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Abstract: Laboratory realizations and numerical simulations of buoyant, gravity-driven coastal plumes are summarized and compared to the inviscid geostrophic theory of . The lengths, widths and velocities of the buoyant currents, as well as their internal structure and dynamics, are studied. Agreement between the laboratory and numerical experiments and the geostrophic theory is found to depend on two non-dimensional parameters which characterize, respectively, the steepness of the plumes isopycnal interface (I) and the strength of horizontal viscous forces (Ek H , the horizontal Ekman number). In general, the numerical and laboratory experiments are in good agreement when conducted at comparable values of I and Ek H . The best agreement between experiments (both laboratory and numerical) and the geostrophic theory are found for the least viscous flows, though important departures from the theoretical predictions are nonetheless found, particularly in the early development of the plume system. At elevated values of the horizontal Ekman number, laboratory and numerical experiments depart more significantly from theory, e.g., in the rate of plume movement along the coast. A simple extension to the geostrophic theory suggests that the discrepancy between the theoretical and experimental propagation speed should be proportional to the square root of the horizontal Ekman number. The numerical simulations confirm this relationship. For some combinations of the non-dimensional parameters, instabilities develop in the seaward edge of the buoyant plumes. The laboratory and numerical experiments are used together to infer the region within parameter space within which the instabilities occur. Mixing of ambient and buoyant fluids by the plume-edge instabilities is explored using the numerical results. [Copyright &y& Elsevier]

Abstract: In this article, we consider a non-autonomous three-dimensional planetary geostrophic model of the ocean with a singulary oscillating external force depending on a small parameter . We prove the existence of the uniform global attractor . Furthermore, using the method of Chepyzhov and Vishik (2007) in the case of the two-dimensional Navier–Stokes systems, we study the convergence of as goes to zero. [Copyright &y& Elsevier]

Abstract: Accurate representation of geostrophic and hydrostatic balance is an essential requirement for numerical modelling of geophysical flows. Potentially, unstructured mesh numerical methods offer significant benefits over conventional structured meshes, including the ability to conform to arbitrary bounding topography in a natural manner and the ability to apply dynamic mesh adaptivity. However, there is a need to develop robust schemes with accurate representation of physical balance on arbitrary unstructured meshes. We discuss the origin of physical balance errors in a finite element discretisation of the Navier–Stokes equations using the fractional timestep pressure projection method. By considering the Helmholtz decomposition of forcing terms in the momentum equation, it is shown that the components of the buoyancy and Coriolis accelerations that project onto the non-divergent velocity tendency are the small residuals between two terms of comparable magnitude. Hence there is a potential for significant injection of imbalance by a numerical method that does not compute these residuals accurately. This observation is used to motivate a balanced pressure decomposition method whereby an additional “balanced pressure” field, associated with buoyancy and Coriolis accelerations, is solved for at increased accuracy and used to precondition the solution for the dynamical pressure. The utility of this approach is quantified in a fully non-linear system in exact geostrophic balance. The approach is further tested via quantitative comparison of unstructured mesh simulations of the thermally driven rotating annulus against laboratory data. Using a piecewise linear discretisation for velocity and pressure (a stabilised P 1 P 1 discretisation), it is demonstrated that the balanced pressure decomposition method is required for a physically realistic representation of the system. [Copyright &y& Elsevier]

Abstract: The cold-dome off northeastern Taiwan is commonly observed by remote-sensing of Sea Surface Temperature (SST) and in-situ observation. The recent remote-sensing SST and subsurface Argo profiles were analyzed to investigate possible formation mechanisms and dynamics. The observed time series of SST anomaly suggested that the surface cold-dome occurred more frequently in summer, including an unusual contribution due to the cold water residual associated with typhoon events. Subsurface hydrographic features from Argo float data indicated that the near-shore thermocline can be lifted up about 85m by Kuroshio dynamics, and the cold saline deep water (100m deep off northeastern Taiwan) can only result from subsurface Kuroshio. We examined the possible formation mechanisms using a duo-grids North Pacific Ocean model (DUPOM) with a horizontal resolution of 1/8° for the East Asian Seas and 1/4° for the remaining North Pacific. The model reproduced several cold-dome formation events and displayed typical cold-dome features. Further analysis shows that the geostrophic component of Kuroshio transport is the main contributor to the cold-dome formation (57.4% of the total isotherm uplift) and dominates seasonal occurrence of the cold-dome. The contribution resulting from the associated cyclonic eddy is only 3.3% of the total isotherm uplift. Additional sensitivity tests suggested that the remaining contribution (39.6% of the total isotherm uplift) is mainly due to the topographically controlled upwelling in this region. Moreover, the local boundary Ekman transport may enhance the surface appearance of the cold-dome, but plays only a minor role. [Copyright &y& Elsevier]

Abstract: Multiscale asymptotics are used to derive three systems of equations connecting the planetary geostrophic (PG) equations for gyre-scale flow to a quasigeostrophic (QG) equation set for mesoscale eddies. , following similar analysis, found eddy buoyancy fluxes to have only a small effect on the large-scale flow; however, numerical simulations disagree. While the impact of eddies is relatively small in most regions, in keeping with Pedlosky’s result, eddies have a significant effect on the mean flow in the vicinity of strong, narrow currents. First, the multiple-scales analysis of Pedlosky is reviewed and amplified. Novel results of this analysis include new multiple-scales models connecting large-scale PG equations to sets of QG eddy equations. However, only introducing anisotropic scaling of the large-scale coordinates allows us to derive a model with strong two-way coupling between the QG eddies and the PG mean flow. This finding reconciles the analysis with simulations, viz. that strong two-way coupling is observed in the vicinity of anisotropic features of the mean flow like boundary currents and jets. The relevant coupling terms are shown to be eddy buoyancy fluxes. Using the Gent-McWilliams parameterization to approximate these fluxes allows solution of the PG equations with closed tracer fluxes in a closed domain, which is not possible without mesoscale eddy (or other small-scale) effects. The boundary layer width is comparable to an eddy mixing length when the typical eddy velocity is taken to be the long Rossby wave phase speed, which is the same result found by in a reduced gravity layer. [Copyright &y& Elsevier]

Abstract: Surface frontogenesis and thermohaline intrusion are examined in a submesoscale eddy-resolving primitive-equation model simulation of an idealized summer shelfbreak front of the Middle Atlantic Bight (USA). The initial front evolves into fully developed geostrophic turbulence characterized by large Rossby number, strong vortical asymmetry, and k −3 eddy kinetic energy and density spectra (k is the horizontal wavenumber). The baroclinic eddies are trapped in the upper 20m, and their growth is limited by conversion from the eddy to mean kinetic energy. The surface frontogenesis drives vigorous thermohaline intrusions of density-compensated temperature and salinity anomalies. Warmer saltier slope waters are subducted in the wave troughs, while colder fresher shelf waters are upwelled in the wave crests. The model results compare well with the observed distribution of subsurface salinity maxima. The total eddy induced onshore salt flux is comparable to the estimated salt budget in the Mid-Atlantic shelf. [Copyright &y& Elsevier]

Abstract: Closed loop mesoscale eddies were identified and tracked in the Ulleung Basin of the southwestern Japan/East Sea (JES) using the winding-angle (WA) methodology, for mapping the absolute geostrophic currents into surface streamlines of flow. The geostrophic velocity used here was the sum of the Archiving, Validation and Interpretation of Satellite Oceanographic data (AVISO), time variable velocity and the 1992–2007 mean geostrophic velocity. Local sampling bias was removed using the drifter observations. This WA methodology of deriving the Lagrangian path lines that drifters followed over a 7-day period was validated by individual drifter tracks and it demonstrated closed looping eddy motions. The WA method demonstrated that less than 6% of the closed streamlines appeared when drifters did not show a closed loop in their vicinity, compared to 30% of the excess detection rate by the Okubo–Weiss method of locating closed loop structures. Three groups of eddies were identified: (1) Coastal Cold and Warm Eddies, which appeared in the area between the coast of southern Korea and the East Korean Warm Current (EKWC), when a southward coastal current was present, (2) Frontal Cold and Warm Eddies, which were formed in the region of the seaward extension of the meandering EKWC, north of Ulleung Island and (3) Ulleung Warm Eddies (UWE) and Dok Cold Eddies (DCE), which appeared during meanders of the EKWC, in the Ulleung Basin. No seasonal concentration for eddy generation and eddy population was found. The average radius of eddies was about 38–60km. These were born, moved in an erratic pattern and then died in the vicinity where the EKWC separated from the coast and formed a large meander. The time-mean large meander formed meridionally concentrated bands of positive and negative relative vorticity. The cyclonic (cold) eddies tend to reside within the band of positive time-mean relative vorticity, and the anticyclonic (warm) eddies reside within the bands of negative relative vorticity. Six UWE and four warm eddies, in the Yamato Basin (about 10% of warm eddies), were sustained longer than a year. Because the large meander of the EKWC appeared to be controlled by topography, and the JES is a nearly enclosed basin with rapid flow-out to the east through the narrow Tsugaru Strait, there was little eddy energy propagation to the west. The warm eddies in the southwestern part of the JES appeared to be interacting very locally with the mean flow. [Copyright &y& Elsevier]

Abstract: The mean circulation of the surface layer of the southwestern Japan/East Sea (JES) was examined using current measurements collected at 15m by satellite-tracked drifters and merged sea level anomalies from satellite altimeters. The study of circulation patterns in this paper focused on the inflow passing through the western channel of the Korea Strait from the East China Sea. Empirical Orthogonal Function (EOF) analysis of non-seasonal sea level anomalies revealed that significant energy in the circulation pattern of Ulleung Basin was controlled by the inflow conditions through the Korea Strait. Three circulation patterns were identified that depended on the initial relative vorticity of the inflow. When inflow had initially large negative vorticity, the flow gained more negative vorticity due to deepening of the bottom (stretching) and then turned right after entering the JES. The inflow then followed the path of the Tsushima Warm Current along the coast of Japan. When the inflow was strong, with a speed in excess of 55cm/s and with a large positive vorticity, potential vorticity appeared to be conserved. In this case, the EKWC followed isobaths along the coast and then left the coast, following topographic features north of Ulleung-Do. The northward flowing jet developed inertial meandering after leaving the coast, which is a characteristic of many western boundary currents. The regular, bimonthly deployments of drifters in the western portion of the Korea Strait revealed that splitting or branching of the flow through the western channel of the Korea Strait occurred only 15% of the time. And splitting or branching rarely occurred during the fall and winter seasons, when the inflow splitting was previously reported in hydrographic surveys. The time-averaged circulation map of the EKWC and its seaward extension were considerably enhanced by using regularly sampled geostrophic velocities calculated from sea level anomalies to remove biases in the mean velocity that were caused by irregular spatial and temporal drifter observations. The East Korean Warm Current, a mean coastal current along the Korean coast, behaved like the simple model by in which the generation of the Ulleung Warm Eddy and the meandering circulation pattern were well reproduced. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: Inter-annual variability in the magnitude and timing of the spring bloom was investigated for the Oyashio region (40 °-48 °N, 143 °E-152 °E) using 10 years (from 1998 to 2007) of satellite ocean-color data. Geostrophic currents were examined using satellite altimeter data. Early spring blooms (>1.5mgm−3) occurred in early April 2001 and late March 2002. The 2001 bloom continued for one month. Late blooms occurred from mid-May 1999, early June 2004 and late April 2006, continuing for about 1 month, 8 days and 16 days, respectively. A strong bloom (4.7mgm−3) also occurred in mid-April 1998; however, it terminated in early May. We classified the Oyashio region based on the pattern of temporal variation of Chl-a concentration from March to June. The spatio-temporal variability in Chl-a concentration during spring was different among years. The area where Chl-a concentration was highest in April was more extensive in 2001, 2002 and 2006 than usual. In 1999, the area where Chl-a concentration was highest in May was the widest among the 10 years. Mesoscale eddies and currents with high velocity were frequently observed in the area of high Chl-a concentration east of Hokkaido, propagating Coastal Oyashio Water of low salinity and low density into the oceanic region. That strengthened stratification in the surface layer. We suggest that this seaward transfer of coastal water could be one of the important factors for phytoplankton distribution in two ways: (1) horizontal advection of water with high Chl-a concentration and (2) enhancement of stratification in the oceanic region. [Copyright &y& Elsevier]

Abstract: The ECCO–GODAE global estimate of the ocean circulation 1992–2007 is analyzed in the region of the Indonesian Throughflow (ITF), including the Southern Ocean flow south of Australia. General characteristics are an intense month-to-month noise, only weak trends, and an important annual cycle (which is not the focus of attention). Apart from the details of the unresolved flows within the various passages, and right on the equator, the region and its large-scale climate effects appears to be accurately diagnosed by large-scale geostrophic balance, so that the ITF can be calculated either from the upstream or the downstream balanced flow (but no simple reference level can be defined). The INSTANT program occurs during a more or less typical three-year period. Indications of response to the large 1997–1998 El Niño are weak. [Copyright &y& Elsevier]

Seven whale sharks were tracked using satellite-linked tags from Ningaloo Reef, off northern Western Australia, following tagging in April and June 2002 and April–May 2005. We investigated how the movements of those whale shark tracks were influenced by geostrophic surface currents during sequential one-week periods by using a passive diffusion model parameterised with observed starting locations of the sharks and weekly maps of surface current velocity and direction (derived from altimetry). We compared the outputs from the passive diffusion model and maps of chlorophyll- a concentration (SeaWiFs/MODIS) and with the actual tracks of the sharks using GIS and generalized linear mixed-effects models (GLMM). The GLMM indicated very little support for passive diffusion with sea-surface ocean currents influencing whale shark distributions in the north eastern Indian Ocean. Moreover, the sharks' movements correlated only weakly with the spatial distribution of sea-surface chlorophyll- a concentrations. The seven whale sharks had average swimming speeds comparable with those recorded in other satellite tracking studies of this species. Swimming speeds of the seven sharks were similar to those reported in previous studies and up to three times greater than the maximum sea-surface current velocities that the sharks encountered while traversing into lower southerly latitudes (moving northward towards the equator). Our results indicate that whale sharks departing from Ningaloo travel actively and independently of near-surface currents where they spend most of their time despite additional metabolic costs of this behaviour. [ABSTRACT FROM AUTHOR]

Abstract: Flow fluctuations inside an anticyclonic eddy in summertime Funka Bay were examined using three moorings and hydrographic data. The flow pattern above a sharp pycnocline with a concave isopycnal structure during the mooring period was characterized by high mean kinetic energy and relatively low eddy kinetic energy. The ratios of eddy to mean kinetic energy were equal to or less than one, and the mean flow field and isopycnal structure indicated the existence of a stable anticyclonic eddy above the sharp pycnocline under approximate geostrophic balance. Larger flow fluctuations with periods longer than 7 days were dominant inside the eddy. The low-frequency flow fluctuations are accompanied by north to northeastward movement of the eddy with deepening of the pycnocline and spin-up of the anticyclonic circulation. The wind field over Funka Bay is characterized by bay-scale wind fluctuations. The bay-scale winds are greatly influenced by the land topography around Funka Bay, resulting in non-uniform structure with significant wind stress curl. The bay-scale wind fluctuations are termed “locally modified wind” in the present study. The locally modified wind has a negative (positive) wind stress curl in the central–northeastern (southwestern) region of Funka Bay. The north to northeastward movement of the eddy is caused by horizontal non-uniform supply of vorticity from the locally modified wind forcing by the Ekman pumping process. Through this process, the anticyclonic circulation is enhanced (weakened) in the central–northeastern (southwestern) part of the eddy, resulting in the eddy moving north to northeastward with the pycnocline deepening and spin-up of the anticyclonic circulation. The locally modified wind forcing induces low-frequency flow fluctuations through the movement of the eddy in summertime Funka Bay. [Copyright &y& Elsevier]

Abstract: Changes in the behavior of individual animals in response to environmental characteristics can provide important information about habitat preference, as well as the relative risk that animals may face based on the amount of time spent in hazardous areas. We analyzed movement and habitat affinities of ten loggerhead turtles (Caretta caretta) tagged with satellite transmitters in the spring and fall of 1998 near Madeira, Portugal for periods of 2–10months. We analyzed the behavior of these individuals in relation to the marine environment they occupied. As a measure of behavior we calculated the straightness index (SI), the ratio of the displacement of the animal to the total distance traveled, for individual weekly segments of the 10 tracks. We then extracted information about chlorophyll a concentration, sea-surface temperature (SST), bathymetry, and geostrophic current of the ocean in a 20-km buffer surrounding the tracks, and examined their relationship to the straightness index using generalized linear models. Chlorophyll a value, bathymetry and SST were significantly related to the straightness index of the tracks of all ten animals, as was the circular standard deviation of the geostrophic current (Wald’s test: p =0.001, p =0.008, p =0.025, and p =0.049, respectively). We found a significant negative relationship between straightness index and chlorophyll, and positive relationships with ocean depth and SST indicating that animals are spending more time and searching more thoroughly in areas with high chlorophyll concentrations and in areas that are shallower, while moving in straight paths through very warm areas. We also found a positive relationship between straightness index and the circular standard deviation of surrounding geostrophic currents suggesting that these turtles are more likely to move in a straight line when in the presence of diffuse, less-powerful currents. Based on these relationships, we propose that conservation planning to reduce overlap of turtles with fishing operations should take into account the locations of bathymetric features such as seamounts and upwelling locations where chlorophyll concentrations are high. This analysis is an effective way to characterize areas of high-use habitat for satellite-tagged marine vertebrates, and allows for comparisons of these characteristics between species and among individuals. [Copyright &y& Elsevier]

Abstract: Pacific bluefin tuna (Thunnus orientalis) have spawning grounds in waters stretching from south of Okinawa to east of Taiwan. This species is typical of fishes that spawn seasonally in small, limited areas. Any marked change in the marine environment of the spawning grounds is likely to have a direct impact on larval survival and growth. We conducted rearing experiments on larvae to investigate these impacts and found that a reduction in temperature resulted in poor growth during the juvenile stage, even if larval survival rates did not change. In the wild, this reduced growth rate is likely to reduce survival rates because smaller juveniles have poorer swimming ability and their ability to avoid predators is also reduced. This is especially important since the Kuroshio current, which connects the spawning grounds to the nursery grounds, transports larvae rapidly because of its faster surface current (the western boundary current), thus larvae arriving too quickly in coastal waters can be exposed to very cold temperatures. An ocean model (MIROC) simulation under a climate warming scenario () predicted that the temperature in the spawning ground would be 3°C higher in 2100 than in present time, while the transport to nursery grounds would also be faster. In this case, the combination of several mechanisms would control the recruitment of juvenile bluefin. On the spawning grounds, high temperatures exceeding the optimal range would increase larvae mortality and any surviving larvae would reach the nursery grounds more quickly, but warmer coastal waters would have less negative impact on their growth. We forced a model of larval drift with MIROC output fields to study the complex response of bluefin tuna recruitment. As a result, the predicted survival rates of larvae arriving in Japanese coastal waters in 2100 would decline to 36% of present recruitment levels. [Copyright &y& Elsevier]

Abstract: Within the framework of the TUNIBAL project that focused on Atlantic bluefin tuna (Thunnus thynnus) larval ecology, ichthyoplankton surveys were conducted from 2001 to 2005 off the Balearic archipelago, which is recognized as one of the main spawning areas of the eastern Atlantic stock of this species. In each survey, a regular sampling grid of about 200 stations, 10 nautical miles apart were sampled. CTD casts and oblique Bongo 60 and surface Bongo 90 plankton tows were carried out. The occurrence frequencies of Atlantic bluefin tuna, albacore tuna (Thunnus alalunga) and bullet tuna (Auxis rochei) larvae in quantitative Bongo 60 samples were 0.14, 0.29 and 0.49 respectively. Mean larval abundances in these positive samples were relatively high: 31 larvae 10m−2 for Atlantic bluefin tuna, 17 for albacore tuna and 31 for bullet tuna. All species had patchy distributions since more than 90% of the stations showed larval densities under 10 larvae 100m−3 (70% showed even less than 2 larvae 100m−3), whereas in some isolated spots, we recorded abundances as high as 867 (Atlantic bluefin) or 872 (bullet tuna) larvae 10m−2. These results allowed us to relate larval distribution to mesoscale hydrographic features and to characterize the spawning habitat of these species. Single Quotient Parameter analyses were applied to spatial (depth), physical (temperature, salinity, dissolved oxygen and geostrophic current velocities) and biological (mesozooplankton biomass) variables to determine the environmental preferences of each species for spawning. Results showed that the complex hydrodynamic scenarios around the Balearic Islands, due to the interaction between the inflowing surface Atlantic water masses (AW) and Mediterranean surface waters (MW), play a key role in determining the abundance and distribution of tuna larvae in this area, especially in the case of Atlantic bluefin tuna. Spawning of this species seems to take place mainly in offshore mixed waters, as suggested by their preferences for waters with salinities between 36.9 and 37.7, located near frontal areas in the confluence of AW and MW. Atlantic bluefin tuna start to spawn once sea surface temperatures (SST) are over 20.5°C, and preferentially in the range of 21.5–26.5°C. Its larval distribution suggests that spawners reach the Balearic Sea in association with the inflowing AW. However, bullet tuna and albacore tuna larvae, species whose Mediterranean stocks stay in this sea year round, had a more widespread distribution and were found both in MW and AW. Bullet tuna starts to spawn in shallower waters near the shelf break once the SST reaches 19°C, and shows significant preferences for waters over 23.5°C. Similar to Atlantic bluefin tuna, albacore tuna spawn in offshore waters, but its spawning peak is later than its congeneric species, since it has a significant preference for even warmer waters, over 27°C. [Copyright &y& Elsevier]

Abstract: Data from Argo floats indicate that significant salinity changes have occurred in the North Pacific thermocline relative to data collected in the previous two decades, including observations obtained as part of the WOCE hydrographic program. Such a salinity decrease on both isopyncals and isobars implies a freshening scenario in the near-surface source region of this water mass. The frequently repeated meridional section P16 supports this inference. The subsurface salinity freshening likely began in the early 1990s, strengthened through 1997, and continued into the 2000s; the surface salinity freshening had commenced by 1984 and continued through the first decade of the 21st century. The spatial distribution of salinity change on the density surface σθ=25.5 is examined through comparisons of Argo and most of the North Pacific WOCE sections (1985-1994) and between Argo and the Hydrobase climatology, largely composed of data from the late 1970s through the mid-1980s. Both comparisons show a large-scale, basin-wide decrease in subsurface salinity through the Argo time period used in this analysis (2003-2006). The salinity difference is maximum in the northeast area and spreads southward and westward, approximately following geostrophic streamlines. [Copyright &y& Elsevier]

Abstract: Altimetry has become a powerful tool to understand the dynamics of the deep-sea ocean circulation. Despite the technical problems encountered in the coastal zone by this observational technique, resulting in large data gaps in those areas, solutions already exist to mitigate this issue and to allow the retrieval of coastal information from existing altimetric data. Using some of these solutions, we have reprocessed a new set of 14.5years of the TOPEX/Poseidon and Jason-1 satellite altimeter data over the Northwestern Mediterranean Sea, leading to a significant increase in the quantity of available data near coastlines. Time series of geostrophic surface velocity anomalies have been computed from the along-track altimeter sea level anomalies. In this paper, we evaluate the ability of these altimeter-derived currents to capture the main surface circulation features and the associated seasonal variability in the area of interest. In-situ ADCP current measurements are used to estimate the accuracy of altimeter geostrophic surface velocity anomalies at different locations on the shelf edge. The results indicate good qualitative altimeter performances at seasonal time scales, confirming that altimetry is reliable to observe synoptic variations of the Liguro–Provençal–Catalan Current System. The seasonal evolution of the shelf edge flow is then documented using results from satellite altimetry and from sea surface temperature (SST). The regional picture of the shelf edge circulation that emerges agrees fairly well with previous knowledge (the flow is much stronger during winter than during summer) but also reveals interesting aspects of the coastal current system: (1) the characteristics of the seasonal cycle observed appear highly consistent along the Northwestern Mediterranean shelf break, suggesting a continuous current from the Tyrrhenian to the Balearic Seas, (2) the relationship with the Balearic Current appears somewhat more complex and suggests that its evolution is controlled by another inflow contribution, at least in spring, (3) the seasonal variations of the shelf edge flow over a particular year can show large discrepancies with the averaged picture presented in this study, since large year to year differences are observed. [Copyright &y& Elsevier]

Abstract: A field experiment was conducted across the Luzon Strait in July 2007, and a total of 51 profiles covering variables of horizontal velocity, temperature, salinity, and pressure were collected at 11 stations. Using this observation, the volume transport through the Luzon Strait, its differences between July 2007 and October 2005, and the distribution of subtidal flow and geostrophic flow have been investigated. The net transport has a two-layer vertical structure, which is eastward both in the upper layer (<26kgm−3 σ 0), and in the intermediate layer (26–27.3kgm−3 σ 0), while it is westward in the deeper layer (>27.3kgm−3 σ 0), with respective values of 3.0, 4.0, and −1.5Sv. The net transport is eastward, and estimated to be 5.5Sv. The distribution of the subtidal flow in the intermediate layer shows that a westward flow exists in the northern part, countered by an eastward flow existing in the southern part of the strait. This distribution is in direct contrast to the previous results obtained in October 2005, in which a westward flow occurs in the south countered by an eastward flow in the north in the intermediate layer. This suggests that the flow pattern varies greatly from October 2005 to July 2007 not only in the upper layer but also in the intermediate layer. The deep layer, on the other hand, shows few changes between the two observation periods. [Copyright &y& Elsevier]

Abstract: Samples obtained in the entrance of the Sea of Cortés were used to study the distribution of euphausiids. This area has a complex hydrography with mixing of the California Current water from the north with Gulf of California and tropical waters arriving from the south probably from the warm pool in southern México, as shown by satellite images and hydrography. The origin of the different water masses is also reflected in their species composition. Three sectors can be recognized according to hydrographic evidence: North, South, and East, with each showing differences in species composition. The dominant species was the neritic low- oxygen-affinity species Euphausia lamelligera, followed by Euphausia eximia, Euphausia tenera, and Euphausia distinguenda. Significant differences exist in postlarval abundance between the three sectors. Early larval stages were found everywhere, but frontal areas of the southern open-ocean sector showed higher abundances, implying greater reproductive activity. E. lamelligera was dominant near the coast in the east sector, and E. eximia, E. distinguenda and E. tenera were dominant in the northern and southern open-ocean sectors. E. tenera was the most abundant species in the western open-ocean transect, but was found mixed with other non-neritic species. Higher diversity indices were found in the northern and southern (open-ocean) sectors; however, diversity indexes were higher at night. This mixing of species was presumably caused by horizontal mixing induced from a large eddy that covers both sectors as shown by the geostrophic currents derived from altimeter data. Complex summer species distributions reflect the complex hydrographic conditions of the area, with water masses mixing, and, consequently, mixing of species with different water mass affinities. [Copyright &y& Elsevier]

Abstract: The dynamics of large-scale river plumes are investigated in idealized numerical experiments using the HYbrid Coordinate Ocean Model (HYCOM). The focus of this study is to address how the development and structure of a buoyant plume are affected by the outflow properties, as impacted by processes within the estuary and at the point of discharge to the coastal basin. Changes in the outflow properties involved vertical and horizontal redistribution of the river inflow and enhanced vertical mixing inside an idealized estuary. The development of the buoyant plume was evaluated in a rectangular, f-plane basin with flat and sloping bottom conditions and in the absence of other external forcing. The general behavior of a mid-latitude river plume was reproduced, with the development of a surface anticyclonic bulge off the estuary mouth and a surface along-shore coastal current which flows in the direction of Kelvin wave propagation (“downstream”); the momentum balance was predominantly geostrophic. Conditions within the estuary and the outflow properties at the river mouth (where observed profiles may be available) greatly impacted the fate of riverine waters. In flat bottom conditions, larger mixing at the freshwater source enhanced the estuarine gravitational circulation, promoting larger upward entrainment and stronger outflow velocities. Although the overall geostrophic balance was maintained, estuarine mixing led to an asymmetry of the currents reaching the river mouth and to a sharp anticyclonic veering within the estuary, resulting in reduced upstream flow and enhanced downstream coastal current. These patterns were altered when the plumes evolved in the presence of a bottom slope. The anticyclonic veering of the buoyant outflow was suppressed, the offshore intrusion decreased and the recirculating bulge was displaced upstream. The sloping bottom impacts were accompanied by enhanced transport and increased downstream extent of the coastal current in most cases. No major changes in the general properties and especially the vertical structure of the plumes were observed when the vertical coordinates were changed from cartesian–isopycnal, to sigma or to sigma–isopycnal. The findings offer a benchmark for coastal studies with HYCOM, where plume dynamics should be examined in tandem with additional circulation forcing mechanisms, resulting in transitions of the vertical coordinate system that are dictated by the prevailing dynamics. [Copyright &y& Elsevier]

Abstract: Discussions of the dynamics of the Antarctic Circumpolar Current (ACC) generally focus on eddies. The linear, analytical models are discussed only infrequently, and none of these models has gained widespread acceptance. These models nevertheless exist and exhibit interesting, and often realistic, features. We revisit those models, to understand their dynamics and to assess their relevance to the ACC. We focus specifically on the steady, linear, wind-driven models, and those with either a barotropic or equivalent barotropic vertical structure. The most important feature distinguishing them is their choice of geostrophic contours ( or the equivalent), whether closed or blocked. We first examine the flat bottom models. With closed geostrophic contours, the solutions have a flow which is primarily along the contours and a transport which is inversely proportional to the bottom drag coefficient. For realistic parameters, this transport is excessively large. Solution with blocked contours instead exhibit gyres, with cross-contour flow and western boundary currents. But they also have one or more circumpolar jets, which follow the geostrophic contours over most of the domain. In contrast to the closed contour models, these jets have a transport which asymptotes to a constant value when the bottom drag is vanishingly weak. We then discuss solutions with bottom topography, focusing in particular on the equivalent barotropic solution. The central parameter here is the vertical scale of the current, which determines the extent of the interaction with topography and the degree to which the geostrophic contours are blocked. The solutions with a shallow current are less affected by topography and have closed geostrophic contours and large transports. Solutions with too large vertical extent are overly-controlled by topography and exhibit only weak circumpolar transport. Solutions with an intermediate vertical scale have blocked contours and also reasonable circumpolar transport. Furthermore, these solutions exhibit strikingly realistic surface height fields. As in the flat bottom case, the solutions have an interior in Sverdrup balance and a circumpolar transport which asymptotes with vanishing bottom friction. We demonstrate that this transport can be estimated via a contour integral; the result agrees well with the full equivalent barotropic solution. Both are nevertheless roughly 50% larger than observed in Drake Passage. However, the transport can be reduced to realistic values by adding lateral dissipation to the model. Thus the equivalent barotropic model is successful at capturing the steering of the ACC by topography, given the vertical scale of the current. However, it remains to understand what determines that scale. Thermohaline forcing and lateral mixing by eddies are likely to be important. [Copyright &y& Elsevier]

Abstract: The vortex in cell (VIC) method has been found to be an attractive computational choice for solving a number of fluid dynamical problems. The Lagrangian advection of particles leads to stability of the method even for long time steps. Moreover, conservation of particle properties, such as potential vorticity, can be enshrined at the heart of the numerical procedure. In this paper we describe a numerical implementation of the VIC method for a reduced gravity, quasi-geostrophic model and make use of its novel aspects to explore the interaction of waves and turbulence on the sphere. The Lagrangian advection of particles is performed using a fourth order Runge–Kutta method and the stream-function is obtained by the inversion of potential vorticity using an underlying Eulerian grid. The scheme is tested in the simulation of Rossby and Rossby–Haurwitz waves. Encouraging results are obtained for various radii of deformations corresponding to both the atmosphere and ocean. [Copyright &y& Elsevier]

Abstract: An approximate expression is derived for the geostrophic streamfunction in approximately neutral surfaces, φ n, namelyThis expression involves the specific volume anomaly defined with respect to a reference point on the surface, Δp and ΔΘ are the differences in pressure and Conservative Temperature with respect to and , respectively, and is the thermobaric coefficient. This geostrophic streamfunction is shown to be more accurate than previously available choices of geostrophic streamfunction such as the Montgomery streamfunction. Also, by writing expressions for the horizontal differences on a regular horizontal grid of a localized form of the above geostrophic streamfunction, an over-determined set of equations is developed and solved to numerically obtain a very accurate geostrophic streamfunction on an approximately neutral surface; the remaining error in this streamfunction is caused only by neutral helicity. [Copyright &y& Elsevier]

Abstract: The Colorado University Princeton Ocean Model (CUPOM) is used here to study the early stages in the life of Millennium, a mesoscale anticyclonic ring that detached from the Loop Current on April 2001 and lasted for more than 100days. The numerical near-surface velocity field for the Gulf of Mexico is validated with the altimetry geostrophic velocities. The first 30days of numerical data, before Millennium interacts with other mesoscalar features, are closely examined both from Eulerian and Lagrangian perspectives. During this time Millennium had a near-constant rotation period of 6.5days, and particles do not leave the ring. Nevertheless, the distributions of temperature, salinity, and angular velocity confirm the existence of significant (possibly numerical) radial diffusion. Polar-coordinate phase plots for temperature–salinity anomalies and tangential–radial velocities, at several depths, illustrate the presence of an evolving oscillating pattern. Radial and tangential velocities change in phase, associated with vertical displacements of the isothermal and isohaline surfaces. A simple diffusion model with an effective diffusion coefficient of 200m2 s−1 is appropriate to grossly simulate the temporal evolution of angular velocity within Millennium. [Copyright &y& Elsevier]

Abstract: The mechanisms governing dispersion processes in the northern Yucatan coast are investigated using a barotropic numerical model of coastal circulation, which includes wind-generated and large scale currents (i.e. Yucatan Current). This work provides the foundations for studying the dispersion of harmful algal blooms (HABs) in the area. Modelling experiments include effects of climatic wind (from long term monthly mean NCEP reanalysis), short term wind events (from in situ point measurements), and Yucatan Current (YC) characteristics. Its magnitude was approximated from published reports, and its trajectory from geostrophic current fields derived from altimeter data. These provided a range of real and climatic conditions to study the routes in which phytoplankton blooms may travel. The 2-D model results show that a synthetic and conservative bloom seeded in the Cabo Catoche (CC) region (where it usually grows), moves along the coast to the west up to San Felipe (SF), where it can either move offshore, or carry on travelling westwards. The transport to the west up to SF is greatly influenced by the trajectory, intensity and proximity of the YC jet to the peninsula, which enhances the westward circulation in the Yucatan Shelf. Numerical experiments show that patch dispersion is consistently to the west even under the influence of northerly winds. When the YC flows westward towards the Campeche Bank, momentum transfer caused by the YC jet dominates the dispersion processes over wind stress. On the other hand, when it flows closer to Cuba, the local processes (i.e. wind and bathymetry) become dominant. Coastal orientation and the Coriolis force may be responsible for driving the patch offshore at SF if external forcing decreases. [Copyright &y& Elsevier]

Abstract: The probability density functions (PDFs) of sea level and geostrophic relative vorticity are examined using satellite altimeter data. It is shown that departures from a Gaussian distribution can generally be represented by two functions, and that the spatial distribution of these two functions is closely linked to the skewness and kurtosis of the PDF. The patterns indicate that strong jets tend to be identified by a zero contour in skewness coinciding with a low value of kurtosis. A simple model of the statistics of a meandering frontal region is presented which reproduces these features. Comparisons with mean currents and sea surface temperature gradients confirm the identification of these features as jets, and confirm the existence of several Southern Ocean jets unresolved by drifter data. Diagnostics from a range of idealized eddying model simulations show that there is a strong, simple relationship between kurtosis of potential vorticity and effective diffusivity. This suggests that kurtosis may provide a simple method of mapping mixing barriers in the ocean. [Copyright &y& Elsevier]

Abstract: Temperature and salinity anomalies derived from observations obtained in the period 1997–2008 are used to study the changes in physical properties off the Baja California west coast (24–31N). Near surface anomalies were used to characterize four periods of distinctive variability: (1) a warm and saline phase of El Niño 1997–1998, (2) a saline period from 1999 to 2002, (3) fresh subarctic water in 2002–2006, and (4) a saline-fresh (El Niño-La Niña) phase in late 2006 to early 2008. Subsurface (200m) salinity anomalies depicted a trend towards saltier conditions (ΔS∼0.1) from 2001 onwards, and did not show the four periods discernible near surface. EOF analysis of sea surface wind stress and wind stress curl suggested that after the intense westerly winds in late 2001, freshening during late 2002–2006 was due to the weakening (strengthening) of the North Pacific Current (Aleutian Low), and to a decrease of wind stress curl produced upwelling. Data also showed differences in the timing and magnitude of anomalies observed between the north (poleward of 28N) and the south (equatorward of 28N). Subsurface geostrophic currents demonstrated the existence of two large scale cyclonic gyres, one associated with a subarctic domain in the northern region, and another having tropical characteristics. The likely role of subsurface cyclonic pairs in the definition of a provincial boundary, and the importance in influencing the CCS ecosystem, are discussed. [Copyright &y& Elsevier]

Abstract: During the February 1981 cruise FIBEX MD-25 between 30–50°E and 61–64°S, hydrography showed the presence of two gyres, confirmed by the geostrophic circulation relative to 1000 m from Levitus climatology, at the borders of these gyres concentrations of highly morphologically differentiated krill were found. Gaussian component analysis of krill samples, pooled by sectors, showed three cohorts of Euphausia superba in the western sector and one in the eastern sector. Across the sampling area, Thysanoessa macrura and E. superba occurred at separate stations. Analysis of cohorts in T. macrura separated two size groups in both the western and the eastern sectors. The use of a Differentiation Index (D.I.) [Färber-Lorda, J., 1990. Somatic length relationships and ontogenetic morphometric differentiation of Euphausia superba and Thysanoessa macrura of the southwest Indian Ocean during summer (February 1981). Deep-Sea Res. 37, 1135–1143.], based on somatic lengths, allows studying certain morphological differences within the populations sampled. Morphologically different and bigger males II (D.I. from 2.8 to 3.5) were present only in the southern transect while smaller males I (D.I. from 3.5 to 5.0) were present over the entire area. Biochemical composition of both species showed significant differences among stations for protein, lipids, and carbohydrates. A significant difference in lipid content was found between males I, and males II. For T. macrura, percentage of lipid content in mature animals was much higher than that in E. superba. The D.I. size distribution showed that when populations of E. superba were highly differentiated (corresponding to mature animals) in morphology, lipid content was high, and they were located near a gyre. Differences in morphometry can influence distribution of the species, because different developing stages have different swimming capacities. It is shown that, together with hydrography and trophic conditions, lipid content and morphometry of krill populations, are different but complementary aspects that help to understand krill ecology and distribution. [Copyright &y& Elsevier]

Abstract: Northern Norwegian shelf regions are highly productive, supporting fisheries rich in commercially important species such as cod, herring and capelin. It has been long recognized that the mesoscale jets, meanders and eddies associated with interactions between the North Atlantic Current, Norwegian Coastal Current and regional bottom topographic features such as troughs, banks and shelfbreaks play important roles in transporting and retaining zooplankton. To investigate zooplankton distributions and their correspondence with the physical fields, three large-scale surveys with mesoscale resolutions on physical and biological fields were conducted in northern Norwegian shelf regions between latitudes 68°15′N and 70°15′N in springs of 2000–2002. Survey results provide insights into the relationships between zooplankton distributions and the physical features such as fronts, the Norwegian Coastal Current and eddies related to topographic features. The physical and biological data are integrated and analyzed focusing on water types, estimation of geostrophic currents from direct current measurements, along-shelf transport of zooplankton, and retention of zooplankton by the mesoscale meander–eddy over a typical bank area on the shelf. The estimated mean transport in the upper 100m on the shelf in the survey region is approximately 6.4×103 tonneswetweightday−1 northward. High zooplankton abundances were found over both Malangsgrunnen and Sveinsgrunnen banks. The specific accumulation rate from northward–southward transport in the upper 100m over Malangsgrunnen was approximately 0.08day−1, while variable currents with an offshore gradient of zooplankton abundance over Sveinsgrunnen implies an offshore dispersion of coastal-originated zooplankton cohort. [Copyright &y& Elsevier]

Abstract: A new high-resolution Eulerian numerical method is proposed for modelling quasigeostrophic ocean dynamics in eddying regimes. The method is based on a novel, second-order non-dissipative and low-dispersive conservative advection scheme called CABARET. The properties of the new method are compared with those of several high-resolution Eulerian methods for linear advection and gas dynamics. Then, the CABARET method is applied to the classical model of the double-gyre ocean circulation and its performance is contrasted against that of the common vorticity-preserving Arakawa method. In turbulent regimes, the new method permits credible numerical simulations on much coarser computational grids. [Copyright &y& Elsevier]

Abstract: In this paper we prove the local-in-time well-posedness for the 2D non-dissipative quasi-geostrophic equation, and study the blow-up criterion in the critical Besov spaces. These results improve the previous one by Constantin et al. [P. Constantin, A. Majda, E. Tabak, Formation of strong fronts in the 2D quasi-geostrophic thermal active scalar, Nonlinearity 7 (1994) 1495–1533]. [Copyright &y& Elsevier]

Abstract: The Ushant tidal front is the dominant feature of the summer season hydrological structure of the Iroise Sea. It separates tidally mixed coastal waters from thermally stratified open Celtic Sea waters. This article reports on observations made in September 2007 during two short cruises that took place aboard R/V “Côtes de la Manche”, and gives a general account of the physical structure of the front along one cross-frontal transect. The data set comprises data from a 4 month ADCP mooring, short CTD/fluorescence/nutrients transects, Lagrangian drifter trajectories, and HF radar surface current measurements. One finding is that the surface and bottom fronts, being affected by different dynamical influences, are not necessarily coincident in the vertical. This entails that the opposite density gradients located above and below the thermocline depth do not necessarily compensate, and can each be associated with a significant surface geostrophic expression. A second finding is that mixing effects bear a very strong influence on the thermal structure of the warm-water intrusions associated with frontal cyclonic eddies of the kind described by Pingree [1978. Cyclonic eddies and cross-frontal mixing. Journal of the Marine Biological Association of the United Kingdom 58 (4), 955–963]. [Copyright &y& Elsevier]

Abstract: Inferring geostrophic velocity fields from CTD data distributions can be handicapped by the impossibility of referring dynamic height to a no-motion level. This is often the case over the continental shelf, but also at open sea, even when velocity measurements (e.g. from a vessel mounted ADCP) are available. In this paper we test and compare four different methods aimed to estimate the geostrophic and total velocity fields from hydrodynamical data. Two of them can either use only CTD data (then relying on the election of a no-motion level) or incorporate ADCP data (through a multivariate interpolation); the other two methods always combine CTD and ADCP data. A 3D primitive equation model is used to reproduce realistic scenarios that provide control velocity fields and typical CTD and ADCP data profiles. The chosen scenarios represent different dynamic situations (in terms of data quality, bathymetric constrictions and dynamical characteristics such as the relative ageostrophic/geostrophic velocity variance) and make possible a broad discussion on the capabilities and limitations of the examined methods. Results show that the performance of the methods is highly dependent on the dynamics to be resolved. The combination of CTD and ADCP data constitutes the best approach for most of the analyzed situations, though special attention has to be paid when dealing with low quality ADCP data and when the circulation is characterized by intense non-divergent ageostrophic velocities. [Copyright &y& Elsevier]

Abstract: Spiny lobsters have a relatively long larval phase with a planktonic duration of about 1 year. Phyllosomas lack efficient swimming ability and large-scale oceanic geostrophic currents are responsible for long-distance transport of larvae away from the spawning area. This raises the possibility that adult stocks might be connected across large distances by larvae transport. We investigated larval dispersion across the Tropical Atlantic (20°N–15°S; 15°E–45°W) using a simple advection–diffusion model. The model updates the position of each virtual larva every day, over 365 days using the surface geostrophic velocity fields derived from satellite altimetry. The diffusive part of the model was calculated from drifting buoy velocities. We calculated the mean zonal and meridional diffusivity (kx =3.97×107 cm2/s and ky =2.05×107 cm2/s) to incorporate into the model. The velocities obtained from the altimeter data were correlated with drifting buoy velocities resulting in a good agreement for both zonal (r =0.94, p =0.05) and meridional (r =0.65, p =0.05) components. This suggests that satellite-derived geostrophic flow is a good estimation for the real mean surface velocity field in the study region. Simulations indicate that Brazilian continental shelf adult stocks are connected to larvae released from oceanic islands, such as São Pedro and São Paulo Archipelago, Atol das Rocas and Fernando de Noronha Archipelago. Simulations also indicate that virtual larvae from the Ivory Coast are retained in the eastern side of the basin, whereas Cape Verde Archipelago virtual larvae do not spread far from the spawning area because of the local mesoscale eddy activity. [Copyright &y& Elsevier]

Abstract: Atmospheric phenomena such as the quasi-stationary Rossby waves, teleconnection patterns, ultralong persistent blockings and the polar/subtropical jet are characterized by planetary spatial scales, i.e. scales of the order of the earth’s radius. This motivates our interest in the relevant physical processes acting on the planetary scales. Using an asymptotic approach, we systematically derive reduced model equations valid for atmospheric motions with planetary spatial scales and a temporal scale of the order of about 1 week. We assume variations of the background potential temperature comparable in magnitude with those adopted in the classical quasi-geostrophic theory. At leading order, the resulting equations include the planetary geostrophic balance. In order to apply these equations to the atmosphere, one has to prescribe a closure for the vertically averaged pressure. We present an evolution equation for this component of the pressure which was derived in a systematic way from the asymptotic analysis. Relative to the prognostic closures adopted in existing reduced-complexity planetary models, this new dynamical closure may provide for more realistic increased large-scale, long-time variability in future implementations. [Copyright &y& Elsevier]

Abstract: We introduce a mixed discontinuous/continuous finite element pair for ocean modelling, with continuous quadratic layer thickness and discontinuous velocity. We investigate the finite element pair applied to the linear shallow-water equations on an f-plane. The element pair has the property that all geostrophically balanced states which strongly satisfy the boundary conditions have discrete divergence equal to exactly zero and hence are exactly steady states of the discretised equations. This means that the finite element pair has excellent geostrophic balance properties. We also show that the element pair applied to the non-rotating linear shallow-water equations does not have any spurious small eigenvalues. We illustrate these properties using numerical tests and provide convergence calculations which show that the numerical solutions have errors which decay quadratically with element edge length for both velocity and layer thickness. [Copyright &y& Elsevier]

Abstract: The circulation of the Gulf of Lion, a large continental shelf north of the western basin of the Mediterranean Sea, is complex and highly variable. During stratified conditions, unexpected barotropic eastward currents can be detected, mostly in the western part of the gulf. Care is given to retrieve inertial oscillations when necessary. The primitive-equation free-surface model Symphonie is used to investigate the processes which can generate and influence these eastward currents. Three main wind forcing create these barotropic eastward currents: northwesterlies channelled in the western part of the gulf, northwesterlies and north winds both homogeneous throughout the gulf. In the first case, the wind stress curl of the channeled northwesterlies generates an elongated cyclonic circulation in the western part of the Gulf of Lion. The southern part of this cyclonic circulation is a barotropic eastward current, detected west of longitude 4.5°E. In the second case, a homogeneous northwesterly wind creates an intrusion of the along-slope geostrophic current on the shelf, generating a strong coastal jet going northward above Cap Creus. In stratified conditions, intrusion at this western end of the continental shelf only occurs during this type of wind forcing. The coastal jet goes north then detaches itself from the coast and goes eastward, north of the 100 m isobath. In the third case, a homogeneous north wind creates an eastward current which occupies the whole shelf north of latitude 43°N. The first two cases are studied in more details since cruise data corroborate the model simulations. The striking characteristic of these eastward currents is that they are barotropic despite the stratified conditions. Otherwise, their amplitude and exact locations are slightly different for the different cases of circulation. These eastward currents probably have an impact on the residence time of water masses in the Gulf of Lion, and hence on the total water budget of the gulf, as well as on primary production and biogeochemical fluxes. [Copyright &y& Elsevier]

Abstract: An eddy-resolving numerical simulation for the Peru–Chile system between 1993 and 2000 is analyzed, mainly for the 1997–1998 El Niño. Atmospheric and lateral oceanic forcings are realistic and contain a wide range of scales from days to interannual. The solution is validated against altimetric observations and the few in situ observations available. The simulated 1997–1998 El Niño closely resembles the real 1997–1998 El Niño in its time sequence of events. The two well-marked, sea-level peaks in May–June and November–December 1997 are reproduced with amplitudes close to those observed. Other sub-periods of the El Niño seem to be captured adequately. Simple dynamical analyses are performed to explain the 1997–1998 evolution of the upwelling in the model. The intensity of the upwelling appears to be determined by an interplay between alongshore, poleward advection (related to coastal trapped waves) and wind intensity, but also by the cross-shore geostrophic flow and distribution of the water masses on a scale of 1000km or more (involving Rossby waves westward propagation and advection from equatorial currents). In particular, the delay of upwelling recovery until fall 1998 (i.e., well after the second El Niño peak) is partly due to the persistent advection of offshore stratified water toward the coast of Peru. Altimetry data suggest that these interpretations of the numerical solution also apply to the real ocean. [Copyright &y& Elsevier]

• Simple biogeochemical model reproduces phosphate variability in Oyashio region. • Coastally trapped current system is a major factor of phosphate transport in winter. • Winter monsoon strength is an indicator for coastally trapped current. • Ekman upwelling in the Sea of Okhotsk is driving force of decadal variability. • West Pacific teleconnection pattern is key factor for decadal variability of phosphate. In the Oyashio region, remarkable climatic signals are observed in biogeochemical parameters such as phosphate (PO 4) concentration and debate continues regarding possible causes. Using a regional ice–ocean coupled model with a simple biogeochemical cycle, this study investigated the mechanisms controlling interannual–decadal variations in surface PO 4 in the Oyashio region and their relationships to climate change. Hindcast experiments forced with atmospheric reanalysis data for 1980–2010 and 18.6-year tidal mixing strength in the Kuril Straits qualitatively simulated interannual–decadal variations of surface PO 4 , including a realistic seasonal cycle. Interannual fluctuations of simulated PO 4 in the Oyashio region are prominent in winter and characterized by year-to-year variability. Budget analysis of PO 4 in the mixed layer showed that the wintertime increase in PO 4 is caused by lateral advection as well as by local vertical convection. The geostrophic current variability responsible for lateral advection of PO 4 is related primarily to the barotropic response of arrested topographic waves in the Sea of Okhotsk as well as the wind-driven gyre in the North Pacific, both of which are regulated by the strength of the wintertime monsoon atmospheric pattern. On a decadal timescale (>7 years), temporal variations of surface PO 4 in the Oyashio region are characterized by decadal-scale fluctuation with positive (negative) peaks around 1985, 1995, and 2005 (1990 and 2000). A series of sensitivity experiments demonstrated that the decadal variability of PO 4 is largely explained by atmospheric wind conditions; however, modulation by 18.6-year tidal mixing is not negligible. Diagnostic analysis of wind-forced-experiment data revealed that the decadal PO 4 signal is advected from the Sea of Okhotsk, where 8-year leading wintertime Ekman upwelling supplies PO 4 -rich water in the northern shelf region, and that the responsible atmospheric circulation is related to the West Pacific pattern. Our model simulation suggests that the wintertime wind-driven current system in the Sea of Okhotsk is important to the system feeding surface nutrients into the Oyashio region on an interannual–decadal timescale. [ABSTRACT FROM AUTHOR]

Upcoming satellite missions will observe the sea surface height (SSH) fields at a very high spatial resolution, which has generated an urgent need to better understand how well geostrophy can represent the ocean current field at finer scales, particularly in coastal regions characterized by complex flow geometry. We conduct statistical and spectral analyses of high-resolution surface currents and SSHs off the Oregon coast to examine the relative contribution of geostrophy and ageostrophy in coastal ocean currents. We analyze forward numerical simulations based primarily on a regional ocean model (ROMS) and use regional observations of high-frequency radar (HFR)-derived surface currents and altimeter-derived geostrophic currents and a subset of global domain numerical simulations (MITgcm) as secondary resources. Regional submesoscale ageostrophic currents account for up to 50% of the total variance and are primarily associated with near-inertial currents and internal tides. Geostrophy becomes dominant at time scales longer than 3 to 10 days and at spatial scales longer than 50 km, and is dependent on the depth and distance from the coast in the cross-shore direction. Ageostrophy dominates in the near-inertial and super-inertial frequency bands, which correspond to near-inertial motions (Coriolis force dominates) and high-frequency internal waves/tides (pressure gradient dominates), respectively. Because of ageostrophy, it may not be possible to estimate submesoscale currents from SSHs obtained from upcoming satellite missions using the geostrophic relationship. Thus, other concurrent high-resolution in-situ observations such as HFR-derived surface currents, together with data assimilation techniques, should be used for constructive data integration to resolve submesoscale currents. • Dynamical relationships between coastal surface currents and SSHs are examined. • Delineation of geostrophy and ageostrophy and their balance are presented. • Coastal ageostrophy is attributed to near-inertial variance and internal tides. [ABSTRACT FROM AUTHOR]

• Subbottom profiler data in Canada Basin, Arctic Ocean, reveal contourites. • Contourites are within mixed systems of turbidity and contour current origin. • Contourites suggest cyclonic movement of Arctic Ocean Bottom Current (AOBC). • Higher sediment flux and more vigorous AOBC were likely during past glacial epochs. Canada Basin Abyssal Plain (CBAP) of the Arctic Ocean is incredibly flat and featureless at first appearance. Sediments of the basin have been interpreted to be turbidites interbedded with hemipelagic sediments. It is hypothesised, however, that deep-ocean geostrophic currents are active here as they are in most ocean basins. Compilations of modern bathymetry and subbottom profiler data are used to assess the possibility of ocean currents and their influence on sediment distribution within Canada Basin. Off of the Alaska-Beaufort margin, eastwardly deflected levees and fans in 3000 to 3800 m water depth along with oblique sediment waves on top of these features suggest a mixed system of turbidity currents influenced by cyclonic flowing geostrophic currents. These features probably formed during glaciations and lower sea level stands when the adjacent Chukchi Shelf was subaerial. Sediment delivery to the margin was likely more pronounced than today, and bottom current activity was presumably intensified. A large (100 km-wide) plastered drift and smaller bedforms were revealed by subbottom profile data along the Canadian Arctic Archipelago margin, in 3000 to 3850 m water depth. It is presumed that these deposits were formed as plumes of sediment, input through glacial outwash or outwash via the Mackenzie River. These plumes were then affected by deep contour-following currents to produce contourites. Large (up to 30 km wavelength) migrating bedforms within northern CBAP are believed to have resulted from turbidity current plumes sourced from the Mackenzie Fan that were additionally influenced by contour current reworking as part of returning cyclonic flow of deep geostrophic currents. There is little to no age control to groundtruth the stratigraphy observed in seismic profiles, but it seems likely, given their near-surface appearance, that sediment input and bottom current intensity was heavily influenced by climatic conditions related to past glaciations and associated relative sea level changes. [ABSTRACT FROM AUTHOR]

Abstract: In this article, we study some robust control problems associated with the multilayer quasi-geostrophic equations of the ocean and related to data assimilation in oceanography. We consider higher norms (compared to [T. Tachim Medjo, Robust control problems associated with the multilayer quasi-geostrophic equations of the ocean, Appl. Math. Optim. 51(3) (2005) 333–360]) in the definition of the cost functionals. We prove the existence and uniqueness of solutions. The result relies on better a priori estimates on the solutions to the multilayer quasi-geostrophic system obtained using a new formulation that we introduce for the multilayer quasi-geostrophic equation of the ocean. The new formulation replaces the non-homogenous boundary conditions (and the non-local constraint) on the stream-function by a simple homogenous Dirichlet boundary condition. [Copyright &y& Elsevier]

• Heat and salt are redistributred from east to west by mean and eddy fluxes. • 2/3 of the heat lost to the atmosphere occurs in the cyclonic boundary currents. • Winds force exchange of fresh water between the Greenland Sea and shelf. The locations, times, and mechanisms by which heat and salt are transported through and within the Nordic Seas are discussed. The analysis is based on a regional, high resolution coupled sea ice-ocean numerical model, a climatological hydrographic data set, and atmospheric reanalysis. The model and climatology are broadly consistent in terms of heat loss, water masses, and mean geostrophic currents. The model fields are used to demonstrate that the dominant exchange between basins is an export of warm, salty water from the Norwegian Sea into the Greenland and Iceland Seas, with both the mean cyclonic boundary current system and eddy fluxes playing important roles. In both the model and the climatology, approximately 2/3 of the heat loss to the atmosphere over the Nordic Seas is found over the mean cyclonic flow and 1/3 takes place within the closed recirculations in the interior of each of the basin gyres, with the Norwegian Sea having the largest heat loss. The seasonal cycle is dominated by local air-sea heat flux within the gyres while it is dominated by lateral advection in the cyclonic boundary current, particularly in the northern Norwegian and Greenland Seas. The freshwater flux off the east Greenland shelf is correlated with the local winds such that in winter, when winds are generally towards the southwest, freshwater is advected onto the shelf and in summer, when winds are weak or towards the northeast, freshwater is advected into the Greenland Sea, which leads to salinification in winter and freshening in summer. [ABSTRACT FROM AUTHOR]

Abstract: Terrestrial organic matter (TOM) in surface sediments from the lower Yangtze River and adjacent East China Sea (ECS) shelf was characterized using elemental, stable carbon isotope and molecular analysis. The results show that it is heterogeneous and derives from various sources in the lower river transect (RC transect) and inner shelf transect (ZJ transect), but is more homogeneous and presumably derives from a single source in the cross-shelf transect (PN transect). The trends in sedimentary TOM abundance indicated by high molecular weight n-alkane abundances and distributions, lignin-derived products, δ 13C values of total organic carbon (δ 13CTOC) and ratio of TOC to total nitrogen (C/N) suggest a southward (off-estuary) transport mode of TOM along the inner shelf transect while, counter intuitively, the opposite or no trend in TOM off-estuary transport occur along the cross-shelf transect. We therefore suggest that Yangtze-discharged OM is transported southwards along the Zhejiang-Fujian coast (ZJ transect) and enters the Southern Okinawa Trough via near bottom currents, from where it is ultimately delivered back upslope to the middle shelf by the Kuroshio invading water, consistent with the hydro-chemical characteristics of the ECS. [Copyright &y& Elsevier]

Using the method of process-oriented hydrodynamic modelling, this work investigates the dispersal of particles in stratified fluids on continental margins. The fundamental principle underlying this work is that particles can be upwelled across isopycnal surfaces, given that turbulent fluctuations do generally not offset the advective displacement of a particle. This principle is validated here with the diapycnal upslope sediment transport in a bottom Ekman layer that forms under a stratified geostrophic slope current. Similarly, this study indicates that the interaction between slope currents with a submarine channel can facilitate a continuous diapycnal upslope flux of particles, confined to the lowermost 10–20 m of the water column. Velocity anomalies that facilitate this upslope sediment flux are the signature of standing topographic Rossby waves that only develop for slope currents that are left-bounded (right-bounded) by shallower water in the northern (southern) hemisphere. Findings of sensitivity studies confirm the existence of up-channel flows for a wide range of parameter values. Under the assumption that particles remain suspended in the water column, the inclusion of gravitational settling significantly increases the up-channel sediment flux. Sediment settling operates to trap particles close to the seafloor within the core of bottom-intensified up-channel flow. The author postulates that this mechanism plays an important role in biogeochemical cycles at continental margins. • Explores the dispersal of sediment particles in stratified flows on continental margins. • Interaction of slope current with submarine channel can induce upslope sediment flux. • Sediment settling enhances this upslope sediment flux. [ABSTRACT FROM AUTHOR]

Cyclothone braueri (Stomiiformes, Gonostomatidae) is a widely distributed fish inhabiting the mesopelagic zone of marine tropical and temperate waters. Constituting one of the largest biomasses of the ocean, C. braueri is a key element in most of the ecological processes occurring in the twilight layer. We focused on the ecological processes linked to early life stages in relation to marine pelagic environmental drivers (temperature, salinity, food availability and geostrophic currents) considering different regions of the Central Mediterranean Sea. A multivariate morphometric analysis was carried out using six parameters with the aim of discerning different larval morphotypes, while a fragment of 367 bp representing the 12S ribosomal RNA gene was used to perform molecular analyses aimed at determining the intraspecific genetic variability. Analysis highlighted two geographically distinct morphotypes not genetically discernible and related to the different nutritional conditions due to spatial heterogeneities in terms of temperature and food availability. The body depth (BD) emerged as an appropriate morphometric parameter to detect the larval condition in this species. Molecular analysis highlighted a moderate genetic divergence in the fish population, showing the recurrence of two phylogroups not geographically separated. • Two larval morphotypes not genetically discernible were found in the regions. • Larval morphotypes were related to temperature and trophic conditions. • The body diameter emerged as an appropriate parameter to detect the larval condition. • Molecular analysis evidenced not geographically separated haplogroups. [ABSTRACT FROM AUTHOR]

Abstract: The geostrophic circulation between the Costa Rica Dome and Central America is described from CTD observations collected in two surveys: (a) The Wet Cruise in September–October 1993, and the Jet Cruise in February–March 1994. Poleward coastal flow was present on both occasions, but the transition from flow around the dome to the poleward Costa Rica Coastal Current flow was quite tortuous because of the presence of mesoscale eddies. In particular, a warm anticyclonic eddy was found off the Gulf of Fonseca during both cruises, at an almost identical position and with similar dimensions (150m deep, 250km in diameter) and surface speed (0.5ms−1). In the Gulf of Panama, poleward flow was also observed, weaker in February–March 1994 than in September–October 1993, when it penetrated to 600m depth and transported 8.5Sv. In September–October 1993, the current between the dome and the coast was mostly ∼100m deep and weak (∼0.15ms−1), although in its southern side it was deeper (∼450m) and faster at 0.3ms−1. The poleward transport between the dome and the coast was ∼7Sv. In February–March 1994 the Costa Rica Dome was a closed ring adjacent to the continental shelf, ∼500km in diameter, at least 400m deep, had geostrophic surface speeds ∼0.25ms−1, and subsurface maximum speed (0.15–0.20ms−1) at ∼180m depth; the associated uplift of the isotherms was ∼150m. The flow in the south part of the dome splits into two branches, the weakest one going around the dome and the strongest one continuing east and turning south before reaching the Gulf of Panama. [Copyright &y& Elsevier]

Abstract: The main components of large-scale circulation of the eastern tropical Pacific were identified in the mid 20th century, but the details of the circulation at length scales of 102 km or less, the mesoscale field, are less well known particularly during summer. The winter circulation is characterized by large mesoscale eddies generated by intense cross-shore wind pulses. These eddies propagate offshore to provide an important source of mesoscale variability for the eastern tropical Pacific. The summer circulation has not commanded similar attention, the main reason being that the frequent generation of hurricanes in the area renders in situ observations difficult. Before the experiment presented here, the large-scale summer circulation of the Gulf of Tehuantepec was thought to be dominated by a poleward flow along the coast. A drifter-deployment experiment carried out in June 2000, supported by satellite altimetry and wind data, was designed to characterize this hypothesized Costa Rica Coastal Current. We present a detailed comparison between altimetry-estimated geostrophic and in situ currents estimated from drifters. Contrary to expectation, no evidence of a coherent poleward coastal flow across the gulf was found. During the 10-week period of observations, we documented a recurrent pattern of circulation within 500km of shore, forced by a combination of local winds and the regional-scale flow. Instead of the Costa Rica Coastal Current, we found a summer eddy field capable of influencing large areas of the eastern tropical Pacific. Even in summer, the cross-isthmus wind jet is capable of inducing eddy formation. [Copyright &y& Elsevier]

Abstract: A historical data set is used to describe the coastal transition zone off Northwest Africa during spring 1973 and fall 1975, from 17° to 26°N, with special emphasis on the interaction between subtropical (North Atlantic Central Waters) and tropical (South Atlantic Central Waters) gyres. The near-surface geostrophic circulation, relative to 300m, is quite complex. Major features are a large cyclonic pattern north of Cape Blanc (21°N) and offshore flow at the Cape Verde front. The large cyclone occurs in the region of most intense winds, and resembles a large meander of the baroclinic southward upwelling jet. The Cape Verde frontal system displays substantial interleaving that may partly originate as mesoscale features at the coastal upwelling front. Property–property diagrams show that the front is an effective barrier to all properties except temperature. The analysis of the Turner angle suggests that the frontal system is characterized by large heat horizontal diffusion as a result of intense double diffusion, which results in the smoothing of the temperature horizontal gradients. Nine cross-shore sections are used to calculate along-shore geostrophic water-mass and nutrient transports and to infer exchanges between the coastal transition zone and the deep ocean (import: deep ocean to transition zone; export: transition zone to deep ocean). These exchanges compare well with mean wind-induced transports and actual geostrophic cross-shore transport estimates. The region is divided into three areas: southern (18–21°N), central (21–23.5°N), and northern (23.5–26°N). In the northern area geostrophic import is roughly compensated with wind-induced export during both seasons. In the central area geostrophic import is greater than wind-induced export during spring, resulting in net import of both water (0.8Sv) and nitrate (14kmols−1), but during fall both factors again roughly cancel. In the southern area geostrophy and wind join to export water and nutrients during both seasons, they increase from 0.6Sv and 3kmols−1 during fall to 2.9Sv and 53kmols−1 during spring. [Copyright &y& Elsevier]