Dynamics of river plumes in the South Brazilian Bight and South Brazil

Abstract

The plumes from the rivers of the South Brazilian Bight (SBB) and South Brazil (SB) were studied using a realistic model configuration. River plume variability on continental shelves is driven by the input of river runoff into the shelf, by wind variability, and also by ambient currents and its seasonal variability, especially the Brazil Current, which are realistically modelled in this study. It is presented a simulation of 4 years using a nested configuration, which allows resolving the region around Florianópolis with very high resolution (∼150 m). The dispersion of river plumes was assessed not only with the hydrodynamical model results but also by using passive tracers whose dynamics was analyzed seasonally. Several dyes were released together with the river discharges. This approach allowed calculating the depths of the riverine freshwater, and the resulting regions affected by the plumes. Northward intrusions of waters from the southern region, under the potential influence of the distant La Plata river plume, were evaluated with a Lagrangian approach. The local river plumes are confined to the inner shelf, except south of 30°S where discharges from Lagoa dos Patos disperse over the shelf in the spring and summer. The Brazil Current flowing southward over the slope prevents the river plumes from interaction with oceanic mesoscale dynamics. The river plumes are, thus, mainly controlled by the wind forcing. The plumes from SBB are able to disperse until SB following the southward wind regime typical of the summer. And both the SB and La Plata river plumes are also able to reach SBB, forced by the northward wind typical of the winter season, until the latitude of 25.5°S. A low salinity belt (below 35) is present along the coastal region of SB and SBB year-round, supported by contributions from both the large and small rivers. The interaction between the different plumes influences the dispersion patterns, shielding the Florianṕolis coastal region from plumes of distant rivers, and dispersing the plume of SBB rivers away from Santa Catarina Island as it disperses southward during the summer months.

Impact of Mesoscale Circulation on the Structure of River Plumes During Large Rainfall Events Inshore of the East Australian Current

“…In the South Brazilian Bight and South Brazil, a permanent continuous Brazil Current flows southward along the slope. By releasing passive dyes together with the river discharge in the hydrodynamical model, Marta-Almeida et al (2021) showed that the local river plumes are confined to the inner shelf because the strong and persistent large-scale Brazil Current flowing southward over the slope prevents the river plumes from interaction with offshore oceanic mesoscale dynamics. The effect of mesoscale eddies on river plumes was conducted in the Agulhas Mozambique Channel region (Malauene et al, 2018), where the circulation is dominated by trains of intermittent, passing mesoscale eddies.…”

“…Previous studies have used numerical models to trace the riverine freshwater by releasing dyes into the rivers in many coastal regions, such as the New York Bight (Zhang et al, 2010), the Rhine Region (Rijnsburger et al, 2021), the South Brazilian Bight (Marta-Almeida et al, 2021), the Yangtze River estuary (Yu et al, 2020;Wu et al, 2021), and the Great Barrier Reef (Colberg et al, 2020). Three-dimensional structure and evolution of the river plumes have been presented in these numerical simulations.…”

Impact of Flash Flood Events on the Coastal Waters Around Madeira Island: The “Land Mass Effect”

“…For each baroclinic timestep, 30 s barotropic timestep was defined. ROMS was successfully applied in previous studies focused on Madeira Island to investigate island-induced oceanic processes (Caldeira and Sangrà, 2012;Couvelard et al, 2012;Caldeira et al, 2016;Alves et al, 2021) and has also been used in idealized and realistic studies to investigate plume dynamics generated by the Columbia, Pearl, and South Brazilian rivers (Chen et al, 2009;Liu et al, 2009;Pan et al, 2014;Basdurak et al, 2020;Branch et al, 2020;Marta-Almeida et al, 2020). Despite the lack of in situ data to assess the accuracy of the coupled ROMS model outputs during February 2010, Vieira et al (in preparation) are (at the time of publication) assessing the general capability of our numerical framework to represent island-scale geophysical processes, including warm wakes, storm events, and land runoff.…”

“…Such torrential discharge often generates buoyant river plumes that are easily identified by the high levels of suspended matter that spread from river mouths and mix with the surrounding oceanic waters. According to Osadchiev and Zavialov (2020), the formation, mixing, and spreading of buoyant river plumes depends on several factors that may be divided into two groups: (i) site characteristics, such as the geometry of the coastline and river mouths, bathymetry, and latitudedependent Coriolis force (Chao and Boicourt, 1986;Simpson, 1997;Garvine, 1999;Horner-Devine et al, 2006, 2015McCabe et al, 2009;Warrick and Farnsworth, 2017); and (ii) external forcing mechanisms, such as river flow, wind, coastal currents, tides, waves, and water column stratification Geyer, 2001, 2002;Yankovsky et al, 2001;Wu et al, 2011;Korotenko et al, 2014;Osadchiev, 2018;Yuan et al, 2018;Zhao et al, 2018;Marta-Almeida et al, 2020). Thus, the land-sea discharges of freshwater, terrigenous sediments, nutrients, suspended matter, and anthropogenic contaminants or pollutants affect the physical, chemical, biological, and geological processes in the coastal environment (Milliman and Syvitski, 1992;Meybeck et al, 2003;Brodie et al, 2010;Hilton et al, 2011;Bao et al, 2015;Warrick and Farnsworth, 2017;Osadchiev, 2018;Osadchiev and Zavialov, 2020).…”

The 11th International Workshop on Modeling the Ocean (IWMO 2019) in Wuxi, China, on June 17–20, 2019

“…Marta-Almeida et al ( 2021 ) used a very high-resolution nested configuration of the Regional Ocean Modeling System (ROMS) to study the dynamics of river plumes in the South Brazilian Bight and the influence of the Brazil Current (BC). Results show that the BC prevents the river plumes from interaction with oceanic mesoscale features, so that river plumes are mainly controlled by wind forcing.…”