Here, we report about recent and upcoming expeditions.
SO 232 'SLIP' - taking RV Sonne to the Mozambique Ridge
Tectono-magmatic evolution of the Mozambique Ridge and development of the circulation system
Understanding the origin of oceanic plateaux and ridges has a direct impact on understanding the development of the oceanic circulation since these structures represent obstacles for the flow of bottom, deep and surface water masses. The interoceanic exchange of heat and salt via the South African gateway maintains the global thermohaline circulation. Modifications of this 'interface' Atlantic-Indian Ocean thus also results in changes in the glocal oceanic circulation. Gateways, e.g. between Africa and Madagascar, are opened and closed as the result of tectonic movements and lead to a relocation of the pathways of oceanic currents. Volcanic extrusions result in the formation and/or enlargement of plateaux and ridges such as the Agulhas Plateau hindering the flow of water masses.
The detailed reconstruction of the break-up of Gondwana, the accompanying processes and the circumstantial impact of the evolving circulation system has formed a focus of the Section Geophysics at AWI (see e.g. South African gateway).The large scale plate tectonic development since the Gondwana break-up and its impact on the general oceanic currents such as the Antarctic Circumpolar Current are generally understood. The role of the smaller scaled crustal fragments Agulhas Plateau, Maud Rise, Mozambique Rücken, Astrid Rücken, Madagaskar Rücken and Gunnerus Rücken on the local circulation pathways and intensities have remained unknown. With their location and size these structures influence the pathways of the currents, e.g. North Atlantic Deepwater and Agulhas Current, and in this way the exchange of heat and energy between the two oceans, which is essential for the maintenance of the global 'conveyor belt'. A reconstruction of the volcanic events and depositional history of the sedimentary sequences will provide further information about the geodynamic and oceanographic-climatic evolution of this important gateway.
Three theories interpret the formation and development of the Mozambique Ridge and surrounding basins totally differently (continental crustal fragment vs independent micro plate vs Large Igneous Province). This has significant implications on (a) our comprehension of the dimension of the Cretaceous volcanism and associated processes in this region, (b) the opening of the gateway south of South Africa, and (c) the development of the circulation system in relation to the seafloor topography.
FS Sonne cruise SO 232 'SLIP'
Cruise Leg So 232 with RV /Sonne/, leaving Durban, South Africa on 30.3.14, returning to Cape Town, South Africa on 13.5.14, comprised seismic reflection and petrological studies of the Mozambique Ridge, a Large Igneous Province (LIP) in the south western Indian Ocean. The Mozambique Ridge consists of four major geomorphological units: Segments 1 to 4. The major goal of the expedition has been the role of the Mozambique Ridge within the break-up of Gondwana and its direct and indirect influence on climate and oceanic circulation. Seismic reflection data were gathered to study the basement structure of the ridge, its development after the initial formation as well as the distribution of sedimentary sequences and depositional environment.
Petrological dredge samples will provide information on composition and age of the Mozambique Ridge. In total ~4200 km of high resolution seismic reflection data were recorded. Bathymetric data were recorded parallel to the seismic profiling. Both datasets have additionally been used to pick significant locations for the petrological sampling. 59 dredges have been taken to sample the basement.
In particular, we intended to answer the following questions:
- How can we characterise the magmatic rocks of the southern Mozambique Ridge? A systematic sampling of the southern Mozambique Ridge will provide information on age (133-125 Ma or younger?) and the geochemical composition (e.g. ocean island basalt OIB or mid ocean ridge basalt MORB or a blend of both?) to distinguish between the above mentioned models for the formation process. A few dredge samples recovered during FS Sonne cruise So 183 AISTEK-II supplied basaltic breccias at three locations on the southern Mozambique Ridge. The questions raised here regarding origin, evolution, extent and age of the volcanism can only be answered with a comprehensive sampling of all geomorphological units of the study area. This way we will be able to identify different phases of magmatic activity and possible variations in the composition of the rocks.
- A renewed phase of excessive volcanism has been observed for the separation of the Agulhas Plateau from the Maud Rise. This is documented in up to 15 km long lava flows, which form an at least 2.5 km thick sequence. Can we identify evidence that the Mozambique Ridge volcanism is a result of the separation of Mozambique Ridge and its conjugate, the Astrid Ridge? Which dimension did this magmatism reach? Do the magmatic rock show a geochemical signature similar to other Gondwana floodbasalts, e.g. Etendeka floodbasalts? This would indicate that the Mozambique Ridge belongs to the world wide suite of Large Igneous Provinces. According to Leitchenkov et al. (2008), König und Jokat and Gohl et al. the northern Astrid Ridge formed already during the early spreading between Antarctica and Africa 160 Ma. Results of the FS Sonne project AISTEK-I show southwards inclined reflection in the upper basement of the southern Mozambique Ridge, which have been interpreted as the result of excessive volcanism. High resolution, deep penetrating seismic reflection data will be collected and combined with sediment echosoundig and swath bathymetric data to study structure and build up of the volcanic layers. This way we will gather information on the topography of the basement top, the distribution and areal extent of inclined reflectors and possible faults of the upper crust. Furthermore, we will map the transition into the surrounding 'normal' oceanic crust. We will sample the volcanic sequences to retrieve information on origin and age of the material.
- Results of the Sonne project AISTEK-I point towards a reorganisation of hte circulation pathways in the Transkei Basin at the Miocene/Pliocene boundary. An E-W oriented sediment drift then was covered by a N-S striking sediment drift. Ben-Avraham et al. (1994) observed similar things in the Natal Valley. There, the Oribi Drift was formed by a geostrophic current following the southeast African continental margin during the Oligocene (Niemi et al., 2000), which was relocated southwards during the Miocene. Ben-Avraham et al (1994) consider a tectonic uplift of the Mozambqiue Ridge as the trigger for this modification in flowpath. To test this hypothesis and check, whether a thermal subsidence can be identified for the ridge instead, we will collect seismic reflection data extending from the Mozambique Ridge into the Natal Valley and connect the lines to the seismic profiles collected during FS Sonne cruise So 182. The seismic data will image the sedimentary structures both on the Mozambique Ridge and into the surrounding basins. This way, we will collect further information on development and modfication of the circulation system south of South Africa and their origin.
This project has been funded by the Bundesministerium für Bildung, Forschung und Technologie under contract No 03G0232A 'SLIP'.
MSM 44 'BAFFEAST' - with FS Maria S. Merian into the northeastern Baffin Bay
In the Baffin Bay, palaeoclimate, palaeoceanography and the past development of the Greenland Ice Sheet are tightly coupled. For the northeast Baffin Bay, in which 27% of the western Greenland Ice Sheet drain, this connection has not yet been established due to the lack of data and samples. In order to model responses of the GIS to changing climatic conditions, and hence, changing oceanographic conditions, it is important to better understand the nature of these ocean-ice sheet couplings and related ice sheet dynamics in this area.
For this reason, the bathymetry working group at the AWI systematically maps the shelf and slope of the northeast Baffin Bay for seabed features associated to past Greenland Ice Sheet advances and retreats and bottom current activity. These studies are supplemented by proxy-studies done at the MARUM to date these features and events. These combined bathymetric/palaeoceanographic studies aim to provide information on the ocean circulation patterns in the northeast Baffin Bay, and thus, the palaeoceanographic influences on the northwest Greenland Ice Sheet.
During July 2015, an expedition to the Baffin Bay on RV Maria S. Merian will take place.
impressions from the mess room... ;-)
...strange things happen at Neumayer base