PS109 - Weekly Report No. 2 | 18 - 24 September 2017
At the 79°N Glacier
We are looking back on a very active and exciting week. In the beginning our work was still concentrated on the area of the shelf break of Northeast Greenland at the mouth of Westwind Trough, with the latter representing a depression leading toward the inner shelf. In the trough relatively warm Atlantic Water can be found near the sea floor.
Besides hydrographic measurements, geological sediment investigations using the gravity corer were a major focus. By means of this, we try to establish the area over which the Greenland ice sheet extended during the time of the last ice age, and in which succession it subsequently retreated. Also, we were able to collect sea floor samples using corer and lander systems based on which the impact of the glacial meltwater input into the ocean on benthic-biogeochemical processes shall be investigated.
Passing a number of icebergs, Polarstern followed toward the west along the axis of the trough, in which geological and benthic work were pursued. From thereon, also the geodesists, seismologists and glaciologists, all of which either carrying out research on the mainland of Greenland or on the 79°N glacier, could commence their helicopter-based operations.
We continued our way towards the coast of Greenland into Djimphna Sound. Dense ice fields allowed us only to move ahead rather slowly. Wedged between steep mountain ranges, Djimphna Sound leads toward the relatively small, northern calving front of the 79°N Glacier. We succeeded to recover an oceanographic mooring at the mouth of the sound, which had been measuring the outflow of the glacier-influenced ocean waters since August 2016. Given the presence of deep-reaching icebergs, we are very pleased about the save recovery of the instrumentation.
Subsequently, Polarstern sailed approximately 30 miles toward the south, and then entered the breathtakingly beautiful bay in front of the main calving front of the 79°N glacier, framed by snow-covered mountain ranges. This area represents a very important target of our expedition. The glacier exhibits a floating ice tongue, below which an 80 kilometers long cavity filled with sea water can be found. We succeeded to recover all four oceanographic moorings deployed last year in close vicinity of the calving front. Thus, the first-ever time series measurements from the ocean-glacier interface of the 79°N Glacier have become available. Apart from that a vessel-based measurement programme of the Atlantic Water and meltwater circulations in the bay and a chemical water sampling programme were carried out. In addition successful biogeochemical benthic samplings as well as geological coring efforts related to the ocean-glacier interaction were executed. We can further report a successful dive of the autonomous underwater vehicle PAUL along the complex circulation pathway along the Atlantic Water toward the 79°N glacier. The work programme was accompanied by outside temperatures of up to -15°C and rapidly progressing new-ice formation. It is a result to the tireless efforts and the enormous experience of both the bridge and deck crews of Polarstern that we can operate complex measurement systems like the CTD rosette, the benthic landers or the underwater vehicle successfully. Owing to the persistent readiness of the helicopter team and the reliable predictions of the weather service on board, also the flight-based operations show some successes despite the unfavourable variable and winterly conditions. The geodesists and seismologists have been able to install measurement systems on the mainland while the glaciologists succeeded in performing a series of thickness measurements of the ice tongue of the 79°N Glacier.
I am sending kind greetings on behalf of the entire science team of the expedition,