Ocean Mixing

Turbulence has been modeled by a two equation k-ω turbulence model to investigate the wind induced circulation patterns in coastal waters. Predictions of the model have been compared by the predictions of two equation k-ε turbulence model. Kinetic energy of turbulence is k, dissipation rate of turbulence is ε, and frequency of turbulence is ω. In the three dimensional modeling of turbulence by k-ε model and by k-ω model, a composite finite element-finite difference method has been used. The governing equations are solved by the Galerkin Weighted Residual Method in the vertical plane and by finite difference approximations in the horizontal plane. The water depths in coastal waters are divided into the same number of layers following the bottom topography. Therefore, the vertical layer thickness is proportional to the local water depth. It has been seen that two equation k-ω turbulence model leads to better predictions compared to k-ε model in the prediction of wind induced circulation in coastal waters.

Turbulence and wave motion driven by horizontal shear layers below/above stably stratified regions MOHAMED MOUSTAOOUI, Arizopna State University, JULIAN C.R. HUNT, University College London, ALEX MA-HALOV, Arizona State University -Analytical studies and high resolution 3dimensional numerical simulations of a jet show how eddies in turbulent shear flows moving with mean velocity ∆U relative to external upper or lower stably stratified regions with buoyancy frequency N o interact with these regions. Internal waves are not generated if the Richardson number is less than a critical value Ri * . If Ri< Ri the stratification only perturbs the irrotational motions outside the shear layer. But if Ri <Ri<Ri * intense interfacial shear layers forms at the top of the shear layer and then a second layer forms at a height of order w + /N o , that bounds a mixed layer of trapped turbulent eddies and weak mean shear. This double layer structure has similar scales as the natural layering process in turbulent stratified flows. When Ri>Ri * , first the upper and then the lower interfacial layers break up, the peak shear in the interface decreases and a narrow band spectrum of internal waves are generated which propagate upwards although they do not significantly interact with the turbulence in the shear layer. The Reynolds shear stress associated with the waves varies with Ri, but over a wide range of Ri is as much as about 1/5 of the peak shear in the shear layer; when normalised on the vertical variance at the interface it increases in proportion to √ Ri -1.

Turbulence and wave motion driven by horizontal shear layers below/above stably stratified regions MOHAMED MOUSTAOOUI, Arizopna State University, JULIAN C.R. HUNT, University College London, ALEX MA-HALOV, Arizona State University -Analytical studies and high resolution 3dimensional numerical simulations of a jet show how eddies in turbulent shear flows moving with mean velocity ∆U relative to external upper or lower stably stratified regions with buoyancy frequency N o interact with these regions. Internal waves are not generated if the Richardson number is less than a critical value Ri * . If Ri< Ri the stratification only perturbs the irrotational motions outside the shear layer. But if Ri <Ri<Ri * intense interfacial shear layers forms at the top of the shear layer and then a second layer forms at a height of order w + /N o , that bounds a mixed layer of trapped turbulent eddies and weak mean shear. This double layer structure has similar scales as the natural layering process in turbulent stratified flows. When Ri>Ri * , first the upper and then the lower interfacial layers break up, the peak shear in the interface decreases and a narrow band spectrum of internal waves are generated which propagate upwards although they do not significantly interact with the turbulence in the shear layer. The Reynolds shear stress associated with the waves varies with Ri, but over a wide range of Ri is as much as about 1/5 of the peak shear in the shear layer; when normalised on the vertical variance at the interface it increases in proportion to √ Ri -1.

We present a comprehensive multi-proxy analysis spanning 550,000 years from the outer Labrador Sea region at the Integrated Ocean Drilling Program (IODP) Sites U1302/1303. We combine new benthic foraminiferal stable oxygen (δ 18 O) and carbon (δ 13 C) isotope records, with sediment elemental composition and authigenic neodymium isotope measurements, to provide insights into deep-water mass sourcing and changes of the Deep Western Boundary Current (DWBC), which exports North Atlantic Deep Water (NADW) into the wider North Atlantic as part of the lower limb of the Atlantic Meridional Overturning Circulation. We find that a prominent DWBC likely remained a persistent feature within the Labrador Sea region throughout the past 550 kyr. However, glacial peaks of marine isotope stage (MIS) 14 to MIS 2 were consistently characterized by a weaker or shallower DWBC, while all interglacial periods of MIS 13a to MIS 1, with the exception of MIS 7e, were marked by enhanced DWBC. Additionally, the dominant deep-water masses feeding into the DWBC during these glacial-interglacial periods varied from regional (K-rich sediment, unradiogenic εNd) to more distal sources from the Nordic Seas (Ti-rich sediment, radiogenic εNd). Yet, these changes in deep-water provenance did not consistently correlate with DWBC strength, suggesting that additional factors may have played a significant role in shaping the DWBC strength or core depth throughout the geological past.

Recibido en junio de 1995; aceptado en marzo de 1996 RESUMEN Con base en un modelo lineal, se estiman los principales parámetros de las mareas y ondas internas semidiumas de altas frecuencias para la plataforma y pendiente continental cerca de las costas mexicanas de los estados de Jalisco y Colima. Por datos de la distribución vertical de la frecuencia de Brunt-Väisälä y por medio de cartas batimttricas actualizadas, se calculan las trayectorias de los flujos de energía (y) de la marea interna y la pendiente del fondo marino (a) en el talud continental, respectivamente. Se muestra que para la mayoría de las secciones del fondo se encuentran valores cercanos al crítico aly = 1, lo cual testifica que existen las condiciones favorables para la generación de las mareas internas en el area de estudio de la costa del Océano Pacífico. Con base en el modelo de Baines (1982), se realizan los cálculos del flujo de energía de la onda barotrópica M2 a las ondas internas y se estiman sus amplitudes. Se muestra que los flujos de energía y amplitud de la marea interna dependen no sólo de la intensidad de la marea barotrópica, sino también de los iingulos de su llegada al borde de la plataforma.

Les processus de mélange sont essentiels au fond de l&#39;océan car ils permettent la remontée des eaux froides abyssales vers la surface. Une grande question de la communauté océanographique concerne la contribution des ondes internes à ces processus car ces ondes, bien que peu énergétiques en regard des courants marins par exemple, sont présentes partout dans l&#39;océan et y déferlent. Les principales sources d&#39;énergie des ondes internes sont le vent et l&#39;interaction de la marée avec la topographie sous-marine. C&#39;est cette dernière configuration que nous considérons ici, au travers d&#39;expériences de laboratoire et numériques, dans le contexte académique d&#39;un talus continental bidimensionnel dans un océan uniformément stratifié. Nous examinons plus particulièrement le processus de génération du champ d&#39;ondes internes et la structure cinématique de ce champ. Nous discutons également de la manifestation des effets non linéaires lorsque le champ d&#39;ondes se ...

 The ocean cavity near the grounding zone of the Ross Ice Shelf is vertically stratified with a boundary layer freshened by ice melting.  A tidally-mixed zone and tidal currents are absent from this 10 m thick ocean cavity in the flexure zone.  The observed stratification and low current velocities result in low melt rates (7 cm yr - 1 ).

Observations suggest that enhanced turbulent dissipation and mixing over rough topography are modulated by the transient eddy field through the generation and breaking of lee waves in the Southern Ocean. Idealized simulations also suggest that lee waves are important in the energy pathway from eddies to turbulence. However, the energy loss from eddies due to lee wave generation remains poorly estimated. This study quantifies the relative energy loss from the time-mean and transient eddy flow in the Southern Ocean due to lee wave generation using an eddy-resolving global ocean model and three independent topographic datasets. The authors find that the energy loss from the transient eddy flow (0.12 TW; 1 TW 5 10 12 W) is larger than that from the time-mean flow (0.04 TW) due to lee wave generation; lee wave generation makes a larger contribution (0.12 TW) to the energy loss from the transient eddy flow than the dissipation in turbulent bottom boundary layer (0.05 TW). This study also shows that the energy loss from the time-mean flow is regulated by the transient eddy flow, and energy loss from the transient eddy flow is sensitive to the representation of anisotropy in small-scale topography. It is implied that lee waves should be parameterized in eddy-resolving global ocean models to improve the energetics of resolved flow.

Sites of ice-stream discharge to the continental slope build trough-mouth fans from glacigenic debris flows (GDFs), subglacial meltwater flows, and suspended sediment. Thus, past ice configurations may be interpreted from the sedimentological record. This study links the records in cores, high-resolution seismic profiles, and multibeam swath bathymetry of Hatton Slope and Fan to the changing glaciological history in Hudson Strait, one of the largest ice streams of the late Pleistocene Laurentide Ice Sheet. 14 C-AMS dates, X-ray fluorescence geochemical profiles, and oxygen isotopes in sixteen cores document sediment supply during the last glacial cycle, and earlier history is interpreted from seismic data. The Frobisher Bay slope sector has a long record of GDF deposits from severe glacial periods between MIS 6 and 22, with little impact of meltwater discharge. Masstransport events and aggrading gravel-floored valleys dominate the northern Hatton slope sector. The central slope sector shows the greatest shelf

Barotropic tidal currents flowing over rough topography may be slowed by two bottom boundary-related processes: tangential stress of the bottom boundary layer, which is generally well represented by a quadratic drag law, and normal stress from bottom pressure, known as form drag. Form drag is rarely estimated from oceanic observations because it is difficult to measure the bottom pressure over a large spatial domain. The ''external'' and ''internal'' components of the form drag are associated, respectively, with sea surface and isopycnals deformations. This study presents model and observational estimates of the components of drag for Three Tree Point, a sloping ridge projecting 1 km into Puget Sound, Washington. Internal form drag was integrated from repeat microstructure sections and exceeded the net drag due to bottom friction by a factor of 10-50 during maximum flood. In observations and numerical simulations, form drag was produced by a lee wave, as well as by horizontal flow separation in the model. The external form drag was not measured, but in numerical simulations was found to be comparable to the internal form drag. Form drag appears to be the primary mechanism for extracting energy from the barotropic tide. Turbulent buoyancy flux is strongest near the ridge in both observations and model results.

Past orbital analogues to the current interglacial, such as Marine Isotope Stage 19c (MIS 19c, ca. 800 ka), can provide reliable reference intervals for evaluating the timing and the duration of the Holocene and factors inherent in its climatic progression. Here we present the first high-resolution paleoclimatic record for MIS 19 anchored to a high-precision 40 Ar/ 39 Ar chronology, thus fully independent of any a priori assumptions on the orbital mechanisms underlying the climatic changes. It is based on the oxygen isotope compositions of Italian lake sediments showing orbital-to millennial-scale hydrological variability over the Mediterranean between 810 and 750 ka. Our record indicates that the MIS 19c interglacial lasted 10.8 ± 3.7 k.y., comparable to the time elapsed since the onset of the Holocene, and that the orbital configuration at the time of the following glacial inception was very similar to the present one. By analogy, the current interglacial should be close to its end. However, greenhouse gas concentrations at the time of the MIS 19 glacial inception were significantly lower than those of the late Holocene, suggesting that the current interglacial could have already been prolonged by the progressive increase of the greenhouse gases since 8-6 ka, possibly due to early anthropogenic disturbance of vegetation.

We experience three dimensions of space as a fixed reference system in which movement occurs in our normal lives. The movement is translation in some direction over time, which we know as velocity (speed and direction). The three spatial dimensions are normally taken as orthogonal (mutually perpendicular, as the edges of a box at a corner) and distance along each is determined with a ruler. Time is normally considered not to be a temporal dimension, because in our lives we have no access to times other than that of which we are conscious. We try to access times in the past via history and memory, and times in the future via hope and mythology, but we cannot act in either.
Fluid Dynamics is a portion of the physical science of Fluid Mechanics, or the mechanics of fluids, including both liquids and gases. The term mechanics is used as a general category in Physics to refer to the study of matter and its motion, including force, acceleration, momentum, and interactions between bodies. Specialties include Celestial Mechanics, Fluid Mechanics, and Quantum Mechanics.
Contents:  Space-time and Fluid Dynamics On Space-Time (~1990) On Fluid Dynamics (~1990) Journal Extracts-The Solution (~1987) On Time (~1990) On Waves (~1990)

Internal tides power much of the observed small-scale turbulence in the ocean interior. To represent mixing induced by this turbulence in ocean climate models, the cascade of internal tide energy to dissipation scales must be understood and mapped. Here, we present a framework for estimating the geography of internal tide energy sinks. The mapping relies on the following ingredients: (i) a global observational climatology of stratification; (ii) maps of the generation of M 2 , S 2 and K 1 internal tides decomposed into vertical normal modes; (iii) simplified representations of the dissipation of low-mode internal tides due to wave-wave interactions, scattering by smallscale topography, interaction with critical slopes and shoaling; (iv) Lagrangian tracking of low-mode energy beams through observed stratification, including refraction and reflection. We thus obtain a global map of the column-integrated energy dissipation for each of the four considered dissipative processes, each of the three tidal constituents and each of the first five modes. Modes ≥6 are inferred to dissipate within the local water column at the employed half-degree horizontal resolution. Combining all processes, modes and constituents, we construct a map of the total internal tide energy dissipation, which compares well with observational inferences of internal wave energy dissipation. This result suggests that tides largely shape observed spatial contrasts of dissipation, and that the framework has potential in improving understanding and modelling of ocean mixing. However, sensitivity to poorly constrained parameters and simplifying assumptions entering the parameterized energy sinks calls for additional investigation. The attenuation of low-mode internal tides by wave-wave interactions needs particular attention.

1. un mapeado rápido al principio y al fin de la campaña para localizar el filamento y observar los cambios en el contexto general durante el estudio; Agradecimientos Quisieramos agredecer al Capitán Ramón Argibay Fernández y a la tripulación del barco por su apoyo magnífico durante la campaña. También agradecemos al equipo de la UTM sin el cuál no hubiese sido posible llevar a cabo el estudio. Damos las gracias al servicio NEODAAS del Plymouth Marine Laboratory, UK, especialmente a Dr Peter Miller, que nos proporcionó diariamente las imagenes AVHRR y Modis Aqua durante el trabajo de campo. CAIBEX es un proyecto del Plan Nacional financiado por el Ministerio de Ciencia e Innovación (CTM2007-66408).

In this study, Arctic Ocean patterns of deep water circulation and sediment provenance during the Last Glacial (LG) were compared with the recent situation by investigating the Nd and Sr isotopic composition (143 Nd/ 144 Nd, expressed as ε Nd , 87 Sr/ 86 Sr) of the leachable and lithogenic sediment fractions as well as the elemental composition (Mn, Ca, Mg, total inorganic carbon (TIC)) on a spatially extended scale encompassing 11 sediment cores from several Arctic Ocean basins and ridges. The leachable, authigenic signature of the surface sediments implies a North Atlantic deep water source and a late Holocene circulation regime that leads to well-mixed, mostly uniform, ε Nd values of −10.9 to −10.3. Sediments from the LG have overall more variable authigenic ε Nd values (−13.9 to −7.4). Lower values specifically occur in the Amerasian and Amundsen Basins, documenting an enhanced flow of deep waters from the Makarov Basin to the Amundsen Basin probably via the Lomonosov Ridge intra-basin. In terms of detrital provenance areas, the lithogenic material deposited at the core locations cannot be unambiguously assigned to distinct source areas based on its radiogenic isotope composition, but represents a diverse mixture. Nevertheless, the Nd and Sr isotope signatures of surface sediments from the Amerasian Basin are dominated by western Arctic sources (ε Nd = −12.8 to −11.0; 87 Sr/ 86 Sr = 0.7214 to 0.7251), while Eurasian Basin surface sediments are dominated by Eurasian sources (ε Nd = − 10.9 to − 9.7, 87 Sr/ 86 Sr = 0.7178 to 0.7299), which is in agreement with previous studies. Bulk element patterns (Ca, Mg, TIC) of the studied sediments support these differences in provenance. The LG samples show the same trends with low ε Nd (−16.1 to −13.7) and high 87 Sr/ 86 Sr (0.7294) in the Canada Basin, and higher ε Nd (− 12.6 to − 8.8) and lower 87 Sr/ 86 Sr (0.7154 to 0.7249) in the Eurasian Basin sediments. However, LG samples have mostly lower and more heterogenous ε Nd and 87 Sr/ 86 Sr values than the surface samples. Our geochemical study shows that the overall circulation pattern of the deep water masses during the LG was locally influenced by brine formation but was generally similar to today. The isotopic composition of the lithogenic material from the LG is different from modern times, presumably due to shorter transport pathways of lithogenic material to the Arctic Ocean because of a lower sea level and exposed shelves during the LG. Nevertheless, the lithogenic fraction still represents a mixture from several sources.

Western boundary currents act as transport pathways for nutrient-rich waters from low to high latitudes (nutrient streams) and are responsible for maintaining midlatitude and high-latitude productivity in the North Atlantic and North Pacific. This study investigates the centennial oxygen (O 2) and nutrient changes over the Northern Hemisphere in the context of the projected warming and general weakening of the Atlantic Meridional Overturning Circulation (AMOC) in a subset of Earth system models included in the CMIP5 catalogue. In all models examined, the Atlantic warms faster than the Pacific Ocean, resulting in a greater basin-scale solubility decrease. However, this thermodynamic tendency is compensated by changes in the biologically driven O 2 consumption which dominates the overall O 2 budget. These changes are linked to the slowdown of the nutrient stream in this basin, in response to the AMOC weakening. The North Atlantic resists the warming-induced deoxygenation due to the weakened biological carbon export and remineralization, leading to higher O 2 levels. Conversely, the projected nutrient stream and macronutrient inventory in the North Pacific remain nearly unchanged.

Nd isotopes and Sm-Nd concentrations have been investigated in the clay size fraction of surface and late Quaternary sediments of the northern North Atlantic. Four sources of Nd have been identified in the surface sediments: (1) a radiogenic Nd typical of the Iceland volcanism; (2) a "Pan-African" Nd issued from eastern Greenland; (3) a "Variscan" Nd derived from the Arctic Ocean; (4) an old unradiogenic Nd related to the North American Shield. In the Iceland and Irminger basins, the major sources of Nd are the Variscan Nd derived from the Arctic Ocean and the Iceland Nd, except in the western Irminger Basin where the Pan-African Nd originating from eastern Greenland is dominant and labels sedimentary supplies linked to the Denmark Strait Ovefflow Water. Nd derived from Icelandic volcanism is never clearly dominant, even on the Reykjanes Ridge, and the Nd derived from the American Shield becomes dominant only in the Labrador Sea. Sediments lying in the pathway of the Western Boundary Undercurrent have Nd isotopic compositions which are shifted towards more radiogenic values indicating an input of material from the eastern basins, carried by this deep current. Late Quatemary sediments were cored from the southern Greenland Rise (core 90-013-013) and eastern Labrador Rise (Orphan Knoll; core 91-045-094). In core 90-013-013, ENd values during the Last Glacial Maximum are as low as-20, but subsequently rose to-9 in the modem sediments, indicating that the sedimentary material during the Last Glacial Maximum was dominated by unradiogenic Nd from the North American Shield. This may be related to a lesser outflow of the Western Boundary Undercurrent. In core 91-045-094, located along the Labrador Current trajectory, a dominant supply of North American Shield Nd is recorded, perhaps originating at least partially from the Hudson Strait. The Sm-Nd data are compatible with smectite vs. illite studies at the same sites which suggest a continuous but more modest Western Boundary Undercurrent supply during Last Glacial Maximum.

Fluorometric measurements were taken from a CTD at San Jorge Bay (northern Chile) to adjust a Gaussian model, in order to determine the vertical distribution of phytoplankton biomass using satellite-derived chlorophyll a data. Calibration was done using two in situ data sets. Each chlorophyll a profile was smoothed by a moving average and adjusted with a Gaussian model, obtaining the mean Gaussian parameters for both data sets. The mean Gaussian model obtained for one of the data sets was valid for a chlorophyll a range between 1.17 and 51.8 mg m-3 , and the maximum concentration was located at 19.20 and 0.25 m depth, respectively. The 20 January 2011 color image was analyzed for the study area, and the modal concentration was 0.78 mg m-3 , with 95% of the data varying between 0.5 and 20.0 mg m-3. The adjusted mean Gaussian model was valid for 80.26% of the study area. The analysis was expanded to the rest of January 2011 (14 images), and the model was valid for 84.40% (±12.48%) of the study area. The same procedure was followed but without applying the moving average to the in situ data, and the Gaussian model obtained in this case was valid for 93.72% (±8.89%) of the study area. Other studies of the optical properties of water are required for a better interpretation of the color images for this coastal system.

Fluorometric measurements were taken from a CTD at San Jorge Bay (northern Chile) to adjust a Gaussian model, in order to determine the vertical distribution of phytoplankton biomass using satellite-derived chlorophyll a data. Calibration was done using two in situ data sets. Each chlorophyll a profile was smoothed by a moving average and adjusted with a Gaussian model, obtaining the mean Gaussian parameters for both data sets. The mean Gaussian model obtained for one of the data sets was valid for a chlorophyll a range between 1.17 and 51.8 mg m–3, and the maximum concentration was located at 19.20 and 0.25 m depth, respectively. The 20 January 2011 color image was analyzed for the study area, and the modal concentration was 0.78 mg m–3, with 95% of the data varying between 0.5 and 20.0 mg m–3. The adjusted mean Gaussian model was valid for 80.26% of the study area. The analysis was expanded to the rest of January 2011 (14 images), and the model was valid for 84.40% (±12.48%) of th...

Enhanced biological production associated with flow disturbance due to island or shallow seamounts is known as the "Island Mass Effect" (IME) (Doty & Oguri, 1956). Because ridges topped by multiple small islands and seamounts are a consistent feature along the Kuroshio flow path (Hasegawa, 2019), several studies since the 1950s have reported that the Kuroshio induces IMEs (e.g., Furuya et al., 1986; Uda & Ishino, 1958, and others). However, in these earlier studies, the detailed physical processes of the IMEs were not thoroughly studied due to the complexities of the flow disturbance associated with the abrupt topographic features. Since the reporting of extremely large upwelling velocities of O(0.01 m s −1) and turbulence kinetic energy dissipation rates of O(10 −4 W kg −1) in lees of small islands located along the Kuroshio main axis (Hasegawa et al., 2008, 2004), the ridges (I-Lan, Tokara, and Izu) over which the Kuroshio passes have been recognized as key locations for open-ocean upwelling and mixing. In recent years, multiple intensive field campaigns have been carried out with the latest observational instruments, building a quantitative understanding of the detailed physical mechanisms of flow-topography interactions in the Kuroshio Current at these ridges. For example, Chang et al. (2016) used an echo-sounder to observe 100 m-scale Kelvin-Helmholtz billows, which are structures resembling a cat's eye generated by the interaction of the Kuroshio with a seamount north of Green Island along the east coast of Taiwan. Nagai et al. (2017) developed a tow-yo-style turbulence profiling system (Underway VMP), that was used to observe layers of strong turbulence associated with bands of near-inertial wave shear excited by flow-topography interactions in the Tokara Strait. Tsutsumi et al. (2017) conducted a transect survey crossing the Kuroshio Current on the lee sides of small islands and seamounts with a turbulence microstructure profiler in order to grasp the overall distribution of turbulent vertical mixing in the Tokara Strait. Moreover, some studies have observed cold surface water formation on the lee sides of small islands in the Kuroshio and have taken these observations as evidence for the

Observations suggest that the tropical Pacific Ocean has lost oxygen since the 1960s leading to the expansion of its oxygen minimum zone (OMZ). Attribution to anthropogenic forcing is, however, difficult because of limited data availability and the large natural variability introduced by the Pacific Decadal Oscillation (PDO). Here, we evaluate the PDO influence on oxygen dynamics and OMZ extent using observations and hindcast simulations from two global ocean circulation models (NEMO-PISCES, MOM6-COBALT). In both models, the tropical Pacific oxygen content decreases by about 30 Tmol.

Observations suggest that the tropical Pacific Ocean has lost oxygen since the 1960s leading to the expansion of its oxygen minimum zone (OMZ). Attribution to anthropogenic forcing is, however, difficult because of limited data availability and the large natural variability introduced by the Pacific Decadal Oscillation (PDO). Here, we evaluate the PDO influence on oxygen dynamics and OMZ extent using observations and hindcast simulations from two global ocean circulation models (NEMO-PISCES, MOM6-COBALT). In both models, the tropical Pacific oxygen content decreases by about 30 Tmol.

The application of the classical logarithmic layer model for wall-bounded shear flows to marine bottom boundary layer (BBL) usually leads to an overestimation of the friction velocity u * due possibly to the influence of form drag, stratification, and rotation of the flow vector. To gain insights on the BBL velocity scaling, acoustic Doppler current profiler (ADCP) measurements taken in the East China Sea were analyzed (a total of 270 sixteen-minute averaged velocity profiles). Single and double log-layer models, a log-wake model, and a modified log-layer (MLL) model that accounts for stratification in the upper part of the BBL (Perlin, Moum, Klymak, Levine et al. 2005) were explored. Although the first three models fit well for a majority of the profiles, the friction velocities appeared to be substantially overestimated, leading to unreasonably high drag coefficients. The friction velocity u * ml inferred from a slightly modified MLL, however, is half of that estimated using the classical log-layer assumption u * l. In a weakly stratified extended BBL, the dissipation rate ε decreases with the height from the seafloor ζ much faster than that in a homogeneous stationary BBL. This observation could be well approximated (in terms of r 2) by an exponential ε (ζ) = ε 0 e −ζ/L m or a power law decrease. The mixing length scale L m = c L h BL , whereh BL = 19-20 m is the BBL height and c L = 0.17, as well as the characteristic dissipation ε 0 , should vary in time, depending on the tidal currents and stratification in the BBL. The eddy diffusivity K N = 0.2ε/N 2 showed an inverse dependence on the Richardson number Ri according to K N = K 0 / (1 + Ri/R c), where R c is a constant and the diffusivity in nonstratified flow near the seafloor K 0 = u * κζ is specified using u * = u * ml .

The shoaling of horizontally propagating internal waves may represent an important source of mixing and transport in estuaries and coastal seas. Including such effects in numerical models demands improvements in the understanding of several aspects of the energetics, especially those relating to turbulence generation, and observations are needed to build this understanding. To address some of these issues in the estuarine context, we undertook an intensive field program for 10 days in the summer of 2008 in the St. Lawrence Estuary. The sampling involved shore-based photogrammetry, ship-based surveys, and an array of moorings in the shoaling region that held both conventional and turbulence-resolving sensors. The measurements shed light on many aspects of the wave shoaling process. Wave arrivals were generally phase-locked with the M 2 tide, providing hints about far-field forcing. In the deeper part of the study domain, the waves propagated according to the predictions of linear theory. In intermediate-depth waters, the waves traversed the field site perpendicularly to isobaths, a pattern that continued as the waves transformed nonlinearly. Acoustic Doppler velocimeters permitted inference of the turbulent energetics, and two main features were studied. First, during a period of shoaling internal waves, turbulence dissipation rates exceeded values associated with tidal shear by an order of magnitude. Second, the evolving spectral signatures associated with a particular wave-shoaling event suggest that the turbulence is at least partly locally generated. Overall, the results of this study suggest that parameterizations of wave-induced mixing could employ relatively simple dynamics in deep water, but may have to handle a wide suite of turbulence generation and transport mechanisms in inshore regions.

The shoaling of horizontally propagating internal waves may represent an important source of mixing and transport in estuaries and coastal seas. Including such effects in numerical models demands improvements in the understanding of several aspects of the energetics, especially those relating to turbulence generation, and observations are needed to build this understanding. To address some of these issues in the estuarine context, we undertook an intensive field program for 10 days in the summer of 2008 in the St. Lawrence Estuary. The sampling involved shore-based photogrammetry, ship-based surveys, and an array of moorings in the shoaling region that held both conventional and turbulence-resolving sensors. The measurements shed light on many aspects of the wave shoaling process. Wave arrivals were generally phase-locked with the M 2 tide, providing hints about far-field forcing. In the deeper part of the study domain, the waves propagated according to the predictions of linear theory. In intermediate-depth waters, the waves traversed the field site perpendicularly to isobaths, a pattern that continued as the waves transformed nonlinearly. Acoustic Doppler velocimeters permitted inference of the turbulent energetics, and two main features were studied. First, during a period of shoaling internal waves, turbulence dissipation rates exceeded values associated with tidal shear by an order of magnitude. Second, the evolving spectral signatures associated with a particular wave-shoaling event suggest that the turbulence is at least partly locally generated. Overall, the results of this study suggest that parameterizations of wave-induced mixing could employ relatively simple dynamics in deep water, but may have to handle a wide suite of turbulence generation and transport mechanisms in inshore regions.

Special volume: Advances in Spanish physical oceanography. Scientia Marina 76(Suppl.1) 2012.-- 13 pages, 12 figures, 1 table[EN] Turbidity, CTD, and temperature and shear microstructure data recorded along a 25 km transect from 8 to 69 m depth across the Ebro Delta shelf (northwestern Mediterranean) are presented. The water column was stratified and prior to the campaign the regional southwest flow was measured to have superimposed diurnal and sub-inertial components. The bottom boundary layer (BBL) at all stations deeper than 20 m has a vertical extension of 3 to 9 m, increasing to 12 m at the deeper stations and even to 14 m at a station at 45 m depth outside the studied transect. The law of the wall was identified at almost all stations with an extension ranging from 40% to 100% of that of the BBL. At some stations high dissipation rates were found in the interior of the bottom layer. The study shows the correspondence between the turbidity contents and the local mixing processes...

Field data collected during June 2005 were used to determine the relationship between the second fluorescence maximum (FMax), the top of the oxygen minimum zone (OMZ), and physical processes (coastal currents, eddies, and upwelling) in the northern region of the Eastern Tropical Pacific off Mexico (ETPM). A recurrent second FMax was observed in the ETPM, which was formed only when the upper limit of the OMZ (9.0 µmol L–1) overlapped with the 1% downwelling blue irradiance depth (Ed490). The presence of the second FMax increased the total integrated water column chlorophyll from 20% to 40%. The second FMax was absent from areas where oxygenated California Current Water (CCW) deepened the upper limit of the OMZ below 1% Ed490. The poleward Mexican Coastal Current carried less oxygenated Subtropical Subsurface Water into the area, and enabled the formation of the second FMax. The variability of the second FMax driven by mesoscale physical processes was related to coastal upwelling and ...

In this work, 16 stations in Cienfuegos Bay were optically classified in the period from 2009 to 2014 and the spatio-temporal variation of the average attenuation coefficient of light was determined, as well as its relationship with chlorophyll a and suspended solids. The average attenuation coefficient was estimated from an empirical relationship ReVIsTA INVesTIGACIONes MARINAs

Internal tide driven mixing plays a key role in sustaining the deep ocean stratification and meridional overturning circulation. Internal tides can be generated by topographic horizontal scales ranging from hundreds of meters to tens of kilometers. State of the art topographic products barely resolve scales smaller than 10 km in the deep ocean. On these scales abyssal hills dominate ocean floor roughness. The impact of abyssal hill roughness on internal-tide generation is evaluated in this study. The conversion of M 2 barotropic to baroclinic tidal energy is calculated based on linear wave theory both in real and spectral space using the Shuttle Radar Topography Mission SRTM30_PLUS bathymetric product at 1/120 resolution with and without the addition of synthetic abyssal hill roughness. Internal tide generation by abyssal hills integrates to 0.1 TW globally or 0.03 TW when the energy flux is empirically corrected for supercritical slope (i.e., 10% of the energy flux due to larger topographic scales resolved in standard products in both cases). The abyssal hill driven energy conversion is dominated by mid-ocean ridges, where abyssal hill roughness is large. Focusing on two regions located over the Mid-Atlantic Ridge and the East Pacific Rise, it is shown that regionally linear theory predicts an increase of the energy flux due to abyssal hills of up to 100% or 60% when an empirical correction for supercritical slopes is attempted. Therefore, abyssal hills, unresolved in state of the art topographic products, can have a strong impact on internal tide generation, especially over mid-ocean ridges.

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We have retrieved radiogenic hafnium (Hf) isotope compositions (3 Hf) from authigenic FeeMn oxyhydroxides of deep northwest Atlantic sediments deposited over the past 26 ka to investigate the oceanic evidence of changes in dissolved weathering inputs from NE America during the last deglaciation. The extraction of seawater-derived Hf isotopic compositions from FeeMn oxyhydroxides is not a standard procedure. Comparisons between the Al/Hf ratios and Hf isotopic compositions of the chemically extracted authigenic phase on the one hand, and those of the corresponding detrital fractions on the other, provide evidence that the composition of past seawater has been reliably obtained for most sampled depths with our leaching procedures. This is endorsed most strongly by data for a sediment core from 4250 m water depth at the deeper Blake Ridge, for which consistent replicates were produced throughout. The Hf isotopic composition of the most recent sample in this core also closely matches that of nearby present day central North Atlantic seawater. Comparison with previously published seawater Nd and Pb isotope compositions obtained on the same cores shows that both Hf and Pb were released incongruently during incipient chemical weathering, but responded differently to the deglacial retreat of the Laurentide Ice Sheet. Hafnium was released more congruently during peak glacial conditions of the Last Glacial Maximum (LGM) and changed to typical incongruent interglacial 3 Hf signatures either during or shortly after the LGM. This indicates that some zircon-derived Hf was released to seawater during the LGM. Conversely, there is no clear evidence for an increase in the influence of weathering of Lu-rich mineral phases during deglaciation, possibly since relatively unradiogenic Hf contributions from feldspar weathering were superimposed. While the authigenic Pb isotope signal in the same marine sediment samples traced peak chemical weathering rates on continental North America during the transition to the Holocene a similar incongruent excursion is notably absent in the Hf isotope record. The early change towards more radiogenic 3 Hf in relation to the LGM may provide direct evidence for the transition from a cold-based to a warm-based Laurentide Ice Sheet on the Atlantic sector of North America.

Between 1989 and 1991 the authors made observations that confirm and elucidate the coupling between harbor seiches at Puerto Princesa on Palawan Island in the Philippines and tide-generated internal solitons in the Sulu Sea. Published tidal current predictions for Basilan Strait in the Sulu Archipeligo were used to produce an index to the daily ebb tidal flows nea•r Pearl Bank where the solitons originate. The coherence between predicted maximum ebb tidal current speed and observed seiche activity was 0.60 and the phase lag between the two quantities closely matched published estimates of the time required for solitons to cross the Sulu Sea. Arrival of the Sulu Sea waves immediately offshore of Puerto Princesa in the form of internal bores corresponded in time to the initiation of harbor seiche activity. A more precise estimate of soliton travel time was determined from the time difference between predicted maximum ebb current and the initiation •of seiche activity, and it was found to have a remarkably regular seasonal pattern, which can be largely explained by seasonal variations in Sulu Sea temperature and salinity stratification. Therefore, the timing of seiche events at Puerto Princesa can be forecast based on Sulu Archipeligo tide predictions and soliton travel time. In general, the fortnightly pattern of seiche magnitude follows that of tidal current predictions, but day-today deviations are common. Seiche magnitude varies seasonally with generally low activity during the winter (northeast) monsoon and usually maximum activity late in the summer (southwest) monsoon. VOLUME 28 * Woods Hole Oceanographic Institution Contribution Number 9343.

Vertical temperature profiles were measured near the shelf edge off the coast of Palawan Island (Philippines) during the passage of several "rip bands" of choppy surface waves. Such rip bands are commonly associated with internal waves. Coincident with the passage of one of the rip bands, the temperature near the bottom decreased by 2.5°C within 1.4 min, becoming colder than any water on the shelf. Furthermore, the apparent depth of our CTD decreased by about 8 m despite the fact that the "line-out" was held fixed. We interpret these limited data, along with a sea-level record, as evidence of internal swash created by breaking internal solitary waves which are generated by tidal flow over a shallow bank in the southeastern Sulu Sea (described by

 Tidal discharges are computed by integration of the continuity equation, based on known water levels, upriver inflows and river geometry  Improvements include the use of temporally and spatially continuous nonstationary tidal data and computation of time-varying wetted areas  Mean error ratios of modeled to observed tidal flows amount to 4.5 % of the tidal discharge amplitudes in the St. Lawrence fluvial estuary

Elevated levels of productivity in the wake of Southern Ocean island systems are common despite the fact that they are encircled by high nutrient low chlorophyll (HNLC) waters. In the Crozet Plateau region, it has been hypothesized that iron from island runoff or sediments of the plateau could be fueling the austral summer phytoplankton bloom. Here, we use radium isotopes to quantify the rates of surface ocean iron supply fueling the bloom in the Crozet Plateau region. A 1-D eddy-diffusion-mixing model applied to a 228 Ra profile (t 1/2 = 5.75 yr) at a station north of the islands suggested fast vertical mixing in the upper 300 m (K z = 11-100 cm 2 s-1) with slower mixing between 300 and 1000 m (K z = 1.5 cm 2 s-1). This estimate is discussed in the context of K z derived from the CTD/LADCP data. In combination with the dissolved Fe profile at this location, we estimated a vertical flux of between 5.6 and 31 nmol Fe m-2 d-1. The cross-plateau gradients in the short-lived radium isotopes, 224 Ra (t 1/2 = 3.66 d) and 223 Ra (t 1/2 = 11.4 d), yielded horizontal eddy diffusivities (K h) of 39 m 2 s-1 and 6.6 m 2 s-1 , respectively. If we assume that the islands (surface runoff) alone were supplying dissolved Fe to the bloom region, then the flux estimates range from 2.3 to 14 nmol Fe m-2 d-1. If the plateau sediments are considered a source of Fe, and conveyed to the bloom region through deep winter mixing combined with horizontal transport, then this flux may be as high as 64 to 390 nmol Fe m-2 d-1. Combined, these Fe sources are sufficient to initiate and maintain the annual phytoplankton bloom.

Abstract. Form drag is a central process linking rough topography to ocean mixing processes. The history of the measurement of form drag in the ocean and atmosphere is reviewed. The basic equations governing form drag and its role in energy conversion are ...

We use hydrographic, velocity and drifter data from a cruise carried out in November 2008 to describe the continental slope current system in the upper thermocline (down to 600 m) between Cape Verde and the Canary Islands. The major feature in the region is the Cape Verde Frontal Zone (CVFZ), separating waters from tropical (southern) and subtropical (northern) origin. The CVFZ is found to intersect the slope north of Cape Blanc, between 22°N and 23°N, but we find that southern waters are predominant over the slope as far north as 24°N. South of Cape Blanc (21.25°N) the Poleward Undercurrent (PUC) is a prominent northward jet (50 km wide), reaching down to 300 m and indistinguishable from the surface Mauritanian Current. North of Cape Blanc the upwelling front is found far offshore, opening a near-slope northward path to the PUC. Nevertheless, the northward PUC transport decreases from 2.8 Sv at 18°N to 1.7 Sv at 24°N, with about 1 Sv recirculating ofshore just south of Cape Blanc, in agreement with the trajectory of subsurface drifters. South of the CVFZ there is an abrupt thermohaline transition at s q =26.85 kg m-3 , which indicates the lower limit of the relatively pure (low salt and high oxygen content) South Atlantic Central Water (SACW) variety that coexists with the dominant locallydiluted (salinity increases through mixing with North Atlantic Central Water but oxygen diminishes because of enhanced remineralization) Cape Verde (SACWcv) variety. At 16°N about 70% of the PUC transport corresponds to the SACW variety but but this is transformed into 40% SACWcv at 24°N. However, between Cape Verde and Cape Blanc and in the 26.85<s q <27.1 layer, we measure up to 0.8 Sv of SACWcv being transported south. The results strongly endorse the idea that the slope current system plays a major role in tropical-subtropical water-mass exchange.

Our long-term goal is to develop a parallel ocean simulation tool that is capable of simulating processes on a wide range of scales by coupling two vastly different codes, namely the Regional Ocean Modeling System (ROMS, Shchepetkin and McWilliams (2005)), and the Stanford Unstructured Nonhydrostatic Terrain-following Adaptive Navier-Stokes Simulator (SUNTANS, Fringer et al. (2006a)). The tool will adaptively nest SUNTANS, an unstructured-grid, coastal-scale code, into ROMS, a curvilinear grid, regional-scale code, in regions where the motions are small-scale and so nonhydrostatic. The nested tool will be applied to study highly nonlinear internal waves in the South China Sea in order to develop an improved understanding of mechanisms that govern their generation, propagation, and dissipation. OBJECTIVES In support of the long term goal of applying a two-way nested simulation tool to study internal waves in the South China Sea, our objectives are threefold. The first is to study internal waves in Monterey Bay in support of the AESOP DRI (Assessing the Effects of Submesoscale Ocean Parameterizations), and the second is to study fundamental internal wave processes in the South China Sea in support of the NLIWI DRI (Nonlinear Internal Waves Initiative). The third objective is to develop a two-way coupled SUNTANS-ROMS simulation tool that can be applied to an arbitrary domain of interest. Because recent work employing separate SUNTANS and ROMS simulations has focused on the California coastal current and internal waves in the Monterey Bay region, the west coast was the 14 19a. NAME OF RESPONSIBLE PERSON

A coupled biophysical model is used to examine the impact of the great Arctic cyclone of early August 2012 on the marine planktonic ecosystem in the Pacific sector of the Arctic Ocean (PSA). Model results indicate that the cyclone influences the marine planktonic ecosystem by enhancing productivity on the shelves of the Chukchi, East Siberian, and Laptev seas during the storm. Although the cyclone's passage in the PSA lasted only a few days, the simulated biological effects on the shelves last 1 month or longer. At some locations on the shelves, primary productivity (PP) increases by up to 90% and phytoplankton biomass by up to 40% in the wake of the cyclone. The increase in zooplankton biomass is up to 18% on 31 August and remains 10% on 15 September, more than 1 month after the storm. In the central PSA, however, model simulations indicate a decrease in PP and plankton biomass. The biological gain on the shelves and loss in the central PSA are linked to two factors. (1) The cyclone enhances mixing in the upper ocean, which increases nutrient availability in the surface waters of the shelves; enhanced mixing in the central PSA does not increase productivity because nutrients there are mostly depleted through summer draw down by the time of the cyclone's passage. (2) The cyclone also induces divergence, resulting from the cyclone's low-pressure system that drives cyclonic sea ice and upper ocean circulation, which transports more plankton biomass onto the shelves from the central PSA. The simulated biological gain on the shelves is greater than the loss in the central PSA, and therefore, the production on average over the entire PSA is increased by the cyclone. Because the gain on the shelves is offset by the loss in the central PSA, the average increase over the entire PSA is moderate and lasts only about 10 days. The generally positive impact of cyclones on the marine ecosystem in the Arctic, particularly on the shelves, is likely to grow with increasing summer cyclone activity if the Arctic continues to warm and the ice cover continues to shrink.

Isotopic compositions of animal tissue are an intrinsic marker commonly used to trace animal origins and migrations; however, few isotopes are effective for this purpose in marine environments, especially on a local scale. The isotope ratio of the lanthanoid element neodymium (Nd) is a promising tracer for coastal animal migrations. Neodymium derives from the same geologic materials as strontium, well known as an isotopic tracer (87 Sr/ 86 Sr) for terrestrial and anadromous animals. The advantage of the Nd isotope ratio (143 Nd/ 144 Nd, expressed as e Nd) is that it varies greatly in the ocean according to the geology of the neighboring continents, whereas oceanic 87 Sr/ 86 Sr is highly uniform. This study explored the utility of the Nd isotope ratio as a marine tracer by investigating the variation of e Nd preserved in tissues of coastal species, and the causes of that variation, in a region of northeastern Japan where the bedrock geology is highly variable. We measured e Nd and 87 Sr/ 86 Sr in seawater, river water, and soft tissues of sedentary suspension feeders: the mussels Mytilus galloprovincialis and Mytilus coruscus and the oyster Crassostrea gigas. We also measured concentrations of three lanthanoids (La, Ce, and Pr) in shellfish bodies to determine whether the Nd in shellfish tissue was derived from solution in seawater or from suspended particulates. The e Nd values in shellfish tissue varied regionally (À6 to +1), matching the ambient seawater, whereas all 87 Sr/ 86 Sr values were homogeneous and typical of seawater (0.7091-0.7092). The seawater e Nd values were in turn correlated with those in the adjacent rivers, linking shellfish e Nd to the geology of river catchments. The depletion of Ce compared to La and Pr (negative Ce anomaly) suggested that the Nd in shellfish was derived from the dissolved phase in seawater. Our results indicate that the distinct Nd isotope ratio derived from local geology is imprinted, through seawater, on the soft tissues of shellfish. This result underscores the potential of e Nd as a tracer of coastal marine animals.

This paper investigates the dynamics of the deep chlorophyll maximu m layer (DCM L) along the Fernando de Noronha Ridge in the oligotrophic western equatorial Atlantic off northeast Brazil. M ixing processes between water masses above and below the thermocline may occur in a scale of tens of meters around the 24.5 to 25.5 isopycnals, where photoautotrophs are concentrate at the bottom of the euphotic zone. The primary production at the DCM L can provide 210 (±170) metric tons of Carbon per day to the benthic community at the Rocas atoll. The behavior of isopycnals in deeper and strongly stratified waters suggest that internal waves may imp rove primary production, by lift ing the deeper and nutrient-rich South Atlantic Central Water upwards and carrying the autotrophs to brighter depths.

Western boundary currents act as transport pathways for nutrient-rich waters from low to high latitudes (nutrient streams) and are responsible for maintaining mid-and high-latitude productivity in the North Atlantic and North Pacific. This study investigates the centennial oxygen (O2) and nutrient changes over the Northern Hemisphere in the context of the projected warming and general weakening of the Atlantic Meridional Overturning Circulation (AMOC) in a subset of Earth System Models included in the CMIP5 catalogue. In all models examined, the Atlantic warms faster than the Pacific Ocean, resulting in a greater basin-scale solubility decrease. However, this thermodynamic tendency is compensated by the changes in the biologically-driven O2 consumption which dominates the overall O2 budget. These changes are linked to the slow-down of the nutrient stream in this basin, in response to the AMOC weakening. The North Atlantic resists the warming-induced deoxygenation due to the weakened biological carbon export and remineralization, leading to higher O2 levels. On the contrary, the projected nutrient stream and macro-nutrient inventory in the North Pacific remain nearly unchanged.