Influence of the Gulf of Guinea Islands on the Atlantic Equatorial Undercurrent Circulation

Napolitano, Dante Campagnoli; Alory, Gaël; Dadou, Isabelle; Morel, Yves; Jouanno, Julien; Morvan, Guillaume

doi:10.1029/2021jc017999

Cited by 4 publications

(6 citation statements)

References 104 publications

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“…In this case P V = ∂ x v−∂ y u + f is the expected absolute vertical vorticity with a value at rest corresponding to the Coriolis parameter. As argued in previous studies (Delpech et al, 2020;Assene et al, 2020;Aguedjou et al, 2021;Napolitano et al, 2022;Ernst et al, 2023), in the general case, ρ * should correspond to the stratification at rest, obtained from the Lorenz's (Lorenz, 1955) rearranged stratification (see also Nakamura, 1995;Winters and D'Asaro, 1996). Indeed, in this case only, the rescaled PV at rest is still given by the Coriolis parameter P V rest rescaled = f and, at first order, the anomaly from this reference corresponds to the quasigeostrophic PV, which is again directly linked to the geostrophic circulation.…”

Section: An Objective Definition Of Potential Vorticitysupporting

confidence: 68%

“…However, the link between Ertel PV and the dynamics (vorticity and velocity fields) is not straightforward, which makes the physical analysis inconvenient. Morel et al (2019) (see also Assene et al, 2020;Delpech et al, 2020;Aguedjou et al, 2021;Napolitano et al, 2022;Ernst et al, 2023) proposed a rescaled PV, which is calculated taking into account a reference density profile "representative of the background stratification at rest". The interest of the rescaled PV is that it is a generalization of the QG PV.…”

Section: Introductionmentioning

confidence: 99%

“…The interest of the rescaled PV is that it is a generalization of the QG PV. It scales as a vorticity with a reference value at rest equal to the Coriolis parameter (Morel et al, 2019;Assene et al, 2020;Napolitano et al, 2022) and deviations of the rescaled PV from its background value at each latitude (also called PV anomalies) are the signature of the vortical geostrophic circulation and can be linked to the dynamics following the QG framework (Morel and McWilliams, 2001;Herbette et al, 2003Herbette et al, , 2005Morel and Thomas, 2009; Le Hénaff et al, 2012). The rescaled PV is conserved for each fluid particle in adiabatic dynamics, but its evolution under diabatic conditions follows similar constraints as the classical Ertel PV (Morel et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

“…The generated anomalies are therefore easier to link to the dynamics. Thanks to these properties, the rescaled PV is very useful to analyze the importance of adiabatic and diabatic processes on the generation and evolution of vortices (Assene et al, 2020;Delpech et al, 2020;Aguedjou et al, 2021;Napolitano et al, 2022;Ernst et al, 2023).…”

Section: Introductionmentioning

confidence: 99%

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An “objective” definition of potential vorticity. Generalized evolution equation and application to the study of coastal upwelling instability

Morel,

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et al. 2023

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Section: An Objective Definition Of Potential Vorticitysupporting

confidence: 68%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

An “objective” definition of potential vorticity. Generalized evolution equation and application to the study of coastal upwelling instability

Morel,

Morvan,

Benshila

et al. 2023

Ocean Modelling

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“…Rather, there is a general enhancement of surface chlorophyll around the islands, resemblant of the so‐called island mass effect first described by Doty and Oguri (1956) and implicated at other off‐equatorial island archipelagos such as the Marquesas (Signorini et al., 1999) and French Polynesia (James et al., 2020). Interactions of the Atlantic EUC with São Tomé, roughly the size of a single atoll in the Gilbert Islands and located ∼240 km offshore of Africa, have only recently begun to be investigated but new model experiments suggest that it may have important impacts on the coastal circulation and environment in the Gulf of Guinea (Napolitano et al., 2021).…”

Section: Summary and Discussionmentioning

confidence: 99%

Argo Reveals the Scales and Provenance of Equatorial Island Upwelling Systems

Karnauskas

Giglio

2022

Geophysical Research Letters

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Upwelling is a ubiquitous feature of the equatorial ocean, as easterly trade winds drive poleward Ekman transport on either side of the equator (Cromwell, 1953;Ekman, 1905). While vertical ocean velocities are prohibitively slow to measure directly, their crucial role in fueling primary productivity, driving air-sea carbon flux, cooling the sea surface, and modulating the coupled ocean-atmosphere system has long been recognized (Bjerknes, 1969;Field et al., 1998). One analysis of shipboard observations in the Pacific during the 1990s estimated peak equatorial upwelling at 0.9-2.4 m per day (Johnson et al., 2001)-roughly consistent with earlier estimates ranging from 1.0 m day -1 (Wyrtki, 1981) to 2.5 m day −1 (Bryden & Brady, 1985). These values describe the large-scale upwelling velocity in the open equatorial ocean. Amid this broad stretch of upwelling across the equatorial Pacific commonly referred to as the "cold tongue" are several islands and the archipelagos with markedly stronger signals of cool sea surface temperature (SST) and high productivity. Found immediately west of the Gilbert and Galápagos Islands are localized enhancements of the surface characteristics of the cold tongue (Figure 1). For example, to the west of Isla Isabela, the Galápagos in the eastern equatorial Pacific has a further SST reduction by 2°C and an order of magnitude higher surface chlorophyll concentration. At the Gilbert Islands in the western Pacific, the signals are roughly −0.2°C in SST and doubling of chlorophyll-smaller but nonetheless clearly evident in satellite observations. The same phenomenon has been documented at islands as small as Jarvis Island (0.4°S, 160°W, and 4.5 km 2

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Unravelling nutrient dynamics and mixed layer depth variability in the equatorial Atlantic: insights from 10°W meridional section monitoring

Kouame,

N’Guessan,

Kouassi

et al. 2024

Front. Mar. Sci.

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The ocean, a pivotal component of the Earth’s climate system, exerts a profound global influence through intricate physical and biological interactions within its surface layer. This interplay centers around the mixed layer (ML), integral for energy exchange driven by oceanic currents. An essential regulatory function of the ocean involves orchestrating the distribution of chemical elements, with nitrate assuming a pivotal role in oceanic primary production. Nutrient availability, a cornerstone of primary production, hinges on the mixed layer depth (MLD) dynamics, modulated by many mechanisms, including upwelling and convection. This study unravels the interplay between nutrient variability and MLD depth, focusing on the Gulf of Guinea (GG) region in the equatorial Atlantic. Characterization of the study area reveals distinctive sea surface temperature (SST), salinity (SSS), and current patterns. The South Equatorial Undercurrent (SEUC) and Equatorial Undercurrent (EUC) play vital roles in surface nutrient transport. Nitrate distribution unveils latitudinal variations, exhibiting pronounced enrichment during boreal summer and winter. The equatorial region experiences a strengthening of MLDs from 10.5 to 35.33 m in summer, which increases the nitrate input from 0 to 2.06 mmol m-3 in the surface layers in the mixed layer. In contrast, boreal winters experience more intense MLDs that vary between 20.5 and 64.50 m, supporting high nitrate concentrations of 2.96 to 7.49 mmol m-3, challenging previous hypotheses. This equatorial enrichment is supported by low nitracline ranging from 5.47 to 46.19 m. Beyond the equator, the subequatorial and subtropical regions, despite the observed deepening of the ML, present low nitrate concentrations (less than 0.5 mmol m-3) with a nitracline that does not reach the ML. However, at 6°S and 9°S, a respective increase in nitrate content of 0.66 mmol m-3 and 1.2 mmol m-3 influenced by internal waves, advection and surface currents is observed. Temperature, salinity, and atmospheric fluxes shape nutrient distribution and primary production dynamics. These findings illuminate the intricate relationships between oceanographic processes, nutrient availability, and marine ecosystem productivity. A holistic understanding is crucial for sustainable resource management and fisheries in the equatorial Atlantic and beyond.

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Influence of the Gulf of Guinea Islands on the Atlantic Equatorial Undercurrent Circulation

Cited by 4 publications

References 104 publications

An “objective” definition of potential vorticity. Generalized evolution equation and application to the study of coastal upwelling instability

An “objective” definition of potential vorticity. Generalized evolution equation and application to the study of coastal upwelling instability

Argo Reveals the Scales and Provenance of Equatorial Island Upwelling Systems

Unravelling nutrient dynamics and mixed layer depth variability in the equatorial Atlantic: insights from 10°W meridional section monitoring

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