Northeastern Atlantic Ocean Research Articles

Weight–length relationships of four intertidal mollusc species from the northeastern Atlantic Ocean and their potential for conservation

ABSTRACT Weight-length relationships (WLRs) are frequently used for the development of comparative studies of life history, population dynamics, ecosystem modelling and estimation of the production and biomass of populations among regions. WLRs provide information about growth, wellbeing and fitness of a population in a marine environment. WLRs for four topshells (Phorcus atratus, Phorcus lineatus, Phorcus mariae, Phorcus sauciatus) caught in North-eastern Atlantic Ocean (Azores, Canaries, Cape Verde, Madeira and Mainland Portugal) were established and their relative growth was assessed. The results showed that almost all species exhibited a positive allometric growth. A comparative study on the effect of harvest in the relative growth of P. sauciatus in the archipelago of Madeira showed that all the populations from exploited areas exhibited a negative allometric growth in contrast to the populations from the Marine Protected Areas (MPAs) which were predominantly isometric. The present results indicate that the conservation measures established in the protected areas promoted a positive effect in the protected populations and are valuable for establishing a set of monitoring and management measures aiming at the sustainable exploitation and conservation of these species. These results are important to demonstrate the role of MPAs in the conservation of these keystone species in the north eastern Atlantic Ocean rocky shore ecosystems.

Toxic Metals (Al, Cd, Pb) and Trace Element (B, Ba, Co, Cu, Cr, Fe, Li, Mn, Mo, Ni, Sr, V, Zn) Levels in Sarpa Salpa from the North-Eastern Atlantic Ocean Region.

Sarpa salpa is a fish belonging to the Sparidae family and is usually found in local markets. Toxic metals such as aluminum (Al), cadmium (Cd), lead (Pb) and trace elements such as boron (B), barium (Ba), cobalt (Co), copper (Cu), chromium (Cr), iron (Fe), lithium (Li), manganese (Mn), molybdenum (Mo), nickel (Ni), strontium (Sr), vanadium (V) and zinc (Zn) are incorporated into fish tissues and remain there. The liver has the highest concentrations of all the analyzed toxic metals and almost all the analyzed trace elements. The consumption of 100 g/day of S. salpa muscle tissue does not pose a health risk. However, 100 g/day of liver consumption may pose a serious health risk due to the intake of Cd (572% of the tolerable weekly intake for adults with a body weight of 68.48 kg) and Pb (117% of the tolerable daily intake for adults weighing 68.48 kg). The consumption of liver of this species is not recommended due to its possible harmful effects on health.

Atmospheric Dynamics of a Saharan Dust Outbreak Over Mindelo, Cape Verde Islands, Preceded by Rossby Wave Breaking: Multiscale Observational Analyses and Simulations

AbstractWe investigate the synoptic precursors to the Harmattan wind and dust frontogenesis during the high impact Saharan dust outbreak over the Cape Verde Islands on 13 November 2017. We employ multiscale observations and the Weather Research and Forecasting model Coupled with Chemistry simulations. The analyses indicate that the dust storm was initiated on the lee side of the Saharan Atlas Mountains (SAM) in Algeria on 10 November 2017. This dust storm was associated with a double Rossby wave break linked through nonlinear wave reflection. Two successive Rossby wave breaks contributed to the wave amplification over the Eastern North Atlantic Ocean which transported large magnitude potential vorticity air into the North African continent. The resulting coupled pressure surge was associated with cold air advected equatorward over the SAM which organized the strong near‐surface wind that ablated the dust. The simulation results indicate that the dust front was initially related to a density current‐like cold front which formed due to the downslope transport of cold airflow over the SAM and then triggered undular bores on the lee side. Each bore perturbed the dust loading and then the subsequent diurnal heating generated differential planetary boundary layer turbulence kinetic energy strengthening the dust frontogenesis. Dust became confined behind the cold surge and interacted with the daytime Saharan planetary boundary layer leading to increased dust loading, while the dust front propagated equatorward. Two distinct dust plumes arrived successively at low levels at Mindelo, Cape Verde Islands: (1) from the coasts of Mauritania and Senegal and (2) from the SAM southern flank.

Persistence and Nonpersistence of East and Southeast Asian Rainfall Anomaly Pattern From Spring to Summer

AbstractThe present study analyzes the connection of rainfall anomalies over East and Southeast Asia between spring and summer. Spatial patterns of contrasting rainfall anomalies between East Asia and the Indochina Peninsula are identified in both spring and summer. The persistence of more rainfall over East Asia and less rainfall over the Indochina Peninsula from spring to summer is associated with the maintenance of an anomalous low‐level anticyclone over the tropical western North Pacific. Further analysis shows that this anomalous anticyclone is attributed to the combined effects of persisting positive sea surface temperature anomalies (SSTAs) in the tropical Indian Ocean and negative SSTAs in the subtropical western Pacific. In contrast, in the nonpersistent rainfall anomaly years, the anomalous anticyclone over the western North Pacific displaces southward from spring to summer. One factor accounting for such a change is the dissipation of the negative SSTAs in the subtropical western Pacific from spring to summer, which weakens the SST forcing on the western North Pacific anticyclone. The other factor is an atmospheric wave train associated with the negative SSTAs in the eastern North Atlantic Ocean. The atmospheric wave train propagates eastward across the Eurasian continent and reaches East Asia. The wave pattern contributes to the development and southward displacement of an anomalous cyclone over East Asia, which causes a southward shift in the western North Pacific anticyclone. The effect of the North Atlantic negative SSTAs on the atmospheric wave pattern is supported by numerical experiments.

Observations of Aerosol, Cloud, Turbulence, and Radiation Properties at the Top of the Marine Boundary Layer over the Eastern North Atlantic Ocean: The ACORES Campaign

AbstractWe report on the Azores Stratocumulus Measurements of Radiation, Turbulence and Aerosols (ACORES) campaign, which took place around Graciosa and Pico Islands/Azores in July 2017. The main objective was to investigate the vertical distribution of aerosol particles, stratocumulus microphysical and radiative properties, and turbulence parameters in the eastern North Atlantic. The vertical exchange of mass, momentum, and energy between the free troposphere (FT) and the cloudy marine boundary layer (MBL) was explored over a range of scales from submeters to kilometers. To cover these spatial scales with appropriate measurements, helicopter-borne observations with unprecedented high resolution were realized using the Airborne Cloud Turbulence Observation System (ACTOS) and Spectral Modular Airborne Radiation Measurement System–Helicopter-Borne Observations (SMART-HELIOS) instrumental payloads. The helicopter-borne observations were combined with ground-based aerosol measurements collected at two continuously running field stations on Pico Mountain (2,225 m above sea level, in the FT), and at the Atmospheric Radiation Measurement (ARM) station on Graciosa (at sea level). First findings from the ACORES observations we are discussing in the paper are as follows: (i) we have observed a high variability of the turbulent cloud-top structure on horizontal scales below 100 m with local temperature gradients of up to 4 K over less than 1 m vertical distance, (ii) we have collected strictly collocated radiation measurements supporting the relevance of small-scale processes by revealing significant inhomogeneities in cloud-top brightness temperature to scales well below 100 m, and (iii) we have concluded that aerosol properties are completely different in the MBL and FT with often-complex stratification and frequently observed burst-like new particle formation.

Contrasting decadal trends of subsurface excess nitrate in the western and eastern North Atlantic Ocean

Abstract. Temporal variations in excess nitrate (DINxs) relative to dissolved inorganic phosphorus (DIP) were evaluated using datasets derived from repeated measurements along meridional and zonal transects in the upper (200–600 m) North Atlantic (NAtl) between the 1980s and 2010s. The analysis revealed that the DINxs trend in the western NAtl differed from that in the eastern NAtl. In the western NAtl, which has been subject to atmospheric nitrogen deposition (AND) from the USA, the subsurface DINxs concentrations have increased over the last 2 decades. This increase was associated with the increase in AND measured along the US East Coast, with a mean lag period of 15 years. This time lag was approximately equivalent to the time elapsed since the subsurface waters in the western NAtl were last in contact with the atmosphere (the ventilation age), suggesting a major role for a physical mechanism in transporting the AND signals to the subsurface. Our finding provides evidence that the DINxs dynamics in the western NAtl in recent years has been affected by anthropogenic nitrogen inputs, although this influence is weak relative to that in the western North Pacific. In contrast, a decreasing trend in subsurface DINxs was observed after the 2000s in the eastern NAtl, particularly in the high latitudes. This finding was not associated with the comparable decrease in AND from Europe. Other natural processes (a possible decline in tropical N2 fixation and weakening of the Atlantic meridional overturning circulation) may be responsible, but lack of time-resolved data on N2 fixation and meridional circulation is an impediment to assessment of these processes. Our results highlight the importance of both anthropogenic and natural forcing in impacting the nutrient dynamics in the upper NAtl.

First insights into the phylogeography and demographic history of the common hermit crab Pagurus bernhardus (Linnaeus, 1758) (Decapoda: Anomura: Paguridae) across the Eastern Atlantic and North Sea

AbstractThe common hermit crab Pagurus bernhardus (Linnaeus, 1758) is an abundant and ecologically important benthic crustacean in the northeastern Atlantic Ocean. While this species has been intensively studied in terms of its ecology, physiology, behavior, and larval development, knowledge about its population structure and demographic history is still lacking. We examined, for the first time, the genetic variability of P. bernhardus by analyzing two mitochondrial gene fragments (CO1 and 16S) from more than 150 specimens collected from various locations from the Iberian Peninsula to Norway. Our results provide evidence for a significant genetic structure according to the sampled regions for both genetic markers. Furthermore, a comprehensive demographic history reconstruction, mainly based on neutrality tests and a Bayesian Skyline Plot (CO1), revealed a recent demographic expansion of P. bernhardus that preceded the Last Glacial Maximum. Such pattern of retrieved demographic trend could have been likely a successive process to historical contraction of the species into potential climate refugia within the surveyed geographic spectrum.

Facing extremes: Cory’s shearwaters adjust their foraging behaviour differently in response to contrasting phases of North Atlantic Oscillation

Climate projections predict increases in the frequency and severity of extreme climate events over the next decades. Hence, phases of extreme climatic indices are emerging as one of the most dangerous effects of climate change, though their impacts on wildlife populations are still poorly understood. Here, we studied the foraging behaviour, body condition and breeding performance of a neritic (Berlenga Island) and oceanic (Corvo Island) population of Cory’s shearwaters (Calonectris borealis) in the mid-North Atlantic, during the two most positive and negative phases of North Atlantic Oscillation (NAO) reported in recent decades. We showed that during an extreme negative NAO phase, birds from Berlenga spent less time foraging and provided less food to their chicks, which subsequently grew more slowly and were in poorer body condition. In contrast, the opposite pattern was found during the strong positive NAO phase in this population. Interestingly, during the same extreme negative NAO phase, birds from Corvo were more successful in terms of their foraging and breeding performance, taking advantage of the enhanced productivity associated with the cyclonic eddies (negative sea surface height anomalies) which occurred close to the colony. However, when anticyclonic eddies (positive sea surface height anomalies) were prevalent near the colony during the strong positive NAO phase, birds travelled longer distances, which negatively impacted their own body condition and that of their chicks. Our study shows that populations breeding in neritic and oceanic areas of the eastern North Atlantic Ocean make contrasting foraging behavioural decisions in response to climate extremes and highlights the importance of mesoscale eddies for oceanic populations of pelagic seabirds.

Hierarchical genetic structuring in the cool boreal kelp, Laminaria digitata: implications for conservation and management

AbstractKelp are foundation species threatened by ongoing warming trends and increased harvesting pressure. This emphasizes the need to study genetic structure over various spatial scales to resolve demographic and genetic processes underpinning resilience. Here, we investigate the genetic diversity in the kelp, Laminaria digitata, in previously understudied southern (trailing-edge) and northern (range-centre) regions in the Northeastern Atlantic Ocean. There was strong hierarchical spatial structuring with significantly lower genetic variability and gene flow among southern populations. As these span the area of the Hurd’s deep Pleistocene glacial refuge, the current low variation likely reflects a fraction of previous levels that has been eroded at the species southern edge. Northern variability and private alleles also indicate contributions from cryptic northern glacial refugia. Contrary to expectations of a positive relationship between neutral genetic diversity and resilience, a previous study reported individuals from the same genetically impoverished southern populations to be better adapted to cope with thermal stress than northern individuals. This not only demonstrates that neutral genetic diversity may be a poor indicator of resilience to environmental stress but also confirms that extirpation of southern populations will result in the loss of evolved, not just potential, adaptations for resilience.

Bryozoa from deep-sea habitats of the northern Gulf of Cádiz (Northeastern Atlantic)

This study examines material collected in the northern part of the Gulf of Cádiz, in the Northeastern Atlantic Ocean, between the Iberian Peninsula and northern Africa, at 300-1200 m depth, within the Site of Community Importance "Volcanes de fango del Golfo de Cádiz" (Mud volcanoes of the Gulf of Cádiz, ESZZ-12002). Several previous studies were carried out in the Iberian Peninsula and Moroccan area (shallow and deep waters), recording ca. 300 bryozoan species from the Gulf of Cádiz. In the present study a total of 40 bryozoan taxa were identified, including two species new to science-Antropora gemarita n. sp. and Microporella funbio n. sp.-and three new records for the area.

Setaphyes elenae sp. nov., a new species of mud dragon (Kinorhyncha: Allomalorhagida) from Skagerrak (north-eastern Atlantic Ocean)

Meiofauna sampling in the proximity of Syd-Hällsö Island (Strömstad, Sweden) revealed a new species of Kinorhyncha from the Skagerrak. The species, Setaphyes elenae sp. nov., is distinguished from its congeners by the arrangement of the middorsal cuticular specializations (it has shortened, distally rounded middorsal processes on segments 1 and 9 and middorsal elevations throughout segments 2–8), as well as by the presence of paired laterodorsal setae on segments 3, 5, 7 and 9 and ventromedial setae on segments 3, 5 and 7 in both males and females. The finding of a new species from the north-eastern Atlantic Ocean, provides new valuable information for the recently established genus in the Allomalorhagida.

Mapping of Eastern North Atlantic Ocean seismicity from Po/So observations at a mid-aperture seismological broad-band deep sea array

SUMMARYA mid-aperture broad-band test array (OBS array DOCTAR) was deployed from June 2011 to April 2012 about 100 km north of the Gloria fault in the Eastern North Atlantic in about 5000 m water depth. In addition arrays were installed on Madeira Island and in western Portugal mainland. For the first time in the Eastern North Atlantic, we recorded a large number of high frequency Po and So waves from local and regional small and moderate earthquakes (ML < 4). An incoherent beamforming method was adapted to scan continuous data for such Po and So arrivals applying a sliding window waveform migration and frequency–wavenumber technique. We identify about 320 Po and 1550 So arrivals and compare the phase onsets with the ISC catalogue (ISC 2015) for the same time span. Up to a distance of 6° to the DOCTAR stations all events listed in the ISC catalogue could be associated to Po and So phases. Arrivals from events in more than 10° distance could be identified only in some cases. Only few Po and/or So arrivals were detected for earthquakes from the European and African continental area, the continental shelf regions and for earthquakes within or northwest of the Azores plateau. Unexpectedly, earthquake clusters are detected within the oceanic plates north and south of the Gloria fault and far from plate boundaries, indicating active intraplate structures. We also observe and locate numerous small magnitude earthquakes on the segment of the Gloria fault directly south of DOCTAR, which likely coincides with the rupture of the 25 November 1941 event. Local small magnitude earthquakes located beneath DOCTAR show hypocentres up to 30 km depth and strike-slip focal mechanisms. A comparison with detections at temporary mid-aperture arrays on Madeira and in western Portugal shows that the deep ocean array performs much better than the island and the continental array regarding the detection threshold for events in the oceanic plates.We conclude that sparsely distributed mid-aperture seismic arrays in the deep ocean could decrease the detection and location threshold for seismicity with ML < 4 in the oceanic plate and might constitute a valuable tool to monitor oceanic plate seismicity.

Simulation of Ship Radiated Noise Field in Deep Sea Based on Statistical Characteristics of Sound Source

The radiated noise of a ship is mainly composed of a low-frequency line spectrum and a medium-high frequency broadband continuum spectrum. In the ocean, the low-frequency sound signal decays slowly, so the low-frequency line spectrum of ship radiated noise can be transmitted over long distances. Based on the statistical analysis method, the inherent source characteristics of radiated noise are obtained from the measured data in shallow sea waveguides. Different deep sea sound velocity distribution conditions, such as the northeastern Atlantic Ocean, the Norwegian Sea deep sea, the Norwegian sea surface channel and the polar regions, were selected, and the propagation characteristics of the low-frequency radiation noise field of the ship were simulated at a horizontal distance of 150 km. The effects of different sound velocity distributions on the propagation of low-frequency acoustic signals are obtained. The research results have important practical significance for the utilization of low-frequency radiation noise characteristics of ships in deep sea.

Oceanic cooling recorded in shells spanning the Medieval Climate Anomaly in the subtropical eastern North Atlantic Ocean

Oceanic cooling recorded in shells spanning the Medieval Climate Anomaly in the subtropical eastern North Atlantic Ocean

Phylogeography highlights two different Atlantic/Mediterranean lineages and a phenotypic latitudinal gradient for the deep-sea morid codling Lepidion lepidion (Gadiformes: Moridae)

In spite of our awareness that the biosphere is represented to a greater extent in the oceans than elsewhere, little is still known about the genetic structure and phylogeography of most deep-sea fish species. Here, different questions regarding the phenotypic and genetic diversity of deep-sea morid cod Lepidion lepidion across its distribution area have been investigated. Principal Component Analyses of 17 different morphological measurements indicated no differences between Atlantic Ocean and Mediterranean Sea, but the presence of a latitudinal phenotypic gradient. The genetic analyses comprised three mitochondrial and two nuclear markers. Neutrality tests and mismatch distributions indicated events of demographic expansion in the western Mediterranean Sea and the northeastern Atlantic Ocean that should be interpreted with caution due to the limited sample size. In addition, two different nuclear lineages partially mixed have been detected, suggesting isolation with secondary contact between the Atlantic Ocean and the Mediterranean Sea. Moderate genetic structure was found in Aviles Canyon (NW Iberian Peninsula) showing limitations to gene flow and asymmetric migration, probably due to the oceanographic conditions in the area. The results suggest that genetic connectivity of L. lepidion is probably due to its pelagic stages.

North Atlantic Integrated Water Vapor Transport—From 850 to 2100 CE: Impacts on Western European Rainfall

AbstractMoisture transport over the northeastern Atlantic Ocean is an important process governing precipitation distribution and variability over western Europe. To assess its long-term variability, the vertically integrated horizontal water vapor transport (IVT) from a long-term climate simulation spanning the period 850–2100 CE was used. Results show a steady increase in moisture transport toward western Europe since the late-nineteenth century that is projected to expand during the twenty-first century under the RCP8.5 scenario. The projected IVT for 2070–99 significantly exceeds the range given by interannual–interdecadal variability of the last millennium. Changes in IVT are in line with significant increases in tropospheric moisture content, driven by the concurrent rise in surface temperatures associated with the anthropogenic climate trend. On regional scales, recent and projected precipitation changes over the British Isles follow the global positive IVT trend, whereas a robust precipitation decrease over Iberia is identified in the twenty-first century, particularly during autumn. This indicates a possible extension of stable and dry summer conditions and a decoupling between moisture availability and dynamical forcing. The investigation of circulation features reveals a mean poleward shift of moisture corridors and associated atmospheric rivers. In particular, in Iberia, a significant increase in the frequency of dry weather types is observed, accompanied by a decrease in the frequency of wet types. An opposite response is observed over the British Isles. These changes imply a stronger meridional north–south dipole in terms of pressure and precipitation distributions, enhancing the transport toward central Europe rather than to Iberia.

Strong Dependence of Wintertime Arctic Moisture and Cloud Distributions on Atmospheric Large-Scale Circulation

AbstractThis study gives a comprehensive picture of how atmospheric large-scale circulation is related to moisture transport and to distributions of moisture, clouds, and surface downward longwave radiation in the Arctic in winter. Anomaly distributions of the abovementioned variables are compared in 30 characteristic wintertime atmospheric circulation regimes, which are allocated from 15 years (2003–17) of mean sea level pressure data of ERA-Interim reanalysis applying the self-organizing map method. The characteristic circulation regimes are further related to known climate indices—the North Atlantic Oscillation (NAO), the Arctic Oscillation (AO), and Greenland blocking index—as well as to a frequent high pressure pattern across the Arctic Ocean from Siberia to North America, herein called the Arctic bridge. Effects of large-scale circulation on moisture, cloud, and longwave radiation are to a large extent occurring through the impact of horizontal moisture transport. Evaporation is typically not efficient enough to shape those distributions, and much of the moisture evaporated in the Arctic is transported southward. The positive phase of the NAO and AO increases moisture and clouds in northern Europe and the eastern North Atlantic Ocean, and a strong Greenland blocking typically increases those in the southwest of Greenland. When the Arctic bridge is lacking, the amount of moisture, clouds, and downward longwave radiation is anomalously high near the North Pole. Our results reveal a strong dependence of moisture, clouds, and longwave radiation on atmospheric pressure fields, which also appears to be important from a climate change perspective.

Análisis de la pesca española en el Atlántico noreste 1980-2012: Papel de Galicia en la explotación de las principales especies marinas

The Spanish fishing fleet is one of the most important in the European Union and is exploiting marine resources in the FAO area 27 (North-eastern Atlantic Ocean). The Galician Region has a relevant role in the fishing industry. The number of boats decreased significantly between 1980 and 2012. But the landing quantities of the main marine species exploited (small pelagic fishes and tuna species mainly) decreased faster that the fleet during the same period. In contrast, landing quantities of Elasmobranchs (sharks and rays) and Cephalopods increased. This analysis shows the overexploitation of the Atlantic fishing grounds.

Revision of the circumglobal genus Barathronus (Ophidiiformes, Bythitidae) with a new species from the eastern North Atlantic Ocean.

The viviparous genus Barathronus Goode Bean, 1886 is known from 11 species. Examination of 68 specimens, not earlier published upon, and re-examination of older material have resulted in taxonomical changes and new distributions. B. unicolor Nielsen, 1984 has become a junior synonym of B. pacificus Nielsen Eagle, 1974, now known from the Atlantic and Pacific Oceans. The number of specimens of B. parfaiti Vaillant, 1888 is restricted to the holotype and a specimen from off the Azores (MOM P01-0003665), often referred to B. parfaiti, represents a new species, B. roulei, herein described. B. diaphanus Brauer, 1906 is now recorded from off Madagascar eastwards to Tonga and Fiji Islands.

Size at sex change and reproductive cycle of the limpets Patella vulgata and Patella ulyssiponensis (Mollusca: Patellogastropoda) from intertidal rocky shores of the Algarve coast (southern Portugal)

ABSTRACTThis study describes the reproductive cycle of the common limpet (Patella vulgata) and rough limpet (Patella ulyssiponensis) from the Algarve coast (southern Portugal). Individuals of both species were sampled monthly during two consecutive years, and subjected to gonad histology and calculation of the mean gonadal index (GI). Both species had balanced sex ratios (P. vulgata = 1M: 0.98F; P. ulyssiponensis = 1M: 1.03F), similar size-frequency distribution between sexes, and equivalent mean shell lengths (SL) and total weights (TW) between males and females. In these protandrous hermaphrodites, the estimated size at sex change was slightly smaller in P. vulgata (SL50 ≈ 29 mm) than in P. ulyssiponensis (SL50 ≈ 36 mm). The reproductive cycles of both species were characterised by a main spawning season in early spring to early summer, sometimes including subsidiary spawning events. A comparison of the main spawning season throughout the species distributional ranges revealed that populations of P. vulgata and P. ulyssiponensis from southern Portugal have later spawning periods than other populations from the northeastern Atlantic Ocean. The present information is relevant for conservation purposes and for the proposal of management measures for the harvesting activity targeting P. vulgata and P. ulyssiponensis in southern Portugal.