Sedimentology and 24h ADCP
We continued the scientific data acquisition in the working area, the Saya de Malha Bank. From September 29th to October 2nd, we conducted a seismic survey in the two working areas in the southern part of the Saya the Malha Bank (WA-2 and WA-3). WA-2 is of particular interest for the project as this is the area where internal waves approach the platform from the southwest. Understanding the sedimentary processes associated with these internal waves is one of the main aims of the expedition.
The seismic- and hydroacoustic survey data were also instrumental to select a series of sediment sampling stations covering a deep- (basin) to shallow-water transect (platform edge to inner platform). The aim of this part of the project is to document the sediment distribution across the carbonate platform in order to understand why the present-day Saya de Malha platform does not show any reefal environment situated close to present-day sea level but instead shows carbonate sediment production in fairly deep water.
The shallower stations show a clear dominance of coralline algae and large benthic foraminifera in contrast to the deeper stations. This might be related to the reduced light at the sea floor as the result of comparable great water depths and turbidity within the water column in this area, and probably represent mesophotic conditions (low light) favouring the large benthic foraminifers and coralline algae production.
In the early morning of October 4th we reached a station scheduled for 24 hrs of continuous ADCP (Acoustic Doppler Current Profiler) and CTD measurements as well as recording of the water column using the multibeam echosounder. These measurements aimed on a better understanding of the internal waves. These waves propagate along discontinuity layers in the water column and are expected to move sediment if they break along the shoaling margins of the Saya de Malha Bank. We remained at this station until midnight and were able to observe the passage of internal waves with amplitudes of up to 35 m.