On the outer shelf

Here the autonomous underwater vehicle Paul was launched one more time, in order to observe the detailed structure of the boundary current. This was accompanied by vessel-based measurements (CTD, microstructure, LADCP, benthic sediment samples), which confirmed the presence of the boundary current. Upon completion of the task, we headed eastward along a course located to the north of Norske Trough toward the outer shelf, only to return southward along 10°E to the area of Norkse Trough. Along the passage we operated hydrographic measurements, complemented by biological sampling based on the bongo net. We were able to show, that even in this relatively shallow area of the shelf, warm Atlantic Water was present near the sea floor. Three moorings in total were deployed, that shall be recovered again in 2018. Subsequent analyses shall show, whether Atlantic Water from this region is injected into the trough, such that it is transported to coast of Greenland.

On Wednesday we continued our way toward the shelf edge along the axis of Norske Trough. Here we were able to recover an oceanographic mooring, took sediment samples for biogeochemical studies and subsequently deployed a lander at the same site. We then pursued a programme along a section across the shelf edge onto the continental slope, composed of hydrographic measurements, gravity corer operations, biological net catches and sediment sampling.

Here, stormy winds challenged our progress during Thursday and the night to Friday. A lander deployment had to be cancelled and for many hours any deployment of scientific gear became impossible. In significantly calmer conditions on Friday morning we deployed an oceanographic mooring in the East Greenland Current, in order to be able to connect the circulation in Norske Trough with the large-scale current system in Fram Strait. We then successfully recovered the lander we had deployed two days earlier and in the following night we completed the somewhat shortened measurement programme on the continental slope that we had started on the previous day.

Over the course of Saturday we left the continental slope in a southeasterly direction toward Greenland Sea. Here two deep-sea CTD casts were performed for instrument calibration purposes in a region in which AWI had started a time series station many years back. Compared to the historical observations our measurements suggest, that the long-term increase of the bottom water temperatures in Greenland Sea has steadily progressed further – most likely as a result of the shift from deep to shallower winter-time convection in this area. In the night to Sunday we started the transit to Bremerhaven, where we are scheduled to arrive in the evening of 13 October.

In the context of global sea level rise and the widespread retreat of the Greenland ice sheet, the expedition PS109 served the study of both the interaction between the ocean and glaciers in Northeast Greenland and the impact of this interaction on the regional marine ecosystem. It was especially during the second and third week of the expedition, when we conducted our field programme in the vicinity of the coast – in sight of the 79°N Glacier within dense sea ice in winterly conditions, surrounded by icebergs – that we were able to make a strong visual connection between our measurement programme and the rough nature of Northeast Greenland. We return home with many valuable data sets and samples, memories of spectacular sights und full of thanks to the captain and the crew of Polarstern.

Many greetings on behalf of the scientific crew on board,

Torsten Kanzow