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van der Schrier, Gerad, Sybren S. Drijfhout, Wilco Hazeleger et Ludovic Noulin. « Increasing the Atlantic subtropical jet cools the circum-North Atlantic Region ». Meteorologische Zeitschrift 16, no 6 (17 décembre 2007) : 675–84. http://dx.doi.org/10.1127/0941-2948/2007/0252.
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Wall-Palmer, Deborah, Mona Hegmann, Erica Goetze et Katja T. C. A. Peijnenburg. « Resolving species boundaries in the Atlanta brunnea species group (Gastropoda, Pterotracheoidea) ». ZooKeys 899 (12 décembre 2019) : 59–84. http://dx.doi.org/10.3897/zookeys.899.38892.
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Atlantid heteropods are a family of holoplanktonic marine gastropods that occur primarily in tropical and subtropical latitudes. Atlantids bear a delicate aragonitic shell (<14 mm) and live in the upper ocean, where ocean acidification and ocean warming have a pronounced effect. Therefore, atlantids are likely to be sensitive to these ocean changes. However, we lack sufficiently detailed information on atlantid taxonomy and biogeography, which is needed to gain a deeper understanding of the consequences of a changing ocean. To date, atlantid taxonomy has mainly relied on morphometrics and shell ornamentation, but recent molecular work has highlighted hidden diversity. This study uses an integrated approach in a global analysis of biogeography, variation in shell morphology and molecular phylogenies based on three genes (CO1, 28S and 18S) to resolve the species boundaries within the Atlanta brunnea group. Results identify a new species, Atlanta vanderspoeli, from the Equatorial and South Pacific Ocean, and suggest that individuals of A. brunnea living in the Atlantic Ocean are an incipient species. Our results provide an important advance in atlantid taxonomy and will enable identification of these species in future studies of living and fossil plankton.
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Silva, Bruna Andrelina, Michelle Simões Reboita, Natália Machado Crespo, Rosmeri Porfírio Da Rocha et Lívia Márcia Mosso Dutra. « Ciclones Subtropicais Guará e Lexi Parte I : Estrutura Térmica e Características Gerais ». Revista Brasileira de Geografia Física 15, no 1 (23 mars 2022) : 333. http://dx.doi.org/10.26848/rbgf.v15.1.p333-342.
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Enquanto para o Oceano Atlântico Sul (OAS) o número de estudos sobre ciclones subtropicais tem aumentado, no oceano Pacífico Sudeste (OPS) estes ainda são raros. Diante disso, objetiva-se contribuir para o entendimento dos processos físicos associados aos ciclones subtropicais Guará, com gênese subtropical pura e ocorrido em dezembro de 2017 no OAS, e Lexi, com transição subtropical e ocorrido em maio de 2018 no OPS. O estudo encontra-se dividido em Parte I e Parte II. A Parte I apresenta a caracterização da estrutura térmica dos dois ciclones, o Índice do Potencial de Gênese (IPG) bem como as características desses sistemas em termos de pressão, ventos e precipitação ao longo do ciclo de vida. Já a Parte II enfoca os processos físicos associados à gênese do Guará e a transição subtropical do Lexi. Para tanto, são utilizados dados da reanálise ERA5. Entre os principais resultados obtidos no estudo Parte I, têm-se que o diagrama de fase confirmou a gênese subtropical pura do ciclone Guará e a gênese extratropical do Lexi com a posterior transição para a categoria subtropical. O IPG mostrou que, no ambiente de gênese/transição subtropical, havia condições ambientais favoráveis a sistemas com núcleo quente, sendo mais intensas no OPS, região conhecida por apresentar temperatura da superfície do mar fria e, por consequência, inviabilizar a formação de ciclones tropicais e subtropicais. O Guará propiciou chuva de cerca de 40 mm no leste da Bahia causando alagamentos. Já o Lexi propiciou chuva somente no oceano.Palavras-Chave: Ciclones Subtropicais, Oceano Atlântico Sul, Oceano Pacífico Sudeste, estrutura térmica, precipitação, ventos Subtropical Cyclones Guará and Lexi Part I - Thermal Structure and General Characteristics A B S T R A C TWhile for the South Atlantic Ocean (SAO) the number of studies focusing on the occurrences of subtropical cyclones has increased, in the Southeast Pacific Ocean (SPO) these studies are rare. Therefore, the objective of this work is to contribute to the understanding of the physical processes associated with pure subtropical cyclogenesis of Guará, which occurred in December 2017 in the SAO, and Lexi, with subtropical transition occurred in May 2018 in PSO. The study is divided into Part I and Part II. Part I presents the characterization of the thermal structure of the two cyclones, the Genesis Potential Index (GPI) as well as the characteristics of these systems in terms of pressure, winds and precipitation over the life cycle. On the other hand, Part II focuses on the physical processes associated with the genesis of Guará and the subtropical transition of Lexi. For this purpose, data from the ERA5 reanalysis are used. Among the main results of the study Part I, we obtained that the phase diagram confirmed the pure subtropical genesis of Guará and the extratropical genesis of Lexi with the subsequent transition to the subtropical category. The GPI showed that, in the subtropical genesis/transition environment, there were favorable environmental conditions for warm core systems, being more intense in the SPO, a region known for presenting cold sea surface temperature and, consequently, making the formation of tropical and subtropical cyclones unfeasible. Guará caused rain of about 40 mm on the eastern sector of Bahia State leading to flooding. Lexi provided rain only in the ocean.Keywords: Subtropical Cyclones, South Atlantic Ocean, South Pacific Ocean, thermal structure, precipitation, winds
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Mill, Guilherme Nogueira, et Afonso De Moraes Paiva. « SUBDUCTION OF SOUTH ATLANTIC SUBTROPICAL MODE WATERS ». Revista Brasileira de Geofísica 31, no 3 (1 septembre 2013) : 495. http://dx.doi.org/10.22564/rbgf.v31i3.323.
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ABSTRACT. The formation of the Subtropical Mode Waters (STMW) in the South Atlantic, part of the South Atlantic Central Water (SACW), by the subduction process, transferring mixed layer fluid into the permanent thermocline, is investigated using results of numerical simulations with the HYbrid Coordinate Ocean Model (HYCOM). Subduction rates were estimated by the kinematic method, adding the lateral induction of fluid through the sloping base of winter mixed layer with the vertical velocities at the base of winter mixed layer. Subduction rates above 100 m/year were found over the South Atlantic Subtropical Front, with maximum rates larger than 200 m/year in three distinct regions. The subduction pattern is dominated by the contribution of lateral induction, specially over the Subtropical Front, with rates significantly larger than the maximum rate of Ekman pumping. Different STMW were identified, associated with maximum layers thickness in isopycnals representative of upper and middle portion of SACW. The regions of maximum subduction rates were associated with the formation of the STMW.Keywords: mixed layer, ventilation, SACW, permanent thermocline, lateral induction. RESUMO. A formação de Águas Modais Subtropicais (AMS) no Atlântico Sul, que fazem parte da Água Central do Atlântico Sul (ACAS), transferindo fluido da camada de mistura para a termoclina permantente pelo processo de subducção, foi estudada a partir dos resultados de simulações numéricas com um modelo oceânico de coordenadas híbridas (HYCOM – Hybrid Coordinate Ocean Model). A subducção foi calculada pelo método cinemático, somando as contribuições da indução lateral de fluido através da base da camada de mistura e as velocidades verticais na base da camada de mistura de inverno. Foram encontradas taxas de subducção superiores a 100 m/ano ao longo da Frente Subtropical do Atlântico Sul, com três núcleos distintos de máxima subducção atingindo mais de 200 m/ano. A indução lateral mostrou-se o processo dominante na subducção, especialmente ao longo da frente, com taxas significativamente superiores ao bombeamento de Ekman. Foram identificadas diferentes AMS associadas às máximas espessuras de camadas representativas das porções média e superior da Água Central do Atlântico Sul (ACAS). As regiões de máximas taxas de subducção estão associadas à formação das AMS.Palavras-chave: camada de mistura, ventilação, ACAS, termoclina permanente, indução lateral.
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He, Chao, Bo Wu, Liwei Zou et Tianjun Zhou. « Responses of the Summertime Subtropical Anticyclones to Global Warming ». Journal of Climate 30, no 16 (août 2017) : 6465–79. http://dx.doi.org/10.1175/jcli-d-16-0529.1.
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Subtropical anticyclones dominate the subtropical ocean basins in summer. Using the multimodel output from phase 5 of the Coupled Model Intercomparison Project (CMIP5), the future changes of the subtropical anticyclones as a response to global warming are investigated, based on the changes in subsidence, low-level divergence, and rotational wind. The subtropical anticyclones over the North Pacific, South Atlantic, and south Indian Ocean are projected to become weaker, whereas the North Atlantic subtropical anticyclone (NASA) intensifies, and the South Pacific subtropical anticyclone (SPSA) shows uncertainty but is likely to intensify. Diagnostic analyses and idealized simulations suggest that the projected changes in the subtropical anticyclones are well explained by the combined effect of increased tropospheric static stability and changes in diabatic heating. Increased static stability acts to reduce the intensity of all the subtropical anticyclones, through the positive mean advection of stratification change (MASC) over the subsidence regions of the subtropical anticyclones. The pattern of change in diabatic heating is dominated by latent heating associated with changes in precipitation, which is enhanced over the western North Pacific under the “richest get richer” mechanism but is reduced over subtropical North Atlantic and South Pacific due to a local minimum of SST warming amplitude. The change in the diabatic heating pattern substantially enhances the subtropical anticyclones over the North Atlantic and South Pacific but weakens the North Pacific subtropical anticyclone.
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Zhang, Dongxiao, Michael J. McPhaden et William E. Johns. « Observational Evidence for Flow between the Subtropical and Tropical Atlantic : The Atlantic Subtropical Cells* ». Journal of Physical Oceanography 33, no 8 (1 août 2003) : 1783–97. http://dx.doi.org/10.1175/2408.1.
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Abstract This study determines the mean pathways and volume transports in the pycnocline and surface layer for water flowing between the subtropical and tropical Atlantic Ocean, using potential vorticity, salinity, geostrophic flow maps on isopycnal surfaces, and surface drifter velocities. In both hemispheres, subducted salinity maximum waters flow into the Tropics in the pycnocline along both interior and western boundary pathways. The North Atlantic ventilating trajectories are confined to densities between about 23.2 and 26.0 σθ, and only about 2 Sv (Sv ≡ 106 m3 s–1) of water reaches the Tropics through the interior pathway, whereas the western boundary contributes about 3 Sv to the equatorward thermocline flow. Flow on shallower surfaces of this density range originates from the central Atlantic near 40°W between 12° and 16°N whereas flow on the deeper surfaces originates from near 20°W just off the coast of Africa at higher latitudes. The pathways skirt around the potential vorticity barrier located under the intertropical convergence zone and reach their westernmost location at about 10°N. In the South Atlantic, about 10 Sv of thermocline water reaches the equator through the combination of interior (4 Sv) and western boundary (6 Sv) routes in a slightly higher density range than in the North Atlantic. Similar to the North Atlantic, the shallower layers originate in the central part of the basin (along 10°–30°W at 10°–15°S) and the deeper layers originate at higher latitudes from the eastern part of the basin. However, the ventilation pathways are spread over a much wider interior window in the Southern Hemisphere than in the Northern Hemisphere that at 6°S extends from 10°W to the western boundary. The equatorward convergent flows in the thermocline upwell into the surface layer and return to the subtropics through surface poleward divergence. As much as 70% of the tropical Atlantic upwelling into the surface layer is associated with these subtropical circulation cells, with the remainder contributed by the warm return flow of the large-scale thermohaline overturning circulation.
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MOLINARI, R. L., G. A. MAUL, F. CHEW, W. D. WILSON, M. BUSHEELL, D. MAYER, K. LEAMAN et al. « Subtropical Atlantic Climate Studies : Introduction ». Science 227, no 4684 (18 janvier 1985) : 292–95. http://dx.doi.org/10.1126/science.227.4684.292.
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Davis, Robert E., Bruce P. Hayden, David A. Gay, William L. Phillips et Gregory V. Jones. « The North Atlantic Subtropical Anticyclone ». Journal of Climate 10, no 4 (avril 1997) : 728–44. http://dx.doi.org/10.1175/1520-0442(1997)010<0728:tnasa>2.0.co;2.
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Silva, Bruna Andrelina, Michelle Simões Reboita, Lívia Márcia Mosso Dutra, Natália Machado Crespo et Rosmeri Porfírio Da Rocha. « Ciclones Subtropicais Guará e Lexi Parte II : Processos Físicos Responsáveis pelas Características Subtropicais ». Revista Brasileira de Geografia Física 15, no 1 (23 mars 2022) : 359. http://dx.doi.org/10.26848/rbgf.v15.1.p359-372.
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Nesse estudo, os processos físicos responsáveis pela ciclogênese subtropical pura do ciclone Guará e da transição subtropical do Lexi são investigados. O ciclone Guará teve gênese no oceano Atlântico Sul em dezembro de 2017 e o ciclone Lexi teve gênese no oceano Pacífico Sudeste em maio de 2018. Como no estudo Parte I, aqui também se utiliza a reanálise ERA5. Para cada ciclone é realizada a análise sinótica e dos balanços de calor e vorticidade. Entre os principais resultados desse estudo têm-se que a transição subtropical do ciclone Lexi foi influenciada pela interação com uma cutoff low, que favoreceu um ambiente com fraco cisalhamento vertical do vento horizontal, à medida que estava se acoplando com o ciclone extratropical em superfície. O ciclone subtropical Guará se formou associado tanto a processos dinâmicos (presença de um cavado de onda curta de pequena amplitude em 500 hPa), cisalhamento horizontal do vento induzindo vorticidade ciclônica em baixos níveis da atmosfera e o fraco cisalhamento vertical do vento horizontal, quanto à processos termodinâmicos, como a influência da transferência turbulenta de calor e umidade na interface mar-ar. Os balanços de calor e vorticidade nas imediações de cada um dos ciclones contribuíram para confirmar a ocorrência dos processos descritos, assim como evidenciam o papel relevante da liberação de calor latente associada à convecção na fase de formação do Guará e de transição subtropical do Lexi. Palavras-chave: Ciclones Subtropicais, Oceano Atlântico Sul, Oceano Pacífico Sudeste, balanços de calor e vorticidade Subtropical cyclones Guará and LexiPart II: physical processes responsible for the subtropical characteristics A B S T R A C TIn this study, the physical processes responsible for the pure subtropical cyclogenesis of Guará and the subtropical transition of Lexi are investigated. Cyclone Guará had its genesis in the South Atlantic Ocean in December 2017 and cyclone Lexi had its genesis in the Southeast Pacific Ocean in May 2018. As in the study Part I, ERA5 reanalysis is also used here. Synoptic analysis and heat and vorticity balances are performed for each cyclone. Among the main results of this study we obtained that the Lexi's subtropical transition was influenced by the interaction with a cutoff low, which favored an environment with weak vertical shear of horizontal wind, as it was coupling with the extratropical cyclone at surface. The subtropical cyclone Guará was formed associated with dynamic processes (presence of a short wave trough with small amplitude at 500 hPa), horizontal wind shear inducing cyclonic vorticity at low-levels of the atmosphere and weak vertical shear of horizontal wind, and thermodynamic processes, as the influence of turbulent transfer of heat and moisture at the sea-air interface. The heat and vorticity budgets equations of each cyclone contributed to confirm the occurrence of the described processes, as well highlight the relevant role of the release of the latent heat associated with the convection in the Guará formation and Lexi subtropical transition.Keywords: Subtropical Cyclones, South Atlantic Ocean, South Pacific Ocean, Cutoff Low, heat and vorticity budgets
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Mulitza, Stefan, et Carsten Rühlemann. « African Monsoonal Precipitation Modulated by Interhemispheric Temperature Gradients ». Quaternary Research 53, no 2 (mars 2000) : 270–74. http://dx.doi.org/10.1006/qres.1999.2110.
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AbstractThe deglacial pattern of a high-resolution alkenone-derived temperature record from the southeastern tropical Atlantic was compared with one from the northeastern subtropical Atlantic. During Termination 1b, surface waters in the eastern tropical Atlantic (6°S) reached modern temperatures, whereas those in the subtropical northeastern Atlantic (21°N) were still considerably colder than today. This asymmetrical warming may reflect meltwater-induced reductions in the northward heat transport and helps to explain rapid changes in monsoonal precipitation over Africa during the early Holocene.
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MORENO-ALCÁNTARA, MARÍA. « Atlantidae (Pterotracheoidea) of the northeast Pacific ». Zoosymposia 13, no 1 (28 février 2019) : 139–46. http://dx.doi.org/10.11646/zoosymposia.13.1.14.
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Atlantids are holoplanktonic snails found in epipelagic waters of all oceans mostly tropical and subtropical but some temperate. There are three genera within Atlantidae, which can be identified by a dextrally coiled, laterally flattened, transparent, discoid (Atlanta, Protatlanta) or involute (Oxygyrus) shell. They can be found in samples collected with plankton nets or sediment traps. Of the 23 species recognized worldwide, eight are known in the northeast Pacific. Herein distribution range extensions are reported for the atlantid species Atlanta oligogyra and Protatlanta souleyeti.
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Abatzoglou, John T., et Gudrun Magnusdottir. « Opposing Effects of Reflective and Nonreflective Planetary Wave Breaking on the NAO ». Journal of the Atmospheric Sciences 63, no 12 (décembre 2006) : 3448–57. http://dx.doi.org/10.1175/jas3809.1.
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Planetary wave breaking (PWB) over the subtropical North Atlantic is observed over 45 winters (December 1958–March 2003) using NCEP–NCAR reanalysis data. PWB is manifested in the rapid, large-scale and irreversible overturning of potential vorticity (PV) contours on isentropic surfaces in the subtropical upper troposphere. As breaking occurs over the subtropical North Atlantic, an upper-tropospheric PV tripole anomaly forms with nodes over the subtropical, midlatitude, and subpolar North Atlantic. The northern two nodes of this tripole are quite similar to the spatial structure of the North Atlantic Oscillation (NAO), with positive polarity. Nonlinear reflection is identified in approximately a quarter of all PWB events. Following breaking, two distinct circulation regimes arise, one in response to reflective events and the other in response to nonreflective events. For reflective events, anomalies over the North Atlantic rapidly propagate away from the breaking region along a poleward arching wave train over the Eurasian continent. The quasi-stationary wave activity flux indicates that wave activity is exported out of the Atlantic basin. At the same time, the regional poleward eddy momentum flux goes through a sign reversal, as does the polarity of the NAO. For nonreflective events, the dipole anomaly over the North Atlantic amplifies. Diagnostics for nonreflective events suggest that wave activity over the Azores gets absorbed, allowing continued enhancement of both the regional poleward eddy momentum flux and the positive NAO.
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Xu, Xiaobiao, Peter B. Rhines et Eric P. Chassignet. « On Mapping the Diapycnal Water Mass Transformation of the Upper North Atlantic Ocean ». Journal of Physical Oceanography 48, no 10 (octobre 2018) : 2233–58. http://dx.doi.org/10.1175/jpo-d-17-0223.1.
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AbstractDiapycnal water mass transformation is the essence behind the Atlantic meridional overturning circulation (AMOC) and the associated heat/freshwater transports. Existing studies have mostly focused on the transformation that is forced by surface buoyancy fluxes, and the role of interior mixing is much less known. This study maps the three-dimensional structure of the diapycnal transformation, both surface forced and mixing induced, using results of a high-resolution numerical model that have been shown to represent the large-scale structure of the AMOC and the North Atlantic subpolar/subtropical gyres well. The analyses show that 1) annual mean transformation takes place seamlessly from the subtropical to the subpolar North Atlantic following the surface buoyancy loss along the northward-flowing upper AMOC limb; 2) mixing, including wintertime convection and warm-season restratification by mesoscale eddies in the mixed layer and submixed layer diapycnal mixing, drives transformations of (i) Subtropical Mode Water in the southern part of the subtropical gyre and (ii) Labrador Sea Water in the Labrador Sea and on its southward path in the western Newfoundland Basin; and 3) patterns of diapycnal transformations toward lighter and denser water do not align zonally—the net three-dimensional transformation is significantly stronger than the zonally integrated, two-dimensional AMOC streamfunction (50% in the southern subtropical North Atlantic and 60% in the western subpolar North Atlantic).
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Repschläger, Janne, Dieter Garbe-Schönberg, Mara Weinelt et Ralph Schneider. « Holocene evolution of the North Atlantic subsurface transport ». Climate of the Past 13, no 4 (10 avril 2017) : 333–44. http://dx.doi.org/10.5194/cp-13-333-2017.
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Abstract. Previous studies suggested that short-term freshening events in the subpolar gyre can be counterbalanced by advection of saline waters from the subtropical gyre and thus stabilize the Atlantic Meridional Overturning Circulation (AMOC). However, little is known about the inter-gyre transport pathways. Here, we infer changes in surface and subsurface transport between the subtropical and polar North Atlantic during the last 11 000 years, by combining new temperature and salinity reconstructions obtained from combined δ18O and Mg ∕ Ca measurements on surface and subsurface dwelling foraminifera with published foraminiferal abundance data from the subtropical North Atlantic, and with salinity and temperature data from the tropical and subpolar North Atlantic. This compilation implies an overall stable subtropical warm surface water transport since 10 ka BP. In contrast, subsurface warm water transport started at about 8 ka but still with subsurface heat storage in the subtropical gyre. The full strength of intergyre exchange was probably reached only after the onset of northward transport of warm saline subsurface waters at about 7 ka BP, associated with the onset of the modern AMOC mode. A critical evaluation of different potential forcing mechanisms leads to the assumption that freshwater supply from the Laurentide Ice Sheet was the main control on subtropical to subpolar ocean transport at surface and subsurface levels.
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Evans, Jenni L., et Aviva Braun. « A Climatology of Subtropical Cyclones in the South Atlantic ». Journal of Climate 25, no 21 (novembre 2012) : 7328–40. http://dx.doi.org/10.1175/jcli-d-11-00212.1.
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A 50-yr climatology (1957–2007) of subtropical cyclones (STs) in the South Atlantic is developed and analyzed. A subtropical cyclone is a hybrid structure (upper-level cold core and lower-level warm core) with associated surface gale-force winds. The tendency for warm season development of North Atlantic STs has resulted in these systems being confused as tropical cyclones (TCs). In fact, North Atlantic STs are a regular source of the incipient vortices leading to North Atlantic TC genesis. In 2004, Hurricane Catarina developed in the South Atlantic and made landfall in Brazil. A TC system had been previously unobserved in the South Atlantic, so the incidence of Catarina highlighted the lack of an ST climatology for the region to provide a context for the likelihood of future systems. Sixty-three South Atlantic STs are documented over the 50-yr period analyzed in this climatology. In contrast to the North Atlantic, South Atlantic STs occur relatively uniformly throughout the year; however, their preferred location of genesis and mechanisms for this genesis do exhibit some seasonal variability. Rossby wave breaking was identified as the mechanism for the ST vortex initiation for North Atlantic STs. A subset of South Atlantic STs forms via this mechanism, however, an additional mechanism for ST genesis is identified here: lee cyclogenesis downstream of the Andes in the Brazil Current region—an area favorable for convection. This formation mechanism is similar to development of type-2 east coast lows in the Tasman Sea off eastern Australia.
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Xu, Xiaobiao, Peter B. Rhines et Eric P. Chassignet. « Temperature–Salinity Structure of the North Atlantic Circulation and Associated Heat and Freshwater Transports ». Journal of Climate 29, no 21 (6 octobre 2016) : 7723–42. http://dx.doi.org/10.1175/jcli-d-15-0798.1.
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Abstract This study investigates the circulation structure and relative contribution of circulation components to the time-mean meridional heat and freshwater transports in the North Atlantic, using numerical results of a high-resolution ocean model that are shown to be in excellent agreement with the observations. The North Atlantic circulation can be separated into the large-scale Atlantic meridional overturning circulation (AMOC) that is diapycnal and the subtropical and subpolar gyres that largely flow along isopycnal surfaces but also include prominent gyre-scale diapycnal overturning in the Subtropical Mode Water and Labrador Sea Water. Integrals of the meridional volume transport as a function of potential temperature θ and salinity S yield streamfunctions with respect to θ and to S, and heat functions. These argue for a significant contribution to the heat transport by the southward circulation of North Atlantic Deep Water. At 26.5°N, the isopycnic component of the subtropical gyre is colder and fresher in the northward-flowing western boundary currents than the southward return flows, and it carries heat southward and freshwater northward, opposite of that of the diapycnal component. When combined, the subtropical gyre contributes virtually zero to the heat transport and the AMOC is responsible for all the heat transport across this latitude. The subtropical gyre however significantly contributes to the freshwater transport, reducing the 0.5-Sv (1 Sv ≡ 106 m3 s–1) southward AMOC freshwater transport by 0.13 Sv. In the subpolar North Atlantic near 58°N, the diapycnal component of the circulation, or the transformation of warm saline upper Atlantic water into colder fresher deep waters, is responsible for essentially all of the heat and freshwater transports.
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Guishard, Mark P., Jenni L. Evans et Robert E. Hart. « Atlantic Subtropical Storms. Part II : Climatology ». Journal of Climate 22, no 13 (1 juillet 2009) : 3574–94. http://dx.doi.org/10.1175/2008jcli2346.1.
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Abstract A 45-yr climatology of subtropical cyclones (ST) for the North Atlantic is presented and analyzed. The STs pose a warm-season forecasting problem for subtropical locations such as Bermuda and the southern United States because of the potentially rapid onset of gale-force winds close to land. Criteria for identification of ST have been developed based on an accompanying case-study analysis. These criteria are applied here to the 40-yr European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-40) to construct a consistent historical database of 197 North Atlantic ST in 45 yr. Because ST may eventually evolve into tropical cyclones, sea surface temperatures (SST) and vertical wind shear conditions for tropical cyclogenesis are contrasted with the conditions for ST genesis identified here. Around 60% of the 197 ST formed over SST in excess of 25°C in a region of weak static stability. Further, the mean environmental vertical wind shear at formation for these storms is 10.7 m s−1, a magnitude generally considered to be unfavorable for tropical cyclogenesis. The STs have hybrid structure, so the potential for baroclinic and thermodynamic development is explored through the baroclinic zone (characterized by the Eady growth rate σ) and SST field. Seasonal evolution in the location and frequency of ST formation in the basin is demonstrated to correspond well to the changing region of overlap between SST > 25°C and σ > 0.1 day−1. This climatology is contrasted with two alternative ST datasets. The STs contribute to 12% of tropical cyclones (TC) in the current National Hurricane Center (NHC) Hurricane Database (HURDAT); this equivalent to about 1 in 8 genesis events from an incipient ST disturbance. However, with the addition of 144 ST that are newly identified in this climatology (and not presently in HURDAT) and the reclassification (as not ST) of 65 existing storms in HURDAT, 197/597 storms (33%) in the newly combined database are ST, which emphasizes the potential importance of these warm-season storms.
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Molinari, Robert. « Subtropical Atlantic Climate Studies (STACS) revisited ». Eos, Transactions American Geophysical Union 67, no 5 (1986) : 59. http://dx.doi.org/10.1029/eo067i005p00059.
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Hernández-Guerra, Alonso, Federico López-Laatzen, Francisco Machín, Demetrio De Armas et J. L. Pelegrí. « Water masses, circulation and transport in the eastern boundary current of the North Atlantic subtropical gyre ». Scientia Marina 65, S1 (30 juillet 2001) : 177–86. http://dx.doi.org/10.3989/scimar.2001.65s1177.
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Marrero-Díaz, Ángeles, Ángel Rodríguez-Santana, Francisco Machín et Josep Lluis Pelegrí. « Analytic salinity-temperature relations for the upper-thermocline waters of the eastern North Atlantic subtropical gyre ». Scientia Marina 70, no 2 (30 juin 2006) : 167–75. http://dx.doi.org/10.3989/scimar.2006.70n2167.
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Drumond, Anita, Erica Taboada, Raquel Nieto, Luis Gimeno, Sergio M. Vicente-Serrano et Juan Ignacio López-Moreno. « A Lagrangian analysis of the present-day sources of moisture for major ice-core sites ». Earth System Dynamics 7, no 3 (8 juillet 2016) : 549–58. http://dx.doi.org/10.5194/esd-7-549-2016.
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Abstract. A Lagrangian approach was used to identify the moisture sources for 14 ice-core sites located worldwide for the period of 1980–2012. The sites were classified into three domains: Arctic, Central (Andes, Alps, and Kilimanjaro), and Antarctic. The approach was used to compute budgets of evaporation minus precipitation by calculating changes in the specific humidity along 10-day backward trajectories. The results indicate that the oceanic regions around the subtropical high-pressure centres provide most of moisture, and their contribution varies throughout the year following the annual cycles of the centres. For the Arctic Domain, the sources lie in the subtropical North Atlantic and Pacific. The subtropical South Atlantic, Indian, and Pacific oceans provide moisture for the Antarctic Domain. The sources for South America are the Atlantic and South Pacific, for Europe the sources are in the Mediterranean and the North Atlantic, and for Asia the sources are the Indian Ocean and the Arabian Sea.
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Tang, Xinxin, Jianping Li, Yazhou Zhang, Yanjie Li et Sen Zhao. « Synergistic Effect of El Niño and Negative Phase of North Atlantic Oscillation on Winter Precipitation in the Southeastern United States ». Journal of Climate 36, no 6 (15 mars 2023) : 1767–91. http://dx.doi.org/10.1175/jcli-d-22-0293.1.
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Abstract This study reveals that the significant increase of winter precipitation over the southeastern United States (SEUS) is associated with El Niño and the negative phase of North Atlantic Oscillation (NAO−). Diagnosis of large-scale dynamics shows that El Niño and NAO− have a synergistic effect on the enhancement of transient eddies and stationary waves in the eastern Pacific, the southern United States, and the North Atlantic. These enhanced transient eddies are associated with subtropical jet stream acceleration and maintenance of subtropical low from the eastern Pacific to the Atlantic, influencing stronger stationary waves propagation from the tropical Pacific to the SEUS and North Atlantic, and from the northwestern Atlantic to the SEUS and Pacific. This favors a positive phase of the meridional dipole in geopotential height anomalies between the tropics and subtropics in the Western Hemisphere (WTSD) during the co-occurrence of El Niño and NAO−. The strong positive WTSD-like pattern, accompanied by a zonally extended and southerly shifted subtropical westerly jet, induces a northward-tilted secondary circulation with ascending motion over the SEUS and Gulf of Mexico. Simultaneously, an intensified trough over the SEUS promotes moisture and warm advection from the subtropical and tropical Pacific converging with cold advection from the northwestern North Atlantic in the adjacent Gulf of Mexico, which is beneficial for front and cyclone generation, and induces precipitation in the SEUS. This study suggests that the synergistic effects of El Niño and NAO− help to understand the variability of winter SEUS precipitation.
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Bates, N. R. « Multi-decadal uptake of carbon dioxide into subtropical mode water of the North Atlantic Ocean ». Biogeosciences Discussions 8, no 6 (21 décembre 2011) : 12451–76. http://dx.doi.org/10.5194/bgd-8-12451-2011.
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Abstract. Natural climate variability impacts the multi-decadal uptake of anthropogenic carbon dioxide (Cant) into the North Atlantic Ocean subpolar and subtropical gyres. Previous studies have shown that there is significant uptake of CO2 into the subtropical mode water (STMW) that forms south of the Gulf Stream in winter and constitutes the dominant upper-ocean water mass in the subtropical gyre of the North Atlantic Ocean. Observations at the Bermuda Atlantic Time-series Study (BATS) site near Bermuda show an increase in dissolved inorganic carbon (DIC) of +1.51 ± 0.08 μmol kg−1 yr−1 between 1988 and 2011. It is estimated that the sink of CO2 into STMW was 0.985 ± 0.018 Pg C (Pg = 1015 g C) between 1988 and 2011 (~70 % of which is due to uptake of Cant). However, the STMW sink of CO2 was strongly coupled to the North Atlantic Oscillation (NAO) with large uptake of CO2 into STMW during the 1990s (NAO positive phase). In contrast, uptake of CO2 into STMW was much reduced in the 2000s during the NAO neutral/negative phase. Thus, NAO induced variability of the STMW CO2 sink is important when evaluating multi-decadal changes in North Atlantic Ocean CO2 sinks.
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Liu, Hao, Shujiang Li et Zexun Wei. « Interannual variability in the subduction of the South Atlantic subtropical underwater ». Climate Dynamics 57, no 3-4 (10 avril 2021) : 1061–77. http://dx.doi.org/10.1007/s00382-021-05758-0.
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AbstractThe South Atlantic subtropical underwater (STUW) is a high-salinity water mass formed by subduction within the subtropical gyre. It is a major component of the subtropical cell and affects stratification in the downstream direction due to its high salinity characteristics. Understanding the interannual variability in STUW subduction is essential for quantifying the impact of subtropical variability on the tropical Atlantic. Using the output from the ocean state estimate of the Consortium for Estimating the Circulation and Climate of the Ocean (ECCO), this study investigates the interannual variability in STUW subduction from 1992 to 2016. We find that heat fluxes, wind stress, and wind stress curl cause interannual variability in the subduction rate. Heat fluxes over the subduction area modulate the sea surface buoyancy and regulate the mixed layer depth (MLD) during its deepening and shoaling phases. Additionally, the wind stress curl and zonal wind stress can modulate the size of the subduction area by regulating the probability of particles entrained into the mixed layer within 1 year of tracing. This analysis evaluates the influence of subtropical wind patterns on the South Atlantic subsurface high-salinity water mass, highlighting the impact of heat and wind on the interannual changes in the oceanic component of the hydrological cycle.
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Wu, Lixin, et Zhengyu Liu. « North Atlantic Decadal Variability : Air–Sea Coupling, Oceanic Memory, and Potential Northern Hemisphere Resonance* ». Journal of Climate 18, no 2 (15 janvier 2005) : 331–49. http://dx.doi.org/10.1175/jcli-3264.1.
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Abstract In this paper, the causes and mechanisms of North Atlantic decadal variability are explored in a series of coupled ocean–atmosphere simulations. The model captures the major features of the observed North Atlantic decadal variability. The North Atlantic SST anomalies in the model control simulation exhibit a prominent decadal cycle of 12–16 yr, and a coherent propagation from the western subtropical Atlantic to the subpolar region. A series of additional modeling experiments are conducted in which the air–sea coupling is systematically modified in order to evaluate the importance of air–sea coupling for the North Atlantic decadal variability being studied. This shall be referred to as “modeling surgery.” The results suggest the critical role of ocean–atmosphere coupling in sustaining the North Atlantic decadal oscillation at selected time scales. The coupling in the North Atlantic is characterized by a robust North Atlantic Oscillation (NAO)-like atmospheric response to the SST tripole anomaly, which tends to intensify the SST anomaly and, meanwhile, also provide a delayed negative feedback. This delayed negative feedback is predominantly associated with the adjustment of the subtropical gyre in response to the anomalous wind stress curl in the subtropical Atlantic. Atmospheric stochastic forcing can drive SST patterns similar to those in the fully coupled ocean–atmosphere system, but fails to generate any preferred decadal time scales. The simulated North Atlantic decadal variability, therefore, can be viewed as a coupled ocean–atmosphere mode under the influence of stochastic forcing. This modeling study also suggests some potential resonance between the Pacific and the North Atlantic decadal fluctuations mediated by the atmosphere. The modeling surgery indicates that the Pacific climate, although not a necessary precondition, can impact the North Atlantic climate variability substantially.
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Walter, S., H. W. Bange, U. Breitenbach et D. W. R. Wallace. « Nitrous oxide in the North Atlantic Ocean ». Biogeosciences Discussions 3, no 4 (17 juillet 2006) : 993–1022. http://dx.doi.org/10.5194/bgd-3-993-2006.
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Abstract. In order to investigate the role of the North Atlantic Ocean as a source of atmospheric nitrous oxide and to decipher the major formation pathways of nitrous oxide, measurements of dissolved nitrous oxide were made during three cruises in the tropical, subtropical and subpolar North Atlantic in October/November 2002, March/April 2004, and May 2002, respectively. Nitrous oxide was close to equilibrium or slightly supersaturated in the surface layers suggesting that the North Atlantic acts as a weak source of nitrous oxide to the atmosphere. Depth profiles showed supersaturation throughout the water column with a distinct increasing trend from the subpolar to the tropical region. Lowest nitrous oxide concentrations, near equilibrium and with an average of 11.0±1.7 nmol L−1, were found in the subpolar North Atlantic where the profiles showed no clear maxima. Highest values up to 37.3 nmol L−1 occurred in the tropical North Atlantic with clear maxima at approximately 400 m. A positive correlation of nitrous oxide with nitrate, as well as excess nitrous oxide with AOU, was only observed in the subtropical and tropical regions. Therefore, we conclude that the formation of nitrous oxide occurs in the tropical region rather than in the subpolar region of the North Atlantic and suggest nitrification is the dominant formation pathway in the subtropical and tropical regions.
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Rodrigues, Regina R., Edmo J. D. Campos et Reindert Haarsma. « The Impact of ENSO on the South Atlantic Subtropical Dipole Mode ». Journal of Climate 28, no 7 (27 mars 2015) : 2691–705. http://dx.doi.org/10.1175/jcli-d-14-00483.1.
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Abstract The impact of El Niño–Southern Oscillation (ENSO) on the South Atlantic subtropical dipole mode (SASD) is investigated using both observations and model simulations. The SASD is the dominant mode of coupled ocean–atmosphere variability in the South Atlantic. This study focuses on austral summer, when both ENSO and SASD peak. It is shown that negative SASD events are associated with central Pacific El Niño events by triggering the Pacific–South American wave train (PSA). The latter resembles the third leading mode of atmospheric variability in the Southern Hemisphere (PSA2) and causes a weakening and meridional shift of the South Atlantic subtropical high, which then generates the negative SASD events. On the other hand, a strengthening of the South Atlantic subtropical high related to central La Niña teleconnections causes positive SASD events. The results herein show that the PSA2, triggered by central Pacific ENSO events, connects the tropical Pacific to the Atlantic. This connection is absent from eastern Pacific ENSO events, which appear to initiate the second leading mode of atmospheric variability in the Southern Hemisphere (PSA1). It is for this reason that previous studies have found weak correlations between ENSO and SASD. These findings can improve the climate prediction of southeastern South America and southern Africa since these regions are affected by sea surface temperature anomalies of both the Pacific and Atlantic Oceans.
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Yu, Lejiang, Shiyuan Zhong, Timo Vihma, Cuijuan Sui et Bo Sun. « A change in the relation between the Subtropical Indian Ocean Dipole and the South Atlantic Ocean Dipole indices in the past four decades ». Atmospheric Chemistry and Physics 23, no 1 (10 janvier 2023) : 345–53. http://dx.doi.org/10.5194/acp-23-345-2023.
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Abstract. We utilized the global atmospheric reanalysis ERA5 and reconstructed sea surface temperature (SST) data from 1979 through 2020 to examine the stability of the relationship between the SST oscillations in the southern Indian Ocean and the Atlantic Ocean, as described by the Subtropical Indian Ocean Dipole (SIOD) and South Atlantic Ocean Dipole (SAOD) indices, respectively. We note a significant positive correlation between the two indices prior to the year 2000 but practically no correlation afterwards. We show that in the two decades prior to 2000, a positive phase of the SAOD is associated with more convective activities over the subtropical southern Atlantic Ocean and eastern Brazil, which trigger a stronger upper-atmosphere wavetrain. This produces stronger southern subtropical highs and surface anti-cyclonic circulations and therefore a stronger correlation between the two indices. The situation is reversed after 2000. Our results are potentially applicable to predictions of precipitation in southern Africa and South America.
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Gozzo, Luiz Felippe, Rosmeri P. da Rocha, Michelle S. Reboita et Shigetoshi Sugahara. « Subtropical Cyclones over the Southwestern South Atlantic : Climatological Aspects and Case Study ». Journal of Climate 27, no 22 (4 novembre 2014) : 8543–62. http://dx.doi.org/10.1175/jcli-d-14-00149.1.
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Abstract Hurricane Catarina (2004) and subtropical storm Anita (2010) called attention to the development of subtropical cyclones (SCs) over the South Atlantic basin. Besides strong and organized storms, a large number of weaker, shallower cyclones with both extratropical and tropical characteristics form in the region, impacting the South American coast. The main focus of this study is to simulate a climatology of subtropical cyclones and their synoptic pattern over the South Atlantic, proposing a broader definition of these systems. In addition, a case study is presented to discuss the main characteristics of one weak SC. The Interim ECMWF Re-Analysis (ERA-Interim) and NCEP–NCAR reanalysis are used to construct the 33-yr (1979–2011) climatology, and a comparison between them is established. Both reanalyses show good agreement in the SCs’ intensity, geographical distribution, and seasonal variability, but the interannual variability is poorly correlated. Anomaly composites for austral summer show that subtropical cyclogenesis occurs under a dipole-blocking pattern in upper levels. Upward motion is enhanced by the vertical temperature gradient between a midtropospheric cold cutoff low/trough and the intense low-level warm air advection by the South Atlantic subtropical high. Turbulent fluxes in the cyclone region are not above average during cyclogenesis, but the subtropical high flow advects great amounts of moisture from distant regions to fuel the convective activity. Although most of the SCs develop during austral summer (December–February), it is in autumn (March–May) that the most “tropical” environment is found (stronger surface fluxes and weaker vertical wind shear), leading to the most intense episodes.
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Duarte, Carlos M., Susana Agustí, Javier Arístegui, Natalia González et Ricardo Anadón. « Evidence for a heterotrophic subtropical northeast Atlantic ». Limnology and Oceanography 46, no 2 (mars 2001) : 425–28. http://dx.doi.org/10.4319/lo.2001.46.2.0425.
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Molinari, Robert. « Subtropical Atlantic Climate Studies (STACS) : An Update ». Oceanography 2, no 2 (1989) : 32–35. http://dx.doi.org/10.5670/oceanog.1989.08.
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Ter Halle, Alexandra, Laurent Jeanneau, Marion Martignac, Emilie Jardé, Boris Pedrono, Laurent Brach et Julien Gigault. « Nanoplastic in the North Atlantic Subtropical Gyre ». Environmental Science & ; Technology 51, no 23 (21 novembre 2017) : 13689–97. http://dx.doi.org/10.1021/acs.est.7b03667.
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Maslin, M., M. Sarnthein et J. J. Knaack. « Subtropical Eastern Atlantic climate during the Eemian ». Naturwissenschaften 83, no 3 (mars 1996) : 122–26. http://dx.doi.org/10.1007/bf01142176.
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Tuchen, Franz Philip, Joke F. Lübbecke, Sunke Schmidtko, Rebecca Hummels et Claus W. Böning. « The Atlantic Subtropical Cells Inferred from Observations ». Journal of Geophysical Research : Oceans 124, no 11 (novembre 2019) : 7591–605. http://dx.doi.org/10.1029/2019jc015396.
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Maslin, M., M. Sarnthein et J. J. Knaack. « Subtropical Eastern Atlantic Climate During the Eemian ». Naturwissenschaften 83, no 3 (1 mars 1996) : 122–26. http://dx.doi.org/10.1007/s001140050258.
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Bates, N. R. « Multi-decadal uptake of carbon dioxide into subtropical mode water of the North Atlantic Ocean ». Biogeosciences 9, no 7 (18 juillet 2012) : 2649–59. http://dx.doi.org/10.5194/bg-9-2649-2012.
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Abstract. Natural climate variability impacts the multi-decadal uptake of anthropogenic carbon dioxide (Cant) into the North Atlantic Ocean subpolar and subtropical gyres. Previous studies have shown that there is significant uptake of CO2 into subtropical mode water (STMW) of the North Atlantic. STMW forms south of the Gulf Stream in winter and constitutes the dominant upper-ocean water mass in the subtropical gyre of the North Atlantic Ocean. Observations at the Bermuda Atlantic Time-series Study (BATS) site near Bermuda show an increase in dissolved inorganic carbon (DIC) of +1.51 ± 0.08 μmol kg−1 yr−1 between 1988 and 2011, but also an increase in ocean acidification indicators such as pH at rates (−0.0022 ± 0.0002 yr−1) higher than the surface ocean (Bates et al., 2012). It is estimated that the sink of CO2 into STMW was 0.985 ± 0.018 Pg C (Pg = 1015 g C) between 1988 and 2011 (70 ± 1.8% of which is due to uptake of Cant). The sink of CO2 into the STMW is 20% of the CO2 uptake in the North Atlantic Ocean between 14°–50° N (Takahashi et al., 2009). However, the STMW sink of CO2 was strongly coupled to the North Atlantic Oscillation (NAO), with large uptake of CO2 into STMW during the 1990s during a predominantly NAO positive phase. In contrast, uptake of CO2 into STMW was much reduced in the 2000s during the NAO neutral/negative phase. Thus, NAO induced variability of the STMW CO2 sink is important when evaluating multi-decadal changes in North Atlantic Ocean CO2 sinks.
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Wilson, Brent, et Michael A. Kaminski. « Rare species of West Indian aspect in the Holocene of Liverpool Bay and their biogeographic and environmental significance ». Micropaleontology 69, no 1 (2023) : 103–12. http://dx.doi.org/10.47894/mpal.69.1.03.
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The Gulf Stream, although not directly responsible for the mild, temperate climate of the British Isles, transports vast quantities of water across the North Atlantic Ocean. An extension of the Caribbean-Loop-Florida current system, this strong current cools and becomes more saline by evaporation as it flows NE across the North Atlantic Ocean. Nevertheless, it is able to transport benthic foraminifera across oceanic distances, the fauna around Bermuda containing many species described from the Caribbean Sea. Examining two cores taken from the shallow middle neritic Holocene Surface Sands Formation of the temperate Liverpool Bay, England, we found rare specimens of eight species recorded also from the neritic of the tropical Caribbean and subtropical Atlantic South Shelf Provinces: Asterigerina carinata, Dyocibicides biserialis, Elphidium discoidale, Nonionoides grateloupii, Quinqueloculina lamarckiana, Reussella atlantica and Sahulia conica. We are confident in our identifications of A. carinata and E. discoidale, but suggest that these names may have been applied to several cryptospecies. Some of these may have been transported on floating phytal debris, A. carinata, which supports algal symbionts, having been recorded at abyssal depths in the eastern North Atlantic. Othersmay have been transported as small propagules (proloculi). Although there may be a constant rain of such specimens into Liverpool Bay, we conclude on the basis of their rarity that the exotic species are unlikely to be able to overwinter there. We suggest, however, that these may have potential as invasive species for Liverpool Bay as climates continue to warm. This is not the earliest instance of transport of exotic species across the North Atlantic. The Late Eocene species Asterocyclina soldadoensis has been recorded from both the southern Caribbean region and offshore Ireland.
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Polkova, Iuliia, Armin Köhl et Detlef Stammer. « Predictive Skill for Regional Interannual Steric Sea Level and Mechanisms for Predictability* ». Journal of Climate 28, no 18 (11 septembre 2015) : 7407–19. http://dx.doi.org/10.1175/jcli-d-14-00811.1.
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Abstract Based on decadal hindcasts initialized every five years over the period 1960–2000, the predictive skill of annual-mean regional steric sea level and associated mechanisms are investigated. Predictive skill for steric sea level is found over large areas of the World Ocean, notably over the subtropical Atlantic and Pacific Oceans, along the path of the North Atlantic Current, and over the Indian and Southern Oceans. Mechanisms for the predictability of the thermosteric and halosteric contributions to the steric signal are studied by separating these components into signals originating from processes within and beneath the mixed layer. Contributions originating from below the mixed layer are further decomposed into density-related (isopycnal motion term) and density-compensated (spice term) changes. In regions of the subtropical Pacific and Atlantic Oceans, predictive skill results from the interannual variability associated with the contribution from isopycnal motion to thermosteric sea level. Skill related to thermosteric mixed layer processes is found to be important in the subtropical Atlantic, while the spice contribution shows skill over the subpolar North Atlantic. In the subtropics, the high predictive skill can be rationalized in terms of westward-propagating baroclinic Rossby waves for a lead time of 2–5 yr, as demonstrated using an initialized Rossby wave model. Because of the low Rossby wave speed in high latitudes, this process is not separable from the persistence there.
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Maneveldt, Gavin William, Elizabeht Van der Merwe et Derek Keats. « Taxonomic review of Hydrolithon samoënse (Corallinaceae, Corallinales, Rhodophyta) and other taxa found to be conspecific ». Phytotaxa 192, no 4 (15 janvier 2015) : 230. http://dx.doi.org/10.11646/phytotaxa.192.4.2.
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Based on new studies of the type and of specimens from various localities in the Indian and Pacific oceans, Hydrolithon samoënse was reaffirmed as a distinct species. The following taxa were found to be heterotypic synonyms thereof: Neogoniolithon caribaeum, N. erosum and N. rugulosum. Based on morphological and anatomical data H. samoënse not only occurs extensively throughout the Indo-Pacific and northern, southern and subtropical eastern Atlantic oceans, but as a result of the present study, is now known to occur throughout the tropical and subtropical regions of the western Atlantic Ocean.
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Morioka, Yushi, Tomoki Tozuka, Sebastien Masson, Pascal Terray, Jing-Jia Luo et Toshio Yamagata. « Subtropical Dipole Modes Simulated in a Coupled General Circulation Model ». Journal of Climate 25, no 12 (15 juin 2012) : 4029–47. http://dx.doi.org/10.1175/jcli-d-11-00396.1.
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Abstract The growth and decay mechanisms of subtropical dipole modes in the southern Indian and South Atlantic Oceans and their impacts on southern African rainfall are investigated using results from a coupled general circulation model originally developed for predicting tropical climate variations. The second (most) dominant mode of interannual sea surface temperature (SST) variations in the southern Indian (South Atlantic) Ocean represents a northeast–southwest oriented dipole, now called subtropical dipole mode. The positive (negative) SST interannual anomaly pole starts to grow in austral spring and reaches its peak in February. In austral late spring, the suppressed (enhanced) latent heat flux loss associated with the variations in the subtropical high causes a thinner (thicker) than normal mixed layer thickness that, in turn, enhances (reduces) the warming of the mixed layer by the climatological shortwave radiation. The positive (negative) pole gradually decays in austral fall because the mixed layer cooling by the entrainment is enhanced (reduced), mostly owing to the larger (smaller) temperature difference between the mixed layer and the entrained water. The increased (decreased) latent heat loss due to the warmer (colder) SST also contributes to the decay of the positive (negative) pole. Although further verification using longer observational data is required, the present coupled model suggests that the South Atlantic subtropical dipole may play a more important role in rainfall variations over the southern African region than the Indian Ocean subtropical dipole.
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Alexander-Astiz Le Bras, Isabela, Maike Sonnewald et John M. Toole. « A Barotropic Vorticity Budget for the Subtropical North Atlantic Based on Observations ». Journal of Physical Oceanography 49, no 11 (novembre 2019) : 2781–97. http://dx.doi.org/10.1175/jpo-d-19-0111.1.
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AbstractTo ground truth the large-scale dynamical balance of the North Atlantic subtropical gyre with observations, a barotropic vorticity budget is constructed in the ECCO state estimate and compared with hydrographic observations and wind stress data products. The hydrographic dataset at the center of this work is the A22 WOCE section, which lies along 66°W and creates a closed volume with the North and South American coasts to its west. The planetary vorticity flux across A22 is quantified, providing a metric for the net meridional flow in the western subtropical gyre. The wind stress forcing over the subtropical gyre to the west and east of the A22 section is calculated from several wind stress data products. These observational budget terms are found to be consistent with an approximate barotropic Sverdrup balance in the eastern subtropical gyre and are on the same order as budget terms in the ECCO state estimate. The ECCO vorticity budget is closed by bottom pressure torques in the western subtropical gyre, which is consistent with previous studies. In sum, the analysis provides observational ground truth for the North Atlantic subtropical vorticity balance and explores the seasonal variability of this balance for the first time using the ECCO state estimate. This balance is found to hold on monthly time scales in ECCO, suggesting that the integrated subtropical gyre responds to forcing through fast barotropic adjustment.
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Milovanovic, Bosko, Milan Radovanovic et Tamara Jojic-Glavonjic. « Linkage between water temperature of the subtropical Atlantic, the Azores maximum and air temperature in Serbia ». Glasnik Srpskog geografskog drustva 90, no 2 (2010) : 69–84. http://dx.doi.org/10.2298/gsgd1002069m.
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The paper explores the link between water temperature of the subtropical part of the Atlantic Ocean (the belt of 25 to 40? N), atmospheric pressure and air temperature in Belgrade and Serbia. The main point of the research is to examine the linkage between the Azores air pressure maximum with the changes of water temperature in the subtropical belt of the Atlantic (given in the net 5x5?). Using the hierarchical cluster analyses, 10 clusters of water temperature of the subtropical part of the Atlantic Ocean were selected. Their linkage between the position and the intensity of the Azores maximum was examined by multiple-linear regression. It was established which of the clusters influenced most the geographical latitude, geographical longitude and the intensity of the Azores maximum, as well as which of the grid cells represented the most significant predictors within each of the clusters. Examining the relation between the position and the intensity of the Azores maximum with the air temperature in Belgrade, i.e. Serbia, it was established that the linkage with the geographical latitude of this action centre was the most significant. .
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Ryoo, J. M., D. W. Waugh et A. Gettelman. « Variability of subtropical upper tropospheric humidity ». Atmospheric Chemistry and Physics Discussions 8, no 1 (22 janvier 2008) : 1041–67. http://dx.doi.org/10.5194/acpd-8-1041-2008.
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Abstract. Analysis of Atmospheric Infrared Sounder (AIRS) measurements for five northern winters shows significant longitudinal variations in subtropical upper tropospheric relative humidity (RH), not only in the climatological mean values but also in the local distributions and temporal variability. The largest climatological mean values in the northern subtropics occur over the eastern Pacific and Atlantic oceans, where there is also large day-to-day variability. In contrast, there are smaller mean values, and smaller variability that occurs at lower frequency, over the Indian and western Pacific oceans. These differences in the distribution and variability of subtropical RH are related to differences in the key transport processes in the different sectors. The large variability and intermittent high and low RH over the Eastern Pacific and Atlantic oceans, and to a smaller extent over the Indian ocean, are due to intrusions of high potential vorticity air into the subtropics. Intrusions seldom occur over the eastern Indian and western Pacific oceans, and here the subtropical RH is more closely linked to the location and strength of subtropical anticyclones. In this region there are eastward propagating features in the subtropical RH that are out of phase with the tropical RH, and are caused by modulation of the subtropical anticyclones by the Madden-Julian Oscillation.
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Ryoo, J. M., D. W. Waugh et A. Gettelman. « Variability of subtropical upper tropospheric humidity ». Atmospheric Chemistry and Physics 8, no 10 (20 mai 2008) : 2643–55. http://dx.doi.org/10.5194/acp-8-2643-2008.
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Abstract. Analysis of Atmospheric Infrared Sounder (AIRS) measurements for five years shows significant longitudinal variations in the winter subtropical upper tropospheric relative humidity (RH), not only in the climatological mean values but also in the local distributions and temporal variability. The largest climatological mean values occur over the central-eastern Pacific and Atlantic oceans, where there is also large day-to-day variability. In contrast, there are smaller mean values, and smaller variability that occurs at lower frequency, over the Indian and western Pacific oceans. These differences in the distribution and variability of subtropical RH are related to differences in the key transport processes in the different sectors. The large variability and intermittent high and low RH over the central-eastern Pacific and Atlantic oceans are due to intrusions of high potential vorticity air into the subtropics. Intrusions seldom occur over the eastern Indian and western Pacific oceans, and here the subtropical RH is more closely linked to the location and strength of subtropical anticyclones. During northern winter there are eastward propagating features in the subtropical RH in this region that are out of phase with the tropical RH, and are caused by modulation of the subtropical anticyclones by the Madden-Julian Oscillation.
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YANES, YURENA, GERALDINE A. HOLYOAK, DAVID T. HOLYOAK, MARIA R. ALONSO et MIGUEL IBÁÑEZ. « A new Discidae subgenus and two new species (Gastropoda : Pulmonata) from the Canary Islands ». Zootaxa 2911, no 1 (9 juin 2011) : 43. http://dx.doi.org/10.11646/zootaxa.2911.1.2.
Texte intégralRésumé :
The family Discidae has undergone extensive speciation in the Macaronesian region (eastern Atlantic Ocean), with 11 endemic species recognised from Madeira and the Canary Islands in recent checklists (Bank, Groh & Ripken 2002; Seddon 2008; Fauna Europaea database project 2011), grouped into the genera Keraea Gude, 1911 and Discus Fitzinger, 1833: K. deflorata (R.T. Lowe, 1855) and D. (Atlantica) guerinianus (R.T. Lowe, 1852), from Madeira; and nine species from the Canary Islands: K. garachicoensis (Wollaston, 1878), D. scutula, (Shuttleworth, 1852), D. engonatus (Shuttleworth, 1852), D. textilis (Shuttleworth, 1852), D. retextus, (Shuttleworth, 1852), D. putrescens (R.T. Lowe, 1861), D. ganodus (J. Mabille, 1882), D. gomerensis Rähle, 1994, and D. kompsus (J. Mabille, 1883). In contrast with the anatomical data known for the European and North American genera Discus and Anguispira Morse, 1864 (Uminski 1962; Pilsbry 1948), there has hitherto been no information published on the internal anatomy of the Canary Islands and Madeiran species, which are known only by their shell characters. In this paper we raise Atlantica to the rank of genus in the Discidae and describe shell and anatomical characters for two new species from La Gomera and Tenerife, respectively. They are grouped in a new subgenus of Atlantica, largely restricted to the laurisilva. This laurel-rich forest occurs in humid subtropical and warm-temperate regions with little variability in temperatures and is developed between 600 and 1,200 m above sea level in the Canary Islands (Yanes et al. 2009b: Fig. 2).
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Huang, Bohua, et J. Shukla. « Ocean–Atmosphere Interactions in the Tropical and Subtropical Atlantic Ocean ». Journal of Climate 18, no 11 (1 juin 2005) : 1652–72. http://dx.doi.org/10.1175/jcli3368.1.
Texte intégralRésumé :
Abstract A 110-yr simulation is conducted using a specially designed coupled ocean–atmosphere general circulation model that only allows air–sea interaction over the Atlantic Ocean within 30°S–60°N. Since the influence from the Pacific El Niño–Southern Oscillation (ENSO) over the Atlantic is removed in this run, it provides a better view of the extratropical influences on the tropical air–sea interaction within the Atlantic sector. The model results are compared with the observations that also have their ENSO components subtracted. The model reproduces the two major anomalous patterns of the sea surface temperature (SST) in the southern subtropical Atlantic (SSA) and the northern tropical Atlantic (NTA) Ocean. The SSA pattern is phase locked to the annual cycle. Its enhancement in austral summer is associated with atmospheric disturbances from the South Atlantic during late austral spring. The extratropical atmospheric disturbances induce anomalous trade winds and surface heat fluxes in its northern flank, which generate SST anomalies in the subtropics during austral summer. The forced SST anomalies then change the local sea level pressure and winds, which in turn affect the northward shift of the atmospheric disturbance and cause further SST changes in the deep Tropics during austral fall. The NTA pattern is significant throughout a year. Like the SSA pattern, the NTA pattern in boreal winter–spring is usually associated with the heat flux change caused by extratropical atmospheric disturbances, such as the North Atlantic Oscillation. The SST anomalies then feed back with the tropical atmosphere and expand equatorward. From summer to fall, however, the NTA SST anomalies are likely to persist within the subtropics for more than one season after it is generated. Our model results suggest that this feature is associated with a local feedback between the NTA SST anomalies and the atmospheric subtropical anticyclone from late boreal summer to early winter. The significance of this potential feedback in reality needs to be further examined with more observational evidence.
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Scussolini, P., E. van Sebille et J. V. Durgadoo. « Paleo Agulhas rings enter the subtropical gyre during the penultimate deglaciation ». Climate of the Past 9, no 6 (25 novembre 2013) : 2631–39. http://dx.doi.org/10.5194/cp-9-2631-2013.
Texte intégralRésumé :
Abstract. A maximum in the strength of Agulhas leakage has been registered at the interface between the Indian and South Atlantic oceans during glacial Termination II (T-II). This presumably transported the salt and heat necessary for maintaining the Atlantic circulation at rates similar to the present day. However, it was never shown whether these waters were effectively incorporated into the South Atlantic gyre, or whether they retroflected into the Indian and/or Southern oceans. To resolve this question, we investigate the presence of paleo Agulhas rings from a sediment core on the central Walvis Ridge, almost 1800 km farther into the Atlantic Basin than previously studied. Analysis of a 60 yr data set from the global-nested INALT01 model allows us to relate density perturbations at the depth of the thermocline to the passage of individual rings over the core site. Using this relation from the numerical model as the basis for a proxy, we generate a time series of variability of individual Globorotalia truncatulinoides δ18O. We reveal high levels of pycnocline depth variability at the site, suggesting enhanced numbers of Agulhas rings moving into the South Atlantic Gyre around T-II. Our record closely follows the published quantifications of Agulhas leakage from the east of the Cape Basin, and thus shows that Indian Ocean waters entered the South Atlantic circulation. This provides crucial support for the view of a prominent role of the Agulhas leakage in the shift from a glacial to an interglacial mode of the Atlantic circulation.
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Falcón, Luisa I., Frank Cipriano, Andrei Y. Chistoserdov et Edward J. Carpenter. « Diversity of Diazotrophic Unicellular Cyanobacteria in the Tropical North Atlantic Ocean ». Applied and Environmental Microbiology 68, no 11 (novembre 2002) : 5760–64. http://dx.doi.org/10.1128/aem.68.11.5760-5764.2002.
Texte intégralRésumé :
ABSTRACT We present data on the genetic diversity and phylogenetic affinities of N2-fixing unicellular cyanobacteria in the plankton of the tropical North Atlantic Ocean. Our dinitrogenase gene (nifH) sequences grouped together with a group of cyanobacteria from the subtropical North Pacific; another subtropical North Pacific group was only distantly related. Most of the 16S ribosomal DNA sequences from our tropical North Atlantic samples were closely allied with sequences from a symbiont of the diatom Climacodium frauenfeldianum. These findings suggest a complex pattern of evolutionary and ecological divergence among unicellular cyanobacteria within and between ocean basins.
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Beven, John L., Lixion A. Avila, Eric S. Blake, Daniel P. Brown, James L. Franklin, Richard D. Knabb, Richard J. Pasch, Jamie R. Rhome et Stacy R. Stewart. « Atlantic Hurricane Season of 2005 ». Monthly Weather Review 136, no 3 (1 mars 2008) : 1109–73. http://dx.doi.org/10.1175/2007mwr2074.1.
Texte intégralRésumé :
Abstract The 2005 Atlantic hurricane season was the most active of record. Twenty-eight storms occurred, including 27 tropical storms and one subtropical storm. Fifteen of the storms became hurricanes, and seven of these became major hurricanes. Additionally, there were two tropical depressions and one subtropical depression. Numerous records for single-season activity were set, including most storms, most hurricanes, and highest accumulated cyclone energy index. Five hurricanes and two tropical storms made landfall in the United States, including four major hurricanes. Eight other cyclones made landfall elsewhere in the basin, and five systems that did not make landfall nonetheless impacted land areas. The 2005 storms directly caused nearly 1700 deaths. This includes approximately 1500 in the United States from Hurricane Katrina—the deadliest U.S. hurricane since 1928. The storms also caused well over $100 billion in damages in the United States alone, making 2005 the costliest hurricane season of record.
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Yang, Haijun, et Lu Wang. « Tropical Oceanic Response to Extratropical Thermal Forcing in a Coupled Climate Model : A Comparison between the Atlantic and Pacific Oceans* ». Journal of Climate 24, no 15 (1 août 2011) : 3850–66. http://dx.doi.org/10.1175/2011jcli3927.1.
Texte intégralRésumé :
Abstract The tropical oceanic response to the extratropical thermal forcing is quantitatively estimated in a coupled climate model. This work focuses on comparison of the responses between the tropical Atlantic and Pacific. Under the same extratropical forcing, the tropical sea surface temperature responses are comparable. However, the responses in the tropical subsurface in the two oceans are distinct. The tropical subsurface response in the Atlantic can be twice of that in the Pacific. The maximum subsurface temperature change in the tropical Pacific occurs in the eastern lower thermocline, while that in the tropical Atlantic occurs in the west and well below the lower thermocline. The different responses in the tropical Atlantic and Pacific are closely related to the different changes in the meridional overturning circulations. The Pacific shallow overturning circulation, or the subtropical cell, tends to slow down (speed up) in response to the extratropical warming (cooling) forcing. The changes in the upwelling in the eastern equatorial Pacific as well as the shallow subduction from the extratropical southern Pacific along the eastern boundary are accountable for the eastern Pacific temperature change. The Atlantic overturning circulation consists of the shallow subtropical cell and the deep thermohaline circulation. A weakened thermohaline circulation will result in a strengthened northern subtropical cell, in which the change in the lower branch, or the low-latitude North Brazil Current, can cause strong response below the western tropical thermocline. Here the coastal Kelvin wave along the western boundary on the intermediate isopycnal level also plays an important role in the equatorward conveying of the climate anomalies in the mid-to-high-latitude Atlantic, particularly during the initial stage of the extratropical forcing.