Orals: Wed, 30 Apr | Room L2
This study explores the oceanic connection between the equatorial dynamics and the coastal variability along the northern coast of the Gulf of Guinea on interannual timescales, based on experiments with a high-resolution tropical Atlantic Ocean model over 1958-2015. Equatorial Kelvin waves, forced by wind-stress anomalies in the west-central equatorial basin, significantly control the interannual fluctuations of the coastal sea-level and subsurface temperature near the thermocline (>70%), leaving only a marginal role for the local forcing contribution. The dynamical coastal response exhibits a clear propagative nature, with poleward propagations (0.75-1.2 m.s-1) from Cameroon to Liberia. Because the northern coast of the Gulf of Guinea is close to the equatorial waveguide, the coastal variability is influenced by both equatorially-forced coastal trapped waves and reflected equatorial Rossby waves. Furthermore, remote equatorial forcing explains more of the surface temperature variance for the coastal systems associated with clear upwelling characteristics such as Côte d’Ivoire and Ghana, where subsurface/surface coupling is more efficient. The surface thermal amplitude and timing is shaped by the coastal stratification and circulation and exhibits a marked seasonal modulation, so that the timing of the SST anomalies relative to the dynamical signature lacks consistency, making SST a less reliable variable for tracking coastal propagations in the Gulf of Guinea. Our findings open the possibility of predicting interannual changes in coastal conditions off Côte d’Ivoire and Ghana a few months in advance, to anticipate impacts on fish habitats and resources, and to facilitate proactive measures for sustainable management and conservation efforts.
How to cite: Illig, S., Djakouré, S., and Mitchodigni, T.: Influence of the remote equatorial dynamics on the interannual variability along the northern coast of the Gulf of Guinea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19497, https://doi.org/10.5194/egusphere-egu25-19497, 2025.
The equatorial Atlantic plays a critical role in regional and global climates, yet the influence of Saharan dust in this region remains underexplored. While Saharan dust’s effects on sea surface temperature variability in the North Tropical Atlantic are well-documented, its impact near the equator, particularly during boreal winter, when dust transport reaches its southernmost extent, has received limited attention. Using observational and reanalysis data, we investigate the effects of Saharan dust on equatorial Atlantic variability. We observe a distinct and complex response contrary to the expected cooling from reduced solar radiation. Dust-induced warming in the lower troposphere drives significant sea surface temperature warming off northwestern Africa through changes in latent heat fluxes and Ekman convergence, leading to an off-equatorial warm front. This warm front generates cross-equatorial winds that shift the Atlantic rain belt northward, cool the equatorial region, and trigger wave activity, ultimately causing delayed warming. This study highlights the need to understand complex dust-climate interactions, identifying Saharan dust as a potential driver of equatorial Atlantic variability with broader climatic implications.
How to cite: Vallès Casanova, I., Adam, O., and Martín Rey, M.: Influence of winter Saharan dust on equatorial Atlantic variability, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20043, https://doi.org/10.5194/egusphere-egu25-20043, 2025.
Previous studies have identified diverse spatial patterns of the Atlantic Niño (AN) linked to different teleconnections. The emergence of these structures coincides with different mean conditions and driving mechanisms. Here, we explore the role of the tropical Atlantic background state in changing the effectiveness of the dynamic mechanisms that generate the AN, and in shaping the distinct AN patterns.
To this aim, we use simulations from five models of the Extratropical-Tropical Interaction Model Intercomparison Project (ETIN-MIP), where changes in the background state are induced by perturbations in incoming solar radiation across three different latitudinal bands.
Our results reveal that modifying the ocean background state could induce the reported changes in the AN pattern through the alteration of ocean wave dynamics and air-sea coupling.
Mean thermocline slope and stratification in the equatorial Atlantic have a pronounced impact on the Bjerknes Feedback (BF), shaping the AN pattern. In particular, a less tilted equatorial mean thermocline (shallower in the west) in spring could strengthen wind-thermocline coupling under strong anomalous interannual westerlies. Additionally, a tilted mean thermocline, shallower in the east and less stratified in June-August, favors the thermocline-SST coupling.
Consequently, the stronger BF produces an eastward AN, with SST anomalies confined to the east of the basin and the coast of Africa. Conversely, when the mean state is less favorable, a weaker BF, combined with less effective wave dynamics, results in a westward AN structure.
How to cite: Montoya-Carramolino, L., Losada, T., and Martín-Rey, M.: Influence of ocean background state in Atlantic Niño diversity, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19250, https://doi.org/10.5194/egusphere-egu25-19250, 2025.
The Atlantic Niño/Niña is a dominant climate variability, exerting substantial climate impacts. Besides interannual variability, the observed Atlantic Niño/Niña also demonstrates robust variations at decadal timescale (decadal ATL). The underlying mechanisms, however, remain unclear. Here, we conduct a 300yr picontrol experiment using CESM that reasonably captures mean climate of the Atlantic cold tongue and decadal ATL. A warming of the Atlantic cold tongue weakens St. Helena anticyclone via triggering atmospheric Rossby wave, which decreases the subtropical cell and suppresses the equatorial upwelling, amplifying the initial warming. Meanwhile, the weakened anticyclone enhances wind speed over the southwestern Atlantic and cools local SST. Such cooling propagates with mean current toward east, driving an eastward propagation of negative wind stress curl anomalies and thus a cooling along thermocline over 5S-12S, with a cross basin time of 6yr. This cooling is further advected with mean current at thermocline to reach the equator, after which it develops following the Bjerknes feedback and shifts the phase of decadal ATL.
How to cite: Yang, Y., Wu, L., Wang, H., Chen, Y., and Yang, C.: On the mechanisms of Atlantic Niño/Niña decadal variability, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4268, https://doi.org/10.5194/egusphere-egu25-4268, 2025.
The eastern equatorial Atlantic hosts a productive marine ecosystem that depends on upward supply of nitrate, the primary limiting nutrient in this region. The annual productivity peak, indicated by elevated surface chlorophyll levels, occurs in the Northern Hemisphere summer, roughly coinciding with strengthened easterly winds. For enhanced productivity in the equatorial Atlantic, nitrate-rich water must rise into the turbulent layer above the Equatorial Undercurrent. Using data from two trans-Atlantic equatorial surveys, along with extended time series from equatorial moorings, we demonstrate how three independent wind-driven processes shape the seasonality of equatorial Atlantic productivity: (1) the nitracline shoals in response to intensifying easterly winds; (2) the depth of the Equatorial Undercurrent core, defined by maximum eastward velocity, is controlled by an annual oscillation of basin-scale standing equatorial waves and (3) mixing intensity in the shear zone above the Equatorial Undercurrent core is governed by local and instantaneous winds. The interplay of these three mechanisms shapes a unique seasonal cycle of nutrient supply and productivity in the equatorial Atlantic, with a productivity minimum in April due to a shallow Equatorial Undercurrent and a productivity maximum in July resulting from a shallow nitracline coupled with enhanced mixing.
How to cite: Brandt, P., Körner, M., Moum, J. N., Roch, M., Subramaniam, A., Czeschel, R., Krahmann, G., Dengler, M., and Kiko, R.: Seasonal productivity of the equatorialAtlantic shaped by distinct wind-drivenprocesses, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-337, https://doi.org/10.5194/egusphere-egu25-337, 2025.
Tropical Atlantic Variability (TAV) exerts a significant influence on the climate of different regions. Understanding these teleconnections and their impacts can improve predictability, particularly in the North Atlantic-European (NAE) region. The Atlantic Niño (ATLN) or Equatorial Mode is known for being the dominant pattern of TAV. This study aims at exploring the atmospheric response to winter ATLN, as it has been much less documented than the summer ATLN. Coupled simulations and atmosphere-only experiments with the CMIP6 version of the climate model EC-EARTH (T255L91) have been performed and analysed to revisit the ATLN-NAE teleconnection and further improve process understanding. The coupled simulation consists in a 250-year long integration, after spin-up, with fixed radiative forcing at present conditions; the atmospheric response is estimated by linear regression onto the winter ATLN index defined by Okumura&Xie. The atmosphere-only experiments comprise two 150-year long integrations keeping again the radiative forcing fixed, a control run with climatological SSTs and a sensitivity run prescribing the observed ATLN with climatology elsewhere; the atmospheric response is evaluated by comparing both experiments. Results show a local Gill-type structure, symmetrically straddling the equator, whose amplitude increases from November-December to January-February. In the extratropics, the upper-tropospheric circulation displays a dipolar structure with cyclonic anomalies at mid-latitudes and anticyclonic anomalies at subpolar latitudes, which is different from the North Atlantic Oscillation (NAO). The associated precipitation anomalies show a robust and approximately-linear signal on the European continent.
How to cite: Gil Reyes, L., García-Serrano, J., and Kucharski, F.: Teleconnection of the winter Atlantic Niño to the North Atlantic-European atmospheric circulation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16700, https://doi.org/10.5194/egusphere-egu25-16700, 2025.
The Atlantic Niño is the primary interannual variability mode in the tropical Atlantic, with far-reaching impacts on global climate. A recent study identified two types of the Atlantic Niño, each with its maximum warming centered in the central and eastern equatorial Atlantic, respectively. Through analysis of observational data and numerical model experiments, we find that the two Atlantic Niño types have distinct climatic impacts on Europe. This is because the central Atlantic Niño is associated with a pronounced increase in precipitation in the western tropical Atlantic, while the positive precipitation anomalies during the eastern type are mainly located in the eastern basin with weaker amplitudes. Consequently, compared to the eastern Atlantic Niño, the extra-tropical atmospheric waves and the associated precipitation and temperature anomalies in Europe during the central type are stronger and shifted westward. Therefore, distinguishing between the two Atlantic Niño types may help improve seasonal climate predictions in Europe.
How to cite: Chen, B., Zhang, L., and Wang, C.: Distinct Impacts of the Central and Eastern Atlantic Niño on the European Climate, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3073, https://doi.org/10.5194/egusphere-egu25-3073, 2025.
Variability of sea surface temperature (SST) in the north tropical Atlantic (NTA) exerts a substantial impact on Atlantic hurricane activity. Referred to as the NTA mode, its positive phase features warm SST anomalies, conducive to increased intensity and frequency of North Atlantic hurricanes. The period 2023-2024 saw two consecutive positive NTA events, featuring a broad warm anomaly pattern in 2024 following the 2023/24 strong El Niño, but a localized SST warm anomaly in the coastal region off northwest Africa in 2023 following a La Niña. Whether there exists inherent diversity in NTA dynamics and impact is unclear. Here we find that the NTA possesses two distinctive flavors: the basin-wide (BNTA) mode and coastal (CNTA) mode. Such diversity is underpinned by an asymmetric response of air-sea heat flux at the SST anomaly centers of the two NTA modes. The BNTA has an overall stronger impact on Atlantic hurricane activity due to its more westward and persistent warm anomaly pattern. Furthermore, since 1990s, the well-known impact from El Niño-Southern Oscillation on the north tropical Atlantic is felt through its influence on the BNTA mode. Our finding highlights the importance of distinguishing and understanding NTA flavors in assessing and predicting their climatic impacts.
How to cite: Liu, Y., McPhaden, M., Cai, W., Zhang, Y., Zhao, J., Nnamchi, H., Lin, X., Li, Z., and Yang, J.-C.: Two flavors of north tropical Atlantic climate variability with distinct impact on Atlantic hurricanes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2963, https://doi.org/10.5194/egusphere-egu25-2963, 2025.
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 1st 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.
