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1.
Fresh water flowing from the Arctic Ocean via the East Greenland Current influences deep water formation in the Nordic Seas as well as the salinity of the surface and deep waters flowing from there. This fresh water has three sources: Pacific water (relatively fresh cf. Atlantic water), river runoff, and sea ice meltwater. To determine the relative amounts of the three sources of fresh water, in May 2002 we collected water samples across the East Greenland Current in sections from 81.5°N to the Irminger Sea south of Denmark Strait. We used nitrate-phosphate relationships to distinguish Pacific waters from Atlantic waters, salinity to obtain the sum of sea ice melt water and river runoff water, and total alkalinity to distinguish the latter. River runoff contributed the largest part of the total fresh water component, in some regions with some inventories exceeding 12 m. Pacific fresh water (Pacific source water S ∼ 32 cf. Atlantic source water S ∼ 34.9) typically provided about 1/3 of the river runoff contribution. Sea ice meltwater was very nearly non-existent in the surface waters of all sections, likely at least in part as a result of the samples being collected before the onset of the melt season. The fresh water from the Arctic Ocean was strongly confined to near the Greenland coast. We thus conjecture that the main source of fresh water from the Arctic Ocean most strongly impacting deep convection in the Nordic Seas would be sea ice as opposed to fresh water in the liquid phase, i.e., river runoff, Pacific fresh water, and sea ice meltwater.  相似文献   

2.
The main water transformations in the Arctic Mediterranean take place in the boundary current of Atlantic Water, which crosses the Greenland–Scotland ridge from the North Atlantic into the eastern Norwegian Sea. It enters and flows around the Arctic Ocean before it exits the Arctic Mediterranean as the East Greenland Current, primarily through Denmark Strait. On route, it experiences numerous branchings and mergings. By examining how the properties of this “circumpolar” boundary current evolve, it is possible to identify and describe the processes causing the water mass transformations in the Arctic Mediterranean. It is also possible to follow the Arctic Ocean deep waters as they spread into the Nordic Seas and eventually provide 40% of the overflow water supplying the North Atlantic Deep Water.  相似文献   

3.
To determine the exchanges between the Nordic Seas and the Arctic Ocean through Fram Strait is one of the most important aspects, and one of the major challenges, in describing the circulation in the Arctic Mediterranean Sea. Especially the northward transport of Arctic Intermediate Water (AIW) from the Nordic Seas into the Arctic Ocean is little known. In the two-ship study of the circulation in the Nordic Seas, Arctic Ocean - 2002, the Swedish icebreaker Oden operated in the ice-covered areas in and north of Fram Strait and in the western margins of Greenland and Iceland seas, while RV Knorr of Woods Hole worked in the ice free part of the Nordic Seas. Here two hydrographic sections obtained by Oden, augmented by tracer and velocity measurements with Lowered Acoustic Doppler Current Profiler (LADCP), are examined. The first section, reaching from the Svalbard shelf across the Yermak Plateau, covers the region north of Svalbard where inflow to the Arctic Ocean takes place. The second, western, section spans the outflow area extending from west of the Yermak Plateau onto the Greenland shelf. Geostrophic and LADCP derived velocities are both used to estimate the exchanges of water masses between the Nordic Seas and the Arctic Ocean. The geostrophic computations indicate a total flow of 3.6 Sv entering the Arctic on the eastern section. The southward flow on the western section is found to be 5.1 Sv. The total inflow to the Arctic Ocean obtained using the LADCP derived velocities is much larger, 13.6 Sv, and the southward transport on the western section is 13.7 Sv, equal to the northward transport north of Svalbard. Sulphur hexafluoride (SF6) originating from a tracer release experiment in the Greenland Sea in 1996 has become a marker for the circulation of AIW. From the geostrophic velocities we obtain 0.5 Sv and from the LADCP derived velocities 2.8 Sv of AIW flowing into the Arctic. The annual transport of SF6 into the Arctic Ocean derived from geostrophy is 5 kg/year, which is of the same magnitude as the observed total annual transport into the North Atlantic, while the LADCP measurements (19 kg/year) imply that it is substantially larger. Little SF6 was found on the western section, confirming the dominance of the Arctic Ocean water masses and indicating that the major recirculation in Fram Strait takes place farther to the south.  相似文献   

4.
The flow of Atlantic water between Iceland and the Faroe Islands is one of three current branches flowing from the Atlantic Ocean into the Nordic Seas across the Greenland–Scotland Ridge. By the heat that it carries along, it keeps the subarctic regions abnormally warm and by its import of salt, it helps maintain a high salinity and hence density in the surface waters as a precondition for thermohaline ventilation. From 1997 to 2001, a number of ADCPs have been moored on a section going north from the Faroes, crossing the inflow. Combining these measurements with decade-long CTD observations from research vessel cruises along this section, we compute the fluxes of water (volume), heat, and salt. For the period June 1997–June 2001, we found the average volume flux of Atlantic water to be 3.5±0.5 Sv (1 Sv=106 m3·s−1). When compared to recent estimates of the other branches, this implies that the Iceland–Faroe inflow is the strongest branch in terms of volume flux, transporting 47% of the total Atlantic inflow to the Arctic Mediterranean (Nordic Seas and Arctic Ocean with shelf areas). If all of the Atlantic inflow were assumed to be cooled to 0 °C, before returning to the Atlantic, the Iceland–Faroe inflow carries a heat flux of 124±15 TW (1 TW=1012 W), which is about the same as the heat carried by the inflow through the Faroe–Shetland Channel. The Iceland–Faroe Atlantic water volume flux was found to have a negligible seasonal variation and to be remarkably stable with no reversals, even on daily time scales. Out of a total of 1348 daily flux estimates, not one was directed westwards towards the Atlantic.  相似文献   

5.
The importance of the circulation of fresh water within the Nordic Seas has frequently been pointed out, especially its effect on deep water formation and therefore possibly on the thermohaline circulation. The main source of fresh water is the East Greenland Current entering the Nordic Seas through Fram Strait. The Jan Mayen Polar Current and the East Icelandic Current (EIC) carry a part of the fresh water into the Greenland and Iceland Seas respectively. As a part of the EU project VEINS, Aanderaa current meters were deployed on two moorings within the EIC from June 1997 to June 1998 on a standard CTD section from Langanes, Northeast Iceland, to the central Iceland Sea in the direction towards Jan Mayen. The current was mainly concentrated along the slope where it was baroclinic, while over the deeper part a weak barotropic flow was observed. Geostrophic calculations, referenced to the current meter data, were used for estimating the volume flux and fresh water transport with the current. The total transport over the section towards the east was found to be 2.5 Sv. The fresh water transport relative to a salinity of 34.93, above 170 m, amounted to 5.5 mSv. This is roughly 4% of the fresh water transport through Fram Strait. This transport is put into a long-term perspective using hydrographic data from the Langanes section.  相似文献   

6.
北极河流径流是北冰洋淡水的最大来源,其变化会对北冰洋中的诸多过程有重要影响。本文基于全球高分辨率海洋?海冰耦合模式的模拟结果,研究北冰洋温盐、海冰以及环流对北极河流径流的敏感性。通过对比有气候态北极河流径流输入的控制实验结果和径流完全关闭的敏感性实验结果,研究发现北极径流对北冰洋温度、盐度、海冰以及海洋环流等有显著的影响。关闭北极河流径流后,在河口附近的陆架上温度降低、盐度升高,且导致500 m深度处温度下降以及盐度升高;河口附近的陆架处,海冰密集度与海冰厚度增加。关闭北极河流径流也对北冰洋内的环流有影响:由于缺少来自欧亚大陆的北极径流的输入,穿极漂流与东格陵兰流流速减小且盐度增加;关闭北极径流导致近岸海表面高度降低,沿欧亚陆架的北冰洋边界流减弱,白令海入流增强。通过对比关闭北极径流实验与控制实验的温度和盐度剖面,发现关闭北极径流后大西洋层温度降低,各陆架海盐跃层的梯度减小,盐跃层厚度减小。  相似文献   

7.
Few basins in the world exhibit such a wide range of water properties as those of the Nordic Seas with cold freshwaters from the Arctic in the western basins and warm saline waters from the Atlantic in the eastern basins. In this study we present a 50-year hydrographic climatology of the Nordic Seas in terms of depth and temperature patterns on four upper ocean specific volume anomaly surfaces. This approach allows us to better distinguish between change due to variations along such surfaces and change due to depth variations of the stratified water column. Depth variations indicate changes in the mass field while property variations along isopycnals give insight into isopycnal advection and mixing, as well as diapycnal processes. We find that the warmest waters on each surface are found in the north, close to where the isopycnal outcrops, a clear indication of downward mixing of the warmer, more saline waters on shallower isopycnals due to convective cooling at the surface. These saline waters come from the Norwegian Atlantic Slope Current by means of a very high level of eddy activity in the Lofoten Basin.The isopycnal analyses further show that the principal water mass boundary between the waters of Arctic origin in the west and Atlantic waters in the east aligns quite tightly with the Jan Mayen, Mohn, Knipovich Ridge system suggesting little cross-ridge exchange. Instead, the main routes of exchange between the eastern and western basins appear to be limited to the northern and southern ends of ridge system: Atlantic waters into the Greenland Sea in the Fram St and Artic waters into the southern Norwegian Sea just north of the Iceland-Faroe Ridge.Analysis of a representative isopycnal in the main pycnocline shows it to be stable over time with only small variations with season (except where it outcrops in winter in the Greenland and Iceland Seas). However, two very cold winters, 1968–1969, led to greater than average heat losses across the entire Lofoten Basin that eroded away much of the Lofoten eddy and induced the greatest temperature anomaly in the entire 50-year record. Interannual variations in isopycnal layer temperature correlate with the NAO index such that waters in the Iceland Sea become warmer than average with warming air temperatures and conversely in the Lofoten Basin.  相似文献   

8.
1972-2013年北欧海深层水增暖   总被引：2，自引：1，他引：1  
The warming of deep waters in the Nordic seas is identified based on observations during Chinese 5th Arctic Expedition in 2012 and historical hydrographic data. The most obvious and earliest warming occurrs in the Greenland Basin(GB) and shows a coincident accelerated trend between depths 2 000 and 3 500 m. The observations at a depth of 3 000 m in the GB reveal that the potential temperature had increased from-1.30°C in the early 1970 s to-0.93°C in 2013, with an increase of about 0.37°C(the maximum spatial deviation is 0.06°C) in the past more than 40 years. This remarkable change results in that deep waters in the center of the Lofton Basin(LB) has been colder than that in the GB since the year 2007. As for the Norwegian Basin(NB), only a slight trend of warming have been shown at a depth around 2 000 m since the early 1980 s, and the warming amplitude at deeper waters is just slightly above the maximum spatial deviation, implying no obvious trend of warming near the bottom. The water exchange rate of the Greenland Basin is estimated to be 86% for the period from 1982 to 2013, meaning that the residence time of the Greenland Sea deep water(GSDW) is about 35 years. As the weakening of deep-reaching convection is going on, the abyssal Nordic seas are playing a role of heat reservoir in the subarctic region and this may cause a positive feedback on the deep-sea warming in both the Arctic Ocean and the Nordic seas.  相似文献   

9.
Sensitivity of a global ocean model to increased run-off from Greenland   总被引：2，自引：0，他引：2  
We study the reaction of a global ocean–sea ice model to an increase of fresh water input into the northern North Atlantic under different surface boundary conditions, ranging from simple restoring of surface salinity to the use of an energy balance model (EBM) for the atmosphere. The anomalous fresh water flux is distributed around Greenland, reflecting increased melting of the Greenland ice sheet and increasing fresh water export from the Arctic Ocean. Depending on the type of surface boundary condition, the large circulation reacts with a slow-down of overturning and gyre circulations. Restoring of the total or mean surface salinity prevents a large scale redistribution of the salinity field that is apparent under mixed boundary conditions and with the EBM. The control run under mixed boundary conditions exhibits large and unrealistic oscillations of the meridional overturning. Although the reaction to the fresh water flux anomaly is similar to the response with the EBM, mixed boundary conditions must thus be considered unreliable. With the EBM, the waters in the deep western boundary current initially become saltier and a new fresh water mass forms in the north-eastern North Atlantic in response to the fresh water flux anomaly around Greenland. After an accumulation period of several decades duration, this new North East Atlantic Intermediate Water spreads towards the western boundary and opens a new southward pathway at intermediate depths along the western boundary for the fresh waters of high northern latitudes.  相似文献   

10.
In summer 1996, a tracer release experiment using sulphur hexafluoride (SF6) was launched in the intermediate-depth waters of the central Greenland Sea (GS), to study the mixing and ventilation processes in the region and its role in the northern limb of the Atlantic overturning circulation. Here we describe the hydrographic context of the experiment, the methods adopted and the results from the monitoring of the horizontal tracer spread for the 1996-2002 period documented by ∼10 shipboard surveys. The tracer marked “Greenland Sea Arctic Intermediate Water” (GSAIW). This was redistributed in the gyre by variable winter convection penetrating only to mid-depths, reaching at most 1800 m depth during the strongest event observed in 2002.For the first 18 months, the tracer remained mainly in the Greenland Sea. Vigorous horizontal mixing within the Greenland Sea gyre and a tight circulation of the gyre interacting slowly with the other basins under strong topographic influences were identified. We use the tracer distributions to derive the horizontal shear at the scale of the Greenland Sea gyre, and rates of horizontal mixing at ∼10 and ∼300 km scales. Mixing rates at small scale are high, several times those observed at comparable depths at lower latitudes. Horizontal stirring at the sub-gyre scale is mediated by numerous and vigorous eddies. Evidence obtained during the tracer release suggests that these play an important role in mixing water masses to form the intermediate waters of the central Greenland Sea.By year two, the tracer had entered the surrounding current systems at intermediate depths and small concentrations were in proximity to the overflows into the North Atlantic. After 3 years, the tracer had spread over the Nordic Seas basins. Finally by year six, an intensive large survey provided an overall synoptic documentation of the spreading of the tagged GSAIW in the Nordic Seas. A circulation scheme of the tagged water originating from the centre of the GS is deduced from the horizontal spread of the tracer. We present this circulation and evaluate the transport budgets of the tracer between the GS and the surroundings basins. The overall residence time for the tagged GSAIW in the Greenland Sea was about 2.5 years. We infer an export of intermediate water of GSAIW from the GS of 1 to 1.85 Sv (1 Sv = 106 m3 s−1) for the period from September 1998 to June 2002 based on the evolution of the amount of tracer leaving the GS gyre. There is strong exchange between the Greenland Sea and Arctic Ocean via Fram Strait, but the contribution of the Greenland Sea to the Denmark Strait and Iceland Scotland overflows is modest, probably not exceeding 6% during the period under study.  相似文献   

11.
The depth distributions of the radiolarian fauna in the Chukchi and Beaufort Seas, marginal seas of the western Arctic Ocean, were examined quantitatively in depth-stratified plankton tows from 4 or 5 intervals above 500 m and in surface sediments from various depths between 163 and 2907 m. The radiolarian assemblage from the water column in September 2000 was dominated by Amphimelissa setosa and followed by the Actinomma boreale/leptoderma group, Pseudodictyophimus gracilipes and Spongotrochus glacialis. These species are related to the Arctic Surface Water shallower than 150 m. This assemblage is similar to that in the Greenland Sea relating to the ice edge, but did not contain typical Pacific radiolarians in spite of the flow of water of Pacific origin in this region. The living depth of Ceratocyrtis historicosa was restricted to the relatively warm water between 300 and 500 m corresponding to the upper Arctic Intermediate Water (AIW) originating from the Atlantic Ocean. Radiolarian assemblages in the surface sediments are similar to those in the plankton tows, except for common Cycladophora davisiana in sediment samples below 500 m. C. davisiana is probably a deep-water species adapted to the lower AIW or the Canadian Basin Deep Water ventilated from the shelves.  相似文献   

12.
观测显示过去几十年间北极入海径流呈现增加趋势,CMIP5耦合模式预测表明21世纪北极入海径流仍会增加,在RCP8.5路径下,21世纪末北极入海径流量将会是1950年的1.4倍。本文利用冰-海耦合数值模式研究了北极径流增加对大西洋经向翻转环流的影响。基于两个数值实验的结果表明,如果北极入海径流按每年0.22%的速度（与RCP8.5路径下的速度相当）增加,大西洋经向翻转环流的强度在100、150和200年后将会分别减弱0.6（3%）、1.2（7%）和1.8（11%） Sv。北极入海径流增加导致大西洋经向翻转环流减弱的主要原因是,北极入海径流增加的淡水被输运到北大西洋后,会抑制北大西洋深层水的生成,这也会导致北大西洋深层水海水年龄的增加。  相似文献   

13.
北欧海作为连接北冰洋和北大西洋的重要海域,其由热效应产生的辐合场值得关注。本文利用NECP/NCAR的速度势函数(Velocity Potential,VP)数据表征北欧海辐合辐散场,发现在秋冬季北欧海上空大气低层存在一个独立的辐合区域。经验正交函数分解结果表明,北欧海上空的VP显示出除了表征北极涛动的全区一致型模态外,还表现出一个东西向辐合辐散反位相的东西振荡型模态。该模态与一支连接北大西洋涛动(NAO)和欧亚遥相关(EU)的复合型大气遥相关波列有关,北欧海表层潜热和感热异常加热通过影响低空大气的异常辐合辐散,与北大西洋偶极子型海温异常加热共同作用,加强了NAO异常环流;同时高空急流波导作用加强了从北欧海到东亚的EU波列,使得位于NAO和EU之间的北欧海成为连接NAO和EU大气遥相关波列的“中继站”,进而通过这种复合型大气遥相关波列将北大西洋与东亚大气环流联系起来,形成对东亚地区天气气候的远程影响。  相似文献   

14.
Data from the East Greenland Current in 2002 are evaluated using optimum multiparameter analysis. The current is followed from north of Fram Strait to the Denmark Strait Sill and the contributions of different source waters, in mass fractions, are deduced. From the results it can be concluded that, at least in spring 2002, the East Greenland Current was the main source for the waters found at the Denmark Strait Sill, contributing to the overflow into the North Atlantic. The East Greenland Current carried water masses from different source regions in the Arctic Ocean, the West Spitsbergen Current and the Greenland Sea. The results agree well with the known circulation of the western Nordic Seas but also add knowledge both to the quantification and to the mixing processes, showing the importance of the locally formed Greenland Sea Arctic Intermediate Water for the East Greenland Current and the Denmark Strait.  相似文献   

15.
Many of the changes observed during the last two decades in the Arctic Ocean and adjacent seas have been linked to the concomitant abrupt decrease of the sea level pressure in the central Arctic at the end of the 1980s. The decrease was associated with a shift of the Arctic Oscillation (AO) to a positive phase, which persisted throughout the mid 1990s. The Arctic salinity distribution is expected to respond to these dramatic changes via modifications in the ocean circulation and in the fresh water storage and transport by sea ice. The present study investigates these different contributions in the context of idealized ice-ocean experiments forced by atmospheric surface wind-stress or temperature anomalies representative of a positive AO index.Wind stress anomalies representative of a positive AO index generate a decrease of the fresh water content of the upper Arctic Ocean, which is mainly concentrated in the eastern Arctic with almost no compensation from the western Arctic. Sea ice contributes to about two-third of this salinification, another third being provided by an increased supply of salt by the Atlantic inflow and increased fresh water export through the Canadian Archipelago and Fram Strait. The signature of a saltier Atlantic Current in the Norwegian Sea is not found further north in both the Barents Sea and the Fram Strait branches of the Atlantic inflow where instead a widespread freshening is observed. The latter is the result of import of fresh anomalies from the subpolar North Atlantic through the Iceland-Scotland Passage and enhanced advection of low salinity waters via the East Icelandic Current. The volume of ice exported through Fram Strait increases by 20% primarily due to thicker ice advected into the strait from the northern Greenland sector, the increase of ice drift velocities having comparatively less influence. The export anomaly is comparable to those observed during events of Great Salinity Anomalies and induces substantial freshening in the Greenland Sea, which in turn contributes to increasing the fresh water export to the North Atlantic via Denmark Strait. With a fresh water export anomaly of 7 mSv, the latter is the main fresh water supplier to the subpolar North Atlantic, the Canadian Archipelago contributing to 4.4 mSv.The removal of fresh water by sea ice under a positive winter AO index mainly occurs through enhanced thin ice growth in the eastern Arctic. Winter SAT anomalies have little impact on the thermodynamic sea ice response, which is rather dictated by wind driven ice deformation changes. The global sea ice mass balance of the western Arctic indicates almost no net sea ice melt due to competing seasonal thermodynamic processes. The surface freshening and likely enhanced sea ice melt observed in the western Arctic during the 1990s should therefore be attributed to extra-winter atmospheric effects, such as the noticeable recent spring-summer warming in the Canada-Alaska sector, or to other modes of atmospheric circulations than the AO, especially in relation to the North Pacific variability.  相似文献   

16.
Pelagic-Benthic Coupling in the Nordic Seas: The Role of Episodic Events   总被引：3，自引：0，他引：3  
Abstract. The consequences of the following episodic phenomena for the pelagic-benthic coupling in the Nordic Seas are illustrated: (1) Advection of water masses between fjords and shelf environments, (2) freshwater run-off and vertical stability, (3) dynamics of the marginal ice zone in the central and northern Barents Sea and the Polar Ocean, (4) drift patterns of sinking particles along the North Norwegian coast, (5) advection of zooplankton into subarctic fjords and the southern Barents Sea, zooplankton overwintering and composition, and (6) transport of organic particulate matter from the Barents Sea shelf. It is shown that physical processes in the north-eastern North Atlantic and Polar Ocean can be strongly variable on time scales of days to decades. They have a significant influence on the dynamics of pelagic-benthic coupling. The physical oceanography influences the vertical and horizontal particle flux not only directly (mixing, advection, up- and down-welling), but also indirectly through its impact on the biota (for example radiation, wind, ice cover, freshwater run-off and overwintering, advection and retention of zooplankton). Understanding pelagic-benthic coupling at high latitudes depends even more on a best possible understanding of the physical oceanography and the time scales involved than elsewhere.  相似文献   

17.
A slowdown of sea surface height(SSH) rise occurred in the Nordic(GIN) seas around 2004.In this study,SSH satellite data and constructed steric height data for the decades before and after 2004(i.e.,May 1994 to April 2014)were used for comparative analysis.The findings indicate that the rate of slowdown of SSH rises in the GIN seas(3.0 mm/a) far exceeded that of the global mean(0.6 mm/a).In particular,the mean steric height of the GIN seas increased at a rate of 4.5 mm/a and then decreased at a slower pace.This was the main factor responsible for the stagnation of the SSH rises,while the mass factor only increased slightly.The Norwegian Sea particularly experienced the most prominent slowdown in SSH rises,mainly due to decreased warming of the 0–600 m layer.The controlling factors of this decreased warming were cessation in the increase of volume of the Atlantic inflow and stagnation of warming of the inflow.However,variations in air-sea thermal flux were not a major factor.In the recent two decades,mean halosteric components of the GIN seas decreased steadily and remained at a rate of 2 mm/a or more because of increased flow and salinity of the Atlantic inflow during the first decade,and reduction in freshwater inputs from the Arctic Ocean in the second decade.  相似文献   

18.
The principal features of the marine ecosystems in the Barents and Norwegian Seas and some of their responses to climate variations are described. The physical oceanography is dominated by the influx of warm, high-salinity Atlantic Waters from the south and cold, low-salinity waters from the Arctic. Seasonal ice forms in the Barents Sea with maximum coverage typically in March–April. The total mean annual primary production rates are similar in the Barents and Norwegian Seas (80–90 g C m−2), although in the Barents, the production is higher in the Atlantic than in the ice covered Arctic Waters. The zooplankton is dominated by Calanus species, C. finmarchicus in the Atlantic Waters of the Norwegian and Barents Seas, and C. glacialis in the Arctic Waters of the Barents Sea. The fish species in the Norwegian Sea are mostly pelagics such as herring (Clupea harengus) and blue whiting (Micromesistius poutassou), while in the Barents Sea there are both pelagics (capelin (Mallotus villosus Müller), herring, and polar cod (Boreogadus saida Lepechin)) and demersals (cod (Gadus morhua L.) and haddock (Melanogrammus aeglefinus)). The latter two species spawn in the Norwegian Sea along the slope edge (haddock) or along the coast (cod) and drift into the Barents Sea. Marine mammals and seabirds, although comprising only a relatively small percentage of the biomass and production in the region, play an important role as consumers of zooplankton and small fish. While top-down control by predators certainly is significant within the two regions, there is also ample evidence of bottom-up control. Climate variability influences the distribution of several fish species, such as cod, herring and blue whiting, with northward shifts during extended warm periods and southward movements during cool periods. Climate-driven increases in primary and secondary production also lead to increased fish production through higher abundance and improved growth rates.  相似文献   

19.
The variability of the ice and freshwater transports through the main openings of the Nordic Seas is studied based on a 200-year simulation with a sea ice–ocean model forced by stochastic surface wind stress anomalies representative of Northern annular mode (NAM). The spectrum of the ice export through Fram Strait (FS), which constitutes the main contribution to the total freshwater export anomaly from the Arctic, shows no significant peak though half of the variance is concentrated at periods longer than a year. The standard deviation of the freshwater export to the subpolar gyre through Denmark Strait only amounts to 40% of the standard deviation of the total (ice+liquid) freshwater export through FS, with a comparatively larger variance in the low-frequency range, suggesting that the Greenland Sea could act as a low-pass filter. In the upper layer of the Iceland–Scotland Passage, positive phases of the NAM lead to a fast increase of the northward volume and salt transports. Within 2 years, the salt transport anomaly, however, changes sign due to advection of negative salinity anomalies which originate in the subpolar gyre and can be traced up to the Barents Sea.  相似文献   

20.
The annual mean volume and heat transport sketches through the inter-basin passages and transoceanic sections have been constructed based on 1 400-year spin up results of the MOM4p1. The spin up starts from a state of rest, driven by the monthly climatological mean force from the NOAA World Ocean Atlas(1994). The volume transport sketch reveals the northward transport throughout the Pacific and southward transport at all latitudes in the Atlantic. The annual mean strength of the Pacific-Arctic-Atlantic through flow is 0.63×106 m3/s in the Bering Strait. The majority of the northward volume transport in the southern Pacific turns into the Indonesian through flow(ITF) and joins the Indian Ocean equatorial current, which subsequently flows out southward from the Mozambique Channel, with its majority superimposed on the Antarctic Circumpolar Current(ACC). This anti-cyclonic circulation around Australia has a strength of 11×106 m3/s according to the model-produced result. The atmospheric fresh water transport, known as P-E+R(precipitation minus evaporation plus runoff), constructs a complement to the horizontal volume transport of the ocean. The annual mean heat transport sketch exhibits a northward heat transport in the Atlantic and poleward heat transport in the global ocean. The surface heat flux acts as a complement to the horizontal heat transport of the ocean. The climatological volume transports describe the most important features through the inter-basin passages and in the associated basins, including: the positive P-E+R in the Arctic substantially strengthening the East Greenland Current in summer; semiannual variability of the volume transport in the Drake Passage and the southern Atlantic-Indian Ocean passage; and annual transport variability of the ITF intensifying in the boreal summer. The climatological heat transports show heat storage in July and heat deficit in January in the Arctic; heat storage in January and heat deficit in July in the Antarctic circumpolar current regime(ACCR); and intensified heat transport of the ITF in July. The volume transport of the ITF is synchronous with the volume transport through the southern Indo-Pacific sections, but the year-long southward heat transport of the ITF is out of phase with the heat transport through the equatorial Pacific, which is northward before May and southward after May. This clarifies the majority of the ITF originating from the southern Pacific Ocean.  相似文献   

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