A mosaic of silence, storm, sea ice and kastenlot

Friday (29 Sep), 06:00 in the morning – ready to run the geological gears. Meanwhile, however, waves have become higher and higher, a strong swell has been established. The ship is moving up and down, and the work with the heavy geological gear becomes difficult and – even more important – dangerous. After a short inspection of this situation on the aft deck, captain, chief mate and chief scientist immediately decide to stop all running activities, the geological station is cancelled. Instead, we are steaming towards the east into the ice (Fig. 2), looking for a station where ice and swell conditions allow hazardless operation of our geological gear.

Four hours later, around 10:00, we stop for running a geological station with giant box corer, multicorer and kastenlot corer. As the weather and visibility conditions are good enough as well, contemporaneously to the geo-station work two helicopter flights are scheduled, making our ice people happy (to have happy people around is always good and important for the whole life onboard). They get the chance for ice observations and the deployment of a drift buoy.

Ice observations from the helicopter and the deployment of drift buoys, these are two key aspects of interest of our ice people onboard. Thus, they should get the chance to introduce themselves and  tell us what they are doing here and why. Go ahead, ice people!

Our sea ice team focuses on three different topics. Niels Fuchs, Gerit Birnbaum and Marcel König investigate melt ponds, which presently refreeze. They are currently only present on second-year ice floes, which did not melt completely during the summer season. The new ice on the melt ponds is considerably darker than the surrounding floe surface. Hence, melt ponds decrease sea ice albedo also in the period of refreezing. The project aims at increasing the quality of areal fraction and melt pond albedo derived from airborne and satellite remote sensing measurements. Heike Zimmermann is mainly interested in the bottom part of the second-year floes and the ice algae that live there. She develops methods to search for ice algae DNA in sediments that are thousands of years old, and with a little luck, to find clues about the sea ice extension of the past. Gunnar Spreen deploys buoys in our working areas to contribute measurements of air temperature and air pressure to the Year of Polar Prediction (YOPP). Additionally, a dense net of buoys is deployed, which allows to analyze ice drift and ice deformation on a local scale.

In their project, Niels, Gerit and Marcel link airborne measurements by using the “Polarstern” helicopter to ground-based measurements on the ice. In order to obtain so-called ground-truth data and to validate the airborne measurements, ideally an area with melt ponds should be first observed with the airborne cameras followed by ground-based measurements. This ideal combination of measurements could not be performed so far due to unfavourable ice and weather conditions. Up to now, Niels and Gerit have carried out four measurement flights. Images taken by an RGB-camera and a hyperspectral camera will allow to derive pond characteristics (areal fraction, albedo) in a radius of 90 km around Polarstern. Almost all ponds on smaller and bigger ice floes in our working areas were melted entirely through during summer. A 5-10 cm thick layer of grey ice with a bulk salinity of about 10 g/kg is now covering them. Only their shape makes them distinguishable from new ice in intermediate floe areas.

In the Arctic, and especially in the remote location of the Arctic we are in, there is only a small amount of weather observations like air pressure and temperature available. Numerical models therefore have problems to reliably predict the weather and climate in the Arctic, which also influences the quality of weather forecasts for more southerly latitudes like Europe. It is the goal of the Year of Polar Prediction (YOPP) to change that. From 2017 to 2019 a huge amount of extra observations are taken in Polar regions, models are getting improved, and also we are a small part of this international project. By now Gunnar deployed seven of the nine YOPP buoys, which measure air temperature, pressure, and sea ice drift. These buoys will drift with the ice for more than a year and every hour transmit their observations by satellite to observational centers. The drift of the buoys can be followed under http://meereisportal.de. Some of the buoys already traveled more than 100 km since their deployment. The YOPP buoys were deployed equally along the route from the ship or by helicopter to sample an as large area as possible (Fig. 4, red diamonds).

In a second experiment, an array of buoys measures the drift and deformation of the sea ice on a more local scale (Fig. 4, orange diamonds). Next year in October, “Polarstern” will be frozen in and drift with the sea ice for one complete year, starting from a location a bit north of the one we are currently. In the framework of this large international MOSAiC project also an array of autonomous measuring stations will be deployed in a radius of 40 km around “Polarstern”. The eight buoys deployed by us will provide data about sea ice drift and deformation from this year, to have a comparison to and as an outlook on the expected situation during MOSAiC next year.