Atlantic Ocean Research Articles

Socio-ecological vulnerability assessment to Sargassum arrivals

The proliferation of holopelagic Sargassum spp. (Sargassum) in the tropical North Atlantic Ocean is of concern for populations and coastal ecosystems in the Caribbean Sea, Gulf of Mexico, and West Africa. Satellite detections have enabled rough assessments of the quantity of algae that drifts seasonally in the open ocean, with seasonal peaks of Sargassum biomass reaching 10 to 20 million tons since 2018. Although the impacts on the coast have been widely publicized, there are no estimates of the quantities of Sargassum that accumulate on the coasts. This study proposes novel vulnerability indicators that combine information on Sargassum stranded biomass, ecosystem and socioeconomic factors to assess risks posed by Sargassum on coastal regions. Quantities of Sargassum that accumulate in the coastal strip at the regional scale were derived by combining the satellite detections in the open ocean with an algal growth-transport-stranding model. It shows that the amount of Sargassum accumulating on the Atlantic coast is of the order of 10% of the biomass estimated offshore and has accumulated between 2 and 10 million tons per year over the last five years. Vulnerability indices identify the Mexican Caribbean, northern Lesser Antilles, and eastern Great Antilles as the most vulnerable regions, facing significant ecosystemic and socioeconomic pressures from Sargassum influxes.

Reduced North Pacific Deep Water formation across the Northern Hemisphere Glaciation

Today, deep waters do not form in the northern high latitudes of the Pacific Ocean, but this may not have been the case during the Pliocene. Evidence suggests there was a Pacific Meridional Overturning Circulation during the warm Late Pliocene, similar to the modern Atlantic Ocean with a weak halocline in the subpolar North Pacific resulting in North Pacific Deep Water (NPDW) formation. However, much of this evidence comes from proxies that can be biased by changes in local productivity. We present a coupled Mg/Ca-δ18O record from the North Pacific which shows two distinct water masses in the Pliocene North Pacific Ocean, with NPDW colder and fresher than the underlying deeper water. Here, we show a decline in NPDW formation during glacials from 2.7 million years ago, which we suggest demonstrates the strong sensitivity of ocean gateways to sea level and ice volume change in shaping deep water circulation, and thus the climate system.

The response of tropical cyclone hazard to natural and forced patterns of warming

This study quantifies the influence of the pattern of sea surface temperature change in the tropical Pacific on tropical cyclone hazard. After downscaling a climate model with an “El Niño-like” forced response, it is found that the “El Niño-like” pattern of warming induces an “El Niño-like” change to tropical cyclone hazard. The magnitude of hazard change owing to the “El Niño-like” pattern of warming is estimated to be around the same order of magnitude as that driven by the forced response that does not project onto the same pattern of warming, highlighting the sensitivity of local tropical cyclone hazard to the pattern of warming. Given the uncertainty around the future pattern of Pacific warming, a storyline with a “La Niña-like” pattern of warming, of similar magnitude to the observations, is created. In this scenario, near-term tropical cyclone hazard over coastal Asia and the Atlantic basin significantly increases.

River discharge impacts coastal southeastern tropical Atlantic sea surface temperature and circulation: a model-based analysis

Abstract. The southeastern tropical Atlantic (SETA) coastal region sustains highly productive fisheries and marine ecosystems, thus having immeasurable socio-economic importance for southwestern African coastal countries. It is characterized by high sea surface temperature (SST) variability and significant freshwater input from land mainly due to Congo River discharge. In this study, using high-resolution ocean model sensitivity experiments, we show that the presence of low-salinity waters from the river discharge increases the mean state SST in the SETA coastal fringe by about 0.26 °C on average and by up to 0.9 °C from south of the Congo River to the Angola–Benguela Front (ABF). North of the Congo River up to about 4° S, this input significantly reduces the mean state SST by more than 1 °C. We demonstrate that the impact of river discharge on SST is associated with a halosteric effect, which modifies the sea surface height gradient and alters geostrophic currents, producing a southward coastal geostrophic flow, with an onshore geostrophic component to the south of the Congo River. Hence, advective warming and downwelling are generated south of the river mouth. Furthermore, the southward advection generated by the low-salinity waters pushes the ABF further south. Concomitantly north of the Congo's mouth, the sea surface height gradient generates a northward geostrophic coastal current with an offshore geostrophic component, which is associated with advective cooling and upwelling north of 6° S. These results draw attention to the freshwater impact on SSTs and ocean surface dynamics, especially in the projected climate change scenario of continuously increasing land-to-ocean discharge.

Comparative Diets of Invasive Blue Catfish: Differences Across Rivers and Ontogenetic Stages

ABSTRACTBlue Catfish (Ictalurus furcatus) are an invasive species with expanding populations in freshwater systems, posing significant ecological challenges to native fauna. To assess their potential impacts in diverse aquatic ecosystems, we examined and compared the diets of non‐native Blue Catfish from four rivers in Georgia, USA, two of which drain into the Atlantic Ocean. A total of 936 Blue Catfish were collected from the Altamaha, Ocmulgee, Oconee, and Satilla rivers, with 90.38% of stomachs containing identifiable prey. Stomach content analysis revealed that Asian Clam (Corbicula fluminea) dominated their diet in terms of number (96.76%), weight (69.33%), and to a lesser degree, frequency (36.96%). Across rivers, smaller Blue Catfish (≤ 300 mm TL) had diets with a higher relative importance of insects and vegetation. Ontogenetic dietary trends showed increasing consumption of fishes and crustaceans as fish size increased in the Altamaha, Ocmulgee, and Oconee rivers. In contrast, the Satilla River population exhibited broader dietary diversity and distinct ontogenetic shifts. Stable isotope analysis (δ13C and δ15N) revealed significant differences between Blue Catfish from the Altamaha and Satilla rivers, underscoring their opportunistic feeding strategies in varying habitats. Bayesian niche overlap analysis indicated that size classes within the Altamaha and Satilla rivers had substantial intraspecific overlap, with Satilla subadults exhibiting the broadest niche (SEAB: 3.83). Factors such as prey availability, density dependence, and environmental conditions likely influence prey selection and feeding strategies in these systems. Understanding these dynamics is crucial for managing the ecological impacts of invasive Blue Catfish in freshwater systems of North America.

Occurrence of parasites in fishery species along the Moroccan coastline.

The fishing industry in Morocco is a fundamental pillar of the national economy. However, it is important to acknowledge that fishery products can potentially transmit parasitic agents to humans. These parasites primarily belong to the Anisakidae family, consisting of two main genera: Anisakis and Pseudoterranova. The main objective of this study is to assess the occurrence of parasitism in fishery species along the Atlantic Ocean and Mediterranean Sea coasts in Morocco. A total of 1808 specimens from 24 species were collected and examined for parasites between August 2022 and May 2023. The results show that 279 samples were infested, giving an overall prevalence of 15.43%, which is very low; 3918 parasites were detected in 14 of the 24 species examined, giving an overall abundance of 2.17 and an intensity of 14.04. Gymnorhynchus gigas were exclusively found in the Atlantic Pomfret (Brama brama), exhibiting a high prevalence of 78.26%. In contrast, xenomas were observed in Axillary seabream (Pagellus acarne) (p=16.19%) and Atlantic horse mackerel (Trachurus trachurus) (p=1.01%). The parasites belonging to the Anisakidae family are the most widespread, with a percentage of 68.70%, and the silver scabbardfish (Lepidopus caudatus) has the highest prevalence, which is 87.14%. The examination of the correlation between its weight and the number of larvae yielded a correlation coefficient of r=0.52, while the correlation between its length and larvae count resulted in r=0.41. Both cases demonstrated a positive correlation. These findings underscore the necessity of prioritizing the safety of fishery species to safeguard public health and ensure sustainable consumption practices.

Arsenic Speciation, an Evaluation of Health Risk Due to the Consumption of Two Fishes from Coastal Marine Areas of the Southwestern Atlantic Ocean (SWAO).

Arsenic (As) is naturally occurring and is found in different forms, some of which are considered toxic to human health and frequently present in fishery resources. The aim of this work was to determine the contribution of toxic As species to the total As in muscle of two commercial fish species (Micropogonias furnieri and Urophycis brasiliensis) and to assess the toxicological risk associated with their consumption, considering different exposed groups. The total As concentrations found exceeded local guideline recommendations (> 1mgkg-1 wet weight), but the concentrations of the toxic As species were below this threshold. The inorganic As levels do not exceed the international guideline recommendations (0.03-0.15μgkg-1 bw per day of iAs). Both interspecific and intraspecific differences in As concentrations were found. Non-carcinogenic and carcinogenic risk values indicated that the exposed groups would not experience health risks through consumption of either fish species. However, due to the lack of an established safe consumption limit for iAs or As species worldwide, there are currently no legal tools to ensure that these fish species are safe for human consumption.

A Comparison of Arctic and Atlantic Basin Cyclone Track and Intensity Forecast Uncertainty

A Comparison of Arctic and Atlantic Basin Cyclone Track and Intensity Forecast Uncertainty

Prey Selection by Walrus (Odobenus rosmarus rosmarus) in the Dutch Wadden Sea, the Netherlands

Between February 2021 and April 2022, a female walrus (Odobenus rosmarus rosmarus) was observed multiple times along the North Sea and Norwegian coasts. Scat samples from the walrus were collected on two occasions when it visited the Dutch Wadden Sea between September and November 2021. It was assumed that the walrus fed locally, so to determine the animal’s diet, scat samples were analyzed using molecular methods. In both scats, only the Atlantic razor (jackknife) clam (Ensis leei, M. Huber, 1843), a mollusk species invasive to the region, was found; this species had invaded the area relatively recently and is very abundant. The walrus did not seem to suffer from the warm water temperature, which reached more than 20°C in summer. We hypothesize that the temperature is not the reason for the walrus’s distribution being restricted in the Arctic, but, instead, it was potentially overhunting and ongoing disturbance. The concurrence of the recovering walrus population in the Northeast Atlantic and global warming causing loss of sea-ice for haul out and augmenting human pressure in the Arctic might drive an increase in walrus visits at lower latitudes in the future. We therefore suggest adequate management plans be drawn up to anticipate this.

Stranding of Beaked Whales in Santa Cruz Province, Southern Patagonia, Argentina (1895-2023)

A total of 49 records of beaked whales stranded along approximately 900 km of coast of Santa Cruz Province, Argentina, were documented between 1895 and March 2023. These include 29 previously published and unpublished records (including one specimen re-identified through DNA analysis) and 20 new records. All of these involve at least seven species in five genera. All strandings correspond to single individuals. The most frequent species found stranded were Cuvier’s beaked whales (Ziphius cavirostris) with 14 records, followed by strap-toothed whales (Mesoplodon layardii; n = 13). Species identities were based on skull morphology, tooth morphology and position in the jaw, and morphometric measurements. Additionally, mitochondrial control region DNA was sequenced to confirm species identification for 10 individuals, although confirmation was only possible in seven individuals. This study provides the first record of Arnoux’s beaked whale and Hector’s beaked whale from Santa Cruz Province and emphasizes the importance of the Southwest Atlantic Ocean for multiple beaked whale species. The potential impacts on these whale species of changing sea surface temperatures and ocean warming are unknown.

Tracing acid mine drainage from an accidental spill on the Estuary of Huelva (SW Spain).

Tracing acid mine drainage from an accidental spill on the Estuary of Huelva (SW Spain).

The DOE E3SM version 2.1: overview and assessment of the impacts of parameterized ocean submesoscales

Abstract. The U.S. Department of Energy's Energy Exascale Earth System Model (E3SM) version 2.1 builds on E3SMv2 with several changes, with the most notable being the addition of the Fox-Kemper et al. (2011) mixed-layer eddy parameterization. This parameterization captures the effect of finite-amplitude, mixed-layer eddies as an overturning streamfunction and has the primary function of restratification. Herein, we outline the changes to the mean climate state of E3SM that were introduced by the addition of this parameterization. Overall, the presence of the submesoscale parameterization improves the fidelity of the v2.1 simulation by reducing the ocean surface biases in the North Atlantic present in v2, as illustrated by changes in the climatological sea surface temperature and salinity and the Arctic sea-ice extent. Other impacts include a slight shoaling of the mixed-layer depths in the North Atlantic and a small improvement in the Atlantic Meridional Overturning Circulation (AMOC). We note that the expected shoaling due to the parameterization is regionally dependent in our coupled configuration. In addition, we investigate why the parameterization and its impacts on mixed-layer depth have little impact on the simulated AMOC: despite increased dense-water formation in the Norwegian Sea, only a small fraction of the water formed makes its way south into the North Atlantic basin. Version 2.1 also exhibits small improvements in the atmospheric climatology, with smaller biases in many notable quantities and modes of variability.

A new soft coral species from the Gulf of Mexico (Octocorallia: Scleralcyonacea: Parasphaerascleridae)

A new species of soft coral, Parasphaerasclera mcfaddenae (Octocorallia: Scleralcyonacea: Parasphaerascleridae), is described from mesophotic hardbottom habitats of the Gulf of Mexico, western North Atlantic Ocean. Previously, this family was only known from the tropical Indo-Pacific and South Africa; therefore, we extend the distribution of the family Parasphaerascleridae into the North Atlantic Ocean. This diminutive species differs from other parasphaerasclerids by a capitate growth form, non-retractile polyps, and presence of tuberculated spindles. Notably, this species was also detected in environmental (e)DNA samples from locations where it was not physically collected, highlighting the importance of both eDNA for biodiversity surveys as well as specimen collections for building comprehensive reference databases for eDNA analyses.

Cryptic diversity within the Gonyaulax spinifera species complex, its relation to the cyst‐defined species Spiniferites bentorii, S. mirabilis and S. membranaceus, with the description of Gonyaulax carbonell‐mooreae sp. nov. (Gonyaulacales, Dinophyceae)

AbstractThe fossil dinoflagellates Spiniferites bentorii, S. mirabilis, and S. membranaceus are known to inhabit recent sediments and are often used to reconstruct past sea‐surface conditions. However, information on their corresponding motile cells has been rare. We isolated single cysts resembling these fossil species from China and France to yield Gonyaulax spinifera‐like cells. Gonyaulax strains were also established from Viet Nam and South Korea by isolating single cells. Both cysts and cells were examined by light and scanning electron microscopy, and their LSU rRNA genes were sequenced. A new Gonyaulax species, G. carbonell‐mooreae, was obtained from S. bentorii‐like cysts and considered the equivalent of Spiniferites bullatus, dating back to the Campanian. Gonyaulax kunsanensis was related to S. mirabilis‐like cysts. A typical S. membranaceus cyst from France yielded cells resembling G. lewisiae but shared only 75% similarity in LSU rRNA gene sequence with those from South Korea. Molecular phylogeny revealed that the pronounced apical boss is systematically significant, whereas the presence of intergonal processes is insignificant. Two ASVs of 18S rRNA V4 region were respectively identified as G. kunsanensis and G. lewisiae from the Tara Oceans metabarcoding data. Gonyaulax kunsanensis has a wide distribution in the Pacific, Indian, and Atlantic Oceans, but G. lewisiae has a restricted distribution. One strain of G. kunsanensis was examined for yessotoxin content using liquid chromatography coupled with tandem mass spectrometry (LC–MS/MS), but no detectable amounts of toxins were observed. Our results uncover the hidden diversity within the G. spinifera species complex and stress the significance of cyst morphology in the taxonomy of Gonyaulax.

Biogeochemical Controls on Latitudinal (42°N to 70°S) and Depth Distribution of Organophosphate Esters in the Atlantic and Southern Oceans

Biogeochemical Controls on Latitudinal (42°N to 70°S) and Depth Distribution of Organophosphate Esters in the Atlantic and Southern Oceans

Comparative Analysis of Climate Change Trend and Change-point for Daily Rainfall Annual Maximum Time Series Data in Four Gauging Stations in South-East Nigeria

The aim of the study was to conduct a comparative analysis of climate change trends and change-point detection in long-term daily rainfall annual maximum series (AMS) data across four gauging stations in South-Eastern Nigeria: Abakaliki, Enugu, Owerri and Umuahia. Utilizing 31-year rainfall records (1992–2022) from the Nigerian Meteorological Agency (NIMET), the research employed the Indian Meteorological Department (IMD) method to downscale daily rainfall to sub-daily durations. Trend analysis utilizing Mann-Kendall test and Sen’s slope estimator revealed statistically significant increasing rainfall trends in Abakaliki (Z = 2.75, p < 0.01) and Umuahia (Z = 2.75, p < 0.01), with Sen’s slope magnitudes ranging from 0.35–2.28 mm/year and 0.14–0.90 mm/year, respectively. Conversely, Enugu and Owerri exhibited non-significant decreasing trends. Change-point analysis using distribution-free CUSUM and sequential Mann-Kendall (SQMK) tests identified a significant shift in rainfall patterns in Umuahia (2002–2003), while other stations showed no statistically meaningful change points. The spatial variability in trends underscores the influence of geographical proximity to the Atlantic Ocean and localized urbanization. These findings emphasize the necessity of region-specific climate adaptation strategies, particularly for infrastructure design in regions with intensifying rainfall. The study advocates integrating non-stationary approaches in hydrological modeling especially at Abakaliki and Umuahia to address evolving climate risks in those regions.

Deep-sea Echinoids from the Galician Bank (North Atlantic Ocean)

The Galician Bank (GB) is a seamount in the Northeast Atlantic Ocean (Northwest Spain) at 180 km from the Galician coast. Its summit is between 650 and 1500 m below the surface as it rises from the abyssal plain at 4000 m depth. The dynamics of water masses and the geomorphology of the area favour the retention of nutrients and larvae, augmenting the diversity of benthic communities. The present study aims to inventory and reviewing of the echinoid fauna collected during the LIFE+ INDEMARES project carried out on the Galician Bank. New findings are compared with previous studies of the Official Spanish Checklist (IEEM: “Inventario Español de Especies Marinas”, 2017, 2020) to update our knowledge of the diversity and distribution of echinoid species in the study region. During the surveys carried out under the auspices of project LIFE+INDEMARES on the Galician Bank (2010–2011), a total of 139 echinoids belonging to 8 different species were sampled from 27 stations, between 744 and 1764 m depth. The most frequently collected species were Cidaris cidaris (Linnaeus, 1758) and Sperosoma grimaldii Koehler, 1897. After public datasets analysis, it turns out that one species should be considered as a new record in Spanish waters: Echinocyamus grandiporus Mortensen, 1907, and two for the North Atlantic Spanish Marine Sub-Division: Holanthus expergitus (Loven, 1871) and Plexechinus hirsutus Mortensen, 1905. In addition, the bathymetric range of Echinocyamus pusillus (O.F. Müller, 1776) was extended to 1313 m depth.

Intense and localized export of selected marine snow types at eddy edges in the South Atlantic Ocean

Abstract. The biological carbon pump (BCP) comprises a wide variety of processes involved in transferring organic carbon from the surface to the deep ocean. This results in long-term carbon sequestration. Without the BCP, atmospheric CO2 concentrations would be around 200 ppm higher. This study reveals that ocean dynamics at the mesoscale and submesoscale could have a major impact on particulate organic matter (POM) vertical distribution. Our results indicate that intense submesoscale frontal regions, such as those between mesoscale eddies, could lead to an important accumulation and transport of POM from the mixed-layer depth (MLD) down to the mesopelagic zone. To reach these conclusions, a multifaceted approach was applied. It included in situ measurements and marine snow images from a BGC-Argo float equipped with an Underwater Vision Profiler (UVP6), satellite altimetry data, and Lagrangian diagnostics. We focused our study on three intense features in marine snow distribution, observed during the 17-month-long float mission in the Cape Basin in the southwest of Africa. These features were located in the frontal region between mesoscale eddies. Our study suggests that a particle injection pump induced by a frontogenesis-driven mechanism has the potential to enhance the effectiveness of the biological pump by increasing the depth at which carbon is injected into the water column. This work also emphasizes the importance of establishing repeated sampling campaigns targeting the interface zones between eddies. This could improve our understanding of the mechanisms involved in the deep accumulation of marine snow observed at eddy interfaces.

Mixing, spatial resolution and argon saturation in a suite of coupled general ocean circulation biogeochemical models off Mauritania

Abstract. Numerical coupled ocean circulation biogeochemical modules are routinely employed in Earth system models that provide projections into our warming future to the Intergovernmental Panel on Climate Change (IPCC). Previous studies have shown that a major source of uncertainties in the biogeochemical ocean component is vertical, or rather diapycnal, ocean mixing. The representation of diapycnal mixing in models is affected by several factors, including the (poorly constrained) parameter choices of the background diffusivity, the choice of the underlying advection numerics and the spatial discretization. This study adds to the discussion by exploring these effects in a suite of regional coupled ocean circulation biogeochemical model configurations. The configurations comprise the Atlantic Ocean off Mauritania – a region renowned for its complex ocean circulation driven by seasonal wind patterns, coastal upwelling and peculiar mode water eddies featuring toxically low levels of dissolved oxygen. Based on simulated argon saturation as a proxy for effective mixing, we conclude that the resolution effect beyond mesoscale on diapycnal mixing is comparable to other infamous spurious effects, such as the choice of advection numerics or a change in the background diffusivity of less than 60 %.

Consistent Coupled Patterns of Teleconnection Between Rainfall in the Ogooué River Basin and Sea Surface Temperature in Tropical Oceans

This study investigates teleconnections between rainfall in the Ogooué River Basin (ORB) and sea surface temperature (SST) in the tropical ocean basins. The Maximum Covariance Analysis (MCA) is used to determine coupled patterns of SST in the tropical oceans and rainfall in the ORB, depicting regions and modes of SST dynamics that influence rainfall in the ORB. The application of MCA to rainfall and SST fields results in three coupled patterns with squared covariance fractions of 84.5%, 76.5%, and 77.5% for the Atlantic, Pacific, and Indian tropical basins, respectively. Computation of the correlations of the Savitzky–Golay-filtered resulting expansion coefficients reached 0.65, 0.5 and 0.72, respectively. The SST variation modes identified in this study can be related to the Atlantic Meridional Mode for the tropical Atlantic and the El Niño Southern Oscillation for the tropical Pacific. Over the Indian Ocean, it is a homogeneous mode over the entire basin, instead of the popular dipole mode. Then, the time-dependent correlation method is used to remove any ambiguity on the relationships established from the MCA.