The last week
We have made our way towards the east through the entire platform and finished the CTD and Multi Closing Net (MCN) transect located along 65° E. On the morning of October 21st, the Sonne started her transit towards the harbour of Port Louis (Mauritius). Port call was on October 23rd.
Multibeam (EM122, EM710) and Parasound data revealed a slope deeply incised by canyons. Based on this data, the current rate of material export from the platform towards the west seems to be very low. We expect to gain more detailed information on this from the sediment cores and the surface samples that we obtained from the sediment fans in front of the mouth of one of these canyons and from the canyon course. Hydroacoustic data also show how the canyons are connected to the shallow water areas of the carbonate platform. Here and during this cruise in general, hydroacoustic data were instrumental for the selection of distinct sampling sites. They not only allow studying the sediment geometries of the selected sedimentary archive, but also provide information on the sediment type, highly valuable for the selection of the sampling tool.
In the further course of the last week we continued with sediment sampling and OFOS transects along our way towards the eastern margin of Saya de Malha. Beside numerous surface samples, we were also able to obtain two gravity cores from the region of the platform interior.
By means of OFOS we also studied the shallowest parts of our working areas, with water depths less than 40 m. Located well in the mesophotic zone, with enough light available, the sea floor in these areas is populated by coralline algae, colony forming corals, and green algae (Halimeda); all of them important carbonate producers.
The last OFOS transect was on the eastern slope of Saya de Malha; from 280 to 750 m of water depth. The slope here is comparable steep (up to 40°), which led to slope collapses and slumps in the geological past. The upper part of the slope is formed by outcropping limestone, partly with a black coat; slumps composed of fine grained material and blocks cover the lower slope (Fig. 2).
Our work at Saya de Malha Bank terminated with a last seismic survey of the eastern platform slope. After 4 weeks of intensive work, we leaved the Saya de Malha carbonate platform with a very comprehensive data set and are looking forward to start analyses and interpretation.