Распространение плотных придонных вод на шельфе Арктических морей Dense bottom water transport over the shelf of Arctic seas Платов Г. А. (Platov G. A.) ИВМиМГ СОРАН, Новосибирск ICMMG, Novosibirsk
Problems with numerical simulation of deep water formation Regions of dense water formation have distant location from deep ocean Characteristic length scale of corresponding dynamics is small Diurnal variations are important
The Sources of deep water in Arctic According to Aagaard et al. (1981), to maintain the Arctic halocline about 1 2 Sv of high salinity (34.75 ) and low temperature (-1ºC) water is to be contributed. The main sources are: New ice formation in pack ice and in polynias 0.7-1.2 Sv (Björk, 1989, 1990), Cooling and freshening of Atlantic water, passing through the Fram strait and Barents Sea 0.6-1.0 Sv (Steele et al,1995), Deep water passing from Norwegian Sea (Jones, 1995).
The geographic location of significant polynia regions in Kara and Barents Seas An approximate position of shelf break line Some polynias are located close to the shelf break (1,2,7,8), some others are quite distant up to thousand km s apart (3,4,5,6). The analyzes of ICMMG model results shows that most productive polynia region from 1948 to 2008 is the vicinity of the Novaya Zemlya islands (4,5,6).
Mechanisms of dense shelf water deepening in higher scale ocean models (z-coordinates) Bottom Ekman layer Diffusioni Density anomaly forms an anticyclonic Horizontal diffusion spreads the dense (northern hemisphere) circulation water out of the dense core Ekman transport moves the dense Vertical mixing water out of the dense core Vertical mixing
The disadvantages of vertical mixing, applied as a mechanism of deep water formation Vertical mixing means the mixing of all cells situated along the path of dense water trajectory. That is the source of dense water must be strong and last for a long enough period, which is quite unusual situation in Arctic. In reality the dense water motion occurs along the topographic canyons and troughs, so that the mixing with ambient water is reduced substantially.
Numerical model region configuration Земля Франца Иосифа North-Eastern part of Franz Josef Land vicinity Horizontal resolutions are 1х1 km and 10х10 km (Rossby radius 5-6 km) Period of numerical integration is 40 days (winter season, February 1983) Initial temperature and salinity distribution corresponds to the horizontal mean for the open part of the basin ( ) and density anomaly for the shelf region ( )
Comparison of the Results 1x1 km 10x10 km
Propagation along the right side of the canyon (trough)
Theoretical background of the direction of dense water propagation The linear equation of non-viscid barotropic eddy is The right side corresponds to JEBAR (joint effect of baroclinity i and relief). If Х-axis directed along density gradient then JEBAR has the form I. e. the density gradient contributes only if depth gradient has a normal component.
Sloping convection Forced by the gravity component (-g HΔρ/ρ) Divergence of the dense core near the bottom leads to its anticyclonic rotation (northern hemisphere). Convergence of the light water at the top of the dense water column leads to its cyclonic rotation.
Propagation of the dense core along the coast line or sloping bottom. Anticyclonic rotation moves dense water from the rare to the front side, so that the whole core is shifted forward leaving the coast or slope on its right Similarity with the Kelvin waves
Parameterization of sloping convection The dense water subducts the ambient water, pushes it upward, where it fills the top of the dense water column. According to Wang (1984) the bottom velocity is u=½(ghδρ/ρ) ½
Dense water route parameterization If we know which way the bottom dense water would propagate then we can build a whole map of deep water motion which is similar to the river routes
parameterization 5 Comparison of the Results High Resolution Model Low Resolution Model Low Resolution Model with proposed 15 35
Arctic deep water volume The results show that application of this method to the Arctic and North Atlantic sea-ice model gives rize of deep water volume (S>34.91 and T<-0.1), but lower the volume of deepest water (S>34.94 and T<- 0.8) The reasons are an extra vertical mixing occurred due to vertical interpolation applied for a large vertical spacing near the bottom of the z- coordinate model increased transport of the dense water from the Arctic region toward the North Atlantic
Some conclusions Large scale models are not capable to simulate the sinking of the dense water along the shelf slope The introduced dense water route parameterization is able to move dense bottom water anomalies distant from the shelf breaks without substancial lost of their original properties. The approbation of new parameterization shows that additional justification of vertical mixing is necessary to apply for the higher depths in z-coordinate models Спасибо за внимание Thank you!