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  • 1
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    Dissolved Organic Matter Fluorescence as a Tracer of Upwelling and Microbial Activities in Two Cyclonic Eddies in the Eastern Tropical North Atlantic (2023)
    Details
    Publication Date: 2024-01-24
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Mesoscale eddies are frequently observed in the Eastern Tropical North Atlantic (ETNA), yet their effects on the transport and distribution of biogeochemical solutes, and specifically on the production and remineralization of dissolved organic matter (DOM) remain difficult to elucidate. Here, we investigated the submesoscale variability of chromophoric DOM (CDOM) and fluorescent DOM (FDOM) together with microbial production and remineralization processes in two cyclonic eddies (CEs) in the ETNA during summer and winter 2019. One CE, formed near the coast off Mauritania during the post‐upwelling season, was sampled along a ∼900 km zonal corridor between Mauritania and the Cape Verde Islands. The other CE, formed nearby Brava Island, was out of coastal influence. Four fluorescent components were identified with parallel factor analysis, two humic‐like, and two protein‐like components. Humic‐like FDOM components correlated to optode‐based community respiration and were also good indicators of upwelling associated with the Brava Island CE as they correlated to physical parameters (e.g., temperature) and to dissolved inorganic nitrogen. The tryptophan‐like FDOM components correlated with the carbon and nitrogen content of semi‐labile DOM, phytoplankton biomass, community respiration, and bacterial production. Overall, our study revealed that DOM optical properties are suitable for tracing freshly produced organic matter and the transport of remineralized DOM within offshore eddies.〈/p〉
    Description: Plain Language Summary: Mesoscale eddies are ubiquitous circulation features in the ocean with horizontal scales on the order of 100 km and lifetimes of days to months. Their swirling motion can cause nutrients from deeper waters to be transported to the surface, stimulating phytoplankton biomass and resulting in the production of dissolved organic matter. However, these effects are difficult to quantify and proxies (biomarkers) are needed to monitor the impact of eddies at high resolution. In this work, we used the optical properties of the dissolved organic matter, especially the fraction capable of fluorescence (FDOM) as biomarker in two cyclonic eddies, one formed in an eastern boundary upwelling system and one formed offshore by winds/Island interaction. We identified four FDOM components, among which an indicator of cyclonic eddy productivity and two indicators of dissolved organic matter recycling, which also tracked nutrient transport in the offshore cyclonic eddy. Our study highlights that continuous FDOM data obtained with sensors could help to follow eddy development and influence on seawater biogeochemistry.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉Four fluorescent dissolved organic matter (FDOM) components were studied in two cyclonic eddies (CEs) in the Eastern Tropical North Atlantic〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Tryptophan‐like FDOM was an indicator of the CEs' productivity as it correlated with semi‐labile dissolved organic matter and microbial metabolic activities〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Humic‐like FDOM was a by‐product of microbial respiration; its distribution within an offshore CE covaried with nutrient upwelling〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Keywords: ddc:https://doi.pangaea.de/10.1594/PANGAEA.959742 ; ddc:https://doi.org/10.1594/PANGAEA.950510 ; ddc:577.7 ; PARAFAC ; Atlantic Ocean ; Mauritanian upwelling system ; mesoscale eddies ; fluorescence dissolved organic matter (FDOM) ; DOC
    Language: English
    Type: doc-type:article
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    CITATION GEO-LEO
  • 2
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    Temperature, salinity and oxygen measured on CTD water bottle samples and apparent oxygen utilization and relative precentage of South Atlantic Central Water (SACW) during METEOR cruise M160 (2023)
    PANGAEA
    Details
    Publication Date: 2024-02-02
    Description: Temperature, salinity, and oxygen were obtained from a Seabird 911 plus CTD system equipped with two independently working sets of temperature–conductivity–oxygen. The apparent oxygen utilization was calculated as the difference between saturation concentrations of O2 and measured O2 concentrations: AOU= [O2sat (θ, S)] − [O2], with S = salinity and θ = potential temperature (Redfield, 1942; Redfield et al., 1963; Pytkowicz, 1971). The saturated oxygen (O2sat) was computed using measured temperature and salinity following 212 Garcia and Gordon (1992). Relative percentage of South Atlantic Central Water was determined as in Klenz et al., (2018).
    Keywords: apparent oxygen utilization; Cast number; CTD; CTD/Rosette; CTD-RO; Date/time end; Date/time start; DEPTH, water; Event label; LATITUDE; LONGITUDE; M160; M160_106-1; M160_132-1; M160_134-1; M160_136-1; M160_141-1; M160_149-1; M160_165-1; M160_168-1; M160_17-1; M160_175-1; M160_180-1; M160_184-1; M160_188-1; M160_194-1; M160_200-1; M160_21-1; M160_38-1; M160_40-1; M160_43-1; M160_63-1; M160_65-1; M160_67-1; M160_69-1; M160_73-1; M160_75-1; M160_84-1; M160_88-1; M160_94-1; M160_96-1; M160_98-1; Meteor (1986); Oxygen; Oxygen, apparent utilization; REEBUS; Role of Eddies for the Carbon Pump in Coastal upwelling Areas; SACW; Salinity; Sample ID; South Atlantic Ocean; Station label; Temperature; Temperature, water; Water mass
    Type: Dataset
    Format: text/tab-separated-values, 1620 data points
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    DATA PANGAEA
  • 3
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    Apparent oxygen utilization and relative percentage of South Atlantic Central Water (SACW) during METEOR cruise M156 (2023)
    PANGAEA
    Details
    Publication Date: 2024-02-02
    Description: This dataset includes calculated data over the epi-mesopelagic layer (0-800 m depth) of 26 stations with 14 of them inside or in the vicinity of a cyclonic eddy that formed off Mauritania along the ∼ 900 km zonal corridor between Mauritania and the Cabo Verde islands in the eastern Tropical North Atlantic during the M156 cruise on the RV Meteor from July 3rd to August 1st 2019. The apparent oxygen utilization was calculated as the difference between saturation concentrations of O2 and measured O2 concentrations: AOU= [O2sat ({*}{*}θ{*}{*}, S)] − [O2], with S = salinity and θ = potential temperature (Redfield, 1942; Redfield et al., 1963; Pytkowicz, 1971). The saturated oxygen (O2sat) was computed using measured temperature and salinity following 212 Garcia and Gordon (1992). Relative percentage of South Atlantic Central Water was determined as in Klenz et al., (2018).
    Keywords: apparent oxygen utilization; CTD/Rosette; CTD-RO; DATE/TIME; DEPTH, water; Event label; LATITUDE; LONGITUDE; M156; M156_107-1; M156_113-1; M156_125-1; M156_130-1; M156_13-1; M156_135-1; M156_138-1; M156_143-1; M156_151-1; M156_155-1; M156_158-1; M156_21-1; M156_26-1; M156_3-1; M156_43-1; M156_50-1; M156_58-1; M156_59-1; M156_66-1; M156_70-1; M156_7-1; M156_79-1; M156_87-1; M156_91-1; M156_98-1; Meteor (1986); Oxygen, apparent utilization; REEBUS; Role of Eddies for the Carbon Pump in Coastal upwelling Areas; SACW; South Atlantic Ocean; Station label; Water mass
    Type: Dataset
    Format: text/tab-separated-values, 513 data points
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    DATA PANGAEA
  • 4
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    A Model Investigation of the Influences of the South‐East Madagascar Current on the South‐East Madagascar Bloom (2020)
    AGU (American Geophysical Union)
    Details
    Publication Date: 2023-02-08
    Description: The South-East Madagascar Bloom, one of the most compelling biogeochemical features of the Indian Ocean, occurs sporadically during austral summer in the oligotrophic waters south-east of Madagascar, where it can cover up to 1% of the global ocean surface area. Its spatial extension and its timing are highly variable. A high-resolution biophysical model is used to investigate a previous hypothesis that the onset of a particular circulation of the South-East Madagascar Current advects fresher and nutrient-rich waters eastward, feeding the bloom. The model is able to reproduce an intermittent phytoplankton bloom with large spatial variability but in the subsurface layers, as well as the presence of an irregular retroflection of the South-East Madagascar Current. The simulated bloom occurs within a shallow stratified mixed layer, with fresher waters at the surface, parallel to the water mass in an observed bloom. The model results suggest, from a nutrient flux analysis, that horizontal advection of low-salinity nutrient-rich Madagascan coastal waters can indeed trigger a phytoplankton bloom. The coupled model is also able to resolve a bloom that is atmospherically forced by cyclonic activity.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Eddies in the Canary eastern boundary upwelling system (2022)
    Details
    Publication Date: 2022-10-17
    Type: Conference or Workshop Item , NonPeerReviewed
    Format: text
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    OceanRep: Talk
  • 6
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    Spreading of Lagrangian Particles in the Black Sea: A Comparison between Drifters and a High-Resolution Ocean Model (2021)
    MDPI
    Details
    Publication Date: 2024-02-07
    Description: The Lagrangian dispersion statistics of the Black Sea are estimated using satellite-tracked drifters, satellite altimeter data and a high-resolution ocean model. Comparison between the in-situ measurements and the model reveals good agreement in terms of the surface dispersion. The mean sub-basin coherent structures and currents of the Black Sea are well reproduced by the model. Seasonal variability of the dispersion in the upper (15 m), intermediate (150 m) and deep (750 m) layers are discussed with a special focus of the role of sub-basin scale structures and currents on the turbulent dispersion regimes. In terms of the surface relative dispersion, the results show the presence of the three known turbulent exponential, Richardson and diffusive-like regimes. The non-local exponential regime is only detected by the model for scales 〈10 km, while the local Richardson regime occurs between 10 and 100 km in all cases due to the presence of an inverse energy cascade range, and the diffusive-like regime is well detected for the largest distance by drifters (100–300 km) in winter/spring. Regarding the surface absolute dispersion, it reflects the occurrence of both quasi-ballistic and random-walk regimes at small and large times, respectively, while the two anomalous hyperbolic (5/4) and elliptic (5/3) regimes, which are related to the topology of the Black Sea, are detected at intermediate times. At depth, the signatures of the relative and absolute dispersion regimes shown in the surface layer are still valid in most cases. The absolute dispersion is anisotropic; the zonal component grows faster than the meridional component in any scenario.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    Generation mechanisms of mesoscale eddies in the Mauritanian Upwelling Region (2022)
    AMS (American Meteorological Society)
    Details
    Publication Date: 2024-02-07
    Description: The physical processes driving the genesis of surface- and subsurface-intensified cyclonic and anticyclonic eddies originating from the coastal current system of the Mauritanian Upwelling Region are investigated using a high-resolution (~1.5 km) configuration of GFDL’s Modular Ocean Model. Estimating an energy budget for the boundary current reveals a baroclinically unstable state during its intensification phase in boreal summer and which is driving eddy generation within the near-coastal region. The mean poleward coastal flow’s interaction with the sloping topography induces enhanced anticyclonic vorticity, with potential vorticity close to zero generated in the bottom boundary layer. Flow separation at sharp topographic bends intensifies the anticyclonic vorticity, and submesoscale structures of low PV coalesce to form anticyclonic vortices. A combination of offshore Ekman transport and horizontal advection determined the amount of SACW in an anticyclonic eddy. A vortex with a relatively dense and low PV core will form an anticyclonic mode-water eddy, which will subduct along isopycnals while propagating offshore and hence be shielded from surface buoyancy forcing. Less contribution of dense SACW promotes the generation of surface anticyclonic eddies as the core is composed of a lighter water mass, which causes the eddy to stay closer to the surface and hence be exposed to surface buoyancy forcing. Simulated cyclonic eddies are formed between the rotational flow of an offshore anticyclonic vortex and a poleward flowing boundary current, with eddy potential energy being the dominant source of eddy kinetic energy. All three types of eddies play a key role in the exchange between the Mauritanian Coastal currents system and the adjacent eastern boundary shadow zone region.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    Dissolved Organic Matter Fluorescence as a Tracer of Upwelling and Microbial Activities in Two Cyclonic Eddies in the Eastern Tropical North Atlantic (2023)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2024-02-07
    Description: Mesoscale eddies are frequently observed in the Eastern Tropical North Atlantic (ETNA), yet their effects on the transport and distribution of biogeochemical solutes, and specifically on the production and remineralization of dissolved organic matter (DOM) remain difficult to elucidate. Here, we investigated the submesoscale variability of chromophoric DOM (CDOM) and fluorescent DOM (FDOM) together with microbial production and remineralization processes in two cyclonic eddies (CEs) in the ETNA during summer and winter 2019. One CE, formed near the coast off Mauritania during the post-upwelling season, was sampled along a ∼900 km zonal corridor between Mauritania and the Cape Verde Islands. The other CE, formed nearby Brava Island, was out of coastal influence. Four fluorescent components were identified with parallel factor analysis, two humic-like, and two protein-like components. Humic-like FDOM components correlated to optode-based community respiration and were also good indicators of upwelling associated with the Brava Island CE as they correlated to physical parameters (e.g., temperature) and to dissolved inorganic nitrogen. The tryptophan-like FDOM components correlated with the carbon and nitrogen content of semi-labile DOM, phytoplankton biomass, community respiration, and bacterial production. Overall, our study revealed that DOM optical properties are suitable for tracing freshly produced organic matter and the transport of remineralized DOM within offshore eddies. Key Points: - Four fluorescent dissolved organic matter (FDOM) components were studied in two cyclonic eddies (CEs) in the Eastern Tropical North Atlantic - Tryptophan-like FDOM was an indicator of the CEs' productivity as it correlated with semi-labile dissolved organic matter and microbial metabolic activities - Humic-like FDOM was a by-product of microbial respiration; its distribution within an offshore CE covaried with nutrient upwelling
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Format: text
    Location Call Number Limitation Availability
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 9
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    Where and How the East Madagascar Current Retroflection Originates? (2021)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2024-02-07
    Description: The East Madagascar Current (EMC) is one of the western boundary currents of the South Indian Ocean. As such, it plays an important role in the climate system by transporting water and heat toward the pole and recirculating to the large-scale Indian Ocean through retroflection modes of its southern extension. Five cruise data sets and remote sensing data from different sensors are used to identify three states of the southern extension of the EMC: early retroflection, canonical retroflection, and no retroflection. Retroflections occur 47% of the time. EMC strength regulates the retroflection state, although impinged mesoscale eddies also contribute to retroflection formation. Early retroflection is linked with EMC volume transport. Anticyclonic eddies drifting from the central Indian Ocean to the coast favor early retroflection formation, anticyclonic eddies near the southern tip of Madagascar promote the generation of canonical retroflection, and no retroflection appears to be associated with a lower eddy kinetic energy (EKE). Knowledge of the EMC retroflection state could help predict (a) coastal upwelling south of Madagascar, (b) the southeastern Madagascar phytoplankton bloom, and (c) the formation of the South Indian Ocean Counter Current (SICC).
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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