New observations of the spreading and variability of the Antarctic Intermediate Water in the Atlantic

The new and unique Argo data set currently available, in conjunction with other data previously collected, increases our understanding of the spreading of the Antarctic Intermediate Water in the southern and tropical Atlantic Ocean and to verify previous results. The combination of velocity and salinity data collected with Argo floats verified the main patterns of circulation at intermediate (800 to 1100 dbar) depths. Interesting new features in the pathways are found: (1) the existence of a new, third, branch of westward to northwestward flow that is fed by the Benguela Current; (2) two pathways through which the water from the Benguela Current Extension feeds into the Intermediate Western Boundary Current, one turns north at the western boundary while the other one turns north about 10° farther offshore; (3) the core of the South Atlantic Current is located farther north than was thought earlier (at 35 to 38°S instead of south at about 40°S); (4) significant flow of water from the South Atlantic Current to the Antarctic Circumpolar Current occurs east of the Zapiola Eddy (at about 45°S, 35°W); (5) a quite robust eastward current exists at about 20°S; and (6) there are indications, only in the salinity distribution, for southward spreading of Antarctic Intermediate Water from the equator near the eastern boundary. Transport estimates for the 800 to 1100 dbar layer show that the transports of the zonal currents in the subtropical gyre at intermediate depth increase from east to west, and that this trend is nearly linear. The transport of the South Atlantic Current near the western boundary is between 5 and 10 Sv, while it is close to 1 Sv near the eastern boundary of the Atlantic. The transport of the Benguela Current Extension is about 8 Sv near 45°W and only about 1 Sv near 14°E. It is also found that at the bifurcation of the Benguela Current Extension (at 28.5°S) about two thirds of the Antarctic Intermediate Water recirculate in the subtropical gyre, which is a smaller portion than the three quarters reported previously. Zonally integrated transports in the Antarctic Intermediate Water layer show that, as a meridional average, about 3 Sv are transported northward in the 800 to 1100 dbar layer. At 35°S this transport is 2.8 Sv, which amounts to 16% of the total northward transport of the Meridional Overturning Circulation (18 Sv). An analysis of the variability shows that the confluence of the Malvinas Current and the Brazil Current undergo seasonal variations at intermediate depth. The confluence is at its northernmost location (36°S) in July-September. On average the confluence is at 38°S. Both, the variability and the mean location of the confluence at the depth of Antarctic Intermediate Water is similar to what has been observed at the surface

New observations of the intermediate depth circulation in the tropical Atlantic

The intermediate depth (around 1000 m) circulation in the interior tropical Atlantic has been described as several narrow flow bands. Due to a lack of data, these currents have previously been poorly resolved in space and time. Recent observations, obtained during the mid-1997 Seward Johnson cruise and from PALACE floats which cover the period Summer 1997 to Spring 2000, allow a more detailed description of the intermediate depth circulation in the tropical Atlantic. The PALACE trajectories display several well defined currents between the equator and 4N at 800 to 1100 m. Two regimes separated by the eastern edge of the Mid-Atlantic Ridge seem to exist at these latitudes. Velocities in the eastern regime are lower than in the western regime and at some latitudes, the zonal flow in the two regimes is going in opposite directions. Farther south, between 4S and 2S, westward velocities of the central South Equatorial Current dominate the circulation. The flow north of 4N and south of 4S is governed by up to several month-long periods of eastward or westward flow, with only weak preferences for either direction. The southern region is characterized by the (meandering) transition between the central South Equatorial Current and the South Equatorial Countercurrent. It has been proposed earlier that these two currents do not extend eastward beyond about 10W, and that the intermediate water follows a cyclonic path east of 10W between about 5S and 25S. This could be interpreted as an intermediate expression of the Angola Gyre. Such a circulation is not found in the present data set. It is also noted that no significant cross-equatorial flow is found in the PALACE data

Liquid and vapour phase of lavandin (Lavandula × intermedia) essential oil: chemical composition and antimicrobial activity

Essential oils from Lavandula genus and the obtained hybrids are widely used for different purposes such as perfume production in the cosmetic field and for its biological properties. This is the first study on the liquid and vapour phase of Lavandula × intermedia “Grosso” essential oil grown in the Lazio Region, Italy, investigated using headspace coupled to gas chromatography and mass spectrometry (HS-GC/MS). The results showed the most abundant components were linalool and linalyl acetate, followed by 1,8-cineole and terpinen-4-ol, while lavandulyl acetate and borneol were identified as minor compounds, maintaining the same proportion in both the liquid and vapour phase. Furthermore, we tested lavandin liquid and vapour phase essential oil on gram-negative bacteria (Escherichia coli, Acinetobacter bohemicus, and Pseudomonas fluorescens) and gram-positive bacteria (Bacillus cereus and Kocuria marina)

Chemical investigation of a biologically active schinus molle L. leaf extract

The pepper tree Schinus molle L. is an evergreen ornamental plant belonging to the Anacardiaceae family, native to South America and widespread throughout the world. It has biological activities and is used in folk medicine. This paper aims to contribute to a deeper knowledge of its chemical composition and biological properties. S. molle leaf extracts were obtained by sequential extraction with solvents of different polarities and subsequently tested on the HL-60 human leukaemia cell line to define a possible cytotoxic activity. Among the investigated extracts, the petroleum ether extract revealed a high cytotoxic activity, and its chemical composition was further investigated. By a silica column chromatography, eight fractions were obtained, and their compositions were determined by GC-MS analysis. Compounds and relative abundance differed widely among the fractions; sesquiterpenes resulted the main component and alcoholic sesquiterpenes the most abundant

Dynamics of the Makassar Strait

Data collected as part of the Arlindo Project ( Arlindo is an acronym for Arus Lintas Indonesia, meaning throughflow in Bahasa Indonesia) from October 1996 to March 1998 are analyzed to study the characteristics of the flow through the Makassar Strait. Analysis of inverted echo sounders (IES) and bottom pressure data (PIES) combined with TOPEX/POSEIDON satellite-derived sea height anomaly suggest that a minimum of three-layer approximation is necessary to explain the dynamics of the flow in the Makassar Strait. The simple two-layer model used in several studies of the throughflow is rejected based on total incompatibility with the data sets. A three-layer model with significant contributions by the middle layer provides a consistent interpretation of PIES and satellite data. Results are interpreted in the framework of the large-scale circulation

Variability and sources of the southeastern Atlantic circulation

The 1992–1993 Benguela Sources and Transport (BEST) time series provide a quantitative view of the Benguela Current transport and the eddy field crossing 30S, as well as an estimate of the relation between its barotropic and baroclinic components. This is done by a simultaneous analysis of the BEST data derived from inverted echo sounders, pressure sensors, current meter moorings, CTD, and ADCP stations. The analysis of the time series indicates that the annual mean baroclinic transport of the Benguela Current is 13 Sv with a total transport of 16 Sv. Through the combination of instruments the total baroclinic plus barotropic transport of the upper 2600 m was obtained without making any assumption about the level of no motion. Results from this calculation corroborated the assumption that 1000 m as a level of no motion could be used as a fairly good approximation. The stationary flow of the Benguela Current is mostly confined near the African Continent while a transient flow, composed by large eddies shed from the Agulhas retroflection, dominates the western portion of the Benguela Current. In the stationary part of the Benguela Current, both barotropic and baroclinic components are equally important while in the transient part, the barotropic is more substantial. Several rings were observed during the experiment that migrated toward the west. An initial speed of 12 km/day diminished to 6 to 7 km/day at the Walvis Ridge. The water mass source of the Benguela Current includes Indian and South Atlantic subtropical thermocline water; relatively saline, low oxygen tropical Atlantic water; and the cooler, fresher subantarctic water. Changes in thermocline salinity correlate with transport: in general when the northward transport is increasing the thermocline salinity also increases, without a decrease in oxygen. This indicates that the Benguela Current increases in strength by bringing in more subtropical thermocline water. As the Agulhas input is most effective in boosting the salinity of the upper thermocline (the South Atlantic Current water being deficit in salinity relative to the Indian Ocean source) we suggest that the spatial variations in transport are tied to Agulhas water influx, presumably associated with the eddy field

Monitoring the upper southeastern Atlantic transports using altimeter data

A large in-situ data set, collected in the southeastern Atlantic Ocean, is merged with the TOPEX/POSEIDON altimeter observations in order to verify the use of altimeter data in monitoring the transports of the Agulhas/Benguela system. Comparisons between altimeter observations and either moored current meters or inverted echo sounder measurements shows that the sea-surface elevation anomaly is significantly correlated with the thermocline depth and the surface dynamic height, respectively. Knowing the least-squares regression parameters, it is possible to calculate the transports by using geostrophy and either a two-layer or a continuously-stratified model. The transports obtained from fits of dynamic height to altimeter sea-surface height are similar to the ones calculated with the moored instruments. In the southern part of the area under analysis, around 35S, close to the Agulhas retroflection, the transports obtained from the two-layer model are overestimated. Across the Benguela Current, at 30S, transports are still overestimated but of the same order as the measured ones. In this part of the region, the two-layer model can be successfully used to calculate the total and barotropic transports of the Benguela Current. Analysis of the three years of geostrophic transport obtained from the altimeter data indicate that the mean Benguela Current transport does not change interannually more than 20%. However, the primary interannual variability derives from the source water that forms the Benguela Current

Variability and motion of the Brazil-Malvinas front

The temporal evolution of the thermal field associated with frontal motions in the South Western Atlantic is studied. The analysis is based on data collected with an array of inverted echo sounders (IES) deployed during the Confluence Program (1988-1990) at the Brazil/Malvinas Confluence. The travel time series obtained with the IES are scaled to mean temperatures of the upper 500 m (Tsoo) of the ocean and series of T500 horizontal distributions are constructed. A description of the evolution of the thermal field, emphasizing the frontal motions and some mesoscaie features, is presented. Three well-defined northward penetrations of the Malvinas current with fairly variable periods of permanence (15-60 days) and mean frontal motion velocities of 0.2 m/s are observed. Cross-correlation of the T500 time series analysis leads to a plausible explanation of some features of the observed variability. Comparison with previous results in the area indicate a marked interannual variability and sources of variability are discussed.Se estudia la evolución temporal del campo de isotermas asociados con movimientos frontales en el océano Atlántico Sudoccidental. El análisis está basado en datos obtenidos de ecosondas invertidos (IES) fondeados durante la ejecución del Programa Confluencia (1988-1990) en la confluencia de las corrientes de Malvinas y Brasil. Las series de tiempo obtenidas con los IES fueron estandarizados con las temperaturas medias de los primeros 500 m (T500) del océano y de esta forma se obtuvo la distribución horizontal de T500. Se presenta una descripción de la evolución del campo térmico en relación con los movimientos frontales y las características de mesoescala de esa zona. Se observaron tres penetraciones bien definidas de la corriente de Malvinas con períodos variables de permanencia (15 -60 días) y velocidades del frente de 0.2 m/s. Del análisis de la correlación cruzada de la serie de T500 se obtiene una posible explicación de la variabilidad observada. La comparación con resultados previos indican una variabilidad interanual. Se discuten las fuentes de variabilidad.Material digitalizado en SEDICI gracias a la colaboración de la Facultad de Ciencias Astronómicas y Geofísicas (UNLP).Asociación Argentina de Geofísicos y Geodesta

Agulhas ring dynamics from TOPEX/POSEIDON satellite altimeter data

The transfer of warm water from the Indian Ocean into the South Atlantic subtropical gyre takes place in the form of rings and filaments formed when the Agulhas Current retroflects south of Africa between 15 and 25E. A survey of the rings formed from September 1992 until December 1995 in the Retroflection region was carried out using TOPEX/POSEIDON altimeter data. A two-layer model was used to estimate the upper layer thickness from the altimeter-derived sea-surface height anomaly data. An objective analysis scheme was used to construct a map of upper layer thickness every ten days. Seventeen rings and their trajectories were identified using these maps. The shedding of rings from the Agulhas Current was neither continuous nor periodic, and for long periods there is no formation of rings. Several rings remained in the region for more than a year and, at any given time, 2 to 6 rings coexisted in the region east of the Walvis Ridge. The results showed that the number of rings translating simultaneously in this region is larger during the first half of each year. The upper layer transport of the Agulhas Current in the Retroflection region was computed and a close association between high variations in transport and ring shedding was found. Rings translated WNW at translation speeds ranging from 5 to 16 km day−1 following formation. The values of available potential energy computed for the rings place them among the most energetic rings observed in the world oceans, with values of up to 70 × 1015 J. Transport computations indicate that each ring contributes in the average approximately 1 Sv of Agulhas Current waters to the Benguela Current

Study of the outer galactic structure for 288°≤l≤310°, −7°≤b≤2°

The structure of the outer part of the Galaxy is studied, based upon 21-cm line observations of Hi in the region 288°≤l≤310°, −7°≤b≤2°. In this longitude range the galactic plane is strongly bend toward negative latitudes. The principal outer structure is a spiral arm which has a pitch angle of 10º and is formed by several concentrations differing in shape and size. There exists also a secondary concentration which could be a split from the previous structure. Possible hypotheses about the origin of the later feature are discussed.Instituto Argentino de RadioastronomíaComisión de Investigaciones Científicas de la provincia de Buenos Aire