ISSN 0916-7390

九州大学大学院理学研究院紀要

M E M O I R S
OF THEFACULTYOFSCIENCESKYUSHU UNIVERSITY

Series D Earth and Planetary Sciences
VOLUME XXXII
No. 3

FUKUOKA, JAPANMarch, 2011

Contents

Takahito Ikenoue, Kozo Takahashi, Tatsuhiko Sakamoto, Saburo Sakai
and Koichi Iijima:
Occurrences of radiolarian biostratigraphic markers Lychnocanoma
nipponica sakaii and Amphimelissa setosa in Core YK07-12 PC3B
from the Okhotsk Sea …………………………………………………………

1

Takashi Ninomiya:
Chemosynthetic fossil molluscan faunas from the Neogene
Taishu Group, distributed in Tsushima Islands, Nagasaki Prefecture,
the southwest Japan ………………………………………………………… 11
Hideto Tsutsui and Kozo Takahashi:
Cell size variation of Anoplosolenia brasiliensis (calcareous nannoplankton)in the central equatorial Pacific Ocean ……………………………………… 27
Jonaotaro Onodera, Yusuke Okazaki, Kozo Takahashi, Kei Okamura,and Masafumi Murayama:
Distribution of polycystine Radiolaria, Phaeodaria and Acantharia
in the Kuroshio Current off Shikoku Island and in Tosa Bay during Cruise
KT07-19 in August 2007 …………………………………………………… 39
Terumasa Tokunaga, Kiyohumi Yumoto, Teiji Uozumi and CPMN Group:
Identification of full-substorm onset from ground-magnetometer databy singular value transformation …………………………………………… 63

Editorial Board
Kozo TAKAHASHI, Chief Editor
Hiroshi TAKENAKA
Syoichi SHIMOYAMAAll communications relating to this Memoirs should be
addressed to the Dean of the Faculty of Sciences, Kyushu University
Hakozaki, Fukuoka 812-8581, JAPANMem. Fac. Sci., Kyushu Univ., Ser. D, Earth ＆ Planet. Sci., Vol. XXXⅡ, No. 3,
pp. 1-10, March 10, 2011

Occurrences of radiolarian biostratigraphic markers Lychnocanoma nipponica sakaii andAmphimelissa setosa in Core YK07-12 PC3B from the Okhotsk Sea
Takahito Ikenoue*, Kozo Takahashi*, Tatsuhiko Sakamoto**,Saburo Sakai** and Koichi Iijima**

AbstractCore YK07-12 PC03B obtained from the central Okhotsk plain (52°36’N, 150°08’E ; water depth: 1049m) was analyzed every 5 cm, focusing on two radiolarian biostratigraphic markers in the late Pleistocene:
Lychnocanoma nipponica sakaii and Amphimelissa setosa. The last occurrence (LO) datum of A. setosa at
67 ka conformed with those of the LO of the previously published studies. However, the LO of L.
nipponica sakaii at 25 ka was off set and significantly younger than those published in the previous studies
in the North Pacific and the marginal seas. We introduce herein the conceptual use of the last common
occurrence (LCO) of L. nipponica sakaii as the LCO conforms with the LO of this taxon publishedelsewhere and hence more reliable, especially out side of the northern part of the central Okhotsk plain.
The LCO of L. nipponica sakaii is 46 ka, 21 kyrs older than the LO, but is approximately the same as theLOs published elsewhere. We postulate the LCO as a practical datum which can be compared with the datafrom out side of the studied region. As alternative explanations, the obtained significantly younger LO thanthe LOs of other studies from the out side of the study region may stem from the following two reasons.
Because that the present study is specifically focused on the two biostratigraphic marker radiolarian taxa
with details our microscopic counts are significantly greater than those performed in the previous studies.
This may have caused the documentation of the LO with the rare microscopic counts on multiple
microslides, which could have been missed had we counted only one microslide. It is also possible that theeffect of bioturbation due to upward transport in the slow sedimentation rate regime caused the appearanceof the rare specimens of L. nipponica sakaii well above the LCO.
Keywords: Radiolarian biostratigraphy, last occurrence (LO), last common occurrence (LCO), Lychnocanoma
nipponica sakaii, Amphimelissa setosa, Okhotsk Sea, late Pleistocene

1. Introduction
The Okhotsk Sea represents as one of the lowest latitude regions with extensive sea-ice cover in the world.
Environmental conditions of the Okhotsk Sea with such sea-ice formation can alter global water circulations
because that the formation results in the generation of dense Okhotsk intermediate water which exits into theNorth Pacific (e.g., Talley, 1991). The Okhotsk Sea is also characterized by a high biological productivity andthus it serves as an efficient biological pump to absorb atmospheric CO2. Therefore, for further understanding the
global carbon cycle it is important to study the region including the past environmental conditions (Takahashi,1998).
Radiolarians represent as one of the common microzooplankton groups in the pelagic and hemipelagic realms.
Their siliceous skeletons are often well preserved in the sediments and hence they can be used in biostratigraphy

Manuscript received on 1 November 2010; accepted on 7 January 2011
Department of Earth & Planetary Sciences, Graduate School of Sciences, Kyushu University, 6-10-1 Hakozaki,
Higashi-ku, Fukuoka 812-8581, JAPAN; Corresponding authorʼs e-mail: ikenoue@geo.kyushu-u.ac.jp** Earth and Life History Research Program, Institute of Biogeosciences, Japan Agency for Marine-Earth Science andTechnology (JAMSTEC), Natsushima-cho 2-15, Yokosuka, 237-0061, JAPAN*2

Takahito Ikenoue, Kozo Takahashi, Tatsuhiko Sakamoto, Saburo Sakai and Koichi Iijima

of deep-sea sediments and reconstruction of paleoceanographic conditions. Pertinent previous works onradiolarian biostratigraphy in the Okhotsk Sea are, for example, published by Takahashi et al. (2000), Matul et al.
(2002, 2009), and Okazaki et al. (2003, 2005). The purpose of this study is to examine radiolarian biostratigraphic
markers of the late Pleistocene in detail employing Core YK07-12 PC03B obtained in the northern part of thecentral Okhotsk plain.

2. Materials and Methods
During Cruise YK07-12 of R/V Yokosuka belonging to Japan Agency for Marine-Earth Science andTechnology (JAMSTEC) in summer 2007, Core YK07-12 PC03B was obtained from the northern part of thecentral Okhotsk plain (52°36’N, 150°08’E ; water depth: 1,049 m; Fig. 1). The recovered core length is 14.09 m.
Sediment samples were continuously sliced every 1 cm in thickness throughout the core. In this study, samples
were analyzed at every 5 cm interval.

60°
N

Okhotsk Sea

MD01-2415

YK07-12 PC03B
LV28-42-4

XP98-PC2

XP98-PC1

50°

XP98-PC4

MD01-2412

140°

150°

160°E

Fig. 1. Location map of Core YK07-12 PC03B (solid circle) together with other relevant cores (open circles) in the Okhotsk Sea.

Fig. 1Radiolarian biostratigraphic markers Lychnocanoma nipponica sakaii and Amphimelissa setosa in the Okhotsk Sea

3

An age model of Core YK07-12 PC3B was established based on δ18O stratigraphy with subordinate magnetic
susceptibility (MS). Graphic correlations of δ18O records were established between the δ18O variations of benthic
foraminifer shells (Uvigerina spp.) in Core PC3B and the standard curve of LR04 Benthic δ18O global stack
constructed by Lisiecki and Raymo (2005) (Fig. 2). As results of the analyses, Marine Isotope Stages (MIS)
1-12.3 were identified, and it was determined that Core PC3B recorded at least 450 kyrs of the environmental
conditions of the northern part of the central Okhotsk plain.

YK07-12 PC3B
MS (SI)050

100 150 200

YK07-12 PC3B
Uvigerina spp.
Benthic b18O (‰, PDB)

LR04 Global Stack
Benthic b18O (‰, PDB)
5.5

5.0

4.5

4.0

3.5

3.0

0

0
2.2

200
5.1

100
5.5

6.2

400

600

6.6

MR2

200

Age (ka)Core depth (cm)

6.3

MR3
800
300

1000

10.2

400
1200

11.3

12.2
12.3

5.0

4.5

4.0

3.5

3.0

2.5

(Lisiecki and Raymo, 2005)

Fig. 2. An age model of Core YK07-12 PC3B based on δ18O stratigraphy and subordinated by MS. Changes in (a) MS of Core
YK07-12-PC3B; (b) benthic foraminiferal (Uvigerina spp.) δ18O of Core YK07-12-PC3B; and (c) stacked benthic foraminiferal
oxygen isotope curve LR04 (Lisiecki and Raymo, 2005), Lines MR2 and MR3 are tephra horizons recovered in Core YK07-12
PC3B.

Fig. 2

4

Takahito Ikenoue, Kozo Takahashi, Tatsuhiko Sakamoto, Saburo Sakai and Koichi Iijima

Radiolarian counts were conducted on 53 selected samples whose ages ranged from 133 ka at 264.5 cm depth
to the present at the core top. Wet samples of 100-1,100 mg were weighed after freeze-drying for 24 hrs. They
were treated with 5 ml of 1N hydrochloric acid, 10 ml of 30% hydrogen peroxide, and heated on a hot plate at
90℃ for 1 hr in order to remove organic matter and calcium carbonate. Then, Calgon® (hexametaphosphate,surfactant) solution was added to the mixture to further disaggregate the sediments. Our samples contained a large
amount of lithogenic grains and thus we employed the elutriation method for extracting opal particles from theresidues according to Itaki (2003). After the elutriation, samples were sieved through a stainless screen with 45
μm mesh and filtered through Gellman® membrane filters with a nominal pore size of 0.45 μm. The filteredsamples were washed with distilled water to remove salts, dried in an oven at 50°C, and then permanently
mounted with Canada Balsam® on microslides. We counted the number of all radiolarian specimens on the slides
under a compound light-microscope at x100-200 magnifications. Normally, counts were made on an entire area ofTable 1. Radiolarian counts in Core YK07-12 PC3B.
Total Radiolaria
Total depth
Sectionat cubecenter (cm)

Age
(ka)

Dry
NumberDry bulk
density
SR sediment of slides(g cm-3) (cm ky-1)(g)countedCount

Lychnocanoma nipponika sakaii

Amphimelissa setosa

AR(No. rads cm-2 ky-1)

Count

AR
(No. rads cm-2 ky-1)%

Specimens(g dry sed.-1)

Count

AR
(No. rads cm-2 ky-1)%

Specimens(g dry sed.-1)

1

9.3

0.00

0.324

2.49

0.042

1

434

8381

0

0

0

0

0

0

0

0

1

16.0

2.79

0.459

2.49

0.040

1

630

17896

0

0

0

0

0

0

0

0

1

20.5

5.59

0.564

2.49

0.043

1

563

18559

0

0

0

0

0

0

0

0

1

25.0

8.38

0.617

2.49

0.050

1

323

9901

0

0

0

0

0

0

0

0

1

29.5

11.18

0.526

2.49

0.051

1

130

3374

0

0

0

0

0

0

0

0

1

34.0

13.97

0.742

2.49

0.057

1

168

5418

0

0

0

0

0

0

0

0

1

40.9

16.76

0.976

2.49

0.096

1

34

860

0

0

0

0

0

0

0

0

1

45.4

19.69

1.010

1.43

0.118

1

79

970

0

0

0

0

0

0

0

0

1

50.0

23.16

1.005

1.43

0.413

4

282

981

0

0

0

0

0

0

0

0

1

54.5

26.63

0.968

1.43

0.420

4

426

1404

1

3

0

2

0

0

0

0

1

59.1

30.10

1.057

1.43

0.982

8

721

1110

4

6

0.55

4

0

0

0

0

1

66.0

33.57

1.045

1.43

0.408

3

561

2055

12

44

2.14

29

0

0

0

0

1

70.6

37.03

1.002

1.43

0.419

2

1382

4727

2

7

0

5

0

0

0

0

1

75.2

40.50

0.957

1.43

0.427

2

1600

5134

2

6

0

5

0

0

0

0

1

79.3

43.97

1.058

1.43

0.095

1

239

3819

3

48

1.26

32

0

0

0

0

2

79.3

44.66

1.002

1.43

0.096

1

192

2861

0

0

0

0

0

0

0

0

2

84.8

48.13

1.020

1.43

0.441

2

972

3218

89

295

9.16

202

0

0

0

0

2

89.4

51.60

0.938

1.43

0.491

5

326

891

222

606

68.10

452

0

0

0

0

2

94.0

55.07

0.967

1.43

0.527

5

252

661

122

320

48.41

231

0

0

0

0

2

100.9

58.54

0.966

1.43

0.452

8

309

945

195

596

63.11

432

0

0

0

0

2

105.5

62.01

0.914

1.43

0.407

3

590

1894

335

1075

56.78

823

0

0

0

0

2

110.1

65.47

0.946

1.43

0.071

1

122

2331

35

669

28.69

494

0

0

0

0

2

114.7

68.94

1.151

1.43

0.139

1

189

2235

32

378

16.93

230

1

12

0.53

7

2

119.2

72.41

0.730

1.43

0.066

1

232

3670

38

601

16.38

576

0

0

0

0
35

2

126.1

75.88

0.700

1.43

0.058

1

305

5304

56

974

18.36

972

2

35

0.66

2

130.6

79.20

0.706

1.43

0.057

1

279

4979

60

1071

21.51

1060

2

36

0.72

35

2

135.2

81.15

0.493

2.5

0.027

1

223

10294

41

1893

18.39

1536

4

185

1.79

150

2

139.8

83.10

0.566

2.5

0.049

1

357

10352

63

1827

17.65

1291

3

87

0.84

61

2

144.4

85.06

0.619

2.5

0.046

1

359

12211

44

1497

12.26

967

1

34

0.28

22

2

149.0

87.01

0.584

2.5

0.043

1

194

6522

25

840

12.89

576

4

134

2.06

92

2

155.9

88.97

0.652

2.5

0.060

1

495

13505

48

1310

9.70

804

2

55

0.40

34

2

160.5

90.92

0.502

2.5

0.062

1

631

12741

56

1131

8.87

900

19

384

3.01

305

2

165.1

92.88

0.578

2.5

0.056

1

476

12328

71

1839

14.92

1272

7

181

1.47

125

2

169.7

94.83

0.622

2.5

0.056

1

322

8926

71

1968

22.05

1266

7

194

2.17

125

2

174.3

96.79

0.665

2.5

0.064

1

309

8085

33

863

10.68

520

9

235

2.91

142

3

178.9

98.94

0.724

2.5

0.051

1

366

12984

38

1348

10.38

745

9

319

2.46

176

3

184.6

100.89

0.659

2.5

0.067

1

331

8206

6

149

1.81

90

11

273

3.32

165

3

189.0

102.85

0.595

2.5

0.052

1

790

22408

24

681

3.04

458

42

1191

5.32

802

3

195.8

104.80

0.740

2.5

0.058

1

804

25809

22

706

2.74

382

50

1605

6.22

868

3

200.2

106.75

0.626

2.5

0.063

1

2166

53544

23

569

1.06

363

149

3683

6.88

2354

3

204.8

108.71

0.588

2.5

0.061

1

2522

60421

18

431

0.71

293

199

4768

7.89

3241

3

209.4

110.66

0.575

2.5

0.064

1

4001

89649

26

583

0.65

405

642

14385

16.05

10000

3

214.1

112.62

0.518

2.5

0.037

1

3002

104436

36

1252

1.20

968

578

20108

19.25

15538

3

221.1

114.57

0.510

2.5

0.046

1

2810

78002

30

833

1.07

654

506

14046

18.01

11024

3

225.7

116.53

0.585

2.5

0.049

1

2925

87846

26

781

0.89

534

470

14115

16.07

9651

3

230.3

118.48

0.561

2.5

0.033

1

1939

81672

27

1137

1.39

811

203

8551

10.47

6096

3

234.9

120.44

0.601

2.5

0.043

1

1651

58251

22

776

1.33

516

86

3034

5.21

2019

3

239.5

122.41

0.626

2.5

0.056

1

1367

37905

14

388

1.02

248

111

3078

8.12

1968

3

244.1

124.44

0.638

1.85

0.059

1

557

11132

5

100

0.90

85

48

959

8.62

812

3

250.9

126.47

0.687

1.85

0.059

1

762

16461

9

194

1.18

153

45

972

5.91

765

3

255.5

128.50

0.917

1.85

0.081

1

421

8875

8

169

1.90

99

46

970

10.93

571

3

260.0

130.53

0.973

1.85

0.101

1

278

4934

7

124

2.52

69

21

373

7.55

207

3

264.5

132.56

1.021

1.85

0.076

1

344

8582

3

75

0.87

40

22

549

6.40

291

Radiolarian biostratigraphic markers Lychnocanoma nipponica sakaii and Amphimelissa setosa in the Okhotsk Sea

5

one microslide with a goal of counting >300 specimens. The counts of <200 specimens were resulted in eight cases outof the total of 55 cases whereas the counts exceeding 500 specimens resulted in 22 cases (11 cases >1,000 specimens)(Table 1). In two extremely cases of rare radiolarian occurrences (Samples 59.1 cm and 100.9 cm) eightmicroslides were prepared and all the slides were counted in order to fulfill the initial goal of counting sufficientnumber of specimens. In order to achieve the goal as close as possible, multiple microslides were counted ineleven cases in total (Table 1). The classification of Lychnocanoma nipponica (Nakaseko) sakaii (Morley and
Nigrini) and Amphimelissa setosa (Cleve) in the samples follow that of Morley and Nigrini (1995) for the former
and Bjørklund et al. for the latter (1998), respectively.
A radiolarian accumulation rate (RAR) was calculated using the following equation: RAR (No. radiolarians
cm-2 kyr -1)= [No. radiolarians g-1 dry sediment] (No. g-1) × [dry bulk density] (g cm-3) × [sedimentation rate] (cmkyr -1 ). Dry bulk density was determined from weights of each of 10 cc sediment samples taken with apolypropylene cube. It was calculated from the wet bulk density multiplied by the water contents (%). The watercontents of each sample were determined from weights of the wet and dry samples. The samples were weighed
before and after drying in an oven at 50℃ for 24 hrs. Sedimentation rates (SR) were assumed between the age
control points.

3. Results and Discussion
The temporal changes in total RAR in Core YK07-12 PC3B are shown in Fig. 3. Its pattern tends to follow the
temporal patterns displayed by the global δ18O changes during the glacial-interglacial cycles (e.g., Lisiecki andRaymo, 2005); total RAR increased during the interglacial periods and decreased during the glacial periods atleast for the time span examined. The values during MIS 1 and MIS 5 were relatively high compared to those of
the other MIS stages.

Total RAR
3

0

-1

(×10 No. specimens cm-2 kyr )0 20 40 60 80 100
MIS
1

20

Age (ka)

40

2

3

60

4
80

100

5
120

140
Fig. 3. Changes in total RAR in Core YK07-12 PC3B during the last 130 kyrs. Gray areas indicate cold
MIS.

Fig. 3

6

Takahito Ikenoue, Kozo Takahashi, Tatsuhiko Sakamoto, Saburo Sakai and Koichi Iijima

In this study we focused on two important radiolarian taxa as biostratigraphic markers in the late Pleistocene:
Lychnocanoma nipponica (Nakaseko) sakaii (Morley and Nigrini) and Amphimelissa setosa (Cleve) (Fig. 4).
They are quite useful markers in the North Pacific and marginal seas (Bjørklund and Swanberg, 1987; Morley etal., 1995; Matul et al., 2002). In Core YK07-12 PC3B, the LO of L. nipponica sakaii occurred in the upper MIS 3
at 25 ka, and the L. nipponica sakaii acme event occurred at 81 ka (Table 1, Fig. 5). Our data displayed several
differences compared to the results shown by the previous studies. The LO of L. nipponica sakaii in the previous
studies are listed in Table 2. Specifically, the LO of L. nipponica sakaii was 49 ka (Morley et al., 1982) and 50 ka(Morley et al., 1995) in the North Pacific. Tanaka and Takahashi (2005) and Itaki et al. (2009) dated the LO of L.
nipponica sakaii at 46-52 ka using sediment samples from the Bering Sea. Itaki et al. (2007) also estimated the
LO to be 54 ka using sediment samples from the Japan Sea. The LO in four piston cores XP98-PC1, XP98-PC2,
XP98-PC4, MD01-2412 from the Okhotsk Sea were determined also as ca. 50 ka (Takahashi et al., 2000; Okazaki
at al., 2005). The locations of these four core sites are further south of the core site of the present study.

a

c

b

d

1
Fig. 4. Radiolarian taxa Fig.
from Core
4 YK07-12 PC03B discussed in the text. All scale bars equal to 50 μm. a.
Lychnocanoma nipponica (Nakaseko) sakaii (Morley and Nigrini), Sample 230.3 cm. b. Lychnocanoma nipponica(Nakaseko) sakaii (Morley and Nigrini), Sample 230.3 cm. c. Amphimelissa setosa (Cleve), sample 230.3 cm. d.
Amphimelissa setosa (Cleve), Sample 230.3 cm.

On the contrary to the majority of the LOs of ca, 50 ka mentioned above, Matul et al. (2002) and Matul et al.
(2009) proposed the LO to have occurred at 28 ka and 34 ka in the central Okhotsk Sea, which is fundamentallythe same region as that in our study. As mentioned earlier, the results of our study also show that the LO to be at
25 ka level, approximately the same age as those in Matul et al. (2002, 2009). These LOs from the three piston
cores (LV28-42-4, MD01-2412, and YK07-12 PC03B) from the same general region collectively displayed
significantly younger ages than those from other previous studies. While there is a discrepancy in the timing of
the LOs between the older (ca. 50 ka) and younger (34-25 ka) groups, the overall patterns of the population
change with time appear to be conformable between the two groups. Namely, the AR, abundance and relative
abundance of L. nipponica sakaii increased steadily from ca. 120 ka towards 50 ka and rapidly declined after 50

Radiolarian biostratigraphic markers Lychnocanoma nipponica sakaii and Amphimelissa setosa in the Okhotsk Sea

7

Lychnocanoma nipponica sakaii

0

AR
3
-1
(×10 No. specimens cm -2 kyr )0
1
2

Relative abundance
(%)

0

20

40

60

Abundance
3（×10 No. specimens/g dry sed.）
0
0.8
1.6 MIS120

Age (ka)

40

LO
25 ka

2

LCO
46 ka

3

60

Acme
81 ka

80

4

100

5
120

140

5
Fig. 5.Fig.
Changesin AR, relative abundance and abundance of L. nipponica sakaii in Core YK07-12 PC03B. The LO, LCO and Acme
datums are shown with arrows.

Amphimelissa setosa

0

AR
3
-1
(×10 No. specimens cm -2 kyr )
0
5
10
15
20

0

Abundance
Relative abundance
3(%)（×10 No. specimens/g dry sed.）
MIS
10
20 0
8
16

1
2

20

Age (ka)

40

60

80

3
LO
67 ka
LCO
74 ka

4

100

5
120

140

Fig. 6
Fig. 6. Changes in AR, relative abundance and abundance of A. setosa in Core YK07-12 PC03B. The LO and LCO are shown witharrows.

8

Takahito Ikenoue, Kozo Takahashi, Tatsuhiko Sakamoto, Saburo Sakai and Koichi Iijima

ka. Thus, the trend of the changes in AR, abundance and relative abundance in our study are roughly conformablewith those in the previous studies.
Furthermore, the LO of A. setosa is placed at 67 ka within MIS 4, slightly above the MIS 4/5 boundary (Fig.
6). Thus, the LO of L. nipponica sakaii and A. setosa obtained from Core YK07-12 PC3B correspond to the LOsof Core LV28-42-4 (Matul et al., 2002) fairly well. It is quite possible that the LO of L. nipponica sakaii in thenorthern part of the central Okhotsk plain is diachronous with respect to the LO of this taxon further south in the
Okhotsk plain and in other basins, considering the consistency of the LOs from the same region. It is plausiblethat the environmental conditions between ca. 50 ka and ca. 34-25 ka in the northern part of the central Okhotsk
plain were still favorable for the survival of L. nipponica sakaii whereas those of the further south were severe
enough to cause an extinction of this taxon at ca. 50 ka. This could well be due to the distribution of the sea-ice
cover during the interval in question in the region. It is noteworthy to mention here that the sea-ice cover was
more extensive at Site XP98-PC1 than Site XP98-PC2 (Fig. 1), according to Okazaki et al. (2005). Shiga andKoizumi (2000) also reported more open water conditions in the eastern Okhotsk Sea than in the western area
during the time period around 22 ka and the last glacial maximum. Based on these pieces of information weinterpret that the survival of L. nipponica sakaii was prolonged at our study site than the western area and perhaps
further south in the Okhotsk Sea. Thus, one of the possible three reasons (see below for the remainders) for thesignificantly young 25 ka as the LO is the diachronous extinction of this taxon within the entire Okhotsk Sea.
As a part of the second explanation of the discrepancy, we herein propose the introduction of “the lastcommon occurrence (LCO)” concept as a practical biostratigraphic datum. This datum should be far more reliable
than the LO for the following details which we have encountered in the present piston core. The tail end of theoccurrence of L. nipponica sakaii prior to ca. 25 ka (Fig. 5) may well be due to the detailed radiolarian counts
performed in our study, which is specifically devoted to illustrate the exact occurrences. Specifically, the total
radiolarian counts of 426 (4 microslides) at 27 ka and 721 (8 microslides) at 30 ka were performed (Table 1).
These values are apparently far more greater than those proceeded in other published data whereas their exact
counts were not published nor available in their results. Our microscopic counts for L. nipponica sakaii were one
specimen at 27 ka and four specimens at 30 ka, respectively (Table 1). These relatively small count values could
well have been missed and recorded as zeros, had the significantly smaller counts (1 microslide or portion of it)
than the present study were made. In that case our LO would have been 46 ka in stead. Thus, it makes a sense to
use the 46 ka level as the LCO, which is graphically illustrated as the rapid decrease interval in AR, abundance
and %L. nipponica sakaii.
Table
2.
Table 2(a) List of the LO / LCO of L. nipponica sakaii and SR for cores used in the recent studies.
Age (ka) SR (cm kyr -1 ) Reference

Core/ SiteArea

YK07-12 PC03B

Okhotsk Sea 52°36.01' N

150°08.25' E

25 / 46

2.86

This paper

LV28-42-4

Okhotsk Sea 51°42.89' N

150°59.13' E

28

2-4

Matul et al. (2002)

MD01-2415

Okhotsk Sea 53°57.09' N

149°57.52' E

34

2-4

Matul et al. (2009)

MD01-2412

Okhotsk Sea 44°31' N

145°00' E

47-48

46

Okazaki et al. (2005)

XP98-PC1

Okhotsk Sea 51°00.9' N

152°00.5' E

43-44

8.1

Takahashi et al. (2000)

XP98-PC2

Okhotsk Sea 50°23.7' N

148°19.4' E

53-55

10.5

Takahashi et al. (2000)

XP98-PC4

Okhotsk Sea 49°29.3' N

146°07.7' E

55-56

12.6

Takahashi et al. (2000)

PC-23A

Bering Sea

48.6

Itaki et al. (2009)

ES

Bering Sea

45.9

Tanaka and Takahashi (2005)

BOW-8A

Bering Sea

49.5

Tanaka and Takahashi (2005)

BOW-9A

Bering Sea

49.7

Tanaka and Takahashi (2005)

BOW-12A

Bering Sea

51.7

Tanaka and Takahashi (2005)

Japan Sea

54

Itaki et al. (2007)

MD01-2407

othersV20-120, RC14-103

others North Pacific49

Morley et al. (1982)

ODP Sites 881, 883

others North Pacific

50

Morley et al. (1995)(b) List of the LO / LCO of A. setosa and SR for cores used in the recent studies.
Age (ka) SR (cm kyr -1 ) Reference

Core/ SiteArea

YK07-12 PC03B

Okhotsk Sea 52°36.01' N

150°08.25' E

67 / 74

2.86

This paper

LV28-42-4

Okhotsk Sea 51°42.89' N

150°59.13' E

72

2-4

Matul et al. (2002)

MD01-2415

Okhotsk Sea 53°57.09' N

149°57.52' E

64

2-4

Matul et al. (2009)

ES

Bering Sea

85.1

Tanaka and Takahashi (2005)

BOW-8A

Bering Sea

111.5

Tanaka and Takahashi (2005)

BOW-9A

Bering Sea

68

Tanaka and Takahashi (2005)

GAT-3A

Bering Sea

82.6

Tanaka and Takahashi (2005)

North Pacific70

Bjørklund and Swanberg (1987)

Radiolarian biostratigraphic markers Lychnocanoma nipponica sakaii and Amphimelissa setosa in the Okhotsk Sea

9

As a second alternative, the slow SR observed in the central Okhotsk Sea may have caused the discrepancy in
the LO levels. Itaki et al. (2009) speculated that the delay of the LO of L. nipponica sakaii by Matul et al. (2002)
might be due to the effect of bioturbation in the slow SR environment. When sedimentation rates are slow fossil
radiolarian specimens initially located at several cm deep (or even deeper sometimes) in sediments, for example,
could have been subsequently transported upward to the sediment surface or nearby by organisms living near thesurface or within sediments, causing a bioturbation. Such an activity can alter the sequentially deposited initialsignature in a drastic manner. On the other hand, the chances of the effect in high SR regime can minimize suchan action because faster burial than the artifact of the bioturbation. The sedimentation rates of the previously
studied cores from the Okhotsk Sea are shown in Table 2. The sediment cores with higher SRs than the threepiston cores (LV28-42-4, MD01-2412, and PC03B) may have led the LO of L. nipponica sakaii to be ca. 50 ka.
Thus, the time lag of the LO of L. nipponica sakaii with respect to the LCO in YK07-12 PC03B could possibly
be due to the effect of bioturbation in the slow SR regime. Note that the first disappearances of L. nipponica
sakaii and A. setosa after the major occurrence maxima are 46 ka and 74 ka, respectively. These ages are nearly
equal to the LO of other previously published studies. One drawback of such an explanation with the slow SR isthat the LO of A. setosa at 68 ka did not cause any significant time lag compared to the data from the fast SR
regimes. Because that the occurrence of total radiolarians is about the same at both at 25 ka and 67 ka (Table 1,
Fig. 3) it is difficult to explain why we did not encounter a time lag problem in the LO of A. setosa in the present
piston core.

4. Conclusions
A focused detailed study on two important radiolarian biostratigraphic markers of the late Pleistocene was
performed in the northern part of the central Okhotsk plain: Lychnocanoma nipponica (Nakaseko) sakaii (Morley
and Nigrini) and Amphimelissa setosa (Cleve). We have employed Core YK07-12 PC3B from the northern part ofthe central Okhotsk plain with the aid of benthic foraminiferal δ18O stratigraphy. The introduction of the conceptof “the last common occurrence (LCO)” makes a sense where the LO and the LCO differ significantly in age,especially in the case of the present study. The LCO of the 46 ka in the present study serves as a comparable
datum with respect to the LO at ca. 50 ka of L. nipponica sakaii found further south in the Okhotsk Sea andelsewhere in the marginal seas of the North Pacific and subarctic Pacific. It is possible that the extinction datumof L. nipponica sakaii in the northern part of the central Okhotsk plain (25 ka) specifically lagged behind of thatof elsewhere by ca. 25 kyrs. This may well have caused the diachronous LO compared to those of elsewhere. We
interpret that the sea-ice conditions were favorable to allow the survival of L. nipponica sakaii for additional ca.
16-25 kyrs in the study region compared to elsewhere. As alternative explanations for the discrepancy in the LOs,
we also offer (1) the detailed counts of the radiolarians in this devoted study; and (2) the slow SR where
bioturbation may have caused the apparent time lag of the LO at 25 ka compared to the LO of ca. 50 ka in thestudies performed other than in the northern part of the central Okhotsk plain. Furthermore, the LO ofAmphimelissa setosa at 67 ka obtained from the present study was conformable with that of Core LV28-42-4.

5. Acknowledgments
We thank scientists, Captain and crew participated in Cruise YK07-12 of R/V Yokosuka who assisted us on
board for this work. We thank Dr. Yusuke Okazaki of JAMSTEC for his constructive review of an early draft ofthis paper as well as further discussion. The senior author received and benefitted by the Professor Tatsuro
Matsumoto Scholarship Fund.

6. References
Bjørklund, K.R., and Swanberg, N.R. (1987) The distribution of two morphotypes of the radiolarian
Amphimelissa setosa Cleve (Nassellarida): a result of environmental variability. Sarsia, 72, 245-254.
Bjørklund, K.R., Cortese, G., Swanberg, N., and Schrader, H.J. (1998) Radiolarian faunal provinces in surface
sediments of the Greenland, Iceland and Norwegian (GIN) Seas. Marine Micropaleontology, 35, 105-140.
Itaki, T. (2003) Elutriation technique for the extraction of radiolarian skeletons from sandy sediment. Fossils, 73,

10Takahito Ikenoue, Kozo Takahashi, Tatsuhiko Sakamoto, Saburo Sakai and Koichi Iijima

38-41.
Itaki, T., Komatsu, N., and Motoyama, I. (2007) Orbital- and millennial-scale changes of radiolarian assemblages
during the last 220 kyrs in the Japan Sea. Palaeogeography, Palaeoclimatology, Palaeoecology, 247, 115-130.
Itaki, T., Uchida, M., Kim, S., Shin, H-S., and Tada, R. (2009) Late Pleistocene stratigraphy and palaeoceanographic
implications in northern Bering Sea slope sediments: evidence from the radiolarian species Cycladophoradavisiana. Journal of Quaternary Science, 24, 856-865.
Lisiecki. L.E., and Raymo, M.E., 2005. A Plio-Pleistocene stack of 57 globally distributed benthic δ18O records.
Paleoceanography, 20, 1003.
Morley, J.J., and Nigrini, J.D. (1995) Miocene to Pleistocene radiolarian biostratigraphy of North Pacific sites
881, 884, 885, 886, and 887. In: Rea, D.K., Basov, I.A., Scholl, D.W., Allan, J.F. (Eds.), Proc. ODP, Sci.
Results, 145, College Station, TX (Ocean Drilling Program), 55-91.
Morley, J.J., Hays, J.D., and Robertson, J.H. (1982) Stratigraphic framework for the late Pleistocene in thenorthwest Pacific Ocean. Deep-Sea Research, 29, 1485-1499.
Morley, J.J., Tiase, V.L., Ashby, M.M., and Kashgarian, M. (1995) A high-resolution stratigraphy for Pleistocene
sediments from North Pacific Sites 881, 883, and 887 based on abundance variations of the radiolarian
Cycladophora davisiana. In: Rea, D.K, Basov, I.A, Scholl D.W., Allen, J.F. (Eds), Proc. ODP, Sci. Results,
145, College Station, TX (Ocean Drilling Program), 133-140.
Matul, A., Abelmann, A., Tiedemann, R., Kaiser, A., and Nürnberg, D. (2002) Late Quaternary polycystineradiolarian datum events in the Sea of Okhotsk. Geo-Marine Letters, 22(1), 25-32.
Matul, A., Abelmann, A., Nürnberg, D., and Tiedemann, R. (2009) Stratigraphy and major paleoenvironmental
changes in the Sea of Okhotsk during the last million years inferred from radiolarian data. Oceanology, 49(1),93-100.
Okazaki, Y., Takahashi, K., Yoshitani, H., Nakatsuka, T., Ikehara, M., and Wakatsuchi, M. (2003) Radiolarians
under the seasonally sea-ice covered conditions in the Okhotsk Sea: flux and their implications forpaleoceanography. Marine Micropaleontology, 49(3), 195-230.
Okazaki, Y., Takahashi, K., Katsuki, K., Ono, A., Hori, J., Sakamoto, T., Uchida, M., Shibata, Y., Ikehara, M., andAoki, K. (2005) Late Quaternary paleoceanographic changes in the southwestern Okhotsk Sea: evidence fromgeochemical, radiolarian, and diatom records. Deep-Sea Research II, 52, 2332-2350.
Shiga, K., and Koizumi, I., (2000) Latest Quaternary oceanographic changes in the Okhotsk Sea based on diatom
records. Mar. Micropaleontol. 38, 91-117.
Takahashi, K. (1998) The Bering and Okhotsk Seas: modern and past paleoceanographic changes and gateway
impact. Journal Asian Earth Science, 16, 49-58.
Takahashi, K., Okazaki, Y., and Yoshitani, H. (2000) Radiolarian fossils and paleoceanography: accumulation
changes in the Okhotsk Sea. Chikyu Monthly. 22, 623-630. [in Japanese]
Talley, L. D. (1991) An Okhotsk Sea water anomaly: implications for ventilation in the North Pacific. Deep-Sea
Research, 38, S171-S190.
Tanaka, S. and Takahashi, K. (2005) Late Quaternary paleoceanographic changes in the Bering Sea and thewestern subarctic Pacific based on radiolarian assemblage. Deep-Sea Research II, 52, 2131-2149.

Mem. Fac. Sci., Kyushu Univ., Ser. D, Earth ＆ Planet. Sci., Vol. XXXⅡ, No. 3,
pp. 11-26, March 10, 2011

Chemosynthetic fossil molluscan faunas from the Neogene Taishu Group, distributed in
Tsushima Islands, Nagasaki Prefecture, the southwest Japan
Takashi Ninomiya*

Abstract
The middle of the Neogene Taishu Group, distributed in Tsushima Islands, Nagasaki Prefecture, thesouthwest Japan, is considered to include the authigenic carbonates originated from cold-seep and thechemosynthetic molluscan faunas deposited in deep sea environment of greater than 500 m depth. In thisstudy, the author examined classification of the bivalves occurred in the middle of the Taishu Group.
Consequently, the molluscan faunas are assigned into the following ten species belonging to seven genera:
Bathymodiolus sp., Adipicola sp., Calyptogena spp., Acharax spp., Acila sp., Nuculana sp., and Yoldia sp.
Keywords: the Neogene Taishu Group, deep sea environment, chemosynthetic molluscan faunas

1. Introduction
The formation of the Sea of Japan is thought to be the results of the following processes. (1) The east marginof the Eurasian Continent subsided in the late Cenozoic; (2) the spreading of the Sea of Japan reached the climax
opening stage in the Early Miocene; and (3) the Japanese Archipelago was formed in the middle Miocene (Otofuji
and Matsuda, 1983, 1985). The Taishu Group distributed in Tsushima Islands, which is located in the southwest
part of the Sea of Japan, has been regarded as the conformable marine deposits and they can be compared with
the Paleogene strata distributed in the northwest Kyushu (Nakajo and Funakawa, 1996; Nakajo et al., 2006).
Therefore, Tsushima Islands are important area in reconstructing the formation history of the Sea of Japan and theJapanese Archipelago. However, our knowledge concerning the sedimentary environments of the Taishu Groupwas fragmental and there are many unsettled discussions about the formation age (Okada and Fujiyama, 1970;
Nakajo and Maejima, 1998; Nakajo et al., 2006; Yamaguchi and Oho, 2007). Furthermore, the maga-fossils foundin the Taishu Group are of mainly shallow marine fossil faunas. However, the maga-fossils are scarce and poorly
preserved (Matsumoto, 1969; Masuda, 1970; Takahashi and Nishida, 1975). The author has been studying about
the Taishu Group distributed in Tsushima Islands to understand the formation processes of the Sea of Japan andthe depositional environments of the deep sea sediments in the southwestern Sea of Japan. Recently, small-scalecarbonate and fossil assemblages are found successively in the middle of the Taishu Group (Aoki and Nishida,
1999; Ninomiya et al., 2008). In our study, it has been shown that they are authigenic carbonates originated fromcold-seep and that the fossil molluscan faunas are chemosynthetically formed (Ninomiya et al., 2008). They statethat the middle of the Taishu Group was deposited in deep-sea environments at greater than 500 m depth(Ninomiya et al., 2010). Therefore, cold-seep carbonates and chemosynthetic fossil assemblages from the Taishu
Group are important in deciphering the paleoenvironments of the opening stage of the Sea of Japan. The author
reports the classification of chemosynthetic bivalves occurred from the Taishu Group in this paper.

Manuscript received on 24 December 2010; accepted on 27 January 2011

* Department of Earth and Planetary Sciences, Graduate School of Science, Kyushu University, Hakozaki6-10-1,

Fukuoka, 812-8581, JAPAN; authorʼs e-mail: sc308031@s.kyushu-u.ac.jp

12

Takashi Ninomiya

2. Geological setting of Tsushima Islands
Tsushima Islands are located at 120 km off Kyushu in the southwestern Sea of Japan (Fig. 1). The Taishu
Group is conformable marine formation with the thickness of greater than 5,400 m and it is classified into theLower Formation, Middle Formation and Upper Formation based on lithology and distribution of T3 Tuff (MITI,
1973). The layer of T3 Tuff can be tracked in distance of greater than 40 km (Fig. 2). Anticlinorium andsynclinorium structures with a northeast-southwest axis are observed in Tsushima Islands. In the south of
Tsushima Islands, where granite as intrusive rock is observed the Taishu Group was affected by contact
metamorphism. Also observed are rhyolite, quartz porphyry, plagiophyre and dolerite as intrusive rocks. The
formation age of the Taishu Group has been regarded as the early Eocene-early Miocene (Ibaragi, 1994; Nakajo
and Funakawa, 1996; Sakai and Yuasa, 1998). However, the author and his colleagues dated T3 Tuff andsubaqueous pyroclastics of the Upper Formation. Consequently, we learned that the main part of the Taishu
Group was deposited at approximately 16 Ma which was in the middle Miocene (Ninomiya et al., 2010).
Furthermore, the lower most of the Taishu Group with the reported early Eocene radiolarians may be comparedwith the Paleogene strata distributed in the northwest Kyushu.

40°N

Sea of Japan

Tsushima Islands

35°N

Fig. 230°N
130°E
Fig. 1. Location of Tsushima Islands.

135°E

140°E

Chemosynthetic fossil molluscs from the Neogene Taishu Group, the southwest JapanN

13

Legendfold axes
Upper Formation

Tanohama Limestone

Middle Formation
Lower Formation

Nita Limestone
Nita Mudstone

2000
10

20 km

Upper Form.

Kanoura Limestone
Nita Mudstone
Tanohama Limestone
Nita Limestone
Fukusaki Limestone

0

1000

0

Middle Form.

3000

Fukusaki Limestone

Lower Form.

4000

5000 mKanoura Limestone

mudstonesandstone/
alternation ofsandstone and mudstone

T3 Tuff

Fig. 2. Geologic map of Tsushima Islands and lithological column of the Taishu Group based on MITI (1972, 1973, 1974). Circles
show the locality of limestone and chemosynthetic fossil assemblages.

3. Chemosynthetic bivalves from the Taishu GroupMITI (1972) reported Adulomya cf. uchimuraensis, Calyptogena akanudaensis from the limestone boulder at
Tanohama, where the upper part of the Lower Formation is located. Aoki and Nishida (1999) found a lenticular
limestone including small Adulomya sp. from the same horizon. Moreover, fossil molluscan faunas are dominatedby Acharax spp. with occurrences of Sacella, Yoldia and Portlandia. These fossil molluscan faunas are quite
dense in population and they are regarded as chemosynthetic fossil assemblages.
Ninomiya et al. (2010) reported that fossil assemblages of the authigenic cold-seep carbonates and mudstone arechemosynthetic bivalves which are mytilids, vesicomyids and solemyids. As Aoki and Nishida (1999) indicated, thecalcareous shells are absent in mudstones but are preserved in carbonates. Based on these conditions, the middle part of
the Taishu Group is considered to be deposited at deep-sea floor greater than 500 m depth (Ninomiya et al., 2010).

14

Takashi Ninomiya

4. Description of molluscan fossils
Class Bivalvia Linnaeus, 1758
Family Solemyidae Gray, 1840
Genus Acharax Dall, 1908
Type species: Solemya johnsoni Dall, 1891; Recent,Northeast Pacific.
Acharax sp. A
Plate 1, fig. 1
Acharax sp. A, Aoki and Nishida, 1999.
Locality: Nita (Basal part of the Middle Formation;
Aoki and Nishida, 1999)
Measurements (in mm) :SumpleNo.

valve

LengthLa

HeightHeight/LengthLa/L

Rib
numberPlate

Aok-001

right
balve

49.7

14.2

23.7

0.48

0.29

20

Plate 1,
fig. 1

La: Length of anterior margin.
Description: Shell is of middle size. Ligament external.
Dorsal margin straight, antero-postero margin rounded.
Ventral margin nearly straight. Umbo located at anterior
one and third of valve of shell length. Radial ribs count
18-20, and marginal portion degitated beyond shell
margin. The ribs are strong at anterior-posterior end, but
weak and obscure at center of valve.
Remarks: According to Aoki and Nishida (1999), thisspecies resembles Acharax tokunagai. As Sasaki et al.
(2005) indicated, Solemya (Acharax) agasizii, Solemya
tokunagai, Solemya (Acharax) tibai, and Solemya
tokunagai elongata are synonymyzed with Solemya
johnsoni (Coan et al., 2000). This species resembles
Acharax johnsoni in many points. However, umbo of
Acharax johnsoni situates posteriorly, 78%. Therefore,
this species may be distinguished from Acharax
johnsoni.
Acharax sp. B
Plate 1, figs. 2-6
Acharax sp. B, Aoki and Nishida, 1999.
Locality: Nita (Basal part of the Middle Formation;
Aoki and Nishida, 1999)
Measurements (in mm) :Sumple No.

valve

LengthLa

Height Height/
LengthLa/L

Rib
numberPlate

Aok-002 right balve

38.3

8.8

13.8

0.36

0.23

17

Plate 1, fig. 2

GK-L12000 left valve

29.4

8.2

10.4

0.35

0.28

17

Plate 1, fig. 3

Aok-003 right balve

44.2

10.6

13.3

0.30

0.24

15+

Plate 1, fig. 4

GK-L12001 right balve 59.5+

16.1

－

－

－

18

Plate 1, fig. 5, 6

Description: Shell is small to middle size and elongated.
Ligament external. Dorsal margin straight, anteropostero margin rounded. Ventral margin nearly straight.
Umbo located at anterior about three of quarter of valve
length. Radial ribs count 17, and marginal portion
digitated beyond shell margin. The ribs are strong at
anterior-posterior end, but weak and obscure at center ofvalve.
Remarks: Bivalves of geneus Acharax is reported atleast in eight species (Baba, 1990; Hatai and
Koike1956; Kamada, 1962; Kanehara, 1937; Kanno,
1960; Kanie and Kuramochi, 1995; Kanie et al, 1995;
Kanie et al., 1999; Natori, 1964). This species
resembles Acharax yessoensis, Acharax dalli, Acharax
muroensis, and Acharax gigas. However, radial rib
numbers of A. yessoensis are 18-20. Shell length of A.
dalli is smaller than that of this species and radial rib
numbers are 10-11. Shell length of A. muroensis isless than that of this species. Acharax bosoana islarger than Acharax sp. B and has 10-11 ribs. Shell
size of Acharax gigas is much larger than those of A.
yessoensis, A. dalli, A. muroensis and Acharax sp. B.
Therefore, Acharax sp. B can clearly be distinguishedfrom other species. It appears necessary in the future
to discuss about the possibility of erecting this taxon
as a new species.
Acharax sp. C
Plate 2, figs. 1-2
Locality: Kanoura (Lower part of the Middle Formation)
Description: Shell size and outline unknown. Ligamentis external. Radial ribs marginal portion digitatedbeyond shell margin. Frequently, this species is observedin mudstones around Kanoura Limestone. However,shells are imperfect, shell outline is unknown. This
species may be identified as Acharax sp. A or Acharax
sp. B. In this paper, the author assigns this taxon as
Acharax sp. C.
Class Bivalvia Linnaeus, 1758
Family Nuculidae Adams and Adams, 1858
Genus Acila Adams and Adams, 1858
Type species: Nucula divaricata Hinds, 1843; Recent,
China
Acila sp.
Plate 2, fig. 3
Locality: mudstone around Fukusaki Limestone (Upper
part of the Lower Formation)

15

Chemosynthetic fossil molluscs from the Neogene Taishu Group, the southwest Japan

Measurements (in mm):

Aoki and Nishida, 1999).

Sample No.

valve

LengthHeightPlate

GK-L12004

left valve

26+

34.7+

Plate 2, fig. 3

Description: Shell length greater than 26 mm and height
reaching about 35 mm. Shell subovate, inequilateral, notso inflated well-defined rostral portion. Posterior side isvery short. Umbo located at nearly posterior margin.
Anterior dorsal margin gently sloping, but anterior end isabsent. Ventral margin regularly arched. Posterior
margin form and lunula cannot be observed. Sculpture
consisting of divaricating oblique threads, the line ofmain devarication is slightly posterior to the middle.
Remarks: This species resembles Acila submirabilis
and is common in the Neogene of Japan. However,u m b o , l i n u l e a n d p o s t e r i o r m a rg i n f o r m s a r e
unknown. Therefore, the author tentatively assigns
this taxon as Acila sp. until well-preserved specimens
with visible structures are studied.
Family Nuculanidae Adams and Adams, 1858
Genus Nuculana Link, 1807
Type species: Arca rostrata Bruguière, 1791= Mya
pernula Müller, 1779; Recent, North Atlantic.
Nuculana sp.
Plate 2, fig. 4
Locality: Nita (Basal part of the Middle Formation;
Aoki and Nishida, 1999).
Measurements (in mm):
Sample No.

valve

LengthLa

Plate

Aok-004

left valve

8.7

3.2

Plate 2, fig. 4

Description: Shell small, long-ovate, inflated, nearlyveneriform. Escutcheon is obscure. Umbo located atnearly anterior margin. Strong concentric regular
growth line presents on surface. Hinge structure
unknown.
Remarks: Shell form and only growth line are observedon surface. However, hinge structure is unknown.
Therefore, the author assigns this taxon as Nuculana sp.
until well-preserved specimens are studied.
Genus Yoldia Möller, 1842
Type species: Yoldia hyperbore Torell, 1859= Nucula
hyperborea Gould, 1841; Recent, North Atlantic.
Yoldia sp.
Plate 2, figs. 5-6
Locality: Nita (Basal part of the Middle Formation;

Measurements (in mm):
Sample No.

valve

LengthLa

HeightHeight/LengthPlate

Aok-005

right valve

13.7

3.2

10.1

0.74

Plate 2, fig. 5

Aok-006

left valve

14.9

5.0

8.2

0.55

Plate 2, fig. 6

Description: Shell small, long-ovate, anterior marginrounded, anterior side slightly shorter than posterior
side. Postero-dorsal corner pointed. Postero-dorsal
border concaved. Strong concentric regular growth line
is observed on surface. Hinge structure and escutcheon
are unknown.
Remarks: Shells are deformed, umbo area structures
cannot be observed. Therefore, the author assigns thistaxon as Yoldia sp.
Unidentified species
Plate 2, fig. 6
Locality: Nita (Basal part of the Middle Formation; Aoki
and Nishida, 1999).
Measurements (in mm):
Sample No.

valve

LengthLa

Plate

GK-L12005

left valve

42.1+

13.2

Plate 2, fig. 6

Description: Shell moderate, elongated, anterior marginrounded, ventral margin slightly arcuated. Posterior
dorsal margin is straight. Strong concentric regular
growth line presents on surface. Hinge structure is
unknown. Therefore, it will be necessary to describe
more details in the future based on well-preserved
specimens whose structures can be observed.
Class Bivalvia Linnaeus, 1758
Order Mytiloida Férussac, 1822
Family Mytilidae Rafinesque, 1815
Subfamily Bathymodiolinae Kenk and Wilson, 1985
Genus Bathymodiolus Kenk and Wilson, 1985
Type species: Bathymodiolus thermophilis Kenk andWilson, 1985; Recent, Galapagos Rift zone.
Bathymodiolus sp.
Plate 3, figs. 1-6
Locality: Fukusaki Limestone (Upper part of theLower Formation).

16

Takashi Ninomiya

Measurements (in mm):
Sample No.

valve

LengthLa

HeightPlate

GK-L12006

right valve

36

1.3

−

Plate 3, ﬁg. 1

GK-L12007

right valve

38.1+

4.6

21.8

Plate 3, ﬁg. 2

GK-L12008

right valve

41.5

−

−

Plate 3, ﬁg. 3

GK-L12009

left valve

29.5+

−

17.7

Plate 3, ﬁg. 4

GK-L12010

right valve

46.7+

−

−

Plate 3, ﬁg. 5

GK-L12011

left valve

33.0+

−

17.5

Plate 3, ﬁg. 6

Description: The largest one reaches about 47 mm inlength, although the present specimen is broken atanterior, posterior, and dorsal sides. All the specimens
are imperfect and height/length ratio and width/length
ratio unknown. Shell rather thick and solid,
modioliform, inflated, elliptical equivalve. Umbo
subterminal, prosogyrated at nearly anterior margin.
Anterior margin is located slightly forward thanumbo. Anterior margin rounded, dorsal margin
convex, postero-dorsal corner rounded, posterior
margin broadly rounded, ventral margin straight.
Feeble radial threads present in mid-portion. Inner
structures are unknown.
Remarks: This species resembles Bathymodiolus
platifrons, B. japonicus and B. hirtus described by
Hashimoto and Okutani (1994) and Okutani et al. (2004)
from Japanese waters. However, this species isdistinguished from the similar taxa listed above based onumbo projection from anterior margin, strait ventral
margin, as well as shell length of 50 mm. Nobuhara et al.
(2008) indicated that bathymodiolin became large in the
middle Miocene. However, this species is 50 mm in shelllength. It may be necessary in the future to discuss about
the possibility of erecting this taxon as a new species.
Genus Adipicola Dautzenberg, 1927
Type species: Myrina denhami Adams and Adams, 1854
=Modiolus pelagica Woodward, 1854 (by monotypy);
Recent, South Atlantic.
Adipicola sp.
Plate 3, fig. 7
Locality: Kanoura (Lower part of the Middle Formation).
Measurements (in mm):
Sample No.

valve

LengthLa

HeightHeight/LengthPlate

GK-L12012

right valve

37.4

11.2

14

0.37

Plate 3, fig. 7

Description: Shell small (length: 37.4 mm), elongate
quadrangular, ligament external. Antero-posterodorsal margin nearly straight. Anterior margin slightly
narrow, rounded, posterior margin smoothly rounded,
ventral margin slightly concave. Umbo directed

forwards, situated at between anterior about one andthird. Growth line distinct at posterior margin of shell.
Remarks: Bivalves belonging to genus Adipicola are
known as whale-fall community of the present or the
past (Amano and Little, 2005; Dell, 1995; Okutani etal., 2004; Tsuchida and Tabakotani, 1997). Okutani
and Miyazaki (2007) described Benthomodiolus
geikotsucola from deep sea floor of the northeast
Pacific. This species closely resembles Adipicola
pacifica. However, the calcareous shell has not beenpreserved and thus the inner structure cannot be
observed. This species occurred from the mudstonearound Kanoura Limestone which is the authigenic
cold-seep carbonate. Consequently, in this study, theauthor assigns this taxon as Adipicola sp. until wellpreserved specimens with structures are studied.
Class Bivalvia Linnaeus, 1758
Order Veneroida Adams and Adams, 1856
Superfamily Glossaceae Gray, 1847
Family Vesicomyidae Dall and Simpson, 1901
Genus Calyptogena Dall, 1891
Type species: Calyptogena pacifica Dall, 1891 (bymonotypy); Recent, East Pacific.
Calyptogena sp. A
Plate 4, figs. 1-4, Plate 5, figs. 1-6, Plate 6, figs. 1-4
Locality: Kanoura Limestone (Lower part of the
Middle Formation), Tanohama Limestone (Upper partof the Lower Formation) and mudstone around
Kanoura Limestone (Lower part of the Middle
Formation).
Measurements (in mm):
Sample No.

valve

LengthLa

Height Height/
Length

Width

Plate

GK-L12013

left valve

41.9

6.9

16.5

0.39

−

Plate 4, ﬁg. 1

Aok-007

right valve

40.3+

9.6

−

−

−

Plate 4, ﬁg. 2

Aok-008

left valve

39.0+

−

13.2

−

−

Plate 4, ﬁg. 3

GK-L12014

right valve

44.4+

−

−

−

−

Plate 4, ﬁg. 4

GK-L12015

right valve

45.4

6.1

18.2

−

13.2

Plate 5, ﬁgs. 1, 2

GK-L12016

left valve

35.3

5.1

15.3

0.43

−

Plate 5, ﬁgs. 3, 4

GK-L12017

right valve

32.7+

4.9

17.3

−

−

Plate 5, ﬁg. 5

GK-L12018

right valve

37.9+

−

15.5

−

−

Plate 5, ﬁg. 6

GK-L12020

right valve

37.3

8.5

−

−

−

Plate 6, ﬁg. 1

GK-L12021

left valve

37.5+

6.5

11.3

−

−

Plate 6, ﬁg. 2

GK-L12022

left valve

36.9+

−

9.1

−

−

Plate 6, ﬁg. 3

GK-L12023

left valve

46.5

6.3

11.3

−

−

Plate 6, ﬁg. 4

Description: The largest one can be measured about
47mm in length, although it is deformed. Shell thick,not so inflated, elongated slightly inequivalve.

Chemosynthetic fossil molluscs from the Neogene Taishu Group, the southwest Japan

Ligament external. Anterior margin rounded, ventral
margin strait. Posterior margin slightly broad,smoothly rounded. Postero-dorsal margin nearlystraight. Umbo low, reaching slightly above hingeline and is located at between anterior about one sixthof valve length. Hinge structures are unknown.
Calyptogena sp. B
Plate 4, figs. 5-6, Plate 5, figs.7-8, Plate 6, fig. 5
Locality: Kanoura Limestone (Lower part of the Middle
Formation), Tanohama Limestone (Upper part of theLower Formation) and mudstone around Kanoura
Limestone (Lower part of the Middle Formation)
Measurements (in mm):
Sample No.

valve

LengthLa

Height

Width

Plate

Aok-009

right valve

51.1+

7.5

15.5

8.5

Plate 4, ﬁg. 5, 6

GK-L12019

right valve

32.1+

4.2

12.4

8.5

Plate 5, ﬁg. 7, 8

GK-L12024

right valve

43.9

5

−

−

Plate 6, ﬁg. 5

Description: The largest one can be measured about 51
mm in length, although posterior end is not observed.
Shell rather thick, antero-posteriorly significantly
elongated, inequilateral slightly inequivalve. Ligament isexternal along dorsal side. Anterior margin rounded,
ventral margin long, rather strongly concave centrally.
Anterior dorsal margin descending at an angle of about
30° from umbo. Umbo quite low, reaching slightly
above hinge line and located at anterior side and one
seventh of valve length. Hinge structure is unknown.
Remarks on Calyptogena spp.: In Japan, many fossil
species and present species of Calyptogena are17

described thus far (Amano and Kiel, 2006; Kanno etal., 1998; Métivier et al., 1986; Kojima and Ohta,
1997; Kuroda, 1943; Okutani, 1957, 2000, 2008;
Okutani and Métivier, 1986; Okutani et al., 1992,
1993, 1996, 1997, 2000, 2002).
Calyptogena sp. A closely resembles Calyptogena(Archivesica) similaris described by Okutani et al.
(1997). However, there are differences in that Calyptogena
sp. A of shell length is a half size or less and anterior
margin and antero-dorsal margin are rounded.
Adulomya cf. uchimuraensis reported by MITI (1972) islong as 150 mm (Kanno et al., 1998). And Calyptogena
sp. A is more elongated than C. akanudaensis. Therefore,
this species is different from these two species. This
species closely resembles Adulomya hokkaidoensis inshell length and form, which is described by Amanoand Kiel (2006) from the Miocene Chikubetsu
Formation as a part of whale-fall community. However,
Adulomya hokkaidoensis is known only from thewhale-fall community. However, hinge structure of
Calyptogena sp. A cannot be observed. Consequently,
in this study, the author assigns this taxon as
Calyptogena sp. A. Most of fossil bivalves frommudstone around Kanoura Limestone are consideredas this species, although they are deformed.
Calyptogena sp. B resembles the modern species
Calyptogena (Ectenagena) phaseoliformis. However,Calyptogena sp. B is distinguished from the thickshell and 50 mm or less in shell length. Adulomya
uchimuraensis is different from this species becausethat ventral margin is straight or only a little concave
toward dorsal. It is considered that this species is thesame as that occurred from mudstone, but the
specimen is significantly deformed. Hinge structure
cannot be observed. Therefore, in this study, theauthor assigns this taxon as Calyptogena sp. B.

5. Conclusions
The middle part of the Neogene Taishu Group including the cold-seep carbonates was originated from theauthigenic chemosynthetic fossil molluscan faunas, which are distributed in Tsushima Islands, Nagasaki
Prefecture. It is considered that the Taishu Group was deposited in deep sea environments of greater than 500 m
depth. In this paper, the author classified the bivalves from the cold-seep carbonates and mudstones. The
assemblages are identified as ten species belonging to seven genera as follows: Bathymodiolus sp., Adipicola sp.,
Calyptogena spp., Acharax spp., Acila sp., Nuculana sp., and Yoldia sp. These fossil bivalves may be considered
to be new species pending on further studies. It will be necessary in the future to classify them based on detailed
hinge structures of well-preserved specimens.

6. Acknowledgements
The author is grateful to Mr. Takahiro Aoki (Shinwa Techno Co., Ltd.) for lending many specimens from hiscollections. Dr. Shoichi Shimoyama (Kyushu University) is gratefully acknowledged for providing helpful advice
and suggestions. Thanks are extended to Dr. Kozo Takahashi (Kyushu University) for providing opportunity towrite this manuscript and for his helpful suggestions and improving the English text. The author is also greatly

18

Takashi Ninomiya

indebted to Dr. Tamio Nishida (Professor Emeritus of Saga University), who acted as an external reviewer, forproviding valuable comments and suggestions.

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Okutani, T., Fujiwara, Y., Fujikura, K., Miyake, H., and Kawato, M. (2004) A mass aggregation of the mussel Adipicola
pacifica (Bivalvia: Mytilidae) on submerged whale bones. Venus (Japanese Journal of Malacology), 63, 61-64.
Okutani, T., Hashimoto J., and Fujikura, K. (1992) A new species of vesicomyid bivalve associated withhydrothermal vents near Amami-Ohshima Island, Japan. Venus (Japanese Journal of Malacology), 51, 225233.
Otofuji, Y., and Matsuda, T. (1983) Paleomagnetic evidence for the clockwise rotation of Southwest Japan. Earthand Planetary Science Letters, 62, 349-359.
Otofuji, Y., and Matsuda, T. (1987) Amount of clockwise rotation of Southwest Japan-fan shape opening of thesouthwestern part of the Japan Sea. Earth and Planetary Science Letters, 85, 289-301.
Rafinesque, C.S. (1815) Analyse de la nature ou tableau de l’univers et des corps organisés. 224 pp. Barravecheia,
Palermo.
Sakai, H., and Yuasa, T. (1998) K-Ar Ages of the Mogi and Ugetsuiwa Subaqueous Pyroclastic Flow Deposits in
the Taishu Group, Tsushima Islands. Memoirs of Natural Science Museum Tokyo, 31, 23-28
Sasaki, T., Okutani, T., and Fujikura, K. (2005) Molluscs from hydrothermal vents and cold seeps in Japan: Areview of taxa recorded in twenty recent years (1984-2004). Venus (Japanese Journal of Malacology), 64,
87-133.
Takahashi, K., and Nishida, T. (1974) On the molluscan fossils from the Lower Formation of the Taishu Group in
the Kamiagata district of Tsushima Islands. Bulletin of Faculty of Liberal Arts, Nagasaki University. Naturalscience, 15, 15-21. (In Japanese with English abstract)
Torell, O.M. (1859) Bidrag till Spitsbergen Mollusk-fauna. Jemte en allman oversigt af Arktiska regionens
naturforahallanden och forntida ubtredning, 154 pp. Boktrycheri, Stocholm.
Tsuchida, E., and Tabakotani, Y. (1997) Deep-sea mytilid bivalve assemblage on whale bone collected from theentrance of Tokyo Bay. Venus (Journal of Malacological Society of Japan), 56, 77-78. (In Japanese)
Woodward, S.P. (1851-1856) A manual of the Mollusca; or a rudimentary treatise on Recent and fossil shells, 486
pp. John Weale, London.
Yamaguchi, Y., and Oho, Y. (2007) Sedimentological history of Tertiary slope facies in the northern area of the
Tsushima Islands, Japan. Journal of Geological Society of Japan, 113, 113-126. (In Japanese with English
abstract)Chemosynthetic fossil molluscs from the Neogene Taishu Group, the southwest Japan

21

Plate 1

1

2

1 cm

1 cm

3

4

1 cm

5

1 cm

6

1 cm

1 cm

Plate 1. 1-6. Acharax spp. from Nita (fig. 1: Acharax sp. A [Sample ID: Aok-001]; fig. 2: Acharax sp. B [Aok-002]; fig. 3: Leftvalve of Acharax sp. B [GK-L12000]; fig. 4: Acharax sp. B [Aok-003]; figs. 5, 6: Acharax sp. B [GK-L12001], fig. 5: Anterior side;
fig. 6: Posterior side).

22

Takashi Ninomiya
Plate 2

2

1

1 cm
1 cm

3

4

5 mm

1 cm

5

6

5 mm

5 mm

7

1 cm

Plate 2. 1, 2. Acharax sp. C from Kanoura (fig. 1: Acharax sp. C [GK-L12002]; fig. 2: Acharax sp. C [GK-L12003]), 3. Acila sp.
from Fukusaki [GK-L12004], 4-7. Nuculanidiae, Unidentified species from Nita (fig. 4: Left valve of Nuculana sp. [Aok-003]; fig.
5: Right valve of Yoldia sp. [Aok-004]; fig. 6: Right valve of Yoldia sp. [Aok-005]; fig. 7: Unidentified species [GK-L12005]).

Chemosynthetic fossil molluscs from the Neogene Taishu Group, the southwest Japan

23

Plate 3

1

2

1 cm

3

1 cm

4

1 cm

5

1 cm

6

1 cm

1 cm

7

1 cm

Plate 3. 1-6. Bathymodiolus sp. from Fukusaki Limestone (fig. 1: Right valve [GK-L12006]; fig. 2: Right valve [GK-L12007]; fig.
3: Right valve [GK-L12008]; fig. 4: Left valve [GK-L12009]; fig. 5: Right valve [GK-L12010]; fig. 6: Left valve [GK-L12011]]]),
7. Adipicola sp. [GK-L12012].

24

Takashi Ninomiya
Plate 4

1

2

1 cm

3

1 cm
4

1 cm
1 cm

5

6

1 cm

Plate 4. Calyptogena spp. from Kanoura Limestone. 1-4. Calyptogena sp. A (fig. 1: Left valve [GK-L12013]; fig. 2: Right valve[Aok-007]; fig. 3: Dorsal side (Aok-008). fig. 4: Left valve (GK-L12014)), 5, 6. Calyptogena sp. B [Aok-009] (fig. 5: Right valve;fig. 6. Left valve).

Chemosynthetic fossil molluscs from the Neogene Taishu Group, the southwest Japan

25

Plate 5

1

2

1 cm

3

4

1 cm

5

6

1 cm

7

1 cm

8

1 cm

Plate 5. Calyptogena spp. from Tanohama Limestone. 1-6. Calyptogena sp. A. 1, 2. Calyptogena sp. A ([GK-L12015]: fig. 1: Right
valve; fig. 2: Left valve), 3, 4. Calyptogena sp. A ([GK-L12016]: fig. 3: Right valve; fig. 4: Left valve), 5. Calyptogena sp. A[GK-L12017]. 6. Calyptogena sp. A [GK-L12018], 7, 8. Calyptogena sp. B ([GK-L12019]: fig. 7: Right valve; fig. 8: Left valve).

26

Takashi Ninomiya
Plate 6

1

2

1 cm

3

1 cm

4

1 cm

1 cm

5

1 cm

Plate 6. Calyptogena spp. from mudstone around Kanoura Limestone. 1-4. Calyptogena sp. A (fig. 1: Right valve [GK-L12020];
fig. 2: Right valve [GK-L12021]; fig. 3: Left valve Right valve [GK-L12022]; fig. 4: Left valve [GK-L12023]), fig. 5. Left valve of
Calyptogena sp. B [GK-L12024].

Mem. Fac. Sci., Kyushu Univ., Ser. D, Earth ＆ Planet. Sci., Vol. XXXⅡ, No. 3,
pp. 27-38, March 10, 2011

Cell size variation of Anoplosolenia brasiliensis (calcareous nannoplankton) in the central
equatorial Pacific Ocean
Hideto Tsutsui and Kozo Takahashi*
Abstract
A morphometric analysis on Anoplosolenia brasiliensis (calcareous nannoplankton) was conductedemploying samples obtained from 0 to 120 m water depths in the central equatorial Pacific Ocean along theequator ranging from 166.3°E to 170.1°W. Measured cell length of A. brasiliensis showed the minimum of
39 µm to the maximum of 165 µm. The cell width ranged from the minimum of 1 μm to the maximum of
10 µm. Measured cell volumes ranged from the minimum of 28.3 µm3 to the maximum of 2,741 µm3. In
addition, length/width ratios ranged from the minimum of 6.8 to the maximum of 37.5. The cell size of thistaxon is very large compared to that of other calcareous nannoplankton taxa such as Emiliania huxleyi.
Related factors for such a large cell size appears to be: (1) population density of the own taxon; (2)ambient temperature; (3) ambient dissolved oxygen concentration; and (4) other phytoplankton population
density such as that of E. huxleyi. The life adaptation of A. brasiliensis is interpreted as fundamentally
pursuing a K-strategy, but this taxon is also pursuing an r-strategy when appropriate situation arises. The
population density of this taxon may be related to ambient nutrient concentrations, intricate balance among
several species of nutrients, and competitions with other coccolithophore taxa such as E. huxleyi.
Keywords: Anoplosolenia brasiliensis, calcareous nannoplankton, morphometrics, cell size, K-strategy, central
equatorial Pacific Ocean

1. Introduction
In the recent years, we have seen a steady progress in morphometric studies (e.g., de Meuter and Symons,
1975; Lazarus, 1986a; Lazarus, 1986b; Lazarus, 1986c; Kurihara and Takahashi, 2002; Schmidt et al., 2004;
Tsutsui and Takahashi, 2009a; Tsutsui et al., 2009b). However, these studies were limited by the following
reasons. (1) In general, the plankton groups included in the above-cited literature are microscopic in size.
Therefore, the work concerning size measurement requires substantial labor employing a light microscope (LM)or a scanning electronic microscope (SEM) under high magnifications. (2) Significant amount of time must be
expended when one wisheds to employ an SEM.
Calcareous nannoplankton can be very useful as indicators for deciphering environmental conditions inoceanography and paleoceanography. It is important to characterize basic information for population, distribution,
and/or cell size since the nannoplankton can tell us about environmental conditions such as nutrient
concentrations.
Therefore, our present study is focused on morphometric analysis of Anoplosolenia brasiliensis. This taxon
has a comparatively large-sized cell among many calcareous nannoplankton taxa and hence measurements areeasier compared to that of other nannoplankton taxa. The cell form of this taxon appears as a very slim figure likethe shape of a javelin. Simply put, the exterior calcareous shield of this taxon is composed of a large number ofvery slim rhomboids, which are geometrically arranged in an orderly manner (Fig. 2). Each member of such ashield is classified as a ‘scapholith’ type. A scapholith of this taxon represents an appearance like hair comb slits
in the central area called as a ‘lath’ (Winter and Siesser, 1994). The first description of this species was given by*

Manuscript received on 27 December 2010; accepted on 10 February 2011
Department of Earth and Planetary Sciences, Graduate School of Sciences, Kyushu University, Hakozaki6-10-1,
Fukuoka, 812-8581, JAPAN; Corresponding authorʼs e-mail: hideto@geo.kyushu-u.ac.jp

28

Hideto Tsutsui and Kozo Takahashi

Lohmann (1919), followed by a re-description by Deflandre (1952). In recent years, Young et al. (2003)
transferred and emended A. brasiliensis into genus Calciosolenia due to the significant similarity in fine coccolith
structure of Calciosolenia murrayi. Furthermore, Young et al. (2003) also discussed about classification of A.
brasiliensis based on the presence/absence by dimorphism: Anoplosolenia brasiliensis represents a monomorphic
stage, and C. murrayi represents a dimorphic stage. In our study, we respect the differences in the coccoliths andcoccosphere morphology by lath and cell form of genus Anoplosolenia and genus Calciosolenia, thus this species
in question is tentatively defined as A. brasiliensis as done by Deflandre (1952). This species belongs to Kingdom
Protista, Phylum Haptophyta, Class Haptophyceae, Order Coccolithophorales, Family Calciosoleniaceae (Mantonand Oates, 1985; Jordan and Kelijne, 1994; Heimdal, 1997; Young et al., 2003; Edvardsen and Medlin, 2007).
Anoplosolenia brasiliensis belongs to heterococcolithophores group (Jordan and Kelijne, 1994). Rutten (1972)
discussed about this species based on sediment trap samples collected at approximately 3,000 m depth at Station
UM15 in the Bannock basin in the Mediterranean Sea and A. brasiliensis was described as a member ofcalcareous nannoplankton fluxes. Nishida (1979) discussed about this species from the central Pacific Ocean.
Manton and Oates (1985) studied morphology of this species in the Galapagos Islands. Manton and Oates (1985)
sampled A. brasiliensis and Calciosolenia aff. murrayi from 8 to 19 m depths from Academy Bay, Barrington(Fernandina) Island of the Galapagos Islands. Manton and Oates (1985) discussed fine structures including lathemploying LM, SEM and transmission electron microscopy (TEM) and suggested a morphological difference
between genus Anoplosolenia and genus Calciosolenia. Steinmetz (1991) reported about this species in the flux
material collected by sediment traps deployed in the equatorial Atlantic, central Pacific and Panama Basin.
Nishida et al. (2000) investigated the assemblages and populations of nannoplankton in the central equatorial
Pacific Ocean and discussed about this species among other nannoplankton taxa. Ziveri and Thunell (2000)
discussed and described this species as a member of coccolithophore flux in sediment trap samples collected fromthe Gulf of California. Malinverno (2004) observed fine coccolith morphology of A. brasiliensis employing an
SEM and discussed/classified the results of scapholith morphometrics. The scapholith length of A. brasiliensis is
5.8 to 7 µm and the width is 1.9 to 2.3 µm (Malinverno, 2004). In contrast, when A. brasilieneis is living in themodern ocean, A. brasilieneis has large cell size compared to major calcareous nannoplankton taxa such as genus
Emiliania and genus Gephyrocapsa, but fine details of A. brasiliensis size is not well understood. If a populationof A. brasiliensis were found in a sediment trap sample, it would be possible to predict that the total mass flux ofthat sample would be very large for the reasons discussed in Discussion section of this paper. Therefore, we
discuss about the variations in A. brasiliensis population and cell size of living A. brasiliensis in the modern
ocean.

2. Materials and Methods
2.1. Sampling logistics

Seawater samples containing nannoplankton were collected on R/V Mirai of JAMSTEC during Cruise MR99K07, November to December 1999 in the central equatorial Pacific Ocean (Nishida et al., 2000). The sampled
depths were limited down to 200 m and the sample water volumes were approximately two to three liters. The
sampled stations are shown (Fig. 1). Cruise MR99-K07 started at 04.2°N/135.6°E as Station 1 and the ship
steamed along the equator from 145°E to 170.1°W in the central equatorial Pacific Ocean. Stations 1 to 12 wereassigned from the east to west as identification numbers (ID) for the samples. Significantly large populations of
A. brasiliensis were observed at Stations 7, 8, 9 and 12 and hence the populations of A. brasiliensis at the four
stations were used for a morphometric analysis. Size variations of this taxon can effectively be measured at thefour stations by the following reasons: (1) The populations present are sufficient at the four stations among
Stations 1 to 12 with statistically satisfactory numbers. (2) The area of high population density is found at
Stations 8 and 9 and Station 7 is located at the margin of the high density. Therefore, the cell size variations of A.
brasiliensis are set to be measured at the three stations plus Station 12, which provides a fair population density.
The logistics for sampling is given (Table 1). Our study depths for A. brasiliensis ranged as follows: 0, 10, 30,
40, 50, 60, 80, 100 and 120 m. This is because that below 120 m depth the population density of this taxon was
expected to be nearly zero and thus there was no need of taking additional samples from further down depths. The
pertinent environmental data such as water temperature, salinity and nutrients were summarized by Kawano(2000).
The seawater samples were filtered and sieved through 200 µm stainless steel mesh and large-sized plankton
particles were excluded: no filtered seawater samples include, for example, copepods and planktonic foraminifers.
Finally, the calcareous nannoplankton samples were filtered onto MilliporeR HA type membrane filters with anominal pore size of 0.45 µm. After this process, the filters were dried at room temperature in the shipboard

Size variation of Anoplosolenia brasiliensis in the central equatorial Pacific Ocean

29laboratory.
After the filters were brought back to the shore laboratory, circular subsamples of 6 mm in diameter were cut
off. The observation for A. brasiliensis was conducted on an SEM. The logistic details of the SEM observation
are as follows: JSM-6300PS with the acceleration voltage of 10 to 15 kv; and samples coated with carbon vapor
using JFE-400 carbon coater (both made by Japan Electron Optics Laboratory (JEOL)).

140

160

180°

160°W

40

0

120°E

20°N

20°S
120°E

140

12

9

8

7

160°E

10
11

3

EQ

4
5
6

2

St

.1

20°N

180°

EQ

160°W

Fig. 1. Map showing the sampled locations

2.2. Morphometric technique

itu
th de
e
Eq (all
ua
rto
Sa
r)
m
D ple
at d
e
(a
ll
19
99
Sa
)
m
Ti pl
m ed
e

St. 7
8
9
12

166.3°E
171.4°E
174.5°E
170.1°W

at

Lo

ng

St

at
io

n

ID

Table 1. Logistics for the sampling.

4 Dec.
5 Dec.
6 Dec.
9 Dec.

10:33-11:20
10:35-11:16
11:05-11:43
10:30-11:32

SEM images of A. brasiliensis are shown (Fig 2). The morphometric techniques are kept as simplest andfastest as possible in this study. We focused on measuring cell “length”, scaling the distance from one tip to the
opposite tip. Analogously, “width” represents the widest part of a cell. In practice, A. brasiliensis often exhibits abending feature like an arch. In that case, the length is manually measured with a flexible lead ruler on a TV
screen of the SEM. The morphometric concept employed here is illustrated (Fig. 3). Cell volumes can becalculated based on the measurements of length and width, assuming a cell is made of a pair of ideal geometriccones. The numerical formula for a cell volume is also shown (Fig. 3).

30

Hideto Tsutsui and Kozo Takahashi

Fig. 2. (a) SEM photograph of Anoplosolenia brasiliensis from the equatorial Pacific Ocean (theEquator, 178°05.26W), at 50 m depth at Station 10. (b) An enlarged view of the thickest part ofphotograph (a).

LW
1
V=2(1 1 w2 L)
3 2 2
Fig. 3. Graphic representation of the morphometric method. 'V' is a cell volume.

3. Results
3.1. Population of A. brasiliensis along the equator

Distribution of A. brasiliensis during Cruise MR99-K07 is illustrated (Fig. 4). Among all sampled stations, themaximum population density of calcareous nannoplankton was 3,333 individualsℓ-1, and the mean value
throughout all stations was 614 individualsℓ-1. The depth of the maximum population found was at 40 m at
Station 8 (171.4°E). The samples from Station 8 and Station 9 (174.5°E) represented 43% of the specimens of
total populations, followed by Station 12 (170.1°W) as the third rank representing 14% of the total. The
remaining 43% of the population was represented by those from Stations 1 through 6, 10 and 11 (Fig. 4).
On the other hand, when we pay our attention to vertical distribution, 85% of the population concentrations
are located between 0 to 70 m depths (Fig. 4). The highest population density is found at 50 m, contributing 15%
of total at all depths. The population contributions at 40 m and 60 m are 12% at both depths. In summary, fromthe surface to 50 m depth the populations increased gradually, but below 50 m the populations decreased and the
populations became very small representing only less than 1% below 100 m.

0°
E

10

1°
W
0.

4°
W
6.

11

17

9

0°
W

5°
E

4°
E

8

17

7

8.

6

17

5

4.

4

17

3

1.

3°
E
6.

2

17

5°
E

16

9.

2°
E

15

7.

0°
E

15

2.
15

1

0

12

0

Individual (%)
6
12 15

(b)

Ind. liter -1
3500

20

20

2800
40

Water depth (m)Water depth (m)

31

0.
14

0°
E

14

5.

°N
05

.3

04

.2

°N

13

5.

6°
E

Size variation of Anoplosolenia brasiliensis in the central equatorial Pacific Ocean

60

40

2100
60

1400
80

80

700
100

100

0

Individual (%)

120
25
20

120

(a)

10
0

1

2

3

4

5

6
7
Station ID

8

9

10

11

12

Fig. 4. Distribution of A. brasiliensis populations. Crosses represent sampled locations/depths.
Bottom line graph: % contribution by each station in total populations throughout the stations; left line graph: %contribution by each depth in total populations throughout the depths.

3.2. Morphometric results

A total of 1,026 of A. brasiliensis specimens were initially attempted to measure for size. Some specimens
were, however, physically damaged and the seriously damaged specimens were rejected in the analysis, making
the number of valid specimens 963 individuals for length and 1,003 for width. The statistical results of themorphometrics are based on total specimens from all depths and they are summarized including the following
parameters: minimum, maximum, mean, standard deviation (S.D.), skewness and kurtosis (Table 2). The resultsin skewness and kurtosis represent good proxies for the measure of normal distribution (Ichikawa and Ohashi,1987).
The measured cell length ranged from a minimum of 39 µm to a maximum of 165 µm. At Station 8 (171.4°E)
cell length showed a wide range of values compared to that from other stations. The mean cell length also showeda wide range compared to other parameters: the mean value was approximately 10 µm; and the S.D. was greaterthan 15 µm. In contrast, width showed a narrow range compared to length: the measured cell width ranged from aminimum of 1 µm to a maximum of 10 µm. The mean width also showed a narrow range: the mean value wasapproximately 5 µm; and the S.D. was approximately 1 µm. In summary, the measured length varied significantly
greater than that of the width. The cell length and width can be used to calculate cell volume (Table 2). At Station
7 (166.3°E) and Station 9 (174.5°E) the mean cell volume is greater than 700 µm3. On the other hand, the mean

32

Hideto Tsutsui and Kozo Takahashi

cell volumes at Station 8 and Station 12 (170.1°W) showed both approximately 300 µm3, which was roughly one
half of the volume measured at the other two stations. The measured kurtosis values are very large except at
Station 9.
Table 2. Summary of the statistical analysis performed.

90.7
83.8
79.2
85.4

17.9
17.0
16.4
17.9

St
at
io

1.02

1003

1

10

5.5

1.1

0.50

1.02

0.49 -0.07
0.86 2.15
0.46 0.50
0.62 1.20

124
297
408
174

3
2
3
1

10
9
9
7

5.6
5.4
5.8
5.0

1.1
0.9
1.1
1.0

0.91
0.51
0.59
0.04

2.48
1.20
0.43
0.46

(c) Length/Width
Min.
(µm3)

Max.
(µm3)

Mean
(µm3)

S.D.
(µm3)

Sk
ew

Ku
rto
si

1.48

963

28.3 2741.0

702.2

354.1 1.62

4.39

2734.52741.02092.82056.3

789.4
329.2
731.3
298.8

398.3
329.2
367.2
298.8

2.19
1.98
1.18
1.36

7.56
7.01
1.40
3.49

N

Min. Max. Mean S.D.

Sk
ew

s

N

ne
s

Ku
rto
si

s

(d) Cell volume

Statistics

963

6.8 37.5 15.4

3.9

0.87

St. 7 166.3°E
St. 8 171.4°E
St. 9 174.5°E
St. 12 170.1°W

119
286
395
163

9.3
7.3
7.2
6.8

16.4
15.6
13.9
17.4

3.8
3.7
3.2
4.5

0.32 -0.68
0.54 0.47
0.83 1.36
1.00 2.04

25.1
28.7
28.0
37.4

119 234.8
286 120.6
395 200.9
163 28.3

3.3. Relationship between length and width and summarized results for a normal distribution

s

147
165
149
162

s

55
42
39
46

Ku
rto
si

119
286
395
163

0.62

ne
ss

St. 7 166.3°E
St. 8 171.4°E
St. 9 174.5°E
St. 12 170.1°W

ness

83.1 17.4

N

Sk
ew

165

s

39

Ku
rto
si

963

n

Lo

(b) Width
Min. Max. Mean S.D.
(µm) (µm) (µm) (µm)

Sk
ew

ID

StatisticsnN

Min. Max. Mean S.D.
(µm) (µm) (µm) (µm)ness(a) Length

de

tu
gi

The plot for length versus width is illustrated (Fig. 5). The two morphometric parameters did not show any
strong correlations each other, but a vague trend can be read along two lines drawn at the upper and lower ends.
The morphometric results of A. brasiliensis are summarized (Fig. 6). The high kurtosis value for cell length at
Station 8 (Table 2) is represented by a sharp peak compared to those at other stations. The frequency distribution
curves indicate a dull shape at the top compared to those at other stations, but almost all of the peaks areconcentrated between 90 µm and 100 µm in length. In addition, the values for width are concentrated between 5µm and 6 µm. The peaks for a normal distribution columns are shifted to the left side.

Width (µm)

12N
St. 7 166.3°E 119
St. 8 171.4°E 286
St. 9 174.5°E 395
St. 12 170.1°W 163

8

4

0

60

Fig. 5. Plot for length vs. width.

120
Length (µm)

180Size variation of Anoplosolenia brasiliensis in the central equatorial Pacific Ocean

250

N
St. 7 166.3°E 119 400
St. 8 171.4°E 286
St. 9 174.5°E 395
St. 12 170.1°W 163

(a)

200

33

N
St. 7 124
St. 8 297
St. 9 408
St. 12 174(b)

Individuals

300

150

200

100

100

50

0

0

300

50

100

Length (µm)

150

200

St. 7
St. 8
St. 9
St. 12(c)

0N
119 350
286
395
163

2

4

6

8

Width (µm)

10

12

N
St. 7 119
St. 8 286
St. 9 395
St. 12 163

(d)

250

Individuals

200

150

100

50
0

15

30

Length/Width

45

0

0

1000

2000

Cell volume (µm3)

3000Fig. 6. Histograms for length, width, length/width and cell volume, respectively (columns: sum of the four stations); eachof the line graphs represents a histogram curve for a given sampled station.

4. Discussion
4.1. Difference in cell volume at each station

At this step, the variations in cell volume of A. brasiliensis are confirmed by t-test: a statistical difference inlength can be evaluated depending on depth and station. The results of t-value are summarized (Table 3). First, theresults of t-test suggest that there is a statistical difference between the verge point covered by Station 7 and thedense populations covering Station 8 to Station 9. In contrast, the t-test results between Station 8 and Station 9shows no statistical difference.
Therefore, concerning the cell volume of A. barasiliensis belonging to three discrete sample groups we
performed another round of t-test again: Station 7, Station 12 and the group of high population density consistingof Stations 8 and 9. The results are summarized in Table 3. The cell volumes of A. brasiliensis appear different
depending on the verge point of high population density at Station 7 or the dense population group represented by
Stations 8 and 9. Therefore, we performed a third round of t-test of A. brasiliensis cell volume in opposite sides:
the cell volumes in low and high population density, respectively. The borderline between the low population andhigh population density appears approximately at 1,000 individualsℓ-1. The results of the t-test show a statisticaldifference in A. brasiliensis cell volume between the values less than 1,000 individualsℓ-1 and greater than 1,000

34Hideto Tsutsui and Kozo Takahashi

individuals ℓ-1. The relationship between cell length and population density is illustrated (Fig. 6). The density of
1,000 individualsℓ-1 appears to represent a reasonable boundary between the following two cases. The case withfewer than 1,000 individualsℓ-1 shows a wide range in length from approximately 55 to 110 µm. For the casewith greater than 1,000 individualsℓ-1, the measured cell length is concentrated at approximately 75 to 100 µm. In
summary, the variation in cell length of A. brasiliensis can be represented by two separate modes depending onhigh or low population density.
Table 3. Results of t-test matrix: (a) among four stations; (b) among Station 7,
Station 12, and the sum of Stations 8 and 9; and (c) between the population density<1,000 individualsℓ-1 and >1,000 individualsℓ-1. The results with significant
differences are shown in bold face.

(a) among four stations
Class
St. 7
St. 8
St. 9

St. 8 St. 9 St. 12
2.72** 1.47 4.58**-1.70 2.75**
4.09**

Class
St. 7
St. 12

St. 8+St. 9-2.16*
4.18**

(b)

(c)
Class
<1000

>1000 ind. liter -1
2.58*
Prob.: ** (1%), * (5%)

Mean cell length (µm)

120

90

60

30
0

St. 7 166.3°E
St. 8 171.4°E
St. 9 174.5°E
St. 12 170.1°W
2Population density (x103 ind. liter -1)

4

Fig. 7. Relationship between mean cell length and population density. The dashed line is the result of a regression analysis.

4.2. Environmental conditions as related factors for cell size

In general, nannoplankton-sized marine life requires metabolic substance from ambient waters such as
nutrients for growth. The obtained cell volumes of A. brasiliensis at the four stations are compared with theSize variation of Anoplosolenia brasiliensis in the central equatorial Pacific Ocean

35

measured pertinent oceanographic conditions acquired during Cruise MR99-K07 (Fig. 1): temperature anddissolved oxygen (DO) among many parameters available (Kawano, 2000). In the case of temperature,
approximately 27°C appears as the most popular level accounting for the majority of the populations that weinvestigated. Approximately 190 µmol kg-1 is the most popular condition for DO (Fig. 8). Temperature is an
important factor as a prerequisite, but the relationships with cell volume variations and DO are unknown. Related
factors for cell volumes of A. brasiliensis are the followings: (1) population density of this own taxon; (2) watertemperature; and (3) DO. Nishida et al. (2000) discussed the changes in population density of the majorcalcareous nannoplankton taxa encountered in the same samples as this study: they are Umbellosphaera
irregularis, Emiliania huxleyi, Florisphaera profunda and Thorosphaera flabellate. The relationship between the
populations of A. brasiliensis and E. huxleyi is of interested and illustrated (Fig. 9). It is quite cleat that these two
distinctively different taxa in shape and size were behaving quite differently each other. When the population
density of the latter is fairly high (Stations 7, 11-12) that of the former is low. On the contrary to this, the former
picks up its populations at Station 8-9 where the latter declines its populations. Such a mirror image trend
observed from Stations 12 to 7 may be a hint showing a biological competition for nutrient uptake while it is hardto prove. For example, Gephyrocapsa oceanica is one of the major taxa in population besides E. huxleyi, but the
population of G. oceanica decreased from Station 9 to the west towards Station 7 (not shown). The nutrient levelof PO4 is the highest at Station 12, which is located within the equatorial upwelling region (Fig. 9). There is a
general decreasing trend in nutrient concentrations from Station 12 to the west towards Station 1. However, from
Station 9 to the west towards Station 6 significant changes are observed in trend and ranks of nutrient
concentrations for NH3 and NO2, especially relative to those of PO4 (Fig. 9). The maximum concentrations forNH3 and NO2, are found at Station 8 and Station 7, respectively. It may be that A. brasiliensis expands its
population density at the nutrient level somewhat intermediate rather than the highest. Whether the biologicalcompetition is important or ambient nutrient concentrations are more influential must be evaluated in light offurther data in future studies.

28

(a)

Dissolved oxygen (µmol kg -1 )Temperature (°C)

27

180

26

St. 7 166.3°E
St. 8 171.4°E
St. 9 174.5°E
St. 12 170.1°W

25

24

(b)

200

0

1000
2000
Cell volume (µm3)

3000

160

150

0

1000
2000
Cell volume (µm3)

3000Fig. 8. Relationships between cell volumes and temperature as well as DO as environmental indices.

4.4. Reproductive strategy of A. brasiliensis

Organisms are surrounded by environments and thus they are depended on the ambient conditions.
Anoplosolenia brasiliensis, a coccolithophore taxon, is not an exception for such dependency on environments.
Anoplosolenia brasiliensis pursues an adaptation strategy called a ”K-strategy”, which is a commonly used termin ecology. The following features, which are encountered in this taxon, fit in a K-strategy: (1) large body size
(Table 2, Figs. 5, 6); (2) low population density compared to that of an r-strategy type (low population density
shown at Stations 1 through 12, with respect to those of E. huxleyi except for at Stations 8-9 (Figs. 4, 9)); (3)36Hideto Tsutsui and Kozo Takahashi

Anoplosolenia brasiliensis
Emiliania huxleyi

4

4

2

01
6

2

(b)

3

4

5

6

7

8

9

10 11

12

6 7
8
Station ID

9

10 11

12

NH3
NO2
PO4

(µmol liter -1)

Nutrients concentration(a)(x10 Ind. liter -1)

Population density

5

4
2
0

1

2

3

4

5

Fig. 9. (a) Changes in population density of A. brasiliensis and E. huxleyi for Cruise MR99-K07. (b) Also potted are nutrientsconcentrations for NH3, NO2, and PO4 obtained during Cruise MR99-K07 (Kawano, 2000).

possessing a monomorphic stage; and (4) responsive to low nutrient concentrations (e.g., Foster, 1964;
MacArthur and Wilson, 1967; Kimoto, 1979; Tuomi, 1980; Iwasa, 1981; Young et al., 2003; Malinverno, 2004
and Litchman et al., 2007). Young et al. (2003) and Malinverno (2004) described this taxon as possessing a
haploid, and this taxon did not show any positive response for specific nutrients (Fig. 9). The above four features
represent as evidence for a K-strategy. In addition to a K-strategy, MacArthur and Wilson (1967) proposed
another way of life adaptation as an ”r-strategy”. With an r-strategy in stable environments organisms adapt
opposite features and characteristics with respect to those of a K-strategy such as high fecundity, small body size,
early maturity, and short generation time. A K-strategy can also be seen in other coccolithophore taxa than A.
brasiliensis. For example, it is known that Coccolithus braarudi represents two different ecological niches
depending on environmental conditions, representing a haploid stage when nutrient concentrations are low and adiploid stage when nutrient concentrations are high (Houdan et al., 2006).
However, at Stations 8 and 9 A. brasiliensis showed remarkably large populations compared to that of otherstations (Fig. 4). When the population density of A. brasiliensis is greater than 1,000 individualsℓ-1, cell length
decrease ca. 25% from low to high population density groups along the regressions line (Fig. 7). When the
population density of A. brasiliensis is greater than 1,000 individualsℓ-1, this taxon appears to have modified
growth strategy for adaptation. In other word, the greater the population density becomes, smaller the variance ofcell length becomes. We interpret that this taxon has adapted an r-strategy in the situation with relatively highpopulation density. Such a trend can also be observed in body size and litter size of mammals (Tuomi, 1980).
Moreover, it is known that major phytoplankton groups and size classes use skillful tactics for nutrient utilization
along nutrient availability gradients (Litchman et al., 2007). When the major species of coccolithophores such as
A. brasiliensis and E. huxleyi swapped their population maxima between Stations 8 and 9, A. brasiliensis
appeared to have won the competition against E. huxleyi. Therefore, A. brasiliensis fundamentally pursues aK-strategy, but this taxon is also pursuing an r-strategy when the situations become appropriate such as in theabove case. According to Lewis (1985), natural selection in phytoplankton could optimize the utilization andstorage of nitrogen and phosphorus, and render an advantage to haploid organisms with lower requirements ofSize variation of Anoplosolenia brasiliensis in the central equatorial Pacific Ocean

37

these elements in ambient environmental conditions. Margalef (1978) and Houdan et al. (2006) strongly
recommended needs for observations on nutrient response in r-strategy and K-strategy in phytoplankton.

5. Summary
The maximum population density of Anopsolenia brasiliensis was 3,333 individualsℓ-1 located at 40 m depth
at Station 8. A total of 963 individuals were measured for size analysis. The measured cell length ranged from theminimum of 39 µm to the maximum of 165 µm; width from the minimum of 1 µm to the maximum of 10 µm;
and cell volume from the minimum of 28 µm3 to the maximum of 2,741 µm3. The length/width ratios showed theminimum of seven to the maximum of thirty-seven. One of the related factors for cell length of A. brasiliensis
appears to be own population density. When the population density is less than 1,000 individualsℓ-1 the measured
cell length ranged from 55 to 110 µm. In contrast, when the population density is greater than 1,000 individualsℓ-1,
the values for cell length are clustered in the range of 75 to 100 µm. As other related factors attributing to such alarge cell size, the following hydrographic conditions appear important enough to report among many parameters
available: water temperature is ca. 27°C; and DO is ca. 190 µmol kg -1. The cell volume variations in A.
brasiliensis may be negatively influenced by the presence of E. huxleyi populations. Intricate nutrient levels witha balance among nutrient species must be considered as one of the factors contributing in high population densityof A. brasiliensis encountered at Stations 8 and 9. Fundamentally, A. brasiliensis pursues a K-strategy for survival
because that this taxon presents: (1) large cell size; (2) low population density compared to that of E. huxleyi; and (3)responsive to low nutrient conditions. Nevertheless, this taxon is also pursuing an r-strategy when ambient situation
becomes appropriate.

6. Acknowledgements
We thank Associate Professor Yutaka Wada of Department of Earth Sciences, Faculty of Education at Nara
University of Education; he provided a use of SEM JSM-6300PS and carbon coater JFE-400 for this work.
Professor Niichi Nishiwaki of Faculty of Sociology, at Nara University checked the statistic results in the
manuscript and provided useful discussions as the first reviewer. Professor Emeritus Shiro Nishida of Nara
University of Education provided critical comments and discussions as the second reviewer. Professor Tetsukazu
Yahara of Department of Biology, Faculty of Sciences at Kyushu University, who guided us on life strategy andfunction of phytoplankton, including providing useful references. Ms. Chiho Yamamoto, the technical engineer ofthe Aero Asahi Corp., checked English in early draft. Ms. Hisako Miyazaki, the CEO and Vice President Ms.
Masako Ito of the Miyazaki Insurance Firm and Co., Ltd., helped the senior author with a private scholarship. We
also thank Mr. and Ms. Muraoka for their kind assistance in lodging for the senior author while the work on the
SEM observation was conducted.

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Mem. Fac. Sci., Kyushu Univ., Ser. D, Earth ＆ Planet. Sci., Vol. XXXⅡ, No. 3,
pp. 39-61, March 10, 2011

Distribution of polycystine Radiolaria, Phaeodaria and Acantharia in the Kuroshio Current
off Shikoku Island and Tosa Bay during Cruise KT07-19 in August 2007
Jonaotaro Onodera*, Yusuke Okazaki*, Kozo Takahashi**, Kei Okamura***, and Masafumi Murayama***

Abstract
The occurrences of polycystine Radiolaria, Phaeodaria, and Acantharia are reported from plankton net
samples, which were obtained in the transect covering from the Kuroshio Current off Shikoku Island to
Tosa Bay during Cruise KT07-19 in August 2007. We employed 100 µm as the mesh size of the plankton
nets, which was coarser than the mesh size of many recent radiolarian studies (e.g., 44 or 63 µm). The
obtained specimens in the samples were categorized into 130 polycystine radiolarian, and 17 phaeodarian,and 3 acantharian taxa. The marked similarity of the polycystine radiolarian assemblages encountered inthis study to those reported from the tropical and subtropical oceans in the literature clearly indicates thesignificant influence by the warm Kuroshio Current. Furthermore, the observed polycystine radiolarianassemblages are similar to those of the previous result from the same specific study area. However, thevertical distribution patterns of some of the major polycystine radiolarian and phaeodarian taxa aredifferent from the previous results from the same region. The differences in vertical distribution may be
primarily due to the differences in vertical water mass conditions due to different sampling seasons. In
spite of the lengthy sample storage for seven months after the sampling in the shore laboratory, many
acantharian specimens were still preserved and encountered in the laboratory census, representing theacantharian presence in the summer sea surface waters in the Kuroshio Current area.
Keywords: Radiolaria, Phaeodaria, Acantharia, Kuroshio, MTD-net, subtropical assemblage

1. Introduction
In the subtropical oceans Radiolaria normally represent one of the major biosiliceous planktonic particles(e.g., Boltovskoy et al., 2010; Ishitani and Takahashi, 2007). In addition to calcareous microplankton particles,
together with diatoms the siliceous skeletons of Radiolaria and Phaeodaria significantly contribute as the ballastof sinking particles to the vertical transport of organic material to the interior of the deep oceans (Honjo et al.,2008). Thus, it is important to study them in detail. However, the information concerning the distributio ofRadiolaria and related groups in the water column is still meager and hence further studies are warranted.
Phaeodaria had been traditionally considered as one group of Radiolaria (see discussion in Takahashi andAnderson, 2002) whereas it has recently been often treated as one of Cercozoa (Poulet et al., 2004). As thetaxonomy of polycystine Radiolaria, Class Polycystinea is one of the representative groups in Subphylum
Radiolaria (Müller) Cavalier-Smith 1993. Class Polycystinea is subdivided into two Orders: Spumellaria
Ehrenberg 1875 and Nassellaria Ehrenberg 1875 (Anderson et al., 2002). Class Acantharia, which is classified
into Radiolaria with recent substantial molecular support, was traditionally treated separately from Radiolaria.
This is because that they bear celestite (SrSO4 ) skeletons, which are different from polycystine Radiolaria withbiogenic opal skeletons. Although there have been many studies on polycystine Radiolaria, works concerning

Manuscript received on 1 Dember 2010; accepted on 20 January 2011
Research Institute for Global Change, Japan Agency for Marine Earth Science and Technology, Natsushima-cho 2-15,
Yokosuka, 237-0061, JAPAN; Corresponding authorʼs e-mail: onoderaj@jamstec.go.jp** Department of Earth and Planetary Sciences, Graduate School of Science, Kyushu University, Hakozaki6-10-1,
Fukuoka, 812-8581, JAPAN*** Center for Advanced Marine Core Research, Kochi University, B200 Monobe, Nankoku, 783-8502, JAPAN*40

Jonaotaro Onodera, Yusuke Okazaki, Kozo Takahashi, Kei Okamura, and Masafumi Murayama

Acantharia are quite limited due to readily dissolved nature of their celestite skeletons. However, in the viewpointof geochemical cycle, acantharian production in the subtropical oceans may significantly influence, for instance,
the distribution of Sr/Ca ratios in the upper water column (De Deckker, 2004). Based on the microscopic
examinations on plankton tow and surficial bottom sediment samples we report the distribution of polycystineRadiolaria, Phaeodaria and Acantharia in this paper in order to serve a basis for the future studies.

2. Materials and Methods
2.1. Study Materials

The study area is located off Shikoku Island and Tosa Bay in the western North Pacific (Fig. 1). While this isin the temperate region with northern latitude of the Tropic of Cancer the watermasses here are largely influencd
by the northernly flow of the Kuroship Current and hence this region is conceptually close to the subtropics. The
studied materials were obtained at six sites during Cruise KT07-19 on board R/V Tansei-Maru of Japan Agency
for Marine Earth Science and Technology (JAMSTEC), which took place during 8-10 August 2007 (Table 1; Fig.
1). One of the two microplankton sampling methods was proceeded, employing a standard twin North Pacific net(NORPAC net: Motoda, 1957), at Sites M1, M2, and M3. The other sampling method employed involves Motoda
horizontal nets (MTD plankton net; lateral tow: Motoda, 1971); the plankton tow samples were obtained fromseven discrete depth layers at Sites M5, M7, and M9. During the lateral towing of the MTD plankton nets for ahalf an hour, the ship speed was controlled (~2 knot) in order to keep the wire angle of 45°. The applied mesh sizeof the plankton nets for the both moethods is 100 µm because of the primary objective in foraminifer sampling.
The obtained plankton samples were immediately fixed by 5% sample volume of buffered (pH 7.8) formaldehydewith sodium tetraborate. The rose bengal stain was added to the MTD samples in order to distinguish live
specimens (stained) from dead specimens (stain-free). The twin NORPAC net was towed without a flow meter
132°E
35°
N

133°

shu
Hon

Isla

134°

135°

nd

34°

S

ku
hiko

Isla

nd

M1
M2
M3

33°

M5
E

32°

-5000

-4000

M7
M9

-3000
-2000
Water Depth (m)

-1000

0

Fig. 1. Map of the studied area configured with GMT. The symbol with circles represents the sampling locations for the verticaltowing. The symbol with stars represents the locations for the lateral towing (MTD) and surface sediment sampling. The symbolwith a cross is the location where Station E was occupied in a previous study (Ishitani and Takahashi, 2007). Two bold arrows
designate the northern and southern boundaries of the Kuroshio Current on 7 August 2007, among the arrows representing theestimated lines of sea surface stream, (JHOD, JCG, 2007).

Radiolarians in Tosa Bay and off Shikoku Island in August 200741

attached. Furthermore, a flow meter test for the MTD net could not be conducted due to the limited ship time.
Therefore, reliable standing stocks cannot be estimated in this study. The results of specimen counts are shown as
relative abundance in total numbers of encountered polycystine radiolarian, phaeodarian and acantharianspecimens. Unexpected small number of live sea surface and subsurface dwellers were observed in deep MTD
samples. Such rare occurrences are considered as the result of contamination in the upper water column during
the cast of the net from sea surface to the deep depth. Therefore, some sampling error is included in the obtained% data in deep MTD samples.

Table 1. Summary for microzooplankton and microfossil samples obtained during Cruise KT07-19 ofTable 1. Summary for microzooplankton and microfossil samples in R/V Tansei-maru
R/V Tansei-maru.
cruise KT07-19.

Site ID Coordinate

Start Dateand Time(yr/m/d, JST)

Water
Depth
(m)

Sample Type

TargetTowing
Depth
Speed
(m)

Flow
Meter
Read

M1

33°26'N133°30'E

2007/8/8 9:40

31

Twin NORPAC(mesh: 100µm)

0.5 m/s

0-20

---

M2

33°24'N133°32'E

2007/8/8 7:20

70

Twin NORPAC(mesh: 100µm)

0.5 m/s

0-50

---

M3

33°14'N133°38'E

2007/8/10 5:10

231

Twin NORPAC(mesh: 100µm)

0.5 m/s

0-50

---

M5

32°40'N133°46'E

2007/8/8 21:30

990

Closing MTD + 2 knot
open net at 0m(mesh: 100µm);
surface sediment
by Multiple Core
sampler (MC)

0
50
100
200
300
500
750
M7
32°20'N
2007/8/9 13:55 1935 Closing MTD + 2 knot
0
134°00'E
50
open net at 0m
100(mesh: 100µm);
200
MC
300
500
1000
M9
33°09'N
2007/8/9 22:00 2750 Closing MTD + 2 knot
0
134°03'E
50
open net at 0m
100(mesh: 100µm);
200
MC
300
500
750
b
a
: plankton net tangled during towing; : plankton net mesh was torn during towing

2869
4345
442 a
14475
3522 a
21460
24280
4162
7522 b
17513
13038
28240
245
3395
4501
7045
369
919
1482
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5611 bThe obtained samples had been kept in a refrigerator (4°C) in a shore laboratory. All of the sample treatment
for this study was conducted in March 2008, seven months after the collection at sea. Portions of samples weresieved through stainless screens of 1000, 500, and 63 µm mesh size, respectively. The residue on these mesh sizes
was filtered onto a membrane filter (with 3 mm grid printed) and desalted. The filter was dried in an oven at 40˚Cand the sample was mounted on a glass slide with Canada BalsamR. In order to observe skeletons of polycystineRadiolaria and Phaeodaria employing a field emission scanning electron microscope (FE-SEM), portions ofplankton net samples and surface sediments taken by multiple core sampler (MC) were treated with hydrogen peroxideand sodium hexametaphosphate. The skeletal counts were proceeded under a light microscope (LM) to distinguishthe live/dead status of each of the specimens. The polycystine radiolarian and phaeodarian skeletons werenormally identified at genus or family level based on the illustrations published by Boltovskoy and Riedel (1987)
and Takahashi (1991). Concerning the encountered living specimens of a radiolarian Sphaerozoum, both numbersof their spicules and protoplasm were counted (Table 2).

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42Jonaotaro Onodera, Yusuke Okazaki, Kozo Takahashi, Kei Okamura, and Masafumi Murayama

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Radiolarians in Tosa Bay and off Shikoku Island in August 2007

43

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44

Jonaotaro Onodera, Yusuke Okazaki, Kozo Takahashi, Kei Okamura, and Masafumi Murayama

Radiolarians in Tosa Bay and off Shikoku Island in August 2007

45

3. Results and Discussion
3.1. Oceanographic conditions

Sea surface temperatures ranged from 25.3°C (Site M1) to 29.4°C (M7). According to the daily report on the
Kuroshio Current provided by Japan Coast Guard, Site M5 on 7th August 2007 was located in the central part of
the Kuroshio Current (Fig. 1). Site M7 was located in the southern part of the Kuroshio Current. While thesouthern edge of the Kuroshio Current was unclear, Site M9 appeared to be out side of the Kuroshio Current
based on the on-site CTD vertical profiles. Water temperature became colder with increased water depth. Below
200 m the isotherm depth shoaled from Site M9 towards Site M5. Sea surface salinity was the lowest at Site M1(33.1 psu) and the highest at Site M9 (34.5 psu). The high salinity waters (>34.5 psu) in the subsurface at Sites
M5-M9 reflect the lateral advection of the central subtropical waters. The maximum of chlorophyll concentration
was observed around the pycnocline depth at each site. In the plankton tow samples at Site M2, a diatom
Coscinodiscus sp. was dominant and conspicuous in the net phytoplankton (>100µm).
3.2. Polycystine Radiolaria

Among the observed microzooplankton groups, polycystine Radiolaria represented the major component in all
the samples except for the sea surface at Sites M5 and M7 (Fig. 2). The encountered polycystine radiolarianspecimens in all the sample slides were categorized into the following two orders (Anderson et al., 2002):
Spumellaria: 64 taxa; and Nassellaria 66 taxa (Table 2). While the sampled locations spans from 32.15°N to33.43˙N, which are within the temperate climatic region of the world, the obtained polycystine radiolarian(a) St. M1
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



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

(c) St. M3

Temp. (°C)



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     (b) St. M2

Temp. (°C)







Sal.







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Temp. (°C)

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Spumellaria
Nassellaria
Acantharia
Phaeodaria

for Sites M5-M9
Live



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

Chl-a (g L-1)

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Dead

Fig. 2. CTD profiles and relative abundances of Polycystine Radiolaria, Acantharia, and Phaeodaria at Sites M1-M9. The distinction ! was"given #
$M5-M9.
"  ! % && " ' ' " % "between live
and
dead
specimensat Sites   ()(*+  "  ! # ," "   -  "    ()(*+46

Jonaotaro Onodera, Yusuke Okazaki, Kozo Takahashi, Kei Okamura, and Masafumi Murayama

assemblages clearly show the affinity to the subtropic to the tropic assemblages. This is due to the influence of theKuroshio Current, which laterally advects the warm subtropical water mass from the lower latitudes along thewestern boundary of the North Pacific. The major encountered taxa in this study are essentially the same as thosereported in the previous study at Station E in June 2002 (Fig. 1; Ishitani and Takahashi, 2007). However,thevertical distribution of characteristic species indicated by Ishitani and Takahashi (2007) were different from theresults in this study. The differences in the vertical distribution of polycystine Radiolaria are primarily due to theseasonal difference in water mass conditions in the upper water column.
The relative abundance of Order Spumellaria was usually at similar level or higher than that of Order
Nassellaria. The spumellarian assemblages were represented by Didymocyrtis tetrathulumus, Tetrapyleoctacantha group. Tetrapyle octacantha group and Didymocyrtis tetrathalamus; they commonly occur in thesubtropical and tropical oceans (Kling, 1979; Yamashita et al., 2002; Boltovskoy et al., 2010). In addition to
Family Collosphaeridae, abundant Spaherozoum spicules were the main cause of high %Spumellaria in theshallow layers at Sites M5-M9. In particular, radiolarian assemblage at sea surface at Site M9 was characterized
by the high abundance of Sphaerozoum with Siphonosphaera spp. and Solenosphaera spp., all of which belong tocolonial radiolarians. Because that the colonial radiolarians prosper better in the pelagic waters than in moreeutrophic waters the result shown here are conformable with the known distribution (Takahashi et al., 1995).
Interestingly, Tetrapyle octacantha group and Didymocyrtis tetrathalamus, which commonly occur in thesubtropical and tropical oceans (Kling, 1979; Yamashita et al., 2002; Boltovskoy et al., 2010), were commonly
observed in many samples. Living Dictyocoryne spp. were observed in many samples at Sites M5 and M7
whereas the living specimens of this taxon were encountered only at 50 m at Site M9.
The vertical trend of %Nassellaria at Sites M5-M9 shows the maximum depth at 200 m or 300 m, whichcorrespond to the lower part of high salinity layer (Fig. 2). The increase in %Nassellaria from the surface layer tothe deeper layer is the same characteristics as in the previous observation in the oligotrophic tropical ocean(Yamashita et al., 2002). Lophophaena spp. and Lophospyris spp. were found in many samples. The highabundance of these taxa were also reported in the subtropical and tropical oceans (Kling, 1979; Yamashita et al.,2002). The nassellarian assemblage at Sites M1-M3 was mainly composed of Pseudocubus obeliscus, Zygocircus
productus, Plagoniidae spp., and juvenile of Nassellaria spp. (Table 2). Psudocubus obeliscus and Z. productus
were characteristically observed in the surface waters (Yamashita et al., 2002). The high abundances of P.
obeliscus at coastal sites rather than pelagic sites appear to be related to the high primary productivity (Ishitani
and Takahashi, 2007) and high nutrient supply in the equatorial upwelling (Yamashita et al., 2002). At Sites
M5-M9, %Nassellaria was significantly minor at the sea surface. There are two possible reasons for the minor%Nassellaria representations. The first reason is the relative dominance of Spaherozoum spicules or Acantharia.
Another reason is the limited standing stock of Nassellaria at sea surface at Sites M5-M9; Nassellaria were absent
at Site M9 or 4-5 specimens only at Sites M5 and M7 whereas the encountered Spumellaria were greater than 100
specimens except for Sphaerozoum spicules. In the deep layer at Site M5-M9, Eucecryphalus spp. wereencountered.
3.3. Phaeodaria

Seventeen phaeodarian taxa were observed mainly below the depth of chlorophyll concentration maximum at
Sites M5-M9 (Fig. 2). The relative abundance of total Phaeodaria in the studied microplankton groups was higher
than that of total Nassellaria at 500 m and 750 m at Site M5. The major taxon at Site M5 was Challengeron
willemoesii in addition to Protocystis xiphodon and Challengeriidae spp. (Table 2). The depths with abundant
Challengeron willemoesii were deeper than the previous result in the equatorial Pacific (as subsurface dwellers in
120-200 m: Yamashita et al., 2002). While phaeodarian specimens at Site M2 were absent in the census sample
slides (Table 2), few skeletons of Medusetta ansata were found in the treated sample for photomicrographs (Plate
13, fig. 1).
The relative increase of phaeodarian abundance with respect to polycystine radiolarians in the deep layers iscommon in the tropical oceans (Dworetzky and Morley, 1987; Yamashita et al., 2002). When the relatively highstanding stocks of Phaeodaria relative to polycystine Radiolaria were observed in the subsurface layers (40-200m) around Japan, salinity and water temperature were about 34 psu and 5-13°C, according to the CTD profile
figure in Ishitani and Takahashi (2007). Such values in salinity and water temperature were also observed in thisstudy in the deep layers, which roughly correspond to the sampled depths with the observed living phaeodarianspecimens (Fig. 2).
3.4. Acantharia

In spite of the fact that the studied samples had been stored in a refrigerator for seven months after sampling,Radiolarians in Tosa Bay and off Shikoku Island in August 200747

common to dominant acantharian specimens were encountered in the samples from the sea surface and upper
waters of Sites M5 and M7 (Fig. 2). The dominant acantharian taxon at Sites M5 and M7 was Holacanthida(?) sp.
as shown in Plate 13, figs. 7 and 8. Most acantharian specimens at Site M5 had the stained protoplasm, suggesting
living conditions at the time of sampling. However, many specimens at the sea surface at Site M7 were deadwithout protoplasm (Fig. 2). The acantharian occurrences were trace level at Sites M3 and M9 and absent at Sites
M1 and M2.
In general, acantharian skeletons are readily dissolved after death (Beers and Stewart, 1970) because of theunsaturated strontium sulfate concentrations in sea waters. The high abundance of acantharians at Sites M5 andM7 are unusual. This is because that addition of strontium for the sake of skeletal preservation (Michaels, 1988)
was not proceeded to the acquired samples, which were kept in the buffered formaldehyde solution. Although thestrontium concentration in the waters of the plankton net samples has not yet been analyzed, we suspect that some
portion of acantharian skeletons may have been dissolved prior to the point where strontium concentration
became saturated in the stored samples. The skeletal abundance ratios of acantharian versus polycystineradiolarians at sea surface at Sites M5 and M7 were two orders of magnitude less than those in the previous
results without significant acantharian skeleton dissolution (Beers et al., 1975 in the central North Pacific gyre;
De Deckker, 2004 in Indian Ocean). Therefore, the relative abundance of acanthaians at Sites M5 and M7 may
originally have been significantly higher than our obtained results.
Based on the biogeographic occurrence pattern in this study, the high abundance of acantharians can be related
to the summer surface waters of the Kuroshio Current. According to De Deckker (2004), the acantharianassemblage in the Mediterranean Sea around Italy suggested an ecological relationship to salinity gradient(Bottazzi, 1978; Bottazzi and Andreoli, 1978). In this study, the σt values determined by both salinity and watertemperature were lower than that in the Mediterranean data when acantharians dominated relative to polycystineradiolarians and phaeodarians. Sigma-t (σt) at 0 m at Sites M5 and M7 were 21.2 and 21.3, respectively, whichwere lower than σt at sea surface at nearshore Site M1 (σt = 22.1) and offshore Site M9 (σt = 22.1). Not only
salinity difference but also higher water temperature appear be related to the biogeographic patterns ofacantharian distribution in this study. However, at Site M3 with the lowest σt at sea surface, %Acantharia wasminor (Fig. 2). Such a low %Acantharia is explained by the difference in the sampling method (vertical towing
for 0-50 m at Site M3). The previous study shows that the vertical distribution of acantharian abundance steeply
decreases below 20 m water depth (Michaels, 1988). Therefore, the %Acantharia in the vertical tow sample at
Site M3 appears to be suppressed, with the view that the standing stock of polycystine radiolarians just below thesea surface was relatively abundant compared to the acantharian standing stock.

4. Acknowledgements
We thank the captain, crew, technical staff, and scientists on board R/V Tansei-Maru of JAMSTEC for theirefforts in the CTD observations and plankton two sampling employed in this study. We are grateful to Dr.
Yoshiyuki Ishitani at JAMSTEC who reviewed the manuscript of this paper for his critical and constructive
comments, which were greatly helpful in revising the manuscript. This work was financially supported by the
Kochi University President's Discretionary Grant in 2007 and 2008.

5. References
Anderson, O. R., Nigrini, C., Boltovskoy, D., Takahashi, K., and Swanberg, N. R. (2002) Class Polycystina. In:
The Second Illustrated Guide to the Protozoa, Lee, J.J., Leedale, G.F., and Bradbury, P., (eds.), Society ofProtozoologists, Lawrence, KS. 994-1022.
Beers, J. R., and Stewart, G. L. (1970) The preservation of acantharians in fixed plankton samples. Limnology
and Oceanography, 15, 825-827.
Beers, J. R., Reid, F.M.H., and Stewart, G. L. (1975) Microplankton of the North Pacific Central Gyre. Population
structure and abundance, June 1973. Internationale Revue Gesamtes Hydrobiologie, 60, 607-638.
Boltovskoy, D., and Riedel, W.R. (1987) Polycystine Radiolaria of the California Current region: seasonal andgeographic patterns. Marine Micropaleontology, 12, 65-104.
Boltovskoy, D., Kling, S. A. Takahashi, K. and Bjørklund. K. (2010) World atlas of distribution of recent
Polycystina (Radiolaria). Paleotologia Electronica, Article Number: 13.3.18A; http://palaeo-electronica.
org/2010_3/215/index.html.
Bottazzi, E.M. (1978) Systematic-ecological aspects of Radiolaria with special reference to Acantharia. Bolletino

48

Jonaotaro Onodera, Yusuke Okazaki, Kozo Takahashi, Kei Okamura, and Masafumi Murayama

Zoologica, 45, 133-144.
Bottazzi, E. M., and Andreoli, M.G. (1978) Distribuzione stagionale degli Acantari e dei Radiolari (Protozoa,
Sarcodina) in diverse zone costiere dei mari italiani. L’ Ateneo Parmense Acta Naturalia, 14, 477-500.
De Deckker, P. (2004) On the celestite-secreting Acantharia and their effect on seawater strontium to calcium
ratios. Hydrobiologia, 517, 1-13.
Dworetzky, B.A., and Morley, J.J. (1987) Vertical distribution of radiolaria in the eastern Equatorial Atlantic:
analysis of a multiple series of closely-spaced plankton tows. Marine Micropaleontology, 12, 1-19.
Honjo, S., Manganini, S.J., Krishfield, R.A., Francois,R. (2008) Particulate organic carbon fluxes to the oceaninterior and factors controlling the biological pump: A synthesis of global sediment trap programs since 1983.
Progress in Oceanography, 76, 217-285.
Ishitani, Y., and Takahashi, K. (2007) The vertical distribution of Radiolaria in the waters surrounding Japan.
Marine Micropaleontology, 65, 113-136.
Kling, A.S. (1979) Vertical distribution of polycystine radiolarians in the central North Pacific. Marine
Micropaleontology, 4, 295-318.
Michaels, A.F. (1988) Vertical distribution and abundance of Acantharia and their symbionts. Marine Biology, 97,
559-569.
Motoda, S. (1957) North Pacific standard plankton net. Information Bulletin on Planktology in Japan, 4, 13-15.
Motoda, S. (1971) Devices of simple plankton apparatus V. Bulletin of the Faculty of Fisheries Hokkaido
University, 22, 101-106.
Poulet, S., Berney, C., Fahrni, J., and Pawlowski, J.A.N. (2004) Small-subunit ribosomal RNA gene sequences of
Phaeodarea challenge the monophyly of Haeckel's Radiolaria. Protist, 155, 53-63.
Takahashi, K. (1991) Radiolaria: Flux, ecology, and taxonomy in the Pacific and Atlantic. In: Honjo, S. (Ed.),
Ocean Biocoenosis Series, 3. Woods Hole Oceanography Inst. Press, Woods Hole, MA. pp. 303.
Takahashi, K., Oba, T., Yamazaki, H., and Ohkouchi, N. (1995) Paleoceanographic changes based on radiolarianfossils during the past 80 ky in the western Tropical Pacific. Kaiyo Monthly, 27 (8), 466-473. [in Japanesewith English fig. & table captions.]
Takahashi, K., and Anderson, O. R. (2002) Class Phaeodaria. In: The Second Illustrated Guide to the Protozoa ,Lee, J.J., Leedale, G.F., and Bradbury, P., (eds.), Society of Protozoologists, Lawrence, Kansas. 981-994.
Yamashita, H., Takahashi, K., and Fujitani, N. (2002) Zonal and vertical distribution of radiolarians in the westernand central Equatorial Pacific in January 1999. Deep-Sea Research II, 49, 2823-2862.
.

Radiolarians in Tosa Bay and off Shikoku Island in August 2007

49

Plate 1

Plate 1. Spumellaria. All scale bars = 50 μm. The sample ID of each photomicrograph is represented in parenthesis. 1, 2.
Acrosphaera spinosa, 3. Collosphaera macropora, 4, 5. Collosphaera tuberosa, 6-10. Siphonosphaera spp., 11. 12. Solenosphaera
quadrata, 13, 14. Solenosphaera zanquebarica, 15-17. Solenosphaera spp., 18. Sphaerozoum sp., 19, 20. Plegmosphaera
entodictyon (figs. 1-3, 5, 6, 10-12, 14-17, 19, 20.: Sample Site M9, Multiple Core Sample (MC), 0-1 cm; figs. 4, 7, 8.: M5, MC, 0-1
cm; 9. M9,: MTD net sample (MTD), 50 m; 13. M7, MTD, 50 m; fig. 18.: M9, MTD, 0 m)

50

Jonaotaro Onodera, Yusuke Okazaki, Kozo Takahashi, Kei Okamura, and Masafumi Murayama
Plate 2

Plate 2. Spumellaria. All scale bars = 50 μm. Spongosphaera polycantha, 2. Spongosphaera streptacantha, 3. Actinomma
antarcticum Group?, 4-5, 6? Actinomma arcadophorum, 7-13. Actinomma spp. (figs. 1, 2, 6, 7, 9, 11, 12.: M9, MC, 0-1 cm; fig.3.:
M7, MC, 0-1 cm; figs. 4, 5, 8, 10, 13.: M5, MC, 0-1 cm)

Radiolarians in Tosa Bay and off Shikoku Island in August 2007

51

Plate 3

Plate 3. Spumellaria. All scale bars = 50 μm. 1. Acanthosphaera actinota, 2, 3. Actinoshapera spp., 4. Arachnosphaera myriacantha,
5. Cladococcus cervicornis, 6. Cladococcus scoparius, 7. Cladococcus viminalis, 8. Astrosphaera hexagonalis, 9. Drymosphaera
dendrophora, 10. Hexacontium hostile, 11. Hexacontium melpomene, 12. Hexacontium spp. (figs. 1, 11.: M5, MC, 0-1cm; figs. 2, 7,
9, 10.: M9, MC, 0-1 cm; fig. 3.: M7, MTD, 300 m; fig. 4.: M2, NORPAC net sample (NORPAC), 0-50 m; fig. 5.: M7, MTD, 300 m; fig.
6.: M7, MTD, 50 m; fig. 8.: M7, MC, 0-1 cm).

52

Jonaotaro Onodera, Yusuke Okazaki, Kozo Takahashi, Kei Okamura, and Masafumi Murayama
Plate 4

Plate 4. Spumellaria. All scale bars = 50 μm. 1-3. Hexacontium spp., 4, 5. Hexalonche amphisiphon, 6, 7. Axoprunum stauraxonium,
8, 9. Druppatractus sp., 10-13. Actinomiidae spp.(figs. 1-9, 13.: M9, MC, 0-1 cm; fig. 10.: M5, MC, 0-1 cm; fig. 11.: M7, MTD, 300m; fig. 12.: M9, MTD, 750 m)

Radiolarians in Tosa Bay and off Shikoku Island in August 2007

53

Plate 5

Plate 5. Spumellaria. All scale bars = 50 μm. 1, 2. Actinomiidae spp., 3-8. Didymocyrtis tetrathalamus tetrathalamus, 9.
Didymocyrtis aff. tetrathalamus, 10-12. Euchitonia elegans, 13, 14. Amphirhopalum ypsilon, 15. Spongopyle osculosa, 16.
Stylochlamydium venustum, 17, 18. Stylodictya asteriscus, (figs. 1, 4, 9, 10, 12.: M5, MC, 0-1 cm; figs. 2, 3. 5-8, 11, 13-15, 17, 18.:
M9, MC, 0-1 cm; fig. 16.: M9, MTD, 750 m)

54Jonaotaro Onodera, Yusuke Okazaki, Kozo Takahashi, Kei Okamura, and Masafumi Murayama
Plate 6

Plate 6. Spumellaria. All scale bars = 50 μm. 1, 2. Stylodictya validispina, 3-7. Spongodiscidae spp., 8-10. Dictyocoryne spp., 11.
Spongurus cylindricus, 12. Spongurus spindalis, 13, 14. Spongaster tetras tetras, 15, 16. Heliodiscus macrococcus, 17, 18.
Tetrapyple octacantha group (figs. 1, 5, 7, 14: M5, MC, 0-1 cm; figs. 2-4, 8-13, 15- 18.: M9, MC, 0-1 cm).

Radiolarians in Tosa Bay and off Shikoku Island in August 2007

55

Plate 7

Plate 7. Spumellaria. All scale bars = 50 μm. 1, 2. Tholospira cervicornis group, 3. Tholospira? sp., 4-6. Larcopyle buetschlii, 7, 8.
Lithelius spp.?, 9, 10. Larcospira quadrangular, 11-20. Spumellaria spp. (figs. 1-3, 5, 6, 9-13, 17-20.: M9, MC, 0-1 cm: figs. 4, 7, 8,
15, 16.: M5, MC, 0-1 cm; fig. 14.: M7, MC, 0-1 cm)

56

Jonaotaro Onodera, Yusuke Okazaki, Kozo Takahashi, Kei Okamura, and Masafumi Murayama
Plate 8

Plate 8. Nassellaria. All scale bars except for figs. 3 and 4 = 50μm. 1. Peridium sp., 2. Peromelissa phalacra, 3, 4. Plagoniidae spp., 5.
Plectacantha sp., 6. Pseudodictyophimus sp.?, 7-9. Arachnocorys umbellifera, 10-12. Lophophaena spp., 13. Pseudocubus obeliscus, 14,
15. Zygocircus productus, 16, 17. Acanthodesmia vinculata, 18, 19. Lophospyris spp., 20. Lophospyris pentagona pentagona, 21, 22.
Phormospyris herdisae, 23. Ceratospyris borealis, 24. Phormospyris stabilis scaphipes, 25. Liriospyris reticulata? (figs. 1, 5, 9-11, 18,
20-24.: M9, MC, 0-1 cm; figs. 2-4, 7, 8, 12-14, 17, 25.: M5, MC, 0-1 cm; fig. 6.: M7, MTD, 300 m; fig. 19.: M9, MTD, 50 m)

Radiolarians in Tosa Bay and off Shikoku Island in August 200757

Plate 9Plate 9. Nassellaria. All scale bars = 50μm. 1, 2. Androspyris huxley, 3. Clathrocanium coarctatum, 4. Callimitra sp., 5.
Tetraphormis rotula, 6. Tetraphormis dodecaster, 7-9. Lampromitra spp., 10, 11. Eucecryphalus cervus, 12. Eucecryphalus
tricostatus (inside view), 13, 14. Eucecryphalus spp., 15, 16. Peripyramis circumtexta, 17. Lithrachnium eupilium (figs. 1, 2.: M7,
MC, 0-1 cm; figs. 3-6, 8-10, 12-14, 16, 17.: M9, MC, 0-1 cm; fig. 7.: M7, MTD, 300 m; fig. 15.: M5, MC, 0-1 cm)

58

Jonaotaro Onodera, Yusuke Okazaki, Kozo Takahashi, Kei Okamura, and Masafumi Murayama
Plate 10

Plate 10. Nassellaria. All scale bars = 50μm. 1, 2. Pterocanium trilobum, 3. Pterocanium praetextum eucolpum, 4-6. Pterocanium
praetextum praetextum, 7. Conarachnium parabolicum, 8-10. Stichopilium bicorne, 11, 12. Theocorythium trachelium, 13. Lipmanella
bombus, 14. Lipmanella sp., 15. Cycladophora bicornis, 16. Cycladophora davisiana, 17. Cycladophora cornutoides, 18. Pterocyrtidium
dogieli, 19. Theoperidae sp., (figs. 1-4 , 6-9, 13, 18.: M5, MC, 0-1 cm; figs. 5, 10-12, 15-17, 19.: M9, MC, 0-1 cm; fig. 14.: M9, MTD, 50m).

Radiolarians in Tosa Bay and off Shikoku Island in August 2007

59

Plate 11

Plate 11. Nassellaria. All scale bars = 50 μm. 1. Tetracorethra tetracorethra, 2, 3. Pterocorys zancleus, 4, 5. Eucyrtidium
acuminatum, 6, 7. Eucyrtidium anomalum, 8, 9. Eucyrtidium dictyopodium, 10. Eucyrtidium hexastichum, 11-13. Eucyrtidium spp.,
14, 15. Anthocyrtidium ophirense, 16, 17. Anthocyrtidium zanguebaricum (fig. 1.: M9, MTD, 50 m; figs. 2-9, 11, 12, 15, 16.: M9,
MC, 0-1 cm; figs. 10, 14, 17.: M5, MC, 0-1cm; fig. 13.: M7, MTD, 300 m)

60

Jonaotaro Onodera, Yusuke Okazaki, Kozo Takahashi, Kei Okamura, and Masafumi Murayama
Plate 12

Plate 12. Nassellaria and Phaeodaria. All scale bars = 50 μm. 1-3. Lamprocyclas maritalis group?, 4. Botryostrobus auritus/
australis, 5, 6. Carpocanistrum spp., 7. Conchidium caudatum, 8, 9. Conchellium capsula, 10. Challengerosium? sp., 11. Protocystis
auriculata, 12. Protocystis xiphodon, 13, 14. Challengeron willemoesii, 15. Challengellanium diodon?, 16, 17. Euphycetta lucani(figs. 1, 2, 5, 6.: M9, MC, 0-1 cm; figs. 3, 4.: M5, MC, 0-1 cm; fig. 7.: M9, MTD, 200 m; figs. 8, 9.: M7, MTD, 300m; fig. 10.: M5,
MTD, 300 m; figs. 11, 15.: M5, MTD, 500 m; figs. 12, 13, 16.: M5, MTD, 200 m; fig. 14.: M7, MTD, 1000 m; fig. 17.: M9, MTD,
750 m)

Radiolarians in Tosa Bay and off Shikoku Island in August 2007

61

Plate 13

Plate 13. Phaeodaria and Acantharia. All scale bars = 50μm. 1. Medusetta ansata, 2. Gazelletta cyrtonema, 3. Porospathis? sp., 4.
Castanidium longispinum?, 5. Aularia ternaria, 6. Aulographis? sp., 7, 8. Acantharia sp. 1 , 9, 11-14. Acantharia spp., 10. Acantharia sp. 2,(fig. 1.: M2, NORPAC, 0-50 m; fig. 2.: M7, MTD, 50 m; fig. 3.: M7, MTD, 750 m; fig. 4.: M7, MTD, 100 m; fig. 5.: M7, MTD, 300 m;
fig. 6.: M9, MTD, 750 m; figs. 7-14.: M5, MTD, 0 m)

Mem. Fac. Sci., Kyushu Univ., Ser. D, Earth ＆ Planet. Sci., Vol. XXXⅡ, No. 3,
pp. 63-73, March 10, 2011

Identification of full-substorm onset from ground-magnetometer data by singular valuetransformation
Terumasa Tokunaga*, Kiyohumi Yumoto**, Teiji Uozumi** and CPMN Group

Abstract
Pi 2 magnetic pulsations observed on the ground are a good indicator of the auroral breakup. However,they have not only corresponding full-substorm onsets but also most pseudobreakups. Another well-known
substorm related phenomenon observed on the ground is positive bays. In order to identify full-substorm
onsets from ground-magnetometer data, we developed a new algorithm based on “Singular Spectrum
Analysis (SSA)”. The algorithm enables us to screen Pi 2 pulsations accompanied by the magnetic positivebay. We applied proposed algorithm to ground-magnetometer data and compared to the obtained resultswith Polar/UVI data. As a result, we succeeded in identifying 62% of the full-substorm onsets fromground-magnetometer data obtained in the nighttime sector between 21 and 03LT.
Keywords: auroral substorm, Pi 2 pulsation, positive bay, Singular Value Transformation

1. Introduction
Pi 2 magnetic pulsations are defined as impulsive hydromagnetic oscillations with a period of 40-150s. It is
well-known that Pi 2 pulsations has one-to-one correspondence with auroral breakups (Jacobs et al., 1964; Saito,
1969; Yumoto and CPMN Group, 2001). The excitation of the Pi 2 wave is closely related to the substorm trigger(Saito, 1976) and therefore Pi 2 onsets are often used for identifying substorm onsets. Although Pi 2 pulsations
have been accepted as a good indicator of auroral breakups, they correspond to not only full-substorm onsets but
also most pseudobreakups (Rostoker et al., 1980). Hsu and McPherron (2007) examined statistical properties of
Pi 2 pulsations. They reported that the most probable number of Pi 2 bursts per substorm is 2. Pseudobreakups arecharacterized by short lifetimes, extreme locations, and weak magnetic perturbations on the ground (McPherron,1991). In the previous substorm researches, geophysical differences between pseudobreakups and full substorms
have been studied (Ohtani et al., 1993; Nakamura et al., 1994; Ohtani et al., 2002; Partamies et al., 2003).
However, the physical difference in the magnetosphere and on the ground has not been clarified yet. In otherwords, to figure out the physical difference is a key subject for understanding the substorm onset mechanism.
From this viewpoint, it is important to detect Pi 2 pulsations that correspond to full-substorm onset.
In 1990s, some studies have been made on the automatic detection of ground-observed Pi 2 pulsations.
Takahashi et al. (1995) utilized wave power in the Pi 2 frequency band, which is calculated by applying thediscrete Fourier transform, for selecting Pi 2 pulsations. An wavelet analysis has also been used to detect Pi 2
pulsations (Nose et al., 1998; Murphy et al., 2009). Recently, Hilbert-Huang Transformation used as ULF (Ultra
Low Frequency) wave diagnosis of substorm expansion phase onset (Kataoka et al., 2009). Furthermore, thepattern recognition capabilities of artificial neural networks (ANN) have been used to identify Pi 2 pulsations(Sutcliffe, 2007). However, these methods cannot determine whether the Pi 2 pulsation corresponds to fullsubstorm onsets or to psedobreakups.
Another well-known substorm related phenomenon measured on the ground is positive bays. At the onset ofManuscript received on 15 December 2010; accepted on 13 January 2011
Department of Earth & Planetary Sciences, Graduate School of Sciences, Kyushu University, 6-10-1 Hakozaki,
Higashi-ku, Fukuoka 812-8581, JAPAN; Corresponding authorʼs e-mal: tokunaga@geo.kyushu-u.ac.jp** Space Environment Research Center, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, JAPAN*64

Terumasa Tokunaga, Kiyohumi Yumoto, Teiji Uozumi and CPMN Groupthe substorm expansion phase, the crosstail current is diverted down the magnetic filed lines. The current thenflows in the ionosphere as the westward electrojet and returns to the tail along the magnetic field line. The
perturbation of tail current can be represented by an equivalent eastward current, which completes the threedimensional current wedge. The mid-latitude and low-latitude signature of this wedge is a positive perturbation in
the north-south component (McPherron et al., 1973a; Clauer and McPherron, 1974). The positive perturbation iscalled substorm positive bay (Akasofu and Meng, 1969; Meng and Akasofu, 1969). It is widely accepted that thesudden formation of the current wedge is essential to complete substorm onset. Hence, positive bays at mid andlow latitudes could be an evidence for the occurrence of full substorms. From these arguments, we can say that Pi
2 pulsations accompanied by positive bays are one of the most reliable indicators of full-substorm onsets.
In order to identify full-substorm onsets from ground-magnetometer data, we propose a new algorithm toscreen Pi 2 pulsations that accompanied by positive bays. As mentioned earlier, there are some works about
automatic detections of Pi 2 pulsations. However, these methods are limited only to detecting wave packets. To
screen Pi 2 pulsations that accompanied by positive bays, we should detect wave packets and changes of slopes
simultaneously in ground-magnetometer data. Recently, singular spectrum analysis (SSA) has been used forchange-point detections in time series (Moskvina and Zhigljavsky, 2003). Ide and Inoue (2005) developed the
SSA-based change-point detection method, named singular spectrum transformations (SST), and showed that it
was useful in knowledge discovery of causal relationships from a set of heterogeneous time series. Recently, theSST has been applied to determine the onset of positive bays (Tokunaga et al., 2010a, b). Unlike otherconventional approaches, the SSA is data adaptive and does not employ any specific generative models. Further,
SSA can extract simultaneously complex trends and periodic components. Hence, SSA-based change-point
detection method likely fills our purpose, that is, to detect wave packets and changes of slopes simultaneously. In
this paper, we introduce a new SSA-based change-point detection method, named Singular Value Transformation(SVT), to screen Pi 2 pulsations that accompanied by positive bays.
The outline of the rest of the paper is as follows. In Section 2, we describe the basic concept of SSA. Further,
we introduce “bay-score” that provides information to determine whether the Pi 2 pulsation accompanied by the
positive bay is present or not. Then, we define the framework of SVT. In Section 3, we apply our algorithm to theground-magnetometer data and compare the result with auroral images obtained by Polar Ultra Violet Imager(Polar/UVI). Furthermore, we evaluated the practical performance of the algorithm in a statistical study.

2. Singular Value Transformation
In this section, we introduce the new method, named SVT, to detect substorm positive bays from groundmagnetometer data. The SVT can be regard as an applied technique of SSA. Thus, we first describe the basic
concept of SSA.
2. 1. Pattern Extraction by SSA

First of all, let us consider a transformation of a sequence time series
into the multidimensional series, where the X i denotes a subsequence that can be described as. Vectors Xi’s and the matrix X are called L-lagged vectors and an L-trajectory
matrix, respectively. Note that an L-trajectory matrix X is an L× K Hankel matrix described as‥‥(1)
We call K and L a window width and an embedding dimension, respectively.
The second step of the SSA is the SVD of the Hankel matrix X. Let us denoteas squared. Now the SVD of the Hankel
singular values of XXT in decreasing order of the magnitude
matrix X can be described as X=ULVT, where Λ denotes a diagonal matrix whose diagonal element equal to thesquared singular values, U denotes a left singular matrix and V denotes a right singular matrix. Superscript T
denotes the transpose of a matrix. Then, the Hankel matrix X can be described as a sum of rank-one bi-orthogonalIdentification of full-substorm onset from ground-magnetometer data65

elementary matrices. The ith elementary matrix can be described by using the ith left
singular vector and the ith right singular vector as. A set of these three notations
consists of singular value , empirical orthogonal functions
and principal components . Note that L
corresponds to the number of singular vectors.
Now let us define representative patterns using empirical orthogonal functions(1≤ i ≤ L). As describedabove, the method to extract dominant structures in time series via the SVD on the Hankel matrix is referred to as
the SSA.
2. 2. Preliminary procedure for SVT

Let us consider to create a L× K Hankel matrix

according to the procedure shown in Figure 1.

‥‥(2)

Fig. 1. Schematic illustration of the preliminary procedure for SVT.

Here, we call K and L a window width and an embedding dimension.
represents a shift length. Next, weconsider a SVD of the matrix . Let us denote () as squared singular values ofin decreasing), where the subscript T denotes transpose of a matrix. Now the SVD oforder of the magnitude (the Hankel matrix
can be described asdenotes a diagonal matrix whose diagonal, whereelement equal to the squared singular values,
denotes a left singular matrix anddenotes a right singularmatrix. For simplicity, now we assume that is a square matrix, that is, K=L. Then, can be described as‥‥(3)
Now let the ith column vector of matrix
and the ith row vector of matrix
beand , respectively.
andcalled empirical orthogonal functions and principal components, respectively. The magnitude ofcorrespond to powers of empirical orthogonal functions and principal components.

66

Terumasa Tokunaga, Kiyohumi Yumoto, Teiji Uozumi and CPMN Group. In Figure 2, we show the test data, which we created
Next, we focus attention on the time variation of
based on a mid- and low-latitude magnetic variation around a substorm onset. Figure 3a shows the time variationof(). Figure 3b shows() at t=250s and Figure 3c shows() att=1400s.

Fig. 2. Test data, which we created based on a mid- and low-latitude magnetic variation around a substorm onset.
The vertical dashed line at t=1200s represents the start time of extraordinary oscillations.

Fig. 3. (a) A time variation of singular values for the test data shown in Fig. 2 calculated with the procedure described in Section 2.2.
Hankel matrices were created with K=80, L=80, M=20, τ=30. (b) Singular values at t=250s. (c) Singular values at t=1400s.

Identification of full-substorm onset from ground-magnetometer data67

As shown in Figure 3b, we see that the first eigenvalue
is extraordinary large. In contrast,() arealmost the same. So it is likely that empirical orthogonal functions() or principal components() represent noise. Also, this indicates that the essential structure of the test data around t=250s
can be represented by the first empirical orthogonal functions or the first principal component.
Next, let us focus on Figure 3c which shows() at t=1400s. At this time, the extraordinary
oscillation has already begun. We see that the magnitudes of singular values decrease from i=1 to i=4. However,() are the almost same. So it is likely that empirical orthogonal functions() or
principal components() represent noise. This indicates that the essential structure of the test dataaround t=1400s can be represented by a linear combination of first to fourth empirical orthogonal functions() or of first to fourth principal components(). From what we have seen, it is clear thatthe distribution of singular values obtained by SVD of the Hankel matrix reflects the complexity of thesubsequence.
2. 3. Bay-score

We introduce a relative anomaly metric of time series at the present time, named "bay-score". It provides
information to determine whether the Pi 2 pulsation that accompanied by the positive bay is present or not. As wediscussed in Section 2.2, the distribution of singular values calculated by SVD of the Hankel matrix reflects thecomplexity of the subsequence. The top panel of Figure 4 shows H-component of ground-magnetometer dataobtained at KAG. The second panel of Figure 4 shows the time variations of the largest singular value calculatedby the procedure described in Section 2.2. Similarly, the third panel and the fourth panel of Figure 4 shows thetime variations of the second-largest singular value and that of the third-largest singular value, respectively. The
vertical dashed lines in red show Pi 2 pulsations accompanied by positive bays selected by visual inspection. We
see that singular values around substorm positive bays decreased. By taking account into the feature, we define
the bay-score Z(t) as‥‥(4)Here, M is the number of singular values to be included for the bay-score. The selection of M affects thesensibility of the SVT.
is the usual Euclidean norm.
is the ith-largest singular value. Note that Z(t) is nondimensional parameter and positive value by definition. The calculation of the bay-score can be viewed also as anonlinear transformation from an original time-series
to a new time-series , i.e.
‥‥(5)
We call this transformation "Singular Value Transformation (SVT)". The algorithm detects Pi 2 pulsations that
accompanied by positive bays, if the bay-score Z(t) be larger than a predetermined threshold value.
2.4. Choice of parameters

As shown in Eq. 5, the SVT algorithm includes four parameters, namely, K, L, M and . By nature of SVT,
these parameters needed to be determined experimentally. In change-point detection methods based on SSA, thechoice of K depends on the kind of structural changes to be detected (Moskvina and Zhigljavsky, 2003). A generalrule is to choose K reasonably large. However, if we allow small gradual changes in the time series then we could
not take K very large. The feature is most likely valid in the SVT. Since the onset of Pi 2 pulsations is gradual, we
should not take K as a large value. In this paper, we set to K=80s, which is the typical period of Pi 2 pulsations.
Remaining parameters, K=80, L=80, M=20, τ=30 were determined empirically. In the following application,these parameters were set to L=K, M=20, τ=30s.

68

Terumasa Tokunaga, Kiyohumi Yumoto, Teiji Uozumi and CPMN Group

Fig. 4. (Top panel) H-component of ground-magnetometer data obtained at KAG station on 10:00-18:00UT 27 January 1997. The
vertical dashed lines in red show the onset of positive bays determined by visual inspection. (Second panel) The largest singularvalues calculated with K=80, L=80, M=20, τ =30 for the ground-magnetometer data that shown in the top panel. (Third panel) The
second-largest singular values. (Fourth panel) The third-largest singular values.

3. Application to Ground-magnetometer Data
3. 1. Data Sets
3. 1. 1. Ground-magnetometer data

Ground magnetometer data obtained from the CPMN (Circum-pan Pacific Magnetometer Network) stations in
the 210° magnetic meridian (MM) chain (Yumoto and CPMN Group, 2001) have been used in the following
applications. CPMN consists of about 50 stations. In this study, the data obtained at KAG were used for the
analysis. The locations of these stations are listed in Table 1. The observations were based on vector
measurements by fluxgate magnetometers with a sampling rate of 1Hz.
Table 1. Locations of geomagnetic observatories used in this paper.

Station
KAG

Geographic Latitude Geographic Longitude
31.48

130.72

Identification of full-substorm onset from ground-magnetometer data

69

3. 1. 2. Polar Ultra Violet Imager

In this study, Polar Satellite Ultra Violet Imager (Polar/UVI) to check the global auroral activities. The Polarsatellite is in a highly elliptical polar orbit with an apogee at about 9RE, and it collects data from a high-altitude
perspective on auroral activities. In this paper, we referenced the specification of Polar/UVI is described in Liouet al. (1999). UVI is a narrow-angle larger-aperture design. In Figure 5a, we present a sequence of nightside UV
auroral images from Polar/UVI. The images were obtained by a combination of Lyman-Birge-Hopfield bands (14001600 A ) on 4 January 1997. We see that the auroral intensity started to enhance exponentially between
15:45:08UT and 15:46:22UT.

Fig. 5. Polar/UVI images at N2 Lyman-Birge-Hopfield bands (1400-1600 A) on 4 January 1997.

3. 2. Case Studies

In two case studies, we evaluate the performance of the SVT. The top panel of Figure 6 shows the keogram ofauroral brightening observed by Polar/UVI in the Southern Hemisphere on 8 January 1997. The luminescenceintensity averaged over magnetic local time of 21-03 h. The vertical axis shows magnetic latitude. The verticaldashed line in red shows full-substorm onsets visually identified by checking the keogram. Here, we define thefull-substorm onset as the auroral breakup that is followed by rapid poleward motion of the brightened arc. The
middle panel of Figure 6 shows H-component of ground-magnetometer data obtained at KAG station on 8
January 1997. The bottom panel of Figure 6 shows the resulting SVT series calculated with K=80, L=80, M=20,
τ=30. The dashed horizontal line in blue shows the threshold value (0.05) for the detection of Pi 2 pulsations
accompanied by positive bays.
We can see that the result shows two high scores that exceed 0.05 at around 14:20UT and at around 14:40UT.
These two high scores most likely correspond to second and third full-substorm onsets shown as vertical dashedlines. However, we see that the first full-substorm onset at around 13:10UT was not detected. This is likely due tothe fact that the amplitude of the positive bay at around 13:10UT was small.
Similarly, the top panel of Figure 7 shows the keogram of auroral brightening observed by Polar/UVI in theSouthern Hemisphere on 27 January 1997. The middle panel of Figure 7 shows H-component of groundmagnetometer data obtained at KAG station on 27 January 1997. The bottom panel of Figure 7 shows theresulting SVT series calculated with K=80, L=80, M=20, τ=30. The presentation format is the same as Figure 6.
We can see that the result shows two high scores that exceed 0.05 at around 10:00UT, at around 15:30UT, ataround 15:15UT and at around 17:10UT. It is likely that four full-substorm onsets were detected successfully by
the proposed algorithm.

70

Terumasa Tokunaga, Kiyohumi Yumoto, Teiji Uozumi and CPMN Group

Fig. 6.(Top) Keogram of auroral brightening observed by Polar/UVI in the Southern Hemisphere on 8 January 1997. The
luminescence intensity averaged over magnetic local time of 21-03LT. (Middle) H-component of ground-magnetometer data
observed at KAG station on 8 January 1997. (Bottom). The resulting SVT series calculated from H-component of KAG data. The
SVT parameters were set to K=80, L=80, M=20, τ =30. The dashed horizontal line in blue shows the threshold value for the detectionof Pi 2 pulsations accompanied by positive bays.

Fig. 7.(Top panel) Keogram of auroral brightening observed by Polar/UVI in the Southern Hemisphere on 27 January 1997. The
luminescence intensity averaged over magnetic local time of 21-03LT. (Middle) H-component of ground-magnetometer data
observed at KAG station on 27 January 1997. (Bottom panel) The resulting SVT series calculated from H-component of KAG data.
The SVT parameters were set to K=80, L=80, M=20, τ =30. The dashed horizontal line in blue shows the threshold value for thedetection of Pi 2 pulsations accompanied by positive bays.

71

Identification of full-substorm onset from ground-magnetometer data
3. 3. Statistical Evaluation

Next, let us evaluate the performance of the full-substorm onset detection algorithm based on SVT in astatistical study. By checking the keogram of auroral brightening observed by Polar/UVI, we identified 69 auroral
breakups for the period from 3 January 1997 through 4 February 1997. We applied the SVT to H-component ofground-magnetometer data obtained at KAG. The investigation was limited in a time period from 10:00-18:00UT,
which KAG was located in/around the midnight sector in the period. The SVT parameters were set to K=80,
L=80, M=20, τ=30. The threshold value for detecting auroral breakups was set to 0.05. The evaluation procedure
is as follows. (1) Detected Events: If the bay-score exceed 0.05 during poleward motion of aurora. (2) False
Positive: If the bay-score exceed 0.05 during there is no poleward motion of aurora. (3) False Negative: If thebay-score does not exceed 0.05 during poleward motion of aurora. As we mentioned in Section 1, the mostprobable number of Pi 2 bursts per substorm is 2 (Hsu and McPherron, 2007). In other words, about half of Pi 2
pulsations is not accompanied by poleward expansion and positive bays. Thus, it is our expectation that thealgorithm possibly detect almost equal numbers of full-substorm onsets and false positives.
A test result of the algorithm is summarized in Table 2. The algorithm detected 51 possible full-substorm
onsets. Forty three out of 51 events were in good agreement with full-substorm onsets. Eight out of 51 eventswere false positives. The number of false positive was lower than expected. Twenty six out of 69 events wereoverlooked. Thus the rate of successful detection is calculated to be about 62%. We consider that our algorithm
gives fairly good results on the nightside (21-03LT).
Table 2. Test result of the full-substorm onset detection algorithm based on SVT for the KAG data in the nighttime(21--03LT).

Date
3 Jan. 1997
4 Jan. 1997
5 Jan. 1997
6 Jan. 1997
7 Jan. 1997
8 Jan. 1997
9 Jan. 1997
11 Jan. 1997
12 Jan. 1997
13 Jan. 199714 Jan. 199715 Jan. 199716 Jan. 199717 Jan. 1997
18 Jan. 199719 Jan. 1997
20 Jan. 1997
21 Jan. 1997
22 Jan. 1997
23 Jan. 1997
24 Jan. 1997
25 Jan. 1997
27 Jan. 1997
28 Jan. 1997
29 Jan. 1997
30 Jan. 1997
31 Jan. 1997
1 Feb. 1997
2 Feb. 1997
3 Feb. 1997
4 Feb. 1997
Total

Event Number
1
1
2
1
4
3
0
4
3
5
2
1
0
3
0
3
1
5
1
0
4
1
4
4
1
4
1
1
4
1
4
69

Successful
Detection
1
1
2
0
4
2
0
3
3
3
2
1
0
1
0
1
0
3
1
0
1
0
4
4
1
2
0
0
1
1
1
43

False Negative False Positive
0
0
0
1
0
1
0
1
0
2
0
0
0
2
0
2
1
2
0
0
3
1
0
0
0
2
1
1
3
0
3
26

0
0
0
0
3
0
0
1
0
0
0
0
0
0
0
0
0
1
0
0
0
0
0
2
0
0
0
0
0
0
1
8

72

Terumasa Tokunaga, Kiyohumi Yumoto, Teiji Uozumi and CPMN Group

4. Conclusions
In order to identify the onset of full-substorms from ground-magnetometer data, we developed a newalgorithm to detect Pi 2 pulsations that accompanied by positive bays. There are some works about automatic
detection of Pi 2 pulsations. However, the previous studies are limited in detecting only wave packets. Thus, wedefined the “bay-score” which provides information to determine whether positive bay is present or not. The
transformation from an original time-series to a new time series of the bay-score named “Singular Value
Transformation (SVT)”. We have applied the SVT to ground-magnetometer data and showed that high scores ofresulting SVT series are in good agreement with that full-substorm onsets. Further, we evaluated the practical
performance of the SVT in a statistical study. By checking the keogram of auroral brightening observed by Polar/
UVI, 69 full-substorm onsets were identified for the period from 3 January 1997 through 4 February 1997. Forty
three events of them were detected successfully from ground-magnetometer data by proposed algorithm. On theother hand, 26 events were overlooked. This is mainly due to a local time dependence of positive bays
(McPherron, 1973b). As mentioned in Section 1, it is thought that the substorm positive bay is caused by thesubstorm current wedge. Hence, the positive bay intensity strongly depends the positional relationship between
the auroral breakup and the station. If KAG station was located outside the current wedge, the detection of
positive bay likely failed regardless of the SVT parameter setting. By using the network data that covers wide
range of longitude, the detection ratio will be improved. Whereas, the number of false positive was lower than
expected. Hence, we conclude that the proposed algorithm is a strong method to detect positive bays fromground-magnetometer data. In other words, it will enable us to identify full-substorm onsets from groundmagnetometer data.

5. Acknowledgments
We would like to thank Prof. J. Dowell of the University of Iowa for providing the Polar/PWI data, Dr. C.
Meng and Dr. K. Liou of Johns Hopkins University for providing Polar/UVI data. We thank all the members of
the CPMN project (PI; K. YUMOTO) for their ceaseless support. The CPMN project is financially supported by
the Ministry of Education, Science, and Culture of Japan (and Japan Society for the Promotion of Science (JSPS))
as the Grants-in-Aid for Overseas Scientific Survey (05041060, 0841105, 10041122, 12373003). The seniorauthor (T. Tokunaga) was supported by the JSPS under Grant-in-Aid for Scientific Research 2005443. We would
like to thank Dr. H. Kawano for his great assistance in evaluating and improving this paper as a reviewer.

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Memoirs of the Faculty of Sciences, Kyushu University
Series D, Earth and Planetary Sciences
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Memoirs of the Faculty of Science, Kyushu Imperial University. Series D, Geology.
Vol. 1 No. 1 (July, 1940), No. 2 (Mar., 1941), No. 3 (July, 1942).
Vol. 2 No. 1 (Feb., 1943), No. 2 (Aug.,1944).
Vol. 3 No. 1 (Apr., 1947).
Memoirs of the Faculty of Science, Kyushu University. Series D, Geology.
Vol. 3 No. 2 (Nov., 1949), No. 3 (May.,1952), No. 4 (Dec., 1952).
Vol. 4 No. 1 (June, 1954), No. 2 (July, 1954).
Vol. 5 No. 1 (Aug., 1954), No. 2 (Oct., 1954), No. 3 (Dec., 1955), No. 4 (Jan., 1957).
Vol. 6 No. 1 (Feb., 1957), No. 2 (May.,1957), No. 3 (May.,1958).
Vol. 7 No. 1 (Mar., 1958).
Vol. 8 No. 1 (Mar., 1958), No. 2 (May.,1958), No. 3 (Mar.,1959), No. 4 (May.,1959).
Vol. 9 No. 1 (Dec., 1959), No. 2 (Nov., 1959), No. 3 (Mar.,1960).
Special Issue No. 1 (Nov., 1959), No. 2 (Jan., 1960).
Vol. 10 No. 1 (Dec., 1960), No. 2 (Mar.,1961).
Vol. 11 No. 1 (Mar., 1961), No. 2 (Nov., 1961), No. 3 (Dec., 1961).
Vol. 12 No. 1 (Mar., 1962), No. 2 (June, 1962), No. 3 (June, 1962).
Vol. 13 No. 1 (Feb., 1963).
Vol. 14 No. 1 (Jan., 1963), No. 2 (Mar.,1963), No. 3 (Jan., 1964).
Vol. 15 No. 1 (June, 1964), No. 2 (Mar.,1965).
Vol. 16 No. 1 (Mar., 1965), No. 2 (May.,1965), No. 3 (Nov., 1965).
Vol. 17 No. 1 (Nov., 1965), No. 2 (Dec., 1965), No. 3 (Sept.,1966).
Vol. 18 No. 1 (Feb., 1967), No. 2 (Dec., 1967).
Vol. 19 No. 1 (Jan., 1969), No. 2 (Jan., 1969), No. 3 (Nov., 1969).
Vol. 20 No. 1 (Jan., 1970), No. 2 (Nov., 1970).
Vol. 21 No. 1 (Oct., 1971), No. 2 (Dec., 1972).
Vol. 22 No. 1 (Nov., 1973), No. 2 (Feb., 1975).
Vol. 23 No. 1 (Mar., 1975), No. 2 (Nov., 1975), No. 3 (Feb., 1977).
Vol. 24 No. 1 (Nov., 1978), No. 2 (Nov., 1979), No. 3 (Jan., 1981), No. 4 (Dec.,1981).
Vol. 25 No. 1 (Nov., 1983), No. 2 (Nov., 1984), No. 3 (Feb., 1985).
Vol. 26 No. 1 (Jan., 1986), No. 2 (Jan., 1988), No. 3 (Dec., 1989).
Memoirs of the Faculty of Science, Kyushu University. Series D, Earth and Planetary Sciences.
Vol. 27 No. 1 (Jan., 1991), No. 2 (Feb., 1992).
Vol. 28 No. 1 (Dec., 1993), No. 2 (Dec., 1994).
Vol. 29 No. 1 (Dec., 1995), No. 2 (Dec., 1996).
Vol. 30 No. 1 (Jan., 1998), No. 2 (Dec., 1998), No. 3 (Dec., 1999).
Vol. 31 No. 1 (Dec., 2000), No. 2 (Feb., 2002), No. 3 (Feb., 2005), No. 4 (Feb., 2007).
Vol. 32 No. 1 (Feb., 2008), No. 2 (Mar.,2009), No. 3 (Mar.,2011).
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Kyushu University
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