THERMOHALINE STRUCTURE ON THE SURFACE OF THE SEA OF OKHOTSK INCLUDING THE ICE COVER

Transcription

1 THERMOHALINE STRUCTURE ON THE SURFACE OF THE SEA OF OKHOTSK INCLUDING THE ICE COVER Mariya M. Shutova 1 and Lev P. Jakunin 1 1 Far-Eastern State University, Vladivostok, Russia ABSTRACT Data on distribution of temperature, salinity and water density on the surface under an ice cover of the Sea of Okhotsk practically are absent. The natural observations of temperature and water salinity of basins, free from ice, and also data of ice patrols, have allowed to approximate position of an ice edge in February with an isotherm of water below -1 C, and boundary of broken ice with an isotherm -1,7 C. In offshore water areas, according to coastal stations where there is a constant pushing of ice from coast, the temperature of water is reduced up to -1,8 1,9 C. On basins without an ice cover actual observations of salinity have been used, and under an ice cover water salinity on the surface was accepted depending on temperature of freezing. The number of deep-water and passing observations of water temperature in February has made about 800 cases. Measurements of water temperature at coastal stations have exceeded 180, and observations of salinity were carried out only at deep-water stations on pure water in a southeast part of the sea and have made 273 cases. Data, and also materials of observations of ice cover were given from the archive of air observations of Far East State University. In the paper the generalized data are resulted. In result maps of water temperature, water salinity and water density on the surface of the Sea of Okhotsk in February of severe, moderate and warm years have been made. KEY WORDS: Sea of Okhotsk; Ice cover; Water temperature; Water salinity; Water density. ICE COVER RESULTS The ice cover distribution was determined as average value from three years on three ten-day periods. For each type of ice cover the averaging was made to 9 ten-day periods (Figure 1). In Table 1 the years, subjected to averaging, and also average percent of the sea area, covered by ice in February, are shown

2 TEMPERATURE OF WATER ON THE SURFACE IN FEBRUARY In February on the surface, free from ice, in years with maximum ice cover distribution warmer waters are observed, in comparison with all water area. The temperature changes from -0,4 to -1,7 C (Figure 2,а), that is consequence of advection of warm Pacific waters. At border of an ice edge the temperature of water has values from -1,0 to -1,7 C, at boundary of broken ice from -1,7 to -2,0 C. Table 1 Years Average Average Average Average long-term ice cover distribution The ice area, in % from the sea area Types of winters February 89,4 90,3 85,1 88,3 Severe 46,8 48,6 61,9 52,4 Moderate 77,8 71,0 71,7 73,5 Warm 70,9 At the Kamchatka coast the temperature of water changes from -1,5 to -2,0 C. On the northern part of the Sea of Okhotsk and in the Shelikhov Gulf the minimum values of water temperature from -1,8 to -2,0 C is observed. On the Sakhalin offshore values of water temperature from -1,6 to -1,8 C are observed, and the lower-range value of water temperature -1.8 C was registered in the Aniva Gulf. At moderate winters the area, occupied by ice, is less (73,5%) in comparison with the years of maximum ice cover distribution (88,3%). On the surface, free from ice, the temperature of water has positive values that are connected to advection of the Pacific waters, and changes in limits from 0,5 to 2,6 C (Figure 2,b). Between boundaries of ice edge and broken ice the temperature of water has values from 0,43 to -1,7 C. At the Kamchatka coast the temperature of water changes in limits from 1,0 up to -1,47 C, on northern part of the Sea of Okhotsk and in the Shelikhov Gulf from -1.6 to -1.8 C. The Pacific warm waters are distributed to the large area in comparison with severe years of maximum ice cover. On the Sakhalin shelf the temperature of water has values in limits from -1,55 to -1,7 C. The lower-range value of water temperature -1.7 C was registered in the Aniva Gulf on water area with grey ice. The ice area in years with minimum ice cover distribution (warm winters) is 52.4%. The extensive water area, free from ice, has positive values of water temperature, changing in limits -302-

3 from 3,0 to -1,0 C (Figure 2,c). Typical convolution of isotherms obviously specifies on inflow of Pacific waters. Positive values of water temperature extend from the south up to latitude 57 N. Near to boundaries of an edge of ice the water temperature changes in limits from 0,0 till - 1,0 C, at boundaries of broken ice from -1,0 to -1,7 C. Warmer waters adjoin to the Kamchatka coast, in comparison with years of moderate and warm winters; the temperature here changes in limits from 2,0 to -1,0 C. Negative values of water temperature are observed closer to the coast. On the northern part of the Sea of Okhotsk and in the Shelikhov Gulf the water temperature changes in limits from -1,7 to -1,8 C, more cold waters also are located closer to coast. On the Sakhalin shelf the water temperature is -1,6 1,7 C, the minimum values of water temperature are observed in the Aniva Gulf. WATER SALINITY ON THE SURFACE IN FEBRUARY Water salinity has the maximum values as a result of salinization of waters due to ice formation in the winter. In severe years with maximum ice cover distribution on all water area of the sea the high salinity of water which changes in limits from 33,0 up to 33,25 (Figure 3,а) is observed. On the surface, free from ice, the lower-range values of water salinity 33,0 are obtained. The high values of water salinity 33,25 are observed on water area with grey ice. Variation of water salinity in years with moderate winters changes in limits from 32.9 up to 33,25 (Figure 3,b). On all water area of the sea they less saline, than in the severe years with maximum ice cover. The lower-range values of water salinity 32,9 33,0 are observed on the surface, free from ice. The greatest values of water salinity 33,25 are observed in areas of formation of grey ice on the northern part of the Sea of Okhotsk and in the Shelikhov Gulf. In years with warm winters water salinity of the Sea of Okhotsk changes in limits from 32,8 up to 33,25 (Figure 3,c). On the surface, free from ice and occupying the larger area, than in other types of years, the lower-range values of water salinity from 32,8 up to 33,0 are observed. Waters with the lowered salinity (32,9 ) are observed to the latitude 57 N. The greatest values of water salinity (33,25 ) are observed in area of formation of grey ice. The received maps have allowed calculating fields of water density on the middle of the winter period in different types of years in according to ice cover distribution. WATER DENSITY ON THE SURFACE IN FEBRUARY Water density in the Sea of Okhotsk increases in the autumn, before to the ice formation. It happens due to reduction of water temperature. Then process of ice formation has been started, and the increase in density depends from salting-out of ice. In February the water density of the Sea of Okhotsk increases only due to raising of water salinity at ice formation. In severe years with maximum ice cover the water density has the greatest values, changing in limits: on the surface, free from ice, from 26,51 to 26,76 standard units; on the area of the sea, occupied by ice, from 26,63 to 26,76 standard units (Figure 4,а). In years with moderate winters waters of the Sea of Okhotsk less dense and change in limits: on the surface, free from ice, from 26,25 to 26,55 standard units; on the area of the sea, occupied by ice, from 26,35 to 26,74 standard units (Figure 4,b)

4 In warm years with minimum ice cover waters have the lowered salinity and smaller density, in comparison with winters of other types of ice cover. Their density amounts: on the surface, free from ice, from 26,21 to 26,72 standard units; on the area of the sea, occupied by ice, from 26,36 to 26,76 standard units (Figure 4,c). Similar maps, including the ice cover, are made for the first time and can be used for calculation of currents on the surface layer, ecological characteristics, biological parameters and other hydrological factors. REFERENCES Luchin, V.A. (1998), Hydrological regime, In Hydrometeorology and hydrochemistry of the seas, Vol. IХ: Sea of Okhotsk, Part 1: Hydrometeorological conditions, Saint-Petersburg, Hydrometeoizdat, Russia, pp (in Russian). Chernyavsky, V.I. (1973), About some questions of forecasting such as a thermal regime in the Sea of Okhotsk, News of Pacific Research Fish Centre, Vladivostok, Russia, Vol. 86, pp (in Russian). Chernyavsky, V.I. (1992), Features of thermal formation an active layer of the Sea of Okhotsk, Oceanologic bases of biological efficiency of waters of a northwest part of Pacific, News of Pacific Research Fish Centre, Vladivostok, Russia, pp (in Russian). Yakunin, L.P. (1993), Temperature and Salinity of Surface Water of the Okhotsk Sea of Extremal Periods of Year, Abstracts of the 8 th International Symposium on Okhotsk Sea&Sea Ice, Mombetsu, Japan, pp Maximum ice cover distribution Moderate ice cover distribution Minimum ice cover distribution Figure 1. Expansion of boundaries of ice edge (1), broken ice (2), grey ice (3) (maximum ice cover distribution): - 1 _ - 2 _. _ pure water -304-

5 a) maximum ice cover distribution b) moderate ice cover distribution -305-

6 c) minimum ice cover distribution Figure 2. Distribution of water temperature ( 0 С) on surface of the Sea of Okhotsk in February. а) maximum ice cover distribution -306-

7 b) moderate ice cover distribution c) minimum ice cover distribution Figure 3. Distribution of water salinity ( ) on surface of the Sea of Okhotsk in February

8 а) maximum ice cover distribution b) moderate ice cover distribution c) minimum ice cover distribution Figure 4. Distribution of water density (sigma-t) on surface of the Sea of Okhotsk in February