ARK-XXV/3, Weekly Report No. 7

Reykjavik – Bremerhaven, 13 September - 19 September 2010

The reflection seismic data acquisition along the predominantly E-W trending profiles in the Smith Sound which started on Sunday were continued in the first half of the week. We want to study the internal structure of the thick sedimentary sequences and to define the extension of pre-Cenozoic sediment basins and Proterozoic rock units in the north Baffin Bay. Very hard sediments occur in particular areas of less than 500 m water depth, obviously due the load of overlaying icebergs. Changing sea levels in the Earth’s history and the influence of tides may produce this high density of near surface sediments. Their reflectivity of seismic energy is very high and strong multiple surface reflections mask reflections from the deeper structures. Special and careful data processing is necessary before interpretation. A first step is done by the onboard processing. In addition to the normal processing sequence, it is of great benefit to consider seismic velocities of individual layers which were derived from sonobouys data. Besides the multi-channel reflection seismic data we are able to record wide-angle reflection data by means of these one-way sonobouy instruments. The data are radio transmitted up to a distance of 30 km and provide information on propagation velocities in the sediment layers.

Close to the end of a seismic line off Cape York R/V POLARSTERN navigated into an area with numerous icebergs. With the increasing amount of icebergs ahead and the risk of damage to the 3900 m long seismic cable it was decided to stop data acquisition along this profile. Thanks to the highly skilled and routineous navigation officers during the line change as they navigated R/V POLARSTERN safely through the labyrinth of icebergs without any collision with the seismic outboard systems.

The newly recorded seismic data in Smith Sound will extend the already existing database acquired during a previous research cruise of BGR in 2001. The comprehensive data set will be used to map sediment basins in the area and help to understand the tectonic processing of their formation.

Besides the marine geophysical investigations, numerous aeromagnetic survey flights were conducted during last week. Due to good flying conditions up to three helicopter flights per day were possible. The aeromagnetic data with a line spacing of 12 km will supplement the marine magnetic data. The whole data set already covers a substantial part of the Greenland side of northern Baffin Bay. The data will be used to study the nature of the crust underlying the thick sediments and identify possible oceanic crust.

Currently ocean bottom seismometers are being deployed along the last two refraction seismic lines of our expedition. Following one of these lines R/V POLARSTERN is heading south for another 150 nm of deploying ocean bottom seismometers to the end of profile at position 71°30’N.

Still in Arctic waters but back to milder temperatures all colleagues send greetings home. 

Volkmar Damm
September 19th, 2010, Baffin Bay, 5°C