Catherine Guigue
email: catherine.guigue@mio.osupytheas.fr

Javier Angel Tesán-Onrubia

Léa Guyomarc'h

Daniela Bănaru

François Carlotti

Marc Pagano

Sandrine Chifflet

Deny Malengros

Léa Guyomarc'h A

Lassaad Chouba

Jacek Tronczynski

Marc Tedetti

Hydrocarbons in size-fractionated plankton of the Mediterranean Sea (MERITE-HIPPOCAMPE campaign)

Keywords: Hydrocarbons, PAHs, plankton, size fractions, bioaccumulation, Mediterranean Sea

published or not. The documents may come

Introduction

Hydrocarbons, in particular polycyclic aromatic hydrocarbons (PAHs), are among the most widespread organic pollutants in the marine environment [START_REF] Hylland | Polycyclic Aromatic Hydrocarbon (PAH) ecotoxicology in marine ecosystems[END_REF][START_REF] Duran | Role of environmental factors and microorganisms in determining the fate of polycyclic aromatic hydrocarbons in the marine environment[END_REF][START_REF] Ben Othman | Effects of polycyclic aromatic hydrocarbons on marine and freshwater microalgae -A review[END_REF]. PAHs are considered to be almost exclusively of anthropogenic origin, possibly coming from crude oil or its derivatives (petrogenic PAHs) or from the combustion of fossil fuels and biomass (pyrogenic PAHs) [START_REF] Wang | Oil spill identification[END_REF][START_REF] Yunker | PAHs in the Fraser River basin: A critical appraisal of PAH ratios as indicators of PAH source and composition[END_REF][START_REF] Stogiannidis | Source characterization of polycyclic aromatic hydrocarbons by using their molecular indices: an overview of possibilities[END_REF]. Aliphatic hydrocarbons (AHs), which also represent an important class of hydrocarbons in the marine environment, can be of anthropogenic (petroleum) and biogenic (terrestrial or marine) origin [START_REF] Volkman | Identification of natural, anthropogenic and petroleum hydrocarbons in aquatic sediments[END_REF][START_REF] Bouloubassi | Investigation of anthropogenic and natural organic inputs in estuarine sediments using hydrocarbon markers (NAH, LAB, PAH)[END_REF]Love et al., 2021). PAHs are listed as priority pollutants by various international organizations (US-EPA, 2012; EU-Directive, 2013) due to their deleterious effects on living organisms [START_REF] Honda | Toxicities of polycyclic aromatic hydrocarbons for aquatic animals[END_REF]. Thus, for many years, PAHs, and to a lesser extent AHs, have been studied in different matrices of the marine ecosystems, such as surface sediments [START_REF] Mille | Hydrocarbons in coastal sediments from the Mediterranean Sea (Gulf of Fos area, France)[END_REF][START_REF] Zaghden | Origin and distribution of hydrocarbons and organic matter in the surficial sediments of the Sfax-Kerkennah channel (Tunisia, Southern Mediterranean Sea)[END_REF][START_REF] Mandić | Polycyclic aromatic hydrocarbons in surface sediments of the mid-Adriatic and along the Croatian coast: Levels, distributions and sources[END_REF], the dissolved phase of water [START_REF] Guigue | Spatial and seasonal variabilities of dissolved hydrocarbons in surface waters from the Northwestern Mediterranean Sea: Results from one-year intensive sampling[END_REF][START_REF] Adhikari | Vertical fluxes of polycyclic aromatic hydrocarbons in the northern Gulf of Mexico[END_REF][START_REF] Tong | Distribution, sources an ecological risk assessment of PAHs in surface seawater from coastal Bohai Bay, China[END_REF], suspended particles [START_REF] Bouloubassi | PAH transport by sinking particles in the open Mediterranean Sea: A 1 year sediment trap study[END_REF][START_REF] Mzoughi | Distribution and partitioning of aliphatic hydrocarbons and polycyclic aromatic hydrocarbons between water, suspended particulate matter, and sediment in harbours of the West coastal of the Gulf of Tunis (Tunisia)[END_REF][START_REF] Rocha | Concentrations, sources and risks of PAHs in dissolved and suspended material particulate fractions from the Northwest Atlantic Coast of the Iberian Peninsula[END_REF], surface microlayer [START_REF] Stortini | n-Alkanes, PAHs and surfactants in the sea surface microlayer and sea water samples of the Gerlache Inlet sea (Antartica)[END_REF][START_REF] Guitart | Effect of the accumulation of polycyclic aromatic hydrocarbons in the sea surface microlayer on their coastal air-sea exchanges[END_REF][START_REF] Guigue | Occurrence and distribution of hydrocarbons in the surface microlayer and subsurface water from the urban coastal marine area off Marseilles, Northwestern Mediterranean Sea[END_REF], and biota, especially macro-organisms [START_REF] Baumard | Polycyclic aromatic hydrocarbons in sediments and mussels of the western Mediterranean Sea[END_REF][START_REF] Tolosa | Aliphatic and aromatic hydrocarbons in marine biota and coastal sediments from the Gulf and the Gulf of Oman[END_REF][START_REF] Pirsaheb | Evaluation of polycyclic aromatic hydrocarbons (PAHs) in fish: a review and meta-analysis[END_REF].

The incorporation and transfer of PAHs within marine food webs is known to induce major disturbances of ecosystems, and to have negative impacts on the exploitation of marine resources and habitats, socio-economic activities, and human health [START_REF] Islam | Impacts of pollution on coastal and marine ecosystems including coastal and marine fisheries and approach for management: a review and synthesis[END_REF][START_REF] Balcıoğlu | Potential effects of polycyclic aromatic hydrocarbons (PAHs) in marine foods on human health: a critical review[END_REF][START_REF] Romero | Decadal Assessment of Polycyclic Aromatic Hydrocarbons in Mesopelagic Fishes from the Gulf of Mexico Reveals Exposure to Oil-Derived Sources[END_REF]. However, even though the concentrations of PAHs in upper food webs has been quite well documented so far, they have been much less investigated in plankton, i.e., the first trophic levels of pelagic marine ecosystems. Yet, plankton, which includes phytoplankton (mostly unicellular photosynthetic autotrophic organisms), zooplankton (heterotrophic eukaryotes), and bacterioplankton (heterotrophic prokaryotes), is recognized as a key gateway and playing a major role in the transfer of contaminants from water to upper food webs [START_REF] Berrojalbiz | Biogeochemical and physical controls on concentrations of polycyclic aromatic hydrocarbons in water and plankton of the Mediterranean and Black Seas[END_REF][START_REF] Tiano | PCB concentrations in plankton size classes, a temporal study in Marseille Bay, Western Mediterranean Sea[END_REF][START_REF] Tao | Factors affecting annual occurrence, bioaccumulation, and biomagnification of polycyclic aromatic hydrocarbons in plankton food webs of subtropical eutrophic lakes[END_REF][START_REF] Chouvelon | Patterns of trace metal bioaccumulation and trophic transfer in a phytoplankton-zooplankton-small pelagic fish marine food web[END_REF][START_REF] Tedetti | Contamination of planktonic food webs in the Mediterranean Sea: Setting the frame for the MERITE-HIPPOCAMPE oceanographic cruise (spring 2019)[END_REF].

Given their high surface area/volume ratio and the subsequent large areas of exchanges, phytoplankton cells display high bioconcentration capacities (bioconcentration referring to the accumulation of contaminants in a given organism relative to surrounding water by direct absorption from the latter) [START_REF] Martin | The elemental composition of plankton[END_REF][START_REF] Fan | Phenanthrene Accumulation Kinetics in Marine Diatoms[END_REF][START_REF] Heimbürger | Methylmercury distributions in relation to the presence of nano and picophytoplankton in an oceanic water column (Ligurian Sea, North-western Mediterranean)[END_REF][START_REF] Chouvelon | Patterns of trace metal bioaccumulation and trophic transfer in a phytoplankton-zooplankton-small pelagic fish marine food web[END_REF]. Assuming partition equilibrium processes between the cells and the surrounding water [START_REF] Frouin | Partitioning and bioaccumulation of PCBs and PBDEs in marine plankton from the Strait of Georgia, British Columbia, Canada[END_REF], the bioconcentration of organic contaminants in phytoplankton may be directly related to their octanol-water partitioning coefficient (Log KOW), i.e., their degree of hydrophobicity (the higher the Log KOW, the greater the contaminant bioconcentration) [START_REF] Swackhamer | Bioaccumulation of PCBs by algae: kinetics versus equilibrium[END_REF][START_REF] Nizzetto | Biological pump control of the fate and distribution of hydrophobic organic pollutants in water and plankton[END_REF][START_REF] Li | Impact of trophic levels on partitioning and bioaccumulation of polycyclic aromatic hydrocarbons in particulate organic matter and plankton[END_REF], and to the size of the phytoplankton species (the smaller the cell size, the greater the contaminant bioconcentration) [START_REF] Fan | Phenanthrene Accumulation Kinetics in Marine Diatoms[END_REF]. On the other side, bioaccumulation processes in zooplankton (bioaccumulation referring to the accumulation of contaminants in a given organism relative to surrounding water by both direct absorption from water and the consumption of contaminated prey) are made complex by 1) the influence of trophic interactions and transfers between phytoplankton and zooplankton and within zooplanktonic compartment, and 2) the removal processes of contaminants implemented by these organisms, including metabolization, passive release and excretion [START_REF] Berrojalbiz | Accumulation and cycling of polycyclic aromatic hydrocarbons in zooplankton[END_REF][START_REF] Tiano | PCB concentrations in plankton size classes, a temporal study in Marseille Bay, Western Mediterranean Sea[END_REF][START_REF] Alekseenko | Modeling of PCB trophic transfer in the Gulf of Lions; 3D coupled model application[END_REF][START_REF] Tao | Factors affecting annual occurrence, bioaccumulation, and biomagnification of polycyclic aromatic hydrocarbons in plankton food webs of subtropical eutrophic lakes[END_REF][START_REF] Li | Impact of trophic levels on partitioning and bioaccumulation of polycyclic aromatic hydrocarbons in particulate organic matter and plankton[END_REF]. Ultimately, all these processes, which can act concurrently in the same or opposite directions, makes it difficult to understand and predict the pattern of contaminant concentrations within the planktonic food web [START_REF] Nizzetto | Biological pump control of the fate and distribution of hydrophobic organic pollutants in water and plankton[END_REF][START_REF] Strady | 210 Po and 210 Pb trophic transfer within the phytoplankton-zooplanktonanchovy/sardine food web: a case study from the Gulf of Lion (NW Mediterranean Sea[END_REF][START_REF] Alekseenko | Modeling of PCB trophic transfer in the Gulf of Lions; 3D coupled model application[END_REF][START_REF] Castro-Jiménez | Persistent organic pollutants burden, trophic magnification and risk in a pelagic food web from coastal NW Mediterranean Sea[END_REF][START_REF] Li | Characteristics of plankton Hg bioaccumulations based on a global data set and the implications for aquatic systems with aggravating nutrient imbalance[END_REF].

Recently, some works have focused on the bioaccumulation of PAHs in the planktonic compartment (here and below the term bioaccumulation includes bioconcentration for simplicity, the latter being a direct form of bioaccumulation) [START_REF] Berrojalbiz | Accumulation and cycling of polycyclic aromatic hydrocarbons in zooplankton[END_REF][START_REF] Berrojalbiz | Biogeochemical and physical controls on concentrations of polycyclic aromatic hydrocarbons in water and plankton of the Mediterranean and Black Seas[END_REF]Tao et al., 2017a[START_REF] Tao | Factors affecting annual occurrence, bioaccumulation, and biomagnification of polycyclic aromatic hydrocarbons in plankton food webs of subtropical eutrophic lakes[END_REF]González-Gaya et al., 2019). These have provided a very interesting insight of the PAH bioaccumulation pattern within the plankton and showed a link between this bioaccumulation and the surrounding biogeochemical parameters. Nevertheless, in these studies, plankton has been generally taken as an entire compartment, without any separation into size fractions. Furthermore, the lipid content was not taken into account, even though, due to their hydrophobic nature, lipids represent a major matrix contributing to the bioaccumulation of the organic contaminants within marine and planktonic organisms [START_REF] Mackay | Bioaccumulation of Persistent Organic Chemicals: Mechanisms and Models[END_REF][START_REF] Arnot | A Review of Bioconcentration Factor (BCF) and Bioaccumulation Factor (BAF) Assessments for Organic Chemicals in Aquatic Organisms[END_REF][START_REF] Lee | Lipid storage in marine zooplankton[END_REF]Tesán-Onrubia et al., 2023).

In this context, the objectives of the present work were to 1) determine the contents in hydrocarbons (AHs and PAHs) in the dissolved fraction (< 0.7 µm) of surface water and in various particulate/planktonic size fractions (0.7-60, 60-200, 200-500 and 500-1000 µm) from sampling in the deep chlorophyll maximum (DCM), along a North-South transect in the Mediterranean Sea during the MERITE-HIPPOCAMPE campaign. For these different size fractions, suspended particulate matter (SPM), biomass, total chlorophyll a (TChla), particulate organic carbon (POC), C and N isotopic ratios (δ 13 C, δ 15 N) and lipid biomarkers were also determined. 2) Evaluate the spatial variations (between stations) and the distributions within the planktonic size fractions of these parameters (mainly AHs, PAHs, POC, lipids), as well as the correlations between them. 3) Investigate the concentration patterns and bioaccumulation of PAHs within plankton according to the size fraction, trophic level, organic carbon partitioning and biomass. 4) Assess, via the estimation of hydrocarbon vertical fluxes, the role of Mediterranean plankton as biological pump for hydrocarbons.

Material and Methods

Study area

The MERITE-HIPPOCAMPE cruise took place in spring 2019 (from April 13 to May 14), aboard the R/V Antea, along a North-South transect in the Mediterranean Sea, from the French coast (La Seyne-sur-Mer, Northwestern Mediterranean) to the Gulf of Gabès in Tunisia (Southeastern Mediterranean). Leg 1 (13-28 April) covered the southward transect, between La Seyne-sur-Mer and Tunis, with sampling of stations St2, St4, St3, St10 and St11.

Leg 2 (30 April-14 May) included the end of the southward transect (from Tunis to the Gulf of Gabès), and the return trip back northward to La Seyne-sur-Mer, with sampling of stations St15, St17, St19, St9 and St1 (Fig. 1a,b) [START_REF] Tedetti | HIPPOCAMPE cruise, RV Antea[END_REF][START_REF] Tedetti | Contamination of planktonic food webs in the Mediterranean Sea: Setting the frame for the MERITE-HIPPOCAMPE oceanographic cruise (spring 2019)[END_REF]. The ten stations were chosen according to criteria of physical, biological and biogeochemical conditions and level of anthropogenic pressures, as well as the location of bloom areas and ecoregions of the Mediterranean (see full description in [START_REF] Tedetti | Contamination of planktonic food webs in the Mediterranean Sea: Setting the frame for the MERITE-HIPPOCAMPE oceanographic cruise (spring 2019)[END_REF].

Sampling, filtration, sieving and conditioning

At each station, a conductivity-temperature-depth probe (CTD; Seabird SBE 911plus) equipped with a TChla fluorescence sensor (Chelsea ctg) was deployed over the depth range 0-250 m (or 0-bottom when depth was < 250 m) to identify the DCM. For each station, the sampling depth ranges in the DCM are reported Table S1.

In situ filtration. Two

McLane in situ pumps (WTS6-142LV, 4-8 L min -1 ) were used to collect high amounts of particles/plankton in the DCM. Each pump was mounted with a regular 142-mm filter holder for hosting a pre-combusted (450 °C, 6 h), pre-weighted 142mm diameter glass fiber (GF/F) filter (Whatman). The holder was covered with a sock-type pre-filter of 60-µm pore size, so as to collect on the filters the size fraction 0.7-60 µm. Both pumps were deployed at the same time by the ship's Moon-Pool on the hydrographic cable to reach the DCM. At the DCM, the pumping lasted 40-60 min, so that ~ 250 L of seawater was passed over each GF/F filter. Back on board, the filters were recovered and dried. One filter was used for the analysis of SPM and hydrocarbons, while the other filter was dedicated to SPM, TChla, POC, and δ 13 C/δ 15 N. Before drying, this second filter was also rinsed with ultrapure water to remove residues of the seawater salts. Finally, the GF/F filters were placed in glass boxes and stored at -18 °C on board and then in the laboratory before analysis. It should be noted that molecular lipid analyzes were not conducted on these filters/size fraction 0.7-60 µm.

Plankton sampling.

Multiple Plankton Sampler (Midi type, Hydro-Bios), here referred to as "MultiNet", was used to collect plankton in the DCM. The MultiNet was made of 5 individual opening and closing nets with 0.25-m 2 aperture, 60-µm mesh size, and cod ends of 60-µm mesh size, as well as two flowing meters to measure the volume of water filtered by the nets, a CTD sensor and a TChla fluorometer. The MultiNet was deployed horizontally in the DCM from the rear of the ship via the electromechanical cable. The Multinet position was maintained stable at the defined depth by means of a V-fin deflector, a helicoidal bucket connector gathering the cod ends, a controlled vessel speed, and real-time control of its position from the on board desk unit. Once the five nets were filled, the MultiNet was brought on board, the cod ends rinsed out with local seawater, and their content transferred into pre-cleaned 10-L HDPE bottles. The device was then returned to the water as many times as necessary until sufficient quantities of plankton were obtained.

In the on board clean lab container, plankton was then fractionated on a column of five stainless steel sieves (60, 200, 500, 1000 and 2000-µm mesh size) by wet-sieving with GF/F filtered seawater previously retrieved from ASTI pump/in-line filtration system and stored in a stainless steel jerry can (see section 2.2.3). The planktonic size fractions recovered on the stainless-steel sieves (i.e., 60-200, 200-500, 500-1000, 1000-2000 and > 2000 µm) were shared out for the different analyzes. For the analyzes of hydrocarbons, lipids, POC and δ 13 C/δ 15 N, each size fraction was transferred into two pre-combusted 150-mL amber glass flasks. It is worth noting that the quantities obtained for the size fractions 1000-2000 and > 2000 μm were not sufficient enough for PAH analyzes. Hence, only the fractions 60-200, 200-500 and 500-1000 µm are exploited in the present work. The glass flasks were stored at -18 °C on board and then in the laboratory before analysis.

Water sampling and in-line filtration.

Seawater was sampled at ~ 5-20-m depth, depending on the stations, with a pneumatically-operated Teflon ASTI pump (model PFD2) set up on board, connected to Teflon tubing, which was weighted down and immersed with the hydrology gallows. The pump was connected to a clean dry air supply. The seawater brought on board in the Teflon tubing was then filtered in-line onto a pre-combusted GF/F 142-mm filter using a Teflon filtration holder. The seawater filtered through GF/F was stored in two stainless steel jerry cans of 20 L each. The seawater of the first jerry can was used exclusively for sieving the plankton collected with the MultiNet. The seawater of the second jerry can was amended with 50 mL of dichloromethane (CH2Cl2) for subsequent analyzes of dissolved (< 0.7 µm) AHs and PAHs. This jerry can was stored at ~ 20 °C on board and then in the laboratory before analysis. Before filling the jerry cans, several liters of filtered seawater were thrown away.

Analysis

2.3.1. SPM, Biomass. SPM was measured on the size fraction 0.7-60 µm by weighing, with a precision balance, the tare, the entire (142-mm GF/F) filters before filtration, and the entire filters, wet and dry (freeze dried), after filtration, taking into account the volumes of water filtered with the McLane pumps (Tesán-Onrubia et al., 2023). Dry-weight biomasses of the size fractions 60-200, 200-500 and 500-1000 µm were determined after drying samples on pre-weighed GF/F filters (60 °C, 24 h) and then re-weighed with a precision balance, taking into consideration the volumes of water filtered by the MultiNet (Fierro-González et al., 2023). The contributions of zooplankton, phytoplankton and detritus components to the total weighted biomass were estimated according to Fierro-González et al. (2023). SPM is expressed in mg L -1 , and biomass concentrations in µg (or mg) dry weight (dw) L -1 . 13 C, δ 15 N. The determination of TChla concentration on the size fraction 0.7-60 µm was performed on a 22-mm diameter aliquot of the 142-mm GF/F filter by fluorescence method after methanol (MeOH) extraction according to [START_REF] Welschmeyer | Fluorometric analysis of chlorophyll a in the presence of chlorophyll b and pheopigments[END_REF] and [START_REF] Raimbault | Dosage rapide de la chlorophylle a et des phéopigments a par fluorimétrie après extraction au méthanol. Comparaison avec la méthode classique d'extraction à l'acétone[END_REF]. TChla concentration is expressed in µg L -1 . POC concentration and δ 13 C/δ 15 N were determined on the size fractions 0.7-60 to 500-1000 µm.

TChla, POC, δ

POC samples, i.e., 22-mm diameter aliquots of the freeze dried 142-mm GF/F filters (0.7-60 µm) and ~ 1 mg of the freeze dried plankton material (60-200 to 500-1000 µm), were analyzed using the persulfate wet-oxidation procedure according to [START_REF] Raimbault | Wet-oxidation and automated colorimetry for simultaneous determination of organic carbon, nitrogen and phosphorus dissolved in seawater[END_REF].

For the fraction 0.7-60 µm, POC concentration is expressed either in mg L -1 or in mg g -1 dw (when normalized by SPM). For the fractions 60-200 to 500-1000 µm, POC concentration is expressed in mg g -1 dw. Concerning δ 13 C/δ 15 N samples, the SPM collected on the GF/F filters were scraped off with a scalpel, whereas plankton fractions were ground to fine powder. Samples were then acidified (for δ 13 C) or not (for δ 15 N) and analyzed using an elemental analyzer (Flash EA 2000, Thermo Scientific ® ) coupled with a continuous flow isotope ratio mass spectrometer (Delta V Plus, Thermo Scientific ® ) (see details in Tesán-Onrubia et al., 2023). Isotope compositions are expressed in ‰ as deviations from the standard reference materials (N2 in air for δ 15 N and Vienna Pee Dee Belemnite for δ 13 C).

Lipid biomarkers.

Lipid biomarkers were determined on the size fractions 60-200 to 500-1000 µm. For each fraction, ~ 10 mg of freeze dried plankton were mixed with 15 mL MeOH and reduced with excess sodium borohydride (NaBH4). This process was conducted to reduce any hydroperoxides in samples [START_REF] Galeron | Seasonal survey of the composition and degradation state of particulate organic matter in the Rhône River using lipid tracers[END_REF], which are known to induce autoxidative damage of some lipids during the hot saponification step.

Saponification was carried out on each reduced sample. After NaBH4 reduction, water and potassium hydroxide (KOH) were added and the mixture directly saponified by refluxing.

After cooling, the contents of the flask were acidified with hydrochloric acid (HCl) to pH 1, and extracted 3 times with 30-mL CH2Cl2. The combined CH2Cl2 extracts were dried over anhydrous sodium sulfate (Na2SO4), filtered and concentrated to give the total lipid extract. These latter were derivatized by dissolution in 300 µL pyridine/bis(trimethylsilyl)trifluoroacetamide (BSTFA, Supelco) (2:1, v/v) and silylated.

After evaporation to dryness under a stream of N2, the derivatized residue was dissolved in hexane/BSTFA (2:1, v/v) to avoid desilylation and analyzed using gas chromatographyelectron ionization quadrupole time of flight mass spectrometry (GC-QTOF). Individual fatty acids, fatty alcohols and sterols were identified and quantified using an Agilent 7890B/7200 GC-QTOF System (Agilent Technologies, France) according to [START_REF] Rontani | Identification of diand triterpenoid lipid tracers confirms the significant role of autoxidation in the degradation of terrestrial vascular plant material in the Canadian Arctic[END_REF]. It should be noticed that the polyunsaturated fatty acid concentrations must be regarded as minimal values because they might have been affected by oxidative losses occurring during the 2-year storage of samples at -18 °C before analysis. Concentrations of individual and total lipid biomarkers (fatty acids, fatty alcohols and sterols) are expressed in mg g -1 dw.

2.3.4.

Hydrocarbons. Twenty-eight AHs, i.e., a series of n-alkanes from n-C15 to n-C40 and two isoprenoids, pristane (Pr) and phytane (Phy), were determined in this study.

Unresolved complex mixture (UCM) was not detected or negligible in our samples. For PAHs, we determined the concentrations of 17 parent PAHs, namely naphthalene (Nap), acenaphthylene (Acy), acenaphtene (Ace), fluorene (Flu), dibenzothiophene (DBT), phenanthrene (Phe), anthracene (Ant), fluoranthene (Flt), pyrene (Pyr), benz[a]anthracene

(BaA), chrysene (Chr), benzo[b]fluoranthene (BbF), benzo[k]fluoranthene (BkF), benzo[a]pyrene (BaP), dibenz[a,h]anthracene (DahA), benzo[g,h,i]perylene (BP),
indeno [1,2,3-cd]pyrene (IndP), as well as the concentrations of methylated derivatives (methyl-= C1-, dimethyl-= C2-, trimethyl-= C3-) of the five compounds Nap (C1, C2, C3), Flu (C1, C2), DBT (C1, C2), Phe/Ant (C1, C2) and Flt/Pyr (C1), which lead to a total of 27 PAHs (or groups of PAHs). AHs and PAHs were determined on the dissolved fraction (< 0.7 µm) of seawater, as well as on the size fractions 0.7-60, 60-200, 200-500 and 500-1000 µm.

For the fractions > 0.7 µm, samples (entire GF/F filters and plankton) were freeze dried for 24-96 h, then spiked with a multi-standard mixture containing surrogate standards for AHs (C16-d34, C24-d50 and C36-d74) and PAHs (Nap-d8, Flu-d10, Phe-d10, Flt-d10 and BaP-d12), and extracted with CH2Cl2 using accelerated solvent extraction (ASE 350, Dionex, Thermo Scientific) with the following procedure: 150 °C, 110 bars, 3 cycles of 10 min, 100% of rinsing and purging for 60 s [START_REF] Guigue | Remobilization of polycyclic aromatic hydrocarbons and organic matter in seawater during sediment resuspension experiments from a polluted coastal environment: insights from Toulon Bay (France)[END_REF]Fourati et al., 2018a). For the fraction < 0.7 µm, samples, i.e., 20 L of filtered seawater with 50 mL of CH2Cl2, were spiked with the multi-standard mixture and extracted by liquid-liquid extraction with CH2Cl2 (3 × 60 mL per liter) according to [START_REF] Guigue | Spatial and seasonal variabilities of dissolved hydrocarbons in surface waters from the Northwestern Mediterranean Sea: Results from one-year intensive sampling[END_REF] and Fourati et al. (2018b). All CH2Cl2 extracts were concentrated and solvent was exchanged by n-hexane. Extracts were reduced to ~ 1 mL, and cleaned with a silica-alumina column (10 mm i.d., made of glass) packed from bottom to top with 1-3 g deactivated alumina (by 3% ultra-pure water w/w), 1-3 g activated silica, and 1 g dehydrated Na2SO4, depending on the quantity of extracted matter. First, the sorbents were conditioned with 20 mL n-hexane, then the extract was deposited on the top of the column and both AHs and PAHs were eluted with 50-mL n-hexane:CH2Cl2 (9:1 v/v). This was followed by solvent reduction to 200-500 µL, and deuterated mixtures for AHs (C19-d40 and C30-d62) and PAHs (Ace-d10, Ant-d10, Pyr-d10, Chr-d12 and Per-d12) were spiked as internal standards before analysis.

AHs and PAHs were analyzed separately by gas chromatography (Trace ISQ, Thermo Electron) equipped with a mass spectrometry (MS) detector operating at an ionization energy of 70 eV, with hydrogen (1.2 mL min -1 ) as carry gas. The capillary column (HP-5MS, Agilent Technologies, USA) was 30 m in length with an internal diameter of 0.25 mm and a film thickness of 0.25 μm. The injector (used in splitless mode) and detector temperatures were 250 and 320 °C, respectively. The column temperature was initially held at 70 °C for 3 min, increased to 150 °C at 15 °C min -1 , then increased to 320 °C at 7 °C min -1 and finally held for 10 min. AHs and PAHs were identified and quantified in full scan and selected ion monitoring (SIM) modes simultaneously using two distinct methods [START_REF] Guigue | Occurrence and distribution of hydrocarbons in the surface microlayer and subsurface water from the urban coastal marine area off Marseilles, Northwestern Mediterranean Sea[END_REF][START_REF] Guigue | Spatial and seasonal variabilities of dissolved hydrocarbons in surface waters from the Northwestern Mediterranean Sea: Results from one-year intensive sampling[END_REF][START_REF] Guigue | Remobilization of polycyclic aromatic hydrocarbons and organic matter in seawater during sediment resuspension experiments from a polluted coastal environment: insights from Toulon Bay (France)[END_REF]. All solvents and chemicals used were of high purity grade. Ʃ AHs and Ʃ PAHs represented the sum of the targeted AH and PAH compounds, respectively. Concentrations of dissolved AHs and PAHs are expressed in ng L -1 . Concentrations of AHs and PAHs for the fractions > 0.7 µm are expressed in µg g -1 dw and ng g -1 dw, respectively.

The quality control procedures were strictly followed throughout the whole sampling and laboratory treatments. They included control/validation of GC-MS calibration and tuning, laboratory and field blanks, method limit of detection/quantification (LODs/LOQs), as well as surrogate recoveries. Field and laboratory blanks were prepared, processed and analyzed in the same manner as the real samples. LOQs ranged from 30 to 100 pg L -1 and from 10 to 50 pg L -1 in water for AHs and PAHs, respectively. They ranged from 0.3 to 1 ng g -1 and from 0.1 to 0.5 ng g -1 in plankton for AHs and PAHs, respectively. Blank values were below LODs or LOQs and surrogate recoveries were > 75 and > 70% for AHs and PAHs, respectively. All the concentrations reported here were not neither blank-nor recovery-corrected.

Data handling

To fully compare our PAH concentrations in the planktonic size fractions with those in literature, we estimated the concentrations of individual PAHs (and of POC) in the entire size fraction 60-1000 µm by summing the concentrations of individual PAHs (and of POC) in the fractions 60-200, 200-500 and 500-1000 µm, each of these concentrations being weighted (multiplied) by the contribution of the biomass of the given fraction to the total biomass of the fraction 60-1000 µm (fBiomass = biomass of the given fraction / biomass 60-1000 µm).

According to González-Gaya et al. (2019), we estimated the biological pump fluxes of PAHs, i.e., the vertical fluxes of PAHs exported in depth through the biological pump process (in ng m -2 day -1 ), for the Western basin of the Mediterranean Sea. For this, we normalized the PAH concentrations in the size fraction 60-1000 µm at each station (in ng g -1 dw) by the corresponding organic carbon (OC) content (in g C g -1 dw). Then, we averaged these OCnormalized PAH concentrations (in ng g -1 C dw), and multiplied this obtained mean concentration by the vertical settling flux of POC (in g C m -2 day -1 ) below 100-m depth for the Western Mediterranean Sea estimated by [START_REF] Guyennon | New insights into the organic carbon export in the Mediterranean Sea from 3-D modeling[END_REF], where POC is defined as being fueled by the natural mortality of the largest organisms (mesozooplankton, diatoms and ciliates) and by the excretion of fecal pellets and sloppy feeding by mesozooplankton. This calculation was performed for total PAHs (sum of our 27 parent and alkylated compounds; Ʃ27PAHs) but also for Phe alone, which was the dominant PAH in the planktonic fractions.

The partition coefficient between particulate matter and water (KD in L kg -1 ) was calculated for seven individual PAHs (the ones present both in water and particulate/planktonic phases, namely Nap, Flu, Phe, Flt, Pyr, BaA and Chr) in each size fraction (0.7-60, 60-200, 200-500, 500-1000 and 60-1000 µm) as (CP / CW) × 1000 where CP is the concentration of the given PAH in the given size fraction in ng g -1 dw, and CW is the concentration of the PAH in the dissolved phase (size fraction < 0.7 µm) in ng L -1 . The partition coefficient between organic carbon and water (KOC in L kg -1 ) was then determined for the seven individual PAHs in each size fraction as KD / fOC where fOC is the contribution of the OC mass (in g) to the total matter mass (in g) for a given size fraction (fOC = POC in mg g - 1 dw / 1000).

According to the previous works by [START_REF] Berrojalbiz | Biogeochemical and physical controls on concentrations of polycyclic aromatic hydrocarbons in water and plankton of the Mediterranean and Black Seas[END_REF] and González-Gaya et al.

(2019), we assume that the relationships between SPM or biomass concentration in a given size fraction and the concentration of individual PAHs in this size fraction can be approximated by a power function of the form: CP = aSPM -m or aBiomass -m where a is the constant and m the slope of the regression. In the present study, the Log KOC and slope (m) values were exploited to highlight the influence of plankton on the PAH bioaccumulation.

Statistics

Statistical analyzes were performed using XLSTAT software (version 2021.1.1).

Student's parametric test (t-test) was used to determine significant differences between the means of two groups, i.e., the mean concentrations in two size fractions over the 10 stations.

Results and Discussion

TChla, POC and SPM/biomass

In the size fraction 0.7-60 µm sampled from the DCM, TChla, POC and SPM concentrations followed substantially the same spatial distribution (Fig. 2a; Table S1), and were thus significantly positively correlated with each other (r = 0.70-0.93, n = 10, p < 0.05).

The lowest concentrations were found at two southern coastal stations, St17 and St15. Low values were also recorded at St3 and St11. The highest concentrations were observed at the offshore station St9. High values were also found at two coastal stations, St19 and St1 (Fig. 2a; Table S1).

These results are in accordance with the observations by [START_REF] Tedetti | Contamination of planktonic food webs in the Mediterranean Sea: Setting the frame for the MERITE-HIPPOCAMPE oceanographic cruise (spring 2019)[END_REF] who highlighted that St9 displayed the highest contents in silicates [Si(OH)4] and nitrates (NO3 -), and the highest concentrations in POC and TChla in the size fraction > 0.7 µm in the DCM compared to the other stations. The high levels of TChla in St9 during the sampling period were also confirmed from satellite data [START_REF] Tedetti | Contamination of planktonic food webs in the Mediterranean Sea: Setting the frame for the MERITE-HIPPOCAMPE oceanographic cruise (spring 2019)[END_REF]. Indeed, St9, situated at the boundary of the Ligurian consensus region [START_REF] Ayata | Regionalisation of the Mediterranean basin, a MERMEX synthesis[END_REF] in the deep convection area, benefited from a relatively intense phytoplankton bloom in late March 2019 (still visible in May), consecutive to a pronounced winter convection process [START_REF] Margirier | Abrupt warming and salinification of intermediate waters interplays with decline of deep convection in the Northwestern Mediterranean Sea[END_REF][START_REF] Bosse | LION observatory data[END_REF]. In line with our results, [START_REF] Tedetti | Contamination of planktonic food webs in the Mediterranean Sea: Setting the frame for the MERITE-HIPPOCAMPE oceanographic cruise (spring 2019)[END_REF] also reported high concentrations in Si(OH)4 and phosphates (PO4 3-), as well as TChla and POC in the fraction > 0.7 µm at St19. This enrichment could be related to nutrient inputs and the subsequent stimulation of phytoplankton activity from Saharan dust deposition event that occurred in the south of the Gulf of Gabès during sampling. Such Saharan dust deposition events have been already reported and recognized to provide nutrients in this area [START_REF] Béjaoui | Synthesis review of the Gulf of Gabes (eastern Mediterranean Sea, Tunisia): morphological, climatic, physical oceanographic, biogeochemical and fisheries features[END_REF]. Apart from St9 and St19, the fraction 0.7-60 µm exhibited higher TChla, POC and SPM contents for the northern stations (St1-St4) than for the offshore and southern stations (St10-St17) (Fig. 2a), which is consistent with their positioning in terms of bloom-condition areas and consensus regions defined by D' Ortenzio and d'Alcalà (2009) and [START_REF] Ayata | Regionalisation of the Mediterranean basin, a MERMEX synthesis[END_REF].

The highest biomasses of the size fractions 60-200 to 500-1000 µm recovered from the DCM sampling were determined at the southern (St17, St19) andnorthern (St4, St1) coastal stations. The lowest ones were recorded at St3 and St10 (Fig. 2b; Table S1). The fractions 60-200 and 200-500 µm contributed the most to the total biomass (37 and 41% on average, respectively), while the contribution of the fraction 500-1000 µm was smaller (22% on average) (Fig. 2b; Table S1).

The spatial distribution pattern of the biomasses of the size fractions 60-200 to 500-1000 µm (Fig. 2b) did not really correspond to that of the SPM of the fraction 0.7-60 µm (Fig. 2a). According to Fierro-González et al. (2023) and Tesán-Onrubia et al. (2023), the biomass of the fractions 60-200 and 200-500 µm was dominated by detritus and phytoplankton, which represented on average 68.8% (fraction 60-200 µm) and 59.2% (fraction 200-500 µm) of the total biomass (against 31.2 and 40.8% for zooplankton, respectively). An inverse pattern was found for the fraction 500-1000 µm whose biomass was dominated by zooplankton (69.8% on average). Zooplankton was mainly composed of copepods, which accounted for 48.9, 91.9 and 69.7% of total zooplankton in the fractions 60-200, 200-500 and500-1000 µm, respectively (Fierro-González et al., 2023;Tesán-Onrubia et al., 2023). Compared to the other stations, the fraction 60-200 µm at St4 was enriched in phytoplankton, while the fractions 60-200 and 200-500 µm at St17 were enriched in detritus.

The POC concentrations in the fractions 60-200 to 500-1000 µm were the highest in the three offshore stations (St9-St11) and at the coastal station St1. They were the lowest at the coastal stations St17, St4 and St3 (Fig. 2c; Table S1). The low POC levels at St17 could be related to the high proportion of detritus within the biomass at this site. The POC concentrations were generally the highest for the fraction 200-500 µm, and the lowest for the 60-200 µm. The POC concentrations of the three size fractions were quite well correlated with each other (r = 0.87-0.91, n = 9-10, p < 0.05). However, the latter were not at all correlated with the those of the 0.7-60-µm fraction, as seen from Fig. 2a,c.

Lipids

Concentrations of total lipid biomarkers in the planktonic fractions 60-200 to 500-1000 µm from the DCM are shown in Fig. 3. Concentrations of individual compounds are also presented in Table S2. Concentration of total (Ʃ39) lipids (= concentrations of Ʃ25fatty acids + Ʃ8fatty alcohols + Ʃ6sterols) ranged from 3.5 mg g -1 dw (equivalent to 0.35%) at St2, fraction 500-1000 µm to 35.6 mg g -1 dw (equivalent to 3.6%) at St9, fraction 200-500 µm (Fig. 3a).

The highest Ʃ39lipid concentrations were recorded in the three offshore stations St9-St11, as well as in the southern coastal stations St15 and St19, while the lowest ones were found at St17 and St3 (Fig. 3a). Ʃ39lipid concentrations in the three fractions were significantly positively correlated with each other (r = 0.79-0.86, n = 9-10, p < 0.05) and no significant difference was detected between the mean concentrations of the three fractions over the 10 stations (t-test, p > 0.05). The distribution of Ʃ39lipid concentrations throughout stations and fractions was very close to that of POC (Fig. 2c). Logically, a significant positive relationship appeared between Ʃ39lipid and POC concentrations when considering the fractions 60-200 to 500-1000 µm (r = 0.69, n = 29, p < 0.05) (Fig. S1a). This underlines the strong link between the lipid and POC contents in the planktonic compartment. Interestingly, our Ʃ39lipid concentrations (determined by GC-MS) were compared to those obtained by colorimetric method by Tesán-Onrubia et al. (2023) on the same samples. Both were rather well correlated (r = 0.75, n = 29, p < 0.05) albeit the colorimetric method gave slightly higher concentrations (Fig. S1b).

The Ʃ39lipid concentrations we measured here in the three fractions (0.35-3.6%) were quite low compared to works by [START_REF] Båmstedt | Chemical composition and energy content[END_REF] who found up to 61% lipid in some copepod species from temperate areas. However, they were of the same order of magnitude as a previous study conducted in the Mediterranean waters (3.0 ± 2.8%; [START_REF] Tiano | PCB concentrations in plankton size classes, a temporal study in Marseille Bay, Western Mediterranean Sea[END_REF].

According to [START_REF] Lee | Lipid storage in marine zooplankton[END_REF], the plankton that has a year-round low-level supply of food available do not accumulate lipid reserves. This is in agreement with the oligotrophic character of the Mediterranean waters along with poor seasonality of food supply for plankton. In addition, even though zooplankton is known to have a higher content in lipids than phytoplankton, the occurrence of phytoplankton and detritus in addition to zooplankton species (mainly copepods) in each of our size fractions tended to lower their lipid content (Tesán-Onrubia et al., 2023), as for St17 where the high proportion of detritus was accompanied by a very low lipid content.

Concentrations of Ʃ25fatty acids, Ʃ8fatty alcohols and Ʃ6sterols represented 80 ± 7.9%, 15 ± 8.6% and 5.0 ± 2.5% of the Ʃ39lipid concentration, respectively (Fig. 3b-d). The distribution of Ʃ25fatty acid concentrations throughout stations and fractions (Fig. 3b) was very similar to that of Ʃ39lipid concentrations. While the distribution of Ʃ6sterol concentrations (Fig. 3d) followed also quite well those of Ʃ39lipids and Ʃ25fatty acids, the distribution of Ʃ8fatty alcohol concentrations (Fig. 3c) was rather different from the three others. Overall, as for Ʃ39lipids and Ʃ25fatty acids, the highest Ʃ8fatty alcohol and Ʃ6sterol concentrations were measured in St9-St11, followed by St15, St19 and St1 (Fig. 3c,d).

The prevalence of 16:0, 14:0, 18:1w9, 18:0 and 16:1w7 compounds for fatty acids, and of 16:0 and 14:0 compounds for fatty alcohols (Table S2) reflected the overall dominance of the carnivorous/omnivorous zooplankton [START_REF] Lee | Lipid storage in marine zooplankton[END_REF]. Nevertheless, some indicators allowed us to point out substantial differences between stations. Indeed, some phytoplankton (organisms or detrital matter) biomarkers, such as 16:1w7/18:1w9 and 16:1w7/16:0 fatty acid ratios and the relative abundance of phytol among the fatty alcohols, were abundant at St4 and St17 (Fig. S2a-c). This could be related to the much higher contributions of phytoplankton and detritus found within the total biomass for the fractions 60-200 to 500-1000 µm at these two stations (Fierro-González et al., 2023;Tesán-Onrubia et al., 2023). These phytoplankton biomarkers revealed more pronounced signatures of diatoms and/or organisms feeding on phytoplankton residues [START_REF] Falk-Petersen | Ecological investigation on the zooplankton community in Balsfjorden, northern Norway: Seasonal changes in the lipid class composition of Meganyctiphanes norvegia (M. Sars), Thysanoessa raschii (M Sars), T. inermis (Krøyer)[END_REF][START_REF] Falk-Petersen | Ecological investigations on the zooplankton community of Balsfjorden, northern Norway: lipids in the euphausiids Thysanoessa raschii and T. inermis during the spring[END_REF][START_REF] Sargent | Ecological investigations on the zooplankton community in Balsfjorden, northern Norway: Lipids and fatty acids in Meganyctiphanes norvegia, Thysanoessa raschi, and T. inermis during midwinter[END_REF][START_REF] Tolosa | Distribution of pigments and fatty acid biomarkers in particulate matter from the frontal structure of the Alboran Sea (SW Mediterranean Sea)[END_REF]. Zooplankton biomarkers were also used: the relative abundance of 22:1, 20:5 and 22:6 fatty acids. The latter were higher in offshore stations, especially at St11 in the fraction 500-1000 µm, and St15 (Fig. S3a-c). They could highlight together the presence of herbivorous zooplankton feeding on diatoms [START_REF] Kates | Lipid components of diatoms[END_REF][START_REF] Harrington | The polyunsaturated fatty acids of dinoflagellates[END_REF][START_REF] Graeve | Umsatz und Verteilung von Lipiden in arktischen marinen Organismen unter besonderer Berücksichtigung unterer trophischer Stufen[END_REF][START_REF] Lee | Lipid storage in marine zooplankton[END_REF]. Indeed, according to Fierro-González et al. ( 2023), there was a high % (in biomass) of large crustaceans which could be euphausiids, actually potential consumers of diatoms, in the fractions 500-100 and 1000-2000 µm at St11 and St15.

Moreover, according to the taxonomy results (M. Pagano personal communication), the % (in number) of herbivorous filter feeders (large calanides of the Calanus type) over the entire water column was the highest at these two stations, especially St11.

Among sterols, cholesterol (Cholest-5-en-3ß-ol) was the dominant compound (63.5 ± 6.5%) followed by Cholesta-5,22E-dien-3ß-ol (14.4 ± 6.5%) (Table S2). These % are in agreement with previous values found in crustaceans from the Northern Adriatic Sea [START_REF] Serrazanetti | ALIPHATIC HYDROCARBON AND STEROL CONTENT OF ZOOPLANKTON OF THE EMILIA-ROMAGNA COAST (NORTHERN ADRIATIC)[END_REF]. The concentrations of cholesterol were low, in accordance with the overall low lipid content. This may be due not only to the composition of the zooplankton diet, but also to the absence in these organisms of biochemical mechanisms capable of converting into cholesterol some of the most diffused sterols in the marine environment [START_REF] Serrazanetti | ALIPHATIC HYDROCARBON AND STEROL CONTENT OF ZOOPLANKTON OF THE EMILIA-ROMAGNA COAST (NORTHERN ADRIATIC)[END_REF].

Hydrocarbons

AH distribution

In seawater, dissolved Ʃ28AH concentrations varied from 18 ng L -1 (St10) to 489 ng L -1 (St1) (Fig. S4a; Table S3). The highest values were recorded at St1, St9, St11, and at the Tunisian coasts (St15-St19), and were associated with monomodal molecular profiles in the range n-C22-n-C36 without predominance of odd over even carbon numbered n-alkanes, which reflected anthropogenic inputs from uncombusted oil-derived products (Fig. S4b) [START_REF] Bouloubassi | Investigation of anthropogenic and natural organic inputs in estuarine sediments using hydrocarbon markers (NAH, LAB, PAH)[END_REF][START_REF] Wang | Differentiation of the source of spilled oil and monitoring of the oil weathering process using gas chromatography-mass spectrometry[END_REF]. The lower concentrations recorded at St2-St4 and St10 were associated with bimodal molecular profiles exhibiting, in the range n-C24n-C36, anthropogenic input residues, and in the range n-C15-n-C24, the peculiar abundance of n-C16 and n-C18 linked to microorganism contribution (bacteria, fungi, yeast) and their action on algal detritus (Fig. S4c) [START_REF] Elias | Even n-alkanes on the Amazon shelf and a northeast Pacific hydrothermal system[END_REF]. These molecular profiles have been already observed in the dissolved phase of variably anthropogenic-stressed marine coastal areas [START_REF] Guigue | Spatial and seasonal variabilities of dissolved hydrocarbons in surface waters from the Northwestern Mediterranean Sea: Results from one-year intensive sampling[END_REF].

In the fraction 0.7-60 µm, Ʃ28AH concentrations varied from 3.9 µg g -1 dw (St9) to 104 µg g -1 dw (St11) (Fig. 4a; Table S4). The molecular profiles were dominated by n-C15 and n-C17 (Fig. 4b), indicative of phytoplanktonic contribution linked to high primary production [START_REF] Blumer | Hydrocarbons of marine phytoplankton[END_REF][START_REF] Goutx | Relationship between dissolved and particulate fatty acids and hydrocarbons, chlorophyll-a and zooplankton biomass in Villefranche Bay, Mediterranean Sea[END_REF]. Despite these predominant biological fingerprints, no correlation was found between n-C15 or n-C17 and TChla concentrations (r = -0.12 to 0.23, n = 19, p > 0.05). n-pentadecane (n-C15) has been shown to be produced by cyanobacteria, mainly in the lower euphotic zone, and rapidly consumed by heterotrophic prokaryotes in the ocean (Love et al., 2021). This could explain the absence of correlation between n-C15 and TChla concentrations.

In the fractions 60-200 to 500-1000 µm, Ʃ28AH concentrations ranged from 3.4 µg g -1 dw (St17, 60-200 µm) to 55 µg g -1 dw (St11, 500-1000 µm) (Fig. 4c; Table S4). While Ʃ28AH concentrations in these three fractions were significantly positively correlated with each other (r = 0.62-0.88, n = 9-10, p < 0.05), they were all weakly correlated with that of the fraction 0.7-60 µm (r = 0.24-0.64, n = 9-10, p < 0.05 or > 0.05). No significant difference was detected between the mean concentrations of the four fractions over the 10 stations (t-test, p > 0.05). Interestingly, Ʃ28AH concentration was significantly positively correlated to Ʃ39lipid and POC concentrations only in the fraction 60-200 µm (r = 0.62-0.65, n = 10, p < 0.05).

Pristane was one of the main compounds within the low molecular weight range (< n-C22) (Fig. 4d; Table S4), which is in line with the presence of zooplankton, especially the dominance of copepods [START_REF] Blumer | Pristane in Zooplankton[END_REF]. Indeed, the high values of pristane in the fractions 200-500 and 500-1000 µm at St11 (Table S4) coincided with very high proportions of zooplankton (Fierro-González et al., 2023). Also, the abundance of n-C15 and n-C17 revealed the presence of phytoplanktonic residues (Fig. 4d), although no significant correlation was observed with these two latter biomarkers and the 16:1w7 diatom biomarker (r = -0.28 to 0.16, n = 29, p > 0.05) [START_REF] Blumer | Hydrocarbons of marine phytoplankton[END_REF]. The high molecular weight compounds (> n-C22) displayed the predominance of odd over even carbon numbered compounds (n-C27, n-C29, n-C31, n-C33) (Fig. 4d; Table S4), illustrating the presence of terrigenous higher plant debris in the samples [START_REF] Douglas | Distribution of Alkanes[END_REF]. It is unlikely that these debris were ingested by the organisms. It seems more likely that they were part of some allochthonous detritus collected along with zooplankton as observed by imagery analyzes (Fierro-González et al., 2023). Moreover, a background series of n-alkanes with no predominance of odd over even compounds was visible and may originate from anthropogenic inputs with minor occurrence. These results (AH concentrations and their molecular profiles in plankton) are in good agreement with previous studies from neighboring areas [START_REF] Serrazanetti | ALIPHATIC HYDROCARBON AND STEROL CONTENT OF ZOOPLANKTON OF THE EMILIA-ROMAGNA COAST (NORTHERN ADRIATIC)[END_REF][START_REF] Serrazanetti | ALIPHATIC HYDROCARBON AND STEROL CONTENT OF ZOOPLANKTON OF THE EMILIA-ROMAGNA COAST (NORTHERN ADRIATIC)[END_REF][START_REF] Salas | Fingerprinting petroleum hydrocarbons in plankton and surface sediments during the spring and early summer blooms in the Galician coast (NW Spain) after the Prestige oil spill[END_REF]. This class of compounds is very useful to better assess the sources of hydrocarbons in planktonic organisms. Nevertheless, the dominance of biogenic signatures observed here makes AH biomarkers not very explanatory in the study of the bioaccumulation of hydrocarbons.

PAH distribution

In seawater, the dissolved Ʃ14PAH concentrations ranged from 0.9 ng L -1 (St11) to 16 ng L -1 (St4) (Fig. S5a; Table S5). The concentrations were quite low (< 5 ng L -1 ) and the methylated derivatives were not really identifiable, except at St4 (Fig. S5b,c). At this station, the concentration reached 16 ng L -1 due to significant inputs of C1-, C2-and C3-Nap (Fig. S5c). The 2-3 ring PAHs were the major compounds representing 71 ± 16% of the total PAHs, which is in accordance with their lower hydrophobicity (Fig. S5b,c; Table S5). The quite low levels of concentrations along with the highly altered methylated derivatives at almost all sites reflected remote or aged (weathered/photo-and bio-degraded) inputs, except at St4, where local and recent moderate petrogenic inputs were suspected [START_REF] Wang | Differentiation of the source of spilled oil and monitoring of the oil weathering process using gas chromatography-mass spectrometry[END_REF][START_REF] Chifflet | Distribution and accumulation of metals and metalloids in planktonic food webs of the Mediterranean Sea (MERITE-HIPPOCAMPE campaign)[END_REF].

In the fraction 0.7-60 µm, the Ʃ27PAH concentrations ranged from 53 ng g -1 dw (St9) to ~ 220 ng g -1 dw (St3 and St11) (Fig. 5a; Table S6). The PAH profiles in the fraction 0.7-60 µm (Fig. 5b) were different from those found in water (Fig. S5b,c), the 2-3 ring PAHs being less abundant (49 ± 9% of total PAHs) and the 4-6 ring PAHs more abundant (Fig. 5b), which is consistent with previous studies on particles in the Mediterranean Sea [START_REF] Dachs | Spatial, Vertical Distribution and Budget of Polycyclic Aromatic Hydrocarbons in the Western Mediterranean Seawater[END_REF]Marti et al., 2001). However, as for PAHs in water (Fig. S5b,c), the methylated derivatives were not well visible in this fraction and suspected to be highly degraded. Hence, the PAH profiles in the fraction 0.7-60 µm might be explained by a high microbial degradation which rather affected LMW PAHs, especially methylated derivatives [START_REF] Lipiatou | Sediment trap fluxes of polycyclic aromatic hydrocarbons in the Mediterranean Sea[END_REF]Dachs et al., 1997). Another explanation could be inputs of atmospheric aerosols or from sediments [START_REF] Chifflet | Distribution and accumulation of metals and metalloids in planktonic food webs of the Mediterranean Sea (MERITE-HIPPOCAMPE campaign)[END_REF], which are important sources of pyrogenic PAHs (HMW PAHs with a low proportion of methylated derivatives) [START_REF] Lipiatou | Mass budget and dynamics of polycyclic aromatic hydrocarbons in the Mediterranean Sea[END_REF], but the lack of 5-6 ring compounds suggests that these inputs were minor.

In the fractions 60-200 to 500-1000 µm, the Ʃ27PAH concentrations ranged from 35 ng g -1 dw (St19, 200-500 µm) to 255 ng g -1 dw (St1, 60-200 µm) (Fig. 5c; Table S6). The lowest Ʃ27PAH concentrations were found at St9, St17 and St19 (Fig. 5c). Two of them, St9 and St19, showed the highest TChla concentrations. These two stations displayed a particular biogeochemical context with regard to the other stations, as explained in section 3.1. Ʃ27PAH concentrations in these three fractions were rather well positively correlated with each other (r = 0.50-0.73, n = 9-10, p < 0.05 or > 0.05), but not significantly correlated with that in the fraction 0.7-60 µm (r = 0.14-0.55, n = 9-10, p > 0.05). The mean Ʃ27PAH concentration of the fraction 60-200 µm was significantly higher than those of the fractions 200-500 and 500-1000 µm (Fig. 5c) (t-test, p < 0.05). Ʃ27PAH concentration was significantly positively correlated to Ʃ28AH concentration only in the fraction 0.7-60 µm (r = 0.84, n = 10, p < 0.05), while Ʃ27PAH concentrations were not correlated with Ʃ39lipid and POC concentrations whatever the size fraction. The PAH molecular profiles in the three fractions, i.e., dominance (80 ± 12%) of the 2-3 ring compounds (parents and methylated), especially Phe, and very low abundance of the 4-6 ring compounds (Fig. 5d), were in agreement with those reported by [START_REF] Salas | Fingerprinting petroleum hydrocarbons in plankton and surface sediments during the spring and early summer blooms in the Galician coast (NW Spain) after the Prestige oil spill[END_REF] and [START_REF] Berrojalbiz | Biogeochemical and physical controls on concentrations of polycyclic aromatic hydrocarbons in water and plankton of the Mediterranean and Black Seas[END_REF].

Comparison of plankton PAH concentrations and biological pump fluxes of PAHs

It is important to note that comparisons of our concentrations/fluxes of PAHs and individual Phe (the dominant PAH in our study and also in most of previously works) with those reported in the literature should be taken with caution since the methodologies for sampling/separations of planktonic fractions, the planktonic size fractions, analyzes of PAHs and the number of PAHs analyzed are not the same. Despite these limitations, these comparisons still allow us to situate our data in relation to those obtained formerly.

The Ʃ27PAH and Phe concentrations in plankton we determined here in the Western Mediterranean Sea were globally lower than those measured in the Western and Eastern Mediterranean Sea [START_REF] Berrojalbiz | Biogeochemical and physical controls on concentrations of polycyclic aromatic hydrocarbons in water and plankton of the Mediterranean and Black Seas[END_REF], and in the Atlantic, Pacific and Indian Oceans (González-Gaya et al., 2019), when taking into account maximal and mean values (see data in Table 1). [START_REF] Salas | Fingerprinting petroleum hydrocarbons in plankton and surface sediments during the spring and early summer blooms in the Galician coast (NW Spain) after the Prestige oil spill[END_REF] also found higher concentrations in the Galician coast (NW Spain) after the Prestige oil spill (353-2035 ng g -1 dw; not reported in Table 1). However, when considering minimal and median values, our Ʃ27PAH concentrations were very close to those of other oceanic areas, and our Phe concentrations were even slightly higher (Table 1).

From the vertical settling flux of POC (in Table 1) and OC-normalized PAH concentrations (not in Table 1), we estimated the biological pump fluxes of Ʃ27PAHs and Phe below 100-m depth in the Western Mediterranean Sea at 15 ± 10 and 4 ± 2 ng m -2 day -1 , respectively (Table 1). González-Gaya et al. (2019) found mean biological pump fluxes of Ʃ64PAHs and Phe below the surface mixed layer depth of 172 and 23 ng m -2 day -1 in the North Atlantic, 91 and 6 ng m -2 day -1 in the South Atlantic, 55 and 7 ng m -2 day -1 in the North Pacific, 14 and 1 ng m -2 day -1 in the South Pacific, and 22 and 2 ng m -2 day -1 in the Indian Ocean (Table 1). Therefore, our biological pump fluxes were lower than those in the Atlantic and North Pacific but comparable to those in the South Pacific and Indian Ocean. From our results, the annual biological pump flux of Ʃ27PAHs for the whole Western Mediterranean Sea would be of 5274 ± 3467 kg yr -1 .

Concentration patterns and bioaccumulation of PAHs within plankton

It is important to note that only seven parent PAHs (Nap, Flu, Phe, Flt, Pyr, BaA and Chr) were found both in water and all particulate/planktonic size fractions (Table S7). They were thus selected to investigate the concentration patterns and bioaccumulation of PAHs within plankton (see below).

Concentration pattern with the size fraction and trophic level

The concentrations of Ʃ7PAHs and Ʃ6PAHs (without Phe) significantly decreased from the fractions 0.7-60 or 60-200 µm to the fractions 200-500 or 500-1000 µm (t-test, p < 0.05) (Fig. 6a,b), highlighting the bioreduction process of PAHs within the planktonic food web, i.e., decreasing concentration with increasing organism size/trophic level. The fact that the highest concentrations were found in the smallest fraction (0.7-60 µm) is in agreement with recent observations (Berroralbiz et al., 2011;[START_REF] Tao | Factors affecting annual occurrence, bioaccumulation, and biomagnification of polycyclic aromatic hydrocarbons in plankton food webs of subtropical eutrophic lakes[END_REF]González-Gaya et al., 2019) and related to the strong capacity of small cells to bioaccumulate contaminants due to their high surface/volume ratio [START_REF] Fan | Phenanthrene Accumulation Kinetics in Marine Diatoms[END_REF][START_REF] Heimbürger | Methylmercury distributions in relation to the presence of nano and picophytoplankton in an oceanic water column (Ligurian Sea, North-western Mediterranean)[END_REF][START_REF] Chouvelon | Patterns of trace metal bioaccumulation and trophic transfer in a phytoplankton-zooplankton-small pelagic fish marine food web[END_REF]. Fig. 7 shows the concentrations in relation with the trophic levels, given by δ 13 C and δ 15 N. It appears that the fraction 0.7-60 µm was trophically decoupled from the three other ones. In other words, the bioaccumulation of PAHs in the upper 60-200-µm fraction would not take place by trophic transfer from the 0.7-60-µm fraction but rather by water.

Then, considering the trophic proximity between the fractions 60-200, 200-500 and 500-1000 µm, it is possible that besides transfer from water, the PAHs were also transferred by ingestion/diet between these three fractions (Fig. 7a,b). The overall bioreduction observed along the planktonic food web would be due to the fact that when going up in the trophic levels, even if there was trophic transfer of PAHs, the processes of absorption directly by the water would have been less and less effective and the removal processes of PAHs (such as depuration or metabolization) likely more effective, which ultimately would have led to this decrease of PAH concentrations within the planktonic food web.

Phe presented a different pattern from the other compounds, with the highest concentrations mainly found in the fraction 60-200 µm (Fig. 6c; Fig. 7c). Phe was the most abundant compound representing for all sites 14, 51, 48 and 41% of Ʃ7PAHs in the fractions 0.7-60, 60-200, 200-500 and 500-1000 µm, respectively. [START_REF] Berrojalbiz | Biogeochemical and physical controls on concentrations of polycyclic aromatic hydrocarbons in water and plankton of the Mediterranean and Black Seas[END_REF] also reported Phe (and alkylated homologues) as dominant compound in particles and plankton along a West-East transect in the Mediterranean Sea. In the present work, the peculiar Phe bioaccumulation in the fraction 60-200 µm, systematically observed at all stations (see Table S6), is intriguing. It could originate from a biogenic production within the collected plankton, as already suggested by [START_REF] Nizzetto | PAHs in air and seawater along north-south Atlantic transect: trends, processes and possible sources[END_REF]. However, since there were no correlations between Phe concentrations, neither with POC, TChla, nor lipids (in both fractions 0.7-60 and 60-200 µm) (r = -0.33 to -0.04, n = 20, p > 0.05), this suggests that even if this process had occurred, it would have been minor and hidden within the complex dynamics of Phe in plankton. Another explanation for the Phe bioaccumulation in the 60-200-µm fraction could be that this compound was less subjected to depuration/metabolization processes than the other compounds and than in the other fractions.

Water-OC partitioning and influence of biomass

For each fraction at each station, the water-particulate matter coefficients (KD in L kg -1 ), then the water-organic carbon partition coefficients (KOC in L kg -1 ) were calculated for the 7 targeted PAHs (Tables S7-S9). It should be noticed that KD and KOC values were determined using dissolved PAH concentrations measured in surface waters (at ~ 5-20-m depth depending on stations) and particulate/plankton PAH concentrations measured in the DCM (at ~ 20-60 depth depending on the stations). Despite these depth discrepancies, and the possible differences in the dissolved PAH concentrations between surface waters and the DCM, the use of KOC as determined here remains very likely more suitable and reflects the PAH biogeochemistry much better than the use of KOW that are theoretical values provided under partition equilibrium conditions (these equilibrium conditions certainly did not prevail in the water at the time of sampling). Consistent with the concentration patterns, Log KOC values clearly decreased with the size fractions, which confirms the higher PAH bioaccumulation in the smaller size fractions (Fig. 8a). Moreover, for each individual compound and each station, the PAH concentrations in size fractions (ng g -1 dw) were plotted against the plankton biomass concentrations (mg dw L -1 ). For most of PAHs and size fractions (except 500-1000 µm), the concentrations decreased with biomass, following a power function equation [PAH] = a[Biomass] -m (Fig. 8b; Table S10), reinforcing the results presented above (Fig. 6,7). This highlights the biodilution process, which reflects the decrease in PAH concentrations with plankton biomass [START_REF] Berrojalbiz | Biogeochemical and physical controls on concentrations of polycyclic aromatic hydrocarbons in water and plankton of the Mediterranean and Black Seas[END_REF][START_REF] Nizzetto | Biological pump control of the fate and distribution of hydrophobic organic pollutants in water and plankton[END_REF][START_REF] Everaert | Multidecadal field data support intimate links between phytoplankton dynamics and PCB concentrations in marine sediments and biota[END_REF][START_REF] Morales | Oceanic sink and biogeochemical controls on the accumulation of polychlorinated dibenzo-pdioxins, dibenzofurans, and biphenyls in plankton[END_REF][START_REF] Ding | The biological pump effects of phytoplankton on the occurrence and benthic bioaccumulation of hydrophobic organic contaminants (HOCs) in a hypereutrophic lake[END_REF].

The -m slope values originating from the power function equations were further examined because they are indicative of the influence level of the SPM or biomass load on the PAH concentration [START_REF] Berrojalbiz | Biogeochemical and physical controls on concentrations of polycyclic aromatic hydrocarbons in water and plankton of the Mediterranean and Black Seas[END_REF]. As for Log KOC, the -m values noticeably decreased with the size fraction (Fig. 8b), which illustrates once again the more important role of the smaller fractions in the bioaccumulation of PAH, as well as the biodilution process. These m values were then plotted against Log KOC. Finally, a positive significant relationship was found between "-m" and the Log KOC for the 7 PAHs and the different size fractions (0.7-60 to 500-1000 µm, as well as 60-1000 µm) (Fig. S6; Table S11). Such a linear relationship highlighted the strong link between the PAH bioaccumulation and the impact of the planktonic biomass on the PAH concentrations in plankton, implying also the biological pump process for the PAHs. González-Gaya et al. (2019) observed the same type of relationship between -m slope and Log KOW. [START_REF] Tao | Factors affecting annual occurrence, bioaccumulation, and biomagnification of polycyclic aromatic hydrocarbons in plankton food webs of subtropical eutrophic lakes[END_REF] also reported a decrease in the PAH concentration along with phyto-and zooplankton biomass, but without any obvious linear relationship between Log KOW et -m. The present results show that through the bioaccumulation process, the plankton, and in particular its smallest fractions, plays a key role in the PAH cycling in the Mediterranean Sea. Besides, biotransformation/degradation is another essential fate for PAHs in the ocean. This biological reworking has already been reported by González-Gaya et al. (2019), who observed a linear negative relationship between Log Kow and -m for some LMW PAHs. In our study, the biological removal was very likely present, especially in the fraction 60-200 µm, for which we also found a negative linear relationship between Log KOC et -m for the LMW HAPs, as well as the low abundance of methylated derivatives.

Conclusion

In this study, we determined the hydrocarbon (AH and PAH) content in water and sizefractionated plankton to help characterizing the bioaccumulation of these compounds at the water-plankton interface in the Western Mediterranean Sea. Zooplankton was mainly composed of copepods and its low lipid content was in accordance with the oligotrophic character of the Mediterranean waters, along with poor seasonality of food supply for plankton. Concerning AHs, anthropogenic inputs were recorded in water at all sites, even though these inputs were masked in plankton by major biogenic signatures. Regarding PAHs, profiles in water and in the 0.7-60-µm size fraction were quite similar but distinct from those in zooplankton, highlighting differences in the bioaccumulation processes. The peculiar bioaccumulation of Phe in the 60-200 µm is intriguing and could be related to reduced metabolization/depuration processes. We also demonstrate the strong PAH bioaccumulation in the 0.7-60-µm fraction (relative to water), followed by a limited transfer to higher size fractions, ultimately underscoring a bioreduction process along the planktonic food web. Furthermore, the biodilution process (the decrease in concentration at higher SPM/biomass) was evidenced for the fractions 0.7-60 and 60-200 µm. Finally, our results point out the key role of the smallest size fractions of plankton in the PAH cycling in the Mediterranean Sea. andc) indicate significant differences between the means of the distributions (t-test; p < 0.05). Log KOC and -m were determined in each fraction, at the 10 stations, for each of the 7 PAHs (Nap, Flu, Phe, Flt, Pyr, BaA, Chr). For each size fraction, the value m is the slope of the regression (power function) between the SPM/biomass concentration (in mg L -1 dw) and the concentration of the given PAH (in ng g -1 dw) for the 10 stations. Examples of SPM/biomass versus PAH power relationships and associated -m values are presented for Phe for each size fraction. The detailed regression parameters of the power functions for the 7 PAHs, including m values, are found in Table S10. The plankton fraction corresponds to the size fraction 60-1000 µm; c Total PAHs = sum of 19 compounds (Ʃ19PAHs); d The plankton fraction corresponds to the size fraction > 50 µm; e Total PAHs = sum of 64 compounds (Ʃ64PAHs); f Vertical settling flux of POC below 100-m depth for the western Mediterranean Sea estimated by [START_REF] Guyennon | New insights into the organic carbon export in the Mediterranean Sea from 3-D modeling[END_REF], where POC is defined as being fueled by the natural mortality of the largest organisms (mesozooplankton, diatoms and ciliates) and by the excretion of fecal pellets and sloppy feeding by mesozooplankton; g Vertical settling flux of POC from the surface mixed layer due to phytoplankton and to zooplanktonassociated pellets estimated from [START_REF] Siegel | Global assessment of ocean carbon export by combining satellite observations and foodweb models[END_REF]'s global climatology.

MERMEX-MERITE and CHARMEX subprograms). The project also

n-C16 n-C17 Pr n-C18 Phy n-C19 n-C20 n-C21 n-C22 n-C23 n-C24 n-C25 n-C26 n-C27 n-C28 n-C29 n-C30 n-C31 n-C32 n-C33 n-C34 n-C35 n-C36 n-C37 n-C38 n-C39 n-C40 0
-C15 n-C16 n-C17 Pr n-C18 Phy n-C19 n-C20 n-C21 n-C22 n-C23 n-C24 n-C25 n-C26 n-C27 n-C28 n-C29 n-C30 n-C31 n-C32 n-C33 n-C34 n-C35 n-C36 n-C37 n-C38 n-C39 n-C40
Relative abundance (%)

Supplementary Material

The supplementary material contains 26 pages, and includes 11 tables and 6 figures. 3.2 3.1 2.9 3.6 2.0 3.6 3.5 3.6 1.9 1.5 200-500 3.7 3.3 3.4 3.6 2.7 3.9 3.8 3.9 2.4 1.6 500-1000 4.4 3.5 3.4 3.5 3.9 4.5 4.2 3.3 na 2.5 na: not available; TChla: total chlorophyll a; SPM: suspended particulate matter; Biomass: total biomass including the biomasses of zooplankton, phytoplankton and detritus (see Fierro-González et al., 2023); POC: particulate organic carbon; δ 13 C and δ 15 N: C and N stable isotopic ratios.

Table S2. Concentrations (in mg g -1 dw) of individual and total lipid biomarkers (fatty acids, fatty alcohols and sterols) in the planktonic size fractions 60-200, 200-500 and 500-1000 µm recovered from the DCM at the 10 stations. 0.03 0.01 0.01 0.02 0.04 0.01 0.02 0.02 0.04 0.01 0.04 0.01 0.12 0.08 0.06 Cholesta-5,22E-dien-3-ol 0.05 0.04 0.02 0.04 0.10 0.02 0.02 0.03 0.06 0.04 0.12 0.05 0.17 0.13 0.12 Cholest-5-en-3-ol 0.18 0.16 0.16 0.17 0.45 0.08 0.07 0.15 0.21 0.06 0.29 0.13 0.99 0.82 1.01 Cholesta-5,24-dien-3-ol 0.02 0.01 0.01 0.01 0.03 nd nd 0.01 0.01 nd 0.02 0.01 0.17 0.12 0.09 24-Methylcholesta-5,22E-dien-3-ol 0.01 0.01 0.01 0.01 0.05 0.01 0.01 0.02 0. Ʃ6sterols (mg g -1 dw) 1.50 1.85 1.15 0.75 2.03 1.08 1.16 0.72 2.23 0.11 0.28 na 1.18 1.69 1.62 24-Norcholesta-5,22E-dien-3-ol 0.06 0.04 0.04 0.03 0.08 0.03 0.04 0.04 0.11 0.00 0.01 na 0.04 0.00 0.05 5-Cholestan-3-ol 0.14 0.11 0.10 0.09 0.16 0.08 0.09 0.05 0.07 0.02 0.04 na 0.09 0.10 0.07 Cholesta-5,22E-dien-3-ol 0.20 0.22 0.16 0.10 0.25 0.13 0.18 0.11 0.21 0.02 0.04 na 0.12 0.15 0.14 Cholest-5-en-3-ol 0.95 1.31 0.70 0.42 1.30 0.70 0.67 0.42 1.67 0.06 0.16 na 0.75 1.18 1.20 Cholesta-5,24-dien-3-ol 0.06 0.08 0.04 0.07 0.11 0.07 0.08 0.03 0.06 0.01 0.01 na 0.07 0.11 0.06 24-Methylcholesta-5,22E-dien-3-ol 0.09 0.09 0.10 0.03 0.13 0.07 0.10 0.07 0.11 0.01 0.02 na 0.12 0.15 0.10 na: not available; nd: not detected; Ʃ39lipids = Ʃ25fatty acids + Ʃ8fatty alcohols + Ʃ6sterols; Ʃ25fatty acids = Ʃ 14:0-isomeric dihydroxy 16:0 (25 compounds); Ʃ8fatty alcohols = Ʃ 14:0-phytol (8 compounds); Ʃ6sterols = Ʃ 24-Norcholesta-5,22E-dien-3-ol-24-Methylcholesta-5,22E-dien-3-ol (6 compounds). Table S3. Concentrations (in ng L -1 ) of individual and total aliphatic hydrocarbons (AHs) in the dissolved phase (< 0.7 µm) of water collected at 5-20-m depth at the 10 stations. na: not available. fBiomass: contribution of the biomass of a given size fraction to the total biomass of the fraction 60-1000 µm (i.e., fBiomass x = biomass fraction x / biomass 60-1000 µm), with biomass 60-1000 µm = biomass 60-200 µm + biomass 200-500 µm + biomass 500-1000 µm. fOC: contribution of the OC mass (in g) to the total matter mass (in g) for a given size fraction (i.e., fOC = POC in mg g -1 dw / 1000). Concentrations of POC and individual PAHs in the size fraction 60-1000 µm were calculated by summing the concentrations of POC/PAH in the fractions 60-200, 200-500 and 500-1000 µm, each of these concentrations being weighted (multiplied) by the corresponding fBiomass value.

Table S8. Partition coefficient between particulate matter and water (KD in L kg -1 ) and Log KD for the 7 individual PAHs in each particulate/ planktonic size fraction (0.7-60, 60-200, 200-500, 500-1000 and 60-1000 µm) Table S10. Nonlinear regression parameters (power function) between SPM (in mg L -1 ) or biomass (in mg dw L -1 ; horizontal axis) and PAH concentration (Cp in ng g -1 dw; vertical axis) for each particulate/planktonic size fraction (0.7-60, 60-200, 200-500, 500-1000 and 60-1000 µm) and individual PAH; The power functions are of the form: y = ax -m (i.e., Cp = aSPM -m or aBiomass -m ).

The number of samples n correspond to the stations. Power functions for Phe are shown Fig. 8.

  received financial support from the IRD French-Tunisian International Joint Laboratory (LMI) COSYS-Med. The MERITE-HIPPOCAMPE cruise was organized and supported by the French Oceanographic Fleet (FOF), CNRS/INSU, IFREMER, IRD, the Tunisian Ministry of Agriculture, Water Resources and Fisheries, and the Tunisian Ministry of Higher Education and Scientific Research. The project also benefited from additional funding by IFREMER, by the MIO Action Sud and Transverse Axis programs (CONTAM Transverse Axis), by the IRD Ocean Department, and by the CONTAMPUMP project (ANR JCJC #19-CE34-0001-01). We are grateful to the captains and crew of the R/V Antea for their help and assistance during the cruise. Various MIO platforms also provided valuable support: the Service Atmosphère-Mer (SAM), the Plateforme Analytique de Chimie des Environnements Marins (PACEM platform) and the Platforme Microscopie et Imagerie (MIM platform). We warmly thank J.-F. Rontani for his expertise on lipid biomarkers. Finally, we acknowledge two Reviewers for their relevant and helpful comments.

Figure caption Figure 1

 caption1 Figure caption

Figure 2 .

 2 Figure2. a) Concentrations of total chlorophyll a (TChla, in µg L -1 ), suspended particulate matter (SPM, in mg L -1 ) and particulate organic carbon (POC, in mg L -1 ) in the size fraction 0.7-60 µm, b) total biomass (in µg dw L -1 ) (seeFierro-González et al., 2023, this cumulates phytoplankton, zooplankton and detritus biomasses), and c) concentration of POC (in mg g -1

Figure 3 .

 3 Figure 3. Concentrations of total lipid biomarkers (in mg g -1 dw) in the planktonic size

Figure 4 .

 4 Figure 4. Concentrations of total aliphatic hydrocarbons (Ʃ28AHs, in µg g -1 dw) in the

Figure 5 .

 5 Figure 5. Concentrations of total polycyclic aromatic hydrocarbons (Ʃ27PAHs, in ng g -1 dw)

Figure 6 .

 6 Figure 6. Concentrations (in ng g -1 dw) of a) Ʃ7PAHs (= Nap + Flu + Phe + Flt + Pyr + BaA

Figure 7 .

 7 Figure 7. Concentrations (in ng g -1 dw) of a) Ʃ7PAHs (= Nap + Flu + Phe + Flt + Pyr + BaA

Figure 8 .

 8 Figure 8. Distribution of a) Log KOC and b) slope value (-m) in the particulate/planktonic size

  Figure 1

  Figure 5

  Figure 6

Figure S1 .Figure S2 .

 S1S2 Figure S1. Relationships between the concentration of Ʃ39lipids (= Ʃ25fatty acids + Ʃ8fatty alcohols + Ʃ6sterols; in mg g -1 dw) measured in the present study (horizontal axis), and a) the concentration of POC (in mg g -1 dw) measured in the present study and b) the concentration of total lipids (in mg g -1 dw) determined by Tésan Onrubia et al. (2023) using a global method (vertical axes), on the same planktonic size fractions (60-200, 200-500 and 500-1000 µm) recovered from the DCM at the 10 stations.

Figure S3 .

 S3 Figure S3. Zooplankton biomarkers in the planktonic size fractions 60-200, 200-500 and 500-1000 µm, recovered from the DCM at the 10 stations: relative abundances of a) 20:5, b) 22:1 and c) 22:6 within fatty acids (in %).

Figure

  Figure S4. a) Concentrations of total aliphatic hydrocarbons (Ʃ28AHs, in ng L -1 ) at the 10 stations, and b) mean relative abundances of individual AHs (in %) for stations St1, St9, St11,

Figure

  Figure S5. a) Concentrations of total polycyclic aromatic hydrocarbons (Ʃ14PAHs, in ng L -1 ) at the 10 stations, and b) mean relative abundances of individual PAHs (in %) for stations St1, St2, St3, St9, St10, St11, St15, St17, St19 and c) station St4 only, for the dissolved phase (< 0.7 µm) of water collected at 5-20m depth. Ʃ14PAHs = Ʃ Nap-Chr (14 compounds).

Table 1 .

 1 Comparison of plankton PAH concentrations and biological pump fluxes of PAHs determined here for the Western Mediterranean Sea (over our ten stations) with those reported previously in the same and other oceanic areas. We present the data for total PAHs (sum of individual compounds) and individual phenanthrene. Phe: phenanthrene; POC: particulate organic carbon; a Total PAHs = sum of 27 compounds (Ʃ27PAHs); b

	This study a, b	Berrojalbiz et al.		González-Gaya et al. (2019) d, e
		(2011) c, d
	Western Med.	Western and	North	South	North	South	Indian
	Sea	Eastern Med. Sea	Atlantic	Atlantic	Pacific	Pacific	Ocean

Table S1 .

 S1 Biogeochemical parameters measured in the different particulate/planktonic size fractions(0.7-60, 60-200, 200-500 and 500-1000 µm) recovered from the deep chlorophyll maximum (DCM) at the 10 stations.

				St1	St2	St3	St4	St9	St10	St11	St15	St17	St19
	Sampling depth range in the DCM (m)	20-24	25-53	53-58	13-35	20	40-60	30-58	60-68	37-46	30-46
	Parameter Unit	Size fraction (µm)
	TChla	µg L -1	0.7-60	0.46	0.33	0.37	0.38	0.65	0.41	0.24	0.29	0.12	0.54
	SPM	mg L -1	0.7-60	0.35	0.32	0.21	0.22	0.67	0.25	0.15	0.12	0.29	0.34
	Biomass	µg dw L -1 60-200	20.0	7.1	1.9	68.3	17.3	3.5	3.9	6.4	83.1	28.5
			200-500	37.4	6.8	2.3	28.5	23.3	4.1	5.4	10.0	71.8	38.2
			500-1000	4.7	6.7	4.0	6.8	3.6	2.0	8.6	8.7	2.1	11.2
			Tot 60-1000	62.1	20.6	8.2	103.5	44.2	9.6	17.9	25.2	157.0	77.9
	POC	mg L -1	0.7-60	0.047	0.022	0.016	0.035	0.175	0.030	0.018	0.014	0.024	0.048
		mg g -1 dw 0.7-60	134.5	67.3	78.3	159.5	261.8	118.6	121.7	120.6	80.9	141.9
			60-200	263.4	129.4	81.9	103.5	249.8	240.3	271.5	153.7	43.5	156.0
			200-500	246.4	238.0	179.6	139.4	341.0	269.8	299.9	199.6	75.9	204.7
			500-1000	284.9	207.1	168.5	109.7	326.2	222.8	311.4	228.9	na	190.5
		%	0.7-60	13.5	6.7	7.8	15.9	26.2	11.9	12.2	12.1	8.1	14.2
			60-200	26.3	12.9	8.2	10.4	25.0	24.0	27.1	15.4	4.4	15.6
			200-500	24.6	23.8	18.0	13.9	34.1	27.0	30.0	20.0	7.6	20.5
			500-1000	28.5	20.7	16.9	11.0	32.6	22.3	31.1	22.9	na	19.1
	δ 13 C	‰	0.7-60	-24.5	-24.8	-23.6	-23.2	-24.2	-24.6	-24.1	-25.1	-23.7	-23.6
			60-200	-22.8	-22.7	-21.7	-20.5	-22.7	-22.8	-22.9	-22.8	-21.8	-22.3
			200-500	-23.9	-23.9	-23.0	-21.5	-23.2	-23.7	-24.0	-23.4	-17.4	-21.8
			500-1000	-23.4	-23.8	-22.7	-22.2	-22.9	-23.3	-23.4	-22.7	na	-23.1
	δ 15 N		0.7-60	1.8	0.9	0.1	2.1	-1.3	0.4	0.9	1.6	0.8	0.3
			60-200

Table S5 .

 S5 Concentrations (in ng L -1 ) of individual and total polycyclic aromatic hydrocarbons (PAHs) in the dissolved phase (< 0.7 µm) of water collected at 5-20-m depth at the 10 stations.

		St1	St2	St3	St4	St9	St10	St11	St15	St17	St19
	Nap	0.29	0.69	0.24	0.93	0.11	0.44	0.06	0.34	0.18	0.41
	C1-Nap	nd	nd	nd	3.13	nd	nd	nd	nd	nd	nd
	C2-Nap	nd	nd	nd	7.06	nd	nd	nd	nd	nd	nd
	C3-Nap	nd	nd	nd	2.43	nd	nd	nd	nd	nd	nd
	Acy	0.01	nd	nd	nd	nd	nd	nd	nd	0.01	0.01
	Ace	0.08	0.10	0.12	0.12	0.08	0.09	0.04	0.06	0.06	0.06
	Flu	0.27	0.26	0.21	0.40	0.14	0.23	0.09	0.16	0.15	0.19
	DBT	0.01	0.07	0.03	0.18	0.03	0.02	0.02	0.01	0.01	0.01
	Phe	0.43	1.06	0.91	1.14	3.52	0.46	0.33	0.34	0.28	0.32
	Ant	0.03	nd	0.07	nd	nd	nd	nd	0.05	0.03	0.06
	Flt	0.17	0.34	0.82	0.17	0.13	0.15	0.13	0.14	0.15	0.12
	Pyr	0.10	0.29	0.65	0.12	0.10	0.13	0.09	0.12	0.12	0.12
	BaA	0.05	0.04	0.13	0.05	0.04	0.03	0.04	0.05	0.05	0.05
	Chr	0.10	0.13	0.62	0.06	0.09	0.11	0.08	0.12	0.18	0.11
	Ʃ14PAHs	1.5	3.0	3.8	16	4.2	1.7	0.9	1.4	1.2	1.4
	Ʃ7PAHs	1.4	2.8	3.6	2.9	4.1	1.6	0.8	1.3	1.1	1.3
	LMW PAHs (%)	73	73	42	97	92	74	61	69	59	73
	HMW PAHs (%)	27	27	58	3	8	26	39	31	41	27
	nd: not detected; C1: methyl; C2: di-methyl; C3: tri-methyl; Ʃ14PAHs = Ʃ Nap-Chr (14 compounds); Ʃ7PAHs = Ʃ Nap, Flu, Phe, Flt, Pyr, BaA, Chr; LMW:
	low molecular weight, i.e., 2-3 rings; HMW: high molecular weight, i.e., 4-6 rings.

Table S6 .

 S6 Concentrations (in ng g -1 dw) of individual and total polycyclic aromatic hydrocarbons (PAHs) in the particulate/planktonic size fractions 0.7-60, 60-200, 200-500 and 500-1000 µm recovered from the DCM at the 10 stations.

	Size fraction (µm) Nap C1-Nap C2-Nap C3-Nap Acy Ace Flu C1-Flu C2-Flu DBT C1-DBT C2-DBT Phe Ant C1-Phe/Ant C2-Phe/Ant Flt Pyr C1-Flt/Pyr BaA Chr Size fraction (µm) Nap C1-Nap C2-Nap C3-Nap Acy Ace Flu C1-Flu C2-Flu DBT C1-DBT C2-DBT Phe Ant C1-Phe/Ant C2-Phe/Ant Flt Pyr C1-Flt/Pyr BaA Chr BbF BkF BaP IndP DahA	St1 0.7-60 18 nd nd nd nd nd 14 nd nd 0.6 nd nd 16 nd nd nd 23 31 nd 9.0 19 0.7-60 23 nd nd nd nd nd 14 nd nd 0.2 nd nd 9.4 nd nd nd 9.1 21 nd 7.6 9.4 nd nd nd nd 1.2 St10 St2 St3 St4 St9 60-200 200-500 500-1000 0.7-60 60-200 200-500 500-1000 0.7-60 60-200 200-500 500-1000 0.7-60 60-200 200-500 500-1000 0.7-60 60-200 200-500 500-1000 8.0 2.9 13 25 31 7.0 7.0 36 14 5.6 3.6 20 6.2 7.8 18 11 3.9 2.1 5.2 4.5 1.3 2.9 nd 8.1 2.1 1.7 nd 5.0 2.4 1.2 nd 3.9 5.1 4.7 nd 1.5 0.9 1.5 16 4.4 8.1 nd 18 2.0 5.9 nd 18 14 7.8 nd nd nd nd nd 6.4 4.0 5.9 16 0.2 6.1 nd 17 5.4 5.9 nd 16 12.5 5.8 nd 10.3 14 10 nd 6.4 4.0 5.8 1.8 3.1 1.4 nd nd nd nd nd 0.9 0.4 0.3 nd nd 1.2 0.8 nd 0.5 0.2 nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd 0.5 0.4 nd 4.3 3.4 7.6 20 19 5.5 6.9 38 15 4.9 2.2 18 5.5 14 11 9.7 3.1 2.7 2.3 6.8 3.6 4.0 nd 7.5 4.5 4.5 nd 7.9 7.8 4.0 nd 4.9 4.4 3.0 nd 3.6 2.9 2.1 5.7 nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd 2.1 nd 0.5 nd nd nd nd nd 1.9 0.8 0.4 0.5 0.8 1.1 0.0 0.2 0.4 0.1 0.2 1.7 nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd 2.4 nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd 39 16 17 21 71 20 24 51 79 29 14 19 32 26 25 5.3 19 9.1 6.8 1.7 nd 1.3 nd nd 7.0 0.0 10 3.8 1.1 0.5 nd 2.1 1.9 2.4 nd 0.7 0.4 0.3 16 6.0 8.1 nd nd 2.6 8.7 nd 9.1 6.9 4.7 nd 17 14 0.0 nd 6.9 5.1 4.0 12 nd 4.0 nd nd nd nd nd 5.7 5.1 2.9 nd 9.0 12 0.0 nd 4.8 2.8 1.4 24 12 9.3 7.0 14 4.3 8.3 22 10 5.1 3.4 17 16 13 12 6.6 3.4 3.4 2.1 21 12 8.6 19 12 5.2 7.3 41 8.4 3.6 2.4 14 13 11 12 13 2.9 1.6 1.1 17 6.1 4.7 nd nd nd nd nd nd nd nd nd 7.8 5.6 0.0 nd 2.2 3.0 1.2 14 0.3 3.6 8.2 2.9 1.1 1.6 11 2.5 1.3 0.6 14 5.9 4.9 4.7 4.4 2.3 0.4 0.7 17 4.8 8.2 12 5.1 2.6 6.1 12 3.9 3.0 3.5 35 13 8.9 16 3.5 3.0 2.4 St11 St15 St17 St19 60-200 200-500 500-1000 0.7-60 60-200 200-500 500-1000 0.7-60 60-200 200-500 500-1000 0.7-60 60-200 200-500 500-1000 0.7-60 60-200 200-500 500-1000 8.9 3.0 8.2 64 5.5 4.0 3.0 29 11 2.9 4.3 15 2.7 3.8 na 13 2.9 2.7 11 2.4 2.0 1.9 nd 2.2 1.6 1.4 nd 4.1 2.7 1.4 nd 1.5 1.6 na nd 1.1 0.9 nd 8.4 14 6.7 nd 10 9.1 7.4 nd 0.0 17 8.8 nd nd nd na nd 6.2 5.5 nd 19 0.0 6.3 nd 12 13 8.5 nd 17 16 8.6 nd 5.1 4.2 na nd 4.0 4.9 nd 1.2 0.6 0.7 nd 0.5 0.2 0.2 nd nd 0.6 0.2 nd nd nd na nd nd nd nd nd nd nd nd nd 1.0 0.9 nd nd 1.8 1.1 nd nd nd na nd 0.6 0.3 nd 7.7 5.6 7.1 41 6.8 4.8 4.5 20 12 8.5 4.8 13 3.1 4.2 na 11 2.9 2.5 6.9 6.3 9.3 4.9 nd 7.8 7.8 7.0 nd 4.1 8.2 3.9 nd nd nd na nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd na nd nd nd nd 0.8 0.7 0.3 nd 1.1 0.5 0.3 0.6 1.9 1.0 0.5 nd 0.4 0.3 na 0.2 0.4 0.3 0.4 nd nd nd nd nd nd nd nd nd nd nd nd nd nd na nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd na nd nd nd nd 38 24 21 41 46 23 15 22 67 37 21 8.7 15 14 na 8.7 14 8.6 17 1.2 1.1 0.6 nd 1.4 0.6 0.4 nd nd 1.3 0.7 nd nd nd na nd 0.3 0.1 0.0 9.9 10 6.7 nd 5.4 7.2 6.8 nd 9.3 9.8 7.0 nd 6.0 5.4 na nd 5.7 3.3 0.0 6.0 5.9 3.1 nd 4.5 3.6 3.6 nd 0.0 11 8.6 nd 4.8 4.0 na nd 3.5 2.6 0.0 7.3 4.8 4.9 20 7.2 2.6 2.3 24 5.2 3.6 3.2 11 1.4 1.7 na 9.0 1.1 1.0 2.0 5.9 3.1 4.4 24 4.8 1.6 1.4 31 8.3 2.6 4.0 19 2.1 3.1 na 18 1.4 1.0 2.7 nd nd nd nd nd nd nd nd nd nd nd nd nd nd na nd nd nd nd 1.3 0.8 1.0 18 1.9 0.6 0.6 19 0.0 1.3 0.9 7.3 0.3 0.4 na 6.9 0.3 0.3 1.5 4.1 2.9 2.7 11 4.4 1.6 1.8 18 2.1 2.0 2.0 15 0.9 0.9 na 4.3 0.5 0.5 1.0 nd nd nd nd nd nd nd nd nd nd nd nd nd nd na nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd na nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd na nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd na nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd na nd nd nd nd
	BP	nd	nd	nd	nd	nd	2.0	nd	nd	nd	nd	nd	nd	nd	nd	nd	na	nd	nd	nd	nd
	Ʃ27PAHs	94	128 87	80	219 124 83	65	163 141 126 81	89	43	44	na	71	45	35	43
	Ʃ7PAHs	94	73	44	49	219 76	38	28	163 105 58	40	89	25	28	na	71	23	17	42
	LMW PAHs	50	85	87	84	66	84	92	90	43	89	92	87	41	89	86	na	47	93	92	83
	PAHs (%) HMW PAHs	50	15	13	16	34	16	8	10	57	11	8	13	59	11	14	na	53	7	8	17
	PAHs (%) na: not available; nd: not detected; C1: methyl; C2: di-methyl; C3: tri-methyl; Ʃ27PAHs = Ʃ Nap-BP (27 compounds); Ʃ7PAHs = Ʃ Nap, Flu, Phe, Flt, Pyr, BaA,
	Chr; LMW: low molecular weight, i.e., 2-3 rings; HMW: high molecular weight, i.e., 4-6 rings.

Table S7 .

 S7 Summary of SPM, biomass, POC and individual PAH concentration data for the particulate/planktonic size fractions 0.7-60,60-200, 200-500, 500-1000 µm, but also 60-1000 µm, recovered from the DCM at the 10 stations.

		500-1000 0.009	0.5	311.4	0.311 3.0	4.5	14.5 2.3	1.4	0.6	1.8
		60-1000	0.018	1.0	299.1	0.299 3.9	5.1	23.9 3.5	2.2	0.9	2.4
	St15 < 0.7	na	na	na	na	0.34 0.16 0.34 0.14 0.12 0.05 0.12
		0.7-60	0.120	na	120.6	0.121 28.6 19.7 22.0 24.0 31.0 18.8 18.4
		60-200	0.006	0.3	153.7	0.154 10.5 12.0 66.9 5.2	8.3	na	2.1
		Size 200-500	Biomass 0.010	fBiomass POC 0.4 199.6	fOC 0.200 2.9 ng L -1 for < 0.7 µm, ng g -1 dw for other fractions 8.5 37.0 3.6 2.6 1.3 2.0
		fractions 500-1000 0.009 (mg dw L -1 )	0.3	(mg g -1 228.9	Nap Flu 0.229 4.3 4.8	Phe 20.6 3.2 Flt	Pyr 4.0	BaA Chr 0.9 2.0
		(µm) 60-1000	or SPM 0.025	1.0	dw) 198.1	0.198 5.3	8.1	38.9 3.9	4.5	0.8	2.0
	St17 < 0.7	(mg L -1 ) na	na	na	na	0.18 0.15 0.28 0.15 0.12 0.05 0.18
	St1	< 0.7 0.7-60	na 0.290	na na	na 80.9	na 0.081 15.0 13.1 8.7 0.29 0.27 0.43 0.17 0.10 0.05 0.10 10.7 18.9 7.3 15.1
		0.7-60 60-200	0.347 0.083	na 0.5	134.5 43.5	0.135 18.0 13.6 16.1 22.8 31.2 9.0 0.044 2.7 3.1 14.5 1.4 2.1 0.3	18.7 0.9
		60-200 200-500	0.020 0.072	0.3 0.5	263.4 75.9	0.263 8.0 0.076 3.8	4.3 4.2	39.1 23.8 20.5 13.7 17.4 14.0 1.7 3.1 0.4 0.9
		200-500 500-1000 0.002 0.037	0.6 0.0	246.4 na	0.246 2.9 0.000 na	3.4 na	16.3 12.0 11.9 0.3 na na na na	4.8 na
		500-1000 0.005 60-1000 0.157	0.1 1.0	284.9 57.7	0.285 13.3 7.6 0.058 3.2 3.6	16.5 9.3 14.1 1.5	8.6 2.6	3.6 0.4	8.2 0.9
	60-1000 St19 < 0.7	0.062 na	1.0 na	254.8 na	0.255 5.3 na 0.41 0.19 0.32 0.12 0.12 0.05 0.11 4.0 23.6 15.6 14.4 4.8 9.1
	St2	< 0.7 0.7-60	na 0.340	na na	na 141.9	na 0.142 13.4 10.7 8.7 0.69 0.26 1.06 0.34 0.29 0.04 0.13 9.0 17.6 6.9 4.3
		0.7-60 60-200	0.320 0.029	na 0.4	67.3 156.0	0.067 25.3 19.6 20.7 7.0 0.156 2.9 2.9 14.0 1.1	18.5 8.2 1.4 0.3	12.2 0.5
		60-200 200-500	0.007 0.038	0.3 0.5	129.4 204.7	0.129 31.2 19.0 71.2 13.9 12.1 2.9 0.205 2.7 2.5 8.6 1.0 1.0 0.3	5.1 0.5
		200-500 500-1000 0.011 0.007	0.3 0.1	238.0 190.5	0.238 7.0 0.191 10.8 6.9 5.5	20.1 4.3 17.3 2.0	5.2 2.7	1.1 1.5	2.6 1.0
		500-1000 0.007 60-1000 0.078	0.3 1.0	207.1 184.9	0.207 7.0 0.185 3.9	6.9 3.3	23.9 8.3 11.8 1.2	7.3 1.4	1.6 0.5	6.1 0.6
		60-1000	0.021	1.0	190.7	0.191 15.3 10.6 38.9 8.9	8.3	1.9	4.6
	St3	< 0.7	na	na	na	na	0.24 0.21 0.91 0.82 0.65 0.13 0.62
		0.7-60	0.210	na	78.3	0.078 36.3 38.1 50.8 22.2 40.6 11.2 11.6
		60-200	0.002	0.2	81.9	0.082 14.0 15.4 78.5 10.2 8.4	2.5	3.9
		200-500	0.002	0.3	179.6	0.180 5.6	4.9	28.5 5.1	3.6	1.3	3.0
		500-1000 0.004	0.5	168.5	0.169 3.6	2.2	13.5 3.4	2.4	0.6	3.5
		60-1000	0.008	1.0	152.0	0.152 6.5	5.9	32.5 5.4	4.1	1.2	3.4
	St4	< 0.7	na	na	na	na	0.93 0.4	1.14 0.17 0.12 0.05 0.06
		0.7-60	0.220	na	159.5	0.159 19.7 17.5 18.8 16.5 14.4 14.0 34.9
		60-200	0.068	0.7	103.5	0.104 6.2	5.5	31.7 16.4 13.2 5.9	12.6
		200-500	0.028	0.3	139.4	0.139 7.8	13.5 26.4 12.5 10.9 4.9	8.9
		500-1000 0.007	0.1	109.7	0.110 18.2 11.4 24.6 12.0 11.6 4.7	15.5
		60-1000	0.104	1.0	113.8	0.114 7.4	8.1	29.8 15.0 12.5 5.5	11.8
	St9	< 0.7	na	na	na	na	0.11 0.14 3.52 0.13 0.1	0.04 0.09
		0.7-60	0.670	na	261.8	0.262 10.5 9.7	5.3	6.6	13.2 4.4	3.5
		60-200	0.017	0.4	249.8	0.250 3.9	3.1	18.7 3.4	2.9	2.3	3.0
		200-500	0.023	0.5	341.0	0.341 2.1	2.7	9.1	3.4	1.6	0.4	2.4
		500-1000 0.004	0.1	326.2	0.326 5.2	2.3	6.8	2.1	1.1	0.7	1.2
		60-1000	0.044	1.0	304.2	0.304 3.1	2.8	12.7 3.3	2.1	1.2	2.6
	St10 < 0.7	na	na	na	na	0.44 0.23 0.46 0.15 0.13 0.03 0.11
		0.7-60	0.250	na	118.6	0.119 23.1 14.3 9.4	9.1	20.5 7.6	9.4
		60-200	0.003	0.4	240.3	0.240 8.9	7.7	37.9 7.3	5.9	1.3	4.1
		200-500	0.004	0.4	269.8	0.270 3.0	5.6	24.0 4.8	3.1	0.8	2.9
		500-1000 0.002	0.2	222.8	0.223 8.2	7.1	20.5 4.9	4.4	1.0	2.7
		60-1000	0.010	1.0	249.1	0.249 6.3	6.7	28.3 5.7	4.4	1.0	3.3
	St11 < 0.7	na	na	na	na	0.06 0.09 0.33 0.13 0.09 0.04 0.08
		0.7-60	0.150	na	121.7	0.122 64.2 40.5 40.7 20.4 24.3 17.6 11.3
		60-200	0.004	0.2	271.5	0.271 5.5	6.8	45.9 7.2	4.8	1.9	4.4
		200-500	0.005	0.3	299.9	0.300 4.0	4.8	22.8 2.6	1.6	0.6	1.6

Table S9 .

 S9 and station. Partition coefficient between particulate organic carbon and water (KOC in L kg -1 ) and Log Koc for the 7 individual PAHs in each particulate/planktonic size fraction(0.7-60, 60-200, 200-500, 500-1000 and 60-1000 µm) and station.

		Size Size				KD (L kg -1 ) KOC (L kg -1 )							Log KD Log KOC
		fractions (µm) fractions (µm)	Nap Nap	Flu Flu	Phe Phe	Flt Flt	Pyr Pyr	BaA BaA	Chr Chr	Nap Nap	Flu Flu	Phe Phe	Flt Flt	Pyr Pyr	BaA BaA	Chr Chr
	St1	0.7-60	61968	50402	37546	133838 311743 180191 186903 4.79	4.70	4.57	5.13	5.49	5.26	5.27
		60-200	27589	16089	90814	140275 205392 274689 173735 4.44	4.21	4.96	5.15	5.31	5.44	5.24
		200-500	9828	12537	37820	70311	118644 5214	48387	3.99	4.10	4.58	4.85	5.07	3.72	4.68
		500-1000 45902	28186	38282	54476	86145	71473	82200	4.66	4.45	4.58	4.74	4.94	4.85	4.91
		60-1000	18260	14858	54904	91627	144104 96901	91261	4.26	4.17	4.74	4.96	5.16	4.99	4.96
	St2	0.7-60	36609	75278	19529	20684	63624	204506 93689	4.56	4.88	4.29	4.32	4.80	5.31	4.97
		60-200	45212	73198	67132	40743	41854	72886	39568	4.66	4.86	4.83	4.61	4.62	4.86	4.60
		200-500	10146	21025	18963	12569	17848	27888	19819	4.01	4.32	4.28	4.10	4.25	4.45	4.30
		500-1000 10112	26496	22549	24554	25330	39204	46882	4.00	4.42	4.35	4.39	4.40	4.59	4.67
		60-1000	22158	40704	36652	26149	28527	47018	35442	4.35	4.61	4.56	4.42	4.46	4.67	4.55
	St3	0.7-60	151402 181259 55817	27024	62409	86410	18700	5.18	5.26	4.75	4.43	4.80	4.94	4.27
		60-200	58158	73373	86227	12394	12911	19161	6264	4.76	4.87	4.94	4.09	4.11	4.28	3.80
		200-500	23466	23460	31367	6262	5549	10291	4771	4.37	4.37	4.50	3.80	3.74	4.01	3.68
		500-1000 14877	10256	14874	4152	3625	4582	5674	4.17	4.01	4.17	3.62	3.56	3.66	3.75
		60-1000	27090	28257	35665	6611	6268	9488	5553	4.43	4.45	4.55	3.82	3.80	3.98	3.74
	St4	0.7-60	21168	43669	16528	96979	120318 279300 582278 4.33	4.64	4.22	4.99	5.08	5.45	5.77
		60-200	6636	13871	27774	96459	109872 117408 210352 3.82	4.14	4.44	4.98	5.04	5.07	5.32
		200-500	8399	33723	23161	73713	90808	98657	148349 3.92	4.53	4.36	4.87	4.96	4.99	5.17
		500-1000 19537	28604	21574	70335	96549	94223	259076 4.29	4.46	4.33	4.85	4.98	4.97	5.41
		60-1000	7969	20296	26098	88489	103755 110729 196512 3.90	4.31	4.42	4.95	5.02	5.04	5.29
	St9	0.7-60	95270	68960	1493	50734	132374 110649 39342	4.98	4.84	3.17	4.71	5.12	5.04	4.59
		60-200	35853	21900	5322	25968	28505	57125	33596	4.55	4.34	3.73	4.41	4.45	4.76	4.53
		200-500	19084	19166	2576	26267	16184	10828	26720	4.28	4.28	3.41	4.42	4.21	4.03	4.43
		500-1000 47133	16105	1925	16116	10509	17476	13828	4.67	4.21	3.28	4.21	4.02	4.24	4.14
		60-1000	27946	19982	3595	25313	20528	29460	28343	4.45	4.30	3.56	4.40	4.31	4.47	4.45

Acknowledgments

The MERITE-HIPPOCAMPE project was initiated and funded by the cross-disciplinary

Pollution & Contaminants axis of the CNRS-INSU MISTRALS program (joint action of the

Data availability

All data from this paper is stored in the MISTRALS-SEDOO database (https://mistrals.sedoo.fr/MERITE/) and will be made publicly accessible once all the articles related to the MERITE-HIPPOCAMPE cruise are published. In the meantime, data can be obtained upon request from the corresponding author. St15, St17, St19 and c) stations St 2, St3, St4, St10, for the dissolved phase (< 0.7 µm) of water collected at 5-20-m depth. Ʃ28AHs = Ʃ n-C15-n-C40, Pr, Phy (28 compounds). a) Ʃ 28 AHs (ng L -1 ) b St2, St3, St4, St10)

Author contribution statement

All the authors participated in the MERITE-HIPPOCAMPE project and design of the manuscript.

Conception and design of

Supplementary information

Supplementary material related to this article is available online at: xxx Table S4. Concentrations (in µg g -1 dw) of individual and total aliphatic hydrocarbons (AHs) in the particulate/planktonic size fractions 0.7-60, 60-200, 200-500 and 500-1000 µm recovered from the DCM at the 10 stations. andS9, respectively. Slope values are also reported Table S10. S11) for all the particulate/planktonic size fractions, i.e., 0.7-60, 60-200, 200-500, 500-1000 and60-1000 μm, andthe 7 PAHs (Nap, Flu, Phe, Flt, Pyr, BaA, Chr). The darker blue dot is not taken into account in the linear regression.