The PAVE project is based on a combination of observational and modeling studies to investigate the varying inflow of AW into the Arctic Ocean. The historical data collected by the project partners and obtained from other sources will be used to describe the long-term variability the AW transformations along the two main pathways towards the Arctic Ocean.
Since 2000 IOPAS has carried out the summer hydrographic surveys covering the AW inflow region between the northern Norway and Fram Strait. These observations will be continue during three field campaigns during PAVE and used in a combination with hydrographic data collected by IMR to determine the spatial transformation and temporal variation of AW properties, in particular splitting of the AW flow between the Barents Sea and Fram Strait and recirculation in the Fram Strait in WP2. The hydrographic sections will be augmented with the ship-borne current measurements using Lowered Acoustic Doppler Current Profiler (LADCP) and vessel mounted ADCP (VMADCP) to provide data for the inverse model FEMSECT. The ship-borne CTD system will be equipped with fluorescence sensor to collect the chlorophyll data for validation of the biological model. Additional high-resolution sections will be measured in the regions of high mesoscale activity and frontal zones with a towed undulating CTD system.
The Atlantic inflow trough Fram Strait to the Arctic Ocean boundary current will by observed with two moored systems, deployed north of Svalbard. Two existing moorings equipped with McLane Moored Profilers and deployed in 2012 in the collaboration with the Norwegian project A TWAIN will be augmented with ADCPs and CTD sensors (MicroCats) in WP2 of the PAVE project to better monitor changes in the properties and inflow of Atlantic Water. To maintain the existing time series moorings will be deployed at the same locations (one in the A-TWAIN line along the 30°E meridian, the second one upstream, at 15°E).
The transport series of the Atlantic inflow to the Barents Sea will be also updated throughout the PAVE project in WP3. We will improve the quality of these estimates by including profiling current meters. We will collocate hydrographic data over the same period of year as the annual Polish cruises in the WSC (summer) over the period the arrays have been operated since 1997. This should provide a robust description of relations between the ocean transports and hydrography. Further these data sets will be compared to atmospheric reanalysis fields. There are several ocean model hindcasts covering the study area and a candidate readily available for us is the SVIM reanalysis (WP4). This was recently finished in the SVIM project (Spatiotemporal Variability In Mortality and growth of fish larvae in the Lofoten-Barents Sea ecosystem). Work is presently going on to validate the results. The SVIM results are obtained by the Regional Ocean Model System (ROMS), which has a resolution of 4 km. A finer resolution ROMS hindcast (2 km) is planned and will be used for PAVE if ready in time. In WP5 the model results will be compared with the observational data used in WP 2 and 3. The model fields and their atmospheric forcing will be analysed to identify the pathways of Atlantic Water and the transformation of this water mass. The variability will be examined by extracting time series of volume, heat and salt fluxes through selected sections. More advanced methods like empirical orthogonal functions will be used to identify patterns in the modelled pathways. Atmospheric modes corresponding to the variability in the branches will be extracted.
Changes in the physical environment will then be related to changes in the zooplankton, and also integrated biomass estimates. The coupled HYCOM-NORWECOM modeling system will be used for this study in WP4. A nested model configuration, where the TOPAZ system (http://topaz.nersc.no/) will provide the boundary condition for a high-resolution (3.5 km) model for the Fram Strait will the used. HYCOM is a hybrid-coordinate Ocean model designed to have good representation of both deep water (by isopycnal coordinates) and the upper water column (by z-coordinates). HYCom has been coupled to the biogeochemical model NORWECOM and used for several studies in the North Atlantic and the Norwegian Sea (e.g. Hansen et al., 2009). NORWECOM is nitrate-based and contains 3 nutrients, diatoms, flagellates, detritus as well as two size-classes of zooplankton. The model has been validated and tuned against in-situ data from the Norwegian and the Barents Sea, however in-situ observation in the Fram Strait has until now not been available for use and will be provided by the PAVE project for analysis in WP6.
In WP6 the zooplankton samples will be collected during the IOPAS summer cruises in 2013 and 2014 from transects covering the depth gradient from the deep parts of the Greenland and Norwegian Seas to the shallower shelf areas of the Barents Sea and Svalbard. The existing time series of the zooplankton data (1987-2012 in Fram Strait from IOPAS and 1985-2012 in the Barents Sea from IMR) will be prolonged for 2013 and 2014, with extended sampling to fill the gaps in our knowledge on vertical zooplankton distribution in those complex systems as well as on the proportion of small size fraction taxa (Microcalanus, Oithona, Triconia) in the mesozooplankton communities. Parallel to the high-resolution CTD sections, the plankton abundance will be measured with acoustical and optical (with Laser Optical Particle Counter, LOPC) methods.
Zooplankton samples will be collected from discrete water layers with Judy and MPS nets (mesh sizes 0.056 and 0.180mm, respectively). Zooplankton sampling will be vertically stratified in a manner reflecting the hydrographical structure of the water column revealed by temperature and salinity measurements taken prior to the net sampling. Standard methodology for the qualitative/quantitative analyses of zooplankton will be applied. Calanus will be identified to species for each developmental stage based on the description given in Kwasniewski et al. (2003). The importance of environmental controls for the studied biota will be assessed via statistical analysis of biological and environmental data. The impact of varying AW flow on Calanus species diversity and development will be assess based on comparison of Calanus composition and demographic structure from study locations with different temperature and advective characteristics to be found in individual branches of the Atlantic water flow.