Seasonal variability of the equatorial undercurrent termination and associated salinity maximum in the Gulf of Guinea

Kolodziejczyk, Nicolas; Marin, Frédéric; Bourlès, Bernard; Gouriou, Yves; Berger, Henrick

doi:10.1007/s00382-014-2107-7

Cited by 21 publications

(67 citation statements)

References 56 publications

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“…The structures of the thermocline and halocline in June and September were in association with the EUC shoaling in June and deepening in September. The imprint of the EUC salinity maximum was absent at the mean depths of the EUC core in June 2005, which is an indication of an intense mixing of the EUC water with the surface waters in June, as reported by Voituriez and Herbland (1979) and Kolodziejczyk et al (2014). Higher AOU values at the surface in June are indicative of lower oxygen saturation, whereas the constant AOU value from the surface to about 50 m in September indicates little or no oxygen-consuming processes within this depth range.…”

Section: Seasonal Upwelling Influencementioning

confidence: 64%

“…The general track of the six EGEE cruises conducted between 2005 and 2007 is presented in Figure 1 (Kolodziejczyk et al, 2009(Kolodziejczyk et al, , 2014Nubi et al, 2014 for additional details). Seawater samples were collected in 11 or 22 (depending on the cruise/research vessel used) hydrological bottles attached to a rosette, together with a CTD-O2 (bathysonde) and ship-mounted acoustic Doppler current profiler (SADCP).…”

Section: Sampling and Quality Controlmentioning

confidence: 99%

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On the Nutrient distribution and phytoplankton biomass in the Gulf of Guinea equatorial band as inferred from In-situ measurements

Nubi

Edokpayi²,

Hounkonnou³

2016

J. Oceanogr. Mar. Sci.

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Oceanographic in situ data collected in the Gulf of Guinea during six cruises carried out between 2005 and 2007 were analysed to study the influence of equatorial upwelling on the productivity of the region. At 10°W, observations during boreal summer and autumn cruises captured seasonal upwelling influences. In response to the shoaling pycnocline in June 2005, higher concentrations of nitrate and chlorophyll fluorescence were recorded at the ocean surface in June than in September. Our findings challenge the paradigm that westward advection from the nutrient-rich African coast is responsible for equatorial enrichment in the Gulf of Guinea. Vertical sections of the parameters under study in the summer of 2005 showed no westward advection from 3°E to 10°W within the equatorial band. This emphasizes the important role of vertical processes in equatorial enrichment at 10°W. An additional aspect of our study provides evidence of the impact on nutrient and chlorophyll distribution of offequatorial westward recirculation of equatorial undercurrent waters (observed between 2°and 3°S).

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Section: Seasonal Upwelling Influencementioning

confidence: 64%

Section: Sampling and Quality Controlmentioning

confidence: 99%

On the Nutrient distribution and phytoplankton biomass in the Gulf of Guinea equatorial band as inferred from In-situ measurements

Nubi

Edokpayi²,

Hounkonnou³

2016

J. Oceanogr. Mar. Sci.

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“…Therefore, the SSS starts to decrease in June–July, while the upward cooling flux remains intense up to July owing to the vertical distribution of temperature against salinity. This erosion of the equatorial salinity maximum during boreal summer was also reported by several authors based on observations and models [ Gouriou and Reverdin , ; Kolodziejczyk et al ., ; Johns et al ., ].…”

Section: Discussionmentioning

confidence: 99%

“…To understand the disappearance of the EUC salinity maximum during the boreal summer, a seasonal salinity budget of the EUC in the ACT has been analyzed. We find that the major reason for the EUC salinity maximum erosion in July and August is due to the weakening of the zonal salt advection which is mainly related to the weakening of the EUC [ Kolodziejczyk et al ., ; Johns et al ., ]. The vertical turbulent salt driven by the vertical shear between the surface and the upper thermocline currents is negative throughout the year and also contributes to decrease the salinity of the EUC.…”

Section: Discussionmentioning

confidence: 99%

“…A similar result was found in the eastern part of the basin by Kolodziejczyk et al . []. Based on a seasonal box‐averaged salinity budget in the upper thermocline delimited by

σ_{θ} = 24.5 kg m^{- 3}

and

σ_{θ} = 26 .2 kg m^{- 3}

isopycnals in the eastern Gulf of Guinea (east of 4°W), these authors also suggested that the main cause of the equatorial EUC salinity core erosion is due to the intense vertical mixing during the boreal summer although the role of horizontal advection cannot be neglected.…”

Section: Discussionmentioning

confidence: 99%

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Importance of the Equatorial Undercurrent on the sea surface salinity in the eastern equatorial Atlantic in boreal spring

et al. 2017

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The physical processes implied in the sea surface salinity (SSS) increase in the equatorial Atlantic Cold Tongue (ACT) region during boreal spring and the lag observed between boreal spring SSS maximum and sea surface temperature (SST) summer minimum are examined using mixed‐layer salinity budgets computed from observations and model during the period 2010–2012. The boreal spring SSS maximum is mainly explained by an upward flux of high salinity originating from the core of the Equatorial Undercurrent (EUC) through vertical mixing and advection. The vertical mixing contribution to the mixed‐layer salt budget peaks in April–May. It is controlled primarily by (i) an increased zonal shear between the surface South Equatorial Current and the subsurface EUC and (ii) the presence of a strong salinity stratification at the mixed‐layer base from December to May. This haline stratification that is due to both high precipitations below the Inter Tropical Convergence Zone and zonal advection of low‐salinity water from the Gulf of Guinea explains largely the seasonal cycle of the vertical advection contribution to the mixed‐layer salt budget. In the ACT region, the SST reaches its maximum in March/April and minimum in July/August. This SST minimum appears 1 month after the maximum of SSS. The 1 month lag observed between the maximum of SSS in June and the minimum of SST in July is explained by the shallowing of the EUC salinity core in June, then the weakening/erosion of the EUC in June–July which dramatically reduces the lateral subsurface supply of high‐saline waters.

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Mixed layer heat and salinity budgets during the onset of the 2011 Atlantic cold tongue

Schlundt

Brandt

Dengler

et al. 2014

J. Geophys. Res. Oceans

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The mixed layer (ML) temperature and salinity changes in the central tropical Atlantic have been studied by a dedicated experiment (Cold Tongue Experiment (CTE)) carried out from May to July 2011. The CTE was based on two successive research cruises, a glider swarm, and moored observations. The acquired in situ data sets together with satellite, reanalysis, and assimilation model data were used to evaluate box-averaged ML heat and salinity budgets for two subregions: (1) the western equatorial Atlantic cold tongue (ACT) (23 -10 W) and (2) the region north of the ACT. The strong ML heat loss in the ACT region during the CTE was found to be the result of the balance of warming due to net surface heat flux and cooling due to zonal advection and diapycnal mixing. The northern region was characterized by weak cooling and the dominant balance of net surface heat flux and zonal advection. A strong salinity increase occurred at the equator, 10 W, just before the CTE. During the CTE, ML salinity in the ACT region slightly increased.Largest contributions to the ML salinity budget were zonal advection and the net surface freshwater flux. While essential for the ML heat budget in the ACT region, diapycnal mixing played only a minor role for the ML salinity budget. In the region north of the ACT, the ML freshened at the beginning of the CTE due to precipitation, followed by a weak salinity increase. Zonal advection changed sign contributing to ML freshening at the beginning of the CTE and salinity increase afterward.

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Seasonal variability of the equatorial undercurrent termination and associated salinity maximum in the Gulf of Guinea

Abstract: International audienc

Cited by 21 publications

References 56 publications

On the Nutrient distribution and phytoplankton biomass in the Gulf of Guinea equatorial band as inferred from In-situ measurements

On the Nutrient distribution and phytoplankton biomass in the Gulf of Guinea equatorial band as inferred from In-situ measurements

Importance of the Equatorial Undercurrent on the sea surface salinity in the eastern equatorial Atlantic in boreal spring

Mixed layer heat and salinity budgets during the onset of the 2011 Atlantic cold tongue

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