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ANT-XXIX/6, Weekly Report No. 8

29 July - 6 August 2013

The end of a research campaign


 

Cruise Track

EM-Bird above sea ice. Photo: M. Hoppmann

Aerial photograph of Polarstern at an ice floe.

Unmanned aircraft M²AV of the TU Braunschweig.

The SUMO observer of the Finnish group. Photo: M. Hoppmann

On Monday we completed the hydrographic transect from Joinville Island – the tip of the peninsula – to the position of the AWI mooring 207 at 63°43’ South and 50°51’ West. Despite the fact that we only reached a depth of 2500 Meters on the continental slope, and had actually intended to reach the deep trough at 4000 meters, we were still able to satisfy a major intention, which was to do a CTD at the location from where we have the longest oceanographic record. We were thus able to complement the series with a rare winter record. Because of the heavy pack ice, which during the past few days slowed our progress and due to the little expedition time left, the captain and I decided not to progress further south, but instead to head for the ice edge and towards Elephant Island.


Prior to that, however, we again carried out a 4 day station on the sea ice to do physical and biogeochemical investigations. The weather during this station was not very pleasant and temperatures dropped to below -25°C, which together with the strong winds on the first two days resulted in wind-chill temperatures of -60°C. The subsequent two days were sunny and the pleasant weather and wonderful colours provided some consolation to the scientist who had really worked hard under the harsh conditions. During these days the helicopters flew for ice thickness measurements and the small recording aeroplanes were also deployed.


S
ince we have been cruising in ice-covered waters the members of the sea ice physics group have measured sea ice thickness whenever weather conditions allowed. They use an instrument, which is suspended 20 meters below the helicopter and towed just 10 to 15 meters above the ice surface. The sensor, a so-called EM-Bird, uses electromagnetic radiation to measure sea ice thickness 10 times per second.


During the cruise, they accomplished 16 airborne surveys with a total distance of more than 2000 km. They gathered valuable datasets of young first year sea ice near the winter ice edge, as well as thick multi-year sea ice, which made ice navigation difficult near the Antarctic Peninsula. No prior datasets from airborne surveys have so far been obtained during this period of the year. They provide a much more detailed view on sea ice thickness than icestation work does. But besides the capability to measure sea ice thickness, the EM-Bird is also equipped with a downward looking camera. With this the members of the sea ice physics group are able to not only document the ice surface, but also to measure the size of ice floes.


The aim of the meteorological group is to investigate atmospheric processes above the Antarctic sea ice. Meteorological parameters like temperature, humidity, pressure and wind are measured by unmanned aircraft. Vertical profiles up to 2000 m provide reliable data of the atmospheric boundary layer, which is the lowest part of the atmosphere. We are particularly interested in the turbulence of the atmospheric boundary layer.


The working group of the Technical University Braunschweig uses the M²AV (Meteorological Mini Aerial Vehicle), which has a wing span of 2 m and an approximate weight of 6 kg. The take-off is realized by a winch system that is fixed to the ice. During this week, successful horizontal flights
have been undertaken above sea ice and leads. The influence of leads on the atmosphere is not well known. An enormous energy exchange is caused by a high temperature difference between relatively warm sea water and the very cold atmosphere. The resulting energy exchange influences the surface energy balance and has an impact on the entire atmospheric boundary layer.


The fleet of the Finnish part of the atmosphere working group consists of the small unmanned aircraft SUMO (Small Unmanned Meteorological Observer) and a quadrocopter, both equipped with numerous sensors for temperature, wind and humidity observations. The typical flight pattern for SUMO consists of vertical profiles up to 2km altitude, while the quadrocopter is used for more precise measurements in the lowest 100m layer of the atmosphere. During this week they performed 22 flights with SUMO and 3 flights with the quadrocopter. All flight operations were supplemented by near-surface measurements from small weather station on the ice floe.


The measurements taken by the atmospheric working group are of high value for improving weather and climate models, because observations are rare in winter.


The largest inhabitant of the winter pack ice is the Antarctic minke whale, which can reach a length of 10 m and a weight of 10 t. It is the only great whale species, which has adapted to a permanent life in the ice. Knowledge about the species is scarce, and population estimates differ from 360.000 to 1.000.000 individuals. Whether the stock is increasing or decreasing also remains under dispute. Minkes are mainly known to the public as being the primary target of contemporary whaling. Yet little is known about their voice. But because all other whales communicate acoustically and several so far unassigned sounds appear to exist in the ocean, the bioacoustics group aims to find these specific vocalizations. Once known, these can later be used to detect and count the whales and enables an acoustic analysis of their behaviour. However, an animal must be simultaneously observed visually and acoustically to establish that link. For this goal an infrared camera in the ship’s crow’s nest is employed, which can detect the warm blow of whales automatically, together with sonobuoys, which transmit underwater sounds remotely up to 30 km distance by radio. During this cruise this method allowed us to relate several so far unidentified underwater sounds to minke whales.


On the 6th August we successfully concluded our research activities. All scientists are returning home with invaluable data records and will be busy for the coming months to analyse these.


On the coming Monday we are expecting to arrive in Punta Arenas, which concludes our expedition. A total of 49 scientists and technicians (including 2 helicopter pilots) from 13 countries participated. We were superbly supported by 44 crewmembers, who enabled us to so successfully do our research programme.


In the name of all members of the expedition I send greetings from the tip of the Antarctic Peninsula, bid you farewell from my position as Chief Scientist, and wish you all the best.

Yours
Peter Lemke

 

Further reports and photos can be found – in German – on the website of the Meereisportal (www.meereisportal.de).

 


 
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