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A 3‐km resolution regional ocean model is used to investigate the role of wind‐driven coastal circulation and mesoscale variability on the inter‐annual variability of transport success in the southern Benguela between Cape Point (34°S) and St Helena Bay (32°S) from 1992 to 2011. Lagrangian particles are released within the top 100 m of the water column along an across‐shore transect off Cape Point. Transport success is given by the ratio of the number of particles that reach St Helena Bay over the total number of particles released. The analysis of transport success anomalies and their relationship with the local circulation and wind forcing reveal that there is no single driver of the inter‐annual variability. The transport success variability of particles released on the shelf (depths <300 m) mainly depends on their capacity to remain embedded within the coastal Benguela Jet. Nevertheless, peaks in offshore Ekman transport and episodic occurrence of a poleward inner‐shelf counter‐current contribute to negative anomalies. For particles released on the outer shelf edge (depths >500 m), across‐shore transports induced by mesoscale eddies are the main contributors to transport success variability. Rare passage of Agulhas rings near the shelf edge can induce strong offshore advection of particles into the open ocean. In contrast, shelf‐edge cyclonic eddies favor the onshore transport of particles originating from the outer shelf edge and thus contribute to increasing transport success. Plain Language Summary: This study investigates the inter‐annual variation of Lagrangian transport in the southern Benguela Current upwelling system using a high‐resolution regional ocean model and particle tracking experiments. Transport of fish eggs and larvae by upper ocean currents is crucial for the marine ecosystem in this highly productive region since the spawning and nursery areas used by anchovies are separated by large distances (∼400 km). The alongshore connectivity between the Cape Peninsula and St Helena Bay from 1992 to 2011 is analyzed and linked to the regional ocean circulation and wind‐forcing on an inter‐annual time scale. We find that transport success is influenced by several drivers including the Benguela Jet, Ekman transport, the coastal inner‐shelf poleward counter‐current, and occasional interactions with eddies such as Agulhas rings and shelf‐edge cyclonic eddies. These findings provide a valuable information for future studies on the role of the physical drivers that impact the transport of larvae and eggs in the southern Benguela, underlining that no single driver can account solely for extreme positive or negative events in transport success. Key Points: There are multiple physical drivers of the interannual variability of along‐shore transport success in the southern Benguela upwellingPositive anomalies of transport success are associated with a strong Benguela Jet, reduced offshore and southward transportNegative anomalies are associated with enhanced offshore and southward particles transport, and anticyclonic eddies [ABSTRACT FROM AUTHOR]

The Weddell Sea is of global importance in the formation of dense bottom waters associated with sea ice formation and ocean‐ice sheet interaction occurring on the shelf areas. In this context, the Weddell Sea boundary current system (BCS) presents a major conduit for transporting relatively warm water to the Weddell Sea ice shelves and for exporting some modified form of Wedell Sea deep and bottom waters into the open ocean. This study investigates the downstream evolution of the structure and the seasonality of the BCS along the Weddell Sea continental slope, combining ocean data collected for the past two decades at three study locations. The interannual‐mean geostrophic flow, which follows planetary potential vorticity contours, shifts from being surface intensified to bottom intensified along stream. The shift occurs due to the densification of water masses and the decreasing surface stress that occurs westward, toward the Antarctic Peninsula. A coherent along‐slope seasonal acceleration of the barotropic flow exists, with maximum speed in austral autumn and minimum speed in austral summer. The barotropic flow significantly contributes to the seasonal variability in bottom velocity along the tip of the Antarctic Peninsula. Our analysis suggests that the winds on the eastern/northeastern side of the gyre determines the seasonal acceleration of the barotropic flow. In turn, they might control the export of Weddell Sea Bottom Water on seasonal time scales. The processes controlling the baroclinic seasonality of the flow need further investigation.Plain Language Summary: In the Weddell Sea, large amounts of seawater are cooled to become dense and sink, carrying signals of human‐induced changes such as atmospheric carbon into the abyss of the ocean. Understanding the variability of the ocean currents at the Antarctic continental margin is critical because it controls both the export of the dense water formed in these areas and the access of warm water that may melt the Antarctic ice sheet. This study investigates the structure and the seasonality of the flow at the continental margin in the Atlantic sector of the Southern Ocean, using in situ observations upstream and downstream of the dense water formation regions. Following the bathymetry, ocean currents flow from East to West along the continental shelf edge. As water densifies along this path, the flow speed changes from being maximum at the ocean surface to be maximum at the bottom. The depth‐averaged current varies with a synchronized seasonality along the continental shelf break, reaching a maximum in austral autumn. Our analysis suggests that the winds on the eastern/northeastern margin drives the seasonality of the depth‐averaged flow along the shelf break, significantly contributing to changes in bottom velocity near the export region.Key Points: The coherent seasonal acceleration of the barotropic flow significantly contributes to the seasonal variability in dense water outflowThe seasonal flow strength is in phase with the intensification of the surface stress upstream of the dense water formation regionOur results suggest a teleconnection to exist between the eastern/northeastern Weddell Sea winds and the barotropic flow [ABSTRACT FROM AUTHOR]

The land‐sea breeze is resonant with the inertial response of the ocean at the critical latitude of 30°N/S. 1‐D vertical numerical experiments were undertaken to study the key drivers of enhanced diapycnal mixing in coastal upwelling systems driven by diurnal‐inertial resonance near the critical latitude. The effect of the land boundary was implicitly included in the model through the "Craig approximation" for first‐order cross‐shore surface elevation gradient response. The model indicates that for shallow water depths (<∼100 m), bottom shear stresses must be accounted for in the formulation of the "Craig approximation," as they serve to enhance the cross‐shore surface elevation gradient response, while reducing shear and mixing at the thermocline. The model was able to predict the observed temperature and current features during an upwelling/mixing event in 60 m water depth in St Helena Bay (∼32.5°S, southern Benguela), indicating that the locally forced response to the land‐sea breeze is a key driver of diapycnal mixing over the event. Alignment of the subinertial Ekman transport with the surface inertial oscillation produces shear spikes at the diurnal‐inertial frequency; however their impact on mixing is secondary when compared with the diurnal‐inertial resonance phenomenon. The amplitude of the diurnal anticyclonic rotary component of the wind stress represents a good diagnostic for the prediction of diapycnal mixing due to diurnal‐inertial resonance. The local enhancement of this quantity over St Helena Bay provides strong evidence for the importance of the land‐sea breeze in contributing to primary production in this region through nutrient enrichment of the surface layer. Plain Language Summary: Winds near the coast often have a daily cycle known as the land‐sea breeze. Near latitudes of 30°N/S ubiquitous rotating ocean currents also have a daily frequency and therefore become enhanced by daily winds at these latitudes. The ocean currents result in vertical mixing of subsurface and surface water layers, bringing subsurface nutrients to the surface where they stimulate phytoplankton growth. In this study we use a simple model of the ocean (composed of the vertical dimension only) to study the key drivers of vertical mixing due to the land‐sea breeze. We show how vertical mixing is reduced in shallow water (<∼100 m) near the coast, where currents are slowed down by friction at the seabed. We find that vertical mixing can be predicted by a parameter computed from wind speed and direction over time. This parameter is shown to be enhanced over St Helena Bay on the west coast of South Africa, where phytoplankton blooms are known to be particularly prevalent. The results suggest that the land‐sea breeze is likely to be an important contributor to phytoplankton bloom development in this region. Similar processes are likely to be at play in other coastal regions. Key Points: Land‐sea breeze driven vertical mixing is studied using a 1‐D model including the land boundary effectThe land boundary effect dampens vertical mixing, particularly when bottom friction is nonnegligibleThe diurnal anticyclonic rotary component of the wind stress provides a diagnostic for diapycnal mixing [ABSTRACT FROM AUTHOR]

This study applied a previously used Lagrangian individual‐based model (IBM) for sardine in the Southern Benguela to an improved and more robust hydrodynamic model to investigate whether a more representative spatial coverage, greater horizontal and vertical resolution, more realistic winds and improved representation of mesoscale features such as eddies and filaments would give different results for transport and retention of early life stages. Despite major differences between the old and new hydrodynamic models, overall the IBM results were quite similar to the previous southern Benguela sardine IBM study. This surprising result indicates that it is the macroscale circulation features resolved by the two hydrodynamic models that are controlling transport and retention of sardine early life stages. The contribution of transient mesoscale features such as eddies and filaments appears to be less important when transport patterns are averaged over the 21‐year‐long experiment. Another aim of this study was to better estimate the contribution of south coast spawning to west coast sardine recruitment. This was possible because of an eastward extension of the geographical domain of the new hydrodynamic model which provided a more realistic representation of the south coast spawning ground. Three main spawning and nursery area systems, similar to those identified in the previous sardine IBM, were identified: west coast and west coast (WC‐WC), south coast and west coast (SC‐WC), and south coast and south coast (SC‐SC). Spawning area proved to be an important determinant of modelled retention and transport success, with spawning depth also playing an important role on the west coast. The main difference observed from the previous study was an increase in the average percentage of particles released on the south coast and transported to the west coast (P0, 17.4%). This indicates more connectivity between the southern and western sardine stocks than previously thought and is therefore important for fishery management. Standardized anomalies from the modelled retention/transport were compared with recruitment estimates from stock assessment models but there was no correlation between the two sets of anomalies. However, a significant correlation was observed between the modelled retention/transport anomalies for the west coast and total cumulative upwelling anomalies for the Southern Benguela (r = −0.67, p <.001). [ABSTRACT FROM AUTHOR]

The effect of ocean currents on fish eggs and larvae during their journey from spawning to nursery grounds in the Southern Benguela upwelling system is poorly understood. The survival and successful transport of fish eggs and larvae results from complex biological and physical processes. This study focuses on the advective processes, more specifically on how the dynamics and characteristics of the ocean currents shape the Lagrangian pathways in the Southern Benguela. A mesoscale eddy resolving interannual (1989–2010) simulation of the region, with a horizontal resolution of 7.5 km, is used to study processes impacting the connectivity between the western edge of the Agulhas Bank and the west coast upwelling region. A set of Lagrangian experiments are conducted with particles being released within the top 100 m of the water column along an across-shore transect off Cape Point (34∘ S). Transport success is given by the ratio of the number of particles that reach St Helena Bay (32∘ S) over the total number of particles released. The model results show a strong seasonal cycle in transport success which is governed by the complex three-dimensional structure of the along-shore jets, their variability, together with the wind-induced Ekman drift. Transport success is most efficient in spring when the Benguela Jet consists of one coherent intensified single-core branch that flows over the 300 m isobath, and when wind-induced Ekman transport favours the retention of particles within the jet. At this time of the year, the pathway leading to successful transport is located inshore, with 90% of particles released inshore the 300 m isobath being successfully transported to St Helena Bay in <15 days. This pathway is also characterized by low eddy kinetic energy values. During the upwelling season (December–March), transport success becomes less efficient, and less sensitive to the initial across-shore position of the particles. The inshore route no longer dominates, as the majority of particles follow offshore pathways. The Benguela Jet shifts offshore and splits into several branches due to the shoaling of the poleward undercurrent. The entrainment of particles within the offshore branch of the jet is favored by the dominating offshore wind-induced Ekman transport. Particles trapped in the offshore branch get exposed to higher mesoscale variability. Their northward progression is slower, which leads to journeys generally exceeding 20 days. This study shows that successful transport from the Agulhas Bank to the west coast upwelling region cannot be attributed to only a simple wind induced modulation of the jet. It explores how the seasonal modulation of the Benguela Jet, poleward undercurrent and offshore Ekman transport combine together with the turbulent off-shelf eddy field to set-up the characteristics of transport success. • Fish larvae pathways in the Southern Benguela Upwelling System • A 300 miles along shore fast route for fish larvae in the Southern Benguela • Lagrangian pathways in the Southern Benguela Upwelling System [ABSTRACT FROM AUTHOR]

When a source-sink dipole forces a fluid on a-plane limited by a western boundary, the linear steady solution can be obtained analytically and consists of zonally elongated gyres that extend west of the forcing and close as western boundary currents. The nondimensional parameter(withthe zonal velocity of the flow andthe distance between the source and sink) is used to characterize the nonlinearity of the flow. Whenreaches 0.1, the numerical shallow-water solution shows that the configuration with the source to the north of the sink becomes unstable, while the reverse configuration remains steady. Indeed, that reverse configuration remains steady for much larger values of the nonlinearity parameter, and begins to share some of the characteristics of a pure inertial circulation. The asymmetry of the stability properties of the two configurations, also found in the laboratory experiments of Colin de Verdière [Quasigeostrophic flows and turbulence in a rotating homogeneous fluid, 1977], is rationalized herein through the stability properties of the zonal central jet that flows between the source and sink. We consider, in turn, (i) the Kuo’s [J. Meteor.1949,6, 105–122] zero potential vorticity gradient necessary criteria (valid for an infinite zonal jet), (ii) enstrophy budgets and (iii) linear stability analysis of the mean flow. All three methods point out to the enhanced instability of the westward jet. We show that the transition regime has the characteristics of a super critical Hopf bifurcation. [ABSTRACT FROM PUBLISHER]

This study deals with the separation of western boundary currents within a reduced-gravity framework, and it analyzes the formation of eddies in the separation region and the conditions of their shedding into the open ocean. It shows that the separation point of the current oscillates along the coast so that the retroflected eastward current develops meanders. These meanders grow, drift westward under the influence of β, and finally hit the coastal current, which leads to the periodic formation of eddies. This study also highlights the impact by the geometrical configurations of the flow and coastline upon the existence or lack of a subsequent shedding of these eddies: a shedding occurs when no obstacle hinders the β-induced westward drift of the eddies. This happens when either (i) the current retroflects far enough beyond the tip of the coast so that, because of β, the eddies can propagate westward without being blocked, or (ii) the tilt of the coast is small enough so that the alongshore component of the β-induced velocity is enhanced and the eddies can escape from the retroflection region. [ABSTRACT FROM AUTHOR]

This paper investigates the behavior of a surface-intensified anticyclone encountering a seamount on the β plane in a stratified ocean. The eddy may be strongly eroded, and sometimes subdivided, provided that it gets close enough to the seamount. In case of subdivision, the detached part has a vertical structure different from that of the initial eddy, and a subsurface vortex may result. The basic erosion mechanism previously observed with f-plane experiments is still active on the β plane. Deep fluid motions induced by the initial vortex across the isobaths generate topographic vortices whose upper parts exert a shear/strain on the initial eddy, causing its filamentation. On the β plane, this process is further complicated by the presence of additional eddies created by fluid motion across the planetary vorticity gradient. Experiments without any topography show that these eddies by themselves can erode the initial vortex. In particular, a deep positive potential vorticity pole influences the near-bottom signature of the original vortex with a strong temporal variability. This reflects on the manner in which the surface eddy feels an underlying seamount. Sensitivity experiments show that the eddy erosion rate after encountering a seamount can no longer be related to basic parameters such as the minimum eddy–seamount distance, as it was on the f plane. The additional vorticity poles influencing the eddy on the β plane make the result of the eddy–seamount encounter very sensitive to small variations of the initial conditions, and impossible to predict. [ABSTRACT FROM AUTHOR]

The possibility for a preexisting surface-intensified anticyclone to subduct beneath a surface front is investigated using an isopycnal numerical model. Subduction occurs for strong coherent vortices and is usually accompanied by strong dissipation. Two main mechanisms cause the erosion of the vortex core. The first one is induced by the velocity shear associated with the front. It results in the peeling of the vortex potential vorticity (PV) core, sometimes leading to its complete disappearance. The second mechanism occurs after the vortex has subducted. Entrainment of high positive PV fluid parcels from the front above the vortex low negative PV core modifies the stability properties of the latter. Meanders are observed to grow at the rim of the structure, which favors the formation of PV filaments. The erosion rates caused by each mechanism are discussed in relation to the jet and vortex characteristics, and to the background stratification. The trapping of high PV fluid parcels above the vortex is also shown to be partly responsible for the decrease and eventual loss of the eddy altimetric signal, after it has subducted. [ABSTRACT FROM AUTHOR]

Numerical experiments are carried out on the f plane, using a shallow-water isopycnal model, to analyze the behavior of a surface-intensified anticyclonic vortex when it encounters an isolated seamount. The advection by the vortex of deep fluid parcels across the isobaths is known to generate deep anticyclonic and cyclonic circulations above and near the bathymetry, respectively. These circulations are shown to exert a strong shear on the upper layers, which causes an erosion of the initial vortex by filamentation. The erosion often results in a subdivision of the eddy. While the eroded original structure forms a dipole with the deep cyclone and is advected away, the filaments torn off from the original core aggregate into a new eddy above the seamount. Splitting in more than two structures is sometimes observed. The erosion process is quantified by the bulk volume integral of the eddy potential vorticity anomaly. A sensitivity study to different parameters of the configuration (distance between vortex and seamount, vortex radius, seamount radius, seamount height, or stratification) shows that the intensities of the deep anticyclonic and cyclonic circulations and the vortex erosion are governed both by the reservoir of positive potential vorticity associated with the seamount and by the strength of the cross-isobath flow induced by the eddy. [ABSTRACT FROM AUTHOR]

More than twelve satellite scatterometers have operated since 1992 through the present, providing the main source of surface wind vector observations over global oceans. In this study, these scatterometer winds are used in combination with radiometers and synthetic aperture radars (SAR) for the better determination and characterization of high spatial and temporal resolution of regional surface wind parameters, including wind speed and direction, wind stress components, wind stress curl, and divergence. In this paper, a 27-year-long (1992–2018) 6-h satellite wind analysis with a spatial resolution of 0.125° in latitude and longitude is calculated using spatial structure functions derived from high-resolution SAR data. The main objective is to improve regional winds over three major upwelling regions (the Canary, Benguela, and California regions) through the use of accurate and homogenized wind observations and region-specific spatial and temporal wind variation structure functions derived from buoy and SAR data. The long time series of satellite wind analysis over the California upwelling, where a significant number of moorings is available, are used for assessing the accuracy of the analysis. The latter is close to scatterometer wind retrieval accuracy. This assessment shows that the root mean square difference between collocated 6-h satellite wind analysis and buoys is lower than 1.50 and 1.80 m s−1 for offshore and nearshore locations, respectively. The temporal correlation between buoy and satellite analysis winds exceeds 0.90. The analysis accuracy is lower for 1992–1999 when satellite winds were mostly retrieved from ERS-1 and/or ERS-2 scatterometers. To further assess the improvement brought by this new wind analysis, its data and data from three independent products (ERA5, CMEMS, and CCMP) are compared with purely scatterometer winds over the Canary and Benguela regions. Even though the four products are generally similar, the new satellite analysis shows significant improvements, particularly in the upwelling areas. [ABSTRACT FROM AUTHOR]

Based on satellite and in situ data, the dynamic characteristics and vertical structure of a surface intensified mesoscale eddy dipole recently expelled from the South East Madagascar Current (SEMC) is described for the first time. The dipole was surveyed 250 nautical miles south of Madagascar between 14 and 23 November 2016, during west-east and south-north transects carried out over the northern Madagascar Ridge. The dipole consisted of two counter-rotating vortices of similar size (100 km) and intensity (0.7 f), and an intense southwestward jet (150 cm s-1) in the frontal region between the two eddies. The cyclonic eddy was lying on the western side of the anticyclonic eddy. With azimuthal velocities reaching 100 cm s-1 at the surface and decreasing slowly with depth (40 cm s-1 at -600 m), this dipole was defined as a highly non-linear (Ro ~ 0.7) isolated eddy-type structure (c β ~ 11 cm s–1 and U / c β ~ 0.7) capable of trapping and advecting water masses over large distances. The enhanced concentration of chlorophyll- a found in the cyclone relative to the anticyclone could be tracked back to the spin-up phase of the two eddies and attributed to eddy-pumping. The eddy cores were located above the pycnocline (1026.4 kg m-3), within the upper 600 m, and consisted of varieties of Subtropical Underwater (STUW) found within the SEMC. The STUW found in the anticyclone was more saline and oxygenated than in the cyclone, highlighting mixing with the inshore shelf waters from the southeastern coastal upwelling cell off Madagascar. Observations suggest that the dipole interacted strongly with the chaotic bathymetry of the region, characterized by a group of five seamounts lying between -240 m and -1200 m. The bathymetry blocked its westward advection, trapping it in the vicinity of one shallow seamount for more than 4 weeks, so enhancing the role of the eddy-induced velocities in stirring the surrounding water masses. Squeezed between the southern Madagascan shelf and the northern flank of the anticyclone, two filament-like dynamic features with very different water-mass properties could be observed on the south-north transect: i) one filament highly concentrated in chlorophyll- a demonstrating the capacity of the eddy to export shelf water offshore; ii) intrusions of southern-type STUW generally found south of the South Indian Counter Current (SICC) recirculating on the external flanks of the anticyclone. Although the observed circulation and hydrography were largely constrained by the presence of the mesoscale eddy dipole, unmistakable fine-scale dynamics were also observed in the vicinity of the MAD-Ridge seamount, superimposed onto the mesoscale eddy flow. [ABSTRACT FROM AUTHOR]

Surface winds (equivalent neutral wind velocities at 10 m) from scatterometer missions since 1992 have been used to build up a 20-year climate series. Optimal interpolation and kriging methods have been applied to continuously provide surface wind speed and direction estimates over the global ocean on a regular grid in space and time. The use of other data sources such as radiometer data (SSM/I) and atmospheric wind reanalyses (ERA-Interim) has allowed building a blended product available at 1/4° spatial resolution and every 6 h from 1992 to 2012. Sampling issues throughout the different missions (ERS-1, ERS-2, QuikSCAT, and ASCAT) and their possible impact on the homogeneity of the gridded product are discussed. In addition, we assess carefully the quality of the blended product in the absence of scatterometer data (1992 to 1999). Data selection experiments show that the description of the surface wind is significantly improved by including the scatterometer winds. The blended winds compare well with buoy winds (1992–2012) and they resolve finer spatial scales than atmospheric reanalyses, which make them suitable for studying air-sea interactions at mesoscale. The seasonal cycle and interannual variability of the product compare well with other long-term wind analyses. The product is used to calculate 20-year trends in wind speed, as well as in zonal and meridional wind components. These trends show an important asymmetry between the southern and northern hemispheres, which may be an important issue for climate studies. [ABSTRACT FROM AUTHOR]

This work is part of the MADRidge Project special issue which aims to describe pelagic ecosystems in the vicinity of three prominent shallow seamounts in the South West Indian Ocean: one here named MAD-Ridge (240 m below the surface) plus Walters Shoal (18 m) on the Madagascar Ridge, and La Pérouse (60 m) on the abyssal plain east of Madagascar. The three span latitudes 20°S and 33°S, some 1500 km. The study provides the background oceanography for the once-off, multidisciplinary snapshot cruise studies around the seamounts. As life on seamounts is determined by factors such as summit depth, proximity to the light layers of the ocean, and the ambient circulation, a first description of regional spatial-field climatologies (16–22 years) and monthly along-ridge gradients of surface wind (driving force), water column properties of sea surface temperature, mixed layer depth, chlorophyll- a and eddy kinetic energy, plus ocean currents is provided. Being relevant to many applications in the study domain, these properties in particular reveal contrasting environments along the Madagascar Ridge and between the three seamounts that should drive biological differences. Relative to the other two seamounts, MAD-Ridge is in the more extreme situation, being at the end of the East Madagascar Current, where it experiences sturdy, albeit variable, currents and the frequent passing of mesoscale eddies. [ABSTRACT FROM AUTHOR]

An investigation of the vertical and horizontal distributions of micronekton, as influenced by mesoscale eddies, the Madagascar shelf and shallow seamounts, was undertaken using acoustic data collected during two research cruises at an unnamed pinnacle (summit depth ~240 m) thereafter named "MAD-Ridge", and at La Pérouse seamount (~60 m) in the south-western Indian Ocean. MAD-Ridge is located to the south of Madagascar, in an "eddy corridor", known both for its high mesoscale activity and high primary productivity. In contrast, La Pérouse is located on the outskirts of the Indian South Subtropical Gyre (ISSG) province, characterised by low mesoscale activity and low primary productivity. During the MAD-Ridge cruise, a dipole was located in the vicinity of the seamount, with the anticyclone being almost stationary on the pinnacle. Total micronekton acoustic densities were greater at MAD-Ridge than at La Pérouse. Micronekton acoustic densities of the total water column were lower within the anticyclone than within the cyclone during MAD-Ridge. Micronekton followed the usual diel vertical migration (DVM) pattern, except within the cyclone during MAD-Ridge where greater acoustic densities were recorded in the daytime surface layer. The backscatter intensities were stronger at the 38 kHz than at the 70 and 120 kHz frequencies in the daytime surface layer at MAD-Ridge cyclonic stations. These backscatter intensities likely correspond to gas-filled swimbladders of epi- and mesopelagic fish actively swimming and feeding within the cyclone or gelatinous organisms with gas inclusions. Our findings evidenced that the distributions of micronekton and DVM patterns are complex and are influenced significantly by physical processes within mesoscale eddies. The mesoscale eddies' effects were dominant over any potential seamount effects at the highly dynamic environment prevailing at MAD-Ridge during the cruise. No significant increase in total micronekton acoustic densities was observed over either seamount, but dense aggregations of biological scatterers were observed on their summits during both day and night. [ABSTRACT FROM AUTHOR]