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«Reports can be ordered from: Monika Bachur Forschungszentrum Ozeanränder, RCOM Universität Bremen Postfach 330 440 D 28334 BREMEN Phone: (49) 421 ...»

-- [ Page 1 ] --

The "Berichte aus dem Fachbereich Geowissenschaften" are produced at irregular intervals by the Department

of Geosciences, Bremen University.

They serve for the publication of experimental works, Ph.D.-theses and scientific contributions made by

members of the department.

Reports can be ordered from:

Monika Bachur

Forschungszentrum Ozeanränder, RCOM

Universität Bremen

Postfach 330 440

D 28334 BREMEN

Phone: (49) 421 218-65516

Fax: (49) 421 218-65515 e-mail: MBachur@uni-bremen.de http://elib3.suub.uni-bremen.de/publications/diss/html

Citation:

Bohrmann, G., and cruise participants Report and preliminary results of R/V Meteor Cruise M74/3, Fujairah – Male, 30 October - 28 November, 2007.

Cold Seeps of the Makran Subduction Zone (Continental Margin of Pakistan).

Berichte, Fachbereich Geowissenschaften, Universität Bremen, No. 266, 161 pages. Bremen, 2008.

ISSN 0931-0800 R/V METEOR Cruise Report M74/3 Cold Seeps of the Makran Subduction Zone (Continental Margin of Pakistan) M74, Leg 3 Fujairah – Male 30 October – 28 November, 2007 Cruise within the framework of the DFG financed Research Center Ocean Margins, project area E: "Fluid and gas seepage at ocean margins" Edited by Gerhard Bohrmann and Greta Ohling with contributions of cruise participants The cruise was performed by MARUM Center for Marine Environmental Sciences R/V METEOR Cruise Report M74/3 Table of contents Preface 1 Personnel aboard R/V METEOR M74/3 3 List of Participants and Institutions 4 1 Introduction 6

1.1 Geology of Makran Accretionary Wedge 6

1.2 Objectives 10 2 Cruise Narrative 12 3 Multibeam Swathmapping 18 4 Subbottom Profiling and Flare Imaging 22 5 TV-sled Investigations 25 6 Remotely Operated Vehicle (ROV) QUEST 32

6.1 Technical Description and System Performance 32

6.2 Dive Observations and Protocols 36

6.3 Bubblemeter

–  –  –

Preface R/V METEOR Cruise M74/3 investigated fluid venting at the sea floor along the Makran subduction zone (Continental slope of Pakistan). The expedition was strongly related to the previous cruise of METEOR M74/2, during which geophysical investigations on fluid seepage were conducted in the same area. Both cruises were planned together as part of research area E of the DFG Research Center Ocean Margins at the University of Bremen (RCOM). Fluid and gas seepage (cold seeps) at the sea floor is of global importance and leads to a major material exchange between sediments of the ocean, the hydrosphere and/or the atmosphere.

Scientists from RCOM are currently working on various types of cold seeps to understand the mechanisms of fluid and gas exchange as well as to measure and estimate the amount of sea floor emissions and to learn about the influence of emissions to the environment.

–  –  –

RCOM scientists had been limited so far to the study of the cold seeps at passive margin sites in the Gulf of Mexico, in the Mediterranean and the Niger deep sea fan. During this cruise research activities for the first time took place at an active margin where fluid and gas circulation by dewatering of sediments is characterized by the compression tectonic regime of the plate convergence. Thus in the investigation area the Arabic plate, and/or a micro plate is pushing against the continental slope of Pakistan, whereby very thick sediments in the collision zone are squeezed and should produce an intensive fluid and gas circulation within the accretionary wedge. R/V Meteor Cruise M74/3 brought together interdisciplinary groups from RCOM Research Areas B and E.

Fig. 2: Research vessel METEOR in the northern Indian Ocean (left). Preparation of ROV QUEST on the working deck; in the heat of the day parts of the ROV have been protected from direct sun light (right).

The cruise and the research programs were planned, coordinated and carried out by the Department of Earth Sciences and the MARUM Center for Marine Environmental Sciences of the University of Bremen. The National Institute of Oceanography of Pakistan NIO and the Office of Hydrographer of Pakistan Navy HPN helped in preparing the cruise and are involved in the scientific analyses and interpretation of the data.

Fig. 3: Important equipment for work within the oxygen minimum zone of the Arabic sea. Water sampling by hydro casts (left); fast treatment in the sediment laboratory is needed because of the rapid hydrate decomposition (right).

R/V METEOR Cruise Report M74/3 Preface

The German Embassy in Islamabad and the Ministry of Foreign Affairs in Berlin helped in obtaining the permission necessary to work within the EEZ of Pakistan. Thanks to all of them.

The cruise was financed in Germany by the German Research Foundation (DFG). The shipping operator (Reederei F. Laeisz GmbH, Bremerhaven) provided technical support on the vessel in order to accommodate the large variety of technical challenges required for the complex sea-going operations. We would like to especially acknowledge the master of the vessel, Walter Baschek, and his crew for the continued contribution to a pleasant and professional atmosphere aboard R/V METEOR.

Personnel aboard R/V METEOR M74/3 Table 1: Scientific crew.

–  –  –





Participating Institutions AWI Alfred-Wegener-Institut für Polar- und Meeresforschung, 27570 Bremerhaven, Germany DWD Deutscher Wetterdienst, Geschäftsfeld Seeschifffahrt, Bernhard-Nocht-Straße 76, 20359 Hamburg, Germany GeoB Fachbereich Geowissenschaften, University of Bremen, Klagenfurter Str., 28359 Bremen, Germany HBHV Hochschule Bremerhaven, An der Karlstadt 8, 27568 Bremerhaven, Germany MPI Max-Planck Institut für Marine Mikrobiologie, Celsiusstr. 1, 28359 Bremen, Germany HPN Office of Hydrographer of Pakistan Navy II, Liaquat Barracks, Karachi, Pakistan NIO National Institute of Oceanography, St 47, Block 1, Clifton, Karachi-75600, Pakistan NOC National Oceanographic Centre, University of Southampton, Waterfront Campus, European Way, Southampton SO14 3ZH, UK RCOM DFG-Forschungszentrum Ozeanränder University of Bremen, P.O.Box 30440, 28334 Bremen, Germany Fig. 4: Scientists, technicians, and guests sailed during R/V METEOR Cruise M74/3.

–  –  –

The accretionary wedge of the Makran subduction zone is one of the largest on earth and is forming at the plate boundary between the Eurasian Plate in the north to the Arabian Plate in the south. The Arabian plate is subducting at an angle of 2o and with a rate of 3-5 cm/a towards north under the Eurasian Plate. This subducting process is ongoing and active at least since Cretaceous times (DeJong, 1982). The Makran accretionary wedge developed throughout the Cenozoic period and its sequence was mainly influenced by Himalayan turbidites (Harms et al., 1984). Terrestrial sediment input created a sediment of thickness 7 km above the oceanic basement (White 1982).

Fig. 5: Plate tectonic setting of the Arabian sea (from Kopp et al. 2000). Compared to surrounding plate boundaries, the Makran subduction is characterised by sparse earthquake activity (black dots).

MF = Minab Fault system, MR = Murray Ridge, BVA = Baluchistan volcanic arc, ONF = Ornach-Nal Fault, OFZ = Owen Fracture Zone, CR = Carlsberg Ridge, rectangle = research area.

The extension of the total Makran accretionary wedge is approximately 800 km from east to west (Pakistan-Iran). Its southern offshore boundary is approximately 150 km where it reaches at the maximum depth 3200 m below sea level and it extends heights of 1500 m above sea level in the north approximately 500 km north of its deformation front. In the south and southwest the Oman abyssal plain is bounded by the Murray Ridge, which separates the Arabian and the Indian Plates (Fig. 5). To the east, the abyssal plain narrows due to

R/V METEOR Cruise Report M74/3 Introduction

convergence of the Murray Ridge and the Makran accretionary wedge and disappears at about 65o30’E (Fig. 5).

Fig. 6: Plate boundaries in the area of the Arabian-Indian-Eurasian convergence zone (from Kukowski et al. 2000). Direction of convergence is shown by arrows as well as the area (dark-shaded box) of swath mapping during Cruise SO-123.

Fig. 7: Section of Multi-channel seismic profile SO 122-04A (from von Rad et al. 2000). Record covering First and Nascent Ridges (left). Interpretation of a larger part of the section (right).

Offshore, the Makran accretionary wedge consists of a number of ridges with long, narrow in parallel sequences, orientated from east to west. It can be divided into three sections: the upper slope, the mid-slope terrace and the lower slope. The upper slope is shallow, narrow and less steep than the lower slope (Pratson and Haxby, 1996), the accreted wedges continue in further north 400-500 km across the Iran and Pakistan. The deformation front of the Makran accretionary prism lies approximately 150 km south from the coast (Kukowski et al., 2000). Two major seasonal rivers (Shadi and Hingol) transport sediments onto the continental slope and turbidity currents form deep erosive canyons “Shadi and Save” (Underwood 1991, Gnibidenko and Sarichevskaya, 1983).

–  –  –

Fig. 8: Map taken from von Rad et al. (2000) showing main features of seepage recovered during SO 122/130 cruises.

The Northern Arabian Sea is the highest biological productive area in the world especially during the summer monsoon. High oxygen consumption due to organic matter degradation results in a stable and mid-water oxygen minimum zone (OMZ) between about 150-1100 m water depths in the Arabian Sea (Wyrtki, 1973). Productivity derived organic matter and terrestrial organic rich mud input lead to lamination of the ocean floor deposits. The sedimentation rate of the slope sediments is extremely high up to 0.2-1 mm/a (von Rad et al., 2000) because of rapid tectonic uplift, the narrow shelf, and the effective erosion of the hinterland because of the lack of extensive vegetation. The burial of organic matter in the sediments, particularly on continental margins also provides a unique palaeoenvironmental record as well as the main potential source for fossil fuels (Berner, 1989).

During bathymetry surveys of several cruises with the German research vessel SONNE in 1997 and 1998 (SO-122, SO-123, SO-124 and SO-130), gas seepage from shallow ridges near the OMZ were documented (von Rad et al., 2000). Associated to those seep sites a number of white microbial mats composed of large sulphur oxidizing bacteria (such as Beggiatoa and Thioploca) were found. Furthermore in a deeply incised submarine canyon at 2100-2500 m water depth seeps of methane and H2S-rich fluids were found (von Rad et al. 2000). The fluid flux was explained by the tectonic stress within the zone of convergence. The occurrence of gas hydrates was shown by the presence of a well pronounced bottom-simulating seismic reflector (BSR) documented in most of the seismic profiles (Figs. 7 and 9). Driven by the dynamic of the accretionary wedge the landward part of the gas hydrate-bearing sediments are being progressively uplifted which should lead to progressively decomposition of gas hydrates since they move out of their stability field. At least enhanced seepage at sea floor above 800 m water depth was explained by this process (Fig. 9).

–  –  –

Fig. 9: Schematic cross section of the Makran accretionary margin summarizing seep related features in relation to the tectonic situation and the location of the oxygen minimum zone (from von Rad et al.

2000).



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