Amazon water lenses and the influence of the North Brazil Current on the continental shelf

Prestes, Yuri Onça; Silva, Alex Costa da; Jeandel, Catherine

doi:10.1016/j.csr.2018.04.002

Cited by 14 publications

(5 citation statements)

References 33 publications

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“…Our two extreme cases (tidal vs. nontidal ocean) can be put in parallel with the two opposed cases observed in the AMASSEDS cruises, during spring and neap tides (Beardsley et al, 1995;Geyer, 1995;Geyer & Kineke, 1995; as well as in the AMANDES moorings (Prestes et al, 2018), and simulated in the idealized model of Fontes et al (2008): According to these studies, during spring tides the production of vertical turbulence is strong enough to push offshore the location of the northwestward deflection of the plume waters, whereas during neap tides the system behaves virtually like in our NoTide experiment, with a plume being deflected northwestward right upon entering the ocean and subsequently remaining much closer to the shore. We verified this by compositing the currents and SSS of our Model experiment, during the spring tides as well as during the neap tides, over 1 year (2015).…”

Section: Discussionsupporting

confidence: 72%

Role of the Tide on the Structure of the Amazon Plume: A Numerical Modeling Approach

et al. 2020

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The dynamical balance on the Amazon shelf and its implication on the properties of the Amazon River plume is not fully understood and poorly represented in global‐ and basin‐scale ocean models. In this study, the sensitivity of the Amazon shelf dynamics to tidal forcing is explored with a set of high‐resolution numerical simulations (1/36°) with and without the tide. A comparison of the simulations with sea surface salinity in situ measurements at 5°N (a location where the plume seasonally detaches from the coast and retroflects toward the east) revealed that the explicit resolution of the tide significantly improves the representation of the offshore spread of the river plume. This study further highlights the finding that tidal currents affect the properties of the whole Amazon plume. This sensitivity is explained by a near total collapse of the northwestward alongshore mean flow located near the river mouth, once the tidal forcing is included. This weakening of the ambient flow reduces (i) the dilution ratio between the ambient salty shelf waters and the riverine freshwaters and (ii) the constraint on the cross‐shore extension of the low‐salinity bulge. With tides, the plume is fresher near the river mouth (by up to 5 units), more extended in the cross‐shore direction, and more easily exported offshore by the North Brazil Current at the shelf break.

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Section: Discussionsupporting

confidence: 72%

Role of the Tide on the Structure of the Amazon Plume: A Numerical Modeling Approach

et al. 2020

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“…During the AMANDES project, a mooring was deployed at the continental shelf, which recorded the transport rate of the northwestward current at 10 m depth (location 1.1°N, 46.7°W at the 50 m isobaths). Highly temporal variable transport rates were observed with a maximum value up to 100 cm s −1 and a minimum value when currents are flowing toward southeast (Prestes et al 2018). Drifters launched at the Amazon mouth during AmasSeds program revealed transport rates in the range of 41–128 cm s −1 (Limeburner et al 1995).…”

Section: Discussionmentioning

confidence: 99%

“…While 224 Ra, 226 Ra, and 228 Ra activities have been reported in this region in a previous study (Moore et al 1995), the AZ4R cruise provided the earliest samples measured for 224 Ra and 223 Ra data offshore the Amazon mouth. The second set of samples originated from the AMANDES project (2007–2008); (Le Bars et al 2010; Rousseau et al 2015; Prestes et al 2018). These latter campaigns aimed at better understanding the physico‐chemical exchange processes that take place in the Amazon delta and along the Brazilian continental shelf and at evaluating the impact on the chemical composition of the Atlantic Ocean waters.…”

Section: Methodsmentioning

confidence: 99%

Use of ²²³Ra and ²²⁴Ra as chronometers to estimate the residence time of Amazon waters on the Brazilian continental shelf

Léon

Beek

Scholten

et al. 2022

Limnology & Oceanography

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When rivers mix into the ocean, radium isotopes are released into the dissolved phase allowing us to apply these isotopes as powerful tracers of river plumes spreading into the ocean. We report 223 Ra and 224 Ra radium activities that were determined in the Amazon River mouth and along the Amazon plume that extends off the coasts of Brazil and French Guyana into the Atlantic Ocean. We summarize 223 Ra and 224 Ra data from AmasSeds (1991), AMANDES (GEOTRACES process study GApr01;-2008 and M147 (2018) projects, which were conducted in different seasons corresponding to different Amazon discharge rates. We determined the 224 Ra ex / 223 Ra activity ratios (AR) along the Amazon plume to derive apparent ages and to estimate the residence time of the Amazon waters on the Brazilian continental shelf. Our data suggest that it takes 9-14 d for the Amazon waters to reach the northern continental shelf off French Guyana and 12-21 d to reach the eastern part of the Brazilian continental shelf. These time scales are in good agreement with those derived from a high-resolution numerical simulation of the regional ocean dynamics. We do not find any relationship between the discharge rate of the Amazon River and the residence time of the waters on the Brazilian continental shelf, suggesting that the residence time of the Amazon waters is primarily driven by the ambient northwestward current. Using the apparent ages along the plume, we estimate an average velocity of 26 cm s À1 for the northward transport of the Amazon waters on the continental shelf.

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“…Another relevant aspect to be considered is that the mean values used to calculate the mixing models and the sediment accumulation have quite some variation, even within one zone (Table 1). In addition, the flux in the Amazon river and the direction of the river plume changes radically over the hydrological seasons, due to the periodic floods and the marine currents (Coles et al, 2015;Molleri, et al, 2010;Prestesa et al, 2018). Thus, our results did not include all the events and processes that could affect the quantification of carbon burial in the continental shelf and marine sites.…”

Section: Accumulation Of Continental and Marine Organic Carbon Transe...mentioning

confidence: 99%

A multiproxy approach to characterize the sedimentation of organic carbon in the Amazon continental shelf

et al. 2021

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Amazon water lenses and the influence of the North Brazil Current on the continental shelf

Cited by 14 publications

References 33 publications

Role of the Tide on the Structure of the Amazon Plume: A Numerical Modeling Approach

Role of the Tide on the Structure of the Amazon Plume: A Numerical Modeling Approach

Use of ²²³Ra and ²²⁴Ra as chronometers to estimate the residence time of Amazon waters on the Brazilian continental shelf

A multiproxy approach to characterize the sedimentation of organic carbon in the Amazon continental shelf

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Amazon water lenses and the influence of the North Brazil Current on the continental shelf

Cited by 14 publications

References 33 publications

Role of the Tide on the Structure of the Amazon Plume: A Numerical Modeling Approach

Role of the Tide on the Structure of the Amazon Plume: A Numerical Modeling Approach

Use of 223Ra and 224Ra as chronometers to estimate the residence time of Amazon waters on the Brazilian continental shelf

A multiproxy approach to characterize the sedimentation of organic carbon in the Amazon continental shelf

Contact Info

Product

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Use of ²²³Ra and ²²⁴Ra as chronometers to estimate the residence time of Amazon waters on the Brazilian continental shelf