PS111 – Weekly Report No. 3 | 3 - 9 February 2018
This week’s work on PS111 was focused on moorings. Instruments, which have stayed in the water for up to 4 years, were retrieved and re-deployed.
The instruments are attached to a rope with a heavy weight (500 kilograms) at the bottom and floats at the top to keep the rope straight in the water column. The length of the rope is determined by water depth minus 200 m to keep it clear of deep-drafting passing icebergs. The instruments include current meters, sound sources to guide free drifting floats (see Weekly Report #1), acoustic releases, and CTDs – Conductivity (to calculate salinity), Temperature, Depth (= Pressure). We recovered 4 moorings, which all arrived on board in perfect shape and ‘delivered’ well-recorded ocean parameters. All together 7 moorings, 4 from AWI and 3 from the University of Bergen, Norway, have now been deployed at 76°S at the northeastern slope of the Filchner Trough to monitor for another 2 or 3 years the outflow of very cold (< -2°C) and the inflow of relatively warm (< -1.3°C) water masses. Recovery and deployment is quite complicated and requires a fair number of people on deck. However, the deck crew is very experienced - who knows how many times they have done it - therefore, our last mooring in 500-m water depth was deployed in just 14 minutes.
At each mooring position a CTD is lowered to measure the above-mentioned ocean parameters and to collect water by closing 24 Niskin bottles at different depths. The samples will be analyzed onboard or at home by the different groups including micro-biology, chemistry, geochemistry, and tracer oceanography.
For navigation and location of specific areas of interest we use satellite images. The sea ice concentration has a huge impact on the ship’s mobility and the use of our instruments. Because of favorable sea ice concentrations indicating less sea ice to the west of the grounded iceberg A23-A and a coastal polynya in front of the Ronne Ice Shelf, we decided to head south; a polynya is an ice-free area in the sea ice cover caused by winds and/or relatively high ocean temperatures. The 3 days we needed from the Filchner Sill to the Ronne Ice Shelf were used for working on samples, scientific talks, and, as always when the ship is moving, surveying previously uncharted areas of the sea floor using the side-scan sonar and the sediment echo sounder.
On Friday noon Polarstern arrived at the edge of Ronne Ice Shelf.
Best wishes from all members of PS111.
Dr Michael Schröder