Underwater worlds

100% ice cover +++ 70° 15’S, 9° 30’W +++ -3°C, sunshine +++
15 January 2015
(by Stefanie Arndt and Marcel Nicolaus, translation: Ina Lefering)

Turquois-blue underwater worlds, small caves under the sea ice, a krill swarm passing by. Thanks to Siri’s video camera, we are able to explore all these fascinating under worlds. We took Siri, our small remotely operated vehicle (ROV), along on this cruise as a diving platform for our radiation sensors. We measure how much of the sunlight passes through the sea ice and enters the ocean. Sunlight is one of the energy sources in the marine ecosystem and a main driver for heating of sea ice and ocean as well as photosynthesis. Not only the organisms living on the surface but also the ones living under the ice need light to live and grow. Let’s got back two hours: Every ice station starts with lifting the ROV control hut, equipped with four computers and five screens, onto an ice floe, either with the ship’s crane or by helicopter. Preparing the ice station on the sea ice: we have to drill holes to set up a grid of markers that will hang under the sea ice. They will help to guide the ROV during our dives. Additionally, we prepare the floe edge by removing all snow and preparing a small platform. Such we make sure that Siri, weighing 80 kg, gets safely in and out of the water. We then test our instruments on the sea ice and if everything works well we are good to go! Our chief pilot, Martin Schiller, has to be fully focused when steering the ROV in from the control hut. Operating our ‘young lady’ can be quite tricky, because the rough bottom topography of the sea ice and strong ocean currents impact the movements and finally the path of the robot. However, it is very important for our measurements to keep the ROV in a stable position. Light conditions and visibility vary strongly with the properties of snow and ice above us. The measured spectra show that there is a lot of life in the sea ice. Algae absorb a major portion of light and have a characteristic fingerprint in the spectra. Later, we remove the snow from a defined area and repeat our measurements to study the effect of the snow cover on top of the sea ice. At the end of the day we have recorded several hours of video and thousands of light measurements – this will keep us busy for months.