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An overview is given of the surface-to-bottom thermohaline, oxygen, nutrient, and baroclinic flow structures in the Aleutian Basin of the Bering Sea and the adjacent North Pacific, based on high-resolution field measurements in July 1993. A basic fourlayer vertical structure is observed in the upper 1500 m. The 30-m top layer is warm, low in salinity and nutrients, and high in oxygen. Beneath it a 100-to 150-m thick temperature minimum layer is found, believed to be a remnant of winter convection. This is followed by a 300-m thick warm layer in which the main halocline, oxycline, and nutricline are located. Below it lies a layer of minimum oxygens and maximum nitrates and phosphates, centered at a depth of 900 rn in the Bering Sea but rising to 400 rn south of the Aleutians. This basic structure is disrupted in the vicinity of Amchitka Pass due to strong tidal mixing. The deep and abyssal waters of the Aleutian Basin differ substantially from those at comparable depth in the adjacent Pacific by being warmer (A = 0.1øC), less saline (A = 0.01%o), less dense (A -0.01 kg/m3), poorer in oxygen (A = 50 txmol/kg), and richer in silicates (A: 80 txmol/kg), nitrates (A = 1.0 txmol/kg), and phosphates (A = 0.3 txmol/ kg). The highest silicate concentrations (>240 txmol/kg) occur at the foot of the Bering shelf. Unusual hydrographic conditions exist in an isolated tidal mixing basin in Amchitka Pass, where the bottom mixed layer is 600 rn thick, 0.7øC warmer, 0.14%o less saline, and 21 txmol/kg less oxygenated than at comparable depths outside. Baroclinic currents indicate strong, deep, jetlike flows on both sides of the Aleutian ridge, weak shallow eddies in the middle of the Aleutian Basin, and somehat enhanced flows near the Bering shelf edge. The Alaska Stream in July 1993 was 100 km wide, had a double core with a top speed of 0.54 m/s, and had a westward volume transport of 38 Sv, with 14 Sv below 1000 dbar. The north Aleutian current had a speed of 0.2 m/s and an eastward transport of 10 Sv, with 4 Sv below 1000 dbar. Off the Bering slope, both eastward and westward flows were observed, with volume transports near 7 Sv. The Bering Sea is one of the major marginal seas of the North Pacific, with a surface area of about 2.3 x 10 6 km 2 and a volume of 3.7 x 10 6 km 3. It is bounded in the north by the shallow (45 m) and narrow (85 km) Bering Strait, in the west by the Kamchatka Peninsula, in the east by Alaska, and in the south by a perforated island chain encompassing the Commander and Aleutian Islands. Topographically, the Bering Sea can be divided into a wide shallow shelf in the north and east and three deep basins in the south and west. The largest of these is the Aleutian Basin, followed by the Kamchatka and Bowers Basins, which are separated from each other by the Shirshov and Bowers ridges (Figure 1). In the uppermost layers the waters of the Bering Sea communicate freely with those of the North Pacific through Kamchatka and Near Straits and through the Aleutian passes (Table 1). Most of the Aleutian passes are...

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The subarctic‐subtropical transition zone in the eastern North Pacific is investigated and an attempt is made to relate the observed features to the heat and salt flux divergence fields. These are linked to the atmospheric and oceanic circulation and are shown to depend upon the vertical stability, the divergence of the Ekman and geostrophic mass transports, and the horizontal advection of density, salinity, and pressure. Field measurements of the thermohaline structure made in November 1969 are presented. The transition zone is found to occupy the latitude belt between 30° and 40°N in the western part of the region and to turn southeastward as it approaches the North American continent. The boundaries of the transition zone are marked by sharp horizontal salinity gradients and by a break in the thin high‐stability layer, commonly encountered between 60 and 80 m. Very complicated thermohaline structure is encountered in the vicinity of Cabo San Lucas, Mexico, where the subarctic‐subtropical transition zone meets with the north equatorial current and the outflow from the Gulf of California.

The frontal features observed at the boundaries of the subarctic-subtropical transition zone in the western Pacific are investigated. The subarctic front occurs near 42'N and is characterized by horizontal temperature gradients of 8'C/36 kin, horizontal salinity gradients of 1%o/36 km, and horizontal sound velocity gradients of 28 m sec-•/36 kin. The horizontal temperatur• and salinity gradients in the upper 100 meters balanc e each other in such a way that thb resulting density gradients are small. Very low hydrostatic stabilifies occur just south of the subarctiC front and result in a 300-meter-deep isøthermal and isohaline surface layer. The depth of the Solar axis increases from 40 to 600 meters at the front, and the sound velocities along the axis increase from 1464 to 1478 m sec -x. The subtropical front occurs in the vicinity of 30*N and differs from the subarctic front by the presence of significant horizontal density gradients in the upper 100 meters. Low hydrostatic stabilia]es are found just north of the subtropical front, whereas the region to the south is marked by a thin layer of high stability centered at 30 meters. Characteristi c horizontal gradients are 1øC/36 km for temperature, 0.1%o./36 km for salinity, and 4 m seC•/36 km for sound velocity. At 154øE a marked change in the color of the sea was observed. Both the subtropic and the subarctic fronts are related to the wind stress and geostroPhic flow fields and to the heat and salt flux divergence. One of the outstanding features of the western North Pacific is the well-defined transition zone between the subarctic and subtropical water masses. The boundaries of this zone are marked by large temperature and salinity gradients and by low hydrostatic stabilities. At the northern boundary in particular the gradients are frequently strong enough to assume the character of a front. This front is referred to as the polar front [Uda, 1963] or the subarctic front [Bu/gake•v, 1967]. The term subtropical front is used occasionally to describe the. southern boundary of the transition zone [Muromtsev, 1970], though it is usually much less pronounced than the subarctic front. Best known, from an observational point of view, are the temperature fronts at the sea surface. 'They can be seen regularly on the 10-day maps prepared by the Japan Meteorological Agency [1971]. Most of these occur between 40 ø and 45øN and are stronger near X Contribution 0672 from the Japan than further to the east. Less well known is the subsurface structure of fronts. From past hydrographic cruises and recent investigations in the ocean area between Japan and 150øE in connection with the Cooperative Study of the Kuroshio it has been found that the fronts are