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1.
《Ocean Modelling》2004,6(3-4):245-263
Astronomical data reveals that approximately 3.5 terawatts (TW) of tidal energy is dissipated in the ocean. Tidal models and satellite altimetry suggest that 1 TW of this energy is converted from the barotropic to internal tides in the deep ocean, predominantly around regions of rough topography such as mid-ocean ridges. A global tidal model is used to compute turbulent energy levels associated with the dissipation of internal tides, and the diapycnal mixing supported by this energy flux is computed using a simple parameterization.The mixing parameterization has been incorporated into a coarse resolution numerical model of the global ocean. This parameterization offers an energetically consistent and practical means of improving the representation of ocean mixing processes in climate models. Novel features of this implementation are that the model explicitly accounts for the tidal energy source for mixing, and that the mixing evolves both spatially and temporally with the model state. At equilibrium, the globally averaged diffusivity profile ranges from 0.3 cm2 s−1 at thermocline depths to 7.7 cm2 s−1 in the abyss with a depth average of 0.9 cm2 s−1, in close agreement with inferences from global balances. Water properties are strongly influenced by the combination of weak mixing in the main thermocline and enhanced mixing in the deep ocean. Climatological comparisons show that the parameterized mixing scheme results in a substantial reduction of temperature/salinity bias relative to model solutions with either a uniform vertical diffusivity of 0.9 cm2 s−1 or a horizontally uniform bottom-intensified arctangent mixing profile. This suggests that spatially varying bottom intensified mixing is an essential component of the balances required for the maintenance of the ocean’s abyssal stratification. 相似文献
2.
Walter Munk 《Progress in Oceanography》1997,40(1-4)
Topex/Poseidon (T/P) altimetry has reopened the problem of how tidal dissipation is to be allocated. There is now general agreement of a M2 dissipation by 2.5 Terawatts (1 TW = 1012 W), based on four quite separate astronomic observational programs. Allowing for the bodily tide dissipation of 0.1 TW leaves 2.4 TW for ocean dissipation. The traditional disposal sites since
(1920) have been in the turbulent bottom boundary layer (BBL) of marginal seas, and the modern estimate of about 2.1 TW is in this tradition (but the distribution among the shallow seas has changed radically from time to time). Independent estimates of energy flux into the marginal seas are not in good agreement with the BBL estimates.T/P altimetry has contributed to the tidal problem in two important ways. The assimilation of global altimetry into Laplace tidal solutions has led to accurate representations of the global tides, as evidenced by the very close agreement between the astronomic measurements and the computed 2.4 TW working of the Moon on the global ocean. Second, the detection by
and
(1996) of small surface manifestation of internal tides radiating away from the Hawaiian chain has led to global estimates of 0.2 to 0.4 TW of conversion of surface tides to internal tides. Measurements of ocean microstructure yields 0.2 TW of global dissipation by pelagic turbulence (away from topography). We propose that pelagic turbulence is maintained by topographic scattering of barotropic into baroclinic tidal energy, via internal tides and internal waves. Previous estimates by
(1974);
, (1982)) of this conversion along 150,000 km of continental coastlines gave a negligible 0.02 TW; evidently the important conversion takes place along mid-ocean ridges.The maintenance of the abyssal global stratification requires a much larger expenditure of power. 2 TW versus 0.2 TW. This is usually attributed to wind forcing. If tidal power is to play a significant role here, then the BBL estimates need to be reduced. The challenge is to estimate dissipation from the energy flux divergence in the T/P adjusted tidal models, without prior assumptions concerning the dissipation processes. 相似文献
3.
The mean available potential energy released by baroclinic instability into the meso-scale eddy field has to be dissipated in some way and Tandon and Garrett [Tandon, A., Garrett, C., 1996. On a recent parameterization of mesoscale eddies. J. Phys. Oceanogr. 26 (3), 406–416] suggested that this dissipation could ultimately involve irreversible mixing of buoyancy by molecular processes at the small-scale end of the turbulence cascade. We revisit this idea and argue that the presence of dissipation within the thermocline automatically requires that a component of the eddy flux associated with meso-scale eddies must be associated with irreversible mixing of buoyancy within the thermocline. We offer a parameterisation of the implied diapycnal diffusivity based on (i) the dissipation rate for eddy kinetic energy given by the meso-scale eddy closure of Eden and Greatbatch [Eden, C., Greatbatch, R.J., 2008. Towards a meso-scale eddy closure. Ocean Modell. 20, 223–239.] and (ii) a fixed mixing efficiency. The implied eddy-induced diapycnal diffusivity (κ) is implemented in a coarse resolution model of the North Atlantic. In contrast to the vertical diffusivity given by a standard vertical mixing scheme, large lateral inhomogeneities can be found for κ in the interior of the ocean. In general, κ is large, i.e. up to o(10) cm2/s, near the western boundaries and almost vanishing in the interior of the ocean. 相似文献
4.
2012年夏季海南岛东岸上升流区的混合观测 总被引：1，自引：0，他引：1
The turbulent mixing in the upwelling region east of Hainan Island in the South China Sea is analyzed based on in situ microstructure observations made in July 2012. During the observation, strong upwelling appears in the coastal waters, which are 3℃ cooler than the offshore waters and have a salinity 1.0 greater than that of the offshore waters. The magnitude of the dissipation rate of turbulent kinetic energy ε in the upwelling region is O(10–9 W/kg), which is comparable to the general oceanic dissipation. The inferred eddy diffusivity K_ρ is O(10–6 m~2/s), which is one order of magnitude lower than that in the open ocean. The values are elevated to K_ρ≈O(10–4 m~2/s) near the boundaries. Weak mixing in the upwelling region is consistent with weak instability as a result of moderate shears versus strong stratifications by the joint influence of surface heating and upwelling of cold water.The validity of two fine-scale structure mixing parameterization models are tested by comparison with the observed dissipation rates. The results indicate that the model developed by Mac Kinnon and Gregg in 2003 provides relatively better estimates with magnitudes close to the observations. Mixing parameterization models need to be further improved in the coastal upwelling region. 相似文献
5.
《Ocean Modelling》2011,40(3-4):262-274
The impact of topographically catalysed diapycnal mixing on ocean and atmospheric circulation as well as marine biogeochemistry is studied using an earth system model of intermediate complexity. The results of a model run in which diapycnal mixing depends on seafloor roughness are compared to a control run that uses a simple depth-dependent parametrization for vertical background diffusivity. A third model run is conducted that uses the horizontal mean of the topographically catalysed mixing as vertical profile in order to distinguish between the overall effect of larger diffusivities and the spatial heterogeneity of the novel mixing parametrization.The new mixing scheme results in a strengthening of the deep overturning cell and enhances equatorial upwelling. Surface temperatures in the Southern Ocean increase by about 1 K (in the overall effect) whereas cooling of a similar magnitude in low latitudes is generated by the spatial heterogeneity of the mixing. The corresponding changes in the atmospheric circulation involve a weakening of the southern hemispheric Westerlies and a strengthening of the Walker circulation. Biogeochemical changes are dominated by an improved ventilation of the deep ocean from the south. Water mass ages decline significantly in the deep Indian Ocean and the deep North Pacific whereas oxygen increases in the two ocean basins. The representation of the global volume of water with an oxygen concentration lower than 90 μmol/kg in the model is improved using the topography catalysed mixing. Furthermore, primary production is stimulated in equatorial regions through increased upwelling of nutrients and reduced in the oligotrophic gyres. 相似文献
6.
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
7.
The pattern and magnitude of the global ocean overturning circulation is believed to be strongly controlled by the distribution
of diapycnal diffusivity below 1000 m depth. Although wind stress fluctuation is a candidate for the major energy sources
of diapycnal mixing processes, the global distribution of wind-induced diapycnal diffusivity is still uncertain. It has been
believed that internal waves generated by wind stress fluctuations at middle and high latitudes propagate equatorward until
their frequency is twice the local inertial frequency and break down via parametric subharmonic instabilities, causing diapycnal
mixing. In order to check the proposed scenario, we use a vertically two-dimensional primitive equation model to examine the
spatial distribution of “mixing hotspots” caused by wind stress fluctuations. It is shown that most of the wind-induced energy
fed into the ocean interior is dissipated within the top 1000 m depth in the wind-forced area and the energy dissipation rate
at low latitudes is very small. Consequently, the energy supplied to diapycnal mixing processes below 1000 m depth falls short
of the level required to sustain the global ocean overturning circulation. 相似文献
8.
Using an idealized ocean general circulation model, we examine the effect of “mixing hotspots” (localized regions of intense
diapycnal mixing) predicted based on internal wave-wave interaction theory (Hibiya et al., 2006) on the meridional overturning circulation of the Pacific Ocean. Although the assumed diapycnal diffusivity in the
mixing hotspots is a little larger than the predicted value, the upwelling in the mixing hotspots is not sufficient to balance
the deep-water production; out of 17 Sv of the downwelled water along the southern boundary, only 9.2 Sv is found to upwell
in the mixing hotspots. The imbalance as much as 7.8 Sv is compensated by entrainment into the surface mixed layer in the
vicinity of the downwelling region. As a result, the northward transport of the deep water crossing the equator is limited
to 5.5 Sv, much less than estimated from previous current meter moorings and hydrographic surveys. One plausible explanation
for this is that the magnitude of the meridional overturning circulation of the Pacific Ocean has been overestimated by these
observations. We raise doubts about the validity of the previous ocean general circulation models where diapycnal diffusivity
is assigned ad hoc to attain the current magnitude suggested from current meter moorings and hydrographic surveys. 相似文献
9.
The variation of turbulent diapycnal mixing at 18°N in the South China Sea stirred by wind stress 总被引：1，自引：0，他引：1
The spatial and temporal variations of turbulent diapycnal mixing along 18°N in the South China Sea(SCS) are estimated by a fine-scale parameterization method based on strain, which is obtained from CTD measurements in yearly September from 2004 to 2010. The section mean diffusivity can reach ~10~(–4)m~2/s, which is an order of magnitude larger than the value in the open ocean. Both internal tides and wind-generated near-inertial internal waves play an important role in furnishing the diapycnal mixing here. The former dominates the diapycnal mixing in the deep ocean and makes nonnegligible contribution in the upper ocean, leading to enhanced diapycnal mixing throughout the water column over rough topography. In contrast, the influence of the wind-induced nearinertial internal wave is mainly confined to the upper ocean. Over both flat and rough bathymetries, the diapycnal diffusivity has a growth trend from 2005 to 2010 in the upper 700 m, which results from the increase of wind work on the near-inertial motions. 相似文献
10.
Estimates of Energy Dissipation Rates in the Three-Dimensional Deep Ocean Internal Wave Field 总被引：2，自引：0，他引：2
Using the “Eikonal Approach” (Henyey et al., 1986), we estimate energy dissipation rates in the three-dimensional Garrett-Munk internal wave field. The total energy dissipation rate within the undisturbed GM internal wave field is found to be 4.34 × 10−9 W kg−1. This corresponds to a diapycnal diffusivity of about 0.3 × 10−4 m2s−1, which is less than the value 10−4 m2s−1 required to sustain the global ocean overturning circulation. Only when the high vertical wavenumber, near-inertial current shear is enhanced can diapycnal diffusivity reach ∼10−4 m2s−1. It follows that the energy supplied at low vertical wavenumbers and low frequencies is efficiently transferred to high vertical wavenumbers and near-inertial frequencies in the mixing hotspots in the real ocean. 相似文献
11.
This study presents an analysis of the CTD data and the turbulent microstructure data collected in 2014, the turbulent mixing environment above the Atlantic Water(AW) around the Chukchi Borderland region is studied.Surface wind becomes more efficient in driving the upper ocean movement along with the rapid decline of sea ice,thus results in a more restless interior of the Arctic Ocean. The turbulent dissipation rate is in the range of4.60×10~(–10)~(–3.31×10~(–9) W/kg with a mean value of 1.33×10~(–9) W/kg, while the diapycnal diffusivity is in the range of1.45×10~(–6)–1.46×10~(–5)m~2/s with a mean value of 4.84×10~(–6) m~2/s in 200–300 m(above the AW). After investigating on the traditional factors(i.e., wind, topography and tides) that may contribute to the turbulent dissipation rate, the results show that the tidal kinetic energy plays a dominating role in the vertical mixing above the AW. Besides, the swing of the Beaufort Gyre(BG) has an impact on the vertical shear of the geostrophic current and may contribute to the regional difference of turbulent mixing. The parameterized method for the double-diffusive convection flux above the AW is validated by the direct turbulent microstructure results. 相似文献
12.
Shizuo Tsunogai 《Journal of Oceanography》1972,28(4):145-152
A simple advection-diffusion model is applied to the deep water of the North Pacific Ocean. The physical mixing parameter, i.e., the ratio of vertical advection velocity (W) to vertical eddy diffusivity (D), is obtained from the vertical distribution of a conservative property such as salinity. The rate of decomposition of organic matter is estimated from the oxygen consumption rate which is obtained from dissolved oxygen content. The calcium carbonate flux in the deep water is obtained from alkalinity. Using these values and the vertical distribution of a radioisotope,14C or226Ra, the vertical eddy diffusivity and the upwelling velocity are found to be 1.2 cm2/sec and 1.4 ×10–5 cm/sec, respectively, at the Geosecs 1969 station. The oxygen consumption rate at 3 km depth of the station is found to be 1.4×10–3ml/l/yr. 相似文献
13.
Shizuo Tsunogai 《Journal of Oceanography》1987,43(1):77-87
A simple dissolved silica (Si) and dissolved oxygen (O) diagram method was applied to study the deep-water circulation in the North Pacific and the following results and conclusion have been obtained. In the abyssal water flowing northward in the western Pacific Si increases with a constant ratio of Si to decreasing O(Si/O=–0.30). The water is designated as the main sequence. In the eastern Pacific the Si-O diagram is characteristic of the location and reflects the degrees of mixing with older waters and of alteration due to decomposition of biogenic material. The Bay of Alaska is found to be a great source of silica in the North Pacific and its bottom water spreads out to the central North Pacific north of 40°N, called here the abyssal front. The younger abyssal water in the Aleutian Trench flowing to the eastern North Pacific north of 40°N comes through the north end of the Kuril-Kamchatka Trench instead of the gap in the Emperor Seamounts at about 46°N. The deep water is almost completely homogenized by active isopycnal mixing and advection when the deep water reaches its upper boundary by upwelling in the western North Pacific including the Bering Sea. Thus the high productivity in the Bering Sea is principally caused neither by the direct supply of abyssal water rich in nutrients nor by the extremely active vertical mixing reaching depths greater than 500 m, but it may be caused simply by the shallower upper boundary of the deep water mass in the Bering Sea, from which nutrients are easily transported to the surface. 相似文献
14.
引潮力对海洋环流模式的影响 总被引：2，自引：1，他引：1
The eight main tidal constituents have been implemented in the global ocean general circulation model with approximate 1° horizontal resolution.Compared with the observation data,the patterns of the tidal amplitudes and phases had been simulated fairly well.The responses of mean circulation,temperature and salinity are further investigated in the global sense.When implementing the tidal forcing,wind-driven circulations are reduced,especially those in coastal regions.It is also found that the upper cell transport of the Atlantic meridional overturning circulation(AMOC) reduces significantly,while its deep cell transport is slightly enhanced from 9×106m3/s to 10×106 m3/s.The changes of circulations are all related to the increase of a bottom friction and a vertical viscosity due to the tidal forcing.The temperature and salinity of the model are also significantly affected by the tidal forcing through the enhanced bottom friction,mixing and the changes in mean circulation.The largest changes occur in the coastal regions,where the water is cooled and freshened.In the open ocean,the changes are divided into three layers:cooled and freshened on the surface and below 3 000 m,and warmed and salted in the middle in the open ocean.In the upper two layers,the changes are mainly caused by the enhanced mixing,as warm and salty water sinks and cold and fresh water rises;whereas in the deep layer,the enhancement of the deep overturning circulation accounts for the cold and fresh changes in the deep ocean. 相似文献
15.
Locally enhanced turbulent mixing over rough bottom bathymetry is one of the candidates that might make up for the lack of
diapycnal diffusivity in maintaining the global overturning circulation. In the present study, using a two-dimensional vertical
numerical model for the Brazil Basin, we numerically examine the intensity and vertical structure of tide-induced mixing over
multi-beam bottom bathymetry via the comparison with those over somewhat smoothed bottom bathymetry. Note that even this smoothed
bottom bathymetry is finer than in commonly used datasets. In comparison to the response over the smoothed bottom bathymetry,
energy dissipation rates are enhanced within a few hundred meters over the multi-beam bottom bathymetry. In spite of several
limitations of the two-dimensional vertical numerical model, the magnitude and vertical distribution of the calculated dissipation
rates agree well with those from microstructure measurements. We find that tidal interaction with fine-scale (≤2 km) bottom
bathymetry efficiently generates high wavenumber internal waves, which are subject to local energy dissipation and hence strongly
control the abyssal mixing; the most important finding is that the intensity and vertical decay scale of abyssal mixing are
in a trade-off relationship with each other, which is not taken into account in the existing parameterizations. 相似文献
16.
The global diapycnal transport in the ocean interior is one of the significant branches to return the deep water back toward near-surface. However, the amount of the diapycnal transport and the seasonal variations are not determined yet. This paper estimates the dissipation rate and the associated diapycnal transports at 500 m, 750 m and 1 000 m depth throughout the global ocean from the wide-spread Argo profiles, using the finescale parameterizations and classic advection-diff usion balance. The net upwelling is ~5.2±0.81 Sv (Sverdrup) which is approximately one fifth in magnitude of the formation of the deep water. The Southern Ocean is the major region with the upward diapycnal transport, while the downwelling emerges mainly in the northern North Atlantic. The upwelling in the Southern Ocean accounts for over 50% of the amount of the global summation. The seasonal cycle is obvious at 500 m and vanishes with depth, indicating the energy source at surface. The enhancement of diapycnal transport occurs at 1000min the Southern Ocean, which is pertinent with the internal wave generation due to the interaction between the robust deep-reaching flows and the rough topography. Our estimates of the diapycnal transport in the ocean interior have implications for the closure of the oceanic energy budget and the understanding of global Meridional Overturning Circulation. 相似文献
17.
Hydrographic data show that the meridional deep current at 47°N is weak and southward in northeastern North Pacific; the strong
northward current expected for an upwelling in a flat-bottom ocean is absent. This may imply that the eastward-rising bottom
slope in the Northeast Pacific Basin contributes to the overturning circulation. After analysis of observational data, we
examine the bottom-slope effect using models in which deep water enters the lower deep layer, upwells to the upper deep layer,
and exits laterally. The analytical model is based on geostrophic hydrostatic balance, Sverdrup relation, and vertical advection–diffusion
balance of density, and incorporates a small bottom slope and an eastward-increasing upwelling. Due to the sloping bottom,
current in the lower deep layer intensifies bottomward, and the intensification is weaker for larger vertical eddy diffusivity
(K
V), weaker stratification, and smaller eastward increase in upwelling. Varying the value of K
V changes the vertical structure and direction of the current; the current is more barotropic and flows further eastward as
K
V increases. The eastward current is reproduced with the numerical model that incorporates the realistic bottom-slope gradient
and includes boundary currents. The interior current flows eastward primarily, runs up the bottom slope, and produces an upwelling.
The eastward current has a realistic volume transport that is similar to the net inflow, unlike the large northward current
for a flat bottom. The upwelling water in the upper deep layer flows southward and then westward in the southern region, although
it may partly upwell further into the intermediate layer. 相似文献
18.
In this study we estimate diffusive nutrient fluxes in the northern region of Cape Ghir upwelling system (Northwest Africa) during autumn 2010. The contribution of two co-existing vertical mixing processes (turbulence and salt fingers) is estimated through micro- and fine-structure scale observations. The boundary between coastal upwelling and open ocean waters becomes apparent when nitrate is used as a tracer. Below the mixed layer (56.15±15.56 m), the water column is favorable to the occurrence of a salt finger regime. Vertical eddy diffusivity for salt (Ks) at the reference layer (57.86±8.51 m, CI 95%) was 3×10−5 (±1.89×10−9, CI 95%) m2 s−1. Average diapycnal fluxes indicate that there was a deficit in phosphate supply to the surface layer (6.61×10−4 mmol m−2 d−1), while these fluxes were 0.09 and 0.03 mmol m−2 d−1 for nitrate and silicate, respectively. There is a need to conduct more studies to obtain accurate estimations of vertical eddy diffusivity and nutrient supply in complex transitional zones, like Cape Ghir. This will provide us with information about salt and nutrients exchange in onshore–offshore zones. 相似文献
19.
David Kadko William Johns 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(6):647-657
Ocean upwelling rates are difficult to measure because of the relatively small velocities involved, and therefore are typically inferred from indirect methods such as heat budget estimates or tracer observations. Here we present the first results using a novel technique, based on the isotope 7Be, to infer rates of upwelling along the equator. Beryllium-7 (half-life=53.3 d) is a cosmic-ray produced radioactive nuclide that is deposited by rainfall upon the ocean surface and subsequently enriched and homogenized within the mixed layer. Previous investigations have utilized the penetration of characteristically high mixed layer concentrations into the upper thermocline to trace ocean ventilation and subduction over seasonal timescales. Here, the tracer is used in a reverse sense; that is, the 7Be concentration in the usually 7Be-rich surface mixed layer will be diluted from penetration of 7Be “dead” water upwelled from below. This dilution provides a means to infer upwelling rates. Furthermore, with knowledge of upwelling rates, 7Be profiles can be used to constrain vertical diffusivity within the upper thermocline. These ideas were tested with samples collected during the Tropical Atlantic Climate Experiment (TACE) cruise (May 22-June 27, 2009). The observations indicated a nearly linear relationship between 7Be inventory and mixed layer temperature, as with increased upwelling, lower mixed layer temperatures correspond to greater 7Be dilution from depth. With this data, upwelling rates were estimated at a number of stations near the equator between 0°E and 30°W within and adjacent to the equatorial cold tongue. The derived upwelling rates ranged from 0 to 2.2 m/d, with maximum values found between the equator and 2°S. The corresponding Kz values derived for the upper thermocline were in the range 1-4×10−4 m2/s. 相似文献
20.
《Deep Sea Research Part I: Oceanographic Research Papers》1999,46(1):109-148
The realization of North Atlantic Deep Water (NADW) replacement in the deep northern Indian Ocean is crucial to the “conveyor belt” scheme. This was investigated with the updated 1994 Levitus climatological atlas. The study was performed on four selected neutral surfaces, encompassing the Indian deep water from 2000 to 3500 m. The Indian deep water comprises three major water masses: NADW, Circumpolar Deep Water (CDW) and North Indian Deep Water (NIDW). Since NADW flowing into the southwest Indian Ocean is largely blocked by the ridges (the Madagascar Ridge in the east and Davie Ridge in the north in the Mozambique Channel) and NIDW is the only source in the northern Indian Ocean that cannot provide a large amount of volume transport, CDW has to be a major source for the Indian deep circulation and ventilation in the north. Thus the question of NADW replacement becomes that of how the advective flows of CDW from the south are changed to be upwelled flows in the north—a water-mass transformation scenario. This study considered various processes causing motion across neutral surfaces. It is found that dianeutral mixing is vital to achieve CDW transformation. Basin-wide uniform dianeutral upwelling is detected in the entire Indian deep water north of 32°S, somewhat concentrated in the eastern Indian Ocean on the lowest surface. However, the integrated dianeutral transport is quite low, about a net of 0.2 Sv (1 Sv=106 m3 s-1) across the lowermost neutral surface upward and 0.4 Sv across the uppermost surface upward north of 32°S with an error band of about 10–20% when an uncertainty of half-order change in diffusivities is assumed. Given about 10–15% of rough ridge area where dianeutral diffusivity could be about one order of magnitude higher (10-4 m2 s-1) due to internal-wave breaking, the additional amount of increased net dianeutral transport across the lowest neutral surface is still within that error band. The averaged net upward transport in the north is matched with a net downward transport of 0.3 Sv integrated in the Southern Ocean south of 45°S across the lowermost surface. With the previous works of You (1996. Deep Sea Research 43, 291–320) in the thermocline and You (Journal of Geophysical Research) in the intermediate water combined, a schematic dianeutral circulation of the Indian Ocean emerges. The integrated net dianeutral upwelling transport shows a steady increase from the deep water to the upper thermocline (from 0.2 to 4.6) north of 32°S. The dianeutral upwelling transport is accumulated upward as the northward advective transport provided from the Southern Ocean increases. As a result, the dianeutral upwelling transport north of 32°S can provide at least 4.6 Sv to south of 32°S from the upper main thermocline, most likely to the Agulhas Current system. This amount of dianeutral upwelling transport does not include the top 150–200 m, which may contribute much more volume transport to the south. 相似文献