carlsberg ridge & andaman sea...carlsberg ridge (cr), a part of the central indian ridge and the...

RV SONNE

CRUISE: NIO-RVS2

17 Oct - 01 Dec 2007

AREA OF SURVEY

CARLSBERG RIDGE & ANDAMAN SEA Goa - CR- Andaman Sea – Port Blair

NATIONAL INSTITUTE OF OCEANOGRAPHY (Council of Scientific & Industrial Research)

Dona Paula, Goa – 403 004

REPORT ON THE CRUISE NIO-RVS2 OF RV SONNE CONTENTS 1. Summary

2. Cruise track

3. Introduction

4. Itinerary

5. Cruise participants

5.1. Scientific component

5.2. Ship’s complement

6. Objectives

7. Survey Plan

8. Work accomplished

8.1. Equipment Used

8.2. Geological sampling

8.2.1 TV Grab Operations

8.2.2 Dredging Operations

8.2.3 OFOS Stations

8.3. Deep -Tow Operations

8.4. Water Column Physics- Chemistry- Biology

8.4.1 Water Column Survey

8.4.2 Highlights of deep-tow and hydrocast observations

8.4.3 Onboard collection/ processing / analysis of sea water samples

8.4.4 Benthic biology

9. Performance of ship and equipment used

10. Conclusions

11. Recommendations

12. Acknowledgements

Annexure I : Table1 - 7

II : Fig. 3 - 11

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1. SUMMARY

The NIO-RVS2 cruise onboard RV Sonne was planned for the second phase of field program of CSIR Network Program titled “Tectonic and Oceanic processes along the Indian ridge system and the back arc basins”. The main objective of the cruise is to acquire multiparameter data together with deep-tow and seafloor imaging over the segments of Carlsberg Ridge and Andaman Backarc Spreading Ridge regions. The observations include multibeam mapping, magnetics, Deep-Tow survey along the rift valley, Ocean floor imaging with OFOS (Ocean Floor Observing System) at selected locations and seabed sampling using TV-Grab, Dredge, Spade core and Gravity Core. Water column sampling and CTD observations have been carried out over the Carlsberg Ridge (CR) and Andaman Backarc Spreading Center (ABSC) segments.

About 600 km long segment of the Carlsberg Ridge and part of ABSC and a region off Nicobar Islands covering the Off Nicobar Swarm are covered in the cruise. The cruise is organized in to two legs the first on CR and the second leg in the Andaman Sea. Starting from Goa (Marmugao, Port) we surveyed the CR region in the Arabian Sea first and then conducted investigations in the Andaman Sea and disembarked at Port Blair, Andamans. We have planned deep-tow tracks along the rift valley based on the multibeam data acquired during earlier cruises. Conducted CTD observations at anomalous tectonic regions identified from the deep-tow side-scan and MAPR data. Systematic seabed sampling followed by OFOS observations were carried out at selected locations. Deep-tow system IMI-30, hired from Hawaii Mapping Research Group, Hawaii was operated along 11 tows. Six tows are along the CR and five are in the Andaman Sea. Seabed sampling included, 10 dredge operations, 14 TV-Grab operations, one spade core and 4 Gravity core operations. OFOS was operated at five locations on CR and one location in the Andaman Sea. 21 operations of CTD including a circular towed CTD were conducted. Besides, benthic and microbial studies were carried out over the seabed samples and water column samples respectively. The marine magnetometer was towed between the station and during transit. The water samples were filtered and stored for onshore analysis. Onboard analysis was carried out for pH, DO and SiO4. Water samples were collected in specially designed copper tubes for the analysis of Helium. Onboard analysis of methane has been carried out on selected water samples. Prominent optical signatures indicative of an active hydrothermal filed were noticed over the Carlsberg Ridge. Further investigations are required to locate the origin of the identified plume. In the Andaman Sea the off Nicobar earthquake swarm region has been mapped and seabed samples have been collected.

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2. CRUISE TRACK

The Cruise track from GOA to Carlsberg Ridge

Fig. 1 The Cruise Track from Goa to Carlsberg Ridge

Fig. 2 The Cruise Track from Carlsberg to Andaman

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3. INTRODUCTION

Mid-oceanic ridges are the primary sites of volcanic activity and generation of new crust. They exert major influence on the evolution of the solid earth, affect the composition of the ocean waters and support unique forms of life. It is estimated that about 25% of the Earth's total heat flux is transferred to the hydrosphere through thermal convection related to volcanic and hydrothermal activity associated with mid oceanic ridges.

The mid-ocean ridge systems in the Indian Ocean comprise of Carlsberg ridge (CR), Central Indian Ridge (CIR), South West Indian Ridge (SWIR), South East Indian Ridge (SEIR). The back arc spreading system in the Andaman Sea region is an illustration of the spreading systems in the backarc basins. The CIR, SWIR and SEIR meet at the Rodriguez Triple Junction (RTJ) in a inverted Y shaped junction. These ridge systems together with the back arc spreading system in the Andaman Sea provides an opportunity to study a broad range of characters related to the global ridge systematics. Among these ridge systems the SWIR and a part of the SEIR are comparatively better explored than the CR, CIR and Andaman back arc systems.

The ridge program aims to concentrate on CR-CIR and Andaman backarc spreading systems by launching an inter-disciplinary exploration program to understand the tectonic and oceanic processes that are occurring at these dynamic plate boundaries. A joint CSIR-DOD Network program has been formulated to undertake the ridge research. Under this program a segment of the Carlsberg Ridge (CR), a part of the Central Indian Ridge and the Andaman back arc basin (ABAB) and the back arc spreading center have been mapped during the cruises of ORV Sagar Kanya.

The well mapped Carlsberg Ridge segment and the Andaman backarc spreading center are chosen for second phase of investigations using deep-tow and underwater photography. For this purpose the services of RV Sonne were hired by the National Institute of Oceanography. RV Sonne is equipped with special tools such as TV-Grab and underwater camera sledge namely the Ocean Floor Mapping System (OFOS). Besides RV Sonne also has a multibeam, CTD system and fiber optic cable to facilitate installation of deep-tow equipment, the vessel has excellent navigation capability and onboard computer network system to carry out data logging and data processing. The vessel provided ideal platform to conduct complex deep-sea experiments. We have hired deep-tow mapping system IMI-30 from Hawaii University to image the rift valley floor in greater detail. Also deployed in this cruise in the ridge region are Miniature Autonomous Plume Recorders (MAPRs). These can be deployed along with a variety of sampling devices to sense the physical properties of the plume water. In this cruise the MAPRs are used with Deep-tow, CTD, OFOS and TV-Grab operations.

The NIO-RVS2 cruise onboard RV Sonne is the second cruise during the charter of RV Sonne by NIO in the year 2007. The funding for the program is provided by the CSIR under the Network program, titled “Tectonic and Oceanic processes along the Indian ridge system and the back arc basin”.

4. ITINERARY

Departure : Goa, 17th October 2007 Arrival : Port Blair, 1st December 2007

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5. CRUISE PARTICIPANTS

5.1 Scientific Component National Institute of Oceanography 1. Dr. K.A. Kamesh Raju, Chief Scientist 2. Dr. A. B. Valsangkar Scientist F 3. Dr. Abhay Mudholkar Scientist F 4. Mr. G.P.S. Murty Scientist EII 5. Mr. Durbar Ray Scientist B 6. Mr. B.R. Rao Technical Officer 7. Mr. Desmond Gracias Technical Officer 8. Mr. Imran Mirza Project Assistant III 9. Mr. Jayant Kumar Singh Project Assistant III 10. Mr. Bijin K. Project Assistant III 11. Mr. Robin Mathew Project Assistant III 12. Mr. Ratheesh R. Project Assistant III 13. Ms. Runa Antony Project Assistant III 14. Mr. L. Surya Prakash Project Assistant III 15. Mr. Sabyasachi Sautya Project Assistant III 16. Mr. Vipin M. G. Project Assistant III 17. Ms. Nilima Chintalapati Project Assistant III 18. Ms. Bernadette Rebeiro Project Assistant II

National Geophysical Research Institute 19. Mr. T. Vijaya Kumar Scientist B

HMRG, Univ. of Hawaii, Hawaii 20. Dr. Paul Johnson UH, Hawaii 21. Dr. Roger Davis UH, Hawaii 22. Mr. Mark Rognstand UH, Hawaii 23. Mr. Steven Tottori UH, Hawaii 24. Mr. Todd Ericksen UH, Hawaii 25. Mr. Jonathan Weiss UH, Hawaii

5.2 Ship’s Complement

1. Capt. Lutz Malon Master 2. Nils Arne Aden Chief Mate 3. Jenes Gobel 2nd Officer 4. Ulrich Buchele 2nd Officer 5. Werner Guzman-Navarrete Ch. Engineer 6. Klaus Klinder 2nd Engineer 7. Jorg Buss 2nd Engineer 8. Jorg Leppin Chief Electrician 9. Uwe Rieper Electrician 10. Mathias Grossmann Sys. Manager 11. Sabine Heuser Doctor 12. Wilhelm Wieden Ch. Cook 13. Ganakaraj Antony 2nd Cook 14. Werner Slotta Ch. Steward 15. Gerlinde Grube 2nd Stewardess 16. Rainer Rosemeyer Deck Locksmith 17. Winfried Jahns Boatman 18. Werner Hodi Seaman 19. Jurgen Kraft Seaman 20. Andreas Schrapel Seaman 21. Henning Schnur Seaman 22. Michael Barkow Seaman

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6. OBJECTIVES

The objective of the cruise is to acquire high resolution deep-tow data (side-scan image and phase derived bathymetry) along the rift valley floor of a part of the Carlsberg Ridge and the Andaman backarc spreading center.

The data acquisition involves multibeam mapping, underway geophysical data such as magnetics, and acquisition of CTD data, collection of water column samples and seabed samples. These studies are aimed at imaging the seafloor at high resolution to characterize the rift valley floor in terms of magmatic activity and to explore for the plume signature in the water column using CTD and MAPR data. Water samples are collected to identify the chemical and biological signatures and thereby identify the plume waters indicative of hydrothermal mineralization at the seafloor.

7. SURVEY PLAN

The survey during NIO-RVS2 was planned to acquire high-resolution seafloor image of the rift valley using deep-tow and Multibeam data. MAPRs are attached below and above the depressor weight of the deep-tow system to record the temperature and turbidity signatures within the water column. The plan to conduct the deep-tow survey first is to select the specific CTD and sampling locations. Based on the deep-tow, MAPR and CTD data, the OFOS and TV-Grab locations was planned. It is proposed to cover the entire length of the Carlsberg Ridge (about 600 km) in a phased manner. Each deep-tow track was planned for a period of 48 hours followed by sampling. The survey tracks are planned based on the hydrosweep multibeam data acquired using ORV Sagar Kanya.

The Figs. 1 and 2 represents the cruise tracks from Goa to CR and CR to Andaman respectively. The detailed track maps of CR and Andaman regions provide the list of operations carried out during the cruise.

8. WORK ACCOMPLISHED

8.1 Equipment used The following Equipments were used:

1. Global Positioning System receiver 2. IMRAD EM-120 Multibeam Echosounder 3. ATLAS PARASOUND parametric Sediment Survey Echosounder 4. IMI-30 Deep-Tow side scan sonar 5. Magnetometer 6. CTD – Seabird CTD system (SBE 9/11 plus) 7. Miniature Autonomous Plume Recorders (MAPRs) 8. Ocean Floor Observing System (OFOS) 9. TV Guided Grab (TV GRAB)

IMI-30 Deep – Tow side scan data:

A total number of 6 deep-tow tracks in the Carlsberg region (Fig. 10) covered about 550 km along axis rift valley floor. The deep-tow fish was flown at an altitude of about 500 to 600 m from the seafloor and provided a swath coverage of 1500 m to 2000 m on either side of the fish. The survey was conducted at an average speed of 2.0 knots/hr. The depth to the rift valley floor in the region varied from 3500 to 4800 m. The deeper seafloor demanded more wire to be lowered and to reduce the speed of the vessel. The system functioned satisfactorily throughout the cruise.

The deep-tow system is monitored by Linux stations using the software developed by the University of Hawaii. The data acquisition and control systems used the Linux servers. All the parameters of

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the Deep-tow are monitored by the system and the pilots on watch continuously monitor the fish altitude with respect to the seafloor and give commands to the winch operator and the bridge.

The acquired data is post processed onboard and the gray scale images of the illuminated seafloor are generated (Fig. 11). GMT was used for the presentation of the data. The onboard A0 plotters are used to generate the plots.

EM120 Multibeam System:

The EM120 multibeam system was operated through out the cruise to provide depth information. The data acquired along the deep-tow tracks and during transits was processed separately to generate A0 plots. Onboard Neptune software was used to process the data. GMT is used for the presentation. MB-SYSTEM will be used to post-process the data in the lab.

The EM 120 is designed to do mapping to full ocean depth with a hitherto unsurpassed resolution, coverage and accuracy. The receive transducer is wide band and in conjunction with a separate Low frequency transmit transducer, the EM120 may optionally be able to deliver sub-bottom profiling capabilities with a very narrow beam width. The nominal sonar frequency is 12 kHz with an angular coverage sector of up to 150° and 191 beams per ping as narrow as 1°. The angular coverage sector and beam pointing angles may be set to vary automatically with depth according to achievable coverage. This maximizes the number of usable beams. The beam spacing is normally equidistant with equiangle available. The transmit fan is split in several individual sectors with independent active steering according to vessel roll, pitch and yaw. This places all soundings on a “best fit” to a line perpendicular to the survey line, thus ensuring a uniform sampling of the bottom and 100% coverage. The sectors are frequency coded (11.25 to 12.60 kHz), and they are all transmitted sequentially at each ping. The steering is fully taken into account when the position and depth of each sounding is calculated, as is the refraction due to the sound speed profile, vessel attitude and installation angles. Pulse length and range sampling rate was variable with depth for best resolution, and in shallow waters due care taken to the near field effects. The ping rate is only limited by the round trip travel time in the water up to a ping rate of 5 Hz. The EM 120 transducers are linear arrays in a Mills cross configuration with separate units for transmit and receive. The arrays are divided into modules, these may be replaced by a diver. The number of modules used (and hence the beam width) may be adjusted according to particular installation requirements. For both arrays 1° and 2° beam widths are standard options, and 4° beam width is available for the receive array. The resulting array lengths are between 2 and 8 m. The Kongsberg Simrad EM 120 is a complete system. All necessary sensor interfaces, data displays for quality control and sensor calibration, seabed visualization, and data logging are a standard part of the system, as is integrated seabed acoustical imaging capability (sidescan).

Ocean Floor Observing System [OFOS]:

The basic function of the system is to provide the online seafloor image using an array of cameras. The array consists of one color video and one black and white video camera, one still camera. Besides there is a CTD mounted on the frame to provide online conductivity temperature data during the tow. There is an altimeter, control electronics and the lights for the video and photography. The system is typically towed along a predefined track at a speed of 0.2 to 0.5 knots and covers an area of about 2 Sq.m region. The system is connected by the optical fiber cable for powering the lights and subsystems and for high speed data transmission (Fig. 4). The system is continuously monitored by the winch operator and maintained at optimum altitude (~5 m) above the seafloor to obtain well-focused image of the seafloor. The video output is recorded on hard disc and then transferred to DVD. During the first leg of operations over the Carlsberg Ridge, the OFOS was operated at 5 locations (Table-4).

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TV-Grab system:

The TV-Grab is a very useful tool to collect samples from a precise location. The user has the advantage of seeing the ocean-floor and selecting the precise location to pick-up the sample. The system uses the same optics as that of OFOS with a color and still camera options (Fig. 5). The system is battery powered. The closing of the grab can be activated from onboard by the observer and the grab closes by hydraulic motors. The photography and grab operations consume lot of power and this limits the amount of time the sampler can stay near to the seafloor, usually it is about 3 hrs. The operations during the cruise were successful and the system functioned satisfactorily.

Miniature Autonomous Plume Recorders (MAPRs):

The Miniature Autonomous Plume Recorder (Figure 6) is a self contained unit having temperature, pressure and optical back-scatter sensors, these units can be attached with the cables of different sampling devices and instrument packages used for survey and sampling work. Data is recorded internally and can be retrieved after recovery of the unit upon completion of the sampling/survey operation. Deployment time is limited by the number of records that can be stored in the MAPR’s memory (1 MB), it is sufficient to record data for 7.2 days with an interval of 5 seconds. MAPR data is available in binary format using the macro GET BINARY DATA given in MAPR work book, these data can be retrieved.

During the Carlsberg leg of RV Sonne-2 Cruise, six MAPRs, provided by Dr. Edward T. Baker, Pacific Marine Environmental Laboratory (PMEL), NOAA, USA, were used.

8.2 Geological Sampling The Geological sampling during the cruise was conducted using TV-Grab, dredge, coring and spade core devices. TV grab and dredge were used for recovering well constrained geological samples from the deep axial-valley of the Carlsberg Ridge, north Indian Ocean and in the Andaman Sea. During the Carlsberg Ridge leg of the RVS-2, nine (9) dredge operations were carried out of which seven (7) were successful in recovering rocks from the valley floor. Similarly TV Grab (Bodo) was used at eight (8) locations and samples were recovered from four (4) locations (Fig. 8). The second leg of the RVS-2 cruise was in Andaman Back-Arc Basin (ABAB) during which dredging, coring (gravity and spade) and TV Grab operations were carried out (Fig. 9). From ABAB, variety of rock samples were recovered, specially noted is the TV Grab over the northern seamount brought up the sediments along with the large pieces of pumice which is a light density rock when dry floats on the water. Off Nicobar, over the earthquake swarm region, from a shallow depth rhyolitic rocks and few unaltered but mostly in different stages of alteration were recovered. The details of coring operations in the Andaman region is given in Table-2.

8.2.1 TV-Grab operations During the cruise TV-Grab was operated at 14 stations (Table-3). Out of the 14 stations, 8 operations are in Carlsberg Ridge and 6 in the Andaman Sea region. TV Grab has a TV camera on the top, with the help of the Camera continuous video images can be seen onboard in a monitor screen these images can also be recorded in a DVD. Exact sampling location can be selected based on the video image and the grab can be closed from onboard by transmitting a command to the hydraulic arms of the grab. After TV grab closes, it can be confirmed that the sample that are present in the grab with the desired samples. With the TV grab the samples recovered are position and depth controlled. TV Grab can be operated independent of collecting the geological samples when other video gear on board is non-operational.

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8.2.2 Dredging operations Most of the dredge locations are located within the axial valley of the Carlsberg Ridge. In general the dredging sites were selected on the basis of the axial highs within the valley or along the valley flanks (Table-1).

Operational details of dredge

The dredge locations were decided based on the multi-beam bathymetry map. After finalizing the location and after the ship stopped, lowering of the dredge starts and ship’s position is maintained till the dredge the reaches the sea-floor. After that ship is allowed to move in the desired direction and slowly the wire rope is lowered till total rope length is about 400-500 m more than the water depth. Slowly the dredging is carried out for about 25-30 minutes and the rope is heaved in slowly (~0.2 m/sec). During the heaving the tension develops on the rope. Out of nine dredge operation at seven locations rock samples were recovered. After putting the nylon net inside the dredge, two time sediment was also collected from the dredging.

8.2.3 OFOS stations During the RVS-2 cruise the camera sledge OFOS (Ocean Floor Observation System) on board RV Sonne which has B/W and colour camera with still colour camera was used over Carlsberg Ridge and over the Andaman Backarc Spreading Center (ABSC). Apart from visual sensors, the sledge has CTD sensors. OFOS was operated at 6 locations, 5 are over Carlsberg Ridge and one station was in the Andaman Sea (Table-4).

8.3 Deep-Tow Operations The Imaging and Mapping Instrument (IMI-30) is a new 30 kHz phase-bathymetric sidescan sonar developed and operated by the Hawaii Mapping Research Group at the University of Hawaii at Manoa (Fig. 3).

Two power amplifiers drive the port and starboard sidescan arrays, and one drives the sub bottom transducers. Each 30 kHz power amplifier has a 9000 µF capacitor bank to store energy for the transmitted signal; the sub bottom capacitor bank is 18000 µF to support longer pulse lengths. A four channel capacitor charging board controls the voltage of each bank, recharging to the desired level after each transmission. The IMI-30 system contains three receiver-processor modules: two for the 30 kHz swath mapping sonar, and one for the sub bottom. Each receiver-processor is capable of acquiring data on two channels.

Capable of operation at depths of up to 6000 m and altitudes above the seafloor of approximately 500 m, it maps a swath up to 5 Kms in width. Eleven Tracks for Deep-Tow (six in Carlsberg and five in Andaman) were operated. The tracks were planned based on previous studies and the survey was completed successfully. 550 Kms of Axial valley was covered on the Carlsberg Ridge (Fig. 10). Five deep-tow tracks were completed in the Andaman region, two in the Andaman back-arc spreading centre, two in the Seamount just south of the spreading centre and one over the Nicobar swarm region.

The dredge stations, TV Grab locations, OFOS stations, Gravity Core locations, Spade Core locations for Andaman region is given in Tables 4,5,6,7,8 respectively. Gravity core was used to recover long sediment cores from the Andaman Basin for deciphering the past geological records of tsunami deposits. A spade core was operated close to the GC-4 location to get the undisturbed top of the core for further laboratory studies. This core in tandem with the GC–4 will be helpful in understanding the geochemical behavior of various elements within the sediment column.

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8.4 Water Column Physics-Chemistry-Biology 8.4.1 Water column survey: The cruise NIO-RVS2, on board RV Sonne aimed to explore a segment of Carlsberg ridge, Northern Indian Ocean and Andaman Backarc Spreading Center (ABSC) for sea floor hydrothermal activities. As a part of this programme, detailed water column investigations with CTD hydrocast sampling was carried out between 5o33’ and 3o40’N and in the Andaman Sea (Fig. 9).

Strategies for deep sea water survey and sampling Based on preliminary deep tow survey along the axial valley as well as hydro graphic (viz. in-situ temperature and turbidity) data obtained from Miniature Autonomous Plume Recorder (MAPRs), attached along with deep tow cable, we have selected the CTD hydrocasts locations for deep sea water sampling. The deep tow and MAPRs data were analysed immediately after their recovery to trace out possible plume signatures along the rift valley. The locations with near sea floor temperature highs (from deep tow survey) and water column having considerable nephelometric signals (from MAPR data) were chosen for further plume investigations. Nephelometric anomalies of about 0.01 nephels or more above the back ground are considered for detailed hydrographic investigations. To trace out the possible plume source, repeated hydrocast sampling was carried out around the particular location(s) with prominent optical signatures.

Miniature Autonomous Plume Recorder (MAPR) survey During the Carlsberg leg of RV Sonne-2 Cruise, six MAPRs, received from Dr. Edward T. Baker, Pacific Marine Environmental Laboratory, NOAA, USA, were used for the first time along with CTD, DEEP TOW, OFOS & TV-GRAB to observe the water column plume signatures in the survey area.

Initially all six MAPRs (nos: 09, 12, 13, 06, 08 & 29) were used with first four Deep Tow (ie, DT-01 to DT-04) operations, three above and three below the depressor of the deep tow. The O-ring of the MAPR 06 was damaged during the DT-04 operation. The details of MAPRs attatched with DEEP-TOW is given in Table-5. Two MAPRs were used at 10 m and 20 m above the rosette during every CTD hydrocasts.

CTD hydrocasts summary There were a total of seventeen (17) CTD casts during the first leg of the cruise over Carlsberg Ridge (Fig. 7). All the CTD stations were mostly located over the axial valley or either side of valley wall with average water column depth ranging between 3500 to 4200 m. The water column hydro graphic profiles were obtained with a Seabird CTD system (SBE 9/11 plus) along with additional transmissometer and backscatter (Wetlab-633/634) or Seapoint turbidity sensors. Two MAPRs (10 and 20 m. above the CTD rosette) also has been used along every CTD hydrocasts. Mostly deep water (> 2500 m) having intense optical backscatter and /or minute insitu temperature signature were sampled with 10 Lt Teflon coated Niskin samplers (24 nos.) mounted on CTD rosette. All the Niskin samplers were cleaned and rinsed with dilute (~1.0 N) supra-pure nitric acid before CTD deployment. The CTD hydrocasts summary is given in Table-6.

8.4.2 Highlights of deep-tow and hydrocast observations During second and third phase (DT02 and DT03) of deep tow operations, at two locations prominent optical signature has been recorded with MAPR along the axial rift valley. The optical signatures of possible plume sources were confirmed with vertical CTD hydrocasts (CTD05 and CTD06 respectively) at those same locations. Although CTD05 did not revealed with any major anomalies while the latter showed an optical backscatter anomaly of ~0.007 nephels in the water column 800 m above the sea floor. About 100m thick turbid layer, typical plume profile with minimum

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backscatter voltage immediately above and below has been found at CTD06. To locate the possible plume source, a set of close grid CTD operations (CTD07-CTD11) were carried out at relatively shallow (~3600 m) flanks on either side of rift valley wall. During towing the CTD at constant depth of 3300 m, over a circular track around CTD06 we noticed consistent optical signatures in south-west of CTD06. A deep tow survey (DT06) also carried out from west to east across the rift valley. The maximum optical anomaly (0.033 nephels above the background) has been recoded at the water depth 3200m, near the western flank. The close spaced CTDs14 to 17 hydrocasts were made near that anomalous area and also revealed with consistent signatures over a depth ranging 2900 to 3200 m. The CTD16 showed small temperature and salinity highs within the same depth range. During all CTD casts water sample were collected for further chemical and microbial analysis.

8.4.3 Onboard collection/ processing/ analysis of sea water samples Among 17 CTD casts, twelve (CTDs-06 to 17) were made within a small segment (between 03o39´ and 03o48´N), where maximum optical anomalies were observed with MAPR and optical sensors attached with CTD rosette. Water samples were collected in duplicate for certain geochemical (volatiles, trace and major elements) and microbial tracers analysis.

8.4.3.1 Chemical tracers a) Helium isotopes

Water samples for helium isotopes analysis were collected in nitrogen flushed copper tubing (2.0 cm diameter) in duplicate. After flushing with enough (~2.0L) seawater sample, copper tubes were crimped immediately with crimper provided by Dr John Lupton, PMEL, NOAA. The tubes are checked for leaks and carefully stored for further mass spectrometer analysis at Helium Isotope Laboratory, PMEL, NOAA, OR, USA.

b) Dissolved oxygen

Immediately after helium sampling the dissolved oxygen was measured with a D.O. meter (Eutech Instrument, DO 300) in samples taken from same Niskin sampler, used for helium sampling.

c) Dissolved methane

Water samples for dissolved methane estimation were collected from duplicate Niskin sampler. Total volatiles were extracted and stored in crimped glass vials from water samples with a ultra sonic bath following Schmitt et.al. (1991).

d) pH and Eh

pH and Eh of individual water samples were measured onboard using pH meter (PHAN, Labindia) calibrated with standard solutions of pH 7.0 and 9.2.

e) Dissolved trace metals

About 2.0 L of each sample was filtered through 0.45 µm Millipore mixed cellulose ester filter paper and acidified with ultra pure (60%) nitric acid to pH 1.5. Those preserved samples were stored carefully in acid washed plastic bottles for dissolved trace metals (e.g. Mn and Fe) analysis with GFAAS or ICPMS on shore.

f) Dissolved major elements

0.5 L unfiltered water from individual samples were stored in plastic bottles for major sea water components analysis.

g) Particulate trace metals

10 L water sample from eight selected CTD stations were filtered through 0.45 µm filter paper. After filtration, filter papers are oven dried and packed in separate pertiplates for further trace metal analysis in particulate fractions.

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8.4.3.2 Biological tracers a) Total bacterial counts:

5.0 ml of water sample was dispensed in TC vials and fixed with buffered formalin. Samples were stored in cool, dark place.

Analysis in laboratory: Total bacterial counts will be recorded using epifluorescence microscope after filtering the samples through GSWP 0.22 µm filter paper, and staining with acridine orange.

b) Retrievable counts:

100 µl of sample was surface plated on quarter strength nutrient agar for the enumeration of heterotrophs and dilute nutrient agar (1.3 gmL-1 nutrient broth + 2% agar in aged offshore sea water) supplemented with 1mM MnCl2 and 1mM CoCl2 for enumeration of metal tolerant bacteria. Enumeration of nitrifiers and sulphur oxidizers was done on N1 and TDLO medium.

Analysis in laboratory: Retrievable counts in the form of colony forming units will be recorded from plate counts. Representative isolation will be done based on variability in colony morphology. Well isolated colonies will be further characterized based on biochemical analysis.

c) Native ATP:

500ml of water sample was filtered through sterile GSWP 0.22 µm filter paper. Filter paper was boiled in tris buffer and supernatant collected and stored at -20˚C.

Analysis in laboratory: The samples will be analysed spectrophotometrically using luminometer

d) Native DNA:

Water sample (2.0 L) was filtered through sterile 0.22 µm filter paper. Filter paper was stored in vials at -85˚C.

Analysis in laboratory: DNA from filter paper will be extracted using extraction buffer and purified by agarose gel electophoresis. Purity and quantity of DNA will be estimated using NanoDrop. Purified DNA samples will be amplified by PCR and sequenced.

e) Metal immobilization studies:

5.0ml of water sample was dispensed in sterile tubes and spiked with metal. Tests were done at metal amendments of 10, 50, 100, 200, 300 and 400 µM. 5.0% triphenyl tetrazolium chloride (TTC) was added to each tube so as to obtain a final concentration of 0.025% TTC. Heat killed controls were also maintained. Initial metal concentration was estimated spectrophotometrically using BIO-RAD microplate reader. The samples were incubated in dark at 4˚C.

Analysis in laboratory: The rate of metal immobilized by bacteria will be determined by measuring the amount of residual metal. Respiration rate will be determined based on the amount of TTC reduced to formazan. Samples for both respiring activity and metal uptake will be analysed spectrophotometrically.

8.4.4 Benthic biology Description of benthic samples : One Brittle star under the phylum Echinodermata was recovered from rocks brought up by TV grab at station RVS-2/TVG-1. It was attached to a plant (unidentified). Variety of samples (slime moulds, coral fragments, sea plant ?) were found at station RVS-2/TVG-4. Some of the samples of this station include slime moulds and one appears to be sea anemone and others are yet to be identified. Samples were preserved with 5.0% formalin/absolute alcohol

Brachiopoda (species unidentified) recorded at stations RVS-2/TVG-4, RVS-2/TVG-7, and RVS-2/DR-9. Two varieties of coral fragment found at station RVS-2/TVG-1 and RVS-2/TVG-7.

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Twelve quadrants sediment was taken for macrofaunal analysis at station RVS-2/TVG-7. All quadrant samples were sieved through 300 µm sieve and preserved with 5.0% formalin mixed with rose Bengal. All samples were stored in polyethylene bags.

Analysis in laboratory: All sieved samples have to be sorted out and identified under the microscope up to the lowest possible taxonomic position. Unidentified crabs were caught by hand net and preserved with 5.0% formalin. Collection of Benthic samples is given in Table-7

9. PERFORMANCE OF SHIP AND EQUIPMENT USED

The team found the performance of the vessel is excellent in terms of average speed, maneuverability and scientific operations. We have got excellent support from Master, Officers and deck crew during our work. The database and system management are excellent. Computational and plotting facilities onboard are maintained well by the system manager.

10. CONCLUSION

The cruise onboard RV Sonne was essentially planned for the exploration of selected areas over Carlsberg Ridge and the Andaman back arc basin regions with high end tools such as deep-tow, TV-Grab and OFOS equipment. MAPRs hired from NOAA were used for the first time to detect hydrothermal plume signatures in the water column. With these tools valuable multi-parameter data and well located seabed samples have been acquired. A probable location for the occurrence of hydrothermal vent system has been delineated based on the plume signature. Further investigations are required to locate the origin/source of this hydrothermal plume.

11. RECOMMENDATIONS

High degree of accuracy and precision are required in the exploration for deep-sea hydrothermal fields that occur at a depth of 3000 to 4500 m water depth. It is required to position the vessel with respect to a feature on the seafloor for long duration of time to obtain well controlled samples and to get seafloor images using underwater camera systems. Usually it is required to tow the underwater instrument packages close to the seabed along a predetermined path to image and to sense the hydrothermal plumes using optical and chemical sensors. The deployment and recovery of Deep-tow and ROV systems requires highly skilled technicians, deck crew and navigation officers. Dedicated teams are required to achieve the desired levels of expertise. It is therefore recommended that research vessels with proven experience in the planned field of exploration may be chartered. RV Sonne cruise has been successful since it has efficient team to man the vessel and also to operate the scientific equipment. Further it is desirable to develop capabilities in handling deep-tow and ROV systems, as these will be commonly used in future deep-sea exploration.

12. ACKNOWLEDGEMENTS

Master, RV Sonne, and his team of Officers and Engineers are thanked for extending their support and co-operation during the cruise. Dr. S.R. Shetye, Director, N.I.O., Goa is thanked for encouragement and constant support. Dr. V.P. Dimri, Director, NGRI, Hyderabad is thanked for NGRI participation and encouragement. We thank Ship Cell and PME of NIO for their support and help at various stages of charter of the research vessel. This work has been carried out under the CSIR Network Program on Ridges. We thank CSIR, New Delhi for the funding support and encouragement.

14

ANNEXURE I Table - 1 RV-Sonne Dredge Locations a) Carlsberg Ridge

Location Sr. No.

Station No. Latitude (N) Longitude (E)

Depth (m)

Sample recovery

1 CR/DR-1 05012.664’ 61058.144’ 3322 Three pieces of basalt 2 CR/DR-2 05008.401’ 62000.281’ 3028 Two rock pieces 3 CR/DR-3 04050.472’ 62012.397’ 3490 No sample 4 CR/DR-4 04041.459’ 62016.040’ 3365 Two pieces of basalt 5 CR/DR-5 04026.314’ 62030.467’ 3215 One large basalt boulder 6 CR/DR-6 04000.036’ 63015.832’ 2907 No sample 7 CR/DR-7 03000.669’ 65009.284’ 2750 ~80-90 kg rocks. 8 CR/DR-8 03008.824’ 64049.311 3067 ~40 kg rocks 9 CR/DR-9 03044.132’ 64002.912’ 3532 Granulated basalt pieces.

b) Andaman Back Arc Basin

Location Sr. No.

Station No. Latitude (N) Longitude(E)

Depth (m)

Sample recovery

10 DR-10 09 19.961’ 94 20.477’ 2917 Few grams of sediment along with few pieces of rocks came in the net and on the dredge head.

Table - 2

RV-Sonne Gravity-Core and Spade-Core Locations a) Gravity Core locations in Andaman

Location Sr. No.


Depth (m)

Sample recovery

1 GC – 1 12 15.000’ 91 33.717’ 3218 0.65 m long core recovered 2 GC – 2 06 56.534’ 92 23.220’ 4252 2.36 m long core recovered 3 GC – 3 07 42.501’ 93 58.001’ 2301 5.44 m long core recovered 4 GC – 4 10 55.007’ 94 45.003’ 3618 3.80 m long core recovered

b) Spade-Core Location in Andaman

Location Sr. No.


Depth (m)

Sample recovery

1 SPC – 1 10 56.010’ 94 44.997’ 3553 26 cm long core recovered

15

Table - 3 RV-Sonne TV-Grab Locations a) Carlsberg Ridge

Sr. No

Station No.

Duration ( Date & Time) UTC

Start Location

End Location

Depth (m)

Sample recovery

1. TVG-1 24/10/2007; 1710 to 24/10/2007; 2019

05051.932’ 610 11.203

050 52.391’ 61011.695’

3628 - 3676

One larger pillow

2. TVG-2 25/10/2007; 0429 to 25/10/2007;0920

050 26.513’ 610 26.524’

050 27.071 61026.193’

1643 - 1486

No sample

3. TVG-3 25/10/2007; 0934 to 25/10/2007;1210

05026.452’ 610 26.578’

050 26.684’ 61026.459’

1834 - 1656

Few pieces of basalts

4. TVG-4 03/11/2007; 2241 to 04/11/2007; 0200

03058.505’ 630 01.000

030 58.556’ 63001.041’

3558-3365

Variety of basalts (~100kg)

5. TVG-5 11/11/2007; 0955 to 11/11/2007; 1458

030 40.291’ 630 44.794’

030 39.749’ 630 45.032’

3339 - 3413

Communication failure

6. TVG-6 12/11/2007; 1715 to 12/11/2007; 2316

030 40.325’ 630 45.156’

030 39.821’ 630 45.026’

3565 - 3436

Grab did not close.

7. TVG-7 13/11/2007; 0038 to 13/11/2007; 0414

030 39.649’ 630 44.474’

030 40.144’ 630 44.907’

3669 - 3417

Grab came full of sediments and rocks.

8. TVG-8 13/11/2007; 0652 to 13/11/2007; 1151

030 40.356’ 630 44.958’

030 40.009’ 630 44.779’

3589 - 3529

B/W camera not worked. Grab up without closing.

b) Andaman

Sr. No

Station No.

Duration (Date & Time) UTC

Start Location

End Location

Depth (m)

Sample recovery

1 TVG –9 25/11/2007; 2146 to 25/11/20072255

07 55.924’ 94 03.139’

07 56.036 94 03.026

671 – 517

Different types of rocks have been recovered.

2 TVG –10 26/11/2007; 0004 to 26/11/2007; 0037

07 56.330’ 94 02.638

07 56.255’ 94 02.693’

494 – 373

Mostly rhyolite in various alteration conditions.

3 TVG – 11 27/11/2007; 0417 to27/11/2007; 0520

09 59.500’ 93 57.137’

09 59.526’ 93 57.260’

1424 – 1299

Mostly volcanic breccia with rhyolitic cement and ultramafic (?) clasts or xenoliths.

4 TVG – 12 27/11/2007; 0726 to27/11/2007; 0800

10 00.243’ 94 00.784

10.00.255’ 94 00.813’

1372 – 1299

Few rock pieces of samples which have ~4 mm thick coating of Fe-Mn oxide.

5 TVG – 13 30/11/2007; 0610 to30/11/2007; 0910

10 27.200’ 94 09.500’

10 27.590’ 94 09.590’

2917 – 2876

Only brown and dull cream coloured sediment recovered.

6 TVG – 14 30/11/2007; 1217 To 30/11/2007;1335

10 33.599’ 93 51.978’

10 33.646’ 93 52.149’

1814 – 1767

Grab came full of dull whitish coloured light density pumice along with sediments.

16

Table - 4 RV-Sonne OFOS Locations a) Carlsberg Ridge

Sr. No

Station Duration Date &time UTC

Start Location

End Location

Depth (m)

Remarks

1 OFOS – 1 29/10/2007; 2100 to 30/10/2007;0816

050 13.647’610 58.616’

050 14.304’ 610 58.592’

3513 - 3548

No. Photos:440 DVD files: 7

2 OFOS – 2 06/11/2007; 1108 hr to 06/11/2007; 1447 hr

030 47.932’630 37.594’

030 47.758’ 630 37.739’

3272 - 3291

Poor quality of pictures.

3 OFOS – 3 06/11/2007; 1624hr to 07/11/2007; 0326 hr

030 47.786’630 37.736’

030 45.057’ 630 37.265’

3288 - 4236

No. of Photos: 280 No. of DVD files: 7 Noise on the TV at 0246 hr 07/11/2007.

4 OFOS – 4 11/11/2007; 1555 hr to 11/11/2007; 2050hr

030 39.965’630 45.839

030 40.010’ 630 45.823’

3103 - 3094

Operation abandoned after camera failed twice. Second time deployed without still camera.

5 OFOS – 5 12/11/2007; 1429 hr to 12/11/2007;15.40 hr

030 40.294’630 45.094’

030 40.342’ 630 45.110’

2810 - 3587

Operation abandoned. First B/W camera failed at 2500 and then 2800 color camera also failed.

b) Andaman

Sr. No

Station Date & time UTC

Start Location

End Location

Depth (m)

Remarks

1 OFOS -6 30/11/2007; 0047 hr to 30/11/2007; 0405 hr

10 24.915’ 94 07.599’

10 25.226’ 94 08.228’

3575 –3553

17

Table - 5 Details of the DEEP-TOW Tracks a) Carlsberg Ridge

Sr. No.

Deep Tow No.

Start Date/ Time (UTC)

Deep tow start location

(Latitude/ Longitude)

End Date/ Time (UTC)

Deep tow end location

(Latitude/ Longitude)

MAPR position

above the sea floor

Remarks

01.

DT01

23.10.07

09:33

5°36.846’N

61°36.458’E

24.10.07

10:52

6°05.653’N

60°54.118’E

M-081320m M-06 820m M-29 320m M-13 220m M-12 120m M-09 20m

MAPR started at 06:30hrs. Data recovered.

02.

DT02

25.10.07

16:35

5°21.967’N

61°35.789’E

26.10.07

03:30

5°14.268’N

61°58.872’E

M-081320m M-06 820m M-29 320m M-13 220m M-12 120m M-09 20m


03.

DT03

26.10.07

02:08

4°15.649’N

62°38.361’E

28.10.07

19:14

5°13.812’N

61°55.488’E

M-081320m M-06 820m M-29 320m M-13 220m M-12 120m M-09 20m

MAPR started at 00:10 hrs. M-29 did not respond. Other data recovered.

04.

DT04

01.11.07

08:56

3°44.126’N

63°57.989’E

03.11.07

10:56

4°31.99’N

62°55.73’E

M-06 720m M-13 520m M-08 320m M-29 220m M-12 120m M-09 20m

MAPR started at 08:20hrs. Battery leakage in M-06. Other data recovered.

05.

DT05

07.11.07

06:57

3°39.605’N

64°06.120’E

09.11.07

08:17

2°01.58’N

65°00.41’E

M-29 505m M-08 305m M-13 205m M-12 105m

M-09 5m

MAPR started at 06:30 hrs. M-09 lost its header information. Data not recovered.

06.

DT06

10.11.07

11:28

3°37.658’N

63°49.238’E

11.11.07

03:17

3°46.877’N

63°31.124’E

M-09 705m M-29 605m M-13 205m M-12 105m

M-08 5m

MAPR started at 11:00hrs. M-09 data not recovered.

07.

DT07

23.11.07

21:25

7°39.43’N

93°58.11’E

25.11.07

03:31

7°68.85’N

94°13.950’E

M-29 405m M-13 205m M-12 105m M-08 05m


18

Table - 5 (continued) b) Andaman

Sr. No.

Deep Tow No.

Start Date/ Time (UTC)

Deep tow

start location (Latitude/

Longitude)

End

Date/ Time (UTC)

Deep tow

end location (Latitude/

Longitude)

MAPR

position above the sea floor

Remarks

08.

DT08

26.11.07

17:45

10°08.00’N

94°10.00’E

27.11.07

02:30

9°99.48’N

94°01.74’E

M-13 170m M-12 70m M-08 20m

MAPR started at 17:40hrs. MAPRs were attached above the depressor. Data recovered.

09.

DT09

27.11.07

09:50

10°02.04’N

94°05.36’E

27.11.07

19:14

9°99.9’N

94°03.47’E

M-08 320m M-29 170m M-13 70m M-12 20m

MAPR started at 09:30 hrs. MAPRs were attached above the depressor. Data recovered.

10.

DT10

27.11.07

22:05

10°17.20’N

93°50.00’E

28.11.07

11:25

10°45.25’N

94°15.78’E

M-29 405m M-13 205m M-12 105m M-08 5m


11.

DT11

28.11.07

14:20

10°39.560’N

94°28.530’E

29.11.07

03:20

10°48.33’N

94°19.18’E

M-29 405m M-13 205m M-12 105m M-08 5m

MAPR started at 13:50 hrs. M-12 data not recovered.

19

Table - 6 CTD Hydrocasts summary

Sr. No.

CTD

Station No.

Date

CTD locations

Water Depth

(m)

MAPR

information No. Depth

Remarks

01.

Ref stn

21.10.07

5°33.000’N 61°38.000’E

3524

No

Completed successfully

02.

CTD 01

24.10.07

5°44.985’N 61°23.010’E

3746

M-29 10m

Completed successfully

03.

CTD 02

26.10.07

5°15.946’N 61°49.511’E

3873

M-08 10m M-29 30m

Deployed twice due to communication failure.

04.

CTD 02

26.10.07

5°16.065’N 61°49.482’E

3766

M-08 10m M-29 30m

Stn abondoned for the day after thrird attempts.

05.

CTD 03

29.10.07

5°14.617’N 61°57.989’E

3488

No

CTD tested till 3450m, bottles were fired and water samples were collected.

06.

CTD 03a

29.10.07

5°14.619’N 61°58.012’E

3523

M-06 10m M-13 30m

MAPR data recovered

07.

CTD 04

31.10.07

4°39.558’N 62°18.039’E

3487

M-06 10m M-08 20m

19 bottles fired at the bottom itself, problem found with software

08.

CTD04/2

31.10.07

4°35.075’N 62°24.301’E

3565

M-08 10m M-13 20m

MAPR data recovered

09.

CTD 05

03.11.07

3°58.507’N 63°00.997’E

3527

M-08 10m M-13 20m

Completed successfully MAPR data recovered

10.

CTD 06

04.11.07

3°45.233’N 63°37.255’E

4240

M-08 10m M-13 20m


11.

CTD 07

04.11.07

3°43.007’N 63°35.508’E

3849

M-08 10m M-13 20m


12. CTD 08 04.11.07 3°47.000’N 63°38.500’E

3954 M-08 10m M-13 20m


13. CTD 09 05.11.07 3°47.000’N 63°38.50’E

4192 M-08 10m M-13 20m


14.

CTD 10

05.11.07

3°46.553’N 63°37.066’E

3976

M-08 10m M-13 20m

Communication failed at 150m, CTD brought back to deck and turbidity sensor was changed. Again deployed successfully. MAPR data recovered

15.

CTD 11

05.11.07

3°46.236’N 63°37.227’E

4131

M-08 10m M-13 20m

CTD towed on a circular path at depth of 3300 m. MAPR data recovered

16. CTD 12 09.11.07 3°02.493’N 65°00.562’E

3322 M-08 10m M-13 20m


20

Table – 6 (continued)

17.

CTD 13

10.11.07

3°30.647’N 64°18.707’E

3793

M-08 10m M-13 20m


18.

CTD 14

11.11.07

3°41.500’N 63°39.400’E

3398

M-08 10m M-13 20m


19.

CTD 15

11.11.07

3°39.000’N 63°44.800’E

3606

M-08 10m M-13 20m


20.

CTD 16

11.11.07

3°40.007’N 63°45.597’E

3292

M-08 10m M-13 20m


21.

CTD 17

12.11.07

3°40.000’N 63°44.800’E

3553

M-08 10m M-13 20m


Table - 7 Collection of Benthic Samples TV-grab/ dredge

Start Location End Location

Depth (m)

Sample recovery

TVG-1 05051.932’N 610 11.203É

050 52.391’N 61011.695’E

3628 - 3676

One large Brittle star attached to a plant and few coral parts were obtained.

TVG-4 03058.505’N 630 01.000E

030 58.556’N 63001.041’E

3558-3365

Variety of organisms were attached to the rocks.

TVG-7 030 39.649’N 630 44.474’E

030 40.144’N 630 44.907’E

3669 - 3417

One Brachipoda, one coral and plant body were recovered attached to rocks. 12 quadrant of sediment taken for macrofaunal analysis.

Dredge Latitude (N) Longitude (E) Depth DR-9 03044.132’N

64002.912’E 3532 Two Brachiopoda and an unidentified plant

were recovered from the rocks.

03044.747’N

63036.358’E 3857 Four crabs caught by hand net.

21

ANNEXURE II

(a)

(b)

Fig. 3 (a) Fish and Depressor of IMI-30 on board RV SONNE (b) Fish being lowered

22

(a)

(b)

Fig. 4 (a) OFOS onboard RV SONNE (b) OFOS back to deck

23

(b) OFOS back to deck

(a)

(b)

Fig. 5 (a) TV Grab onboard RV SONNE (b) Lowering of TV Grab

24

(a)

(b)

Fig. 6 (a) MAPR (b) MAPR coming out of water

25

26

26

Fig. 7 CTD locations in Carlsberg Region

27

Fig. 8 Geological Sampling locations in Carlsberg Region

27

Fig. 9 Sampling and CTD locations in Andaman

28

29

Fig. 10 Deep-tow track in Carlsberg region

29

30

Fig. 11 EM120 & Deep-tow side-scan image over a segment - Carlsberg Ridge

30

carlsberg ridge & andaman sea...carlsberg ridge (cr), a part of the central indian ridge and the...

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