By Erika Allhusen, Robert Ricker, Hazel Hartman-Jenkins, Andreas Krell, Gerhard Diekmann, Ellen Damm |
As Miss Smilla searched snow and ice for clues to solve an arctic crime; similarly, we search the arctic icepack to for answers to a variety of scientific questions. How is biomass distributed throughout the ice? What is the small-scale current structure directly under the ice and how thick is the ice? Which processes in the ice are important for the , that affect our climate? Answering these questions requires cross-disciplinary co-operation: physicists, oceanographers, geochemists, and biologists working together.
An icestation takes planning. We need appropriate weather and ice conditions; we need the agreement of the chief scientist, the captain, the meteorologists, and last but not least, everyone else working on the Polarstern, since an 8-hour icestation affects everyone’s schedule. Then we hunt for a suitable ice floe, from the bridge and from the helicopter. It must be big enough for everyone’s work, and the ship must be able to come alongside and lower the gangway.
We move onto the ice with Nansen sledges and pulkas, loaded with a gallimaufry of tools: ice augers, generators, shovels, winches, pumps, measuring instruments of all types. And a stepladder. We’ll come to the stepladder.
The oceanographers bring the heaviest equipment. They pull winches and other instruments on Nansen sledges, which can make you sweating, even with -5 C° air temperature. They build their measuring site rather far away from the ship, that their measurements are not disturbed.
They bore a hole through the ice, through which they lower a CTD, which is an instrument that measures salinity and temperature along with the depth. With the portable winch, they also lower further instruments for currents and turbulence measurements down to 400 m.
The biologists stay closer to the ship. They lay out a drilling area, and take dozens of closely-spaced ice cores. These will be used for a variety of analyses.
The biologists see the ice as a habitat. They study the microscopic organisms (mostly diatoms) which colonise the tiny liquid channels in the ice. Already refrozen meltponds on top of the ice are also of interest. Their water will be analysed later on the ship.
The geochemists want to learn more about the processes that lead to the formation of DMS and methane (climate relevant trace gases) in the sea ice. Also the questions, how and when these gases are released from the ice to the ocean, will be investigated. Therefore, they sample ice cores, the water directly below the ice as well as the brines (saline channels in the ice), which then need to be analysed as soon as possible.
Finally, the ice physicists explore the physical parameters of the ice: temperature, salinity, texture, and optical properties. They measure the translucency of the ice and the snow cover, and map the ice thickness of the entire floe, pulling electromagnetic instruments over the surface in a sledge. The ice-thickness sensors are calibrated by placing them at a variety of distances from the ice; that’s what the stepladder’s for.
A good characterization of the ice uses all these measurements. Scientists from all disciplines benefit from the simultaneous data collection; each subject contributes its own puzzle pieces to our picture of the sea ice.
Beside all this data and ice cores, an important gift from the ice stations is fresh water ice from the melt ponds as an ingredient for some after work drinks.