Estudios de la circulación forzada por el viento en el estuario del Río de la Plata y sus implicancias en la estratificación: resultados del análisis de datos y simulaciones numéricas

En esta Tesis, por primera vez, se combina el análisis de los datos históricos de salinidad disponibles con series de tiempo de corriente y simulaciones numéricas de alta resolución, en un esfuerzo por comprender los procesos que ocurren en el activo e importante sistema estuarino del Río de la Plata. Con ese fin, se analizan las primeras series relativamente largas de corrientes ADCP colectadas en dos puntos del estuario. Se encuentra que la marea sólo explica alrededor de un 25% de la varianza. Aproximadamente otro 25% está asociado con actividad de ondas internas en los puntos de adquisición de datos, que corresponden a zonas de fuerte estratificación. Estas ondas son forzadas por la brisa tierra-mar y por la marea y son muy frecuentes durante la primavera y el verano. El 50% restante de energía está forzado por el viento en las escalas de tiempo sinóptica a intra-estacional. El estuario responde en una escala de tiempo de alrededor de 6 horas a la variabilidad del viento, con una estructura esencialmente barotrópica frente a vientos con una componente dominante perpendicular al eje del estuario y con una fuerte estructura baroclínica, con inversión en la dirección de las corrientes entre capas superiores e inferiores, para vientos con una componente paralela al eje del estuario. Aunque este tipo de respuesta es característica de cuencas semi-cerradas, no es típica de estuarios y es observada en el Río de la Plata como consecuencia de su gran ancho. Se utilizó el modelo hidrodinámico Estuary Coastal and Ocean Model (ECOM) juntos con datos CTD de campañas sinópticas históricas para evaluar las implicancias de la circulación forzada por el viento en la estratificación. Se encuentra que, aunque la estructura de cuña salina es una consecuencia de la intensa descarga continental en la región, los vientos predominantes favorecen su mantenimiento. Solamente bajo vientos intensos o persistentes del sudeste la estratificación puede quebrarse completamente. Sin embargo, la estructura vuelve a establecerse en un período de tiempo relativamente corto después de que los vientos se relajan. Los eventos con estas características son poco frecuentes en la región. Esto tiene un fuerte impacto sobre la biología ya que las especies que alberga el estuario requieren de ciertas condiciones de salinidad para su reproducción exitosa. Además, se caracterizó la respuesta de los campos de salinidad al forzante del viento y se encontraron indicios de eventos de surgencia a lo largo de la costa uruguaya frente a vientos del noreste, característicos de la estación cálida. Los resultados modifican el esquema conceptual vigente respecto de la señal estacional como principal característica del campo de salinidad en el Río de la Plata. Esta señal es el resultado de la mayor frecuencia de ocurrencia de vientos provenientes de direcciones determinadas a lo largo de las diversas estaciones. Situaciones caracterizadas como típicas de “invierno” o “verano” pueden ocurrir a lo largo de todo el año con gran variabilidad. La pluma de agua de baja salinidad impactaría en la plataforma continental en forma de pulsos alternativos hacia el noreste o el sudoeste en una escala del orden de los tres a cuatro días. Se identificaron los principales forzantes de variabilidad en las diferentes escalas de tiempo mediante una simulación de largo período realizada con el modelo Hamburg Shelf Ocean Model (HamSOM). Se encuentra que el primer modo de variabilidad en la escala interanual de la elevación de la superficie libre está forzado simultáneamente por la descarga continental y por el viento y ambos están asociados a los ciclos del ENSO. La variabilidad en la escala estacional explica un muy bajo porcentaje de varianza y está compuesta por una onda anual y una semianual, forzada por viento y descarga, respectivamente. La variabilidad en la escala subanual explica alrededor del 90% de la varianza y está forzada por el viento. Se encontró que los eventos extremos de crecidas en el estuario presentan a lo largo del tiempo una mayor frecuencia de ocurrencia y una mayor intensidad de respuesta. Por último, la arquitectura de modelado aplicada a la circulación barotrópica resultó exitosa mostrando ser una herramienta robusta para pronóstico y para el estudio de la variabilidad climática futura en respuesta al cambio climático.In this Thesis, for the first time, the analysis of historical salinity data and new current series is combined with high resolution numerical simulations, with the aim of understanding the processes that occur in the active and important Río de la Plata estuary. With that objective, the first relatively long ADCP current series collected in two points of the estuary are analyzed. Only 25% of the currents’ variance is accounted by the tide. Approximately another 25% is associated with internal wave activity at the sampling locations, where a strong stratification exists. These waves are forced by land-sea breeze and tide and are very frequent during spring and summer. The remaining 50% of the energy is wind driven and occurs in synoptic to intra-seasonal time scales. The estuary responds to wind variability in a time scale of approximately 6 hours. Response displays an essentially barotropic structure to winds with a dominant component perpendicular to the estuary axis and with a strong baroclinic structure, with inversion in current direction between upper and lower layers, to winds with a dominant component along the estuary axis. Although this kind of response is characteristic of semi-enclose basins, it is not a typical response in estuaries, and it is observed in the Río de la Plata due to its huge width. To evaluate the implications of the wind forced circulation on stratification, Estuary, Coastal and Ocean Model (ECOM) together with CTD data from synoptic campaigns were used. It is observed that, even though the salt wedge structure is a consequence of the intense discharge, its existence is favoured by winds that prevail in the region. The stratification can only be completely destroyed by strong or persistent south-easterly winds. Nevertheless, the structure is reconstructed in a relatively short period of time after wind relaxation, and that kind of events are not frequent in the region. This has a strong impact on biology because the species housed by the estuary require specific salinity conditions for their successful reproduction. Additionally, the response of the salinity field to wind forcing was characterized. High surface salinity, consistent with upwelling along the Uruguayan coast is observed for north-easterly winds, which are typical of the warm season. The present conceptual scheme involving the seasonal signal as the main feature of the salinity filed variability is modified by the results of this Thesis. This signal result of a larger frequency of occurrence of some wind direction along the different seasons, and conditions classically though as characteristic of “winter” or “summer” can take place during any season with high variability. The fresh water plume would impact the continental shelf in the form of alternating pulses toward the northeast or to the southwest in a time scale around three to four days. The main forcings of estuarine variability in different time scales were identified by means of a long term numerical simulation using Hamburg, Shelf Ocean Model (HamSOM). The first mode of the sea surface height variability on inter-annual time scale is forced simultaneously by runoff and wind. Results show clear evidence that both forcings are associated to ENSO cycles. The seasonal scale variability accounts by a very low percentage of variance and it is a combination of an annual and a semi-annual signal forced by wind and runoff, respectively. Approximately 90% of the variance is accounted by sub-annual scale variability, essentially wind driven. Extreme flood events in the estuary increase their frequency of occurrence and intensity over the time. Finally, the model hierarchy applied for barotropic circulation shows to be a robust tool for forecasting and for the study of estuarine climate variability in response to climate change.Fil:Meccia, Virna Loana. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Interactive ocean bathymetry and coastlines for simulating the last deglaciation with the Max Planck Institute Earth System Model (MPI-ESM-v1.2)

As ice sheets grow or decay, the net flux of freshwater into the ocean changes and the bedrock adjusts due to isostatic adjustments, leading to variations in the bottom topography and the oceanic boundaries. This process was particularly intense during the last deglaciation due to the high rates of ice-sheet melting. It is, therefore, necessary to consider transient ocean bathymetry and coastlines when attempting to simulate the last deglaciation with Earth system models (ESMs). However, in most standard ESMs the land-sea mask is fixed throughout simulations because the generation of a new ocean model bathymetry implies several levels of manual corrections, a procedure that is hardly doable very often for long runs. This is one of the main technical problems towards simulating a complete glacial cycle with general circulation models. For the first time, we present a tool allowing for an automatic computation of bathymetry and land-sea mask changes in the Max Planck Institute Earth System Model (MPI-ESM). The algorithms developed in this paper can easily be adapted to any free-surface ocean model that uses the Arakawa-C grid in the horizontal and z-grid in the vertical including partial bottom cells. The strategy applied is described in detail and the algorithms are tested in a long-term simulation demonstrating the reliable behaviour. Our approach guarantees the conservation of mass and tracers at global and regional scales; that is, changes in a single grid point are only propagated regionally. The procedures presented here are an important contribution to the development of a fully coupled ice sheet–solid Earth–climate model system with time-varying topography and will allow for transient simulations of the last deglaciation considering interactive bathymetry and land-sea mask

Rio de la Plata estuary response to wind variability in synoptic to intraseasonal scales: 2. Currents' vertical structure and its implications for the salt wedge structure

The first acoustic Doppler current profiler current data collected at two locations of the Río de la Plata salt wedge during a period of around 6 months and salinity profiles gathered at and around those locations are used to study the vertical structure of currents' response to wind variability in synoptic to intraseasonal timescales and its implications for stratification. Results indicate that the estuary rapidly responds to prevailing southwesterlies/northeasterlies with currents that decay toward the bottom with only little rotation in depth. For the less frequent southeasterlies/northwesterlies the estuary develops a strong vertical structure with a defined inversion in current direction between surface and bottom layers. These patterns derive from the estuary's geometry and bathymetry. Results have important implications for the salinity vertical structure that are verified on the analyzed profiles. First, the combination of the bathymetry and coastline with the prevailing wind variability is highly favorable to the maintenance of a salt wedge structure in this estuary. Second, weakening and eventually breakdown of stratification can only occur for intense and/or persistent southeasterly winds, which even can be very strong, are not frequent. This can explain why the Río de la Plata displays the unusual feature of being an area of spawning and a nursery for a number of coastal species that use the wedge as an essential element for their reproduction. Results show that stratification is highly affected by short-term wind variability, which is its major characteristic in the area, changing the classical concept of summer-winter seasonality as the main feature of estuarine variability.Fil: Simionato, Claudia Gloria. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; ArgentinaFil: Meccia, Virna Loana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; ArgentinaFil: Guerrero, Raul. Instituto Nacional de Investigaciones y Desarrollo Pesquero; Argentina. Universidad Nacional de Mar del Plata; ArgentinaFil: Dragani, Walter Cesar. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; Argentina. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval; ArgentinaFil: Nuñez, Mario Nestor. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; Argentin

Deep mixed ocean volume in the Labrador Sea in HighResMIP models

Simulations from seven global coupled climate models performed at high and standard resolution as part of the high resolution model intercomparison project (HighResMIP) are analyzed to study deep ocean mixing in the Labrador Sea and the impact of increased horizontal resolution. The representation of convection varies strongly among models. Compared to observations from ARGO-floats and the EN4 data set, most models substantially overestimate deep convection in the Labrador Sea. In four out of five models, all four using the NEMO-ocean model, increasing the ocean resolution from 1° to 1/4° leads to increased deep mixing in the Labrador Sea. Increasing the atmospheric resolution has a smaller effect than increasing the ocean resolution. Simulated convection in the Labrador Sea is mainly governed by the release of heat from the ocean to the atmosphere and by the vertical stratification of the water masses in the Labrador Sea in late autumn. Models with stronger sub-polar gyre circulation have generally higher surface salinity in the Labrador Sea and a deeper convection. While the high-resolution models show more realistic ocean stratification in the Labrador Sea than the standard resolution models, they generally overestimate the convection. The results indicate that the representation of sub-grid scale mixing processes might be imperfect in the models and contribute to the biases in deep convection. Since in more than half of the models, the Labrador Sea convection is important for the Atlantic Meridional Overturning Circulation (AMOC), this raises questions about the future behavior of the AMOC in the models

Sensitivity of the Atlantic meridional overturning circulation to model resolution in CMIP6 HighResMIP simulations and implications for future changes

A multi‐model, multi‐resolution ensemble using CMIP6 HighResMIP coupled experiments is used to assess the performance of key aspects of the North Atlantic circulation. The Atlantic Meridional Overturning Circulation (AMOC), and related heat transport, tends to become stronger as ocean model resolution is enhanced, better agreeing with observations at 26.5°N. However for most models the circulation remains too shallow compared to observations, and has a smaller temperature contrast between the northward and southward limbs of the AMOC. These biases cause the northward heat transport to be systematically too low for a given overturning strength. The higher resolution models also tend to have too much deep mixing in the subpolar gyre. In the period 2015‐2050 the overturning circulation tends to decline more rapidly in the higher resolution models, which is related to both the mean state and to the subpolar gyre contribution to deep water formation. The main part of the decline comes from the Florida Current component of the circulation. Such large declines in AMOC are not seen in the models with resolutions more typically used for climate studies, suggesting an enhanced risk for Northern Hemisphere climate change. However, only a small number of different ocean models are included in the study

North Atlantic gyre circulation in PRIMAVERA models

AbstractWe study the impact of horizontal resolution in setting the North Atlantic gyre circulation and representing the ocean–atmosphere interactions that modulate the low-frequency variability in the region. Simulations from five state-of-the-art climate models performed at standard and high-resolution as part of the High-Resolution Model Inter-comparison Project (HighResMIP) were analysed. In some models, the resolution is enhanced in the atmospheric and oceanic components whereas, in some other models, the resolution is increased only in the atmosphere. Enhancing the horizontal resolution from non-eddy to eddy-permitting ocean produces stronger barotropic mass transports inside the subpolar and subtropical gyres. The first mode of inter-annual variability is associated with the North Atlantic Oscillation (NAO) in all the cases. The rapid ocean response to it consists of a shift in the position of the inter-gyre zone and it is better captured by the non-eddy models. The delayed ocean response consists of an intensification of the subpolar gyre (SPG) after around 3 years of a positive phase of NAO and it is better represented by the eddy-permitting oceans. A lagged relationship between the intensity of the SPG and the Atlantic Meridional Overturning Circulation (AMOC) is stronger in the cases of the non-eddy ocean. Then, the SPG is more tightly coupled to the AMOC in low-resolution models

Decadal variability of the Turner Angle in the Mediterranean Sea and its implications for double diffusion

The physical reanalysis component of the Mediterranean Forecasting System is used to construct a high- resolution three-dimensional atlas of the Turner Angle. An assessment of the model quality shows a maximum degree of agreement with observations in the water column between 150 and 1000 m depth. The mean state of the favourable conditions for double diffusion processes is evaluated and the recent decadal variability is studied in terms of changes in the water mass properties. The results show that approximately 50% of the Mediterranean Sea is favourable to double diffusion processes, from which around 47% is associated with salt fingering. The Tyrrhenian, Ionian and southwestern Mediterranean are the most vulnerable basins to salt fingering, and the strongest processes can occur in the Tyrrhenian deep waters. Diffusive convection is most likely to occur in the Ionian, Aegean and eastern Mediterranean at vertical levels deeper than 1000 m. The observed gradual warming and salinification of the Medi- terranean after 1997 decreased and increased the possibilities of the occurrence of salt fingers and double diffusive convections, respectively. The climatological atlas that is presented in this paper pro- vides a three-dimensional picture of the regions that are either doubly stable or favourable to double diffusion instability and allows for the characterization of the diffusive properties of the water masses.Published64-774A. Oceanografia e climaJCR Journa

Modelling biogeochemical fluxes across a Mediterranean fish cage farm

An integrated approach is described for modelling interactions between off-shore fish cages and biogeochemical fluxes of carbon (C), nitrogen (N) and phosphorus (P). Two individ- ual-based population dynamic models for European seabass Dicentrarchus labrax and gilthead seabream Sparus aurata were coupled with a Lagrangian deposition and a benthic degradation model. The individual models explicitly take into account the effects of water temperature and feed availability on fish growth. The integrated model was tested at a Mediterranean fish farm where a comprehensive set of in situ environmental and husbandry data was available. Tests were performed to compare the predicted and observed total organic carbon (TOC) concentrations in surface sediment under and near fish cages. At a local scale, the model output simulated the spa- tial distribution of 4 biogeochemical indicators, namely: TOC concentrations, C fluxes towards the seabed and C:N and C:P ratios. These allowed the most impacted areas and more extended areas of intermediate organic enrichment to be identified. The model was also used for estimating the mass balance of C, N and P, in order to determine the potential cumulative effects of multiple fish farms in the same area. The C, N and P fluxes among feed, fish and environment were calculated for each fish species over 24 mo of farm activity. The results showed that the amount of dissolved N directly released into the water column in inorganic form (ammonia/urea) was comparable to that deposited on the seafloor in particulate form as uneaten feed and faeces. A larger fraction of P (about 65%) was released as faeces. Results from the integrated model yielded useful informa- tion for assessing the sustainability of an area for aquaculture activities that could be used to pro- vide a scientific rationale for fish farm development in new areas

Deep mixed ocean volume in the Labrador Sea in HighResMIP models

Simulations from seven global coupled climate models performed at high and standard resolution as part of the high resolution model intercomparison project (HighResMIP) are analyzed to study deep ocean mixing in the Labrador Sea and the impact of increased horizontal resolution. The representation of convection varies strongly among models. Compared to observations from ARGO-floats and the EN4 data set, most models substantially overestimate deep convection in the Labrador Sea. In four out of five models, all four using the NEMO-ocean model, increasing the ocean resolution from 1° to 1/4° leads to increased deep mixing in the Labrador Sea. Increasing the atmospheric resolution has a smaller effect than increasing the ocean resolution. Simulated convection in the Labrador Sea is mainly governed by the release of heat from the ocean to the atmosphere and by the vertical stratification of the water masses in the Labrador Sea in late autumn. Models with stronger sub-polar gyre circulation have generally higher surface salinity in the Labrador Sea and a deeper convection. While the high-resolution models show more realistic ocean stratification in the Labrador Sea than the standard resolution models, they generally overestimate the convection. The results indicate that the representation of sub-grid scale mixing processes might be imperfect in the models and contribute to the biases in deep convection. Since in more than half of the models, the Labrador Sea convection is important for the Atlantic Meridional Overturning Circulation (AMOC), this raises questions about the future behavior of the AMOC in the models.This work has been funded by the PRIMAVERA project, which is funded by the European Union's Horizon 2020 programme, Grant Agreement No. 641727PRIMAVERA. D. V. Sein was also supported by the state assignment of the Ministry of Science and Higher Education of Russia (theme No. 0128-2021-0014). PO was supported by the Spanish Ministry of Economy, Industry and Competiveness through the Ramon y Cajal grant (RYC-2017-22772). The global ocean heat flux and evaporation products were provided by the WHOI OAFlux project (http://oaflux.whoi.edu) funded by the NOAA Climate Observations and Monitoring (COM) program.Peer Reviewed"Article signat per 12 autors/es: Torben Koenigk, Ramon Fuentes-Franco, Virna L. Meccia, Oliver Gutjahr, Laura C. Jackson, Adrian L. New, Pablo Ortega, Christopher D. Roberts, Malcolm J. Roberts, Thomas Arsouze, Doroteaciro Iovino, Marie-Pierre Moine & Dmitry V. Sein "Postprint (published version

The potential role of wind variability on plankton retention in the Río de la Plata Estuary: a numerical study

The Río de la Plata is one of the most important estuarine systems of the world. It drains the waters of the Paraná and Uruguay rivers, which constitute the second largest basin of South America. As a result, it has a huge discharge with a mean of around 25,000 m3 s-1, and maximum values as high as 50,000 m3 s-1 under extreme conditions. Water stratification is controlled by the confluence of high buoyancy continental discharge advecting offshore, lying on denser shelf waters that intrude into the estuary as a topographically controlled wedge, typically between 100 and 250 km long. The upstream reach of the wedge defines a bottom salinity front, located over a submersed bar named Barra del Indio shoal following the 10 m isobath. Several authors have pointed out the importance of this bottom salinity front in structuring plankton communities as well as in the development of spawning grounds for several coastal fishes. It has been suggested that observed patterns result from retention processes associated to the bottom salinity front. However neither the occurrence of this retention nor the physical and/or behavioral mechanisms involved have been well studied. It has been classically thought that retention would be a natural consequence of the theoretical circulation associated to a salt wedge: salty water incoming from the bottom would push plankton upstream to the bottom salinity front. Nevertheless, several recent papers based on numerical simulations and ADCP current observations have shown that estuarine circulation does not necessarily follow this pattern and, moreover, that it is highly variable and essentially wind dominated. These papers indicate that estuarine scales of variability replicate atmospheric ones, and that currents response to changes in the wind field is very fast, occurring in a lapse of around 6 hours. They also demonstrated that estuarine response to winds can be explained in terms of two modes, both implying currents with a phase lag with respect to winds that depends on the location in the estuary, but that in any case, produce a response in the bottom layer. As a result of the described features, in the time scales relevant to biota, the Río de la Plata would display weather and climate, as the atmosphere does. Atmospheric circulation in the region is characterized in synoptic to intra-seasonal scales by a high variability. As winds in the region rarely blow from the same direction for more than a few days, currents present the same feature. A striking question is, then, whether this highly variable system can favor retention and if this is the fact, what are the involved mechanisms. The aim of this paper is to explore this matter. A set of process oriented numerical experiments in which neutral particles are released along the frontal zone of the Río de la Plata and its vicinity and tracked for different wind conditions in short time scales is conducted. Results of numerical experiments are complemented with an analysis of local wind statistics. As a result a possible mechanism for plankton retention is suggested.Pages: 1383-139