A Survey of Water Masses in The and The Bussol Strait

by

Colin E. Taylor

B.Sc. The University of British Columbia, 1986

A Thesis Submitted In Partial Fulfillment Of The Requirements For The Degree of Master Of Science

in

The Faculty Of Graduate Studies (Department of Physics)

We accept this thesis as conforming to the required standard:

The University of British Columbia

December 1996

© C. E. Taylor, 1996 f

In presenting this thesis in partial fulfilment of the requirements for an advanced

degree at the University of British Columbia, I agree; that the Library shall make it

freely available for reference and study. I further agree that permission for extensive

copying of this thesis for scholarly purposes may be granted by the head of my

department or by his or her representatives. It is understood that copying or

publication of this thesis for financial gain shall not be allowed without my written

permission.

QL • Department of \j ^ c_S The University of British Columbia Vancouver, Canada

Date 0,,. r u

DE-6 (2/88) II

Abstract

In September of 1993, a World Ocean Circulation Experiment (WOCE) expedition to the Sea of Okhotsk collected hydrological data along a transect of the sea, located next to the northwest Pacific. Hydrological sampling was conducted at several stations over the Kuril Trench, and continued along a line passing through the Bussol Strait and across the Sea of Okhotsk to the continental mainland. The data collected on this voyage suggest that the Sea of Okhotsk plays only an indirect role in the formation of North Pacific Intermediate Water (NPIW) and that much of the water in the Sea of Okhotsk has resided there for some time. An exchange of waters at depth over the Bussol Sill is also suggested. This paper will discuss the properties of the water masses in the Sea of Okhotsk with respect to the collected data and focus on the exchange across the Bussol Strait. The residence time of water masses and the effect of winter cooling will also be described. Table of Contents:

Abstract ii Table of Contents iii List of Figures v Acknowledgement vii

1. Introduction 1 1.1. Physical Geography of the Sea of Okhotsk 1 1.2. Oceanographic Features of the Sea of Okhotsk 3 1.2.1. Sea Ice Formation 3 1.2.2. Currents in the Sea of Okhotsk Region 5 1.2.3. Tides 6 1.2.4. Water Properties 8 1.3. World Ocean Circulation Experiment Expedition 1993 9 1.3.1. World Ocean Circulation Experiment (WOCE) 9 1.3.2. North Pacific Intermediate Water 10 1.3.3. The 1993 Okhotsk Sea Expedition 11 2. Description of Data 13 2.1. Collection Methods 13 2.2. Data Processing 14 2.3. Overview of Data 15 3. Results 17 3.1. Water Masses in the Sea of Okhotsk 17 3.1.1. Surface Waters 18 3.1.2. the Deryugin Basin Water 20 3.1.3. Water Masses near the Bussol Sill 21 3.2. Water Properties 24 3.2.1. Chlorofluorocarbon Dating of Okhotsk Waters 24 3.2.2. The Okhotsk Gyre and the Bussol Eddy 26 iv

3.2.3. Tidal Mixing over the Bussol Sill 29 4. Discussion 33

References 34 Summary of Figures 37 Appendix A. - Using CFC's to date ocean water masses 78 Appendix B. - Niskin Bottle Salinity Data. 80 V

List of Figures:

Fig. 1: The Sea of Okhotsk and the North Pacific 39 Fig. 2: Oceanographic features of Okhotsk Sea (Alfultis and 40 Martin, 1987) Fig. 3: The and Straits from PICES 41 Fig. 3 Captions 42 Fig. 4: Bathymetry of Sea of Okhotsk from U.S. Naval 43 Oceanographic Office. Fig. 5: a) Development of Sea Ice over winter months (Japanese 44 Meteorological Agency, 1990) b) February sea ice extent 1973-76 (Parkinson, 1990) 45 c) Interannual sea ice cover as a % of total area from H. 46 Freeland, compiled with data sent by Alex Bychov, POI. Fig. 6: a) Circulation of SoO in summer by Watanabe 47 b) Circulation of SoO according to Leonov 48 c) Circulation of SoO according to Moroshkin 49 d) Estimates of surface currents from lida 50 (in knots: 1 knot = 0.514 m/s) e) The presence of the Bussol Eddy (Rogachev,1993) 51 f) Gyres of the North Pacific (Ohtani et al, 1991) 52 Fig. 7: a) Amplitudes of tidal components (Suzuki and Kanari) 53 b) Tidal components in the Kurils from Luchin 54 c) Tidal parameters near the Bussol Strait from Luchin 55 Fig. 8: Temperature distribution along north-south line at 56 approximately 150° E (Kitani, 1973) Fig. 9: WOCE survey lines in the Northwest Pacific 57 Fig. 10: Survey Stations of WOCE Expedition 9316 (Sept. 1993) 58 Fig. 11: NPIW low salinity intrusion from H. Freeland 59 - solid lines are 5, 6 and 7 degree isotherms vi

- clashed lines are 26.7, 26.7 and 26.8 isopycnals Fig. 12 a) Potential temperature over the transect 60 b) Potential temperature for first 500 meters 61 Fig. 13 a) Salinity over the transect 62 b) Salinity for first 500 meters 63

Fig. 14 a) Potential Density over the transect 64 b) Potential Density for first 500 meters 65

Fig. 15 Profiles of S, T, 0 at various stations along the transect 66 Fig. 16 TS plot for above stations 67

Fig. 17 a) Temperature-salinity profiles for all 30 stations. 68 b) TS profiles divided into 3 regions 69 c) TS plots with density contours and freezing point. 70 Fig. 18 Potential Density Contour illustrating 3 regions 71

Fig. 19 Dissolved 02 contour plot 72 Fig. 20 Dissolved silicate contour plot 73 Fig. 21 Potential density near the Bussol Sill 74

Fig. 22 TS plot for depths below 1000 meters 75 Fig- 23 CFC age contours for the SoO. 76 Fig. 24 Dynamic heights relative to 1000 dBar surface for stations 77 where depth exceeds 1000 rri (stations 1 to 23) VII

Acknowledgements:

For my long-suffering wife, Angela and the other members of my family who helped along the way. 1

1. Introduction

1.1. Physical Geography of the Sea of Okhotsk

The Sea of Okhotsk is located in the Northwest Pacific (figure 1); it is a marginal sea separated from the Pacific by the chain of Kuril Islands. The Kuril island chain runs northeast from the Japanese Island of Hokkaido to the southern tip of Kamchatka. The Sea of Okhotsk (SoO) is bordered by land on three sides. In the east, the Kamchatka Peninsula extends from the Kurils to the northeast corner of the SoO. The western border of the SoO is marked by Sakhalin Island, stretching 800 kilometers north-south along the flank. The northern shore of the SoO is outlined by the coast of continental Asia sweeping from the base of the Kamchatka Peninsula to the far western reaches of the sea. There are few large islands in the Sea of Okhotsk itself, the largest being the Shantarsky Island group, in Shantarsky Bay on the northwest continental shelf. In all, the SoO stretches from 43° to 63° north latitude and from 135° to 165° east longitude.

The waters of the Sea of Okhotsk are separated from the Pacific Ocean by the Kuril Ridge (figure 2). There are many islands and straits along this span . There are both Russian and Japanese names for the oceanographic features (figure 3 + captions). On the Okhotsk side of the ridge, the sea floor drops into the Kuril Basin; on the Pacific side the depth increases more rapidly, falling into the Kuril Trench. Exchange between the two bodies of water is accomplished through the many straits. The Bussol Strait, in the middle of the island chain, has the deepest sill at about 2300 meters. To the north, the Kruzenshtern Strait is the second deepest 2 passage with a sill depth of 1400 meters. Other important straits include Friza and Nemuro Straits among the southern Kurils. These straits will be mentioned again later when currents and exchange are discussed. The Sea of Okhotsk is also connected to the Japan Sea by two shallow straits. The southern tip of Sakhalin Island and the northern end of Hokkaido are separated by the Soya Strait, about 42 kilometers wide and 55 meters deep. There is also a narrow strait between Sakhalin Island and the Tartarin Peninsula; the Tartar Strait is only 8 kilometers wide at its narrowest with a sill depth of 12 meters at low tide.

The bathymetric features of the Sea of Okhotsk are shown on figures 2 and 4. It can be noted that the depth contours on these two plots are not entirely in agreement; this is an example of the lack of solid information about the Sea of Okhotsk. However, this discrepancy is minor and the main features are apparent on both graphics. The deepest part of the SoO, the Kuril Basin, is located in the southern portion of the sea and reaches a maximum depth of about 3200 m. The Deryugin Basin, located off the east coast of Sakhalin Island, drops to a depth of about 1700 meters. To the northeast, the shallow Tinro Basin parallels the Kamchatka coast. The sea also has a few notable rises. The Kashevorova Bank, in the northwest SoO, rises above 200 meters in depth. Two other rises, the Institute of Oceanology Rise and the Academy of Science Rise, lie between the Kuril and Deryugin Basins. The overall area of the SoO is about 1.5 million square kilometers and the average depth is approximately 800 meters. 3

1.2. Oceanographic Features of the Sea of Okhotsk

The details of oceanographic properties of the Okhotsk Sea are not well known. This body of water has been sampled extensively by Soviet scientists but there is a lack of quantitative information available in English. This section will attempt to outline those features that have been chronicled by a number of research efforts.

1.2.1. Sea Ice Formation

Although within temperate latitudes, the Sea of Okhotsk is covered by a substantial amount of pack ice every winter. There are two primary reasons why this occurs. In the northern winter, an atmospheric high is generally situated over the Siberian land mass. The dominant wind pattern has outflow winds passing from the cold continent, traveling over the Okhotsk Sea towards the low pressure system near the Aleutian Islands of Alaska. This flow of cold air has a drastic effect on cooling the SoO and causing the formation of sea ice. In addition, there is a layer of relatively fresh water trapped near the surface of the SoO. This layer is fed by the many rivers draining into the Okhotsk Sea; the largest of these rivers, the Amur River, supplies fresh water directly into Shantarsky Bay. This water is carried southward by the East Sakhalin Current promoting the creation of sea ice very early along the east coast of Sakhalin Island. The ice pack first begins forming in Shantarsky Bay in the western end of the SoO and in Penzhinskaya Bay in the northeast corner (PICES,1995). The ice can start forming as early as November and grows south to a latitude of 45° N at the period of peak ice buildup, in early March. The typical growth of the ice pack is shown in monthly steps in figure 5a. At its fullest extent, the ice 4

pack reaches to the northern coast of Hokkaido. The winter ice pack is first year ice as all of it melts the following summer, sometimes as late as July.

There is some interannual variability to the extent of sea ice formation. The spread of the ice pack to the south can vary greatly from year to year. Figure 5b shows the ranges of the ice pack for four successive Februarys. The long term variation in ice coverage is shown in figure 5c as a percentage of total surface area. It should also be noted that there appears to be an inverse correlation between ice formation on the Okhotsk and Bering Seas. That is, when the ice pack is large one winter on the Sea of Okhotsk, it is typically a lean year for ice on the Bering Sea and vice versa. This may be explained by relative movements of the key atmospheric features: the Siberian High and the Aleutian Low. As for the thickness of the ice pack, little data is available. Visual observations suggest a thickness of 1.5 m at the northern edge, decreasing to 0.5 m in the south (Akagawa, 1969). Another feature the Okhotsk Sea exhibits are polynyas. A polynya forms consistently along the northern Siberian coast from Tauyskaya Bay westward past the city of Okhotsk. This polynya is probably formed by the prevailing north-northwest winds that occur in the winter. Another polynya is often reported near the Kashevarova Bank; this is most probably caused by upwelling or tidal mixing. The effect these features have on water mass modification will be mentioned with the discussion of Sea of Okhotsk water masses. 5

1.2.2. Currents in the Sea of Okhotsk Region

Although there is only limited information regarding the strengths of the currents in the SoO, it is evident that the circulation pattern has a strong seasonal variation. Indicated by the presence of sea ice, the currents in the summer are markedly different from those in the winter. Perhaps the clearest available summary of currents for summertime within this sea is shown in figure 6a (Watanabe, 1963b). This map outlines the general cyclonic nature of the surface circulation in the SoO. From the diagram it is evident that there is one large gyre in the central Okhotsk with subgyres in the northwest over Tinro Basin, around Tarpeniya Bay in the west and over the Kuril Basin in the south. More detailed pictures of the current pattern in the Okhotsk sea are shown in figures 6b (Leonov,1960) and 6c (Moroshkin,1964). Both of these schematic diagrams of the surface circulation in the SoO indicate a large number of smaller eddies which may be of a temporal nature. The main gyre over the Kuril basin appears to be anticyclonic in nature while the general flow over the SoO is cyclonic. There is also evidence of a persistent anticyclonic eddy on the Pacific side of the Bussol Strait (Rogachev,1991) shown in figure 6e. The complex interaction between the Okhotsk Sea and the North Pacific currents, primarily the Oyashio, is illustrated in figure 6f. Traveling in a southwest direction past the southern tip of Kamchatka, the Oyashio parallels the chain of Kuril Islands just outside the SoO. Branching off the Oyashio and entering the Okhotsk Sea through the Kruzenshtern Strait, the West Kamchatka Current travels northward in the Sea of Okhotsk beginning the main cyclonic gyre of the SoO. The East Sakhalin Current flows southward along the western boundary of the SoO. These are the two most marked currents in 6

the sea; however, they can only be described in qualitative terms because of the lack of a consistent series of measurements over time. Another important current enters the Okhotsk Sea through the Soya Strait. The Soya Current carries warm saline water from the Japan Sea. This intrusion typically flows closely along the northern coast of Hokkaido.

The pattern of circulation changes in the colder months. With the onset of the winter ice, the strength of the East Sakhalin Current increases, carrying pack ice to the northern shores of Hokkaido. Also at this time, the strength of the incoming Soya Current decreases and this warmer, more saline water entering the SoO is subducted by the colder waters approaching from the north. On the other side of the Sea of Okhotsk, the West Kamchatka Current continues to bring in warmer Pacific water and this impedes the formation of the ice pack in the eastern side of the SoO. Since many of the estimates of currents in the Okhotsk Sea have been obtained with satellite tracked instruments, the formation of winter pack ice has prohibited the collection of surface current measurements by these means.

1.2.3. Tides

The Sea of Okhotsk experiences some of the largest tides in the world's oceans; several studies have found evidence of large tidal dissipation. In a recent analysis using satellite altimetric data (Kantha,1995), the Okhotsk Sea was found to be one of the world's primary sites for dissipation of the diurnal Ki tidal component. In another paper by Japanese scientists (Suzuki and Kanari,1986), data collected in the early 1920's by Ogura and Schureman was used to model the tides in the SoO. This model of the different tidal 7 components (figure 7a) shows large amplitudes in the Sea of Okhotsk, especially in the areas of Shelikof Bay in the northeast and Shantarsky Bay in the west. The model also shows currents due to tidal flows are strong in the regions of the Kuril Straits, near cape Tarpeniya, over the Kasheverova Bank and in Shelikof Bay. Suzuki and Kanari suggest maximum tidal currents in the Kuril Straits on the order of 20-30 cm/s. This is somewhat low compared with the findings of Efimor (Efimor,1985), who suggested velocities in the straits over 1 m/s. Efimor, who suggested large Oi tidal components, concurs with the two previously mentioned studies that the dissipation of tidal energy over the Okhotsk Sea is primarily diurnal in nature. However, in the region of greatest interest - the Kuril Straits, where exchange between the Okhotsk and Pacific takes place - the picture is less clear. There is some suggestion that the flows in the straits themselves are of a semi-diurnal nature (Rabinovich,1993). A graphic provided by V.A. Luchin (PICES,1995: App. B) shows the tidal flow in this region to be quite complex in nature (figure 7b), a mixture of diurnal and semi-diurnal components. Luchin also suggests tidal flows in the Bussol Strait on the order of 2 to 4 knots, or about 1 to 2 m/s (figure 7c). The currents associated with the tidal flows through the Kuril islands are so large in magnitude they may overwhelm the steady currents. This may be one reason for the lack quantitative values for steady currents in the SoO. Tides may also be responsible for much of the vertical mixing in the Sea of Okhotsk; this will be mentioned when vertical mixing is later discussed. 8

1.2.4. Water Properties

The waters of the Sea of Okhotsk can only be described qualitatively at this point. Oceanographic sampling has been conducted for over a century but there is a lack of published data. There have been several thorough studies of the SoO by Russian scientists, particularly those of Leonov (1960) and Moroshkin (1964). The work of Kitani (1973) also provides a digest of information on the subject. Despite this, there is no aggregate understanding of the formation, variability and interaction of the water masses in the Sea of Okhotsk. There is only a general picture of the nature of Okhotsk waters.

The most obvious feature of the water column in the Okhotsk Sea is a distinct partition between surface and deep waters, illustrated in the temperature contours of Kitani (figure 8). This plot shows a cold fresh layer of water directly below the sea surface and extending down to about 200 meters. Below that depth, the temperature and salinity vary only slightly. This upper layer is present over the entire SoO and is probably the result of ice melt and continental run-off. Little is known however about how this subsurface layer interacts with the waters below. In contrast to the temperature minimum in the upper layer, the waters below 200 meters tend to exhibit a weak temperature maximum at a depth of about 1000 meters. Below that depth, in the Kuril and Deryugin Basins, the temperature falls only slightly, dropping at most half of one degree from 1000 meters depth to the bottom. How this bottom water mass interacts with the colder layers above is to this point conjecture. This then is the initial depiction of water properties in the SoO: a cold, fresh layer of water just below the sea's surface 9 below which is a comparatively uniform water mass extending to the bottom of the sea's basins, with subtle variations in depth.

1.3. World Ocean Circulation Experiment Expedition

This research effort was conducted as a very small part of the international World Ocean Circulation Experiment (WOCE). The expedition was undertaken to improve oceanographic knowledge of the Okhotsk Sea and northwest Pacific by completing the westernmost segment of WOCE survey line Pacific One (P1). This study is an attempt to bring to light some of the features of a small part of the world's oceans and add to the global WOCE picture.

1.3.1. The World Ocean Circulation Experiment

I The WOCE is an international undertaking by scientists from more than 30 countries, concluding in 1997. The goal of the program is to develop better modeling techniques of world ocean circulation and to gain a better understanding of how the oceans and atmosphere affect long-term global climates. At present, there is no worldwide system in place for monitoring global oceanic changes; the WOCE will hopefully provide some direction in the design of an observing system. With the presence of more reliable oceanic and atmospheric data, better predictions could be made of how human and natural influences are affecting climate. Part of the WOCE program involves active sampling of ocean waters along many transects. Figure 9 shows the WOCE sampling regime for the Pacific; note line Pacific One (P1). Line P1 transects the Pacific east-west at a latitude of about 45° N, from the mainland 10

US coast to near the Kuril Islands. At this point, line P1 breaks up into two sections: one going southwest towards Japan, and one going northwest to the Siberian mainland. The line going northwest through the Sea of Okhotsk completes the Pacific crossing, and is referred to as line Pacific One West (P1W). This is the survey described in this thesis, with station positions given in figure 10.

1.3.2. North Pacific Intermediate Water

This study is important for a number of reasons. First of all, there is the absence of quality oceanographic data available for this part of the world's oceans. Secondly, there is the question of the formation of North Pacific Intermediate Water (NPIW). The Northeast Pacific maintains a salinity minimum in the top 1000 meters of the water column; the water mass in a narrow band of densities on either side of this minimum has been dubbed North Pacific Intermediate Water. Its presence throughout the North Pacific has been well documented and described by Reid (1965) and Talley (1991). Its presence along a north-south transect at 165° W is shown graphically in figure 11 (provided by H. Freeland). This picture shows a tongue of low salinity water reaching to a depth of about 600 meters and extending as far south as 15° N latitude. The origin of this fresher water is believed to be in the Mixed Water Region of the Kuroshio and Oyashio currents, to the east of Japan. However, the process leading to its formation is poorly understood. It was suggested by Wust (1930) that the Sea of Okhotsk was the formation site for NPIW and that this fresher, denser water spilled out through the Bussol Strait into the Pacific. Others have also suggested that a great deal of water mass modification takes place in the SoO. Favorite (1976) suggests that much of the East Kamchatka Current, 11 flowing south along the Kurils, enters the Okhotsk, is modified and then re-enters the Pacific as a large part of the Oyashio Current. This recirculated water, colder and fresher as a result of modification, subsides under warmer Kuroshib water to form NPIW. Kitani (1973) added further weight to this argument, suggesting that water mass modification on the northern continental shelf of the SoO due to winter ventilation would produce dense water that might then flow into the Pacific. However, Reid (1973) believes that the amount of water produced in the Sea of Okhotsk would not be adequate to form the large NPIW water mass. In a recent study (Talley et al, 1994), it is suggested that direct ventilation on the northern continental shelf of the Okhotsk Sea plays an important role in producing this water mass. The role of the Okhotsk Sea on the formation of North Pacific Intermediate Water has remained unclear, mainly from lack of data. This paper will discuss the data taken from this expedition concerning this question.

1.3.3. The 1993 Okhotsk Sea Expedition

A WOCE expedition to the Sea of Okhotsk was conducted in the fall of 1993. In cooperation with the Pacific Oceanological Institute, (POI), the ship Aleksandr Nesmeyanov was used as the platform for all experimental work. The ship left Vladivostok, home of POI, on August 31, 1993 and was at sea for 22 days. The objective of the sampling program was to complete oceanographic survey line P1W (Pacific One West) and so continue the line P1 across the Pacific. To this end, 30 hydrological survey stations were chosen to transect the Sea of Okhotsk (fig. 10). Beginning outside the SoO, over the Kuril Trench, the survey line passes through the Bussol Strait, over the Kuril and Deryugin Basins, past the Kashevorova Rise and to the 12

Siberian continental shelf. Along with the thirty stations along this line, another eight stations to the west of P1W were also sampled. The main survey line, stations 1 to 30, crosses the deepest oceanographic features of the Sea of Okhotsk and completes the Pacific survey line, P1.

The data recorded from this voyage do not suggest a large scale exchange of water between the Okhotsk Sea and the Pacific Ocean at the depths and densities of the North Pacific Intermediate Water mass. However, it must be recognized that this study looked at only one of the many straits through the Kuril Islands and sampling was only conducted at the height of summer. Again, little is known about Okhotsk water behaviors in winter and others (Bobkov,1993 and Ohtani,1991) have suggested that outflow of Okhotsk waters may occur in straits farther to the southwest. Whatever the case, the data from this study imply that the Sea of Okhotsk may play only a minor role in the ventilation of North Pacific water and that much of the water in the Sea of Okhotsk has been there for some years. The data will also illustrate that there is little horizontal mixing of Pacific and Okhotsk waters in the relevant first 1000 meters of depth. However, since these data were taken in a single summer month and do not include any estimates of transport between the Okhotsk and Pacific, the complete picture of water mass production remains unresolved. The data presented will also show many of the water properties of the Sea of Okhotsk not available until this time. 13

2. Description of Data

2.1. Collection Methods

Sampling was performed with instruments provided by the Institute of Ocean Sciences (IOS), Sidney, BC, Canada. The Conductivity- Temperature-Depth Probe (CTD) profiler was a Guildline 8736 device calibrated just before shipment to Vladivostok; this calibration was confirmed when the unit was returned to IOS after the expedition. The CTD was transported from IOS to Vladivostok aboard a shipping container as was other scientific equipment. The probe itself was attached to an array of 23 10-litre Niskin Sampling Bottles; the whole unit was lowered together by an onboard winch. After considering the weight of the sampling unit, the weight of released cable and safety, a maximum sampling depth of 3400 meters was possible. The signals sent from the probe along a transmission wire inside the main cable were logged at 40 samples per second. The unit was lowered and raised at a rate of approximately 1 meter per second in the water column; the depth of the CTD was measured with a pressure sensor. The data were stored on hard disk for later analysis.

The CTD Probe and Niskin Bottles were first tested at a station (station 'A') on the way to the beginning of the transect. The 10 litre Niskin bottles occasionally did not fire during this test but that problem was corrected for subsequent trials. The CTD profiler did not exhibit any problems during this test; sampling began on the south end of the transect, at station 1 (figure 10). The deep stations (stations 1 through 5), where the probe was dropped to its maximum depth of 3400 meters, took about 45 minutes to sample 14

going one direction. Of course, the depth of water at the first few stations was well over 3400 meters as these stations were over the Kuril Trench so only the top of the water column could be sampled. However, for all the shallower stations from the Bussol Strait to the continental shelf, the probe was dropped to within 50 meters of the bottom. It took about three hours to steam between the hydrological sampling stations, which were about 30 nautical miles apart. For the most part, the seas were fairly calm and the waves light; sampling was not performed during heavy seas. A storm system did disrupt sampling after station 18. The A. Nesmeyanov steamed north out of the system to continue sampling at station 24 before returning a few days later to complete stations 19 through 23. Hence, the stations were not sampled in consistent numerical order The position of the A. Nesmeyanov was determined by GPS monitors located on the bridge and in the data collection area.

The focus of this paper will be on the data logged by the CTD probe; however, a number of others parameters were measured using sea water samples retrieved with the Niskin bottles. These water samples were analyzed for salinity and chlorofluorocarbon (CFC-11 and CFC-12) concentration as well as dissolved oxygen, nitrate, phosphate and a number of other chemical parameters. The results obtained for salinity from the water samples were checked against the CTD data; similarly, reversing thermometers triggered at various depths were used as cross checks on the CTD temperature results (see Appendix B).

2.2. Data Processing

The raw data taken from each station were initially processed on board ship. This was done in a number of steps. First of all, the 15

data were sorted by pressure to align the samples taken as the probe was lowered with records collected as it was raised. These data were then filtered to remove spikes in the profiles of conductivity and temperature. As mentioned above, data were collected at a rate of 40 samples/second. The CTD probe was moved through the water column at approximately 1 meter per second so there were about 80 samples taken in each meter of water traversed in both directions of travel. This of course makes for very large data files; to get the data in a more useful form, one meter average files were produced. All the records within one meter intervals were averaged and the pressure measurements converted to depth. The potential density for each record was also calculated. The end result was tabular data showing potential density, temperature, salinity at each one meter depth for each station.

2.3. Overview of Data

Contour plots of the three principal properties sampled with the CTD device over the transect are shown in figures 12, 13, 14. For example, figure 12 shows the temperature distribution over the entire passage; both to full depth and a more detailed plot for the top 500 meters. Figures 13 and 14 show similar graphics for salinity and potential density. The bottom shown on these plots represents the maximum depth of each CTD cast of 3400 meters, not the actual sea bottom for the very deep stations. A notable feature of all three of these plots is the dramatic changes near the sea's surface, in the top 100 meters. This variation is better resolved in profiles. Figure 15 shows T, S and a profiles for several stations: one outside the SoO, one over the Bussol Sill, one in each of the Kuril and 16

Deryugina Basins. A temperature versus salinity plot is also shown for these select stations - figure 16. These figures illustrate the general overall properties of the water masses in the Okhotsk Sea as sampled during this expedition; the next section will attempt to describe some of the more specific findings of the expedition. 17

3. Results

3.1. Water Masses in the Sea of Okhotsk

A common method of typifying water masses is by plotting a temperature versus salinity (TS) characteristic diagram. This approach was first used early this century (Helland-Hansen, 1916) and provides a good method of breaking water samples at various depths into different water masses. All water samples with similar TS characteristics can be grouped as a single water mass. The TS plot for the data taken for the Sea of Okhotsk stations reveal some cogent features (figure 17a). The TS profiles on this figure have been categorized by colour into groups: one group for those plots from stations outside the SoO, one for those in the Kuril Basin, one for the Deryugin Basin and the shallower stations on the northwest continental shelf. All 30 profiles have a similar form down to 100 meters of depth, i.e. the TS profiles for all the stations show an abrupt drop in temperature from the surface to 100 meters. The stations in the Deryugin Basin and Continental Shelf group (in red) appear to have a lower surface salinity than the stations farther south. Below that depth, the curves separate into families describing the basin waters in the Okhotsk Sea and a region encompassing the Pacific water outside the Bussol Strait. There is an obvious separation of water masses between open Pacific water and Okhotsk water between the depths of 750 meters down to about 1800 meters. In this depth range, the open Pacific waters (in black) are slightly warmer than those in the SoO. Below 1800 meters, the Okhotsk water in the Kuril Basin has similar characteristics to open Pacific waters. Roughly, the sampled water can be divided into the 18 three regions on the TS diagram; these also appear geographically on the potential density contour plot (figure 18). First of all, there is the uppermost 200 meters where salinity and especially temperature undergo dramatic changes with depth (Surface Water). Then there is the region below this where there is little change to the bottom of the Deryugin Basin (Deryugin Basin Water). Finally, there is the region of mixing between the Pacific and the Kuril Basin near the Bussol Strait (Bussol Sill Water). This section of the report will attempt to describe these three regions and discuss the possibility of exchange with water outside the Sea of Okhotsk.

3.1.1. Surface Water

The water in the first 200 meters exhibits spme extremely cold temperatures. The water directly at the sea surface has a temperature of a few degrees Celsius, presumably warmed by contact with the atmosphere; however the subsurface water at about 100 meters depth is much colder. This water mass, first identified by Kitani (1973), shows potential temperatures as low as -1.1 °C. Shown best in figure 12b, this water appears coldest at the noted depth in a layer centered over the Deryugin Basin. Another pocket of cold water exists outside the Bussol Strait but it should be noted that this cold water is significantly warmer than that in the SoO at the same depth. Presumably, this cold water is left over from last winter's ice pack which has subsequently melted in the spring. The water mass is also quite fresh, with salinities less than 33.2. The freshness of this water mass is probably best attributed to inflow from the many rivers surrounding the SoO. The largest river to flow into the Okhotsk Sea, the Amur River, has a mean annual outflow of

315 km3 (UNESCO, 1974). Presumably, the outflow from the Amur 19 and other rivers occurs mainly during the summer months so that this water has a chance to mix with Okhotsk surface water. Discharge from other rivers and a net precipitation surplus amount to another 530 km3 (Aota, 1991). Spread over the average 60% of the SoO that exhibits sea ice each year, this fresh water input accounts for an even layer about a meter thick. This fresh water is strongly buoyant and creates a sharp pynocline preventing vertical mixing with the water below; note the rapid increase of density with depth in the first 100 meters for all of the density profiles in figure 15. It is the low salinity of the surface water that produces the pynocline, maintaining the surface layer. This is another significant reason for sea ice forming at the low latitudes in the south of the sea; the fresh water layer freezes readily in the winter. Although the expedition data were collected in the summer, even the saltiest water at the sea surface, at 32.9 , can only reach a potential density of 26.5 before freezing at T* -1.5° C (figure 17c). At this density, the water can only ventilate down to 200 meters or so as shown on the density contours. That is, water of this density is found at a depth of about 200 meters in the SoO. Therefore, the surface waters are somewhat isolated from the deeper waters, below 200 meters. It is interesting to note that this density, 26.5, is slightly below the range of the densities for North Pacific Intermediate Water, discussed earlier. The NPIW generally has a density of 26.7 to 26.9 (Talley, 1993), It has been shown by Kitani that direct ventilation of surface water occurs in the SoO during the winter along the northern continental shelf. It is believed that this advected water then spills into the deeper Deryugin Basin. However, if this cold, fresh surface water undergoes downwelling during the winter, it could not reach the depths of the NPIW mass, at least not in the Sea of Okhotsk, according to the potential density 20

contours collected for this study. It must be remembered however that this data set was established in the summer and the potential density contours may be quite different in the winter, allowing deeper ventilation. Also, the production of an Okhotsk component of NPIW may take place to the east or west of the transect line and not appear on these contours. Nonetheless, one might expect some evidence of this ventilation to show up in the Deryugin Basin, the deepest basin in the northern part of the sea and it is not readily apparent. The water in this basin will be examined in the next section. It may be possible to produce water of sufficient density and freshness for NPIW through other processes such as diffusion but this requires a long time period, suggesting production is slow. Presumably, the great quantities of water composing the NPIW could not be formed by direct overturn of surface waters. Finally, it should be noted that the cold fresh surface layer extends over the entire transect. However, in the 500 meter temperature and salinity contours (figures 12b and 13b) there appears to be a discontinuity over the Bussol Sill around station 7. This may be evidence of tidal mixing over the sill and will be discussed in 3.2.3.

3.1.2. The Deryugin Basin Water

The physical properties of the water mass in this region seem to suggest that there is little change in the deep waters and that this water mass has resided there for some time. The potential density and salinity contours are both fairly flat in this region. The slight doming of the isopychals near the surface (figure 14b) is indicative of the general cyclonic circulation pattern suggested for the Sea of Okhotsk. An estimate is made of the strength of this circulation in section 3.2.2. There is also little variation in temperature; from 600 21

meters to the bottom, the temperature varies less than 0.25 C° (figure 12a). These factors suggest that this water mass has resided in the Deryugin Basin for some time and has not been flushed out yearly by direct ventilation. There is no evidence for the appearance of colder fresher water from the northern continental shelf. The potential density contours actually rise at the northern end of the Deryugin Basin; this may be evidence of tidal mixing. The dissolved oxygen concentration (figure 19) is very low at the bottom of the basin; as well, the dissolved silicate concentration increases with depth (figure 20). If the water in the Deryugin Basin was ventilated frequently, the concentration of O2 would be similar throughout the water column. In fact, the deep waters in this basin exhibit the lowest oxygen concentrations throughout the transect with the exception of water just outside the Bussol Strait. The Deryugin Basin water also has a higher silicate concentration than this other water mass; the silicate concentration at the bottom of the basin is the highest found. All these factors, the flat contours and the tracer concentrations, suggest that this water mass has not been disturbed recently by vertical mixing or convective ventilation.

3.1.3. Water Masses near the Bussol Sill

It is evident from the contour plots of all the dynamic properties that there is a disjunction at the Bussol Sill. This is displayed most clearly on the potential temperature contours (figure 12a and 12b). There is a clear separation of water masses on either side of the Bussol Sill in the upper 600 meters of the water column. The contours of salinity and density also show a discontinuity in this region. The contours for salinity fall to a minimum at station 3, rise again at station 5, and then dip once more on the other side on the 22

sill near station 7. The local isopycnals mirror the variation in salinity; the change in temperature below 60 meters depth is too slight to significantly alter the density. These properties, as well as the oxygen and silicate profiles, suggest that there is some vertical mixing in the first 800 meters of the water column.

As discussed earlier, this mixing is in part the result of tidal flows through the Bussol Strait, estimated to be some of the largest in the world and this process is discussed in 3.2.3. The isopycnal contours also suggest the existence of a strong surface eddy near the Bussol Strait. The circulation of this eddy is discussed in 3.2.2. At the sea surface immediately over the sill, between stations 6 & 7, the cooler temperature contours approach the surface: evidence of vertical mixing of the cold subsurface water with the slightly warmer water from below. This mixing appears to extend down a few hundred meters; this is mentioned in 3.2.3. However, on either side of the sill, the cold water masses centered at about 100 meters depth have different characteristics. The cold water mass located entirely within the SoO has a significantly lower temperature than that sampled at the same depth in the Pacific: at station 20, the temperature minimum approaches -1.0 °C while its counterpart in the Pacific is warmer at about 1.5 °C. Thus, the variation in the contours and the temperature difference of these water masses suggest that though there is some vertical mixing, net horizontal exchange of water across the Bussol Strait is weak, at least in the upper 800 meters of the water column.

Below that depth, the picture is different. There appears to be a portion of the water column between about 800 and 1800 meters in which little vertical mixing takes place. Directly over the Bussol Sill, between stations 6 and 7, the isopycnals are fairly flat (figure 14a). This suggests there is little vertical movement of water. Also, there 23 appears to be a distinct separation of water masses on either side of the sill. A magnified TS diagram for those stations in the Kuril Basin and those in the Pacific show a significant temperature difference for the two groups of stations (Figure 22). The Pacific waters are slightly warmer than those in the Kuril Basin and this distinction exists between the depths of around 800 and 1800 meters. Below these depths, the TS signatures reconverge. This gap between the two families of curves indicates that there is little horizontal passage of water from the Pacific to the Okhotsk Sea at the depths mentioned.

A closer look at the potential density structure (figure 21) suggests that there has been an inflow into the Kuril Basin from the Pacific. This was also hypothesized by Yasuoka (1967-1968). Near the depth of the Bussol Sill, it seems some horizontal exchange is taking place. The contour plots of potential temperature, salinity and density exhibit similar water properties at depths of 2000 meters in the open Pacific with those at 3000 meters near the bottom of the Kuril Basin. This suggests there is an exchange of waters over the Bussol Sill below 1800 meters, primarily an inflow from the Pacific into the Kuril Basin. The isopycnals lead from the sill down into the basin, suggesting a flow parallel to the bottom down into the Kuril Basin. Therefore, it is unlikely that water is flowing out from the Okhotsk Sea and entering the Pacific at this depth. This is well below the depths relevant to the North Pacific Intermediate Water mass and the water in this region has too high a density for NPIW. It is unclear how this deep inflow affects the circulation in the Kuril Basin but it may be part of an anticyclonic current suggested for the basin. 24

In summary, the water column over the Bussol Sill has three parts: mixing in the surface layer down to a few hundred meters, a stratified middle layer, and a deep inflow at depth. 3.2. Other Features of the Sea of Okhotsk

The data collected from the waters of the Sea of Okhotsk also exhibit other interesting characteristics. Chlorofluorocarbons will be used as a chemical tracer in this section to attempt to date the basin waters in the SoO. These anthropogenic chemicals have grown in use as an oceanographic tracer since the early 1980's; see Appendix A for a more complete discussion of their use and development. Estimates of the strength of the cyclonic flow also will be made from the isopycnal data. Finally, tidal mixing over the Bussol Sill and Kashevorova Bank will be discussed.

3.2.1. Chlorofluorocarbon Dating of Okhotsk Waters

Further evidence of the relative age of basin waters in the Sea of Okhotsk is shown through the use of chlorofluorocarbons (CFCs) as chemical tracers. Trichlorofluoromethane (CFC-11) and dichlorofluoromethane (CFC-12) are manmade substances manufactured since the early 1900's. Produced in great amounts since 1950, these unreactive chemicals have been dispersed through the atmosphere and subsequently dissolved in the oceans. Warner and Weiss (1985) have described the solubility of these CFCs as a function of ocean temperature and salinity. The ratio of the amount of CFC-11 to CFC-12 in the atmosphere has changed over time. Therefore, a water sample tested for these freons and then corrected for solubility can have its CFC ratio compared to that of the atmosphere. Assuming that the CFC ratio of the water 25 sampled has not changed since the CFCs were absorbed, the data can infer a time when the water sample was last in contact with the atmosphere. The dating technique is described by Doney and Bullister (1992).

Unfortunately, there are some limitations to this process. The CFC ratio is only good for dating water masses that were last in equilibrium with the atmosphere between the years 1950 and 1980. Outside of this period of years the CFC ratio levels off, producing ambiguity it the dating process (see Appendix A). Mixing can also have an effect on the dating results. The blending of a younger, more recently at surface water mass with an older one will produce an age more heavily weighted to the younger sample because the concentrations of both CFCs have increased with time. Consequently, the technique provides only a lower bound of the true age, or number of years since the tested water samples were last at the surface. Despite these restrictions, the CFC ratio can present insight into the age of a submerged water mass. Figure 23 shows the age contours for the Sea of Okhotsk transect given as years in last contact with the atmosphere. These contours give a rough estimate of the residence time of basin waters.

The CFC data suggests that the waters occupying the bottom of the Deryugin Basin have resided there for some 20 to 30 years. Fortunately, this era lies within the span of years which can be uniquely determined by CFC dating. Of course, at the surface the water cannot be accurately dated because all years after 1980 have similar CFC ratios. This generates some ambiguity in the top 200 meters of the water column. It is evident that in the depths of interest to NPIW formation, down to 1000 meters or so, that the water mass has resided in the sea's basin for a span of many years. 26

This is another indication that the Sea of Okhotsk is not ventilated to this depth with colder fresh surface waters on a frequent basis.

3.2.2. The Okhotsk Gyre and the Bussol Eddy

As mentioned earlier, the cyclonic circulation of the surface waters is evident in the general doming of the isopycnals over the center of the Sea of Okhotsk. Using a geostrophic model, the strength of this gyre's flow can be estimated. The geostrophic technique assumes a balance between Coriolis and pressure forces. Horizontal differences in density, apparent in the sloped isopycnal contours, create horizontal pressure gradients. In a section of water with sloped isopycnals (p's), there is a corresponding set of isobars (P's), contours of equal pressure, which have opposite slopes:

p3

^ ""~P"3 Force due to Coriolis Force due to Horizontal motion of water

p2 Pressure Gradient down gradient

0?

Pi Direction of current is

p1 out of page for Po Northern Hemisphere Po The slopes in the isobaric surfaces are created by the density field; the horizontal difference in pressure creates a force which drives water down the slopes of the isobars. As the water flows down the isobars, it is acted on by the Coriolis force which deflects the flow either into or out of the page. When the flow attains a certain speed, the pressure gradient force will be balanced by the Coriolis force: 27

Coriolis Force = 2vQsin d> = — = Pressure Force p ax. where v=current speed, Q=angular rotation speed of the earth (7.29x10"5/second), <|)=latitude, p=average density and dPIdx is the horizontal pressure gradient. At this point, the flow of water is no longer down the isobars but along them at right angles to the gradient. In the Northern Hemisphere, water flowing to the right is deflected out of the page by the Coriolis force while flows to the left are shifted into the page. The opposite holds true in the Southern Hemisphere. For the density contours from the SoO, therefore, isopycnals sloping up from south (station 1) to north (station 30) suggest a flow to the east while those sloping down suggest a flow to the west. Over the Kuril and Deryugin Basins, the slopes of the isopycnals are consistent with the suggested cyclonic flow of the Okhotsk Gyre. It is important to note that the geostrophic model relies on there being a reference level where the slopes of the isopycnals and isobars are considered level. This level of no motion is the baseline from which the slopes of the pressure gradients above and below are calculated. This is one limitation of applying the geostrophic model: all the currents calculated are relative to the current at the reference level. The reference level is usually chosen at some depth where the current is considered to be almost zero but this cannot always practically be determined. A better alternative is to use a reference level where the current is well monitored: a level of known motion. From this point, all the other currents can be found relative to this established value. However, data on the steady state transport of water is not always available or consistent. Since geostrophic estimates of current assume no friction and ignore transient currents, using a measured value of current for a 28

reference value must be done carefully. In any case, no such current values are presently available for the Sea of Okhotsk. Another way of looking at the pressure distribution is to create a varying dynamic height at the sea surface which similarly accounts for the higher pressure at certain locations. Differences in dynamic height represent pressure differences which reflect the horizontal pressure gradient; larger dynamic heights coincide with higher pressures and vice versa. Again, these dynamic heights are calculated relative to a reference level. Figure 24 shows the dynamic height along the transect where the station depth is deeper than 1000 meters. The reference level is the 1000 dBar pressure surface. The south end of the transect is on the left side of the figure and the north end, station 23, at the right. North of station 23, the depth is less than the reference level and the geostrophic model breaks down as friction with the bottom becomes a significant factor; there is probably some interference from recirculation of water off the northern continental shelf. In this diagram, the dynamic height sloping up to the right represents current flowing to the west and sloping down, flow to the east. The steeper the slope, the larger the magnitude of the current.

The graphic of dynamic height has some obvious features. The anticyclonic Bussol Eddy is readily apparent, centered around station 3. This eddy may be temporary, its variability with time is not well known. The dynamic height plot can be used to estimate the strength of surface currents. The current velocity on either side of the eddy has a magnitude of « 1 m/s; this is somewhat higher than that collected from satellite tracked drifter data (Thomson et al., 1996). However, this circulation is difficult to estimate because of the close packing of the isopycnals near the surface. The isopycnal contours suggest that this eddy appears to penetrate to at 29 least the depth of the Bussol Sill at 2300 meters. The main Okhotsk Gyre is also apparent between stations 8 and 22. Unlike the Bussol Eddy, this gyre has a lower dynamic height at its center, being cyclonic. The current appears to be larger at the south end with a magnitude of between 40-50 cm/s. The current at the north end is about half that, around 20 cm/s. These estimates are in the range for surface currents given by lida (1969) shown in figure 6d. The magnitudes of these currents are small, probably on the same order as the local tidal currents discussed earlier. This is not an uncommon situation near coastal areas. Between stations 5 and 8, directly over the Bussol Sill and between the Bussol Eddy and the Okhotsk Gyre, there is a large change in the dynamic height. This feature is probably more due to the mixing mentioned in the next section than any east-west flow, although some may be occurring. It is unlikely, however, that any steady state geostrophic current would occur between the islands of the Kuril Island chain. Although the geostrophic model does provide some useful estimates of large scale currents, it is limited being applied to short term data. It must be remembered that these current estimates are based on a 'snapshot' of data collected over a few days at one time of the year.

3.2.3. Tidal Mixing over the Bussol Sill

The Sea of Okhotsk is the site of large tidal flows. There is considerable tidal friction in the straits between the Kuril Islands. The data collected from this expedition give some idea of what is happening in the Bussol Strait. The contour plots of the physical properties - temperature, salinity, density - all indicate an unstratified water mass near the sea surface directly over the sill 30 down to a depth of about 800 meters. Presumably, the large tidal currents through the strait are responsible for this mixing. The strength of vertical mixing can be estimated from energy arguments (Garrett, 1978). For a heat flux Q flowing into a unit

surface area of depth h with specific heat cp and thermal expansion

coefficient a, potential energy is created at a rate of gccQh/2cp if complete vertical mixing is assumed. Mechanical energy from tidal friction is supplied at a rate of 4ypu3/37t where y is the bottom friction coefficient, p the density and u the average tidal strength. Therefore, the ratio of the required energy for mixing to the actual energy dissipated provides a quantitative mixing efficiency:

3 37T.gaQh/8cpypu . In a water column where Q, cp, a, p, and y are fairly constant, the mixing parameter boils down to h/u3. This is the Hunter-Simpson parameter, first used to describe the level of mixing in the Irish Sea (Hunter, 1974). As a tidal current with a mean amplitude u flows across a sea of mean depth h, the tidal action stirs the water column producing a well-mixed lower layer. In very deep water, the bottom boundary layer is distinct from the surface and the water column is stratified. At shallower depths, however, where h is low or at site where the tidal current u is large, the entire column water is mixed: the bottom boundary layer reaches the surface. This transition from a partially mixed water column to a fully mixed one can be predicted by a characteristic value of h/u3 «

100 m"2s3 (Garrett, 1978). Of course, in many areas the assumption of uniform water properties made to resolve the parameter of h/u3 is misleading. In addition, there are other factors including fresh water run-off and wind mixing which effect vertical structure. However, Garrett was able to use the H-S parameter to effectively describe mixing of tidal fronts in the Bay of Fundy. 31

At the Bussol Sill, where the depth is 2300 meters and the tidal currents are estimated to be about 1-2 m/s, the value of h/u3 is too high to anticipate full mixing of the water column at the full depth of the sill. This is of course what is observed, as discussed earlier (3.1.3) where it was mentioned that vertical mixing had only occurred in the first few hundred meters. However, the Bussol Sill is a saddle point between two islands and more complete mixing of the water column may occur on the sides of the strait where the water is shallower. Turning this equation around and using h/u3 = 100 and giving u a maximum value of 2 m/s, the depth of full mixing can be estimated to be about 500-600 meters and this can occur on either side of the strait: Cross-section of Bussol Strait

mixed areas on the sides of stratified Bussol Strait deep water ^--^_L-^-^

Of course, this estimate generates a mixing depth that the Hunter-

Simpson parameter was not designed to predict. In fact, the h/u3 parameter was originally to describe tidal flows into shallow seas, not over deep sills. However, this estimate agrees well with the previous observations and with Rogachev (1995) who suggested mixing does take place down to depths of 400-500 meters. The Rogachev estimates are for neighboring Vries (Friza) Strait, rather than Bussol Strait but one might assume similar structure. If the water column was entirely mixed at the sides of the strait, this would provide a mechanism for the downward vertical movement of the cold fresh surface water. As the tidal currents moved back and forth 32 over the sill, this water would be mixed across the strait and carried out to the Pacific. It is also interesting to note that the water in the Bussol Strait has a density range of 26.6 at 100 meters to 27.0 at 600 meters. This density range is very similar to that of NPIW and at similar depths. North Pacific Intermediate Water (figure 11) appears across the subarctic gyre of the North Pacific as a low salinity intrusion. There is nothing to suggest, however, that large quantities of this mixed water are being produced since its properties are dependent on the small quantity of water in the thin subsurface layer. Also, the water in the Bussol Strait is somewhat cooler and fresher than the main body of NPIW while of similar density. The mixed surface water in the Bussol Strait may be further transformed but how this occurs is unknown; surely the Oyashio current and the Bussol Eddy play a role. Until current measurements at all depths and transport estimates can be made, the strength of the influence of water mixed in the Bussol Strait cannot be determined. 33

4. Discussion

The Sea of Okhotsk has been suggested as a possible source for North Pacific Intermediate Water, a water mass characterized by a salinity minimum in the top 1000 meters. It is believed that deep convection could occur down to this depth as result of winter cooling of surface waters in the SoO. The data gathered from the WOCE Expedition 1993 indicate that vertical mixing is taking place near the surface of the Bussol Strait, primarily due to tidal flows. There is no evidence of large scale exchange of Okhotsk and Pacific water at the density and depths ascribed to NPIW. That said, it should also be noted that this account only examines water properties as recorded in one summer month in 1993. There is no examination of annual and interannual variability in the conditions in the Sea of Okhotsk. As well, this paper only examines the exchange of waters through a single strait in the Kuril Island chain, albeit the deepest one. The circulation patterns and mixing processes in this sea are not well known and this may account for the difference in opinion as to the role of the Sea of Okhotsk plays in water mass formation. On the positive side, the data did confirm the general cyclonic flow of the Okhotsk Gyre and also substantiated the deep inflow of Pacific water over the Bussol Sill. Until tidal effects are accounted for and transport estimates are undertaken in the Bussol Strait, exchange between the Pacific and the Sea of Okhotsk will be obfuscated. Further study is needed to discern the true nature of what may be a complex interaction between these bodies of water. 34

References:

Akagawa M. Sea ice in the Okhotsk Sea. Kisho-Kenkyuu Note, 101, 47-77, 1969. (In Japanese).

Aota M. and M. Ishikawa. Fresh water supply to the Sea of Okhotsk and volume transport of Soya Warm Current. Bull. Hokkaido Nat. Fish. Res. Inst., 55, 109-113, 1991. (In Japanese).

Alfultis M.A., and S. Martin. Satellite passive microwave studies of the Sea of Okhotsk ice cover and its relation to oceanic processes. J. Geophys. Res., 92, 13, 13-13028, 1987.

Bathymetric Atlas of the North Pacific Ocean, U.S. Naval Oceanographic Office, Washington D.C., 1973.

Bobkov A.A. New schema of the circulation and water mass distribution in the southern Kuril area. Umi to Sora, 69:41-52 1993.

Doney S.C. and J. L.Bullister. A chlorofluorocarbon section in the eastern North Atlantic. Deep-Sea Res. 39, 1857-1883, 1992.

Efimor V.V., E.A. Kulikov, A.B.Rabinovich and I.V. Fain. Waves on Boundary Regions of the Ocean. Hydrometeoizdat, Saint Petersburg, 1985.

Favorite F., A.J. Dodimead and K. Nasu. Oceanography of the Subarctic Pacific Region, 1960-71. International North Pacific Fisheries Commission, 33, 187pp., 1976.

Garrett C.J.R., J.R. Keeley and D.A. Greenburg. Tidal Mixing versus Thermal Stratification in the Bay of Fundy and Gulf of Maine. Atmosphere-Ocean 16 (4) 403-423, 1978.

Hunter J.R. and J.H. Simpson. Fronts in the Irish Sea. Nature, vol.250, Aug. 2, 1974.

Helland-Hansen B. Nogen hydrografiscke metodor. Forh. Skandinaviske Naturforske mote, 16, 357-359, 1916. lida H. Oceanographic Conditions of the Okhotsk Sea. Kisho- Kenkyuu Note. 101:480-491, 1969. (In Japanese) 35

Kantha L.H., C. Tiemey, J.W. Lopez, S.D. Desai, M.E. Parke and L. Drexler. Barotropic tides in the global oceans from a nonliear model assimilating altimetric tides. 2. Altimetric and geophysical implications. Journal of Geophysical Research, Vol. 100, No. C12, pp 25309-25317, Dec. 15, 1995.

Kitani K., An oceanographic study of the Sea of Okhtosk - Particularly in regard to cold waters. Bull. Far Seas Fish. Res. Lab. 9, 45-77, 1973.

Leonov A.K. The Sea of Okhotsk. NTIS AD 639 585, 95pp., Natl. Tech. Inf. Serv., Springfield, Va, 1960.

Luchin V.A. 1. Russian Hydrological Studies in the Okhotsk Sea - Historical Background. 2. System of Currents and Pecularities of Temperature Distribution in the Okhotsk Sea. Hydrometeorology and Hydrochemistry of the Seas, Saint Petersburg, 1993.

Ohtani K. Re-consideration on the definition of the Oyashio. Bull. Tohoku Reg. Fish. Res. Lab., 55, 1-24, 1991.

Parkinson C.L., The impact of the Siberian High and Aleutian Low on the sea-ice cover of the Sea of Okhotsk. Annals of Glaciology, 14, 226-229. 1990.

PICES Scientific Report No. 2. The Okhotsk Sea and Oyashio Region (Report of Working Group 1). Ed. by L.D. Talley and Y. Nagata. April, 1995.

Moroshkin K.V. New Scheme of the surface Okhtosk Sea currents. Oceanology 1(4):641 -643, 1964.

Rabinovich A.B. Long Gravitational Waves in the Ocean: Trapping, Resonance and Scattering. Hydrometeoizdat, Saint Petersburg, 1993.

Reid J.L., Intermediate waters of the Pacific Ocean. John Hopkins Press, Baltimore, MD., U.S.A., 85pp., 1965.

Reid J.L., Northwest Pacific Ocean waters in winter. John Hopkins Press, Baltimore, MD., U.S.A., 96pp., 1973. 36

Rogachev K.A..A.S. Bychkov, P.Y. Tishchenko, E.C. Carmack, C.S. Wong and P.H. Leblond. Circulation and Mixing Processes influencing carbon dioxide partial pressure during summer in the Kuril Island region between the Sea of Okhotsk and the western subarctic Pacific. Draft, July 1995.

Rogachev K.A., E.C. Carmack, G.I. Yurasov, M. Miyake and V. Sosnin. Structure of warm core rings and volume transport of the Oyashio and Kamchatka Current in Autumn 1990. Proceedings of the Nemuro Workshop on western subarctic circulation, PICES 1993.

Rogachev K.A. and V. Goryachev. Mixing in the warm core ring of the Kuroshio. J. of Geophys. Res., 96:8773-8777, 1991.

Suzuki K. and S. Kanari. Tidal Simulation of the Sea of Okhtosk. Kaiyo Kagaku, 18:455-463, 1986. (In Japanese)

Talley L.D. An Okhotsk Sea water anomaly: implications for ventilation in the North Pacific. Deep-Sea Res., 38, supp. 1, s171- s190, 1991.

Talley L. D., Distribution and Formation of North Pacific Intermediate Water. J. Phys. Oceanogr. 23, 517-537, 1993.

Thomson R.E., P.H. Leblond and A.B. Rabinovich. Oceanic odyssey of a satellite tracked drifter: North Pacific variability delineated by a single drifter trajectory. Submitted to: Journal of Oceanography, 1996.

Warner M.J. and R.F. Weiss. Solubilities of chlorofluorocarbons 11 and 12 in water and seawater. Deep-Sea Res. 32, 1485-1497, 1985.

Watanabe K. On the reinforcement drift of the East Sakhalin Current preceding to the ice season off the coast of Hokkaido - Study in sea ice in the Okhotsk Sea (IV). Oceanography Mag., 14, 117-130, 1963b.

Wust G., Meridionale Schichtung und Tiefenzirkulation in der Westhalften der drei Ozeane. Journal du Conseil, Conseil International pour I'Exploration de la mer, 5, 21pp., 1930. 37

Summary of Figures:

Fig. 1: The Sea of Okhotsk and the North Pacific Fig. 2: Oceanographic features of Okhotsk Sea (Alfultis and Martin, 1987) Fig. 3: The Kuril Islands and Straits from PICES Fig. 4: Bathymetry of Sea of Okhotsk from U.S. Naval Oceanographic Office. Fig. 5: a) Development of Sea Ice over winter months (Japanese Meteorological Agency, 1990) b) February sea ice extent 1973-76 (Parkinson, 1990) c) Interannual sea ice cover as a % of total area from H. Freeland, compiled with data sent by Alex Bychov, POL Fig. 6: a) Circulation of SoO in summer by Watanabe b) Circulation of SoO according to Leonov c) Circulation of SoO according to Moroshkin d) Estimates of surface currents from lida (in knots: 1 knot = 0.514 m/s) e) the presence of the Bussol Eddy (Rogachev, 1993) f) Gyres of the North Pacific (Ohtani et al, 1991) Fig. 7: a) Amplitudes of tidal components (Suzuki and Kanari) b) Tidal components in the Kurils from Luchin c) Tidal parameters near the Bussol Strait from Luchin Fig. 8: Temperature distribution along north-south line at approximately 150° E (Kitani, 1973) Fig. 9: WOCE survey lines in the Northwest Pacific Fig. 10: Survey Stations of WOCE Expedition 9316 (Sept. 1993) Fig. 11: NPIW low salinity intrusion from H. Freeland

- solid lines are 5, 6 and 7 degree isotherms - dashed lines are 26.7, 26.7 and 26.8 isopycnals 38

Fig. 12: a) Potential temperature over the transect b) Potential temperature for first 500 meters Fig. 13: a) Salinity over the transect b) Salinity for first 500 meters Fig. 14: a) Potential Density over the transect b) Potential Density for first 500 meters Fig. 15: Profiles of S, T, 0 at various stations along the transect Fig. 16: TS plot for above stations Fig. 17: a) Temperature-salinity profiles for all 30 stations. b) TS profiles divided into 3 regions c) TS plots with density contours and freezing point. Fig. 18: Potential Density Contour illustrating 3 regions

Fig. 19: Dissolved 02 contour plot Fig. 20: Dissolved silicate contour plot Fig. 21: Potential density near the Bussol Sill Fig. 22: TS plot for depths below 1000 meters Fig. 23: CFC age contours for the SoO. Fig. 24: Dynamic heights relative to 1000 dBar surface for stations where depth exceeds 1000 m (stations 1 to 23) 39

Figure 1 Figure 2 41

1U* 150' 156*

Figure 3 42

Table 1. Geographical locations in the Okhotsk Sea region: (old) indicates that the Russian is preferred

Label Russian Japanese Note a Pervyy Kuril'sky Proliv Simusyu Kaikyo (old) strait b Ostrov Simusyu To (old) island c Ostrov Paramusir ParamusiruTo (old) island d Chetvertyy Kuril'skiy Proliv Kaikyo (old) strait e Ostrov Onekotan Onekotan To (old) island f Proliv Krenitsyna Harumukotan Kaikyo (old) strait g Proliv Cevergina Syasukotan Kaikyo (old) strait h Proliv Kruzenshtema Musiru Kaikyo (old) strait i Proliv Nadezhdy Rasyuwa Kaikyo (old) strait j Proliv Rikorda Ketoi Kaikyo (old) strait k Proliv Diany Simusiru Kaikyo (old) strait 1 Ostrov Shimushir Simusiru To (old) island m Proliv Bussol' Kita-Uruppu Suido (old) strait n Proliv Minami-Uruppu Suido (old) strait o Ostrov Urup UruppuTo (old) island p Proliv Friza Etorohu Kaikyo strait q Ostrov Etorohu To (old) island r Proliv Ekaterina Kunasiri Kaikyo island

s Ostrov Kunasir Kunasiri To , , . island t ? Nemuro Kaikyo strait u Siretoko Misaki cape v Soya Misaki cape w La Perouse (strait) Soya Kaikyo strait x Mys Kril'on Nisi-Notoro Misaki (old) cape y ZalivAniva AniwaWan (old) bay z Mys Aniwa Naka-Siretoko Misaki (old) cape A Zaliv Terpeniya TaraikaWan (old) bay B Mys Terpeniya Kita-Siretoko Misaki (old) cape C Gulf of Tartary strait D Mys Telizavety cape E Sakhalinskiy Zaliv bay F Ostrov Iony island G Kashevarov Bank rise H Deryugin Basin basin I Instituta Okeanologii Rise rise J Akademii Nauk Rise , rise K Kuril Basin basin L Penzhinsky Zaliv (Shelikova Zaliv) bay M Tinro Basin basin

Figure 3 Captions 43 Figure 5a 45 46

o o o o o o o o o o ejj CO in CN o o o o9 00 1 CD 00 6 C6O m 6 C6O C6M T6— o CO o • • • • CD • • 0 • Q

9m* WISE ^—^Z^Sk."* -1.6-06 IFfl "'••.'^•••k ••! tW ^A 68- 88 ^11 Ik. Ik W~JM Z8-98 i JV i .^IIJI if iiir J • irjipmj|. ^jr ji *w Q8-fr8

88-28 C3 0 CO 1.8- 08 c B »1 II ',"»**"v w o -6Z-8Z 3 n\r\. yrn^jk .^/siit O •o 11-91 c (0 •W /• o 0) "Ilk. -9Z-W. <5 ki o ^IBk^i**kf A IlV 9 > o ZtZL iRi lai llllllllili^^ % ; II r (0 l[f # ".'.*V"""I*_K \ikV JH j - IL-0L

flj 69- 89 wmr~*y'Sh^. IF Jv Z9-99

99-179

iisBr £9-29

1.9- 09

nkiir .. #*— mw 69-89 sir: Figure 5c Z9-99 )

Al

Figure 6a 48

Figure 6b Figure 6c Figure 6d 51

Dynamic height at the sea surface relative to 1000 dbar in fall, 1990, showing Kuril eddies (Rogachev et al.,1993).

Figure 6e Figure 6f 53

Figure 7a 54

Type of tidal current in the 0-25 m layer

1 - complex with prevailing semidiurnal tides 2 - complex with prevailing diurnal 3 - diurnal

(Luchin)

Figure 7b Figure 7c Figure 8 57

WOCE Survey Lines in the Pacific (from the WOCE Homepage)

Figure 9 58

-135 -140 -145 -150 -155 -1B0

-135 -140 -IMS -150 -155 -160

WOCE EXPOCOPE 90BM9316/1 "flK. R. NESMEYNOV SEPTEMBER 19

Figure 10 59

o o o o o

CN ^ CO 00 O

Figure 11 (sjd)eiu) mdaQ Figure 12a Figure 12b (SJ9J8UJ) i\\tidQ Figure 13a (sjajaui) ijjdea Figure 13b (sjejeiu) qjdea Figure 14a (sjd)diu) MJdaa Figure 14b

67

Figure Figure 17a Figure 17b

71

-Q E ZD z oc co

3 c o o o JC O

(0 0) c CD (0 c Q o c o 0.

(sjajeiu) qjdea Figure 18 72

Figure 19 73

Station Number

Distance (km.) Figure 20 74 75

Figure 22 76

Figure 23 77 78

Appendix A: The Use of Chlorofluorocarbons as Oceanographic

Tracers

Two industrially produced CFCs, freon-11 and freon-12, have found recent use as chemical tracers in oceanographic work. These substances are anthropogenic, produced only by human industrial activity beginning around 1912. The technique was pioneered by Bullister and Weiss in the early 1980's and has been developed to "age" water masses. That is, the sampling of these CFCs is used to find out how long a deep water sample has remained below the surface, out of contact with the atmosphere. Using industrial output figures, the concentrations of the two freons have been monitored over time. The concentrations of both CFC-11 (C11) and CFC- 12(C12) were present in trace amounts in the atmosphere as early as 1930 and have risen steadily ever since:

C11 and C12 over time

1930 1938 1947 1955 1963 1972 1980 1988 Year

It is primarily the ratio of these two concentrations that is used to find the age of a water sample. First of all, the level of each CFC in a sample must be normalized according to their solubilities at the sampled temperature and salinity. After that, the ratio of their concentrations can be compared to that estimated for the atmosphere: 79

Ratio of Freon Concentrations over Time [C11/C12] -r 0.6 " 4- 0.5 - 0.4 - 0.3 - 0.2 - 0.1 4- o 1930 1940 1950 1960 1970 1980 1990 Year

This gives an idea of when the water sample was last in contact and mixing with the atmosphere. The freon concentrations given for the atmosphere are assumed to be constant over the northern hemisphere and testing to date (1993) has so far concurred. Two things should be noted from this plot. Most obviously, the freon dating system can only uniquely identify water samples that were last in equilibrium with the atmosphere between 1950 and 1980. Outside of these limits, the concentration ratio cannot distinguish between different years. Mixing can also play a role. The blending of an "older" and a "younger" water sample will give more weight to the younger sample since the amount of CFCs in the younger sample will dominate the proportions. The result is that a water sample is always at least as old as the CFC ratio suggests on the average. CFCs are unreactive and their concentrations change only with mixing when taken out of contact with the atmosphere.

This method of dating water samples relies on several assumptions, listed above, but used in conjunction with other techniques can provide some unique information about the sample under test. 80

Appendix B. A Comparison of CTD and Niskin Bottle Salinitv(Conductivity) Data.

The following Data table contains the raw data collected for salinity from the expedition. All values are in psu, using the PSS-78 convention. The depth of sampling is roughly described by the pressure in decibars (1dBar - 1 meter). The values listed for measured bottle salinity which are negative indicate a missing sample. Since the comparison data is long (14 pages), one comparison has been selected from each station. No reversing thermometer data was available.

Station No.# Bottle No.# Depth (dBar) CTD Salinity Measured Bottle Salinity

1 13 1000.3 34.4220 34.4112 2 14 1001.8 34.3656 34.3541 3 13 999.1 34.2907 34.2766 4 14 999.7 34.3758 34.3634 5 13 999.7 34.3989 34.3865 6 10 1005.2 34.2996 34.2846 7 13 1001.1 34.2925 34.2792 8 14 1001.5 34.2084 34.1937 9 14 1000.9 34.2593 34.2484 10 9 1001.3 34.2959 34.2820 11 4 999.2 34.3364 34.3175 12 3 898.8 34.3085 34.2881 13 3 997.7 34.3523 34.3327 14 5 998.7 34.3354 34.3160 15 3 1001.6 34.3355 34.3160 16 3 998.3 34.3362 34.3190 17 3 999.9 34.3219 34.3030 18 4 999.4 34.3357 34.3210 19 5 998.1 34.3297 34.3150 20 5 999.6 34.3406 34.3230 21 4 1001.4 34.3522 34.3360 22 6 998.9 34.3333 34.3180 23 3 996.7 34.2835 34.2630 24 3 199.7 33.5935 33.5720 25 2 198.6 33.3981 33.3700 26 2 200.7 33.3194 33.2800 27 10 100.5 33.1508 33.0980 28 17 99.3 33.2978 33.2490 29 2 99.3 33.3116 33.2590 30 9 49.7 33.0324 32.9890