PS118 - Weekly Report No. 7 | 25 - 31 March 2019

Western South Scotia Ridge

[02. April 2019] 

During the past week, science has focused on bathymetry, oceanography and heat flow/geology transects along the western end of the South Scotia Ridge between the Antarctic Peninsula and the South Orkney Plateau. Our work was only briefly interrupted by a gale-force storm that passed through our area.

During the past week, science has focused on bathymetry, oceanography and heat flow/geology transects along the western end of the South Scotia Ridge between the Antarctic Peninsula and the South Orkney Plateau. Our work was only briefly interrupted by a gale-force storm that passed through our area.

Surveying was slow and difficult. Therefore, we stopped the survey and worked on an oceanography transect from the South Scotia Ridge southward across the slope into the Powell Basin. Across the slope, stations were quite narrowly spaced to resolve relative small-scale oceanographic processes in this area. At the site furthest into the basin, we combined the oceanography station with geo-sampling and collected a gravity core and two multi-cores for sediment analysis. After this, we travelled back to the flanks of the South Scotia Ridge to deploy the second of our oceanographic gliders. In addition to the normal oceanographic payload, this glider was also equipped with a microstructure system. Microstructure is a term used to refer to very small-scale (mm to cm) turbulent processes in the water. The microstructure system on the glider carries two probes: a very fast thermistor to measure rapid changes in temperature and a fast shear probe to measure changes in the horizontal currents. This information can be used to assess mixing in the water column, and estimate the rate at which turbulent kinetic energy is dissipating.

Another microstructure sensor was operated in parallel from Polarstern, the MicroStructure Sonde or MSS. This instrument carries two shear probes, a fast thermistor, and additional sensors measuring conductivity, chlorophyll fluoresence, and the transmission of light through the water. The idea was to have simultaneous shipboard and glider measurements. In this way, the shipboard data provided a spatially distributed snapshot for the area while the glider recorded a longer time series for a small section.

 

Once the oceanographic measurements were finished, we transited to the northeast Powell Basin to conduct a geothermal heat flow transect. Geothermal heat flow is the flow of geothermal heat energy from the interior of the earth to the earth surface. It depends on geological factors including heat transport mechanisms from the mantle, heat production in the crust by radioactive decay, and tectonic processes. Estimating geothermal heat flow requires observations of geothermal gradients and thermophysical sediment properties. In our case, temperature loggers were attached to a gravity core to record heat flow data and to collect sediments at each deployment. Prior to the geothermal heat flow measurements, sediment thicknesses were analysed with Polarstern’s sediment echosounder in the northeast Powell Basin. Based on this information, we selected suitable sites for geothermal heat flow measurements and coring.

Along the selected sites, we worked our way westward coring and measuring. After four sites, however, we had to interrupt our activities. A gale system crossed the area where we were working. Fortunately, this system moved quickly and we experienced only one shaky night from Friday to Saturday. Already on Saturday morning, we were able to resume our work and started a bathymetric survey. During the following night, an OFOBS dive covered the flanks of a gap in the South Scotia Ridge. Once again, we were not disappointed. OFOBS covered fields of pillow lava, basalt breccia and sediment waves interrupted by cliff faces and overhangs. And all these habitats showed a truly amazing density of mobile and sessile organisms (sessile meaning organisms which do not move, such as sponges and corals).

At the moment, we are collecting a glider we deployed last Tuesday. It has been spotted on our starboard side and will hopefully be on board soon.

The departure date is approaching fast and preparations for our return have already intensified as the first teams start to pack their equipment. Never the less, we will use the remaining time to explore as much as possible.

With less than a week in Antarctic waters ahead of us, I sent best regards on behalf of all expedition participants.

Boris Dorschel

Contact

Science

Boris Dorschel
+49(471)4831-1222
boris.dorschel@awi.de

Scientific Coordination

Rainer Knust
+49(471)4831-1709
Rainer Knust

Assistant

Sanne Bochert
+49(471)4831-1859
Sanne Bochert