ALBERT

Description: The multidisciplinary research cruise 64PE350 was conducted in the central part of the Red Sea to strengthen our understanding of volcanism and tectonics and related hydrothermal processes in this young rifting system. Therefore we extended our intense multibeam mapping campaign, which had started during the PO408 cruise in 2011, by mainly focusing on the hydrothermally active “Multi Deep” area. Detailed geological mapping was performed by selective rock sampling (dredging, coring) in areas of special interest (i.e. fresh basalt flows, or zones with signals of recent volcanic activities). Moreover, a geochemical sampling campaign (i.e. gravity coring, Niskin water sampling) was conducted in brine-filled Red Sea deeps where variable hydrothermal activity is expected. The geochemical characteristics of sediment (pore water and mineral composition) and brine will help to identify sources and sinks relative to hydrothermal activity (e.g. hydrocarbon inflow, heavy metal concentrations in brine and sediment, etc.). Transport and degradation processes (biogeochemical cycles) at the brine- seawater interfaces were investigated by high-resolution water sampling and subsequent onboard membrane inlet mass spectrometry, gas chromatography, and major and trace element sampling. Biomarker studies are being performed by sampling/ filtering water column and brine to decipher allochthonous from autochthonous organic matter input to the Red Sea Deeps. Moreover, microbiological studies will be performed on selected brine and sediment samples. Hydrocarbon seepage at the pockmark area was investigated by hydroacoustic and geophysical methods (water column imaging, sparker reflection seismics). Additionally, sediment cores were retrieved from selected pockmark structures to investigate gas/ fluid seepage activities during Holocene. The recently described subsea salt glacier phenomenon was investigated by seismic reflection studies and comparative multibeam profiling (salt glacier flow velocities will be calculated).

Description: The underlying scientific motivation of SO227 was to constrain the geological processes that control the distribution and saturation of hydrate in marine sediments. The most important objective of the cruise was to observe the effect of additional fluid advection along blind thrusts into the gas hydrate stability zone. With its clear distinction into a passive margin and an active margin the area SW of Taiwan is particularly well suited for this kind of research because it is very well studied and it is known where the tectonic structures of the compression and subduction zone disturb the otherwise fairly homogeneous surface sediments of the margin. After a reconnaissance survey using multi beam echo sounder and side scan sonar we selected two sites that are typical for the active and passive margin, respectively. At these two sites we carried out comprehensive geophysical experiments including high-resolution 3D seismic imaging with the P-Cable system, ocean bottom seismometer (OBS) deployments, controlled source electromagnetic (CSEM) measurements, heat flow measurements, and ground-truthing using HyBis and TV grab. While the P-Cable data allow us to determine the internal structure of the study areas down to a depth of approximately 500 m below sea floor, the OBS and CSEM data will constrain the hydrate and free gas saturation along twodimensional transect through the 3D seismic cubes. The heat flow data will provide information on the thermal conditions of the sediments. The first site covers the Formosa Ridge on the passive margin of the South China Sea. The ridge is the result of canyon erosion in the north, west, and east. The high-resolution threedimensional seismic data show a continuous bottom simulating reflector (BSR) marking the base of the hydrate stability zone. Particularly, underneath the canyon in the north the BSR is much shallower than underneath the centre of the ridge. This may indicates that the canyon incision has changed the hydrate stability field and that hydrate formation at depth has not been able to adjust to the new pressure and temperature conditions. The second site includes a roll over anticline called Four-Way-Closure Ridge which is the surface expression of an underlying blind thrust. In this area numerous high amplitude reflectors occur above the BSR. This unusual observation may suggest very high gas hydrate saturations and coeval presence of free gas and gas hydrate in the sediments. Evaluation of the OBS and CSEM data will allow to test this hypothesis. The 3D seismic data clearly show fluid migration pathways through the gas hydrate stability to the sea floor. Sea floor video footage and sampling confirmed the presence of on-going methane seepage at the Formosa Ridge above the fluid migration pathway imaged in the 3D seismic data. They also establish that there is at least one seep on the Four-Way-Closure Ridge at which methane is released into the ocean above another seismically imaged fluid migration pathway. This is the first active seep site with chemosynthetic ecosystems discovered on the active margin SW off Taiwan.

Description: 13.04. – 27.04.2013 Port Calls: Gdynia, Poland 19. – 21.04.2013

Description: R/V SONNE cruises SO-224 and SO-225 are part of the cooperative project MANIHIKI II between GEOMAR Helmholtz Centre for Ocean Research Kiel and the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI), funded by the German Ministry of Education and Research (BMBF). This multidisciplinary project continues previous research at the Manihiki Plateau conducted since 2007 (SO-193) on morphological, volcanological, geochemical, and geochronological studies and is now broadened by geophysical and paleoceanographic research foci. SO-225 focused on stratigraphically controlled sampling of the igneous successions of the Manihiki Plateau. This has been accomplished by using the remotely operated vehicle ROV Kiel 6000 and chain bag dredges. Coring of deep sea sediments and sampling of the overlying water column has been added to the program. SO-225 and subsequent shore-based research in the home institutes mainly address (1) the temporal, spatial, and compositional evolution of the igneous basement of Manihiki Plateau, (2) the environmental impact of the large volcanic eruptions, which formed the Manihiki Plateau, (3) the Plio-Pleistocene dynamics and evolution of the West Pacific Warm Pool during the last ~3 million years, and (4) the potential oceanographic interaction between the equatorial Pacific and the Southern Ocean (“ocean tunnel hypothesis”) and its climatic responses. The integration of scientific results from SO-224 and SO-225 with existing data from the West Pacific large igneous provinces Manihiki, Hikurangi, and Ontong Java will contribute towards a better understanding of the origin and effects of volcanic mega events, the formation of large igneous provinces, and the paleoceanography and paleoclimate of the equatorial West Pacific. R/V SONNE cruise SO-225 started in Suva/Fiji on November 21st, 2012, and ended in Auckland/New Zealand on Januar 5th, 2013. Complementing 2,940 nm multi-beam mapping and 2,250 nm sediment echo-sounding, a total of 62 deployments of various devices have been carried out during SO-225. Ten of 11 multi corers yielded sediment samples, 16 piston corer and 3 gravity corer deployments recovered altogether 131.6 m sediment cores. The sampling of the water column by CTD and multi net was successful. Foraminiferal sand and ooze dominate among the sediment samples, some cores also contained sandy clayey silt rich in foraminifers and nanno ooze. The sediment cores cover a more than 1,100 km core transect extending from the ocean floor to the north of the Manihiki Plateau to the southern foothills of the High Plateau. Preliminary studies on board showed that the SO-225 sediment sampling yielded excellent paleoceanographic archives which can be correlated along the entire core transect and dated back to Pliocene. Further preliminary results include that past climate changes significantly affected the West Pacific Warm Pool. The sediment samples also will allow to reconstruct the Plio/Pleistocene variability of equatorial currents and the Antarctic intermediate water. Four ROV dives yielded 32 rock samples from two profiles across the slopes in the northern and central part of the Manihiki Plateau (North Plateau and Danger Island Troughs). Stratigraphically controlled sampling along c. 3 km long profile reaching from 4,600 m up to 3,260 m water depth across the flank of the south-eastern foothills of the North Plateau was particularly successful. Due to a series of unfortunate circumstances beyond our control, further ROV sampling on SO-225 had to be cancelled. Instead we decided to run dredges to considerably broaden the range of samples from the Manihiki Plateau basement by dredging. Twenty-three dredge hauls have been conducted in an average water depth of 4,380 m. Of these, 20 delivered magmatic rocks, 12 volcaniclastics, 8 sedimentary rocks, and 13 Mn-Fe-Oxide crusts. Notably, some of the dredged rocks show spinifex textures indicating unusual high eruption temperatures and several dredges contained fresh volcanic glass. The recovery of fresh glass from a presumably c. 120 million years old flood basalt province is a great achievement which will enable detailed petrological and geochemical studies of the plateau forming melts. Finally, mapping of submarine volcano Monowai en route on the transit to Auckland SO-225 should contribute to a time series of maps which continuously document the evolution of the volcano. During profiling, however, a sudden and significant increase in volcanic activity hindered us in mapping the top area of Monowai.