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Journal of Oceanography, Vol. 56, pp. 439 to 447, 2000

Keywords:⋅ Kashevarov Bank,⋅ Sea of Okhotsk,⋅ tidal mixing.

* Corresponding author. E-mail: pacific@online.marine.su

Copyright © The Oceanographic Society of Japan.

Strong Tidal Mixing and Ventilation of Cold IntermediateWater at Kashevarov Bank, Sea of Okhotsk

KONSTANTIN A. ROGACHEV1*, EDDY C. CARMACK2 and ALEXANDR S. SALOMATIN1

1Pacific Oceanological Institute, Baltiyskay 43, Vladivostok, 690041, Russia2Institute of Ocean Sciences, 9860 West Saanich Road, Sidney, B.C., Canada

(Received 13 May 1999; in revised form 4 January 2000; accepted 10 January 2000)

Tidal mixing at the Kashevarov Bank, Sea of Okhotsk, has been investigated usingobservations of bottom pressure and currents. The tides are dominated by the diur-nal constituents. The water motion over the Bank is predominantly controlled by strongdiurnal tidal currents, which bring cold water on the bank from its source, a coldintermediate layer. The temperature fluctuations are about 1.2°C at the southern edgeof the bank. The maximum observed velocity is about 164 cm/s at the top of the bank.A superposition of the original diurnal constituents K1 and O1 reveals a strong fort-nightly (Mf) variability of the current speed. Tidal-induced mixing is responsible forventilation of the cold intermediate layer of the Sea of Okhotsk. Strong tidal mixingcreates a well-defined tidally mixed front around the bank. This front acts like a bar-rier separating well-mixed water on the bank from stratified water on its flanks. Thereis a residual current of the order of 10 cm/s.

tral Okhotsk Sea and the vertically well-mixed waters inareas of strong tidal mixing. The coldest, most saline bot-tom water occurs at depths of 150–200 m on the North-west shelf (NWS) and extends southeast (Martin et al.,1998). Dense water polynyas occur along the northernshelf of Okhotsk Sea. Yasuda (1997) and Martin et al.(1998), estimate that the maintenance of the North Pa-cific Intermediate Water requires 0.5 Sv of this dense shelfwater. The NWS is strongly affected by tides (Kowalikand Polyakov, 1998). The local mixing of the surfacewater with the cold bottom shelf water and intermediateDeryugin Basin water maintains an extremely high sur-face CO2 partial pressure at the bank in summer(Rogachev et al., 1997). High values of carbon dioxidepartial pressure (of 550 µatm) are the result of shelf bot-tom water and intermediate water ventilation. This valueis much greater than the partial pressure for the KurilStraits and Oyashio eddies, where tidal mixing is strong(Rogachev et al., 1996, 1997).

Recently, Kowalik and Polyakov (1998, 1999)showed that trapping of the tidal energy at the bank ispronounced: the K1 current is amplified 20–30 times rela-tive to off-bank values. Amplification of the diurnal am-plitudes and currents is associated with the trapping oftidal energy by the bank and its steep slopes (Fig. 3).Observations over Kashevarov bank show almost homo-geneous vertical structures of the temperature, salinityand oxygen (Rogachev et al., 1997). These observations

1. IntroductionThe Kashevarov Bank is a unique region. It lies on

the continental margin north of the Deryugin Basin andhas a maximum length of 170 km along the 200-m isobath(Fig. 1). In summer, the bank is identified as a spot ofcold water at the surface (Fig. 2), but with relatively warmwater at a depth of 100 m (Figs. 3 and 4). The northwest-ern shelf of the Sea of Okhotsk, northwest of the bank, isan important region of dense bottom water production dueto ice formation in winter (Martin et al., 1998). Satelliteimages demonstrate the polynya positioned over theKashevarov Bank during winter (Alfultis and Martin,1987). The polynya is likely maintained by a vertical heatflux driven by tidal mixing. The distribution of sedimentsalso suggests that strong tidal currents create unfavorableconditions for the deposition of fine materials. For ex-ample, sediments surrounding the bank are mainly mud,while at depth of 135 m on the bank, the bottom is cov-ered by well-sorted pebbles.

Satellite infrared images of the Okhotsk Sea revealthat there are strong and persistent summertime fronts insea surface temperature on the Kashevarov Bank. In mostcases these fronts are the surface signatures of the transi-tion zones between the stratified waters of the deep cen-

440 K. A. Rogachev et al.

suggest that the vertical mixing and the thermohaline frontaround the bank are due to strong tidal mixing. However,hitherto there have been no direct observations of tidesand tidal currents.

The Okhotsk Sea is an area where the currents andtides are not well known. Tidal ranges along the west coastof Kamchatka and the northwest part of the sea are someof the largest in the world. Analysis of the tidal energybudget in the Sea of Okhotsk and in other regions (Ffieldand Gordon, 1996; Lueck and Mudge, 1997) shows thata small area may play an extremely important role in thedissipation of tidal energy. For example, the total energydissipated in the Sea of Okhotsk is greater than the en-ergy dissipated in the Arctic Ocean (Kowalik and

Polyakov, 1998). Thus, small volumes of water, such asthe Kashevarov Bank, can be significant sinks of tidalenergy and play an important role in water mass transfor-mation.

Fig. 1. Sea of Okhotsk bathymetry, general circulation schemeand bathymetry of Kashevarov Bank. Stars show locationof the tide gauges and current meter (southern star—in 1994,mooring A, northern star—in 1996, mooring B). LS—LaPerouse Strait (Soya Strait).

Fig. 2. Infrared (AVHRR) image obtained on September 13,1993 by the NOAA-10 satellite. Image show surface cool-ing signature associated with the slope region of theKashevarov Bank (KB). Light color = low temperature; darkcolor = high temperature.

Fig. 3. Map of stations used on TS diagram and temperaturesections. Stars show the mooring locations. CTD observa-tion depth was deeper than 1000 dbar, or to the bottom ifdepth is shallow than 1000 dbar.

Kashevarov Bank Tides and Mixing 441

There have been numerous tidal charts produced forthis region based on coastal measurements (Kowalik andPolyakov, 1998). Owing to the shallow depth of the north-ern part of the Okhotsk Sea and the large amplitudes ofthe primary tides, tides at the bank are expected to have asignificant role but have not yet been quantified. Thenumerical model of Kowalik and Polyakov (1998) showsthat the largest tides occur in the northeastern part of theOkhotsk Sea, in Penzhin Bay (northwest of Kamchatka),where it has a maximum tidal range of 13 m. Smaller butsignificant tides occur along the NWS, where tidal am-plitudes increase to the west. Measurements of currentsand tidal elevations in the Okhotsk Sea interior are verydifficult to obtain because of severe ice conditions andthe intense level of fishing and trawling. Hence suchmeasurements are relatively scarce.

The main purpose of these measurements was to gaina better understanding of the currents at the bank. Themain questions addressed in this paper are how large thecurrents are and how these currents determine water massstructures within the bank. In this paper, both measure-ments of elevations and current speeds are analyzed fortidal constituents. In addition, the current measurementsare analyzed to determine the residual circulation.

The focus of this study is on an investigation of tides,tidal currents and their effects on water mass mixing over

the bank. There are two strong diurnal components, O1and K1, at Kashevarov Bank. The superposition of thesetwo diurnal constituents gives strong fortnightly varia-tions in current magnitude, and the degree of tidal mix-ing. The residual anticyclonic circulation over the bankis of the order of 10 cm/s.

2. DataData used for the Kashevarov Bank area were ob-

tained from the observations by R/V Vityaz, Akademik A.Nesmeyanov, Akademik M.A. Lavrentyev and ProfessorGagarinskiy (Table 1). Current meter and pressure gaugemoorings were deployed on Kashevarov bank during eachof three cruises in 1994, 1995 and 1996. The first moor-ing had only a pressure gauge, and the last one both apressure gauge and a current meter at a depth of 10 mabove the bottom. The 1995 mooring was lost. The pres-sure gauge in 1994 also recorded temperature. Table 2and Fig. 1 show the position and duration of these moor-ings.

The moorings had water level recorder (WLR) andcurrent meter manufactured by Aanderaa Instruments,Victoria, B.C., British Columbia, Canada. These weredeployed on June 22, 1996 and recovered on September24, 1996. The 1996 mooring was the longest among threeattempts at the bank to be recovered.

Fig. 4. (a), (b) Temperature sections across the bank in August 1–2 and 23–24, 1994. (c), (d) Sigma-theta (kg m3) sections acrossthe bank for the same periods. Shaded areas represent temperature range 1.5°–2.5°C and sigma-theta range 26.4–26.5. Notechange in stratification between these periods corresponded to the different phases of the fortnightly cycle.

442 K. A. Rogachev et al.

The pressure transducer used in the WLR is a spe-cial quartz crystal resonator with stress induced by theapplied pressure. The WLR would measure the depth ofthe water in which it was installed to about ±2.7 cm, butmeasurements of water height variations could be madeto within ±2.7 mm approximately. Atmospheric pressurevariations are a significant factor in the reduction of purewater level variations from ocean hydrostatic pressurerecords. The inverted barometer correction was appliedto the bottom pressure records. This correction compen-sates for the effect of changing of atmospheric pressureon the height of the ocean surface, adding approximately1 cm to sea surface height measurements for each increaseof 1 mb of atmospheric pressure. Extrapolating informa-tion from the meteorological weather report can give anestimate of barometric pressure changes. This will onlybe accurate to within a few millibars. Therefore, the ac-

Research vessel Period of observations Institution

Vityaz 1949, Aug.–Sept., bottles Institute of OceanologyAkademik Nesmeyanov 1992, Aug., CTD POI (Pacific Oceanological Institute)Akademik Nesmeyanov 1993, Aug., CTD POIAkademik Nesmeyanov 1993, Sept., CTD POIAkademik M.A. Lavrentyev 1994, Aug., CTD, mooring POIAkademik M.A. Lavrentyev 1995, May, CTD POIProfessor Gagarinskiy 1996, June–July, CTD, mooring POI

Station Latitude, N Longitude, E Start day End day Water depth Year

Pressure Gauge A 55°31.3 145°11.9 1 Aug. 23 Aug. 135 m 1994Pressure Gauge B 55°40 145°20 22 June 19 Sept. 141 m 1996

Table 1. Primary CTD data set.

Table 2. Position and period of moorings A and B.

curacy of each pressure gauge is about 3 cm. Since onlymean atmospheric pressure was removed from the pres-sure data during processing, fluctuations in atmosphericpressure during the passage of storms may result in er-rors of 3–5 cm in height. Monthly mean fluctuations ofatmospheric pressure at the bank in June–September 1996were about 5 mbar.

Seasonal changes of geopotential anomaly at the bankare small. For example, our CTD data (Table 1) show thatgeopotential anomaly variations from August 1994 to May1995 are less than 1 dyn. cm. The TS diagram for stationsat the bank in May and August clearly shows that densityvariations from August 1994 to May 1995 are small be-cause a significant temperature decrease in winter is com-pensated by a large decrease in salinity.

Bottom pressure was recorded every 30 minutes andcurrent magnitude was recorded every hour. The current

Table 3. Tidal amplitude and phases for major constituents at moorings A and B.

Constituent Amplitude, m Phase, grad.

Name Frequency, cycle hour–1 Mooring A Mooring B Mooring A Mooring B

Mm 0.00151215 0.0178 356.62Fortnight 0.00305009 0.0292 0.0365 301.45 2.14Q1 0.0372185 0.111 23.48O1 0.03873065 0.507 0.4727 51.23 42.35K1 0.04178075 0.5266 0.5319 113.52 94.38M2 0.08051140 0.3185 0.3408 332.56 307.09S2 0.08333333 0.1210 0.1140 41.53 12.69M3 0.12076710 0.0034 0.0051 169.77 133.15MK3 0.12229215 0.0082 67.77SK3 0.12511408 0.0038 0.0041 215.85 164.84

Kashevarov Bank Tides and Mixing 443

components u (east-west) and v (north-south) were cal-culated using direction of current. The 1994 pressuregauge records were spike free and required no editing.The pressure time series has a range of 2 m. Tides domi-nate the pressure records. Tides also dominate the cur-rent records. A representative time series of pressure andtemperature as a function of time over a 23 day period atmooring A is presented in Figs. 5 and 6.

3. ResultsThe pressure gauge data are analyzed with tidal

analysis software (Foreman, 1977) which uses a leastsquares analysis method incorporating nodal modulation,astronomical corrections and inference calculations fortidal amplitudes and phases. A maximum of 146 possibletidal constituents can be included in the tidal analysis; 45of these are astronomical in origin (main constituents),while the remaining 101 are shallow water constituents.Amplitudes and Greenwich phases for the largest indi-vidual constituents are given in Table 3.

The primary diurnal tides over the bank were the O1(25.82 hour) and K1 (23.93 hour) components. These tides

were greatly amplified above the bank. Temperature os-cillations at the diurnal tidal frequencies were large(>1.2°C). The K1 constituent has the largest amplitudefor each of the pressure gauge records. The next largestamplitudes are from O1 and M2 constituents and then ei-ther S2 or Q1 constituents (for mooring B), whose ampli-tudes of which are comparable. The amplitudes of themajor constituents are high for both mooring sites. Tidalrange is greater than 2 m for both moorings. Tides arefound to account for at least 90% of the sea surface heightvariance at the bank. Shallow water tides are relativelysmall.

Fig. 5. Bottom pressure and temperature at Kashevarov Bankin August 1994.

Fig. 6. Relation between bottom pressure and temperature forone tidal cycle at mooring A, August 1994. Numbers arehours.

Fig. 7. Current speed at Kashevarov Bank in 1996. Fortnightlyvariability is superposition of two strong original diurnalconstituents K1 and O1.

444 K. A. Rogachev et al.

Table 4. Comparison of tidal ellipses obtained from observations (italic) at mooring B and from 3-D modeling in stratified case(Kowalik and Polyakov, 1999).

Fig. 8. Observed major tidal current ellipses. The arrow at eachellipse shows the direction of the current vector rotation.

Fig. 9. Height (a), temperature (b) and (c) velocity (v-compo-nent) spectra. Note high temperature signal at diurnal fre-quency and low signal at semidiurnal frequency.

Tides are the dominant source of current variability(Figs. 7–9). We used least-squares tidal analysis (Fore-man, 1978) to determine properties of 18 separate tidalconstituents ranging from Zo (mean flow) to M8 (periodabout 3 h). Ellipse parameters (Fig. 8) demonstrate thatthe diurnal currents are dominated by O1 and K1, and theyhave low ellipticity (1.3). The semidiurnal tide, which isdominated by M2, is small, but shows larger ellipticity(3). The rotation direction is clockwise, except for thefortnightly component (Table 4). The same rotation of thefortnightly constituent was found by Kowalik andPolyakov (1999) using a three-dimensional model. Thesense of rotation is indicated by the sign of the minoraxis: positive signifies counterclockwise rotation andnegative signifies clockwise rotation. Current ellipses areshown for the O1, K1, Q1 and M2 components in Fig. 8.Note that the sense of rotation of the fortnightly compo-nent is cyclonic and opposite to the sense of rotation atthe three diurnal components O1, K1 and Q1. This con-clusion is in agreement with model results obtained byKowalik and Polyakov (1999). Current ellipses for M2and Q1 are smaller than the other analyzed constituents.

Kashevarov Bank Tides and Mixing 445

The mean lengths of the major axes of the tidal currentellipses (amplitude of the tidal current) are 65.6 cm/s forO1 tide, 58.6 cm/s for K1, 14.9 cm/s for M2 and 12 cm/sfor Q1. The large axes of O1 and K1 current ellipses areabout five times as large as that of the M2 current ellipse.The diurnal current dominates over the semidiurnal cur-rents at mooring B.

It is evident that K1 + O1 tidal currents are the majorcontributors over the bank. The general pattern of the O1constituent is similar to that for K1. The maximum of theO1 and K1 currents is close to the model results of Kowalikand Polyakov (1999). The most pronounced effect is fort-nightly variability of the total current. The temporal vari-ability of the current over the bank is shown on Fig. 7. Asuperposition of the original diurnal constituents K1 andO1 reveals strong fortnightly (Mf) variability. The energysource for the fortnightly variations is primarily due tothe K1-O1 interaction, since the region has strong diurnalcurrents. The nonlinear interaction is reflected in an asym-metry of the fortnightly signal. The spectrum of the tidalcurrent magnitude shows that the fortnightly signal hasthe largest amplitude. This fortnightly signal is five timesgreater than the diurnal variations of the current speed.Therefore we should expect these variations in the de-gree of water mass mixing. Meanwhile, the spectra ofvelocity and tidal elevations have small signals at the fort-nightly frequency. This again confirms that the nature ofthe fortnightly variations in temperature signal and incurrent speed lies in the interaction of the original diur-nal constituents K1 and O1. Large variations of the mixedwater volume were observed at different stages of thefortnightly cycle (Fig. 4). A geostrophic current at thenorthern edge of the bank between stations 147 and 148(see Fig. 3 for position of stations) at 50 dbar relative to250 dbar is 13.3 cm s–1. This speed is less than that cal-culated by Kowalik and Polyakov (1999). This current isdue to the existence of the tidal front between the well-mixed layer on the bank and the stratified waters aroundit. The geostrophic current is also pronounced on thesouthern edge of the bank, and forms an anticyclonic cir-culation around the bank. However, the current was sig-nificantly reduced during the first survey (August 1–2,1994). Figure 10 shows a progressive vector diagram forobservations at mooring B. The mean current is directedsouthward. There are also fortnightly variations in me-ridional and zonal displacement, as well as in the sizes ofthe tidal loops.

The temperature section from south to north has beenmade across the bank just before the first mooring de-ployment (Fig. 4). It is evident that the core of the coldintermediate layer lies at a depth of 120 m and reachesthe edge of the bank. Figures 5 and 6 show the measuredbottom pressure and temperature variations in August

1994, made after this CTD section. The temperature andbottom pressure vary in phase—temperature decreases asfor when sea level increases, suggesting that cold wateris coming in with the flood. Figure 9 shows pressure, tem-perature and velocity spectra. It is evident that the tem-perature and meriodional component of current havestrong diurnal peaks, while the pressure signal has bothdiurnal and semidiurnal signals. Thus, the data also sug-gest that temperature variations are due to cold wateradvection by strong diurnal tidal currents.

The TS diagram for the stations at the bank (Fig. 11)shows that well-mixed water at the bank (stations 144–145) is the product of mixing of the cold intermediatewater from the southern (station 142) and south-westernedges with the surface water and the water from the north-ern part of the region (station 148). It is evident from thisfigure that water at 100-m depth has a minimum tempera-ture at the southern station (142), while there is a maxi-mum temperature at this depth at the northern station(148). As the result of such mixing, there is relativelywarm salty water at a depth of 100 m within the bank,while the temperature is lower everywhere around it.

Fig. 10. Progressive vector diagram for mooring B. Currentmeters 7910, 10 m above the bottom, days 58–90 of obser-vations, August–September 1996. Records are annotatedwith a day of observation every 24 hour, marked with acircle. The direction of true north is shown with a 100-kmscale. The fortnightly (Mf) periodicity is evident in meridi-onal displacement and tidal loops. Diurnal tidal excursionis about 35 km.

446 K. A. Rogachev et al.

Fig. 11. TS diagram for stations on Kashevarov Bank in August 1994. Thin lines represent CTD casts. Symbols mark 50-dbarintervals. Station on the Kashevarov Bank (144) is one point.

4. DiscussionInfrared satellite images in summer reveal a cold

water pool within the bank very close to what is observedat the tidal fronts of the Sea of Okhotsk. There are twosources of cold water in the Sea of Okhotsk: the first isthe cold intermediate layer in the deep central part of thesea, and the other is from the north and northwestern shelf.The major feature over the northwestern shelf of theOkhotsk Sea is the cold bottom water with its high salin-ity. During the warm period this layer allows thermalstratification to develop, when the temperature of the sur-face layer sharply increases in the lack of tidal mixing.The halocline at the northern shelf is maintained by theadvection of this dense and salt water from the continen-tal shelf (Aagaard et al., 1981). It appears that the denseshelf water loses its high-salinity nature before it flowsout into the central part of the Sea of Okhotsk. The salin-ity of the temperature minimum of this dense water isshifted towards the low salinity side roughly along theline of the freezing point in the TS diagram. This indi-cates that the water is mixed with low-salinity cold wateras it flows along its path to the central Okhotsk Sea. Onepossible mechanism for this is the strong tidal mixing atthe Kashevarov Bank. The forced vertical mixing trans-

ports a considerable quantity of salt without effectivewater transport. Without this vertical mixing the salinityin the surface water cannot be maintained, and the for-mation of the dense shelf water will cease (Yang andHonjo, 1996).

This work corroborates previous studies suggestingthat tidal currents are responsible for most of the mixingin the halocline that transports salt and nutrients from thedeeper layers over the bank to the surface layer (Rogachevet al., 1997). The mechanism by which this flux occurs,however, is not yet clear. It is possible that higher fre-quency internal waves, which are generated from tidalcurrents at the slope region, provide an important sourceof turbulent energy. We believe that these waves can begenerated by the interaction of tidal currents with thebottom topography. For example, such internal waves area likely source of energy for the strong turbulence aroundCobb Seamount (Lueck and Mudge, 1997). Without thismixing, the sea would turn within a few years (Yang andHonjo, 1996) into a stagnant pool with a cold intermedi-ate layer and a fresh surface layer. The tides and windsare the only possible source of mechanical energy to drivethe internal mixing. Since nearly all tidal dissipation hastraditionally been located in the turbulent bottom bound-

Kashevarov Bank Tides and Mixing 447

ary layers of marginal seas (Lueck and Mudge, 1997),we suggest that the mixing at Kashevarov Bank plays thecentral role in the dynamics of the Sea of Okhotsk.

The formation of tidal fronts is considered bySimpson and Hunter (1974), Fearnhead (1975), andSchumacher et al. (1979). For shallow seas the simplecritical parameter which determines the rate of mixingcan be introduced as a depth divided by the cube of maxi-mum tidal current (Simpson and Hunter, 1974; Fearnhead,1975; Yanagi and Takahashi, 1988). If its value is about70 s3/m2 (as it is for the Bay of Main shelf), then a tidalcurrent of 1.26 m/s can keep a water layer of 140 m depthwell mixed. Figure 7 shows the current magnitude atmooring B. The maximum observed current speed is 1.64m/s above the bottom. Moreover, the contours of the maxi-mum K1 + O1 tidal currents at depth of 2.5 m show aclear maximum in total currents above the bank top, whichattains 2.64 m/s at the surface and 1.77 m/s at the 80-mdepth (Kowalik and Polyakov, 1999). This supports thehypothesis that the observed homogeneous vertical dis-tribution over the bank summit is due to tidal mixing. Itis quite plausible that the mechanism underluing the di-urnal temperature variations is the advection of cold wa-ter to the bank during tidal excursion. Therefore, there isan intensive transportation of the Okhotsk Sea cold inter-mediate water at the bank. Tidal mixing in the KashevarovBank region results in a shelf-break cooling. This workdemonstrates the role of tidal mixing in establishing thehomogeneous stratification over the Kashevarov Bank andits strong fortnightly variability.

AcknowledgementsRobert Lake from IOS supported this work. Doug

Sieberg from IOS made a significant contribution to pre-paring the mooring B. Deployment and recovery werepossible with support of Viktor A. Akulichev and Cap-tain V. Osynny. Many thanks to Marina Alexanina forsatellite images. Comments on the manuscript from threereviewers were also appreciated.

ReferencesAagaard, K., L. K. Coachman and E. Carmack (1981): On the

halocline of the Arctic Ocean. Deep-Sea Res., 28, 529–546.Alfultis, M. A. and S. Martin (1987): Satellite passive micro-

wave studies of the sea of Okhotsk ice cover and its rela-

tion to oceanic processes, 1978–1982. J. Geophys. Res., 92,13013–13028.

Fearnhead, P. G. (1975): On the formation of fronts by tidalmixing around the British Isles. Deep-Sea Res., 22, 311–321.

Ffield, A. and A. L. Gordon (1996): Tidal mixing signatures inthe Indonesian Seas. J. Phys. Oceanogr., 26, 1924–1937.

Foreman, M. G. (1977): Manual for Tidal Heights Analysis andPrediction. Institute of Ocean Sciences, Victoria, B.C.,Canada, 98 pp.

Foreman, M. G. (1978): Manual for Tidal Currents Analysisand Prediction. Institute of Ocean Sciences, Sidney, B.C.,Canada, 70 pp.

Kowalik, Z. and I. Polyakov (1998): Tides in the Sea of Okhotsk.J. Phys. Oceanogr., 28, 1389–1409.

Kowalik, Z. and I. Polyakov (1999): Diurnal tides overKashevarov Bank, Sea of Okhotsk. J. Geophys. Res., 104,5361–5380.

Lueck, R. G. and T. D. Mudge (1997): Topographically inducedmixing around a shallow seamount. Science, 276, 1831–1833.

Martin, S., R. Drucker and K. Yamashita (1998): The produc-tion of ice and dense shelf water in the Okhotsk Seapolynyas. J. Geophys. Res., 103, 27,771–27,782.

Rogachev, K. A., P. Ya. Tishchenko, G. Yu. Pavlova, A. S.Bychkov, E. C. Carmack, C. S. Wong and G. I. Yurasov(1996): The influence of fresh-core rings on chemical con-centrations (CO2, PO4, O2 and pH) in the western subarcticPacific Ocean. J. Geophys. Res., 101, 999–1010.

Rogachev, K. A., A. S. Bychkov, E. C. Carmack, P. Ya.Tishchenko, A. P. Nedashkovskiy and C. S. Wong (1997):Regional carbon dioxide distribution near Kashevarov Bank:effect of tidal mixing. p. 52–69. In Biogeochemical Proc-esses in the North Pacific, ed. by S. Tsunogai, Japan Ma-rine Science Foundation, Tokyo.

Schumacher, J. D., T. H. Kinder, D. J. Pashinski and R. L.Charnell (1979): A structural front over the continental shelfof the eastern Bering Sea. J. Phys. Oceanogr., 9, 79–87.

Simpson, J. H. and R. J. Hunter (1974): Fronts in the Irish Sea.Nature, 250, 404–406.

Yanagi, T. and S. Takahashi (1988): A tidal front influenced byriver discharge. Dyn. Atmos. Oceans., 12, 191–206.

Yasuda, I. (1997): The origin of the North Pacific IntermediateWater. J. Geophys. Res., 102, 893–909.

Yang, J. and S. Honjo (1996): Modelling the near-freezingdichothermal layer in the Sea of Okhotsk and its interannualvariations. J. Geophys. Res., 101, 16421–16433.