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The animation below shows temperature on the level of the constant potential density (an isopycnal level) of 26.6 kg/m3. In the ocean interior this level is placed at approximately 300 m below the surface (but it would rise closer to the surface over the shelf in summer). In absence of strong vertical mixing, fluid particles found on this level away will tend to remain on it (as the effect of the ocean stratification that tends to inhibit vertical motions). Because of low mixing at the depth of the layer, the potential temperature sampled on this level can be viewed as a passive scalar (a quantity that is conserved following the fluid element). The animation shows influence of cold subarctic and warm subtropical waters. In particular, in winter the northward slope flow associated with the wind-driven downwelling regime separates the subarctic waters from the shelf. Subsurface eddy variability in spring stirs subarctic and subtropical waters, preparing a mixture that will be upwelled onto the shelf in summer. The northward transport of subtropical waters and horizontal stirring is more vigorous in 2010 (influenced by El Nino). [model and animation: courtesy S. Durski