Tada et al. Progress in Earth and Planetary Science (2018) 5:19
https://doi.org/10.1186/s40645-018-0167-8

Progress in Earth andPlanetary Science

PAPER WITH FULL DATA ATTACHEDOpen Access

High-resolution and high-precision
correlation of dark and light layers in the
Quaternary hemipelagic sediments of theJapan Sea recovered during IODP
Expedition 346
Ryuji Tada1* , Tomohisa Irino2, Ken Ikehara3, Akinori Karasuda1, Saiko Sugisaki3, Chuang Xuan4, Takuya Sagawa5,
Takuya Itaki3, Yoshimi Kubota6, Song Lu2, Arisa Seki1, Richard W. Murray7, Carlos Alvarez-Zarikian8,
William T. Anderson Jr9, Maria-Angela Bassetti10, Bobbi J. Brace11, Steven C. Clemens12,
Marcio H. da Costa Gurgel13, Gerald R. Dickens14, Ann G. Dunlea16, Stephen J. Gallagher15, Liviu Giosan16,
Andrew C. G. Henderson17, Ann E. Holbourn18, Christopher W. Kinsley19, Gwang Soo Lee20, Kyung Eun Lee21,
Johanna Lofi22, Christina I. C. D. Lopes23, Mariem Saavedra-Pellitero24, Larry C. Peterson25, Raj K. Singh26,
Samuel Toucanne27, Shiming Wan28, Hongbo Zheng29 and Martin Ziegler30

Abstract
The Quaternary hemipelagic sediments of the Japan Sea are characterized by centimeter- to decimeter-scalealternation of dark and light clay to silty clay, which are bio-siliceous and/or bio-calcareous to a various degree.
Each of the dark and light layers are considered as deposited synchronously throughout the deeper (> 500 m) partof the sea. However, attempts for correlation and age estimation of individual layers are limited to the upper few
tens of meters. In addition, the exact timing of the depositional onset of these dark and light layers and its
synchronicity throughout the deeper part of the sea have not been explored previously, although the onset timing
was roughly estimated as ~ 1.5 Ma based on the result of Ocean Drilling Program legs 127/128. Consequently, it is
not certain exactly when their deposition started, whether deposition of dark and light layers was synchronous andwhether they are correlatable also in the earlier part of their depositional history.
The Quaternary hemipelagic sediments of the Japan Sea were drilled at seven sites during Integrated Ocean
Drilling Program Expedition 346 in 2013. Alternation of dark and light layers was recovered at six sites whose water
depths are > ~ 900 m, and continuous composite columns were constructed at each site. Here, we report our effort
to correlate individual dark layers and estimate their ages based on a newly constructed age model at Site U1424
using the best available paleomagnetic datum and marker tephras. The age model is further tuned to LR04 δ18O
curve using gamma ray attenuation density (GRA) since it reflects diatom contents that are higher during
interglacial high-stands. The constructed age model for Site U1424 is projected to other sites using correlation ofdark layers to form a high-resolution and high-precision paleo-observatory network that allows to reconstructchanges in material fluxes with high spatio-temporal resolutions.
Keywords: Quaternary sediments, Japan Sea, Inter-site correlation, High-resolution age model, IODP,
Expedition 346, U1424, U1425, U1426, U1430* Correspondence: ryuji@eps.s.u-tokyo.ac.jp
1
Graduate School of Science, The University of Tokyo, Tokyo, Japan
Full list of author information is available at the end of the article© 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.

Tada et al. Progress in Earth and Planetary Science (2018) 5:19

Introduction
Background

The Japan Sea is one of the marginal seas on the western
rim of northern Pacific that were formed more or lesssimultaneously during the Cenozoic. It is the most isolated marginal sea that is connected to neighboring
oceans only with shallow (< 130 m in sill depth) and narrow (< 90 km in width) straits (Fig. 1). Partly because of
its semi-isolation, the Japan Sea has its own deep water(called Japan Sea Proper Water), which ventilates thedeeper part of the sea with the residence time of ~100 years (Gamo et al. 2014), and thus, the sea is occasionally called a miniature ocean (Gamo et al. 2014).
The deep water below the water depth of ~ 2000 m ishighly homogenous with low and nearly constanttemperature of 0.04~0.07 °C, slightly low salinity of
34.07‰, low phosphorous of 1.9~2.2 μmol/kg, and highdissolved oxygen of 200~ 230 μmol/kg (Talley et al.
2006; Gamo et al. 2014). Consequently, the modern
Japan Sea is one of the most oxic ocean basins in theworld and relatively poor in nutrients. However, the situation was not necessarily the same in the geological pastwhen sea level and the properties of the inflowing waters
were different (e.g., Gallagher et al. 2015). We understand that the marginal sea discussed here is known bydifferent names, including the “Japan Sea” and “EastPage 2 of 10

Sea”. In this paper, we use “Japan Sea” given the order ofauthorship.
Previous studies

In the summer of 1989, JOIDES Resolution entered theJapan Sea and drilled at six sites during Ocean Drilling
Program (ODP) legs 127/128 (Tamaki et al. 1990) to explore its tectonic and paleoceanographic histories. Basedon the results of these legs, Tada et al. (1992) reported
that Quaternary sediments in the deeper part of the sea
are characterized by centimeter- to meter-scale alternations of dark, organic-rich layers and light, organic-poor
layers. They further demonstrated that their deposition
was synchronous basin-wide and the dark (and light)
layers can be correlated in-between sites. Tada et al.
(1999) demonstrated that alternation of dark and lightlayers reflects millennial-scale changes in the contribution of nutrient-rich East China Sea coastal water to the
influx through the Tsushima Strait, which probably reflects changes in Yangtze River discharge caused by thechanges in East Asian Summer Monsoon intensity in association with the Dansgaard-Oeschger Cycle (DOC)
with dark layers deposited during interstadials (see also
Tada 2005, 2012). Consequently, the onset timing of thedark and light layer deposition and temporal changes in
the amplitude and frequency of their alternation

Fig. 1 A map showing locations of studied sites (red circles) together with unstudied sites (white circles) drilled during IODP Expedition 346 in theJapan Sea and northern East China Sea. Surface currents within the sea, water depths of each sites, and sill depths of each straits are also indicatedTada et al. Progress in Earth and Planetary Science (2018) 5:19

collected wide attention. Tada (2005) estimated the onset
timing of the deposition of dark and light layers at approximately 1.5 Ma. However, since drilling was conducted in a single hole, the correlation gaps existed
between cores and correlation among the sites was not
perfect. Consequently, correlation went back only to
0.7 Ma (Tada et al. 1992). In addition, the age model wasof lower resolution and precision since drilling was in asingle hole and only limited paleomagnetic and biostratigraphic events were available at that time (e.g., Tada 1994).
Objective of this study

In order to specify the onset timing of deposition of dark
and light layers, to examine the origin and the nature of theiralternations, and to explore their temporal changes in frequency and amplitude, Integrated Ocean Drilling Program(IODP) Expedition 346 was conducted in the summer of2013 and drilled at seven sites in the Japan Sea and two sites
in the northern tip of the East China Sea (Fig. 1). To accomplish the objectives described above, high-resolution andhigh-precision correlation of sedimentary sequences among
the sites within the sea is critical, especially for the Quaternary interval. Here, we present a result of group effort tocorrelate the dark and light layers in the Quaternary interval among six sites located in the deeper (> 900 m) parts ofthe sea where dark and light color contrast is distinct.

Construction and content
Studied sites

Seven sites were drilled during the IODP Expedition 346.
Sites were selected so that they cover wide ranges of latitude, longitude, and water depths to form a “paleo-observatory network”. With respect to the present water depth,
Site U1427 is the shallowest site at ~ 320 m water depth,
Sites U1426 and U1430 are shallower depth sites of around1000 m, Sites U1425 and U1423 are intermediate depthsites of slightly less than 2000 m, and Sites U1422 andU1424 are the deepest sites in excess of 2800 m water
depth (Fig. 1). Sites U1426 and U1430 are on the bank, Site
U1425 is on a terrace within the failed rift in the middle of
the Yamato Rise, Sites U1423 and U1427 are on gentle
slopes, and Sites U1422 and U1424 are on the basin floor.
Sites U1427, U1424, and U1423 are under the influence ofthe first branch of the Tsushima Warm Current (TWC),
Site U1426 is under the influence of the second branch,and Sites U1430 and U1425 are under the influence of thethird branch of TWC, respectively. Site U1422 is under the
influence of the Liman Cold Current. Sites U1422, U1423,
and U1424 were influenced by sea ice at least during thelast glacial period (Ikehara 2003). Sites U1427, U1426, andU1425, as well as Sites U1424, U1423, and U1422 can form
latitudinal transects; Sites U1427, U1426, U1425, andU1424, as well as Sites U1423 and U1422 can form depth

Page 3 of 10

transects; and U1430, U1425, and U1424 can form a longitudinal transect, respectively.
Three to five holes are drilled at each site at least to thedepth of ~ 100 m so that we can construct a continuous
stratigraphic column at each site by core splicing, at least
for the Quaternary interval (Tada et al. 2015). Since Sites
U1424 and U1426 are drilled approximately at the same
locations as ODP Sites 794 and 798, respectively, whereprevious drilling (legs 127/128) drilled deeper into Miocene, it is possible to use the cores from these sites tocomplement stratigraphic information on the older part.
Studied methods
Inter-hole correlations and construction of composite columns

It is important to construct perfectly continuous composite
columns at all the sites to conduct high-resolution andhigh-precision correlations of dark and light layers inbetween the sites. We conducted inter-hole correlation of
all the recovered cores covering the lithological Unit I (Tadaet al. 2015) at each site for this purpose. In addition, interhole correlation of cores enables us to precisely correlate
off-splice parts of cores to the composite columns (spliced
sections) so that we can use samples taken from off-spliceparts of cores in the same way as those taken from the
spliced parts and thus can drastically increase the amountof samples utilized for high-resolution studies.
Preliminary inter-hole correlation of cores was conductedonboard by stratigraphic correlators based on RGB (redgreen-blue), GRA (gamma ray attenuation), and NGR (natural gamma ray) profiles taken immediately after core retrieval (Tada et al. 2015). However, there was no time
onboard to examine core photographs in detail to crosscheck the validity of inter-hole correlations. For this reason,
there were possibilities that stratigraphic gaps and/or repetitions of the sequence caused by small faults mostly
formed during drilling were overlooked. Also, drilling disturbance may affect physical properties such as GRA andNGR and even color in some cases, but they are easily
overlooked just by examining profiles of physical properties
and/or color especially if disturbances are minor. If the coresediments are homogeneous or heavily bioturbated, suchsmall faults or disturbances are difficult to identify. However, in the case of the Quaternary part of the Japan Sea
sediments, centimeter- to meter-scale dark and light layers
serve as good markers to detect such minor faults and disturbances. We went back to high-resolution core photos ofUnit I to identify minor faults, core disturbances, and artificial modifications such as plugging sponges in interstitialwater (IW) sampling intervals and modified tie points toavoid such intervals. Details of procedures of inter-hole correlation, revision of tie points, and construction of composite sections are presented in Irino et al. (in press), and weadopt their results (revised composite sections) in thisstudy.

Tada et al. Progress in Earth and Planetary Science (2018) 5:19

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Inter-site correlations

Inter-site correlations of dark and light layers are conductedbased on visual inspection of composite columns of the six
sites. First, we make a continuous composite column ateach site using high-resolution core photographs (Irino etal., in press) and pick up relatively thick and distinct darklayers as marker layers. We set the bottom of marker darklayers as correlation tie points since many of the dark layers
are laminated especially at their bottoms; thus, the effect of
bioturbation is minimal (Watanabe et al. 2007). We use acomposite column of Site U1424 as a reference column
since its preliminary age model (Tada et al. 2015) suggeststhat the linear sedimentation rate (LSR) is more or lessconstant throughout the Quaternary and no significant
sedimentation break exists. In addition, magnetostratigraphic events are best identified (Xuan et al., 2018, personal communication) and the largest number of tephra
layers is found at this site. Next, we visually correlatemarker dark layers at Site U1424 with those at other sites
from the top of the column downward. We use marker
tephra layers (Sagawa et al., in press) and magnetostratigraphic events (Xuan et al., 2018, personal communication)
as guides to correlate marker dark layers among the sites.
After inter-site correlation is completed, photographs ofcomposite columnar sections of each sites are adjusted intheir lengths at the core top and the Brunhes/Matsuyama
boundary so that we can visually check the appropriateness of inter-site correlation of marker dark layers(Additional file 1: Figure S1).
Construction of the age model

The master age model of Unit I is constructed for Site
U1424 where sedimentation seems continuous with relatively constant LSR, magnetostratigraphic events are best
defined, and the largest number of tephra are identified
among the six deeper sites drilled in the Japan Sea during Exp. 346. We use the revised magnetostratigraphy of
Xuan et al. 2018 (personal communication) and tephrochronology of Sagawa et al. (in press) and Satoguchi andNagahashi (2012) to construct an age model, which wecall a tephra-p-mag-based age model (Fig. 2). The datum
used to construct the age model is listed in Table 1.
A tephra-p-mag-tuned age model is further tuned to
LR04 age model (Lisiecki and Raymo 2005) by visuallycorrelating GRA and NGR composite profiles of U1424 to
LR04 δ18O stack of benthic foraminifers. It is well known
that GRA decreases with the increase in diatom contents
because diatom frustules have high internal porosity (Tadaand Iijima 1983). NGR also decreases with the increase indiatom contents because diatoms dilute detrital material.
In case of the Quaternary sediments of the Japan Sea, diatom abundance strongly links to glacio-eustatic sea level
because surface productivity of the sea is controlled by nutrient influx through the Tsushima Strait, which in turnFig. 2 A diagram showing age versus depth relationship at Site
U1424 based on marker tephras and magnetostratigraphic events
listed in Table 1. Depth is in CCSFD_patched meter scale

has been modulated by glacio-eustatic sea level changes(Tada et al. 1992, 1999; Tada 2012). Because the Tsushima
Strait is only 130 m deep and its width and depth increase
with the rise in sea level, the influx of the TWC is expected to increase drastically with the rise in sea level.
Thus, diatom abundance can be used as a sea level proxy.
Tuning of U1424 age to LR04 age is conducted for thelast ~ 3 m.y. based on visual correlation of the GRA andNGR composite profiles with LR04 δ18O stack profile.
We put priority on GRA over NGR for correlation because GRA data has higher resolution than NGR. We
then cross-check the correlation by comparing LR04
stack profile with NGR profile. For most of glacialinterglacial cycles, GRA and NGR profiles show patterns
similar to each other without phase shift and thus confirm the correlation based on GRA. For several intervals
where the GRA profile does not show a clear patternsimilar to LR04 δ18O stack profile, NGR profile is used
for correlation. The correlation of GRA and NGR with
LR04 δ18O stack is shown in Additional file 2: Figure S2
and CCSF-D_patched depth and age for each correlation
point are listed in Table 2 where CCSF-D_patched depth
is the depth scale for the revised composite section. A
resulted LR04-tuned age model is shown in Fig. 3.

Results and discussion
Age estimation of marker dark layers

In this study, we first constructed perfectly continuouscomposite columns for the entire Quaternary sequencesat the six deeper sites studied, and using these composite
columns, we correlated distinct dark layers among the sites

Tada et al. Progress in Earth and Planetary Science (2018) 5:19

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Table 1 A list of tephras and magnetostratigraphic events, their composite depths (CCSFD_patched), ages, and references used toconstruct a tephra and p-mag based age model shown in Fig. 2
Control No.

Event name

Other name0Core top

0

0.000

0.000

T01

AT

0.03

1.659

1.350

T02

BT22

Aso-4

0.09

3.960

3.860

T03

JS72

Toya

0.10

4.750

4.650

TK01

Aso-1

0.26

10.85211.002

TK02

B-Og

0.45

16.67516.215

T04

Ka1

0.7

24.45824.358T05

Imakuma1

Hkd-Ku0.75

26.52726.427

PM01

Bot C1n

B/M

0.78

27.54227.442

T06

Yamada1

0.95

33.87133.751PM02

Top C1r.1n

Top Jarallillo

0.99

34.94134.821

T07

Pink

SS-Pnk

1.02

36.79537.121PM03

Bot C1r.1n

Bot Jarallillo

1.07

37.74138.101PM04

Top C1r.2n

Top Cobb Mountain

1.17

40.63540.995

PM05

Bot C1r.2n

Bot Cobb Mountain

1.19

40.84541.205T08

Kd18?

Ak-Kd18

1.45

47.58648.436

T09

FukudaEb-Fkd1.75

57.81258.662PM06

Top C2nTop Olduvai

1.78

59.69260.542

PM07

Bot C2n

Bot Olduvai

1.95

63.90264.752PM08

Top C2r.1n

Top Reunion

2.13

67.91368.763

PM09

Bot C2r.1n

Bot Reunion

2.15

68.40669.256

T10

MushonoMsn-Jwg4

2.3

74.72775.577PM10Top C2An.1n

M/G

2.58

81.39682.246

T11

Asashiro

Ass-Tmd2

2.62

83.23184.451PM11

Top C2An.1r

Top Kaena

3.03

97.68298.992PM12

Bot C2An.1r

Bot Kaena

3.12

98.53799.847

T12

Souri

Sr-Ity3.55

114.662115.972

T16

Ohta

Znp-Ohta

3.95

142.667

143.977

for the interval covering the last 1.5 My corresponding to
the lithological Subunit IA (Additional file 1: Figure S1).
Then, we constructed a high-resolution and high-precision
age model at Site U1424 based on correlation of GRA andNGR with LR04 δ18O stack (Additional file 2: Figure S2).
By using this age model, it is possible to estimate the ages
of individual marker dark layers and thus project their ages
to other sites.
Coding of dark layers

As is described above, dark layers are useful markers tomake a high-resolution correlation between sites and assign
precise ages to the sedimentary sequences in the deeper
part of the Japan Sea. Consequently, it is useful to give themcode numbers so that we can easily identify dark layers of
our interest and estimate their ages. As to the last glacial
period, thinly laminated (TL) layer numbering was

Age (Ma)CCSF-D (m)CCSF-D _Patched (m)conducted in the way so that TL numbers agree with interstadial numbers of DOC (Tada et al. 1999; Dansgaard et al.
1993). No numbering has been made on dark layers deposited before Marine isotope stage (MIS) 6 except by Tada etal. (1992) who made tentative naming of distinct dark layers
at ODP Sites 794, 795, and 797. However, their naming was
not systematic and went back to only ca. 0.7 Ma.
In this study, we conduct numbering of the marker
dark layers in Subunit IA covering the last 1.45 Ma. We
first identify relatively thick and distinct dark layers
as marker layers for the purpose of inter-site correlation as is described above. Then, using these marker
dark layers and tephra layers as guides, we further
identify thinner but distinct dark layers that can becorrelated among the deeper six sites and can be usedas second order marker layers. The results are listed
in Additional file 3: Table S1.

Tada et al. Progress in Earth and Planetary Science (2018) 5:19

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Table 2 A list of correlation point numbers, their depths (CCSFD_patched) on U1424 composite column, and their corresponding
ages on LR04 δ18O stack profile. Correlation points are also shown in Additional file 2: Figure S2
Exp Site

Hole Core Type Sect A/W Offset (cm) CSF-A (m) CCSF-A (m) CCSF-D_Patched (m) Age Control No. LR04-tuned Age (Ma)346 U1424 A

1

H

1

A

97.0

0.97

0.97

0.97

1

0.018

346 U1424 A

1

H

3

A

20.0

3.20

3.20

3.10

2

0.069

346 U1424 B

2

H

1

A

120.0

3.90

6.05

5.95

3

0.135

346 U1424 B

2

H

2

A

6.0

4.26

6.41

6.31

4

0.156

346 U1424 B

2

H

3

A

144.0

7.14

9.29

9.19

5

0.223

346 U1424 B

2

H

4

A

125.0

8.45

10.60

10.50

6

0.246

346 U1424 B

2

H

5

A

78.0

9.48

11.63

11.53

7

0.278

346 U1424 B

2

H

5

A

135.5

10.06

12.21

12.11

8

0.294

346 U1424 A

2

H

5

A

29.0

13.09

13.86

13.76

9

0.341

346 U1424 B

3

H

2

A

28.0

13.98

16.44

16.34

10

0.431

346 U1424 B

3

H

3

A

130.5

16.51

18.97

18.87

11

0.513

346 U1424 B

3

H

4

A

52.5

17.23

19.69

19.59

12

0.536

346 U1424 A

3

H

2

A

127.5

19.08

20.97

20.87

13

0.583

346 U1424 A

3

H

4

A

15.0

20.95

22.85

22.75

14

0.630

346 U1424 B

4

H

1

A

87.5

22.58

25.79

25.69

15

0.718

346 U1424 A

3

H

6

A

74.0

24.54

26.44

26.34

16

0.746

346 U1424 B

4

H

2

A

147.0

24.67

27.89

27.79

17

0.794

346 U1424 B

4

H

4

A

102.5

27.23

30.44

30.34

18

0.872

346 U1424 A

4

H

2

A

104.0

28.34

31.64

31.54

19

0.922

346 U1424 A

4

H

4

A

30.0

30.60

33.90

33.78

20

0.964

346 U1424 A

4

H

4

A

122.5

31.53

34.83

34.71

21

0.986

346 U1424 C

4

H

5

A

119.5

33.10

36.42

36.33

22

1.038

346 U1424 B

5

H

3

A

107.0

34.73

38.13

38.49

23

1.098

346 U1424 B

5

H

4

A

72.5

35.89

39.29

39.65

24

1.122

346 U1424 B

5

H

5

A

79.0

37.45

40.85

41.21

25

1.198

346 U1424 A

5

H

2

A

134.5

38.15

42.14

42.50

26

1.248

346 U1424 C

5

H

3

A

85.0

39.25

43.30

44.06

27

1.290

346 U1424 A

5

H

4

A

102.5

40.83

44.82

45.59

28

1.336

346 U1424 A

5

H

5

A

114.0

42.44

46.44

47.25

29

1.412

346 U1424 B

6

H

2

A

135.5

43.43

47.79

48.64

30

1.456

346 U1424 B

6

H

4

A

17.5

45.25

49.61

50.46

31

1.496

346 U1424 B

6

H

5

A

112.0

47.69

52.06

52.91

32

1.535

346 U1424 A

6

H

3

A

58.0

48.38

52.95

53.80

33

1.575

346 U1424 A

6

H

4

A

62.5

49.93

54.49

55.34

34

1.613

346 U1424 A

6

H

5

A

37.0

51.17

55.74

56.59

35

1.655

346 U1424 A

6

H

5

A

129.5

52.10

56.66

57.51

36

1.700

346 U1424 B

7

H

2

A

137.0

53.07

58.30

59.15

37

1.748

346 U1424 B

7

H

4

A

37.5

55.08

60.31

61.16

38

1.795

346 U1424 B

7

H

5

A

21.5

56.42

61.65

62.50

39

1.863

346 U1424 B

7

H

6

A

36.5

58.07

63.30

64.15

40

1.900

346 U1424 A

7

H

4

A

55.0

59.35

64.48

65.33

41

1.948

346 U1424 A

7

H

5

A

7.0

60.37

65.50

66.35

42

2.000

346 U1424 A

7

H

5

A

142.0

61.72

66.85

67.70

43

2.065

Tada et al. Progress in Earth and Planetary Science (2018) 5:19

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Table 2 A list of correlation point numbers, their depths (CCSFD_patched) on U1424 composite column, and their corresponding
ages on LR04 δ18O stack profile. Correlation points are also shown in Additional file 2: Figure S2 (Continued)
Exp Site

Hole Core Type Sect A/W Offset (cm) CSF-A (m) CCSF-A (m) CCSF-D_Patched (m) Age Control No. LR04-tuned Age (Ma)346 U1424 B

8

H

3

A

11.5

62.82

68.88

69.73

44

2.155

346 U1424 B

8

H

3

A

149.0

64.19

70.25

71.10

45

2.200

346 U1424 B

8

H

4

A

117.5

65.38

71.44

72.29

46

2.240

346 U1424 B

8

H

5

A

49.0

66.19

72.25

73.10

47

2.275

346 U1424 A

8

H

4

A

52.5

68.83

73.44

74.29

48

2.313

346 U1424 A

8

H

5

A

52.0

70.32

74.94

75.79

49

2.358

346 U1424 B

9

H

1

A

130.0

70.50

77.14

77.99

50

2.433

346 U1424 B

9

H

2

A

110.5

71.77

78.41

79.26

51

2.488

346 U1424 B

9

H

3

A

74.5

72.91

79.55

80.40

52

2.518

346 U1424 B

9

H

4

A

60.0

74.26

80.90

81.75

53

2.565

346 U1424 A

9

H

3

A

50.5

76.81

82.15

83.09

54

2.600

346 U1424 B

9

H

5

A

139.5

76.56

83.20

84.42

55

2.645

346 U1424 B

9

H

6

A

124.5

77.91

84.55

85.86

56

2.688

346 U1424 A

9

H

5

A

66.5

79.97

85.31

86.62

57

2.715

346 U1424 B

10

H

3

A

122.5

82.93

89.75

91.06

58

2.805

346 U1424 B

10

H

5

A

89.0

85.59

92.41

93.72

59

2.878

346 U1424 A

10

H

4

A

102.5

88.33

94.18

95.49

60

2.920

346 U1424 A

10

H

5

A

117.0

89.97

95.83

97.14

61

2.975

Fig. 3 A diagram showing age versus depth relationship at Site
1424 based on tuning of GRA and NGR profile at U1424 and LR04
benthic δ18O record of Lisiecki and Raymo (2005). All tuned points
fall in an age versus depth relationship based on marker tephras andmagnetostratigraphic events within uncertainties

The relatively thick and distinct dark layers occur every
several meters and they tend to be associated with quasicyclic changes in amplitude and frequency of sediment lightness (L*) in Subunit IA, which seems to be associated withglacial-interglacial sea level changes as will be discussed
later. In brief, thicker dark layers tend to occur during glacial
maxima especially when sea level was lowered by more than
100 m and euxinic deep water emerged due to developmentof low-salinity surface water (Tada et al. 1999; Kido et al.
2007; also Seki 2017). Thick dark layers accumulated undereuxinic deep water were found during MIS 2, 6, 10, 12, 16,
20, and 22 (Seki 2017). Such dark layers are overlain by thicklight layers which were deposited during interglacial
maxima. These characteristics are less clear before MIS 22(~ 0.9 Ma) when thick diatomaceous dark layers frequently
deposited during interglacial maxima.
We define a cycle of such several meter-scale change in
amplitude and frequency of lightness as starting from the
top of a relatively thick and distinct dark layer downward
to the base of the relatively thick light layer so that one
cycle basically corresponds to one glacial-interglacial
cycle. From the core top downward, cycle number starts
from 0 and increases downward. Because we tunechanges in sea level proxies such as GRA and NGR to
LR04 δ18O stack so as to construct high-resolution age
model for Unit I as described above, and because one
cycle basically represents one glacial-interglacial cycle,
there is a relation between a cycle number and MIS number. Namely,Tada et al. Progress in Earth and Planetary Science (2018) 5:19

X ¼ Y =2−1
where X is a cycle number and Y is an MIS number when
the thick dark layer at the top of cycle X deposited. Exceptions are cycle 0 that corresponds to the Holocene whenno thick dark layer exists at the top, cycle 1 whose top
thick dark layer corresponds to MIS 2 and thus X = Y/2,
cycle 20 whose thick and dark layer deposited during MIS
45 (interglacial period) and thus X = Y/2 − 2.5, and cycle
21 whose thick dark layer deposited at MIS 46 and thus X= Y/2 − 2. A relatively thick and distinct dark layer at a topof cycle X is named Dark Layer (DL)-X-1 (Additional file
1: Figure S1; Additional file 3: Table S1). Every cycle contains several thinner but still distinct dark layers thatare possible to correlate in-between sites. We put
numbers 2, 3, … on them in descending order and described as suffixes to the cycle number. Namely, Zthdark layer in cycle X is DL-X-Z. In Additional file 3:
Table S1, we list ages at the base of each dark layer
based on tephra-p-mag-tuned and LR04-tuned age
models for the last ~ 3 My. We also list depths andages at the top of marker dark layer that define the
top of each cycle, although it should be noted that theirdepths and ages may be less well defined and could beslightly diachronous due to the result of bioturbation.
Temporal and spatial changes in linear sedimentation
rates (LSRs) in the Japan Sea during the last 1.45 My

As is described in the previous section, we estimatedthe age at the base of each marker dark layer at Site
1424 and projected its age to other sites based oninter-site correlation described above (Table 2). By
using these data, it is possible to calculate linear sedimentation rates (LSRs) at all the six sites with hightime resolution (Additional file 4: Table S2). Additional file 5: Figure S3 shows temporal changes in
LSRs at all sites. LSRs are more or less constant at ~4 and ~ 3 cm/ky at Sites U1422 and U1424 (deeper
sites); gradually increasing from ~ 3 to ~ 10 cm/ky,
from ~ 2 to ~ 7 cm/ky, and from ~ 2 to ~ 8 cm/ky at
Sites U1423, U1425, and U1430 (intermediate depths
sites); and relatively high and more or less constantat ~ 10 cm/ky at Site U1426 (shallow site), respectively.
Exceptions are between ~ 850 and ~ 1200 ka when LSRs
are slightly higher and variable and after ~ 250 ka when
LSRs increase upward. At Site U1430, extremely low LSR
is observed at ~ 800 ka.
In general, LSR tends to be lower at deeper sites,
which probably reflects dissolution of carbonate (andbiogenic silica to some extent). The upward increase in
LSRs after ~ 250 ka is probably because near-surface
sediments are less compacted. The gradually increasing
trend of LSR at intermediate depth sites can be partly
due to lesser degree of compaction, but the increasing

Page 8 of 10

trends started from deeper parts. The upward increasing
trend of LSRs could be explained by the upward increasein biogenic carbonate content due to deepening of calcium carbonate compensation depth (CCD) that crossed
the intermediate depths of 1000 to 2000 m at ~ 1.0 Ma.
Variable LSRs between ~ 850 and ~ 1200 ka could be related to large amplitude changes of CCD during transition from shallower CCD before 1200 ka to deeper CCD
after 850 ka. Mass accumulation rate (MAR) calculationof carbonate at these sites based on high-resolution
XRF core scanner and gamma ray attenuation (GRA)
porosity data combined with LSR data will be necessary to test this possibility.

Establishment of paleo-observatory network

Reconstruction of material cycling such as carbon, sulfur, and phosphorous within the earth surface is criticalto understand dynamics and controlling mechanisms ofclimatic changes in the past and preparing for the future.
Especially, changes in centennial to millennial timescales are of prime importance since they are beyond thecoverage of observational records, but still, climaticchanges of such time scales are relevant to the society.
Spatial coverage is also important since spatial changes
in mass flux often give clues to understand the processes
within the system of interest and their controlling factors. However, it is generally difficult to correlate geological records from different localities with high time
precision and resolution. In this respect, Quaternary
hemipelagic sediments of the Japan Sea provide a rareopportunity to study spatiotemporal changes of massflux with high time precision and resolution. Namely,marker dark layers and tephra layers can be correlatedwith the time precision of less than 100 years, and approximately 250 marker layers are defined during thelast 1.45 Ma, providing ~ 6 ky resolution in average.
These time precision and resolution are an order ofmagnitude higher than those for other correlation
methods such as biostratigraphy, paleomagnetism, andradiometric dating. In addition, dry bulk density of thesediments can be estimated from GRA data measured
onboard. Thus, it is possible to reconstruct MARs withan average time resolution of ~ 6 ky at the six deeper
IODP sites that cover the area more than a half of theJapan Sea. Moreover, we can calculate MAR of individual chemical element and/or mineral by combining
high-resolution MAR data with high-resolution chemical
and/or mineralogical analyses data.
In this study, we propose to utilize the six IODP sites in
the Japan Sea as paleo-observatory network since highprecision age data and high-resolution LSRs and GRA
data are available; the sites cover wide latitude, longitude,
and water depth ranges; proxy data at each site can beTada et al. Progress in Earth and Planetary Science (2018) 5:19

correlated with precision of less than 100 years; and goodamount of samples are still available from IODP.

Conclusions
The Quaternary hemipelagic sediments in the Japan
Sea (Subunit IA) are characterized by centimeter- to
decimeter-scale alternation of dark and light layers.
Over 250 dark layers are present and 64 distinct darklayers are chosen that are traceable throughout the
deeper (> 500 m water depth) part of the basin andcorrelated in-between the six sites (U1422, 1423, 1424,
1425, 1426, and 1430) drilled by IODP Expedition 346.
An age model covering the last 3 My is constructed at
Site U1424 based on tephra-chronology and magnetostratigraphy, which is further tuned to LR04 age using
GRA profile, a proxy for sea level change in the Quaternary Japan Sea, correlated to LR0 4 δ18O stack profile.
We estimate ages of marker dark layers at Site U1424,
which are projected to other sites based on inter-sitecorrelation of marker dark layers. In this way, we establish paleo-observatory network covering the last
1.45 My in the Southeastern half of the Japan Sea. This
network will greatly enhance our understanding onmaterial cycling in the Japan Sea.
Additional files
Additional file 1: Figure S1. Figures showing inter-site correlation ofmarker dark layers in Subunit IA among six deeper sites in the Japan Sea
drilled during Expedition 346. a From 0 to 0.8 Ma and b from 0.8 to 1.5
Ma. Code numbers of marker dark layers (in Additional file 3: Table S1),
marker tephras, and paleomagnetic event boundaries (in Table 1) are also
shown. (TIF 6.55 mb)
Additional file 2: Figure S2. a-d Correlation of GRA and NGR profiles at
Site U1424 with LR04 benthic δ18O record of Lisiecki and Raymo (2005)
during the last 3 My to construct LR04-tuned age model. Correlation
points are numbered and listed in Table 2. Also shown at the bottom is
L* profile with marker dark layer numbers during the last 1.5 Ma, whoseages and depths are listed in Additional file 3: Table S1. (TIF 8.26 mb)
Additional file 3: Table S1. Code numbers and ages of marker darklayers and their composite depths (CCSFD_patched) at Sites U1422,
U1423, U1424, U1425, U1426, and U1430. (XLSX 21 kb)
Additional file 4: Table S2. A list of linear sedimentation rates (LSRs)
between two adjacent marker dark layer horizons at each site during thelast 1.4 Ma (corresponding to Subunit IA) based on the two age models.
(XLSX 69 kb)
Additional file 5: Figure S3. Temporal changes in linear sedimentation
rates (LSRs) at all the studied sites during the last 1.45 Ma calculated
based on ages of marker dark layers whose ages are estimated based on
LR04-tuned age model of U1424 (blue) and tephras and paleomagnetic
events (orange). (TIF 4.45 mb)

Abbreviations
CCD: Calcium carbonate compensation depth; CCSF: Core composite depth
below sea floor; DL: Dark Layer; DOC: Dansgaard-Oeschger Cycle;
GRA: Gamma ray attenuation; IODP: Integrated Ocean Drilling Program;
IW: Interstitial water; LSR: Linear sedimentation rate; MAR: Mass accumulation
rate; MIS: Marine isotope stage; NGR: Natural gamma ray; ODP: Ocean Drilling
Program; RGB: Red-green-blue; TL: Thinly laminated; TWC: Tsushima Warm
Current; XRF: X-ray fluorescence

Page 9 of 10

Acknowledgements
We thank the technicians and crews of IODP Expedition 346 for their
dedicated efforts to help us in retrieving high-quality cores and shipboard
data that were used in this study. This research used samples and/or data
provided by the Integrated Ocean Drilling Program (IODP).
Funding
This work was supported by a grant from IODP Exp. 346 After Cruise
Research Program, JAMSTEC, awarded to TR, IK, Irino T, Itaki T, ST, KY, SS, andKA and from JSPS KAKENHI grant number 16H01765 awarded to TR.
Authors’ contributions
Exp. 346 scientists collected basic data for this study during IODP Expedition to
the Japan Sea. TR, MRW, and ZCA directed AWT Jr., BMA, BBJ, CSC, GMHC, DGR,
GSJ, GL, HACG, HAE, IK, Irino T, Itaki T, KA, KCW, KY, LGS, LKE, LJ, LCICD, PMS, PLC,
SRK, SS, ST, TS, WS, XC, ZH, and ZM to collect data. TR, Irino T, and IK proposed
the topic and conceived and designed the study. TR, Irino T, IK, TS, KA, LS, and SA
conducted detailed inter-site correlation of dark layers, SS and XC conducted
revision of magneto-stratigraphy, and Itaki T and KY conducted revision ofbiostratigraphy. TR, Irino T, Itaki T, KA, LS, and SA drew figures, and TR wrote a
draft of the manuscript. All authors read and approved the final manuscript.
Authors’ information
TR and MRW were co-chief scientists, ZCA is a staff scientist, and IK, Irino T,
Itaki T, ST, KY, SS, KA, XC, AWT Jr., BMA, BBJ, CSC, GMHC, DGR, GSJ, GL, HACG,
HAE, KCW, LGS, LKE, LJ, LCICD, PMS, PLC, SRK, TS, WS, ZH, and ZM were
shipboard scientists of IODP Expedition 346. KA and SA are students of TR,
and LS is a student of Irino T.
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
Graduate School of Science, The University of Tokyo, Tokyo, Japan. 2Facultyof Environmental Earth Science, Hokkaido University, Sapporo, Japan.
3
Research Institute of Geology and Geoinformation, Geological Survey ofJapan, AIST, Tsukuba, Japan. 4National Oceanography Centre Southampton,
Southampton, UK. 5Institute of Science and Engineering, Kanazawa
University, Kanazawa, Japan. 6Department of Geology and Paleontology,
National Museum of Nature and Science, Tsukuba, Japan. 7Department ofEarth and Environment, Boston University, Boston, USA. 8International Ocean
Descovery Program, Texas A&M University, College Station, USA. 9Marine
Sciences, Florida International University, Miami, USA. 10Laboratoire CEFREM,
Université de Perpignan, Perpignan, France. 11Department of Earth andAtmospheric Sciences, University of Nebraska, Lincoln, USA. 12Earth,Environmental, and Planetary Sciences, Brown University, Providence, USA.
13
Escola de Artes, Ciencias e Humanidades (EACH), Universidade de São
Paulo, São Paulo, Brazil. 14Department of Earth, Environmental, and Planetary
Science, Rice University, Houston, USA. 15School of Earth Sciences, Universityof Melbourne, Melbourne, Australia. 16Present Address: Department of
Geology and Geophysics, Woods Hole Oceanographic Institution, Woods
Hole, USA. 17School of Geography, Politics and Sociology, University of
Newcastle Upon Tyne, Newcastle Upon Tyne, UK. 18Institute for Geosciences,
Christian-Albrechts-Universitat zu Kiel (IFM), Kiel, Germany. 19Department ofEarth, Atmospheric and Planetary Sciences, Massachusetts Institute ofTechnology, Cambridge, USA. 20Petroleum and Marine Research Division,
Korea Institute of Geoscience and Mineral Resources, Daejeon, South Korea.
21
Department of Ocean Science, Korea Maritime and Ocean University,
Busan, South Korea. 22Géosciences Montpellier, Université Montpellier II,
Montpellier, France. 23IPMA, Lisbon, Portugal. 24Department of Geosciences,
FB5, University of Bremen, Bremen, Germany. 25Rosenstiel School of Marine
and Atmospheric Science, University of Miami, Miami, USA. 26School of Earth,
Ocean and Climate Sciences, Indian Institute of Technology Bhubaneshwar,
Bhubaneshwar, India. 27Centre Bretagne, IFREMER, Plouzané cedex, France.
28
Institute of Oceanology, Chinese Academy of Sciences, Beijing, China.
29
Present Address: Research Center for Earth System Science, Yunnan

Tada et al. Progress in Earth and Planetary Science (2018) 5:19

University, Kunming, China. 30Present Address: Department of Earth Sciences,
Utrecht University, Utrecht, Netherlands.
Received: 30 November 2016 Accepted: 21 November 2017

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