Post-2011 variability of the great Atlantic Sargassum belt attributed to changing winds and currents

2021 ◽  
Author(s):  
Robert Marsh ◽  
Nikolaos Skliris ◽  
Hazel Oxenford ◽  
Kwazi Appeaning Addo
Keyword(s):  
Ocean Model ◽  
Recirculation Region ◽  
Circulation System ◽  
Tropical Atlantic ◽  
Virtual Particle ◽  
The North ◽  
Brazil Current ◽  
North Brazil ◽  
North Equatorial Counter Current ◽  
Amazon River Plume

<p><span>Since 2011, <em>Sargassum </em>seaweed has proliferated across the tropical North Atlantic, evident in Floating Algae Index (FAI) images for the Central Atlantic region (38-63°W, 0-22°N) over 2000-2020. To investigate the role of physical drivers in post-2011 <em>Sargassum </em>blooms, conditions are examined across the wider tropical Atlantic. Of particular consequence for the growth and drift of Sargassum are patterns and seasonality of winds and currents. In years when the FAI index is high (2015, 2018), the </span><span>Intertropical Convergence Zone (where <em>Sargassum </em>accumulates) was displaced southward, towards nutrient-rich waters of the Amazon river plume and the equatorial upwelling zone. </span><span>Strong enhancement of the North Brazil Current retroflection and North Equatorial Counter Current circulation system in 2015 and 2018 may have increased nutrient availability/uptake for <em>Sargassum </em>in the North Equatorial Recirculation Region. </span><span>To first order, these changes are associated with modes of </span><span>natural variability in the tropical Atlantic, notably a negative phase of the Atlantic Meridional Mode in 2015 and 2018, and a positive phase of the Atlantic Niño in 2018. </span><span>The influence of </span><span>anomalous winds and currents on <em>Sargassum </em>drift during years of high and low FAI are explored with virtual particle tracking, using surface currents from an eddy-resolving ocean model hindcast and </span><span>optional % </span><span>windage, to quantify the variable partitioning between <em>Sargassum </em>that is westward-bound to the Caribbean and eastward-bound to west Africa.</span></p>

Impact of mesoscale eddies on salinity and CO2 ocean parameters in the western tropical Atlantic in February 2020

2021 ◽  
Author(s):  
Léa Olivier ◽  
Jacqueline Boutin ◽  
Nathalie Lefèvre ◽  
Gilles Reverdin ◽  
Peter Landschützer ◽  
...  
Keyword(s):  
Dissolved Inorganic Carbon ◽  
Salinity Gradient ◽  
Sea Surface Salinity ◽  
Amazon River ◽  
Tropical Atlantic ◽  
Surface Salinity ◽  
The North ◽  
Brazil Current ◽  
North Brazil

<p>Large oceanic eddies are formed by the retroflection of the North Brazil Current (NBC) near 8°N in the western tropical Atlantic. The EUREC<sup>4</sup>A-OA/Atomic cruise took place in January - February 2020, and extensively documented two NBC rings. The NBC flows northward across the Equator and pass the mouth of the Amazon River, entraining fresh and nutrient-rich water along its nearshore edge. From December to March, the Amazon river discharge is low but a freshwater filament stirred by a NBC ring was nevertheless observed. The strong salinity gradient can be used to delineate the NBC ring during its initial phase and its westward propagation. Using satellite sea surface salinity and ocean color associated to in-situ measurements of salinity, temperature, dissolved inorganic carbon, alkalinity and fugacity of CO<sub>2</sub> we characterize the salinity and biogeochemical signature of NBC rings.</p>

Jet Streams of the Tropical Atlantic: Observing and Forecasting the North Brazil Current Retroflection

2013 ◽  
Author(s):  
Michael Christensen ◽  
Ashwanth Srinivasan ◽  
Jill Nelson ◽  
Neha Sharma ◽  
Peter Brickley
Keyword(s):  
Tropical Atlantic ◽  
Jet Streams ◽  
The North ◽  
Brazil Current ◽  
North Brazil ◽  
North Brazil Current

scholarly journals Investigation of the Intra-Annual Variability of the North Equatorial Countercurrent/North Brazil Current Eddies and of the Instability Waves of the North Tropical Atlantic Ocean Using Satellite Altimetry and Empirical Mode Decomposition

2017 ◽  
Vol 34 (10) ◽  
pp. 2295-2310 ◽  
Author(s):  
Jean-Luc Mélice ◽  
Sabine Arnault
Keyword(s):  
Atlantic Ocean ◽  
Empirical Mode Decomposition ◽  
Satellite Altimetry ◽  
Tropical Atlantic ◽  
Instability Waves ◽  
The North ◽  
Brazil Current ◽  
Mode Decomposition ◽  
North Brazil ◽  
North Brazil Current

AbstractThe intra-annual variability of the tropical Atlantic Ocean north of the equator is investigated with satellite altimetry mean sea level anomaly data and with an algorithm based on empirical mode decomposition (EMD) methods. Two regions of high variability are identified. The first region, between 3° and 12°N, is characterized by the presence of westward-propagating eddies linked to the North Brazil Current (NBC) retroflection in the vicinity of the Brazilian coast. They show a strong annual cycle. In this paper the EMD algorithm points out that this signal is frequency modulated shifting from large length-scale structures in October to smaller ones in March. Consequently, the number of “eddies” per year can be aliased, according to the time and location of sampling, and can impact the percentage they explain of the interhemispheric exchange of mass and heat associated with the meridional overturning circulation’s upper limb. A scenario concerning this dynamics is proposed. The second region reveals the presence of westward-propagating instability waves centered north of the equator (3°–7°N) between 50° and 10°W. These instability waves are also frequency modulated and show a strong seasonal cycle with maximum amplitude around August.

Retroflections of the North Brazil Current during February 2002

2005 ◽  
Vol 52 (4) ◽  
pp. 647-667 ◽  
Author(s):  
Marlos Goes ◽  
Robert Molinari ◽  
Ilson da Silveira ◽  
Ilana Wainer
Keyword(s):  
The North ◽  
Brazil Current ◽  
North Brazil ◽  
North Brazil Current

Using Satellite Altimeter and SST Observations of the 1997-1998 El Nino to Check the Key Ocean Processes Involved in a Strong El Nino.

2021 ◽  
Author(s):  
David Webb ◽  
Andrew Coward ◽  
Helen Snaith
Keyword(s):  
El Niño ◽  
Large Scale ◽  
El Nino ◽  
Ocean Model ◽  
Satellite Altimeter ◽  
The North ◽  
Satellite Sst ◽  
Model Study ◽  
North Equatorial Counter Current ◽  
Equatorial Current

<p>A recent high-resolution ocean model study of the strong El Ninos of 1982-1983 and 1997-1998 highlighted a previously neglected ocean mechanism which was active during their growth.   The mechanism involved a weakening of both the Equatorial Current and the tropical instability eddies in mid-ocean.  It also involved an increase in the strength of the North Equatorial Counter Current due to the passage of the annual Rossby wave.</p><p>      This presentation reports how satellite altimeter and satellite SST data was used to validate the model results the key areas, confirming the changes in the current and eddy fields and the resulting eastward extension of the region of highest SST values.  The SST changes were sufficient to trigger new regions deep-atmospheric convection and so had the potential to have a significant impact on the development of the El Nino and the resulting changes in the large scale atmospheric circulation.</p>

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