Description of work
Task 5.1: Study the response of the inland seas to changing conditions of atmospheric forcing and fluvial continental discharges (Black and Caspian seas)
5.1.1) The mesoscale circulation of the Black Sea and the Caspian Sea. The approach is to use a numerical model with the least possible amount of horizontal dissipation, in order to allow the instabilities of the flow to develop as freely as possible and to handle abrupt topography, such as the steep channels and escarpments off the Caucasian and Turkish coasts. DieCAST stands as the model of choice, because of its 4th-order resolution in the horizontal (allowing large Reynolds numbers at the grid level) and its z-level discretization in the vertical (best suited for the representation of topographic steps). The application of this model to the BS basin must also ensure that the grid resolution is sufficiently high to resolve scales below the radius of deformation, that is, a few kilometres. Using high resolution DieCAST for the Adriatic Sea gave encouraging results for the modelling of mesoscale variability. A high resolution (two nautical miles) version of the DieCAST has already been developed for and implemented in the Black Sea to reproduce the main structures of the circulation and mesoscale variability.
5.1.2) Horizontal mixing. The reaction of horizontal mixing processes in the Black Sea and the Caspian Sea to the climate change based on DieCAST numerical results will be evaluated. The analysis will focus on the horizontal mixing linked to the study of cyclogenesis and anticyclogenesis of mesoscale eddies within and shoreward of the boundary current, their trajectories, interactions and eventual senescence.
Task 5.2: Study the effect of sea level variations in the dynamics of inland seas (Caspian and Aral)
5.2.1) Topographic mixing. After data validation, numerical simulations will be run to evaluate the relevance of bottom and side effects for different surface levels. POM, a model widely used in operational simulations, will be used because of its low computational cost, due to the splitting procedure with different time steps for the baroclinic and barotropic modes. The effect of internal mixing on the sea surface temperature and their space variability will be studied for different sea levels.
5.2.2) Vertical mixing. The effect of different atmospheric forcings, including extreme events, on the extension of the upper mixed layer of the Caspian and Aral seas and on their seasonal warming-cooling cycle will be studied. Background stratifications for the seas will be designed to be compatible with the historical hydric balance of the future climatic scenarios. Simpler models and even dimensional analysis will also be used for this analysis and compared with POM simulations. When possible, results will be compared with those derived by the simulations performed in 5.1.1).
5.2.3) Heat Budget. 1D-mixing models will be run in parallel to study how well they can be fitted to capture the horizontal variability under different scenarios. Variation of the heat budget of the seas and the location of active and dead mixing zones will also be studied.
Task 5.3: Parameterisation of vertical mixing in inland seas
5.3.1) Shear mixing in highly-stratified systems. The applicability of standard closures for shear mixing in open ocean will be tested for high stratification conditions. This study will be done by a) testing different closures with either measured or historical data (see WP2) or obtained within the programme (WP4) and b) performing K-H laboratory experiments within the range of the Ri number expected in inland seas as determined from hydrophysical measurements and numerical modelling. The Ri range for inland seas under present and future climate change scenarios will be estimated.
5.3.2) Convective process. Due to characteristics of inland seas, single and multi-component could be expected to be relevant mixing mechanisms. In the Aral Sea three types of convection have been identified: winter thermal, winter thermohaline associated with ice growth (and salt rejection) and summer convection due to evaporation. Dimensional analysis and laboratory work will be carried out to determine the relative importance these processes can have on the mixing of inland seas according to historical measurements and new data obtained in the field campaigns included in WP4. Existing parameterisations of convective fluxes will be tested with new field data, if available.
5.3.3) Mixing variability. The intermittency of mixing and the horizontal variability will be studied based on numerical results and field data. Statistics of different turbulent parameters in highly-stratified inland seas will be compared with existing results in the ocean and in lakes.
Task 5.4: Quantify the effect of vegetation change on albedo at a regional scale
We will use satellite data over the last 30 years to transfer the changes of vegetation into changes in albedo. Additional data will be derived from documentary evidence and proxy data. A Leaf Area Index will be applied.
Task 5.5: To obtain a precise assessment of changes in the relative sea level and changes in water parameters
5.5.1) Geomorphology (Aral Sea) : Using available remotely sensed imagery and field survey supported by precise DGPS, we will identify and map shoreline features such as wave-formed depositional ridges, deltas and erosional platforms. In the Aral Sea, this work will be initially focused on the eastern and southern shorelines as the shallow sloping, depositional nature of these areas is likely to have produced a well-preserved sequence of identifiable features. A second phase of the work will consider the interaction between littoral processes and slopes on the steeper western shore of the Aral Sea as this may be a significant source for sediment and nutrients and so influence a range of processes within the sea.
5.5.2) Sedimentology (Black, Aral and Caspian Seas): We will identify the processes responsible for deposition at key locations, thereby providing information on littoral conditions leading up to, during and following marine regression/transgression. Specific techniques will include high-resolution site stratigraphy, similar to that used in palaeoseismic studies, particle size analysis, environmental magnetism, organic content, geochemistry and thin section analysis. We will also assess pedogenic and diagenetic features for evidence of groundwater behaviours over time,
5.5.3) Palaeoecology/Biostratigraphy (Aral, Black and Caspian Seas): Where fossil material is present (particularly molluscs and pollen, but possibly also fish, diatoms and seeds), these will be identified to help construct a more complete picture of contemporary conditions (e.g. changes in local energy state, salinity). The fossil record will be assessed for use in creating a high-resolution biostratigraphy to assist in correlation between sites. The data assessed for this will be in the form of indicator species, assemblage characteristics and morphological changes.
5.5.4) Chronology (Aral, Black and Caspian Seas): A relative chronology for features and events will be constructed using a morphostratigraphical approach. A more precise chronology will use the radionuclide record in accumulations of terrestrially-derived sediment in depressions on the exposed former littoral zone and in shallow water. The focus will be upon 210Pb and 137Cs, measured through alpha and gamma spectroscopy, as these are widely applied dating tools.