130,851 research outputs found
Eddy-Induced Modulation of Turbulent Dissipation over Rough Topography in the Southern Ocean
No full textMesoscale eddies are universal features of the ocean circulation, yet the processes by which their energy is dissipated remain poorly understood. One hypothesis argues that the interaction of strong geostrophic flows with rough bottom topography effects an energy transfer between eddies and internal waves, with the breaking of these waves causing locally elevated dissipation focused near the sea floor. This study uses hydrographic and velocity data from a 1-yr mooring cluster deployment in the Southern Ocean to test this hypothesis. The moorings were located over a small (~10 km) topographic obstacle to the east of Drake Passage in a region of high eddy kinetic energy, and one was equipped with an ADCP at 2800-m depth from which internal wave shear variance and dissipation rates were calculated. Examination of the ADCP time series revealed a predominance of upward-propagating internal wave energy and a significant correlation (r = 0.45) between shear variance levels and subinertial near-bottom current speeds. Periods of strong near-bottom flow coincided with increased convergence of eddy-induced interfacial form stress in the bottom 1500 m. Predictions of internal wave energy radiation were made from theory using measured near-bottom current speeds, and the mean value of wave radiation (5.3 mW m−2) was sufficient to support the dissipated power calculated from the ADCP. A significant temporal correlation was also observed between radiated and dissipated power. Given the ubiquity of strong eddy flows and rough topography in the Southern Ocean, the transfer from eddy to internal wave energy is likely to be an important term in closing the ocean energy budget
Acceleration of the Antarctic Circumpolar Current by Wind Stress along the Coast of Antarctica
No full textThe influence of wind forcing on variability of the Antarctic Circumpolar Current (ACC) is investigated using a series of eddy-permitting ocean–sea ice models. At interannual and decadal time scales the ACC transport is sensitive to both the mean strength of westerly winds along the ACC circumpolar path, consistent with zonal momentum balance theories, and sensitive to the wind stresses along the coast of Antarctica, consistent with the “free mode” theory of Hughes et al. A linear combination of the two factors explains differences in ACC transport across 11 regional quasi-equilibrium experiments. Repeated single-year global experiments show that the ACC can be robustly accelerated by both processes. Across an ensemble of simulations with realistic forcing over the second half of the twentieth century, interannual ACC transport variability owing to the free-mode mechanism exceeds that due to the zonal momentum balance mechanism by a factor of between 3.5 and 5 to one. While the ACC transport may not accelerate significantly owing to projected increases in along-ACC winds in future decades, significant changes in transport could still occur because of changes in the stress along the coast of Antarctica
Global patterns of diapycnal mixing from measurements of the turbulent dissipation rate
No full textThe authors present inferences of diapycnal diffusivity from a compilation of over 5200 microstructure profiles. As microstructure observations are sparse, these are supplemented with indirect measurements of mixing obtained from (i) Thorpe-scale overturns from moored profilers, a finescale parameterization applied to (ii) shipboard observations of upper-ocean shear, (iii) strain as measured by profiling floats, and (iv) shear and strain from full-depth lowered acoustic Doppler current profilers (LADCP) and CTD profiles. Vertical profiles of the turbulent dissipation rate are bottom enhanced over rough topography and abrupt, isolated ridges. The geography of depth-integrated dissipation rate shows spatial variability related to internal wave generation, suggesting one direct energy pathway to turbulence. The global-averaged diapycnal diffusivity below 1000-m depth is O(10?4) m2 s?1 and above 1000-m depth is O(10?5) m2 s?1. The compiled microstructure observations sample a wide range of internal wave power inputs and topographic roughness, providing a dataset with which to estimate a representative global-averaged dissipation rate and diffusivity. However, there is strong regional variability in the ratio between local internal wave generation and local dissipation. In some regions, the depth-integrated dissipation rate is comparable to the estimated power input into the local internal wave field. In a few cases, more internal wave power is dissipated than locally generated, suggesting remote internal wave sources. However, at most locations the total power lost through turbulent dissipation is less than the input into the local internal wave field. This suggests dissipation elsewhere, such as continental margins
Equilibration of the Antarctic Circumpolar Current by standing meanders
No full textThe insensitivity of the Antarctic Circumpolar Current (ACC)’s prominent isopycnal slope to changes in wind stress is thought to stem from the action of mesoscale eddies that counterbalance the wind-driven Ekman overturning—a framework verified in zonally symmetric circumpolar flows. Substantial zonal variations in eddy characteristics suggest that local dynamics may modify this balance along the path of the ACC. Analysis of an eddy-resolving ocean GCM shows that the ACC can be broken into broad regions of weak eddy activity, where surface winds steepen isopycnals, and a small number of standing meanders, across which the isopycnals relax. Meanders are coincident with sites of (i) strong eddy-induced modification of the mean flow and its vertical structure as measured by the divergence of the Eliassen–Palm flux and (ii) enhancement of deep eddy kinetic energy by up to two orders of magnitude over surrounding regions. Within meanders, the vorticity budget shows a balance between the advection of relative vorticity and horizontal divergence, providing a mechanism for the generation of strong vertical velocities and rapid changes in stratification. Temporal fluctuations in these diagnostics are correlated with variability in both the Eliassen–Palm flux and bottom speed, implying a link to dissipative processes at the ocean floor. At larger scales, bottom pressure torque is spatially correlated with the barotropic advection of planetary vorticity, which links to variations in meander structure. From these results, it is proposed that the “flexing” of standing meanders provides an alternative mechanism for reducing the sensitivity of the ACC’s baroclinicity to changes in forcing, separate from an ACC-wide change in transient eddy characteristics
La Consulta Terapéutica y el Juego del Garabato de D. W. Winnicott: sus alcances teóricos y clínicos.
No full textEn este trabajo se realiza una investigación teórica sobre dos desarrollos originales de D. W. Winnicott denominados Consulta Terapéutica, espacio del psicoanálisis aplicado que consiste en el aprovechamiento del primer o los primeros encuentros con el paciente, y Juego del Garabato, el singular método que el psicoanalista inglés implementa para ponerse en contacto con sus pacientes niños y adolescentes. Resulta necesario, para dar cuenta del complejo entramado de estos desarrollos, profundizar en conceptos centrales de la obra del autor, tales como el juego y psicoterapia, los objetos y fenómenos transicionales, la teoría del desarrollo emocional del individuo, la teoría de la comunicación y el objeto subjetivo, entre otros. Se concluye que la propuesta de Winnicott posee absoluta vigencia en sí misma, siendo a su vez extensible a otros abordajes psicoterapéuticos. Finalmente, se propone utilizar el juego del garabato como un modelo para pensar novedosas intervenciones en psicoterapia, en especial en el trabajo clínico con adolescentes.Baños, Juan Manuel. UNR; Argentina
Finescale parameterizations of turbulent dissipation
No full textThis article (1) reviews and clarifies the basic physics underpinning finescale parameterizations of turbulent dissipation due to internal wave breaking and (2) provides advice on the implementation of the parameterizations in a way that is most consistent with the underlying physics, with due consideration given to common instrumental issues. Potential biases in the parameterization results are discussed in light of both (1) and (2), and illustrated with examples in the literature. The value of finescale parameterizations for studies of the large-scale ocean circulation in the presence of common biases is assessed. We conclude that the parameterizations can contribute significantly to the resolution of large-scale circulation problems associated with plausible ranges in the rates of turbulent dissipation and diapycnal mixing spanning an order of magnitude or more
RRS James Cook Cruise 090, 30 Aug - 17 Sep 2013. Ocean Surface Mixing, Ocean Sub-mesoscale Interaction Study (OSMOSIS)
No full textThe RRS James Cook 090 cruise (Vigo, 30 August 2013 - Santander, 17 September 2013) was the concluding phase of the fieldwork for the Ocean Surface Mixing, Ocean Sub-mesoscale Interaction Study (OSMOSIS) consortium. The primary goal of the fieldwork element of OSMOSIS was to obtain a year-long time series of the properties of the ocean surface boundary layer and its controlling 3-d physical processes with an array of moorings (two nested clusters of 4 moorings each centred around a central mooring) and gliders deployed near the Porcupine Abyssal Plain (PAP) observatory, with a view to gaining understanding of and developing parameterizations for those processes. The JC090 cruise sought to recover the moorings and gliders, to conduct hydrographic and biogeochemical measurements for mooring and glider calibration, and to obtain opportunistic measurements of upper-ocean microstructure and air-sea CO2 fluxes. Operations were very successful. All moorings and gliders were safely recovered, with near-complete data return. Three out of the four guard buoys that had been deployed around the inner mooring cluster were also recovered, with the fourth guard buoy (which had sunk upon deployment) failing to rise to the surface after release. Nearly 700 upper-ocean microstructure profiles were obtained in several transects within the mooring area. 9 CTDs were conducted, and underway measurements of biogeochemical parameters and air-sea CO2 fluxes obtained throughout much of the cruise. The meteorological buoy at the PAP observatory was also serviced successfully
Deep boundary current disintegration in Drake Passage
No full textThe fate of a deep boundary current that originates in the Southeast Pacific and flows southward along the continental slope of South America is elucidated. The current transports poorly ventilated water of low salinity (a type of Pacific Deep Water; PDW), into Drake Passage. East of Drake Passage, the boundary current breaks into fresh anticyclonic eddies, nine examples of which were observed in mooring data from December 2009 to March 2012. The observed eddies appear to originate mainly from a topographic separation point close to 60°W, have typical diameters of 20–60 km and accompanying Rossby numbers of 0.1–0.3. These features are likely to be responsible for transporting PDW meridionally across the ACC, explaining the near-homogenization of Circumpolar Deep Water properties downstream of Drake Passage. This mechanism of boundary current breakdown may constitute an important process in the Southern Ocean overturning circulation
Internal waves and turbulence in the Antarctic Circumpolar Current
No full textAuthor Posting. © American Meteorological Society, 2013. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 43 (2013): 259–282, doi:10.1175/JPO-D-11-0194.1.This study reports on observations of turbulent dissipation and internal wave-scale flow properties in a standing meander of the Antarctic Circumpolar Current (ACC) north of the Kerguelen Plateau. The authors characterize the intensity and spatial distribution of the observed turbulent dissipation and the derived turbulent mixing, and consider underpinning mechanisms in the context of the internal wave field and the processes governing the waves’ generation and evolution.
The turbulent dissipation rate and the derived diapycnal diffusivity are highly variable with systematic depth dependence. The dissipation rate is generally enhanced in the upper 1000–1500 m of the water column, and both the dissipation rate and diapycnal diffusivity are enhanced in some places near the seafloor, commonly in regions of rough topography and in the vicinity of strong bottom flows associated with the ACC jets. Turbulent dissipation is high in regions where internal wave energy is high, consistent with the idea that interior dissipation is related to a breaking internal wave field. Elevated turbulence occurs in association with downward-propagating near-inertial waves within 1–2 km of the surface, as well as with upward-propagating, relatively high-frequency waves within 1–2 km of the seafloor. While an interpretation of these near-bottom waves as lee waves generated by ACC jets flowing over small-scale topographic roughness is supported by the qualitative match between the spatial patterns in predicted lee wave radiation and observed near-bottom dissipation, the observed dissipation is found to be only a small percentage of the energy flux predicted by theory. The mismatch suggests an alternative fate to local dissipation for a significant fraction of the radiated energy.SW acknowledges the support of the Grantham Institute for Climate Change, Imperial College London. ACNG acknowledges the support of a NERC Advanced Research
Fellowship (Grant NE/C517633/1). KLP acknowledges support from Woods Hole Oceanographic Institution
bridge support funds.2013-08-0
Identification of Southern Ocean upwelling from biogeochemical‐argo float
No full textThe Southern Ocean surrounds the continent of Antarctica, linking the southern regions of the Atlantic, Indian, and Pacific Oceans. It plays a fundamental role in the global overturning circulation, and is a location of intense upwelling of deep water. The deep water that upwells is rich in nutrients, depleted in oxygen (O 2), and enriched in carbon dioxide (CO 2). Southern Ocean upwelling is thus important to the global carbon cycle through its impact on global ocean productivity and through its influence on air-sea CO 2 exchange. However, because of its widespread nature in time and space, and its underpinning weak vertical flows, it is challenging to detect Southern Ocean upwelling from observations. In a novel approach, we utilize measurements from Biogeochemical-Argo floats deployed throughout the Southern Ocean by the Southern Ocean Carbon and Climate Observations and Modeling project, to identify Southern Ocean upwelling through its biogeochemical fingerprint. Our approach detects upwelling by examining surface carbon dioxide ([CO 2]) and oxygen ([O 2]) concentration Relative to Saturation (CORS). Differences between observed (calculated from pH for CO 2) and saturating gas concentrations are used to fingerprint upwelling. Spatial analysis of the identified upwelling reveals a latitudinal gradient in upwelling, with the maximum toward the south of the Antarctic Circumpolar Current. Furthermore, our observational diagnostics provides some support of previous model-based propositions of a focalization of Southern Ocean upwelling on hotspots of complex topography. Ongoing analysis with our approach can provide further insight into the nature and spatio-temporal variability of Southern Ocean upwelling.</p
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