YOKOSUKA Cruise Report YK10-08

Transcription

1 YOKOSUKA Cruise Report YK10-08 Eastern argin of Japan Sea July 10 th, 2010 July 26 st, 2010 Japan Agency for Marine-Earth Science and Technology (JAMSTEC)

2 Contents 1. Cruise Inforation 2 2. Researchers 5 3. Research Suary Background and overview Cruise Log AUV Dives (A) AUV Urashia 9 (B) AUV TunaSand AUV Dive Suary AUV Urashia Dives 11 (A) MBES High Resolution Bathyetry 16 (B) Sub Botto Profiler AUV Tuna Sand Dives SCS survey 23 Notice on Using 25 Acknowledgeents 25 1

3 1. Cruise Inforation Cruise nuber: YK10-08 Ship nae: R/V Yokosuka, AUV Urashia, AUV TunaSand Title of the cruise: Joetsu Basin, Eastern argin of Japan Sea Title of proposal: Analysis and acquisition of high resolution ap data of the accuulation and auto-collapse processes of the sea-floor gas hydrates Cruise period: July 10 th, 2010 July 26 th, 2010 Port call: July 10 th Departure JAMSTEC, Yokosuka, Kanagawa Prefecture July 26 st Arrival Matsugae Pier, Nagasaki, Nagasaki Prefecture Research area: Eastern argin of Japan Sea (Fig. 1) Joetsu Basin, Uitaka Spur and Joetsu Knoll (Figs. 2A and 2B) 2

4 Fig. 1. Ship track of the YK10-08 Cruise. 3

5 Fig.2A. Bathyetry and research area, Joetsu Basin, SW of Sado island. Fig.2B. Joetsu knoll and Uitaka Spur of the Joetsu Basin. 4

6 2. Researchers (Science Party) Chief Scientist (Representative of the Science Party): Matsuoto, Ryo (University of Tokyo) Onboard Scientists: Ura, Taaki (University of Tokyo) Nakatani, Takeshi (University of Tokyo) Ki, Kansu (University of Tokyo) Sakaaki, Takashi (University of Tokyo) Toaru, Minero (University of Tokyo) Hiroatsu, Minero (University of Breen) Eanuel Fonseca de Costa (University of Tokyo) Alfeus E. Kaban (University of Tokyo) Sato, Mikio (Institute for Advanced Industrial Science and Technology) Machiyaa, Hideaki (JAMSTEC) Shiizu, Ken (Nippon Marine Enterprises) Takaesu, Morifui (Nippon Marine Enterprises) Okada, Satoshi (Nippon Marine Enterprises) Machida, Shuusuke (Nippon Marine Enterprises) Shore-based Scientists: Kinoshita, Masataka (JAMSTEC) Ogihara, Shigenori (University of Tokyo) Ito, Kaori (University of Tokyo) Yaano, Makoto (Earthquake Research Institute, University of Tokyo) Yanagawa, Katsunori (University of Tokyo) 5

7 3. Research Suary 3.1 Background and Overview Gas hydrates accuulate in shallow sedients on the ounds, 300 to 500 in diaeter and 30 to 40 high, on the Uitaka spur and Joetsu knoll in Joetsu basin, at the depth of water of 880 to 1200, Japan Sea. All of the hydrate ounds develop on gas chineys as observed by single channel seisic profiles. Soe of the ounds are associated with active ethane plues, 600 to 700 high. During the R/V Yokosuka YK10-08 cruise in July 2010, we conducted (1) Multi Bea Echo Sounder (MBES), Side Scan Sonar (SSS) and Sub-Botto Profiler (SBP) by eans of AUV URASHIMA, (2) osaic photo survey by AUV Tuna Sand of the Institute of Industrial Science and Technology, Tokyo University, and (3) Single Channel Seisic surveys. (1) The AUV operated geophysical surveys have revealed ultra-high resolution topographic features and subsurface structures of the ounds and adjacent areas. AUV URASHIMA ran over the spur and knoll at 50 to 80 above seafloor at a cruising speed of 2.4 knots. MBES and SSS discriinated two types of ounds; one is a low swell with sooth surface and weak reflections, while the other is characterized by rough and uneven topographic features with strong SSS iages, probably due to incrustation by ethane-induced carbonate concretions and gas hydrates. SBP penetrated down to 50 bsf to 80 bsf and recognized three stratigraphic units: I upper assive unit (5-10 thick), II iddle evenly bedded unit (15-25 thick) and III lower slightly bedded unit (> thick). Deep gas chineys grow up toward the seafloor through the lithologic Units III, II, and I. When the ceiling of gas chiney stays within Unit III or II, the ounds above are either low swell or nearly flat, while the ceiling reaches up to Unit I or seafloor, ounds grow up high. Finally, the ceiling breaks through the seafloor and protrudes to for gas hydrate ound. The ounds continue to grow up to 40 to 50 high, and then start to decay due to echanical collapse and cheical dissolution of gas hydrates. The protruded ounds with uneven rough surface and strong SSS iages correspond to this stage. The ceiling of gas chineys is often represented by high aplitude, uneven acoustic reflectors on SBP, even within the sedients. 6

8 (2) We conducted 5 dives of AUV Tuna Sand over active ethane seep sites, gas hydrate exposures, and bacterial at zones. We had identified high concentration of snow crab on and around gas hydrate ounds, which seeed to suggest that snow crabs depend on cheosynthetic counity. AUV Tuna Sand took about 600 high resolution photos during her 7 to 8 hours dive, covering about 20 x 40 area. The resolution of the photos is a few or less, enabled to identify very sall crabs, and discriinate ale and feale, and old and young ones. Highest concentration ( population ) was 2945 feale crabs and 416 ales in about area. This eans that about 4 crabs in 1 2. This population is 100 ties high than average crab population in Japan Sea. Crabs tend to concentrate around high ethane concentration area, however, the direct relation between the cheosynthetic counities was not recognized. Lithology and icro-topography ay also control the population of snow crabs. (3) Single Channel Seisic profiles were taken for about 20 track lines over the Uitaka Spur and Joetsu Knoll. We had already revealed the structure and distribution of the botto siulating reflectors on the knoll and spur, but the stratigraphic relation between the knoll and spur was not fully understood SCS surveys were focused on the connection between the knoll and spur. We confired that the Joetsu knoll is younger than the Uitaka spur. 3.2 Cruise Log Date Activity & Operation Area July 10 Ebarkation/Departure JAMSTEC Pier, Yokosuka Brifing July 11 Transit Science Talk and Science Meeting July 12 Transit Turnout at Ryotsu harbor due to high waves July 13 Transit Ebarkation of 3 scientists Naoetsu port 7

9 Site survey for crab-fishing XGT/Bathyetry (MBES) SCS on the Uitaka Spur July 14 AUV Urashia dive#114(150 interval) Uitaka spur SCS on the Uitaka spur July 15 AUV Urashia dive#115(75 interval) Uitaka spur SCS on the Uitaka spur July 16 AUV Tuna Sand dive#46 & #47 Uitaka spur SCS on the Uitaka spur to the Un-naed ridge July 17 AUV Tuna Sand dive #48 & #49 Uitaka spur SCS on the Uitaka spur to the Un-naed ridge July 18 AUV Tuna Sand dive #50 & #51 Uitaka spur Science eeting July 19 AUV Urashia dive#116 (75 interval) Joetsu knoll SCS on the Uitaka spur Uitaka spur July 20 AUV Tuna Sand dive #52 & #53 Uitaka spur SCS on the Uitaka spur and Joetsu knoll July 21 AUV Tuna Sand dive #54 & #55 Joetsu knoll SCS on the Uitaka spur and Joetsu knoll July 22 AUV Tuna Sand dive #56 & #57 Joetsu knoll July 23 AUV Urashia dive #117 (75 interval) Joesu knoll Disebarkation of 3 scientists Naoetsu port Transit to Nagasaki July 24 Transit off Shiane-Torrori Science eeting July 25 Transit Genkai nada July 26 Disebarkation Matsugae Pier, Nagasaki 8

10 3.3 AUV (Autonoous Underwater Vehicle) Dives (A) AUV Urashia Multi Narrow Bea Echo Sounder (MBES), Side Scan Sonar (SSS) and Sub-Botto Profiler (SBP) surveys were conducted by AUV Urashia about 80 to 100 eters above seafloor at cruising speed of 2.4 knots. Urashia also carried 24 Niskin bottles to collect seawater saples during the cruise. AUV Urashia: Max. detph Max. cruising range Cruising speed Length Width Height k (by fuel cell) 2.0 to 4.0 knots Fig. 3. AUV Urashia onboard R/V Yokosuka in Joetsu Basin, Japan Sea. 9

11 Fig. 4. MBES, SSS, SBP, and other instruents below the Urashia. Fig. 5. Niskin bottles onboard AUV Urashia. 10

12 (B) AUV Tuna Sand Hovering type AUV Tuna Sand was used for close observation and photo-iaging of gas hydrate bearing, ethane venting sea-floor. Basin diension of Tuna-Sand is, Length Weight Max depth kg (in the air) 1500 Tuna Sand is specially designed for taking high resolution photographs of the seafloor fro about 2.2 above seafloor. The vehicle can dive into depression and rise up cliff guided by its forward laser sensor. For 7 to 8 hours dive, it takes 600 shots covering 20 x 40 area. These photos are to be copiled to construct a osaic photo soon after the recovery onboard. Fig. 6. AUV Tuna-Sand onboard R/V Yokosuka in Joetsu Basin. 3.4 AUV Dive Suary AUV Urashia Dives AUV Urashia conducted 4 dives (Dive#114, #115, #116 and #117) over the Uitaka spur and Joetsu knoll, and collected high resolution data for bathyetry apping (MBES), surface expression (reflection profiles/sss), and sub-seafloor iaging (SBP). Aong these apping and iaging, MBES has revealed a series of evolution of gas hydrate ounds fro sooth doed swell with gentle slope to unusual ound with central crater-like depressions, valleys and rough and irregular surface. Evolved ounds are also characterized by high reflections on SSS iages. SBP has revealed 11

13 high resolution acoustic stratigraphy down to 40 eters below seafloor. Track lines of the dives are shown in Figs. 7 to 10. Fig. 7. SSBL track lines of AUV Urashia dive #114 on the Uitaka spur 12

14 Fig. 8. SSBL track lines of AUV Urashia Dive #115 on the Uitaka spur. 13

15 Fig. 9. SSBL track lines of AUV Urashia Dive #116 on the Joetsu knoll. 14

16 Fig. 10. SSBL track lines of AUV Urashia Dive #117 on the Joetsu knoll. 15

17 (A) MBES High Resolution Bathyetry Gas hydrate occurs in and on ounds of the Uitaka spur and Joetsu knoll. The ounds are often observed as siple swell or oval shaped ounds. However, the Urashia MBES has revealed that ost of gas hydrate ounds have central crater-like depressions with rough surface. Fig. 11. MBES apping by R/V Natsushia (left) and AUV Urashia (UT spur). Fig. 12. MBES apping by R/V Natsushia (left) and AUV Urashia (JE knoll). 16

18 (B) Sub-Botto Profiles SBP has revealed acoustic blanking structures below gas hydrate ounds and high resolution stratigraphy around the ounds. SBP penetrated about 40 bsf. Mounds are observed as exposed/extruded hard ceiling of gas chiney structures. SBP has also revealed hidden ound under the seafloor. Fig. 13. SBP showing exposed gas chineys. Gas hydrate and carbonate concretions have been recovered fro the top of the ounds. 17

19 Fig. 14. SBP showing hidden ound under the seafloor. Blanking zone indicates extensve distribution of free gas while strong reflectors see to correspond carbonate and gas hydrate ixed hard cap of gas chiney structure AUV Tuna-Sand Dives Main objectives of the Tuna Sand Dives were to take high resolution photos of seep sites and gas hydrate exposures. According to high resolution apping of the Urashia, 12 dives were conducted on the selected sites of the ounds. Mosaic photos have clearly revealed 3 to 6, circular depressions on the outer ridge of ounds. This type of depressions are considered to represent initial phase of the collapse of gas hydrate ounds. Unexpectedly, large nuber of snow crabs were observed on ounds, in particular, around carbonate concretions and depression areas. No crabs were found on ud flat far away fro gas hydrate ounds, whereas, high concentration of crabs are coon on the ounds, in particular, well developed ounds with rough surfaces. Nuber of crabs sees to be related with bacterial at as well as carbonate hard-ground and seep sites. 18

20 '**#(+(% !(*#'"') (&)#%"' 12 )% )* 37 32'N 'N )) 'N 'N 'N !"!&!*!%, )+ )$ 'N!"#$%& ''#$$ 105 (!#'** '&#'" )*#)!$ +# 'E k 37 22'N 'N ベニズワイガニ 雄, 雌 の個体数 (40x20) 'E 'E 'E 'E 'E 'E Fig. 15. Nuber of snow crabs in on and around gas hydrate ounds. No crabs were recognized at Site 46, which is ore than 1 k away fro active seep sites

21 Fig. 16. Snow crabs on carbonate concretions near CH4 seep sites on the Joetsu knoll. Fig. 17. Snow crabs on bacterial at, central ound of the Uitaka spur. 20

22 Fig. 18. Mosaic photo of gas hydrate ound on the Joetsu knoll. 10 x 20 oval shaped depression is found on the right of the survey area. White zone indicates bacterial ats. Fig. 19. Distribution of snow crab (orange dot = ale, blue=feale) in the upper center area of Fig

23 Fig. 20. Densely populated area at Site 57 on the Joetsu knoll. &!! ()*+&!,-./01 %!! $!! #!! "!!!!"####$%!"####&!"' '()*+,-./01 Fig. 21. Relation between the coverage of bacterial at and nuber of snow crabs. 22

24 !$&## 3.5 SCS survey SCS survey has clearly indentified different history of evolution between the Uitaka spur and Joetsu knoll. Also, the profiles has revealed wide distribution of debris flow deposits. Considering the structures observed by SBP, gas chineys are playing a critical role to carry gas and gas-bearing fluid to the surface. SCS survey lines are shown in Fig. 22.!"#$!$%&'()*+,-&".)//&0& &6748&696 $-/!+#01 $-/!++01 $-%!##01 $-%!#+01 $-%!$#01 -/!"+02 k -/!"+02 # + -/!"# $!& 6789$!% -/!"#02 345/-$ 345+$+ 6789$!" /! 6789$!!5+ $!+ ##$ 6789$!. 6789$!#5+!"# 6789$&$ 345&!/ 345&/# 6789$!/ 6789$$%5+ %#$ ##$ 6789$$!;! 345&%! 345% $!+!$"##!$!## +#$ 345%#" ##$ +#$ 6789$#&1 345!##$ 345!#"- -/!-#02 -/!-# %" 6789$!-5+ ##$ 345&%& -/!-+02 $"- 6789&! -/!-+02 ##$ ##$ 345&&# 6789$&! 6789$!$5+ 345/%/!$!##!$###!$###!$!##!/. 345!+. ##$ 345!+#$ 6789$#%: 6789%$ 6789/$ 6789$#& ##$ +#$.#$.!# 6789$#! 345%&# 6789+! 345//+ +#$ "$& 6789$$#1 6789$#- ##$ ##$ +#$ 6789-$ /$! 345%/! +#$ ##$ #&. +#$ ##$ 6789-# 6789$#$ ##$ "&/!$###!$!## 345!##$ 6789$$.5+ ##$ 6789!/1 345%-$ #// 6789!+ ##$ +#$& !$;!;<=>>5<?@ ##$ ##$ ##$ +#$ /$/ 6789$& ##$ 345!##$ 6789$#" 345&&! 6789$" 6789$!5+ 345&-% +#$&-#!+% 6789$# $#%1 ##$ +.+ +#$ ##$ -/!!+02 -/!!+02!$### 345!"%! 6789! 6789$ 345&/# +#$ 345&%% &$& &$!%##!&## $-/!+#01!#$#'()*'!+'$%,-.,#+ $-/!++01 $-%!##01 Bathyetric data../grd/sado_05_06_07_08_scsix50neg.grd $-%!#+01 $-%!$#01 Fig. 22. SCS track lines conducted during the YK10-08 in the Joetsu basin. 23

25 Fig. 23. W-E seisic section of the Uitaka Spur showing distinct 5 seisic facies. Fig. 24. Interpretation of Seisic section L12.5 (above). 24

26 Notice on using This cruise report is a preliinary docuentation as of the end of the cruise. It ay not be corrected even if changes on content (i.e. taxonoic classifications) are found after publication. It ay also be changed without notice. Data on the cruise report ay be raw or not processed. Please ask the Chief Scientist for the latest inforation. Acknowledgeents We thank the captain and crew of R/V Yokosuka and AUV Urashia, Japan Agency for Marine-Earth Science and Technology (JAMSTEC). We are also grateful to technical staffs fro Nippon Marine Enterprises, Ltd. for aking this cruise a success. This research is financially supported in part by the Grant-in-Aid of the Ministry of Education, Culture, Sport, Science and Technology of Japan (MEXT), University of Tokyo, Japan Agency for Marine-Science and Technology (JAMSTEC), Japan Oil, Gas, Metals National Corporation (JOGMEC), and Petrobras-Brazil. 25