Net Volume Transport Research Articles

High-resolution numerical modelling of seasonal volume, freshwater, and heat transport along the Indian coast

Abstract. Seasonal reversal of winds and equatorial remote forcing influences the circulation of the Arabian Sea (AS) and Bay of Bengal (BoB) basins in the northern Indian Ocean. In this study, we numerically modelled the physical characteristics of the AS and BoB, using the Massachusetts Institute of Technology general circulation model (MITgcm) at a high spatial resolution of 1/20° forced with climatological initial and boundary conditions. The simulated temperature, salinity, and flow fields were validated with satellite and in situ datasets. We then studied the exchange of coastal waters by evaluating transports computed from the model simulations. The alongshore volume transport on the eastern coast is stronger with high seasonal variability due to the poleward-flowing western boundary current and equatorward-flowing East Indian Coastal Current. West coast transport is influenced by large intraseasonal oscillations. The alongshore freshwater transport is an order less than the alongshore volume transport. Out of the net volume transport, freshwater accounts for a maximum of 6.03 % during the southwestern monsoon season, followed by 4.85 % in the post-monsoon season. We observe an inverse relationship between alongshore freshwater and volume transport on the western coast and a direct relationship on the eastern coast. The contribution of eddy-induced heat and freshwater transport was also examined. The relation between net heat transport and net heat flux illustrates the role of coastal currents and equatorial forcing in dissipating heat within the coastal waters. We observed that meridional heat transport over the AS is stronger than over the BoB. Both basins act as a heat source during the summer monsoon and heat sink during the winter. This high-resolution model setup simulates all the important physical climatological patterns, leading to a better understanding of the state of the northern Indian Ocean.

Wind‐Driven Seasonal Variability of Deep‐Water Overflow From the Pacific Ocean to the South China Sea

AbstractThe South China Sea (SCS) is a semi‐enclosed marginal sea linked to the broader oceans via various geographically constrained channels. Beneath the main thermocline depth, Luzon Strait is the only conduit for water‐mass exchanges. Observations indicate a substantial seasonal variability in the inflow transport of deep water from the Pacific Ocean. This study aims to identify and examine key drivers for such seasonal changes. It is found that seasonal variability of the deep‐water transport into the SCS is primarily driven by surface wind stress. An imbalance in wind‐driven exchanges of surface water between the SCS and external seas demands compensational transports in subsurface layers so that the net volume transport into the SCS is conserved, resulting in seasonal variations in deep‐water overflow. Changes in Karimata Strait exert a particularly influential impact on deep‐water inflow, likely due to its unique position as the sole connecting channel across the Equator.

Influence of Caribbean eddies on the Loop current system evolution

The Loop Current (LC) system dynamics are an essential component of the processes influencing circulation and transport in the Gulf of Mexico (GoM). The LC evolution is influenced by various factors, including the rich eddy field of the region and the flow exchange through the Yucatan Strait with the neighboring Caribbean Sea. These factors contribute to the complexity of the LC and, as a result, to the limitations in the predictability of the system. The focus of this study is to further elucidate the evolution of the LC, by quantifying the influence of coherent eddy fluxes originating in the Caribbean Sea. This is achieved by employing the Lagrangian-Averaged Vorticity Deviation (LAVD) method, an objective metric to evaluate eddy coherence in the Caribbean Sea that allows, for the first time, to quantify at different depths the evolution of coherent Caribbean eddies through the Yucatan Channel towards the GoM. The physical connectivity between the Caribbean Sea and the GoM is addressed using Lagrangian techniques to analyze processes that take place south of the Yucatan Channel and help quantify their strong relationship with the GoM eddy field. Coherent anticyclonic vorticity fluxes, as well as the net coherent anticyclonic volume transport between the Caribbean Sea and the GoM are associated with Loop Current Eddy (LCE) detachments through direct connectivity between the coherent Caribbean anticyclones and the forming LCE. The findings have important implications for understanding and predicting the LC system and the physical connectivity processes between the GoM and the Caribbean Sea.

Multi-layer flow field mapping in a small-scale shallow water reservoir by coastal acoustic tomography

Long-term, high-precision and spatiotemporal observation of current structure in small-scale waters is important for underwater research and water resources management. In this paper, a reciprocal sound transmission experiment was conducted using three Coastal Acoustic tomography (CAT) systems within 300 m spacing in Huangcai reservoir, Hunan, China from 14 to 16, Sep 2020. The multi-arrival reciprocal paths between each pair of stations were identified with the help of ray simulation. 3-D CAT data which penetrated the full depth of water were obtained. The flow field along vertical slice were mapped and showed consistency with Acoustic Doppler Current Profiler (ADCP) and Temperature Depth (TD) data. A standard deviation of 0.73 m/s at the bottom layer were observed, indicating strong bottom flows in the reservoir. Furthermore, to visualize the strong bottom flow, the horizontal flow fields in the bottom layer were mapped by 3-D inversion technique. The feasibility of the technique was validated by three measures: 1) comparison between range average current and horizontal flow field; 2) Uncertainty analysis; 3) Check net volume transport. This work proves the CAT combined with 3-D inversion technique has the potentials to provide real-time 3-D current data for water researches.

Eddy Induced Cross-Shelf Exchanges in the Black Sea

Cross-shelf exchanges in the Black Sea were investigated using remote sensing data and an ocean circulation model to which an eddy-tracking algorithm and Lagrangian particle tracking model was applied. An anticyclonic eddy in 1998 and a cyclonic eddy in 2000 were investigated in detail. Eddy-induced cross-shelf transport of low salinity and high Chl-a waters reached a maximum in the presence of filaments associated with these eddies. The daily mean volume transport by the eddies was comparable with the previously documented transport by eddies of similar size in the north-western shelf region. Lagrangian particle tracking results showed that 59% of particles initially released over the shelf were transported offshore within 30 days by the 1998 anticyclone and 27% by the 2000 cyclone. The net volume transport across the Black Sea shelf-break reached the maxima in winter, coinciding with the increase in wind stress curl and mean kinetic energy that is a measure of the intensity of the boundary current. Ekman transport directly influences the cross-shelf exchanges in the surface layer. The south-eastern Black Sea is presented as an important area for cross-shelf transport. The total cross-shelf transport can be divided into its “large-scale” and “eddy-induced” components. Eddy-induced transport was 34% and 37% of the total cross-shelf transport (1998–2014) in the Black Sea in the off-shelf and on-shelf directions, respectively, but these values ranged between 25% and 65% depending on the eddy activity over time.

The roles of wind and baroclinic processes in cross-isobath water exchange within the Bohai Sea

Considering the significance of water exchange between the nearshore and offshore waters to shallow-water biogeochemical processes, the influences of wind and baroclinic processes on water exchanges across the 10-m (E10) and 20-m isobaths (E20) in the Bohai Sea during ice-free cycles of 1998–2019 were investigated using a three-dimensional Finite Volume Community Ocean Model (FVCOM). The two-way analysis of variance illustrated that both E10 and E20 showed significant seasonal and spatial variations. The cross-isobath fluxes were the strongest during summer and the weakest during fall, with offshore (onshore) transport in the upper (bottom) layer. The net volume transport was at O (10−2) Mm3/s (millions of cubic meters per second) in Bohai and Liaodong Bays, which was an order of magnitude greater than that in Laizhou Bay. Further numerical experiments revealed that wind regulated the upper-layer E10 via the wind-induced advection, while it altered E20 mainly through the enhanced mixing and the subsequent weakening of the baroclinic pressure gradient force in the subsurface layer. In addition, the thermal gradient driven cross-isobath volume transports in Bohai and Liaodong Bays were most prominent during summer but negligible during fall. Those along the 10-m isobath in Laizhou Bay, however, were induced by the salinity gradient from the buoyant fluxes of the Yellow River all year round. With supplemental contributions of the baroclinic processes related to the cold pool of the Bohai Sea, and the wind-induced advection and mixing in the surface and subsurface layers, respectively, Laizhou Bay's E20 had a four-layer vertical structure during summer.

Variation of water mass exchange on tidal scale in Balikpapan Bay

Balikpapan Bay is enclosed water influenced by freshwater from river runoff and saline water from Makassar Strait. The exchange of water mass was examined by 3D numerical model simulation-Hamburg Shelf Ocean Model (HAMSOM) with horizontal resolutions approx. 150 m and 10 vertical layers applied in Balikpapan Bay. The thirteen tidal components, daily river runoff, atmospheric forcing, subsurface temperature, and Salinity in 3D used for model input. The tidal elevation from Geospatial Information Agency (BIG) model fits with this result from 01/03/2020 to 31/03/2020. It has coefficient correlation 0,99 with a significant level of 95% and Root Mean Square Error (RMSE) is 0,1 m. The volume and salt transport in the mouth (Line-A) and middle (Line-B) of bay was examined. The maximum transport in Line-A during spring (neap) high to low tide and low to high tide is −18364.72 m3/s (−1717.57 m3/s) and −17532.27 m3/s (4258.86 m3/s) for volume. Then, 531,947,898.90 kg.psu./s (−45,127,135.38 kg.psu./s) and −536,410,944.50 kg.psu./s (140,700,437.97 kg.psu./s) for salinity. Positive (negative) of water transport is inflow (outflow) to Balikpapan Bay. The net transport in a day during the spring (neap) is −832.45 m3/s (5976.43 m3/s) for volume and −4,463,045.58 kg.psu./s (185,827,573.35 kg.pau./s) for salt. The vertical structure of net volume and salt transport bot in Line-A and Line-B shows the water goes to outer bay in surface and inner bay in subsurface. While in the spring tide the surface deeper than neap tide. It indicated that water mass exchange dominantly influenced by river in surface and tidal in subsurface. It also shows that water mass from inner bay more easy flushing during spring tide than neap tide and vice versa

Comparison of volume transport in the Halmahera Sea between La Nina 2011 and El Nino 2015 events based on numerical model

Variations of volume transport in the Halmahera Sea are strongly influenced by the El Nino Southern Oscillation (ENSO). Based on the Southern Oscillation Index (SOI), in 2011 La Nina event took place with a strength of 3.02, while in 2015 El Nino occurred with a strength of -2.6. This paper discusses the variation of transport volume caused by the ENSO phenomenon based on the results of the Regional Ocean Model System (ROMS). On the Halmahera Sea at a latitude of 0.3°S with a width of 67 km and a depth of down to 200 m, net volume transport always moves southward. The largest volume transport in La Nina 2011 occurred in September-October, which was -8.9 Sv. Meanwhile, in El Nino 2015 the largest volume transport occurred in July-August, which was equal to -4.9 Sv. The cross correlation coefficient between volume transport and SOI in 2011 and 2015 was r = 0.55 and r = 0.61 respectively, where these results indicate a strong relationship.

Mapping Small-Scale Horizontal Velocity Field in Panzhinan Waterway by Coastal Acoustic Tomography.

Mapping small-scale high-precision velocity fields is of great significance to oceanic environment research. Coastal acoustic tomography (CAT) is a frontier technology used to observe large-scale velocity field in the horizontal slice. Nonetheless, it is difficult to observe the velocity field using the CAT in small-scale areas, specifically where the flow field is complex such as ocean ranch and artificial upwelling areas. This paper conducted a sound transmission experiment using four 50 kHz CAT systems in the Panzhinan waterway. Notably, sound transmission based on the round-robin method was recommended for small-scale CAT observation. The travel time between stations, obtained by correlation of raw data, was applied to reconstruct the horizontal velocity fields using Tapered Least Square inversion. The minimum net volume transport was 8.7 m3/s at 12:32, 1.63% of the total inflow volume transport indicating that the observational errors were acceptable. The relative errors of the range-average velocity calculated by differential travel time were 1.54% (path 2) and 0.92% (path 6), respectively. Moreover, the inversion velocity root-mean-square errors (RMSEs) were 0.5163, 0.1494, 0.2103, 0.2804 and 0.2817 m/s for paths 1, 2, 3, 4 and 6, respectively. The feasibility and acceptable accuracy of the CAT method in the small-scale velocity profiling measurement were validated. Furthermore, a three-dimensional (3-D) velocity field mapping should be performed with combined analysis in horizontal and vertical slices.

Revisiting a coastal acoustic tomography experiment in Hiroshima Bay: Temporal variations in path-averaged currents and its relation to wind

Remote sensing is a desirable method for measuring ocean currents on various spatial and temporal scales. Coastal acoustic tomography (CAT) can measure current velocity in coastal and shallow seas, but the application of this method in stratified shallow estuaries has not been sufficiently tested. This study revisits the acoustic transmission data obtained from the 2013 Hiroshima Bay CAT experiment and investigates what information could be obtained from acoustic data when a relatively strong southward wind blew in the bay. We determined path-averaged currents of the first arrival rays and compared the temporal variations in this path-averaged current with those in the wind, water temperature, and detided sea level. When the southward wind was intensifying, the sea level at the northern coast of the bay decreased and then recovered when the southward wind subsided. These sea level variations must be accompanied by net volume transport variations. When sea level was recovering, the path-averaged current exhibited a positive bias, reflecting an increase of volume transport toward the inner part of the bay. In contrast, the path-averaged current did not show a noticeable variation when the sea level was decreasing although the surface layer current was expected to be intensified southward. This is because the first arrival ray did not propagate through the surface layer during the period, and therefore, the path-averaged current from the first arrival rays did not contain surface current velocity information. CAT is promising method for measuring variations in current velocity fields associated with winds; however, in the application to stratified and shallow estuaries such as Hiroshima Bay, it is crucial to consider acoustic ray-path variations when analyzing and interpreting travel time data time series.

Bidirectional Volume Exchange Between Kuroshio and East China Sea Shelf Water Based on a Whole‐Region Passive‐Tracing Method

AbstractThe Kuroshio intrusion has a profound influence on the marine dynamic and ecological environment in the East China Sea (ECS) shelf. In most previous studies, the intrusion has been evaluated by the volume transport across the 200 m isobath. However, this approximate substitution leads to an underestimation of the Kuroshio intruding flux as it fails to separate the onshore and offshore transport of Kuroshio and shelf water. In this paper, a whole‐region passive‐tracing modeling method is proposed to quantitatively explore the bidirectional exchange of Kuroshio and shelf water, by introducing the Kuroshio water concentration as a passive tracer into the flux calculations. In terms of the climatological annual mean, the Kuroshio intrusion onto the ECS shelf is as high as 1.85 Sv (1 Sv = 106 m3 s−1), with a shelf water outflow rate of 0.42 Sv. The real Kuroshio intruding flux is about 30% higher than the net volume transport across the 200 m isobath (1.43 Sv), which indicates that the influence of the Kuroshio intrusion on the ECS may be far greater than believed before. The volume exchange on the inner shelf of the ECS is also discussed. Analyses of the momentum balances indicate that the exchanges on both the shelf break and the inner shelf are generally dominated by the geostrophic balance, but the exchange on the shelf break is more susceptible to nonlinear effects. The results of a set of sensitivity experiments show that variation of the Kuroshio intrusion is mainly regulated by the combined effect of the Kuroshio transport, the Taiwan Strait current, and the local wind stress. In contrast, the local wind stress has a predominant effect on the outflow of shelf water.

Bifurcation and Upwelling of the Equatorial Undercurrent West of the Galápagos Archipelago

AbstractThe Equatorial Undercurrent (EUC) encounters the Galápagos Archipelago on the equator as it flows eastward across the Pacific. The impact of the Galápagos Archipelago on the EUC in the eastern equatorial Pacific remains largely unknown. In this study, the path of the EUC as it reaches the Galápagos Archipelago is measured directly using high-resolution observations obtained by autonomous underwater gliders. Gliders were deployed along three lines that define a closed region with the Galápagos Archipelago as the eastern boundary and 93°W from 2°S to 2°N as the western boundary. Twelve transects were simultaneously occupied along the three lines during 52 days in April–May 2016. Analysis of individual glider transects and average sections along each line show that the EUC splits around the Galápagos Archipelago. Velocity normal to the transects is used to estimate net horizontal volume transport into the volume. Downward integration of the net horizontal transport profile provides an estimate of the time- and areal-averaged vertical velocity profile over the 52-day time period. Local maxima in vertical velocity occur at depths of 25 and 280 m with magnitudes of (1.7 ± 0.6) × 10−5 m s−1 and (8.0 ± 1.6) × 10−5 m s−1, respectively. Volume transport as a function of salinity indicates that water crossing 93°W south (north) of 0.4°S tends to flow around the south (north) side of the Galápagos Archipelago. Comparisons are made between previous observational and modeling studies with differences attributed to effects of the strong 2015/16 El Niño event, the annual cycle of local winds, and varying longitudes between studies of the equatorial Pacific.

Variation in Water Masses on Shelf of Northern Bering Sea in September 2016-2018

Based on hydrological data obtained during the 7th to 9th Chinese National Arctic Research Expeditions in the summers of 2016–2018, the main water structure on the shelf of the northern Bering Sea and the volume and heat fluxes of the Bering Strait throughflow were analyzed. Distinct variability was identified in the three Pacific water masses feeding the strait - Anadyr Water (AW), Bering Shelf Water (BSW) and Alaskan coastal water (ACW). Overall, the temperature and salinity of the entire section increased each year, with 2018 showing significant anomalies, i.e., a temperature anomaly of up to 1 °C and a maximum salinity anomaly of 2. From 2016 to 2018, the extent of the ACW gradually narrowed in the eastern part of this section, while the AW expanded eastward each year. The net volume transport through each of the three sections increased poleward from 1.65 Sv to 2.76 Sv, with the AW increasing from 0 Sv to 1.03 Sv, the BSW varying between 0.52–1.65 Sv, and the ACW gradually decreasing from 1.04 Sv to disappearing completely. The net heat fluxes were also poleward, varying between 25.77 TW and 61.50 TW, and showing a significant increase. Significant variations in magnitude and extent were observed in each water mass of the Bering Strait throughflow, which could produce widespread effects in the Arctic Ocean and the global ocean beyond.

Topographic Control of Southern Ocean Gyres and the Antarctic Circumpolar Current: A Barotropic Perspective

AbstractIn the Southern Ocean the Antarctic Circumpolar Current is significantly steered by large topographic features, and subpolar gyres form in their lee. The geometry of topographic features in the Southern Ocean is highly variable, but the influence of this variation on the large-scale flow is poorly understood. Using idealized barotropic simulations of a zonal channel with a meridional ridge, it is found that the ridge geometry is important for determining the net zonal volume transport. A relationship is observed between ridge width and volume transport that is determined by the form stress generated by the ridge. Gyre formation is also highly reliant on the ridge geometry. A steep ridge allows gyres to form within regions of unblocked geostrophic (f/H) contours, with an increase in gyre strength as the ridge width is reduced. These relationships among ridge width, gyre strength, and net zonal volume transport emerge to simultaneously satisfy the conservation of momentum and vorticity.

Origin and formation of the Ryukyu Current revealed by HYCOM reanalysis

The origin of the Ryukyu Current (RC) and the formation of its subsurface velocity core were investigated using a 23-year (1993–2015) global Hybrid Coordinate Ocean Model (HYCOM) dataset. The volume transport of the RC comes from the Kuroshio eastward branch (KEB) east of Taiwan and part of the North Pacific Subtropical Gyre (p-NPSG). From the surface to 2 000 m depth, the KEB (p-NPSG) transport contributes 41.5% (58.5%) to the mean total RC transport. The KEB originally forms the subsurface velocity core of the RC east of Taiwan due to blockage of the subsurface Kuroshio by the Ilan Ridge (sill depth: 700 m). Above 700 m, the Kuroshio can enter the East China Sea (ECS) over the Ilan Ridge, meanwhile, the blocked Kuroshio below 700 m turns to the right and flows along the Ryukyu Islands. With the RC flowing northeastward, the p-NPSG contribution strengthens the subsurface maximum structure of the RC owing to the blockage of the Ryukyu Ridge. In the surface layer, the p-NPSG cannot form a stable northeastward current due to frequent disturbance by mesoscale eddies and water exchange through the gaps (with net volume transport into ECS) between the Ryukyu Islands.

Variability of Southern Ocean Transports

AbstractThe Southern Ocean (SO) is capable of transporting vast amounts of salt, heat, and nutrients, which allows it to influence and regulate global climate. The variability of depth- and density-integrated volume transports in the SO is studied using the Estimating the Circulation and Climate of the Ocean (ECCO), version 4, release 3 (1992–2015), ocean state estimate. The estimate has a net eastward transport of 150.6 ± 5.5, 162.6 ± 7.4, and 148.2 ± 5.4 Sv (1 Sv ≡ 106 m3 s−1) between the Atlantic–Indian, Indian–Pacific, and Pacific–Atlantic basins, respectively. The time-mean meridional volume transport across 30°S in the Atlantic is estimated to be −1.4 ± 0.6 Sv, −14.4 ± 3.5 Sv in the Indian basin, and 15.5 ± 4.1 Sv in the Pacific, where negative values are southward. Trends in net volume transport between the basins are statistically insignificant. Within the water column, however, the middle and lower branches of the meridional overturning circulation have trends of −0.289 and 0.248 Sv decade−1 in the Atlantic basin. The Indian and Pacific basins have decreasing trends in their lower overturning cells. These results indicate increased overturning circulation within the lower branch in the South Atlantic and decreased lower branch circulation within the Indian and Pacific basins and have implications on the thermohaline-driven circulation. Using ECCO, we estimate a southward potential temperature transport of −176.2° ± 197.2°C Sv and salinity transport of −1.71 ± 22.4 psu Sv into the SO and indicate potential temperature transport is increasing by −15.0° ± 13.2°C Sv decade−1.

The Cross-Sectional Characteristic and Spring-Neap Variation of Residual Current and Net Volume Transport at the Yeomha Channel

The Cross-Sectional Characteristic and Spring-Neap Variation of Residual Current and Net Volume Transport at the Yeomha Channel

Composition and variability of the Denmark Strait Overflow Water in a high‐resolution numerical model hindcast simulation

AbstractThe upstream sources and pathways of the Denmark Strait Overflow Water and their variability have been investigated using a high‐resolution model hindcast. This global simulation covers the period from 1948 to 2009 and uses a fine model mesh (1/20°) to resolve mesoscale features and the complex current structure north of Iceland explicitly. The three sources of the Denmark Strait Overflow, the shelfbreak East Greenland Current (EGC), the separated EGC, and the North Icelandic Jet, have been analyzed using Eulerian and Lagrangian diagnostics. The shelfbreak EGC contributes the largest fraction in terms of volume and freshwater transport to the Denmark Strait Overflow and is the main driver of the overflow variability. The North Icelandic Jet contributes the densest water to the Denmark Strait Overflow and shows only small temporal transport variations. During summer, the net volume and freshwater transports to the south are reduced. On interannual time scales, these transports are highly correlated with the large‐scale wind stress curl around Iceland and, to some extent, influenced by the North Atlantic Oscillation, with enhanced southward transports during positive phases. The Lagrangian trajectories support the existence of a hypothesized overturning loop along the shelfbreak north of Iceland, where water carried by the North Icelandic Irminger Current is transformed and feeds the North Icelandic Jet. Monitoring these two currents and the region north of the Iceland shelfbreak could provide the potential to track long‐term changes in the Denmark Strait Overflow and thus also the AMOC.

Tidal currents and Kuroshio transport variations in the Tokara Strait estimated from ferryboat ADCP data

AbstractFrom 2003 to 2011, current surveys, using an acoustic Doppler current profiler (ADCP) mounted on the Ferry Naminoue, were conducted across the Tokara Strait (TkS). Resulting velocity sections (1234) were used to estimate major tidal current constituents in the TkS. The semidiurnal M2 tidal current (maximum amplitude 27 cm s−1) was dominant among all the tidal constituents, and the diurnal K1 tidal current (maximum amplitude 21 cm s−1) was the largest among all the diurnal tidal constituents. Over the section, the ratios, relative to M2, of averaged amplitudes of M2, S2, N2, K2, K1, O1, P1, and Q1 tidal currents were 1.00:0.44:0.21:0.12:0.56:0.33:0.14:0.10. Tidal currents estimated from the ship‐mounted ADCP data were in good agreement with those from the mooring ADCP data. Their root‐mean‐square difference for the M2 tidal current amplitude was 2.0 cm s−1. After removing the tidal currents, the annual‐mean of the net volume transport (NVT) through the TkS ± its standard derivation was 23.03 ± 3.31 Sv (Sv = 106 m3 s−1). The maximum (minimum) monthly mean NVT occurred in July (November) with 24.60 (21.47) Sv. NVT values from the ship‐mounted ADCP were in good agreement with previous geostrophic volume transports calculated from conductivity temperature depth data, but the former showed much finer temporal structure than those from the geostrophic calculation.

Abyssal Upwelling and Downwelling Driven by Near-Boundary Mixing

AbstractA buoyancy and volume budget analysis of bottom-intensified mixing in the abyssal ocean reveals simple expressions for the strong upwelling in very thin continental boundary layers and the interior near-boundary downwelling in the stratified ocean interior. For a given amount of Antarctic Bottom Water that is upwelled through neutral density surfaces in the abyssal ocean (between 2000 and 5000 m), up to 5 times this volume flux is upwelled in narrow, turbulent, sloping bottom boundary layers, while up to 4 times the net upward volume transport of Bottom Water flows downward across isopycnals in the near-boundary stratified ocean interior. These ratios are a direct result of a buoyancy budget with respect to buoyancy surfaces, and these ratios are calculated from knowledge of the stratification in the abyss along with the assumed e-folding height that characterizes the decrease of the magnitude of the turbulent diapycnal buoyancy flux away from the seafloor. These strong diapycnal upward and downward volume transports are confined to a few hundred kilometers of the continental boundaries, with no appreciable diapycnal motion in the bulk of the interior ocean.