Lu et al. Progress in Earth and Planetary Science
https://doi.org/10.1186/s40645-018-0206-5(2018) 5:53

Progress in Earth andPlanetary Science

RESEARCH ARTICLE

Open Access

Biomass burning history in East Asia
during the last 4 million years recorded inelemental carbon variability at IODP site
U1423
Song Lu1* , Tomohisa Irino2 and Yaeko Igarashi3

Abstract
The burning of trees and grasses produces charred particles, such as charcoal and soot, that can be transported over long
distances via winds and rivers to coastal, deltaic, and ocean environments, where they are preserved in sediments.
Charcoal contained in sediments has been widely used as a proxy for biomass burning and human activities as well asclimate change. Charcoal and soot in Cenozoic marine sediments at Integrated Ocean Drilling Program (IODP) Expedition(Exp.) 346 Site U1423 were measured to examine the regional history of biomass burning in East Asia. Charcoal and sootwere measured as elemental carbon (EC) in coarse (> 2 μm) and fine (< 2 μm) fractions using grain size separation byrepeated settling followed by application of a thermal optical transmittance (TOT) method. Organic carbon (OC) was also
quantified during the process. EC and OC in both coarse and fine fractions are higher from 0 to 1.8 Ma and lower from 1.
8 to 4.3 Ma but have large variations, which suggest more frequent or intense biomass burning since 1.8 Ma. Terrestrial
biomass and precipitation could be major controls on the EC supply. Fine EC varies independently from coarse EC, whichsuggests a remote origin of fine EC. Large increases in terrestrial vegetation cover have led to high-temperature burning,which is associated with interglacial stages.

Introduction
Elemental carbon (EC) is a combustion residue defined as“combustion produced black particulate carbon having agraphitic microstructure” (Novakov 1984). Thermal
optical analyses have been widely used as analyticalmethods that could provide reasonable estimates of EC
contents in marine sediments (Buseck et al. 2014). Referring to the previous research results, EC could be definedas the high-temperature component of thermal opticalanalyses, whereas organic carbon (OC) was the
low-temperature component of the analyses. EC is also
called soot, black carbon, charcoal, spheroidal carbonaceous particles, or charged particles (Gustafsson and
Gschwend 1998; Glaser and Amelung 2003; Preston andSchmidt 2006). The chemical properties of EC are stable
and have a long mean residence time in soil (Swift 2001).
* Correspondence: lusong@ees.hokudai.ac.jp
1
Graduate School of Environmental Science, Hokkaido University, N10W5,
Kita-ku, Sapporo 060-0810, Japan
Full list of author information is available at the end of the article

EC generally originates from the residues of fossil fuel orbiomass burning, and the color is dark, mostly nearly
black or brown (Andreae and Gelencsér 2006). The colorof EC allows them to absorb a large amount of radiationenergy in the atmosphere, which has a significant impact
on climate (Buseck et al. 2014; Oshima et al. 2012).
Biomass burning is related to the volume of vegetation, frequency of ignition events, and connectivity of
the fuel bed (Archibald et al. 2012), where these factors
could be controlled by climate change as well as humanactivity. Biomass may be ignited by lightning strikes, volcanic activity, sparks from rockfalls, and spontaneous
combustion. A most important trigger is lightning(Batchelder 1967; Komarek Sr. 1967). Increased precipitation may limit the spreading of fires in wet environments (Bowman et al. 2011; Marlon et al. 2013).
However, precipitation and charcoal content could bedecreased at the same time because a precipitation
decrease could cause a decrease in the frequency of ignition events, such as lightning strikes. Drought conditions© The Author(s). 2018 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, andreproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to
the Creative Commons license, and indicate if changes were made.

Lu et al. Progress in Earth and Planetary Science(2018) 5:53

may lead to reductions in biomass burning by decreasing
vegetation volume and areal cover, breaking the connectivity of the fuel bed, and reducing the frequency of ignition events (Archibald et al. 2012). Based on the HYDE
dataset, it is speculated that the human population before 12 ka in the Asian monsoon area was less than 1
million, and human activities could not have had a large
influence on fire regimes before the Holocene (Marlon
et al. 2013). Therefore, natural conditions, such as climate and vegetation, were the main controlling factorsof EC variability on a million year time scale.
The range of transport of macroscopic EC is limited(Peters and Higuera 2007), although coarse particles ofEC may be transported out of a fire site by water (Scott2010). On the other hand, fine EC can be transported
over long distances as an aerosol (Thevenon et al. 2010).
Previous studies of EC dispersion had shown that morethan 90% of the EC with diameters > 2 μm fell out of theatmosphere, whereas more than 80% of the EC with diameters < 2 μm could remain airborne (Masiello 2004).
The diameter of 2 μm is critical for whether EC particles
can be transported by winds. Research on modern aerosol (Han et al. 2008; Wang et al. 2012; Huang et al.
2014) and past eolian dust variability showed that thesource of fine terrigenous clastic particles in the northPacific was central and northern Eurasia, and their flux
could be a proxy for the continental aridity (Irino andTada 2003) or the length of dust season (Ono and Irino
2004). In this study, the relationship between biomassburning and vegetation (climate) changes in East Asia
on a time-scale longer than 100 ky is examined using
marine sediments that are anticipated to receive biomassburning products from the East Asian monsoon region.
U1423 stratigraphy and samples

Integrated Ocean Drilling Program (IODP) Expedition(Exp.) 346 Site U1423 is located in the eastern part of
the Japan Basin at 41° 41.95′ N, 139° 4.98′ E and wasrecovered from a 1785 m water depth (Fig. 1; Igarashi etal. 2018). Site U1423 is situated on the middle of theslope at Oshima Island and is under the direct influenceof the Tsushima Warm Current (TWC). The TWC flows
toward the Tsugaru Strait and the Soya Strait (Yoon and
Kim 2009). Because the depth of the Soya Strait is only
55 m, sea level changes could significantly affect thestrength of the TWC, which can transport materials
downstream.
The sediment cores taken from Site U1423 extend
from the Holocene to the early Pliocene and are dominated by clay, silty clay, and diatom ooze. The depth
scales used during the cruise were CSF-A, CCSF-A, and
CCSF-D (Tada et al. 2015). CSF-A is the depth (m)drilled from the sea floor regardless of potential gaps
and overlaps between cores. Because more than one hole

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was drilled at each site during Exp. 346, the core gaps
recognized at one hole were fulfilled with the corresponding interval found at an adjacent hole, and a composite depth scale (CCSF-A) was defined by adjusting
the original drilled depth (CSF-A) for each hole. Splicing
continuous intervals from the multi-hole sequences, asingle continuous sediment sequence was established,
the depth scale of which was called CCSF-D. The sediment sequence is divided into two units based on lithology (Tada et al. 2015). Unit I (0–107 m CCSF-D)
mainly consists of silty clay and clay, exhibiting cycles ofdark (organic matter rich) and light (organic matterpoor) colored layers. Unit II (107–240 m CCSF-D)
mainly consists of diatomaceous silty clay, clay, and diatom ooze, which is homogeneous or bioturbated.
The initial stratigraphic frameworks and spliced depth
scale (m CCSF-D) established onboard were mainly
based on the sediments’ physical properties, such ascolor (RGB or reflectance spectrum and colorimetry(RSC)), gamma-ray attenuation density (GRA), natural
gamma-ray radiation (NGR), and magnetic susceptibility(MS). However, disturbances in the half cut core, suchas Styrofoam (filled for voids and interstitial-water/
paleontological sampling intervals), core liquefaction,
rotated ash layers, scratched surfaces, deformations, anddrilling faults, can be only recognized by visual inspection, which may lead to noises in the profile of physicalproperties. Such disturbed stratigraphic intervals
involved in the spliced sequence could be removed andreplaced with the corresponding undisturbed intervals
found in the other hole. By these amendments of theoriginal spliced sequence, a nearly continuous sequence
was established (Irino et al. 2018). The revised depth
scale is defined as m CCSF-D_Patched. Using thispatched stratigraphic sequence, we could establish amore accurate stratigraphic framework.
Because the resolution of the initial age model is nothigh and one of the control points is ambiguous (Tadaet al. 2015), the age model for U1423 was also revised.
U1424 is located at the southeastern margin of the Japan
Basin at 40° 11.40′ N, 138° 13.90′ E (Tada et al. 2015)
and is close to Site U1423. Both sites are under the influence of the first branch of the TWC. At Site U1424,
GRA and NGR were tuned onto the LR04 benthic
isotope stratigraphy (Lisiecki and Raymo 2005) by Tada
et al. (2018). We projected this “U1424_LR04 tuned age”
to Site U1423 based on the inter-site correlation using
dark–light cycles (Tada et al. 2018) from 0 to 75 m
CCSF-D_Patched. From 75 to 127 m CCSF-D_Patched,
the GRA density of Site U1423 was directly tuned onto
the LR04 oxygen isotope stratigraphy (Fig. 2; Lisiecki
and Raymo 2005). We used a total of 200 control points
to maintain a high-resolution age model for the last 3
Myr, and the control points are shown in Figs. 2 and 3

Lu et al. Progress in Earth and Planetary Science(2018) 5:53

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Fig. 1 Map showing the studied sea area and location of Site U1423. The locations of ① Site 795, ② Site 794, and ③ Site 797 in Heusser (1992)
and ④ Site GH02–1030 in Igarashi et al. (2011) are also shown (from Igarashi et al. 2018)

and listed in Additional file 1: Table S1. GRA at U1423
could be regarded as a proxy for sea level change in theJapan Sea because a low GRA associated with high diatom content indicates high sea level (Tada et al. 1999).
Below 146.7 m CCSF-D_Patched, age control points
adopted in the cruise report were used (Fig. 3; Tada etal. 2015). The 109 samples between 0 and 200 m
CCSF-D_Patched were collected for this study, which
covered the last 4.3 Myr.

Analytical methods
Sample preparation

Sediments were freeze-dried, after which 100 mg of eachsample were treated with 1.2 N hydrochloric acid atroom temperature overnight to remove carbonate andrinsed with milli-Q water twice to remove salts. The
samples were dispersed in milli-Q water and separated
into < 2 μm (fine fraction) and > 2 μm (coarse fraction)by the repeated settling method (Folk 1980). The fine(2018) 5:53

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Age (Myr)

Age (Myr)

Benthic d18O (per mil) Bulk density (g/cm3)

Benthic d18O (per mil) Bulk density (g/cm3)

Benthic d18O (per mil) Bulk density (g/cm3)

Lu et al. Progress in Earth and Planetary Science

Age (Myr)
Fig. 2 Revised age model for U1423 based on projection of the “U1424_LR04 tuned age” (Tada et al. 2018) to site U1423 by the inter-site correlationof dark-light cycles for the last 1.5 Ma (red inverted triangles) and tuning of the GRA profile to the LR04 stack (vertical lines). Assuming that a high GRA
represents glacial maxima, 118 horizons have been correlated to maxima of the oxygen isotope profile of LR04 for the last 2.975 Myr

Lu et al. Progress in Earth and Planetary Science(2018) 5:53

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Fig. 3 The age-depth relationship of the revised age model for site U1423 used in this study. The age control points from the Expedition Report(Tada et al. 2015) is also indicated by the black dots and lines

fractions were collected on Φ49 mm quartz fiber filters
using suction filtration, while the coarse fractions werecollected by centrifugation at 3000 rpm for 30 min
followed by freeze drying and weighing.
Thermal optical transmittance analysis

The analysis was conducted using a Semi-Continuous
OCEC Carbon Aerosol Analyzer manufactured bySunset Laboratory (Miyazaki et al. 2007) at the Instituteof Low Temperature Science, Hokkaido University. Thisapparatus is equipped with a thermal optical transmittance (TOT) system that uses a highly sensitive analytical method for determining the content of EC. The
contents of EC in both fine and coarse fractions of Site
U1423 samples were measured as a proxy for biomassburning. For the fine fraction, a Φ14 mm part waspunched out from the Φ49 mm quartz fiber filter andcovered with another blank Φ14 mm quartz fiber filter.
For the coarse fraction, a known amount (approximately
10 mg) of the freeze dried fraction was sandwiched bytwo Φ14 mm quartz fiber filters. These preparedΦ14 mm quartz fiber filters were set in the quartz glass
tube of the apparatus.
In this study, we used a temperature protocol basedon that proposed by the Institute of Low Temperature
Science (Miyazaki et al. 2007). A single sample wasplaced immediately into the apparatus. Figure 4a shows

an example thermogram used in this study. The combustion temperature was increased from room
temperature to a high temperature in five steps (250 °C,
350 °C, 550 °C, 750 °C, and 850 °C). The duration ofeach temperature step and heating rate were set as constants and routinely controlled by a computer program.
The ambient environment was a complete helium
atmosphere from 0 to 370 s at three temperature steps(250°, 350°, and 550 °C) to remove non-fire-resistantorganic carbon (OC), and, then, from 371 to 820 s, theatmosphere was switched to a 2% oxygen/helium mixture at temperature steps of 550 °C, 750 °C, and 850 °C
to combust the residual carbon. Carbon fractions
extracted at each temperature step were detected andquantified by a non-dispersive infrared (NDIR) sensor
and defined as six carbon fractions from C1 to C6(Fig. 4a). From 821 s, a fixed volume of methane wasinjected into the quartz tube, providing a known quantity of carbon. The carbon amount of the introduced
methane was calibrated using sucrose standards before
measurement.
During the entire combustion sequence above, lasertransmission was also monitored to determine how theblackness of the sample filter changed (Fig. 4a). The
laser transmission data generated by the apparatus werenecessary to calibrate for its temperature dependency
and convert the value to a “transmission ratio,” whereLu et al. Progress in Earth and Planetary Science(2018) 5:53

Page 6 of 13abFig. 4 a An example thermal optical transmittance (TOT) thermogram. Temperature change is represented as red line, and the corrected laser transmission
ratio is represented by orange line. The carbon fraction detected by NDIR response is represented as black line. b The relationship between the ambient
temperature and the original laser transmission generated by a Semi-Continuous OCEC Carbon Aerosol Analyzer manufactured by Sunset Laboratory. The
temperature dependency of the raw laser transmission values was calibrated using a quadratic relationship, with the ambient temperatures
shown as red dots

the laser transmission with no carbon fraction (after themeasurement sequence) was set to unity (Fig. 4a). The
relationship between the laser transmission andtemperature can be expressed as a quadratic function(Fig. 4b; red dots), where all the “black” carbon materials
had been removed. The quadratic function could provide
the laser transmission value anticipated at a temperature
with no “black” carbon in the sample. The laser transmission at each temperature during the measurement
was divided by this anticipated laser transmission value,
which yielded the “transmission ratio.” Under the helium

atmosphere, part of the carbon was charred, the sample
became darker, and the laser transmission ratio decreased. Then, under an oxygen atmosphere, charredcarbon was burned, and the laser transmission ratio wasrecovered to the original level. We defined the carbon
generated from 0 s to this time as OC, and the carbon
extracted between the time when the laser transmission
was recovered to the original level and 820 s was
regarded as EC (Fig. 4a).
Analytical errors were introduced during the determination of carbon amount and the distinction of OC

Lu et al. Progress in Earth and Planetary Science(2018) 5:53

and EC. The uncertainty during carbon determination
was ± 1.8 μgC for a single measurement, whereas theerror related to distinguishing OC-EC was ± 0.4 μgC due
to the uncertainty of the initial laser transmission.
Depending on the sample amount (~ 10 mg and 10–30 mg for coarse and fine fractions, respectively) collected on the quartz fiber filter, the total EC determination errors were ± 0.22 mgC/g sediment for the coarse
fraction and ± 0.7 mgC/g sediment for the fine fraction.

Results
The contents of OC and EC during the last 4.3 Myr at
Site U1423 are shown in Fig. 5a, b, respectively. The
contents of OC and EC are high in subunit IA (0–1.8 Ma) and decrease rapidly downward in the upper
part of subunit IB (1.8–2.2 Ma), and low levels are maintained in aubunits IIA (2.2–3.0 Ma) and IIB (> 3.0 Ma).
OC and EC in the coarse (> 2 μm) fraction are 5–10
times higher than those in the fine (< 2 μm) fraction.
The OC content is much higher than the EC content of
the coarse fraction, whereas the EC content of the fine
fraction is occasionally much higher than the OC content. The content of coarse EC is steady in subunit IIB(> 3.0 Ma), whereas the content of fine EC shows significant fluctuations in the same subunit.

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To compare the data showing different absolute values
and dynamic ranges, conversions of raw data into standard scores (Z-score) were conducted and are shown in
Fig. 5c. Photo RGB-B can be used as a proxy for sediment brightness, which is also shown in Fig. 5c. In general, the contents of coarse OC and EC are high in thedark layers and low in the light layers for all the lithological units. The high OC contents in the fine fraction
are not necessarily associated with low sedimentbrightness.

Discussion
Sediment brightness and carbon content

The general tendency that high coarse OC and EC areassociated with darker color layers (Fig. 5c) suggests a
significant effect of OC-EC supply to the dark layer
formation in spite of a potential influence of carbonate
fraction on the sediment brightness. However, the sediment at Site U1423 had only a small amount of calcium
carbonate content ranging from 0.2 to 1.0 wt% (average
0.4 wt%; Tada et al. 2015), and the high calcium carbonate contents were exceptional and restricted only inseveral layers rich in foraminifers, whose calcium
carbonate contents were up to 14 wt%. Therefore, thecalcium carbonate at this site could have a weak effectFig. 5 Temporal variations in EC (a) and OC (b) contents and the relationship between Z-scores of brightness and carbon contents in the coarse
fraction (c), abundance of Taxodiaceae pollen (d), and Tp value (e) at site U1423. EC and OC in the coarse fraction are represented as black solidline. EC and OC in the fine fraction are represented as red solid line. Z-scores for OC content, EC content, and brightness (RGB-B) are shown as
black solid line, red solid line, and gray shades, respectively. The proportion of Taxodiaceae and Tp are shown as blue shades and orange
shades, respectively

Lu et al. Progress in Earth and Planetary Science(2018) 5:53

on the brightness of sediments, whereas the OC and EC
contents in the coarse fraction could be major controlling factors of sediment brightness.
Previous reports have also shown that the high organic
matter contents in the sediments of the Japan Sea werecorrelated to the dark layers that were deposited during
interstadials due to stronger summer monsoon precipitation (Tada et al. 1999). Research on fire-regime indicates that the EC content is controlled by fire intensity,
which could be related to climate as well as fuel typeand load (terrestrial vegetation; Iglesias and Whitlock2014), and coarse EC particles (> 2 μm), such as
charcoals, are usually an important part of river suspended solids (C. A. Masiello and Druffel 2001; Schmidt
et al. 2002). The dark layers at Site U1423 also containhigher coarse EC as well as OC, while the light layers
contain lower amounts. This observation suggested thatcoarse EC was generated by more frequent paleofires innorthern Japan and transported by river during interstadials rather than during stadials. During the interstadials,
higher summer precipitation could have promoted alarger terrestrial biomass in northern Japan, and thelarge amounts of fuel load were consumed, which produced rich EC.
Pollen assemblage and carbon contents

The pollen assemblage could reveal more information
on vegetation and climate. Here, we compared ourEC analysis results with pollen assemblage data collected from the same sample set (Igarashi et al.
2018). To understand the relationship between OC/
EC supply to Site U1423 and paleoclimate, we examine the proportion of broadleaf (Tw) and the sum of
broadleaf (Tw) and conifer (Tc), which is defined as
Tp% (= [Tw / (Tw + Tc)] × 100); Fig. 5e). Tp was
regarded as a proxy of air temperature, while Taxodiaceae% was considered to be a precipitation proxy(Igarashi et al. 2018; Fig. 5d). Using these two pollen
proxies, we classified climatic regime into four categories, which were cool-dry, cool-wet, warm-dry, andwarm-wet. The threshold used to distinguish the cooland warm categories was set to a median value of
Tp%, whereas that for the cool and warm categories
was set to the median value of Taxodiaceae%. Because
each sample was attributed to its own climate
category, we calculated the average OC and EC contents for each climate category shown in Table 1.
Coarse OC was higher during warm climates than incool climates, regardless of dry/wet conditions. The
content of fine OC/EC was not sensitive to any of
the climate categories. On the other hand, coarse EC
shows higher values under a wet condition thanunder a dry condition, although there was no significant difference between cool and warm conditions.

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Table 1 The averages of OC and EC contents for the four climatic
categories
Dry

Wet

Cool

5.6

5.5

Warm

7.5

8.7

Cool

0.8

1.2

Warm

0.9

1.4

Cool

2.1

2.5

Warm

1.9

2.7

Cool

0.3

0.4

Warm

0.3

0.4

Coarse OC (mg/g)

Coarse EC (mg/g)

Fine OC (mg/g)

Fine EC (mg/g)

This suggests that precipitation might be a potential
control on coarse EC supplied to Site U1423.
The total pollen number was a proxy for the volumeof terrestrial vegetation that could be a major part ofbiomass fuel load for fires. The relationship between
pollen count and coarse EC content shows a weak positive correlation (R2 = 0.417, p < 0.001; Fig.6), with an
exceptional outlier with high pollen number (92,022/g)
and low coarse EC (0.689 mg/g). Despite the weak positive correlation between them, a larger biomass or highbiomass fuel load could be a first-order control oncoarse EC supply. The relationship between total number of pollen and fine EC content shows no significant
correlation (not shown).
The Taxodiaceae% is a proxy for humid climate (Igarashi et al. 2018). Figure 5d shows that Taxodiaceae%
shows rapid and intense changes in unit I (0–2.2 Ma)
but becomes flat in unit II (> 2.2 Ma), which is consistent with the variabilities of coarse EC (Fig. 5a) and sediment brightness (RGB-B) (Fig. 5c). Coarse EC also
shows a weak positive correlation with Taxodiaceae%(R2 = 0.230, p < 0.001; Fig. 7), which suggests that heavy
rain after a wildfire could also carry abundant EC to thesea through the rivers (Scott 2010). In the case of highcoarse EC associated with low precipitation (Taxodiaceae%; Fig. 7), a time lag between EC generation andtransport might be responsible. Based on a study ofpotential charcoal source areas, the coarse EC comesfrom local fires (Peters and Higuera 2007), and soils act
as an intermediate stage for the aging of EC prior to deposition in the ocean (Schmidt et al. 2002).
Factors controlling EC grain size

Fine EC content varies independently from coarse EC
content (Fig. 5a), which suggests a remote origin of fineEC. The fine particles of EC might be transported out of

Lu et al. Progress in Earth and Planetary Science(2018) 5:53

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Fig. 6 Relationship between pollen content and EC content in the coarse fraction at site U1423. The gray lines represent the 95% of confidence
interval envelopes

a fire site by wind, which is different from coarse EC(Scott 2010). In particular, canopy fires can produce fineEC particles that are susceptible to wind dispersal. Taking into account the fact that the fine particles could betransported over long distances as aerosols, unusuallyhigh contents of fine EC suggest contributions fromremote fires. Wildfires occur mainly in spring and autumn in East Asia because fires are mostly triggered by asudden change in environment. Usually autumn and late
winter or early spring experience numerous wildfires.
Therefore, fine EC and Asian Dust could have similartransport processes. Based on modern aerosol research(Huang et al. 2014) and high-resolution variations ineolian dust research (Irino and Tada 2003), eastern andnorthwest China and Mongolia could be sources of fineEC. Strong westerly winds can carry large amounts offine particulate matter over long distances and could
finally deposit them in the Japan Sea.
Our high-resolution age model covers the last 3
Myr, which enables us to examine the relationship between EC grain size and glacial–interglacial cycles. Six
maxima events in fine EC/coarse EC occurred during
interglacial (low GRA) intervals (Fig. 8). In interglacial
stages, large-scale terrestrial vegetation could provide
ample loads of fuel and higher chances for ignition

events, where lightning might be a main ignition
event (Marlon et al. 2013). These conditions could
provide the possibility of large-scale biomass burning,which could generate fine elemental carbon in East
Asia. We note that the high interglacial precipitation
was not sufficiently powerful to drive a linear change
in local fires (Fig. 6), and their correlation was weak.
When precipitation exceeded a threshold, it may suppressed or promoted fires. However, it is difficult toquantify this threshold simply by relying on current
pollen data. Such large-scale biomass burning at a remote fire site could have served as a fine EC supply
for Site U1423.
A set of second-highest peaks of Fine EC/Coarse EC
appeared in the glacial stages, which were found during267~279 ka and 358~370 ka (Fig. 8). Lower peaks also
appeared in the glacial stages, which were found during
1.60~1.63 Ma and 2.11~2.13 Ma (Fig. 8). Under normal
circumstances, the amount of coarse EC is much higher
than that for fine EC. Changes in wind strength could
significantly affect fine EC flux. Therefore, these exceptionally high fine EC contents suggest a special condition of enhanced winds during particular glacial stages,
which corresponded to MIS 8, MIS 10, MIS 56, andMIS 80.

Lu et al. Progress in Earth and Planetary Science(2018) 5:53

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Fig. 7 Relationship between Taxodiaceae and EC content in the coarse fraction at site U1423. The gray lines represent the 95% of confidence
interval envelopes

Fig. 8 Temporal variation of fine EC/course EC and LR04 standard benthic δ18O (Lisiecki and Raymo 2005. Significant maxima observed in temporalvariations of fine EC/coarse EC are marked as blue and red vertical lines that correspond to glacial and interglacial stages, respectively

Lu et al. Progress in Earth and Planetary Science(2018) 5:53

The strong winds during glacial stages could carrygreat amounts of terrigenous clastic particles, which
could cause abnormal increases in the contents of certain terrestrial substances, such as freshwater diatoms(Pokras and Mix 1987; Verardo and Ruddiman 1996).
During the glacial period, the surface of mainland China
was heavily weathered, and a large number of debris particles were formed. Under the influence of strong winds,
this newborn terrigenous clastic debris could have beentransported into the ocean. The wind strength or direction during glacial stages could also affect the change intempo of charcoal deposition (Verardo and Ruddiman
1996). The biomass burning was relatively stable on theloess plateau (Zhou et al. 2007) for MIS 8 and MIS 10.
Coarse particle content increased significantly on theloess plateau at MIS 8 and MIS 10 (Sun et al. 2003),
and, at the same time, the mean grain size of bulk sample data also indicates a stronger East Asian winter monsoon (Sun et al. 2006). Based on particle sizes and themagnetic susceptibility of the Loess Plateau, weakersummer and stronger winter monsoons were suggested
during MIS 8 and MIS 10 (Wang 2003; Hao et al. 2012).
At MIS 56 and MIS 80, the magnetic susceptibility of
the Loess Plateau shows a slightly stronger winter monsoon (Nie et al. 2008). Although the fine EC concentration increased during those particular glacial phases, itdoes not necessarily mean that the biomass burning or
fuel load had increased. The strong winds could havecarried land-deposited EC particles into the ocean.

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Benefitting from the strong winter monsoon in the surrounding area, larger supplies of fine EC to Site U1423
could have been realized during MIS 8, MIS 10, MIS 56,
and MIS 80.
Paleoenvironment and high-temperature paleofires

Based on the principle of the TOT method, the ratio
between the sixth carbon fraction (C6) and the total elemental carbon (EC) could be an index of thehigh-temperature component of EC. The sixth carbon
fraction (C6) is a refractory component of EC, and its formation conditions could be those of high-temperature
combustion. When this index increases, the biomassburning temperature could be higher. Ordinary temperatures in biomass burning are approximately 400 °C,
whereas canopy fires can be much hotter (more than 800 °C; Scott 2010). Our high-resolution age model for U1423
covers the last 3 Myr, and we can also examine the relationship between the C6/EC variability and glacial–interglacial cycles (Fig. 9).
Local high-temperature paleofires suggested bycoarse EC were more frequent than remotehigh-temperature paleofires suggested by fine EC (Fig.
9). One maximum of C6/EC in both coarse and fine
fractions appeared in the glacial stage, which was
found during 57~68 ka (Fig. 9; blue vertical line). Remote high-temperature paleofire maxima of fine C6/
EC also occurred at approximately 548~560 ka,
1.0 Ma, and 1.7 Ma in glacial stages (Fig. 9; blue

Fig. 9 LR04 standard benthic δ18O (Lisiecki and Raymo 2005) and C6/EC in fine and coarse fractions. The significant maxima observed in thehigher temperature biomass burning proxy (C6/EC) in coarse and fine fractions are marked as blue and red vertical lines corresponding to glacial
and interglacial stages, respectively

Lu et al. Progress in Earth and Planetary Science(2018) 5:53

vertical lines). In most cases, however, maxima of C6/
EC in coarse and fine fractions have very similar
trends, and they mostly occurred in the interglacial
stages (Fig. 9; red vertical lines).
These facts suggest that local high-temperature
paleofires occurred more frequently during interglacial
stages in northern Japan. Remote high-temperature
paleofires also exhibited an enhanced trend during
interglacial stages, and some glacial stages also show
the signal of remote high-temperature burning. However, burning at high temperatures is difficult in acold and dry environment. The sizes of biomass fuelloads during glacial times might have been very small
and were insufficient for large-scale biomass burningor high-temperature burning. Therefore, apparent increases in remote high-temperature burning might be
attributed to the fact that the winter monsoon carried
the old (interglacial) high-temperature EC particles.

Conclusions
During the last 4.2 million years, coarse EC wereenriched in interglacial stages or interstadials withstronger East Asian summer monsoons, suggestingthat the volume of terrestrial plants affected fire
intensity. Larger biomasses or high biomass fuel loads
in northern Japan were dominant controls on coarse
EC content. Therefore, a wet climate was preferable
for coarse EC supplies to IODP Site U1423. The intensity of a local fire also depends on the local fuelload, which contains not only newborn vegetation but
also dead but not decomposed vegetation. This meansthat the local fuel loads could have been high at the
beginning of the glacial stages, which would have led
to exceptionally high concentrations of coarse EC
during glacial stages with apparent low terrestrial
biomass.
The independent behavior of fine EC from that ofcoarse EC suggests its remote origin. Considerable
amounts of biomass burning in the remote source area
during interglacial stages or the wind strength or direction preferable for fine EC emissions from East Asia during glacial stages could have caused unusually high fineEC/coarse EC. Although remote fires were suppressed
during the glacial stage, high concentrations of fine EC
could be expected because of the intense erosion of soils
formed during the previous interglacials and windtransport.
The high-temperature component of coarse and fine
EC could be associated with interglacial stages due topreferable burning conditions, with some exceptions. Exceptional maxima of the high-temperature componentof fine EC might also be attributed to the reworking ofolder EC formed during the previous interglacials.

Page 12 of 13

Additional file
Additional file 1: Table S1. The control points for the revised age model.
(XLS 42 kb)

Abbreviations
CCSF-D: Core composite depth; EC: Elemental carbon; GRA: Gamma-ray
attenuation density; IODP: Integrated Ocean Drilling Program; MS: Magnetic
susceptibility; NDIR: Non-dispersive infrared sensor; NGR: Natural gamma-ray
radiation; OC: Organic carbon; RSC: Reflectance spectrum and color; TOT: Thermal
optical transmittance; Tp: The pollen temperature index; Tw: The sum of
broadleaf; Tc, the sum of conifer
Acknowledgements
The research included in this paper could not been performed without theassistance and supports from Profs. Atsuko Sugimoto, Hisayuki Yoshikawa,
Masanobu Yamamoto, Youhei Yamashita, Ken Sawada in Hokkaido University,
Ryuji Tada in University of Tokyo, and Dr. Ken Ikehara in Geological Survey ofJapan, AIST. And many thanks also go to Profs. Kimitaka Kawamura, Yuzo
Miyazaki, and Ms. Eri Tachibana in Institute of Low Temperature Science,
Hokkaido University for allowing us to use thermal optical transmittance (TOT)system and their instructions. We would also like to acknowledge constructive
feedback provided by four anonymous reviewers as well as editor. This research
was financially supported by JSPS KAKENHI Grant Number 26287130 (to Ken
Sawada) and IODP Exp. 346 After Cruise Research Program, JAMSTEC.
The JpGU classifies reviews and articles into the following six science
sections: (1) space and planetary sciences; (2) atmospheric and hydrosphericsciences; (3) human geosciences; (4) solid earth sciences; (5) biogeosciences;or (6) interdisciplinary research.
Funding
This research was financially supported by JSPS KAKENHI Grant Number
26287130 (to Ken Sawada) and IODP Exp. 346 After Cruise Research Program,
JAMSTEC.
Availability of data and materials
Please contact author for data requests.
Authors’ contributions
SL and TI proposed the topic, conceived and designed the study. SL carriedout the experimental study for EC and OC concentrations. TI provided therevised depth scale for U1423. The high-resolution age model for U1423 wascreated by SL under supervision of TI. YI provided her own pollen data andadvised for the interpretation. All authors read and approved the final
manuscript.
Authors’ information
LU Song was a master course student at Graduate School of Environmental
Science, Hokkaido University under supervision by IRINO Tomohisa. This
paper is a main part of master thesis and the study at 1st year doctor courseof LU Song.
Competing interests
The authors declare that they have no competing interests. All institutionaland national guidelines for the care and use of laboratory animals were
followed.

Publisher’s NoteSpringer Nature remains neutral with regard to jurisdictional claims inpublished maps and institutional affiliations.
Author details
1
Graduate School of Environmental Science, Hokkaido University, N10W5,
Kita-ku, Sapporo 060-0810, Japan. 2Faculty of Environmental Earth Science,
Hokkaido University, N10W5, Kita-ku, Sapporo 060-0810, Japan. 3Institute for
Paleoenvironment of Northern Regions, Koyocho 3-7-5, Kitahiroshim
061-1134, Japan.

Lu et al. Progress in Earth and Planetary Science(2018) 5:53

Received: 1 October 2017 Accepted: 15 August 2018

References
Andreae MO, Gelencsér A (2006) Black carbon or brown carbon? The nature oflight-absorbing carbonaceous aerosols. Atmos Chem Phys Discuss 6(3):3419–
3463 Retrieved (https://doi.org/10.5194/acp-6-3131-2006)
Archibald S, Staver AC, Levin SA (2012) Evolution of human-driven fire
regimes in Africa. Proc Natl Acad Sci 109(3):847–852 Retrieved (http://
www.pnas.org/content/109/3/847.abstract%5Cnhttp://www.pnas.org/
content/109/3/847.full.pdf)
Batchelder RB 1967. Spatial and temporal patterns of fire in the tropical world.
Proceedings Annual (6th) Tall Timbers Fire Ecology Conference (June 1966).
6:171–207.
Bowman DMJS et al (2011) The human dimension of fire regimes on earth. J
Biogeogr 38(12):2223–2236
Buseck PR, Adachi K, Gelencsér A, Tompa É, Pósfai M (2014) Ns-Soot: a materialbased term for strongly light-absorbing carbonaceous particles. Aerosol Sci
Technol 48(7):777–788 Retrieved (https://doi.org/10.1080/02786826.2014.
919374)
Folk RL 1980. Petrologie of sedimentary rocks. 3, p. 15-24. Hemphll Publishing
Company, Austin 170
Glaser B, Amelung W (2003) Pyrogenic carbon in native grassland soils along a
climosequence in North America. Glob Biogeochem Cycles 17(2):n/a Retrieved(https://doi.org/10.1029/2002GB002019)
Gustafsson O, Gschwend PM (1998) The flux of black carbon to surface
sediments on the New England continental shelf. Geochim Cosmochim Acta
62(3):465–472
Han YM et al (2008) Distribution and origin of carbonaceous aerosol over a rural
High-Mountain Lake area, northern China and its transport significance.
Atmos Environ 42(10):2405–2414
Hao Q et al (2012) Delayed build-up of Arctic ice sheets during 400,000-year
minima in insolation variability. Nature 490(7420):393–396 Retrieved (https://doi.org/10.1038/nature11493)
Huang J, Wang T, Wang W, Li Z, Yan H (2014) Climate effects of dustaerosols
over East Asian arid andsemiarid regions. J Geophys Res, 119:11,398–11,416,
https://doi.org/10.1002/2014JD021796
Igarashi Y, Irino T, Sawada K, Lu S, Furota S (2018) Fluctuations in the East Asianmonsoon recorded by pollen assemblages in sediments from the Japan Sea
off the southwestern coast of Hokkaido, Japan from 4.3 ma to the present.
Glob Planet Chang 163:1–9 (https://doi.org/10.1016/j.gloplacha.2018.02.001)
Iglesias V, Whitlock C (2014) Fire responses to postglacial climate change andhuman impact in Northern Patagonia (41–43°S). Proc Natl Acad Sci U S A
111(51):E5545–E5554 Retrieved (https://doi.org/10.1073/pnas.1410443111)
Irino T, Tada R (2003) High-resolution reconstruction of variation in Aeolian dust
(Kosa) deposition at ODP site 797, the Japan Sea, during the last 200 Ka.
Glob Planet Chang 35(1–2):143–156
Irino T, Tada R, Ikehara K, Sagawa T, Karasuda A, Kurokawa S, Seki A, Lu S (2018)
Construction of perfectly continuous records of physical properties for darklight sediment sequences collected from the Japan Sea during Integrated
Ocean Drilling Program Expedition 346 and their potential utilities as
paleoceanographic studies. Prog Earth Planet Sci 5:23. https://doi.org/10.
1186/s40645-018-0176-7
Komarek EV Sr (1967) The nature of Lightning fires. Proc, Annual Tall Timbers
Ecology Conference 7:5–41
Lisiecki LE, Raymo ME (2005) A Pliocene-Pleistocene stack of 57 globally
distributed Benthic ?? 18O records. Paleoceanography 20(1):1–17
Marlon JR et al (2013) Global biomass burning: a synthesis and review of
Holocene Paleofire records and their controls. Quat Sci Rev 65:5–25 Retrieved(http://dx.doi.org/10.1016/j.quascirev.2012.11.029)
Masiello C a (2004) New directions in black carbon organic geochemistry. Mar
Chem 92(1–4):201–213
Masiello CA, Druffel ER (2001) Carbon isotope geochemistry of the Santa Clara
River. Glob Biogeochem Cycles 15(2):407–416
Miyazaki Y et al (2007) Chemical characteristics of water-soluble organic carbon
in the Asian outflow. Journal of Geophysical Research Atmospheres 112(22):
1–18
Nie J et al (2008) Link between benthic oxygen isotopes and magnetic
susceptibility in the red-clay sequence on the Chinese Loess Plateau.
Geophys Res Lett 35(3):L03703 Retrieved (http:/ doi:10.1029/2007GL032817,
2008)

Page 13 of 13

Novakov T (1984) The role of soot and primary oxidants in atmosphericchemistry. Sci Total Environ 36(C):1–10
Oshima N et al (2012) Wet removal of black carbon in Asian outflow: aerosol
Radiative forcing in East Asia (A-FORCE) aircraft campaign. J Geophysical Res
Atmospheres 117(3):1–24
Peters ME, Higuera PE (2007) Quantifying the source area of macroscopic
charcoal with a particle dispersal model. Quat Res 67(2):304–310
Pokras EM, Mix AC (1987) Earth’s precession cycle and quaternary climaticchange in tropical Africa. Nature 326(6112):486–487 Retrieved September 29,
2017 (https://doi.org/10.1038/326486a0
Preston CM, Schmidt MWI (2006) Black (pyrogenic) carbon: a synthesis of current
knowledge and uncertainties with special consideration of boreal regions.
Biogeosciences 3(4):397–420
Schmidt MW, Skjemstad JO, Jäger C (2002) Carbon isotope geochemistry andnanomorphology of soil black carbon: black chernozemic soils in Central
Europe originate from ancient biomass burning. Glob Biogeochem Cycles
16(4):70–1–70–78 Retrieved (https://doi.org/10.1029/2002GB001939)
Scott AC (2010) Charcoal recognition, taphonomy and uses inpalaeoenvironmental analysis. Palaeogeogr Palaeoclimatol Palaeoecol 291(1–2):11–39 Retrieved (http://dx.doi.org/10.1016/j.palaeo.2009.12.012)
Sun X, Luo Y, Huang F, Tian J, Wang P (2003) Deep-sea pollen from the South
China Sea: Pleistocene indicators of East Asian monsoon. Mar Geol 201(1–3):
97–118Sun Y et al (2006) East Asian monsoon variability over the last seven glacial
cycles recorded by a loess sequence from the northwestern Chinese loessplateau. Geochem Geophys Geosyst 7(12):1–16
Swift RS (2001) Sequestration of carbon by soil. Soil Sci 166(11):858–871 Retrieved(https://journals.lww.com/soilsci/Fulltext/2001/11000/SEQUESTRATION_OF_
CARBON_BY_SOIL.10.aspx)
Tada R, Irino T, Ikehara K, Karasuda A, Sugisaki S, Xuan C, Sagawa T, Itaki T, Kubota
Y, Lu S, Seki A, Murray RW, Alvarez-Zarikian C, Anderson WT Jr, Bassetti M-A,
Brace BJ, Clemens SC, da Costa Gurgel MH, Dickens GR, Dunlea AG, Gallagher
SJ, Giosan L, Henderson ACG, Holbourn AE, Kinsley CW, Lee G-S, Lee K-E, Lofi
J, Lopes CICD, Saavedra Pellitero M, Peterson LC, Singh RK, Toucanne S, Wan
S, Zheng H, Ziegler M (2018) High-resolution and -precision correlation ofdark and light layers in the quaternary hemipelagic sediments of the Japan
Sea recovered during IODP expedition 346. Prog Earth Planet Sci 5:19 DOI:
10.1186/s40645-018-0167-8
Tada R, Irino T, Koizumi I (1999) Land-ocean linkages over orbital and millennial
timescales recorded in Late Quaternary sediments of the Japan Sea.
Paleoceanography 14(2):236–247
Tada R et al. 2015. Expedition 346 Scientists (2015) Site U1423. 346, Proceedingsof the Integrated Ocean Drilling Program, Volume 346 Retrieved (https://doi.
org/10.2204/iodp.proc.346.104.2015).
Thevenon F et al (2010) Combining charcoal and elemental black carbon analysis
in sedimentary archives: implications for past fire regimes, the pyrogenic
carbon cycle, and the human-climate interactions. Glob Planet Chang 72(4):381–389 Retrieved (http://dx.doi.org/10.1016/j.gloplacha.2010.01.014)
Verardo DJ, Ruddiman WF (1996) Late Pleistocene charcoal in tropical Atlantic
Deep-Sea sediments: climate and geochemical significance. Geology 24(9):855–857
Wang P (2003) Evolution of the South China Sea and monsoon history revealed
in deep-sea records. Chin Sci Bull 48(23):2549,https://doi.org/10.1360/
03wd0156
Wang R et al (2012) Black carbon emissions in China from 1949 to 2050. Environ
Sci Technol 46(14):7595–7603 Retrieved September 25, 2017Retrieved (https://doi.org/10.1021/es3003684)
Yoon JH, Kim YJ (2009) Review on the seasonal variation of the surface
circulation in the Japan/East Sea. J Mar Syst 78(2):226–236 Retrieved (http://dx.doi.org/10.1016/j.jmarsys.2009.03.003)
Zhou B et al (2007) Elemental carbon record of Paleofire history on the Chinese
loess plateau during the last 420 Ka and its response to environmental andclimate changes. Palaeogeogr Palaeoclimatol Palaeoecol 252(3–4):617–625