Seki et al. Progress in Earth and Planetary Science
https://doi.org/10.1186/s40645-018-0244-z(2019) 6:1

Progress in Earth andPlanetary Science

RESEARCH ARTICLE

Open Access

High-resolution Quaternary record ofmarine organic carbon content in thehemipelagic sediments of the Japan Sea
from bromine counts measured by XRF
core scanner
Arisa Seki1* , Ryuji Tada2, Shunsuke Kurokawa2 and Masafumi Murayama3

Abstract
The marine organic carbon content in sediments is a useful tool for reconstructing past productivity in the ocean.
Bromine has been proposed as a useful proxy for marine organic carbon, since bromine is more concentrated inmarine organic matter compared to terrestrial organic matter.
Here, we present a high-resolution Quaternary record of marine organic carbon in the hemipelagic sediments of
the Japan Sea obtained during Integrated Ocean Drilling Program (IODP) Expedition 346. We measured thebromine content in the sediments using an XRF core scanner (ITRAX). The total organic carbon content, total
nitrogen, and stable carbon isotope values were also measured for discrete samples from the same sediments. The
total organic carbon/total nitrogen ratio and the stable carbon isotope ratio of the total organic carbon are used toestimate the marine organic carbon content within the total organic carbon.
The Br counts and marine organic carbon content show a high correlation, which we used to construct acalibration equation of the marine organic carbon content from the Br counts. Using the calibration equation,
we reconstructed the changes in the marine organic carbon content during the Quaternary with a time
resolution of ~ 50 years using sediment cores from IODP Site U1424 in the east central Japan Sea. The
method to estimate the marine organic carbon content from the Br counts measured by the XRF corescanner proposed in this paper will be a useful tool to reconstruct the organic carbon content with highresolution and high speed.
Keywords: Marine organic carbon, Japan Sea, XRF core scanner, ITRAX, Bromine, IODP, Expedition 346, Site
U1424

Introduction
Br as a potential proxy of marine organic carbon

Br (Bromine) is one of the major elements in seawater. The
concentration of Br in seawater is 6.7 × 107 ng/L (0.84 mM),
which is the eighth highest in seawater (National Astronomical Observatory of Japan 2016). The seawater/crust concentration ratio of Br is second highest next to Cl (The
Geochemical Society of Japan 2012). The average residence* Correspondence: a_seki@shinshu-u.ac.jp
1
Faculty of Science, Shinshu University, 3-1-1 Asahi, Matsumoto, Nagano
390-8621, Japan
Full list of author information is available at the end of the article

time of Br in seawater is 100 × 106 years (Gamo 2014). The
vertical profiles of the Br concentration in the water column
are flat, and Br is thus classified as a conservative element inseawater (Nozaki 1992; National Astronomical Observatoryof Japan 2016). However, a recent study on the biogeochemical cycling of Br casts doubt on the classification of Br as aconservative element (Leri et al. 2010).
Br is known to be present in organic materials of bothmarine and terrestrial origin in the form of organobromine compounds (Leri et al. 2010). More than 1600 naturally occurring organobromine compounds, such as
bromoalkanes, bromopyrroles, and bromophenols have

© The Author(s). 2019 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0
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Seki et al. Progress in Earth and Planetary Science(2019) 6:1

been identified, and many of them are of marine origin(Gribble 2000). It is known that some microalgae andheterotrophic organisms produce brominated organic
compounds (Gribble 1998). Bromoperoxidase enzymes,
which catalyze the formation of organobromine compounds, have been found in organisms such as marine
algae (red, green, and brown), bacteria, and a marine
annelid (Gribble 2000). However, the structures andidentities of the organobromine compounds in the deep
marine sediments have not been well characterized (Bergand Solomon 2016).
In the Japan Sea, Masuzawa et al. (1988) measured the
Br concentrations of zooplankton and found that Br is 3
to 20 times more concentrated in zooplankton compared to seawater. Therefore, Br is expected to be concentrated in the Japan Sea sediments, especially in thosewith high concentrations of marine organic matter.
As a result of the formation of organobromine compounds by biobromination, good correlations between
the bromine content and total organic carbon (TOC)
content are reported for estuarine and marine sediments(Ziegler et al. 2008; Leri et al. 2010). Since the Br concentration in seawater (0.84 mM) is higher than that interrestrial water (National Astronomical Observatory ofJapan 2016), the Br content in marine organic matter ishigher than that in terrestrial organic matter (Berg andSolomon 2016). The reported average Br/TOC molar ratio for marine organic matter is 0.9–1.8 × 10−3, whilethat for terrestrial organic matter is 0.06–0.3 × 10−3
(Berg and Solomon 2016; Mayer et al. 2007; Leri et al.
2010).
Owing to the large difference in Br/TOC ratios
between marine and terrestrial organic matter, Br/TOC
ratios have been used as a proxy to distinguish organic
matter of marine and terrestrial origin in estuary sediments (Mayer et al. 1981, 2007; Malcolm and Price1984). Additionally, based on the high correlation between Br and TOC, Br is used as a proxy for TOC in
deep sea sediments (Ziegler et al. 2008, 2010).
Ziegler et al. (2008) established a method to estimate
the TOC content from Br profiles measured by an X-ray
fluorescence (XRF) core scanner, using sediments fromthe Arabian Sea and a Mediterranean brine basin. They
showed the usefulness of the XRF core scanner to measure the variability of Br and estimate the TOC with highspeed and high resolution. They also pointed out that acalibration for each XRF core scanner is necessary when
applying their method because the peak area counts ofelements are sensitive to the XRF core scanner settings.
They also suggest the possibility of estimating the marine organic carbon (MOC) content from the Br counts
by removing samples where the δ13C values are less than
− 20‰ (the typical value for marine organic carbon) to
improve the correlation between the Br counts and thePage 2 of 12

TOC contents of Arabian Sea sediments. However, therelationship between the Br and MOC content has notbeen evaluated.
XRF core scanner for high-resolution measurement

In recent decades, XRF core scanners have become intensively used for the analysis of sediment cores in many
academic fields including paleoceanographic studies(Rothwell and Croudace 2015a). The advantages of the
XRF core scanner are its nondestructive measurements,
high speed, and high resolution.
In previous studies, the measurement results of XRF
core scanners have generally been expressed as downcore profiles of the element peak area count calculated
from XRF spectra. Rarely have these peak counts been
converted to the concentration of an element in sediments (Rothwell and Croudace 2015b, and references
therein). This fact is because measurement by an XRF
core scanner is a nondestructive method that cananalyze half-round cores or u-channels directly; thus,
the result is easily affected by the sediment surface condition or water content of the sediments (Croudace et al.
2006; Kido et al. 2006; Weltje and Tjallingii 2008; Weltje
et al. 2015). Therefore, the data processing is more complicated even though the measurement itself is simple
and easy. Some studies have made efforts to constructcalibration equations to calculate the concentrations ofelements from their peak area counts, but these efforts
have had limited success, and XRF core scanner measurements are generally used in a qualitative way.
The ITRAX XRF core scanner is one of the mostpopular XRF core scanners and is manufactured andsold by COX Analytical Systems (Croudace et al. 2006;
Rothwell and Croudace 2015a). Owing to the flat-beamtechniques developed for the ITRAX core scanner, it has
advantages for high-resolution measurement, with ahighest resolution of 0.2 mm. Since XRF measurements
using the ITRAX are conducted under the ordinary atmospheric environment, elements lighter than Al cannot
be measured because the absorption effect of X-rays by
air is more significant for the lighter elements. Although
the organic carbon content in sediments is important for
many paleoceanographic studies, the organic carbon
cannot be measured by XRF core scanners.
Aim of this study

In this study, the TOC, total nitrogen (TN), and organic
matter δ13C of selected discrete samples taken fromIODP Expedition 346 Site U1424 are measured andcompared with the Br counts measured by the ITRAXXRF core scanner to evaluate the possibility of estimating MOC contents from Br counts in the Japan Sea sediment. Based on the results obtained, the downcoreorganic carbon variability in the Japan Sea sediments will

Seki et al. Progress in Earth and Planetary Science(2019) 6:1

be reconstructed at Site U1424 to demonstrate the usefulness of the method.

Oceanographic settings
Oceanographic and geological settings

The Japan Sea is a semiclosed marginal sea located along
the northwest margin of the Pacific Ocean. The sea isconnected with the surrounding seas through four shallow channels, the Tsushima Strait (sill depth ~ 130 m),
the Tsugaru Strait (sill depth ~ 130 m), the Soya Strait

Page 3 of 12(sill depth ~ 55 m), and the Mamiya (Tatar) Strait (silldepth ~ 15 m) (Fig. 1). The average depth of the Japan
Sea is more than 1600 m, with a maximum depth of
more than 3700 m (National Astronomical Observatory of Japan 2016). The Japan Sea is composed ofthree basins, the Japan Basin (~ 3800 m), Yamato Basin(~ 3000 m), and Tsushima (Ulleung) Basin (~ 2600 m), divided by the Yamato Rise (Gamo 2016; Fig. 1).
At present, the Tsushima Warm Current (TWC) is the
only current flowing into the Japan Sea through theFig. 1 A map of the Japan Sea with the study site, IODP Site U1424. Main surface currents and name of basins and straits are also indicated.
(Modified after Tada et al. 2015a)

Seki et al. Progress in Earth and Planetary Science(2019) 6:1

Tsushima Strait. The TWC is composed of two components, the Kuroshio Warm Current (KWC) and the
Taiwan Warm Current (TWWC). The TWC originates from the KWC that flows into the Japan Sea
through the southern channel, whereas the TWC
originates from the TWWC flows into the Japan Sea
through the northern channel of the Tsushima Strait.
The TWWC flows from the South China Sea into theEast China Sea (ECS), and then flows northeastward
on the ECS shelf where it is mixed with river watersupplied from the continent to become lower in salinity and higher in nutrients compared to the KWC
flowing northeastward in the Okinawa Trough. Therefore, the surface water salinity in the Japan Sea is easily influenced by the salinity of the TWWC, which, inturn, is affected by the fresh water flux from the continent (Yanagi 2002), and the relative contributions of
the TWWC and the KWC to the influx into theJapan Sea.
The modern Japan Sea produces its own deep water
called the Japan Sea Proper Water (JSPW), which is characterized by a low potential temperature of 0–1 °C andhigh oxygen content (200–300 μmol/kg) throughout the
deeper (> 200 m) part of the Japan Sea (Gamo et al. 2014;
Gamo 2016). The dissolved oxygen levels in the Japan Sea
deep water are more than 200 μmol/kg in all threebasins, and this value is higher than that in the
Northwestern Pacific at the same latitude (~150 μmol kg−1) (Gamo et al. 2014). The potential
temperature deeper than 2000–2500 m is uniform inall three basins with < 0.001 °C fluctuations, suggesting active vertical convection in the deep water(Gamo and Horibe 1983; Gamo et al. 2014). The
current that flows along the western margin of theJapan Sea is cooled by the winter monsoon wind andthe JSPW is formed especially in the area off Vladivostok where strong northwesterly winter monsoon
winds are focused because of a topographic effect due
to a mountain gap.
Since the sill depths of the modern straits are shallow (< 130 m) and the tectonic influences are minimal, especially in the Tsushima Strait (Itaki 2016),
sea level changes should be the major factor that controls the paleoceanographic conditions of the JapanSea during the Quaternary (Tada et al. 1999). During
the Last Glacial Maximum (LGM), when the sea level
dropped to around − 120 m, the surface water inflow
from the Tsushima Strait dramatically decreased, andthe sea became a closed system (Tada et al. 1999).
The surface water salinity in the sea also decreased
due to the excess precipitation plus fresh water inflow
from the surrounding rivers over evaporation (Matsui
et al. 1998). Consequently, the sea became stratified
and the deep water became euxinic because thePage 4 of 12

production of the dense deep water was reduced dueto the low-salinity surface water (Tada et al. 1999).
The Japan Sea is also characterized by its low nutrient content (Yanagi 2002; Tada 2012). In the modern
Japan Sea, the phosphorus content in the JSPW is
low (2.3 μM), and the residence times of phosphorus
and nitrogen are short (2.2 years and 1.6 years in theuppermost 200 m, respectively) (Yanagi 2002, Tada
2012). The phosphorous budget in the Japan Sea reveals that the phosphorus input from the ECS
through the Tsushima Strait is by far the dominantsource (Yanagi 2002). However, 90% of the phosphorus flowing into the sea via the Tsushima Strait
flows out from the Tsugaru Strait in the modern
Japan Sea because the subsurface water, which has ahigher nutrient content than the surface water, flows
out from the Tsugaru Strait, whose sill depth (~130 m) is deeper than the thermocline (Tada 2012).
Thus, the nutrient budget in the Japan Sea is also
thought to have been affected significantly by changes
in the sill depth controlled by sea level changes (Tada
2012).
Study site

In the summer of 2013, the Integrated Ocean Drilling
Program (IODP) Expedition 346 “Asian Monsoon”
drilled hemipelagic sediments at seven sites in the Japan
Sea (Tada et al. 2015a). Among the seven sites, sediments recovered from Site U1424 (water depth 2808 m)
are selected for this study.
Site U1424 is located ~ 150 km to the west of northern
Honshu Island and ~ 200 km to the southwest of the
Tsugaru Strait (40° 11.40′ N, 138° 13.90′ E), close to theboundary of the Japan Basin and Yamato Basin, with awater depth of 2808 m (Fig. 1; Tada et al. 2015c).
The hemipelagic sediments of the Japan Sea are
known to have distinct alternations of dark and lightlayers (e.g., Tada et al. 1999; Tada 2004). During IODP
Expedition 346, these dark and light layers were recovered at six sites in the Japan Sea at water depths deeper
than 900 m (Tada et al. 2015a). The deposition of dark
and light layers started at approximately 2.6 Ma (million years ago) and became increasingly distinct at approximately 1.45 Ma (Tada et al. 2015a; Tada et al.
2018). Distinct dark layers have been correlated among
the six sites (Irino et al. 2018), and their deposition was
synchronous basinwide, suggesting that the Japan Sea
has been acting as a single system responding toclimatic-oceanographic change in climatic-tectonic
coupling in Asia throughout the Quaternary (e.g., Tada
et al. 2016: Clift 2017).
Three holes were drilled at Site U1424 to recover acontinuous sequence of sediments. The sediments backto 5 Ma were continuously recovered. These mainly

Seki et al. Progress in Earth and Planetary Science(2019) 6:1

consist of clay and diatom ooze, with a minor component of volcaniclastic materials (Tada et al. 2015c).
Splice intervals were defined onboard, and a continuous composite column made of each splice interval wasconstructed. The depth scale of this composite column
is expressed as “CCSF-D (m)” (Tada et al. 2015b). The
splice intervals were further revised after the cruise andthe new depth scale for U1424 is called “U1424_
CCSF-D_Patched_rev20170308 (m)” (Irino et al. 2018).
The difference between the shipboard depth scale(CCSF-D) and the new depth scale is less than 1.5 m
throughout the splice (Irino et al. 2018). The new depth
scale is employed in this study unless otherwise noted.
The thickness of the Quaternary sediment is approximately 90 m based on the shipboard age model (Tadaet al. 2015c) and ~ 83 m based on the revised age
model described below (Tada et al. 2018). Since this site
is at the same location as Ocean Drilling Program(ODP) Site 794, the sediment sequence was correlatedwith ODP Site 794 cores (Irino et al. 2018).
One reason to choose Site U1424 is because no
sediment disturbance (such as slumps) or hiatus isobserved at this site (Tada et al. 2015c). In addition,
the color alternations of dark and light layers are distinct at this site compared to sites drilled from shallower water depths (such as Site U1426 drilled at
903 m; Tada et al. 2015a; Irino et al. 2018). Anotherreason to choose Site U1424 is that a high-precisionand high-resolution age model has been constructedat this site (Fig. 2; Tada et al. 2018).
In the Japan Sea hemipelagic sediments, especiallythe sediments deposited at a deep-water depth with

Fig. 2 Age model of IODP Site U1424. Data are from Tada etal. (2018)

Page 5 of 12

alternations of dark and light layers, foraminifer shells
are not continuously found from all horizons (Tada etal. 2015c). Thus, it is difficult to construct a δ18O
stratigraphy of foraminifer shells for the Japan Sea
hemipelagic sediments. Tada et al. (2018) constructeda “LR04-tuned age model” for Site U1424 by tuning
the gamma ray attenuation (GRA) bulk density of theSite U1424 composite section to the LR04 δ18O stack(Lisiecki and Raymo 2005) because the diatom content, which is the major reason for the densitychanges in the Japan Sea sediments, has been changing in association with glacial-interglacial cycles(Tada et al. 1999). Since their age model has a higher
resolution and reliability covering the entire Quaternary compared to the shipboard age model, their age
model (Fig. 2) is employed in this study.

Methods/Experimental
TOC, TN, and δ13C measurements

Discrete samples of U1424 cores were subsampled fromworking halves in August 2016 (Table 1). Since the TOC
content is different in the dark and light layers (Tada etal. 1999), every sample was obtained from the middle ofeither a dark or light layer and represents a 1-cm stratigraphic interval. Although tephra layers sometimes
occur at Site U1424, no discrete sample contained visual
tephra identified from the shipboard visual core description (VCD) and core photographs. In total, 23 samples
were used in this study (Table 1).
The discrete samples were dried at 50 °C for morethan 3 days and were gently ground to powder using anagate mortar. Then, 5- to 50-mg powdered samples were
weighed in an Ag cup (dimensions: φ5, 9 mm) andtreated with 100 μl of 3 M HCl for 3 days at room
temperature to remove carbonate carbon. During the
HCl treatment, the samples were stored in the Ag cups
inside a desiccator with NaOH and P2O5 to remove HCland H2O. After the HCl treatment, each Ag cup was
enfolded by a Sn cup (dimensions: φ9, 10 mm) andstored in a desiccator until the measurement of the
TOC, TN, and δ13C. To estimate any carbon contamination from the HCl, blank Ag cups with HCl treatmentthat were enfolded by Sn cups were also prepared.
The TOC, TN, and δ13C of the samples were measured by an elemental analyzer (Flash EA 1112) coupled
to a ConFlo III and a Thermo Finnigan DeltaPlus
Advantage isotope ratio mass spectrometer at the Center
for Advanced Marine Core Research, Kochi University.
Sulfanilamide was used as a standard for the TOC andTN measurements, and its analytical error (σ) was
within 0.03 wt% for both TOC and TN. L-Alanine (δ13C= 19.6‰ ± 0.2) was used as a standard for the δ13C
measurement, and its analytical error (σ) is 0.89‰.

2

2

2

2

2

2

2

2

1

1

1

1

1

1

1

1

1

1

1

1

1

1

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

1

4

3

3

3

2

2

1

1

4

4

3

3

3

2

2

1

1

1

1

1

1

1

W

W

W

W

W

W

W

W

W

W

W

W

W

W

W

W

W

W

W

W

W

W

W

Ages are calculated based on Tada et al. (2018)

U1424 BU1424 B

23

26

U1424 B

22

U1424 BU1424 B

21

U1424 BU1424 B

20

24

U1424 B

1925

U1424 AU1424 A

17

18

U1424 AU1424 A

14

U1424 A

12

16

U1424 AU1424 A

10

11

U1424 AU1424 A

8

9

U1424 BU1424 A

6

7

U1424 AU1424 B

34U1424 AU1424 A

1

2

1

59

127
33

32

31

6

24

16

149

130

41

15

107

80

26

99

11

126

121

118

117

106

88

76

126

30

5

23

15

148

129

40

14

106

79

25

98

10

125

120

117

116

105

87

75

58

9.57

9.01

8.05

7.80

6.48

6.40

6.23

6.04

4.80

4.54

3.96

3.69

3.15

2.38

1.57

1.25

1.20

1.17

1.13

1.02

0.87

0.75

0.58

0.230 70.219 70.196 70.190 6

0.159 60.157 60.149 60.139 6

0.108 50.102 50.089 50.083 50.070 40.052 30.032 30.025 20.024 20.023 20.022 20.019 20.016 20.014 1

Light

Dark

Dark

Dark

Dark

Dark

Light

Dark

Dark

Dark

Dark

Dark

Dark

Dark

Dark

Light

Dark

Dark

Dark

Dark

Light

Light

Dark

0.26

1.57

3.96

3.24

1.23

0.98

0.30

1.16

3.50

1.25

2.15

1.54

2.49

1.10

2.42

0.48

1.64

1.54

1.40

1.59

0.38

0.58

1.32

Marine Layer TOC
isotope type (%)
stage

0.011 1

Age
Sample(Ma)
top depth
Hole Core Type Sect A/W Offset
Offset Bottom (cm)U1424_Top (cm)
CCSF-D_
Patched_rev20170308 (m)Sample interval

Site

SampleNo.

Table 1 List of discrete samples taken from IODP Site U1424 and their analytical results

0.00

0.01

0.04

0.01

0.01

0.01

0.00

0.01

0.02

0.01

0.01

0.01

0.01

0.01

0.02

0.00

0.01

0.01

0.01

0.01

0.00

0.00

0.01

0.06 0.00

0.18 0.01

0.40 0.04

0.33 0.01

0.12 0.01

0.10 0.01

0.06 0.00

0.11 0.01

0.35 0.02

0.16 0.01

0.23 0.01

0.18 0.01

0.26 0.01

0.14 0.01

0.26 0.02

0.07 0.00

0.17 0.01

0.15 0.01

0.14 0.01

0.16 0.01

0.07 0.00

0.08 0.00

12.3

11.1

11.0

10.9

14.3

14.4

11.9

15.5

11.0

9.8

11.1

10.7

10.9

10.7

10.7

13.4

12.5

13.0

12.8

12.5

10.9

12.0

10.3

0.89

0.89

− 25.10− 24.70

0.89− 27.76

0.89

0.89

− 26.64

0.89

0.89

− 23.99− 23.280.89− 27.57− 23.230.89
0.89− 21.85− 23.46

0.89
0.89− 22.75

0.89− 24.96− 24.410.89
0.89− 24.16− 23.170.89
0.89− 26.40− 23.43

0.89
0.89− 26.94− 26.73

0.89
0.89− 23.80− 26.630.89
0.89− 22.95− 23.47

797

1819

3857

2366

1036

992

872

831

2500

1777

2462

1955

1819

1615

2286

1045

1422

1206

1130

1443

1472

1593

2223

58

88

128

100

66

65

61

59

103

87

102

91

88

83

98

67

78

72

69

78

79

82

97

0.44

0.16

0.27

0.20

0.32

0.14

0.31

0.06

0.21

0.20

0.18

0.20

0.05

0.07

0.17

MOC
error
(%)

0.09

0.84

2.11

0.88

− 0.13

0.05

0.13

0.03

0.20

0.50

0.41

0.16

0.12

0.04

− 0.09 0.15

1.77

0.92

0.80

0.94

0.72

0.60

0.98

0.25

0.14

0.06

0.01

0.08

0.17

0.29

0.76

TN
TOC/(TN- δ13C (‰ δ13C Br
Br error MOC
error (%) 0.035)
VPDB)
error (counts) (counts) (%)‰)

0.16 0.02

TOC
TN
error (%) (%)

Seki et al. Progress in Earth and Planetary Science(2019) 6:1
Page 6 of 12

Seki et al. Progress in Earth and Planetary Science(2019) 6:1

Br measurement using XRF core scanner (ITRAX)

Archive halves of the U1424 cores from the Quaternary intervals were measured by ITRAX, using a Mo X-ray tube
with settings of 30 kV, 55 mA, a 2-mm step size, and a 10-s
measurement time. Outliers in the ITRAX analytical results
due to core surface disturbances (such as cracks) were eliminated after the measurement. Before the sample measurement, five repeated measurements were conducted using
standard samples to evaluate the analytical precision of themeasurement (Seki 2017); the analytical precision of fivetimes repeated measurement for Br was determined to be
2.1*√N (N: peak area counts; Seki 2017). To check the relationship between the Br counts and Br concentration,
standard reference materials (Additional file 1: Table S1)
were measured by ITRAX (Seki 2017). Since the concentration of Br in the standard reference material is not sufficiently high, KBr was added to standard reference materials
and these KBr-supplemented standard reference materials
were also measured by ITRAX (Seki 2017). Based on themeasurement, the Br counts show a high correlation with
the Br concentrations within a range between 0 and
500 ppm (Additional file 2: Figure S1; Seki 2017). Thus, theBr counts can be used as a semiquantitative measure of the
Br concentration in the sediments.
Br counts measured on exactly the same stratigraphic
intervals as the discrete samples used for the TOC, TN,and δ13C measurements (Table 1) were used for comparison with the TOC, TN, and δ13C results. Since
discrete samples represent 1-cm intervals and the step
size of the ITRAX measurement was 2 mm, the ITRAX
results from five adjacent measurements for the same
stratigraphic intervals as the discrete samples were averaged (Table 1).

Page 7 of 12

illite) and is contained in the total nitrogen values. According to their results, inorganic nitrogen significantly affects
the TOC/TN ratios (Schubert and Calvert 2001). Since theJapan Sea sediments contain significant amounts of clay, including illite (Irino and Tada 2000; Tada et al. 2015c), we
investigated the possible influence of inorganic nitrogen on
the TOC/TN ratio. Figure 3 shows the relationship between
the TOC/TN ratio and the TOC. The TOC/TN ratio increases with the TOC, but the rate of increase gradually decreases. This relation can be explained by the presence of
inorganic nitrogen binding to clay minerals. Schubert andCalvert (2001) calculated that the inorganic nitrogen content in the sediments of the central Arctic Ocean is 0.035%,
based on TON and inorganic nitrogen content measurements in sediments taken from the central Arctic Ocean.
Since the reported illite contents in the Japan Sea sediment(~ 14–20%; Irino and Tada 2000) are comparable to thoseof the central Arctic Ocean sediments (~ 20%, Schubert
and Calvert 2001), we assumed an inorganic nitrogen content in the sediment of 0.035% (the same amount as in thecentral Arctic Ocean) for the Japan Sea sediment used inthis study. Based on this assumption, theoretical TOC/TN
ratios were calculated and are shown in Fig. 3. Figure 3 reveals that the TOC/TON ratio of the U1424 samples analyzed in this study is between 9 and 16 when the correction
for the inorganic nitrogen content (estimated as 0.035%) ismade. The calculated TOC/(TN-0.035) ratios have no dependency on the TOC, suggesting that the assumed content of inorganic nitrogen of 0.035% is reasonable for theU1424 samples.
The C/N ratio and δ13C are both used as parameters toevaluate the relative ratio of marine versus terrestrial

Results and discussion
Results of TOC, TN, and δ13C measurements

Table 1 shows the results of the TOC, TN, and δ13C measurements for discrete samples from Site U1424. In general, the TOC is high (typically 1–6%) in dark layers andlow (< 1%) in light layers (Table 1). The TN values ranged
between 0.06 and 0.4% (Table 1), and the stable carbon
isotope values ranged between − 20 and − 28‰ (Table 1).
It is known that the terrestrial organic matter and marineorganic matter have different TOC/total organic nitrogen(TON) ratios (Lamb et al. 2006). Therefore, the TOC/TON
ratio is commonly used to estimate the relative contributions of terrestrial and marine organic matter in sediments(Lamb et al. 2006). However, many paleoceanographic studies use the TOC/TN ratio instead of the TOC/TON ratio
to evaluate the relative contributions because the analysisof the TN is much easier than the TON measurement(Schubert and Calvert 2001). In the Arctic Ocean, Schubert
and Calvert (2001) demonstrated that a significant amountof inorganic nitrogen binds to clay minerals (especiallyFig. 3 TOC versus TOC/TN ratio of samples from IODP Site
U1424 measured in this study. The TOC/TN ratio decreases as
the TOC decreases, suggesting a probable effect of inorganic
nitrogen, especially when the TOC is low. Solid and dashed lines
are theoretical lines for the TOC/TN ratio versus the TOC when
the TOC/TON ratio is assumed as 9 and 16 and inorganic
nitrogen content is assumed as 0.035% (see text for details)

Seki et al. Progress in Earth and Planetary Science(2019) 6:1

Page 8 of 12

organic matter because the two parameters show distinctly different values for marine and terrestrial organic
matter. Marine organic matter has a lower C/N ratio andhigher δ13C compared to terrestrial organic carbon (Lambet al. 2006). The TOC/(TN-0.035) ratio and δ13C obtainedin this study show a high correlation of r2 = 0.64 (Fig. 4),
with samples with a lower C/N ratio having higher δ13C
values. This result suggests that the organic matter in theJapan Sea sediments is a mixture of marine and terrestrialorganic matter. These results suggest that both the TOC/
(TN-0.035) ratio and δ13C in the Japan Sea sediment aregood proxies to distinguish marine from terrestrial organic
matter. In this study, we use δ13C to calculate the percentages of marine and terrestrial organic carbon, because
δ13C is more reliable than the TOC/(TN-0.035) ratio,
which has uncertainty in the inorganic nitrogen estimate.
We assume that the δ13C of marine organic carbon is −20‰, and that of terrestrial organic carbon is − 27‰(Minoura et al. 1997; Ikehara et al. 2009). Then, the MOC
can be calculated as follows (Eq. 1), where “marine organiccarbon fraction” means the percentage of marine organiccarbon within the total organic carbon.
MOC ð%Þ ¼ TOC ð%Þ < marine organic carbon fraction >
¼ TOCð%Þ  δ13 Cterrestrial −δ13 Csample= δ13 Cterrestrial −δ13 Cmarine

ð1Þ
Correlation between Br and marine organic carbon

The relationship between the Br and TOC is shown in the
cross-plot of Br and TOC in Fig. 5. It shows a highcorrelation (R2 = 0.69) and a y-intercept of 739 (Brcounts) (Fig. 5).

Fig. 4 Correlation between TOC/(TN-0.035) ratio and δ13C of the
TOC for samples analyzed in this study. (TN-0.035) represents theestimated organic nitrogen content of the sediments (see text
for details)

Since wet archive halves of cores were used for the
ITRAX measurement, the Br counts include the Br in
the interstitial water. As bromine does not accumulate
in solution as dissolved organobromine compounds(Berg and Solomon 2016), the Br in organic matter and
Br in the interstitial water should behave independently.
The Br concentration in the interstitial water is reported
from a shipboard analysis as being 0.91–1.05 (± 0.03)
mM for the uppermost 10 m of U1424 (Tada et al.
2015b, 2015c). Using water contents measured onboard(Tada et al. 2015c) and the relationship between the Br
counts and concentration, the contribution of the Br in
the interstitial water to the total Br counts of the wetarchive halves is estimated as being between 470 and
880 counts (minimum and maximum estimates). Thus,
the intercept of the Br counts in Fig. 5 (739 counts) isinterpreted as representing the background Br in theinterstitial water.
Since the Br is mainly contained in the MOC, the relation
between the Br and MOC (calculated from TOC and δ13C)
is further examined. Figure 6 shows a cross-plot of Br and
MOC calculated from Eq. 1. For U1424, the Br counts
show a better correlation with the MOC (R2 = 0.85) compared to the TOC (R2 = 0.69) (Figs. 5 and 6).
Since the Br is mainly contained in the MOC, the calibration equation obtained from Fig. 6 is used to estimate
the MOC content from the Br counts in this study.
Br ðcountsÞ ¼ 1143  MOC ð%Þ þ 1060

ð2Þ

MOC ð%Þ ¼ ðBr ðcountsÞ−1060Þ=1143

ð3Þ

Since the analytical error of Br is small (less than 150
counts when the peak area count is less than 5000
counts), the error of this equation mainly comes fromdeviations from the regression curve in Fig. 6. The estimated error of the MOC calculation is approximately

Fig. 5 Cross-plot of Br counts by XRF core scanner and TOC
measured in this study

Seki et al. Progress in Earth and Planetary Science(2019) 6:1

Fig. 6 Cross-plot of Br counts by XRF core scanner and MOC
calculated from TOC and δ13C in this study

Page 9 of 12

0.5% (Fig. 6). It should be noted that Eqs. 2 and 3 arebased on the assumption that the Br in terrestrial organic
matter is negligible because the Br/TOC ratio is much
lower in terrestrial organic matter (0.06–0.3 × 10−3) compared with marine organic matter (0.9–1.8 × 10−3) (Bergand Solomon 2016; Mayer et al. 2007; Leri et al. 2010).
Since analytical data on Br/MOC ratios in marine organic
matter for individual seas are not available, the applicability of the equations for the MOC calculation (Eqs. 2 and
3) for sediments from other seas (such as the open ocean)should be checked in the future. Even given the limitations
described above, this method to estimate the MOC content by the high-resolution, high-speed, and nondestructive measurement of Br using ITRAX is a useful tool for
paleoceanographic studies.
MOC variability in the Japan Sea during the Quaternary

Using Eq. 3, high-resolution temporal variations of the
MOC during the Quaternary were reconstructed forSite U1424 from the Br counts measured by ITRAX(Fig. 7; Additional file 3 and Additional file 4: Table

Fig. 7 Reconstructed MOC for Site U1424. Enhanced photograph, lightness (L*, black; data from Irino et al. 2018) and Br counts (light blue) arealso shown for comparison. The hatched intervals are of a dark color (low L* value) but are low in MOC content (see text for details). a 0–10 m, b
10–20 m, c 20–30 m, d 30–40 m, e 40–50 m, f 50–60 m, g 60–70 m, h 70–80 m, i 80–90 m, j 90–100 m

Seki et al. Progress in Earth and Planetary Science(2019) 6:1

S2). Enhanced core photographs, lightness (L*; datafrom Irino et al. 2018), and Br counts measured by ITRAX
are shown with the MOC in (Fig. 7; Additional file 3). The
MOC values tend to be high (> 1%) in the dark layers (lowL* values) and low (< 0.5%) in the light layers (high L*
values). The concentration of the MOC in the dark layers
occurs throughout the sequence, but more distinct in theuppermost 50 m (Fig. 7; Additional file 3), which corresponds to the last 1.5 Myr (Fig. 2; Tada et al. 2018). Below
50 m (before 1.5 Ma), dark layers are rare, and thus the
low-MOC layers prevail (Fig. 7; Additional file 3).
The reconstructed MOC shows cm-scale variability associated with the dark layers (Fig. 7; Additional file 3),
which correspond to millennial-scale variability (Fig. 2;
Tada et al. 2018). These millennial-scale variations are
more distinct during the last 1.5 Myr (uppermost 50 m
(Fig. 7; Additional file 3). The MOC in the sediments reflects the surface productivity, degradation of marine organic matter within the water column and during earlyburial, and dilution by terrigenous and biogenic materials.
Thus, the reconstructed MOC enables us to discuss possible oceanic condition changes. In the glacial period during
the last 200 kyr, a millennial-scale variation in the TOC was
reported (Tada et al. 1999). This millennial-scale alternationof dark and light layers in the Japan Sea sediments was proposed to reflect the East Asian summer monsoon (EASM)
variability associated with Dansgaard-Oeschger cycles (Tadaet al. 1999; Tada 2004). Tada et al. (1999) proposed a hypothesis on dark and light layer deposition. Namely, when
the EASM became stronger during interstadials, more nutrients was provided to the Japan Sea via the Tsushima
Strait, and the surface productivity in the Japan Sea was enhanced. The reconstructed MOC variability revealed thatmillennial-scale variability occurred not only during the last
200 kyr but also during most of the glacial periods during
the last 1.5 Ma. This suggests the occurrence of climate
perturbations such as Dansgaard-Oeschger cycles in theearlier period. Since exploring the relationship between the Asian monsoon and the oceanography of
the Japan Sea is important (Tada and Murray 2016),
the detailed mechanism and onset timing of themillennial-scale variability of the MOC should be addressed in the future.
As described above, MOC values tend to be high (> 1%)
in the dark layers throughout the sequence (Fig. 7;
Additional file 3). However, there are some exceptions to
the relationship between the lightness (L*) of the sedimentand the MOC content. For example, the dark layers in theintervals of 5.9–6.1 m and 6.3–6.6 m are of a dark color(low L* value) but are low in MOC content (Fig. 7;
Additional file 3). These layers were deposited during
marine isotope stage (MIS) 6, when the eustatic sea level
was more than ~ 100 m lower than it is today (Tada et al.
2018). Similar trends are obvious in the layers depositedPage 10 of 12

during MIS 2, 10, 12, and 16 (Fig. 7; Additional file 3).
These layers have high concentrations of pyrite and areconsidered to have been deposited under euxinic
deep-water conditions (Tada et al. 1999; Kido et al. 2007).
From the results of the δ13C of organic carbon (sample
No. 4, 6, 7, 8, 19, 21, and 22 in Table 1), these layers arealso characterized by high terrestrial/marine organic matter ratios. Since organic matter is the main cause of thedark color in the Japan Sea sediments (Tada et al. 1992),
L* has been used to estimate the TOC content in theJapan Sea because it is easy to measure compared to theconventional TOC measurement methods (Kido et al.
2007). Thus, the Br counts have an advantage over L* as aparameter to reconstruct the paleoproductivity. On theother hand, it may be possible to estimate the fraction ofterrestrial organic carbon within the TOC using a combination of L* and Br counts, which will be tested in the
future.
From the results of this study, it is clear that MOC estimation from Br counts measured by ITRAX has a highpotential to reconstruct the paleoproductivity with highresolution and high speed and in a nondestructive way,
which allows us to examine past marine productivity,
the carbon cycle in the ocean, and oceanographic
changes.

Conclusions
In this paper, a method to estimate the MOC content
from Br as measured by an XRF core scanner is described. For establishing the method, the TOC, TN, andδ13C were measured on discrete sediment samples. The
TOC/TN ratio, which is usually used to distinguish marine organic matter from terrestrial organic matter, is significantly influenced by inorganic nitrogen bound to clay
minerals. The inorganic nitrogen content of the sediment is assumed to be a constant 0.035% based on apreviously reported value for sediments from the Arctic
Ocean (Schubert and Calvert 2001). Both the TOC/
(TN-0.035) ratio and δ13C of the Quaternary Japan Sea
sediments suggest a wide range of mixing of terrestrial
and marine organic matter. The δ13C of the organic
matter is used to calculate the marine organic carbon
fraction, because δ13C is more reliable than the TOC/
(TN-0.035) ratio because the latter contains uncertainty
in the inorganic nitrogen content assumption. Then, the
MOC is calculated from the TOC and the marine organic carbon fraction, which is calculated from the δ13C
value, and the calculated MOC is compared with the Br
counts. A high positive correlation is found between the
MOC and Br counts, and a calibration equation to estimate the MOC from the Br counts is obtained. To demonstrate the usefulness of the equation, it is applied to
the Quaternary sediments of the Japan Sea. The MOC
variability was reconstructed for the entire Quaternary

Seki et al. Progress in Earth and Planetary Science(2019) 6:1

sediment sequence at IODP Site U1424. The reconstructed MOC record reveals that millennial-scale variations exist since 1.5 Ma. Since the millennial-scalevariations reflect climate perturbations similar to
Dansgaard-Oeschger cycles, the reconstructed MOC
may provide useful information to investigate past climate and oceanographic changes. L* is commonly used
as a proxy for the TOC and used to semiquantitatively
estimate the surface productivity. However, the TOC
sometimes contains nonnegligible amounts of terrestrialorganic carbon, the effect of which should be corrected
to estimate the surface productivity. Consequently, Br
counts are superior to L* if one wants to obtain morequantitative information on the surface productivity.
Therefore, the MOC estimation from Br counts measured by ITRAX has a high potential to reconstruct the
paleoproductivity with high resolution and high speed
and in a nondestructive way.

Additional files
Additional file 1: Table S1. Standard reference material used in thisstudy. (DOCX 55 kb)
Additional file 2: Figure S1. Relationship between Br counts and Br
concentration. Results of standard reference material (Additional file 1:
Table S1) and KBr-supplemented standard reference materials are shown.
(JPG 42 kb)
Additional file 3: Reconstructed MOC for Site U1424. Enhanced
photograph, lightness (L*, black; data from Irino et al. 2018) and Br counts(light blue) are also shown for comparison. The hatched intervals are of adark color (low L* value) but are low in MOC content (see text for
details). a 0–10 m, b 10–20 m, c 20–30 m, d 30–40 m, e 40–50 m, f 50–
60 m, g 60–70 m, h 70–80 m, i 80–90 m, j 90–100 m. (PDF 7.79 kb)
Additional file 4: Table S2. Raw data of Br counts and MOC content
shown in Fig. 7. (XLSX 1443 kb)
Abbreviations
EASM: East Asian summer monsoon; ECS: East China Sea; GRA: Gamma ray
attenuation; IODP: Integrated Ocean Drilling Program; JSPW: Japan Sea
Proper Water; KWC: Kuroshio Warm Current; LGM: Last Glacial Maximum;
MIS: Marine isotope stage; MOC: Marine organic carbon; ODP: Ocean Drilling
Program; TN: Total nitrogen; TOC: Total organic carbon; TON: Total organic
nitrogen; TWC: Tsushima Warm Current; TWWC: Taiwan Warm Current;
VCD: Visual core description; XRF: X-ray fluorescenceAcknowledgements
We appreciate Kaz Mitake of the University of Tokyo and Minoru Ikehara,
Takuya Matsuzaki, and the staff of the Kochi Core Center for laboratory
assistance. We appreciate Larry Peterson and an anonymous reviewer for
their constructive comments and helpful suggestions.
This research used samples provided by the International Ocean Discovery
Program (IODP). This study was performed under the cooperative research
program of Center for Advanced Marine Core Research (CMCR), Kochi
University (16A035, 16B031).
Funding
Funding for this research was provided by JSPS KAKENHI Grant Numbers
16H01765 for RT and 25•9053 for AS. This work is also supported by the
Sasakawa Scientific Research Grant from the Japan Science Society for AS.
Authors’ contributions
RT and AS proposed the topic and conceived and designed the study. AS,
SK, and MM carried out the experimental study. AS and SK analyzed thePage 11 of 12

data. All authors took part in discussions about the data analysis andinterpretation. AS drew the figures and wrote a draft of the manuscript. All
authors read and approved the final manuscript.
Authors’ information
RT was cochief scientist of IODP Expedition 346. AS and SK were students of RT.
Competing interests
The authors declare that they have no competing interests.

Publisher’s NoteSpringer Nature remains neutral with regard to jurisdictional claims inpublished maps and institutional affiliations.
Author details
1
Faculty of Science, Shinshu University, 3-1-1 Asahi, Matsumoto, Nagano
390-8621, Japan. 2Graduate School of Science, The University of Tokyo, 7-3-1
Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. 3Faculty of Agriculture andMarine Science, Kochi University, 200 Monobe, Nankoku-shi, Kochi 783-8502,
Japan.
Received: 29 June 2018 Accepted: 19 November 2018

References
Berg RD, Solomon EA (2016) Geochemical constraints on the distribution andrates of debromination in the deep subseafloor biosphere. Geochim
Cosmochim Acta 174:30–41.
Clift PD (2017) Cenozoic sedimentary records of climate-tectonic coupling in theWestern Himalaya. Prog Earth Planet Sci 4:39. https://doi.org/10.1186/s40645017-0151-8.
Croudace IW, Rindby A, Rothwell RG (2006) ITRAX: description and evaluation ofa new multi-function X-ray core scanner. In: Rothwell RG (ed) New
techniques in sediment Core analysis, Special publication, vol 267. GeologicalSociety, London, pp 51–63.
Gamo T (2014) Marine geochemistry. Kodansha Ltd., Japan (In Japanese).
Gamo T (2016) Tha Japan Sea—things happen in the deep sea. Kodansha Ltd.,
Japan (In Japanese).
Gamo T, Horibe Y (1983) Abyssal circulation in the Japan Sea. J Oceanogr Soc
Jpn 39:220–230.
Gamo T, Nakayama N, Takahata N, Sano Y, Zhang J, Yamazaki E, Taniyasu S,
Yamashita N (2014) The Sea of Japan and its unique chemistry revealed bytime-series observations over the last 30 years. Monogr Environ Earth Planets
2(1):1–22. https://doi.org/10.5047/meep.2014.00201.0001.
Gribble GW (1998) Naturally occurring organohalogen compounds. Acc Chem
Res 31:141–152.
Gribble GW (2000) The natural production of organobromine compounds.
Environ Sci Pollut Res 7(1):37–49. https://doi.org/10.1065/espr199910.002.
Ikehara M, Akita D, Matsuda A (2009) Enhanced marine productivity in the
Kuroshio region off Shikoku during the last glacial period inferred from theaccumulation and carbon isotopes of sedimentary organic matter. J Quat Sci
24(8):848–855.
Irino T, Tada R (2000) Quantification of aeolian dust (Kosa) contribution to theJapan Sea sediments and its variation during the last 200 ky. Geochem J
34:59–93.
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 during IODP expedition 346. Prog Earth
Planet Sci 5:19. https://doi.org/10.1186/s40645-018-0167-8I.
Itaki T (2016) Transitional changes in microfossil assemblages in the Japan Sea
from the Late Pliocene to Early Pleistocene related to global climatic andlocal tectonic events. Prog Earth Planet Sci 3:11. https://doi.org/10.1186/
s40645-016-0087-4.
Kido Y, Koshikawa T, Tada R (2006) Rapid and quantitative major element analysis
method for wet fine-grained sediments using an XRF mixroscanner. Mar
Geol 229:209–225.
Kido Y, Minami I, Tada R, Fujine K, Irino T, Ikehara K, Chun JH (2007) Orbital-scale
stratigraphy and high-resolution analysis of biogenic components and deep
water oxygenation conditions in the Japan Sea during the last 640 kyrs using
XRF microscanner. Palaeogeogr Palaeoclimatol Palaeoecol 247:32–49. https://doi.org/10.1016/j.palaeo.2006.11.020.

Seki et al. Progress in Earth and Planetary Science(2019) 6:1

Lamb AL, Wilson GP, Leng MJ (2006) A review of coastal palaeoclimate andrelative sea-level reconstructions using δ13C and C/N ratios in organic
material. Earth-Sci Rev 75:29–57.
Leri AC, Hakala JA, Marcus MA, Lanzirotti A, Reddy CM, Myneni SCB (2010)
Natural organobromine in marine sediments: new evidence ofbiogeochemical Br cycling. Glob Biogeochem Cycles 24:GB4017.
Lisiecki LE, Raymo ME (2005) A Pliocene-Pleistocene stack of 57 globally
distributed benthic δ18O records. Paleoceanography 20(1):PA1003. https://doi.org/10.1029/2004PA001071.
Malcolm SJ, Price NB (1984) The behaviour of iodine and bromine in estuarine
surface sediments. Mar Chem 15:263–271.
Masuzawa T, Koyama M, Terazaki M (1988) A regularity in trace element contents
of marine zooplankton species. Mar Biol 97:587–591. https://doi.org/10.1007/
BF00391056.
Matsui H, Tada R, Oba T (1998) Low-salinity isolation event of the Japan Sea in
response to eustatic sea-level drop during the LGM: reconstruction based on
salinity-balance model. Quatern Res (Daiyonki-kenkyu) 37:221–233 (inJapanese with English abstract).
Mayer LM, Macko SA, Mook WH, Murray SM (1981) The distribution of bromine incoastal sediments and its use as a source indicator for organic matter. Org
Geochem 3:37–42.
Mayer LM, Schick LL, Allison MA, Ruttenberg KC, Bentley SJ (2007) Marine vs.
terrigenous organic matter in Louisiana coastal sediments: the uses ofbromine:organic carbon ratios. Mar Chem 107:244–254.
Minoura K, Hoshino K, Nakamura T, Wada E (1997) Late Pleistocene-Holocene
palcoproductivity circulation in the Japan Sea: sea-level control on δ13C andδ15N records of sediment organic material. Palaeogeogr Palaeoclimatol
Palaeoecol 135:41–50.
National Astronomical Observatory of Japan (ed) (2016) Rika Nenpyo(chronological scientific tables). Maruzen Publishing Co., Ltd., Japan (InJapanese).
Nozaki Y (1992) Trace elements in sea water: their mean concentrations andNorth Pacific profiles. Chikyukagaku (Geochemistry) 26:25–39 (In Japanesewith English abstract).
Rothwell RG, Croudace IW (2015a) Micro-XRF studies of sediment cores: aperspective on capability and application in the environmental sciences. In:
Croudace IW, Rothwell RG (eds) Micro-XRF Studies of sediment cores,
developments in Paleoenvironmental research 17. https://doi.org/10.1007/
978-94-017-9849-51.
Rothwell RG, Croudace IW (2015b) Twenty years of XRF Core scanning marine
sediments: what do geochemical proxies tell us? In: Croudace IW, Rothwell
RG (eds) Micro-XRF studies of sediment cores, developments in
Paleoenvironmental research 17. https://doi.org/10.1007/978-94-017-9849-52.
Schubert CJ, Calvert SE (2001) Nitrogen and carbon isotopic composition ofmarine and terrestrial organic matter in Arctic Ocean sediments: implications
for nutrient utilization and organic matter composition. Deep Sea Res Part I
48:789–810.
Seki A (2017) Reconstruction of marine organic matter content in the sediments
and deep-water redox condition variability of the Japan Sea during thequaternary using high-resolution XRF core scanner. Dissertation, theUniversity of Tokyo, Tokyo.
Tada R (2004) Onset and evolution of millennial-scale variability in the Asian
Monsoon and its impact on paleoceanography of the Japan Sea.
Millennial-Scale Variability in the Asian Monsoon, American Geological
Union, U.S.A, pp 1–16.
Tada R (2012) The Japan Sea sediments and variability of East Asian Monsoon:
toward the IODP drilling of the Japan Sea and East China Sea. Quatern Res
51:151–164 (In Japanese).
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, Exp. 346 Scientists (2018) Highresolution and -precision correlation of dark and light layers in the
Quaternary hemipelagic sediments of the Japan Sea recovered during IODP
expedition 346. Prog Earth Planet Sci 5:19. https://doi.org/10.1186/s40645018-0167-8.
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, Koizumi I, Cramp A, Rahman A (1992) Correlation of dark and light layers,
and the origin of their cyclicity in the Quaternary sediments from the Japan
Sea. In: Pisciotto KA, Ingle JC, von Breymann J et al (eds) Proceedings ofPage 12 of 12

ocean drilling program scientific results, vol 127/128. Ocean Drilling Program,
TX, pp 577–601.
Tada R, Murray RW (2016) Preface for the article collection “Land–Ocean linkages
under the influence of the Asian monsoon”. Prog Earth Planet Sci 3:24.
https://doi.org/10.1186/s40645-016-0100-y.
Tada R, Murray RW, Alvarez Zarikian CA, Anderson WT Jr, Bassetti MA, Brace BJ,
Clemens SC, da Costa Gurgel MH, Dickens GR, Dunlea AG, Gallagher SJ,
Giosan L, Henderson ACG, Holbourn AE, Ikehara K, Irino T, Itaki T, Karasuda A,
Kinsley CW, Kubota Y, Lee GS, Lee KE, Lofi J, Lopes CICD, Peterson LC,
Saavedra-Pellitero M, Sagawa T, Singh RK, Sugisaki S, Toucanne S, Wan S,
Xuan C, Zheng H, Ziegler M (2015a) Expedition 346 summary. In: Tada R,
Murray RW, Alvarez Zarikian CA, the Expedition 346 Scientists (eds) Proc.
IODP, 346. Integrated Ocean Drilling Program, College Station. https://doi.
org/10.2204/iodp.proc.346.101.2015.
Tada R, Murray RW, Alvarez Zarikian CA, Anderson WT Jr, Bassetti MA, Brace BJ,
Clemens SC, da Costa Gurgel MH, Dickens GR, Dunlea AG, Gallagher SJ,
Giosan L, Henderson ACG, Holbourn AE, Ikehara K, Irino T, Itaki T, Karasuda A,
Kinsley CW, Kubota Y, Lee GS, Lee KE, Lofi J, Lopes CICD, Peterson LC,
Saavedra-Pellitero M, Sagawa T, Singh RK, Sugisaki S, Toucanne S, Wan S,
Xuan C, Zheng H, Ziegler M (2015b) Methods. In: Tada R, Murray RW, Alvarez
Zarikian CA, the Expedition 346 Scientists (eds) Proc. IODP, 346. Integrated
Ocean Drilling Program, College Station. https://doi.org/10.2204/iodp.proc.
346.102.2015.
Tada R, Murray RW, Alvarez Zarikian CA, Anderson WT Jr, Bassetti MA, Brace BJ,
Clemens SC, da Costa Gurgel MH, Dickens GR, Dunlea AG, Gallagher SJ,
Giosan L, Henderson ACG, Holbourn AE, Ikehara K, Irino T, Itaki T, Karasuda A,
Kinsley CW, Kubota Y, Lee GS, Lee KE, Lofi J, Lopes CICD, Peterson LC,
Saavedra-Pellitero M, Sagawa T, Singh RK, Sugisaki S, Toucanne S, Wan S,
Xuan C, Zheng H, Ziegler M (2015c) Site U1424. In: Tada R, Murray RW,
Alvarez Zarikian CA, the Expedition 346 Scientists (eds) Proc. IODP, 346.
Integrated Ocean Drilling Program, College Station. https://doi.org/10.2204/
iodp.proc.346.105.2015.
Tada R, Zheng H, Clift PD (2016) Evolution and variability of the Asian monsoon
and its potential linkage with uplift of the Himalaya and Tibetan plateau.
Prog Earth Planet Sci 3:4. https://doi.org/10.1186/s40645-016-0080-y.
The geochemical society of Japan (2012) Encyclopedia of chemistry in earth andspace. Asakura Publishing Co., Ltd., Japan ISBN978-4-254-16057-4 C3544 (inJapanese).
Weltje GJ, Bloemsma MR, Tjallingii R, Heslop D, Röhl U, Croudace IW (2015)
Prediction of geochemical composition from XRF-core-scanner data: a new
multivariate approach including automatic selection of calibration samples
and quantification of uncertainties. In: Croudace IW, Rothwell RG (eds) MicroXRF Studies of Sediment Cores, Developments in Paleoenvironmental
Research 17. https://doi.org/10.1007/978-94-017-9849-5_21.
Weltje GJ, Tjallingii R (2008) Calibration of XRF core scanners for quantitative
geochemical logging of sediment cores: theory and application. Earth Planet
Sci Lett 274:423–438.
Yanagi T (2002) Water, salt, phosphorus and nitrogen budgets of the Japan Sea. J
Oceanogr 58:797–804.
Ziegler M, Jilbert T, de Lange GJ, Lourens LJ, Reichart GJ (2008) Bromine counts
from XRF scanning as an estimate of the marine organic carbon content of
sediment cores. G-cubed 9:Q05009.
Ziegler M, Lourens LJ, Tuenter E, Reichart GJ (2010) High Arabian Sea productivity
conditions during MIS 13—odd monsoon event or intensified overturning
circulation at the end of the mid-Pleistocene transition? Clim Past 6:63–76.