|Author(s) and Affiliation(s)
|Trophic position and benthic-pelagic coupling changes along the depth gradient of habitats used by the Lane snapper, Lutjanus synagris in a tropical protected seascape
|Author(s): Rodrigo Ferreira Bastos,1,2, Gilvan Takeshi Yogui,1,3 Thierry Frédou4, Flavia Frédou4, Fréderic Ménard5, François Le Loc’h6, Alexandre Miranda Garcia7, Mauro Maida1,2, Sergio Rezende8, Jay R. Rooker9 and Beatrice Padovani Ferreira1,2.
1 Post Graduate Program on Oceanography (PPGO), Oceanography Department (DOCEAN), Center of Technology and Geosciences (CTG), Federal University of Pernambuco (UFPE).
2 Reef and Ocean Ecosystem Studies Laboratory (LECOR).
3 Organic Compounds in Coastal and Marine Ecosystems Laboratory (OrganoMAR).
4 Laboratory for Studies of Anthropic Impacts on Marine and Estuarine Biodiversity, BIOIMPACT, Department of Fisheries and Aquaculture, Federal Rural University of Pernambuco (UFRPE)
5 IRD – MIO Marseille
6 IRD – UMR LEMAR
7 Oceanography Institute, Rio Grande Federal University (FURG).
8 CEPENE ICMBio
9 Texas A&M Galveston
|It is known that one of the most important factors regulating Benthic-pelagic coupling of food webs is depth. Here we investigated how the Lane snaper, Lutjanus synagris, changes its trophic positions and connects its benthic habitats with pelagic ones, from coastal shallow seagrass, mangroves and coral reefs, through shallow and mesophotic continental shelf, used along its ontogeny in a Northeast Brazilian Marine complex of MPAs.
We hypothesized that (1) trophic positions will increase with depth because fish size distributions increases, (2) coastal habitats are benthic-pelagic coupled because its short distance, (3) shallow shelf are more benthic supported because benthic production is high while (4) mesophotic conditions will increase benthic-pelagic coupling. Stable isotopes (C, N) from this demersal fish and also benthic and pelagic primary consumers from each site were used to investigate and modeling the TP’s and trophic support. TP’s increased from coastal to continental shelf sites as well as the fish size distributions.
However, fish TP’s did not show differences between shallow and mesophotic sections neither between sub-adults and adults. Mixing models revealed that for seagrass, costal reefs and mesophotic shelf sites fishes were benthic and pelagic supported while for mangrove and shallow shelf individuals benthic support prevail. Along continental shelf, pelagic support was positively related to depth while decreased with fish size.
It’s known that pelagic food webs are longer than benthic ones. Possibly for this reason fish trophic positions were not different between sub-adults and adults. Also, as small Lane snapers fishes were more related to pelagic sources, they are important benthic-pelagic couplers along all habitats. The Pelagic support increases with depth could be fueled by physical process occurring at this shelf break, such as the uplift of deep rich oceanic waters.
The results showed how physical and biological processes can operate over a large spatial area for a single species along the marine seascape, highlighting the importance of maintenance of spatial connectivity for marine protected areas.
|Preliminary study of phytoplankton biomass and pigment composition on Amazon Continental Shelf
|Angelica Viana e Silva (1); Sandrine Hillion (2); Gabriel Bittencourt Farias (1); Claire Carré (3); Arnaud Bertrand (3); Ariane Koch-Larrouy (4); Pedro Augusto Mendes de Castro melo (1)
Departamento de Oceanografia, Universidade Federal de Pernambuco (1); IRD – Instrumentation, Moyens analytiques, Observatoires en Géophysique et Océanographie (2); MARBEC, Univ Montpellier, IRD, Ifremer CNRS (3); IRD – Laboratory for Studies
|The Amazon River has the world largest hydrographic basin being responsible for 20% of all fresh water in the global ocean and forming a plume that transports a high amount of sediments, organic matter and nutrients to the continental shelf (ACS) and adjacent ocean, increasing its productivity. In addition, the plume influences the structure of biological communities due to its role in the stratification of the upper ocean. Among these communities, we highlight the phytoplankton, which is responsible for half of the global primary production.
Several phytoplankton studies have been carried out in ACS, however, still lacks studies considering the contribution of phytoplankton size classes in terms of biomass. The use of HPLC to study phytoplankton allow the quantification of biomass and relative contribution of different taxonomic groups, through quantification of chlorophyll-a and accessory pigments. During the AMAZOMIX project, we determined the biomass and size relative contribution of main groups in 33 stations of the ACS and adjacent oceanic region.
Here, we bring preliminary data of the coast-offshore and vertical variation of the total biomass (chlorophyll-a). The biomass ranged from 0.003 mg.m-3 to 0.207 mg.m-3 on the continental shelf (average of 0.066 mg.m-3), while in oceanic region from 0.002 to 0.470 mg.m-3 (average of 0.073 mg.m-3), although no significant differences were observed between areas (M-W;p = 0.748). Vertically, the biomass was higher in the DCM (M-W;p = <0.001), with mean values of 0.127 mg.m-3 (from 0.016 mg.m-3 to 0.470 mg.m-3), while on the surface the average was 0.039 mg.m-3 (from 0.009 to 0.078 mg.m-3). Despite the absence of a coast-offshore gradient for the total biomass, possibly indicating an effect of the plume beyond the ACS, the next steps of the present research will allow to evaluate the influence of this gradient on the composition and community structure, as well as to relate the biological results with physicochemical data in the area.
|Mesopelagic ichthyoplankton species distribution and composition in the Southwest Atlantic Ocean
|Veronica F. Costa & Jose H. Muelbert
Postgraduate Program in Oceanology (PPGO), Institute of Oceanography (IO), Federal University of Rio Grande (FURG), Brazil
|The Mesopelagic is an important habitat for fish, with Myctophidae being the most abundant and relevant family, contributing to the trophic web and as a fishing resource for human consumption.
This study aims to evaluate the influence of meanders and eddies on the composition, abundance, and spatial and temporal distribution of Myctophidae larvae throughout the Southwestern Subtropical Atlantic Ocean. For this, 40 years of data were investigated, sampled by 12 oceanographic cruises at 203 stations between 1970 and 2011 in the Southern and Southeastern Continental Shelves of Brazil. Ichthyoplankton was collected with plankton nets, the mesh size and area ranging from 140-500 µm and 0.20-0.75 m², respectively. Larvae were identified at the lowest taxonomic level. For meanders and eddies evaluation, 3 periods were selected (i.e. 2007, 2010, and 2011). Temperature, salinity, and depth were measured in situ to identify vertical profiles and eddies structures throughout the water column. Meanders and eddies were also identified by satellite imagery, using Sea Surface Temperature (SST) and Sea Surface High (SSH) Anomaly. Twenty genera of Myctophidae were identified, distributed between 20ºS and 35ºS. Diaphus sp. was the most abundant (30%) genera covering the study area. The oceanic area showed higher larval abundance (75%) than the continental shelf (16%) and shelf break (9%), with the predominance of Diaphus sp. in the three areas. Meanders and eddies were preliminary visually identified by SST and SSH images, corresponding to the location of the presence of Myctophidae.
This is an ongoing study, the next step is to identify the eddies by in situ and satellite data and correlate them with the larval distribution. To this end, dynamic height will be calculated using in situ data and eddies will be identified geometrically using satellite data. To evaluate the influence of the eddies on the larvae, the Moran I Index will be applied, performing a spatial autocorrelation. It is expected that, based on other studies, meanders and eddies affect the spatial distribution, mainly in the intrusion of deep-water species on the continental shelf.
|Unusual onset of the 2021 Atlantic Niño
|Sang-Ki Lee (1), Hosmay Lopez (1), Philip F. Tuchen (1), Dongmin Kim (2,1), and Gregory R. Foltz (1)
(1) NOAA Atlantic Oceanographic and Meteorological Laboratory, Miami, FL,
(2) Cooperative Institute for Marine and Atmospheric Studies, University of Miami, Miami, FL
|In the boreal summer of 2021, extremely warm sea surface temperatures (SSTs) appeared in the eastern equatorial Atlantic Ocean, producing the strongest Atlantic Niño event ever recorded in the satellite period (since early-1970s). During its peak in June-August, the 2021 Atlantic Niño produced heavy rainfall and multiple flooding events in countries bordering the Gulf of Guinea.
The warm event occurred between two consecutive La Niña events of 2020-2021 and 2021-2022. However, it did not follow the usual pathway of La Niña-forced Atlantic Niño onset, which is often mediated by the onset of negative Atlantic Meridional Mode (AMM) in boreal spring and associated northwesterly wind anomalies in the western equatorial Atlantic.
In contrast, the 2021 warm event was preceded by a positive AMM in boreal winter, which is a very rare precondition for the occurrence of historical Atlantic Niño events (i.e., occurred only in 1981 and 2021). The positive AMM and the associated southeasterly wind anomalies in the western equatorial Atlantic dissipated abruptly in boreal spring, ending an anomalous buildup of warm water in the western equatorial Atlantic Ocean.
A strong Madden-Julian Oscillation (MJO) event and its associated westerly wind burst served as a catalyst for terminating the equatorial southeasterly wind anomalies. The wind burst also excited a downwelling equatorial Kelvin wave that initiated the 2021 warm event around May.
In summary, an unusual combination of a precondition in boreal winter (i.e., deepened thermocline in the western equatorial Atlantic maintained by a positive AMM), its abrupt dissipation in boreal spring, and the westerly wind burst (i.e., MJO) triggered the downwelling Kelvin wave. Subsequently, the concomitant positive atmosphere-ocean feedback produced the extreme Atlantic Niño in the boreal summer of 2021.
|Interannual variability of the Guinea Current and its effect on the Gulf of Guinea coastal Upwelling
|S., Djakouré 1, Y., Konaté 1, K. Bosson 1, Y., Kouadio 1, A. Aman, and V. Koné 2
1. Laboratoire des Sciences de la Matière, de l’Environnement et de l’Énergie Solaire, UFR SSMT, Université Félix Houphouët-Boigny, 22 BP 582 Abidjan 22, Côte d’Ivoire
2. UFR Sciences de la Mer, Université de San Pédro (USP), BP V1800, San Pédro, Côte-d’Ivoire
|The ocean circulation in the Gulf of Guinea may affect the ocean dynamics of the tropical Atlantic because of its impact, on the regional climate and the marine resources. The Coastal and Regional Ocean COmmunity model (CROCO) configured in the tropical Atlantic with a nested grid on the Gulf of Guinea is used to study the interannual variability of the Guinea Current (GC).
The model simulation compares reasonably with the EGEE/AMMA cruises data, the Geostrophic and Ekman Current Observatory (GEKCO) and the Prediction and Research Moored Array in the Tropical Atlantic (PIRATA) at 0°N–23°W and 0°N–10°W. The results evidence the eastward Guinea Current as the main surface current of the Gulf of Guinea. The GC flows at depths of 10-20 m, between the African coast and 2°N with speeds of 50-100 cm.s-1. The GC transport is range from 2 Sv to 5 Sv. It appears that the intensification of the GC is observed east of Cape Palmas and Cape Three Points.
The results also show latitudinal displacements and variations in current strength. The interannual variability of the Guinea Current core is found to be associated with the tropical Atlantic climate modes and to affect the coastal upwelling index.
|First Indicators of Mesopelagic fish biomass in the northern central off Angola
|Miguel André1, Filomena Vaz Velho1 Bjørn Axelsen 2
1Instituto Nacional de Investigação Pesqueira e Marinha, Luanda, Angola
2 Institute of Marine Research, Bergen, Norway
|The pelagic ecosystem off Angola has been monitored annually by means of acoustic surveys since 1995, covering the area between the 20 m and 500 m isobaths. Mesopelagic fish are primarily found from the shelf break around 200-250 m bottom depth, where their densities are highest, and further offshore, where abundance levels generally decrease with distance offshore. The principal mesopelagic scattering layers typically occur at 200–400 m depth during daytime and migrate towards the near-surface zone at night.
The abundance of mesopelagic fish off Angola has, however, so far not been estimated systematically due to challenges with acoustic abundance estimation such as their general small body sizes, low aggregation densities, wide depth ranges, as well aggregating in mixed-species assemblages, often with other non-fish scatterers such as crustaceans, cephalopods and mesozooplankters. Further, the acoustic scattering properties of mesopelagic fish may be modulated by depth due to swim bladder compression, altering both their acoustic target strengths (TS) and frequency response patterns (r[f]) crucial for acoustic identification and conversion to abundance, potentially leading to diurnal effects on derived acoustic abundance estimates.
Here, we report on the first attempt to estimate the biomass of mesopelagic fish within the 500 m isobath off Angola from an acoustic survey conducted in 2022. The scattering layers were insonified using a Simrad EK80 echosounder operating at 18, 38, 70, 120, 200 and 333 kHz with continuous wave (CW) pulse form. Acoustic data were collected along predefined pseudo-parallel transect lines perpendicular to the coastline/ isobaths during day and night. Target identification was done by means of trawling using a Multpelt 642 pelagic sampling trawl. Estimates based on day- and night time acoustic data were compared for evaluation of systematic diurnal differences in recorded acoustic backscatter
|Contributions of decapod life history stages to the zooplankton in tropical estuarine, coastal and shelf waters – is the upgrade from abundance only to a semi-automatic quantification of biovolume and biomass relevant?
|Denise Fabiana de Moraes Costa Schwamborn¹,²; Ralf Schwamborn²; Catarina da Rocha Marcolin3; Nathália Lins Silva²; Alexandre Oliveira de Almeida¹
1 Programa de Pós-Graduação em Biologia Animal, Federal University of Pernambuco, Recife, Pernambuco, Brazil
2 Laboratory of Zooplankton, Department of Oceanography, DOCEAN, Federal University of Pernambuco, Recife, Pernambuco, Brazil
3 Federal University of Southern Bahia, Instituto Sosígenes Costa de Humanidades, Artes e Ciências, Porto Seguro, Bahia, Brazil
|Decapod crustaceans are important components of marine ecosystems, yet, there is little known about their contributions to biomass and biovolume in tropical zooplankton. Thus, we analyzed the zooplankton in three tropical coastal areas: Rio Formoso Estuary, Tamandaré Bay, and Pernambuco Continental Shelf off Tamandaré, Brazil. Zooplankton samples were taken bimonthly from June 2013 to May 2015, totalling 120 samples.
Samples were analyzed using ZooScan. All images obtained were semi-automatically classified to identify organisms, and then further validated manually. The most relevant decapods, in terms of biovolume and biomass, were brachyuran zoeae, luciferids (adults and larvae), Penaeus postlarvae, anomuran zoeae, and caridean zoeae (e.g., Alpheidae).
In the three study areas, zooplankton abundance ranged from 0.62 to 5,343.00 ind. m-3, total zooplankton carbon biomass ranged from 2.95 gC L-1 in the Tamandaré Bay, in the dry season of 2014, to 75,349.00 gC L-1 in the Rio Formoso Estuary, in the rainy season of 2013. Decapoda contributed on average 31% of the zooplankton biovolume in the Bay area (median = 29.18 mm3 m-3, min. = 0.22 mm3 m-3, max. = 82.66 mm3 m–3, standard deviation = 25.57 mm3 m-3). Despite the higher absolute values of density, biovolume and biomass and relative abundance (%) found in the Estuary, relative biovolume (%) and relative biomass (%) of decapods were much more relevant in the Bay, due to the presence of larval and advanced pre-settling post-larval stages, which migrated into the Bay at high tide (e.g. brachyuran megalopae and penaeid shrimp post-larvae), especially in the rainy season (June). These pre-settlement stages enter the Bay, an oligotrophic reef-lined environment, that is poor in zooplankton, where they dominate decapod biomass and biovolume.
These results show the importance of quantitative approaches for biomass and biovolume and the relevance of decapod crustacean larvae for pelagic food webs in coastal areas.
|The role of small mesopelagic fish in the food web off Southern Brazil
|Juliano L. Coletto, Laura Alma & José Henrique Muelbert
Programa de Pós-Graduação em Oceanografia Biológica, Instituto de Oceanografia, Universidade Federal do Rio Grande – FURG, Brazil
|The Subtropical Convergence Zone in southern Brazil represents one of the main biodiversity hotspots in the Southern Hemisphere. The confluence between the Brazil Current and the Malvinas Current, together with high nutrient concentrations from Rio de La Plata and Lagoa dos Patos on the continental shelf, result in high biological productivity.
The area serves as a nursery, feeding and breeding grounds for several subantarctic and subtropical species. High biomass of mesopelagic fish, such as lanternfish (Sternoptychidae: Maurolicus stehmanni), and Myctophidae are found in the outer shelf and slope areas, respectively. These fish perform daily vertical migrations, spending daytime hours near the bottom below 150m, and swimming towards the surface during nighttime to feed. They feed mostly on euphausiids and copepods. By serving as food for demersal and pelagic predators, they connect pelagic and benthic compartments and play the role of transferring energy from basal trophic levels to top predators. In this work, we will investigate the role of small mesopelagic fish in the trophic structure on the pelagic food web off Southern Brazil.
The specific objectives are: 1) To conduct a systematic review on the importance of mesopelagic fish in the diet of top predators inhabiting the outer shelf and slope waters; 2) To investigate trophic relationships using ecological networks, and; 3) To identify knowledge gaps and research priorities for ecosystem management. Our results will contribute to the comparative trophic structures analysis on Atlantic Ocean ecosystems within the scope of the TRIATLAS Project.
|Distribution patterns and biodiversity of pelagic and mesopelagic fauna in the Subtropical Southwestern Atlantic Ocean
|Silva, Aline Barbosa; Muelbert, José Henrique;
): Institute of Oceanography. Federal University of Rio Grande – FURG
|The Brazilian Southern Continental Shelf is under the influence of the Brazil/Malvinas Confluence and the input of freshwater from the La Plata River and Lagoa dos Patos, which provide areas with biodiversity hotspots and biological production of ecosystem relevance that may be important for commercial fishing. Mesopelagic animals comprise critical structural and functional links in ocean ecosystems, being an important food source for most commercially caught pelagic species and play an essential role in maintaining ecosystem integrity. However, most mesopelagic species have not yet been described or had their ecology characterized.
The main objective of this study is to analyze the abundance, diversity, and vertical and horizontal distribution of small pelagic and mesopelagic fauna relevant to the fisheries and ecosystem of the region. The analysis will use historical data from literature and oceanographic cruises to estimate species and biomass in the southern Atlantic. Geoprocessing methods and spatial analysis will produce maps showing the location stratification of the main species present in the study area. Comparison with previous studies will allow us to observe the historical evolution of biomass in the studied region.
The work will describe the structure of the components of the mesopelagic ecosystem, their daily vertical migration, distribution patches in relation to oceanographic conditions, and the structure of the size spectrum. Results will contribute to a better understanding of the mesopelagic ecosystem in order to sustainably manage fisheries in the region. Further comparison among the areas covered by TRIATLAS will allow a unique and unprecedented interdisciplinary view on the mesopelagic structure of Tropical and Southern Atlantic key ecosystems.
|Preliminary analysis of CO2 data from PIRATABR-2022 campaign
|Thiago Veloso Franklin; Leticia Cotrim da Cunha; Tainan da Fonseca Fernandes
Chemistry Oceanography laboratory (LABOQUI) – Department of Chemical Oceanography, State University of Rio de Janeiro
|Carbon dioxide (CO2) is an essential metabolic gas involved in organic matter (OM) production (e.g., photosynthesis) and decomposition (e.g., respiration), which may show high daily and spatial variability following changes in temperature, pH and salinity. Based on this, we evaluated daily and spatial variability of CO2 in a Tropical Atlantic waters.
We monitored the gas in surface waters during the PIRATABR-2022 expedition performed throughout on 31 days the trajectory of the oceanographic ship Antares were gently sampled over 24h using a continuous non-turbulent pump in closed system with a CO2 infrared gas analyzer (EGM-4® PPSystems) coupled to air equilibrator. There was of n=30198 CO2 where it ranged from 361 ppm to 599 ppm, with average values of 440 ppm. We observe that along the transect the CO2 in the water tended to be higher than in the atmosphere (410 – 439 ppm). However, when we focus on the transect at 38°W, which extends from the coast of Fortaleza to 15°N, we can observe a drop in CO2 as it crosses the equator, where sightings of large bands of sargassum have occurred.
The presence of large amounts of algae in these waters increases the consumption of CO2 by the process of photosynthesis, can thus reducing the CO2 in these waters than the atmospheric CO2, giving this region the ability to absorb CO2 present in the atmosphere. Tropical regions like this one are commonly considered as sources of CO2 to the atmosphere, but as seen not all the area presents the same trend, the influence of the Amazon River plume that feeds the western region of the Tropical Atlantic favours the formation not only of the sargassum patches observed during the commission, but also the phytoplankton, which will also be responsible for absorbing the CO2 contained in the water. This preliminary analysis reinforces the importance of studies on carbon dynamics in the region and seeks to show the potential of this region for absorbing atmospheric CO2.
|Uncoupled changes in phytoplankton biomass and size structure in the western tropical Atlantic
|Gabriel Bittencourt Farias (1) , Juan-Carlos Molinero (2), Claire Carré (2), Arnaud Bertrand (1,2), Béatrice Bec (2), Pedro Augusto Mendes de Castro Melo (1)
1 Departamento de Oceanografia, Universidade Federal de Pernambuco, Avenida Arquitetura, S/N, 50670-901, Recife, PE, Brazil.
2 MARBEC, Université Montpellier, IRD, Ifremer CNRS, Montpellier, France
|Structural changes in phytoplankton communities have large influence on marine elemental cycling, food web dynamics and carbon export.
Here we used data from two field expeditions, performed in spring and fall, over a coast-offshore gradient to investigate phytoplankton structure and dynamics in the Southwestern Tropical Atlantic (SWTA). Results revealed a predominant role of the thermohaline structure as the main driver of phytoplankton dynamics regardless the season. In fall, the thermocline and nutricline shallowing promoted a biomass increase, which was 3-fold higher around the oceanic islands.
The structure of phytoplankton community mainly varied vertically, with Prochlorococcus pigments contributing greatly to the higher nutrient Deep Chlorophyll Maximum, whereas other Cyanophyceae predominated in nutrient poor surface layers during the two seasons. In addition, a clear coast-offshore variability in the new production (Fp) was observed, with the shelf region displaying higher values (up to 0.21), promoted by larger Bacillariophyceae pigments concentration, thus suggesting a coastal influence on shelf production.
Although the phytoplankton biomass increased seasonally, our results highlighted a predominance of recycled production (Fp) and uncoupled dynamics between biomass and size of phytoplankton structure, with pico- and nanophytoplankton dominating the relative biomass, i.e., ca. 80% of the community in both seasons.
We hypothesize that these patterns may result from a strong nitrogen limitation (N:P of around 3:1), which likely constrain a pronounced growth of the microphytoplankton.
|Physical processes in the Confluence region in Southern Brazil (key area 5)
|Rafael Avila, José Henrique Muelbert
Laboratório de Ecologia do Ictoplâncton, Instituto de Oceanografia, Universidade Federal do Rio Grande
|Key area 5 covers the coastal and open ocean provinces of the Southwestern Atlantic Ocean from Brazil’s southeast coast to Argentina’s northeast coast. The area presents a complex network of hydrographic Interactions, with several water masses, mesoscale processes, and a substantial low-salinity water input, all subjected to a variable wind pattern. Herein is presented a summary of the main physical features in the area and the respective implications in the local circulation based on the available literature and data obtained from the Copernicus Marine Service database.
The local circulation is primarily driven by two features: the Brazil-Malvinas Confluence, a region of convergence of two large-scale currents (Brazil and Malvinas currents), and the discharge from the La Plata River, which yields a large-scale buoyant plume. The Brazil-Malvinas Confluence is one of the greatest mesoscale systems in the world’s ocean, and the meanders and eddies from the convergence between the currents have a strong influence not only on the local circulation but also on the air-sea exchange processes in this portion of the Southwestern Atlantic Ocean. The La Plata discharge onto the continental shelf generates one of the largest estuarine plumes in the world. Also, it creates strong horizontal gradients, a sharp salinity front, and mixes with local water masses.
The area is under the influence of the South Atlantic anticyclone, which leads to a prevailing northeasterly wind regime throughout the year, changing to southwesterly during the passage of cold fronts. These changes in the wind pattern lead to the latitudinal displacements of the confluence and the plume, as well as seasonal upwelling in northern areas of the domain. Both features also have a great impact on the local biological productivity by creating frontal zones of phytoplankton accumulation, and the plume also injects large nutrient concentrations that spread all over the coastal areas of the key area 5.
|Tropical Atlantic recent observations for thermocline depth, heat storage, and wind
|Ana Clara B. Mariani, Maurício R. Rocha, Paulo S. Polito and Olga T. Sato
Oceanographic Institute of the University of São Paulo
|The tropical Atlantic ocean is in a unique position that connects the North Atlantic region of deep water formation with the South Atlantic which has a direct connection to the Southern, Pacific, and Indian Oceans. The ocean upper layer in the tropical Atlantic has become warmer in recent decades.
However, that occurred unevenly along the basin, with large warming trends observed in the eastern tropical Atlantic. In that, the long-term variation in thermocline depth is a crucial aspect of ocean heat balance and transport. We investigate thermocline depth trends over the past decades using two proxy variables: a fixed 20°C isotherm and the hinge point of an adjusted hyperbolic tangent function. We used temperatures from three reanalyses (GECCO3, ORAS4, and IAP) and from PIRATA moorings located at 4°N 23°W, 0°N 23°W, 0°N 10°W, and 0°N 0°W. The thermocline depth showed no significant linear trend in the period between 1999 and 2018. The quest for a trend in thermocline depth proved quite challenging due to data gaps and time series extension, such that the results do not yet support a firm conclusion.
The east side of the basin is a region of positive heat storage (HS) trend, while the wind magnitude has a negative trend. The HS was computed from altimetric data and the wind magnitude was computed from the OAFlux dataset. This warming pattern could be caused either by changes in the heat flux at the air-sea interface due to changes in wind patterns or by oceanic processes, such as the weakening of the atlantic meridional overturning circulation (AMOC), or a combination of both.
However, there is still no agreement on the long-term weakening of the AMOC, and some studies argue that the strength of the AMOC does not show significant long-term trends in recent decades.
|Reconstruction of the marine carbonate system at the Western Tropical Atlantic: trends and variabilities on 20 years of PIRATA project
|Carlos Augusto Musetti de Assis; Leticia Cotrim da Cunha; Luana Queiroz Pinho
|This study aims to reconstruct the surface marine carbonate system from 1998 to 2018 using sea surface temperature (SST) and sea surface salinity (SSS) data from the PIRATA buoy at 8°N 38°W and describe its variability in time.
Two empirical models were used to calculate total alkalinity (TA) and dissolved inorganic carbon (DIC) from SSS, from which pH, in total scale, and CO2 fugacity (fCO2) values were then estimated. Only DIC, pH and fCO2 showed a statistically significant trend in time, where DIC showed an increase of 0.717 ± 0,108 µmol kg-1 year-1, pH decreased 0.0014 ± 0,0001 pH units year-1, and fCO2 had an increase of 1.539 ± 0,028 µatm year-1.
Two different seasons were observed when data were analyzed: a dry season from January to June, when SSTs were lower (27.00 ± 0.61°C) and SSS was higher (35.94 ± 0.34), matching the period when the ITCZ is over the South American continent, Amazon river plume is restricted to western shelf areas and Equatorial upwelling is less intense, and a rainy season from July to December, when SSTs were higher (28.35 ± 0.7°C) and SSS was lower (35.01 ± 0.8), matching the period when the ITCZ is at its northern range, the Amazon plume is spread eastwards through the North Brazil Current’s retroflection and the Equatorial upwelling is more active. Along with that, TA, DIC and pH varied positively with SSS, with higher values (TA: 2352.88 ± 19.74µmol kg-1; DIC: 2013.82 ± 18.6µmol kg-1; pH: 8.0604 ± 0.0121) during dry season and lower values (TA: 2299.3 ± 46.32µmol kg-1; DIC: 1967.61 ± 40.0µmol kg-1; pH: 8.0485 ± 0.0119) during rainy season. On the other hand, fCO2 varied positively with SST, with higher values (391.13 ± 13.76µatm) during rainy, upwelling season and lower values (385.85 ± 12.86µatm) during dry season.
|Stable isotope variability in a tropical zooplankton time series explained by its key species
|Morgana Brito-Lolaia, Gabriela Guerra Araújo Abrantes de Figueiredo, Sigrid Neumann-Leitão, Gilvan Takeshi Yogui, Ralf Schwamborn
Dept. of Oceanography, Federal University of Pernambuco (UFPE), Av. Arquitetura s/n, Cidade Universitária, Recife, PE 50740-550, Brazil
|Time series play an essential role in the study of marine ecosystems, including zooplankton communities and their stable isotope (SI) signatures. SI analysis of ecosystems is generally based on the measurement of a few individuals from a small list of subjectively pre-defined species.
The main objective of this study was to detect species that are significantly associated with the temporal variability of the SI composition of coastal zooplankton in the Tropical West Atlantic. We investigated this by means of a novel species-biomass-isotopes-mixture (SBIM) approach. SBIM was applied to detect key taxa that can be considered bioindicators for important descriptors of ecosystem state (e.g., oligotrophy, carbon sources, mean trophic level). Zooplankton samples (64 µm mesh size) were obtained in Tamandaré Bay (northeastern Brazil) from June 2013 to August 2019 for stable isotope measurements and estimation of size and relative biomass. Zooplankton δ13C ranged from -21.0 to -18.2‰ (mean: -19.7‰ in the dry season and -19.4‰ in the rainy season). Total zooplankton δ15N ranged from 3.8 to 9.0‰ (7.0‰ in the dry season, and 6.5‰ rainy season). Total zooplankton C/N ratios ranged from 3.5 to 5.0 (4.2 in the dry season and 4.2 in the rainy season). The copepod Pseudodiaptomus acutus was the most important species for explaining the variability in δ15N (22% of the total variability). Relative biomass (%) of P. acutus showed a strong positive correlation with δ15N, indicating a high trophic level (TL). Small-sized invertebrate larvae were negatively correlated with δ15N, indicating a TL below average. The tintinnid F. ehrenbergii showed a positive correlation with C/N, being an indicator for turbid “green waters”, during the rainy season, when the ecosystem was in a eutrophic state, with high lipid contents in the zooplankton community. The proposed SBIM approach opens up a novel pathway to understanding the factors and species that shape the temporal variability of food webs and a new way to look at SI data of zooplankton communities.
|Using otolith biochronologies from sardine (Sardinops sagax) in the southern Benguela to identify ecosystem shifts
|Faye Brinkman1, Margit Wilhelm1,2, Yonela Geja3 & Carl D. van der Lingen3,4
1 Department of Fisheries and Aquatic Sciences, University of Namibia, Henties Bay, Namibia.
2 Sam Nujoma Marine and Coastal Resources Research Centre (SANUMARC), University of Namibia, Henties Bay, Namibia.
3 Branch: Fisheries Management, Department of Forestry, Fisheries and the Environment (DFFE), Cape Town, South Africa.
4 Department of Biological Sciences and Marine Research Institute, University of Cape Town, Cape Town, South Africa.
|Southern Benguela sardine Sardinops sagax has shown substantial changes in population size over the past 70 years. We developed a robust 49-year (1962-2010) otolith biochronology of annual increment width to infer long-term growth patterns of sardine sampled off the South African west coast. Linear mixed effect models were applied to separate intrinsic (within individual) and extrinsic (by year – e.g. population density, environment) factors to estimate mean annual growth. Sequential t-test of regime shifts (STARS) analysis performed on the best linear unbiased predictor (BLUP) of the year effect on fish growth indicated three regimes with two alteration points. The first alteration occurred in 1986 from well-below average growth to well-above average growth, and the second in 2006 from well-above average growth to average growth. These three regimes correspond with periods of low, high, and low biomass, respectively; i.e. well-above average growth rates occurred during the high biomass period and vice versa. Sardine is expected to grow faster to reach maturity earlier at low biomass. The pattern of slow growth at low biomass is counter-intuitive and suggests that environmental conditions may have been primarily responsible. These findings indicate that sardine growth is influenced by both biomass levels and environmental conditions, and that the relative effect of each can change over time. Further work is needed to elucidate this, but our study demonstrates the utility for developing otolith increment methods to identify ecosystem shifts in the Benguela ecosystem, and will contribute to an ecosystem approach to management of the fishery.
|Marine heatwaves in the Cape Peninsula Upwelling Cell
|Kirstin Petzer, Prof. Mathieu Rouault and Dr. Tarron Lamont
University of Cape Town, Nansen Tutu Center for Marine Environmental Research
|Due to global warming, marine heatwaves are considered to be one of the emerging threats to marine ecosystems globally. South Africa’s fisheries and coastal communities depend on the Southern Benguela’s upwelling for the high marine productivity. Marine heatwaves are prolonged periods of extreme warm Sea Surface Temperatures (SST) anomalies which could have severe ecological impacts on marine ecosystems by decreasing biodiversity, negatively affecting cold water species and increasing ocean stratification. Council for Scientific and Industrial Research (CSIR) half-hourly in situ SST from the Cape Point station about 5.4 km of the coast, and ECMWF Reanalysis 5th Generation wind speed and direction time series from January 2003 to March 2020 were examined to quantify the occurrence, formation and decay of marine heatwaves in the Southern Benguela. The marine heatwaves were identified using the SST values which exceed the 90th percentile of the timeseries for at least five days. In the CSIR SST time series 18 marine heatwaves were identified at the Cape Point station. The occurrence of strong north-westerly winds was found to be the main driver of marine heatwaves, while southeasterly winds was observed to have a large role in the decay of marine heatwaves. Marine heatwaves are expected to worsen with climate change by lasting longer with high temperature increases but increase in southeasterly winds could decrease the occurrence of marine heatwaves in the Southern Benguela.
Key words: Southern Benguela, marine heatwave, upwelling
|Disentangling the impact of Atlantic Niño on sea-air CO2 fluxes
|Shunya Koseki(1), Jerry Tjiputra(2), Filippa Fransner(1), Lander R. Crespo(1), Noel Keenlyside(1.3)
1: Geophysical Institute, University of Bergen 2: NORCE 3: NERSC
|The Atlantic Niño is a major tropical interannual climate variability mode of the sea surface temperature (SST) occurring during boreal summer that shares many similarities with the tropical Pacific El Niño.
Although the tropical Atlantic is an important source of CO2 to the atmosphere, the impact of Atlantic Niño on the sea-air CO2 exchange is not well understood. We reveal that the Atlantic Niño enhances (weakens) CO2 outgassing in the central (western) tropical Atlantic.
In the western basin, freshwater-induced changes in surface salinity, which considerably modulate the surface ocean CO2 partial pressure (pCO2), is the primary driver for the observed CO2 flux variations. Contrastingly, pCO2 anomaly in the central basin is dominated by the SST-driven solubility change. Here, we reveal that this multi-variable mechanism for pCO2 anomaly differs remarkably from the Pacific where the response is predominantly controlled by upwelling-induced dissolved inorganic carbon anomalies.
The contrasting behavior is characterized by the high CO2 buffering capacity in the Atlantic, where the subsurface water mass contains higher alkalinity than in the Pacific. The different mechanisms driving the interannual variability in sea-air CO2 exchange in the tropical Atlantic and Pacific suggests that they may respond differently to climate change.
|The deep chlorophyll maximum in the tropical Atlantic: is it a phytoplankton biomass maximum?
|Cristina González-García1, Mike V. Zubkov2, Emilio Marañón1
1Departament of Ecology and Animal Biology, University of Vigo, Vigo, Spain
2Scottish Association for Marine Sciences, Scottish Marine Institute, Oban, United Kingdom
|The deep chlorophyll maximum (DCM), a peak in chlorophyll concentration located near the bottom of the euphotic layer, is a widespread biological feature in all stratified oceanic regions. The ecological and biogeochemical significance of the DCM depends on whether it reflects an actual maximum in phytoplankton abundance and biomass, or arises from an increase in chlorophyll cellular content (photoacclimation).
Recent analyses of fluorescence and backscattering profiles from Argo floats have identified the DCM in subtropical gyres as being caused mainly by photoacclimation, whereas the DCM in equatorial regions was classified as a maximum of phytoplankton biomass. However, geographical coverage of available Argo profiles in tropical regions is sparse, particularly in the south Atlantic. In addition, the backscattering signal can be affected by non-phytoplankton material, including heterotrophic bacteria and detritus. It is thus of interest to examine the available evidence on the vertical distribution of phytoplankton abundance in tropical regions, in order to verify if inferences based on fluorescence and backscattering profiles are valid.
Here we use phytoplankton abundance measurements obtained during two Atlantic Meridional Transects to ascertain if the DCM is a maximum of phytoplankton biomass in the Atlantic subtropical gyres and equatorial region.
|Fisheries and environmental variables reveal migration patterns of albacore Thunnus alalunga (Bonnaterre, 1788) in the South Atlantic Ocean
|Previero, M., Travassos, P. and Andrade, H.
Departamento de Pesca e Aquicultura, Universidade Federal Rural de Pernambuco (UFRPE)
|The albacore (Thunnus alalunga) fishery is amongst the main important in the South Atlantic Ocean. Albacore is a migratory species alternating periods in tropical and temperate waters. While adults migrate to tropical warmer waters, with reproductive purposes, juveniles inhabit high southern latitudes.
Here the albacore adults and juveniles migration in the South Atlantic were modeled and mapped. Fishery data (catch, effort and fish sizes) were obtained from ICCAT databases to China Taipei longline fleet. Sea Surface Temperature (SST, ºC) and Chlorophyll-a (mgg) were obtained from NASA. The dataset were compiled by month and 5°x5° spatial resolution to 1997-2020. A Random Forest model by month to juveniles and adults separately relating catch data and environmental variables was performed.
The model results were spatialized using a predict function in rasterized shapefiles of SST and Chlorophyll-a for each 1°x1°. The highest abundance spatial patches were evidenced. The temporal trends of abundance, SST and Chlorophyll-a were also investigated. Different migration patterns were found to adults and juveniles. Between August and September, adults start a migratory movement from the southern African coast to the area off the north-east Brazilian coast, above 20oS. In this tropical warm water zone, from October to February the adults spawn and returns to temperate areas. On the other hand, juveniles remain in subtropical areas (30°S-40°S) throughout the year. The results indicate the tropical migration possibly has reproductive character, being performed mainly by adults and some pre-adults. The SST and Chlorophyll-a seems do not influence this adults migratory pattern. These large-scale displacements may be associated with the fulfillment of species’ reproductive task to seek the same spawning area previously defined throughout its evolutionary cycle. Regarding juveniles being a temperate tuna species, their distribution is restricted to higher latitudes. They begin to participate in this migration to tropical areas when reach sexual maturity, contributing to the stock reproductive process.
The results obtained may contribute both to the species’ spatial management and to future studies on migration in climate change scenarios.
|Evaluation of Benguela Niño-Niña events in the CMIP6 historical simulations
|Marie-Lou Bachelery1, Shunya Koseki1, Noel Keenlyside1
1- Geophysical Institute, University of Bergen, Bjerknes Centre for Climate Research, Bergen, Norway
|Historical Coupled Model Intercomparison Project Phase 6 (CMIP6) model outputs are analyzed to evaluate models’ ability in simulating the seasonal and interannual variability in the South-Eastern Atlantic Ocean. The study focuses on SST in February-March-April, the main season of occurrence of the extreme interannual warm and cold Benguela Niño-Niña events.
In the Angola-Benguela-Area (ABA), the CMIP6 SST ensemble-mean resembles the seasonality of the observations but with a strong bias. Unlike the seasonal cycle, the SST interannual variability in CMIP6 ensemble-mean is underestimated and occurs 3-4 months after the peak of maximum variability in the observations (June/July). Among the model ensemble, 2 groups of models emerge: a group featuring a maximum interannual variability in the right location (ABA) but delayed by about 2/3 months compared to the observation (~60% of the models); a group featuring the maximum variability in the right season (FMA) but in a location shifted southward in the South-Benguela (~30% of models). For the first group, results suggest that the time-shift of the peak in the SST variability is induced by the time-shift of the equatorial zonal wind stress. For the second group results show that the latitudinal-shift of the peak in SST variability is controlled by intense coastal wind activity in the south Benguela rather than by model bias and a southward shift in the position of Angola-Benguela-Frontal Zone.
Finally, we examined the models’ ability in simulating extreme interannual Benguela Niño-Niña events. Very few individual models correctly simulate the phenology of the Benguela events, including the modulation of the equatorial zonal and coastal winds that drive development in the preceding months. Interestingly most of the best models have in common a fairly good representation of the South-Atlantic High pressure system.
|Marine protected areas in face of global warming in the Tropical Western Atlantic (Brazilian Coast)
|A.S. LIRA1; F. LUCENA-FRÉDOU1; M.A.L. LIMA2; L.N. EDUARDO3; L. CAPITANI2; T. FRÉDOU1; A. BERTRAND3; J. STEENBEEK4,5; M. COLL5; R. ANGELINI2
1-Fisheries and Aquaculture Department, Federal Rural University of Pernambuco, Rua D. Manuel de Medeiros s/n, Dois Irmãos, CEP 52171-900, Recife, Pernambuco, Brazil.
2-Civil Engineering Department, Federal University of Rio Grande do Norte, Campus Universitário Lagoa Nova, CEP 59078-970, Natal, Rio Grande do Norte, Brazil.
3-Institut de Recherche pour le Développement (IRD), MARBEC, Univ Montpellier, CNRS, Ifremer, IRD, Sète, France
4-Ecopath International Initiative Research Association, Spain.
5-Institute of Marine Sciences, Spanish National Research Council, Spain.
|Marine ecosystems are threatened by climate change, overfishing and loss of biodiversity, which has led to the use of approaches that consider methods to quantify and mitigate these threats.
The Ecospace model for Northeast Brazil (NE) aims to assess the species distribution, in terms of biomass, catch, and ecological indicators under different climate scenarios (e.g. global warming) and the establishment of Marine Protected Areas (MPAs) to explore their effectiveness for maintenance of biodiversity in the region. The analysis encompasses 31km2 off the NE coast, considering over fifty-five compartments and different layers such as depth, Sea Surface Temperature and Seabed morphology. The multi-decadal to centennial forecasts according to the Fish-MIP protocol were simulated from 2015 to 2100 after the historic trend calibrated, using annual fishing time series (1987-2007). The Earth-System Model from Geophysical Fluid Dynamics Laboratory (GFDL-ESM2M) projections of historic and ssp126 (RCP 2.6) and 585 (RCP 8.5) climate scenarios were used to evaluate the responses of functional groups to changing average water temperatures for the top 150 meters. In addition, the GFDL projections were applied to force phytoplankton biomasses over time. Overall, the increase of temperature not reflected in a significant decrease of biomass and capture of all groups evaluated on the multi-decadal to centennial forecasts. However, some species (e.g., Lutjanus spp and Epinephelus spp) were strongly impacted, mainly in the intense global warming scenarios (RCP8.5). In contrast, the MPAs implementation in face of global warming scenarios was promising, increasing the biomass for some species, mainly in the no-fishing areas, where biomass hot spots were observed. In terms of Ecological indicators (e.g., biodiversity indicators and biomass of fish), differences were observed between the (RCP8.5) and (RCP2.6) scenarios, especially in the year after 2070s. We conclude that the increase of temperature cause negative impacts on the biomass mainly in the commercial species of high trophic level. However, MPAs play an important role in maintaining the biomass of these groups and the biodiversity of the ecosystem.
|ECOSYSTEM INTERACTIONS AND FUTURE SCENARIOS AT THE AMAZON RIVER MOUTH
|Maria Alice L. Lima (Federal University of Rio Grande do Norte);
Flávia Lucena-Frédou (Federal Rural University of Pernambuco);
Bianca Bentes (Federal University of Pará);
Victoria Isaac (Federal University of Pará);
Tommaso Giarrizzo (Federal University of Ceará);
Tatiane Medeiros (Federal University of Pará);
Ronaldo Angelini (Federal University of Rio Grande do Norte)
|Estuarine areas are the most productive ecosystems, concentrating many activities supported by nutrient enrichment of the rivers. The Amazon River is the largest in the world in water discharge. Its adjacent estuary covers a total area of 112,699.7 km², supporting the capture of many fish species and other organisms such as shrimp. This study aims to develop a trophic model for the mouth of the Amazon River, evaluate the crucial shrimp fishery activity in the region, and assess climate change’s effect on fishing activity and natural resources. Using the Ecopath with Ecosim software, we built the trophic model of this area with approximately 50,000 km2. Functional groups to the Amazon River mouth region model were chosen according to a) importance in the fisheries experimental samples in 2019; b) importance in fishing landings; c) vulnerable and charismatic species, such as turtles and dolphins. Other fish species with low biomass were grouped in functional groups according to their trophic categories. The model comprises 56 functional groups, of which 34 are fish and one compartment for detritus. Our complete model is composed of marine (as Lutjanus spp), estuarine (as Cynoscion spp), and freshwater (as Brachyplatysoma spp) species, all of which are important for commercial fisheries. Shrimp species are also key in fisheries, and four of them were included in the model: Farfantepenaeus subtilis, Xiphopenaeus kroyeri, Nematopalaemon schmitti, and Litopenaeus schmitii. The history of fisheries production in the North region was evaluated in the period between 1976 to 2015 from official national databases. The Ecosim module helps assess observed and estimated trends in the time series of catches available for some functional groups. We propose simulating commercial species’ scenarios and responses using temperature changes and effort. The Amazon River ecosystem is expected to be a resilient system, with high cycling and respiration values, in addition to the importance of the detritus chain for the system. These results with ecosystem approaches are designed to help the management and management of natural resources and support the sustainability of commercial capture.
|Tropical Atlantic forcing of different ENSO regime
|Noel Keenlyside, Hui Ding, Marta Martín del Rey, Irene Polo, Belen Rodrigues-Fonseca, Fred Kucharski
University of Bergen, University of Colorado, Universidad Complutense de Madrid, International Centre for Theoretical Physics
|The El Niño Southern Oscillation (ENSO) underwent a major shift in in the 1970’s, become stronger and more predictable. This shift has been attributed to changes in the tropical Pacific mean state. However, around the 1970’s, tropical Atlantic – Pacific variability became coupled, with Atlantic SST leading opposite signed changes in the Pacific by around 6-months.
Here we assess the role of the Atlantic in driving the ENSO regime shift using pacemaker experiments with two climate models: ECHAM5/MPIOM and SPEEDY/RGO. In these experiments, model SST is restored to observations in the tropical Atlantic, while elsewhere the models are fully coupled. Both models capture the observed changes in inter-basin interactions and strengthening on ENSO variability after the 1970’s.
The warming of the equatorial and south Atlantic and southward shift of the inter-tropical convergence zone causes inter-basin interactions to become active after the 1970’s in the models. In ECHAM5/MPIOM, this leads to Atlantic Niño variability driving increased ENSO activity. In SPEEDY/RGO, the increase in ENSO activity appears more related to induced mean state changes in the Pacific.
|Global spatial-temporal trends of tuna ex-vessel price
|Eurico Mesquita Noleto Filho 1; Ronaldo Angelini 1; Paulo Eurico Pires Ferreira 2; Flávia Lucena Frédou 2; Thierry Frédou 2; Sebastian Villasante 3; Vicky Lam 4; Ussif Rashid Sumalia 4; Adriana Rosa Carvalho1
1-Federal University of Rio Grande do Norte, Brazil; 2- Universidade Federal Rural de Pernambuco, Brazil; 3- University of Santiago de Compostela, Spain; 4- University of British Columbia, Canada
|Tuna species are an important economic commodity that plays a critical role in keeping the health of marine ecosystems and are under threat by overfishing. Proper estimation of the tuna ex-vessel prices is difficult, given that most species are highly migratory and exploited all over the globe. So, it is hard for Regional Fisheries Management Organizations (RFMOs) to decide whether or not to establish integrated management policies, since the link between regional markets is not completely understood. The spatial structure might be a key element for successfully estimating a price assessment model for this species. Yet, modeling complex spatial data can be difficult and time-consuming for both frequentist methods and Bayesian models with Monte Carlo Markov Chains (MCMC). The Integrated Nested Laplace Approximation (INLA) is a faster alternative to MCMC and is suitable to model the uncertainties in data. Here we estimate and predict the spatial-temporal patterns of the ex-vessel price of four species of tuna: skipjack (Katsuwonus pelamis), yellowfin (Thunnus albacares), bigeye (Thunnus obesus), and albacore (Thunnus alalunga). For that means, we modeled a dataset from 2001 to 2018 from Sea Around Us, using Bayesian Hierarchical Spatio-Temporal Models. For the majority of species, we discovered significant price elasticity across areas, indicating that country economies may be more closely tied to a species’ global price cointegration than oceanic regions are.
|Adaptation of a bi-frequency discrimination method to the copepods in the Senegalese coast
IRD Lemar/ ISRA, CRODT, BP 2221 Dakar, Senegal
|Underwater acoustics sampling techniques provide an benefit over traditional net sampling for macrozooplankton research due to its high spatial coverage. Estimation of abundance or biomass, using acoustic techniques requires knowledge of the frequency dependent acoustic backscatter characteristics, or target strength (TS) of insonified organisms. The TS of zooplankton is usually estimated from physics-based models but can also be made in field. To do so we applied an inversion method, which combine both acoustic and biological data for discriminating zooplankton copepod. We examined echo sounder data at 38 and 120 kHz, collected during a fisheries acoustics survey carried out off Senegalese over the continental shelf. Biological samples collected with a Multinet were used as ground truth. We identified copepod backscatter using differences in volume backscattering strength (Sv) measured at both frequencies. A close relationship were found between the measured values of copepod from Multinet with those calculated by the standard and simple model used. The correlation between copepod abundance and corresponding Sv were positive. This work showed that acoustic method can provide information on a key component of the lower trophic levels in Senegalese water i.e. the copepods (>1mm). These results are essential to better understand marine ecosystem, and constitute a first step for copepod biomass estimation in the study area.
Keywords: Acoustic, bi-frequency, copepod, volume backscattering strength.
|Variabilidade espaço-temporal da salinidade e transporte no Oceano Atlântico Tropical (N e NE do Brasil) baseados em dados observados e modelagem numérica
|Ricardo Christyan Matos Carvalho, Geórgenes Hilário Cavalcante Segundo
|As variações de longo prazo da Circulação de Revolvimento Meridional do Atlântico podem levar a mudanças regionais na distribuição da temperatura (TSM) e salinidade (SSM) da superfície do mar. Tais processos afetam os transportes latitudinais de calor e sal, e como consequencia final, o estabelecimento das correstes de contorno oeste do Atlântico Sul, como a Corrente Norte do Brasil (CNB) e Corrente do Brasil (CB). Neste trabalho, usaremos produtos de sensores instalados em satélites para medir a salinidade da superfície do mar (SSM), em combinação com dados de modelo numérico (HYCOM), e medições em in situ da salinidade na superfície do mar, a fim de explorar a variação sazonal das correntes de superfície e salinidade médias nas regiões norte e nordeste do Brasil. A análise de ondelatas permitirá decompor as séries temporais em diferentes níveis de resolução tempo-frequência para determinar as componentes da variabilidade dominantes. As análises produziram estimativas da variação sazonal das correntes e salinidade. Esta informação será então aplicada aos produto de satélite SSM para obter mapas de velocidade da água e transporte de sal, levando a um ferramenta para estimar o transporte de água e sal em regiões específicas do Atlântico Tropical.
|Quasi-decadal to interdecadal SST variability in the Benguela Upwelling System
|Folly Serge Tomety and Mathieu Rouault
Nansen-Tutu Centre for Marine Environmental Research, Department of Oceanography, University of Cape Town, South Africa
|The observations and reanalysis datasets are used to investigate the sea surface temperature (SST) decadal fluctuation in the southern Benguela upwelling system and their teleconnections with the global ocean. Two dominant decadal time scales of variability are identified over the twentieth century: the quasi-decadal (9-14 years) and the Interdecadal (19-26 years). The teleconnections between SST in the southern Benguela system and SST over the global ocean are different at both quasi-decadal and interdecadal time scales. At the interdecadal scale, the tropical and subtropical oceans, especially the Pacific Ocean appear to be strongly linked to the southern Benguela SST fluctuations. The teleconnections of the tropical Pacific (the El Niño Southern Oscillation ENSO-like and Pacific Decadal Oscillation (PDO)) with SB SST are statistically significant. At the quasi-decadal time scale, there is no relationship between SB SST and the climate modes used in this study. However, the composite anomalies show a link between the SB SST and the whole South Atlantic Ocean. The pattern of SB SST composite anomalies in the South Atlantic is reminiscent of the South Atlantic Subtropical Dipole mode (SASD), the dominant mode of variability in the South Atlantic Basin.
|A cooperative response to the paraíba oil spill incident: results from a tactical-operational exercise
|Diego Xavier Bezerra
National Institute for Space Research
|The appearance of oil slicks on the beaches of Paraíba, during the days of December 31st, 2021 and January 3rd, 2022, provided an opportunity for the coalition of the Brazilian scientific community on the topic of detection, prediction and monitoring of oil spills at sea, in the interest of deterring future incidents. The search for the best available scientific knowledge is fundamental and a guiding element to improve the correct preparation for potential future oil spill incidents in the Blue Amazon, starting with the establishment of inclusive mechanisms of technical-scientific articulation, aiming to increase detection capacity, impact prevention, and timely response actions. The recent allocation of resources by the MCTI/FINEP to the development of a “multi-user system for the detection, prediction and monitoring of oil slicks at sea” (SisMOM), with the participation of INPE, Science and Technology Institutes, Brazilian Navy and IBAMA, is for the Brazilian nation a fact that brings a better future when faced with incidents of oil spills at sea. The present work constitutes a tactical-operational demonstration of the analysis, synthesis and response capacity of researchers and institutions involved in a multi-user system (SisMOM) to articulate themselves permanently in response to incidents of oil spills at sea. The proposed method, based on oil spill trajectory modelling and analysis of Automatic Identification System (AIS) constitutes a practical solution for improving maritime domain awareness and fast oil spill response.
|A Lagrangian study of cross-basin, seasonal connection in the Tropical Atlantic
|Emanuel Giarolla and Paulo Nobre
Brazilian National Institute for Space Research
Av. dos Astronautas, 1758
|In August of 2021, the presence of marine debris, including plastic materials and tar balls, were reported along the beaches of Fernando de Noronha archipelago, located 354 km offshore from the Brazilian coast (3°51′S, 32°25′W). Here, we investigate the debris’ many possible origins, it was questioned whether such debris could come from regions as far as the African coast.
A set of experiments were performed with a Lagrangian model (Ocean Parcels), using Mercator ocean surface currents (1/12o global analysis forecast “phy_001_024”). The “backward” simulations (going back in time) showed that parcels (or particles), released near the Fernando de Noronha beaches, eventually reach the African coast, spending a whole year in this journey. On the other hand, in “forward” simulations releasing the parcels near the African coast, e.g., close to the Congo river basin, the particles usually keep trapped in that regional ocean circulation for weeks and, under some circumstances depending on the season of the year, ultimately are captured by the main Atlantic ocean circulation, then increasing the chances of those set of particles to reach the archipelago beaches region in the course of time.
|Spatial distribution of Caretta-Caretta turtle and the Florida current transports at interannual timescales
|L. Sánchez-Gabán (1), I. Polo (1), F. Ramírez (2)
(1) Dpto. Física de la Tierra y Astrofísica, UCM, Spain (2) ICM-CSIC, Barcelona, Spain
|The Atlantic Meridional Overturning Circulation (AMOC) is the main system for the exchange of water, heat and carbon across the North Atlantic. It distinguishes a northward flow of warm, shallow water and a southward flow of colder, deeper water. Studies show that variability in the AMOC has an impact on climate and therefore on habitats and biodiversity. Based on observed physical and ecological data, this study aims to test the hypothesis that variability in oceanic transport in the Straits of Florida affects the distribution of Caretta-Caretta turtle. In summer, a higher density of records has been observed in coastal areas and in coastal areas and in the north, as this coincides with the breeding and migratory period. At winter, records were found in the Sargasso Sea due to the return to nesting areas due to the subtropical gyre. The results suggest that, mainly in summer, with an anomalous positive Florida transport, more records are observed in the north Atlantic, probably because the intensified Gulf Stream transports the current transports turtles further away. In contrast, with anomalously negative Florida transport, more records occur in the Gulf of Mexico and around Florida. At winter, with a positive anomalous transport, more observations occur in the Sargasso Sea, probably due to an intensification of the subtropical gyre. Despite the limitations, which mainly affect the ecological data, it is expected that an analysis of turtle trajectories will allow conclusions to be drawn about variations in the AMOC due to climate change.
|Influence of ENSO events on the Atlantic coast of the Iberian Peninsula
|E. Mohino (1), I. Polo (1), B. Rodríguez-Fonseca (1), J. Miguel-Fernández (1), E. Exarchou (2), P. Ortega (2), P. Castellanos (2,3)
(1) Dpto. Física de la Tierra y Astrofísica, UCM, Spain (2) Barcelona Supercomputing Center (BSC), Barcelona, Spain. (3) Marine and Environmental Sciences Centre (MARE), Lisboa, Portugal
|In this study, we analyse the potential influence of the ENSO events in the coastal upwelling of the Iberian Peninsula as part of the Canary Current Upwelling System, considering the chlorophyll concentration as an indicator of upwelling with satellite data since 1997. The results suggest that, on the one hand, El Niño events could be leading by 10-8 months the increased of boreal summer upwelling in the Atlantic coast of the Iberian Peninsula. On the other hand, La Niña events and the increased SLP in the Azores high region, are linked to an enhancement of the coastal upwelling in that region in the month of October. Data from a biogeochemical reanalysis is compared with the observations. The influence of ENSO on Tropical North Atlantic and NAO variability could provide a teleconnection mechanism for the observed link between ENSO and enhanced upwelling in the Iberian coast.