Temporal and Spatial Variability Scales of Salinity at a Large Microtidal Estuary

Michelle Jackson,Mónica Fossati,Gianfranco Sienra,Pablo Santoro

doi:10.3390/jmse9080860

Michelle Jackson, Mónica Fossati + Show 2 more

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https://doi.org/10.3390/jmse9080860

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Abstract

The Río de la Plata is a large fluvial–estuarine–sea system discharging into the southwestern Atlantic Ocean, which has relevant features such as high fluvial discharge, microtidal astronomical tidal scales, a relevant meteorological tide, and a strong atmospheric forcing effect, due to its large width. The objective of this study is to advance the understanding of the estuarine hydrodynamics and salt transport, as well as discussing the main characteristics of the spatiotemporal variability of the salinity field. To achieve this, the results of a 3D model of the Río de la Plata and its maritime front were used, simulating an extensive period of 10 years. In this study, the model was validated using vertical salinity profiles collected at different locations in the estuary. The temporal variability of the salinity stratification was characterised at different temporal scales: annual, monthly, and storm. At the same time, the influences of fluvial flow and winds were determined. The correlation analysis between fluvial flow and the salinity field showed that high annual fluvial flows generate an extension of the freshwater area, with larger longitudinal salinity gradients and a shift of the salinity front towards the ocean. The tendency at the monthly scale is not as clear as that observed at the annual scale. The results show that the effect of a storm coming from the northwest is quite similar to that of storms coming from the southwest, especially in the central and southern zones of the Río de la Plata, where mixing increases and stratification decreases, according to the intensity of the storm. The effect of south–southeasterly storms increases the mixing process and reduces stratification; the opposite effect was identified with respect to northeasterly storms, under the influence of which the stratified area increases. Synthesising the obtained results, a global zonification of the vertical salinity stratification for the Río de la Plata is proposed.

Highlights

The spatiotemporal variability of salinity and stratification in the Río de la Plata was Considering the period between 2006 and 2015, the annual mean fluvial flow from the analysed based on the numerical results of the RPtide model
The results clearly show that high annual average fluvial flow generates the extent of the freshwater area, with a higher longitudinal salinity gradient and the change in the location of the salinity front towards the ocean
Continuous measurements in several vertical positions, in order to analyse the temporal evolution of the vertical salinity profile in the Río de la Plata, are not available

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Estuarine hydrodynamics have been studied through the use of both generic theories and case studies, the latter approach being much more complex ([1,2]; Valle-Levinson, 2010). Under the influence of oceanic and continental dynamics, the flow in estuarine regions generally presents different temporal and spatial variability scales, being more pronounced in large estuaries [3]. This includes flow variables, such as sea level and velocities, as well as water properties, such as salinity and temperature; these, in turn, determine the density of the water

Results

Discussion

Conclusion