The Sonne Cruise SO122 was carried out by the Federal Institute for Geosciences and Natural Resources (BGR, Hannover) from 3rd August to 9th September 1997, in cooperation with GEOMAR (Kiel), the National Institute of Oceanography (NIO, Karachi) and the Hydrocarbon Development Institute of Pakistan (HDIP). During the joint project with R/V SONNE the Makran accretionary wedge off Pakistan should have been investigated in detail with multi-channel reflection seismics, magnetics and gravimetry. Intense fishery offshore Pakistan forced a change of the area of investigation to the south with the following objectives: investigation of the crustal structure and occurrence of the bottom simulating reflector (BSR) in the Makran accretionary wedge; investigation of the structure of the Murray Ridge System in order to reconstruct the geodynamic evolution of the eastern Indian Plate margin; determination of the origin of the crust underlying the Indus Fan and reconnaissance of the sedimentary history of the Indus Fan in order to reveal the uplift and erosion history of the Himalayas.

The multidisciplinary marine geoscientific expedition ARK-25/3 was focused on the Greenland part of northern Baffin Bay and was aimed to acquire new geoscientific data to be used for modelling the evolution of the Greenland continental margin and its hydrocarbon prospective. The data format is Society of Exploration Geophysicists SEG Y. The cruise was performed under the direction of the Federal Institute for Geosciences and Natural Resources Hannover in cooperation with the Alfred-Wegener-Institute for Polar and Marine Research, Bremerhaven. Using 70 days of ship time onboard the research icebreaker R/V POLARSTERN a comprehensive data set was acquired along profiles extending from the deep oceanic basin in the central part of North Baffin Bay onto the Greenland continental margin in an area which was bordered by the Kane Basin in the North and Disko Island in the South. By means of multi-channel seismic, wide angle seismic, gravimetric and magnetic methods the structural inventory of the crust in the NW Baffin Bay was investigated. Additionally, heat flow data and sediment cores were collected along lines crossing the Greenland continental margin. The cores were extracted for geochemical and geomicrobiological analysis to be used for basin modelling, studying the hydrocarbon potential, and the hydrocarbon degradation by microorganisms under polar conditions. Geological sampling in the coastal area was done between Melville Bay and Washington Land. The collected rock material will be used to derive constraints on the erosion history of the coastal area. Aeromagnetic data was acquired covering a substantial part of the marine survey area to investigate magnetic signatures of the oceanic crust and the continental margin. This report summarizes the working programme and contains the documentation of acquired data and first results of the expedition.

In September 1993, the Federal Institute for Geoscience and Natural Resources (BGR) has carried out in cooperation with Sevmorneftegeofizika (SMNG), Murmansk a 2D-seismic survey of the eastern part of the Laptev Sea shelf. The data format is Society of Exploration Geophysicists SEG Y. During the survey with a total length of 3189 km the 70 km wide New Siberian Basin and two other basins were mapped. In the central part of the New Siberian Basin, a Tertiary sediment thickness of more than 4 km overlying older sediments was observed. Further to the east, a large area covered by lava flows of unknown thickness was investigated. There are no indications of a propagation of real seafloor spreading into the Laptev Shelf and thus the Asian continental crust. Therefore seafloor spreading seems impossible at total spreading rates below 0.7 cm/year, at least for crust of the character which is present here.

The cruise leg MSM09/3 was conducted as a cooperative project between the Alfred Wegener Institute for Polar and Marine Research (AWI), the Federal Institute for Geosciences and Resources (BGR), the Geological Survey of Denmark and Greenland (GEUS) and Dalhousie University. The data format is Society of Exploration Geophysicists SEG Y. A geophysical survey covered areas of Baffin Bay and Davis Strait between Greenland and the Canadian Baffin Island. A component of the IPY 2007/08 Lead Project Plate Tectonics and Polar Gateways in the Earth System (PLATES & GATES), this project DAVIS GATE is aimed to develop a tectonic and sedimentary reconstruction of the opening process of this oceanic gateway. Baffin Bay and Davis Strait play an important role in the shallow water exchange from the Arctic to the Atlantic Ocean. The plate-tectonic evolution as well as the magmatic history of this region has been sparsely known and required a careful geophysical investigation in order to construct a set of gridded detailed paleotopographic maps for a complete geodynamic reconstruction of this gateway. With a set of three seismic refraction/wide-angle reflection profiles, using ocean-bottom seismometers on 62 stations, as well as multi-channel reflection seismic recordings with a 3000-m long streamer, data were acquired from the sedimentary cover to the deep crust and even from parts of the uppermost mantle. Additional seismic data supplement these profiles and provide insights into the structures of the basement and dominant fault zones such as the Ungava fault system. A parallel running magnetic survey aimed to resolve the temporal evolution of the oceanic crust of Baffin Bay. The extension and subsidence of the continental and transitional crust in the Davis Strait and the evolution of oceanic crust in the Labrador Sea and Baffin Bay could be investigated with dataset to which continuously recorded gravity anomaly data and sub-bottom profiler data also contribute. This dataset provides the basis of geometrical and physical properties of the crust required for a realistic geodynamic model which will describe the break-up and the ocean basin evolution between Greenland and Canada in terms of detailed paleo-topography.

The structure and tectonics of the Pacific margin of Costa Rica were studied by multichannel seismic measurements in parallel with gravity measurements and swathmapping from the Cocos Ridge to Nicoya Peninsula during R/V SONNE cruise SO81 legs 1 and 2 from 18th August to 15th September 1992. In addition geological sampling has been carried out. Dominant structural feature is the buried Costa Rica Terrrane (CRT), a complex and segmented, wedge-shaped unit characterized by relative high seismic velocities of 4 km/s. The thickness of this several tens of kilometres wide zone varies between 0.5 and 3 s (twt). The CRT forms the backstop against which the sediments of the subducting Cocos plate accrete resulting in accumulation of sedimentary mass beneath and in front of the CRT, as well as in simultaneous uplift and fracturing of the CRT. It appears that the distinct CRT is affected locally by raft tectonics, i.e. a form of thin-skinned extension by normal faulting from gravity sliding over a non-stretched oceanic crust. A unit is recognizable between the base of the CRT and the surface of the subducting oceanic crust on most of the seismic lines. This unit is thought to consist mostly of ductile pelagic to hemipelagic shales. Some segment boundaries of the CRT are associated with morphological furrows, 5 to 10 km wide and up to 30 km long running across the slope. We feel that the data acquired during SONNE cruise SO81, and the preliminary results at hand have already improved our knowledge on the geological processes of active continental margins. We are convinced that plausible concepts for the origin of tsunamis and asperities can be developed on the basis of the data collected during SONNE cruises SO81 and SO76. The research of both SONNE cruises are a contribution to the International Decade of Natural Desaster Reduction (IPNDR).

In July/August 1988 a seismic reconnaisance survey was carried out with F.S. Polarstern on the perennially ice covered East Greenland shelf between latitudes 73°N and 81°N. The data format is Society of Exploration Geophysicists SEG Y. 14 reflection seismic lines with a total length of 2.016 km and 12 sonobuoy refraction profiles were recorded. The following results were obtained: •On the wide Holm Land shelf province north of 79°N three possible Cretaceous rift basins were observed. •A buildup of layered extrusive basaltic rocks forming a wedge of seaward dipping reflectors underlies the Holm Land continental slope. •On the Northeastern Greenland shelf province the existence of a wide sedimentary basin was demonstrated north of 76°N. •South of 76°N four volcanic structures from the continent to ocean were observed: The zone of Early Tertiary plateau basalts (zone I) that occur landward of an escarpment, a flat lying basaltic flow unit immediately seaward of the escarpment (zone II), an elongate wedge of seaward dipping reflectors (zone IIIa), a basaltic flow unit which in places shows seaward dipping beds of short length (zone IIIb), and the oceanic crust. •Dyke swarms and intrusions of inferred Neogene age were recognized at several locations.

The major pre-alpine tectonic lineaments as the Glückstadt Graben and the Avalonia-Baltica suture zone run across the southern Baltic. The BalTec expedition aimed at the gapless imaging of these fault systems from the seafloor down to the Paleozoic basement. Scientifically the expedition was motivated by two hypotheses. We postulated that advances and retreats of icesheets during the glacials initiated and reactivated faulting of the Post-Permian succession, thereby generating several kilometers long near-vertical faults and anticlines. We further postulated that – in contrast to the generally accepted text book models – deformation of the initially up to 1800 m thick Zechstein salt started already during salt deposition as the consequence of salt load induced basin subsidence and resulting salt creep. The profile network was further designed to allow for linking the stratigraphy between previously generated local underground models in the frame of the TUNB project. Altogether we collected during cruise MSM52 onboard of R/V Maria S. Merian 62 reflection seismic profiles of an entire length of 3500 km. This data set contains all seismic lines located in the German EEZ (lines BGR16-212 to BGR16-264) as time-migrated version.

During the cruise with S.V. EXPLORA within the Ross Sea on the second marine-geophysical expedition of the Federal Institute for Geosciences and Natural Resources (BGR) to Antarctica, in total 6,745 km of magnetic, gravity and digital reflection seismic lines and additionally 1,400 km gravity lines were acquired in the period from January 10th to March 2nd 1980. On 43 stations sonobuoy refraction measurements have been carried out. The main results are: (1) In the eastern part of the Ross Sea Shelf two striking discontinuities have been identified in the reflection seismics representing gaps in the sediments at the turn-over of the Upper Miocene to the Pliocene (ca. 7 mio years B.P.) and between the Middle and Upper Miocene (ca. 11.5 mio. years B.P.) according to results of DSDP boreholes. (2) In the southern part of the Ross Sea Shelf the basement is uncovered at depths over 700m due to a thrust of the shelf ice recently. (3) A structural unit extends alongside the meridian of 180° separating the Ross Sea into two different geologic regions. This unit is characterised by two basement highs with seismic velocities exceeding 5 km/sec. (4) In relation with the GANOVEX expedition two profiles have been measured off northern Victoria Land which indicate two large faults with a faulting amount of 2 km. Another area is characterised by intrusive and volcanic bodies.

On the M/V Akademic Nemchinow multichannel seismic measurements were carried out on 34 lines with a total length of 4,000 km. The area covered was the Laptev Sea. The data format is Society of Exploration Geophysicists SEG Y.

Main target of the project GIGICS (Cooperative German-Indonesian Geoscientific Investigations in the Celebes Sea) is the investigation of the internal crustal structure and the plate tectonic evolution of the Celebes Sea and its active continental margins off Mindanao and Northern Sulawesi. These investigations were carried out during the cruise SO98 of RV SONNE by the Federal Institute for Geosciences and Natural Resources (BGR), Hannover; the German Research Centre for Geosciences (GFZ), Potsdam; the GEOMAR, Kiel; the Institute of Oceanography (IfM), Hamburg; the Mines and Geoscience Bureau, Manila; the Agency for the Assessment and Application of Technology, Jakarta, and the Institute of Oceanography, Wormley. The cruise SO98 consisted of three legs of two weeks duration and one leg of four weeks duration. The total amount of data acquired during the cruise were: - 3,300 km of multichannel reflection seismics, - over 6,800 km of gravimetric and magnetic data and approximately 10.000 km of swath bathymetric and sediment echosounder data, - 3 wideangle-/refractionseismic profiles, each of 120 - 150 km length, - geological, geochemical sampling and oceanographical measurements at a total of 37 stations. During the cruise SO98 a widespaced but regular grid of magnetic and gravimetric profiles were acquired in the eastern part of the Celebes Sea from which up to then reliable data were very sparse. WEISSEL (1980) recognized in the western Celebes Sea WSW-ENE striking magnetic lineations, which he interpreted as chrons 18 - 20 (39 - 43 Ma according to the timescale of HARLAND et al. (1990)). The data from cruise SO98 show that there is no continuation of these anomalies to the east. In the eastern part the magnetic field of the Celebes Sea is less clear and much more disturbed. Nevertheless, E-W-striking anomalies are recognizable. Because amplitudes of local magnetic anomalies are higher than the lineations, the correlation of these lineations with the magnetic reversal scale is still somewhat ambiguous. The gravity map compiled from the measured gravimetric data shows elongated positive anomalies in the eastern part of the Celebes Sea. Exceptions occur at the deep sea trenches off North Sulawesi (North Sulawesi Trench) and Mindanao (Cotabatu Trench) and at the Sulu Archipelago where strong negative gravity anomalies were found. A remarkable NW-striking gravity high of up to 60 mgal was found in the central eastern part of the Celebes Sea. Gravimetric modelling suggests that this high can be correlated with the gravimetric effect of the Molucca Sea Plate subducting from the east under the Sangihe Arc. The reflection seismic data from the northern part of the Celebes Sea show indications for a juvenile subduction of oceanic Celebes Sea crust under the Sulu Archipelago. The oceanic crust bends down towards the Sulu Arc with angles between 2° and 5° and the sedimentary sequence above is deformed indicating a compressional stress regime. With the exception of two linear arranged seamount-like basement highs the Celebes Sea is dominated by two different oceanic crustal types showing distinct differences in the topography. The first one is showing a very similar reflection seismic pattern as it is found for oceanic crust of the Atlantic (HINZ et al., 1994). This type is characterized by a small-scale block-faulted relief of the top basement and a low reflectivity in lower crustal levels typically related as to be accreted at slow to intermediate spreading ridges. This type is found in the western, northern and southern part of the investigated area. In the eastern and especially in the southeastern part the igneous crust shows a very different image. The reflection of the top of the basement is less distinct and of lower frequency. The relief is very much smoother than in the previous type. This reflection seismic image indicates a volcanic/magmatic overprinting of the oceanic crust in this part of the Celebes Sea. Another target of cruise SO98 was the area of the active continental margin off North Sulawesi and its accretionary complex. The internal structure of the accretionary complex should be investigated to decide whether this active margin is also of the 'splinter-type' or not. During former geophysical cruises with RV SONNE oceanic crustal splinters were discovered in the accretionary wedges of the Sulu Sea and off Costa Rica (e.g. HINZ et al., 1991). From our reflection seismic measurements this active continental margin is morphologically subdivided into three units and consists of two accretionary complexes of different internal structural style: the lower and middle continental slope is underlain by an intensively thrusted, sedimentary accretionary wedge. This wedge was most probably formed during the last 5 Ma. Landward of this wedge an older and seismically very complex accretionary unit is present which is overlain at its landward termination by a sedimentary fore-arc basin. Within this older accretionary complex, units with a strong, low frequency reflection pattern were found which are interpreted to represent crustal splinters of igneous oceanic or ophiolitic nature. This interpretation is supported by our gravity and magnetic data. The magnetic profiles show an increase of the magnetic field towards the north arm of Sulawesi across the continental margin. This increase of the magnetic field suggests an increase of magnetized material within the older accretionary wedge towards the northern arm of Sulawesi where ophiolites are emplaced. During the interpretation of the reflection seismic data of the project GIGICS BSR's (bottom simulating reflectors) were discovered for the first time along the active continental margin of North-Sulawesi. BSR's are the seismic expression of a velocity decrease at the bottom of a gas hydrate zone. The distribution and depth of the BSR's correlates with the geochemical and geothermal results. Radiometric age dating and geochemical analyses from pillow basalts of a seamount from the southeastern Celebes Sea indicate hot-spot activity in this part of the Celebes Sea during or shortly after the formation of the oceanic crust approximately at 43 Ma ago. Three NW-striking ridges or seamount-chains in the northeastern Celebes Sea were mapped and investigated in detail. They are thought to represent a wrench fault system extending through the northeastern Celebes Sea. At the flank of one of these ridges a strongly alterated plagioclase-olivine basalt sample was dredged which was overlain by non-fossiliferous clay stone. A similar lithostratigraphic sequence was drilled during ODP leg 124 (RANGIN et al., 1990). The geochemical composition of these basalts is different from typical MORB. The existence of a large crustal splinter within the accretionary wedge off southwestern Mindanao obviously is responsible for a high thermal conductivity which in turn could have enhanced heat flow (108.1 mW/m2) and methanogenesis (405 ppb). The heat flow of 103.0 mW/m2 at the deformation front of the Mindanao wedge and the high methane concentration of 5.555 ppb suggests tectonically induced fluid transport within the wedge. High methane concentrations between 8.044 and 49.006 ppb at the lower slope off Sulawesi and in the North Sulawesi Trench are accompanied by high heat flow values of up to 100.5 mW/m2. Heat flow is significantly lower upslope (31.3 mW/m2). This general heat flow distribution pattern is seen over a large portion of the accretionary wedge. The elevated heat flow values and high methane concentrations near the deformation front most likely result from heat transport by fluids squeezed out from vertically and laterally compacting sediments. The reduced heat flow towards the coast is compatible either with a cooling effect of slow subduction of the oceanic crust, or stacking of cool slabs of compacted sediments. A subduction of oceanic crust with a heat flow around 60 mW/m2 over a period of more than 3 million years would have produced the low heat flow values of the upper slope if the wedge consists of claystone with a low thermal conductivity (1.2 - 1.7 W/mK). Even in the low-heat flow area isolated fluid venting is possible. Lateral variations in the heat flow pattern (e.g. broadening of the anomalies in the west) may be due to different thermal regimes within the subducted crust.