Propagation and amplification of tide at the Bransfield and Gerlache Straits, northwestern Antarctic Peninsula

The propagation and amplification of the tide at the Gerlache and Bransfield Straits, northwestern side of the Antarctic Peninsula, was studied by analysis of thirteen series of direct sea level measurements. Harmonic analysis was performed to obtain the amplitudes and phases of the M_2, S_2, O_1 and K_1 tidal constituents. Based on the computed harmonic constants, cotidal and corange charts of these main constituents were prepared. The M_2 cotidal lines are parallel to the coast and show predominantly southeastward propagation, except at the western side of the Trinity Peninsula, where the M_2 wave pivots to enter the Bransfield Strait from the Weddell Sea and turns southwestward. M_2 amplitudes present a southwestward decrease. S_2 cotidal lines are normal to the Antarctic Peninsula coast and show southwestward propagation. S_2 corange lines increase eastward from the Gerlache Strait to the Antarctic Strait. O_1 and K_1 cotidal lines are also normal to the Antarctic Peninsula coast. Diurnal amplitudes are alike in the study area except at the northwestern side of the Antarctic Strait where they present a maximum gradient. Amplitudes of the main tidal constituents are higher in the northwestern Weddell Sea than at the northwestern side of the peninsula. This fact explains the maximum tidal amplitudes observed at the Antarctic Strait in comparison to the Bransfield Strait

Propagation and amplification of tide at the northeastern coast of the Antarctic peninsula: an observational study

The amplification and propagation of the tide at the northeastern coast of the Antarctic Peninsula was studied by analysis of instantaneous sea levels measured at the tidal station of Base Esperanza,at the northern end of the Antarctic Peninsula (63゜22.46\u27S, 56゜59.33\u27W) ,at the northeastern coast of Marambio Island (Seymour Island,64゜14.11\u27S, 56゜34.51\u27W) and near Base Matienzo,Larsen nunatak (64゜54.23\u27S, 60゜2.60\u27W) at the edge of the Larsen ice-shelf. By means of harmonic analysis the amplitudes and phases of the most energetic ten tidal constituents were obtained.The tidal regime was typified by means of the factor F and a preponderantly semidiurnal mixed tide was obtained. Signi ficant southward amplification was observed in the amplitudes of semidiurnal constituents,and a less evident amplification was obtained in diurnal ones.Consequently,slightly southward diminution in factor F,from 0.75 (Esperanza) to 0.6 (Matienzo),was found.Bothsouthward amplification in amplitudes and northward propagation of the main tidal constituents obtained from numerical global models show good agreement with the present observations

A numerical study of the ocean circulation around the northern Antarctic Peninsula: Barotropic response to tidal forcing

A high-resolution shallow water model was implemented to study tidal propagation around the northern Antarctic Peninsula. Numerical experiments were done using a grid with 3.00′longitude and 1.05′latitude resolution. Amplitudes and phases of the four main tidal constituents (M_2, S_2, K_1 and O_1) were used to force the model. Modeled sea levels and currents were compared with observations. The modeled cotidal, corange and tidal ellipse axis obtained by harmonic analysis from model results are in good agreement with those of available observations. Given the good correspondence between harmonic constants obtained from model results and from observed hourly sea levels, the energy flux and dissipation by bottom friction were computed. The most intense energy fluxes are related to the semidiurnal constituents. The highest values are present in the Weddell Sea and the energy flux shows a relative maximum at the Antarctic Strait, flowing from the Weddell Sea to Bransfield Strait. Nearly all the dissipation occurs in the Antarctic Strait (maximum value ～0.25Wm^(-2)) and around the South Shetland Islands. The total tidal energy lost to bottom friction in our 4-constituent model is about 1.5GW, giving a domain-averaged value of ～0.002Wm^(-2)

One-dimensional tidal model of the Ría San Julián, Argentina

Se implementó un modelo numérico unidimensional para sistemas de canales interconectados con el fin de simular la hidrodinámica de la marea de la ría San Julián, Argentina. En posiciones prefijadas dentro del sistema se pronosticaron la altura de la superficie libre y los caudales, utilizando un método implícito en diferencias finitas. Los resultados de la simulación numérica se compararon con mediciones de campo, y se obtuvo una correlación satisfactoria entre marea y corrientes predichas y observadas.A one-dimensional numerical model for a system of interconnected channels was implemented to simulate the tidal hydraulics of the Ría San Julián, Argentina. Free surface displacement and discharge were computed from predetermined locations throughout the system using an implicit, finite-difference technique. The results of the numerical simulation were compared with field measurements, and a satisfactory correlation was obtained between observed and predicted tides and currents.Este documento es bilingüe: español-inglésFacultad de Ciencias Naturales y Muse

About the vertical structure of currents in the intermediate Rio de la Plata: observational study

The Río de la Plata is one of the most important estuarine systems of the world and the most developed basin of eastern South America. Water levels and currents have been measured at many locations of the river and a number of depth-integrated (2-D) models have been applied to determine its circulation. Nevertheless, the three-dimensional characteristics of the currents have been never analyzed neither by means of direct observations nor by means of 3-D models. In this work current data measured using an Acoustic Doppler Current Profiler are presented to show the vertical structure of currents in the intermediate Rio de la Plata. In February 2-3 2000, a transect of approximately 16 Km long was repeated eleven times during 25 hours obtaining 1972 current profiles. After applying a specific processing, sinusoids with M2 (12.42 hours) period was fitted to the data series using least squares fitting method. The M2 amplitudes and phases of the EW and NS components of the current and both components corresponding to the mean flow (residuals) were obtained along the transversal section of the transect. Results showed that currents present strong vertical gradients not only in the phases of the semidiurnal constituent but also in the mean flux in the intermediate zone of the Rio de la Plata. Although the intermediate Rio de la Plata is a very shallow basin results reveal that the current from upper to bottom layers can rotate more than 90°. These results indicate that currents respond strongly to the local winds but their effects are mainly manifested at the upper layer. Finally, results indicate that 3-D baroclinic models (including temperature and salinity fields and a realistic atmospheric forcing) should be used in order to obtain a reliable and complete representation of currents especially at the intermediate and outer zone of the Rio de la Plata.El Rio de la Plata es uno de los sistemas fluviales más importantes del mundo y la cuenca más desarrollada del sudeste sudamericano. Los niveles del agua y las corrientes han sido medidos en un gran número de sitios del río y, por otro lado, diversos modelos integrados en la vertical (2-D) han sido aplicados para determinar su circulación. Sin embargo, hasta el momento, las características tridimensionales de las corrientes no han sido descriptas ni mediante observaciones directas ni por medio de modelos 3-D. En este trabajo los datos de corrientes medidos con un Perfilador de Corrientes Acústico Doppler (del inglés ADCP) son presentados para mostrar la compleja estructura vertical de las corrientes en el Río de la Plata intermedio. Entre el 2 y 3 de febrero de 2000 se repitió once veces durante 25 horas una transecta de aproximadamente 16 Km de longitud obteniéndose un total de 1972 perfiles de corriente. Después de aplicar un procesamiento específico las series fueron ajustadas a sinusoides con periodo correspondiente a la componente de marea M2 (12.42 horas) utilizando el método de mínimos cuadrados. Se obtuvo así las amplitudes y fases de las componentes EW y NS de la corriente correspondientes a la M2 y las dos componentes para el flujo medio (residuos) a lo largo de la transecta estudiada. Los resultados muestran que las corrientes en la zona intermedia del Río de la Plata presentan intensos gradientes verticales no solo en las fases de las componentes semidiurnas sino también en las del flujo medio. Aunque el Río de la Plata intermedio es una cuenca muy somera los resultados revelan que las corrientes pueden variar su dirección en más de 90° entre las capas superior e inferior de la columna de agua. Estos resultados indican que las corrientes responden fuertemente a los vientos locales, pero sus efectos son principalmente manifestados en la capa superior. Finalmente, los resultados indican que para obtener una representación confiable y completa de las corrientes especialmente en las zonas intermedia y exterior del Río de la Plata deberían implementarse modelos baroclínicos 3- D que incluyan tanto los campos térmicos y salinos como así también forzantes atmosféricos realistas.Asociación Argentina de Geofísicos y Geodesta

On the path of plumes of the Río de La Plata Estuary main tributaries and their mixing scales

With a length of 300 km and a width that narrows from 220 km at its mouth to 40 km at its upper end, the Rio de la Plata is one of the largest estuaries of the world. Its three main tributaries -contributing to a total mean runoff of22,000 m3 s’1- have different properties and are object of diverse environmental impact due to dissimilar development conditions on their shores. The knowledge of the paths of the plumes of those tributaries along the estuary and their mixing scales is necessary for management purposes. In this paper, advection-diffusion equations for passive tracers are coupled to the three-dimensional Hamburg Shelf Ocean Model and validated by means of a case study. Then, simulations in which each tributary is characterized by a different dye tracer are done for scenarios resulting of the combination of diverse characteristic atmospheric forcing and runoff conditions. The impact of bathymetry and Earth’s rotation on plumes paths and mixing is also evaluated. Results indicate that, for mean to low discharge conditions, the path of the waters of the tributaries is in the form of two main plumes. The different water speeds of both tributaries, the presence of a bend immediately after their confluence and the varying geometry and bathymetry of the estuary favor a rapid mixing between the Uruguay and Paraná Guazú-Bravo waters, which then flow along the northern portion of the upper estuary channel. The Paraná de las Palmas waters, instead, occupy the southern shallow region of Playa Honda in the upper estuary and then flow following the southern coast. Downstream Colonia, at the intermediate estuary, the occurrence of another large bend and a change in bathymetric features force the flow to concentrate in the central part of the estuary and favor further mixing between the plumes. For high discharge conditions the northern part of the upper estuary is divided into two regions, one with a larger concentration of Uruguay waters between Oyarvide and Martín Garcia islands and the coast and another with a larger concentration of Paraná Guazú-Bravo waters south of the islands. In this case there is a much larger concentration of Uruguay waters along the northern coast, which might be enhanced if a peak runoff occurs for the Uruguay but not for the Paraná River. These conclusions are consistent with what can be inferred from the conductivity field observed at the intermediate estuary, the bottom sediments distribution and satellite images. Results indicate that even though strong winds can favor the mixing of the plumes, especially along Argentinean coast, they preserve their pattern and the effect of the storms only persists for a few days. For mean runoff, the elapsed time to the arrival of the leading edge of the Paraná de las Palmas, Paraná Guazú- Bravo and Uruguay tracer clouds at Buenos Aires is of around 3, 5 and 7 days, respectively. The elapsed time to the peak concentration of the tracer cloud for a typical mean runoff scenario is of around 20 days at Buenos Aires. For that condition, the flushing times of the upper and upper intermediate estuary are of around 10 and 60 days, respectively. Nevertheless, mixing scales can be half (twice) those valúes for high (low) runoff conditions.Con una extensión de 300 km y un ancho que varía entre 220 km en su boca y 40 km en su parte superior, el Río de la Plata es uno de los mayores estuarios del mundo. Sus tres tributarios -que contribuyen con una descarga media total de 22.000 m3s_1- tienen diferentes propiedades y son objeto de distinto impacto medioambiental debido a condiciones disímiles de desarrollo en sus costas. El conocimiento del camino de las plumas de esos tributarios y sus escalas de mezcla es necesario para propósitos de gestión. En este trabajo, se acoplan ecuaciones de advección-diíusión para trazadores pasivos al modelo tridimensional Hamburg Shelf Ocean Model y se las valida por medio de un estudio de casos. Luego se realizan simulaciones en las cuales cada tributario es caracterizado por un trazador diferente para escenarios que resultan de combinar las diversas condiciones características del forzante atmosférico y la descarga. El impacto de la batimetría y la rotación de la Tierra en el camino de las plumas y su mezcla también es evaluado. Los resultados indican que, para condiciones de descarga media a baja el camino de las aguas de los tributarios es en la forma de dos plumas principales. La diferente velocidad del agua en ambos tributarios, la presencia de una curva inmediatamente después de su confluencia y la geometría y batimetría variables del estuario favorecen una rápida mezcla entre las aguas del Uruguay y el Paraná Guazú-Bravo, que luego fluyen a lo largo de la parte norte del estuario superior. Las aguas del Paraná de las Palmas, en cambio, ocupan la región somera de Playa Honda en la porción sur del estuario superior y luego fluyen a lo largo de la costa sur. Aguas abajo de Colonia, en el estuario medio, la ocurrencia de una gran curva y un cambio en las características batimétricas fuerzan al flujo a concentrarse en la parte central del estuario y favorece mayor mezcla entre las plumas. Para condiciones de descarga alta la porción norte del estuario se divide en dos regiones, una con mayor concentración de aguas del Uruguay entre las islas Oyarvide y Martín García y la costa, y otra con mayor concentración del Paraná Guazú-Bravo al sur de dichas islas. En este caso, hay una concentración mucho mayor de aguas del Uruguay a lo largo de la costa norte, característica que podría incrementarse si un pico de descarga ocurre en el Río Uruguay pero no en el Paraná. Estas conclusiones son consistentes que lo que puede inferirse del campo de conductividad observado en el estuario intermedio, con la distribución de sedimentos de fondo y con imágenes satelitales. Los resultados indican que aunque vientos fuertes pueden favorecer la mezcla de las plumas, especialmente a lo largo de la costa argentina, ellas mantienen su estructura y el efecto de las tormentas sólo persiste unos pocos días. Para descarga media, el tiempo de arribo del borde de las nubes de trazadores de los ríos Paraná de las Palmas, Paraná Guazú-Bravo y Uruguay a Buenos Aires es de aproximadamente 3, 5 y 7 días, respectivamente. El tiempo hasta el alcance de la concentración pico de la nube de trazadores para un escenario típico de descarga media es de alrededor de 20 días para Buenos Aires y 60 días para el estuario medio. Para esa condición, el tiempo de lavado en el estuario superior y medio superior es de alrededor de 10 y 60 días. No obstante, las escalas de mezcla pueden ser la mitad (el doble) de esos valores para condiciones de descarga alta (baja).Asociación Argentina de Geofísicos y Geodesta

Estudio de la marea en el borde de la barrera Larsen, Mar de Weddell noroccidental

El objetivo de este trabajo es el estudio de la marea en el borde de la barrera Larsen (latitud: 64° 54' 14" S, longitud: 60° 02' 36" W) en el mar de Weddell noroccidental, Antártida. Los niveles del mar se registraron con un sensor de presión y mediante nivelación geométrica (mira y nivel). El coeficiente de determinación de los niveles del mar obtenidos con ambas técnicas es de 0.96. Se presentan las constantes armónicas de las componentes de marea más energéticas. Se realiza un análisis comparativo entre las constantes calculadas y las que surgen de modelos mareológicos globales y se discute la propagación de la marea en el mar de Weddell noroccidental. Se tipificó el régimen de marea cuantitativamente mediante el coeficiente de Courtier resultando un régimen mixto preponderantemente semidiurno. Los niveles del mar registrados en esta zona de la Antártida son inéditos debido a que el sitio de mediciones fue inaccesible durante muchos años.The objective of this paper is the study of the tide at the Larsen iceshelf boundary (latitude: 64° 54' 14" S, longitude: 60° 02' 36" W), Northwestern Weddell Sea, Antarctica. Sea levels were recorded using pressure sensor and geometric leveling (sight and level). The determination coefficient from sea level gathered with both methods is 0.96. Harmonic constants of the most energetic tidal constituents are presented. A comparative analysis between calculated harmonic constants and those obtained from tidal global models is made and tidal propagation in the Northwestern Weddell Sea is discussed. Tidal regimen is quantified by means of the Courtier coefficient and a preponderantly semidiurnal mixed tide is obtained. Sea levels gathered in this zone of the Antarctica are completely new because the place where the measurements were made was inaccessible for a large period of years.Asociación Argentina de Geofísicos y Geodesta