R/V KAIREI Cruise Report

KR13-14

R/V KAIREI + ROV KAIKO7000II Deep Sea Research Structure and dynamics of subduction channels in intraoceanic

subduction zones (Ohmachi Seamount, Izu-Bonin arc)

August 30, 2013 – September 12, 2013 Yokosuka – Naha

Japan Agency for Marine-Earth Science and Technology (JAMSTEC)

Contents 1. Cruise Information 2. Backgrounds and objectives

3. Operation and preliminary results 3.1 Side scan sonar imaging 3.2 Dive report (7K#609 and7K #610) 3.3 Dredge 3.4 MBES

4. Summary 5. Acknowledgements 6. Notice on using

1. Cruise information

(1) Name of vessel & Cruise ID R/V KAIREI KR13-14

(2) Title of the cruise 2013 Deep Sea Research: R/V KAIREI / KAIKO 7000II:

Ohmachi Seamount, Izu-Ogasawara (Bonin) arc.

(3) Proposal number and scientific title S13-36 Structure and dynamics of subduction channels in intraoceanic arcs.

(4) Period of the cruise From August 30 to September 12, 2013

(5) Port calls Departure: Yokosuka (August 30, 2013)

Arrival: Naha (September 12, 2013)

(6) Research area Ohmachi Seamount (1000 - 4000 m bsl)

28º30.0’ – 29º30.0’N, 140°20.0’E - 141°00.0’E

(7) Researchers [R/V KAIREI Crew]

Captain YOSHIYUKI NAKAMURA Chief Officer HIROYUKI KATO 2nd Officer TOSHIYO OHARA 3rd Officer SATORU YOSHIDA Chief Engineer KIYONORI KAJINISHI 1st Engineer KENZO KATO Jr. 1st Engineer KOJI FUNAE 2nd Engineer RYOZO MIKAMI 3rd Engineer NAOOMI UEMURA Chief Electronics Operator HIROYASU SAITAKE 2nd Electronics Operator YOSHIKAZU KURAMOTO 3rd Electronics Operator TAKAYUKI MABARA Boat Swain YASUYOSHI KYUKI Able Seaman SHUICHI YAMAMOTO Able Seaman HATSUO ODA Able Seaman YUKITO ISHII Able Seaman SAIKAN HIRAI Sailor SHUN MIURA

Sailor FUMIAKI OMACHI Sailor TOSHIYA SAGA No.1 Oiler JUNJI MORI Oiler MASANORI UEDA Assistant Oiler DAIKI SATO Assistant Oiler RYO MATSUUCHI Assistant Oiler SYOTA SHIMOHATA Assistant Oiler ATSUMU HARA Chief Steward YUKIO TACHIKI Steward YOSHINOBU HASATANI Steward TATSUNARI ONOUE Steward SEIJI HONDA Steward RYU KUBOTA

[KAIKO 7000II operating team]

Operation Manager ATSUMORI MIURA 1st ROV Operator HOMARE WAKAMATSU 2nd ROV Operator KIYOSHI TAKISHITA 2nd ROV Operator TETSUYA ISHITSUKA 2nd ROV Operator SHIGERU KIKUYA 2nd ROV Operator SEIJI SHIGETAKE 2nd ROV Operator YUDAI SAKAKIBARA 3rd ROV Operator TAKUMA GOTO 3rd ROV Operator YOICHI YASUE

[Onboard scientific team]

Chief Scientist HAYATO UEDA* Hirosaki University Co-chief Scientist TADASHI USUKI Academia Sinica, Taiwan Scientist MASAKO USUKI National Taiwan University Scientist YUKA NISHIKAWA National Taiwan University Scientist TAKECHIKA KASAI Hirosaki University Scientist ASAMI SAITO Hirosaki University Scientist NATSUMI IIZUKA Hirosaki University Marine Technician HISAORI IWAMOT Nippon Marine Enterprise, Ltd. Marine Technician YUKI MIYAJIMA Marine Works Japan, Ltd. Marine Technician YHEI TAKETOMO Marine Works Japan, Ltd. Marine Technician TETSUHARU IINO Marine Works Japan, Ltd. Marine Technician MASARU YASUNAGA Marine Works Japan, Ltd. * Representative of the scientific theme.

(8) List of scientific operations * Imaging sea-borrom features by KAIKO Launcher side-scan sonar (1 dive)

* Observation and sampling of rock exposures by the KAIKO vehicle (2 dives)

* Dredging rock samples (7 times towing)

* Bathymetry mapping using Multi-beam echo sounder (MBES).

(9) Extra apparatus * Top Clinometer (payloaded by KAIKO vehicle)

* Dredgers (cylinder and box types).

Fig.1 Dimension of the top clinometer.

Fig.2 Apparatus of dredge systems (left: cylinder type; right: box type).

(10) Cruise log Table 1. KR13-14 cruise log

Date Local Time Event Position/Weather/ Sea condition

30-Aug-13 08:00 Scientists onboard. 8/3012:00 (UTC+9h) 34-46.6N,139-41.0E fine but cloudy SW-7 (near gale) 4 (sea moderate) 1 (Low swell sea) Visibly: 5'

09:00 Departure from Sumitomo Heavy Indus., Yokosuka. 10:00-10:40 Lecture for shipboard life and safety. 10:45-11:05 KAIKO briefing. 11:08-11:15 Scientists’ meeting.

31-Aug-13 15:00 Arrived at the research area. 8/31 12:00 (UTC+9h) 29-58.7N,140-42.2E fine but cloudy WSW-3 (gentle breeze) 2 (sea smooth) 2 (Low swell long) Visibly: 8'

15:20 Released XBT. 16:14 Deployed transponder B. 16:36 Deployed transponder A. 16:58 Deployed transponder C. 17:48-18:55 LBL transponder calibration.

01-Sep-13 07:44 Launching KAIKO (KAIKO#608Dive). 9/1 12:00 (UTC+9h) 29-07.2N,140-42.1E fine but cloudy East-1 (light air) 1 (calm) 2 (Low swell long) Visibly: 8'

09:50 KAIKO started SSS survey. 14:00 KAIKO finished SSS survey. 15:55 KAIKO came up to the surface. 18:30-18:50 Scientists’ meeting. 18:46- Began MBES survey.

02-Sep-13 -03:20 Stopped MBES survey. 9/2 12:00 (UTC+9h) 29-07.3N,140-42.3E fine but cloudy East-5 (fresh breeze) 3 (sea slight) 1 (Low swell sea) Visibly: 8'

04:46-04:56 Dive point MBES survey. 08:49 Launching KAIKO (KAIKO#609Dive). 11:10 KAIKO landing (3,372m). 14:37 KAIKO left the bottom (3,345m). 16:46 KAIKO came up to the surface. 19:17- Began MBES survey. 20:00-20:10 Scientists’ meeting.

03-Sep-13 -00:18 Stopped MBES survey. 9/3 12:00 (UTC+9h) 29-07.3N,140-42.3E fine but cloudy ESE-5 (fresh breeze) 3 (sea slight) 1 (Low swell sea) Visibly: 8'

08:39 Launching KAIKO (KAIKO#610Dive). 11:05 KAIKO landing (3,361m). 14:04 KAIKO left the bottom (3,335m). 16:11 KAIKO came up to the surface. 18:45- Began MBES survey.

04-Sep-13 -04:00 Stopped MBES survey. 9/4 12:00 (UTC+9h) 29-06.5N,140-47.5E fine but cloudy SE-5 (fresh breeze) 3 (sea slight) 1 (Low swell sea) Visibly: 8'

08:00-08:42 Recovered transponder B. 08:54-10:43 Recovered transponder A. 10:52-11:28 Recovered transponder C. 12:47-20:34 MBES survey. Transit to off Chichi jima island for rigging.

05-Sep-13 08:00-09:30 Rigging dredge equipments. 9/5 12:00 (UTC+9h) 27-39.0N,141-43.2E fine but cloudy ESE-3 (gentle breeze) 2 (sea smooth) 1 (Low swell sea) Visibly: 8'

18:00-18:20 Scientists’ meeting. 17:14- Began MBES survey.

06-Sep-13 -01:00 Stopped MBES survey. 9/6 12:00 (UTC+9h) 29-07.4N,140-42.4E fine but cloudy East-1 (light air) 1 (calm) 1 (Low swell sea) Visibly: 8'

08:10-11:46 Dredge operation DR101. 13:04-16:37 Dredge operation DR102. 18:10-18:45 Scientists’ meeting. 18:52- Began MBES survey.

Date Local Time Event Position/Weather/ Sea condition

07-Sep-13 -01:32 Stopped MBES survey. 9/7 12:00 (UTC+9h) 29-07.4N,140-42.4E fine but cloudy ESE-3 (gentle breeze) 2 (sea smooth) 1 (Low swell sea) Visibly: 8'

07:54-12:23 Dredge operation DR103. 13:32-17:17 Dredge operation DR104. 19:12- Began MBES survey.

08-Sep-13 01:08 Finished MBES survey. 9/8 12:00 (UTC+9h) 29-07.5N,140-42.3E cloudy SE-3 (gentle breeze) 2 (sea smooth) 1 (Low swell sea) Visibly: 8'

07:48-11:28 Dredge operation DR105. 13:16-16:49 Dredge operation DR106. 18:33-18:54 Eight-figure turn.

09-Sep-13 07:57-12:37 Dredge operation DR107. 9/9 12:00 (UTC+9h) 29-07.4N,140-42.3E fine but cloudy ENE-1 (light air) 1 (calm) 1 (Low swell sea) Visibly: 8'

Transit to OKINAWA.

10-Sep-13 Transit to OKINAWA. 9/10 12:00 (UTC+9h) 27-19.8N,135-08.8E fine but cloudy West-2 (light breeze) 1 (calm) 1 (Low swell sea) Visibly: 8'

11-Sep-13 Transit to OKINAWA. 9/11 12:00 (UTC+9h) 26-01.5N,129-19.2E fine but cloudy East-3 (gentle breeze) 2 (Sea smooth) 1 (Low swell sea) Visibly: 8'

12-Sep-13 09:00 Arrived at NAHA-shinko port, OKINAWA 8/7 12:00 (UTC+9h) OKINAWA

Fig.3 KR13-14 ship track.

2. Backgrounds and objectives

Metamorphic rocks associated with serpentinites have been found in the Ohmachi Seamount as

the only locality of the eclogite facies rocks in the world ocean bottoms. Sea-floor exposure of these

rocks provides composition, structure, and dynamics along deep subduction interface, where

material transport is channelized (“subduction channel”), with minimal later modification by

mountain building processes.

Previously collected metamorphic rocks (five samples in 2001 and one in 2004) are drifted

pebbles on debris apron at the foot of serpentinite exposures (YK01-04 6K#609 R2, R4, R5, & R6),

a presumably float stone on the rock exposure (6K#609 R12), or a dredged stone (KT04-28 D6-1).

Two submersible dives (6K#1064 and 6K#1239) tried to find the outcrop of metamorphic rocks,

however, nothing but serpentinites were found. Therefore, the mode of occurrence of metamorphic

rocks, e.g. precise distribution of the rock bodies and contact relationships with serpentinites, have

been still left unknown.

One of the main purpose of this cruise is addressed to find and observe metamorphic rocks on

outcrop using the ROV “KAIKO 7000II”. The target locality is 6K#609 Loc.4, where the collected

sample (R12) were potentially derived from the same outcrop. Side-scan sonar equipped on the

KAIKO launcher is used to find rock exposures, each of whose location is precisely determined by

LBL. Two dives are taken to find the target, observe field occurrences of metamorphic rocks, collect

samples, and measure orientation of metamorphic foliation.

Another purpose is to increase volume and variation of rock types of metamorphic rocks. The

volume of the previously collected metamorphic rock samples are limited (0.03-1 kg for each sample

is available) and insufficient for crushing and powdering at detailed geochemical and

geochronological examinations. In addition, these samples are classified to three petrographic types,

all of which underwent severe retrograde modification of rock textures and mineral chemistry.

Increasing variation of rock types, as well as obtaining ones preserving early textures and minerals

are necessary for precise analysis of metamorphic conditions and histories. For these purposes,

dredges are performed around localities of metamorphic rocks.

3. Operation and preliminary results

3.1 Side scan sonar imaging In the first dive of this cruise (7K#608), the “KAIKO” launcher collected side scan sonar (SSS)

images covering the survey area (Fig. 2). The launcher was towed along downslope (line 1) and

upslope (line 3) transects, as well as line 2 connecting both the routes, all at a speed of 0.3 knot.

Although only uncorrected SSS raster images were available onboard, they well contrasted relatively

gentle “middle slope terraces”, steep and rocky “lower slopes”, a gravelly debris apron, and a

mud-filled flat basin floor. In addition to these general topography, many more delicate features such

as abreast gullies and channels, their side walls, and intervening ridges were imaged. We compared

these features with MBES bathymetric maps and previous 6K dive results, and finally selected the

tip of a ridge with a pronounced reflection as the most probable identification for 6K# Loc.4. We set

this point as the target for exploration of the 7K#609 dive.

Fig.4 Position of transponders and the trail of side-scan sonar imaging during 7K#608 dive.

3.2 Dive report (7K#609 and7K #610) The purpose of these dives was to revisit the outcrop where a high pressure metamorphic rock

(R12) was previously collected by the dive 6K#609 of (YK01-04) and to collect large amount of

metamorphic rocks there. Two KAIKO7000II (7K#609 and7K #610) dives were conducted at the

same outcrop.

The VCL (dive 7K#609) firstly visited a large serpentinite (antigorite schist) outcrop (X:-904,

Y:916, depth: 3374m) imaged by SSS data. However, we found out that it was not the target. The

target outcrop was found in ~80 m north (X:-823, Y:920, depth: 3349m) from the first outcrop. We

found that the target position was very close to the location estimated from the previous

SHINKAI6500 dive (6K#609). We put two markers on the outcrop for the dive 7K#610 of the next

day. Marker 1 and marker 2 were put on near the bottom of the outcrop and the upper part of it on a

schistose plane of the serpentinite, respectively. We collected several rocks just on up and right sides

of “R12” collection site. We also collected two floats on mud slope in few meter lower part of it. We

collected total 11 samples in this dive.

In the dive 7K#610, we tried to go down just on the same outcrop. However, the VCL arrival

position was 30m southwest of it (X: -867, Y: 916, depth: 3354m). In this dive, we continued

sampling near “R12” collection site and ~2m upper part of the outcrop. We collected total 9 samples

Fig.5 7K#609 dive track.

including one huge sample (R104: ~49 kg). We measured a foliation plane of this outcrop using the

top clinometer.

3.3 Dredge We performed seven dredges, whose locations are listed in Table X, and the apparatus is shown

in Fig. X, DR101. The operation followed the procedure as below:

(a) The main wire length is held for three minutes at the depth where the dredger lies ca. 50 m

above the estimated depth of the landing point.

(b) After the position of the transponder is stabilized, the main wire is paid out. The vessel

begins towing the dredger at a speed of ~0.5 knots.

(c) The wire tension decreases at the time when the dredger landed on bottom. More 30 m

(except for DR102 with 100 m) wires are released and then held.

(d) When the transponder arrives around the target point, the vessel decreases its speed and then

keeps its position as it stopped. The cable begins to be winched up at a speed of 10 m/min.

(e) When the wire tension gradually increases and reaches to the break value of fuse wire, the

cable stops to be winched up and is paid out at a speed of 30 m/min. After the wire tension

decreases, the cable is winched up at a speed of 10 m/min, If the wire tension increases again,

the same procedure is followed two to three times. In the case high wire tension cannot be

Fig.6 7K#610 dive track.

released with the above mentioned procedure, the vessel is backed to the landing point of the

dredger, winching up the cable.

(f) After the tension meter suggested that the dredger has left the bottom, the main wire is

winched up faster at 20 and then 30 m/min. Off-bottom of the dredger can also be

confirmed when the total wire length (main plus lead wires) becomes evidently shorter than

the sea-floor depth,

At the first two dredges (DR101 and 102), the on-bottom target was set around a fault scarp on

the mud basin floor, where a float stone of epidote amphibolite (6K#609R002) was collected, and

the end point was set around the outcrop where the garnet-zoisite amphibolite (6K#609R012) was

collected. In both operations, the dredger began to be towed along the planned lines, however, left

the bottom halfway without any significant hit before it reached to the end points. The hauls

consisted of semi-consolidated sediments as well as soft mud at DR101, and only of soft mud at

DR102.

The on-bottom points for subsequent DR103-107 were placed on the approximate edges of the

steep debris apron much closer to the outcrop, reflecting the results of DR101 and 102. In these later

operations, the tension meter indicated significant and repetitive hits (and locking in cases) as the

transponder passed through the end point, suggesting that the dredger arrived at rock exposures.

Serpentinites and subordinate amounts of amphibolites were collected by these dredges.

Date (JST)

Dredge number

On bottom Off bottom Tension max. (kN) Lat. Lon. Depth Lat. Lon. Depth

2013/9/6 DR101 29°07.2104’N 140°41.9652’E 3,486 29°07.3560’N 140°42.2589’E 3,292 25 2013/9/6 DR102 29°07.1905’N 140°41.8791’E 3,486 29°07.4579’N 140°42.3266’E 3,120 22 2013/9/7 DR103 29°07.3563’N 140°42.1802’E 3,339 29°07.4199’N 140°42.2919’E 3,270 48 2013/9/7 DR104 29°07.3660’N 140°42.1513’E 3,256 29°07.4592’N 140°42.3567’E 3,077 48 2013/9/8 DR105 29°07.3364’N 140°42.1539’E 3,338 29°07.4703’N 140°42.3905’E 3,038 41 2013/9/8 DR106 29°07.3636’N 140°42.1592’E 3,365 29°07.4862’N 140°42.3814’E 2,941 36 2013/9/9 DR107 29°07.3247’N 140°42.1853’E 3,338 29°07.4045’N 140°42.2879’E 3,261 48

3.4 MBES During the intervals of dives and dredges at night, bathymetry around the Ohmachi Seamount

were mapped by KAIREI SeaBeam. The blank areas which had not yet been mapped in the survey

area were almost fully filled with the acquired depth data. Together with the previous data,

bathymetric features on and around the seamount were imaged enough for topographic analyses and

for designing future surveys.

4. Summary Results of this cruise is briefly summarized as:

(1) KAIKO 7000II vehicle successfully revisited to the same outcrop as 6K#609 Loc. 4 (the

locality of an amphibolitized eclogite collected in 2001), whose location was aimed greatly

relying on the side-scan sonar images newly acquired by the KAIKO launcher with LBL

ecolocation. Two markers were left on the outcrop for future exploration.

(2) Detailed observation and sampling concluded that this outcrop probably consists wholly of

serpentinite. Two float stones of amphibolite collected from the outcrop surface close to a

ridge crest suggested that the amphibolite exposure lies a little more upslope, where our

exploration did not reached.

(3) Repetitive dredges around 6K#609 Loc. 4 collected 44 new amphibolite samples of varying

lithotypes as well as numerous antigorite schists. The largest block weighted ~9 kg

voluminous enough both for various kinds of laboratory analysis. Precise positioning of the

transponder attached to the main wire greatly helps to infer distribution of amphibolite

bodies by lithotypes.

(4) Detailed bathymetric map without blanks was completed on and around the Ohmachi

Seamount.

5. Acknowledgements

The scientific team thanks captain and crew of the R/V KAIREI, the KAIKO operation team, JAMSTEC Navigation Group, and scientific supports by Nippon Marine Enterprise Ltd. and Marine Works Japan Ltd. This study is supported by JSPS KAKENHI Grant no. 22540464.

6. Notice on using this cruise report This cruise report is a preliminary documentation as of the end of the cruise. It may not

be corrected even if changes on content (i.e. taxonomic classifications) are found after

publication. It may also be changed without notice. Data on the cruise report may be raw

or not processed. Please ask the Chief Scientist for the latest information before using.