|¤||Poster Title||Author(s) and Affiliation(s)||Abstract|
|55||Seasonal Cycle of Sea Surface Salinity in the Angola Upwelling System||
F. M. Awo1, M. Rouault1, M. Ostrowski3, F. S. Tomety1, C. Y. Da-Allada2,4, and
1Nansen-Tutu Centre for Marine Environmental Research, Department of Oceanography, University of Cape Town, Cape Town, South Africa,
2ICMPA-UNESCO Chair/UAC, Cotonou, Bénin,
3Institute of Marine Research (IMR), Bergen, Norway,
4LaGEA/ENSTP/UNSTIM, Abomey, Bénin,
5LEGOS, CNES/CNRS/IRD/UPS, Toulouse, France
|The seasonal cycle of sea surface salinity (SSS) along the Angolan coast is investigated using observations and a regional ocean model. The model reproduces the main characteristic of the seasonal cycle of SSS along the Angolan coast, such as the freshwater discharge signature off the Congo River plume and the low-salinity observed in February/March and October/November along the Angolan coast. The model also reproduces the two maxima of salinity in June/July and December/January. The analysis of the model salt budget reveals that the semi-annual cycle of SSS is controlled by the meridional advection of surface water, the vertical advection of subsurface water, and the mixing at the base of the mixed layer. The meridional advection is controlled by the Angola Current, which brings low-salinity water from offshore region of the Congolese coast toward the south Angolan coast in February/March and October/November. The vertical advection contribution is modulated by the vertical stratification of salinity and not by vertical velocities, which peak during the main Angolan upwelling season. The vertical stratification is due to the low-salinity intrusion at the Angolan coast that creates a strong vertical salinity gradient, with low-salinity at the surface and high salinity at the subsurface.|
|50||Analysing changes in mesopelagic biomass size spectra||
Normalized biomass size spectra (NBSS) are an important tool to describe organization and matter flow in biological systems, where changes in slopes are considered attributed to changes in community composition (increase or decrease of abundance of smaller or bigger specimens), while changes in intercepts are considered attributed to changes in system’s productivity. However, given that slopes and intercepts are negatively correlated, an approach is developed to distinguish between the inherent slope-intercept relationship and the changes attributed to ecological perturbations. One way is to apply MLE estimation of NBSS slopes, which does not require the calculation of intercepts. The other is based on a randomization (resampling) procedure, so that slope-intercept properties can be analysed for each of the communities as well as for different periods. The mesopelagic data analysed comprise 4 case studies for which paired designs are available, i.e. Southern Benguela 2019 and 2021 (different upwelling seasons), and tropical and subtropical as well as OMZ assemblages from 1966-71 and 2015 (different periods).
A reference vector is defined incorporating all the possible slope-intercept combinations after resampling. The changes of the 4 case studies are investigated in terms of their deviation from the reference vector and the quantity of this deviation by means of the size of the shifting vector in each of the case studies. Biomass difference by period and vector size are correlated, and increases in linear slope were also correlated to increases in MLE slopes. Further data on Northern Benguela mesopelagic assemblages are being analysed, so as to get a fifth case study.
|45||Investigation of the surface and subsurface salinity wakes of tropical cyclones||
Aurpita Saha (1,2), Gregory R. Foltz (2), Claudia Schmid (2)
(1) Cooperative Institute for Marine and Atmospheric Studies, University of Miami, Miami, FL, USA
(2) NOAA/Atlantic Oceanographic and Meteorological Laboratory, Miami, FL, USA
|The northwestern tropical Atlantic Ocean is a breeding ground for devastating tropical cyclones (TC) that are also prominent upper ocean mixing agents. In this region, freshening from TC rainfall and freshwater input from river runoff cause salinity stratification that can reduce TC-induced sea surface temperature cooling. The reduced cooling makes TC rapid intensification more likely. Freshwater anomalies in this region also have the potential to alter the properties of the waters involved in the upper limb of the Atlantic Meridional Overturning Circulation and further north crucially change the water stability in the convection sites of the subpolar gyre, therefore having climatic impacts. Locally and over smaller time-scales, salinity anomalies can induce changes in the tropical surface mixed-layer, upper-ocean salt budgets, and consequently in the position and strength of equatorial and off-equatorial currents. The impact of TCs on heat transport and circulation has been explored, but there is very limited understanding of the impact of TCs on upper-ocean salinity, salinity transport and ocean circulation. It is therefore crucial to understand the role of TC-induced salinity variability in the physics of the upper ocean. In this study, the surface signature and vertical structure of salinity wakes on various timescales are presented using data from Argo floats and satellite observations. Significant differences are found in the characteristics of the TC wakes in the northwestern tropical Atlantic Ocean. A saline surface salinity wake and subsurface freshening dominate in the Amazon plume region and in the northern Gulf of Mexico. In contrast, the southern Gulf of Mexico shows predominantly a fresh wake. We explore the potential of a mixed layer salinity budget to explain these different TC-induced salinity anomalies. Differences in the residence times of the subsurface salinity anomalies and potential implications for the large-scale ocean circulation will also be discussed.|
|44||Mesoscale dynamics in the northern Gulf of Guinea||
Abdoul Karim Thiam (1), Gaël Alory (2), Isabelle Dadou (2), Yves Morel (2), Dante Napolitano (2), Julien Jouanno (2)
The mesoscale represents the spatial scale from 50 km to 500 km. Dynamics associated with this scale, especially the oceanic eddies, is of paramount importance. Indeed, the kinetic energy of the ocean is dominated by these quasi-circular structures which have the property to trap water masses and transport them over distances depending on the characteristics of the eddies. Eddies can locally influence heat fluxes at the ocean-atmosphere interface, but also winds, cloud cover, precipitation and biological productivity.
However, little is known about mesoscale activity in the Gulf of Guinea, especially in its northern part where seasonal coastal upwelling occurs. Thus, the aim of this work is to quantify the mesoscale dynamics and its potential role in exchanges between the coastal and open ocean in the northern Gulf of Guinea, using a realistic NEMO OGCM simulation at 1/36° resolution.
Focusing on the year 2016 and the July-August-September upwelling season, a cyclonic eddy located east of Cape Three Points from mid-July to mid-August was detected. This cyclone is characterized by cold waters trapped within it. To understand the origins of these waters and the mechanism of formation of this eddy, backward lagrangian trajectories were simulated. They show that eddy waters come from active upwelling cells off Ivory Coast and Ghana. Once these waters are brought to the surface, they are trapped and warmed in the cyclone by mixing with the warmer waters of the Guinea Current.
Next, the influence of these dynamics and the contribution of this eddy to the upwelling will be studied by a heat budget. The fate of these waters will also be studied by simulating forward lagrangian trajectories, to evaluate possible exchanges between the coastal and open ocean. General characteristics of the eddies (size, amplitude, lifetime, seasonality) extracted for the NEMO model and from altimetry will be also compared for year 2016.
|33||A comparison of equatorial waves in two regions of the Atlantic separated by the Archipelago of St. Peter and St. Paul||
Paulo S. Polito and Olga T. Sato
University of Sâo Paulo, Oceanographic Institute
|Intraseasonal variability of sea surface temperature (SST) and height (SSH) in the equatorial Atlantic is often associated in the literature to Tropical Instability Waves (TIWs) or, more specifically, to Yanai and Rossby waves. Within the broad equatorial channel there are two distinct regions where these waves are observed, one in the central portion of the basin and another much closer to South America. The tiny Archipelago of St. Peter and St. Paul (ASPSP), near 29°W, 0°, is between these two areas. In this study we separate the intraseasonal signals of equatorial mesoscale from the rest of the variability in the SSH and SST fields, in (t, x, y) dimensions, and in the temperature profiles T(t, z) as measured by the PIRATA moorings. At this initial step we use a least squares fit to remove the seasonal signal and long-term trend, and a simple high-pass filter afterwards. From that we can see how this particular band of variability decays with depth as a way to quantify the vertical limit of its influence on the ecosystem. This region is characterized by a very shallow thermocline, and any phenomenon that moves it vertically has a potential to impact the part of the biota that is temperature and nutrient controlled. These estimates are performed in areas to the east and to the west of the ASPSP for comparison. As a further refinement, we isolate the part of frequency and zonal wavenumber spectrum that characterize the waves at each latitude and re-assemble the filtered fields into maps that contain only waves. That allows us to see the wave-like features apart from everything else, where and when their amplitude is signicant, and whether there is an interconnection between the two regions separated by the ASPSP.|
|31||Mesopelagic fish diversity across the Tropical and South Atlantic||
Henrike Andresen (1)
Leandro Nolé Eduardo (2)
Aline Barbosa da Silva (3)
Heino O. Fock (1)
(1) Thuenen Institute of Sea Fisheries, Bremerhaven, Germany
(2) Institut de Recherche pour le Développement, UMR MARBEC, Sète, France
(3) FURG, Instituto de Oceanografia, Rio Grande – RS Brasil
Mesopelagic fishes inhabit the twilight zone of the open oceans between about 200 and 1000 m depth. They are, collectively, the vertebrates with the highest biomass in the ocean. Many species perform diel vertical migrations, with which they contribute actively to the ocean’s biological carbon pump. For that reason, they are increasingly becoming a focus of scientific attention. In addition, they are a potential new food source. However, due to the low commercial interest in the past and the difficult accessibility of their habitat, comparatively little is known about their ecology.
One of the aims of the TRIATLAS project is a status assessment of Tropical and South Atlantic marine ecosystems. We are investigating and mapping large scale patterns in the biodiversity of mesopelagic fishes in relation to environmental characteristics, also using valuable historical data from net sampling.
Primary production appears to be a main predictor of mesopelagic fish diversity, with lowest diversities observed in the oligotrophic South Atlantic. Remarkably, this effect is more pronounced in shallow catches than at greater depth. Local zones of low oxygen have distinct faunas. Our results can help refine the biogeography of mesopelagic ecoregions. A combination with analyses of the functional composition of the communities will be useful to further identify vulnerable regions and set conservation priorities.
|30||Local ecological responses to global climate processes||
Núria Camps1, Laura Julià1, Francisco Ramírez1, Marta Coll1, Belén Rodríguez de Fonseca2
1-Institute of Marine Science (ICM-CSIC, Spain)
2-Universidad Complutense de Madrid, Grupo Excelente de Invetigación TROPA
Climate variability modes such as El Niño/La Niña are impacting natural systems and processes globally. These modes can have far-reaching consequences on marine ecosystems by atmospheric teleconnections. To our knowledge studies aiming to evaluate, from a wide-scale, holistic, and integrative way; how these signals propagate through local to regional marine food webs are clearly lacking. Here, we evaluate the role of general, large-scale climate indexes (e.g., El Niño Southern Oscillation -ENSO-, North Atlantic Oscillation -NAO- Index) as drivers of local patterns of marine productivity in the Atlantic Ocean, and their ultimate consequences for marine organisms from a wide range of taxa. We used the longest available time-series (1993-2020) of spatially-explicit information on chlorophyll-a concentration (chl-a) to explore the cell-basis correlations between the global indexes and local patterns of marine productivity. These spatial assessments were then combined with an extensive bibliographic review of available scientific literature that used global indexes as predictors of biological responses (e.g., phenological, distributional and demographic responses) in a vast array of marine life.
Our spatial assessments revealed that ENSO is significantly and positively correlated with chl-a in marine regions from the Central Atlantic, particularly in Spring. In the case of NAO, significant and reversed correlations with chl-a were observed for template areas of the North Atlantic. Studies using global indexes as predictors of biological responses are clearly biased towards the Northern Hemisphere (852 out of 1.042 studies). Overall, 57% of screened studies pointed to the significant role of global indexes as drivers of biological responses, particularly demographic responses: changes in abundances or biomasses which represented ca. 70% of significant responses. We observed a large spatial heterogeneity, with no clear spatial congruence between responses in terms of chl-a and the signals reported for the different taxonomic groups. This suggests that other factors (e.g., biodiversity and configuration of the food webs, and fishing pressure) may alter these responses. Further research should be focused on the Central/Southern Atlantic Ocean to gather more information on how climate processes affect the southern marine community.
|27||How can coastally trapped waves explain the productivity season in coastal waters off Angola?||
Mareike Körner (1), Peter Brandt (1,2), Marcus Dengler (1), Ajit Subramaniam (3), Gerd Krahmann (1)
(1) GEOMAR Helmholtz Centre for Ocean Research, Kiel, Germany
(2) Faculty of Mathematics and Natural Sciences, Kiel University, Kiel, Germany
(3) Lamont-Doherthy Earth Observatory, Columbia University, Palisades, NY, United States of America
The tropical Angolan upwelling system is a highly productive ecosystem with a distinct seasonal variability. Productivity peaks in austral winter in a narrow band along the coast. The seasonality cannot be explained by local wind-driven upwelling as upwelling favorable winds experience their minimum during austral winter. The Angolan ecosystem is connected to equatorial dynamics via the propagation of coastally trapped waves (CTWs) producing periodic upwelling and downwelling near the coast. The productivity season off the coast of Angola is associated with the CTW upwelling phase. Here we analyze hydrographic, ocean turbulence and satellite data to investigate how CTWs control the productivity in coastal waters off Angola.
Ocean turbulence data taken during several cruises shows that high mixing rates are found in shallow waters (<100 m) at the Angolan shelf around the year. Thus, seasonal variations in mixing does not explain seasonal differences in productivity. However, associated with the passage of CTWs the thermocline moves vertically ~ 50 m up and down throughout the year. The analysis of nutrient and oxygen data shows that the nutricline follows this movement. Near the coast the upward movement of the nutricline is associated with a horizontal nutrient transport toward the coast, where the nutricline reaches regions of high mixing. Vertical and horizontal nutrient advection by CTWs and near-coastal mixing are suggested to explain seasonal differences in productivity in coastal waters off Angola. Furthermore, interannual variability in the strength of the net primary production correlate with the interannual variability of CTW amplitude. This underlines the role of CTW-driven nutrient supply for the Angolan upwelling system. Additionally, the connection between equatorial dynamics and productivity introduces a possibility for prediction of primary production off Angola.
|19||Investigation of the deep scattering layer along a trans-equatorial transect in the Atlantic Ocean||
Alix Rommel, Tim Dudeck, Werner Ekau, and Heino Fock
Leibniz Centre for Tropical Marine Research (ZMT), Bremen, Germany; Thünen Institute of Sea Fisheries, Bremerhaven, Germany
|The deep scattering layer (DSL) can be observed between 300-800m depth throughout the world oceans. Some DSL organisms undertake diel vertical migration (DVM), thereby playing an important role in the ocean’s biogeochemical cycles. Marked spatio-temporal differences in the DSL vertical distribution and DVM pattern have been observed around the world. The environmental factors responsible for the DSL daytime depth and vertical extension, and the reasons for performing migrating behaviours are still a point of contention in the scientific community. Here we will present the results of investigations on the DSL along a transect between Namibia and Cape Verde and its relationship to observed environmental parameters. Hydroacoustic data collected during a cruise with RV Meteor in 2019 were used to determine the weighted mean depth (WMD) of the DSL in different ecoregions (Sutton et al., 2017) and correlated to oceanographic data. Daytime WMD of the DSL was stable throughout the transect (398.3 ± 25.7m), but the environmental factors affecting the DSL varied between ecoregions. The DSL depth in the Tropical and West Equatorial Atlantic ecoregion showed a negative correlation (-0.597) with the 2.5mL/L isoline of dissolved oxygen. However, in the Guinea Basin and East Equatorial Atlantic ecoregion, the DSL depth was instead correlated with the 50μmol.s-1.m-2 absolute light intensity isolume (0.7689) and salinity (0.560). Nonetheless, no single factor was sufficient to explain the DSL position and movement throughout the water column. The stability of the DSL along the transect could however indicate a stronger dependence on light than other factors.|
|16||Climate and fishing simultaneously impact small pelagic fish in the southernmost tip of Africa||
Francisco Ramírez1, Lynne J. Shannon2, Carl D. van der Lingen2,3, Laura Julià1, Jeroen Steenbeek4, Marta Coll1,4
1 ICM-CSIC, Spain
2 University of Cape Town, South Africa
3 Fisheries Management, Department of Forestry, Fisheries and the Environment.
4 Ecopath International Initiative (EII) Research Association, Spain.
|Climate and fisheries interact, often synergistically, and may challenge marine ecosystems functioning and, ultimately, seafood provision and human wellbeing that depend on them. Holistic and integrative approaches aiming at evaluating the spatial overlap between these major stressors are crucial for identifying marine regions and key fish species that deserve conservation priority to prevent future collapses. Based on highly resolved information on environmental conditions and fishing pressure from the Southern Benguela Ecosystem and the Agulhas Bank system, of South Africa, we identified main areas where the small pelagic fish community (European anchovy Engraulis encrasicolus, South African sardine Sardinops sagax, and West Coast round herring Etrumeus whiteheadi) have been highly impacted in terms of unfavourable environmental conditions and heavy fishing historically (1993-2018). We identified these areas as cumulative “hotspots” of climate change and fishing impact. We also identified fishing grounds where environmental conditions are now more favourable for pelagic fish species, terming these “bright spots” of climate change. Environmental conditions and fishing intensity contrasted between Southern Benguela and the Agulhas Bank system, with the Southern Benguela region accumulating most of cumulative “hotspots”, and showing the most negative trends in CPUE. Contrastingly, neighbouring “bright spots” identified in the Agulhas system and nearby areas showed more positive trends in CPUE, suggesting that they may support sustainable fishing growth in the medium term. These areas may serve as alternatives to allocate fisheries and alleviate pressure on the doubly and highly impacted cumulative hotspots from the west side of the southernmost tip of Africa.|
An inventory of dissolved oxygen conditions along the eastern boundary of tropical
and subtropical Atlantic: building oxygen monitoring capacity in West African countries, 2013-2019
Paulo Coelho el al., 2021
Instituto Nacional de Investigação Pesqueira e Marinha.
Co-Author(s): Pedro Tchipalanga, Marisa Macuéria, Anja van der Plas, Benjamin N’Guessan, Kanga Desiré, Ahmed Makaoui, Ismail Bessa, Mohamed Idrissi, Omar Ettahiri, Karim Hilmi, Issufo Halo, Sunke Schmidtko, Marcus Dengler, Peter Brandt, David Cervantes, Helene Lødemol, Melissa Chierici, Marek Ostrowski, Mamadou Lamba, Abdoulaye Sarre, Saliou Faye.
Climate change is expected to result in a reduction of oceanic oxygen concentration and an expansion of oxygen minimum zones (OMZs) in the tropical ocean. In West Africa, where rich fisheries are essential for supporting the livelihood of coastal populations, the prospect of expanding hypoxic conditions into fishable coastal shelf waters is a major concern. Here, we present an inventory of oxygen content in the coastal fringe off West Africa between 30°N and 30°S. Our aim is to present a unified and fisheries relevant information on oxygen water quality along the entire West African continental boundary. The inventory collates the results of recent international expeditions monitoring trans-regional oxygen data over the shelves of West African countries. The EAF Nansen Programme surveys on board the RV Dr Fridtjof Nansen in 2017 and 2019 provided one source such data. During these surveys, scientists representing regional research fisheries institutes carried out observations on dissolved oxygen conditions within their respective exclusive economic zones (EEZ). These data are complemented by oxygen data collected during different international expeditions particularly including research cruises with RV Meteor covering the EEZ of West African countries during 2013-2019. The Meteor results have long established the baseline for OMZ monitoring. In this presentation, we show the distribution of the mean and extreme oxygen conditions in the coastal fringe along the West African continental boundary, provide insight into the seasonal variability across the region, identify data-poor subregions, and discuss potential impacts of the observed oxygen distributions on local ecosystems and fisheries.
Key words: climate change, oxygen-minimum zones, environmental variable, fisheries.
|3||A global stratification product of the thermocline based on Argo observations||
Marisa Roch (1), Peter Brandt (1), (2), Sunke Schmidtko (1)
(1) GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany, (2) Faculty of Mathematics and Natural Sciences, Kiel University, Germany
Enhanced ocean stratification is projected as a result of a warming climate. Changes of upper-ocean stratification have the potential to impact physical, biogeochemical and ecological processes, such as ocean circulation and redistribution of heat and salt, ocean ventilation and air-sea interactions, nutrient fluxes, primary productivity and fisheries. However, in what terms these processes might be affected still remains uncertain.
This investigation particularly addresses variations of the vertical stratification maximum which is found at the depth of the thermocline/pycnocline. Separation between seasons shows a summertime increase of the thermocline stratification in both hemispheres, respectively. Besides, on global average the Northern Hemisphere’s winter demonstrates an intensifying stratification, while the Southern Hemisphere’s winter vertical stratification maximum does not change much. The enhancing thermocline stratification is accompanied by a warming and partly freshening mixed layer. Additionally, we observe a mixed layer deepening which could further contribute to the increasing stratification, since the summertime thermocline depth does not change much. Focusing locally on the tropical and South Atlantic some different features can be observed. While the tropical Atlantic reveals a mixed layer warming in both seasons, the South Atlantic is warming in its winter, but cooling south of 25°S in its summer. This pattern mirrors the trend of the thermocline stratification in these regions.
The aim of this study is further to produce a global product of the stratification maximum based on Argo observations from 2006-2021. In order to verify our product, we compare the results of the Argo data to other CTD measurements as obtained from research vessels and buoys, e.g., PIRATA. With this we receive a quality-controlled global product which allows us to make a statement about global and regional variability of thermocline stratification.
|29||Population fluctuations predictability||
Rodrigo Crespo-Miguel (a), Francisco J. Cao-García (a,b)
(a) Departamento de Estructura de la Materia, Física Térmica y Electrónica, Facultad de Ciencias Físicas, Universidad Complutense de Madrid. Plaza de Ciencias 1, 28040 Madrid, Spain
(b) Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA-Nanociencia). Calle Faraday 9, 28049 Madrid, Spain.
|Population dynamics is affected by environmental fluctuations (as climate variations) which have a characteristic correlation time. Strikingly, the time scale of predictability can be larger for the population dynamics than for the underlying environmental fluctuations. Here, we present a general mechanism leading to this increase in predictability. We considered colored environmental fluctuation acting on a population close to equilibrium. In this framework, we derived the temporal auto and cross-correlation functions for the environmental and population fluctuations. We found a general correlation time hierarchy leaded by the environmental-population correlation time, closely followed by the population autocorrelation time. The increased predictability of the population fluctuations arises as an increase in its autocorrelation and cross-correlation times. These increases are enhanced by the slow damping of the population fluctuations, which has an integrative effect on the impact of correlated environmental fluctuations. Therefore, population fluctuations predictability is enhanced when the damping time of the population fluctuation is larger than the environmental fluctuations. This general mechanism can be quite frequent in nature and it largely increases the perspectives of doing reliable predictions of population fluctuations.|
|24||Connection between marine ecosystems in the Tropical Atlantic via oceanic wave propagation||
I. Polo, M. Martin-Rey, E. Calvo-Miguélez, I. Gómara, B. Rodríguez-Fonseca, T. Losada, E. Mohino
Dpto. Física de la Tierra y Astrofísica, UCM, Spain
|In the Tropical Atlantic are the equatorial and eastern coastal upwelling systems; in the north the Mauritania/Senegal system and in the south the Angola/Benguela system. These systems provide a large amount of biomass throughout the year and are key to biodiversity in the basins. Previous analyses of the predictability of the Mauritanian upwelling using chlorophyll concentration data have revealed that a La Niña event in the Pacific leads to changes in the Tropical North Atlantic (TNA) that impact the Mauritanian upwelling. Using an index of upwelling in the Mauritania region we analyse the relationship with the other upwelling systems in the tropical Atlantic. Results suggest that the adjustment of the ocean through equatorial ocean waves to anomalous winds in the TNA region allows a connection between the Mauritania and Benguela upwelling systems. These paths give potential predictability to the South Atlantic from atmospheric and oceanic teleconnections in the North Atlantic.|
|13||Marine Heat Waves in the Brazil Current system||
Camila Artana, Marta Coll and Jose Luis Pelegri
Instituto Ciencias del Mar
|Ocean warming has not been homogenous over the past fifty years. One of the regions with the largest warming trends is the Brazil Current. Superimposed to these long-term trends are Marine Heat Waves (MHWs), defined as episodes of anomalous warming in the ocean that can last from a few days to months. These extreme events have been associated with dramatic consequences on marine ecosystems with strong socio-economic impacts. For example, MHWs have contributed to massive fish mortality, toxic algal blooms and temporary closure of recreational beaches (summer 2017), to unprecedented mortality of the coral reefs at 17° S (summer 2019) and to an increase in pollution in the Santa Catarina Bay, where the first recorded episode of anoxia occurred in 2020. MHWs have been mainly explored at the surface, and their signal at depth remains mainly unexplored. With state-of-the-art highly performant models we can now have access to subsurface information of MHWs. In this work, we characterize surface and subsurface signals of MHWs in the Southwestern Atlantic Ocean using a high-resolution (1/12 degree) ocean reanalysis and sea surface temperature satellite data. We find that surface MHWs are well reproduced in the reanalysis regarding amplitude, frequency and duration. We show that characteristics of MHWs in the Brazil Current region change with latitude, with MHWs being more frequent and less persistent in Rio de Janeiro than in Salvador de Bahia. Using the K-means clustering method, MHWs are classified into 7 different types according to their characteristics. The characterization shows that some MHWs are more intense and persistent at depth than at the surface. We investigate the drivers of each type of MHWs and examine their preconditions: ocean stratification, local atmospheric conditions and oceanic heat advection. This characterization paves the road to investigate the impact of each type of MHWs on marine resources and food security and to identify regions of high vulnerability, where increased occurrences of MHWs overlap with areas of high human activities such as fisheries intensity.|
|8||Interaction between upwelling and marine heatwaves events in Cabo Frio/Rio de Janeiro||
Jhoseny S. Santos, Regina. R. Rodrigues, Afonso G. Neto, Daniela L. Corrêa.
Department of Oceanography, Federal University of Santa Catarina, Brazil
|Upwelling is a process by which cold and nutrient-enriched waters are brought into the euphotic zone and, as such, supports some of the most productive ecosystems in the global. In contrast, marine heatwaves are extreme ocean warming events that devastate marine ecosystems. Upwelling in the western South Atlantic, especially during austral summer, occurs more intensely off the coast of Cabo Frio, Brazil. There, the South Atlantic Central Water rises toward the continental shelf and eventually to the surface as a response to the strengthing of northeasterly winds. Even though there is strong evidence that marine heatwaves are becoming more frequent and intense in the western South Atlantic, it is not clear that these events have intensified in the upwelling region of Cabo Frio. In this study, we apply a standard methodology for calculating marine heatwaves and cold spells from satellite sea surface temperature and use the latter as a proxy for upwelling events. We focus on the austral summer for the period from 1982 to 2020. We found a significant reduction in upwelling events during this period. At the same time, marine heatwaves become more frequent and intense. Analysis of daily wind and sea level pressure suggests that there has been a decrease in the occurrence of upwelling favorable winds from the northeast in the region. And this is due to changes in the location and the intensity of the South Atlantic Subtropical High.|
|6||Subsurface marine heatwaves in the equatorial Atlantic||
Daniela L. Corrêa, Regina. R. Rodrigues, Afonso G. Neto, Jhoseny S. Santos
Department of Oceanography, Federal University of Santa Catarina, Brazil
|Marine heatwaves (MHWs) are events of extreme ocean warming and are expected to increase in intensity and frequency under anthropogenic climate change. The temperature anomaly or the intensity during an MHW event can represent the level of acute heat stress for marine ecosystems and is closely linked to the mortality of marine organisms. Despite its impact on marine life, most studies focus on sea surface MHW. Therefore, in this study, we investigate the vertical structure of the MHW in the water column using in situ data from two buoys (0°N-10°W and 0°N-23°W) of the Prediction and Research Moored Array in the Tropical Atlantic (PIRATA). We first compare the in-situ measurements of sea surface temperature from the two buoys with those from the satellite data (NOAA-OISST). Even though they are strongly correlated, the satellite data underestimate in situ measurements. We then apply the standard methodology to calculate MHW for all depths at the two locations along the equatorial Atlantic. From 1999 to 2021, 31% of all MHWs detected had higher duration and intensity in the subsurface than in surface. We investigate then two unprecedented subsurface MHW events in 2010 and 2021 with anomalies of 3°C reaching down to 140 m of depth. These events did not have a surface signature and would not be detected by the traditional satellite-based methodology. Both events happened in November and July, respectively, and are associated with weakening the easterly trade winds, which reduces equatorial upwelling and deepens the thermocline along the equatorial Atlantic. Contrary to initially thought, they are associated with the Atlantic Niño and secondary Atlantic Niño that occurs during the boreal summer and late austral spring.|
|2||Marine heat waves: The added value of a high resolution regional climate model||
Marie Pontoppidan, Jerry Tjiputra, Priscilla Mooney, Chiara De Falco
NORCE Norwegian Research Centre, Bergen, Norway
|Marine heat waves (MHW’s) exert a substantial impact on human life and ecosystems in the ocean. To mitigate future changes in MHW’s it is detrimental to increase our mechanistic understanding, and this must be investigated on a local scale to understand the smaller scale dynamics of the heat waves. Here we compare the simulated MHW on a 12 km grid coupled ocean-atmosphere modelling system (COAWST), which includes the atmospheric model WRF and the ocean model ROMS with those from coarser CMIP6 Earth system models. While the number of MHW days are comparable within the uncertainty range, the mean length and frequency of MHW events are very distinct. We highlight processes driving these differences and potential implications for marine ecosystem predictions.|
|49||Agulhas leakage influence on the Tropical Atlantic Variability Modes||
Teresa Losada Doval*1, Paola Castellanos3, Belén Rodríguez-Fonseca*1,2,
Irene Polo*1, Wlademir Santis, Edmo D. J. Campos4
1 Universidad Complutense de Madrid, Madrid, Spain.
2 Instituto de Geociencias, IGEO, UYCM-CSIC, Madrid, Spain.
3 Marine and Environmental Science Centre, Universidade de Lisboa, Lisbon, Portugal
4.Instituto Oceanográfico da Universidade de São Paulo, Brazil
Output of an eddy-resolving numerical experiment (1/12-degree resolution), forced with NCEP Reanalysis products from 1970 to 2010, has been used for studying the variations in the Agulhas System and their impact on the tropical Atlantic Ocean. A previous work suggested that the increase of the Agulhas transport affects the western boundary system of the tropical Atlantic Ocean, which is directly related to an increase in the precipitation and latent heat flux along the western coast. Parallel to this, other studies found that tropical Atlantic interannual variability modes have changed showing a westward extension in the configuration of the Atlantic Niño.
Using the above-mentioned simulations, the present study tries to conciliate both results and to seed light about the impact of the Agulhas leakage in changes in the south Atlantic heat content and configuration of the oceanic interannual variability.
We find that there is an enhancement of the variability on the western equatorial Atlantic and an enhancement of the dynamic feedbacks in the equatorial Atlantic.
|48||Seasonal prediction of the teleconnections between ENSO and Atlantic Eastern Boundary Upwelling Systems||
Teresa Losada (1), Verónica Martín-Gómez (2), Lara Bober (1), Belén Rodríguez-Fonseca (1,3) Iñigo Gómara (1), Jorge López-Parages (3), Elsa Mohino (1), Irene Polo(1)
(1 )Departamento de Física de la Tierra y Astrofísica. Universidad Complutense de Madrid.
(2) Barcelona Supercomputing Center.
(3) Instituto de Geociencias (CSIC-UCM)
(4) Universidad de Málaga.
Using seasonal predictions from the ECMWF SEAS-5 System, we analyze the relationship between ENSO and two different upwelling indices in the regions of Benguela and Senegal-Mauritantia.
We find that observations and reanalysis show a strong teleconnection between the tropical Pacific and the region of Mauritania-Senegal in FMA. The system performs a very accurate prediction in the Tropics of the SST and wind stress variables leading to a good simulation of El Niño, but to a less realistic simulation of Senegal-Mauritania upwelling. The system shows a clear relationship between ENSO and the upwelling index that is based on the Ekman transport, but not so much between ENSO and the SST-based upwelling index.
Regarding Benguela region, reanalysis also show correlations between ENSO and upwelling indices in FMA. Results from the ECMWF SEAS-5 System fail to produce skillful predictions of Benguela upwelling phenomenon due to problems in the reproduction of the global atmospheric teleconnection pattern related to ENSO.
|41||Variability and predictability of chlorophyll in the major upwelling systems of the tropical Atlantic||
Elena Calvo-Miguélez (1), Belén Rodríguez-Fonseca (1,2), Iñigo Gómara (1,2), Eleftheria Exarchou (3), Pablo Ortega (3)
(1) Depto. Física de la Tierra y Astrofísica, Universidad Complutense de Madrid, Spain
(2) Instituto de Geociencias (IGEO), UCM-CSIC, Madrid, Spain
(3) Barcelona Supercomputing Center, Barcelona, Spain
Marine ecosystems are seriously threatened due to anthropogenic impacts. Knowledge of the drivers that determine the variability of these ecosystems is essential for their prediction, in order to ensure their conservation and sustainable management.
The most productive marine ecosystems worldwide are located in wind-driven upwelling regions, where nutrient-rich subsurface water is brought into the euphotic zone. Many of the changes in wind regimes take place as a consequence of the action of climate teleconnection patterns. Due to the thermal inertia of the ocean, some of these teleconnections can be predicted months ahead considering sea surface temperature information.
As organisms capable of photosynthesis are the first link in the food chain and are affected by wind-driven upwelling, in this work, we will focus on chlorophyll concentration predictability in two highly productive and variable regions: the coast of Mauritania/Senegal (FMAM) and the equatorial Atlantic (JJAS). With this aim, we use chlorophyll-a concentration from Copernicus Satellites and sea surface temperature (SST) anomalies from OISST (January 1998-December 2019).
The main SST drivers of chlorophyll variability have been already identified using a statistical methodology. The cross-validated hindcast based on Maximum Covariance Analysis (MCA) is used to assess predictability. The results show an important role of Pacific El Niño as well as internal modes of tropical Atlantic variability in seasonal chlorophyll prediction.
In pararell, we validate the chlorophyll-a reanalysis performed by the Barcelona Supercomputing Center for the period 1951-2020. Results indicate that this reanalysis can be used as a proxy of observations. As tropical basin interactions are not stationary on time, we take advantage of the use of this reanalysis to further analyze chlorophyll predictability from the mid-20th century.
|40||Biogeochemical and Ecosystem Predictions||
Filippa Fransner et al.
University of Bergen, Bjerknes Centre of Climate Research
|Here I will do a review of biogeochemical and ecosystem predictions, and present some upcoming work on the topic.|
Observing and modelling diurnal ocean mixed layer
in the eastern equatorial Atlantic
F. Gasparin1, H. Giordani2, S. Cravatte3, R. Bourdallé-Badie4, E. Kestenare1, J. Llido1, G. Samson4, B. Bourlès5
1 LEGOS/IRD, toulouse, France
2 CNRM, toulouse, France
3 LEGOS/IRD, New Caledonia, France
4 Mercator Ocean International, toulouse, France
5 LEGOS/IRD, Brest, France
|The diurnal cycle of the oceanic mixed layer has been shown to play a fundamental role in the dynamics of the tropical oceans. It modulates surface currents, air-sea fluxes and sea surface temperature, with climatic impacts since it rectifies into lower frequency. Combined efforts of observation and modelling have been undertaken in the eastern equatorial Atlantic Ocean to capture and improve the representation of the diurnal cycle in stratification, shear, and vertical mixing in the surface layer. During the PIRATA FR-31 and FR-32 cruises in 2021 and 2022, coordinated observations at 10°W, 0° (Argo floats with a dedicated diurnal mission, additional sensors at the PIRATA mooring, 48-h hydrographic stations) have been intercompared to assess our ability to capture diurnal signals with these various platforms. These also provided information on the significant spatial and temporal modulation of the diurnal cycle. At the same time, a new one-dimensional parameterization of the vertical mixing has been developed for ocean general circulation models to properly represent the diffusive and convective processes in a unified approach. We will show that the deepening of dense water in 1D analytic cases of the ocean model NEMO is significantly better captured than with standard diffusion parameterizations thanks to a better representation of the non-local entrainment fluxes. With such reinforcement of tropical observations associated with the refined parameterization of the full vertical mixing, we aim at demonstrating the importance of synergetic approaches between observations and model activities in the tropical Atlantic.|
|26||On the origin of the oil spill in northeast Brazil, 2019: A numerical approach||
Angelo T. Lemos, Paulo Nobre, Emanuel Giarolla, Rosio Camayo, Laercio Namikawa, Milton Kampel, Diego X. Bezerra, João Lorenzzetti, Jorge Gomes, Manoel D. Da Silva Jr.
Universidade Federal do Sul da Bahia, Instituto Nacional de Pesquisas Espaciais.
|Between August and December 2019 the Brazilian coast was reached by tonnes of tar balls and oil slicks in one of the worst environmental disasters in Brazilian history. In this study, we use the OSCAR (Oil Spill Contingency and Response) model in deterministic mode (Reed et al. 1999) to investigate the distribution of coastline positions affected by oil in individual oil spill experiments. A total of 49 simulation experiments were carried out from the initial date of July 29 until December 2, 2019 (127 days), with the oil spill locations between the latitudes of 5°S and 17°S and the longitudes of 32°W and 20°W. The model was forced by daily zonal and meridional velocity components (Mercator) and wind components at 10 m (ERA5). The simulations used 100,000 tons of Bunker oil of °API 14 and viscosity of 28000 cP, as representative oil of the heavy and high viscosity oil group. The experiment’s output was compared with in situ observations throughout the latitudinal distribution of the ashore oil for each experiment (as box plots) compared with the IBAMA sighting data through December 2, 2019. The forward oil spill simulations show a reasonable probability that the oil spill occurred from a mobile source between the latitudes of 10°S and 15°S and the longitudes of 32°W and 28°W, not excluding possible oil tanker routes close to this area. The simulation study suggested a higher probability that the oil came from one or more sources west of 25°W and that the weathering of the oil provided a fast submersion, rapidly reducing the amount of oil present on the surface. The analysis also suggests that the oil spread to the subsurface and reached the seabed of the Brazilian continental shelf before reaching the beaches.|
|25||An Atlas of Climatic Predictors for the Senegal-Mauritania and Equatorial Atlantic Marine Ecosystem Regions||
Iñigo Gómara (1,2), Belén Rodríguez-Fonseca (1,2), Elena Calvo-Miguélez (1), Marta Coll (3), Eleftheria Exarchou (4) and Pablo Ortega (4)
(1) Departamento de Física de la Tierra y Astrofísica, Universidad Complutense de Madrid, Madrid, Spain
(2) Instituto de Geociencias (UCM-CSIC), Madrid, Spain
(3) Instituto de Ciencias del Mar (ICM‐CSIC), Barcelona, Spain
(4) Barcelona Supercomputing Center, Barcelona, Spain
In this study seasonal to multi-annual predictability of Senegal-Mauritania and Equatorial Atlantic marine productivity is assessed considering climatic information. For this purpose, atmospheric (NCEP) and oceanic (GFDL-COBALT and BSC) reanalysis data are considered, together with a historical global marine ecosystem simulation from the FishMIP initiative (EcoOcean).
Leave-one-out cross-validated hindcasts based on Maximum Covariance Analysis reveal a key role of Atlantic Niños and Pacific Niñas as predecessors of enhanced marine primary productivity in the Senegal-Mauritania coast during the upwelling season (February to May). In the equatorial Atlantic, interannual variability of living marine resources is mainly dominated by Atlantic Niños/Niñas. The observed delay between climatic triggers and marine ecosystem responses also offers a potential for seasonal marine productivity prediction in the area. This is an ongoing TRIATLAS work framed within Task 7.3: Synthesis and assessment of key regional drivers of variability, change and stability.
|14||Towards EcoOcean v3: fostering the capacity of global marine ecosystem models to project the cumulative effects of change on the future ocean||
Marta Coll1,2 & Jeroen Steenbeek2
1 Institute of Marine Science (ICM-CSIC), Barcelona, Spain
2 Ecopath International Initiative (EII) Research Association, Barcelona, Spain
|We present progress towards EcoOcean v3, a spatial-temporal ecosystem modelling complex of the global ocean that spans spatial-temporal food-web dynamics from primary producers to top predators. Advancements since the last major update of the model (Coll et al., 2020) are (1) the improvement of the capacity to internally project species distributions, 2) the addition of environmental dynamics and human drivers considered, and (3) the development of validation and uncertainty assessments. Firs, we have complemented the explicit representation of species adaptation through evolutionary responses, and refined the climate-driven dispersal and species invasion dynamics combining statistical, and machine learning tools, with mechanistic tools, while drawing on global databases of species traits and interactions. Second, we have expanded EcoOcean with new spatiotemporal environmental dynamics and new anthropogenic multi-use patterns of the marine space to better forecast the state of future oceans. Finally, we have implemented validation and uncertainty assessments by using state-of-the art methods in distributed computing and statistical Bayesian modelling to advance towards the assessment of MEM uncertainty and to better communicate the results from scenarios. These advancements are integrated into EcoOcean v3 to develop, test and analyse spatial-temporal scenarios of future change of environmental dynamics and key human activities. The aim is to move forward the ability of global ecosystem modelling to quantify the cumulative impacts of spatial multiple stressors and of plausible ocean-based solutions to prevent, mitigate and adapt to global change.|
|95||Optimising Ocean Biogeochemical parameters in an Earth System Model using Ensemble Data Assimilation method in a Real Framework||
Tarkeshwar Singh1, Francois Counillon1, Jerry F. Tjiputra2 and Yiguo Wang1
1Nansen Environmental and Remote Sensing Center and Bjerknes Centre for Climate Research, Bergen, Norway
2NORCE Norwegian Research Centre AS, Bjerknes Centre for Climate Research, Bergen, Norway
Earth System models (ESMs) are powerful tools to study the ocean’s role in the global carbon cycle and estimate the impact of climate change on marine ecosystems. The ocean biogeochemical cycle (BGC) is governed by numerous physical and biological processes that change over space and time. Accurately representing the biological dynamics in an ESM is fundamental to improve the accuracy and reliability of their projections. However, due to limitations in observational data and to reduce model complexity, BGC models utilise many poorly constrained global parameters to mimic unresolved processes. Suboptimal tuning of the parameters could contribute significantly to the errors in the simulated biogeochemical tracers. In this study, we optimise the BGC parameters in the Norwegian Earth System Model (NorESM) using an Ensemble data assimilation (DA) method. The work follows on Singh et al. (2022), which successfully demonstrated the approach in an idealised twin experiment framework. We assimilate climatological observations of physics (salinity and temperature profiles) to constrain error in ocean physics and use BGC observations (Nitrate, Phosphate, Silicate, and Oxygen) to calibrate six BGC parameters. An iterative ensemble smoother technique achieves the best results because it overcomes issues related to ensemble spread collapse. Global parameters estimation outperforms the simulation with standard parameters specifically for nutrients. Estimating spatially varying parameters allows for some further improvements in some regions but also causes large regional degradations. We proposed an efficient and flexible framework to tune model parameters. The parameter estimation converges quickly requiring only a 10-year ensemble spin-up (of 30 members) to build sensitivity in the parameter, and the calibration converges within a 1-year cycle. We foresee that the same approach can be used to constraint error in the other components of the ESM.
Reference: Singh T, Counillon F, Tjiputra J, Wang Y and Gharamti ME (2022): Estimation of Ocean Biogeochemical Parameters in an Earth System Model Using the Dual One Step Ahead Smoother: A Twin Experiment. Front. Mar. Sci. 9:775394. doi: 10.3389/fmars.2022.775394
|10||The crucial role of international cooperation in deep-sea science: a case study of a 7-year French-Brazilian partnership||
Leandro N. Eduardo1 , Flávia Lucena-Frédou2, Michael M. Mincarone3, Arnaud Bertrand1,2
1 MARBEC, Univ. Montpellier, CNRS, Ifremer, IRD, Sète, France.
2Universidade Federal Rural de Pernambuco (UFRPE), Departamento de Pesca e Aquicultura, Recife, PE, Brazil.
3 Universidade Federal do Rio de Janeiro (UFRJ), Instituto de Biodiversidade e Sustentabilidade, Av. São José do Barreto, 764, Macaé, RJ, 27965-045, Brazil.
|Mesopelagic organisms are increasingly threatened, and there is a significant lack of knowledge on all aspects of their ecology, especially in tropical areas where most countries lack funding for deep-sea research. International partnerships therefore can be a powerful tool to foster such critical research. Here we compile the results of a 7-year French-Brazilian partnership to study the mesopelagic region in Brazil and discuss its importance on a regional and global scale. Three oceanographic campaigns aboard French oceanographic vessels have been carried out so far. More than 50 researchers from different scientific areas are involved in mesopelagics, of which 70% are Brazilian and 30% French. Of these, 60% are students, representing a significant investment in human resources for the next generation of deep-sea scientists. At least 10.000 specimens and 300 species of mesopelagic organisms were recorded, including at least ten new species (4%) and 80 (27%) new records for Brazilian waters. This international cooperation (see www.tapioca.fr) allowed us to tackle essential questions, such as (i)which are the main species, (ii)what are the features of their diel vertical migration, (iii) what are their trophic relationships, (iv) how are they related to oceanographic conditions, (v) what are their functional roles, and (vi) what are their main threats? Despite these efforts, the deep waters of Brazil and other developing economies remain mostly unknown. The results of the cooperation presented here show that strengthening international collaboration is an essential path to smooth asymmetries among countries and provide the deep-sea knowledge necessary to achieve global sustainability.|
|22||Dynamics of the Atlantic Marine Intertropical Convergence Zone||
Hervé Giordani and Philippe Peyrillé
This study aims at identifying the processes that force upward motions in the
Atlantic Marine ITCZ (AMI) from a numerical mesoscale simulation of June 2010.
It is shown that the Weak Temperature Gradient (WTG) approximation, based
on the balance between vertical temperature advection and diabatic heating,
fails to restore the simulated vertical velocity in the free troposphere and
within the boundary-layer. This result underlines that dynamic forcings
contribute as much as diabatic forcings to the dynamics of the AMI.
A generalized ω-equation is used to identify thoroughly the diabatic and
dynamic forcings to the vertical velocity in the AMI.
In the free troposphere the ascending motions are driven by the deep convection
heating, as expected by the WTG framework, but also by the ageostrophic
adjustment term within the Tropical Easterly Jet.
In the Marine Atmospheric Boundary-Layer (MABL), the upward motions in the AMI
are induced by the frontogenesis and buoyancy w-components, which are regulated
by the ageostrophic adjustment due to the presence of thermal-wind imbalance.
The balance of these three processes well captures the variability of the
vertical velocity and the associated precipitation, meaning that MABL processes
play a central role in the AMI dynamics.
The frontogenesis and buoyancy w-components were identiﬁed as the primary
components of the engine of the shallow meridional circulation, which is
characterized by a southerly inﬂow below 2000 m, and a northerly return ﬂow in
the layer [2000 − 4000 m], between the equator and 10N.
|94||Extreme Compound Events in the tropical and South Atlantic||
Regina R. Rodrigues1, Afonso Gonçalves Neto1, Noel Keenlyside2, Thomas Frölicher3, Friedrich Burger3, Alistair Hobday4
1. Dept. of Oceanography, Federal University of Santa Catarina, Brazil
2. Bjerknes Centre for Climate Research, University of Bergen, Norway
3. Physics Institute, University of Bern, Switzerland
4. CSIRO Oceans and Atmosphere, Australia
|Marine heatwaves (MHWs) are analogues to atmospheric heatwaves and have devastating effects on marine ecosystems, ranging from habitat shifts and changes in population structure to high mortality of various marine species. The impacts of MHWs can be amplified when combined with other extreme events that can act synergistically. Here we investigate the temporal-spatial distribution of compound events of MHW, high acidity and low chlorophyll in the tropical and South Atlantic, using observational datasets and reanalysis products. We show that the frequency and intensity of these compound events have increased dramatically over the past two decades in the tropical and South Atlantic, peaking in the most recent years, putting in check the capability of the marine ecosystems to recover from these compound extremes. We also show that the strong El Niño event in 2015/16 was responsible not only for generating MHWs but also for compound extremes of low chlorophyll and high acidity in the most biologically rich regions of the tropical and South Atlantic. The teleconnections from the tropical Pacific weakened the southeasterly trade winds that caused the triple compound events in the equatorial Atlantic and Angola Front during austral summer. The southward shift of the South Atlantic subtropical high in the eastern side of the basin caused the triple compound extreme in the Agulhas Leakage in austral summer. Later in austral spring, this shift of the subtropical high combined with a persistent anticyclonic circulation over the western side of the subtropical South Atlantic is responsible for the triple compound extreme in the western subtropical South Atlantic and Brazil-Malvinas Confluence regions. The fact that triple compound extremes are widespread over the tropical and South Atlantic during an El Niño event is important because recent studies have shown that MHWs can be skilful predicted mainly due to ENSO. Thus, the results presented here can help improve models’ performance that, in turn, will be used in early warning systems and integrated into disaster preparedness and long-term adaptation.|
|91||Predictability of climate-driven physical-biogeochemical processes in key regions of the tropical and south Atlantic||
David Rivas; Noel Keenlyside
University of Bergen
|Predictability of climate-induced changes in oceanic biogeochemical processes within the TRIATLAS domain is analyzed from global simulations from the Norwegian Climate Prediction Model (NorCPM) together with the Hamburg Ocean Carbon Cycle Model (HAMOCC). Seasonal-to-decadal variations of physical and biogeochemical ocean variables in key regions, focus of the TRIATLAS project, are identified and evaluated. Effects of such variations on upper tropic levels will be also analyzed. In addition, downscaling experiments for specific areas and periods will be carried out through a mesoscale-resolving regional physical-biogeochemical coupled model to elucidate the role of mesoscale dynamics, not completely resolved by the global models, in the biological processes over the shelf. The combination of these analyses will provide insights about the vulnerability of the ecosystems in the tropical and south Atlantic Ocean.|
|98||Marine heatwaves and availability of sardinella to coastal fisheries: the case of Angola, 1994-2015||
Filomena Vaz Velho1, Marek Ostrowski2, Paulo Coelho1, Virgilio Estevão1, Founi Mesmin Avo3 and Mathieu Rouault3
1Instituto Nacional de Investigação Pesqueira e Marinha, Luanda, Angola
2Oceanography and Climate, Institute of Marine Research, Bergen, Norway
3Nansen-Tutu Centre for Marine Environmental Research, Department of Oceanography, University of Cape Town, Cape Town, South Africa
|Sardinella fish off Angola constitutes about 80% of the total fish landed and 75% of animal protein in the diet of the coastal population. The all-year habitat of Angolan sardinella is in the region of remotely forced, windless upwelling, located north of 13 S. During austral summers, in synchrony with the seasonal poleward warm water intrusions, sardinella migrates south towards the Angola-Benguela Frontal region (ABF). However, the recent signals from fisheries indicate that the spawning and recruitment habitat may have expanded into the ABF. The ABF is a climatic hotspot in the southeastern Atlantic, warming at a steady rate and exposed to extreme climatic events interannually. This paper aims to understand the impacts of those extremes on changes in the southern stock range and structure as observed from 1994 to 2015. We compared the existing time series of data on sardinella distribution and age structure from annual acoustic surveys with climatic trends and marine heatwave indicators obtained from satellite imagery. The fish survey time series exhibited two prominent peaks, during 2006-2009 and 2012-2013; both were associated with the rise in the estimated biomass and the poleward shift of the southern stock range into the ABF. However, whereas the first peak reflected the movement of the adult sardinella stock from Gabon and Congo towards Angola, the second peak manifested successful recruitment in Angolan waters. We attribute the difference to contrasting climatic scenarios; deterioration in the sardinella habitat towards the stock’s northern range due to persistent warming in the first case, in contrast to its sudden improvement in Angolan waters during a climatic hiatus that followed the 2010/2011 Benguela Niño in the second case.|