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1.
A review is made of circulation and currents in the southwestern East/Japan Sea (the Ulleung Basin), and the Korea/Tsushima Strait which is a unique conduit for surface inflow into the Ulleung Basin. The review particularly concentrates on describing some preliminary results from recent extensive measurements made after 1996. Mean flow patterns are different in the upstream and downstream regions of the Korea/Tsushima Strait. A high velocity core occurs in the mid-section in the upstream region, and splits into two cores hugging the coasts of Korea and Japan, the downstream region, after passing around Tsushima Island located in the middle of the strait. Four-year mean transport into the East/Japan Sea through the Korea/Tsushima Strait based on submarine cable data calibrated by direct observations is 2.4 Sv (1 Sv = 106 m3 s−1). A wide range of variability occurs for the subtidal transport variation from subinertial (2–10 days) to interannual scales. While the subinertial variability is shown to arise from the atmospheric pressure disturbances, the longer period variation has been poorly understood.Mean upper circulation of the Ulleung Basin is characterized by the northward flowing East Korean Warm Current along the east coast of Korea and its meander eastward after the separation from the coast, the Offshore Branch along the coast of Japan, and the anticyclonic Ulleung Warm Eddy that forms from a meander of the East Korean Warm Current. Continuous acoustic travel-time measurements between June 1999 and June 2001 suggest five quasi-stable upper circulation patterns that persist for about 3–5 months with transitions between successive patterns occurring in a few months or days. Disappearance of the East Korean Warm Current is triggered by merging the Dok Cold Eddy, originating from the pinching-off of the meander trough, with the coastal cold water carried Southward by the North Korean Cold Current. The Ulleung Warm Eddy persisted for about 20 months in the middle of the Ulleung Basin with changes in its position and spatial scale associated with strengthening and weakening of the transport through the Korea/Tsushima Strait. The variability of upper circulation is partly related to the transport variation through the Korea/Tsushima Strait. Movements of the coastal cold water and the instability of the polar front also appear to be important factors affecting the variability.Deep circulation in the Ulleung Basin is primarily cyclonic and commonly consists of one or more cyclonic cells, and an anticyclonic cell centered near Ulleung Island. The cyclonic circulation is conjectured to be driven by a net inflow through the Ulleung Interplain Gap, which serves as a conduit for the exchange of deep waters between the Japan Basin in the northern East Sea and the Ulleung Basin. Deep currents are characterized by a short correlation scale and the predominance of mesoscale variability with periods of 20–40 days. Seasonality of deep currents is indistinct, and the coupling of upper and deep circulation has not been clarified yet.  相似文献   

2.
Deep circulation in the southwestern East/Japan Sea through the Ulleung Interplain Gap (UIG), a possible pathway for deep-water exchange, was directly measured for the first time. Five concurrent current meter moorings were positioned to effectively span the UIG between the islands of Ulleungdo to the west and Dokdo to the east. They provided a 495-day time series of deep currents below 1800 m depth spanning the full breadth of the East Sea Deep and Bottom Water flowing from the Japan Basin into the Ulleung Basin. The UIG circulation is found to be mainly a two-way flow with relatively weak southward flows directed into the Ulleung Basin over about two-thirds of the western UIG. A strong, persistent, and narrow compensating northward outflow occurs in the eastern UIG near Dokdo and is first referred to here as the Dokdo Abyssal Current. The width of the abyssal current is about 20 km below 1800 m depth. The low-frequency variability of the transports is dominated by fluctuations with a period of about 40 days for inflow and outflow transports. The 40-day fluctuations of both transports are statistically coherent, and occur almost concurrently. The overall mean transport of the deep water below 1800 m into the Ulleung Basin over the 16.5 months is about 0.005 Sv (1 Sv=106 m3 s?1), with an uncertainty of 0.025 Sv indicating net transport is negligible below 1800 m through the UIG.  相似文献   

3.
Circulation in the upper and the intermediate layer of the East Sea is investigated by using a fine resolution, ocean general circulation model. Proper separation of the East Korean Warm Current from the coast is achieved by adopting the isopycnal mixing, and using the observed heat flux (Hirose et al., 1996) and the realistic wind stress (Na et al., 1992). The simulated surface circulation exhibits a remarkable seasonal variation in the flow patterns of the Nearshore Branch, the East Korean Warm Current and the Cold Currents. East of the Oki Bank, the Nearshore Branch follows the isobath of shelf topography from late winter to spring, while in summer and autumn it meanders offshore. The Nearshore Branch is accompanied by cyclonic and anticyclonic eddies in a fully developed meandering phase. The meandering and the eddy formation of the Nearshore Branch control the interior circulation in the Tsushima Current area. A recirculation gyre is developed in the region of the East Korean Warm Current in spring and grown up to an Ulleung Basin scale in summer. A subsurface water is mixed with the fresh surface water by winter convection in the northeastern coastal region of Korea. The well-mixed low salinity water is transported to the south by the Cold Currents, forming the salinity minimum layer (Intermediate Water) beneath the East Korean Warm Current water. The recirculation gyre redistributes the core water of the salinity minimum layer in the Ulleung Basin. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

4.
The Current System in the Yellow and East China Seas   总被引：18，自引：1，他引：18  
During the 1990s, our knowledge and understanding of the current system in the Yellow and East China Seas have grown significantly due primarily to new technologies for measuring surface currents and making high-resolution three-dimensional numerical model calculations. One of the most important new findings in this decade is direct evidence of the northward current west of Kyushu provided by satellite-tracked surface drifters. In the East China Sea shelf region, these recent studies indicate that in winter the Tsushima Warm Current has a single source, the Kuroshio Branch Current in the west of Kyushu, which transports a mixture of Kuroshio Water and Changjiang River Diluted Water northward. In summer the surface Tsushima Warm Current has multiple sources, i.e., the Taiwan Warm Current, the Kuroshio Branch Current to the north of Taiwan, and the Kuroshio Branch Current west of Kyushu. The summer surface circulation pattern in the East China Sea shelf region changes year-to-year corresponding to interannual variations in Changjiang River discharge. Questions concerning the Yellow Sea Warm Current, the Chinese Coastal Current in the Yellow Sea, the current field southwest of Kyushu, and the deep circulation in the Okinawa Trough remain to be addressed in the next decade. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

5.
Mass fluxes in the Canary Basin   总被引：1，自引：1，他引：0  
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6.
Absolute geostrophic velocities were calculated along TOPEX/Poseidon (T/P) groundtracks located in the Ulleung Basin of the southwestern Japan/East Sea (JES) from a combined analysis of nearly a decade of T/P data and two years of pressure-gauge-equipped inverted echo sounder (PIES) data obtained during the United States Office of Naval Research’s JES Program. Geostrophic velocities have been calculated daily for the Ulleung Basin from June 1999 to July 2001 from a three-dimensional mapping of temperature and salinity produced by PIES data interpreted via the Gravest Empirical Mode (GEM) technique combined with the Navy’s Modular Ocean Data Assimilation System (MODAS). These velocities were then used to convert T/P velocity anomalies to absolute velocities for the T/P time period of 1993 to 2002. Current intensities and variabilities associated with the East Korean Warm Current, Ulleung Warm Eddy, and Offshore Branch are examined. Spatial and temporal variations of the sea surface circulation are strong. Intensification of the currents generally occurred during the fall season. The flow pattern in individual years differed greatly from year to year and differed from climatology in important qualitative ways.  相似文献   

7.
The northward outflow of cold, dense water from the Weddell Sea into the world ocean basins plays a key role in balancing the global heat budget. We estimate the geostrophic flow patterns in the northwestern Weddell Sea using box inverse methods applied to quasi-synoptic hydrographic data collected during the Brazilian DOVETAIL 2000 and 2001 austral summer cruises. The analysis is focused on the variations of the deep Weddell Sea outflow into the Scotia Sea within boxes that bound the main deep gaps over the South Scotia Ridge. To determine the geostrophic volume transports in each box, mass, salt, and heat are conserved within neutral density layers that are not in contact with the atmosphere. Implementing the inverse model and using property anomaly equations weighted by the flow estimate uncertainty our results are consistent with those reported in the literature. A bottom triangle extrapolation method is introduced, which improves the estimated property fluxes through hydrographic sections. In the austral summer of 2000 the transports of Weddell Sea Deep Water (WSDW) through the Philip Passage, Orkney Passage, and southwestern Bruce Passage are 0.01±0.01, 1.15±0.33, and 1.03±0.23 Sv (1 Sv=106 m3 s−1, >0 is northward), respectively. After extrapolation within bottom triangles these transports increase to 0.12±0.03, 3.48±1.81, and 1.20±2.16 Sv. Analysis of the hydrographic data reveal distinct oceanographic conditions over the Philip Passage region, with evidence of mesoscale meanders, warmer and saltier Warm Deep Water (WDW) and colder WSDW observed in 2001 than in 2000. Despite these differences the WSDW transport does not present a significant variation between 2000 and 2001. The WSDW transports through the Philip Passage in 2001 are 0.012±0.001 and 0.113±0.001 Sv after extrapolation within bottom triangles. The circulation derived from the inversion in the austral summer of 2001 suggests a sharp weakening of the barotropic cyclonic flow in the Powell Basin, which may be due to northerly and northeasterly winds associated with an atmospheric low-pressure center located west of the Antarctic Peninsula. We suggest that similar variations in atmospheric forcing may explain changes in the intensity of the cyclonic flow observed in the northwestern Weddell Sea and Powell Basin.  相似文献   

8.
Bottom water formation changes the characteristics of water masses entering the southern part of the Weddell Sea through atmosphere-ice-ocean interaction in which both sea and shelf ice play an important role. Modified water, in particular Weddell Sea Bottom Water, recirculates in the west. By comparing the in- and outflowing water masses we have estimated transformation rates on the basis of a data set obtained during the Winter Weddell Gyre Study from September to October 1989. This consisted of a salinity-temperature-depth (CTD) section carried out by R/V “Polarstern” from the northern tip of the Antarctic Peninsula to Kapp Norvegia and data from three current meter moorings maintained from 1989 to 1990 in the eastern boundary current off Kapp Norvegia. Because of the lack of sufficient direct current measurements in the interior and the western boundary current, it was necessary to derive mass transports on the basis of available data combined with physical and geometrical arguments. At the mooring site barotropic currents were measured. They were extrapolated to the interior under the assumption that wind-driven, baroclinic and barotropic current fields are of similar shape. The location of the gyre centre was determined from drifting buoy tracks and geopoten-tial anomaly. A linear current profile from the eastern boundary current to the centre of the gyre was assumed, and the western outflow was determined according to mass conservation. Different assumptions on the transition from the boundary current to the interior and the location of the centre result in a wide range of transports with most likely values between 20 and 56 Sv. The total mass transport was split into individual water masses. Differences between inflow and outflow result in a transformation rate of 3–4 Sv from Winter and Warm Deep Water to Antarctic and Weddell Sea Bottom Water. The net heat and salt transport across the transect implies heat fluxes from the ocean to the atmosphere of 3–10 W m−2 and ice formation rates of 0.2–0.35 m year−1.  相似文献   

9.
Full-depth conductivity-temperature-depth-oxygen profiler (CTDO2) data at low latitudes in the western North Pacific in winter 1999 were analyzed with water-mass analysis and geostrophic calculations. The result shows that the deep circulation carrying the Lower Circumpolar Water (LCPW) bifurcates into eastern and western branch currents after entering the Central Pacific Basin. LCPW colder than 0.98°C is carried by the eastern branch current, while warmer LCPW is carried mainly by the western branch current. The eastern branch current flows northward in the Central Pacific Basin, supplying water above 0.94°C through narrow gaps into an isolated deep valley in the Melanesian Basin, and then passes the Mid-Pacific Seamounts between 162°10′E and 170°10′E at 18°20′N, not only through the Wake Island Passage but also through the western passages. Except near bottom, dissolved oxygen of LCPW decreases greatly in the northern Central Pacific Basin, probably by mixing with the North Pacific Deep Water (NPDW). The western branch current flows northwestward over the lower Solomon Rise in the Melanesian Basin and proceeds westward between 10°40′N and 12°20′N at 150°E in the East Mariana Basin with volume transport of 4.1 Sv (1 Sv=106 m3 s−1). The current turns north, west of 150°E, and bifurcates around 14°N, south of the Magellan Seamounts, where dissolved oxygen decreases sharply by mixing with NPDW. Half of the current turns east, crosses 150°E at 14–15°N, and proceeds northward primarily between 152°E and 156°E at 18°20′N toward the Northwest Pacific Basin (2.1 Sv). The other half flows northward west of 150°E and passes 18°20′N just east of the Mariana Trench (2.2 Sv). It is reversed by a block of topography, proceeds southward along the Mariana Trench, then detours around the south end of the trench, and proceeds eastward along the Caroline Seamounts to the Solomon Rise, partly flowing into the West Mariana and East Caroline Basins. A deep western boundary current at 2000–3000 m depth above LCPW (10.0 Sv) closes to the coast than the deep circulation. The major part of it (8.5 Sv) turns cyclonic around the upper Solomon Rise from the Melanesian Basin and proceeds along the southern boundary of the East Caroline Basin. Nearly half of it proceeds northward in the western East Caroline Basin, joins the current from the east, then passes the northern channel, and mostly enters the West Caroline Basin (4.6 Sv), while another half enters this basin from the southern side (>3.8 Sv). The remaining western boundary current (1.5 Sv) flows over the middle and lower Solomon Rise, proceeds westward, then is divided by the Caroline Seamounts into southern (0.9 Sv) and northern (0.5 Sv) branches. The southern branch current joins that from the south in the East Caroline Basin, as noted above. The northern branch current proceeds along the Caroline Seamounts and enters the West Mariana Basin.  相似文献   

10.
Robust diagnostic modeling of the Japan Sea circulation   总被引：1，自引：0，他引：1  
The Japan Sea circulation is numerically modeled with robust diagnostic terms included. The general features are nearly the same as previous prognostic models though small differences appear in local current fields, and agree with most of existing observation results. This model, however, seems to be more successful than prognostic ones in that the overshooting of the East Korean Warm Current, a northward western boundary current, is much reduced and the North Korean Cold Current, a southward western boundary current, is more enhanced. Based on the model results, discussions are made about the large convective structure and the global kinetic energy budget of the Japan Sea circulation.  相似文献   

11.
Pacific ocean circulation based on observation   总被引：2，自引：1，他引：1  
A thorough understanding of the Pacific Ocean circulation is a necessity to solve global climate and environmental problems. Here we present a new picture of the circulation by integrating observational results. Lower and Upper Circumpolar Deep Waters (LCDW, UCDW) and Antarctic Intermediate Water (AAIW) of 12, 7, and 5 Sv (106 m3s−1) in the lower and upper deep layers and the surface/intermediate layer, respectively, are transported to the North Pacific from the Antarctic Circumpolar Current (ACC). The flow of LCDW separates in the Central Pacific Basin into the western (4 Sv) and eastern (8 Sv) branches, and nearly half of the latter branch is further separated to flow eastward south of the Hawaiian Ridge into the Northeast Pacific Basin (NEPB). A large portion of LCDW on this southern route (4 Sv) upwells in the southern and mid-latitude eastern regions of the NEPB. The remaining eastern branch joins nearly half of the western branch; the confluence flows northward and enters the NEPB along the Aleutian Trench. Most of the LCDW on this northern route (5 Sv) upwells to the upper deep layer in the northern (in particular northeastern) region of the NEPB and is transformed into North Pacific Deep Water (NPDW). NPDW shifts southward in the upper deep layer and is modified by mixing with UCDW around the Hawaiian Islands. The modified NPDW of 13 Sv returns to the ACC. The remaining volume in the North Pacific (11 Sv) flows out to the Indian and Arctic Oceans in the surface/intermediate layer.  相似文献   

12.
东中国海环流及其季节变化的数值模拟   总被引：1，自引：0，他引：1  
关于东中国海环流的研究，国内外学者已做了大量的工作。早期科学家们主要依赖于对温盐资料和少数测流资料的分析研究对渤、黄、东海的环流结构有了较系统和深入的认识。东中国海环流是由一个气旋式的“流涡”组成，东侧主要是北上的黑潮-对马暖流-黄海暖流及其延伸部分；西侧为南下的沿岸流系。黑潮对东中国海环流的影响是如此之大，以致于除了某些局部区域外，上述海域主要流系的冬、夏季分布形式比较相似而无本质上的差异(胡敦欣等，1993)。但本文所研究海域正处于世界上最显著的季风区，冬、夏季盛行风向基本相反，过渡季节(春、秋季)风向多变，风力减弱；海洋热盐结构季节变化明显(如冬季混合强，而夏季层化明显等)，这些因素都使得东中国海环流存在着较明显的季节变化。 自20世纪80年代以来，东中国海环流的数值模拟工作逐步展开，并已成为研究环流结构及其形成机制的强有力工具。但由于数值模式本身以及计算方案的缺陷(如有些学者用固定的风场、温盐场对东中国海环流进行诊断模拟等)和观测资料的不足，数值模拟的结果难以得到验证，渤、黄、东海的环流研究中仍有大量的问题存在争议，以待澄清。例如，台湾暖流的来源、流径;对马暖流的来源;夏季黄海暖流的流径以及黄海冷水团环流等均有不同的论述。对黄、东海环流季节变化的数值模拟工作也较少，多用冬、夏典型月份的风场强迫积分至稳定态，给出冬、夏季环流，这种做法值得商榷。三维环流模式很难在1个月内达到稳定态，尤其是夏季层化明显、风力减弱的情况下，非常定风场的影响更应引起人们的重视。 本文采用比较符合实际的计算方案，用年循环风场和海面热通量场为外强迫，对渤、黄、东海的环流及其季节变化进行了模拟，并对一些争议问题进行了探讨。  相似文献   

13.
Characteristics of the Sôya Warm Current from Abashiri Bay to the area off the coast of the southern Kuril Islands are clarified by water mass analysis. The water flowing into the Okhotsk Sea as the Sôya Warm Current is divided into two: the Forerunner of the Sôya Warm Water (March to May) and the Sôya Warm Water (June to November). It is shown that in May the Sôya Warm Current flows in the subsurface layer (about 200–400m deep) in Abashiri Bay, and flows northeastward just off the coast of the Kuril Islands as a subsurface current reaching a region northwest of Etorofu Island by the end of May. The dissolved oxygen content is fairly effective in identifying the Forerunner of the Sôya Warm Water in the subsurface layer. The Sôya Warm Current shifts upwards to the surface layer in Abashiri Bay by early July, because the Sôya Warm Water with large thermosteric anomaly t begins to flow into the Okhotsk Sea in June. It is shown that, in general, the major portion of the Sôya Warm Current flows northeastward just off the coast of the Kuril Islands during the summer season, although a minor branch of the current flows northward in the area off the Shiretoko Peninsula, and another minor branch flows out to the Pacific Ocean through the Nemuro Straits.  相似文献   

14.
A nonlinear theory for the generation of the Ulleung Warm Eddy (UWE) is proposed. Using the nonlinear reduced gravity (shallow water) equations, it is shown analytically that the eddy is established in order to balance the northward momentum flux (i.e., the flow force) exerted by the separating western boundary current (WBC). In this scenario, the presence of β produces a southward (eddy) force balancing the northward momentum flux imparted by the separating East Korean Warm Current (EKWC).It is found that, for a high Rossby number EKWC (i.e., highly nonlinear current), the eddy radius is roughly 2Rd/ε1/6 (here ε≡βRd/f0, where Rd is the Rossby radius), implying that the UWE has a scale larger than that of most eddies (Rd). This solution suggests that, in contrast to the familiar idea attributing the formation of eddies to instabilities (i.e., the breakdown of a known steady solution), the UWE is an integral part of the steady stable solution. The solution also suggests that a weak WBC does not produce an eddy (due to the absence of nonlinearity).A reduced gravity numerical model is used to further analyze the relationship between β, nonlinearity and the eddy formation. First, we show that a high Rossby number WBC which is forced to separate from the wall on an f plane does not produce an eddy near the separation. To balance the northward momentum force imparted by the nonlinear boundary current, the f plane system moves constantly offshore, producing a southward Coriolis force. We then show that, as β is introduced to the problem, an anticyclonic eddy is formed. The numerical balance of forces shows that, as suggested by the analytical reasoning, the southward force produced by the eddy balances the northward flow force imparted by the boundary current. We also found that the observed eddy scale in the Japan/East Sea agrees with the analytical estimate for a nonlinear current.  相似文献   

15.
Summertime hydrographic features in the southeastern Hwanghae   总被引：1，自引：0，他引：1  
CTD casts in the southeastern Hwanghae (Yellow Sea) were made in August 1983 and 1984 to describe the spatial structure of the summertime hydrographic features. Cold coastal water appeared around the southwestern coast of Korea, which was formed by strong tidal stirring. Tidal mixing in the study area seems to have been enhanced by the presence of many small islands. In the deeper region beyond the tidal front, stratification became much stronger and the bottom layer below seasonal thermocline was occupied mostly by the Hwanghae Cold Water characterized by a temperature lower than 10°C and salinity of 32.5–33.0%.The northeastward extension of the Changjiang Diluted Water was shown by a tongue-like plume of relatively warm fresh water, confined to the thin surface layer 10 m thick. There was no evidence for the Hwanghae Warm Current carrying high salinity water into the eastern Hwanghae along the Korean coast. The warm current was found to flow in a narrow band close to the west and north coast of Chejudo (Cheju Island) and then to pass eastward through the Cheju Strait. Thus the eastern part of the cyclonic circulation in the surface layer cannot be considered to be a northward continuation of the Hwanghae Warm Current. The local salinity maximum in the lower layer off Kunsan and the higher salinity on the west side of the central trough than on the east side would imply a northward flow on the west flank of the trough to compensate for the southward intrusion of the Hwanghae Cold Water, from which an anticyclonic circulation could be expected in the lower layer.  相似文献   

16.
To better understand the cause of high summer primary productivity in the Ulleung Basin located in the southwest part of the East/Japan Sea, the spatial dynamics of primary, new, and regenerated productivities (PP, NP, and RP) were examined along the path of the Tsushima Warm Current system in summer 2008. We compared hydrographic and chemical parameters in the Ulleung Basin with those of the Kuroshio Current in the Western Pacific Ocean and the East China Sea. In summer, integrated primary productivity (IPP, 0.37–0.96 g C m−2 d−1) and integrated new productivity (INP, 26–221 mg N m−2 d−1) within the euphotic zone in the Ulleung Basin were higher than those in the East China Sea and the Western Pacific Ocean (0.17–0.28 g C m−2 d−1, 2−5 mg N m−2 d−1, respectively). In contrast, there was no pronounced spatial variation in integrated regenerated productivity (IRP, 43–824 mg N m−2 d−1). Strong positive correlations between IPP and INP (also the f-ratio), and between nitrate uptake rate in the mixed layer and nitrate upward flux through the top of pycnocline in summer in the Ulleung Basin imply that the high IPP was mainly supported by supply of nitrate from the underlying water in the euphotic zone. Shallowing of the pycnocline depth as the current enters the East/Japan Sea facilitates nitrate supply from the nutrient-replete cold water immediately below the pycnocline through nitrate upward flux. A subsurface maximum in PP at or above the pycnocline and a high f-ratio further support the importance of this source of nitrate for maintaining the high summer PP in the Ulleung Basin. In comparison, the high PP layer was observed at the surface in the following fall and spring in the Ulleung Basin. Our results demonstrate the importance of hydrographic features in enhancing PP in this oligotrophic Tsushima Warm Current system.  相似文献   

17.
The northward intruding eddy along the East coast of Korea   总被引：5，自引：0，他引：5  
The current structures and their seasonal variations in the East Korean Warm Current (EKWC) region, which plays a significant role in the northward transport of warm and saline waters, were described by combining the sea surface temperature (SST) data of consecutive satellite inferred (IR) images and hydrographic data. The SST patterns in winter-spring clearly showed that the small meander of thermal front originating from the Tsushima/Korea Strait formed close to the Korean coast and grew an isolated warm eddy with horizontal dimension of order 100 km. Such warm eddy began to intrude slowly northward from spring to summer. At that time, interactions with neighboring synoptic warm eddy [Ks] around the Ulleung Basin were found to have strongly influence the movement of the intruding eddy and its structural change. In autumn, after the northward movement stopped at the north of eddy [Ks], the relative stable northward current along the Korean coast were formed. The evidence from observational results does not support a persistent branching of the EKWC from the Tsushima/Korea Strait, but a seasonal episodic supply of warm and saline waters due to the northward intruding eddy process described above.  相似文献   

18.
The circulation and hydrography of the north-eastern North Atlantic has been studied with an emphasis on the upper layers and the deep water types which take part in the thermohaline overturning of the Oceanic Conveyor Belt. Over 900 hydrographic stations were used for this study, mainly from the 1987–1991 period. The hydrographic properties of Subpolar Mode Water in the upper layer, which is transported towards the Norwegian Sea, showed large regional variation. The deep water mass was dominated by the cold inflow of deep water from the Norwegian Sea and by a cyclonic recirculation of Lower Deep Water with a high Antarctic Bottom Water content. At intermediate levels the dominating water type was Labrador Sea Water with only minor influence of Mediterranean Sea Water. In the permanent pycnocline traces of Antarctic Intermediate Water were found.Geostrophic transports have been estimated, and these agreed in order of magnitude with the local heat budget, with current measurements, with data from surface drifters, and with the observed water mass modification. A total of 23 Sv of surface water entered the region, of which 20 Sv originated from the North Atlantic Current, while 3 Sv entered via an eastern boundary current. Of this total, 13 Sv of surface water left the area across the Reykjanes Ridge, and 7 Sv entered the Norwegian Sea, while 3 Sv was entrained by the cold overflow across the Iceland-Scotland Ridge. Approximately 1.4 Sv of Norwegian Sea Deep Water was involved in the overflow into the Iceland Basin, which, with about 1.1 Sv of entrained water and 1.1 Sv recirculating Lower Deep Water, formed a deep northern boundary current in the Iceland Basin. At intermediate depths, where Labrador Sea Water formed the dominant water type, about 2 Sv of entrained surface water contributed to a saline water mass which was transported westwards along the south Icelandic slope.  相似文献   

19.
The horizontal structure of deep mean circulation and its seasonal variability in the Japan/East Sea (JES) were studied using profiling float and moored current meter data. The deep circulation in the Japan Basin (JB) flows cyclonically, basically following f/H contours. The correlation between the directions of deep current and f/H contour increases as |▿(f/H)| increases, reaching remarkably high correlation coefficient (>0.8) values in steep slope regions in the JB. In contrast to the JB, the deep mean circulation in the Ulleung/Tsushima Basin (UTB) is generally weak and cyclonic accompanied by sub-basin-scale cyclonic and anticyclonic eddies. The UTB shows a poorer correlation between directions of deep current and f/H contours than other basins. The time-space averaged deep mean current is about 2.8 cm/s and the volume transport in the deep layer (800 m to bottom) in the JB reaches about 10 Sv (10 × 106 m3s−1), which is about four times greater than the inflow transport through the Tsushima Straits. A salient feature is that the amplitude of deep mean current in the JB reveals a remarkable seasonal variation with a maximum in March and minimum in October. The annual range of the seasonal variation is about 30% of the mean velocity, whereas that in the southern JES (UTB and Yamato Basin) is weak.  相似文献   

20.
Repeated hydrographic casts, mooring time series and satellite sea surface temperature collected during the CANALES experiment (1996–98) are used to describe the thermohaline circulation in the Balearic Channels (western Mediterranean) and to analyze its variability. Mass transports are estimated by inverse calculations. The role played by each channel in the meridional water exchange is clarified: the Ibiza Channel funnels southward cool, saline, northern waters whereas the Mallorca Channel appears as the preferred route for the northward progression of warm, fresh, southern waters. A neat interannual trend is revealed by the continuous decrease of the amount of Western Mediterranean Intermediate Waters (WIW) brought by the Northern Current, reflecting the increase in temperature of the winter mixed layer in the northern Mediterranean that occurred each year between 1996 and 1998. A clear seasonal signal was also seen in the transport of the Northern Current which decreased from 1 to 1.4 Sv in winter to < 0.5 Sv in summer. The current intensified again in fall. A number of mesoscale eddies, from 20 to 70 km in size, most of them anticyclonic vortex eddies were brought by the unstable Northern Current, these eddies strongly perturbed the water exchange in the Ibiza Channel forcing retroflections of northern waters back to the north-east into the Balearic Current. These eddies either stayed stalled for several months in the Gulf of Valencia to the north of the channel, or were slowly funnelled southward through the channel narrows. A decreasing trend was observed in the mesoscale activity of the Northern Current between 1996 and 1998. Conversely, large, anticyclonic eddies, 150-km diameter, progressively invaded the Algerian Basin to the south of the channels in 1997–98 and forcing northward inflows (up to 0.75 Sv) of fresh and warm waters of Atlantic origin (AW) into the Mallorca Channel. The marked interannual differences observed in both northern and southern eddy activity may be linked to the interannual variability of the large scale thermohaline circulation.  相似文献   

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