PS100 - Weekly Report No. 5 | 15 - 21 August 2016
Working in Norske Trog
Meanwhile R/V Polarstern has worked her way toward the inner shelf of Northeast Greenland. We have reached the transition from Norske Trough to Westwind Trough, which is where the 79°N glacier meets the sea. In this region, sea ice often prevails the whole year round.
Our expedition is the first one that will conduct detailed measurements of the hydrography, ocean circulation and the sea floor characteristics in this area. Throughout the last week we followed the axis of Norske Trough toward the Northeast. This depression in the shelf serves as a conduit of warm, saline waters (originating from the Atlantic Ocean) from the shelf edge in Fram Strait toward the calving front of the 79°N glacier. One of our work foci in the last days were hydrographic measurements combined with biochemical and geochemical water sampling along the pathway. In addition, we were able to recover all of the seven moorings deployed on the mid-shelf in 2014. They had been equipped with sensors in order to measure the circulation of Atlantic water in the trough. In turn, an array of four moorings was subsequently deployed with a similar sensor arrangement, which shall be recovered during a R/V Polarstern expedition next summer. We further resumed the helicopter-based operations for the recovery and redeployment of several geodetic and one seismological station on the mainland of Greenland. Fortunately the weather conditions allowed us to conduct at least two operations per day.
Geological observations represented another work focus in the last week, as follows. The main aim of the NEGIS project and the geological survey of the Norske Trough has been to establish the extent of the Greenland ice sheet offshore, to map its retreat following the last glacial cycle and to establish the configuration of the ice sheet and the 79N ice shelf at the opening of the Holocene. Using the RV Polarstern Hydrosweep and Parasound systems our strategy has been two-fold. Firstly, to map glacial features on the seafloor and establish grounding line retreat patterns, and secondly to identify and core deglacial and Holocene sedimentary environments.
Our initial surveys of the outer and mid Norske Trough revealed distinctive till wedges, streamlining and mega-scale glacial lineations and intensive iceberg scour. The till wedges mark the progressive retreat of grounded ice northwestwards along the trough and the streamlined bedforms suggest an ice stream operated within the confined trough. The scours across the seafloor point to flotillas of icebergs being released during ice sheet break-up and the prolonged turbation of subglacial and glaciomarine sediments deposited in the trough.
The inner trough and regions peripheral to Zacharriae Isstrom and 79N glacier are the areas where ice sheet retreated at the opening of the Holocene. Our initial survey in these areas has revealed ice moulded bedrock and deep basins harbouring stratified deglacial and Holocene depo-centres. These will provide a long term record of Holocene grounding line and ice shelf fluctuation, as well as an insight into palaeo-oceanographic conditions along the 79N over the last 10,000 yrs. Over the next week we hope to explore along the edge of the 79N ice shelf itself ...... happy days.
Many greetings from R/V Polarstern,
Torsten Kanzow and the geology team