首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 46 毫秒
1.
We survey the recent progress in studies of North Pacific Intermediate Water (NPIW) in SAGE (SubArctic Gyre Experiment), including important results obtained from related projects. Intensive observations have provided the transport distributions relating to NPIW and revealed the existence of the cross-wind-driven gyre Oyashio water transport that flows directly from the subarctic to subtropical gyres through the western boundary current as well as the diffusive contribution across the subarctic front. The anthropogenic CO2 transport into NPIW has been estimated. The northern part of NPIW in the Transition Domain east of Japan is transported to the Gulf of Alaska, feeding the mesothermal (intermediate temperature maximum) structure in the North Pacific subarctic region where deep convection is restricted by the strong halocline maintained by the warm and salty water transport originating from NPIW. This heat and salt transport is mostly balanced by the cooling and freshening in the formation of dense shelf water accompanied by sea-ice formation and convection in the Okhotsk Sea. Intensive observational and modeling studies have substantially altered our view of the intermediate-depth circulation in the North Pacific. NPIW circulations are related to diapycnal-meridional overturning, generated around the Okhotsk Sea due to tide-induced diapycnal mixing and dense shelf water formation accompanied by sea-ice formation in the Okhotsk Sea. This overturning circulation may possibly explain the direct cross-gyre transport through the Oyashio along the western boundary from the subarctic to subtropical gyres. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

2.
A numerical study using a 3-D nonhydrostatic model has been applied to baroclinic processes generated by the K 1 tidal flow in and around the Kuril Straits. The result shows that large-amplitude unsteady lee waves are generated and cause intense diapycnal mixing all along the Kuril Island Chain to levels of a maximum diapycnal diffusivity exceeding 103 cm2s−1. Significant water transformation by the vigorous mixing in shallow regions produces the distinct density and potential vorticity (PV) fronts along the Island Chain. The pinched-off eddies that arise and move away from the fronts have the ability to transport a large amount of mixed water (∼14 Sv) to the offshore regions, roughly half being directed to the North Pacific. These features are consistent with recent satellite imagery and in-situ observations, suggesting that diapycnal mixing within the vicinity of the Kuril Islands has a greater impact than was previously supposed on the Okhotsk Sea and the North Pacific. To examine this influence of tidal processes at the Kurils on circulations in the neighboring two basins, another numerical experiment was conducted using an ocean general circulation model with inclusion of tidal mixing along the islands, which gives a better representation of the Okhotsk Sea Mode Water than in the case without the tidal mixing. This is mainly attributed to the added effect of a significant upward salt flux into the surface layer due to tidal mixing in the Kuril Straits, which is subsequently transported to the interior region of the Okhotsk Sea. With a saline flux into the surface layer, cooling in winter in the northern part of the Okhotsk Sea can produce heavier water and thus enhance subduction, which is capable of reproducing a realistic Okhotsk Sea Mode Water. The associated low PV flux from the Kuril Straits to the open North Pacific excites the 2nd baroclinic-mode Kelvin and Rossby waves in addition to the 1st mode. Interestingly, the meridional overturning in the North Pacific is strengthened as a result of the dynamical adjustment caused by these waves, leading to a more realistic reproduction of the North Pacific Intermediate Water (NPIW) than in the case without tidal mixing. Accordingly, the joint effect of tidally-induced transport and transformation dominating in the Kuril Straits and subsequent eddy-transport is considered to play an important role in the ventilation of both the Okhotsk Sea and the North Pacific Ocean. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

3.
A basin-wide ocean general circulation model of the Pacific Ocean was used to investigate how the interior restoration in the Okhotsk Sea and the isopycnal diffusion affect the circulation and intermediate water masses. Four numerical experiments were conducted, including a run with the same isopycnal and thickness diffusivity of 1.0×103 m2/s, a run employing the interior restoration of temperature and salinity in the Okhotsk Sea with a time scale of 3 months, a run that is the same as the first run except for the enhanced isopycnal mixing, and a final run with the combination of the restoration in the Okhotsk Sea and large isopycnal diffusivity. Simulated results show that the intermediate water masses reproduced in the first run are relatively weak. An increase in isopycnal diffusivity can improve the simulation of both Antarctic and North Pacific intermediate waters, mainly increasing the transport in the interior ocean, but inhibiting the outflow from the Okhotsk Sea. The interior restoration generates the reverse current from the observation in the Okhotsk Sea, whereas the simulation of the temperature and salinity is improved in the high latitude region of the Northern Hemisphere because of the reasonable source of the North Pacific Intermediate Water. A comparison of vertical profiles of temperature and salinity along 50°N between the simulation and observations demonstrates that the vertical mixing in the source region of intermediate water masses is very important.  相似文献   

4.
Hydrographic observations in Hidaka Bay, south of Hokkaido, Japan were carried out in late winter 1996 and 1997 to examine the spatial distributions and circulation features of two different water masses, i.e., Coastal Oyashio Water (COW) and Tsugaru Warm Water (TWW), and their modifications. It is known that COW is mostly composed of cold and low-salinity water of the melted drift ice coming from the Okhotsk Sea and flows into Hidaka Bay from winter to spring and TWW with high-salinity continuously supplies from the Tsugaru Strait to the North Pacific. Cold surface mixed layers (<26.2σθ, 0–100 m depth) were found mainly over the shelf slope, confirming that anti-clockwise flow of COW was formed. TWW was relatively high in salinity and low in potential vorticity, and had some patch-like water masses with a temperature and salinity maximum in the limited area in the further offshore at the deeper density levels of 26.6–26.8σθ. The fine structure of vertical temperature and salinity profiles appeared between TWW and COW is an indication of enhanced vertical mixing (double-diffusive mixing), as inferred from the estimated Turner angles. At a mouth of the Tsugaru Strait in late winter 1997, a significant thermohaline front between TWW and the modified COW was formed and a main path of TWW spreaded south along the Sanriku coast, probably as the bottom controlled flow. Hence, the patch-like TWW observed in late winter is isolated from the Tsugaru Warm Current and then rapidly modified due to a diapycnal mixing. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

5.
The intermediate water masses in the eastern Atlantic Ocean between 31°N and 53°N were studied by analysis of the distributions of potential temperature, salinity, dissolved nutrients and oxygen. Sub-surface salinity minima are encountered everywhere in the area. At the northern and southern boundary they are connected with the presence of Sub-Arctic Intermediate Water and Antarctic Intermediate Water, respectively, but towards the European ocean margin the sub-surface salinity minima shift to shallower density levels. The sub-surface salinity minima observed west of the Iberian Peninsula represent a water mass formed by winter convection in the Porcupine Sea Bight and the northern Bay of Biscay. These minima gain salt by diapycnal mixing with the underlying Mediterranean Sea Outflow water and with the overlying permanent thermocline. The core of Antarctic Intermediate Water appears to contribute to the formation of Mediterranean Sea Outflow Water since it becomes entrained into the overflow near Gibraltar. This entrainment gives rise to an enhanced concentration of the nutrients in the Mediterranean water in the North Atlantic. The deep salinity minimum, due to the presence of Labrador Sea Water, is restricted mainly to the Porcupine Abyssal Plain. In the Bay of Biscay this water type is strongly modified by enhanced diapycnal mixing near the continental slope. At all intermediate levels the continental slope in the Bay of Biscay seems to be a focal point for water mass modification by diapycnal mixing. Below the core of the Mediterranean Sea Outflow Water the Labrador Sea Water is also strongly modified. Its salinity is strongly enhanced by diapycnal mixing with the overlying core of Mediterranean Sea Outflow Water. An analysis of the oxygen and nutrient data indicates that the large spatial concentration differences at the level of the Labrador Sea Water are caused mainly by ageing of the water. The youngest water is observed at 52°N, and, especially in the Bay of Biscay and off south-west Portugal, the water at levels of about 1700 dbar are strongly enriched in nutrients and depleted in oxygen.  相似文献   

6.
Stable oxygen isotopic composition of sea water and stable carbon isotopes of dissolved inorganic carbon (DIC) on the continental shelf in the southern Weddell Sea are presented. Using the stations sampled during the summer 1995 two sections can be constructed, one closely parallel to the ice shelf edge and the other perpendicular to the upper continental slope. Generally, δ18O values clearly separate between different shelf water masses depending on the content of meteoric meltwater added during melting of glacial ice. Extrapolation of the mixing line between the cores of High Salinity Shelf Water (HSSW) and supercooled Ice Shelf Water (ISW) reveals δ18O values of the glacial ice of −27‰, whereas extrapolation of the mixing line between the δ18O values of the most-saline HSSW and lowest temperature ISW results in δ18O values of −34‰ for glacial ice. These values point to an origin of meltwater from below the ice shelf, where ice is less depleted in 18O, since deep beneath the ice shelf close to the grounding line, values may reach −40‰. If values between −34 and −27‰ are used as δ18O end member values for glacial ice, the amount of meltwater from the ice shelf that adds to the formation of ISW off the Filchner–Ronne Ice Shelf ranges from 0.2 to 0.8%, in agreement with previous studies based on δ18O and 4He. Carbon isotopic fractionation due to gas exchange between the atmosphere and the ocean at cold temperatures results in Δδ13CDIC values of 0.20±0.17‰ for Weddell Sea Deep Water, the water mass that ventilates the global abyssal ocean, typically defined as Antarctic Bottom Water (AABW). This confirms the low end of the range estimated previously (0.2–0.4‰), and thus corroborates the dominance of biology in shaping the deep and bottom water δ13C signal. It has been hypothesized that different modes of glacial/interglacial Antarctic bottom water formation may be separated by different stable isotopic compositions of deep-sea foraminiferal calcite. Here I show that differences between Δδ13C and δ18O values of HSSW and ISW, both of which contribute to bottom water formation today, are too small to be resolved in deep and bottom water masses. Therefore, glacial/interglacial changes in relative proportions of these water masses in Antarctic deep and bottom water cannot be separated by stable isotopes of fossil benthic foraminiferal calcite.  相似文献   

7.
Three sections are used to analyze the physical and chemical characteristics of the water masses in the eastern South Pacific and their distributions. Oceanographic data were taken from the SCORPIO (May–June 1967), PIQUERO (May–June 1969), and KRILL (June 1974) cruises. Vertical sections of temperature, salinity, σθ, dissolved oxygen, nitrate, nitrite, phosphate, and silicate were used to analyze the water column structure. Five water masses were identified in the zone through T–S diagrams: Subantarctic Water, Subtropical Water, Equatorial Subsurface Water, Antarctic Intermediate Water, and Pacific Deep Water. Their proportions in the sea water mixture are calculated using the mixing triangle method. Vertical sections were used to describe the geographical distributions of the water mass cores in the upper 1500 m. Several characteristic oceanographic features in the study area were analyzed: the shallow salinity minimum displacement towards the equator, the equatorial subsurface salinity maximum associated with a dissolved oxygen minimum zone and a high nutrient content displacement towards the south, and the equatorward intermediate Antarctic salinity minimum associated with a dissolved oxygen maximum. The nitrate deficit generated in the denitrification area off Peru and northern Chile is proposed as a conservative chemical tracer for the Equatorial Subsurface Waters off the coast of Chile, south of 25°S.  相似文献   

8.
Okhotsk Sea Intermediate Water (OSIW), the source water for ventilation of North Pacific Intermediate Water, exhibits a multidecadal warming trend. Historical data show that OSIW temperatures increased by 0.28, 0.57, 0.31 and 0.10°C during 1955 to 2003 at potential densities of 26.8, 27.0, 27.2 and 27.4σ θ , at depths of approximately 250, 500, 700 and 900 m, respectively. This rate of warming is much faster than that of the global ocean. This OSIW warming is likely linked to the reduced ventilation of cold Dense Shelf Water associated with brine rejection during sea ice formation.  相似文献   

9.
Evidence from geochemical tracers (salinity, oxygen, silicate, nutrients, alkalinity, dissolved inorganic carbon (DIC), carbon isotopes (δ13CDIC) and radiocarbon (Δ14C)) collected during the Pacific Ocean World Ocean Circulation Experiment (WOCE) voyages (P10, P15, P17 and P19) indicate there are three main water types at intermediate depths in the Pacific Ocean; North Pacific Intermediate Water (NPIW), Antarctic Intermediate Water (AAIW) and Equatorial Pacific Intermediate Waters (EqPIW). We support previous suggestions of EqPIW as a separate equatorial intermediate depth water as it displays a distinct geochemical signature characterised by low salinity, low oxygen, high nutrients and low Δ14C (older radiocarbon). Using the geochemical properties of the different intermediate depth waters, we have mapped out their distribution in the main Pacific Basin.From the calculated pre-formed δ13Cair–sea conservative tracer, it is evident that EqPIW is a combination of AAIW parental waters, while quasi-conservative geochemical tracers, such as radiocarbon, also indicate mixing with old upwelling Pacific Deep Waters (PDW). The EqPIW also displays a latitudinal asymmetry in non-conservative geochemical tracers and can be further split into North (NEqPIW) and South (SEqPIW) separated at ～2°N. The reason for this asymmetry is caused by higher surface diatom production in the north driven by higher silicate concentrations.The δ13C signature measured in benthic foraminifera, Cibicidoides spp. (δ13CCib), from four core tops bathed in AAIW, SEqPIW and NPIW, reflects that of the overlying intermediate depth waters. The δ13CCib from these cores show similarities and variations down-core that highlight changes in mixing over the last 30,000 yr BP. The reduced offset between the δ13CCib of AAIW and SEqPIW during the last glacial indicates that AAIW might have had an increased influence in the eastern equatorial Pacific (EEP) region at this time. Additional intermediate depth cores and other paleo-geochemical proxies such as Cd/Ca and radiocarbon are required from the broader Pacific Ocean to further understand changes in intermediate depth water formation, circulation and mixing over glacial/interglacial cycles.  相似文献   

10.
In the southwestern Okhotsk Sea off Hokkaido we observed chemical components related to the carbonate system for 1 year from August 1997 to June 1998. Using the conservative components salinity and water temperature, we confirmed the existence of two water masses flowing into the intermediate layer of the Okhotsk Sea, the East Sakhalin Current Water (ESCW) which becomes denser by mixing of brine water, and the Forerunner of Soya Warm Current Water (FSWW) which becomes denser due to cooling of the saline Kuroshio water. The ΔNTCx values were calculated by comparing the ESCW and the FSWW with the Pacific Deep Water (PDW). The ΔNTCx values obtained are 100–110 μmol/kg and 70–100 μmol/kg for the ESCW and the FSWW off Hokkaido, respectively, which are considerably larger than that of the Kuroshio water. These large ΔNTCx values may be due to both low DIC concentration in the surface water and intense gas exchange under the cold and stormy winter conditions for the ESCW and the cooling of the FSWW as it flows northward. Since the flow rates of dense waters concerned with the ESCW and the FSWW have previously been estimated as 0.9 Sv and 0.2 Sv, respectively, the amount of atmospheric CO2 absorbed and transported to the intermediate layer turns out to be 3.9−4.1 × 1013 gC/yr. This flux is small on a global scale, but the flux divided by the surface layer of the Okhotsk Sea is 30 gC/m2/yr, which is 5 times greater than the mean absorption flux of anthropogenic CO2 in the world's oceans. It is thus considered that atmospheric CO2 is efficiently absorbed in the Okhotsk Sea. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

11.
In this study we used two stable isotopes, δ13C and δ18O, for water mass classification in the coastal region off eastern Hokkaido. δ13C* values, which were corrected for the biological effect, and δ 18O values up to 300 m depth suggested that the isotopic character of the onshore and offshore water in the southern Okhotsk Sea, the Nemuro Strait and the western North Pacific could be explained by the mixing of three source waters: the Oyashio water (OYW), Soya Warm Current water (SWCW) and East Sakhalin Current water (ESCW). In summer, δ 13C*-δ 18O plots indicated mixing between SWCW from the southern Okhotsk Sea and OYW in the Pacific coast of southeastern Hokkaido, while temperature-salinity plots of the onshore water showed minimal difference from the offshore OYW. In winter, on the other hand, the mixed water of ESCW and OYW (or SWCW) appeared in the Pacific coastal region, distributed as cold, low salinity onshore water. Finally, we estimated mixing ratios of OYW, SWCW and ESCW in the coastal region of western North Pacific using their mean values of δ 13C* and δ 18O as endmembers. These results suggest seasonal and yearly changes of water mass combination en route from the southern Okhotsk Sea to the western North Pacific.  相似文献   

12.
Settling particles and surface sediments collected from the western region of the Sea of Okhotsk were analyzed for total organic carbon (TOC), long-chain n-alkanes and their stable carbon isotope ratio (δ13C) to investigate sources and transport of total and terrestrial organic matter in the western region of the sea. The δ13C measurements of TOC in time-series sediment traps indicate lateral transport of resuspended organic matter from the northwestern continental shelf to the area off Sakhalin via the dense shelf water (DSW) flow at intermediate depth. The n-alkanes in the surface sediments showed strong odd carbon number predominance with relatively lighter δ13C values (from −33‰ to −30‰). They fall within the typical values of C3-angiosperms, which is the main vegetation in east Russia, including the Amur River basin. On the other hand, the molecular distributions and δ13C values of n-alkanes in the settling particles clearly showed two different sources: terrestrial plant and petroleum in the Sea of Okhotsk. We reconstructed seasonal change in the fluxes of terrestrial n-alkanes in settling particles using the mixing model proposed by Lichtfouse and Eglinton [1995. 13C and 14C evidence of a soil by fossil fuel and reconstruction of the composition of the pollutant. Organic Geochemistry 23, 969–973]. Results of the terrestrial n-alkane fluxes indicate that there are two transport pathways of terrestrial plant n-alkanes to sediments off Sakhalin, the Sea of Okhotsk. One is lateral transport of resuspended particles with lithogenic material from the northwestern continental shelf by the DSW flow. Another is the vertical transport of terrestrial plant n-alkanes, which is independent of transport of lithogenic material. The latter may include dry/wet deposition of aerosol particles derived from terrestrial higher plants possibly associated with forest fires in Siberia.  相似文献   

13.
The ocean general circulation model for the earth simulator(OFES) products is applied to estimate the transports of the Mindanao Current(MC) and the Mindanao undercurrent(MUC) and explore the relation between them on seasonal scale. In general, the MUC is composed of the lower part of the Southern Pacific Tropical Water(SPTW)and Antarctic Intermediate Water(AAIW). While the deep northward core below 1 500 m is regarded as a portion of MUC. Both salinity and potential density restrictions become more reasonable to estimate the transports of MC/MUC as the properties of water mass having been taken into consideration. The climatological annual mean transport of MC is(37.4±5.81)×10~6 m~3/s while that of MUC is(23.92±6.47)×10~6 m~3/s integrated between 26.5 σ_θ and 27.7 σ_θ, and(17.53±5.45)×10~6 m~3/s integrated between 26.5 σ_θ and 27.5 σ_θ in the OFES. The variations of MC and MUC have good positive correlation with each other on the seasonal scale: The MC is stronger in spring and weaker in fall, which corresponds well with the MUC, and the correlation coefficient of them is 0.67 in the OFES.The same variations are also appeared in hybrid coordinate ocean model(HYCOM) results. Two sensitive experiments based on HYCOM are conducted to explore the relation between MC and MUC. The MUC(26.5σ_θ27.7) is strengthening as the MC increases with the enhancement of zonal wind field. It is shown,however, that the main part of the increasement is the deeper northward high potential density water(HPDW),while the AAIW almost remains stable, SPTW decreases, and vice versa.  相似文献   

14.
Most marginal seas in the North Pacific are fed by nutrients supported mainly by upwelling and many are undersaturated with respect to atmospheric CO2 in the surface water mainly as a result of the biological pump and winter cooling. These seas absorb CO2 at an average rate of 1.1 ± 0.3 mol C m−2yr−1 but release N2/N2O at an average rate of 0.07 ± 0.03 mol N m−2yr−1. Most of primary production, however, is regenerated on the shelves, and only less than 15% is transported to the open oceans as dissolved and particulate organic carbon (POC) with a small amount of POC deposited in the sediments. It is estimated that seawater in the marginal seas in the North Pacific alone may have taken up 1.6 ± 0.3 Gt (1015 g) of excess carbon, including 0.21 ± 0.05 Gt for the Bering Sea, 0.18 ± 0.08 Gt for the Okhotsk Sea; 0.31 ± 0.05 Gt for the Japan/East Sea; 0.07 ± 0.02 Gt for the East China and Yellow Seas; 0.80 ± 0.15 Gt for the South China Sea; and 0.015 ± 0.005 Gt for the Gulf of California. More importantly, high latitude marginal seas such as the Bering and Okhotsk Seas may act as conveyer belts in exporting 0.1 ± 0.08 Gt C anthropogenic, excess CO2 into the North Pacific Intermediate Water per year. The upward migration of calcite and aragonite saturation horizons due to the penetration of excess CO2 may also make the shelf deposits on the Bering and Okhotsk Seas more susceptible to dissolution, which would then neutralize excess CO2 in the near future. Further, because most nutrients come from upwelling, increased water consumption on land and damming of major rivers may reduce freshwater output and the buoyancy effect on the shelves. As a result, upwelling, nutrient input and biological productivity may all be reduced in the future. As a final note, the Japan/East Sea has started to show responses to global warming. Warmer surface layer has reduced upwelling of nutrient-rich subsurface water, resulting in a decline of spring phytoplankton biomass. Less bottom water formation because of less winter cooling may lead to the disappearance of the bottom water as early as 2040. Or else, an anoxic condition may form as early as 2200 AD. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

15.
Vertical profiles of tritium in seawater were determined for samples collected during the period from 1988 to 1990 at fourteen stations in the northwestern North Pacific (the Oyashio region) including the Okhotsk Sea and the Bering Sea. The profiles usually had a maximum in the surface layer and decreased gradually with depth down to 1,000 m. The water column inventory of tritium averaged 63% of the total atmospheric input in this region.The horizontal distribution of tritium showed a maximum in the region facing the Okhotsk Sea near 45°N for every isopycnal surface of 0 ranging from 26.60 to 27.40. The ages of the intermediate water were calculated for the respective isopycnal surfaces in the maximum region. This calculation assumed that the intermediate water was formed by the isopycnal mixing of two water masses—the Okhotsk Sea and the Bering Sea Component Waters, which had been produced in wintertime by the diapycnal mixing of the surface and the deep waters in the respective marginal seas. The results show that the intermediate water in this region was formed in the late 1980's for the water which has 0 of 26.60 to 26.80 and about 1970 for the water which has 0 of 27.00 to 27.40. Although we have estimated the mean ages of the intermediate water, the horizontal profile of dissolved oxygen suggests that the Okhotsk Sea Component Water is younger than the mean age.  相似文献   

16.
The simulation of an ocean general circulation model for the earth simulator （OFES） is transformed to an isopycnal coordinate to investigate the spatial structure and seasonal variability of the Mindanao Under- current （MUC）. The results show that （1） potential density surfaces, δ0=26.5 and δ0=27.5, can be chosen to encompass the M UC layer. Southern Pacilic tropical water （SPTW）, Antarctic Intermediate Water （AAIW） and high potential density water （HPDW） constitute the MUC. （2） Climatologically, the MOC exists in the form of dual-core. In some months, the dual-core structure changes to a single-core structure. （3） Choosing section at 8°N for calculating the transport of the MUC transport is reliable. Potential density constraint provides a good method for calculating the transport of the MOC. （4） The annual mean transport of the MUC is 8.34 × 106 m3/s and varies considerably with seasons： stronger in late spring and weaker in winter.  相似文献   

17.
利用Argo资料和《世界海洋数据集2001版》(WOD01)温盐历史资料,通过对代表性等位势面上盐度分布的分析,探讨了次表层和中层等不同层次上印尼贯通流(ITF)的起源与路径问题.分析结果表明,ITF的次表层水源主要来自北太平洋,中层水源地既包括北太平洋、南太平洋,同时也不能排除有印度洋的可能性.在印度尼西亚海域西部,ITF的次表层和中层水源分别为北太平洋热带水(NPTW)和中层水(NPIW),经苏拉威西海、望加锡海峡到达弗洛勒斯海,层次越深特征越明显.在印度尼西亚海域东部,发现哈马黑拉-新几内亚水道附近存在次表层强盐度锋面,阻隔了南太平洋热带水(SPTW)由此进入ITF海域;中层水具有高于NPIW和来自南太平洋的南极中层水(AAIW)的盐度值,既可能是AAIW和SPTW在当地发生剧烈垂直混合而形成,也可能是来自印度洋的AAIW向北延伸进入ITF的结果.  相似文献   

18.
The salinity minimum frequently occurring in the Mixed Water Region between the Oyashio and Kuroshio Fronts seems to originate from the salinity minimum at the density of 26.8σθ called the North Pacific Intermediate Water. We examined water exchange of this region with the Oyashio and the Kuroshio Extension using mixing ratio RK defined as (θ - θOY)/(θK - θOY) × 100, where θOY, θK, and θ represent potential temperature of the Oyashio and Kuroshio Waters and their mixture on the isopycnal surfaces, respectively. CTD data were obtained by repeated observation from January 1990 to May 1991. RK increases southward from the Oyashio Front to the Kuroshio Front with the range of −20 to 120%. The gradient of RK on the isopycnal surfaces is large around the Oyashio Front above the 26.8σθ surface, while it is large around the Kuroshio Front below it. This agrees with the average RK in the Mixed Water Region decreasing greatly with the increase of density at densities less dense than 26.8σθ. We calculated thickness and volume transport of the Oyashio between the isopycnal surfaces near the coast of Hokkaido. They increase largely with density at densities less dense than 26.8σθ. It is supposed that the salinity minimum in the Mixed Water Region is the upper limit of the water largely influenced by the Oyashio Water. Its density could depend only on the density structure of the Oyashio.  相似文献   

19.
Intensive CTD observations that resolve the mean and tidal components were done with a total of 129 casts in summer of 2001 at Bussol’ Strait. Based on these data and all the available historical data, we have revealed the outflow from Bussol’ Strait to the Pacific and the significant diapycnal mixing in the strait. In the range 27.0−27.3σ θ , the water property in Bussol’ Strait is almost identical to that of the Kuril Basin Water (KBW). The KBW out of Bussol’ Strait forms a water mass front with the East Kamchatka Current Water (EKCW). This front also corresponds to the front of the Oyashio Current. In the lower part of the intermediate layer (27.3−27.6σ θ ), part of the water in the strait is characterized by lower temperature, lower salinity, and higher dissolved oxygen than that of KBW and EKCW, which can be explained only by the diapycnal mixing. The strong diapycnal mixing in the strait can also be shown by the density inversion, occurrence frequency of which corresponds well to the amplitude distribution of the diurnal current. In the density range 26.7−26.8σ θ , the water in Bussol’ Strait has the lowest potential vorticity, suggesting that it is a source region of the low potential vorticity water. Seasonal change of the water can reach up to a density of 26.8σ θ around Bussol’ Strait. This leads us to propose that the combination of winter convection and local tidal mixing leads to effective ventilation of the intermediate layer.  相似文献   

20.
Based on measurements of the 18O isotope composition of 247 samples collected over a 3-year period we have assessed the oxygen isotope composition of water masses in the North Sea. This is the first δ18O data set that covers the entire North Sea basin. The waters lie on a mixing line: δ18O (‰VSMOW) = −9.300 + 0.274(S) with North Atlantic sub-polar mode water (SPMW) and surface waters, and Baltic Sea water representing the saline and freshwater end members respectively. Patterns exhibited in surface and bottom water δ18O distributions are representative of the general circulation of the North Sea. Oxygen-18 enriched waters from the North Atlantic enter the North Sea between Scotland and Norway and to a lesser extent through the English Channel. In contrast, oxygen-18 depleted waters mainly inflow from the Baltic Sea, the rivers Rhine and Elbe, and to a lesser degree, the Norwegian Fjords and other river sources. Locally the δ18O–salinity relationship will be controlled by the isotopic composition of the freshwater inputs. However, the range of local freshwater compositions around the North Sea basin is too narrow to characterise the relative contributions of individual sources to the overall seawater composition. This dataset provides important information for a number of related disciplines including biogeochemical research and oceanographic studies.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号