FEARURES OF FORMATION AND LONGTERM VARIABILITY OF THERMOHALINE STRUCTURE AND OCEAN CIRCULATION OVER THE SIBERIAN CONTINENTAL SL0PE
Vladimir K. Pavlov* and Vladimir V. Stanovoy*
The Arctic and Antarctic Research Institute, St. Petersburg, Russia
1.INTR0DUCTION
Continental slope with sea depths from 200 to 2000 m occupies 4.34 min. sq. km accounting for 29.4% of the total area of the Arctic Ocean (Terms and Notions, 1980). Maximum depth gradients in the region of the continental slope are observed in the Beaufort (0.09), Laptev (0.05), Kara (0.08) and East Siberian (0.02)seas.
Such high gradient values exert significant influence on formation of barotropic ocean circulation and ice drift over the continental slope. The highest drift velocities re registered here(Romanov,1992), as well as maximum velocities of wind-driven and tidal currents (Proshutinsky,1993). Intensive dynamics of ice and water provides prerequisite for formation of numerous cracks, fractures and pressure ridges in this region (Romanov,1992). Presence of ice free areas and areas of thin ice in winter period brings into existence constant convective processes.
The continental slope is a zone, where a complex interaction of shelf water masses of marginal seas, water mass of the Arctic Basin and waters of non-Arctic origin (he Atlantic and Pacific waters) takes place. Appearance of stableand unstable barocline structures is a consequence of this interaction. They are eddies and internal waves contributing to vertical advection of heat and salt.
Possibility of appearance of intensive vertical water motions and the fact, that the warn Atlantic waters have maximum rise to the surface in the region of the continental slope, allow us to include these water areas in the list of the most important investigation objects of climatic variations in the Arctic Ocean.
2. METHODS AND DATA
The following observation data were used for analysis of formation and variability of thermohaline in the region of the continental slope: observation data generalized in the Joint US-Russian Atlas of he Arctic Ocean (1997); gridded data on water temperature and salinity for separate years used by Poliakov and Timokhov (1994) kindly put at our disposal by the authors for this research work; observation data on temperature and salinity in the region of the continental slope collected in the result of joint Russian-Norwegian and Russian-German expeditions to the Barents, Kara and Laptev Seas.
3. DISCUSSION
Analysis of large amount of data for winter period revealed that there was a good correlation between temperature and salinity values in waters over the continental slope in spite of their spatial irregularity (Fig.1).
Water temperature in the surface layer is on average for 0.03-0.005℃ lower than the freezing point. The above-listed features of the spatial temperature and salinity distribution in the surface layer over the continental slope point to the fact, that the convection and vertical advection of water are the main processes of thermohaline structure formation of the water masses at least in winter period.
It is the opinion of a number of authors (Bulgakov, 1975; Shpaikher, 1967; etc) that the density convection developing in autumn-winter can reach the Atlantic water layer and be one of the main mechanisms of heat transfer to the surface especially in the region of the continental slope and deep-water troughs. Typical spatial distribution of the surface temperature and salinity in conditions of intensive development of the winter convection is given in Fig.2.
A narrow stripe of cold and salty water stretched along the continental slope from the Kara to Chukchi Sea can be observed on the surface. Typical vertical structure of the water masses is represented in Fig. 3 at the transect across the continental slope of the Laptev Sea.
We should concentrate our attention on presence of two isolated water masses to the North and to the South off the continental slope divided by the vertical convection zone. The shelf water mass has salinity 28-30 psu andtemperature-1.5-1.7℃.Salinity of the surface waters of the Arctic Basin is close to hat of the shelf waters and equals 29-30 psu, its temperature being close to the freezing point. Salinity of the water mass in the
Corresponding author address. Vladimir K. Pavlov, AARI, Dept. Of Oceanography, 38, Bering St., St.Petersburg, Russia, 199397; e.mail: mod@aari.nw.ru
Vladimir V. Stanovoy, AARI, Dept, Of Oceanograyphy, 38, Bering St,St,Petersburg, Russia, 199397;e-mail:mod@aari.nw.ru
