Retroflections in the tropical Atlantic Ocean

The upper ocean circulation is the area of confluence of two major vertical cells: the large-scale overturning Atlantic Meridional Overturning Circulation (AMOC) and the regional relatively shallow Subtropical Cells (STCs). Both meridional cells interact in a complex system of zonal currents driven by fluctuations of the trade winds. The thermocline waters that subduct in the subtropical South Atlantic join the northward AMOC limb in the western boundary North Brazil Current and Undercurrent system (NBC/NBUC). When the NBC crosses the equator the Coriolis force vanishes and it becomes unstable, therefore it retroflects forced by fluctuations in the easterly winds and associated zonal sea surface height (SSH) gradient . These changes are part of coupled ocean-atmosphere variations that cover a wide range of timescales. A total net transport of 20.6 Sv and 1.0 PW are effectively exported equatorward through the NBC/NBUC system as a result transfer pathways between tropical and subtropical gyres in the South Atlantic. Once at the equator, 11.4 Sv of South Atlantic waters retroflect from the NBC into the eastward Equatorial Undercurrent (EUC) at thermocline layer which join 2.8 Sv arriving from the northern hemisphere. The NBC-EUC retroflection takes place at different latitudinal bands between 3 degrees south and 12 degrees north. A boreal fall maximum is only present in the northernmost retroflection coinciding with the seasonal cycle of the North Equatorial Countercurrent (NECC). At interannual scales the EUC reflects a major increase in the contribution from the South Atlantic tropical waters during 2008-2016 as compared with 1997-2007. The NBC-EUC retroflection occurs within an area where changes in SSH anomalies respond to the two main modes of tropical Atlantic variability: the Meridional Mode and Equatorial Mode. During the development of both events the zonal SSH gradient is modified by the activation of the Rosbby wave (RW) reflected mechanism. Consequently, the zonal current system is altered. Concretely, during a positive Meridional Mode NECC, EUC and north South Equatorial Current (nSEC) intensify, or weaken during negative phase. The associated RW-reflected mechanism results to a Kelvin wave (KW) which reverses the equatorial zonal gradients developing an Equatorial Mode-like pattern. The ocean currents response is not than robust compared with the Meridional Mode. Concretely, the EUC displays a non-linear response probably as a result of external forcings and/or the intrinsic diversity of the Equatorial Mode. The diversity of Equatorial Mode has been studied by applying an empirical orthogonal function (EOF) analysis of a sample of 22 time series of warm Equatorial Mode (or Atlantic Niño) events. This technique reveals four different types of spatio-temporal distributions of SST anomalies (SSTA) in the equatorial Atlantic in the period 1982-2019. These four different types are preceded by different local and remote forcings (i.e: ENSO). Moreover, they are associated with different climatic response on areas in the surrounding continents: northeast region in South America and Western Africa.Dos importants sistemes de circulació meridional conflueixen a l'Atlàntic tropical. La circulació meridional de l'Atlàntic (AMOC, per les seves sigles en anglès) i el sistema regional de cèl·lula subtropicals (STCs). Ambdues cèl·lules circulatòries interactuen en un complex sistema de corrents zonals governat pel patró de vents alisis. Les aigües de la termoclina que s'enfonsen als subtròpics per bombament d'Ekman retornen cap a l'equador mentre es troben amb la branca de retorn de la AMOC al marge occidental, concretament al sistema de la corrent Nord del Brasil (NBC/NBUC). Quan la NBC creua l'equador esdevé inestable per l'absència de Coriolis i dona lloc a un sistema de retroflexió forçat per canvis en els gradients zonals d'altura dinàmica del mar (SSH) associat a fluctuacions de vents dominants de l'est. Aquestes oscil·lacions formen part d'un complex sistema acoblat entre la atmosfera i oceà que es presenta a diferents escales temporals. Un transport net de 20.6 Sv i 1.0 PW, com a resultat de la transferència entre el gir tropical i subtropical de l'Atlàntic Sud, arriba a l'equador a través del sistema NBC/NBUC. Un cop a l'equador, la retroflexió de la NBC alimenta amb 11.4 Sv d'aigües de l'Atlàntic Sud a la corrent equatorial situada a la capa de la termoclina (EUC) que es sumen a 2.8 Sv provinents de l'hemisferi nord. El transport de la retroflexió NBC-EUC es troba repartit en diferents bandes latitudinals entre 3 graus sud i 12 nord que presenten diferents patrons estacionals. Les aigües més septentrionals que tomben cap a l'est mostren un màxim a la tardor boreal que coincideix amb la formació de la contracorrent nord-equatorial (NECC). A escala interanual, el transport la EUC mostra un creixent transport entre el període 2008 al 2016 en comparació amb el període 1997-2007 que es manifesta bàsicament en un increment de les aigües de procedència tropical de l'Atlàntic Sud. La retroflexió de la NBC-EUC succeeix en una àrea on canvis en anomalies de SSH responen als dos modes principals de variabilitat climàtica interanual de l'Atlàntic tropical, el Mode Meridional i el Mode Equatorial. Durant el desenvolupament dels dos modes, el gradient zonal de SSH es veu modificat per l'activitat de la reflexió d'ones Rossby (RW) al marge occidental i en conseqüència el sistema de corrents zonal. Concretament, en situacions de Mode Meridional positiu, la NECC, la EUC i la branca nord de la corrent sud-equatorial (nSEC) s'intensifiquen mostrant una resposta contraria durant el mode negatiu. El sistema de reflexió RW es propaga cap a l'est en forma d'ona Kelvin provocant un canvi de signe en el gradient anòmal zonal de la SSH. El resultat és el desenvolupament d'una situació de mode equatorial del mateix signe. Tanmateix, durant el mode equatorial la resposta de les corrents zonals és menys clara, sobretot per la EUC al marge oriental, indicant la presència d'altres forçaments o la diversitat intrínseca del Mode Equatorial. Mitjançant la tècnica d'anàlisi de funcions ortogonals en mapes de temperatures anòmales de la superfície del mar (SSTA) en l'Atlàntic equatorial s'obté diferents tipus de Mode Equatorial positiu, conegut també com Atlàntic Niño. Concretament entre 1982 i 2019 se'n deriven quatre tipus d'Atlàntic Niño. Cada un d'aquests tipus presenta diferents precondicions que intervenen en el seu desenvolupament, com per exemple teleconnexions atmosfèriques provinents de situacions de Niño en el Pacífic. Addicionalment, els diferents tipus d'Atlàntic Niño estan associats a diferents respostes en el règim de precipitacions tant en el marge nord-est d'Amèrica del Sud com a l'Àfrica Occidental.Postprint (published version

Anàlisi de velocitats en boies de deriva - El problema de detectar la presencia de l'àncora de capa

Treball final presental per n'Ignasi Berenguer Vallès Casanova pel Màster en Canvi Ambiental: Anàlisi i Gestió de la Universitat de Girona (UdG), realitzat sota la direcció del Dr. José Luís Pelegrí Llopart de l'Institut de Ciències del Mar (ICM-CSIC) i de la Dra. Maria Elena Roget Armengol de la Universitat de Girona (UdG).-- 51 pages[EN] Satellite tracked drifting buoys are a useful lagrangian method of studying ocean surface currents and gaining a better understanding of ocean and climate dynamics. Drifting buoys usually have drogues at 15m depth in order to minimize direct wind force. Recent studies detected anomalous trends in data pertaining to the Global Drifter Program suggesting the presence of undrogued buoys in the drifter database even though the buoys were previously believed to be drogued with submergence or tether sensor. Recently, some methods have been developed to detect drogue loss by analysing the correlation between drifter velocities and wind force using altimetry data. However, the results are not useful for weak wind regions such as subtropical gyres. This study proposes a method of analysing drifter velocity time series so as to detect possible drogue loss events in buoys deployed in the North Atlantic Subtropical Gyre zone during the SPURS campaign in 2013 without using any other external data. The results show a potential methodology to keep working with and an interesting way of describing ocean surface dynamics[CAT] Les boies de deriva posicionades per satèl·lit són un mètode lagrangià útil per caracteritzar corrents oceàniques superficials i avançar en la comprensió de la dinàmica del clima i l’oceà. Les boies de deriva normalment tenen una àncora de capa a una profunditat de 15 m per minimitzar l’efecte directe del vent. Estudis recents han detectat que el conjunt de dades proporcionades per el Global Drifter Program contenen error acumulat fruït de boies que han estat erròniament classificades amb presència d’àncora, tot i l’ús d’un sensor de tensió. Recentment s’han desenvolupat metodologies per detectar la pèrdua d’àncora de capa que es basen en un anàlisi de correlació entre les velocitats de les boies i el vent en superfície utilitzant dades altimètriques. Tot i així, els resultats no són útils per zones de vents dèbils com el girs subtropicals. Aquest treball presenta una metodologia basada en l’anàlisi de les sèries de temps de velocitat de les boies per detectar la pèrdua d’àncora de capa en boies llançades el Gir Subtropical Nord Atlàntic durant la campanya SPURS del 2013 sense utilitzar altres fonts de dades. Els resultats mostren el potencial de la metodologia que es presenta per seguir treballant i una manera interessant de descriure la dinàmica superficial de l’oceàPeer Reviewe

Adapting the existing coastal patí a vela fleet for scientic purposes

This paper presents the first results of the Barcelona Institute of Culture’s grant for research and innovation projects under the 2019 Barcelona Science Plan entitled “Development of a citizen monitoring program for the Barcelona waters: The Scientific Pat´i a Vela”. The main objective of this project is to develop a small Pat´i a Vela (PV) fleet that can routinely sample the Barcelona coastal waters and report their observations to an open-access interactive web. The Pat´i a Vela boat was designed in 1942 by the Mong´e brothers. It is a lightweight one- person catamaran with a single Marconi sail and no boom. The main objective of this contribution is to adapt the Pat´i a Vela model attaching an on-board platform with scientific instruments (sensors and devices) and determine the new stability characteristics and seakeeping performance. This will allow an adequate sampling of the Barcelona coast waters and the systematic measurements of the essential physical and biogeochemical variables detecting variations along the coast, hence identifying potential sources of contamination. It will also provide the necessary knowledge of natural and anthropogenic seasonality.Postprint (published version

Water Mass Transports and Pathways in the North Brazil- Equatorial Undercurrent Retroflection

The equatorial retroflection of the North Brazil Current (NBC) into the Equatorial Undercurrent (EUC) and its posterior tropical recirculation is a major regulator for the returning limb of the Atlantic Meridional Overturning Circulation. Indeed, most surface and thermocline NBC waters retroflect at the equator all the way into the central and eastern Atlantic Ocean, before they recirculate back through the tropics to the western boundary. Here, we use cruise data in the western equatorial Atlantic during April 2010 and reanalysis time series for the equatorial and tropical waters in both hemispheres in order to explore the recirculation pathways and transport variability. During the 1998–2016 period, the annual-mean EUC transports 15.1 ± 1.3 Sv at 32°W, with 2.8 ± 0.4 Sv from the North Atlantic and 11.4 ± 1.3 Sv from the South Atlantic. At 32°W most of the total EUC transport comes from the western boundary retroflection south of 3°N (7.2 ± 0.9 Sv), a substantial fraction retroflects north of 3°N (5.6 ± 0.4 Sv), and the remaining flow (2.3 Sv) joins through the interior basin. The South Atlantic subtropical waters feed the EUC at all thermocline depths while the North Atlantic and South Atlantic tropical waters do so at the surface and upper-thermocline levels. The EUC transport at 32°W has a pronounced seasonality, with spring and fall maxima and a range of 8.8 Sv. The 18 yr of reanalysis data shows a weak yet significant correlation with an Atlantic Niño index, and also suggests an enhanced contribution from the South Atlantic tropical waters during 2008–2016 as compared with 1997–2007En prensa3,17

Development of a citizen monitoring program for the Barcelona coastal waters: The Scientific Patí Vela (Patí Científic)

Special issue 9th MARTECH: International Workshop on Marine Technology: 16-18 June 2021, Vigo, Spain.-- 2 pages, 2 figuresThe first results of the PATI CIENTIFIC project are presented. This is a collaborative project funded by a Barcelona Institute of Culture’s grant for research and innovation under the 2019 Barcelona Science Plan. The main objective of this project is to develop a monitoring program for the coastal waters of Barcelona through a small-sailboat feet of the traditional and sustainable Patí de Vela (sailing skate). This pleasure boat is to become a scientifc sailing skate. This feet will acquire the essential oceanographic variables along the Catalan coast, which will be incorporated and accessible in a web platform. We present the initial adaptations done to the Patí de Vela to have an onboard platform holding the scientifc instruments (sensors and devices) for sampling the Barcelona coastal waters. These adaptations allow the systematic measurements of the essential physical and biogeochemical variables. These data, which will allow detecting variations along the coast, hence identifying potential sources of contamination and also providing the necessary knowledge of natural and anthropogenic seasonality, and will be freely available on a web platform. The PATI CIENTIFIC project will increase our knowledge of the coastal waters of the Barcelona coast, encouraging participation in sea monitoring activities and increasing social awareness on the need to love and protect our oceansThe work of Raul Bardaji is supported by the CSIC Intramural Project EMSO – Laboratorios Submarinos Profundos. The work of Carlos Rodero is supported by the H2020 Project MONOCLE (grant agreement No 776480

Development of a citizen monitoring program for the Barcelona coastal waters: the Scientific Patí Vela

The first results of the PATI CIENTIFIC project are presented. This is a collaborative project funded by a Barcelona Institute of Culture’s grant for research and innovation under the 2019 Barcelona Science Plan. The main objective of this project is to develop a monitoring program for the coastal waters of Barcelona through a small -sailboat fleet of the traditional and sustainable Patí de Vela (sailing skate). This pleasure boat is to become a scientific sailing skate. This fleet will acquire the essential oceanographic variables along the Catalan coast, which will be incorporated and accessible in a web platform. We present the initial adaptations done to the Patí de Vela to have an onboard platform holding the scientific instruments (sensors and devices) for sampling the Barcelona coastal waters. These adaptations allow the systematic measurements of the essential physical and biogeochemical variables. These data, which will allow detecting variations along the coast, hence identifying potential sources of contamination and also providing the necessary knowledge of natural and anthropogenic seasonality, and will be freely available on a web platform. The PATI CIENTIFIC project will increase our knowledge of the coastal waters of the Barcelona coast, encouraging participation in sea monitoring activities and increasing social awareness on the need to love and protect our oceans.Postprint (published version

Development of a citizen monitoring program for the Barcelona coastal waters: the Scientific Patí Vela (PATI CIENTIFIC)

The first results of the PATI CIENTIFIC project are presented. This is a collaborative project funded by a Barcelona Institute of Culture’s grant for research and innovation under the 2019 Barcelona Science Plan. The main objective of this project is to develop a monitoring program for the coastal waters of Barcelona through a small-sailboat feet of the traditional and sustainable Patí de Vela (sailing skate). This pleasure boat is to become a scientifc sailing skate. This feet will acquire the essential oceanographic variables along the Catalan coast, which will be incorporated and accessible in a web platform. We present the initial adaptations done to the Patí de Vela to have an onboard platform holding the scientifc instruments (sensors and devices) for sampling the Barcelona coastal waters. These adaptations allow the systematic measurements of the essential physical and biogeochemical variables. These data, which will allow detecting variations along the coast, hence identifying potential sources of contamination and also providing the necessary knowledge of natural and anthropogenic seasonality, and will be freely available on a web platform. The PATI CIENTIFIC project will increase our knowledge of the coastal waters of the Barcelona coast, encouraging participation in sea monitoring activities and increasing social awareness on the need to love and protect our oceans.Peer ReviewedObjectius de Desenvolupament Sostenible::14 - Vida Submarin

Dataset on the RETRO-BMC cruise onboard the R/V Hespérides, April 2017, Brazil-Malvinas Confluence

This dataset, gathered during the RETRO-BMC cruise, reports multiple-scale measurements at the Confluence of the Brazil and Malvinas Currents. The cruise was carried out between 8 and 28 April 2017 onboard R/V Hespérides, departing from Ushuaia and arriving to Santos. Along its track, the vessel recorded near-surface temperature and salinity, as well as the horizontal flow from 20 m down to about 800 m. A total of 33 hydrographic stations were completed in a region off the Patagonian Shelf, within 41.2°S-35.9°S and out to 53.0°W. At each station, a multiparametric probe and velocity sensors were deployed inside the frame of a rosette used to collect water samples at selected depths; these samples were later used for several water analyses, including inorganic nutrient concentrations. Microstructure measurements were carried out in 11 of these hydrographic stations. In addition, two high-resolution three-dimensional surveys were conducted with an instrumented undulating vehicle between 40.6°S-39.0°S and 55.6°W-53.8°W. Lastly, eight high-frequency vertical profilers were deployed in the region and five position-transmitting drifters were launched. These data allow the description of the Confluence from the regional scale to the microscale, and provide a view of the variability of the frontal region on time scales from days to weeks

Barcelona Coastal Monitoring with the “Patí a Vela”, a Traditional Sailboat Turned into an Oceanographic Platform

Special issue Technological Oceanography.-- 16 pages, 12 figures, 3 tables.-- Data supporting reported results can be found at https://paticientific.org/index.php/dades/ (accessed on 13 April 2022) and through https://zenodo.org/search (accessed on 13 April 2022) by searching “pati cientific”.Shelf waters near large cities, such as Barcelona, are affected not only by meteorological episodes but also by anthropogenic influence. Scientists usually use data from on-site coastal platforms to analyze and understand these complex water ecosystems because remote sensing satellites have low spatiotemporal resolution and do not provide reliable data so close to the coast. However, platforms with conventional oceanographic instrumentation are expensive to install and maintain. This study presents the scientific adaptation and initial measurements from a “patí a vela”, which is a very popular unipersonal catamaran in Barcelona. This versatile sailing vessel has been adapted to contain several low-cost sensors and instruments to measure water properties. Here, we describe the setup of a multi-parameter prototype, and then focus on results obtained using a low-cost temperature profiler. First, the temperature data are compared and validated with another conventional oceanographic instrument used in monthly oceanographic cruises. Then, field measurements between July and November 2021 are used to explore the relationship between air and water temperature in the Barcelona coastal area, showing the seasonal evolution of the temperature profile. We conclude that citizen sampling from fully sustainable sailing boats may turn into an effective strategy to monitor the urban coastal watersThis work has been carried out within the framework of the 2019 Barcelona Pla de Ciència, with funding from the Barcelona City Council through the project “Development of a citizen monitoring program for the Barcelona coastal waters: the Scientific Patí Vela” (PATI CIENTIFIC; references 19SO1645-006, 19SO1649-006, 19SO1651-006). [...] The ICM authors also recognize the institutional support of the Spanish Government through the Severo Ochoa Center of Excellence accreditation (CEX2019-000928-S)Peer reviewe

A view of the Brazil-Malvinas confluence, March 2015

The encountering of the subtropical Brazil Current (BC) and the subantarctic Malvinas Current (MC) along the western margin of the Argentine Basin forms the Brazil-Malvinas Confluence (BMC), one of the most intense open-ocean fronts in the world ocean and a site for the formation of intermediate water masses. Here, we provide a comprehensive description of the BMC based on physical and biogeochemical data – hydrographic stations, profiling floats and subsurface drifters – gathered in March 2015. We use these data in order to characterize the impinging and outflowing currents and to describe the cross- and along-frontal thermohaline structure. In addition, we compare the in-situ measurements with both climatological data and the Mercator Ocean eddy-resolving reanalysis. The hydrographic sections illustrate the contrasting properties between the two western boundary currents: warm, salty, nutrient- and oxygen-poor oligotrophic subtropical waters carried southward by the BC and the cold, fresh, oxygen- and nutrient-rich subantarctic waters carried northward by the MC. The frontal system is also characterized by the presence of thermohaline intrusions, with the cross-frontal gradients and along-front velocities sharpening as the colliding currents shape the frontal system. We also observe brackish waters spreading on top of the frontal jet as a result of both the confluence dynamics and off-shelf advection favored by north-easterly winds. These low-salinity waters are positively correlated with surface ageostrophic speeds over the frontal jet. The cruise data illustrates the high regional and mesoscale variability as compared with climatological conditions, and further document the submesoscale subsurface complexity, which is not properly captured by available operational models.Fil: Orúe Echevarría, Dorleta. Consejo Superior de Investigaciones Científicas. Instituto de Ciencias del Mar; EspañaFil: Pelegrí, Josep L.. Consejo Superior de Investigaciones Científicas. Instituto de Ciencias del Mar; EspañaFil: Alonso González, Iván J.. Oceomic, Marine Bio And Technology S.L; EspañaFil: Benítez Barrios, Verónica M.. Oceomic, Marine Bio And Technology S.L; EspañaFil: Emelianov, Mikhail. Consejo Superior de Investigaciones Científicas. Instituto de Ciencias del Mar; EspañaFil: García Olivares, Antonio. Consejo Superior de Investigaciones Científicas. Instituto de Ciencias del Mar; EspañaFil: Gasser i Rubinat, Marc. Consejo Superior de Investigaciones Científicas. Instituto de Ciencias del Mar; EspañaFil: De La Fuente, Patricia. Consejo Superior de Investigaciones Científicas. Instituto de Ciencias del Mar; EspañaFil: Herrero, Carmen. Consejo Superior de Investigaciones Científicas. Instituto de Ciencias del Mar; EspañaFil: Isern Fontanet, Jordi. Consejo Superior de Investigaciones Científicas. Instituto de Ciencias del Mar; EspañaFil: Masdeu Navarro, Marta. Consejo Superior de Investigaciones Científicas. Instituto de Ciencias del Mar; EspañaFil: Peña Izquierdo, Jesús. Consejo Superior de Investigaciones Científicas. Instituto de Ciencias del Mar; EspañaFil: Piola, Alberto Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; ArgentinaFil: Ramírez Garrido, Sergio. Consejo Superior de Investigaciones Científicas. Instituto de Ciencias del Mar; EspañaFil: Rosell Fieschi, Miquel. Consejo Superior de Investigaciones Científicas. Instituto de Ciencias del Mar; EspañaFil: Salvador, Joaquín. Consejo Superior de Investigaciones Científicas. Instituto de Ciencias del Mar; EspañaFil: Saraceno, Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Universidad de Barcelona; EspañaFil: Valla, Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; ArgentinaFil: Vallès Casanova, Ignasi. Consejo Superior de Investigaciones Científicas. Instituto de Ciencias del Mar; EspañaFil: Vidal, Montserrat. Universidad de Barcelona; Españ