The bottom Ekman layer plays a critical role in the exchange of momentum, energy, and materials between the seabed and the overlying deep ocean, yet its detailed features remain poorly understood compared to the upper Ekman layer. Using 222 bottom-reaching velocity profiles obtained in the South China Sea (SCS), we investigated the vertical velocity structure in the bottom layer, and identified three deflection types of the bottom Ekman layer (clockwise, counterclockwise, insignificant) with average deflection angles of 53 ± 34°, 44 ± 26°, and 7 ± 3°, respectively, and thicknesses ranging from 10 to 50 m. The dissipation and diffusivity in the SCS bottom Ekman layer are estimated by assuming a constant value of viscosity coefficient, which show the maximal turbulent dissipation and eddy diffusivity in the Luzon Strait are as high as 10−7 W kg−1 and 10−1 m2 s−1, respectively. The water transport toward the SCS through the bottom Ekman layer via the Luzon Trough is also examined, which reaches 0.03 Sv and contributes 3.6% of the total overflow below the depth of 1920 m. Combined with the suspended sediment concentration of 30 mg L−1 inferred from the backscatter measurements, we estimated a substantial sediment flux of 3.9 Mt y−1 through the bottom Ekman layer from the Luzon Trough to the Manila Trench. This study highlights the significance of bottom Ekman layer in closing energy budget and transporting suspended sediment.

Abstract Ocean turbulence, crucial for regulating Earth systems, is substantially modulated by background dynamic processes. Using 8‐day‐long hourly microstructure observations over the South China Sea shelf in summer, we investigate turbulence evolution under strong stratification and successively modulated by a front and a typhoon. In the mixed layer, the front sustains strong stratification and inhibits shear and convective instabilities, suppressing turbulence and causing low eddy diffusivity Kθ and mixing efficiency Γ. Sporadic intensified subsurface mixing couples with surface‐heating‐induced sharp temperature gradient and elevates daytime Γ throughout the thermocline. Typhoon and subsequent storms then drastically weaken stratification, promote convective instability, and elevate turbulence intensity, Kθ and Γ greatly. The thermocline remains strongly stratified, suppressing turbulence and causing weak dissipation and mixing. Thermocline‐Γ stays low mostly, then rises markedly once near‐inertial waves emerge, averaging 0.15. Scaling of Thermocline‐Γ based on buoyancy Reynolds number Reb and turbulent Froude number Frt suggests Γ∝Reb−1/4Frt0.

Prydz Bay is a major Antarctic Bottom Water production region adjacent to a major cold cavity ice shelf. Its underlying mixing processes are little known, although they determine the intensity of water mass transformation. Using microstructure measurements, we reveal detailed regional variations of dissipation and mixing in Prydz Bay during summer. In the upper layer, turbulence dominates the continental shelf, presenting weak dissipation rate of thermal variance Xo [O(10_10)degrees C2 s_1], but showing the elevated dissipation rate of turbulent kinetic energy s [O(10_8) W kg_1] and thermal eddy diffusivity Ko [O(10_4) m2 s_1]. On the continental slope, diffusive convection prevails, with one-order greater Xo and one-order smaller s and Ko. On the shelf break, turbulence and diffusive convection coexist, with elevated s, Xo, and Ko reaching the orders of 10_8 W kg_1, 10_8 degrees C2 s_1, and 10_4 m2 s_1, respectively. Tidal current's encountering with the ice shelf, background current's impinging on the rough topography, and the intrusion of modified Circumpolar Deep Water all contribute to these spatial variations. The dissipation ratios P for both turbulence (0.05) and diffusive convection (0.14) are statistically smaller than those in waters of mid-and low latitudes because water in Prydz Bay is primarily stratified by salinity; hence, the strong temperature gradient is associated with a weak stratification. Based on these features, we propose a new indicator to differentiate turbulence and double diffusion. This study is helpful for better understanding Antarctic mixing processes, and their contributions to local water mass transformation and to global ocean circulation and climate. SIGNIFICANCE STATEMENT: Prydz Bay is important in producing Antarctic Bottom Water and hence shaping global ocean circulation and climate. This bottom water production and spreading are catalyzed by microscale mixing, yet the local mixing processes remain unclear. Based on field measurements, we reveal the regional differences in dissipation/mixing intensities and its drivers in upper Prydz Bay during the austral summer. Turbulence and diffusive convection dominate the water in and away from the continental shelf, respectively, leading to spatially contrasted mixing intensities. Notably, an important parameter, dissipation ratio, in Prydz Bay is clearly smaller than that of mid-and low latitudes. This is directly linked to the vertical transition of water masses. This study improves our understanding of mixing in Prydz Bay and its influences on other multiscale dynamics.

Abstract. The local dissipation efficiency of internal tides, q, is a critical parameter in tidal mixing parameterizations. However, the conventionally adopted constant value (q ≈ 0.3) in large-scale ocean models neglects its significant spatiotemporal variability. Based on the MITgcm LLC4320 simulation, the internal tidal energy budgets at the Luzon Strait (a source region, LS) and the Nansha Islands (a sink region, Nansha) in the South China Sea (SCS) are analyzed. Results indicate that the barotropic-to-baroclinic energy conversion in the LS reaches approximately 45 GW, with semidiurnal constituents accounting for roughly 60 %, due to the resonance over the double-ridge topography. The value of q in the LS fluctuates between 0.3 and 0.7, primarily modulated by the high-mode local dissipation. Local internal tide generation around the Nansha Islands is less than 1.5 GW; however, this region experiences significant convergence of internal tidal energy flux, which elevates the value of q to generally greater than 1 and occasionally exceeding 2.5. Modal analysis confirms that the intensified dissipation over the Nansha Islands originates predominantly from topographic scattering and breaking of mode-1 internal tides from the far field. Parameterizations for q are developed based on both physical factors and data-driven algorithms, both of which successfully capture the macroscopic clustering of q. In the LS, q is modulated by near-field factors such as the barotropic tidal forcing and the local dissipation of high-mode internal tides. Conversely, q around the Nansha Islands is primarily contributed by mode-1 internal tidal energy coming from the far field, highlighting the jointly modulation of local extreme dissipation by far-field beam interference and nonlinear topographic scattering.

Tropical cyclones (TCs) often undergo track turning when moving over the ocean. However, the influence of track turning on TC-ocean interactions remains little explored. This study systematically investigates sea surface temperature (SST) cooling and TC intensification during TC track-turning stages in global TC-active basins during 1998-2022. Globally, turning TCs induce stronger SST cooling than straight-moving TCs (e.g., -1.53 degrees C vs. -1.08 degrees C for categories 1-2), expand cooling area by 40%-110%, and greatly reduce cooling asymmetry for left-turning (right-turning) TCs in the Northern (Southern) Hemisphere. The translation speed of turning TCs is 1.5 m s-1 slower compared to straight-moving TCs. Numerical experiments demonstrate that the enhanced cooling is attributed to the combined effect of track turning and accompanying slow translation speed. The enhanced cooling effectively suppresses storm intensification of turning TCs. The intensification rate for straight-moving versus turning TCs is 2.98 versus 0.06 m s-1 per 24 hr for categories 1-2. As turning angle increases, cooling magnitude increases and intensification rate decreases. The probability of rapid intensification for turning TCs is about one-third lower than that for straight-moving TCs. Consequently, TCs with smaller turning angles are more likely to develop into intense TCs. Operational forecast models underforecast turning angles of turning TCs and thus overforecast TC intensity with forecast errors increasing with turning angle. This study demonstrates that TC track-turning stages play a crucial role in modulating TC intensification via an oceanic pathway, highlighting that improving track turning forecast will contribute to enhancing TC intensity forecast accuracy.

The close causal link between internal waves (IWs) and IW-driven mixing highlights the importance of investigating IW spectra, especially since IW spectral features vary significantly under different dynamics. In this study, we comprehensively examine the three-dimensional structures of IW spectral levels and their associated features in the South China Sea (SCS), using conductivity-temperature-depth (CTD) and lowered acoustic Doppler current profiler (LADCP) measurements collected simultaneously. We find that the Luzon Strait has higher shear and strain spectral levels compared to the central SCS, but the opposite is true for the shear-to-strain ratio Rv. The shear spectral level shows a more significant increasing trend with depth than the strain spectral level. This results in elevated Rv values in the deep SCS, indicating a substantial presence of near-inertial IWs (NIWs) there, which are always accompanied by strain spectra featuring a pronounced high wavenumber peak and flatter displacement spectra. The analysis of a publicly available numerical simulation output further reveals two main regions of abundant deep-ocean NIWs in the SCS, namely, the region between 11 degrees and 15 degrees N and that around the Xisha Islands, mainly due to the parametric subharmonic instability of diurnal internal tides, wave-eddy interaction, and the breaking and dissipation of internal lee waves. Moreover, we obtain a relationship between Rv and the slope of displacement spectrum qj, Rv 5 100.83qj13.13, which offers novel insights for improving finescale parameterization based solely on strain. These results serve as an inspiration to explicitly link the IW behavior to the finescale parameterization in different regions globally.

Unlike the well-studied South China Sea (SCS) horizontal circulation, the vertical velocity in the SCS, especially in the deep water, is poorly understood. The vertical velocity connects the horizontal circulations at different depths and plays vital roles in modulating vertical material transport and biochemical processes. Using the ECCO4 product, we investigate the distribution of vertical velocities in the deep SCS, and explore the renewal process of the SCS deep water. The vertical velocities deeper than 2500 m all present similar spatial features: the downwelling originates near the Luzon Strait and spreads to the SCS basin interior, while the upwelling mainly takes place near the continental slope and forms an upwelling ring around the downwelling zone. This pattern becomes more and more significant with depth and is temporally stable. The upwelling near the continental slope is dominantly contributed by its diapycnal component, indicating a strong relation to local mixing. The nearbottom vertical velocity field shows a similar spatial-temporal pattern. This vertical velocity distribution suggests the deep-water overflow from the Luzon Strait is the main driving factor of the SCS deep water recycling. The Pacific deep water first sinks into the deep basin interior to supply the SCS deep water; then, it upwells along the slope and returns to the middle layer to accomplish the SCS deep water renewal. These findings not only improve our understanding of the three-dimensional circulation in the SCS, but also serve as an enlightenment for the uplifting of the deep and bottom waters in the open ocean.

Eddy diffusivity is usually estimated using the Osborn relation assuming a constant dissipation ratio of 0.2. In this study, we examine dissipation ratios and eddy diffusivities of turbulent mixing and salt finger mixing based on microstructure datasets. We find that the dissipation ratio of turbulence, ΓT, is highly variable with a median value clearly greater than 0.2, which shows strong seasonal variation and decreases slightly with depth in the western equatorial Pacific but obviously increases with depth in the midlatitude Atlantic. ΓT is jointly modulated by the Ozmidov scale to the Thorpe scale ratio ROT and the buoyancy Reynolds number Reb, namely ΓT∝ROT-4/3 ⋅ Reb1/2. The eddy diffusivity based on observed ΓT is larger than that estimated with 0.2 and presents a much stronger bottom enhancement. The eddy diffusivities of heat and salt for a salt finger are calculated using two “analogical” Osborn equations, and their corresponding “effective” dissipation ratios ΓθF and ΓSF are examined. ΓθF scatters over 2 orders of magnitude with a median value of 0.47 and is mostly linearly correlated with ΓSF as ΓSF≈ 5 ΓθF. The density flux ratio for a salt finger decreases sharply with a density ratio Rρ smaller than 2.4 but regrows to a larger value with Rρ exceeding 2.4. The salt-finger-induced eddy diffusivities also increase with depth, with some being comparable to even stronger ones than the mean turbulent ones. This study highlights the influences of variable dissipation ratios and different mixing types on eddy diffusivity estimates and should help the improvement of mixing estimate and parameterization.

We investigate the interaction between an anticyclonic eddy (AE) and semidiurnal internal tide (SIT) on the continental slope of the northeastern South China Sea (SCS), using a high spatiotemporal resolution numerical model. Two key findings are as follows: first, the AE promotes energy conversion from low-mode to higher-mode SIT. Additionally, production terms indicate that energy is also transferred from the SIT field to the eddy field at an average rate of 3.0 mW m−2 (accounting for 7 % of the incoming energy flux of SIT when integrated over the eddy diameter). Second, the AE can modify the spatial distribution of tidal-induced dissipation by refracting, scattering, and reflecting low-mode SIT. The phase and group velocities of the SIT are significantly influenced by the eddy field, resulting in a northward or southward shift in the internal tidal rays. These findings deepen our understanding of the complex interactions between AE and SIT, as well as their impacts on energy conversion, wave propagation, and coastal processes.

AbstractTropical Cyclones (TCs) are devastating natural disasters. Analyzing four decades of global TC data, here we find that among all global TC-active basins, the South China Sea (SCS) stands out as particularly difficult ocean for TCs to intensify, despite favorable atmosphere and ocean conditions. Over the SCS, TC intensification rate and its probability for a rapid intensification (intensification by ≥ 15.4 m s−1 day−1) are only 1/2 and 1/3, respectively, of those for the rest of the world ocean. Originating from complex interplays between astronomic tides and the SCS topography, gigantic ocean internal tides interact with TC-generated oceanic near-inertial waves and induce a strong ocean cooling effect, suppressing the TC intensification. Inclusion of this interaction between internal tides and TC in operational weather prediction systems is expected to improve forecast of TC intensity in the SCS and in other regions where strong internal tides are present.

The South China Sea (SCS) is abundant with complex multiscale dynamic processes but their spatiotemporal variations, generation and evolution mechanisms, and mutual interactions remain inadequately understood due to the lack of long-term in situ observations. To explore oceanic multiscale dynamics in the SCS, the SCS Mooring Array (SCSMA) was began to be constructed since 2009. The SCSMA consists of ∼40 moorings and is the largest in situ ocean observing system in marginal seas worldwide. The highest spatial resolution of SCSMA is ∼1.5 km, and the longest duration of fixed-location observations reaches ∼15 years. Long-term observations from the SCSMA have allowed significant advances in the understanding of large-scale circulation, mesoscale eddies, submesoscale processes, internal waves, turbulent mixing, and interactions and energy cascades of different processes. In particular, the full chain of forward energy cascade from large-scale currents to turbulence has been revealed. Different dynamic processes in the SCS constitute a three-dimensional multiscale circulation system which transports materials and tracers in a relay. Here, we first describe the SCSMA and its construction process, and then comprehensively review its relevant advances in multiscale dynamics. Prospects for the SCSMA and its future applications are given at the end.

Small-scale turbulent mixing supplies potential energy for the upwelling of deep waters in the abyssal ocean, a key component of the global overturning circulation. This process is particularly significant in critical regions such as the Northwestern Pacific where the upwelling structure of deep waters remains poorly understood due to limited knowledge of deep ocean mixing. Here, we investigate the full-depth spatiotemporal variability of turbulent mixing in the deep Northwestern Pacific based on hydrographic data collected over repeated surveys. Nineteen-year-average diapycnal diffusivity of 1.42 x 10-4 m2 s-1 is reveled in the deep Philippine Sea, indicating significantly stronger mixing compared to the stratified ocean interior. Spatially, turbulent mixing strengthens toward the bottom and intensifies westward from the open Pacific to the Philippine Sea due to rough topography. At certain mixing hotspots, enhanced mixing can penetrate up to 2,500 m above the bottom, suggesting a substantial potential for upwelling. Below 2,000 m, turbulent mixing exhibits pronounced seasonal variation that deep mixing is more intense in summer (winter) than in winter (summer) in the West Caroline Basin (the Parece Vela Basin). This spatially varying seasonality may be attributed to the inhomogeneous internal tidal energy dissipation in the Northwestern Pacific. Our study will serve to clarify the modulation of turbulent mixing to deep-water mass transformation and circulation in the Northwestern Pacific. The global overturning circulation plays an important role in transporting and redistributing climate-sensitive matters such as oxygen and carbon. This circulation is enclosed by the upwelling of deep waters facilitated by turbulence in the deep ocean, which mixes dense waters with the lighter waters above. In the Northwestern Pacific, a significant portion of deep waters from the Southern Ocean continuously intrudes into the Philippine Sea, rendering it a critical region for global circulation. However, the upwelling process of deep water remains largely unknown due to the limited understanding of turbulent mixing in the deep Northwestern Pacific. To fill this gap, we characterize the spatiotemporal distribution of turbulent mixing in the Northwestern Pacific based on long-term observations during 2004-2022. We reveal that turbulent mixing here is highly enhanced by rough topography, 10 to 100 times stronger than that in the open ocean, particularly near some key terrains such like Kyushu-Palau Ridge. Besides, a region-dependent seasonal variation of deep mixing is also observed. Our study contributes to a further understanding of the abyssal mixing and circulation in the Northwestern Pacific. A full-depth distribution of turbulent mixing in the Northwestern Pacific is obtained based on 19-year repeated hydrographic observations Rough topography in the Philippine Sea enhances the deep mixing, with diffusivities even up to O (10-2) m2s-1 near the bottom Latitude dependent seasonality of deep ocean turbulent mixing is revealed, which could be related to spatial variations of internal tides

Abstract A significant portion (∼2.1 Sv, 1 Sv = 106 m3 s−1) of deep water penetrates into the Philippine Sea through the Yap‐Mariana Junction, the sole passage of the Philippine Sea below 4,000 m, and is then upwelled into shallower layers, closing regional overturning circulation. Yet, the structure and variability of this diapycnal upwelling remain poorly understood. Here, we report on a fine‐resolution hydrographic observation conducted at the most significant topographic feature in the Philippine Sea, the Kyushu‐Palau Ridge (KPR). Enhanced mixing up to O(10−2) m2 s−1 near the KPR is manifested, indicating the presence of substantial upwelling herein. Besides, the ridge‐related topography contributes more deep‐water mass transformation than abyssal basins in the Philippine Sea. This study highlights the significant role of rough bathymetry features in generating diapycnal upwelling in the North Pacific.

Internal waves close to the seafloor of abyssal oceans are the key energy suppliers driving near-bottom mixing and the upwelling branches of meridional overturning circulation, but their spatiotemporal variability and intrinsic mechanisms remain largely unclear. In this study, measurements from 10 long-term moorings were used to investigate the internal wave activities in the abyssal South China Sea, which is an important upwelling zone. Strong near-inertial internal waves (NIWs) with current velocity pulses exceeding 5 cm s(-1) were observed to dominate the near-bottom internal wave field at approximately 14 degrees N. These abyssal NIWs were phase-coupled with diurnal internal tides (D-1), and both displayed common seasonal variations that were larger in winter and summer, providing evidence of diurnal parametric subharmonic instability (PSI) near its critical latitudes (CLs). Emitted from the bottom, near-inertial kinetic energy rapidly decreased by one order of magnitude from depths of similar to 120 to similar to 620 m above the bottom. Near rough topographies, the abyssal PSI was shifted poleward to approximately 14.8 degrees N by negative relative vorticities of passing anticyclonic eddies or topographic Rossby waves. Compared with flat topography, PSI near rough topography was significantly promoted by topographic-localized strong D-1 with high-mode structures, creating abyssal NIW bursts. Bottom-reaching shipboard conductivity-temperature-depth profiles revealed that the bottom mixed layers became much thicker when approaching CLs, suggesting that abyssal PSI potentially accelerates the ventilation and upwelling of bottom water. The observational results presented here illustrate notable spatiotemporal variations in abyssal NIWs regulated by PSI and call for consideration of PSI to better understand near-bottom mixing and upwelling.

Data on manuscript entitled "Diapycnal Upwelling over the Kyushu-Palau Ridge in the North Pacific Ocean" in Matlab format. Details about the variables in the mat files are described in Readme.txt.

This study focuses on the statistical features of dissipation flux coefficient gamma in the upper South China Sea (SCS). Based on the microscale measurements collected at 158 stations in the upper SCS and derived dissipation rates of turbulent kinetic energy and temperature variance epsilon and x(T) , via a modified method, we estimate gamma and analyze its spatiotemporal variation in an energetic and a quiescent region. We show that gamma is highly variable, which scatters over three orders of magnitude from 10(-21) to 10(1) in both regions. In the energetic region, gamma is slightly greater than in the quiescent region; their median values are 0.23 and 0.17, respectively. Vertically, gamma presents a clear increasing tendency with depth in both regions, though the increasing rate is greater in the energetic region than in the quiescent region. In the upper SCS, gamma positively depends on the buoyancy Reynolds number Reb and negatively depends on the ratio of the Ozmidov scale to the Thorpe scale R-OT and is scaled as gamma alpha Re-b(1/2) R-OT(-4/3) , which holds for both regions. The vertical decreasing of R-OT is observed, which yields parameterization of R-OT = 10(-0.002z) this parameterization improves the performance of the Thorpe scale method by reducing at least 50% of the bias between the observed and parameterized epsilon. These results shed new light on the spatiotemporal variability and modulating mechanism of gamma in the upper ocean.

Clarifying contributions to the surface mixed layer (SML) dissipation from dynamic processes including winds, waves, buoyancy forcing and submesoscales is of significance for quantifying exchanges between the atmosphere and the ocean. Based on two observation sections across an anticyclonic eddy in the South China Sea, the contributions from different dynamic processes to the SML dissipation rate of turbulence are quantified. The potential vorticity indicates instability events including symmetric instability (SI), gravitational instability and centrifugal instability at the eddy. Despite of a dominant role of wind‐ and wave‐induced dissipation rates, SI is highlighted by a mean estimated depth‐integrated dissipation rate of 4.3 × 10−6 W m kg−1 with a maximum up to 3.2 × 10−5 W m kg−1. The SI dissipation is believed to play a role in the eddy kinetic energy budget by extracting energy from the vertical geostrophic shear at the eddy.

When the bottom current flows over a small-scale topographic feature (with characteristic horizontal scale of 0.1-10.0 km), it generates internal lee waves. These lee waves furnish the energy cascade from mesoscale to dissipative scale, resulting in enhanced turbulent mixing. The existing lee wave theory and parameterization are mostly based on uniform background flow. We improve the linear lee wave theory by considering shear background flow and viscous and diffusive effects, which are ubiquitous in the ocean. In particular, the introduction of vertical viscous and diffusive terms effectively improves the problem of critical layer (where the wave frequency is close to the Coriolis frequency) for linear lee waves under weakly dissipative limit. Then, the influences of different types of shear flow on the frequency, vertical wavelength, group velocity, energy flux, energy density, energy dissipation and irreversible mixing of lee waves are explored through both theory and numerical simulation. A bottom-up decreasing background flow can enhance energy dissipation and irreversible mixing below the critical layer. However, in the real ocean, the dissipation and mixing caused by a decreasing background flow may be weaker than that caused by an increasing background flow in a depth integrated sense, especially when considering a bounded domain. Additionally, the theory of wave action conservation in the absence of dissipation, which is commonly used as a criterion in research of internal waves propagating in varying background fields, is extended to a "modified" wave action equation considering dissipation, which may potentially improve the lee wave parameterization in the future.

Instability within internal solitary waves (ISWs), featured by temperature inversions with vertical lengths of dozens of meters and current reversals in the upper shoreward velocity layer, was observed in the northern South China Sea at a water depth of 982 m by using mooring measurements between June 2017 and May 2018. Regions of shear instability satisfying Ri < 1/4 were found within those unstable ISWs, and some large ISWs were even possibly in the breaking state, indicated by the ratio of L-x (wave width satisfying Ri < 1/4) to lambda(eta/2) (wavelength at half amplitude) larger than 0.86. Wave stability analyses revealed that the observed wave shear instability was induced by strong background current shear associated with multiscale dynamic processes, which greatly strengthened wave shear by introducing sharp perturbations to the fine-scale vertical structures of ISWs. During the observational period, wave shear instability was strong in summer (July-September) while weak in winter (January-March). Sensitivity experiments revealed that the observed shear instability was prone to be triggered within large ISWs by the background current shear and sensitive to the pycnocline depth in the background stratification. However, shear instability within ISWs was observed to be promoted during mid-January, as the near-inertial waves trapped inside an anticyclonic eddy resulted in enhanced background current shear between 150 and 300 m. This work emphasizes the notable impacts of multiscale background processes on ISWs in the oceans.

Turbulent mixing above rough topography is crucial for the vertical motions of deep water and the closure of the meridional overturning circulation. Related to prominent topographic features, turbulent mixing not only exhibits a bottom-intensified vertical structure but also displays substantial lateral variation. How turbulent mixing varies in the upslope direction and its impact on the upwelling of deep water over sloping topography remains poorly understood. In this study, the notable multihump structure of the bottom-intensified turbulent diffusivity in the upslope direction of a seamount in the South China Sea (SCS) is revealed by full-depth fine-resolution microstructure and hydrographic profiles. Numerical experiments indicate that multihump bottom-intensified turbulent mixing around a seamount could lead to multiple cells of locally strengthened circulations consisting of upwelling (downwelling) motions in (above) the bottom boundary layer (BBL) that are induced by bottom convergence (divergence) of the turbulent buoyancy flux. Accompanied by cyclonic (anticyclonic) flow, a three-dimensional spiral circulation manifests around the seamount topography. These findings regarding the turbulent mixing and three-dimensional circulation around a deep seamount provide support for the further interpretation of the abyssal meridional overturning circulation.