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International audience; We report current meter measurements obtained by four moorings deployed across the Malvinas Current (MC) at 44.7ºS during 18 months between December 2015-June 2017. Previous measurements of the MC strength have been reported only close to the Brazil-Malvinas Confluence, hindering the interpretation of the flow variability. The record-length time averaged velocities and variance ellipses indicate a strong northward along-isobath flow with an equivalent-barotropic structure. The meridional velocities at the western and eastern moorings are not correlated and show large amplitude oscillations which are coherent with the passage of mesoscale features over the moorings. Satellite altimetry data, that are highly correlated with 20-day low-pass filtered in situ velocities (r~0.80), show that the MC variability is affected by the propagation of sea level anomalies (SLA) along the Patagonian slope with phase speeds that range between 0.21 ± 0.04 m s-1 and 0.14 ± 0.01 m s-1. SLAs propagate northward along the slope following contours of constant potential vorticity and its phase speeds decrease towards the east across the slope. SLAs that mostly affect the western mooring originate in the northern flank of the North Scotia Ridge while SLAs that mostly affect the eastern mooring originate along the Malvinas Escarpment, along the northern edge of the Malvinas Plateau. We suggest that the interaction between eddies and the complex bathymetry at those locations generate instabilities that enhance the generation of mesoscale structures that propagate in the flow direction along the western boundary of the Argentine Basin affecting the variability of the MC velocities.

The quantification of baseflow is key for water resources management. However, there are few reports on the precision and accuracy in low streamflow measurements. In this paper, we systematically analyze the precision and accuracy of dilution streamflow measurements in headwater channels during baseflow. Precision refers to the variability of the values for repeated measurements and accuracy is how much the measured value approximates the reference one. We measured streamflow in 31 different cross-sections with contributing areas ranging from 0.02 to 5.33 km2. Streamflow measurements with the current meter were adopted as reference for accuracy estimation. A precision error of ±5.0% was found for the measurements. The percent errors compared to reference streamflow ranged from 0.7 to 45.6%, with a median of 6.1%. Precision and accuracy are in the same order of magnitude found in the literature for larger streams. These results can be used for constraining the uncertainty of streamflow measurements and rainfall-runoff modeling of headwater streams.

This study uses global numerical model results of ocean and atmospheric circulation, as well as local wind, wave and current meter data, to investigate the structure of the ocean and coastal circulation potentially associated with the transport of oil that affected thousands of kilometers of the Brazilian coast in 2019. Our analysis suggests the oil was brought close to the continental shelf sometime in August 2019 by the southern branch of South Equatorial Current, and was initially advected towards the north by the North Brazilian Current and shelf currents pushed by SE winds. The onset of negative along-shore winds close to the coast in September–October 2019 turned the coastal along-shore drift south, a situation that persisted throughout the spring and summer seasons. Along the east coast, where observational data was available, landward cross-shelf flows below 17 m of depth, associated with coastal upwelling conditions, advected the oil from the slope onto the outer and mid-shelf. On the inner-shelf the oil was finally pushed towards the beaches by the wave action close to the bottom. Reports of oil arriving on the east coast followed changes in coastal wind and current patterns very closely. It is suggested that before reaching the shelf, the oil drifted at depths larger than 17 m, perhaps reaching several tens of meters.

The removal of the Elwha and Glines Canyon dams from the Elwha River in Washington, USA, resulted in the erosion and transport of over 10 million m 3 of sediment from the former reservoirs and into the river during the first two years of the dam removal process. Approximately 90% of this sediment was transported through the Elwha River and to the coast at the Strait of Juan de Fuca. To evaluate the benthic dynamics of increased sediment loading to the nearshore, we deployed a tripod system in ten meters of water to the east of the Elwha River mouth that included a profiling current meter and a camera system. With these data, we were able to document the frequency and duration of sedimentation and turbidity events, and correlate these events to physical oceanographic and river conditions. We found that seafloor sedimentation occurred regularly during the heaviest sediment loading from the river, but that this sedimentation was ephemeral and exhibited regular cycles of deposition and erosion caused by the strong tidal currents in the region. Understanding the frequency and duration of short-term sediment disturbance events is instrumental to interpreting the ecosystem-wide changes that are occurring in the nearshore habitats around the Elwha River delta.

The coastal ocean circulation off the Chinese Subei (north Jiangsu Province) coasts in the southwestern Yellow Sea in summer is studied using hydrographic data from four research cruises, moored current meter data in the Lunan (south Shandong Province) trough, and Lagrangian trajectories of satellite-tracked ARGOS surface drifters in the summers of 2008 and 2009. The hydrographic data indicate a fresh water plume extending offshore in the northeastward direction from the Sheyang River mouth and a belt of relatively cold surface temperature from the surrounding areas located offshore of the Subei coasts to the south of the plume in summer. The drifter trajectories show that the Subei coastal current, which is traditionally thought to flow southward year round, flows northward in June through July under the forcing of the southerly monsoon. A northward intrusion along the submarine valley off the Changjiang mouth is indicated by the movement of the drifters, which is persistently strong and independent of the winds. Associated with the northward flow, coastal upwelling is generated offshore of the Subei coast to the south of the Sheyang River plume, below which upwelling is generated but is shut down by the buoyancy of the fresh water at the surface. Coastal upwelling is also observed off the coast of Qingdao city in middle July through early August of 2008, which is forced by the along-shore component of the southerly and southwesterly winds. The Qingdao upwelling in summer is reported for the first time in history.

Lagrangian floats and current meter measurements from two moored arrays are analyzed, in combination with altimetry data, in order to investigate the recirculation of Antarctic Intermediate Waters (AAIW), and of the Intermediate Western Boundary Current (IWBC) at the Tubarao Bight, in the vicinity of the Vitoria-Trindade Ridge (VTR), Brazil. Results from a high-resolution numerical simulation provide a complementary view of the flow at intermediate and surface levels. The data depict a topographically-induced cyclonic recirculation at intermediate levels, and five Argo floats are successively trapped inside the bight for two-and-a-half years, performing a total of 10 closed clockwise gyres during this period of time. In situ measurements at the western side of the bight show an intense alongshore flow at intermediate levels, with averaged velocities at 800 m of ~30 cm/s, and peak velocities exceeding 50 cm/s, magnitudes comparable to the Brazil Current (BC) flow at surface levels. The recirculation extends from at least 1000 m deep up to 370 m, reaching sometimes depths as shallow as 150 m, but is mostly uncoupled from the surface flow during the one-and-a-half year long current meter record. Three different flow patterns are observed, and simulated, at surface levels inside the bight during the time the recirculation is well established at intermediate levels: a shallow cyclonic circulation, somewhat akin to the Vitoria Eddy; a recurrent anticyclonic flow that encompasses the entire bight; and a southwestward-oriented circulation, associated with the BC being reorganized in a coherent flow after negotiating its way through the VTR channels. A significant portion (about 50% according to the model) of the inflow of intermediate waters recirculates, enhancing the flow of the IWBC within the bight, and increasing the age of AAIW that will eventually cross the VTR on its way to lower latitudes. Although the data are not conclusive about a preferential pathway of the intermediate flow across the VTR, the simulation indicates that up to 70% will exit through the main channel located between the Besnard Bank and the Vitoria Seamount, while 30% will follow eastward to the south of the VTR, in a region of intense mesoscale activity, and then cross the ridge farther east.

The coastal currents and forcing agents that conduct them are still little-known in the internal continental shelf of Santa Catarina. Therefore, this work aimed to analyze the data of currents measured off the Island of Santa Catarina in order to better comprehend its patterns and forcing agents. The three measuring stations were installed in shallow water near the Arvoredo Biological Marine Reserve (ST01), Jurerê Beach (ST02) and Ingleses Beach (ST03). Data were collected by a current meter from January 22, 2014 to December 17, 2014. In the consisted data set, it was performed a basic statistical analysis, spectral decomposition and harmonic analysis in the tide components. All the stations presented a resulting southward flow, especially the station next to Arvoredo Marine Biological Reserve (ST01). The meteorological forcing has a strong contribution to the magnitude and direction of component v (alongshore). While the tidal component has greater importance in the cross-shore flow (component u). The wind showed a strong correlation with currents and the local level, indicating to be the main forcing agent of the flow in the subtidal frequency. RESUMO As correntes costeiras e as forçantes que as regem ainda são pouco conhecidas na plataforma continental interna de Santa Catarina. Por isso, este trabalha teve como objetivo analisar os dados de correntes medidos ao largo da Ilha de Santa Catarina a fim de compreender melhor os seus padrões e forçamentos. As três estações de medição foram instaladas em águas rasas próximas à Reserva Marinha Biológica do Arvoredo (ST01), Praia de Jurerê (ST02) e Praia dos Ingleses (ST03). Os dados foram coletados por um medidor de correntes no período compreendido entre 22/01/2014 à 17/12/2014. No conjunto de dados consistido foi realizada uma análise estatística básica, decomposição espectral e análise harmônica nas componentes de maré. Todas as estações apresentaram um escoamento resultante para sul, especialmente a estação próxima a Reserva Biológica Marinha o Arvoredo (ST01). A forçante meteorológica possui forte contribuição na magnitude e direção da componente v (ao longo da costa). Enquanto a componente mareal tem maior importância no fluxo através da costa (componente u). O vento apresentou uma forte correlação com as correntes e o nível local, indicando ser a forçante principal do escoamento na frequência submareal.

One of the key factors in determining the accumulation of sediment and soluble nutrients within a lease is water movement. Water masses entering and leaving the farm determine the finfish ecosystem interaction. Understanding the hydrodynamic interaction with the farm is therefore key to understanding the potential ecological effects of individual farms. In addition, finfish farms are now being proposed in exposed offshore environments and have caused concern regarding their potential down stream impacts on currents and wave climate. Seven current meters, oxygen probes and CTD were deployed to examine the hydrodynamic interactions inside and outside a 270 m long Salmon farm in Newfoundland, Canada. Current meter results indicate that the finfish farm cages have a clear shadowing effect on the currents. Currents upstream were found to be considerably faster than those recorded downstream during the sampling period. Current speeds inside the farm were also found to be considerably slower than those found outside of the farm especially during high flow events. In situ observations of currents were found to be similar to those predicted by previous CFD and hydrodynamic modelling studies. Modeling was also undertaken to calculate the energy lost as currents enter and leave a series of fish cages. In comparison to the observed flow the model compares relatively well. Flow recorded downstream of the farm was observed to be in the range predicted by the model as was the flow recorded inside and outside the cages. Current speed downstream of the farm is clearly affected by farm orientation which has important implications for the dispersal of farm debris. Average oxygen saturation within the cages over the 5 day sampling period was 80.2 %± SD 5.7 %, compared to nearly 100 %, 20 m and 50 m from the farm site. Orientation of the farm may play some part in determining the location and amount of oxygen depletion within the farm. The farm also acts to push water from deeper in the water column up into the cages which has implications for farms situated in heavily stratified environments.

The coastal dynamics along the sandy beaches in the Algiers bay is strongly influenced by the hydrodynamic agents, morphological factors, human activities, societal infrastructure and presence of hard structures, which disrupts their hydro-sedimentary balance. The present work contributes to the knowledge of hydrodynamic and morpho-sedimentary forcing mechanisms at sandy beaches by focusing on the impact of extreme sea-weather events of the two most contrasting periods of the year (winter and summer) on coastal processes. Two beaches in the eastern part of Algiers bay were studied by combining field measurements of currents and sediment flux with numerical models (MIKE 21/3 Coupled Model FM). The model validation was done based on the measured nearshore current and sediment transport during low to moderate energy swell conditions with current meter ‘Global water Fp101’ and ‘Krauss sediment traps’. Time series of wind and wave established by Infoplaza Marine weather database were used as input at the open boundaries of the model domain. The results showed a reversal of the dominant direction of the longshore currents, and a very high prevalence of cross-shore sediment transport over longshore sediment transport (LST) due to the coarse grain size of the sediment (very coarse sand). The results indicated that, waves coming from the west prevail in winter have an average wave height varies from 1.5 to 2.1 m, driven a longshore current of 0.17–0.27 m/s, with an estimated seasonal cross-shore sediment transport between 1530 and 5540 m3/year/m. During the summer season, waves approaching from the northeast dominate with an average of Hs that does not exceed 1 m, these waves generate a rip current equal to 0.24 m/s and this current can generate a cross-shore sediment flux in the order of 4000 m3/year/m. The results also reveal the development of morphological landforms represented in the submerged longshore bars at the shallow water depending largely on the hydrodynamic conditions and the cross-shore flux between the land/sea interfaces.

We present long-term current meter records from the Benguela system together with salinity and temperature observations gathered by a mooring on the Namibian shelf across 13 years (2002–2015). From this unique data set a climatological mean state is estimated enabling us to investigate seasonal to interannual variations of these variables on the Namibian shelf. The present study highlights the importance of the alongshore advection for the water mass characteristics in the Benguela system on a seasonal time scale. The annual cycle of the alongshore transport is characterized by a biannual flow reversal. Poleward directed currents dominate from October to April, and from May to September equatorward currents prevail. In addition, we present observational evidence for a biannual intrusion of tropical waters into the Benguela system with maxima in October and February. Based on the in situ temperature data, several anomalous events are described that affect the whole water column. During the outstanding warm event in austral fall 2011 the monthly temperature anomaly exceeds one Kelvin for five consecutive months peaking in March (2.4 K) in the upper layer of the water column. Our study suggests, that the occurrence of such extreme temperature events in the Benguela upwelling system is closely related to the strength of the alongshore advection in austral summer.

Modeling studies of estuary circulation show great sensitivity to the water exchange into and out of adjacent marshes, yet there is significant uncertainty in resolving the processes governing marsh surface flow. The objective of this study is to measure the estuary channel-to-saltmarsh pressure gradient and to guide parameterization for how it affects the surface flow in the high marsh. Current meters and high-resolution pressure transducers were deployed along a transect perpendicular to the nearby Little Ogeechee River in a saltmarsh adjacent to Rose Dhu Island near Savannah, Georgia, USA. The vertical elevations of the transducers were surveyed with static GPS to yield high accuracy water surface elevation data. It is found that water level differences between the Little Ogeechee River and neighboring saltmarsh are up to 15 cm and pressure gradients are up to 0.0017 m of water surface elevation change per m of linear distance during rising and falling tides. The resulting Little-Ogeechee-River-to-saltmarsh pressure gradient substantially affects tidal velocities at all current meter locations. At the velocity measurement station located closest to the Little Ogeechee River bank, the tidal velocity is nearly perpendicular to the bank. At this location, surface flow is effectively modeled as a balance between the pressure gradient force and the drag force due to marsh vegetation and bottom stress using the Darcy–Weisbach/Lindner's equations developed for flow-through-vegetation analysis in open channel flow. The study thus provides a direct connection between the pressure gradient and surface flow velocity in the high marsh, thereby overcoming a long-standing barrier in directly relating flow-through-saltmarsh studies to flow-through-vegetation studies in the open channel flow literature.

Spatiotemporal current variations of coastal-trapped waves (CTWs) were investigated by using a current dataset obtained from daily fishing operations west of the Noto Peninsula (NTP), Japan. Cross-shore lines located in southern, middle, and northern parts of the west coast of the NTP were designed to detect characteristics of CTWs with a time interval of a few days and about 5-km resolution in the cross-shore direction. Accuracy validation by using moored current meter data and sea level data demonstrated that the established dataset expresses accurate variations with periods of several days. The generation and propagation of a CTW event associated with a low-pressure zone passing north of the study area in late May 2010 were analyzed. Along-shore currents with the coast on the right strengthened in every line simultaneously with the domination of the southerly wind, and then weakened in order from south to north simultaneously with weakening of the southerly wind. Although the along-shore currents of the CTWs linearly decreased heading offshore along the south and middle lines, these currents broadened within about 50 km from the coast along the north line, with small variations in the cross-shelf direction, with an increase in shelf width. These generation, propagation and current structure characteristics are clarified and interpreted by the characteristics of the estimated possible CTWs west of the NTP and numerical experiments, which reproduce wind-induced freely propagating CTWs. A change in the propagation characteristics and the structure of the CTWs associated with bottom topography indicates the possibility that adjustments can occur on the order of a few dozen kilometers.

The 500 km long Far Northern Great Barrier Reef (FNGBR) is a semi-enclosed sea with little connectivity with the rest of the GBR further South. Its mean circulation is controlled by the prevailing southeasterly (northwestward) wind that generates a wind-driven mean longshore flow that is enabled by an inflow of oceanic water in the South. From an examination of single-point, mid-depth current meter data at ten sites over one year, it appears that there is no net current during calm weather, which implies that the northward North Queensland Coastal Current in the adjoining Coral Sea does not intrude in the FNGBR. Only about 20–40% of the wind-driven longshore transport continues northward to exit the FNGBR through Torres Strait because of blockage by reefs, shoals and islands and by the tidal friction effect in shallow waters. The remaining 60–80% of the flow appears to be deflected seaward to the Coral Sea in the North, an observation that appears to be supported by oceanographic modelling. This situation differs from that in the central and southern Great Barrier Reef where the southward flowing East Australian Current intrudes on the shelf and generates a net current even during calm weather.

We describe the seasonal cycle of the alongshore flows on the Northwestern Iberian Margin and explain what are the important mechanisms forcing the system. We used a 20-year model simulation at 2.3 km horizontal resolution, with realistic atmospheric forcing and covering the whole Western Iberian Margin. The model results are compared with satellite data, with data measured at two moored buoys and with a compilation of current meter data available for the study region. We show that currents over the slope are divided in three different cores: the Iberian Poleward Current (IPC) occupying the top 350 m, a deeper core at Mediterranean Water levels (∼600–1200 m) and in between the two, an equatorward core centered just beneath the IPC core, the Upper Slope Countercurrent (USCC). The IPC is present almost yearlong, including in summer months, when it is close to the shelf-break and topped by the equatorward upwelling jet. After September, the IPC intensifies and its core surfaces. Heat and salinity budgets on the shelf and slope are dominated by advection, confirming the important role of the IPC in driving the temperature and salinity seasonal cycles. Analysis of the seasonal cycle of the barotropic vorticity equation on the slope, shows that the main forcing mechanism of northward flows is the “Joint Effect of Baroclinicity and Relief” (JEBAR), whose contribution is higher in summer than in winter. In December and January, when the IPC is stronger and surface intensified, the main contribution is from southerly winds. The cross-shore analysis of these terms shows that JEBAR decreases substantially at the core of the IPC because, as advection terms become important, the northward density flux diminishes the local meridional density gradients, resulting in the decrease of JEBAR in the months of strong IPC.

The seasonality of the inshore Labrador Current over the Newfoundland Shelf is investigated using GLORYS (GLobal Ocean ReanalYses and Simulations, hereafter GLORYS) ocean reanalysis product and current meter data. This study finds that the seasonality of the current tends to change as it passes its bifurcation zone between 48 °30′N and 49 °30′N. In this study, the inshore Labrador Current to the north and south of the bifurcation zone are termed as the North Inshore Labrador Current (hereafter NILC) and the South Inshore Labrador Current (hereafter SILC), respectively. The NILC reaches its maximum (~2.7 Sv) in autumn, and relaxes in late winter and early spring (~1 Sv), while the SILC achieves its maximum (~1 Sv) in late autumn and early winter, and weakens in summer (~0.5 Sv). The SILC is significantly weaker than the NILC. In particular, during July and August, the northern segment of SILC is about 4 times weaker than the NILC. Change of wind patterns is found to be linked with the summer weakening of the SILC.

In-situ measurements are labor-intensive, time-consuming, and limited in their ability to observe currents with spatial variations in the surf zone. This paper proposes an optical image-based method of measurement of currents in the surf zone. This method measures nearshore currents by tracking in time wave breaking-induced foam patches from sequential images. Foam patches in images tend to be arrayed with irregular pixel intensity values, which are likely to remain consistent for a short period of time. This irregular intensity feature of a foam patch is characterized and represented as a keypoint using an imagebased object recognition method, i.e., Scale Invariant Feature Transform (SIFT). The keypoints identified by the SIFT method are traced from time sequential images to produce instantaneous velocity fields. In order to remove erroneous velocities, the instantaneous velocity fields are filtered by binding them within upper and lower limits, and averaging the velocity data in time and space with a certain interval. The measurements that are obtained by this method are comparable to the results estimated by an existing image-based method of observing currents, named the Optical Current Meter (OCM).

Polyp expansion state in Lophelia pertusa was studied in situ close to an oil rig during the drilling of a well (Statoil) off mid-Norway, in order to study possible effects on behaviour. The expansion state was monitored visually during the discharge of drill cuttings at one reef exposed to discharges and one not exposed. The reef situated down-current from the discharge point was monitored during 5 days and 15 h with a benthic lander equipped with a stills camera and current meter. This reef was exposed to drill cuttings 11 times during the monitoring. The total exposure time was 13 h 37 min. A remotely operated vehicle was used to provide additional images from both reefs for comparison. The proportion of polyps in different expansion states did not differ significantly between exposed corals and unexposed corals. Rather, changes in polyp behaviour were related to changes in current direction and velocity. A higher proportion of the polyps was expanded during periods with prevailing northeasterl...

© 2014 Elsevier Ltd. The impact of high-frequency winds on the generation and propagation of inertial currents in the Palamós submarine canyon (northwestern Mediterranean) during a severe storm on 9-16 November 2001 is evaluated in an ocean circulation model. Moored current meter time series collected in and around the canyon during the storm are assimilated with an ensemble adjustment Kalman filter (EAKF) to adjust wind forcing through a simultaneous state and parameter estimation approach. Winds are included as time-dependent parameters, which are updated in each assimilation step as part of the model state. A simulation forced by the estimated wind significantly improves simulation with winds from the atmospheric reanalysis (the RMS error reduction is about 50%). This is due to the higher energy for the estimated wind at inertial period in the clockwise rotating component, which enhances generation of near-inertial motions. The surface inertial energy however does not decay as rapidly compared to a simulation with data assimilation. It is suggested that the submesoscales, which are present in the data assimilated simulation, are effective in channeling a spatially heterogeneous vertical propagation of near-inertial motions., This research utilized resources at the New York Center for Computational Sciences at Stony Brook University/Brookhaven National Laboratory which was supported by the U.S. Department of Energy under Contract no. DE-AC02-98CH10886 and by the State of New York. This work was partially carried out in the framework of the CANYONS project, funded by the “Dirección General de Enseñanza Superior e Investigación Científica” (MAR1999-1060). The authors gratefully thank all the personnel involved in the CANYONS project and surveys. A. Jordi's work was supported by a Ramón y Cajal grant (RYC-2010-06898) from the Spanish Ministry of Economy and Competitiveness

From the eleven-year data record at the Southern Adriatic Observatory (E2M3A), we study for the first time in the Adriatic Sea the strength of the backscatter signal from an Acoustic Doppler Current Profiler (ADCP) in relation to zooplankton vertical movement. The signal represents well the general behaviour of the zooplankton to sink at dawn and to emerge at the sunset. The modulation of the signal along the year is linked in particular to the different environmental conditions and the presence of different zooplankton groups. The correlation between the backscatter signal and distinct zooplankton groups (copepods, euphausiids, ostracods, appendicularians, salps) shows that in different seasons and environmental conditions, different groups are responsible for the strength of the signal. Furthermore, the backscatter signal, interpreted in terms of the qualitative composition of the zooplankton community, provides important information on the behaviour and habits of zooplankton in the southern Adriatic. Poorly known aspects of zooplankton behaviour are described in more detail, such as: recovery of zooplankton vertical distribution after mixing events, vertical migration in conditions of increased food availability at depth due to vertical mixing, modulation of vertical migration in dependence of the lunar phase and vertical migration in relation to deep chlorophyll maximum position. In addition, the present study emphasizes the possible influence of gelatinous zooplankton at the open sea on high backscatter values during the warmer part of the year.

The Jan Mayen Ridge, with bottom depths of 1000 m and less, runs southwards from Jan Mayen and separates the warmer and saltier Atlantic Water in the Norwegian Sea from the colder and fresher Arctic water in the Iceland Sea. During the International Polar Year (IPY, 2007–2008), three current meter moorings were deployed with the purpose to investigate water mass exchanges between the Norwegian and Iceland seas over the Ridge and their forcing mechanisms. These are the first in-situ current measurements for this region. The results showed relatively weak currents on the Ridge that frequently shifted direction except near-bottom and at the western slope of the Ridge. All current measurements showed low eddy activity and tidal velocities (less than 0.05 ms − 1 ). Wind-forced near-inertial motion generated from transient atmospheric low pressure systems were observed in the mixed layer being strongest during autumn and winter when ocean velocities reached 0.7 ms − 1 . Near surface currents on the Ridge are influenced by local winds on a time scale of 6 days and longer, but during the two-year deployment no pronounced seasonal variation was observed, mainly due to a lack of seasonality in the local winds. In a 2000 m deep channel that cuts the Ridge, there was pronounced seasonal variation in the currents at all depths below 40 m with stronger flow toward the Iceland Sea during winter compared to summer. The variability of the deep current was found to be influenced by the large-scale wind stress curl. There was a weak net flow with averaged velocities of ~ 0.01 ms − 1 over the Ridge that was directed westward in the upper layer, signifying a small net transport of modified Atlantic Water into the Iceland Sea.

Flocculation and floc break-up dynamics were studied in two field campaigns with calm winds in the northernmost part of the Danish Wadden Sea. The studies were carried out using a LISST-100C together with CTD-instruments and a current meter. A quasi-Lagrangian profiling method was used to assess the dynamics on a short temporal scale ( tidal cycle). The quasi-Lagrangian measurements showed strong flocculation and floc break-up dynamics in the lower part of the water column in the period around slack water. These dynamics were confirmed in the Eulerian deployments and were reoccurring in every tidal cycle. The dynamics were mostly governed by changes in turbulent shear. Strong microflocs with a lower mean threshold diameter of 50–60 μm present at high turbulent shear flocculated to form fragile macroflocs with sizes of several hundred microns and mean diameters above 80 μm around slack water periods. A hysteresis in floc break-up and flocculation was found at high water slack (HWS), as flocs formed at a root mean square velocity gradient ( G ) around 1 s − 1 were not broken up until the shear reached G > 4 s − 1 . As an effect, the flocculation time (time for flocculation from constituent microflocs to fragile macroflocs) was roughly 100 min while the equivalent floc break-up time was roughly 200 min. The asymmetrical, flood-dominated tidal wave showed how longer periods of low turbulent shear enhanced the hysteresis. The study demonstrates how the combination of the two deployment types will give a more adequate description of the flocculation dynamics over tidal cycles. Moreover, it shows the importance of incorporating specific flocculation aspects in numerical models, as a failure to incorporate the flocculation hysteresis results in an underestimation of the net import of sediment by about 30%.

Understanding present-day sediment provenance and transport processes is crucial for studies about the dynamics of ocean circulation, as well as for paleoclimate reconstructions in the Drake Passage (DP), a key area for Earth's global oceanic circulation and climate during past and future. Based on a comprehensive set of surface sediment samples, we used spatial variations in grain-size distribution, bulk sediment mineralogy, silt and clay mineralogy across the entire DP region to elucidate the terrigenous sources and transport mechanisms. The statistical evaluation of these data identifies southern Patagonia (carbonate, illite, chlorite, feldspar and quartz) and the Antarctic Peninsula (chlorite, smectite, and amphibole) as the main sources for terrigenous sediments in the DP region. Different current systems are transporting the sediment material. Here, we provide a new, robust flow speed calibration for silt grain-sizes to enable the reconstruction of Antarctic Circumpolar Current (ACC) dynamics in the DP sector of the Southern Ocean. We correlated the sortable silt mean grain-size records of surface sediments with adjacent long-term current meter data. A clear bottom current speed pattern shows the variability of the ACC in the DP responding to the dynamics of ocean fronts, in agreement with modern observation.

A bottom mounted upward looking Simrad EK60 120-kHz echo sounder was used to study scattering layers (SLs) and individuals of the krill Meganyctiphanes norvegica. The mooring was situated at 150-m depth in the Oslofjord, connected with an onshore cable for power and transmission of digitized data. Records spanned 5 months from late autumn to spring. A current meter and CTD was associated with the acoustic mooring and a shore-based webcam monitored ice conditions in the fjord. The continuous measurements were supplemented with intermittent krill sampling campaigns and their physical and biological environment. The krill carried out diel vertical migration (DVM) throughout the winter, regardless of the distribution of potential prey. The fjord froze over in mid-winter and the daytime distribution of a mid-water SL of krill immediately became shallower associated with snow fall after freezing, likely related to reduction of light intensities. Still, a fraction of the population always descended all the way to the bottom, so that the krill population by day seemed to inhabit waters with light levels spanning up to six orders of magnitude. Deep-living krill ascended in synchrony with the rest of the population in the afternoon, but individuals consistently reappeared in near-bottom waters already

Exchange of water between Prince William Sound and the Gulf of Alaska has a significant impact on its circulation and biological productivity. Current meter records from moored instruments in the two major straits connecting Prince William Sound to the Gulf of Alaska are analyzed to characterize the seasonal variations in water exchange. Eight individual deployments, each lasting for about 6 months, were made during the years 2005–2010. Two moorings were placed across each passage to account for horizontal flow variability. Monthly averaged, depth-integrated transport in winter is characterized by a strong barotropic inflow through Hinchinbrook Entrance and outflow through Montague Strait. The transport through each passage can reach 0.2 Sv, which could replenish the volume of Prince William Sound in as little as 3 months. Depth-integrated transport is weaker and more variable in direction in summer than in winter, implying that Prince William sound is not always a simple flow-through system. Monthly transports range between −0.05 and 0.08 Sv in each passage, and the corresponding flushing times exceed 1 year. The flow through both passages is highly baroclinic in the summer, so that the layer transport can be significant. For example, the deep inflow through Hinchinbrook Entrance can reach 0.05 Sv, which would flush the deep regions of Prince William Sound ( > 400 m ) in only 23 days. The transport imbalance between Montague Strait and Hinchinbrook Entrance cannot be accounted for by considering other terms in a volume budget such as local freshwater input, meaning the imbalance is mostly a result of under-resolving the cross-strait flow variability. The magnitude of the monthly mean depth-integrated transport through Montague Strait and Hinchinbrook Entrance depends non-linearly on the shelf winds. Strong downwelling conditions, characteristic of the winter, drive inflow through Hinchinbrook Entrance, which is balanced by outflow through Montague Strait. Weak downwelling or upwelling conditions, characteristic of the summer, allow deep water from below the shelf break to flow in through Hinchinbrook Entrance.

We measured diel migration with 11 acoustic Doppler current meter profilers and consistently found diel and lunar cycles of vertical migration from 250 m down to the bathypelagic (. 1000 m). These measurements come from year-long deployments in eight locations within the Gulf of Mexico. Diel vertical migration could be characterized, in depth and time, by a pulse of maximum vertical migration activity (PMV), which has a nearly fix phase relation to sunrise and sunset modulated by the lunar cycle. The vertical velocity of migrating biota is in the same direction as the PMV propagation, but it is significantly slower. This difference in velocity implies that the PMV cannot represent the migration pattern of one single population. The lunar cycle is evident down to 1000 m, where the upward migration delays in phase with the full moon. The extension of the diel and lunar cycles over 1000 m depth together with the difference in vertical migration velocity indicate that the surface irradiance signal is transmitted to bathypelagic depth by synchronized depth-tiered populations. A model in which particulate organics are recycled at different depths, similar to a bucket brigade, is consistent with these observations. This daily vertical connectivity is expected to affect the vertical transport of carbon down to the bathypelagic. Zooplankton is a crucial agent in pelagic ecology, linking primary production with higher trophic levels. Zooplankton diel vertical migration is a global phenomenon linking the strata in the ocean transferring organic material toward greater depth (Angel 1989; Buesseler and Boyd 2009). The diel excursion of the ‘sound scattering layer,’ from , 150 m down to , 400 m, is easily observed with echo sounders and serves as a textbook example of negative phototaxis. This migration is commonly explained by a better food supply closer to the surface and predator avoidance by migration to deeper levels during the day, where visual detection is more difficult, a hypothesis calling for strict light control of vertical migration (Cohen and Forward 2009; Ringelberg 2010). The ample literature on diel vertical migration covers aspects of physiological control of the timing, energetic balances, and the effect on vertical transport of organics forming part of the biological carbon pump. Vinogradov (1962) proposed that zooplankton play a role in the vertical transport of organic material within the mesopelagic depth range (bottom of the euphotic zone to 1000 m), suggesting the term ‘ladder of migrations’ for the diel migration of different populations of zooplankton covering different depth ranges. The literature agrees that light triggers the migration; solar eclipses perturb the cycle, and even lunar eclipses have significant effects (Tarling et

During an expedition to the deep-sea long-term observatory HAUSGARTEN in the eastern Fram Strait in summer 2003, the availability of a Remotely Operated Vehicle allowed a targeted sampling of surface sediments around a relatively large dropstone (0.9 m2) to determine suspected differences in community structure and dynamics of nematode assemblages in relation to the confined flow regime and patchy food availability in the immediate vicinity of the stone. The almost rectangular dropstone was about 150 cm in length, 60 cm in width, and up to 15 cm in height. Small-scale current measurements around the dropstone using a MAVS-3 acoustic current meter exhibited a rather complex pattern. A computational fluid dynamics simulation revealed areas of constantly flowing near-bottom currents as well as the generation of vortices in certain areas around the dropstone. Concentrations of biogenic compounds in the sediments surrounding the dropstone generally followed the complex flow pattern. The differences in...

The challenges associated with meso- and submesoscale variability (between 1 and 100 km) require high-resolution observations and integrated approaches. Here we describe a major oceanographic experiment designed to capture the intense but transient vertical motions in an area characterized by strong fronts. Finescale processes were studied in the eastern Alboran Sea (Western Mediterranean) about 400 km east of the Strait of Gibraltar, a relatively sparsely sampled area. In-situ systems were coordinated with satellite data and numerical simulations to provide a full description of the physical and biogeochemical variability. Hydrographic data confirmed the presence of an intense salinity front formed by the confluence of Atlantic Waters, entering from Gibraltar, with the local Mediterranean waters. The drifters coherently followed the northeastern limb of an anticyclonic gyre. Near real time data from acoustic current meter data profiler showed consistent patterns with currents of up to 1 m/s in the southern part of the sampled domain. High-resolution glider data revealed submesoscale structures with tongues of chlorophyll-a and oxygen associated with the frontal zone. Numerical results show large vertical excursions of tracers that could explain the subducted tongues and filaments captured by ocean gliders. A unique aspect of AlborEx is the combination of high-resolution synoptic measurements of vessel-based measurements, autonomous sampling, remote sensing and modeling, enabling the evaluation of the underlying mechanisms responsible for the observed distributions and biogeochemical patchiness. The main findings point to the importance of fine-scale processes enhancing the vertical exchanges between the upper ocean and the ocean interior., The AlborEx experiment was conducted in the framework of PERSEUS EU-funded project (Grant agreement no: 287600). The experiment was led by the Spanish National Research Council (CSIC) institution with strong involvement and cooperation from other national and international partners: Balearic Islands Coastal Observing and Forecasting System (SOCIB, Spain); Consiglio Nazionale delle Ricerche (CNR, Italy), McGill University (Canada); Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS, Italy) and Woods Hole Oceanographic Institution (WHOI, USA). Glider operations were partially funded by JERICO FP7 project. AP acknowledges support from the Spanish National Research Program (E-MOTION/CTM2012-31014 and PRE-SWOT/CTM2016-78607-P). SR and AP are also supported by the Copernicus Marine Environment Monitoring Service (CMEMS) MedSUB project. EM is supported by a post-doctoral grant from the Conselleria d'Educació, Cultura i Universitats del Govern de les Illes Balears (Mallorca, Spain) and the European Social Fund. AC is a FNRS researcher under the FNRS BENTHOX project (Convention T.1009.15).

Current velocities and vertical sediment fluxes in the Var submarine canyon were assessed at three stations respectively at 800 m, 1200 m and 1800 m depth, using moorings deployed for 4 months during winter 2008-2009. During this period, we observed three major sediment gravity flows, all characterized by sudden increases in current velocity that lasted 2-5 h and by downward particle fluxes. Each gravity flow, described using a high frequency current meter and two Acoustic Doppler Current Profiler (75 and 300 kHz ADCP) showed distinctive features. The first event, triggered during a flood of the Var River, was determined to be a hyperpycnal current with a large vertical extent (>100 m high) and relatively low velocity (40 cm s(-1)). The second event, observed after a Var River flood, was more energetic with a maximum horizontal current peak of 60 cm s(-1) with a low vertical extent (30 m high). This event was considered to be a turbidity landslide. The third was the result of a local canyon wall failure. It was characterized by a speed of >85 cm s(-1). These peaks of current speed were associated with large clouds of material that transported sediment along the canyon and reached up to 200 g m(-2) d(-1) of sediment (>1 g m(-2) d(-1) of organic carbon). Our measurements in the Var canyon show the important role of gravity flows transporting particulate matter to the deep-sea floor. These large inputs of sediment and organic carbon may have a significant impact on deep-sea carbon storage in the Mediterranean Sea. (C) 2012 Elsevier Ltd. All rights reserved.

The eastern Canadian seas including Baffin Bay, the Labrador Sea and shelf, the N.E. Newfoundland Shelf, the Scotian Shelf and the Gulf of St. Lawrence form an integrated hydro-dynamical system. The circulation is investigated using current meter data and a high resolution three dimensional coupled ice-ocean circulation model, CECOM (Canadian East Coast Ocean Model) covering the entire area. The model is forced with realistic atmosphere fluxes and the results are compared to the current meter data collected in four selected periods between 1987 and 2008. Many features of the model current fields are similar to those from the previous regional circulation models for the shelves. New findings from CECOM include seasonal differences of the circulation around Davis Strait, the detailed structure of the Labrador Current re-circulation, two cross-shelf currents on the Scotian Shelf, and strong currents in Halibut Channel which connects the waters of the western Grand Banks and Scotian Shelf. The annual variation of the circulation is investigated. Both the model and data show the Labrador Current is strong in fall and weak in spring. The outflow from the Gulf of St. Lawrence through Cabot Strait and the currents on the inner Scotian Shelf are strong in winter and fall and weak in spring, and are in phase with the Labrador Current. The model currents are compared to observations using a qualitative method of visual comparison, and a quantitative method based on statistical analysis. The comparisons indicate that the main features of the current fields from the observations are successfully reproduced by the model. The quantitative analysis indicates that the model currents are in reasonable agreement with the observations. Specifically, a good agreement is found in the Labrador shelf, Newfoundland Shelf and Flemish Pass, a fair agreement is found in Davis Strait, the inner Scotian Shelf and Sable Bank. However, the agreement for Cabot Strait and the Scotian Shelf break is less satisfactory. An analysis of the spatial variability of the current field suggests that the degree of agreement is closely related to the spatial variability of the current field. The regions with low spatial variability generally have good agreements. The volume and freshwater transports through several sections from the model are in good agreement with available estimates based on data.

The effects of sea-state induced vessel motion on the physical performance of the Northeast Fisheries Science Center Yankee 36 survey bottom trawl, rigged with a roller footrope, were investigated. The trawl was instrumented with an acoustic net mensuration system to measure horizontal spread, a head rope mounted acoustic current meter to measure flow at the trawl-mouth, and five sled-mounted inclinometer sensors attached to the wings, quarters and center of the footrope to measure bottom-contact. A vessel motion sensor fixed at the center of the vessel measured roll and pitch. Trawl performance was observed over wave heights of 1–4 m. Vessel motion caused by waves at the sea-surface had a strong effect on trawl motion on the seabed. Vessel heading in relation to wave direction is an influential factor dictating the specific vessel motions occurring in a given sea-state. Of the measured components of vessel motion, pitch had the greatest affect on trawl performance. The speed of vertical stern motion, derived from pitch angles, rather than the magnitude of vertical stern displacement, was the most influential factor controlling variations observed in the footrope bottom-contact data and forward trawl velocity component measured by the current meter. Vertical stern motion speeds of 48 cm/s and greater caused the survey trawl to surge forward and exacerbated the loss of footrope bottom-contact. Since sea-surface conditions had a strong influence on net behavior, it may alter the catch efficiency of a survey trawl, we recommend fish behavior in response to trawl motion be investigated further.

Hypothetical cases of oil spills, caused by ship failure in the northern Adriatic, are analysed with the aim of producing three-dimensional models of sea circulation and oil contaminant transport. Sea surface elevations, sea temperature and salinity fields are applied as a forcing argument on the model’s open boundaries. The Aladin-HR model with a spatial resolution of 8 km and a time interval of 3 hours is used for atmospheric forcing. River discharges along the coastline in question are introduced as point source terms and are assumed to have zero salinity at their respective locations. The results of the numerical modelling of physical oceanography parameters are validated by measurements carried out in the ‘Adriatic Sea monitoring programme’ in a series of current meter and CTD stations in the period from 1 January 2008 to 15 November 2008. The oil spill model uses the current field obtained from a circulation model. Besides the convective dispersive transport of oil pollution (Lagrangian model of discrete particles), the model takes into account a number of reactive processes such as emulsification, dissolution, evaporation and heat balance between the oil, sea and atmosphere. An actual event took place on 6 February 2008, when the ship ‘Und Adriyatik’ caught fire in the vicinity of the town of Rovinj (Croatia) en route from Istanbul (Turkey) to Trieste (Italy). At the time the fire broke out, the ship was carrying around 800 tons of oil. Thanks to the rapid intervention of the fire department, the fire was extinguished during the following 12 hours, preventing possible catastrophic environmental consequences. Based on this occurrence, five hypothetical scenarios of ship failure with a consequent spill of 800 tons of oil over 12 hours were analysed. The main distinction between the simulated scenarios is the time of the start of the oil spill, corresponding to the times when stronger winds were blowing (> 7 m s − 1 ) with a minimum duration of 24 h within the timeframe. Each scenario includes a simulation of oil transport for a period of two months after the beginning of the oil spill. The results show that the coastal belt between the towns of Porec and Rovinj is seriously exposed to an oil pollution load, especially a few days after a strong and persistent bora (NE wind).

Semi-diurnal internal tides and near-inertial waves are investigated using moored current meter measurements at four sites along the shelf break of the East China Sea during August 1987 and May-June 1988. Each mooring is equipped with four current meters spanning from near surface to near bottom. Spectral analyses of all current data reveal dominant spectra at the semi-diurnal frequency band, where the upper and lower current measurements show out-of-phase relationship between them with significant coherences. These are consistent with typical characteristics of the first-mode semi-diurnal internal tide. Strong intensification of the near-bottom baroclinic currents is observed only at one site, where the ratio of the bottom slope to the slope of the internal-wave characteristics at the semi-diurnal frequency is close to unity. An energetic near-inertial wave event is observed during the first half of May-June 1988 observation at two mooring sites. Rotary spectra reveal that the most dominant signal is clockwise rotating motion at the near-inertial frequency band. Upward phase and downward energy propagations, shown in time-depth contour plots of near-inertial bandpass filtered currents, are confirmed by cross correlations between the upper- and lower-layer current measurements. The upward-propagating phase speed is estimated to be about 0.13 ㎝ s?¹ at both sites. Significant coherences and in-phase relationships of near-inertial currents at the same or similar depths between the two sites are observed in spite of their long distance of about 110 ㎞.

The concept of a southward-flowing West Auckland Current off the west coast of Northland has become an accepted feature of the ocean circulation around New Zealand. Knowledge of this flow is based on sparse data collected in the 1950s. Here we quantify the flows in the area for the first time using a current meter array deployed for a year (2003–2004) across the shelf and slope offshore of Hokianga Harbour and three hydrographic surveys along a transect coincident with the current meter array. Flows are found to be weak, and dominated by the variability. There is a southeastward drift in the mean flow offshore of the 1000-m isobath, with a northwestward mean found inshore of this. The offshore flows appear to result from large-scale sea surface height gradients, while the inshore flows respond to wind forcing in a complex manner.

On bottom ( ≈ 2 m ) current velocities in the Puerto Rico Trench ( ≈ 8350 m depth) were measured at 1 Hz for 75 min by acoustic-Doppler current meter at 19.75°N, 66.40°W, via untethered free-descent/ascent vehicle. The April 2008 deployment also recorded 3-axis velocity, temperature, pressure, and instrument heading, pitch, roll, and signal strength during the 153 min free-descent, and while on bottom. No data for the ascent was recorded. Signal strength was above the noise floor for the entire data set, and SNR and velocity STD were within known acceptable bounds above 7000 m. Instrument heading showed a continuous anti-clockwise rotation during descent. Doppler vertical velocity during descent is compared to the pressure time derivative and observed to exhibit extended periods of under-bias, correlated not to low SNR, but to Doppler horizontal velocity fluctuations. Doppler horizontal velocity during descent is interpreted to be tangential to rotation and includes lateral translations. Integration of horizontal velocity during descent suggests a lateral displacement of less than 30 m over the 8.35 km free-fall. Measurements made at impact indicate full functionality of the instrument at depth. Maximum horizontal velocities while on bottom varied between 1 and 5 cm/s and were directed roughly along trench axis to the W.

Hydrographic observations in deep Fram Strait evidence a plume of Storfjorden Brine-enriched Shelf Water in 1986, 1988 and 2002. The plume spreads along the continental slope over 600 km away from its formation area and reaches 2000 m depth. The plume is 30 to 80 m thick in the deep layer of Fram Strait; it is almost 0.4 °C warmer and 0.06 more saline than the ambient water. The velocity of the plume, observed by a moored current meter in Fram Strait, is 12.60±4.70 cm s −1 .The hydrographic properties of the plume are used to study entrainment. A streamtube model with four entrainment parameterizations is applied. Two Froude-number dependent parameterizations lead to mixing mostly happening over the shelf break, where the Froude number is large. This is in agreement with the traditional view, but is inconsistent with the observed temperature and salinity of the Storfjorden plume. Therefore further entrainment assumptions (a constant and a volume-dependent entrainment) are tested. The volume-dependent entrainment scheme yields the best representation of entrainment in the Storfjorden plume. Our results emphasize the necessity of strong mixing in the deep layers in Fram Strait to achieve an agreement with observed properties of the plume.

The relationships between the distribution of different zooplankton and ichthyoplankton stages and physical and chemical variables were studied using samples and data (CTD profiles, ADCP and current meter measurements, nutrients, mesozooplankton, ichthyoplankton) obtained from different strata during two 24-h cycles at two oceanographic stations in a Chilean Patagonian gulf during the CIMAR 10-Fiordos cruise (November, 2004). A station located at the Chacao Channel was dominated by tidal mixing and small increments in surface stratification during high tides, leading to decreased nutrient availability. This agreed with short periods of increased phytoplankton abundance during slack waters at the end of flood currents. Increases in larval density for all zooplankton and ichthyoplankton taxa corresponded to the flooding phases of the tidal cycle. When the larval density data were fit to a sinusoidal model, the regression coefficients were high, suggesting that tides are important features that modulate short-term variations in plankton abundance. All larvae did not vary synchronously with the tidal phase; rather, time lags were observed among species. The abundances of older individuals of the copepodite Rhincalanus nasutus and all zoea stages of the squat lobster Munida gregaria increased during night flood tides, whereas younger stages increased during daytime flood tides. At a station located at the Queullin Pass, which was dominated by vertical stratification patterns, the variations in peak larval density were better fitted to the semi-diurnal sea level fluctuations. Other evidence indicated internal tides below the pycnocline, which could promote larval transport in deeper layers. In the overall picture that emerges from this study, planktonic organisms from different habitats and phylogenetic origins seem to respond to the local tidal regimes. In some cases, this response might be beneficial, transporting these individuals inshore to areas that are rich in food during the peak biological production season.

Seasonal hydrographic conductivity–temperature–depth surveys and moored current meter measurements have been analysed using an inverse approach in order to highlight the main features of the circulation in the western Sicily Strait during 2003. The variational inverse section model combines different types of constraints to seek for a continuous flow field satisfying data and physical assumptions within prescribed prior error bars. It is based on a finite element discretization that allows an appropriate resolution of very irregular topography. The corresponding results, consistent with data and dynamics, are providing new insight into the circulation of the surface and intermediate layers in conjunction with transport and formal error estimates during five hydrographic cruises. In the upper layer, these insights include the southward Atlantic Tunisian Current (ATC) off the Cap Bon Coasts, its high variability at short time-scales and its recirculation during October. For the Levantine Intermediate Water (LIW) regime, a detailed view of the circulation in the western Sicily Strait is given evidencing its recirculation at the western sill during the same period. Transports for both ATC and LIW are computed and found to be maximum in spring and decrease in summer and fall.

Rapid ‘swing’, compass variations O(10°) in O(10 s), and ‘spin’, complete rotations around the vertical axis within a few minutes, are a concern of acoustic current meters moored in-line. Observations are used from fast sampling, at once per 1 and 30 s, instrumentation on deep-ocean moorings mainly outside surface wave and bottom boundary influences. Such instruments do not require a vane common to some historic mechanical current meters and they are often moored in a much easier to handle sub-surface buoy or mounting rack, without vanes. In their mountings they are nearly symmetric, so that they can spin freely in (turbulent; shear) flows. A comparison is made between noise levels of such free spinning instrumentation with those of instruments mounted in a fixed bottom-frame and with those of instruments equipped with a vane to one side. Typical spinning has a single rotation varying between 40 and 200 s. Spinning is shown to be highly binary: on or off. Its effects are found negligible on estimates of ocean currents, provided compass updates are adequate as in existing instrumentation. Acoustic noise is O(10) times larger than noise due to spinning. Some effects of spinning are noticed in the acoustic echo amplitude showing higher noise at frequencies >100 cpd, cycles per day. The character of this noise changes dramatically due to spinning. However, it is mainly in the ocean turbulence range and does not affect measurements of internal waves or periodic zooplankton motions.

Semidiurnal tidal currents on the outer shelf of the Mackenzie Shelf in the Beaufort Sea were found to be strongly influenced by the locally generated baroclinic tide. Two primary factors are involved in this process: (1) the sharp shelf break along the northeastern Mackenzie Shelf, promoting the generation of vigorous internal tidal waves; and (2) the proximity to critical latitudes for M2 and N2 motions locking these waves and preventing them from leaving the source region. As a result, internal tides are resonantly trapped between the shelf and critical latitudes. The physical properties and temporal variations of tidal motions were examined using current meter measurements obtained from 1987–1988 at four sites (SS1, SS2, SS3, and SS4) offshore of the shelf break at depths of ∼200 m. Each mooring had Aanderaa RCM4s positioned at ∼35 m below the surface and ∼50 m above the bottom. Complex demodulation was used to compute the envelopes (amplitude modulation) of these components. A striking difference in the variability of clockwise (CW) and counterclockwise (CCW) tidal currents was found. The CW tides are highly variable, have greater amplitude, exhibit a burst-like character associated with wind events and contain about 80% of the total energy of the semidiurnal tidal currents. In contrast, the CCW components have a more regular temporal regime with distinct monthly, fortnightly and 10-day modulation at astronomical periodicities associated with frequency differences M2–N2 (0.03629 cpd), S2–M2 (0.06773 cpd), and S2–N2 (0.10402 cpd). Significant horizontal correlation of the CW current envelopes was found only between stations near the northeast Mackenzie Shelf, indicating this to be the main area of baroclinic internal wave generation.

Direct velocity measurements undertaken using a nine-system mooring array (M1-M9) from 2004 to 2005 and two additional moorings (M7p and M8p) from 2003 to 2004 reveal the spatial and temporal properties of the deep-circulation currents southwest of the Shatsky Rise in the western North Pacific. The western branch of the deep-circulation current flowing northwestward (270-10°T) is detected almost exclusively at M2 (26°15'N), northeast of the Ogasawara Plateau. It has a width less than the 190km distance between M1 (25°42'N) and M3 (26°48'N). The mean current speed near the bottom at M2 is 3.6 ± 1.3 cm s -1 . The eastern branch of the deep-circulation current is located at the southwestern slope of the Shatsky Rise, flowing northwestward mainly at M8 (30°48'N) on the lower part of the slope of the Shatsky Rise with a mean near-bottom speed of 5.3 ± 1.4 cm s -1 . The eastern branch often expands to M7 (30°19'N) at the foot of the rise with a mean near-bottom speed of 2.8 ± 0.7 cm s -1 and to M9 (31°13'N) on the middle of the slope of the rise with a speed of 2.5 ± 0.7 cm s -1 (nearly 4000m depth); it infrequently expands furthermore to M6 (29°33'N). The width of the eastern branch is 201 ± 70 km on average, exceeding that of the western branch. Temporal variations of the volume transports of the western and eastern branches consist of dominant variations with periods of 3 months and 1 month, varying between almost zero and significant amount; the 3-month-period variations are significantly coherent to each other with a phase lag of about 1 month for the western branch. The almost zero volume transport occurs at intervals of 2-4 months. In the eastern branch, volume transport increases with not only cross-sectional average current velocity but also current width. Because the current meters were too widely spaced to enable accurate estimates of volume transport, mean volume transport is overestimated by a factor of nearly two, yielding values of 4.1 ± 1.2 and 9.8 ± 1.8 Sv (1 Sv = 10 6 m 3 s -1 ) for the western and eastern branches, respectively. In addition, a northwestward current near the bottom at M4 (27°55'N) shows a marked variation in speed between 0 and 20 cm s -1 with a period of 45 days. This current may be part of a clockwise eddy around a seamount located immediately east of M4.

This paper reports on the strength and structure of the Kuroshio Extension and its recirculation gyres. In the time average, quasi-permanent recirculation gyres are found to the north and south of the Kuroshio Extension jet. The characteristics of these recirculations gyres are determined from the combined observations from the Kuroshio Extension System Study (KESS) field program (June 2004–June 2006) and include current meters, pressure and current recording inverted echo sounders, and subsurface floats. The position and strength of the recirculation gyres simulated by a highresolution numerical model are found to be consistent with the observations. The circulation pattern that is revealed is of a complex system of multiple recirculation gyres that are embedded in the crests and troughs of the quasi-permanent meanders of the Kuroshio Extension. At the location of the KESS array, the Kuroshio Extension jet and its recirculation gyres transport of about 114 Sv. This represents a 2.7-fold increase in the transport of the current compared to the Kuroshio’s transport at Cape Ashizuri before it separates from the coast and flows eastward into the open ocean. This enhancement in the current’s transport comes from the development of the flanking recirculation gyres. Estimates from an array of inverted echo sounders and a high-resolution ocean general circulation model are of similar magnitude.

Remote sensing and in situ observations, and model simulations made during the Dynamics of the Adriatic in Real Time (DART) project in the central Adriatic Sea during 2006 reveal intense mesoscale eddy activity in the West Adriatic Current (WAC) system, that flows along the Italian coast. We investigate the origin, scale and rate of evolution of these features, and consider their potential contributions to across-shelf exchange, as a basis for planning future operational coastal prediction and monitoring programs. Predictions from a regional Adriatic Sea implementation of the Navy Coastal Ocean Model (NCOM) are assessed using observations from satellites, current meter moorings, and ship hydrographic transects. Near Cape Gargano in summer, mesoscale eddies and filaments observed in remote sensing imagery and in situ data exhibit horizontal and vertical scales of about 30 km and 25 m, respectively. The observed eddies develop along the WAC front under transient wind conditions, while a quasi-permanent anti-cyclonic circulation appears downstream of the cape. NCOM model predictions show that well-organized, multiple-eddy features appear, grow in unison, then dissipate along the coast west of Cape Gargano in response to transient along-shelf wind forcing, while east of it individual eddies are generated by interaction of the WAC main stream with the bathymetry surrounding the cape. The eddies evolve over time scales of a few days to a week in response to forcing transients. Moderate to strong northwest winds compress the WAC coastward and suppress the instabilities, while relaxing northwest winds or shifts to southeast winds expand the WAC and enhance instability growth. Together with entrained filaments of coastal water, the eddies translate, stretch and rotate in response to WAC horizontal advection and shear. The qualitative character and evolution of the modeled features agree with the observations, and model statistics reveal patterns of variability on monthly and seasonal time scales that are consistent with the appearance of individual eddies in both the model results and observations. In the model, patterns of upwelling and downwelling associated with the WAC main stream and eddies may be linked to dynamical characteristics of the WAC flow and specific bathymetric features. Under wintertime conditions, theoretical arguments predict an upwelling response as flow divergence changes absolute vorticity where the WAC rounds the cape, while Ekman pumping driven by surface winds or bottom stress and associated secondary circulation could explain upwelling and downwelling patches appearing around the rims of individual eddies. The upwelling dynamics are complicated by seasonal stratification effects and bathymetric features, and more work is needed to elucidate these processes. Based on their frequent occurrence, large size compared to the shelf width, high intensity and current shear, and secondary circulations, the eddies and filaments could contribute significantly to across-shelf exchange and coastal/deep-ocean mixing, with important implications for coastal monitoring and prediction. Their generation and evolution present special challenges for coastal prediction, but our results demonstrate that combined use of remote sensing imagery and numerical model simulations can yield valuable insight into such processes, and thereby help plan future monitoring and prediction efforts.

Surf zone drifters and a current meter were used to study the nearshore circulation patterns in the lee of groynes at Cottesloe Beach and City Beach in Western Australia. The circulation patterns revealed that a persistent re-circulation cell was present in the lee of the groyne which was driven by changes in wave set-up resulting from lower wave heights in the lee of the groyne. The re-circulation consisted of a longshore current directed towards the groyne which was deflected offshore due to groyne resulting in a rip current along the groyne face. The offshore-flowing rip current and the incoming waves converged at the offshore extent of this circulation cell, with the deflection of the rip current parallel to the shoreline and then completing the recirculation through an onshore component. The Eulerian measurements revealed that 55% of the currents on the lee side of the groyne were directed offshore and that these currents had a maximum speed of 2 m s −1 . Spectral analysis of the wave heights and the currents revealed several corresponding peaks in the measured spectral densities with timescales between 12 s and 50 min. Numerical simulations of an idealised beach with a shore-normal groyne were conducted using a circulation model driven by waves, and confirmed the formation of a persistent eddy in the lee of the groyne. Sensitivity studies indicated that the incident wave angle, wave period, and especially the wave height controlled the circulation. The eddy vorticity, a measure of an eddy's strength, increased roughly proportional to an increase in the incident wave energy flux.

In order to estimate the contribution of cold Pacific deep water to the Indonesian throughflow (ITF) and the flushing of the deep Banda Sea, a current meter mooring has been deployed for nearly 3 years on the sill in the Lifamatola Passage as part of the International Nusantara Stratification and Transport (INSTANT) programme. The velocity, temperature, and salinity data, obtained from the mooring, reflect vigorous horizontal and vertical motion in the lowest 500 m over the ∼2000 m deep sill, with speeds regularly surpassing 100 cm/s. The strong residual flow over the sill in the passage and internal, mainly diurnal, tides contribute to this bottom intensified motion. The average volume transport of the deep throughflow from the Maluku Sea to the Seram Sea below 1250 m is 2.5 Sv (1 Sv=10 6 m 3 /s), with a transport-weighted mean temperature of 3.2 °C. This result considerably increases existing estimates of the inflow of the ITF into the Indonesian seas by about 25% and lowers the total mean inflow temperature of the ITF to below 13 °C. At shallower levels, between 1250 m and the sea surface, the flow is directed towards the Maluku Sea, north of the passage. The typical residual velocities in this layer are low (∼3 cm/s), contributing to an estimated northward flow of 0.9–1.3 Sv. When more results from the INSTANT programme for the other Indonesian passages become available, a strongly improved estimate of the mass and heat budget of the ITF becomes feasible.

Temperature, salinity and flow variability on the north-west European Shelf west of Scotland are examined. Analyses are derived from a range of marine and atmospheric data sources which together comprise a “proto-observatory” of the European Shelf to the west of the Scottish mainland. The main time series are from a current meter mooring which has been maintained on the northwest European continental shelf since June 1981, and a hydrographic section repeated at least annually across the shelf at ~ 56°N since 1975. With the exception of occasional episodes the water column at the mooring site is well mixed or weakly stratified throughout the year. The mean water temperature was 10.1 °C and the dominant mode of variance in the temperature record is the seasonal cycle (SA), with amplitude of 3.2 °C. The currents are constrained by a passage and are dominated by the semi-diurnal tidal species. There is also significant energy in SA in the along channel velocity but not in the across channel velocity. The along channel residual has mean value of 10.8 cm s − 1 directed towards the north, a clear manifestation of the coastal current, with very few, short duration periods of flow reversal. The monthly temperature anomaly time series are compared with the NE Atlantic upper layer heat content anomalies. Both anomaly time series show highs in the late 1980s and 1990s and lows in the early 1980s and mid 1990s. The overall trend is of warming at a rate of + 0.57 °C per decade, with the timing of maximum annual temperature receding by 12 days per decade through the time series. A simple barotropic dynamic balance for the along channel flow in the passage demonstrates that the near surface wind dominates the variability of the northward flow, and that both the north/south gradient in sea level slope and atmospheric pressure are significant in driving the coastal current northwards. This balance reveals a bias is previous summer-only estimates of the flow rate of the coastal current, and a revised figure approximately double that of previous estimates is suggested. Residual winter flows correlate significantly with the North Atlantic Oscillation index ( r = 0.59). In contradiction to previous published analyses, shelf salinities exhibit only weak seasonality. No single determining factor is found for the longitudinal excursion of surface isohalines across the shelf, however prolonged periods of high NAO index do coincide with a raised salinity of shelf waters.

The Pilot (later termed Prediction) and Research Moored Array in the Tropical Atlantic (PIRATA) programme, developed as a multinational network by Brazil, France and the USA, has deployed and maintained an array of 17 Autonomous Temperature Line Acquisition Systems (ATLAS) buoys in the tropical Atlantic Ocean since 1997. The Benguela Current Large Marine Ecosystem (BCLME) PIRATA buoy, called Kizomba is the south-eastern extension of the original PIRATA array of moorings. It was deployed 4 100 m deep at about 6° S, 8° E on 27 June 2006 and recovered on 9 June 2007. The mooring is fitted with a current meter/temperature sensor deployed 10–13 m deep, five temperature/conductivity sensors deployed at depths of 1, 10, 20, 40 and 120 m, five temperature sensors positioned at depths of 60, 80, 100, 140 and 180 m, and two temperature/pressure sensors at 300 m and 500 m, as well as an anemometer, air temperature, humidity and short-wave solar radiation probes, and a rain gauge. The initial results from the first year of data collected by the buoy are presented with a view to providing scientific and societal motivation for the continuation of the extension of PIRATA in the tropical South-East Atlantic. Keywords: Angola–Benguela Front; ocean observing system; PIRATA; tropical Atlantic; upwellingAfrican Journal of Marine Science 2009, 31(1): 63–71

Deep circulation in the southwestern East/Japan Sea through the Ulleung Interplain Gap (UIG), a possible pathway for deep-water exchange, was directly measured for the first time. Five concurrent current meter moorings were positioned to effectively span the UIG between the islands of Ulleungdo to the west and Dokdo to the east. They provided a 495-day time series of deep currents below 1800 m depth spanning the full breadth of the East Sea Deep and Bottom Water flowing from the Japan Basin into the Ulleung Basin. The UIG circulation is found to be mainly a two-way flow with relatively weak southward flows directed into the Ulleung Basin over about two-thirds of the western UIG. A strong, persistent, and narrow compensating northward outflow occurs in the eastern UIG near Dokdo and is first referred to here as the Dokdo Abyssal Current. The width of the abyssal current is about 20 km below 1800 m depth. The low-frequency variability of the transports is dominated by fluctuations with a period of about 40 days for inflow and outflow transports. The 40-day fluctuations of both transports are statistically coherent, and occur almost concurrently. The overall mean transport of the deep water below 1800 m into the Ulleung Basin over the 16.5 months is about 0.005 Sv (1 Sv=10 6 m 3 s −1 ), with an uncertainty of 0.025 Sv indicating net transport is negligible below 1800 m through the UIG.

The stream-coordinates mean structure of the Gulf Stream at 68°W is derived using new methods for both defining stream coordinates and interpreting bottom pressure and inverted echo sounder travel times collected during the extensive Synoptic Ocean Prediction experiment. These new analyses provide pictures of the vertical structure of Gulf Stream flows that are demonstrably dynamically consistent with the density field at all depths, in contrast to previous work that relies on simple vertical interpolations to fill gaps between sparse current meter measurements. This new view of the Gulf Stream suggests a slightly higher total mean transport, with the increases coming from both baroclinic and barotropic components, and slightly stronger recirculation cells, particularly on the southern side. The recirculation of the Gulf Stream appears to have a weak baroclinic component, perhaps 10% of the total. A significant advantage of the methodology is the ability to obtain sensible vertical and horizontal gradients of currents and density so that the vertical and cross-stream structures of the components of the mean potential vorticity can be clearly imaged. One new feature from this calculation is that the along-stream gradient of the cross-stream velocity, a term that is often ignored in potential vorticity analyses, is non-negligible (though small) and is asymmetric about the current axis. Both the derived structure and implied dynamics of the circulation can be significantly altered by small changes to the method of calculating daily stream coordinates, e.g., by carefully filtering out observations in rings or not. Arrays of pressure-equipped inverted echo sounders provide the opportunity (at reasonable cost) for properly defining the stream coordinates of energetic jets such as the Gulf Stream.

Acoustic Doppler current profiles and current meter data are combined with wind observations to describe the transport of water leaving Florida Bay and moving onto the inner shelf on the Atlantic side of the Florida Keys. A 275-day study in the Long Key Channel reveals strong tidal exchanges, but the average ebb tide volume leaving Florida Bay is 19% greater than the average flood tide volume entering the bay. The long-term net outflow averages 472 m3 s−1. Two studies in shelf waters describe the response to wind forcing during spring and summer months in 2004 and during fall and winter months in 2004–2005. During the spring–summer study, southeasterly winds have a distinct shoreward component, and a two-layer pattern appears. Surface layers move shoreward while near-bottom layers move seaward. During the winter study, the resultant wind direction is parallel to the Keys and to the local isobaths. The entire water column moves in a nearly downwind direction, and across-shelf transport is relatively small. During the summer wet season, Florida Bay water should be warmer, fresher, and thus less dense than Atlantic shelf waters. Ebbing bay water should move onto the shelf as a buoyant plume and be held close to the Keys by southeasterly winds. During the winter dry season, colder and saltier Florida Bay water should leave the tidal channels with relatively high density and be concentrated in the near-bottom layers. But little across-shelf flow occurs with northeasterly winds. The study suggests that seasonally changing wind forcing and hydrographic conditions serve to insulate the reef tract from the impact of low-quality bay water.

The warm and saline deep inflow into the Eastern Gotland Basin (EGB), which lasted from the end of November 1997 until the beginning of May 1998, was the first of a series of warm deep water inflows. Temporal fluctuations of the deep circulation were monitored at 170 m depth by two current meter moorings deployed at the north-eastern and south-western rim. The three-dimensional structure of stratification parameters was inferred from the comparison of two high-resolution hydrographic surveys carried out before and during the end of the 1997/1998 inflow event. The results indicate that near-bottom isopycnals were lifted more than 50 m during the inflow up to a depth of 170–180 m. Since the basin is enclosed at 170 m depth this implies a complete deep water renewal. Detected warm-water intrusions are shown to enhance the temperature variability on isopycnal surfaces at intermediate depth, creating strong inverse temperature gradients below the halocline in an environment with stable stratification due to salinity. Corresponding Turner angles suggest that diffusive convection may significantly contribute to diapycnal mixing in this region. In contrast, for the deepest near-bottom layers only marginally affected by intrusions, basin-scale budgets of heat and salinity suggest comparable diffusivities ( κ s = 1.3–2.1 × 10 − 5 m 2 /s for salt and κ s = 1.6–2.8 × 10 − 5 m 2 /s for potential temperature), implying that double-diffusion does not play a major role in mixing there. For the intermediate layer between 90 and 170 m, where the budget method could not be adopted, we applied an idealized model for the decay of temperature variance associated with the intrusions. The results indicated that the intrusions decay within a few weeks, corresponding to vertical diffusivities of a few times 10 − 5 m 2 /s.