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$B3$I9%G!<%?$,$"$kDxEYC_@Q$5$l$?(B70$BG/Be8eH>0J9_$N8&5f$K$h$j!"CO0hE*$J(B $B3$I90h$NJQF0!"FC$K3$I9LL@Q$NG/!9JQF0$,Bg5$>l$N1F6A$r6/$/l>r7o$N0c$$$,3$I9LL@Q$N0c$$$KH?1G$5$l$k$N$+$O$h$/J,$+$C$F$$$J$$!#$3(B $B$N%W%m%;%9$r2rL@$9$k$3$H$O!"Bg5$>l$,3$I9$K5Z$\$91F6A$NDjNL2=!"$^$?!"(B $B3$0h$K$h$kBg5$$+$i$N1F6A$NFormation of the Okhotsk Sea Intermediate Water (S.V.Gladyshev ) $BH/I=MW;]!'(B
Okhotsk Sea Intermediate Water (OSIW) originated in the Sea of Okhotsk plays an important role in modification of North Pacific Intermediate Water (NPIW) (Talley 1991; Talley 1993; Talley and Nagata 1995; Yasuda 1997; Freeland et al. 1998; Watanabe and Wakatsuchi 1998). According to Talley [1991], the former ventilates NPIW in a wide density range between 26.65-27.6 sigma theta through the entire North Pacific. Analyzing Russian historical data, Moroshkin [1966] defined that the largest difference in water properties between the Sea of Okhotsk and NPIW in the vicinity of Kuril Islands is in a layer 200-800 m. Watanabe and Wakatsuchi [1998] confirmed this result, based on their Japanese data set. This difference is caused by a few reasons that have been already investigated in more or less degree: strong tidal mixing in the Kuril straits, brine rejection in polynyas over northern Okhotsk shelf and Soya Water outflow through Soya Strait to the Deep Kuril Basin (Moroshkin 1966; Kitani 1973; Takizawa 1982; Talley 1991; Wakatsuchi and Martin 1991; Kowalik and Polyakov 1998; Watanabe and Wakatsuchi 1998; Gladyshev et al. 1999). The former mechanism supposed to be predominant in a density range 27.0-27.6 sigma theta (Moroshkin 1966, Talley 1991, Freeland et al. 1998). This process is believed to modify a lower part of OSIW to become colder less saline with high oxygen content in comparison with NPIW. However, evidences of this are still very limited and definitely require further measurements and considerations. Recently, Gladyshev et. al [1999] estimated that brine rejection in polynyas provides annually average flux 0.4 Sv of less saline water close to the freezing point to OSMW in a density range 26.6-26.9 sigma theta. However, they also pointed out strong interannual variability of dense water production over northern Okhotsk shelf. Dense shelf water (DSW) mixes with Forerunner Soya Water (FSW) and NPIW and produce together a new water mass which Yasuda [1996] called Okhotsk Sea Mode Water (OSMW). Gladyshev et.al [1999] estimated annually averaged rate of the OSMW formation about 2 Sv that is close to the result of Alfultis and Martin [1987]. As NPIW contribution is the highest to OSMW, one can consider the latter as strongly modified portion of NPIW. Each source-type component of water contributes different properties to OSMW. If NPIW provides background of OSMW as the basic component, then DSW chills freshens and oxygenates it and FSW increases salinity and oxygen content of OSMW. As a result, OSMW is colder, less saline and more oxygenated than NPIW. OSMW has another remarkable properties. Yasuda [1996] reported high isopycnal thickness of OSMW, suggesting strong influence of some density driven mechanism on it formation. Freeland et al. [1998] also defined upper part of OSIW as low potential vorticity region, interpreting it as recently ventilated layer from the surface. However, Gladyshev et al. [1999] showed that DSW is strongly stratified water and can not be a source of a pycnostad within OSMW. Watanabe and Wakatsuchi [1998] also revealed high volume rate of OSMW in the Okhotsk Sea, assuming that this water formed under the influence of regional conditions. They also pointed out that isopycnals remarkably deepen in the Okhotsk Sea. However up to this time, any explanations of this downwelling does not exist in the oceanographical literature. The main purpose of this report is to clarify the role of the Kuril straits and DSW in the OSIW formation, based on the modern CTD data set and some historical Russian data. Some details of the mixing process between different components of OSIW and possible mechanisms are discussed qualitatively.-----
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mail-to:mizuta@ees.hokudai.ac.jp / Tel: 011-706-2357