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FP5

ASOF-N Sintesi della relazione

Project ID: EVK2-CT-2002-00139
Finanziato nell'ambito di: FP5-EESD
Paese: Norway

Heat Flux in the Western Barents Slope measured from 2003-2005 during ASOF-N

The Barents Sea influences the Arctic Ocean both by providing a pathway for Atlantic Water (AW), but also as a shallow shelf sea producing dense water through cooling and brine release. The Barents Sea provides intermediate water down to 1200 m depth in the Arctic Ocean, and, together with the Kara Sea, is the only source area for shelf waters ventilating the Nansen Basin below the halocline. Thus, knowledge of the variability of the Atlantic inflow to the Barents Sea is important for the understanding of the climatic state of the Arctic Ocean, and for evaluations of climate change.

ASOF-N continued a time series started in 1997 of volume and heat flux through the Western Barents Slope (WBS) using moored instruments. These cover the cross section where the Atlantic inflow takes place -with the exception of heavily fished waters. Temperature and velocity are monitored, allowing to integrate heat fluxes and to distinguish between eastward, westward and net fluxes. The time series is now sufficiently long to determine the variability of the oceanic fluxes through the WBS on inter-annual time scales - and to approach the declared objective of the ASOF cluster to capture variability on decadal time scales.

The long-term mean heat flux is 40 Terrawatt (TW) into the Barents Sea. Considering the inter-annual variability there was a relatively high heat flux into the Barents Sea in the winter of 2002/2003. Thereafter there was a pronounced decrease and 2003/2004 had the lowest heat flux observed during winter. In addition to the moorings, hydrographic measurements with high spatial resolution were used to derive flow field and heat flux six times a year.

Key innovative features and findings:
1) The combination of these two observational methods is one innovation made during the ASOF-N in obtaining an estimate of heat transport as accurate as possible:
2) The splitting of the flow of AW across the WBS was observed to take place in one wide branch but also to be split into several narrower branches, depending on the wind field. Between the branches there might be a weaker inflow or a return flow. At times the flow across the section is dominated by outflow (westward flow) and AW is flowing into the Barents Sea only in the southernmost part of the section.
3) There is no correlation between the fluxes and the temperature of the inflowing water. In fact, in certain periods temperature increases while the volume flux decreases. This shows that the WBS temperature is independent of the volume flux. The reason is that while the temperature of the inflowing water depends on the temperatures upstream in the Norwegian Sea, the volume flux depends mainly on the local wind field. This shows the importance of measuring both volume transport and temperature, since they not always are varying in the same manner. The short-time variations in the heat flux closely resemble the short-time variations in the volume flux, while the temperature variations influence the longer-term variations in the heat flux.
4) A realistic model representation of the Barents Sea region was made possible by another innovation, the coupling of a dynamic-thermodynamic sea ice model to a three-dimensional ocean general circulation model for the purpose of conducting climate dynamical downscaling experiments for the Barents Sea region. The Regional Ocean Model System (ROMS, http://marine.rutgers.edu/po/index.php?model=roms) was chosen as most appropriate since its model architecture is suitable for shelf seas as the Barents Sea. The improvement of the ROMS model is the sea-ice model extension, which performs well also on the high-resolution grid used and is absolutely necessary for realistic Barents Sea simulations. The model will be used to conduct a hind-cast for the period 1990-2005 including 3D fields of velocity and hydrography as well as water level and sea ice thickness and concentration. The horizontal grid resolution is ~10km. The vertical is resolved by 32 terrain following levels. Previous model validation with results from a similar model implementation (i.e. using slightly different and less accurate forcing) against observations show that seasonal and inter-annual variability in the ocean are tracked successfully. Furthermore the model results are used to examine details in space not covered by observations (incl. estimates of the through-flow of AW in the Barents Sea to the Arctic Ocean).

Users:
- Scientists in climate research - the oceanic heat flux through the Barents Sea is an important part in the North Atlantic and Arctic heat balance
- Scientists in Arctic Ocean research - influence of ocean temperature on sea ice, atmosphere, chemical & biological processes
- Offshore technology and shipping in the Barents Sea and the Arctic - oceanic heat is expected to affect the Arctic ice cover
- Commercial fishery - the temperature effect on the distribution of marine organisms
- Advisory panels for national and international policies

Informazioni correlate

Reported by

INSTITUTE OF MARINE RESEARCH
POSTBOKS 1870 NORDNES
5817 BERGEN
Norway
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