The Atlantic Niño controls the boreal summer tropical Atlantic variability at interannual time scales, with pronounced climate impacts in adjacent and remote areas. Changes in the spatial configuration of the Atlantic Niño has been reported during the observational record, coinciding with a modification of the background state and associated teleconnections. The driving mechanisms of the Atlantic Niño have been also changed in recent decades.

The aim of the present study is to explore the role of the ocean background state in the Atlantic Niño diversity and associated air-sea mechanisms. For such purpose, we will use two twin 30-year high-resolution simulations performed in the H2020-EU NEXTGEMS project. Both simulations have the same horizontal resolution (10km) and only differ in the vertical stratification of the upper 20m: 2m layers for the THIN simulation and 10m layers for the THICK one.

To this aim, the Bjerknes feedback and ocean wave propagation are analyzed, and a complete heat budget analysis will be computed and compared in both simulations. Finally, the role of the background state in the modification of air-sea interactions and thus, in Atlantic Niño diversity will be also investigated.

How to cite: Martín-Rey, M., Rodríguez-Fonseca, B., Losada, T., Prigent, A., Polo, I., Abi, A., Mohino, E., Montoya-Carramolino, L., Calvo-Miguélez, E., Wu, J., and Putrasahan, D.: Driving mechanisms of Atlantic Niño under different vertical ocean resolutions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8915, https://doi.org/10.5194/egusphere-egu25-8915, 2025.

How to cite: Deppenmeier, A.-L., Bryan, F., Kessler, W., and Thompson, L.: How alike are diabatic processes in the tropical Atlantic to the Pacific? , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9323, https://doi.org/10.5194/egusphere-egu25-9323, 2025.

The upwelling region off northwest Africa exhibits pronounced seasonal variability and high productivity, playing a critical role in supporting fisheries. The sea surface temperature (SST) difference between the coast and offshore areas serves as a key proxy for upwelling intensity. Using observational data, we found distinct regional dependencies in the response of SST differences to atmospheric forcing. In the permanent upwelling region (21°N-30°N), both upwelling-favorable winds and heat flux enhance the coastal-offshore SST difference, leading the variations by about 70-100 days. In contrast, in the seasonal upwelling region (12°N-19°N),  changes in SST differences precede wind variations by less than one month, particularly during the transition to the downwelling season. Heat flux in this region acts to dampen SST gradients, contrasting with its role in the permanent upwelling zone. Additionally, our results indicate that the response of the SST difference to atmospheric forcing is faster and stronger when the mixed layer is shallower. These results highlight the spatial variability and complexity of air-sea interactions in the northwest African upwelling system, with implications for understanding coastal upwelling dynamics and informing fisheries management.

How to cite: Chen, L. and Juricke, S.: Seasonal cycle of sea surface temperature and air-sea interactions in the Northwest African upwelling region, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11504, https://doi.org/10.5194/egusphere-egu25-11504, 2025.

The rainfall variabilities of the West African and South American summer monsoons, pivotal for local and global climate systems, are strongly influenced by tropical Atlantic sea surface temperature anomalies. This study investigates the impacts of two recently identified Atlantic Niño types, central and eastern Atlantic Niño (CAN and EAN), on these monsoon systems using observational data and numerical experiments. During boreal summer, EAN events exhibit increased rainfall over West Africa compared to CAN events, indicating a strengthened West African summer monsoon. Enhanced moisture flux convergence from eastern Atlantic warming drives these wetting conditions during EAN events. Conversely, CAN events have a more pronounced influence on South American monsoon rainfall during austral summer, causing a rainfall anomaly dipole between the Amazon and eastern Brazil, suggesting an eastward shift in the South American summer monsoon rainfall belt. These rainfall changes are linked to cyclonic circulation anomalies over the southwest Atlantic Ocean, attributed to central Atlantic warming during CAN events. Furthermore, a statistical model assesses hindcast skills of rainfall variability in the two summer monsoon regions, affirming the benefits of separating Atlantic Niño into CAN and EAN events for improved seasonal climate predictions.

How to cite: Xing, W., Wang, C., and Zhang, L.: Influences of Central and Eastern Atlantic Niño on the West African and South American Summer Monsoons, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4950, https://doi.org/10.5194/egusphere-egu25-4950, 2025.

Canary Upwelling System (CUS) is, together with California, Humboldt, and Benguela, one of the four main Eastern Boundary Upwelling Systems (EBUS) across the globe. In particular, small pelagic fishes (hereinafter SPF) dominate the marine biomass in EBUS where they represent a vital intermediate connection between plankton and large predatory species. Regarding the CUS, SPF constitute in weight close to 70% of the total landings of northwest African countries, being the the Sardinella aurita (hereinafter sardinella) one of the dominant SPF species in terms of abundance. This species, for instance, represents the primary source of animal protein in Senegal. However, the absence of systematic observations of sardinella across northwest Africa largely constraint our understanding of how the environmental variability impacts the abundance and distribution of this species. In this work a novel end-to-end (here climate-to-fish) model-based strategy, including explicit representation of sardinella dynamics, has been designed. The results we are obtaining are enabling us to better understand interesting links (and related underlying processes) with well-known climate modes such as NAO and ENSO.

How to cite: López-Parages, J. and Sánchez-Garrido, J. C.: Analysing the climate influence on sardinella abundance in northwest Africa from a novel end-to-end model strategy, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19465, https://doi.org/10.5194/egusphere-egu25-19465, 2025.

The Canary upwelling system, located along the Northwest African coast between approximately 10ºN and 35ºN, is among the most productive marine ecosystems globally. It supports rich marine biodiversity and sustains economically significant fisheries. Notably, the coastal regions off Mauritania and Senegal (9ºN–22ºN), comprising the southern part of this system, exhibit pronounced interannual variability in net primary production (NPP). This variability is influenced by extreme warm and cold events, known as Dakar Niños and Niñas, respectively. In this study, we analyze the physical mechanisms driving the interannual variability of NPP from 2003 to 2022, using a combination of satellite observations, reanalysis data, and ocean model outputs. Our results indicate that the interannual variability of NPP is closely linked to changes in sea surface temperature (SST), with the most pronounced effects occurring during February-March-April, i.e. the main upwelling season. A total of six previously undocumented episodes of strong anomalous coastal high and low NPP were identified, nearly all of which are associated with Dakar Niños and Niñas. Our findings suggest that these events are linked to both local and remote forcing mechanisms. The local forcing is associated with variations of the coastal alongshore winds. The remote forcing involves the propagations of coastal trapped waves, triggered by wind fluctuations in the Gulf of Guinea, or by wind-forced equatorial Kelvin waves originating in the western-to-central equatorial Atlantic. Additional remote influences may stem from large-scale climate modes, including the El Niño-Southern Oscillation (ENSO), the North Atlantic Oscillation (NAO), and the Atlantic Meridional Mode (AMM).

How to cite: Imbol Koungue, R. A., Prigent, A., Lübbecke, J., and Brandt, P.:  Interannual variability of net primary productivity in the Northwest African coastal upwelling system and their relation to Dakar Niños and Niñas., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18521, https://doi.org/10.5194/egusphere-egu25-18521, 2025.

Atlantic Niño, the dominant climate mode in the equatorial Atlantic, is known to remotely force a La Niña-like response in the Pacific, potentially affecting seasonal climate predictions. Here, we use both observations and large-ensemble simulations to explore the physical mechanisms linking the Atlantic to the Pacific. Results indicate that an eastward propagating atmospheric Kelvin wave from the Atlantic, through the Indian Ocean, to the Pacific is the primary pathway. Interaction of this Kelvin wave with the orography of the Maritime Continent induces orographic moisture convergence, contributing to the generation of a local Walker Cell over the Maritime Continent-Western Pacific area. Moreover, land friction over the Maritime Continent dissipates Kelvin wave energy, affecting the strength of the Bjerknes feedback and thus the development of the La Niña-like response. Therefore, improving the representation of land–atmosphere–ocean interactions over the Maritime Continent may be fundamental to realistically simulate Atlantic Niño's impact on El Niño-Southern Oscillation.

How to cite: Liu, S., Chang, P., Wan, X., Yeager, S. G., Richter, I., and Zhang, R.: Role of the Maritime Continent in the remote influence of Atlantic Niño on the Pacific, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5072, https://doi.org/10.5194/egusphere-egu25-5072, 2025.

El Niño-Southern Oscillation (ENSO) is one of the most globally relevant modes of climate variability, playing a crucial role for tropical and extratropical seasonal predictions. During certain decades, specifically in the early and late 20th century, ENSO is coupled with the Atlantic Niño. Since the Atlantic Niño exhibits its maximum variability during the boreal summer (JJA), while ENSO peaks in winter (DJF), it has been shown that the Atlantic Niño can act as a predictor for ENSO in certain decades. This linkage operates on an interannual scale by alterations in the Atlantic Walker cell and, at decadal scales it has been related with changes in certain patterns, such as the Atlantic Multidecadal Variability (AMV), and an increase in pantropical oceanic variability. Nevertheless, further research on the mechanisms of this connection is needed.

This work analyzes this Atlantic-Pacific connection in SEAS5-20C, as well as the decadal and interannual mechanisms that underpin this connection. Furthermore, it discusses the influence of this connection on the decadal variability of ENSO and Atlantic Niño predictive skill. It is found that decadal changes in tropical basin interactions coincide with changes in the predictability of the tropical Atlantic and Pacific. These findings reveal how the connection between tropical basins is associated with improvements in ENSO and Atlantic Niño predictions.

How to cite: Robles Fernández, A. J., Rodriguez-Fonseca, B., Losada Doval, T., Weisheimer, A., and Alonso Balmaseda, M.: Impact of the equatorial Atlantic on ENSO prediction in SEAS5-20C re-forecast, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11559, https://doi.org/10.5194/egusphere-egu25-11559, 2025.

The purpose of this work is to reveal structural features of waters in the tropical Atlantic in the deep and intermediate layers. Based on the data set expanded in recent years, the content of deep and intermediate waters was calculated from conservative chemical variables.

The work includes data obtained from 1873 to 2023 (GLODAPv2.2022, eWOCE, WODB18 databases). Data from expeditions of the MSU Faculty of Geography from 2019 to 2023 were also used.

The following parameters were used to calculate the water mass content:

Results:

1) Broecker calculated the fraction of deep water in the Atlantic using the PO₄*. It was found that the best agreement with the content calculated by PO₄* was shown by the PO parameter with a deviation of 5-10%.

a)  b)   

Fig.1. North Atlantic Deep Water (NADW) distributions calculated by PO₄*(a), PO (b).

2) Deep water contents calculated using PO₄* on the sections were compared with water mass boundaries determined mainly using hydrophysical parameters.

NADW in the western tropical Atlantic is divided into three components: Upper NADW, Middle NADW and Lower NADW. It was found that in most of the analyzed sections, the lower boundaries of MNADW and LNADW practically coincide with the isolines of 85% and 60% of the NADW content.

In addition to large gradients of hydrophysical characteristics, the upper boundary of Antarctic Bottom Water (AABW) is determined by the Si/P=33 ratio (Arzhanova, Artamonova, 2014). In the western Atlantic it most often passes along the isoline of 25% AABW content, in the eastern Atlantic - along the isoline of 15% AABW content.

3) The distribution of AABW is of particular interest because it is transformed as it flows from the western basin to the eastern basin through the Mid-Atlantic Ridge faults. It was decided to refer to the transformed AABW as Northeast Atlantic Bottom Water (NEABW). It has been shown that NEABW is 50% composed of waters entering the eastern Atlantic through the Vema Fracture Zone, and 30% of these waters are “pure” AABW.

4) The PO parameter was used to determine the fraction of Antarctic Intermediate Water (AAIW) and Mediterranean Water (MW):

Fig. 2. Examples of obtained distributions of intermediate waters.

This work was supported by the Russian Science Foundation grant № 23-17-00032.

References:

1) Broecker et al. Radiocarbon decay and oxygen utilization in the Deep Atlantic Ocean // Global geochemical cycles. 1991. V 5, №1. Pp 87-117.

2) Broecker W. "NO" a conservative water-mass tracer // Earth and Planetary Science Letters. V 23. Pp 100-107.

3) Broecker et al. Sources and Flow Patterns of Deep-Ocean Waters as Deduced From Potential Temperature, Salinity, and Initial Phosphate Concentration // J. Geophys. : Oceans.1985. V 90, № C4. Pp 6925-6939.

4) V. Arzhanova, K. V. Artamonova. Hydrochemical structure of water masses in areas of the Antarctic Krill (Euphausia Superba Dana) fisheries // Proceedings of VNIRO. 2014. V 152. Pp. 118-132.

How to cite: Samborskaia, I. and Demidov, A.: Structure of intermediate and deep waters in the tropical Atlantic, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13437, https://doi.org/10.5194/egusphere-egu25-13437, 2025.

Submesoscale coherent vortices (SCVs) have been frequently observed in the eastern tropical Atlantic (between 12°S and 12°N) based on moored and shipboard observations. They are located well below the mixed layer with no surface signature and, thus, undetectable by remote sensing making in-situ observations and modeling indispensable. The SCVs persist and are relatively long-lived and coherent, despite the increasing suppression of geostrophic balance and the rapid change in the Coriolis parameter (ß-effect) near the equator. These factors typically suggest predominant wave-like structures in this region. Additionally, the energetic zonal current system, which stretch and shear the vorticity fields, further complicate the formation of closed vortex structures. Ship-based oxygen measurements conducted in the area between 6°-12°N, 24°-18°W reveal that approximately two-third of these SCVs are associated with low oxygen cores with dissolved oxygen concentrations less than 60 µmol kg^-1 (minimum 40 µmol kg^-1). These values are significantly lower than the climatological averages for this depth range (> 80 µmol kg^-1). Both, observed water mass characteristics and the analysis of an eddy-resolving ocean-biogeochemistry model indicate that the majority of SCVs originate from the eastern boundary and may last for longer than half a year. While propagating westward into a higher potential vorticity environment, anticyclonic SCVs with a low PV core are more effectively isolated and feature longer life times than cyclonic SCVs with a high PV core. The vertical structure of the dominating anticyclonic SCVs is characterized by higher baroclinic modes 4-10, associated with a Rossby radius of 34 -13 km respectively, which is in agreement with the observed eddy radius and well below the 1^st baroclinic Rossby radius of deformation in the region (> 100 km). This study does not only increase our understanding of submesoscale dynamics in equatorial regions, but also how SCVs contribute to the formation of hypoxic zones in the open ocean due to their association with low-oxygen extremes. These hypoxic regimes have the potential to directly impact pelagic fish, biodiversity, and biogeochemical cycles.

How to cite: Schuette, F., Hahn, J., Frenger, I., Bendinger, A., Dilmahamod, F., Schulz, M., and Brandt, P.: Tropical low oxygen extreme events caused by persistent submesoscale coherent vortices, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13553, https://doi.org/10.5194/egusphere-egu25-13553, 2025.