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The study area is strongly influenced by runoff of the Amur River, which leads to significant reduction of salinity of near-surface waters and sharpening of horizontal and vertical density gradients. Another important feature is coastal upwelling induced by the prevailing southern winds during summer. The mean density field for summer was constructed on the 1° grid using the data set included 130 CTD profiles obtained during four cruises of R/V “Professor Khromov” (1998–2000 and 2006, FERHRI) and 120 quality-controlled profiles (1937–1993) from the North Pacific Hydrobase. A four-layer piecewise curvilinear parametric model of vertical density distribution consisted of a homogeneous surface layer, a seasonal pycnocline (represented as two layers) and a deep layer. Ten model coefficients (depth, density and maximum density gradient for each layer interface) were derived for each profile using the nonlinear least squares fitting to observed data, then they were averaged within 1° squares. Comparison with the commonly used isobaric and isopicnal methods of averaging show that for strong stratification and high horizontal density variations a parametric approach is preferable. The isobaric averaging can strongly deform the density structure in the layer 0–150 m: the measured step-like distribution with the sharp pycnocline was fully diffused by averaging procedure on z-levels. This also can change an inclination in the isopycnals, especially near the edge of the continental shelf. The isopycnal approach is of little use in the surface layer.

Palabras clave: parametric model; density; vertical structure

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