Nankai Trough

NT07-E01 CruiseHYPER-DOLPHIN/NATSUSHIMA

Onboard ReportAugust 7, 2007, Yokosuka – August 11, 2007, Kagoshima

Captain: Masayoshi Ishiwata (NME)Operation Manager: Kazuhiro Chiba (NME)

Chief Scientist: Sumito Morita (AIST)

SHIPBOARD SCIENTISTS:Sumito Morita (AIST)Shusaku Goto (AIST)

Satoshi Tonai (Univ. Tokyo)

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Contents

. Introduction

. Shipboard Member List

. Shipboard Log

. Long-Term temperature monitoring system (LTMS)

. Stand-Alone Heat Flow meter (SAHF)

. Dive Record, Track and Log

. Results: Long-term sub-bottom temperature monitoring using LTMS

. Results: Long-term sub-bottom temperature monitoring using LTMS

. Summary

Appendix (digital data on DVD)

1. Introduction

Sumito Morita (GSJ, AIST)

This study has been adapted by a public subscription and was once planned as the research cruise YK07-09 for Shinkai 6500 and Deep tow dives. However, the cruise was cancelled due to a trouble in the Shinkai 6500. As a bailout, this cruise NT07-E01 was executed using the R/V Natsushima and the ROV Hyper Dolphin, aiming only at retrieval of the deep sea equipments that were installed last year.

Purposes: Fluid in plate subduction zone is known to have a big influence on rock mechanics, so that it is very

important to clarify distribution, migration and drainage systems of fluid, for better understanding of development of geologic structure, such as, deformation of a plate boundary fault. Secular change in fluid composition and its flux would also indicate the stress condition in the accretionary prism. The aim of this study is to retrieve long term monitoring systems, the CAT-Meters (Benthic aqueous flux meters) and the LTMS (Long Term Heat Flow Monitoring System) set up on the seafloor on the cruise YK06-03. The data from those recovered equipments have collected about a year records and are available to clarify relations between the variation of the water flux and tidal change, the seismic activity including very-low-frequency earthquakes, etc.

Original research was moreover planned to install CAT-Meters for 2 year fluid monitoring, which was to collect data for combining with those from long term monitoring on IODP Nankai Trough seismogenic zone experiment (NanTroSEIZE) to be operated from this September. Those data would be applied to understand long term variations of fluid migration by water fluxes from both on and below the seafloor. However, this cruise was carried out basically only for retrieval of the above-mentioned deep sea equipments so that the newly planned installation of the equipments was cancelled and observation and subbottom material samplings were kept to the minimum.

Background: In the Nankai Trough, there have been mega earthquakes of magnitude 8 class, repeatedly with

150-250 years interval. Our research group promotes the NanTroSEIZE, the IODP drilling project, which aims to understand the generation process of the mega earthquake that influenced even the outer arc high as rupture zone in the Tonankai Earthquake in 1944. The stage 1 of the drilling project is to start in September, 2007.

Our group has performed submersible dives of the SHINKAI 6500 by the cruises YK01-04, YK02-02 and YK03-03 as site surveys in this survey area, where subbottom observations, push corings, rock samplings, long term temperature monitoring, natural gamma ray analysis were carried out, and we have found that there were, for example, geochemical anomalies of cold seepage, very high thermal gradient and high radionuclide anomalies of uranium series along the splay fault that is a mega-thrust branched from the seismogenic zone.

On the cruise YK06-03, the long term monitoring systems were deployed at the sites Aa and Ca in the Kumano area. The site Aa is located at the top slope of the accretionary prism that is also the southern flank of the

outer arc high. It corresponds to the zone the splay fault reaches to the subsurface. In this zone, a number of bacterial mats have been observed so far by the submersible dives. We set up four CAT-Meters at the site Aa. The site Ca is a primitive mud volcano in the Kumano Basin, which is about 40 meter high and has some cold seep sites at the foot of itself. We deployed a CAT-Meter and a LTMS at the point where huge bacterial mat and Calyptogena colony were found.

Figure 1. Proposed dive sites of the original plans. This cruise was done at the sites of Aa and Ca.

2. Shipboard Member List

Onboard Scientists

Sumito Morita National Institute of Advanced Industrial Science and Technology Shusaku Goto National Institute of Advanced Industrial Science and Technology Satoshi Tonai Ocean Research Institute, University of Tokyo Satoshi Okada Nippon Marine Enterprises,Ltd.

ROV Hyper-Dolphin Operation Team

Operation Manager Kazuhiro CHIBA 1st Submersible Staff Mitsuhiro UEKI 1st Submersible Staff Yoshio OHNO 2nd Submersible Staff Shigeru KIKUYA 2nd Submersible Staff Homare WAKAMATSU 2ndSubmersible Staff Keita MATSUMOTO 2nd Submersible Staff Tetsuya ISHIZUKA 3rd Submersible Staff Teppei KIDO 3rd Submersible Staff Yudai SAKAKIBARA

R/V NATSUSHIMA Crews

Captain Masayoshi ISHIWATA Chief Officer Akihisa TSUJI 1st Officer Koji SAMESHIMA 2nd Officer Yoshiyuki MIZUI 3rd Officer Masaki HAYASHI Chief Engineer Minoru TSUKADA 1st Engineer Kouji FUNAE 2nd Engineer Yoshinobu HIRATSUKA 3rd Engineer Humihiko NATSUI Chief Radio Operator Hiroyasu SAITAKE 2nd Radio Operator Hidehiro ITOH Boat Swain Mikio ISHIMORI Able Seamen Kozo YATOGO Able Seamen Kuniharu KADOGUCHI

Able Seamen Kazushiro OHSAKO Sailer Naoki IWASAKI Sailer Yoshiaki MATSUO Sailer Tomohiro KIMURA No.1 Oiler Kiyoshi YAHATA Oiler Kozo MIURA Oiler Kazuo ABE Oiler Masanori SATOH Oiler Keiya TANIGUCHI Chief Steward Takeshi MIYAUCHI Steward Sueto SASAKI Steward Toshiharu KISHITA Steward Futoshi HATAKEYAMA

3. Shipboard Log

Shipboard Log & Ship Track(NT07-E01 07/08/07 - 07/08/12) Position/Weather/Wind/ Sea condition (Noon)Date Time Description Remark

07,Aug,07 9:00 embarkation science group 8/7 12:00

11:30 departure from JAMSTEC 35-17.0N, 139-45.0E

12:30～13:00 on board seminar for safety NATSUSHIMA life fine

14:00～15:00 on board education & training for emergency operation SSW-4(Moderate breeze)

15:00～15:30 on board seminar for HPD operation Sea smooth

08,Aug,07 6:30 ariived at research area 8/8 12:00

6:48 released XBT 33-35.9N, 136-33.6E

8:10 launched HPD fine

8:27 started HPD#736 dive SE-3(Gentle breeze)

9:36 arrived at bottom D=2066m Sea smooth

15:38 leave the bottom D=2066m

16:43 surfaced HPD

16:59 recovered HPD

17:10 commenced proceeding to reseach area

19:30 ariived at research area

19:42 released XBT

09,Aug,07 6:51 launched HPD 8/9 12:00

7:06 started HPD#737 dive 33-07.2N, 136-29.0E

8:54 arrived at bottom D=2555m fine

10:39 leave the bottom D=2543m S-4(Moderate breeze)

11:54 surfaced HPD Sea slight

12:13 recovered HPD

13:27 launched HPD

13:42 started HPD#738 dive

15:17 arrived at bottom D=2569m

15:54 leave the bottom D=2549m

17:06 surfaced HPD

17:20 recovered HPD

17:30 left the research area for KAGOSHIMA

10,Aug,07 8/10 12:00

33-04.3N, 133-42.9E

fine

NNW-2(Light breeze)

Sea smooth

11,Aug,07 15:30 arrived at KAGOSHIMA KO 8/11 12:00

31-01.0N, 130-36.4E

fine

SSE-6(Strong breeze)

Sea moderate

12,Aug,07 9:00 left the ship and concluded NT07-13 NT07-E01 scientists

4. Long-term temperature monitoring system (LTMS)

Shusaku Goto (GSJ, AIST)

A long-term temperature monitoring system (LTMS, Photos 1 and 2) is designed to monitor bottom-water and sub-bottom temperatures for at least two years. This system is composed of a stainless frame, a titanium pressure case containing a data-logger and battery, and two probes (Probe-1 and Probe-2). The probes, 760mm in length and 13 mm in diameter, contain six thermistors at an interval of 10 cm (Photo 1). The accuracy and resolution of the thermistor are 0.01 K and 0.001 K, respectively. A yellow vinyl band indicates a position of each thermistor (Photo 1). To distinguish between Probe-1 and Probe-2, the handling cylinders are labeled with color vinyl bands (yellow for Probe-1 and red for Probe-2). Pressure sensor is installed at a lid of the pressure case. In order to monitor independently bottom-water temperature, a small temperature recorder is attached to the frame.

On May 4, 2006, LTMS was deployed in biological community area on the northern root of Kumano Knoll No.8 during Shinkai 6500‘s Dive#947, one of research dives during YK06-03 cruise. Probe-2 was inserted into a small bacterial mat. On the other hand, Probe-1 was penetrated into sediment without bacterial mat for reference. On August 8, 2007, LTMS was successfully recovered during Hyper-Dolphin Dive#736 in NT07-E01 cruise. Photo 2 shows LTMS before recovery.

Description Dimension and weight of whole LTMS Dimension of frame: 1200 mm × 430 mm × 510 mm Material of frame:Alloy of stainless steel Weight: 39.6 kg in air (including small temperature sensor and mini-transponder)

22.0 kg in seawater (including small temperature sensor and mini-transponder) External Interface: RS232C (9600BAUD, 8 BIT, Non-Parity, 2 STOP BIT)

Data-logger Model: DHT-60 Length: 1004 mm Diameter: 102 mm Material:Alloy of titanium Depth range: 6000 m Sampling interval: 10 minutes

Pressure meter Depth Rating: 0-6000 m

Temperature probe

1. Probe-1 (handling cylinder is labeled with yellow vinyl band) Material:Alloy of titanium

Diameter of probe: 13 mmDiameter of handling cylinder: 42 mmLength: 760 mmNumber of thermistor: 6Intervals of thermistor: 10 cm (yellow vinyl bands indicate their positions)Accuracy: 0.01 KResolution: 0.001 KCable length: 1.8 m (yellow vinyl band are located at 1 m interval)

2. Probe-2 (handling cylinder is labeled with red vinyl band) Material:Alloy of titanium Diameter of probe: 13 mm Diameter of holding cylinder: 42 mm Length: 760 mm Number of thermistor: 6 Intervals of thermistor: 10 cm (red vinyl bands indicate their positions) Accuracy: 0.01 K Resolution: 0.001 K Cable length: 2.8 m (yellow vinyl bands are located at interval of 1 m)

Notices:1) LTMS turned on 12:10:00 March 15, 2006.2) Temperature measurement stops by hitting “Enter” key until the data-logger responds as “BADCOMMAND”.3) Mini-transponder (#80) is attached to the frame of LTMS.4) LTMS was deployed during Dive #947 on May 4, 2006.

Small temperature meter (Nichiyu Giken Kogyo Co., Ltd.) Model: NWT-DN No: 166 Material of pressure case:Alloy of titanium Length: 212 mm Diameter: 41 mm Number of thermistor: 1 Accuracy: 0.05 K Resolution: 0.001 K Weight: 0.64 kg in air

0.40 kg in seawater Sampling interval: 10 minutes Repeat: 1 Notices: 1) The small temperature meter (NWT-DN#166) was attached to the frame of LTMS. 2) NWT-DN#166 was set that temperature measurements starts on 09:00:00 May 4, 2006.

Photo 1 Recovered long-term temperature monitoring system (LTMS).

Photo 2 LTMS before recovery.

5. Stand-Alone Heat Flow meter (SAHF)

Shusaku Goto (GSJ, AIST)

Stand-Alone Heat Flow meter (SAHF) is designed to measure heat flow using manned submersible and ROV (Fig. 1 and Photo 1). In the pressure case, an electric circuit and battery are contained and five thermistors situated within the probe at 11 cm intervals. The merit of SAHF is “OFF LINE” system so that heat flow can be measured while observer is conducting something else at that position or elsewhere. SAHF can also be used for long-term monitoring of sub-bottom temperature. In this cruise, SAHF6 was used to heat flow measurements on and around Kumano Knoll No.8. The following is description of SAHF.

Description SAHF 6 (Fig. 1 and Photo 1) Material Alloy of titanium Weight 3.1 kg in air

1.5 kg in seawater Length of pressure case 525 mm Diameter of pressure case 58 mm Length of probe 600 mm Diameter of probe 13.8 mm (filled by silicon oil inside) Number of thermistors 5 Intervals of thermistors 110 mm Accuracy 0.01 °C Resolution 0.001 °C External Interface RS232C (9600BAUD, 8 BIT, Non-Parity, 2 STOP BIT)

Heat flow measurement by SAHF While Hyper-Dolphin is descending and ascending, SAHF is located in a basket prepared by

Hyper-Dolphin operational team. After Hyper-Dolphin lands on seafloor, holds SAHF by Hyper-Dolphin’s manipulator and takes the reference temperature for 5 minutes (if SAHF locates enough at same position, temperature measurement for reference can be canceled). And then, penetrate SAHF vertically into sediment and measure temperature gradient for 15 minutes. After end of temperature gradient measurement, pull out SAHF and put into Hyper-Dolphin’s basket.

Fig.1 Schematic illustration of SAHF6

Photo 1 Photograph of SAHF6. Center of each yellow vinyl band on the probe indicates the position of each thermistor.

6. Dive Record, Track and Log

Dive #736

DiveLogHPD Dive #736 Observer: 2007.08.08 Kumano Mudvolcano page:1/__ Time(LCL)hh|mm|ss

Dep.(m)

Alt. (m)

Head (Deg) Observation Remark

9 36 0 2066 0 90 Landing. Clay seaflor. 41 0 2066 1 85 scratch trace

47 0 2066 0.5 46 can. Shell 50 0 2066 0.5 40 seafloor is rough．Scratch trace

54 0 2066 0.5 36 a metal box buried by clay

57 0 2066 0 30 shrimp. Can. 10 2 35 2066 0 5 large box

8 20 2065 0 25 large sheet

13 30 2065 0 28 18 0 2065 0 30 CTDとHPDの水深データに10 m 程度の誤差 22 0 2065 0 30 25 25 2064 0 30 a black driftwood 28 30 2064 0 30 through point 4. Move to point 5 point 4 31 55 2064 0 350 shell. riding slope 33 0 2060 1 350 shell 36 30 2060 0 360 shell 44 40 2061 0.5 0 through point 5 and move to point 6 point 5 49 10 2062 0.5 0 white bucket

50 20 2063 0 2 shell 11 0 30 2065 0 330

7 20 2065 0 330 SAHF start (15 mim.) point 6 22 20 2065 0 330 Recovery SAHF 25 30 2065 0 330 MBARI 29 30 2065 0 230 move to point 7 34 30 2064 0 230 37 40 2064 0 230 Caiibration (5 mim.) point 7 42 40 2064 0 230 waiting for water becoming clear 47 4 2064 0 230 SAHF start (15 mim.)

12 4 48 2065 0 230 Recovery SAHF

5 40 2065 0.5 210 Once HD shifts SSW, then the hedd changes topoint 8

12 30 2044 1.4 330 Head changed to point 8 15 20 2042 0.6 340 Head changed 16 20 2042 0 338 Calibration of SAHF point 8 22 20 2042 0 338 SAHF start (15 mim.)

38 20 2042 0 339 Recover SAHF

40 40 2042 0.5 220 Once HD shifts SSW, then the hedd changes topoint 9

45 24 2046 0.8 220 a black driftwood and shrimp 51 20 2048 0 220 Calibration of SAHF point 9 57 0 2048 0 220 SAHF start (15 mim.)

13 13 45 2048 0 220 Recover SAHF 15 0 2048 0 210 move to point 10 20 20 2046 1.5 300 shell fragments

6. Dive Record, Track and Log

Dive #737

DiveLog

HPD Dive #737 Observer: 2007.08.09 Kumano Accretional Prism page:1/__ Time(LCL)hh|mm|ss

Dep.(m)

Alt.(m)

Head(Deg) Observation Remark

CTD start from 1200 mbsf

8 54 40 2555 1 90 Landing. ROV homer react 60 m.

9 4 0 Fiding CAT-meter.

7 35 2545 3.1 345 Finding tube worm

21 02540 2.6 300 Search Barite Chimny but could not find

58 15 2544 0 58 Retrieve CAT-meter-L.

10 8 5 2541 4 303 Finding CAT-meter

39 44 2543 0 310 Retrieve CAT-meter, LEFT Bottom

6. Dive Record, Track and Log

Dive #738

DiveLogHPD Dive #738 Observer: 2007.08.09 Kumano Accretional Prism page:1/__ Time(LCL)hh|mm|ss

Dep.(m)

Alt. (m)

Head (Deg) Observation Remark

15 17 40 2569 1.6 62 Landing 22 0 2571 1.5 350 Finding shell fragments 27 11 2552 2.4 340 Finding CAT meter #15 37 30 2547 0.5 330 Retrieve CAT meter #15 40 0 2547 0.5 330 barast of 6K? 46 20 2547 4.2 10 Finding CAT meter #6 56 30 2548 1.1 1 Retrieve CAT meter #6 59 30 2549 1 1 Left Bottom

7. Results:

Long-term sub-bottom temperature monitoring using LTMS

Shusaku Goto (GSJ, AIST)

Fig. 1 shows bottom-water and sub-bottom temperatures measured with LTMS (Fig. 1b for Probe-1 and Fig.1 b for Probe-2). The temperatures of P1-6 and P2-6 are of bottom-water. P1-5 and P1-1 are the shallowest and deepest sensors of Probe-1, respectively. Similar, P2-5 and P2-1 are the shallowest and deepest sensors of Probe-2, respectively. For comparison, bottom-water temperatures measured with small temperature recorder are also plotted (Fig. 1a). The measured bottom-water temperatures indicates long-period variations of larger amplitudes with short-period variations of smaller amplitudes. The sub-bottom temperatures respond to the bottom-water temperature variation. For each sub-bottom temperature variation, the amplitude decays and phase delays with increasing depth. By removing the effects of bottom-water temperature variation from these sub-bottom temperatures, heat and fluid flows and their temporal variation will be investigated.

Fig.1 Measured bottom-water and sub-bottom temperatures. (a) Bottom-water temperatures measured with small temperature recorder attached with the frame of LTMS. (b) Bottom-water and sub-bottom temperatures measured at reference point (Probe -1). (c) Bottom-water and sub-bottom temperatures measured within bacterial mat (Probe -2).

8. Results:

Long-term sub-bottom temperature monitoring using LTMS

Shusaku Goto (GSJ, AIST)

During Hyper-Dolphin Dive#736, seven heat flow measurements using SAHF were conducted. In Table 1, positions of the heat flow measurements are listed. Fig. 2 shows measurement positions of heat flow. At the NE root of the knoll, first heat flow measurement (HPD#736-SAHF1) was carried out. At this position, in order to measure thermal conductivity and index properties (porosity and density) of sediment, one sediment core (HPD#736-MBARI1) was recovered near the heat flow measurement position using a MBARI core sampler. Second to fourth heat flow measurements (HPD#736-SAHF2 to HPD#736-SAHF4) were performed on the NE slope of the mud volcano. On the summit area of the mud volcano, fifth heat flow measurement (HPD#736-SAHF5). To investigate heat flow inside bacterial mat, one heat flow measurement (HPD#736-SAHF6) was carried out inside one of bacterial mats in the northern root of the knoll. For reference, one heat flow measurement (HPD#736-SAHF7) was performed outside the bacterial mat. As mentioned above, sub-bottom temperature near the sediment surface includes the effect of bottom-water temperature variation. Using bottom-water temperature data measured with small temperature recorder, the effects of bottom-water temperature variation will be removed from the sub-bottom temperatures and heat flow will be estimated.

Table 1 Positions of heat flow measurements Position

HPD#736-SAHF1

Latitude

33°36.445'N

Longitude

136°33.786'E

Depth (m)

2065

Comment

Sediment sample (HPD#736-MBARI1)wasalsorecovered.

HPD#736-SAHF2 33°36.400'N 136°33.726'E 2065

HPD#736-SAHF3 33°36.350'N 136°33.651'E 2042

HPD#736-SAHF4 33°36.303'N 136°33.603'E 2048

HPD#736-SAHF5 33°36.256'N 136°33.542'E 2034

HPD#736-SAHF6 33°36.427'N 136°33.481'E 2064 Heat flow was measured inside abacterial mat.

HPD#736-SAHF7 33°36.427'N 136°33.481'E 2064 Heat flow was measured sedimentnear the bacterialmatof

HPD#736-SAHF6

Fig.2 Positions of heat flow measurements using SAHF. Solid curve indicates the track of Hyper-Dolphin Dive#736.

Photo 1 Snapshot of heat flow measurement (HPD#736-SAHF4).

Thermal conductivity measurements Shusaku Goto (GSJ, AIST)

Thermal conductivities of sediment recovered using a MBARI core sampler was measured at the four positions of the sample. At each measurement position, nine measurements were conducted and then average thermal conductivity was calculated. In Photo 2, positions of thermal conductivity measurements are indicated. In Table 2, results of thermal conductivity measurements are listed. In order to investigate relation between index properties and thermal conductivity, four cube samples (8 cm3) were picked (Photo 2 and Table 3).

Photo 2 Positions of thermal conductivity merriments and cube samples which will be use measurements of index properties.

Table 2 Results of thermal conductivity measurement Measurement

HPD#736-TC1 Depth (cm)

5.5 Thermal conductivity (W/m/K)

0.777 ± 0.002 HPD#736-TC2 10.0 0.790 ± 0.006 HPD#736-TC3 14.5 0.802 ± 0.004

HPD#736-TC4 19.0 0.837 ± 0.011

Table 3 Sample name and position of cube sample Sample name Depth (cm)

HPD#736-Cube1 4.5 HPD#736- Cube 2 9.0 HPD#736- Cube 3 13.5

HPD#736- Cube 4 18.0

9. Summary

We successfully conducted retrievals of four CAT-meters from the site Aa (OOST scarp site) and one CAT-meter and one LTMS from the site Ca (mud volcano site) by the Hyperdolphin. The dive 736 dove the small knoll (Site Ca) showing incipient stages of mud diapirism in the Kumano Trough. The dive started from the southern flank of the knoll, observed the eastern flank and retrieved the LTMS with the ROV-homer and the CAT-meter. There are considerable amounts of clam fragments during the transit. SAHF measurements and MBARI samplings for LTMS data analysis were also conducted at the northern flank. The dives 737 and 738 were conducted in the fault scarps of OOST (Site Aa). The dive 737 observed tubeworms and bacterial mats, and retrieved two CAT-meters by ROV-homer navigation. The dive 738 also successfully recovered tow CAT-meters by ROV-homer navigation. We are trying to understand variations of fluid expulsions in the subduction zones off Kumano by analyzing flow rates from the CAT-meters, heat flow from the LTMS and SAHFs, and thermal conductivities from MBARI cores on shore.