Work package 1

Work package 2

Work package 3

Work package 4

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Slope convection and overflows off shelves

Work package 3

Key personnel and responsibilities:
Bjørn Ådlandsvik (IMR):
Principal investigator, regional high resolution modelling.

Harald Loeng (IMR): Field work in Bjørnøyrenna, scientific links to ASOF.
Ilker Fer (Bjerknes): Field work in Storfjordrenna, plume physics including microstructure.
Trond Dokken and Eystein Jansen (Bjerknes): Sediment interaction and isotope studies.
Svein Østerhus (Bjerknes): Moorings, scientific links to Greenland-Scotland overflow.
Tor Eldevik (NERSC): Very high resolution outflow modelling.


Activities


Field work 2003-2006: Trawl-proof ADCPs will be deployed in Storfjordrenna and Bjørnøyrenna, recovered and redeployed, in order to provide near continuous time series of cold outflows. Ship-mounted ADCP will add information on the ambient currents. Samples for oxygen and carbon isotope studies will be collected in conjunction with CTD surveys. The nature of intermittency and turbulent mixing within the overflow will be resolved using a profiling microstructure measuring system (to be purchased). Similar measurements will take place in both outflows. Personnel from Bjerknes will take part in cruises organized by IMR and vice versa.
Modelling: The regional modelling will use the ice-ocean model (ROMS) focussing on flow of dense water from the shelf to deep water. High resolution atmospheric forcing fields to be produced in WP2 will be used. The effects of topography on mixing will be examined through idealized very high-resolution experiments with the MITgcm (Marshall et al., 1997). Parameter studies of the topographic drag based on non-resolved bottom-roughness statistics will be performed. The established parameterizations will be used in the ROMS and the MITgcm models that will subsequently be used to simulate the outflow of dense bottom water from the two study areas.
Discussion, description and motivation:
Bottom boundary layers through which dense overflows contribute to the world ocean circulation are poorly represented in large scale models. A large group of today's state-of-the-art ocean models systematically underestimates the cascade, and an improved parameterization of topographic effects is desirable. Recent profiling of the Storfjordrenna outflow (Fer et al., 2002) has demonstrated an internal two-layer structure with implications for the understanding of entrainment and mixing. Detailed structural analysis and long term measurements are required.
Most of the dense water produced in the central Barents Sea leaves the Barents Sea via the northern part of Bjørnøyrenna south of Bjørnøya. As the outflow may be episodic, it is desirable to monitor the outflow for several years. The outflow of Arctic water south of Bjørnøya was not successfully measured during VEINS because the moorings twice were taken by fishing vessels. Also, a mooring in Storfjordrenna deployed during NOClim phase I was lost due to trawling. It is therefore necessary to use trawl proof bottom mounted ADCPs of the same type that have been used with great success during the WOCE experiment and later in the Faroe-Shetland Channel. The EU-funded ASOF-N project measures currents in the deepest part of Bjørnøyrenna and southwards. ADCP measurements from the slope will be an important contribution both to the EU-project and to the international ASOF programme. High precision temperature and pressure will also be recorded at the ADCP locations.
Ongoing projects at NERSC aiming at better turbulence modeling in boundary layers will underpin activities proposed here. Other activities like the planned principal module 2 in RegClim phase III, focussing on downscaling and Atlantic inflow, will benefit from this work package by improved handling of the export of dense water from the Barents Sea in the ROMS model.

 

References

Fer, I., R. Skogseth, P.M. Haugan, and P. Jaccard. 2002. Observations of the Storfjord outflow. submitted to Deep-Sea Res. Part I.

Marshall, J., C. Hill, L. Perelman, and A. Adcroft, 1997: Hydrostatic, quasi-hydrostatic, and nonhydrostatic ocean modelling. J. Geophys. Res., 102, C3, 5733-5752.


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