|Dr. C. Haas, Dr. J. Bareiss
|Marcel Nicolaus, Sascha Willmes, Anja Batzke, John Lobach
|Regionalklima der Polargebiete
|Stiftung Alfred-Wegener-Institut für Polar- und Meeresforschung
|November 2004 bis Februar 2007
1. Boundary conditions of superimposed ice formation
During the spring/summer transition, sea ice and snow properties change considerably in response to warming and the eventual reversal of temperature gradients within the snow and ice. One major process during the onset of melt is superimposed ice formation at the snow/ice-interface. This is due to snow melt water percolating down towards the colder snow/ice interface, where it refreezes. In the Antarctic recent observations show that superimposed ice may actually form layers of some decimeters in thickness. At the end of summer, ice floes in certain areas may consist almost exclusively of superimposed ice, which is responsible for the survival of the floes.Simultaneously, surface gap layers form underneath the superimposed ice. These host extremely high diatom standing stocks. The environmental conditions for their development is not clear so far, and there is a dispute whether they are mainly formed by biotic or abiotic factors. The meteorological boundary conditions for superimposed ice formation are little studied, as it has not been recognized so far to be important for the history of an ice floe. The first objective of this study is to investigate the main processes and boundary conditions for superimposed ice and gap layer formation, in recognition of their importance for Antarctic sea ice, and their possible importance for Arctic sea ice in case of environmental changes due to future climate change. This will be performed by means of combined measurements of ice properties and the energy budget at the ice and snow surface.
We will perform simultaneous measurements of ice and snow properties and of the meteorological boundary conditions. Snow temperature, grain size, density, wetness, snow depth and water equivalent will be determined at selected snow pits on a daily basis. At these sites, ice cores will be extracted and their temperature profile will be measured. In the cold laboratory, they will be analyzed for salinity and crystal texture. To account for lateral heterogeneity, several surface cores will be obtained every 2-4 days. Along extended profiles (several hundred meters), ice thickness will be measured by non-destructive means (EM, radar), and the gap layer development will be observed through small drill holes.The energy budget will be observed continuously with a weather station and radiometers. Thermistor sticks will be used to determine the surface temperature as well as vertical temperature profiles through the ice surface layer.
2. Changes of the ice thickness distribution due to melting and ice deformationThe second goal of this project is the determination of changes in the ice thickness distribution. Clearly, these changes will be dominated by a steady decrease of thickness due to summer melt. However, it is unknown to what extent the ice cover melts inside the closed pack ice, and how it contributes to the freshwater budget before the floes actually fracture and break apart in the MIZ. It is also unknown how thin ice is distributed into thick ice categories during deformation events. A drift station offers the unique opportunity to monitor these changes in a certain ice field. During ISPOL, we will know regional deformation fields from a large number of buoys deployed by several projects within the International Program for Antarctic Buoys (IPAB).Measurements are also performed as ground-truth for satellite radar altimeter measurements of sea ice freeboard.
A helicopter-borne EM ice thickness sensor (HEM bird) will be flown regularly along the same profiles of several ten kilometers length to monitor changes in the ice fields thickness distribution. The profiles will be defined by the trajectories of the drifting buoys, which trace the same ice floes during the expedition. These data will be compared with the thermodynamic and dynamic forcing and used to improve ice thickness estimates of numerical sea-ice models.
3. Satellite remote sensing for operational ship routing and observations of changes of sea ice propertiesSuperimposed ice formation results in marked increases of radar backscatter as visible in satellite data. Snow wetting and melt are detectable by changes in spectral reflectivity in optical and near-infrared imagery. Therefore, our study aims to provide ground-truth information for coincident remote sensing studies. We will obtain a most extensive data set on changes in physical surface properties as well as ice dynamics, and their detection with satellite data.In March 2005, CryoSat will be launched by European Space Agency ESA to measure sea ice freeboard both in the Arctic and Antarctic. As part of CryoSat pre-launch validation activities, we will perform freeboard and snow thickness measurements and compare these with our ice thickness profiles. Measurements will be synchronized with overflights of Envisat carrying a radar altimeter as well.The target area of ISPOL is far within the closed sea ice pack. However, reaching an ice floe far enough south is essential for a successful conductance of the expedition. In order to support ice navigation in possibly heavy second-year ice conditions, a large number of near-real-time high-resolution radar images and visible imagery will be obtained on board, in close cooperation with German Aerospace Center DLR.
During the access voyage to the ice floe ERS-2 Synthetic Aperture Radar (SAR) and MODIS visible and infrared imagery will be received at the German Antarctic Receiving Station O’Higgins and will be transmitted to the ship in near real time to support ice routing. These data will be complemented by passive microwave (SSM/I, AMSR-E) and optical and near infrared (NOAA-AVHRR) data received on board.During the ice drift phase, we will also order acquisition of numerous Envisat-ASAR and Radaraltimeter data.