Physical Oceanography of Polar Seas
Our research will identify and quantify the relevant physical processes which determine the role of the ocean in climate and ecosystems with the objective to provide the basis of prediction in close cooperation with modellers.
Observational oceanography aims to study the status and the variability of circulation and water masses in the ocean in an interdisciplinary context. To understand the observed variability is a major prerequisite to explain the role of the ocean in the global climate system. Physical conditions strongly influence life in the ocean and consequently the CO2 cycle.
The observations include long-time series which allow to detect variations on climatic time scales and well-focussed process studies to understand the interactions of fluctuations on different scales. The data are needed to validate and improve models to predict future change.
Fieldwork is focused on polar and subpolar oceans the implementation of which demands for special instrumentation and methods to cope with ice cover, cold weather and rough seas.
The measurements aim to determine water mass properties, e. g. temperature, salinity, and concentrations of dissolved substances as oxygen, nutrients and the components of the CO2 system, as well as the motion of the water which is mainly due to ocean currents.
The variability is subject to a large range of time and space scales from basin wide currents to turbulence which requires a wide range of instruments and methods.
Research vessels, such as Polarstern, provide the technical facilities for scientific measurements. With the help of winches instruments are lowered into the water to measure water mass properties and the data are electronically transferred to the ship. Conductivity-Temperature-Depth probes (CTD) measure temperature and salinity on vertical profiles in the water column. Water samplers provide water from selected depths to determine the concentration of oxygen, CO2, nutrients, and trace substances.
Platforms equipped with sensors are deployed from ships. They drift at the ocean surface or on sea ice and transmit location and data via satellite. Other systems (floats) sink to a fixed depth level and follow the ocean currents at that level. They are tracked acoustically as SOFAR or RAFOS floats. Significant attention is granted to vertically profiling floats which measure between the surface and a certain depth temperature and salinity of the water column. When reaching the surface, the floats are located and their data transmitted by satellite. Particular attention has to be paid in using such floats in ice-covered areas, since there might be the possibility of them being crashed in the ice while rising to the surface or being located under the ice with no satellite connection, thus requiring the capacity to store the data until back to an ice-free area.
Measurements at fixed locations are obtained by moorings. They consist of lines to which the instruments are fixed and which are moored at the ocean floor with anchors. The instruments record the data internally while moored. After the end of the observation phase, which might take years, the instruments have to be recovered by a research vessel to obtain the data for further evaluation and to use the instruments again for new deployments.
Systems which are able to transmit data from mooring to mooring and finally by a profiling transponder at the surface to satellites are under development.
- Field work in physical oceanography aims to obtain and evaluate measurements in polar and subpolar oceans in order to understand the processes relevant for the determination of the oceans' role in climate and as an ecosystem.
- The obtained data are the basis of model validation and improvement of model quality.
- The results of the obtained data will serve as a major contribution to a better understanding of the earth system in a multidisciplinary context.
- The experience gained from collecting the data will be used to improve measurement techniques and especially to design observation systems to carry out sustained observations in ice covered oceans.