Servizio Comunitario di Informazione in materia di Ricerca e Sviluppo - CORDIS

The optimised observing system for monitoring oceanic fluxes in Fram Strait and western Barents Sea

The long term consolidated data sets necessary to determine the variability of the freshwater and heat fluxes between the Arctic Ocean and the North Atlantic require an innovative design of the cost effective and well-calibrated measurement arrays. The northward flow of the Atlantic water carrying heat into the Arctic Ocean has to be monitored in two main gateways, the eastern Fram Strait and Barents Sea Opening. The southward freshwater flux, which enters the Nordic Seas both as liquid water and sea ice needs to be measured across the western Fram Strait, including the wide shelf east of Greenland. The latter requires current measurements and salinity stratification in shallow depths as well as ice thickness and velocity. To monitor fluxes not only the large cross-sections of the gateways have to be covered by measurements but also intensive variations on a wide range of scales, revealed by earlier observations have to be resolved.

Thus a larger number of moorings and instruments is needed or integral methods, measuring the whole water column have to be used. During ASOF-N observational arrays in Fram Strait and Barents Sea Opening were augmented and optimised in accordance with the observed time-space variability of measured parameters. Newly developed instruments were installed in the moorings, the observational arrays were redesigned for optimal combination of various properties, and transport estimates were proposed based on empirical relations to especially selected instruments. To secure data collected under harsh environmental conditions the possibilities of the near real-time data transfer via satellite link with pop-up buoys was tested. To complement the observing system of mooring arrays a grid of hydrographic stations was designed and repeated every summer to get the spatial variability of the Atlantic water pathways.

Key innovations
The Fram Strait mooring array was optimised to achieve better performance in measurements of temperature, salinity, currents and ice thickness - a prerequisite to derive heat and freshwater fluxes. In the eastern and deep part of the strait additional instruments were added at the depth of ca 700m to resolve the lower boundary of the Atlantic water layer. Two new moorings placed in the deep part of the strait to resolve the recirculation patterns of the Atlantic water and thus to reduce the error in volume transport estimates.

In addition to the moorings, integral measurements were performed with the use of bottom pressure recorders (BPRs) and inverted echo sounders with pressure sensors (PIESs) to estimate the barotropic currents and heat content of the water column. The performance of different current meters and TS sensors during the long-term deployments was evaluated and unreliable instruments were replaced to achieve the highest data recovery rate and the best data quality. The freshwater part of the mooring array in the western Fram Strait was equipped with near surface salinity sensors. Tube moorings in combination with Acoustic Doppler Current Profilers (ADCPs) were successfully deployed on the shelf, surviving the extensive ice cover and drifting icebergs. The moorings in the Barents Sea Opening were combined with a high-resolution hydrographic section repeated 6 times per year. Additionally this moored array was augmented with two bottom-mounted ADCPs in shallow parts. A new strategy was used for tracking the Atlantic water pathways based on combination of moorings, floats and hydrographic sections. The hydrographic sections included not only standard CTD casts but also currents profiles, which were measured by the lowered ADCP and quasi-continuously by the vessel-mounted ADCP. The grid of stations was adjusted to optimise the coverage of spatial structures.

Potential users
Scientists needing information on the physical conditions in the Arctic Ocean. Companies working on development of the novel oceanographic instrumentation. Environmental Protection Agencies and fishery management (recommendation for sustainable observing systems). Climate or ocean observing programmes such as GOOS/GCOS could be interested in recommendations for the Arctic Ocean Observing System regarding methods of measurements, instrumentation, efficiency of the observing system, data transfer, etc.

Expected benefits.
Improvement of the existing observing system to assess Arctic change including additional observed properties, better coverage of the key areas, higher data recovery rate. Improved estimates of the oceanic fluxes due to more reliable and accurate time series, measured in representative locations with higher resolution. This allows for a better model validation and improvements in the potential of the models to predict environmental conditions. The experience gained in the design of a sustainable and cost effective observational system under harsh Arctic conditions.

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POSTFACH 12 0161