From the Northern Transect to Halley Bay

The young investigator group PALICE reconstructs the paleo sea-ice cover from the sediment. A 30-40 cm long MUC core, divided into slices, covers time periods of up to several thousands of years. The so-called biomarkers occur in algae that live at the bottom of the sea ice. Once died off, they become part of the sediment and are therefore a good indicator of the sea-ice extent in the past.

Another corer tube is perforated along its longitudinal axis. From a porous rod, a pore water profile can be extracted in 1 cm increments using syringes. The actual chemical analysis of the samples will then take place at AWI after the expedition. The distribution of nutrients and trace elements provides information on how oxygen-rich the sediment is and whether it can release the amount of iron, necessary for plankton blooms.

The isotope geochemists on board investigate the trace metals lead and neodymium in the MUC core profile in order to reconstruct the ice and meltwater input into the Weddell Sea. The signature of these rare elements is characterized by the composition of the ice-covered geological hinterland. The lead samples must be carefully extracted in a protective argon-atmosphere to avoid contamination. The pore water solution centrifuged from the samples will be analyzed in the labs at GEOMAR.

In additional MUC cores, oxygen profiles were taken and microbial conversion rates were determined. To this aim, sediment cores were incubated on board for 2 days and the decrease in oxygen concentrations was determined, which serves as a measure of the respiration of the organisms living in the soil. The results can be related to surface productivity and general environmental conditions such as the sediment and sea-ice properties.

The sea-ice physics group measured the thickness of the so-called fast ice – the multiyear sea-ice attached to the ice shelf – with means of an electromagnetic probe (EM Bird) which was installed underneath the helicopter for a total of five transect flights. For the first time, the ice thickness distribution of the fast ice in front of Berkner Island could be determined this way.

The deployment of the autonomous platforms (buoys) on ice floes was successfully completed this week. The buoys, including the last snow buoy, two ice-mass balance buoys, one spectral radiation station as well as so-called light and salinity harps, will drift with the ice floes over the coming months and provide real-time data on the snow and ice properties via satellite. The sea-ice group has meanwhile recovered from their last mission - they had worked for 5 hours under strong wind conditions with windchill temperatures down to -50 degrees and heavy snow drift in order to deploy these buoys.

Winter is approaching and with daytime temperatures of -15 to -25 ° C and winds of up to 6-7 Beaufort, even the last areas of open water are freezing over. Drifting snow covers the newly formed sea-ice, so that Polarstern often maneuvers through an ice cover that extends to the horizon. Thanks to the experienced navigators, this is achieved without problems by constantly navigating along the route with the lowest possible ice resistance and thus the lowest fuel consumption.

On Friday, the station work ends at the British Halley station where 16 additional people are coming on board and two pistenbullis, sledges and containers are loaded. En route to the final port of Punta Arenas, the scientific program continues, including seafloor mapping with multibeam echosounder and sediment profiler.

With contributions from Maria-Elena Vorrath, Claudia Hanfland, Marcus Gutjahr and Claudio Richter on the multicorer and sediment cores.

With best wishes from all members of PS111

Michael Schröder

Chief scientist