Charlotte Lefebvre
email: charlotte.lefebvre40@gmail.com

Claire Saraux

Olivier Heitz

Antoine Nowaczyk

Delphine Bonnet

Microplastics FTIR characterisation and distribution in the water column and digestive tracts of small pelagic fish in the Gulf of Lions

Keywords: microplastics, Mediterranean, Sardina pilchardus, Engraulis encrasicolus, FTIR

niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

The first modern plastic, called Bakelite, was made in 1907 [START_REF] Crespy | 100 Years of Bakelite, the Material of a 1000 Uses[END_REF].

Nowadays, all market sectors such as packaging, building, automobile, textile, or cosmetics make use of it. Since its conception, the worldwide global demand in plastic has increased every year, reaching 335 million tons in 2016 (PlasticsEurope, 2018); a number that could be much higher as this estimation does not consider some widely-used plastic fibre types such as polyethylene terephthalate, polyamide, polypropylene and polyacryls. Such a massive use of plastics along with mismanagement raises important environmental issues [START_REF] Barnes | Accumulation and fragmentation of plastic debris in global environments[END_REF]. In particular, plastic is the main litter type in marine environments [START_REF] Andrady | Microplastics in the marine environment[END_REF][START_REF] Bergmann | Le phosphore et l'azote en Mer Méditérranee, bilans et fertilité potentielle[END_REF] and no single place can escape plastic anymore [START_REF] Barnes | Remote Islands Reveal Rapid Rise of Southern Hemisphere Sea Debris[END_REF]: from coasts to open oceans [START_REF] Cózar | Plastic debris in the open ocean[END_REF][START_REF] Desforges | Widespread distribution of microplastics in subsurface seawater in the NE Pacific Ocean[END_REF], or even more remote places such as sea ice from Northern latitudes [START_REF] Obbard | Global warming releases microplastic legacy frozen in Arctic Sea ice: OBBARD ET AL[END_REF] and the deep ocean [START_REF] Chiba | Human footprint in the abyss: 30 year records of deep-sea plastic debris[END_REF]. As such, at least 268 940 tons of plastics currently float at the surface of the ocean [START_REF] Eriksen | Plastic Pollution in the World's Oceans: More than 5 Trillion Plastic Pieces Weighing over 250,000 Tons Afloat at Sea[END_REF] and 206 kg of plastic are still discharged in it every second [START_REF] Jambeck | Plastic waste inputs from land into the ocean[END_REF]. The simplest definition of marine plastic debris is based on three size categories. Macroplastics include plastic pieces measuring more than 2.5 cm, mesoplastics cover the size range from 0.5 cm to 2.5 cm and microplastics (MP) refer to pieces measuring less than 0.5 cm [START_REF] Galgani | Guidance on monitoring of marine litter in European seas[END_REF]. They could display different shapes such as fibre, fragment, film or microbead [START_REF] Hidalgo-Ruz | Microplastics in the Marine Environment: A Review of the Methods Used for Identification and Quantification[END_REF]. MP are scattered in all marine areas and are more abundant than macroplastics as they account for about 92% of total plastic [START_REF] Eriksen | Plastic Pollution in the World's Oceans: More than 5 Trillion Plastic Pieces Weighing over 250,000 Tons Afloat at Sea[END_REF]. Because of their small size, MP can be ingested by a wide range of organisms and trophic levels. In situ ingestion data were thus reported for various organisms such as copepods (Desforges et al., 2015), bivalves [START_REF] Van Cauwenberghe | Microplastics in bivalves cultured for human consumption[END_REF], shrimps (Devriese et al., 2015), cetaceans [START_REF] Lusher | Microplastic and macroplastic ingestion by a deep diving, oceanic cetacean: The True's beaked whale Mesoplodon mirus[END_REF], seabirds [START_REF] Codina-García | Plastic debris in Mediterranean seabirds[END_REF][START_REF] Amélineau | Microplastic pollution in the Greenland Sea: Background levels and selective contamination of planktivorous diving seabirds[END_REF], and fish [START_REF] Nadal | High levels of microplastic ingestion by the semipelagic fish bogue Boops boops (L.) around the Balearic Islands[END_REF][START_REF] Pazos | Microplastics in gut contents of coastal freshwater fish from Río de la Plata estuary[END_REF]. Further, MP can be mixed up with bioresources or even mistaken for prey especially in species, such as planktivorous ones, for which prey and MP exhibit similar sizes [START_REF] Amélineau | Microplastic pollution in the Greenland Sea: Background levels and selective contamination of planktivorous diving seabirds[END_REF][START_REF] Ory | Amberstripe scad Decapterus muroadsi (Carangidae) fish ingest blue microplastics resembling their copepod prey along the coast of Rapa Nui (Easter Island) in the South Pacific subtropical gyre[END_REF]. In the North Pacific gyre, 34% of planktivorous fish had ingested MP [START_REF] Boerger | Plastic ingestion by planktivorous fishes in the North Pacific Central Gyre[END_REF], while in Tokyo Bay, MP were ingested by 77% of Japanese anchovies sampled (Engraulis japonicus; [START_REF] Tanaka | Microplastic fragments and microbeads in digestive tracts of planktivorous fish from urban coastal waters[END_REF].

While some accumulation zones around the oceanic gyres such as the 7 th continent in the North Pacific Ocean are now regrettably infamous [START_REF] Eriksen | Plastic Pollution in the World's Oceans: More than 5 Trillion Plastic Pieces Weighing over 250,000 Tons Afloat at Sea[END_REF], our knowledge on other areas is still very scarce. Yet, according to models [START_REF] Lebreton | Numerical modelling of floating debris in the world's oceans[END_REF], the Mediterranean Sea might be an accumulation zone of plastic debris, due to the long residence time of its waters [START_REF] Lacombe | Response of the Mediterranean to the water and energy fluxes across its surface, on seasonal and interannual scales[END_REF] and few exports to the Atlantic Ocean [START_REF] Cózar | Plastic accumulation in the Mediterranean Sea[END_REF]. [START_REF] Cózar | Plastic accumulation in the Mediterranean Sea[END_REF] found that in the Mediterranean Sea, 83% of the total abundance of plastic were MP.

Consistently, MP were identified in 90% of the sea surface water samples collected in the North Western Mediterranean Sea [START_REF] Collignon | Neustonic microplastic and zooplankton in the North Western Mediterranean Sea[END_REF]. This pollution could be an important threat for biodiversity considering that the Mediterranean Sea holds 4% to 18% of all known marine species (approximately 17 000) despite a very small spatial cover (<1% of the global marine waters in terms of area and volume) and has a high level of endemic wildlife (i.e. 10% of the 635 fish species recorded - [START_REF] Coll | The Biodiversity of the Mediterranean Sea: Estimates, Patterns, and Threats[END_REF].

Although the origins of marine plastic litter are not yet well understood due to a lack of studies focusing on freshwater and terrestrial environments, it was assessed that 80% of inputs are land-based [START_REF] Andrady | Microplastics in the marine environment[END_REF]. In particular, rivers play an important role in discharging plastic in the ocean; an estimation based on floating plastic in river indicated that between 1.15 and 2.41 million tons of plastic are entering the ocean each year by this pathway [START_REF] Lebreton | River plastic emissions to the world's oceans[END_REF][START_REF] Schmidt | Export of Plastic Debris by Rivers into the Sea[END_REF]. As such, areas with important river discharge, such as the Gulf of Lions in which the Rhone river flows, are of particular interest to study. Indeed, the Rhône river is the main freshwater input in the Mediterranean Sea [START_REF] Struglia | River Discharge into the Mediterranean Sea: Climatology and Aspects of the Observed Variability[END_REF] with a mean annual discharge of 1700 m 3 .s -1 (http://hydro.eaufrance.fr; last access : 30/11/2018 ). The Gulf of Lions is a 10 000 km² area with a large continental shelf, in the Northwestern part of the Mediterranean Sea and it is acknowledged as the most productive area of this sea [START_REF] Lacombe | Response of the Mediterranean to the water and energy fluxes across its surface, on seasonal and interannual scales[END_REF] as well as a substantial fishing area. The two main small pelagic species occurring in the Gulf are Sardina pilchardus and Engraulis encrasicolus [START_REF] Palomera | Small pelagic fish in the NW Mediterranean Sea: An ecological review[END_REF]. Along the Mediterranean coasts, sardines and anchovies are widely consumed iconic species. Moreover, in 2015, 15.7% of European sardines and 79.9% of European anchovies of the worldwide captures were caught in the Mediterranean and Black sea (©FAO, 2018, Capture: quantity (t), www.fao.org/figis, last access: 23/01/18). These two Clupeiforme species have trophic similarities in terms of prey types (mostly consisting of copepods -Le [START_REF] Bourg | Trophic niche overlap of sprat and commercial small pelagic teleosts in the Gulf of Lions (NW Mediterranean Sea)[END_REF]. Although they can both use filtration and particulate feeding [START_REF] Costalago | Feeding of European pilchard (Sardina pilchardus) in the northwestern Mediterranean: from late larvae to adults[END_REF][START_REF] Plounevez | Diet, feeding behaviour and trophic activity of the anchovy (Engraulis encrasicolus L.) in the Gulf of Lions (Mediterranean Sea)[END_REF], sardines are thought to favour filtration whereas anchovies select particles [START_REF] Van Der Lingen | Comparative trophodynamics of anchovy Engraulis encrasicolus and sardine Sardinops sagax in the southern Benguela: are species alternations between small pelagic fish trophodynamically mediated?[END_REF]. Therefore, sardines might be more prone to MP ingestion, as their main feeding strategy is non-selective [START_REF] Collard | Morphology of the filtration apparatus of three planktivorous fishes and relation with ingested anthropogenic particles[END_REF]. On the contrary, particulate feeders could be either able to distinguish prey from plastic particles or will mistake plastics for prey, as their feeding strategy is active. Hence, ingestion of MP may not be the same between these two species owing to their different feeding strategy.

To our knowledge, only two publications broach description of MP at sea surface in the Gulf of Lions [START_REF] Collignon | Neustonic microplastic and zooplankton in the North Western Mediterranean Sea[END_REF][START_REF] Schmidt | Occurrence of microplastics in surface waters of the Gulf of Lion (NW Mediterranean Sea)[END_REF] but none of them has described MP abundance in the water column or even the polymer types encountered. Here, our goal was (i) to estimate the amount and chemical nature of MP in the integrated water column of the Gulf of Lions, from bottom to surface, using zooplankton net tows, (ii) to assess MP, in terms of quantity and polymer types, in digestive tracts of two main commercial fish species, (iii) to compare MP in the water column with MP from fish digestive tracts and to investigate whether MP ingestion differed between sardines and anchovies thus translating different feeding behaviours.

Methods

Field Sampling

Water column and fish samples used in MP quantification were collected during the PELMED survey (PELagiques en MEDiterranée) in July 2015. This annual survey takes place in the Gulf of Lions in summer in order to assess small pelagic fish populations. Sampling locations and catches of small pelagic species are shown in Figure 1.

For this study, 169 small pelagic fishes (85 European sardines -Sardina pilchardus-and 84

European anchovies -Engraulis encrasicolus) were sampled using a pelagic trawl net (vertical opening between 15 and 20 m). Individuals were collected at 17 stations in which the two species co-occurred. At each station, five individuals per species (except for station 15, where only 4 anchovies were available) were entirely and directly frozen on board to avoid plastic contamination.

Fish trawls lasted for an average of 44 minutes (31-67 min) at 4 knots and at an average depth of 77 m (from 36 m to 112 m). Zooplankton and debris in the water column were collected after each fish trawl, in the middle of the surface trawled, towing vertically a WP2 plankton net (200 µm mesh), from bottom (or 100 m when bathymetry was higher) to surface. The average maximum depth of water column station was 67 m. A flowmeter was used to calculate the volume of filtered water. Among the 17 stations mentioned above, water column sampling did not occur in 3 of them due to unfavourable weather conditions. Water column samples were stored in 125 ml vials and fixed with formaldehyde 4% allowing identification of the zooplanktonic species and estimation of MP abundance.

Digestive tract dissection

Fish were thawed back at the laboratory, weighed and measured (total length from the tip of the snout to the tip of the tail). Body condition (K) was calculated according to Le Cren (1951) and [START_REF] Van Beveren | Rapid changes in growth, condition, size and age of small pelagic fish in the Mediterranean[END_REF], given that this index is the most adapted to fit these species.

However, Fulton's index (F) described by [START_REF] Froese | Cube law, condition factor and weight-length relationships: history, meta-analysis and recommendations[END_REF] was also calculated in order to compare with Compa et al.'s study (2018). For sardines:

K 1 = Weight 5. 9× 10 -3 × Length 3. 1
For anchovies:

K 2 = Weight 3. 86× 10 -3 × Length 3. 2
During dissection, sex of individuals was determined by macroscopic observations (male, female, immature). Sex-ratio (SR) was calculated according to the following equation:

161 162
Then, the entire digestive tract -from oesophagus until the end of intestine -was isolated and put in a glass petri dish with filtered sea water (0.2 µm). Oesophagus, stomach, pyloric caeca and intestine were cut off and completely emptied of their content with tweezers.

Debris visual sorting

Microplastics were extracted using a common methodology of visual sorting under a stereomicroscope for both water and fish samples (Nikon SMZ25 and Zeiss stemi 2000-c for water and fish samples respectively, ranges of magnification from x6.5 to x50 in both cases) to avoid methodological biases. Visual characteristics described by [START_REF] Zhao | Microscopic anthropogenic litter in terrestrial birds from Shanghai, China: Not only plastics but also natural fibers[END_REF] were used to recognise debris that could be MP. Briefly, identification of non-biological particles was based on surface characteristics, morphology and physical response. No cellular or organic structure, such as segmentation or ornamentation, must be seen. Fibre diameter should be equal along all ends and not tapered.

Collected debris were then placed in Eppendorf tubes with filtered sea water and classified into two categories, fibres and fragments, based on their shape [START_REF] Zhao | Microscopic anthropogenic litter in terrestrial birds from Shanghai, China: Not only plastics but also natural fibers[END_REF].

Colours were also reported and then gathered in four categories: light, dark, blue (frequent colours)

and other (rare colours such as red, pink, yellow or orange).

Size of debris

After homogenisation, each Eppendorf tube was emptied and debris were observed under a Leica M80 stereomicroscope connected to a camera (x7.5 -x60). The Leica Application Suite (V4.5.0) was used to take photos of the debris collected both in the water column and in the fish digestive tracts. Photos were then analysed using Image J (V1.50d) to measure the size of each debris in pixel. Finally, distances in pixels were converted in millimetres through a conversion table established using a photography of a micrometric slide for each magnification. Quantification and comparison of the smallest size class (0 -250µm) could be affected by the 200 µm mesh size of the plankton net, although this size class was found in very small quantity in fish guts as well (<1%).

SR= Number of males Number of males + Number of females

Fourier Transform InfraRed (FTIR) spectroscopy

Polymer types of debris were then characterised by using Fourier Transform InfraRed spectroscopy (PerkinsElmer) in ATR (Attenuated Total Reflection) mode. Infrared light was configured at wavelengths ranging from 4000 to 600 cm -1 . Debris were put individually on the diamond of the spectroscope and then pressed. Given this handling, only a subsample of 1085 debris of the 2165 visually sorted debris was investigated. To define the subsample, debris of each sample were first examined under a stereomicroscope and pooled if they were strongly similar in shape, colours, curves and borders. Spectra were recorded by the software Perkin Elmer version Spectrum (10.4.3; 2014). The quality of each spectrum was assessed by checking peaks, transmittance range, libraries and recurrence of results to be considered as exploitable. Spectra were then compared to spectral libraries (Table S1, supplementary material) to establish a list of potential polymer correspondences. Spectrum identifications were directly validated if they showed a percentage of correspondence superior to 70%. Spectra with lower matches were visually examined for polymer identification and compared with those obtained within the same sample.

Avoiding and quantifying contamination

Throughout the different manipulations, 100% cotton lab coats and nitrile gloves were worn. Working places and all labwares (dissection tools, glass petri dishes, stereomicroscopes, watch glasses, etc.) were cleaned with 75% ethanol. This procedure helps in removing debris from tools and reducing the risks of contamination. Furthermore, air circulation and access to the laboratory were limited.

In order to quantify airborne contamination, glass petri dish filled up with filtered sea water were set up close to the analysed sample and were used as contamination controls (17 controls were realised). Then, they were analysed with the same processes of detection, storage and characterization as other samples.

Statistical analysis

Results such as fish sizes, debris sizes or MP concentrations in water and digestive tracts are presented as mean values ± standard deviation and ranges in square brackets.

Size debris similarity between samples (water, sardines and anchovies) was estimated by calculating the overlap percentage of size class debris between two samples according to the equation:

This index varies between 0 (when no common size is shared between the two samples) and 100% (when all sizes are common between the two samples).

All statistical analyses were run using R software (V. 1.0.143). When using individual data, mixed models were used with the sampling site as a random intercept to consider the nonindependence of data of fish caught in the same trawl. Model selection was performed based on Akaike's Information Criterium (AIC). The model with the lowest AIC was selected, except when the difference between the two AIC was smaller than 2, in which case the most parsimonious model was selected [START_REF] Burnham | Avoiding pitfalls when using information-theoretic methods[END_REF]. Debris sizes were compared using a linear mixed model (LMM) in which species was tested as an explanatory variable. The effect of variables such as species, length, body condition index and sex on the number of debris ingested was tested by using generalized linear mixed models (GLMM) with Poisson distribution.

Additionally, non-parametric statistical tests were run when parametric assumptions were not valid. Correlations between variables or samples were tested with Spearman's rank correlation, and a chi-squared test was used to compare polymer types and colour proportions between different types of samples. For MP ingestion data, a Wilcoxon-Mann-Whitney test was made to compare the number of MP ingested between species. Finally, to determine the potentially non-linear influence of some variables on the number of MP, a regression tree was built. Significance level was fixed at 0.05 for each statistical hypothesis testing.

Results

Pelagic trawls

Anchovy and sardine accounted for 78% of the total biomass of trawled fish in the 17 stations under study (Figure 1). Sardines were more present in coastal stations, while anchovies clearly dominated offshore. Sardines showed a mean length of 11.72 ± 1.00 cm and an average weight of 14.14 ± 4.02 g while anchovies were 11.25 ± 0.90 cm long and weighed 9.53 ± 2.78 g on average (Table S2, supplementary material). Mean body condition (K) was 1.15 ± 0.09 and 1.03 ± 0.11 respectively for sardines and anchovies. Sex ratio was balanced for anchovies (SR = 0.5) whereas there were slightly more males in sardine samples (SR = 0.6).

Amount, composition and size of debris

After visual sorting, debris were discovered in all water column samples and in 98.8% digestive tracts from sardines and anchovies. In the water column, the average concentration was 3.08 ± 3.04 debris.m -3 . Sardines ingested more debris than anchovies (8.56 ± 6.67 debris vs. 7.12 ± 4.81 debris per sardine and anchovy respectively; GLMM, Z = 2.037, p-value = 0.04, N = 169). On average, 0.88 ± 1.36 debris were found in the contamination controls. Debris sizes were very similar whether in the water column or in sardine and anchovy stomach (1.81 ± 1.42 mm [0.24 -4.93 mm], 1.77 ± 1.67 mm [0.10 -4.95 mm] and 1.81 ± 1.52 mm [0.21 -4.99 mm] respectively in the water column, sardines' and anchovies' digestive tracts; LMM: null model being the best model, ΔAIC = 9.332, N = 1618; Figure 2). This was further confirmed by very high overlaps between all three size distributions (≥ 96%; Figure 2). The most represented size classes comprised debris between 0.5 and 1.5 mm (representing 47.4%, 46.8% and 48.3% of the debris ingested by anchovy and sardine or found in the water column respectively). A large majority of fibre-shaped debris was encountered (99.1%) and only a very small portion of debris was fragment-shaped (0.9%). Light colour debris prevailed in all three sample types (58 %, 69 % and 64% respectively for water column samples, sardines' and anchovies' digestives tracts). Dark debris were recovered in 20% of water column samples, 14% and 12% of sardines and anchovies' digestive tracts respectively, while blue debris accounted respectively for 15%, 10% and 15%. Other colours were rarely observed (water column: 7%, sardine: 7%, anchovy: 9%).

Microplastics characterisation

After FTIR analyses, 16% of sample showing an exploitable spectra were microplastics.

Once extrapolated to all debris sorted, MP contribution to total debris amounted to 7.7% for the water column, 2.3% for sardines and 1.5% for anchovies (Table 1). None of the 17 controls showed airborne contamination by MP.

Exclusively fibre-shaped MP were reported in digestive tracts and water column samples.

In total, 61 MP were quantified in water column samples, 17 in sardines' and 9 in anchovies' digestive tracts (Table 1). In the water column, MP were found in 93 % of samples at an average concentration of 0.23 ± 0.20 MP.m -3 , while they were ingested respectively by 12% and 11% of all sardines and anchovies studied. As such, we first studied data in the form of presence/absence to compare length and body condition index of fish with and without MP in their gut. There were no total length or body condition differences between sardines or anchovies that had ingested MP and those without MP in their digestive tract (Figure 3). Furthermore, the number of MP ingested was not correlated to body condition index (K) of sardines (S = 103320, p-value = 0.68, rho = -0.05, N = 85) nor to anchovies (S = 91009, p-value = 0.48, rho = 0.08, N = 84). Sardines ingested 0.20 ± 0.69 MP.ind -1 on average, while anchovies ingested 0.11 ± 0.31 MP.ind -1 (Table 1). Although sardines ingested twice as much MP per individual, this difference was not significant due to a very high inter-individual variability (Wilcoxon-Mann-Whitney, W = 3552, p-value = 0.73, N = 169).

Furthermore, the abundance of ingested MP per station was neither correlated between species (S = 1165, p-value = 0.09, Rho = -0.43, N = 17) nor between species and water column (sardine: S = 484.18, p-value = 0.83, Rho = -0.06; anchovy: S = 550.17, p-value = 0.47, Rho = -0.21; N = 14).

The main polymer types encountered in water column were polyethylene terephthalate (PET; 61%; Table 2) followed by polyamide (PA; 31%), polyvinyl chloride (PVC; 5%), polypropylene (PP; 2%) and polyacrylonitrile (PAN; 2%). In sardines' digestive tracts, 4 types of polymers were detected which first consisted in PET (71%), then polyethylene (PE; 18%), PA (6%) and PP (6%) while in anchovies only 2 kinds of polymers were uncovered and chemically identified: 89% of them being PET and 11% PE (Table 2). Polymer proportions were similar between water and sardine samples (χ² = 20.417, p-value = 0.67, N = 14), water samples and anchovy (χ²= 15.225, p-value = 0.51, N = 14) and between species (χ²= 5.1, p-value = 0.75, N = 17). MP from water column were mostly light coloured (51%) as in sardines' (44%) and anchovies' (59%) digestive tracts (Table 1). Proportions of recorded colours between water column and fish samples and between species were similar (sardine-water: χ²= 29.75, p-value = 0.58; anchovywater: χ²= 19.542, p-value = 0.24, N = 14; sardine-anchovy: χ²= 4.4968, p-value = 0.81, N = 17).

MP spatial distribution

Sardines from the North-eastern part of the Gulf of Lions seemed to have ingested more MP than those caught on the South-western part of the Gulf (Figure 4). The greatest mean ingestion of MP by sardines was at North-East station 26 (1 ± 2.24 MP.ind -1 with one individual presenting up to 5 MP) while fish from several Western stations did not ingest any MP. The number of MP in sardines' digestive tracts was correlated with longitude (S = 76501, p-value = 0.02, rho = 0.25, N = 85). According to regression tree method, combined effects of longitude and distance to the shoreline described three groups. The first one gathered two stations in the Eastern part of the Gulf, located at less than 13.74 Km from the coastline, where ingestion was maximal (mean = 0.8 ± 1.6 MP.ind -1 ). The second group was made up by two Eastern stations located at longitudes superior to 4.389 and at more than 13.74 Km from the coastline, where ingestion was twice higher than the average (mean = 0.4 ± 0.70 MP.ind -1 ). The last group was formed by stations at longitude lower than 4.389, where ingestion was minimal (mean = 0.08 ± 0.32 MP.ind -1 ). Still, there was no direct linear correlation between the number of MP ingested and latitude (S = 85278, p-value = 0.12, rho = 0.17, N = 85), distance from the shoreline (S = 111090, p-value = 0.44, rho = -0.08) or depth (S = 107300, p-value = 0.66; rho = -0.04).

On the contrary, ingestion of MP by anchovies seemed to be lower in North-eastern stations (Figure 4). Maximal ingestion was reported at stations 10 and 28 (0.4 ± 0.52 MP.ind -1 ). Spatial distribution of MP from water column samples was also heterogeneous (Figure 4).

Abundance of ingested MP

Minimal concentration occurred at coastal station 10 (0 MP.m -3 ), located at the North Western part of the Gulf of Lions, while maximal concentration was observed at station 49 (0.7 MP.m -3 ), which is more offshore and situated at the Eastern part of the studied area. Relying on the explanatory variables available, no spatial distribution pattern was indicated by the regression tree method. In addition, no correlation was shown between the concentration of MP and longitude (S = 416, pvalue = 0.77, rho = 0.08, N = 14), latitude (S = 508, p-value = 0.69, rho = -0.11), distance to the coast (S = 327.86, p-value = 0.33, rho = 0.28) or depth (S = 248.96, p-value = 0.10, rho = 0.45).

Discussion

The Mediterranean Sea is prone to several anthropic pressures that could generate marine plastic pollution such as mass tourism, important density of coastal populations, fisheries activities or sea transports. Debris smaller than 5 mm were indeed found in all water column samples and in almost every fish digestive tract in relatively high abundance. Anthropogenic particles may thus be a considerable contaminant in the studied environment and could be frequently encountered by the local fauna. Debris' size and colour found in water column samples and digestive tracts of both species were almost identical (Fig. 2), suggesting that small pelagic fish could be good indicators of environmental conditions.

However, the presence of debris is not synonymous with microplastics occurrence.

Indeed, characterisation of these particles by FTIR indicated that most identifiable debris were not MP [START_REF] Remy | When Microplastic Is Not Plastic: The Ingestion of Artificial Cellulose Fibers by Macrofauna Living in Seagrass Macrophytodetritus[END_REF]. In this study, the contribution of MP to the sorted debris (i.e. percentage of MP among all debris) represents even smaller percentages than what has been observed before in fish digestive tracts (1.5 and 2.3% in this study vs. 7.7%;Zhao et al., 2016 and 29.2%;[START_REF] Obbard | Global warming releases microplastic legacy frozen in Arctic Sea ice: OBBARD ET AL[END_REF] or in the water (7.7% vs. 16.7% in the Arctic Ocean; [START_REF] Amélineau | Microplastic pollution in the Greenland Sea: Background levels and selective contamination of planktivorous diving seabirds[END_REF]. These low contributions underline the importance of polymer determination to avoid MP overestimation after visual sorting despite strict guidelines. Nevertheless, spectral analysis is not yet systematically performed due to time issues and budgetary constraints, impairing the possibility to compare studies and to run meta-analyses.

Most of the debris and absolutely all MP isolated in this study were observed under the shape of fibres, confirming that fibre shape is highly present (Barrow et al., 2018) and likely ubiquitous in marine systems [START_REF] Claessens | Occurrence and distribution of microplastics in marine sediments along the Belgian coast[END_REF][START_REF] Kanhai | Microplastic abundance, distribution and composition along a latitudinal gradient in the Atlantic Ocean[END_REF]. Across the world, fibres

were already found at very high rates in seawaters [START_REF] Lusher | Microplastic pollution in the Northeast Atlantic Ocean: Validated and opportunistic sampling[END_REF][START_REF] Barrows | Marine environment microfiber contamination: Global patterns and the diversity of microparticle origins[END_REF], and in fish digestive tracts [START_REF] Lusher | Occurrence of microplastics in the gastrointestinal tract of pelagic and demersal fish from the English Channel[END_REF][START_REF] Nadal | High levels of microplastic ingestion by the semipelagic fish bogue Boops boops (L.) around the Balearic Islands[END_REF][START_REF] Murphy | The uptake of macroplastic & microplastic by demersal & pelagic fish in the Northeast Atlantic around Scotland[END_REF][START_REF] Pazos | Microplastics in gut contents of coastal freshwater fish from Río de la Plata estuary[END_REF][START_REF] Peters | Foraging preferences influence microplastic ingestion by six marine fish species from the Texas Gulf Coast[END_REF][START_REF] Vendel | Widespread microplastic ingestion by fish assemblages in tropical estuaries subjected to anthropogenic pressures[END_REF]. Nonetheless, fibres are not systematically considered as MP and are sometimes excluded from datasets as they may come from air contamination [START_REF] Dris | Synthetic fibers in atmospheric fallout: A source of microplastics in the environment?[END_REF]. Our results highlight the need for a particular attention to fibre shaped MP due to their ubiquity in aquatic environments and recurrent ingestion.

In the Mediterranean Sea, 90% of the stations sampled at the surface layer of the North Western part presented MP [START_REF] Collignon | Neustonic microplastic and zooplankton in the North Western Mediterranean Sea[END_REF]; 81% in the Central Western part of the sea, [START_REF] Panti | Occurrence, relative abundance and spatial distribution of microplastics and zooplankton NW of Sardinia in the Pelagos Sanctuary Protected Area, Mediterranean Sea[END_REF] and 100% in the Eastern Mediterranean waters [START_REF] Van Der Hal | Exceptionally high abundances of microplastics in the oligotrophic Israeli Mediterranean coastal waters[END_REF]. This is in accordance with our study that also displays a high occurrence of MP in water column samples suggesting that MP are spread all around the Gulf of Lions.

Despite such a broad occurrence, MP concentration seems to vary very importantly across regions, ranging from 0.021 ± 0.015 MP.m -3 along the Portuguese coasts [START_REF] Frias | Evidence of microplastics in samples of zooplankton from Portuguese coastal waters[END_REF] to 7.68 ± 2.38 MP.m -3 in the Israeli Mediterranean surface water [START_REF] Van Der Hal | Exceptionally high abundances of microplastics in the oligotrophic Israeli Mediterranean coastal waters[END_REF], although polymer identification was not performed in the last study and concentrations may thus be overestimated to a certain extent. Such high differences across the world could be explained by (i) differences in methodology to identify MP (e.g. polymer analysis or not), (ii) surface waters sampling versus integration of the entire water column, (iii) oceanographic processes such as local currents or winds, and (iv) socio-geographical factors such as coastal geography, coastal population, and distance from plastic source input [START_REF] Barnes | Accumulation and fragmentation of plastic debris in global environments[END_REF]. Focusing on studies which performed Our results thus indicate that the concentration of MP could be as important in the water column as in the surface layer [START_REF] De Lucia | Amount and distribution of neustonic micro-plastic off the western Sardinian coast (Central-Western Mediterranean Sea)[END_REF][START_REF] Baini | Abundance and characterization of microplastics in the coastal waters of Tuscany (Italy): The application of the MSFD monitoring protocol in the Mediterranean Sea[END_REF]. This reinforces previous work, which showed that MP could be present in the entire water column and that maximal concentration could be found below the surface (between 30 and 60 m during summer in the Baltic Sea, [START_REF] Gorokhova | Screening for microplastic particles in plankton samples: How to integrate marine litter assessment into existing monitoring programs?[END_REF]. Knowledge about MP in the water column is still scarce and more data are needed to have a better understanding on the vertical distribution of MP, the factors influencing it and on describing interactions with pelagic organisms. In particular, physical and hydrodynamic features could affect vertical distribution such as thermo/halocline, with the combined effect of biofouling [START_REF] Lobelle | Early microbial biofilm formation on marine plastic debris[END_REF] or ingestion [START_REF] Cole | Microplastic ingestion by zooplankton[END_REF]. Further, polymer types have different density [START_REF] Hidalgo-Ruz | Microplastics in the Marine Environment: A Review of the Methods Used for Identification and Quantification[END_REF] and thus should be distributed at different depths in the water column. At sea surface, polymers with low density such as PE and PP are commonly characterised [START_REF] Frias | Evidence of microplastics in samples of zooplankton from Portuguese coastal waters[END_REF][START_REF] Enders | Abundance, size and polymer composition of marine microplastics ≥ 10 μm in the Atlantic Ocean and their modelled vertical distribution[END_REF][START_REF] Suaria | The Mediterranean Plastic Soup: synthetic polymers in Mediterranean surface waters[END_REF][START_REF] Ory | Amberstripe scad Decapterus muroadsi (Carangidae) fish ingest blue microplastics resembling their copepod prey along the coast of Rapa Nui (Easter Island) in the South Pacific subtropical gyre[END_REF]. Here, PP and PE (use in packaging) contributions were low probably due to the small water volume collected at sea surface by the vertical plankton tow. On the contrary, polymers like PET and PVC have higher densities [START_REF] Morét-Ferguson | The size, mass, and composition of plastic debris in the western North Atlantic Ocean[END_REF] and are generally less recovered at the surface. In our study, PET, a polymer commonly used for soft drink bottles, was largely dominant in the water column samples, which is consistent with the sampling method (vertical tows). Similarly, PA was the second most abundant polymer found in our study, which may result from the important fisheries activities in this area and its high density [START_REF] Bjordal | The use of technical measures in responsible fisheries: regulation of fishing gear[END_REF].

Finally, in our study, the highest MP concentrations were found in the eastern part of the Gulf, in accordance with the high concentration of plastic predicted by a recent model in this area [START_REF] Liubartseva | Tracking plastics in the Mediterranean: 2D Lagrangian model[END_REF]. Nonetheless, no general spatial pattern was discerned in our results and none of the studied parameters (longitude, latitude, depth, distance to the coast) seemed to drive the spatial distribution of MP in the water column of the Gulf of Lions. In the literature, different and even opposite relationships have been found between MP concentration in the sea and geographical or physical parameters. For instance, MP concentration could either decrease with increasing distance to the coast [START_REF] Desforges | Widespread distribution of microplastics in subsurface seawater in the NE Pacific Ocean[END_REF][START_REF] Panti | Occurrence, relative abundance and spatial distribution of microplastics and zooplankton NW of Sardinia in the Pelagos Sanctuary Protected Area, Mediterranean Sea[END_REF], or remain the same [START_REF] De Lucia | Amount and distribution of neustonic micro-plastic off the western Sardinian coast (Central-Western Mediterranean Sea)[END_REF][START_REF] Baini | Abundance and characterization of microplastics in the coastal waters of Tuscany (Italy): The application of the MSFD monitoring protocol in the Mediterranean Sea[END_REF][START_REF] Gorokhova | Screening for microplastic particles in plankton samples: How to integrate marine litter assessment into existing monitoring programs?[END_REF]. In the Gulf of Lions, the absence of clearly defined spatial pattern could be due to several parameters such as the complex water circulation forming small eddies inside the Gulf (http://marc.ifremer.fr/resultats/courants/modele_mars3d_mediterranee, last access : 10/05/2018), other currents such as the Ligurian Current [START_REF] Ourmieres | The boundary current role on the transport and stranding of floating marine litter: The French Riviera case[END_REF], recurrent strong winds arising in summer [START_REF] Millot | Circulation in the western Mediterranean Sea[END_REF] or storm events [START_REF] Collignon | Neustonic microplastic and zooplankton in the North Western Mediterranean Sea[END_REF].

Despite being present in all but one water sample, microplastics were recovered in only one out of eight or nine fish on average, resulting in a relatively low average concentration of MP in digestive tracts for both species. Such an intermediate level of ingestion is in agreement with a recent similar study (same methods, season and year) in a neighbouring area [START_REF] Compa | Ingestion of microplastics and natural fibres in Sardina pilchardus (Walbaum, 1792) and Engraulis encrasicolus (Linnaeus, 1758) along the Spanish Mediterranean coast[END_REF].

In the North Sea, even lower occurrence of MP were described in fish digestive tracts (0.25% and 2.60%; [START_REF] Foekema | Plastic in North Sea fish[END_REF][START_REF] Hermsen | Detection of low numbers of microplastics in North Sea fish using strict quality assurance criteria[END_REF], while higher occurrences have been found in the Portuguese coast (19.80%; [START_REF] Neves | Ingestion of microplastics by commercial fish off the Portuguese coast[END_REF], the Balearic Islands (27.30%; [START_REF] Alomar | Microplastic ingestion by Mullus surmuletus Linnaeus, 1758 fish and its potential for causing oxidative stress[END_REF] and in Tokyo bay (77%; [START_REF] Tanaka | Microplastic fragments and microbeads in digestive tracts of planktivorous fish from urban coastal waters[END_REF]. This variation in ingestion might of course appear between fish species due to differences in their ecology, spatial distribution and feeding behaviour. Here, both species ingested comparable abundance of MP from similar polymer type and colours, suggesting that their feeding behaviour might be similar and that they are representative of MP occurring in their environment.

Further, previous studies suggested that a single species could also display different levels of MP ingestion (from 0.20 to 2.4 MP.ind -1 for sardines and 0.11 to 0.85 MP.ind -1 for anchovies; see Table 3). Methodological differences could explain part of this variation. Indeed, sample sizes varied between 7 and 105 organisms in these studies and one of these studies considered MP until 10 mm rather than 5 mm. Nevertheless, the heterogeneity of MP concentrations ingested by fish, shown in Table 3, could be due to the to the magnitude of pollution of surrounding waters that probably plays an important part in ingestion. For instance, Japanese anchovies from the heavy polluted area of Tokyo bay displayed the highest ingestion observed (2.3 ± 2.5 MP.ind -1 ; [START_REF] Tanaka | Microplastic fragments and microbeads in digestive tracts of planktivorous fish from urban coastal waters[END_REF]. Looking at a more local scale, no correlation was highlighted between the concentration of MP in fish digestive tracts and in the water column or any of the spatial parameters investigated in our study or in [START_REF] Compa | Ingestion of microplastics and natural fibres in Sardina pilchardus (Walbaum, 1792) and Engraulis encrasicolus (Linnaeus, 1758) along the Spanish Mediterranean coast[END_REF]. Small pelagic fish are constantly moving and can be distributed all around the Gulf of Lions [START_REF] Saraux | Spatial Structure and Distribution of Small Pelagic Fish in the Northwestern Mediterranean Sea[END_REF], so they potentially did not ingest MP at the site they were collected, making correlations harder to underline. Nonetheless, according to the regression tree, longitude and distance to the coast might have an effect on MP ingestion in sardines. Indeed, the two groups presenting the highest MP ingestion were the closest to the Rhone river mouth and therefore to a plastic input source, although the small number of stations in this area prevents conclusive results.

Besides spatial distribution, MP ingestion should also be affected by fish vertical distribution. While small pelagic fish can use the entire water column, they usually stay relatively low in the water column in summer (all trawls used in this study were close to the bottom). As such, pelagic fish may come in contact more frequently with denser polymers than floating MP. This might explain why PET was the most ingested polymer type in this study and others [START_REF] Alomar | Microplastic ingestion by Mullus surmuletus Linnaeus, 1758 fish and its potential for causing oxidative stress[END_REF][START_REF] Compa | Ingestion of microplastics and natural fibres in Sardina pilchardus (Walbaum, 1792) and Engraulis encrasicolus (Linnaeus, 1758) along the Spanish Mediterranean coast[END_REF]. Here, as in [START_REF] Compa | Ingestion of microplastics and natural fibres in Sardina pilchardus (Walbaum, 1792) and Engraulis encrasicolus (Linnaeus, 1758) along the Spanish Mediterranean coast[END_REF]Rummel's et al. (2016), PE was the second MP type occurring in fish gut despite its low density, suggesting that other phenomena might modify their vertical distribution or attractiveness. Actually, polymers could be colonised by microorganisms and biofouling may increase MP density and mass, thus enhancing their bioavailability for pelagic fish [START_REF] Morét-Ferguson | The size, mass, and composition of plastic debris in the western North Atlantic Ocean[END_REF]. Moreover, this biological activity could also lead to a dimethylsufide signature (DMS) acquirement (e.g. for PE and PP; [START_REF] Savoca | Marine plastic debris emits a keystone infochemical for olfactory foraging seabirds[END_REF]. The smell emitted by DMS might play a role in trophic interactions by signalling prey availability as shown for procellariform seabirds [START_REF] Savoca | Marine plastic debris emits a keystone infochemical for olfactory foraging seabirds[END_REF] and suggested for fish [START_REF] Savoca | Odours from marine plastic debris induce food search behaviours in a forage fish[END_REF]. Once ingested, harmful effects of MP on fish are unclear. Laboratory experiments indicate that predatory performance could be affected [START_REF] De Sá | Effects of microplastics on juveniles of the common goby (Pomatoschistus microps): Confusion with prey, reduction of the predatory performance and efficiency, and possible influence of developmental conditions[END_REF], detoxification system induced [START_REF] Alomar | Microplastic ingestion by Mullus surmuletus Linnaeus, 1758 fish and its potential for causing oxidative stress[END_REF] and even that neurotoxic effects could appear (Oliveira et al., 2017). Some studies used body condition to estimate the state of health of wild caught fish. For instance, omnivore fish can show lower body conditions when displaying high abundance of MP ingested [START_REF] Mizraji | Is the feeding type related with the content of microplastics in intertidal fish gut?[END_REF]. [START_REF] Compa | Ingestion of microplastics and natural fibres in Sardina pilchardus (Walbaum, 1792) and Engraulis encrasicolus (Linnaeus, 1758) along the Spanish Mediterranean coast[END_REF] also revealed that sardines with lowest body condition (F) ingested more anthropogenic particles whereas no relationship was described for anchovies. Here, regardless of the body condition index used (K and F), ingestion of MP was not related to the body condition of any of the two studied species as described in North Sea fish [START_REF] Foekema | Plastic in North Sea fish[END_REF]. In the Gulf of Lions, sardine and anchovy have been smaller and thinner for a decade [START_REF] Van Beveren | Rapid changes in growth, condition, size and age of small pelagic fish in the Mediterranean[END_REF]. Here, our results point out that MP ingestion is not responsible for this issue and does not even appear to work in synergy. The main hypothesis for these changes thus remains a shift in plankton community affecting these species' diet [START_REF] Brosset | Condition corporelle et conséquences sur la plasticité des traits d'histoire de vie chez les petits pélagiques de Méditerranée[END_REF][START_REF] Saraux | Small pelagic fish dynamics: A review of mechanisms in the Gulf of Lions[END_REF].

Overall, the average MP concentration recorded in the water column was lower than in accumulation zones but it was comparable with concentrations assessed in the Mediterranean Sea (sea surface and water column) and small pelagic populations are not ingesting high concentration of MP. Further, we showed that in order to monitor MP in seawater and in organisms as advised by the MSFD framework, standardised methods for sampling, extracting and identifying MP need to be developed.

With several questions still being unresolved, it is clear that not only the scientific community is concerned. All stakeholders, such as legislators, manufacturers and citizens must think about using plastics in a more environmentally responsible way. An easy concept, named the "5R", can summarise actions that are possible to take: Reduce, Reuse, Recycle, Redesign, Recover [START_REF] Thompson | Plastics, the environment and human health: current consensus and future trends[END_REF].

List of figures

List of tables

Table 1: Contribution of MP within the sorted debris (%), total number of MP determined, occurrence of MP in total samples (%), concentration of MP in water column (MP.m -3 ) and fish samples (MP.ind -1 ) with standard deviation, contribution of each type of colours (%).

Table 2: Contribution of polymer type for each sample: polyethylene terephtalate (PET), polyamide (PA), polyethylene (PE), polyacrylonitrile (PAN), polyvinyl chloride (PVC), polypropylene (PP).

Table 3: Synthesis of recorded microplastics ingestion by pelagic fish validated by polymer analysis: species, number of individuals studied, area of interest, concentration of MP in fish, occurrence of MP, authors.

  was not correlated to longitude (S = 120710, p-value = 0.10, rho = -0.18, N = 84), latitude (S = 104740, p-value = 0.79, rho = -0.03), distance to the coast (S = 106330, p-value = 0.72, rho = -0.04) or depth (S = 104740, p-value = 0.83, rho = -0.01). No spatial pattern was clearly determined with the regression tree and mean ingestion was 0.11 ± 0.31 MP.ind -1 .

  FTIR identification, MP concentrations varied between 0.021 ± 0.015 MP.m -3 in Portugal (seasurface and 25 m depth samples combined;Frias et al., 2014) and 3.74 ± 10.4 MP.m -3 in sea surface waters that surround Japan[START_REF] Isobe | East Asian seas: A hot spot of pelagic microplastics[END_REF]. In comparison, MP concentration observed in our study was low to intermediate (0.23 ± 0.20 MP.m -3 ), a result similar to the only study conducted in the Mediterranean Sea which integrated the water column and used FTIR analysis (0.22 ± 0.57 MP.m -3 in the North Tyrrhenian sea in spring;[START_REF] Baini | Abundance and characterization of microplastics in the coastal waters of Tuscany (Italy): The application of the MSFD monitoring protocol in the Mediterranean Sea[END_REF] as well as other studies which have sampled only the surface waters in Sardinia (0.17 ± 0.3 MP.m -3 using WP2 plankton net;Panti et al., 2015 and 0.15 MP.m -3 using Manta trawl; de Lucia et al., 2014).

Figure 1 :

 1 Figure 1: Location of sampling stations (numbers) and the relative biomass of collected fish species: Sardina pilchardus (green), Engraulis encrasicolus (red) and other species (purple).

Figure 2 :

 2 Figure2: Back to back histograms of debris size classes found either in the water column (in blue), in the digestive tract of sardine (in green) and anchovy (in red). The difference in size frequency between samples is shown with the black lines, while the overlap percentage and mean size ± SD are indicated on each graph.

Figure 3 :

 3 Figure 3: Le Cren body condition index and length of fish which did not ingest any MP (Without MP) and fish that did (With MP).

Figure 4 :

 4 Figure 4: Spatial distribution and concentration of MP in water column (MP.m -3 ; black circle) and in digestive tracts (MP.ind -1 ) of anchovy (red barplot) and sardine (green barplot).

Figure 1

 1 Figure 1

  Figure 2 504

  Figure 4 508

Table 1 MP

 1

			Total	Occurrence of	Concentration		Colours
		contribution (%)	number of MP determined	MP in total samples (%)	of MP (MP.m -3 ) (MP.ind -1 )	(%) Light Blue Dark Other
	Water column	7.7	61	93	0.23 ± 0.20	51	18	29	2
	S. pilchardus	2.3	17	12	0.20 ± 0.69	59	12	12	17
	E. encrasicolus	1.5	9	11	0.11 ± 0.31	45	22	22	11

*Data corresponding to anthropogenic particles (microplastics and textile fibres not distinguished)

Acknowledgement

The authors thank the captain, the crew and the scientific team of the RV "L'Europe" who made the sampling possible during PELMED surveys (doi: 10.18142/19). PELMED surveys are co-funded by Europe through the Data Collection Framework.

We thank Gilbert Dutto for the use of the camera and binocular at the Palavas-les-flots station of IFREMER. We are grateful to the Institut Universitaire Technologique de Chimie of Sète by means of Michel Granier and Olivier Heitz for use of the FTIR spectroscope. We appreciate the help of Elisa Fabregue, Jose-Manuel Izquierdo Avalos and Henri Desintebin in this study. We also acknowledge Jeffrey Roth from Auburn University for the proofreading and edition of the English.

Sampling was done during the 2015 PELMED survey (https://doi.org/10.18142/19) and was cofunded by Europe through the Data Collection Framework. Part of the work was also funded through the FEAMP project MONALISA, which was co-funded by Europe, the French Ministery of Agriculture and France Filière Pêche. Preference for colour Online version only Declarations of interest: none


Clément Ganino
email: ganino@unice.fr

Guy Libourel

Alain Bernard

Fumarolic incrustations at Kudryavy volcano (Kamchatka) as a guideline for high-temperature (>850 °C) extinct hydrothermal systems

diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Fumaroles, emission of magmatic gases in volcanic environments, have been studied for years with the contrasted objectives (i) to link the chemical composition of the gas with intrusion of magma and to monitor eruptive activity, and (ii) to understand how they leach and carry useful elements that are concentrated in economic minerals. The Kudryavy volcano in the Kurile Islands (Russia) provides a unique natural laboratory to study the formation of fumarolic rocks from high temperature (up to 940°C; [START_REF] Taran | Geochemistry of magmatic gases from Kudryavy volcano, Iturup, Kuril Islands[END_REF]) fluids within a passively degassing volcano. The fumarolic activity of this volcano (e.g. [START_REF] Vlasov | Volcanic Sulfur Ore Deposits and Some Problems of Hydrothermal Ore Formation[END_REF]) is now well constrained, the host-rock being a basaltic andesite (e.g. [START_REF] Taran | Geochemistry of magmatic gases from Kudryavy volcano, Iturup, Kuril Islands[END_REF] and the temperature and elemental and isotopic composition of major gas species having been determined [START_REF] Botcharnikov | Hydrogen isotope geochemistry and heat balance of a fumarolic system: Kudriavy volcano, Kuriles[END_REF][START_REF] Fischer | Fluxes and sources of volatiles discharged from kudryavy, a subduction zone volcano, Kurile Islands[END_REF][START_REF] Taran | Geochemistry of magmatic gases from Kudryavy volcano, Iturup, Kuril Islands[END_REF]. The fumarolic rocks (i.e. rocks altered by the fumarolic activity) of the Kudryavy volcano were particularly characterized because they contain an Re-enrichment [START_REF] Korzhinsky | Discovery of a pure rhenium mineral at Kudriavy volcano[END_REF]. Diverse rare-metal mineralization and high HSE abundances are observed in the fluid and sublimates. The source of the rare-metal mineralization was demonstrated to be the magmatic melt using isotopic Pb and Sm-Nd studies [START_REF] Yudovskaya | Behavior of highly-siderophile elements during magma degassing: A case study at the Kudryavy volcano[END_REF].

The formation of fumarolic rocks is the subtle result of condensation, dissolution and reprecipitation processes. The minerals formed by the condensation are called sublimates whereas the minerals formed by the interactions between the gas phase and the wall rock constitutes the incrustations. The main incrustations of Kudryavy rocks occur as layered filled cavities [START_REF] Africano | High Temperature volcanic gas geochemistry (major and minor elements) at Kudryavy volcano, Iturup Island, Kuril arc, Russia[END_REF] as veins or isolated patches in the rock matrix. Various anhydrous sulfates, Ti-oxide, pyrite and andradite are described in fumaroles with lower temperatures (300-500°C) whereas in addition to the sulfates and andradite, also magnetite, hematite, ilmenite, hercynite, cristobalite, diopside, hedenbergite, sanidine and wollastonite are described in fumaroles with higher temperatures (600-850°C). [START_REF] Africano | High Temperature volcanic gas geochemistry (major and minor elements) at Kudryavy volcano, Iturup Island, Kuril arc, Russia[END_REF] computed thermochemical calculations using the program GASWORKS [START_REF] Symonds | Calculation of multicomponent chemical equilibria in gas-solidliquid systems: calculation methods, thermochemical data, and applications to studies of hightemperature volcanic gases with examples from Mount St[END_REF] to constrain the assemblages produced by the cooling of the high temperature gases and by the gas-rock interaction. They concluded that the leaching of Si, Ca, Mg, Al, Ti and Fe from the wall rock is significant in the formation of silicates in fumaroles. Our shared objective is to understand the formation of incrustations. With this aim, we focused on the assemblages of silicates formed in the fumarolic incrustation of the highest temperature field. Using petrographic observation and a simple thermodynamic modeling, we investigated the characteristics of such low-pressure high-temperature modification of magmatic rocks. Excluding the low-temperature sulfates and focusing on Ca-Fe -rich and Na-Al -rich silicates, we looked for evidences of high temperature in the assemblages and mineral compositions.

Geological setting

The Kudryavy volcano consists of a small cone (996 m elevation) located in the northern end of Iturup island in the south of the Kurile volcanic arc. The last large eruption occurred in 1883 and produced basaltic andesite flows [START_REF] Gorshkov | Volcanism and Upper mantle. Investigation in Kurile Island Arc System[END_REF] but small-scale phreatic eruption occurred more recently in 1999 [START_REF] Korzhinsky | Decade-long study of degassing at Kudriavy volcano, Iturup, Kurile Islands (1990-1999): Gas temperature and composition variations, and occurrence of 1999 phreatic eruption[END_REF]. The Kudryavy basaltic andesite flows are composed of rare olivine, orthopyroxene (hyperstene), clinopyroxene (augite), plagioclase (labradorite to bytownite), and titanomagnetite [START_REF] Africano | Reactive processes during the discharge of high temperature volcanic gases[END_REF] and its chemical composition is typical of the calc-alcaline serie (SiO2=54.52 wt% ; Al2O3 = 17.96 wt% ; Fe2O3 = 3.22 wt% ; FeO = 6.18wt% ; MnO = 0.18 wt% ; MgO = 4.00 wt% ; CaO 8.78 wt% ; Na2O = 2.76 wt% ; K2O = 0.57 wt% ; TiO2 = 0.88 wt% ; P2O5 = 0.13 wt% ; Loss On Ignition (LOI) = 0.44 wt% ; [START_REF] Ostapenko | Petrology of calderas of the Kurilian Islands: Medvezhya and Zavaritsky calderas[END_REF].

Kudryavy volcano is a place of great interest to study fumarolic activity because of the stability of the activity (at least 30 years) and because of the extreme temperatures recorded (up to 940°C) [START_REF] Korzhinsky | Discovery of a pure rhenium mineral at Kudriavy volcano[END_REF][START_REF] Taran | Geochemistry of magmatic gases from Kudryavy volcano, Iturup, Kuril Islands[END_REF]. The long term high temperature degassing is attributed to a steady-state degassing, with volatiles rising continuously from the zones of arc-magma generation at mantle-depth to the surface [START_REF] Fischer | Fluxes and sources of volatiles discharged from kudryavy, a subduction zone volcano, Kurile Islands[END_REF].

The chemical composition of the high temperature Kudryavy gases (T>700°C) is H2O/CO2 = 40 -70 [START_REF] Fischer | Fluxes and sources of volatiles discharged from kudryavy, a subduction zone volcano, Kurile Islands[END_REF][START_REF] Taran | Geochemistry of magmatic gases from Kudryavy volcano, Iturup, Kuril Islands[END_REF][START_REF] Wahrenberger | Some aspects of the chemistry of volcanic gases[END_REF], CO2/Stotal = 1 ± 0.3, Stotal/Cl = 4 ± 1 [START_REF] Fischer | Fluxes and sources of volatiles discharged from kudryavy, a subduction zone volcano, Kurile Islands[END_REF], fH2/fH2O = 10 -2.0 to 10 -2.5 corresponding to an oxygen fugacity between the fayalite-magnetite-quartz (FMQ) buffer and the nickel-nickel oxide (NNO) buffer [START_REF] Taran | Geochemistry of magmatic gases from Kudryavy volcano, Iturup, Kuril Islands[END_REF].

The relative abundances of N2, Ar and He are typical of arc-type volcanic gases [START_REF] Fischer | Fluxes and sources of volatiles discharged from kudryavy, a subduction zone volcano, Kurile Islands[END_REF].

The isotopic compositions are in the range of -4 to 8.9‰ for δ 18 O with a value of δ 18 O = 5 ± 1 ‰ [START_REF] Taran | Geochemistry of magmatic gases from Kudryavy volcano, Iturup, Kuril Islands[END_REF] and δD = -19 ± 3 ‰ [START_REF] Goff | Tritium and stable isotopes of magmatic waters[END_REF] in the highest temperature gas sampled (920°C).

Sublimates of Kudryavy fumaroles have been described by several authors [START_REF] Africano | Reactive processes during the discharge of high temperature volcanic gases[END_REF][START_REF] Bykova | Assemblages and conditions of mineral deposits from gases of Kudryavy volcano[END_REF][START_REF] Korzhinsky | Condensate composition and native metals in sublimates of high temperature gas streams of Kudryavy volcano, Iturup Island, Kuril Islands[END_REF][START_REF] Korzhinsky | Discovery of a pure rhenium mineral at Kudriavy volcano[END_REF][START_REF] Kovalenker | Indium mineralization of Kurile Island Arc[END_REF][START_REF] Magazina | Cd-bearing wurzite from fumarolic field of Kudryavy volcano (SEM data)[END_REF][START_REF] Wahrenberger | Some aspects of the chemistry of volcanic gases[END_REF]. The natural sublimates described in Kudryavy fumarolic rocks are formed by various minerals including, hematite, magnetite, molybdenite, greenockite, wurtzite, cannizzarite, cosalite, pyrite, halite, sylvite, rozenite, ilsemanite, tougarinovite, galena, tungstenite, thenardite and aphtitalite [START_REF] Africano | Reactive processes during the discharge of high temperature volcanic gases[END_REF].

The Kudryavy altered rocks present three main mineralogical assemblages of secondary phases related to the temperatures of the fumaroles at which they were collected. In high temperature assemblages (900 to 500°C) andradite (Ca3Fe2Si3O12), diopside (CaMgSi2O6), salite (Ca(Mg,Fe)Si2O6), hedenbergite (CaFeSi2O6), wollastonite (CaSiO3), sanidine (KAlSi3O8), albite (NaAlSi3O8), Fe oxides, hercynite (FeAl2O4), cristobalite and tridymite (SiO2) are documented [START_REF] Africano | High Temperature volcanic gas geochemistry (major and minor elements) at Kudryavy volcano, Iturup Island, Kuril arc, Russia[END_REF]. These minerals are observed in the incrustations of the natural samples but do not precipitate when sampling the gases in silica tubes, suggesting that their forming cations (Si, Ti, Mg, Al, Ca) were not carried by the gases but were mobilized from the wallrock [START_REF] Africano | High Temperature volcanic gas geochemistry (major and minor elements) at Kudryavy volcano, Iturup Island, Kuril arc, Russia[END_REF]. These minerals replace the primary minerals (pyroxene and plagioclase) in reaction to the remobilization of the rock-bearing cations. Medium temperature (500 to 300°C) assemblages are composed of anhydrite (CaSO4), Al and Fe sulfates, Ti oxide, cristobalite, tridymite, quartz and pyrite or hematite. Low temperatures (< 200°C) rocks are completely silicified.

Methods

Samples were provided by Alain Bernard (ULB, Belgium): three rock samples associated with the highest temperature fumarole (Fig. 1) were examined here (11, 15, and 21, see Fig. 2). They were collected in August 1995 near active fumaroles at temperatures up to ~900°C. The depth of rock sampling was 10 to 30 cm. For each sample we studied several polished sections oriented parallel to the depth profile (e.g. 11A, 11B, 11C for sample 11). Despite some small discrepancies in their mineralogical record (see next section), they were sampled at the same place.

We used a Scanning Electron Microscope (SEM) Philipps FEI XL30 ESEM LaB6 was equipped with a BRUKER Quantax 655 detector, operated at 20 kV and 200 nA beam current at CEMEF-Mines ParisTech in Sophia Antipolis (France). Energy-Dispersive X-ray spectroscopy (EDX) was used to determine the mineral assemblages. Mineral analyses (Table 1) were acquired using Field Emission Electron Probe Micro-Analyzer (EPMA) UH JEOL JXA-8500F operating at 20 kV accelerating voltage, a 50 nA beam current, and 1 µm-sized beam at HIGP, University of Hawai'i at Manoa. Fluorescence was calibrated to the K-lines of Mg in SC olivine (using a TAP crystal), Si in Rockport fayalite (TAP), Cr on magnesio-chromite (LiFH), Fe in fayalite (LiF), Mn in Verma garnet (LiF), and Ni in NiO (LiF).

Standardization was made for Fe and Si on Rockport fayalite (Fe1.9Mn0.1SiO4; USNM85276); Mg and Ni on SC olivine (Mg1.8-Fe0.2SiO4; NMNH111312); Mn on Verma garnet (Fe1.2Mn1.7Al2Si3O12), and Cr on magnesio-chromite (Mg0.7Fe0.4Cr1.6Al0.4O4; NMNH117075), with counting times on peak (and each background) as follows: 90 s (45 s) for Mg, Cr, and Si, 30 s (15 s) for Ni and Mn, and 20 s (10 s) for Fe.

The background fitted to the trace elements magnesium and chromium was an exponential function defined by Probe for EPMA v.929. ZAF matrix corrections [START_REF] Armstrong | Quantitative analysis of silicates and oxide minerals: comparison of Monte-Carlo, ZAF and Phi-Rho-Z procedures[END_REF] were applied. The detection limits were 0.02 wt% for FeO and 0.01 wt% for all other oxides. Thermodynamic analyses and equilibrium phase assemblage diagrams were computed using the Domino program from the Theriak-Domino software [START_REF] De Capitani | The computation of equilibrium assemblage diagrams with Theriak/Domino software[END_REF] and the internally consistent thermodynamic data sets from Holland and Powell (2011) extended with kirschsteinite properties (as explained in [START_REF] Ganino | Reduced and unstratified crust in CV chondrite parent body[END_REF]. In such modeling, the calculated stable mineral assemblage is a combined function of the selected bulk chemical composition (X) of a given volume and the prevailing conditions (P, T) during crystallization.

Results

Petrography of the host-rock and of the incrustations

The fumaroles are located in basaltic andesite flows with a porphyritic-aphanitic texture (Fig. 2) and composed of phenocrystals of olivine (Fo78), orthopyroxene (hyperstene), clinopyroxene (augite), plagioclase (ranging from labradorite to bytownite) and titanomagnetite. The aphanitic groundmass displays a similar primary mineralogy. Our survey of fumarolic rocks confirm [START_REF] Africano | Reactive processes during the discharge of high temperature volcanic gases[END_REF]) that secondary minerals occur as incrustations in pores and alteration veins of primary pyroxenes and plagioclase.

In sample 11 (section 11C shown in Fig. 3), an altered clinopyroxene hosts a pore, probably resulting from aciding leaching (Fig. 3a), that contains euhedral andradite (Ca3Fe2Si3O12). Andradite displays a pronounced oscillatory zoning associated with varying grossular content or Al/Fe ratio (Fig 3b). Veins of Ca-Fe-Mg -rich minerals (hedenbergite CaFeSi2O6, diopside CaMgSi2O6) are also present within the K-Feldspars (Fig. 3c). Larger pores show a zonation at their peripheries (Fig. 3d), including hercynite associated to davyne ((Na,K)6Ca2Si6Al6O24SO4Cl2), albite (NaAlSi3O8), sodalite (Na8Al6Si6O24Cl2), nepheline ((Na,K)AlSiO4) assemblages (Fig. 3e and3f). Area exhibiting the shape of nearly euhedral porphyric primary pyroxene now totally replaced by hedenbergite are cross-cutted by veins of sodalite and K-feldspar (Fig. 3g and3h). The two main types of secondary silicates (Ca-Fe-rich and Na-Al-rich) are frequently observed in association (Fig. 3i). Gypsum (Fig. 3j, 3k and3l) is also present enclosing euhedral andradite or hedenbergite.

Sample 21 (section 21B shown in Fig. 4) displays very similar pattern and assemblage with altered porphyric primary minerals (Fig. 4a). Here pores are incrusted from the periphery to the center with anorthite-hedenbergite-andradite (Fig. 4b,4c,4d 4e,4f,4g). Albite is the unique Na-Al -rich silicate we observed. Magnetite, wollastonite and hercynite are also present, with wollastonite being frequently associated with andradite and magnetite (Fig. 4c, 4g and4i).

Secondary phases in sample 15 (section 15C shown in Fig. 5) are hedenbergite (Fig. 5a), andradite (Fig. 5d), quartz (or other SiO2 minerals; Fig. 5b), and nearly euhedral magnetite (Fig. 5c and5e) in some places covered with hercynite (Fig. 5f).

Mineral composition

In addition to SEM-EDX identification, the compositions of the secondary phases were analyzed using Field Emission Electron Probe Micro-Analyzer and reported in Table 1. Within the secondary phases, we confirm the observation from [START_REF] Africano | High Temperature volcanic gas geochemistry (major and minor elements) at Kudryavy volcano, Iturup Island, Kuril arc, Russia[END_REF] that the secondary pyroxene are present with very contrasted compositions. They consist generally in salite (pyroxene with various Ca-Fe-Mg contents) but some compositions are close to the end-member diopside (Mg0.96Ca0.96Fe0.08Si2O6), hedenbergite (Mg0.02Ca0.98Fe1Si2O6) and wollastonite (Ca0.98Fe0.02SiO3).

The chemical composition of wollastonite varies from nearly pure wollastonite to iron-rich wollastonite (Ca0.82-0.79Fe0.18-0.21SiO3). There is a large gap between the composition of the hedenbergite and the iron-rich wollastonite. Contrary to the large diversity in pyroxenes composition, garnets are present only as andradite. As already shown by [START_REF] Africano | Reactive processes during the discharge of high temperature volcanic gases[END_REF], the oscillatory zoning in andradite (Fig. 3b) is linked to the Al/Fe ratio, with composition varying from Gr69.8 (light gray in Back Scattered Electron (BSE) Image) to Gr61.2 (darker gray). Although not characterized with EPMA, we used EDX-SEM to analyze the composition of nepheline, sodalite and davyne (Table 2).

Discussion

Formation of secondary minerals in fumarolic rocks interpreted as a metamorphic process

The formation of secondary phases is clearly a complex process involving the diverse interactions between the ascending fumarolic gases and the wallrock. Condensation, sublimation, dissolution and precipitation may play a role as well, resulting in the observed textures. The composition of the volcanic vapor was determined [START_REF] Taran | Geochemistry of magmatic gases from Kudryavy volcano, Iturup, Kuril Islands[END_REF] and it has been shown that the elements necessary for the formation of the secondary phases are mobilized in-situ from the altered minerals [START_REF] Africano | Reactive processes during the discharge of high temperature volcanic gases[END_REF]. Following this idea, we attribute the formation of Ca-Fe silicates to various reactions involving the wallrock "primary" mineralogy. With this scenario, we developed a simplistic modeling using Gibbs energy minimization to calculate the stable mineral assemblages. Stability can be expected in such a system characterized by high temperature and the presence of an activating fluid phase.

Secondary high-temperature minerals assemblages and composition and implications on the forming process

Andradite and hederbergite assemblages

Mineral assemblages of the altered rocks collected at the Kudryavy high temperature fumaroles are characterized by the presence of andradite. This mineral was already described in the literature (e.g. [START_REF] Africano | High Temperature volcanic gas geochemistry (major and minor elements) at Kudryavy volcano, Iturup Island, Kuril arc, Russia[END_REF], and we confirm here its presence in all our samples. Andradite typically occurs in skarns [START_REF] Murad | Zoned, birefrengent garnets from Thera Island, Santorini Group (Agean Sea)[END_REF][START_REF] Zharikov | Experimental modelling of wall-rock metasomatism[END_REF] and is associated with hedenbergite and magnetite in Fe-rich skarns [START_REF] Einaudi | Skarn deposits[END_REF][START_REF] Meinert | Skarn, manto, and breccia pipe formation in sedimentary rocks of the Cananea mining district, Sonora, Mexico[END_REF]. It is also present in the calcic metasomatism of igneous rocks [START_REF] Firman | Fissure metasomatism in volcanic rocks adjacent to the Shap Granite[END_REF]. [START_REF] Varet | The origin of fumarolitic andradite at Menoyre, France and Fant'Ale, Ethiopia[END_REF][START_REF] Varet | New discovery of fumarolitic garnets (Fant ale, Ethiopia)[END_REF] reported andradite crystals in lava fractures where fumarolic gases at ~700°C circulated. The andradite-grossular series is widespread in basalts metamorphosed even under low grade (prehnite-pumpellyite and pumpellyite-actinolite facies, possibly extending into the zeolite facies) conditions [START_REF] Coombs | Andradite and andradite-grossular solid solutions in very low-grade regionally metamorphosed rocks in southern New Zealand[END_REF] and may form below 200°C [START_REF] Gutzmer | Formation of jasper and andradite during low-temperature hydrothermal seafloor metamorphism, Ongeluk Formation, South Africa[END_REF]. In conclusion, andradite alone does not bring much information about temperature.

In Kudryavy, andradite is systematically associated with hedenbergite. The association adr + hd is also very common and does not provide any information about temperature (e.g. [START_REF] Gustafson | The stability of andradite, hedenbergite, and related minerals in the system Ca-Fe-Si-O-H[END_REF].

Nevertherless, the stability field is restricted to ±2 log unit of the Fayalite-Magnetite-Quartz (FMQ) oxygen buffer (Fig. 6a) if aSiO2 =1.

Andradite destabilization into wollastonite and magnetite

We documented the occurrence of andradite assemblages with magnetite and wollastonite (Fig. 4c, 4g and4i). This assemblage is an evidence of the following equilibrium [START_REF] Moecher | Experimental investigation of andradite and hedenbergite equilibria employing the hydrogen sensor technique, with revised estimates of ΔfG0m,298 for andradite and hedenbergite[END_REF]): 6 Ca3Fe2Si3O12 (adr) = 4 Fe3O4 (mt) +18 CaSiO3 (wo) + O2 (1) Such an equilibrium requires T>750°C (Fig. 6a) and can be used as a diagnostic of "high" temperature. Here the first "secondary" mineral to form is andradite that is later replaced by a new assemblage (wo + mt). Such replacement suggests an increase in the temperature during the fumarolic activity. The hydrothermal activity may have been continued but with varying temperature driving this destabilization. It is worth noticing that the conditions we described (equilibrium hd+adr and adr=wo+mt; highlighted in green in Fig. 6a) fit perfectly the conditions independently described by [START_REF] Taran | Geochemistry of magmatic gases from Kudryavy volcano, Iturup, Kuril Islands[END_REF] (indicated by the orange stars in Fig. 6a).

Nepheline, Sodalite and the effect of aSiO2 on the stability of Ca-Fe-minerals

Nepheline is abundant in sample 11. This mineral displays textural features of other secondary minerals as it is found as incrustation. Its presence in a magmatic rock saturated with respect to SiO2 confirm its formation as a secondary mineral.

The reaction involved here is the hydrothermal alteration of albite associated to the leaching of SiO2 as follows:

NaAlSi3O8 (ab) = NaAlSiO4 (ne) + 2 SiO2 (silica) (2)
This reaction does not provide much information on the temperature, but the nepheline can occur as three different polymorphs (alpha, beta and gamma) that could be used as thermometers: alphanepheline (25-194°C), beta-nepheline (194-907°C), gamma-nepheline (907-1257°C) [START_REF] Kelley | Thermodynamic properties of sodium-aluminum and potassium-aluminum silicates[END_REF]. If most nepheline is the beta polymorph here, we were close to the stability field of gamma-nepheline and this polymorph would be expected in the very hot fumarole where the samples were collected (T~900°C).

The abundant sodalite also described here can be derived from nepheline [START_REF] Sharp | The stability of sodalite in the system NaAlSiO4-NaCl[END_REF] or directly from albite [START_REF] Drüppel | Metasomatic replacement of albite in nature and experiments[END_REF] according to the following reaction: 6 NaAlSiO4 (ne) + 2 NaCl = Na8Al6Si6O24Cl2 (sdl) (3) 6 NaAlSi3O8 (ab) + 2 NaCl = Na8Al6Si6O24Cl2 (sdl) + 12 SiO2 (silica) (4)

Here again, sodalite does not provide much information on the temperature. Its formation requires a high chlorine content of the fluid phase that interacted with the fumarolic rock in agreement with the composition described by [START_REF] Taran | Geochemistry of magmatic gases from Kudryavy volcano, Iturup, Kuril Islands[END_REF]. Strictly speaking, salinity of the magmatic vapor is quite low (with Na content <41.2 ppm) but chlorine content is high (up to 15380 ppm) leading us to propose that the chlorine involved in the formation of sodalite may come from HCl rather than from NaCl as proposed in reaction (3) and (4).

The stability field of nepheline and sodalite clearly depend on the aSiO2 as it is also the case for the stability of most secondary minerals. Indeed, if we examine andradite in a Ca-Fe-Si-O system, its stability relative to hedenbergite is governed by the reaction 3 Ca3Fe2Si3O12 (adr) + 9 SiO2 (silica) + Fe3O4 (mt) = 9 CaFeSi2O6 (hd) + 2 O2 (fluid) (5)

In a silica-saturated system involving pure phases, this equilibrium lies between the Hematite-Magnetite and FMQ buffers at FMQ ±2 log units (Fig. 6b). In a silica-undersaturated system with pure phases, the equilibrium constant for reaction (5) is log K(5) = 2 log fO2 -9 log aSiO2 (6) Solving for log fO2 gives log fO2 = 1/2 log K(5) -9/2 log aSiO2 (7) and the shift in the equilibrium logfO2 due to the degree of silica undersaturation is ΔK(5) log fO2 = 9/2 log aSiO2 (8) Changes in silica undersaturation that cause the term log aSiO2 to be negative whould then shift then significantly (-4.5 log units fO2 shift per order of magnitude of aSiO2) the equilibrium location of reaction (3). Thus, the effect of the silica activity is significant and should have profound implications on the phase relationships (see also [START_REF] Ganino | Reduced and unstratified crust in CV chondrite parent body[END_REF]. To consider the effect of silica activity, we calculated isothermal stable mineral assemblages as a function of aSiO2 and fO2 for the chemical system Ca-Fe-Mg-Si-O (corresponding to the major components in the primary pyroxenes) at T=800°C and P=1 bar (Fig. 6b). In this system, the equilibrium assemblages observed in Kudryavy high-temperature (700-900°C) fumarolic rocks are di-hd, di-wo-mt and adr di-mt (equilibrium lines highlighted in green in Fig. 6b). These equilibria are compatible with log(aSiO2), in the range -1 to 0 and log fO2 in the range -17 to -12. More specifically, if we consider the equilibrium adr = wo +mt (green line between fields di-wo-mt and adr-di-mt in Fig. 6b) the fO2 is fixed at log fO2 = -13.5, a value that falls perfectly into the range estimated by [START_REF] Taran | Geochemistry of magmatic gases from Kudryavy volcano, Iturup, Kuril Islands[END_REF] and those measured in Kudryavy fumaroles by [START_REF] Rosen | Oxygen fugacity directly measured in fumaroles of the volcano Kudryaviy (Kuril Islands)[END_REF] and [START_REF] Osadchii | FO2 and fS2 Measurements by Electrochemical Sensors in High-Temperature Fumaroles of Active Volcanoes[END_REF]. This good agreement supports the relevance of our simple thermodynamic approach.

We computed equilibrium assemblages in presence of water for FMQ-buffered conditions at 1 bar, for the system Ca-Fe-Mg-Si-O-H and Ca-Na-Al-Si-O-H that may correspond respectively to the hydrothermal alteration of primary pyroxene and plagioclase (Fig. 7). Fig. 6a shows that adr-hd and hd-wo are stable in a large temperature range but are restricted to aSiO2~10 -0.5 . On the other hand, the equilibrium adr = wo + mt requires T~750°C. Fig. 7b suggests a similar silica activity for the equilibrium ab-ne (aSiO2~10 -0.5 ) with little influence of the temperature. In terms of temperature, the rarity of hydrous minerals implies T>220°C for the Ca-Fe-Mg-Si-O-H system and T>400°C for the Ca-Na-Al-Si-O-H system. The relatively low silica activity recorded here during the high temperature phase contrasts with the documented presence of secondary silica (aSiO2>1). We follow the idea of [START_REF] Africano | Reactive processes during the discharge of high temperature volcanic gases[END_REF] of a late and low temperature phase: silica was leached at high temperature and precipitated in pores when the temperature of the fumarolic gases decreased.

Probably because of the high-temperature and the presence of a fluid phase helping the attainment of equilibrium, the mineralogical signature of the fumarolic rocks in Kudryavy can be modelled accurately using a simple thermodynamic equilibrium in a metamorphic process. Solid-solid reactions typical of metamorphic processes are particularly clear when observing the destabilization of andradite into wollastonite and magnetite (reaction 1) or the equilibrium between andradite and hedenbergite (reaction 5). Dissolution may be involved (decrease of aSiO2 / leaching of SiO2) and condensation may also occur (pores filed with SiO2), but most silicates we documented have not been formed by condensation. The textural relationships including pores filled with those minerals, suggest a mobility (fluid phase) rather than a simple replacement. The extremely simple explanation proposed here with secondary phases directly deriving from the primary minerals provide key parameters for the phase stability, but fails to explain their mode of occurrence.

Davyne

Thermodynamic data are not available for davyne in the database from [START_REF] Co Holland | An improved and extended internally consistent thermodynamic dataset for phases of petrological interest, involving a new equation of state for solids[END_REF] and the lack of experimental data on this mineral prevents to implement it into the database.

For this reason, even though this mineral is important, we were not able to model its stability and it does not provide precision on extensive parameters (temperature, aSiO2, fO2). Nevertheless, the occurrence of davyne is not surprising because this mineral is found typically in metasomatized and hydrothermally altered lavas (e.g. [START_REF] Bonaccorsi | Quadridavyne[END_REF]. Its presence documented in other areas where only moderate temperature fumarolic gases are recorded (e.g. Vesuvius, highest temperature in the range 360-445°C, [START_REF] Chiodini | Geochemical evidence for the existence of hightemperature hydrothermal brines at Vesuvio volcano, Italy[END_REF]) makes us propose that davyne alone is not an indicator of high temperature.

Ferro-wollastonite

The mineral composition of the wollastonite-hedenbergite group brings additional information to characterize high-temperature mineralogy: experimental data show a miscibility gap between hedenbergite and wollastonite above about 800° C (Rutstein, 1971 and Fig. 8). The chemical compositions of iron-rich wollastonite in Kudryavy fumarolic rocks fall in the immiscibility gap. With decreasing temperature, iron-rich wollastonite should transform to hedenbergite + wollastonite. Here we assume that the cooling rate was too high for a complete transformation of Fe-rich wollasonite into hd+wo. In summary, the occurrence of iron-rich wollastonite provides an evidence of hightemperature (>800°C) crystallization.

What is remarkable about the secondary phase assemblages observed here is that they are precisely what is predicted from high-temperature alteration of the primary magmatic minerals. No hydration or reverse (low-temperature) metamorphism has altered this high-temperature signature.

A guideline to ancient or planetary fumarolic environment.

Fumarolic activity at the Kudryavy volcano is peculiar because of the high temperature measured, well above most other fumarole fields. Igneous activity and hydrothermal circulation have been present throughout Earth history. The Earth has always recycled buried volatiles including carbon and water back to the surface. During the early Earth's history (e.g. Archean Eon the mantle temperature and surface heat flow would presumably be higher than resulting in a primitive plate tectonics that is different from that of the present (more plate boundaries i.e. more volcanic margins, e.g. [START_REF] Hargraves | Faster spreading or greater ridge length in the Archean? Geology[END_REF]) and a widespread high-temperature volcanic activity (komatiites e.g. [START_REF] Arndt | Komatiite, Komatiite[END_REF]. These two aspects lead us to propose that Kudryavy-like hot volcanic fumaroles might have been more widespread in the early Earth history than now. The mineralogical features we identified here provide a guidance for recognizing high-temperature fumaroles in the rock record. These features (assemblages adr-wo-mt, iron content of wollastonite) are particularly efficient because they formed from the fumarolic alteration of common primary phases as pyroxenes and plagioclase which are very frequent and widespread in most volcanic rocks. The unique limitations are the paucity of Archean outcrops and the possible late retrograde alteration to low-temperature hydrated assemblages that could have affected and erased the high-temperature assemblages.

In a planetary science perspective, our observation could be used to identify ancient hightemperature hydrothermal activity on other planetary bodies. For the case of Mars, several ancient Martian volcanoes display pyroclastic rocks, such as Elysium Mons and Hadriaca Mons. Thus suggests the possibility of high volatile abundances during the earliest period of volcanic activity, and possibly Kudryavy-like hot-temperature hydrothermal system with volcanic vapors. The Kudryavy volcano provides a high-temperature analog with respect to Jaroso hydrothermal system in Spain already proposed as an analog for martian low-temperature hydrothermal field (e.g. [START_REF] Martínez-Frías | Isotopic signatures of extinct low-temperature hydrothermal chimneys in the Jaroso Mars analog[END_REF].

Conclusion

This work characterizes the phase assemblages and mineral compositions that are indicative of high temperature hydrothermal systems. It confirms the presence of hedenbergite, andradite, wollastonite, magnetite, hercynite (Ca-Fe--rich secondary minerals) and shows that a second type of secondary minerals (Na-Al -rich) are also present: nepheline, sodalite and davyne. Some of these minerals do not provide much information on the thermo-chemical conditions, but others can be used as sensors. The best piece of evidences for high-temperatures are the assemblages adr-wo-mt (associated with a >750°C equilibrium), and the iron content of wollastonite (iron-wollastonite stable above 800°C). As a result of the high-temperatures and the presence of a fluid phase helping the completion of equilibrium, a simple modelling of thermodynamic equilibria provides an accurate mineralogical signature of the fumarolic rocks after replacement of the primary minerals. Similar mineralogical features could be of importance when looking at the properties of old extinct hydrothermal systems. Such high-temperature fumarolic fields are rare today, but could have been more frequent in the early history of Earth. High-temperature fumarolic rocks could be widespread in Archean outcrops if late retrograde alteration to low-temperature hydrated assemblage had not affected and erased the high-temperature assemblages. .Our results provide also a guidance for characterizing high-temperature hydrothermal systems on other planets and in particular on Mars.

Figure 1 :

 1 Figure 1: Location of Kudryavy volcano and its associated fumarolic field.

Figure 2 :

 2 Figure 2: BSE-SEM large view images of the three analyzed samples.

Figure 3 :

 3 Figure 3: BSE-SEM images of high-temperature fumarolic rock 11C. (a) large scale view of primary volcanic texture with corodated clinopyroxene and K-felspar; (b) closeup view of sub-euhedral

Figure 5 :

 5 Figure 5: BSE-SEM images of high-temperature fumarolic rock 15C. (a) pores filled with hd. (b)

  Acknowledgements: This study was supported by grants from the COMUE Université de la Côte d'Azur (Idex Academie 3) and BQR Géoazur. We thank Kazuhide Nagashima and Alexander T.Krot for fruitful discussions and Suzanne Jacomet and Olivier Tottereau for their technical support. We gratefully acknowledge reviews by Y. Taran and an anonymous reviewer and the careful reading from M. Wieczorek, which have substantially improved the quality of this manuscript.

Table 1 :

 1 EPMA composition of typical minerals in fumarolic condensates.

Table 2 :

 2 Indicative SEM-EDX analyses of Na-Al -rich minerals.

Table 1 :

 1 Representative EPMA analyses of Ca-Fe-Mg -rich silicates (wt%) Sample SiO 2 TiO 2 Al 2 O 3 Cr 2 O 3 FeO MgO MnO CaO Na 2 O K 2 O TOTAL andradite 21B 34.60 0.03 0.01 0.01 28.73 0.04 0.27 32.27 0.01 0.00 95.97 andradite 11A 34.70 0.05 0.57 0.01 27.25 0.07 0.07 32.30 0.05 0.14 95.21 andradite 11A 34.97 0.01 0.64 0.00 27.67 0.00 0.13 32.42 0.06 0.08 95.99 wollastonite 11C 50.89 0.00 0.05 0.00 1.15 0.04 0.04 47.61 0.01 0.03

	1000 900 T(°C)	Wo ss	Fe-Wo in Kudryavy fumaroles
	800
			Wo ss
		Wo ss		+
	700	(metastable)	Hd
	600
	CaSiO 3	0.9	Composition 0.8 0.7	0.6	Ca 0.5 Fe 0.5 SiO 3
			Ca x Fe 1-x SiO 3

Table 2 :

 2 Indicative SEM-EDX analyses of Na-Al -rich minerals (at%)

	Sample	Na	Mg Al	Si	S	Cl	K	Ca	Fe	O
	Davyne 11A	6.95 0.02 12.18 10.05 1.55 6.49 5.46 5.08 0.25 51.98
	Sodalite 11A	14.82 0.11 14.53 12.39 0.36 5.78 0.97 0.76 0.21 50.06
	Nepheline 11A	10.97 0.28 15.37 13.00 0.46 0.73 2.63 1.79 0.17 54.61
	Plagioclase 11A	4.51 0.00 11.54 17.90 0.28 0.58 1.30 5.18 0.15 58.56
	Hercynite 11A	2.41 4.42 26.76 2.47 0.37 1.31 0.93 0.57 6.36 54.39

Abbreviations : see Fig. 2 Figure 6: (a) Oxygen fugacity vs. temperature plot of the stability field of hedenbergite and andradite.

Both single phases andradite and/or hedenbergite are stable over a range of log fO2 and T and poorly constrained their conditions of formation. When the two phases assemblage andradite + hedenbergite is considered, the redox conditions of formation of the Ca-Fe-rich secondary phases could be a bit more restricted but the temperature remains poorly constrained. The stability field of the Ca-Fe-rich secondary phase assemblages depends on the silica activity: the gray arrow indicates the effect of decreasing the silica activity of the system on the stability field of andradite. (b) Silica activity vs. oxygen fugacity plot of stable phases in the system Ca-Fe-Mg-Si-O at 800 °C and 1 bar. Abbreviations: adr=andradite hd=hedenbergite; kst=kirschsteinite; wo=wollastonite; HM=hematite-magnetite oxygen buffer; FMQ=fayalite-magnetite-quartz oxygen buffer; WM=wustite-magnetite oxygen buffer; IW=iron-wustite oxygen buffer; IM=ironmagnetite oxygen buffer. Abbreviations: ab=albite; adr=andradite; ak=akermanite; da=davyne; di=diopside; gp=gypsum; hc=hercynite; hd=hedenbergite; hem=hematite; kst=kirschsteinite; lrn=larnite; merw=merwinite; mft=magnesioferrite; mont=monticellite; mt=magnetite; ne=nepheline; per=periclase; qz=quartz or silica polymorph; rnk=rankinite; sdl=sodalite; wo=wollastonite