Academic literature on the topic 'Thermohaline variability'
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Journal articles on the topic "Thermohaline variability"
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Greatbatch, Richard J., and K. Andrew Peterson. "Interdecadal variability and oceanic thermohaline adjustment." Journal of Geophysical Research: Oceans 101, no. C9 (September 15, 1996): 20467–82. http://dx.doi.org/10.1029/96jc01531.
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Ferrari, Raffaele, and Daniel L. Rudnick. "Thermohaline variability in the upper ocean." Journal of Geophysical Research: Oceans 105, no. C7 (July 15, 2000): 16857–83. http://dx.doi.org/10.1029/2000jc900057.
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Weaver, Andrew J., Jochem Marotzke, Patrick F. Cummins, and E. S. Sarachik. "Stability and Variability of the Thermohaline Circulation." Journal of Physical Oceanography 23, no. 1 (January 1993): 39–60. http://dx.doi.org/10.1175/1520-0485(1993)023<0039:savott>2.0.co;2.
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Latif, M., C. Böning, J. Willebrand, A. Biastoch, J. Dengg, N. Keenlyside, U. Schweckendiek, and G. Madec. "Is the Thermohaline Circulation Changing?" Journal of Climate 19, no. 18 (September 15, 2006): 4631–37. http://dx.doi.org/10.1175/jcli3876.1.
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Abstract Analyses of ocean observations and model simulations suggest that there have been considerable changes in the thermohaline circulation (THC) during the last century. These changes are likely to be the result of natural multidecadal climate variability and are driven by low-frequency variations of the North Atlantic Oscillation (NAO) through changes in Labrador Sea convection. Indications of a sustained THC weakening are not seen during the last few decades. Instead, a strengthening since the 1980s is observed. The combined assessment of ocean hydrography data and model results indicates that the expected anthropogenic weakening of the THC will remain within the range of natural variability during the next several decades.
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Zhai, Xiaoming, Helen L. Johnson, and David P. Marshall. "A Simple Model of the Response of the Atlantic to the North Atlantic Oscillation." Journal of Climate 27, no. 11 (May 29, 2014): 4052–69. http://dx.doi.org/10.1175/jcli-d-13-00330.1.
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Abstract The response of an idealized Atlantic Ocean to wind and thermohaline forcing associated with the North Atlantic Oscillation (NAO) is investigated both analytically and numerically in the framework of a reduced-gravity model. The NAO-related wind forcing is found to drive a time-dependent “leaky” gyre circulation that integrates basinwide stochastic wind Ekman pumping and initiates low-frequency variability along the western boundary. This is subsequently communicated, together with the stochastic variability induced by thermohaline forcing at high latitudes, to the remainder of the Atlantic via boundary and Rossby waves. At low frequencies, the basinwide ocean heat content changes owing to NAO wind forcing and thermohaline forcing are found to oppose each other. The model further suggests that the recently reported opposing changes of the meridional overturning circulation in the Atlantic subtropical and subpolar gyres between 1950–70 and 1980–2000 may be a generic feature caused by interplay between the NAO wind and thermohaline forcing.
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Bensi, Manuel, Vedrana Kovačević, Leonardo Langone, Stefano Aliani, Laura Ursella, Ilona Goszczko, Thomas Soltwedel, et al. "Deep Flow Variability Offshore South-West Svalbard (Fram Strait)." Water 11, no. 4 (April 2, 2019): 683. http://dx.doi.org/10.3390/w11040683.
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Water mass generation and mixing in the eastern Fram Strait are strongly influenced by the interaction between Atlantic and Arctic waters and by the local atmospheric forcing, which produce dense water that substantially contributes to maintaining the global thermohaline circulation. The West Spitsbergen margin is an ideal area to study such processes. Hence, in order to investigate the deep flow variability on short-term, seasonal, and multiannual timescales, two moorings were deployed at ~1040 m depth on the southwest Spitsbergen continental slope. We present and discuss time series data collected between June 2014 and June 2016. They reveal thermohaline and current fluctuations that were largest from October to April, when the deep layer, typically occupied by Norwegian Sea Deep Water, was perturbed by sporadic intrusions of warmer, saltier, and less dense water. Surprisingly, the observed anomalies occurred quasi-simultaneously at both sites, despite their distance (~170 km). We argue that these anomalies may arise mainly by the effect of topographically trapped waves excited and modulated by atmospheric forcing. Propagation of internal waves causes a change in the vertical distribution of the Atlantic water, which can reach deep layers. During such events, strong currents typically precede thermohaline variations without significant changes in turbidity. However, turbidity increases during April–June in concomitance with enhanced downslope currents. Since prolonged injections of warm water within the deep layer could lead to a progressive reduction of the density of the abyssal water moving toward the Arctic Ocean, understanding the interplay between shelf, slope, and deep waters along the west Spitsbergen margin could be crucial for making projections on future changes in the global thermohaline circulation.
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Hellmer, H. H. "Variability Of Thermohaline Circulation Under An Ice Shelf." Annals of Glaciology 14 (1990): 338. http://dx.doi.org/10.3189/s0260305500009009.
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The production of Antarctic Bottom Water is mainly influenced by Ice Shelf Water, which is formed through the modification of shelf water masses under huge ice shelves. To simulate this modification a two-dimensional thermohaline circulation model has been developed for a section perpendicular to the ice-shelf edge. Hydrographic data from the Filchner Depression enter into the model as boundary conditions. In the outflow region they also serve as a verification of model results.The standard solution reveals two circulation cells. The dominant one transports shelf water near the bottom toward the grounding line, where it begins to ascend along the inclined ice shelf. The contact with the ice shelf causes melting with a maximum rate of 1.5 m a−1 at the grounding line. Freezing and therefore the accumulation of “sea ice” at the bottom of the ice shelf occurs at the end of the melting zone at a rate on the order of 0.1 ma−1. Both rates are comparable with values estimated or predicted by models concerning ice-shelf dynamics.As one example of model sensitivity to changing boundary conditions, a higher sea-ice production in the southern Weddell Sea, as might be expected for a general climatic cooling event, is assumed. The resultant decrease/ increase in temperature/salinity of the inflow (Western Shelf Water) reduces the circulation under the ice shelf and therefore the outflow of Ice Shelf Water by 40%. The maximum melting and freezing rate decreases by 0.1 ma−1 and 0.01 m a−1, respectively. and the freezing zone shifts toward the grounding line by 100 km.In general the intensity of the circulation cells, the characteristics of Ice Shelf Water, the distribution of melting and freezing zones and the melting and freezing rates differ from the standard results with changing boundary conditions. These are the temperature and salinity of the inflow, the surface temperature at the top, and the extension and morphology of the ice shelf.
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Tziperman, Eli, and Petros J. Ioannou. "Transient Growth and Optimal Excitation of Thermohaline Variability." Journal of Physical Oceanography 32, no. 12 (December 2002): 3427–35. http://dx.doi.org/10.1175/1520-0485(2002)032<3427:tgaoeo>2.0.co;2.
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Hellmer, H. H. "Variability Of Thermohaline Circulation Under An Ice Shelf." Annals of Glaciology 14 (1990): 338. http://dx.doi.org/10.1017/s0260305500009009.
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The production of Antarctic Bottom Water is mainly influenced by Ice Shelf Water, which is formed through the modification of shelf water masses under huge ice shelves. To simulate this modification a two-dimensional thermohaline circulation model has been developed for a section perpendicular to the ice-shelf edge. Hydrographic data from the Filchner Depression enter into the model as boundary conditions. In the outflow region they also serve as a verification of model results. The standard solution reveals two circulation cells. The dominant one transports shelf water near the bottom toward the grounding line, where it begins to ascend along the inclined ice shelf. The contact with the ice shelf causes melting with a maximum rate of 1.5 m a−1 at the grounding line. Freezing and therefore the accumulation of “sea ice” at the bottom of the ice shelf occurs at the end of the melting zone at a rate on the order of 0.1 ma−1. Both rates are comparable with values estimated or predicted by models concerning ice-shelf dynamics. As one example of model sensitivity to changing boundary conditions, a higher sea-ice production in the southern Weddell Sea, as might be expected for a general climatic cooling event, is assumed. The resultant decrease/ increase in temperature/salinity of the inflow (Western Shelf Water) reduces the circulation under the ice shelf and therefore the outflow of Ice Shelf Water by 40%. The maximum melting and freezing rate decreases by 0.1 ma−1 and 0.01 m a−1, respectively. and the freezing zone shifts toward the grounding line by 100 km. In general the intensity of the circulation cells, the characteristics of Ice Shelf Water, the distribution of melting and freezing zones and the melting and freezing rates differ from the standard results with changing boundary conditions. These are the temperature and salinity of the inflow, the surface temperature at the top, and the extension and morphology of the ice shelf.
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Lehmann, Andreas, and Hans-Harald Hinrichsen. "On the thermohaline variability of the Baltic Sea." Journal of Marine Systems 25, no. 3-4 (July 2000): 333–57. http://dx.doi.org/10.1016/s0924-7963(00)00026-9.
Full textDissertations / Theses on the topic "Thermohaline variability"
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Hughes, Tertia M. C. "Uniqueness and variability of the ocean's thermohaline circulation." Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=28780.
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A numerical modelling approach is chosen to study equilibrium and time-dependent aspects of the ocean's thermohaline circulation. In the first part, the roles of basin geometry and surface buoyancy forcing in determining the asymmetry of the present-day thermohaline circulation are considered. An idealized flat-bottomed two-basin model of the Atlantic and Pacific is found to favour equilibria with sinking in the southern hemisphere only (Southern Sinking) or also in the North Atlantic (Conveyor), even under a freshwater flux forcing field with more precipitation over the North Atlantic than over the North Pacific.Another new result is the range of Conveyor equilibria found under mixed boundary conditions. Rare cases with North Pacific sinking are characterized by a very fresh halocline in the Southern Ocean and a reversed pole-to-pole surface density contrast. A more quantitative investigation leads to an approximately linear relationship between the Atlantic overturning and the meridional gradient of zonally-averaged depth-integrated steric height from the northern boundary of the ocean to the southern tip of Africa; on the other hand, the local linear relationships postulated in most two-dimensional plane models of the overturning circulation could not be validated.
In the second part, the climatology of a global ocean model is presented, and the importance in the model of the warm water route of the Conveyor through the Indian Ocean relative to the cold water route through Drake Passage is noted. The implied ocean heat and freshwater transports from the Canadian Climate Centre second generation atmospheric general circulation model are then presented, and are shown to be incompatible with the present-day thermohaline circulation.
Finally, in the third part, a simple new parameterization of the sea surface temperature-evaporation feedback is developed as an extension of the traditional mixed boundary conditions. The positive sign of the feedback for the thermohaline circulation is demonstrated, and three examples featuring decadal, century and millennial timescale variability in one-hemisphere idealized basins are discussed. No fundamental alterations of the mechanisms under mixed boundary conditions are found, although the timescale is altered or the variability interrupted sooner in some cases.
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Stuebe, David Allen. "Temperature and salinity variability in thermohaline staircase layers." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/39194.
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Thesis (S.M.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2005.Includes bibliographical references (p. 65-67).
A moored profiler record from the western tropical North Atlantic provides the first continuous time series of temperature, salinity and velocity profiles in a thermohaline staircase. Variations in the intensity of layering and the evolution of layer properties are well documented during the 4.3 month record. Such staircases are the result of strong salt fingering at the interfaces between the mixed layers, and these data provide unique insights into the dynamics of salt fingers. In particular, a striking linear correlation between the temperature and salinity of the layers may be interpreted as resulting from vertical salt finger flux divergences. Data from this record allow new interpretations of previous work on this topic by McDougall (1991).
by David Allen Stuebe.
S.M.
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Tyner, Robin D. "DECADAL variability of thermohaline structure at the SHEBA site." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1999. http://handle.dtic.mil/100.2/ADA365397.
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Thesis (M.S. in Meteorology and Physical Oceanography) Naval Postgraduate School, June 1999."June 1999". Thesis advisor(s): Timothy P. Stanton. Includes bibliographical references (p. 97-100). Also available online.
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Myers, Paul Glen. "Seasonal forcing and low-frequency variability of the thermohaline circulation." Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=60722.
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A series of numerical experiments are conducted using the Bryan-Cox Ocean General Circulation Model to investigate the potential existence of low-frequency variability of the thermohaline circulation under seasonal forcing. Experiments are performed with different combinations of a seasonal cycle being present or not on the restoring temperature, the surface freshwater flux fields (mixed boundary conditions) and the surface wind forcing.Despite the presence of the forcing on the dominant seasonal timescale, it is found that the system may oscillate at the decadal period or longer. The decadal variability is excited by changes in the net surface density flux which are due to the advection of temperature and salinity anomalies in the model domain. The magnitude of the seasonal cycle also plays an important role in determining the timescale of variability. Violent overturning events may occur on the century timescale under seasonal forcing. The magnitudes of the flushes are reduced compared to those found in similar experiments without the presence of a seasonal cycle.
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Bensi, Manuel. "Thermohaline variability and mesoscale dynamics observed at the E2M3A deep-site in the South Adriatic Sea." Doctoral thesis, Università degli studi di Trieste, 2012. http://hdl.handle.net/10077/7387.
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2010/2011Continuous measurements are strictly essential to better understand the deep convection as well as for monitoring the seasonal and interannual thermohaline variability in the ocean. For these reasons, the south Adriatic Sea has been constantly monitored by means of the E2M3A deep observational site, located in its central part (Latitude 41° 50’ N, Longitude 17° 45’ E, maximum depth 1250m) since 2006. Temperature, salinity and current time series collected between 2006 and 2010 are analysed in this thesis and they represent the longest time series available for this region. Moreover, these time series are merged with Conductivity-Temperature-Depth (CTD) profiles obtained from several oceanographic cruises to provide the necessary spatial distribution of data for describing the thermohaline properties in the study area. The analysis of the data presented here shows that winter 2007 was characterized by a weak convection, while winter 2008 and following winters revealed a stronger deep convection able to reach 800-900m in February 2008. Time series highlight the abrupt temperature (T) and salinity (S) decrease, noticeable down to 600-700m depth from March 2008 on. The intermediate layer experienced a maximum decrease in T and S of ~0.4°C and ~0.06 respectively, clearly evident after each strong winter convection phase. The bottom layer (~1200m), instead, shows an opposite behaviour: it suffered a continuous T and S increase (linear trend of ~0.05 °C y-1 and ~0.004 y-1, respectively) during the whole observational period. These changes are discussed in a context of strong relationship between the variability of the Ionian surface circulation recently discovered, and the heat and salt content changes in the South Adriatic presented in this study. The results show that the mechanism triggering the salt content changes in the South Adriatic is based mainly on the winter convection, which transfers surface fresher water towards deeper layers. Nevertheless, current measurements also indicate that the passage of mesoscale eddies in the region can produce sudden thermohaline perturbations along the water column for 10-15 days. Cyclonic eddies seem to be more frequent in the proximity of the observational site than the anticyclonic ones. Interestingly, the comparison between time series and satellite images (Chl-a surface distribution) reveals, for the first time, that the vortices act along the whole water column. Their passage produces a twofold effect: the contribution to the re-stratification of the water column during the post convection phase, by exchanging the buoyancy between the mixed path and the surrounding waters, and the transfer of heat and salt between the deep and the intermediate layers.
Misure oceanografiche in continuo sono essenziali per comprendere meglio il processo di formazione delle acque dense e per monitorare la variabilità termoalina stagionale e interannuale in oceano. Per queste ragioni, a partire dal 2006 il Sud Adriatico è stato costantemente monitorato grazie all’utilizzo del sito di osservazione denominato E2M3A, ancorato nella parte centrale del Sud Adriatico (latitudine 41° 50’ N, longitudine 17° 45’ E, profondità massima 1250m). Le serie temporali di temperatura, salinità e correnti marine raccolte tra il 2006 e il 2010 sono analizzate in questa tesi e rappresentano la serie di dati più lunga mai ottenuta in questa regione. Oltretutto, per fornire la necessaria copertura spaziale dei dati utile a descrivere le proprietà termoaline nell’area di studio, le serie temporali sono state integrate con profili CTD (Conductivity-Temperature-Depth) provenienti da diverse crociere oceanografiche. L’analisi dei dati presentata qui mostra che l’inverno 2007 è stato caratterizzato da una debole convezione, mentre l’inverno 2008 e i successivi hanno mostrato una convezione più intensa, capace di raggiungere 800-900m di profondità a Febbraio 2008. Le serie temporali evidenziano una diminuzione repentina di temperatura (T) e salinità (S), visibile fino a 600-700m a partire da Marzo 2008. Lo strado intermedio ha subito rispettivamente una diminuzione massima di T e S di ~0.4°C e ~0.06, chiaramente evidente a seguito di ogni fase di intensa convezione invernale. Lo strato di fondo (~1200m) ha mostrato invece un comportamento opposto: un inaspettato e continuo aumento di T and S (trend lineare ~0.05 °C y-1 e ~0.004 y-1, rispettivamente) durante tutto il periodo di studio. Questi cambiamenti sono discussi nell’ambito della forte relazione tra la variabilità della circolazione superficiale dello Ionio recentemente scoperta e i cambiamenti nel contenuto di calore e sale del Sud Adriatico presentati in questo studio. I risultati mostrano che il meccanismo in grado di produrre cambiamenti nel contenuto di sale nel Sud Adriatico è principalmente basato sulla convezione invernale, che trasferisce acqua superficiale meno salata verso strati più profondi. Tuttavia, le misure di corrente mostrano che anche il passaggio di vortici a mesoscala può indurre repentine perturbazioni delle proprietà termoaline lungo la colonna d’acqua anche per 10-15 giorni. Vortici di tipo ciclonico sembrano essere più frequenti in prossimità del mooring rispetto a quelli di tipo anticiclonico. È interessante notare che il confronto tra le serie temporali e le immagini da satellite della distribuzione superficiale di clorofilla-a rivela, per la prima volta in questa regione, che i vortici agiscono su tutta la colonna d’acqua. Il loro passaggio produce un duplice effetto: il contributo alla ri-stratificazione della colonna d’acqua a seguito della fase di convezione invernale e il trasferimento di calore e sale tra gli strati intermedio e profondo.
XXIV Ciclo
1978
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Hutchinson, Katherine Alessandra. "Thermohaline variability of AAIW in the Atlantic sector of the Southern Ocean investigated using an Altimetry Gravest Empirical Mode." Master's thesis, University of Cape Town, 2013. http://hdl.handle.net/11427/6648.
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The southeast Atlantic sector of the Southern Ocean connects the Atlantic with the Indian Ocean and the Antarctic Circumpolar Current, thereby acting as a major conduit within global ocean circulation. Thermohaline transports in this region are widely thought to have a critical influence on global climate. Yet magnitudes of the associated heat and salt content variations are poorly understood due to a lack of hydrographic observations and model limitations. An improved Gravest Empirical Mode (GEM) is set up for the Southern Ocean south of Africa using the updated store of hydrographic measurements obtained from CTD transects for the area, combined with the available Argo profiles sampled in the region. Satellite altimetry is combined with the GEM relationships to create an Altimetry GEM (AGEM), thereby generating 20 years of temperature and salinity fields. These thermohaline sections for the region of the ocean south of Africa are found to be proficient at reproducing observations, with associated RMS errors being two orders of magnitude smaller than those reported by other comparable Southern Ocean GEM studies. Confident in the accuracy of the AGEM produced fields, an examination of the temporal evolution of Antarctic Intermediate Water (AAIW) is undertaken. The fluctuation and trends in heat and salt content anomalies and budgets is presented for each Southern Ocean frontal zone, along with the examination of the change in position of the isopycnal limits and resultant water mass thickness. So as to better understand one of the factors that may be influencing some of the changes detected within AAIW, property alterations of eddies identified in the region from 1992 to 2010 are investigated. A general decrease in magnitude and frequency of cyclones, coupled with an increase in absolute dynamic topography (ADT) of anticyclones, designates elevated injection of warm, saline water into the area. The connection identified between eddy property variations and AAIW modification in the region of the ocean south of Africa indicates that the water mass experiences ventilation with the mixed layer at latitudes further north than previously thought to occur. Obtaining an improved image of the magnitudes and variability of AAIW thermohaline properties in the Atlantic sector of the Southern Ocean greatly improves our understanding of its role in the ocean-climate system.
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Kuhlbrodt, Till. "Stability and variability of open-ocean deep convection in deterministic and stochastic simple models." Phd thesis, [S.l. : s.n.], 2002. http://pub.ub.uni-potsdam.de/2002/0033/kuhlb.pdf.
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Houndegnonto, Odilon Joël. "Analyse des variations thermohalines des échelles intrasaisonnière à saisonnière des panaches d'eau douce du Golfe de Guinée." Thesis, Brest, 2021. http://www.theses.fr/2021BRES0105.
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Dans le Golfe de Guinée (GG), les masses d’eau douce provenant des décharges des fleuves et les taux de précipitations élevés contribuent à la stratification en densité de la couche superficielle océanique, et jouent un rôle clé dans la modulation des interactions air-mer. Cependant, les variations thermohalines des couches superficielles au sein des panaches d’eau douce du GG sont encore mal connues, car très peu observées et documentées. L’objectif principal de cette thèse est donc d’étudier et de documenter la variabilité spatiale à mésoéchelle horizontale (10-100 km) et verticale (0-100m), intra-saisonnière à saisonnière de la structure 3D thermohaline dans les panaches d’eau douce du GG, et notamment les panaches des fleuves Congo et Niger. Tout d’abord, à l’aide des données d’observations satellite SSS SMOS, notre étude a montré que les panaches d’eau douce dans cette région s’étendent vers l’océan du large suivant deux régimes de propagation. Durant la période de septembre à janvier, ils se propagent vers le large en direction Nord-Ouest tandis que de janvier à avril, ils se redirigent vers le Sud-Ouest, où leur extension maximale est observée en avril. Le reste de l’année, de mai à août, est marqué par un épisode de salinisation de surface, où les panaches d’eau douce se dissipent avec une extension minimale observée en août. L’analyse du bilan de salinité dans la couche mélangée de surface a permis de mettre en évidence les principaux processus physiques contrôlant la variabilité saisonnière de la salinité au sein de ces panaches d’eau douce. Ce diagnostic a montré que les processus d’advection horizontale et les flux d’eau douce associés aux précipitations et aux décharges des fleuves expliquent principalement de la distribution offshore des masses d’eau de faible salinité dans cette région. Dans le panache du Congo en particulier, l’advection horizontale de salinité est principalement expliquée par la dérive d’Ekman du vent de surface. Ensuite, nous avons montré que la distribution offshore du panache du Congo aux échelles intra-saisonnières est associée à des couches de barrière de sel d’une part, et à des profils verticaux de densité en marches d’escalier d’autre part. Dans une étude de cas (au 31/03/216), nous avons montré que la stratification thermohaline en marches d’escalier observée, résulterait de la dynamique de cisaillement entre le flux d’Ekman de surface associée à la distribution offshore (Nord-Ouest) du panache du Congo, et le flux géostrophique (Sud-Est) associé aux masses d’eau de subsurface de l’océan ouvert à l’Ouest, plus denses et plus salées. Enfin, à partir d’une approche lagrangienne, nous avons mis en évidence l’origine et la structuration à grande échelle des masses d’eau impliquées dans la forte stratification haline observée au large du Congo. Cette étude a montré le fort cisaillement des courants à l’oeuvre au niveau des gradients halins au sein de la colonne d’eau associée à ces profilsIn the Gulf of Guinea (GG), freshwater originated from river discharges and high precipitation rates contribute to the upper ocean density stratification, and play a key role in modulating air-sea interactions. However, the thermohaline variations of the ocean upper layers within the freshwater plumes in the GG are still poorly known, as they are poorly observed and documented. The main objective of this thesis is therefore to study and document the spatial variability at horizontal mesoscale (10-100 km) and vertical (0-100m), from intra-seasonal to seasonal time scales of the thermohaline 3D structure in the freshwater plume areas of the GG: mainly the Congo and Niger Rivers plumes. First, using SSS SMOS satellite data, our study showed that freshwater plumes in this region extend towards the open ocean following two propagation regimes. During September to January, they propagate northwestward while from January to April they redirect to the southwest, where their maximum extension is observed in April. The rest of the year, from May to August, is marked by a surface salinization episode, where the freshwater plumes dissipate with a minimum extension observed in August. A salinity budget analysis in the surface mixed layer allowed highlighting the main physical processes controlling the seasonal variability of salinity within these freshwater plumes. We showed that horizontal advection processes and freshwater fluxes by precipitation and river discharges are the main contributors of low SSS distribution in this region. In the southeastern Gulf of Guinea, off Congo, the horizontal SSS advection is dominated by Ekman wind-driven currents. Second, we showed that the offshore distribution of the Congo plume on intra-seasonal time scales is associated with salt barrier layers and with thermohaline staircases profiles. In a case study (for 2016/03/31), we showed that the observed thermohaline staircases would result from the shear dynamics between the surface Ekman flow associated with the offshore (North-Westward) distribution of the Congo plume, and the geostrophic (South-Eastward) flow associated with the denser and saltier subsurface water masses of the open ocean to the west. Finally, using a Lagrangian approach, we have highlighted the origin and large-scale structuring of water masses involved in the strong haline stratification observed off Congo. This study showed the strong shear of the currents associated with the vertical salinity gradients within the water column associated with the staircases profiles
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Barrier, Nicolas. "Variability of the ocean circulation in the North-Atlantic in response to atmospheric weather regimes." Thesis, Brest, 2013. http://www.theses.fr/2013BRES0064/document.
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Le but de cette thèse est d’analyser les impacts de la variabilité atmosphérique grande échelle sur la circulation océanique. Ceci a déjà fait l’objet de nombreuses publications, dans lesquelles la variabilité atmosphérique est analysée en termes de modes de variabilité, déterminés par analyse en composantes principales (EOF en anglais) des anomalies de pression de surface. Ces modes sont l’Oscillation Nord-Atlantic (NAO), le Pattern Est-Atlantique (EAP) et le Pattern Scandinave (SCAN). La décomposition en EOF implique que les modes sont orthogonaux et symétriques. Cette dernière hypothèse a été montrée comme étant invalide pour la NAO. Par conséquent, un nouveau concept est proposé dans cette étude pour estimer la variabilité atmosphérique, celui des régimes de temps. Ces derniers sont des structures spatiales de grande échelle, récurrents et quasi-Stationnaires qui permettent de capturer la variabilité des forçages atmosphériques. De plus, ils permettent de séparer les patterns spatiaux des deux phases de la NAO. Ces régimes de temps sont donc une alternative prometteuse pour l’analyse de la variabilité océanique forcée par l’atmosphère. A partir d’observation et de modèles numériques (réalistes ou idéalisés), nous avons montré que les régimes Atlantic Ridge (AR), NAO− et NAO+ induisent une réponse rapide (échelles mensuelles à interannuelles) des gyres subtropical et subpolaire (via un mécanisme de Sverdrup topographique) et de la cellule de retournement (MOC, ajustement aux anomalies de transport d’Ekman). Aux échelles décennales, le gyre subpolaire s’intensifie lors de conditions NAO+ et BLK persistantes via un ajustement barocline aux flux de flottabilité et s’affaiblit pour AR via un ajustement barocline aux anomalies de rotationnel de vent. Ce dernier mécanisme explique aussi l’augmentation du gyre subtropical pour une NAO+ persistante et son affaiblissement pour un AR persistant. La réponse des gyres pour des conditions de NAO− persistantes est un déplacement vers le sud des gyres (l’intergyre gyre). L’intensité de la MOC est augmentée pour des conditions de NAO+ et BLK persistantes, dû à l’augmentation de la formation d’eau dense en mer du Labrador, et inversement pour NAO− et AR. Finalement, des bilans de contenu de chaleur dans la gyre subpolaire et les mers nordiques ont été effectués dans quatre modèles océaniques globaux. Les moyennes d’hiver de convergence océanique de chaleur dans la partie ouest de la gyre subpolaire sont positivement corrélées aux occurrences d’hiver de NAO−, ce qui est dû à la présence de l’intergyre, tandis que cette convergence est négativement corrélée aux occurrences d’AR, ce qui est dû à la réduction des deux gyres qui lui est associée. Les flux de chaleur vers l’océan dans la gyre subpolaire sont négativement corrélés aux occurrences d’hiver de la NAO+ et inversement pour la NAO−. Dans les mers Nordiques, ils sont positivement corrélés aux occurrences de BLK et, dans une moindre mesure, aux occurrences de AR. De plus, nous suggérons que la variabilité du contenu de chaleur dans la partie ouest du gyre subpolaire est la réponse décalée (lag de 6 ans) à l’intégration temporelle du forçage lié au régime NAO+, due à la combinaison de la réponse en phase (0-Lag) des flux de chaleur et à la réponse décalée (lag de 3 ans) de la convergence de chaleurThe aim of the PhD is to investigate the impacts of the large-Scale atmospheric variability on the North- Atlantic ocean circulation. This question has already been addressed in a large number of studies, in which the atmospheric variability is decomposed into modes of variability, determined by decomposing sea-Level pressure anomalies into Empirical Orthogonal Function (EOFs). These modes of variability are the North-Atlantic Oscillation (NAO), the East-Atlantic Pattern (EAP) and the Scandinavian Pattern (SCAN). EOF decomposition assumes that the modes are orthogonal and symmetric. The latter assumption, however, has been shown to be inadequate for the NAO. Hence, a different framework is used in this study to assess the atmospheric variability, the so-Called weather regimes. These are large-Scale, recurrent and quasi-Stationary atmospheric patterns that have been shown to capture well the interannual and decadal variability of atmospheric forcing to the ocean. Furthermore, they allow to separate the spatial patterns of the positive and negative NAO phases. Hence, these weather regimes are a promising alternative to modes of variability in the study of the ocean response to atmospheric variability. Using observations and numerical models (realistic or in idealised settings), we have shown that the Atlantic Ridge (AR), NAO− and NAO+ regimes drive a fast (monthly to interannual) wind-Driven response of the subtropical and subpolar gyres (topographic Sverdrup balance) and of the meridional overturning circulation (MOC, driven by Ekman transport anomalies). At decadal timescales, the subpolar gyre strengthens for persistent NAO+ and Scandinavian Blocking (BLK) conditions via baroclinic adjustment to buoyancy fluxes and slackens for persistent AR conditions via baroclinic adjustment to wind-Stress curl anomalies. The latter mechanism also accounts for the strengthening of the subtropical gyre for persistent NAO+ conditions and its weakening for persistent AR conditions. The gyres response to persistent NAO− conditions reflects the southward shift of the gyre system (the intergyre gyre). The MOC spins-Up for persistent NAO+ and BLK conditions via increased deep water formation in the Labrador Sea, and conversely for the NAO− and AR regimes. Last, heat budget calculations in the subpolar gyre and the Nordic Seas have been performed using four global ocean hindcasts. The winter averaged heat convergence in the western subpolar gyre is positively correlated with the NAO− winter occurrences, which is due to the intergyregyre circulation, while it is negatively correlated with AR winter occurrences, because of the wind-Driven reduction of both gyres. Downward surface heat flux anomalies are negatively correlated with NAO+ occurrences, and conversely for the NAO−. In the Nordic Seas, they are positively correlated with BLK and to a lesser extent AR occurrences. Furthermore, we suggest that the heat content variability in the western subpolar gyre is the signature of the delayed response (6-Year lag) to the time-Integrated NAO+ forcing, due to the combination of the immediate (0-Lag) response of surface heat flux and the lagged (3 year lag) response of ocean heat convergence
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Msadek, Rym. "Rôle de la circulation thermohaline dans la variabilité du climat." Paris 6, 2009. http://www.theses.fr/2009PA066087.
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L’objet de cette thèse est l’étude des interactions entre l’océan et l’atmosphère aux échelles de temps décennales. On s’intéresse en particulier au rôle de la circulation thermohaline (ou MOC) dans la variabilité du climat dans des simulations couplées. Dans la première partie de la thèse, nous étudions les mécanismes à l’origine de la variabilité basse fréquence de la MOC dans le modèle du climat de l’IPSL. Nos résultats montrent que les fluctuations basse fréquence de la MOC sont essentiellement forcées par l’EAP, qui est le deuxième mode de variabilité atmosphérique dans l’Atlantique Nord. La MOC a également une influence significative sur l’atmosphère, qui se projette en été sur l’EAP du modèle, suggérant ainsi une faible rétroaction positive sur la MOC. Dans la deuxième partie de la thèse, la réponse atmosphérique d’été est analysée à l’aide d’expériences de sensibilité et des mécanismes physiques sont proposés. La réponse de l’atmosphère aux fluctuations basse fréquence de la MOC est caractérisée par une modification de la circulation subtropicale dans la zone de mousson Indo-Asiatique. Elle est également modulée par l’activité des tourbillons transitoires probablement à l’origine de la forte non linéarité de la réponse. Une influence significative de la MOC sur l’atmosphère est également détectée en hiver et se projette sur la NAO.
Books on the topic "Thermohaline variability"
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Tyner, Robin D. DECADAL variability of thermohaline structure at the SHEBA site. Monterey, Calif: Naval Postgraduate School, 1999.
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Sakai, Kotaro. Late-pleistocene climate variability and the global thermohaline circulation. 1996.
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Decadal Variability of Thermohaline Structure at the Sheba Site. Storming Media, 1999.
Find full textBook chapters on the topic "Thermohaline variability"
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Marotzke, Jochem. "Analysis of Thermohaline Feedbacks." In Decadal Climate Variability, 333–78. Berlin, Heidelberg: Springer Berlin Heidelberg, 1996. http://dx.doi.org/10.1007/978-3-662-03291-6_8.
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Meincke, J., D. Quadfasel, W. H. Berger, K. Brander, R. R. Dickson, P. M. Haugan, M. Latif, et al. "Variability of the Thermohaline Circulation (THC)." In Marine Science Frontiers for Europe, 39–60. Berlin, Heidelberg: Springer Berlin Heidelberg, 2003. http://dx.doi.org/10.1007/978-3-642-55862-7_4.
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Rahmstorf, Stefan. "Decadal Variability of the Thermohaline Ocean Circulation." In Beyond El Niño, 309–31. Berlin, Heidelberg: Springer Berlin Heidelberg, 1999. http://dx.doi.org/10.1007/978-3-642-58369-8_15.
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Ivanova, Elena V. "Variability of the Meridional Overturning Circulation and Paleoceanographic Events in the North Atlantic During the Last Climatic Cycle." In The Global Thermohaline Paleocirculation, 31–59. Dordrecht: Springer Netherlands, 2009. http://dx.doi.org/10.1007/978-90-481-2415-2_3.
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Hofmann, Eileen E., and John M. Klinck. "Thermohaline Variability of the Waters Overlying The West Antarctic Peninsula Continental Shelf." In Ocean, Ice, and Atmosphere: Interactions at the Antarctic Continental Margin, 67–81. Washington, D. C.: American Geophysical Union, 2013. http://dx.doi.org/10.1029/ar075p0067.
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Kurian, Nisha, Joshua Costa, V. Suneel, V. V. Gopalakrishna, R. R. Rao, K. Girish, S. Amritash, M. Ravichandran, Lix John, and C. Ravichandran. "Observed Interannual Variability of the Thermohaline Structure in the South Eastern Arabian Sea." In Remote Sensing of the Changing Oceans, 305–23. Berlin, Heidelberg: Springer Berlin Heidelberg, 2011. http://dx.doi.org/10.1007/978-3-642-16541-2_16.
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Sakai, Kotaro, and W. Richard Peltier. "The Influence of Deep Ocean Diffusivity on the Temporal Variability of the Thermohaline Circulation." In Geophysical Monograph Series, 227–42. Washington, D. C.: American Geophysical Union, 2013. http://dx.doi.org/10.1029/gm126p0227.
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Alekseev, G. V., V. V. Ivanov, and A. A. Korablev. "Interannual Variability of the Thermohaline Structure in the Convective Gyre of the Greenland Sea." In The Polar Oceans and Their Role in Shaping the Global Environment, 485–96. Washington, D. C.: American Geophysical Union, 2013. http://dx.doi.org/10.1029/gm085p0485.
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Marchal, Olivier, Thomas F. Stocker, and Fortunat Joos. "Physical and biogeochemical responses to freshwater-induced thermohaline variability in a zonally averaged ocean model." In Mechanisms of Global Climate Change at Millennial Time Scales, 263–84. Washington, D. C.: American Geophysical Union, 1999. http://dx.doi.org/10.1029/gm112p0263.
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Bensi, Manuel, Vanessa Cardin, and Angelo Rubino. "Thermohaline Variability and Mesoscale Dynamics Observed at the Deep-Ocean Observatory E2M3A in the Southern Adriatic Sea." In The Mediterranean Sea, 139–55. Oxford: John Wiley & Sons, Inc., 2014. http://dx.doi.org/10.1002/9781118847572.ch9.
Full textConference papers on the topic "Thermohaline variability"
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Chu, Peter C., Colleen M. McDonald, Murat Kucukosmanoglu, Albert Judono, Tetyana Margolina, and Chenwu Fan. "Effect of inter- and intra-annual thermohaline variability on acoustic propagation." In SPIE Defense + Security, edited by Weilin (Will) Hou and Robert A. Arnone. SPIE, 2017. http://dx.doi.org/10.1117/12.2258687.
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Demetrashvili, Demuri, Vepkhia Kukhalashvili, Aleksandre Surmava, and Diana Kvaratskhelia. "MODELING OF VARIABILITY OF THE REGIONAL DYNAMIC PROCESSES DEVELOPED DURING 2017-2019 IN THE EASTERNMOST PART OF THE BLACK SEA." In GEOLINKS International Conference. SAIMA Consult Ltd, 2020. http://dx.doi.org/10.32008/geolinks2020/b2/v2/10.
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The study of water circulation and thermohaline processes in the coastal zones of the seas and oceans, subjected to the most intense anthropogenic press, is an important problem of modern Oceanology. According to experimental and theoretical researches the coastal water areas of the Black Sea are dynamically active regions, where intensive generation of mesoscale and submesoscale eddies takes place. Such eddies make a significant contribution to the horizontal and vertical transport of different polluting substances, heat, momentum, etc. Therefore, the modeling and study of main peculiarities of variability of regional dynamic processes is of great scientific and practical interest. The goal of this study is to investigate numerically the structure and spatial –temporal distribution of the sea flow and thermohaline fields taking place during the period 2017-2019 in the easternmost part of the Black Sea, which is limited from the open part of the sea basin with liquid boundary coinciding 39.080E. With this purpose a high-resolution numerical regional model of the Black Sea dynamics of M. Nodia Institute of Geophysics of I. Javakhishvili Tbilisi State University (RM-IG) is used. The RM-IG is nested in the basin-scale model of the Black Sea dynamics of Marine Hydrophysical Institute (Sevastopol) and is based on a primitive system of ocean hydrothermodynamics equations. The RM-IG uses a calculated grid having 215x347 points on horizons with 1 km spatial resolution. Results of researches presented in the paper show significant variability of the regional dynamic processes in the easternmost water area during 2017-2019, where continuously generation, deformation and disappearance of the cyclonic and anticyclonic vortex formations of difference sizes takes plac