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5. Climatic Distribution of the Hydrochemical Characteristics in the Arctic Ocean.

| 5.1. Vertical Profiles.
| 5.2. Transects.
| 5.3. Mean Values and Dispersions at the Standard Depths.
| 5.4. Maps of Climatic Distribution of the Hydrochemical Characteristics at the Standard Depths.

5.1. Vertical Profiles.

Vertical distribution of hydrochemical parameters reflects a complicated, multi-layer water structure in the Arctic Basin and the Arctic seas.

Water column structure in the Arctic Basin is formed under the influence of a complex of external and internal factors. The external factors are: water exchange with the North European Basin through the Fram Strait and the straits between Svalbard and the Franz-Josef Land, with the Pacific Ocean through the Bering Strait, with the Baffin Bay through the straits of the Canadian Archipelago and with the Arctic seas.

The internal factors are: exchange of substance and energy with the atmosphere and ocean bottom, ice melting and freezing, interaction and dynamics of water masses within the basin, physical-chemical and biological processes in water masses.

Extreme values of concentrations of the hydrochemical elements at the vertical profiles demonstrate different origin of the water masses that form the water column in the Arctic Basin.

Unfortunately, investigators have not formulated to the present day a unit approach for description of the Arctic Basin structure and a unit terminology for water mass marking, though the water masses are the main element of the structure. It complicates our understanding of obtained results.

Attention should be paid to the most striking differences in vertical distribution of the hydrochemical parameters in the Eurasian and Canadian parts of the Arctic Basin. Minimum concentrations of oxygen and pH and clearly pronounced maximums of nutrients at the intermediate depths characterize the layer of waters of the Pacific origin mainly circulating in the Canadian part of the basin.

Vertical distribution of the hydrochemical parameters in the Arctic seas is characterized as even more complicated and variable. The most general peculiarities typical for many regions of the Arctic seas are presence of maximum concentration of oxygen and minimum concentration of silicon at the intermediate depths in the zones of river runoff influence. Both these extremes characterize different origin and dynamics complexity of the small in volume and short-lived water masses of the Arctic seas.

5.2. Transects.

Distribution of the hydrochemical parameters at vertical transects illustrates mean locations of the main elements of the water column structure in the Arctic Basin.

Extrema of the hydrochemical parameters in the Eurasian part of the basin are poorly pronounced. The upper quasi-homogeneous layer is saturated with oxygen up to 100% and is characterized with low concentrations of nutrients. Oxygen concentration decreases with depth, however, it is relatively high in deep layers, if compared with the other oceans, and it testifies for a good ventilation of the near-bottom layer. Concentration of nutrients increases with depth, and accumulation of mineral nutrients takes place in the near-bottom waters.

Kernels of low oxygen concentration are clearly seen at the vertical transects in the Canadian part of the basin, kernels of high nutrient concentration corresponding to them can be seen approximately at the same depths. These kernels indicate mean location of the Pacific waters of winter origin.

5.3. Mean Values and Dispersions at the Standard Depths.

Maps of mean values and dispersions of the hydrochemical parameters at the standard depths are given in the Atlas. This information allows us to estimate operatively general variability of the hydrochemical parameters in a given region and at a given depth. Naturally, the regions, located in frontal zones separating the water masses, are characterized by maximum variability. High variability of the hydrochemical parameters is typical also for the Arctic seas and the regions of continental slope.

Spatial and temporal irregularity of oceanographic stations with hydrochemical observations should be taken into account while working with the maps of mean values and dispersions. Moreover, we should mention insufficient accuracy and sensibility of methods of hydrochemical analysis carried out in the Arctic expeditions.

5.4. Maps of Climatic Distribution of the Hydrochemical Characteristics at the Standard Depths.

Maps of climatic distribution of the hydrochemical parameters at the standard depths were constructed using all available data, with the exception of questionable and rejected values. These maps illustrate general regularities of spatial distribution of the hydrochemical characteristics in the Arctic Ocean. The most serious problems by map construction were as follows: spatial and temporal irregularity of oceanographic stations and significant variability of the hydrochemical parameters in the frontal zones.

It should be taken into account that observations at 0 m depth (sea surface) have been performed only in the Arctic seas and only in summer, and the standard depth 5 m is accepted as the first surface horizon in the Arctic Basin.

Zones of river runoff influence can be clearly seen at the surface of the Arctic seas both in winter and in summer on the maps of mean distribution of silicate, alkalinity and pH. The contour of 10 µmol/l of silicate distribution is accepted as the boundary of river runoff influence in the Arctic seas (Rusanov et al., 1979). Distributions of the other hydrochemical elements at the surface of the Arctic seas in summer are determined, to a greater extent, by biological conditions and by a complicated combination of hydrometeorological and ice conditions. Therefore, even mean fields of these parameters have a mosaic structure.

Mean distributions of the hydrochemical parameters on the surface of the Arctic Basin indicate sources and conditions of formation of the surface waters. The water area of the Arctic Basin was divided into five regions by silicate concentration on the surface (Rusanov et al., 1979). The silicate concentration in each region is determined by a combination of biological, physical-chemical, hydrological and meteorological factors. The maximum silicate concentrations are observed in the region adjacent to the Chukchi Sea, and the minimum ones - in the western sector of the Arctic Basin, the surface waters in this region are formed under the influence of the Atlantic Ocean. The increased silicate concentrations in the region of the North Pole are related with upwelling of the Pacific waters from the underlying layers (Rusanov et al., 1979).

Phosphate and nitrate distribution in the Arctic Basin is very similar to that of silicate.

Differences in nutrient distributions in the Eurasian and Canadian sub-basins are most clearly pronounced at the intermediate depths (standard depths: 100, 150, 200 m), where the Pacific intermediate waters of winter origin are located. It should be mentioned that boundaries, separating the Pacific waters and the over- and underlying waters, are located at different depths in different regions of the Arctic Basin. Moreover, the depths, where these waters are deposited, vary with time. Therefore, interchange of regions with increased and decreased concentrations is often observed in distribution fields of the hydrochemical parameters.

Distributions of the hydrochemical parameters at deep and near-bottom horizons are more monotonous. Differences in mean concentrations between the Eurasian and Canadian sub-basins are pronounced not so clear.