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ASOF-N - Arctic Sub-Arctic Ocean Flux array for European Climate: North

Summary information

Funding:FP5 - Research project
Total cost:3773650
Ec contribution:1885078
Start date:2003-01-01
End date:2006-03-31
Duration:39 months
Coordinator:Eberhard Fahrbach (
Organisation:Alfred Wegener Institute for Polar and Marine Research (AWI) – Germany
Themes:Ocean current changes; deep circulation changes; freshwater inflow
Regio:Arctic; North Atlantic
Project name:ASOF-N - Arctic Sub-Arctic Ocean Flux array for European Climate: North
Project summary:Objectives
The main ASOF-N objective is to establish the components of the global observing system in choke points of the Nordic Seas to determine the fluxes between the Arctic Ocean and the North Atlantic and to understand and predict how they respond to climatic forcing. To achieve this goal long time series are needed. For this purpose the main tasks were to perform the field measurements with a special focus on setting up of the long term measuring arrays of moored instruments and floats:
- WP 1 'Atlantic water pathways' - measurements of the track lines of Atlantic water flow by floats and mapping horizontal distributions of the Atlantic water properties;
- WP 2 'Fluxes across the western Barents Sea' - measurements by the mooring array in the Barents Sea opening and carrying out the hydrographic sections;
- WP 3 'Heat flux through Fram Strait' - currents and temperature measurements by the mooring array in the eastern and central Fram Strait and the high resolution vertical section of temperature and salinity across the strait;
- WP 4 'Freshwater flux through Fram Strait' - currents and temperature measurements by the mooring array in the western Fram Strait and the high resolution vertical sections of temperature and salinity across and along the strait.

The tasks included analysis of data sets, obtained during field measurements in WP1, WP2, WP3 and WP4 in the first year of the project. The objective of WP5 'Data Management' was to provide access to the project data and the actual status of field and modelling work and to organize the data flow to the project data centre from all partners. The WP6 'Integration and Synthesis' aimed to develop the adequate water mass classification for Fram Strait including a description of time evolution of the water mass properties and regional correlations between the observed variables.
Project outputs:Scientific achievements
The field work carried out provided repeated hydrographic surveys including vertical sections of temperature and salinity in the observation area (Barents Sea, Greenland Sea, Fram Strait). The ASOF-N mooring arrays maintained during the project provided time series of fluxes in the Barents Sea opening and across Fram Strait. The analysis of the data obtained during ASOF-N in combination with data measured before ASOF-N permitted to describe the longer term variability of the oceanic conditions in the ASOF-N area. On this basis time variability of the water mass properties, heat and volume fluxes were estimated for the three-year long period and beyond. In combination with historical data a nearly decadal time series of fluxes resulted. The variability of volume, heat and freshwater fluxes was analyzed on different time scales from daily to interannual and nearly decadal ones. The contributions of local and remote forcing to the temporal and spatial changes of flow and temperature fields were estimated, giving the insight into the relationship between variability of forcing and of fluxes. High resolution numerical models for the western Barents Sea (NPI) and the Greenland Sea, Fram Strait and Arctic Ocean (AWI) were implemented and runs covering the ASOF-N period were completed. A refined water mass classification for Fram Strait was derived and the possibility was explored to compute the time evolution of heat and salt fluxes through Fram Strait. Variable assessment of the observational system performance during the deployments resulted in a data return of about 90% during the final phase of the project.
A list of publications can be found on the project website.
Socio-economic relevance and policy implications
Variability of the ocean circulation and the water mass distribution in the Nordic Seas lead to changes in the volume, heat and freshwater fluxes between the Arctic Ocean and North Atlantic. Changes in these fluxes can have a strong influence on the role of the ocean in the climate system which includes the potential of abrupt climate changes. The climate variability in particular in the northern North Atlantic has a strong impact on the living conditions in Northwest Europe. This includes energy consumption, sea traffic and marine living resources. Therefore a reliable prediction system is of high value to maintain the present living conditions. Prediction requires understanding and modelling of the relevant processes and monitoring key parameters to validate and constrain the models. Since variability of the relevant time scales can be only studied on the base of the long-term time series, ASOF-N aimed to pave the way towards an observing system consisting of a cost effective array of instruments in the key areas for the exchanges between the North Atlantic and Arctic Ocean. The results of ASOF-N will help to design such a system, to give advice for its implementation and consequently contribute to maintain the quality of life in Northwest Europe.

Results from ASOF-N gave background information to the scientific report from the Arctic Climate Impact Assessment (ACIA) published in 2005 which is a project of the Arctic Council and the International Arctic Science Committee (IASC) a high level intergovernmental forum. The ASOF-N results are included into reports to ICES (the International Council for the Exploration of the Sea), which gives advice to the member countries and helps them manage the North Atlantic Ocean and adjacent seas. ASOF results are a contribution to the formation of the EU-Integrated Project DAMOCLES standing for Developing Arctic Modelling and Observing Capabilities for Long-term Environmental Studies. ASOF results underline the need for a sustained observing system in the Arctic and Subarctic regions in the framework of the Global Ocean Observing System (GOOS) and the Global Climate Observing System (GCOS) which can be maintained beyond the time of individual research projects.

The evaluation of the available historical data together with the results of the ASOF-N field measurements and modelling results revealed a significant warming of the Atlantic Water propagating through the ASOF-N region and an increased heat flux into the Arctic Ocean. The data indicate that variations of the fluxes between the North Atlantic and the Arctic Ocean occur on a wide range of time scales and are interlinked between the main passages. The volume and heat fluxes are also controlled by local and remote atmospheric forcing. Both in the Barents Sea Opening and Fram Strait variability of temperature is independent of the variations in the volume flux. The former is dominated by advective processes and depends mostly on the upstream conditions while the latter is related to the local atmospheric forcing. Observed variations in the Atlantic Water pathways (namely intensification/ weakening of the branches of the Norwegian-Atlantic Current) result in the redistribution of the Atlantic Water in Fram Strait and strongly influence the heat transport into the Arctic Ocean. All these changes occur over long time scales and only quasi-continuous measurements over a decade and more give a chance to identify the nature of these fluctuations. Lacking spatial resolution is a problem in spite of the fact that the major parts of the transports occur in relatively narrow boundary currents. Technical problems with the present day equipment lead to redundancy of equipment. New technology available to replace conventional instruments on an operational basis is under development and a design of optimized observational array has been worked out on the basis of the ASOF-N experience.