PS100 - Weekly Report No. 7 | 29 August - 4 September 2016
The expedition comes to an end
Today we have completed our research programme at the Knipovich Ridge south of Fram Strait. We are now on the transit toward Tromsø, where we will arrive in the morning of 6 September.
In the beginning of the 7th week of the expedition, we found ourselves on the inner shelf of Northeast Greenland at the transition from the 79°N glacier to Westwind Trough. Here we both conducted measurements of the hydrography, circulation and turbulence and carried biochemical and geological sampling. In addition three moorings were deployed for the continuous observation of the circulation of Atlantic water. We then steamed toward Djimphna Sound, which is framed by rocky coastlines decorated by icefields. Also, the 79°N glacier terminates in the fjord comprising a minor calving front. At the sill near the fjord entrance we deployed another mooring and collected sediment samples. This was followed by a transit toward in a south-westerly direction across the sea ice covered shelf toward the shelf edge at 79°36’N. We were able to complete a hydrographic section across the East Greenland Current. In total four such sections have been completed at different latitudes, from which we will be able to derive the spatial structure of the recirculation and the lateral mixing of Atlantic waters. Subsequently we returned to the East Greenland Current at 78°50’N, where we recovered in heavy sea ice the winch mooring deployed for testing purposes earlier in the expedition, and additionally carried out two stations for the GEOTRACES programme still missing. Our subsequent attempts to recover two sound source moorings deployed in 2012 unfortunately failed. We then left the sea ice covered area of the East Greenland Current toward the southeast for Knipovich Ridge. As the last major work programme 13 ocean bottom seismometers were deployed in quick succession, complementing the instruments deployed in this area during the first week of the expedition.
For the two mechanical engineers Keith Soal und Rosca de Waal the research icebreaker Polarstern itself is the object of interest during the expedition, as will be explained in the following. The Polarstern is a great example of a vessel which has enabled the discovery of invaluable knowledge over the last 34 years. Since there is still so much to be learnt about our planet, there is currently a large interest in new polar research vessels. The opportunity is therefore to improve certain aspects of ship design through a better understanding of the physical mechanisms involved. The aim of the project is the characterization of ship dynamic responses due to complex ice-structure and fluid-structure interactions. This will enable investigations into structural health monitoring of the vessel, as well as fatigue life estimations of the vessels hull and shaft line. The preparations for our research started in the shipyard in Bremerhaven with cable and sensor installations, and was completed before departure in Tromsø. During the voyage the measurement systems were configured, tested and maintained. Data processing began on board and revealed high data quality with many interesting phenomena. The first three bending modes of the Polarstern are shown in Figure 1 and the first six propeller modes are shown in Figure 2. In order to understand the mechanisms driving the dynamic response the ships operational parameters were recorded. During ice navigation visual observations were made from the bridge in order to estimate ice thickness, concentration and floe size. The data processing will continue once we are back on land. We feel optimistic about the value of this full scale data set as an opportunity to gain valuable insight from a vessel which has stood the test of time.
This expedition has been successful in every respect. All research groups on board have been able to reach their goals or even superseded them. The success was only possible because of a close and friendly collaboration between the scientists and the Polarstern crew. The fact that we were able to carry out investigations in previously unexplored waters near the 79°N glacier represents a large scientific treasure. During this time we were able to conduct research „with a view“, because we had the important elements (the glacier, the coastline, the rocky coasts sloping steeply into the ocean, icebergs) right in front of us, while seeking the answers to our scientific questions in the water column and on the sea floor. It is not known to me that any other marine expedition accomplished this in the vicinity of the 79°N glacier.
We owe many thanks to Captain Schwarze, the entire Polarstern crew, the helicopter service and the weather service. This was simply an expedition in perfection.
Many greetings from board,