scientific Reports, 5(1), 11186. https://doi.org/10.1038/SREP11186
Chen, F., Yu, Z., Yang, M., Ito, E., Wang, S., Madsen, D. B., etal. (2008). Holocene moisture evolution in arid central Asia and its out-of-phase
relationship with Asian monsoon history. Quaternary Science Reviews, 27(3–4), 351–364. https://doi.org/10.1016/j.quascirev.2007.10.017
Chen, J., Chen, F., Feng, S., Huang, W., Liu, J., & Zhou, A. (2015). Hydroclimatic changes in China and surroundings during the Medieval
Climate Anomaly and Little Ice Age: Spatial patterns and possible mechanisms. Quaternary Science Reviews, 107, 98–111. https://doi.
org/10.1016/J.QUASCIREV.2014.10.012
Chen, S., Liu, J., Xie, C., Chen, J., Wang, H., Wang, Z., et al. (2018). Evolution of integrated lake status since the last deglaciation: A
high-resolution sedimentary record from Lake Gonghai, Shanxi, China. Palaeogeography, Palaeoclimatology, Palaeoecology, 496, 175–
182. https://doi.org/10.1016/J.PALAEO.2018.01.035
Chen, Y., Morton, D. C., Andela, N., Van Der Werf, G. R., Giglio, L., & Randerson, J. T. (2017). A pan-tropical cascade of fire driven by El
Niño/Southern Oscillation. Nature Climate Change, 7(12), 906–911. https://doi.org/10.1038/S41558-017-0014-8
Chýlek, P., Johnson, B., Damiano, P., Taylor, K., & Clement, P. (1995). Biomass burning record and black carbon in the GISP2 ice core.
Geophysical Research Letters, 22(2), 89–92. https://doi.org/10.1029/94GL02841
JI ET AL.
10.1029/2021GL094042
9 of 11
Acknowledgments
The authors sincerely thank Editor
Valerie Trouet and three anonymous re-
viewers for their constructive comments
and suggestions on the manuscript.
This work was supported by the Nation-
al Natural Science Foundation of China
(Grant No. 41790421). The authors also
thank Zhiping Zhang, Lin Chen, Has-
san Azarmdal, and Liangliang Zhang
for collecting sediments core, thank
Jan Bloemendal for suggestion about
paper writing, and thank Junfei Wu for
assistance of data analysis.
19448007, 2021, 16, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021GL094042 by Lanzhou University, Wiley Online Library on [03/07/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License

Geophysical Research Letters
Cordova, C. E., Kirsten, K. L., Scott, L., Meadows, M., & Lücke, A. (2019). Multi-proxy evidence of late-Holocene paleoenvironmental
change at Princessvlei, South Africa: The effects of fire, herbivores, and humans. Quaternary Science Reviews, 221, 105896. https://doi.
org/10.1016/J.QUASCIREV.2019.105896
Dickens, A. F., Gélinas, Y., Masiello, C. A., Wakeham, S., & Hedges, J. I. (2004). Reburial of fossil organic carbon in marine sediments.
Nature, 427(6972), 336–339. https://doi.org/10.1038/NATURE02299
Ditas, J., Ma, N., Zhang, Y., Assmann, D., Neumaier, M., Riede, H., etal. (2018). Strong impact of wildfires on the abundance and aging
of black carbon in the lowermost stratosphere. Proceedings of the National Academy of Sciences, 115(50), E11595–E11603. https://doi.
org/10.1073/PNAS.1806868115
Fang, K., Yao, Q., Guo, Z., Zheng, B., Du, J., Qi, F., etal. (2021). ENSO modulates wildfire activity in China. Nature Communications, 12(1),
1764. https://doi.org/10.1038/s41467-021-21988-6
Fang, X., & Hou, G. (2011). Synthetically reconstructed Holocene temperature change in China. Scientia Geographica Sinica, 31(4), 385–
393. (in Chinese). https://doi.org/10.13249/j.cnki.sgs.2011.04.013
Friedlingstein, P., O'Sullivan, M., Jones, M. W., Andrew, R. M., Hauck, J., Olsen, A., etal. (2020). Global carbon budget 2020. Earth System
Science Data, 12(4), 3269–3340. https://doi.org/10.5194/essd-12-3269-2020
Gélinas, Y., Prentice, K. M., Baldock, J. A., & Hedges, J. I. (2001). An improved thermal oxidation method for the quantification of soot/gra-
phitic black carbon in sediments and soils. Environmental Science & Technology, 35(17), 3519–3525. https://doi.org/10.1021/ES010504C
Goldberg, E. D. (1985). Black carbon in the environment: Properties and distribution (pp. 1–198). John Wiley & Sons.
Gustafsson, Ö., Bucheli, T. D., Kukulska, Z., Andersson, M., Largeau, C., Rouzaud, J.-N., etal. (2001). Evaluation of a protocol for the quan-
tification of black carbon in sediments. Global Biogeochemical Cycles, 15(4), 881–890. https://doi.org/10.1029/2000GB001380
Han, Y., An, Z., Marlon, J. R., Bradley, R. S., Zhan, C., Arimoto, R., etal. (2020). Asian inland wildfires driven by glacial–interglacial climate
change. Proceedings of the National Academy of Sciences, 117(10), 5184–5189. https://doi.org/10.1073/PNAS.1822035117
Han, Y., Cao, J., Yan, B., Kenna, T. C., Jin, Z., Cheng, Y., etal. (2011). Comparison of elemental carbon in lake sediments measured by three
different methods and 150-year pollution history in Eastern China. Environmental Science & Technology, 45(12), 5287–5293. https://doi.
org/10.1021/ES103518C
Kuhlbusch, T. A. (1995). Method for determining black carbon in residues of vegetation fires. Environmental Science & Technology, 29(10),
2695–2702. https://doi.org/10.1021/ES00010A034
Lehndorff, E., Wolf, M., Litt, T., Brauer, A., & Amelung, W. (2015). 15,000 years of black carbon deposition – A post-glacial fire record from
maar lake sediments (Germany). Quaternary Science Reviews, 110, 15–22. https://doi.org/10.1016/J.QUASCIREV.2014.12.014
Li, Y., Nielsen, A. B., Zhao, X., Shan, L., Wang, S., Wu, J., & Zhou, L. (2015). Pollen production estimates (PPEs) and fall speeds for major
tree taxa and relevant source areas of pollen (RSAP) in Changbai Mountain, northeastern China. Review of Palaeobotany and Palynolo-
gy, 216, 92–100. https://doi.org/10.1016/J.REVPALBO.2015.02.003
Liu, J., Chen, J., Kandasamy, S., Chen, S., Xie, C., Chen, Q., etal. (2018). A 14.7 Ka record of earth surface processes from the arid-monsoon
transitional zone of China. Earth Surface Processes and Landforms, 43(3), 723–734. https://doi.org/10.1002/ESP.4265
Liu, S., Deng, C., Xiao, J., Li, J., Paterson, G. A., Chang, L., etal. (2015). Insolation driven biomagnetic response to the Holocene Warm
Period in semi-arid East Asia. Scientific Reports, 5, 8001. https://doi.org/10.1038/srep08001
Marlon, J. R., Bartlein, P. J., Daniau, A.-L., Harrison, S. P., Maezumi, S. Y., Power, M. J., etal. (2013). Global biomass burning: A synthe-
sis and review of Holocene paleofire records and their controls. Quaternary Science Reviews, 65(4), 5–25. https://doi.org/10.1016/J.
QUASCIREV.2012.11.029
Martin, J. P. S., Simon, L. L., Kofi, A.-B., & Carolina, C. (2020). Long-term thermal sensitivity of Earth's tropical forests. Science, 368,
869–874. https://doi.org/10.1126/SCIENCE.AAW7578
Osmont, D., Sigl, M., Eichler, A., Jenk, T. M., & Schwikowski, M. (2019). A Holocene black carbon ice-core record of biomass burning in
the Amazon Basin from Illimani, Bolivia. Climate of the Past, 15(2), 579–592. https://doi.org/10.5194/cp-15-579-2019
Pei, W., Wan, S., Clift, P. D., Dong, J., Liu, X., Lu, J., etal. (2020). Human impact overwhelms long-term climate control of fire in the Yangtze
River Basin since 3.0 ka BP. Quaternary Science Reviews, 230, 106165. https://doi.org/10.1016/J.QUASCIREV.2020.106165
Ramsey, C. B. (2008). Deposition models for chronological records. Quaternary Science Reviews, 27(1–2), 42–60. https://doi.org/10.1016/j.
quascirev.2007.01.019
Reimer, P. J., Bard, E., Bayliss, A., Beck, J. W., Blackwell, P. G., Ramsey, C. B., etal. (2009). IntCal09 and Marine09 radiocarbon age calibra-
tion curves, 0–50,000 years cal BP. Radiocarbon, 51(4), 1111–1150. https://doi.org/10.2458/AZU_JS_RC.55.16947
Ridder, N. N., Pitman, A. J., Westra, S., Ukkola, A., Hong, X. D., Bador, M., etal. (2020). Global hotspots for the occurrence of compound
events. Nature Communications, 11(1), 5956. https://doi.org/10.1038/s41467-020-19639-3
Salvadó, J. A., Bröder, L., Andersson, A., Semiletov, I. P., & Gustafsson, Ö. (2017). Release of black carbon from thawing permafrost esti-
mated by sequestration fluxes in the East Siberian Arctic shelf recipient. Global Biogeochemical Cycles, 31(10), 1501–1515. https://doi.
org/10.1002/2017GB005693
Sherwood, S., Webb, M. J., Annan, J. D., Armour, K. C., Forster, P. M., Hargreaves, J. C., etal. (2020). An assessment of Earth's climate
sensitivity using multiple lines of evidence. Reviews of Geophysics, 58, e2019RG000678. https://doi.org/10.1029/2019RG000678
Smith, D. M., Griffin, J. J., & Goldberg, E. D. (1973). Elemental carbon in marine sediments: A baseline for burning. Nature, 241(5387),
268–270. https://doi.org/10.1038/241268A0
Sugita, S. (2007). Theory of quantitative reconstruction of vegetation II: All you need is LOVE. The Holocene, 17(2), 243–257.
https://doi.org/10.1177/0959683607075838
Sun, W., Zhang, E., Shen, J., Chen, R., & Liu, E. (2016). Black carbon record of the wildfire history of western Sichuan Province in China
over the last 12.8 ka. Frontiers of Earth Science, 10(4), 634–643. https://doi.org/10.1007/S11707-015-0546-Z
Tan, Z., Han, Y., Cao, J., Chang Huang, C., & An, Z. (2015). Holocene wildfire history and human activity from high-resolution charcoal
and elemental black carbon records in the Guanzhong Basin of the Loess Plateau, China. Quaternary Science Reviews, 109, 76–87.
https://doi.org/10.1016/J.QUASCIREV.2014.11.013
Tan, Z., Han, Y., Cao, J., Chang Huang, C., Mao, L., Liu, Z., & An, Z. (2018). The linkages with fires, vegetation composition and human
activity in response to climate changes in the Chinese Loess Plateau during the Holocene. Quaternary International, 488, 18–29. https://
doi.org/10.1016/J.QUAINT.2018.03.041
Thevenon, F., Williamson, D., Bard, E., Anselmetti, F. S., Beaufort, L., & Cachier, H. (2010). Combining charcoal and elemental black
carbon analysis in sedimentary archives: Implications for past fire regimes, the pyrogenic carbon cycle, and the human–climate inter-
actions. Global and Planetary Change, 72(4), 381–389. https://doi.org/10.1016/J.GLOPLACHA.2010.01.014
van der Werf, G. R., Randerson, J. T., Giglio, L., van Leeuwen, T. T., Chen, Y., Rogers, B. M., etal. (2017). Global fire emissions estimates
during 1997–2016. Earth System Science Data, 9(2), 697–720. https://doi.org/10.5194/ESSD-9-697-2017
JI ET AL.
10.1029/2021GL094042
10 of 11
19448007, 2021, 16, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021GL094042 by Lanzhou University, Wiley Online Library on [03/07/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License

Geophysical Research Letters
Wang, X., Cui, L., Yang, S., Xiao, J., & Ding, Z. (2019). Human-induced changes in Holocene nitrogen cycling in North China: An isotopic
perspective from sedimentary pyrogenic material. Geophysical Research Letters, 46(9), 4599–4608. https://doi.org/10.1029/2019GL082306
Wang, X., Xiao, J. L., Cui, L. L., & Ding, Z. L. (2013). Holocene changes in fire frequency in the Daihai Lake region(north-central China):
Indications and implications for an important role of human activity. Quaternary Science Reviews, 59, 18–29. https://doi.org/10.1016/J.
QUASCIREV.2012.10.033
Wu, D., Chen, X., Lv, F., Brenner, M., Curtis, J., Zhou, A., etal. (2018). Decoupled early Holocene summer temperature and monsoon pre-
cipitation in southwest China. Quaternary Science Reviews, 193, 54–67. https://doi.org/10.1016/j.quascirev.2018.05.038
Xu, Q., Chen, F., Zhang, S., Cao, X., Li, J., Li, Y., etal. (2017). Vegetation succession and East Asian summer monsoon changes since the
last deglaciation inferred from high-resolution pollen record in Gonghai Lake, Shanxi Province, China. The Holocene, 27(6), 835–846.
https://doi.org/10.1177/0959683616675941
Xu, X., Zhu, Q., Zhou, Q., Liu, J., Yuan, J., & Wang, J. (2018). An improved method for quantitatively measuring the sequences of total or-
ganic carbon and black carbon in marine sediment cores. Journal of Oceanology and Limnology, 36(1), 105–113. https://doi.org/10.1007/
s00343-017-6229-8
Yang, S., Ding, Z., Li, Y., Wang, X., Jiang, W., & Huang, X. (2015). Warming-induced northwestward migration of the East Asian monsoon
rain belt from the Last Glacial Maximum to the mid-Holocene. Proceedings of the National Academy of Sciences, 112(43), 13178–13183.
https://doi.org/10.1073/pnas.1504688112
Zalasiewicz, J., & Williams, M. (2016). Climate change observed impacts on planet Earth. In Chapter 1 – Climate change through Earth's
history (pp. 3–17). Elsevier. https://doi.org/10.1016/B978-0-444-63524-2.00001-4
Zhang, E., Sun, W., Zhao, C., Wang, Y., Xue, B., & Shen, J. (2015). Linkages between climate, fire and vegetation in southwest China during
the last 18.5 ka based on a sedimentary record of black carbon and its isotopic composition. Palaeogeography, Palaeoclimatology, Palae-
oecology, 435(435), 86–94. https://doi.org/10.1016/J.PALAEO.2015.06.004
Zhang, P., Xu, Q., Marie-jose, G., Mu, H., Zhang, Y., & Lu, J. (2017). Research of main plant species's relative pollen productivities and
relevant source area of temperate coniferous and broad-leaved mixed forest in Northern China. Quaternary Sciences, 37(6), 1429–1443.
(in Chinese with English abstract). https://doi.org/10.11928/j.issn.1001-7410.2017.06.24
Zhou, X., Sun, L., Zhan, T., Huang, W., Zhou, X., Hao, Q., etal. (2016). Time-transgressive onset of the Holocene Optimum in the East
Asian monsoon region. Earth and Planetary Science Letters, 456, 39–46. https://doi.org/10.1016/j.epsl.2016.09.052
JI ET AL.
10.1029/2021GL094042
11 of 11
19448007, 2021, 16, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021GL094042 by Lanzhou University, Wiley Online Library on [03/07/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License