ANT-XXVI/3, Weekly Report No. 2

8 February - 14 February 2010

Having the howling fifties (latitude) crossed, we arrived in the northern Ross Sea of Antarctica at the beginning of the week. Next to the Weddell Sea in the Atlantic sector, the Ross Sea is the second-largest embayment in Antarctica with a wide ice-shelf. Ice-streams and glacier drain more than a third of the West Antarctic ice-sheet into the bay. Since our first scientific targets were located in the ice-free deep sea area of the Ross Sea, we remained at a large distance from the ice-shelf on our route.

A 3000 m long cable (the “yellow snake”) is being spooled from a giant winch into the water behind the stern of Polarstern. The ship’s speed of 5 knots is keeping it at an ideal water depth of 10 m. Every metre, a hydrophone is embedded inside the cable, similar to a microphone, recording acoustic waves. This so-called streamer, together with its electronic recording devices, records the seismic waves which are emitted into the water every 12 seconds by airguns, which are towed behind the ship. With this seismic reflection method, layers of deposited sediments can be imaged down to several kilometres beneath the seafloor. Between the Pacific-Antarctic Ridge and the Ross Sea, we began applying this method to survey sites for a proposed international drilling project (IODP).

Prior to this, the previous cruise leg conducted such pre-site survey studies at various suggested drill sites in the southern Pacific. We continued these surveys at two more locations in the northernmost Ross Sea. This proposed IODP drill project aims to reconstruct the cycles of glacial and interglacial phases of Antarctica from early glaciations at about 34 million years ago until present times. Deep-sea sediments contain micro fossils which provide indications, for instance, on the temperature and salinity of the water masses of the Southern Ocean at a particular geological epoch. Every glacial cycle began with an advance and extension of the Antarctic ice-sheet followed by its retreat, accompanied by changes in environmental conditions of the surrounding Southern Ocean. Decoding this cyclicity using sediments from the deep sea will be a challenge for the marine geologists who will be working with such drill cores. Our seismic survey and a 22 m long sediment core, which was sampled using a so-called piston corer, show that at least the southernmost site may be suitable for future drilling.

After the completion of the pre-site surveys, seismic profiling continues day and night along a 1500 km long seismic survey transect. We want to compare the pattern of sediment deposits on the deep sea-floor from the northern Ross Sea with that of the Amundsen Sea. The difference in sedimentation can tell how variably ice-sheet movements occurred in the different regions of West Antarctica. All seismic survey instruments have been working fine – aided by excellent weather – and the watch team has gotten into a routine mode entertained by lively discussions on the seismic reflection pattern seen on the observer monitors.

Taking advantage of the partly sunny weather, spiced with an iceberg gallery out there, a first barbeque was held on deck on Saturday evening. The cook and his staff prepared a wonderful buffet to be enjoyed by the crew and science teams.


With best regards
Karsten Gohl