Atlantic Ocean Research Articles

Bottom depth carving the pelagic spatial organisation in large marine ecosystem: The case of North West Africa

This study aimed to examine the spatial organization of pelagic communities within the water column along a horizontal gradient extending from the coast to the offshore area, categorized into three zones: inshore, offshore, and transition. Using fisheries acoustics, a total of 29 000 nautical miles of acoustic transects collected during 14 annual standardized surveys were analyzed using two complementary acoustic methods: (i) extraction of sound scattering layers (SSL) and (ii) echointegration (EI) across the entire water column, both horizontally and vertically averaged. The results revealed significant differences between the three bathymetric areas based on SSL and EI descriptors, with micro-nektonic communities in the transition area exhibiting intermediate characteristics between those in the inshore and offshore areas. The relative abundance of micro-nektonic communities decreased from shallow coastal areas to deep offshore areas, with a mean Sv from echointegration of −66.43, −74.39 and −73.65 dB for inshore, transition and offshore, respectively. The inshore area is different from the transition and offshore areas, which is confirmed by diel vertical migration (DVM) analyze through vertical profiles. All areas exhibited classic DVM type I; however, offshore and transition areas also presented unexpected DVMs of type II, i.e., organisms descend deeper during the night, displaying distinct vertical profiles compared to the inshore area. This suggests that the functional and specific composition of pelagic micro-nektonic communities differed between inshore and offshore areas, indicating that organisms adjust their responses to their environment. Over two decades, the three bathymetric areas showed a significant increase in pelagic relative biomass and variation in SSL spatial structure. The number of SSLs significantly increase, from 0.97 to 1.05 inshore, from 1.75 to 2.25 in the transition area and from 2.2 to 2.7 offshore. Nevertheless, micro-nektonic communities reacted differently to interannual changes depending on the bathymetric areas, such as the minimal depth of the shallowest SSL. Fluctuations in SSL descriptors were highlighted over the study period, which may be related to multi-decadal oscillations in the Atlantic Ocean.

Anthropogenic forcing intensified internally driven concurrent heatwaves in August 2022 across the Northern Hemisphere

In August 2022, unprecedented and long-lasting extreme heatwaves attacked the Northern Hemisphere, with simultaneous record-breaking surface air temperature (SAT) in Eastern Europe (EE), Southern China (SC), and Western North America (WNA). However, the underlying physical mechanisms of these concurrent heatwaves, and the extent to which they are driven by anthropogenic forcing versus internal variability remain unclear. Our analysis using the HadGEM3-A-N216 large ensemble attribution model reveals that anthropogenic forcing is responsible for approximately 50% of the heatwaves in EE and SC, and over 80% in WNA. Furthermore, an internally-generated circumglobal atmospheric wave train is identified as a key circulation factor facilitating these simultaneous heatwaves. Observations and numerical simulations indicate that extreme warm sea surface temperature (SST) anomalies in the North Atlantic, North Pacific and Barents Sea, along with extreme cold SST anomalies in the tropical central Pacific, are critical in the formation and maintenance of this atmospheric teleconnection wave train. Under future high-emission scenarios, the influence of the internally-generated atmospheric teleconnection on concurrent heatwaves may be enhanced, particularly in WNA.

Cross-equatorial extension of the Pacific-South American wave train enabled by Southeastern South American rainfall

The Pacific–South American (PSA) pattern is a key mode of climate variability in the mid-to-high latitudes of the Southern Hemisphere, impacting circulation and rainfall anomalies over South America. However, the effect of South American rainfall on the PSA has not been previously explored. This study focuses on the impact of rainfall over southeastern South American (SESA) during the austral summer (December–February). Observational analyses reveal that the PSA pattern remains confined to higher southern latitudes when SESA rainfall anomalies are weak. In contrast, strong SESA rainfall anomalies can generate a quasi-stationary Rossby wave train, which represents a cross-equatorial extension of the PSA. This wave train propagates along a southwest–northeast great circle path from higher latitudes, crosses the equator, and reaches the tropical Atlantic, southern Europe, and northern Africa, inducing a wet and cool weather condition over western and southern Europe. The observed wave train can be reproduced by the linear baroclinic model (LBM) simulations. Given the PSA’s connection to tropical forcing over the central Pacific, we examine differences in the wave response to central Pacific forcing alone versus combined central Pacific and SESA forcings. By incorporating SESA forcing, the wave train originally triggered by central Pacific forcing is amplified and extended. Our findings confirm the significant role of SESA rainfall anomalies in extending the PSA pattern to the Northern Hemisphere and highlight the South American continent as a land bridge that links circulation anomalies across the Pacific and Atlantic Oceans and the Southern and Northern Hemispheres.

Regional differences in salmon post-smolt migration routes can explain variation in individual growth at sea

The low number of Atlantic salmon sampled at sea makes it necessary to use alternative methods to understand their migration routes and interactions with the marine environment. In this study, we use a newly developed individual based model to simulate the ocean migration of Norwegian post-smolts during their first summer in the sea. The model is coupled with a high-resolution hydrodynamic model and dynamic prey fields to investigate how interactions between post-smolts and the dynamic marine environment in the Northeast Atlantic Ocean affect salmon growth and survival. The migration strategy leading to the best fit between the simulated geographic distribution and catches of post-smolts at sea, is to migrate away from shallow, coastal regions and to follow surface currents. Post-smolts originating from the middle parts of Norway can quickly reach the good feeding areas west of the Norwegian continental shelf, while post-smolts leaving rivers further south must start the marine life-stage migrating through the North Sea, where the prey abundance is low, before reaching the feeding areas in the Norwegian Sea. The results indicate that the first weeks at sea is a critical period for post-smolts as the available prey abundance is low, especially for smolts leaving rivers in southern and western Norway. A rapid northward migration to the central or northern Norwegian Sea is associated with faster growth for smolt emigrating from rivers flowing into the North Sea. The presented model is a first attempt to couple salmon and their marine prey in a spatiotemporal model covering the Northeast Atlantic Ocean.

The influence of zooplankton and oxygen on the particulate organic carbon flux in the Benguela Upwelling System

Abstract. We conducted sediment trap experiments in the Benguela Upwelling System (BUS) in the southeastern Atlantic Ocean to study the influence of zooplankton on the flux of particulate organic carbon (POC) through the water column and its sedimentation. A total of 2 long-term moored and 16 short-term free-floating sediment trap systems (drifter systems) were deployed. The mooring experiments were conducted over more than a decade (2009–2022), and the 16 drifters were deployed on three different research cruises between 2019 and 2021. Zooplankton was separated from the trapped material and divided into eight different zooplankton groups. In contrast to zooplankton which actively carries POC into the traps in the form of biomass (active POC flux), the remaining fraction of the trapped material was assumed to fall passively into the traps along with sinking particles (passive POC flux). Our results show, in line with other studies, that copepods dominate the active POC flux, with the active POC flux in the southern BUS (sBUS) being about 3 times higher than in the northern BUS (nBUS). In contrast, the differences between the passive POC fluxes in the nBUS and sBUS were small. Despite large variations, which reflected the variability within the two subsystems, the mean passive POC fluxes from the drifters and the moored traps could be described using a common POC flux attenuation equation. However, the almost equal passive POC flux, on the one hand, and the high POC concentration in the surface sediments of the nBUS in comparison to the sBUS, on the other hand, imply that the intensity of the near-bottom oxygen minimum zone (OMZ), which is more pronounced in the nBUS than in the sBUS, controls the preservation of POC in sediments significantly. This highlights the contrasting effects of the globally observed expansion of OMZs, which on the one hand mitigates the accumulation of CO2 in the atmosphere and the ocean by increasing POC storage in sediments and on the other hand poses a threat to established ecosystems and fisheries.

Hot spot volcano emissions as a source of natural iron fertilization in the ocean

Dust deposition, river runoff and glacial melt are the main sources of trace metals to the surface ocean. In the Canary Islands, deposition is dominated by dry dust deposition from the Saharan desert. However, during 85 days, from 19 September to 13 December 2021, the main source of trace metals on the island of La Palma changed drastically. The eruption of the Tajogaite volcano released tonnes of volcanic ash. Concurrently, several lava flows reached the coastal waters. Volcanic activity on land became the main source of iron (Fe) into the coastal waters. Fe concentrations in seawater reached over 1900 nmol L−1. ∼99 % of the iron was found in the particulate phase (particles >0.2 μm wide; 1920 ± 50 nmol L−1). Colloids, smaller size particles (0.02 μm < colloids < 0.2 μm) represented ∼0.7 % of the iron pool (14.5 ± 0.5 nmol L−1). While the truly soluble phase represented ∼0.03 %. However, the soluble phase presented concentrations reaching 0.66 ± 0.05 nmol L−1, which is ∼10 times higher than generally found in open Atlantic Ocean waters. The results show how the Fe size fractionation evolved during the eruption, from a dominance of large particle phases to smaller-sized compounds.

Depth use of wild Atlantic salmon post-smolts migrating through fjords

Juvenile Atlantic salmon (Salmo salar), known as post-smolt as they enter the sea, undergo an arduous migration from their natal rivers to their feeding grounds in the North Atlantic Ocean. It has become increasingly important to understand how post-smolts use the fjord environment as they migrate in order to properly assess the potential threats posed by large-scale salmon farming. Chief among these threats is the increased numbers of ectoparasitic salmon lice (Lepeophtheirus salmonis) inhabiting the water column, which are known to have specific depth preferences based on light, temperature, and salinity. Here, we present data on the depth use of wild Atlantic salmon post-smolts migrating through fjords. We aimed to investigate to what extent depth use varied throughout the fjord and from year to year. Using acoustic telemetry, tagged fish from four rivers in two fjords in western Norway were monitored as they migrated towards the open sea during two consecutive years. We found that post-smolts predominantly migrated in the top three meters of the water column throughout the length of both fjord systems. Among 61 successful migrants and 7013 detections, 98% of detections were in the top three meters of the water column. This corresponds well with past findings showing similar depth use in hatchery-reared smolt and in adult Atlantic salmon kelts returning to their feeding grounds after spawning. We found little evidence of a consistent diel pattern in depth use. Our results support assumptions of representative sampling when trawling the upper portion of the water column for post-smolts in order to estimate sea lice infection rates and may improve the precision of efforts to model salmon lice infection risk. The results may also be valuable in evaluating other threats to wild salmon.

Towards an understanding of uncertainties in the Lagrangian analysis of moisture sources for tropical cyclone precipitation through a study case

Despite the increasing number of atmospheric moisture tracking tools, their validation is challenging due to the lack of observations. This work contributes to a better understanding of uncertainties in the moisture sources analysis for the precipitation of tropical cyclones (TCs) by assessing eight combinations of threshold values in tracking methods based on the Lagrangian water budget equation. We selected as a study case Hurricane Ida that formed in the North Atlantic basin in late August 2021 and extracted the air parcel trajectories from the global outputs of the Lagrangian FLEXPART model. Results indicate that the choice of relative humidity (RH) threshold for filtering precipitating parcels has a noticeable impact on the Lagrangian precipitation estimates. In addition, methods applying the atmospheric boundary layer restriction produce a weaker moisture source pattern than those accounting for moisture uptakes in the whole atmospheric column. In particular, methods imposing an RH restriction along the air parcel trajectories to filter out noise in moisture losses outperform the others, providing more reliable moisture source contributions. We also introduced a simple bias correction approach that further improves the reliability of moisture source representation.

The Influence of Local Climatic Factors and Water Vapor Transport from North Atlantic Ocean on Winter Snow-Cover Variation on Western Kunlun Mountains and Eastern Pamir Plateau

The Influence of Local Climatic Factors and Water Vapor Transport from North Atlantic Ocean on Winter Snow-Cover Variation on Western Kunlun Mountains and Eastern Pamir Plateau

Spatiotemporal Hotspots of Juvenile Bigeye and Yellowfin Tuna Catches Under Drifting Fish‐Aggregating Devices in the Eastern Atlantic Ocean to Define Moratorium Strata

Spatiotemporal Hotspots of Juvenile Bigeye and Yellowfin Tuna Catches Under Drifting Fish‐Aggregating Devices in the Eastern Atlantic Ocean to Define Moratorium Strata

“The Voice of Agitation Should Roll across the Broad Atlantic”

Abstract Scholars have provided impressive analyses of the transatlantic slave trade to the Americas and its demise over the past four decades, this led by contributions to the Trans-Atlantic Slave Trade Database ( https://www.slavevoyages.org/ ). England played a decisive role in the suppression of that traffic after prohibition of British participation in 1808, this partly achieved by British interceptions of slave vessels by its West Africa Squadron (1819–1867) and the establishment of Courts of Mixed Commission for the Abolition of the Slave Trade (1819–1871). Given a North Atlantic Ocean current clockwise gyre and South Atlantic counterclockwise gyre, a major northern slave vessel route connected Africa to the Caribbean and a second southern route connected Africa to Brazil.1 Africans disembarked in the Caribbean had diverse origins in West Africa (Sierra Leone, Ghana, Togo, Nigeria) and West Central Africa (Congo, Angola). Brazil received fewer Africans from West Africa (there was a long-term connection between Benin and Bahia), large numbers of African slaves from West Central Africa and a small number from Southeast Africa (Mozambique) at or near Rio de Janeiro. Language difference (Spanish, French, English, Dutch, Danish in the North Atlantic, Portuguese in the South Atlantic) contributed to a conceptual separation of those two regions, particularly evident in historiographies related to slavery and abolition. The Scottish diplomat David Turnbull was one of the few observers of the nineteenth century who connected Caribbean islands with Brazil. Turnbull asserted to the British Foreign Office that subaltern resistance by slaves and free blacks in both the British and non-British Caribbean could aid in England’s quest to extinguish the transatlantic slave trade. Turnbull organized a petition campaign in Jamaica in the late 1840s to pressure England’s Foreign Office to pursue more aggressive actions at sea and on land to halt slave disembarkations in Cuba and Brazil. Foreign Secretary Lord Palmerston’s positive response combined with slave resistance in Brazil contributed to Brazil’s imperial government decision to act decisively to halt further slave disembarkations in 1850–1851.

Historical fishing regimes uncover deep-sea productivity hotspots in the SW Atlantic Ocean

Historical fishing regimes uncover deep-sea productivity hotspots in the SW Atlantic Ocean

Rebuilding and Reference Points Under Compensatory and Depensatory Recruitment: A Meta‐Analysis of Northeast Atlantic Fish Stocks

Rebuilding and Reference Points Under Compensatory and Depensatory Recruitment: A Meta‐Analysis of Northeast Atlantic Fish Stocks

The interplay of mineral dust with radiation: analysis of the giant dust intrusion in the Atlantic Ocean on June 2020

The interplay of mineral dust with radiation: analysis of the giant dust intrusion in the Atlantic Ocean on June 2020

The modulation effect of the Victoria mode on the uncertainty connection between ENSO and winter European surface air temperature

While El Niño-Southern Oscillation (ENSO) has widespread impacts on the climate around the Pacific and North America, the relationship between ENSO and winter surface air temperature (SAT) in Europe is less well established. This study investigates the modulation effects of the spring Victoria mode (VM) on the weak ENSO–SAT connection in the following winter based on reanalysis data and numerical experiments. It is shown that the connection between ENSO and the winter SAT in central Europe has a significant and positive (negative) correlation during the positive (negative) VM phase. Further analysis shows that the sea surface temperature (SST) anomalies associated with ENSO play an important role in the VM modulation. For the positive VM phase, ENSO combined with the SST warming mode in the western North Pacific induces the East Atlantic teleconnection pattern, which strengthens the anomalous warm advection and leads to the positive SAT anomalies in central Europe. In contrast, for the negative VM phase, ENSO could trigger a negative North Atlantic Oscillation pattern through intermediate SST anomalies in the tropical North Pacific, favoring the formation of the negative central European SAT anomalies. The remarkable modulation effect of the VM on the connection between ENSO and winter central European SAT is further verified through forced experiments using an atmospheric model. This could provide hope that ENSO can make predictions for the winter SAT in central Europe, considering the phase of the preceding spring VM.

Modulation in Teleconnections of the El Nino Southern Oscillation by Atlantic Multidecadal Sea Surface Temperature Variability

AbstractThis manuscript uses idealized AGCM experiments to explore impacts of observed decadal Atlantic sea surface temperature (SST) changes on El Nino Southern Oscillation teleconnections. Significant regional changes are observed in numerous locations (e.g., Indo‐Pacific and Central Africa) due to the addition of the AMV anomalies. In some regions the teleconnection impacts of AMV forcing appeared to scale with the magnitude of the AMV forcing. However, the AMV induced modulation of temperature and precipitation teleconnections is regionally specific with changes in magnitude, statistical strength, and spatial connection dependent on region. These ENSO teleconnection changes were found to be asymmetric between AMV phases, with negative anomalies appearing to have a larger effect. We hypothesize these changes may be underpinned by a AMV induced modulation and migration of ENSO's equatorial precipitation response.

Automatic Reading and Reporting Weather Information from Surface Fax Charts for Ships Sailing in Actual Northern Pacific and Atlantic Oceans

This study is aimed to improve the intelligence level, efficiency, and accuracy of ship safety and security systems by contributing to the development of marine weather forecasting. The accurate and prompt recognition of weather fax charts is very important for navigation safety. This study employed many artificial intelligent (AI) methods including a vectorization approach and target recognition algorithm to automatically detect the severe weather information from Japanese and US weather charts. This enabled the expansion of an existing auto-response marine forecasting system’s applications toward north Pacific and Atlantic Oceans, thus enhancing decision-making capabilities and response measures for sailing ships at actual sea. The OpenCV image processing method and YOLOv5s/YOLO8vn algorithm were utilized to make template matches and locate warning symbols and weather reports from surface weather charts. After these improvements, the average accuracy of the model significantly increased from 0.920 to 0.928, and the detection rate of a single image reached a maximum of 1.2 ms. Additionally, OCR technology was applied to retract texts from weather reports and highlighted the marine areas where dense fog and great wind conditions are likely to occur. Finally, the field tests confirmed that this auto and intelligent system could assist the navigator within 2–3 min and thus greatly enhance the navigation safety in specific areas in the sailing routes with minor text-based communication costs.

A Marine Barite Perspective of the Late Miocene Biogenic Bloom in the Equatorial Indian Ocean and Equatorial Western Atlantic Ocean

AbstractThe marine biological pump is crucial for removing excess carbon dioxide from the atmosphere to the ocean interior and seafloor sediments. The Late Miocene Biogenic Bloom (LMBB), marked by notable increases in biogenic components in marine sediments, provides insights into the response of the biological pump to climate change. However, understanding the timing, distribution, and cause of the LMBB remains limited. We use marine barite, a refractory mineral precipitating from the water column associated with carbon export, and other proxies to reconstruct productivity in the equatorial Indian Ocean and equatorial western Atlantic between 12 and 5 Ma. Multi‐proxy records reveal the onset of the LMBB in the equatorial Indian Ocean at ∼9 Ma, primarily driven by more vigorous upwelling during global cooling. We suggest that the steepened meridional temperature gradient and the Antarctic ice sheet expansion have strengthened ocean overturning, facilitating nutrient supply and biogenic bloom in upwelling regions.

Analysis of free-living seabirds from Brazil as potential hosts of Toxoplasma gondii and serological investigation for antibodies against Leptospira spp.

Dispersal patterns of zoonotic pathogens can be strongly influenced by mobility and contact among hosts. Toxoplasma gondii infection has been documented in many avian species, however, there is little information regarding free-living seabird populations. Leptospira can infect domestic and wild animals, with birds being potential carriers of the bacteria. The continental shelf of the southwestern Atlantic Ocean is a foraging area for seabirds that breed locally, as well as migratory seabirds wintering in the area, which may come into contact with each other in prey aggregation areas and contribute to T. gondii and Leptospira spread. Therefore, this study aimed to investigate the prevalence of two important zoonotic pathogens in free-living seabirds. Blood samples were collected from 322 birds of three local breeders (Phaethon aethereus, Sula leucogaster and S. dactylatra) in the eastern coast of Brazil (Abrolhos Archipelago), and two migratory species using the area during the pre-laying (Pterodroma arminjoniana) and the non-breeding periods (Thalassarche chlororhynchos). Serological agglutination tests for detection of anti-Toxoplasma gondii and anti-Leptospira spp. antibodies were performed. None of the seabirds in this study was seroreactive to Leptospira spp., whereas 34.5% (n = 111) of the animals presented antibodies anti-T. gondii. Antibody titers in seropositive birds ranged from 10 to 640. There were seropositive birds in all sampled localities. This study provides the first records for P. arminjoniana and T. chlororhynchos as seropositive to T. gondii, suggesting their potential role as sentinels for the environmental contamination by T. gondii and also T. gondii infection. These findings indicate the circulation of the parasite in the Brazilian coastal and oceanic regions, probably due to the ingestion of T. gondii oocysts by birds, the epidemiological involvement of migratory birds as hosts of pathogens, as well as the role of the historical introduction of invasive vertebrates on Brazilian islands. Therefore, due to the serological evidence of infection, the dynamics of toxoplasmosis in seabirds, regarding their susceptibility towards the disease and the possible anthropogenic influence need to be better understood for the colonies to be included in the wildlife cycle of T. gondii.

Letters to the Landscape (or an Alphabet in Ruins)

This article is a crossing through the Anthropocene. Between the body and the landscape, between the past and the future, between concepts and dances, between Edouard Glissant and the Atlantic Ocean, between tremor and uncertainty, between the Forest and Monoculture, between dance and the visual arts, between poetry and concepts, between the body and philosophy, between the animal and the plant, between what I desire and what I get, between Emanuele Coccia and the butterfly, between the thousand names of Gaia, the anthropology and what remains of our planet. They are letters thrown into the sea, directed to the landscapes that inhabit me, written with pieces of images and sounds that were inside my body/computer in these last years of journey. Shared in a list, like an alphabet in ruins, a (un)alphabetical order. Each letter carries a journey in itself: a way of doing and thinking about dance, an invention of a world that is possible to imagine today.