North-eastern Atlantic Waters Research Articles

Coastal and regional marine heatwaves and cold spells in the northeastern Atlantic

Abstract. The latest Intergovernmental Panel on Climate Change (IPCC) report describes an increase in the number and intensity of marine heatwaves (MHWs) and a decrease in marine cold spells (MCSs) in the global ocean. However, these reported changes are not uniform on a regional to local basis, and it remains unknown if coastal areas follow the open-ocean trends. Surface ocean temperature measurements collected by satellites (from 1982–2022) and 13 coastal buoys (from 1990–2022) are analyzed in the northeastern Atlantic and three subregions: the English Channel, Bay of Brest and Bay of Biscay. The activity metric, combining the number of events, intensity, duration and spatial extent, is used to evaluate the magnitude of these extreme events. The results from in situ and satellite datasets for each of the studied regions are quite in agreement, although the satellite dataset underestimates the amplitude of activity for both MHWs and MCSs. This supports the applicability of the method to both in situ and satellite data, albeit with caution on the amplitude of these events. Also, this localized study in European coastal northeastern Atlantic water highlights that similar changes are being seen in coastal and open oceans regarding extreme events of temperature, with MHWs being more frequent and longer and extending over larger areas, while the opposite is seen for MCSs. These trends can be explained by changes in both the mean of and variance in sea-surface temperature. In addition, the pace of evolution and dynamics of marine extreme events differ among the subregions. Among the three studied subregions, the English Channel is the region experiencing the strongest increase in summer MHW activity over the last 4 decades. Summer MHWs were very active in the English Channel in 2022 due to long events, in the Bay of Biscay in 2018 due to intense events and in the Bay of Brest in 2017 due to a high occurrence of events. Winter MCSs were the largest in 1987 and 1986 due to long and intense events in the English Channel. Finally, our findings suggest that at an interannual timescale, the positive North Atlantic Oscillation favors the generation of strong summer MHWs in the northeastern Atlantic, while low-pressure conditions over northern Europe and a high off the Iberian Peninsula in winter dominate for MCSs. A preliminary analysis of air–sea heat fluxes suggests that, in this region, reduced cloud coverage is a key parameter for the generation of summer MHWs, while strong winds and increased cloud coverage are important for the generation of winter MCSs.

A global phylogeny of Elysia Risso, 1818 (Gastropoda: Heterobranchia): molecular systematic insights focusing on European taxa and description of a new species

Abstract The genus Elysia comprises about one-third of the species richness in Sacoglossa. However, the species diversity in the genus remains poorly characterized in some areas like the north-eastern Atlantic and Mediterranean waters. To clarify the systematics of this genus and to characterize the species diversity in undersampled regions, we performed an integrative study based on a thorough literature review, molecular and morphological analyses, and species delimitation approaches. We conducted phylogenetic analyses of partial sequences of two mitochondrial genes (COI and 16S) and two nuclear genes (H3, 28S) using Bayesian inference and maximum likelihood methods, which confirmed the presence of five of the recognized European Elysia species: Elysia viridis, E. timida, E. flava, E. margaritae, and E. rubeni. Moreover, a new species (Elysia azorica sp. nov.) was identified in the Azores, and E. gordanae, currently considered a junior synonym of E. margaritae, was recovered as a distinct species. In addition, we consider E. hetta as a junior synonym of E. gordanae, and E. translucens as a taxon inquirendum. Finally, the tropical E. evelinae is recorded along European coasts for the first time. Our results demonstrate the value of integrative approaches in resolving taxonomic uncertainty surrounding polymorphism and unravelling potential cases of cryptic or pseudocryptic species complexes.

Estimates of humpback and minke whale entanglements in the Scottish static pot (creel) fishery

Entanglement in static fishing gear (pots, or creels as they are called in Scottish fisheries) is a major cause of anthropogenic mortality and morbidity in large whales globally; in northeastern Atlantic waters around the coast of Scotland, entanglement is a particular welfare and conservation concern for minke whales Balaenoptera acutorostrata and humpback whales Megaptera novaeangliae. Reports from strandings, live disentanglements and interviews with Scottish inshore creel fishers were gathered to estimate entanglement rates. Considerably more whale entanglements occur in the Scottish creel fishery than previously thought based on strandings alone, with estimates of 6 humpback whales and 30 minke whales becoming entangled each year. Where entanglement type was reported, 83% of minke and 50% of humpback whales were caught in groundlines between creels. There was a positive correlation between the average amount of gear set by a vessel and the number of minke whale entanglements. For the west coast of Scotland, the estimated annual fatal entanglement rate of minke whales is 2.3% of a recent abundance estimate, suggesting a risk of localised depletion. There are very low densities of humpback whales in Scottish waters, but opportunistic observations suggest numbers are increasing. The estimated number of annual humpback whale entanglements also shows an increasing trend. There are few entanglement estimates for static pot fisheries globally; this study provides an indication of how such data might be derived. Scottish creel fishers have shown a willingness to engage in entanglement mitigation, with suggestions such as the introduction of sinking groundline to the sector, and these options should be urgently pursued.

Empirical leucine-to-carbon conversion factors in north-eastern Atlantic waters (50\u20132000\xa0m) shaped by bacterial community composition and optical signature of DOM

Microbial heterotrophic activity is a major process regulating the flux of dissolved organic matter (DOM) in the ocean, while the characteristics of this DOM strongly influence its microbial utilization and fate in the ocean. In order to broaden the vertical resolution of leucine-to-carbon conversion factors (CFs), needed for converting substrate incorporation into biomass production by heterotrophic bacteria, 20 dilution experiments were performed in the North Atlantic Ocean. We found a depth-stratification in empirical CFs values from epipelagic to bathypelagic waters (4.00 ± 1.09 to 0.10 ± 0.00 kg C mol Leu−1). Our results demonstrated that the customarily used theoretical CF of 1.55 kg C mol Leu−1 in oceanic samples can lead to an underestimation of prokaryotic heterotrophic production in epi- and mesopelagic waters, while it can overestimate it in the bathypelagic ocean. Pearson correlations showed that CFs were related not only to hydrographic variables such as temperature, but also to specific phylogenetic groups and DOM quality and quantity indices. Furthermore, a multiple linear regression model predicting CFs from relatively simple hydrographic and optical spectroscopic measurements was attempted. Taken together, our results suggest that differences in CFs throughout the water column are significantly connected to DOM, and also reflect differences linked to specific prokaryotic groups.

Distribution and life history trait models indicate vulnerability of skates

Elasmobranchs are k-strategy species with low reproduction rate and slow growth lending to increased anthropogenic vulnerability. Specific management measures to improve the conservation of elasmobranchs can be problematic due to insufficient information on their biology and ecology. Here, three sympatric skates occupying north-eastern Atlantic waters, which have differing conservation status were studied within ICES divisions 4.c, 7.d–e, 7.f–h and 8a–b and d. Fisheries-dependent data on skate bycatch and a series of environmental variables were used to model spatio-temporal differences in habitat use between the three species.Raja undulata, the undulate ray (IUCN red listed as ‘Endangered’) was observed to have a coastal distribution within the English Channel and the Bay of Biscay (ICES division 7.d–e and 8.a–b). Raja clavata, the thornback ray (‘Near threatened’), had a broader distribution with higher presence in the eastern English Channel and the southern North Sea (ICES division 7.e and 4.c). Raja montagui, the spotted ray’s probability of presence (‘Least concerned’) was higher off the coast of southern Ireland (ICES division 7.g). Seasonal and life-history trait differences were also observed.From the fisheries-dependent data, wider skate distributions than previously studied were modelled. Although the species do co-occur, spatio-temporal differences between these species were observed. This study contributes to a greater understanding of skate habitat during their different life history stages, and indicates reasons for R. undulata’s increased vulnerability than R. clavata and R. montagui. Information from the distribution models could be used for specific spatio-temporal management measures. Better understanding of the distribution of species can also help reduce bycatch of protected species such as R. undulata.

“Invasion” in the Russian Arctic: is global Climate Changea real driver? A remarkable case of two nudibranch species

In present paper, we report the first findings of two large and conspicuous nudibranch species for Russian waters - Goniodoris nodosa and Flabellina pellucida. Both species show wide distribution in the northeastern Atlantic waters or even in the north-western Atlantic in the case of F. pellucida. The morphology of both species was studied using anatomical dissections and scanning electron microscopy. Molecular diversity was assessed by sequencing of COI marker and reconstruction of haplotype networks. In the Barents Sea, both species show minor genetic differences from their European relatives and similar morphological characters. Putative explanations of new findings for Russian Arctic are discussed.

Weight–length relationships, weight conversion factors and somatic indices from two stocks of black anglerfish (Lophius budegassa) and white anglerfish (L. piscatorius) in north-eastern Atlantic waters

Weight–length relationships, weight conversion factors and somatic indices are presented from a decade (2006 to 2015) for two stocks of Lophius budegassa and L.piscatorius in northern Iberian Atlantic waters (ICES Div. VIIIc–IXa2) and in Celtic Sea, south-western Ireland and Porcupine Bank (Div. VIIb,c,h,j,k). A total of 3298 L.budegassa and 7219 L.piscatorius were sampled from commercial landings and research surveys. Total length (Lt), total weight (Wt), “commercial” weight (Wgl) and “scientific” weight (Wg) were obtained. The parameters (a, b) in the power relationships weight–length for combined sexes in L.budegassa were: 0.020, 2.916; 0.017, 2.929; 0.017, 2.922 for Wt, Wgl and Wg respectively in Div. VIIIc–IXa2; 0.025, 2.841; 0.013, 2.984; 0.013, 2.971 in Div. VIIb,c,h,j,k. For L.piscatorius: 0.025, 2.853; 0.020, 2.868; 0.024, 2.861 in Div. VIIIc–IXa2; 0.027, 2.826; 0.023, 2.825; 0.023, 2.816 in Div. VIIb,c,h,j,k. Significant differences between stocks were found in both species. The conversion factors between total and gutted weight in L.budegassa were: 1.186, 1.236 for Wgl and Wg respectively in Div. VIIIc–IXa2; 1.187, 1.233 in Div. VIIb,c,h,j,k. For L.piscatorius: 1.181, 1.241 in Div. VIIIc–IXa2; 1.210, 1.262 in Div. VIIb,c,h,j,k. The parameters can be used in the process of annual assessment of the state of each stock. Gonadosomatic index (GSI), hepatosomatic index (HSI) and Le Cren’s condition factor, indicators of reproductive and nutritional status, were seasonally analyzed and compared between sexes and stocks. Significant better condition and higher GSI and HSI were found in females. In Div. VIIb,c,h,j,k better condition was found for both species and higher GSI for L.piscatorius. The analysis throughout the year of GSI and HSI for L.budegassa showed seasonality in liver growth previous to spawn and corroborated the spawning season from January to June in VIIIc–IXa2. The parameters obtained were compared with previous ones from these and others Lophiiformes, showing common patterns.

The use of parasites as biological tags for stock identification of blue jack mackerel, Trachurus picturatus, in the northeastern Atlantic waters

The use of parasites as biological tags for stock identification of blue jack mackerel, Trachurus picturatus, in the northeastern Atlantic waters

A revision of the species of the genus Munida (Crustacea, Anomura, Munididae) from Mediterranean and north-eastern Atlantic waters using morphological and molecular characters

A revision of the species of the genus Munida (Crustacea, Anomura, Munididae) from Mediterranean and north-eastern Atlantic waters using morphological and molecular characters

First estimates of age and growth of juvenile black anglerfish (Lophius budegassa), in north-eastern Atlantic waters

Growth increments in the lapilli otoliths of the black anglerfish (Lophius budegassa) were used to investigate its early life history. Assuming that the primary increments are deposited daily, age and hatch dates were determined by counting these increments in the lapilli of 33 juvenile fish collected during autumn bottom trawl surveys in the Bay of Biscay. The estimated ages of juveniles ranged from 71 to 165 days (60 to 202mm total length) while the growth rate ranged from 1.19 to 1.48mmday−1 for that period. The age–length relationship was best described by the power function TL=0.311 age (days)1.26. Hatch date was back-calculated from the date of capture and results indicate a broad spawning season, mainly taking place from May to July. Juveniles of up to 200mm total length collected in October were born the same year and belonged to age class 0. Although the periodicity of the primary increments has not yet been validated, our results, based on this assumption, would corroborate, for the first time using micro-increment analysis, a faster growth pattern of early stages of L. budegassa in Atlantic waters than previously thought, in agreement with the evidence obtained for the species in the Mediterranean Sea.

Genetic and Morphological Approaches Distinguish the Three Sibling Species of theAnisakis simplexSpecies Complex, with a Species Designation asAnisakis berlandin. sp. forA. simplexsp. C (Nematoda: Anisakidae)

Numerous specimens of the 3 sibling species of the Anisakis simplex species complex (A. pegreffii, A. simplex (senso stricto)), and A. simplex sp. C) recovered from cetacean species stranded within the known geographical ranges of these nematodes were studied morphologically and genetically. The genetic characterization was performed on diagnostic allozymes and sequences analysis of nuclear (internal transcribed spacer [ITS] of ribosomal [r]DNA) and mitochondrial (mitochondrial [mt]DNA cox2 and rrnS) genes. These markers showed (1) the occurrence of sympatry of the 2 sibling species A. pegreffii and A. simplex sp. C in the same individual host, the pilot whale, Globicephala melas Traill, from New Zealand waters; (2) the identification of specimens of A. pegreffii in the striped dolphin, Stenella coeruleoalba (Meyen), from the Mediterranean Sea; and (3) the presence of A. simplex (s.s.) in the pilot whale and the minke whale, Balaenoptera acutorostrata Lacépède, from the northeastern Atlantic waters. No F1 hybrids were detected among the 3 species using the nuclear markers. The phylogenetic inference, obtained by maximum parsimony (MP) analysis of separate nuclear (ITS rDNA region), combined mitochondrial (mtDNA cox2 and rrnS) sequences datasets, and by concatenated analysis obtained at both MP and Bayesian inference (BI) of the sequences datasets at the 3 studied genes, resulted in a similar topology. They were congruent in depicting the existence of the 3 species as distinct phylogenetic lineages, and the tree topologies support the finding that A. simplex (s.s.), A. pegreffii, and A. berlandi n. sp. (= A. simplex sp. C) represent a monophyletic group. The morphological and morphometric analyses revealed the presence of morphological features that differed among the 3 biological species. Morphological analysis using principal component analysis, and Procrustes analysis, combining morphological and genetic datasets, showed the specimens clustering into 3 well-defined groups. Nomenclatural designation and formal description are given for A. simplex species C: the name Anisakis berlandi n. sp. is proposed. Key morphological diagnostic traits are as follows between A. berlandi n. sp. and A. simplex (s.s.): ventriculus length, tail shape, tail length/total body length ratio, and left spicule length/total body length ratio; between A. berlandi n. sp. and A. pegreffii: ventriculus length and plectane 1 width/plectane 3 width ratio; and between A. simplex (s.s.) and A. pegreffii: ventriculus length, left and right spicule length/total body length ratios, and tail length/total body length ratio. Ecological data pertaining to the geographical ranges and host distribution of the 3 species are updated.

Preliminary observation on sexual maturity of black anglerfish (Lophius budegassa) in north-eastern Atlantic waters

The reproduction of black anglerfish (Lophius budegassa) was studied from samples collected during 5 years, from January 2006 to December 2010, in Celtic Sea, West and South of Ireland (ICES Div. VIIb–k) and Northern Spanish Atlantic waters (ICES Div. VIIIc–IXa). A total of 1167 specimens (4–99cm) were sampled. The sex ratio, the spawning period and the maturity ogives by length were studied. The sex ratio in both areas studied varied with length, and it was close to 1:1 (male:female), 1:1.22 (54.90% of females) in Div. VIIb–k, and 1:1.01 (50.30% of females) in Div. VIIIc–IXa. A seasonal variation in sex ratio by length was observed at first time in Div VIIIc–IXa, with a very low proportion of intermediate sized females (40–60cm) in the second semester. A seasonal reproductive migratory behavior is discussed. The spawning period was between December and July in Div. VIIIc–IXa. Spawning males were found throughout the year, but fewer spawning females, as in previous studies. The L50 values were estimated in Div. VIIIc–IXa: 38.2cm for combined sexes, 36.0cm for males and 53.0cm for females. These values of sex ratio and L50 are similar to those obtained in closed areas studied.

First record of Ocinebrina nicolai (Mollusca: Gastropoda: Muricidae: Ocenebrinae) in north-eastern Atlantic waters

Ocinebrina nicolai Monterosato, 1884 a marine mollusc belonging to the Muricidae family is reported from Algarve, south coast of Portugal for the first time and is a new record for the biodiversity of the Portuguese malacological fauna and north-eastern Atlantic waters. This species with a medium-size shell for the genus (14–16 mm) was initially sampled during a baseline project that studied marine biotopes in the central Algarve region. This short note presents a brief diagnosis of the species, provides local information on geographical distribution, habitat, and compares it with other congeneric species found in Portugal: Ocinebrina aciculata (Lamarck, 1822) and Ocinebrina edwardsii (Payraudeau, 1826).

Origin, glacial‐interglacial responses, and controlling factors of a cold‐water coral mound in NE Atlantic

Recent deep‐ocean exploration has revealed unexpectedly widespread and diverse coral ecosystems in deep water on continental shelves, slopes, seamounts, and ridge systems around the world. Origin and growth history of these cold‐water coral mounds are poorly known, owing to a lack of complete stratigraphic sections through them. Here we show high‐resolution oxygen isotope records of planktic foraminifers from the base to the top of Challenger Mound, southwest of Ireland, which was drilled during Integrated Ocean Drilling Program Expedition 307. Challenger Mound began to grow during isotope stage 92 (2.24 million years ago (Ma)), immediately after the onset of Northern Hemisphere glaciation and the initiation of modern stratification in the northeast Atlantic. Mound initiation was likely due to reintroduction of Mediterranean Outflow Water (MOW) and ensuing development of a density gradient with overlying northeastern Atlantic water (NEAW), where organic matter was prone to be stagnated and fueled the coral ecosystem. Coral growth continued for 11 glacial‐interglacial cycles until isotopic stage 72 (1.82 Ma) with glacial siliciclastic input from the continental margin. After a long hiatus that separates the lower mound and the upper mound, coral growth restored for a short time in isotope stages 19–18 (0.8–0.7 Ma) in which sediments were either eroded or not deposited during a full glacial stage. The development pattern of the water mass interface between MOW and NEAW might have changed, because of the fluctuations of the MOW production which is responsible for the amplitude in ice volume oscillations from the low‐amplitude 41 ka cycles for the lower mound to the high‐amplitude 100 ka cycles for the upper mound. The average sedimentation and CaCO3 production rates of the lower mound were evaluated 27 cm/ka and 31.1 g/cm2/ka, respectively.

Geographic variability of sardine growth across the northeastern Atlantic and the Mediterranean Sea

This study describes broad-scale spatial variations in sardine growth across the northeastern Atlantic and Mediterranean waters using opportunistic samples collected in recent years. More detailed information on spatial, decadal and seasonal growth variations is provided for the Iberian-Biscay region using data collected in acoustic surveys since the mid-1980s. Growth curves are fitted to annual or monthly length-at-age data using a robust Von Bertalanffy model; parameters for recent samples are compared with literature information using an auximetric plot while differences between areas within the Iberian-Biscay region are tested by log-likelihood ratio tests. Sardine growth performance is generally lower in the Mediterranean and declines across the northeastern Atlantic from the English Channel to north Morocco but increases sharply off Mauritania. Lower growth of Mediterranean sardines is possibly associated to the overall oligotrophy of this Sea while differentiation from the Atlantic is likely sustained by reproductive isolation between populations from the two areas. Within the northeastern Atlantic, size- and age related migrations may partly explain differences in maximum length/age and mean length-at-age between neighbouring areas but the broad-scale latitudinal decline in growth is consistent with adaptation to the north–south decline in seasonal temperature gradients and to the annual cycles of plankton production. Within the Atlantic Iberian waters, sardine grows and improves in condition during spring and summer when the allocation of energetic resources for gonad development cease, temperature is close to the annual maxima and plankton production is high. Variation in sardine length-at-age and growth within the Atlanto-Iberian stock area has implications for stock structure and needs to be taken into account in the calculation of weight and maturity-at-age for assessment purposes. No evidence of broad temporal changes in sardine growth within the Iberian-Biscay region is obtained.

Mitochondrial and nuclear markers reveal isolation by distance and effects of Pleistocene glaciations in the northeastern Atlantic and Mediterranean populations of the white seabream ( Diplodus sargus, L.)

Phylogeography of Diplodus sargus from the northeastern Atlantic and the Mediterranean was assessed using sequences from the mitochondrial control region and the first intron of the S7 ribosomal protein gene. The relationship between genetic and geographic distances supported an isolation by distance model, with the Azores having a peripheral position. The geographic distribution of the genetic diversity, together with the historical demography of the populations studied can be explained by the effect of the Pleistocene glaciations in the northeastern Atlantic warm water fauna. D. sargus might have disappeared from western Europe during glacial peaks and suffered considerable demographic reductions in the Canaries and Mauritania, surviving in less affected areas such as Madeira, Azores and the Mediterranean. The mismatch analysis and the Fu's Fs values provide clear evidence of expansion in western Iberia (S. Pedro), Canaries, Mauritania and also in the eastern Mediterranean. Atlantic and Mediterranean populations of D. sargus showed no signs of genetic differentiation. D. sargus are active swimmers that can undergo extensive movements along the shores. This and the presence of planktonic eggs and larvae would allow rapid mixing between Mediterranean and Atlantic fish, erasing signs of population differentiation.

Total and organic Hg concentrations in cephalopods from the North Eastern Atlantic waters: Influence of geographical origin and feeding ecology

Total (T–Hg) and organic (O–Hg) mercury concentrations and tissue distribution were examined in 20 species of cephalopods (n=278) from the north eastern Atlantic waters, i.e. from the Bay of Biscay to the Faroe Islands. Concentrations of T–Hg in whole cephalopods showed elevated variations among species, i.e. from 40 to 3560ng g−1 dwt, but a low variability within each species (mean CV%=39%). With the exception of oceanic squids, the digestive gland globally displayed higher T–Hg concentrations than the remaining tissues. In contrast, O–Hg concentrations determined in selected species were generally higher in the remaining tissues. Despite higher T–Hg concentrations, the digestive gland weakly contributed to the total body burden of both T–Hg and O–Hg (<25% and <15%, respectively). In fact, from 75% to 95% of the T–Hg and O–Hg were contained in the muscular remaining tissues. Therefore, O–Hg may have a strong affinity to proteins in cephalopods. Sex and size only significantly influenced the bioaccumulation of Hg for the Loliginidae family. T–Hg and O–Hg concentrations were also influenced by geographical origin: Celtic Sea>Bay of Biscay>Faroe Islands, corresponding to the seawater Hg concentrations in these areas. In the Faroe Islands and the Celtic Sea, benthic cephalopods contained significant higher Hg concentrations compared to pelagic ones. This suggests that diet is not the main pathway of Hg uptake in cephalopods as pelagic species were expected to be more exposed to O–Hg through fish consumption than benthic ones.

Determination of the lead and cadmium burden in some northeastern Atlantic and Mediterranean fish species by DPSAV

Lead (Pb) and cadmium (Cd) contents in the edible parts (muscle, fillet) of 68 commercially used fish species from two European regions, the northeastern Atlantic (Tampen, north of the Shetland Islands, Faroe Islands and Copinsay) and the Mediterranean (Izmir Outer Bay, Homa Lagoon/Izmir and Mersin Bay), were determined by means of differential pulse stripping anodic voltammetry. In the sample preparation step, all frozen fish samples were lyophilised, milled in a ball mill and finally decomposed in an oxygen plasma ashing chamber. Among the fishes from northeastern Atlantic waters, the highest average Pb concentration belonged to those from Tampen with 11.25 µg/kg and the average Cd concentration to fish from Copinsay with 2.23 µg/kg. For the Mediterranean fishes, the highest average Pb and Cd concentrations belonged to those from Mersin Bay, with 185.39 µg/kg and 2.12 µg/kg, respectively. The accuracy of the concentrations determined in this study was checked by measurements of the certified reference material CRM No 422 cod muscle from the Commission of the European Communities, Community Bureau of Reference. All Cd and Pb concentrations observed in species of the eastern Mediterranean and the northeastern Atlantic were below the maximum permitted national Turkish and European levels.

Increasing abundance of Calanus finmarchicus in the central and eastern North Atlantic between 1958 and 1996

The abundance of Calanus finmarchicus is known to have fallen between the present and the late 1950s in north-eastern Atlantic shelf waters. Further west in deeper water, however, long-term abundance of the copepod has risen.

Biogeochemical evolution of the outflow of the Mediterranean deep-lying particulate organic matter into the northeastern Atlantic

Abstract Small- and large-size particles were collected in January and August 1989 throughout the water column (50–3000 m) in a northeastern Atlantic area where deep Mediterranean waters outflowing through the Strait of Gibraltar are incorporated at mid-depth into Atlantic waters. Particles collected by water filtration (0.7 μm pore size) and by vertical hauls of a plankton net (50 μm mesh size) were analysed for their organic carbon and lipid composition, namely fatty acids, hydrocarbons, aliphatic and alicyclic alcohols and ketones, and pigments. Small-size particles exhibited POC concentrations two to three orders of magnitude higher (5–50 μg/l) than large particles (0.01–0.32 μg/l). Strong spatial and temporal variations were also observed. Surface small particles collected in January accounted for 15–50 μg/l of POC, whereas in August, these represented only 5–15 μg/l following the seasonal variability of primary production. Concurrently, the variety of lipid components was larger in January. The lipid components of large-size particles were dominated by zooplankton markers, whereas small particles showed evidence of a mixed algal composition (mainly of haptophytes and moderately of diatoms, prasinophytes, chrysophytes and dinoflagellates) with a bacterial contribution. The vertical profiles of the different lipid classes showed a general decrease with depth, particularly significant in the upper 200 m, consistently with the POC contents. Compositional changes were more evident in small particles and included the loss of unsaturated compounds and the increase of diagenetic and bacterial markers. Unusual increases were observed at mid-depths indicating additional particle inputs, either by in situ formation or by advective transport from the Mediterranean. The latter was recognized because small particles in Mediterranean waters entrained large quantities of continental detritic materials that were also found in the Mediterranean water lenses in the Atlantic. From these observations, it was inferred that the outflow of the Mediterranean deep-lying particulate organic matter might still preserve its signature in the mid-depth northeastern Atlantic waters.