SPATIAL STRUCTURE AND DYNAMICS OF INTERME DIATE WATER IN THE NORTHWESTERN PACIFIC

The structure and intraannual variability of the layer of North Pacifi c intermediate water (NPIW) are studied on the basis of analysis of mo re than one thousand Japanese hydrographic stations in the northwester Pacific, NPIW is defined as a minimum on vertical profiles of seawate r salinity. The absence of seasonal variability in the NPIW layer belo w 100m is revealed as well as significant predominance of meridional v ariability of all the parameters compared with the zonal one. A kinema tic model of the NPIW layer, developed for the meridional section alon g 155 degrees E showed the existence of water transport in the equator ial direction caused by vertical mixing. It allowed us to estimate the magnitude of the transport as 1 cm/s, that gives the period of NPIW c omplete renewal equal to 10 years. It is also shown that vertical mixi ng induces density increase in the northern part of the layer while it s buoyancy increases in the southern part. The formalism developed for the description of cabbeling allowed us to show that the contribution of this effect reaches 30% of the local changes of seawater density e verywhere, not only in the Subarctic Front as it was considered before .