Michael Krings

Carla J Harper

Anne-Laure Decombeix

Jean Galtier

The core of Sporocarpon asteroides, an enigmatic fungal fossil from the Carboniferous

Keywords: fossil fungal "sporocarp", Glomeromycota, Lower Coal Measures, Pennsylvanian, pseudoparenchymatous investment, spore wall

The various types of spherical microfossils collectively termed fossil fungal "sporocarps" exhibit basic congruities in morphology that have been used to suggest they all may belong to the same higher taxonomic category. Both the Ascomycota and zygomycete fungi have been discussed in this respect, but features that precisely delimit the nature and taxonomic position of these fossils have not been documented. Here, we present two new specimens of the Pennsylvanian "sporocarp" Sprocarpon asteroides from the Lower Coal Measures of Great Britain. Both provide evidence that a spore with a multi-layered wall was formed in this structure by blastic inflation of a hyphal tip. The outer spore walls appear to be continuous with the wall of the subtending hypha, while the inner wall (the spore wall proper) more likely developed de novo. Sporocarpon asteroides is interpreted as a unisporic sporocarp with a pseudoparenchymatous peridium, likely with affinities to the Glomeromycota. This discovery supports the notion that the fossil fungal "sporocarps" include several biologically different structures.

Introduction

Various types of small spherical structures often collectively termed fossil fungal "sporocarps" 1 are commonly found in Pennsylvanian coal balls and certain chert deposits (surveyed by STUBBLEFIELD et al. 1983;[START_REF] Taylor | Fossil Fungi. 1 st Editionxv + 382[END_REF]. All consist of a central cavity bounded by a contiguous perimeter wall and additionally surrounded by a prominent investment composed of loosely entwined or tightly interwoven hyphae. "Sporocarps" occur singly or in small clusters; hardly any of them provide information on the systems on or in which they were borne. Several different genera, including Dubiocarpon S.A. HUTCH., Mycocarpon S.A. HUTCH., Sporocarpon WILL., and Traquairia CARRUTH., have been erected to accommodate these fossils, which are distinguished from one another based primarily on the construction of the investment. While fossil fungal "sporocarps" are mostly known from the Pennsylvanian, there are also several forms described from the Mississippian [START_REF] Scott | On Traquairia[END_REF][START_REF] Taylor | Fungi from the Lower Carboniferous of central France[END_REF]KRINGS et al. 2010b) and Triassic (WHITE & TAYLOR 1988, 1989a, 1991;TAYLOR & WHITE 1989), and one from the Lower Devonian Rhynie cherts (KRINGS et al. 2014). What relationship, if any, exists between the "sporocarps" and a number of other, structurally similar but generally much smaller Rhynie chert fossils referred to as mantled fungal reproductive units (e.g., KRINGS & TAYLOR 2014, 2015a, 2015b;[START_REF] Krings | Morphology and ontogenetic development of Zwergimyces vestitus, a fungal reproductive unit enveloped in a hyphal mantle from the Lower Devonian Rhynie chert[END_REF][START_REF] Krings | A mantled fungal reproductive unit from the Lower Devonian Windyfield chert, Scotland, with prominent spines and otherwise shaped projections extending out from the mantle[END_REF], 2020) remains uncertain.

Fossil fungal "sporocarps" in general have been attributed to the Ascomycota based on specimens containing one or more spheres believed to represent asci that in turn contain small spherules interpreted as ascospores [START_REF] Hutchinson | A presumed ascomycete from the Upper Carboniferous[END_REF][START_REF] Hutchinson | A review of the genus Sporocarpon Williamson[END_REF]STUBBLEFIELD et al. 1983). According to this idea, the "sporocarp" would be a cleistothecium. Another hypothesis, however, uses specimens that contain a single, large sphere to suggest affinities to the zygomycete fungi [START_REF] Pirozynski | Fossil fungi[END_REF]TAYLOR & WHITE 1989). The sphere is interpreted as a zygospore, while the "sporocarp" would be the zygosporangium enveloped in a hyphal investment equivalent to that seen in certain extant Endogonales (Mucoromycotina). Smaller spheres in some cases present in the large sphere are regarded as intrusive parasites. There is circumstantial evidence to corroborate the latter hypothesis (e.g., KRINGS et al. 2010bKRINGS et al. , 2011a[START_REF] Krings | Fungal sporocarps from the Carboniferous: An unusual specimen of Traquairia[END_REF]KRINGS & TAYLOR 2012), but structural 1 The term sporocarp, used in mycology to refer to a multicellular structure in which spores or spore-producing entities are formed, is put in quotation marks because it may not be applicable to all of these fossils (for details, see [START_REF] Krings | Fungal sporocarps from the Carboniferous: An unusual specimen of Traquairia[END_REF].

features that precisely delimit the nature and taxonomic position of the fungal "sporocarps" have not been documented to date.

Every new specimen that displays features not hitherto seen can provide critical new information on these enigmatic fossils, and thus deserves thoughtful consideration. Here, we present two specimens of Sporocarpon asteroides WILL. from the Lower Coal Measures of Great Britain that both contain a structure suggestive of the formation of a spore with a multilayered wall in this "sporocarp" species. The outer walls appear to be continuous with the wall of a subtending hypha, while the inner wall more likely developed de novo.

Material and Methods

The specimens of Sporocarpon asteroides described in this study are present in a single thin section (c. 60 µm thick) that was prepared from a coal ball from the Lower Coal Measures of Great Britain. The coal ball was collected sometime in the 1970s by John HOLMES, and comes from the Union Seam at Rowley Tip, Burnley (Lancashire), which is Westphalian A or Langsettian (Bashkirian/Lower Pennsylvanian) in age. The Union Seam and its stratigraphic equivalent in Great Britain, the Halifax Hard Seam, together with the contemporaneous Bouxharmont Seam in Belgium and the Finefrau-Nebenbank Seam in the Netherlands and Germany, represent the source strata of the richest European coal ball floras (for details, refer to GALTIER 1997).

The thin section was prepared according to a standard procedure in which a piece of the coal ball was cemented to a glass slide and then ground with abrasive until it was sufficiently thin to be examined with transmitted light [START_REF] Hass | Thin sections and wafering[END_REF]. John HOLMES had already marked the Sporocarpon specimens on a drawing of the cut faces and labelled them as "curious spores 400 µm". The coal ball, offcuts, and slide are deposited in the Collections de Paléobotanique, Université de Montpellier, France, under accession numbers B07 and B07A1aT 01. Fossils were analysed using normal transmitted light microscopy equipment. Digital images were captured with a Leica DFC-480 camera and gently processed in Adobe Photoshop CS4 for brightness and contrast.

Results

Coal ball B07 contains an accumulation of permineralized stigmarian rootlets, fragments of arborescent lycophyte axes, microphylls, megaspores, and Lepidocarpon sp., calamite remains, and several fern rachides, including Botryopteris hirsuta (WILL.) SCOTT and B. ramosa (WILL.) SCOTT, all embedded in a clear matrix interspersed with abundant organic debris, scattered fungal hyphae, and small propagules. Six three-dimensionally preserved specimens of Sporocarpon asteroides in different sectional planes occur in thin section B07A1aT 01. All, except two are, as far as we can see, typical examples of S. asteroides (for details on the morphology of this "sporocarp" species, refer to STUBBLEFIELD et al. 1983).

The two atypical specimens (denoted I and II in Fig. 1A), which are detailed in the paragraphs below, are ideally cut and provide excellent median longitudinal section views of the fossils.

They occur in close proximity to a third specimen (denoted III in Fig. 1A) sectioned slightly off center, and a fourth one (denoted IV in Fig. 1A) of which only a part of the outer surface can be seen because it is located in a different plane.

Specimens I and II correspond in size and overall appearance to typical Sporocarpon asteroides, but differ from all previously described individuals in regard to the outer boundary of the cavity and the cavity contents (Figs. 1B,C,E,). Both specimens exhibit the characteristic, irregularly lobed pseudoparenchymatous investment enveloping a (near-)spherical cavity approximately 300 µm in diameter. A contiguous wall that extends along, and is closely appressed to, the inner surface of the investment, as it occurs in typical S. µm high and 230 µm wide in specimen II. A similar, but distinctly smaller and bulb-shaped vesicle is present in specimen III (arrow in Fig. 1D). What appear to be short fragments of narrow filament-or fiber-like structures of some kind are recognizable here and there in the space between the investment and the vesicle wall, particularly where the two structures are in close proximity to each other (fs in Fig. 1E).

Located within the confines of the vesicle in specimens I and II is a compound structure that comprises a basal, squat-columnar component (less than 40 µm high and 20 µm wide), which is hollow in specimen II (sce in Figs. 1C1,E,2A1) but apparently massive in specimen I (sce in Figs. 1B,2B1). Attached laterally to the columnar component are the remains of at least two walls (w1 and w2 in Figs. 1B, C1, 2A2, B2) of which, unfortunately, only fragments are preserved. Moreover, at the tip of the columnar component is a walled sphere, which is more or less intact and c. 155 µm in diameter in specimen I (cs in Figs. 1B,2B1), but collapsed and mostly disintegrated (but still recognizable) in specimen II (cs in Figs. 1C1,2B1). The wall of this sphere appears to be layered (csw in Fig. 2D). As to whether the sphere was physically connected to the tip of the columnar component or developed freely (de novo) within the confines of the innermost surrounding wall (w2) cannot be determined. The latter seems to be more likely, however, based on the position of the collapsed sphere in specimen II (Fig. 1C1). Specimen II also suggests that the columnar component was connected to, or continued into, some structure on the outside of the "sporocarp" (arrows in Fig. 1C2). Unfortunately, this structure is either not preserved, or not located in the portion (slice) of the "sporocarp" present in the thin section. The vesicle in the cavity of specimen III is empty (Fig. 1D). Tiny, dot-shaped inclusions, which occur in large numbers in the spaces between the individual wall layers (Fig. 2D), are probably remains of the decayed parts of the compound structure (but see below).

Discussion

Fossil fungal "sporocarps" range among the most extensively studied pre-Cretaceous fungal fossils, and their morphology is well understood today (KRINGS et al. 2014). Nevertheless, the biological nature and affinities of these structures have remained a matter of controversy since they were first brought to the attention of the scientific community by [START_REF] Carruthers | On Traquairia, a radiolarian rhizopod from the coal-measures[END_REF] and [START_REF] Williamson | On the organization of the fossil plants of the coal-measures[END_REF][START_REF] Williamson | On the organization of the fossil plants of the coal-measures. Part 10including an examination of the supposed radiolarians of the Carboniferous rocks[END_REF][START_REF] Williamson | On the organization of the fossil plants of the coal-measures: -Part XII[END_REF]. The fact that virtually all "sporocarp" specimens documented to date appear to be fully developed (mature) structures, in tandem with the lack of information on other life cycle stages of the organisms that produced them, and the inconsistency that exists with regard to the cavity contents are the main obstacles to a more complete understanding of these fossils [START_REF] Taylor | Fossil Fungi. 1 st Editionxv + 382[END_REF].

The sac-like vesicle

The most recent taxonomic revision of the "sporocarp" genus Sporocarpon by STUBBLEFIELD et al. (1983) recognizes three species, S. asteroides, S. cellulosum WILL., and S. leismanii STUBBLEFIELD et al., all of them characterized by a prominent, cohesive investment that is pseudoparenchymatous. The species differ primarily in the organization of the investment, which is irregularly lobed in S. asteroides, constructed of radiating files of cells in S. cellulosum, and prolonged into narrow, conical rays in S. leismanii. The cavities of the Sporocarpon specimens figured in literature are either empty or contain small spheres, or they contain a single large sphere, which is either empty or contains one or more smaller spheres [START_REF] Williamson | On the organization of the fossil plants of the coal-measures. Part 10including an examination of the supposed radiolarians of the Carboniferous rocks[END_REF][START_REF] Mclean | On the fossil genus Sporocarpon[END_REF][START_REF] Hutchinson | A review of the genus Sporocarpon Williamson[END_REF][START_REF] Baxter | Sporocarpon and allied genera from the American Pennsylvanian[END_REF][START_REF] Baxter | Fossil fungi from American Pennsylvanian coal balls[END_REF][START_REF] Davis | Further observations on Sporocarpon and allied genera[END_REF]STUBBLEFIELD et al. 1983). However, structures corresponding to the ones present in the fossils described in this study have not been documented previously in Sporocarpon, with the exception of the sac-like vesicle. STUBBLEFIELD et al. (1983) found that the wall lining the inner surface of the investment (i.e. the cavity perimeter wall) in S.

asteroides is multi-layered and granulose on the outer surface of the innermost layer. The saclike vesicles in the specimens described here (sv in Fig. 1B,C, arrow in Fig. 1D) all possess a finely granulose wall (sv in Figs. 1E,2C), suggesting that the vesicle actually is the innermost layer of the perimeter wall that has separated from the outer layers. The outer layers, in turn, no longer exist. They appear to have disintegrated, except for remnants occurring in the form of short filament-or fiber-like fragments in the space between the inner surface of the investment and the vesicle (fs in Fig. 1E). If this is accurate, then the question arises why the vesicle is so much smaller than the cavity? One possible explanation could be that the perimeter wall in vivo was of considerable thickness. However, a thick perimeter wall has not been recorded for any fossil fungal "sporocarp" to date, which renders this hypothesis improbable. More likely, based on the wrinkled wall, is that the vesicle has shrunk during fossilization (see below). An alternative, albeit highly speculative, interpretation of the filament-or fiber-like structures in S. asteroids, and likewise of the dot-shaped inclusions visible in the spaces between the individual wall layers (Fig. 2D), is that they are endosymbionts, perhaps bacteria comparable to the endobacteria found in fungi today (BONFANTE & DESIRÒ 2017), including Endogonales [START_REF] Desirò | Endogone, one of the oldest plant-associated fungi, host unique Mollicutes-related endobacteria[END_REF]) and many species of Glomeromycota (e.g., [START_REF] Desirò | Detection of a novel intracellular microbiome hosted in arbuscular mycorrhizal fungi[END_REF][START_REF] Toomer | Molecular evolution patterns reveal life history features of mycoplasma-related endobacteria associated with arbuscular mycorrhizal fungi[END_REF][START_REF] Venice | Symbiotic responses of Lotus japonicus to two isogenic lines of a mycorrhizal fungus differing in the presence/absence of an endobacterium[END_REF].

The compound structure

The compound structure that occurs in the vesicle in specimens I and II is evidence that a spore of some kind (i.e. the central sphere) was formed inside these "sporocarps," and that this spore had a complex wall comprised of a wall proper (i.e. the layered wall of the central sphere; csw in Fig. 2D) and the two outer walls labelled w1 and w2 in Figs. 1B, C1, 2A2, and B2. A spore-like body bounded by a multi-layered wall has previously been documented solely in the Mississippian "sporocarp" Roannaisia bivitilis T.N. TAYLOR et al. from France (TAYLOR et al. 1994: pl. II, 1). What appear to be concentrically arranged walls or wall layers are also visible in several Pennsylvanian Traquairia specimens from Great Britain and the United States (SCOTT 1911: textfig. 4;STUBBLEFIELD & TAYLOR 1983;[START_REF] Krings | Fungal sporocarps from the Carboniferous: An unusual specimen of Traquairia[END_REF] pl. I, 1). It has been suggested, however, that these layers have formed from the splitting of the cavity perimeter wall during fossilization (STUBBLEFIELD & TAYLOR 1983). By contrast, [START_REF] Krings | Fungal sporocarps from the Carboniferous: An unusual specimen of Traquairia[END_REF] believe that they represent an artefact which came into being during the permineralization process as a result of several successive phases of shrinking of the sporelike body in the cavity. Walls w1 and w2 in Sporocarpon asteroides originate from the base of the compound structure, where they arise from the squat-columnar component, which we interpret as the tip of a subtending hypha. Accordingly, the physical connection between w1 and w2 and the columnar component would imply that these walls were continuous with the wall of the subtending hypha. The wall bounding the central sphere probably formed de novo.

Affinities to Glomeromycota

Based on the preceding considerations, we entertain the possibility that Sporocarpon asteroides was a unisporic sporocarp with a pseudoparenchymatous peridium that enclosed a spore with a multi-layered wall (Fig. 3). The cavity perimeter wall is viewed as a product of the innermost layer of the peridium, rather than as a part of the spore. The origin of the peridium remains elusive. No evidence of paired or single gametangia (and suspensors) has been found, suggesting that the spore developed asexually and by blastic expansion of a hyphal tip, and thus that S. asteroides may have been a member of the Glomeromycota. This concurs with a major counterargument to the interpretation of fossil fungal "sporocarps" in general as zygosporangia containing zygospores, namely the total lack of evidence of gametangia in these structures (KRINGS & TAYLOR 2012;KRINGS et al. 2013a). Even if the gametangia, as argued elsewhere (KRINGS & HARPER 2020; KRINGS 2022), were small and embedded in the investment, if they have existed, then at least some would have been detected, given the large number of "sporocarp" specimens examined to date. Several bona fide zygomycete fungi that also have been described from the Carboniferous and Triassic show zygosporangia with attached gametangia, and investments similar to the ones seen in fossil fungal "sporocarps" (WHITE & TAYLOR 1989b;KRINGS et al. 2012KRINGS et al. , 2013b)).

Glomeromycota are soil-borne fungi that enter into mycorrhizal associations with plants. They produce large (up to more than 800 μm in diameter) spores with multi-layered walls on non-septate hyphae [START_REF] Redecker | Phylogeny of the Glomeromycota (arbuscular mycorrhizal fungi): recent developments and new gene markers[END_REF][START_REF] Walker | Looking for arbuscular mycorrhizal fungi (AMF) in the fossil recordan illustrated guide[END_REF]. The oldest bona fide fossil glomeromycotan spores are Early Devonian in age (e.g., [START_REF] Stubblefield | Fungal remains in the Devonian trimerophyte Psilophyton dawsonii[END_REF][START_REF] Harper | Archaeosporites rhyniensis gen. et sp. nov. (Glomeromycota, Archaeosporaceae), from the Lower Devonian Rhynie cherta fungal lineage morphologically unchanged from more than 400 million years[END_REF][START_REF] Walker | The Early Devonian fungus Mycokidstonia sphaerialoides from the Rhynie chert is a member of the Ambisporaceae (Glomeromycota, Archaeosporales), not an ascomycete[END_REF][START_REF] Lalica | The early fossil record of glomeromycete fungi: New data on spores associated with early tracheophytes in the Lower Devonian (Emsian; c. 400 Ma) of Gaspé (Quebec, Canada)[END_REF], and there is also documented evidence of Glomeromycota from several of those Carboniferous deposits that have yielded "sporocarp" fossils (e.g., [START_REF] Wagner | Evidence for endomycorrhizae in Pennsylvanian age plant fossils[END_REF][START_REF] Wagner | Fungal chlamydospores from the Pennsylvanian of North America[END_REF][START_REF] Stubblefield | Studies of Paleozoic fungi. IV. Wall ultrastructure of fossil endogonaceous chlamydospores[END_REF]KRINGS et al. 2011c). In addition, there are various types of mantled fungal reproductive units from the Lower Devonian Rhynie chert that are morphologically similar to Carboniferous fungal "sporocarps" and demonstrably borne on a simple tubular subtending hypha. These fossils have also been considered to belong to the Glomeromycota (KRINGS & TAYLOR 2014;[START_REF] Krings | A mantled fungal reproductive unit from the Lower Devonian Windyfield chert, Scotland, with prominent spines and otherwise shaped projections extending out from the mantle[END_REF], 2020). Unfortunately, the continuation of the subtending hypha on the outside of Sporocarpon asteroides remains unknown. There is, in fact, very little documented evidence of the structures that gave rise to any of the fossil fungal "sporocarps." One putative subtending structure occurs in a specimen of Mycocarpon cinctum M. KRINGS et al. from the Mississippian of France in the form of an inflated appendage extending from the outer surface of the investment (KRINGS et al. 2010b: pl. 1, fig. 1a, pl. 2, fig. 4). This structure appears to interface the "sporocarp" with its source organism, and is perhaps congruent with the bulbous bases seen in present-day species of the glomeromycotan order Gigasporales [START_REF] Khade | New characteristics for morphotaxonomy of Gigaspora species belonging to arbuscular mycorrhizal fungi[END_REF][START_REF] Walker | Looking for arbuscular mycorrhizal fungi (AMF) in the fossil recordan illustrated guide[END_REF].

Possible objections

The interpretation of Sporocarpon asteroides as a member of the Glomeromycota could be countered by pointing out that the putative spore is considerably smaller than the cavity bounded by the investment. The question therefore is what gave shape to the spherical cavity in this fossil? A peridium typically precedes spore formation or develops concomitantly with the spores, encloses the spores, and expands as the spores grow larger [START_REF] Giovannetti | Morphological, cytochemical, and ontogenetic characteristics of a new species of vesicular-arbuscular mycorrhizal fungus[END_REF]MEIER & CHARVAT 1992, and references therein). We believe that the size difference between the cavity and spore in S. asteroides is a preservation artefact resulting from shrinkage of the spore due to plasmolysis caused by the physico-chemical properties of the depositional environment and the permineralization process (see [START_REF] Scott | The formation and significance of Carboniferous coal balls[END_REF]. A similar effect can be seen in present-day glomeromycotan spores after they have been exposed to certain acidic mounting media. It is known, for instance, that spores embedded in PVLG (polyvinyl-lacto-glycerol) may shrink considerably or collapse with plasmolysis of the spore contents [START_REF] Gamper | Diversispora celata sp. nov.: molecular ecology and phylotaxonomy of an inconspicuous arbuscular mycorrhizal fungus[END_REF]). An ensuing question is, why is there not a spore in every specimen of S. asteroides? We speculate that the pseudoparenchymatous investment may have been durable and remained (largely) intact for an extended period of time after the spore had germinated or become non-viable for some other reason and its walls decayed. If so, then the majority of S. asteroides fossils would be empty investments.

It might also be argued that cohesive, pseudoparenchymatous investments like that of Sporocarpon asteroides do not occur in present-day Glomeromycota (e.g., FURRAZOLA et al. 2016;[START_REF] Gupta | Differential response of arbuscular mycorrhizal sporocarps in longterm trap culturing[END_REF][START_REF] Jobim | New sporocarpic traxa in the phylum Glomeromycota: Sclerocarpum amazonicum gen. et sp. nov. in the family Glomeraceae (Glomerales) and Diversispora sporocarpica sp. nov. in the Diversisporaceae (Diversisporales)[END_REF][START_REF] Yamamoto | A sporocarpic species of Glomeromycotina, Glomus radiatum new to Japan[END_REF]. It is basically correct that the fossil differs from all present-day members of the Glomeromycota producing spores enclosed in an evidently differentiated hyphal peridium. However, there are certain unisporic sporocarps that, in section view, display a relatively high level of organization in the hyphal coverings (e.g., MEIER & CHARVAT 1992: fig. 8). Moreover, we have to consider the possibility that fossil lineages of glomeromycotan fungi, as well as fossil representatives of present-day lineages, have existed that were characterized by structural features unknown in any present-day representative.

Finally, an interesting specimen of Sporocarpon asteroides has been figured by MCLEAN (1922: pl. VIII, fig. 9) and described as "containing a spherical structure apparently dehiscing and extruding a mass of what appear to be small spores united by filaments." It is more likely, however, that the spherical structure and the alleged spores do not belong together. The former appears to correspond to the sac-like vesicle seen in the specimens described here, whereas the latter probably represent an intrusive organism that had entered S. asteroides and produced its own thallus and reproductive units. Support for this view comes from abundant occurrences of spore-like bodies interconnected by filaments in Carboniferous plant parts preserved in coal balls and chert [START_REF] Dotzler | Sphenophyllum (Sphenophyllales) leaves colonized by fungi from the Upper Pennsylvanian Grand-Croix cherts of central France[END_REF]KRINGS et al. 2010aKRINGS et al. , 2011b;;[START_REF] Strullu-Derrien | An expanded diversity of oomycetes in Carboniferous forests: Reinterpretation of Oochytrium lepidodendri (Renault 1894) from the Esnost chert, Massif Central, France[END_REF]. Moreover, there is evidence of mycoparasitism in Dubiocarpon which demonstrates that Carboniferous fungal "sporocarps" were invaded by other organisms and used as a habitat (KRINGS et al. 2011a).

Conclusions

Fossil fungal "sporocarps" continue to invite speculation as to their biological nature and systematic affinities. Although there are morphological differences that have been used to classify the "sporocarps" into a number of fossil genera and species, there are also basic similarities, which could mean that they all belong to the same higher taxonomic category.

Both the Ascomycota and zygomycete fungi have been discussed in this respect, but neither of these attributions has received undivided approval. The specimens presented in this study strongly suggest that the "sporocarp" species Sporocarpon asteroides was a unisporic glomeromycotan sporocarp. This does not necessarily mean, however, that the other Sporocarpon species, let alone the other "sporocarp" genera, were also Glomeromycota.

Rather, we consider it likely that the assemblage of fossils subsumed under fossil fungal "sporocarps" is heterogeneous and includes a range of biologically different structures. Our knowledge of these structures in general continues to be incomplete, and there is need for additional specimens to be discovered, thoroughly investigated, and documented. The present study demonstrates that new features of fossil fungal "sporocarps" can still be found, and can be used to refine current interpretations of these common but as yet enigmatic fossils, and eventually take us to the core of their biological nature and affinities. the characteristic pseudoparenchymatous investment (in), the cavity perimeter wall with its finely granular innermost layer (cpw), two spore walls w1 and w2 that are continuous with the wall of the subtending hypha, and a spore wall proper (csw) that formed de novo.

Figure captions

  asteroides, is present in neither specimen (Figs. 1E, 2C, D). Instead, each of the two cavities contains a single large sac-like vesicle (sv in Figs. 1B, C1, E, 2A1, B1, C, D) with a thin, wrinkled, and finely granulose wall (e.g., Fig. 2C); the position of the vesicle within the cavity is eccentric. The vesicle is c. 230 µm high and 215 µm wide in specimen I and c. 260

Fig. 1 .

 1 Fig. 1. New specimens of the Carboniferous fungal "sporocarp" Sporocarpon asteroides from the Lower Coal Measures of Great Britain. A. Cluster of four specimens (labelled I-IV) in coal ball matrix rich in organic debris; bar = 300 µm. B, C1. Cavities of specimens I and II in higher magnification (in the median longitudinal section view), showing contents; sv = saclike vesicle, sce = squat-columnar component, w1 and w2 = outer walls, cs = central sphere bounded by a layered wall proper; bars = 100 µm. C2. Lower part of specimen II, same magnification as Fig. 1C1 but slightly different focal plane, showing squat-columnar component apparently continuing into some structure on the "sporocarp" outside (arrows); bar = 100 µm. D. Cavity of specimen III, containing an empty sac-like vesicle (arrow); bar = 100 µm. E. Detail of Fig. 1C1, focusing on proximal portion of investment and compound structure; fs = layer of filament-or fiber-like structures between investment and vesicle wall (sv); sce = squat-columnar component; bar = 20 µm.

Fig. 2 .

 2 Fig. 2. New specimens of the Carboniferous fungal "sporocarp" Sporocarpon asteroides from the Lower Coal Measures of Great Britain. A, B. Proximal portions of cavities of specimens I and II (in longitudinal section views) in normal (A1, B1) and, in a slightly different focal plane, inverted (A2, B2) light, showing sac-like vesicle (sv) and compound structure, the latter comprised of squat-columnar component (sce), two outer walls (w1, w2), and central sphere (cs) bounded by layered wall proper; bars = 50 µm. C. Detail of Fig. 1B, showing finely

Fig. 3 .

 3 Fig. 3. Sporocarpon asteroides in vivo, reconstruction. Median longitudinal section, showing

Acknowledgments

This work was supported in part by funds from the United States National Science Foundation (DEB-1441604, subcontract S1696A-A to M.K.). We thank M. FOCKE (Munich, Germany) for preparing Fig. 3 andH. MARTIN (Munich, Germany) for technical assistance. Insightful comments by J.F. WHITE (New Brunswick, NJ, USA) and A.M.F. TOMESCU (Arcata, CA, USA) are greatly appreciated.


Morelle Angue Minto'o Charlie

Bassetti Maria-Angela

Toucanne Samuel

Jouet Gwenael

Charlie Morelle

Angue Minto

La distribution des assemblages d'ostracodes et de foraminifères benthiques le long des derniers 550 ka dans le bassin Est-Corse, Méditerranée occidentale : une reconstitution paléo-environnementale Distribution of ostracod and benthic foraminiferal assemblages during the last 550kyr in the East-Corsica basin, western Mediterranean Sea: A paleo-environmental reconstruction

Keywords: East-Corsica, Ostracoda, Benthic foraminifera, Allochthonous group Est-Corse, Ostracode, Foraminifère benthique, Groupe allochtone

The study of Quaternary sediments covering the last 550 kyr from the borehole GDEC-4-2, East-Corsica basin, was performed through the study of benthic meiofaunal assemblages (ostracoda and benthic foraminifera) whose distribution responds to climate changes, and glacial-interglacial variability in particular. The interglacial ostracod group is mainly composed of the Argilloecia acuminata, Cytheropteron alatum, Henryhowella sp., Polycope sp. and Cytherella sp., which indicate an enhanced surface productivity and possibly high bottom water temperature during these warm intervals. Benthic foraminifera, such as Hoeglundina elegans, Sigmoilopsis schlumbergeri, Bigenerina nodosaria and Hyalinea balthica are predominant during interglacial periods and also show an increasing surface productivity associated to warm intervals. Increase in surface productivity would contribute to an enhanced export of organic matter to sea floor at the GDEC-4-2 site during interglacial periods. The bottom temperature drop coupled with the important sedimentary inputs (associated to a significant quantity of refractory organic matter) during glacial periods was highlighted by the predominance of ostracoda, such as Paradoxostoma sp., Cytheropteron testudo, Bathycythere vanstraateni, Macrocypris sp., Echinocythereis echinata and benthic foraminifera as Bolivina spathulata, Bulimina costata, and Bulimina marginata. The distribution of some benthic foraminifera species describing a turnover system allowed the characterization of the last three climate cycles (MIS 8-9, MIS 6-7, MIS 1-5) probably Please note that this is an author-produced PDF of an article accepted for publication following peer review.

Introduction

Ostracoda and benthic foraminifera are found in most marine environments and are among the most important components of modern and ancient benthic communities. They constitute an important tool for paleo-climatic-environmental-oceanographic reconstructions because of their high sensitivity to environmental conditions (e.g. [START_REF] Barut | Ostracoda as bioindicators of anthropogenic impact in salt lakes, saltpans, and a lagoon: A case study from the Gulf of Saros coast (NE Aegean Sea), Turkey[END_REF][START_REF] Casier | Late Eifelian and Early Givetian Ostracods from Wellin, Hotton and On-Jemelle (Dinant Synclinorium, Belgium)[END_REF][START_REF] Trabelsi | Ostracods from the marginal coastal Lower Cretaceous (Aptian) of the Central Tunisian Atlas (North Africa): paleoenvironment, biostratigraphy and paleobiogeography[END_REF]. As a result, these benthic microfossils are largely studied over the world ( e.g. [START_REF] Zhao | Distribution of the ostracod genera Krithe and Parakrithe in bottom sediments of the East China and Yellow seas[END_REF][START_REF] Wollenburg | Living benthic foraminifers from the central Arctic Ocean: faunal composition, standing stock and diversity[END_REF][START_REF] Redois | Répartition des foraminifères benthiques actuels sur le plateau continental sénégalais au sud de Dakar[END_REF][START_REF] Zhou | Allochthonous ostracods in the South China Sea and their significance in indicating downslope sediment contamination[END_REF][START_REF] Fontanier | Live benthic foraminiferal faunas from the Bay of Biscay: faunal density, composition, and microhabitats[END_REF][START_REF] Triantaphyllou | Foraminiferal and ostracod ecological patterns in coastal environments of SE Andros Island (Middle Aegean Sea, Greece)[END_REF][START_REF] Schumacher | Live (Rose Bengal stained) and dead benthic foraminifera from the oxygen minimum zone of the Pakistan continental margin (Arabian Sea)[END_REF][START_REF] Pascual | A survey of the benthic microfauna (foraminifera, Ostracoda) on the Basque shelf, southern Bay of Biscay[END_REF][START_REF] Hess | Distribution patterns of living benthic foraminifera from Cap Breton canyon, Bay of Biscay: Faunal response to sediment instability[END_REF][START_REF] Nachite | Distribution et écologie des associations d'ostracodes récents de l'estuaire de Tahadart (Maroc Nord-Occidental)[END_REF][START_REF] Drinia | Benthic foraminifer palaeoecology of the Late Quaternary continental outer shelf of a landlocked marine basin in central Aegean Sea, Greece[END_REF][START_REF] Munef | Distribution and taxonomy of shallow marine Ostracods from Northern Socotra Island (Indian Ocean) -Yemen[END_REF][START_REF] Martínez-García | Recent benthic foraminifers of the Basque continental shelf (Bay of Biscay, northern Spain): Oceanographic implications[END_REF]among others).

Studies on variation and distribution of benthic foraminifera and ostracod assemblages East-Corsica basin, western Mediterranean, are very rare. A recent study focusing on both the modern and ancient benthic foraminifera and ostracoda in this area, allowed generating data about the general bathymetric distribution of those in this area [START_REF] Minto'o | Distribution of modern ostracoda and benthic foraminifera from the Golo margin (East-Corsica)[END_REF]. These data are used for interpreting the distribution of benthic microfossils in the 125-m long GDEC-4-2 sedimentary record that covered the last 550 kyr and represents the first long and continuous sedimentary record in the East-Corsica basin [START_REF] Minto'o | Enregistrments sédimentaires des changements climatiques et environnementaux pendant le Quaternaire terminal sur la marge Est-Corse[END_REF]Toucanne et al., 2015). We use these benthic microfossils as a tool to 1) establish the relationship between climatic variations, sea level changes and sedimentary transfer; 2) characterize bottom physical and chemical conditions associated to glacial-interglacial periods.

Study area

The East-Corsica margin, located in the northern part of the Tyrrhenian Sea (Western Mediterranean), is characterized by a narrow continental shelf with a shelf break situated around 110-120 m [START_REF] Gervais | Analyse multi-échelles de la morphologie, de la géométrie et de l'architecture d'un système turbiditique sableux profond (système du Golo, marge est-Corse[END_REF][START_REF] Gervais | Present morphology and depositional architecture of a sandy submarine system: the Golo turbidite system (Eastern margin of Corsica)[END_REF]. This continental shelf is followed by a steep continental slope incised by numerous meandering canyons [START_REF] Gervais | Analyse multi-échelles de la morphologie, de la géométrie et de l'architecture d'un système turbiditique sableux profond (système du Golo, marge est-Corse[END_REF]. The latter open out into a deep basin which is characterized by a depression named Corsican Trough.

The Corsican Trough is narrow (10-30 km) and shallow (400 to ca. 900 m) and is bordered by the Pianosa Ridge on its eastern flank (Fig. 1). The sedimentary transport into the East-Corsica basin is mainly driven by the Golo River (main river of the East-Corsican margin) [START_REF] Calvès | Inferring denudation variations from the sediment record; an example of the last glacial cycle record of the Golo Basin and watershed, East Corsica, western Mediterranean sea[END_REF].

The oceanographic structure of the East-Corsica basin includes a surface layer of Modified Atlantic Water (MAW, down to 200 m water depth) principally constituted by North Atlantic central water drawn into the Mediterranean Sea through the Gibraltar Strait and an intermediate layer of Levantine Intermediate Water below (LIW, down to 600-1.000 m water depth) mainly formed in the Levantine basin (Eastern Mediterranean) [START_REF] Gasparini | The effect of the Eastern Mediterranean Transient on the hydrographic characteristics in the Strait of Sicily and in the Tyrrhenian Sea[END_REF][START_REF] Astraldi | The Seasonal Characteristics of the Circulation in the Tyrrhenian Sea, Seasonal and Interannual Variability of the Western Mediterranean Sea[END_REF]. The LIW enters into the Western Mediterranean Sea through the strait of Sicily. In the northern part of the Tyrrhenian Sea (and in the Corsica Trough especially), a strong seasonal variability of this water mass is noted with a maximal flow observed during winter and early spring [START_REF] Astraldi | The Seasonal Characteristics of the Circulation in the North Mediterranean Basin and Their Relationship With the Atmospheric-Climatic Conditions[END_REF][START_REF] Vidal | Integrated use of altimeter and in situ data for understanding the water exchanges between the Tyrrhenian and Ligurian Seas[END_REF].

Materials and method

The present work is based on the study of 291 samples collected in the borehole GDEC-4-2 drilled at a water depth of 492 m in the East-Corsica margin. Samples were washed and sieved (63 µm) before performing micropaleontological analyses on the sedimentary fraction > 150 µm. Taxonomy of benthic foraminifera was based on [START_REF] Ausseil-Badie | Contribution à l'étude paléoécologique des foraminifères du Quaternaire terminal sur le plateau continental languedocien[END_REF] ;[START_REF] Jorissen | The distribution of benthic foraminifera in the Adriatic Sea[END_REF], [START_REF] Sgarrella | Benthic Foraminifera of the Gulf of Naples (Italy): systematics and autoecology[END_REF][START_REF] Abu-Zied | High resolution LGM-Present paleoceanography of the NE Mediterranean: benthic perspective[END_REF][START_REF] Fontanier | Ecologie des foraminifères benthiques du Golfe de Gascogne: étude de la variabilité spatiale et temporelle des faunes de foraminifères benthiques et de la composition isotopique (δ 18 O, δ 13 C) de leurs tests[END_REF], [START_REF] Aiello | Recent infralittoral Foraminiferida and Ostracoda from the Porto Cesareo Lagoon (Ionian Sea, Mediterranean)[END_REF][START_REF] Milker | Distribution of recent benthic foraminifera in shelf carbonate environments of the Western Mediterranean Sea[END_REF][START_REF] Frezza | Distribution of recent foraminiferal assemblages near the Ombrone River mouth (Northern Tyrrhenian Sea, Italy)[END_REF], [START_REF] Mojtahid | Spatial distribution of live benthic foraminifera in the Rhône prodelta: Faunal response to a continental-marine organic matter gradient[END_REF][START_REF] Mojtahid | Live benthic foraminiferal faunas along a bathymetrical transect (140-4800 m) in the Bay of Biscay(NE Atlantic)[END_REF]. Data on ostracoda systematics are taken from Müller (1894), [START_REF] Bonaduce | Distribution of Ostracoda in the Adriatic Sea[END_REF]; [START_REF] Peypouquet | Les Ostracodes en Méditerranée nord-occidentale[END_REF], [START_REF] Didié | Erratum to "Species composition and glacial-interglacial variations in the ostracode fauna of the northeast Atlantic during the past 200,000 years[END_REF] [START_REF] Aiello | Recent infralittoral Foraminiferida and Ostracoda from the Porto Cesareo Lagoon (Ionian Sea, Mediterranean)[END_REF][START_REF] Triantaphyllou | Foraminiferal and ostracod ecological patterns in coastal environments of SE Andros Island (Middle Aegean Sea, Greece)[END_REF]. Ostracoda and benthic foraminifera stocks were grouped on the basis of their bathymetric and climatologic distribution [START_REF] Lutze | Recent benthic foraminifera from the continental margin of northwest Africa: Community structure and distribution[END_REF][START_REF] Peypouquet | Les Ostracodes en Méditerranée nord-occidentale[END_REF][START_REF] Jorissen | The distribution of benthic foraminifera in the Adriatic Sea[END_REF][START_REF] Babinot | Les ostracodes du quaternaire terminal de la marge marocaine de la mer d'Alboran : Environnements, implications paléoclimatiques et chronologie[END_REF][START_REF] El Hmaidi | Distribution et caractères de la microfaune d'ostracodes dans les dépôts superficiels de la partie occidentale de la marge méditerranéenne marocaine[END_REF][START_REF] Frezza | Distribution of recent foraminiferal assemblages near the Ombrone River mouth (Northern Tyrrhenian Sea, Italy)[END_REF][START_REF] Milker | Distribution of recent benthic foraminifera in shelf carbonate environments of the Western Mediterranean Sea[END_REF][START_REF] Mojtahid | Spatial distribution of live benthic foraminifera in the Rhône prodelta: Faunal response to a continental-marine organic matter gradient[END_REF][START_REF] El Hmaidi | Distribution et caractéristiques des associations d'ostracodes au Pléistocène supérieur et Holocène au niveau de la marge orientale du détroit de Gibraltar (mer d'Alboran, Maroc)[END_REF][START_REF] Zaîbi | Distribution des ostracodes dans les sédiments de subsurface de la Sebkha El-Guettiate (Skhira, golfe de Gabès). Intérêt pour la reconstitution des paléo-environnements de l'Holocène[END_REF][START_REF] Minto'o | Distribution of modern ostracoda and benthic foraminifera from the Golo margin (East-Corsica)[END_REF].

The extension of the continental shelf on the East-Corsica margin is defined by the position of the shelf break around 110-120 m depth [START_REF] Gervais | Analyse multi-échelles de la morphologie, de la géométrie et de l'architecture d'un système turbiditique sableux profond (système du Golo, marge est-Corse[END_REF][START_REF] Gervais | Present morphology and depositional architecture of a sandy submarine system: the Golo turbidite system (Eastern margin of Corsica)[END_REF]. Two mains bathymetric species groups are thus considered. The shallow water species consisting of all species that are known to live in a bathymetric range from 0 to 120 m (Infralittoral to Circalittiral environments). The presence of this species group at a water depth >500 m is considered having been displaced and constitute the allochtonous group in this study. The bathyal species group composed of species living at water depth greater than 120 m, constitute the autochthonous group.

Oxygen stable isotope measurements were performed on specimens of planktonic foraminifera species Globigerina bulloides and Globigerinoides ruber (white) from the 250-315 µm size fraction, Neogloboquadrina pachyderma (dextral) from the 200-250 µm size fraction, and on the epifaunal benthic foraminifera Cibicides wuellerstorfi, Cibicidoides pachyderma and Cibicidoides kullenbergi found in the >150 µm size fraction (Toucanne et al., 2015).

The chronology for GDEC-4-2 was developed by aligning the planktonic δ 18 O (influenced by local hydrography and global ice volume changes) and both the weight percent CaCO 3 and XRF-log(Ca/Ti) records (influenced by carbonate productivity and detrital sedimentation) to the NGRIP ice core isotopes from Greenland for the last 60 ka (GICC05 chronology; [START_REF] Rasmussen | A new Greenland ice core chronology for the last glacial termination[END_REF][START_REF] Svensson | A 60,000 year Greenland stratigraphic ice core chronology[END_REF] and to the synthetic Greenland (GL T -syn) record of [START_REF] Barker | 800,000 Years of Abrupt Climate Variability[END_REF] from 60 to ~550 ka [START_REF] Toucanne | Tracking rainfall in the northern Mediterranean borderlands during sapropel deposition[END_REF]. The synchronization of GDEC-4-2 with the synthetic Greenland record reveals that the 125.7 m long marine sedimentary archive encompasses the last 547 kyr with a mean sedimentation rate of 23 cmkyr -1 . It corresponds to the highest resolution continuous marine sedimentary archive of the last five climatic cycles in the Mediterranean Sea obtained to date [START_REF] Toucanne | Tracking rainfall in the northern Mediterranean borderlands during sapropel deposition[END_REF].

Results

Ostracod groups

A total of 62 ostracoda taxa have been identified. 25 species and genera are considered as part of allochthonous group and the autochthonous group is composed of 37 taxa (Table 1).

The ostracoda autochthonous species is subdivided into three sub-groups: 1) group with species showing a discontinuous distribution; 2) ostracod species with continuous distribution and 3) group with species whose distribution is synchronous with climatic periods.

Autochthonous ostracod group

Ostracod species with discontinuous distribution

The following ostracoda are autochthonous and show a discontinuous distribution along the borehole GDEC-4-2: Buntonia sublatissima Neviani, 1906, Bythocypris sp., Bythocythere turgida Sars, 1866, Bythocythre sp., Krithe compressa Ruggieri, 1952, Pterygocythereis jonesii Baird, 1850, Pterygocythereis sp., Krithe pernoides Bornemann, 1855, Pedicythere polita Colalongo and Pasini, 1980, Pedicythere tessellata Bonaduce, Ciampo and Masoli, 1976, Cytheropteron rotundatum Mueller, 1894, Monoceratina mediterranea Sissingh, 1972 and Cluthia sp. (Table 1).

Ostracod species with continuous distribution

The following ostracoda are part of group with a continuous distribution: Bairdia sp., Pseudocythere caudata Sars, 1866, Parakrithe sp., Phlyctocythere sp. and Xestoleberis sp.

(Table 1). These ostracoda taxa are frequent along borehole.

Ostracoda correlated with climate periods

Interglacial ostracod group

Glacial ostracod group

The following ostracoda present a distribution that seems to correlate with glacial intervals: Cytheropteron hadriaticum Bonaduce, Ciampo & Masoli, 1976

Allochthonous ostracod group

Among the 62 ostracoda taxa identified in this study, 25 species and genera are considered allochthonous (Table 1, Fig. 2). The individual relative abundance of allochthonous varies from 1.5 to 50% (Table 1). The allochthonous elements yielding percentages higher than 10% are the following: Semicytherura spp., Aurila sp., Loxoconcha sp., Hemicytherura videns Mueller, 1894, Pseudocytherura calcarata Seguenza, 1880, Urocythereis favosa Roemer, 1838, Leptocythere sp., Sagmatocythere sp., Callistocythere littoralis Mueller, 1894, Paracypris sp., Costa sp., Heterocythereis sp. (Table 1).

Benthic foraminifera groups

A total of 84 benthic foraminifera species have been identified. Among those, 21 species are considered as allochthonous (Table 2) and they are not taken into account in this study, because do not allow a clear interpretation of the paleo-environmental conditions.

Autochthonous benthic foraminifera species are represented by 63 species and are grouped into three groups: 1) group including species showing a discontinuous distribution; 2) group composed of species with continuous distribution and 3) group including species whose distribution is correlated with climate oscillations.

1. Autochthonous benthic foraminifera groups

1.1. Benthic foraminifera species with discontinuous distribution

A

1.2. Benthic foraminifera species with continuous distribution

Several benthic foraminifera species (21) show a continuous distribution in this study (Table 2) angulosa (36%) and C. pachyderma (29%) (Table 2).

1.3. Benthic foraminifera correlated with climate periods Interglacial Benthic foraminifera group

Several benthic foraminifera show a distribution which can be correlated to interglacials interval (

Glacial Benthic foraminifera group

The following benthic foraminifera present a distribution that can be related to glacial conditions (Table 2,

Benthic foraminifera: turnover across climatic cycles

Looking in details, the distribution of some glacial/interglacial benthic foraminifera show a turnover system following climate cycles (Fig. 3). The time period from 530 to 420 kyr (MIS 13 and MIS 12) is characterized by the occurrence of B. spathulata, B. costata, G, orbicularis and B. marginata. Although they have a continuous distribution, highest relative abundances of these species are recorded during this interval (Fig. 3).

The interglacial-glacial coupled MIS 11-MIS 10 and MIS 9-MIS 8 are characterized by abundant S. schlumbergeri, Spiroloculina sp., B. nodosaria, S. reticulata and (Fig. 3). The observed feature is a relatively high abundance during the interglacial and strong (abrupt) decrease during the glacials (Fig. 3). A similar, but less marked trend is observed for the MIS 7-MIS 6 intervals (Fig. 3). Here, two species are dominant: S. schlumbergeri and B. nodosaria (Fig. 4).

Benthic foraminifer species such as G. altiformis, S. tenuis, S. eckisi and B. dilatata occur during the time interval from 330 to 240 kyr (that includes MIS 9 and MIS 8) where their higher relative abundances are observed (Fig. 3). G. altiformis and S. tenuis are the most abundant during the interglacial MIS 9, whereas S. eckisi peaks are observed during MIS 8 (Fig. 5). Bolivina dilatata occurs only during the MIS 9 (Fig. 5). This group disappears at the end of MIS 8 and it is replaced by group composed of R. phlegeri G. affinis, V. bradyana, C. bradyi, B. albatrossi, N. turgida and U. auberiana during the interval time from 240 to 130 kyr (MIS 7 and MIS 6, Fig. 3). U. auberiana peaks during the MIS 7 and it is absent from glacial interval. While C. bradyi, V. bradyana and B. albatrossi are more abundant during the MIS 6 (191-130 kyr BP), N. turgida, R. phlegeri and G. affinis are found during MIS 7 and MIS 6 (Fig. 6). A. scalaris, R. zitteli, H. balthica, P. crustata are species characterizing the period from 130 kyr to present (from MIS 5 to MIS 1, Fig. 3). In this group, H. balthica is the most abundant species with its higher relative abundance recorded during the MIS 5 (Fig. 7).

P. crustata appears more abundant during the MIS 1. R. zitteli and A. scalaris are found during the MIS 5 and the MIS 1 and they strongly decrease during MIS 4 (71-57 kyr BP), MIS 3 and MIS 2 (Fig. 7).

Discussion

Ostracoda assemblages over the last 550kyr in the East-Corsica basin: downslope transport and physic-chemical bottom conditions

An important number of allochthonous ostracod species is found at the GDEC-4-2 site. There are 25 allochthonous ostracod species among the 62 ostracod species identified. In this group, the most abundant species with higher than 10% (Semicytherura spp., Aurila sp., Loxoconcha sp., H. videns, P. calcarata, Leptocythere sp., U. favosa, Sagmatocythere sp., Paracypris sp., Costa sp., C. littoralis, Bairdia sp., Heterocythereis sp. and B. turgida, Table 1) are found all along the borehole GDEC-4-2.

It is known that ostracoda can be displaced by post-mortem transport more easily than benthic foraminifers [START_REF] Passlow | Late Quaternary history of the Southern Ocean offshore southeastern Australia, based on Ostracoda[END_REF]. This may be caused by their light, bowl-shaped valves, giving them potential as indicators of transport process more than many other microfossil groups [START_REF] Zhou | Allochthonous ostracods in the South China Sea and their significance in indicating downslope sediment contamination[END_REF]. Littoral species can thus be transported as deep as the bathyal waters as shown by several studies [START_REF] Hao | Effect of Quaternary turbidite sedimentation on Ostracoda distribution in the Okinawa Trough[END_REF][START_REF] Drapala | The use of ostracods in detecting fine grained turbidites in deep sea cores[END_REF][START_REF] Sciuto | Initial report on ostracod fauna from the Messina Straits (Ionian Sea, Northeastern Sicily)[END_REF].

The distribution of allochthonous cumulative abundance species plot (Fig. 2) shows that allochthonous ostracoda are more abundant during glacial periods and gradually decrease at the end of the cold stage, as shown by the positive correlation with the δ 18 O curves (Fig. 2, [START_REF] Toucanne | Tracking rainfall in the northern Mediterranean borderlands during sapropel deposition[END_REF]. This result suggests that the shelf-basin sediment transfer is enhanced during the glacial lowstands (in agreement with the former conclusions of [START_REF] Calvès | Inferring denudation variations from the sediment record; an example of the last glacial cycle record of the Golo Basin and watershed, East Corsica, western Mediterranean sea[END_REF][START_REF] Toucanne | Tracking rainfall in the northern Mediterranean borderlands during sapropel deposition[END_REF]. The allochthonous group is constituted by ostracoda shelf species that are considered as affected by reworking processes at the GDEC-4-2 site. Thus, the variations of the allochthonous during climate oscillations (Fig. 2) suggest the major control of eustatic factors in slope sedimentation. During sea level lowstands, gravity-induced mechanisms (i.e. turbidity currents, debris flows) or high energy hydrodynamic processes (i.e. storms, inducing sediment flows at the shelf edge) may increase sediment transport to deeper parts of the continental margins mainly through submarine canyons [START_REF] Shanmugam | Eustatic control of submarine fan development[END_REF][START_REF] Sciuto | Initial report on ostracod fauna from the Messina Straits (Ionian Sea, Northeastern Sicily)[END_REF]. During high sea level the sediment supply might be reduced because sediment is mostly trapped in the inner part of continental shelf, in the delta and prodelta settings, except for the periods with abundant rainfall on land [START_REF] Toucanne | Tracking rainfall in the northern Mediterranean borderlands during sapropel deposition[END_REF]. Submarine canyons are considered as preferential conduits for shelf-slope sediment transport than the adjacent open slope areas (Durrieu de [START_REF] Durrieu De Madron | Hydrography and nepheloid structures in the Grand-Rhône canyon[END_REF]. However, several studies provided information about contemporary sediment-transport processes acting within canyons and sediment resuspension events that is transported to the open slope [START_REF] Puig | Shelf-tocanyon sediment-transport processes on the Eel continental margin (northern California)[END_REF][START_REF] Puig | Storm-induced sediment gravity flows at the head of the Eel submarine canyon, northern California margin[END_REF].

Sediments along the slope are subsequently shaped by bottom current flowing parallel to bathymetric contours that begins the formation of contourites [START_REF] Stow | Contourites: Their recognition in modern and ancient sediments[END_REF][START_REF] Stow | Bottom currents, contourites and deep-sea sediment drifts: current state-of-the-art[END_REF]. Thus, a major role is certainly played by the variable intensity of intermediate currents in the sediment lateral transport in the open slope areas. In western Mediterranean Sea, it has been demonstrated that an intensification of Western Mediterranean Deep Water (WMDW) and Levantine Intermediate Water (LIW) circulation during cold climatic phases [START_REF] Cacho | Evidence for enhanced Mediterranean thermohaline circulation during rapid climatic coolings[END_REF][START_REF] Sierro | Impact of iceberg melting on Mediterranean thermohaline circulation during Heinrich events[END_REF][START_REF] Cacho | Glacial rapid variability in deep-water temperature and δ 18 O from the Western Mediterranean Sea[END_REF][START_REF] Toucanne | A 130,000-year record of Levantine Intermediate Water flow variability in the Corsica Trough, western Mediterranean Sea[END_REF] at Milankovitch to millennial sub-orbital time-scale. On East-Corsica margin, the intensity of downslope and along slope transport is inferred on the basis of the occurrence of allochthonous ostracoda, which suggest that the sea level variations strongly controlled the downslope transport at the glacial-interglacial time scale (Miramontes et al., in press). During glacial stages (positive correlation with δ 18 O values in Fig. 2), high abundances of allochtonous specimens are observed. High sediment supply is expected to be transferred from the shelf to the canyons and slopes during low sea level because of the sediment sources proximity (river mouths) to the shelf edge. Ostracoda from the shelf are thus easily transported in the detritic fraction and found abundant during glacial lowstands.

The abundances of interglacial ostracoda species are negatively correlated to δ 18 O plots (Fig. 2). In the interglacial group, the most significant contribution comes from Argilloecia acuminata, Cytheropteron alatum, Henryhowella sp. Polycope sp. and Cytherella sp.. The genera Argilloecia and Cytheropteron have been effectively observed to be influenced by warm water masses [START_REF] Cronin | Ostracoda and Paleoceanography, The Ostracoda: Applications in Quaternary[END_REF][START_REF] Iwatani | A paleobathymetric transition during the mid-Pliocene warm period: Ostracode evidence from Japan[END_REF] either because sensitive to bottom water temperature changes or to food availability, which is related to surface productivity [START_REF] Alvarez Zarikian | Glacial-interglacial variability in deep sea ostracod assemblage composition at IODP Site U1314 in the subpolar North Atlantic[END_REF] whereas C. alatum and Henryhowella are known to be species preferring oligotrophic conditions [START_REF] Donato | Surface-bottom relationships in the Gulf of Salerno (Tyrrhenian Sea) over the last 34 kyr: Compositional data analysis of palaeontological proxies and geochemical evidence Dingle[END_REF]). The ecological requirements for Henryhowella are still controversial: it is often found dominant in the bathyal zone off West Africa in well oxygenated waters (Dingle et al., 1990) but there is actually no obvious relationship between the abundance of Henryhowella and the oxygen content, according to [START_REF] Bonaduce | The areal and bathymetrical distribution of the genus Henryhowella Puri (Ostracoda) in the Gulf of Naples[END_REF] who studied the distribution of Henryhowella in the Gulf of Naples (Tyrrhenian Sea). Thus, Henryhowella is here considered as belonging to the interglacial group but with giving no specific indications for paleoenvironmental conditions. The genus Cytherella is considered as opportunistic filter-feeders species [START_REF] Russo | Miocene ostracodes of cold seep settings from northern Apennines (Italy) 2012[END_REF]. It is thought to belong to ostracoda species resistant to large decreases in water oxygenation levels because they feed by filtration, ventilate large volumes of water to obtain their food and thus achieve a maximum and optimal state of oxygenation.

At GDEC-4-2 site, the interglacial intervals (e.g., MIS5a, MI7c, 7e) were generally marked by an increase of Golo river discharges due to the increase in the precipitation over the Corsica. Consequently, the runoff increase possibly led to the higher flux of continental detritus (i.e., sediment and organic matter) to the bottom [START_REF] Toucanne | Tracking rainfall in the northern Mediterranean borderlands during sapropel deposition[END_REF]. The increase of interglacial ostracod group during interglacial periods can be linked to organic matter quality arriving at the bottom coupled with higher sea temperature that would favour an enhanced surface productivity. The distribution of these taxa can also be related to high bottom water temperature, as suggested by the perfect correlation with δ 18 O plots (Fig. 2). However, we do not have data from modern ostracoda to confirm this hypothesis and identifying which species are more sensitive to temperature change.

The glacial ostracoda species are not well represented along the borehole GDEC-4-2.

Their cumulative plot shows an important accumulation at the end of MIS 12, during the MIS 8 and MIS 2 (Fig. 2). The dominant taxa being: Paradoxostoma sp., C. testudo; B. vanstraateni, Macrocypris sp., and E. echinata. C. testudo ostracod species is well known as a "cold guest" of the Mediterranean Plio-Pleistocene [START_REF] Bonaduce | The appearance of Cytheropteron testudo Sars (Crustacea: Ostracoda) is a Pliocene event. Evidences from a Sicilian sequence (Italy)[END_REF][START_REF] Ciampo | Ostracods as palaeoenvironmental indicators in the last 30 ky from the Tyrrhenian continental shelf[END_REF]. It have been used to identify the input of "cold" Atlantic waters in the Mediterranean Sea during some cold Quaternary climatic events together with other "Northern guest" ostracod species which include some The study of core MD99-2348 (Gulf of Lions, NW Mediterranean) shows that C. testudo is part of glacial group [START_REF] Bassetti | Response of ostracods to abrupt climate changes in the Western Mediterranean (Gulf of Lions) during the last 30 kyr[END_REF]. In Alboran Sea, the E. echinata-B. vanstraateni-Macrocypris sp. group is known as a deep and cold environment association [START_REF] Babinot | Les ostracodes du quaternaire terminal de la marge marocaine de la mer d'Alboran : Environnements, implications paléoclimatiques et chronologie[END_REF]. E. echinata is considered as probably an indicator of well-ventilated bottom water and sufficient food supply [START_REF] Alvarez Zarikian | Glacial-interglacial variability in deep sea ostracod assemblage composition at IODP Site U1314 in the subpolar North Atlantic[END_REF][START_REF] Bassetti | Response of ostracods to abrupt climate changes in the Western Mediterranean (Gulf of Lions) during the last 30 kyr[END_REF].

In the borehole GDEC-4-2, the glacial ostracoda taxa show high abundance in the upper part of MIS 12, during the MIS 8 and MIS 2. The MIS 12 appears as marked by strong cold conditions with a climate that was colder than more recent glacial intervals [START_REF] Healey | Millennial-scale variability in western subtropical North Atlantic surface and deep water circulation during marine isotope stages 11 and 12[END_REF]. The MIS 8 is known as a relatively weak glacial in terms of global ice volume whereas MIS 2 is on average a very intense glacial phase [START_REF] Lisiecki | A Pliocene-Pleistocene stack of 57 globally distributed benthic d 18 O records[END_REF][START_REF] Lang | Interglacial and glacial variability from the last 800 ka in marine, ice and terrestrial archives[END_REF]. The increase of Paradoxostoma, C. testudo, B. vanstraateni, Macrocypris sp., E. echinata abundances observed in the GDEC-4-2 borehole during these cold climate intervals (MIS 12, MIS 8 and MIS 2) is interpreted as related to temperature drop, but coupled with the trophic level of hosting waters. As discussed above, the glacial intervals correspond to the periods with the highest sediment flux carried by the Golo River that means nutrients enriched waters. In this context, however, it is not possible to disentangle the impact of temperature from the nutrient supply in the distribution of the observed glacial ostracoda.

Ostracoda distribution: Mediterranean Sea vs Atlantic Ocean

The distribution of ostracoda in the Mediterranean seems to not be uniform with respect to the Atlantic during glacial-interglacial transitions. Polycope sp. and E. echinata distribution are here compared in the attempt to correlate their distribution to water masses properties, which are related to climate conditions. The genus Polycope is often associated to fine-grained, organic-rich sediment, possibly linked to interglacial high productivity both in the Mediterranean and Arctic Ocean [START_REF] Breman | The distribution of ostracodes in the bottom sediments of the Adriatic Sea[END_REF][START_REF] Bonaduce | Distribution of Ostracoda in the Adriatic Sea[END_REF][START_REF] Cronin | Quaternary paleoceanography of the deep Arctic Ocean based on quantitative analysis of Ostracoda[END_REF]. [START_REF] Benson | Newfoundland continental slope and rise[END_REF] consider Polycope sp. associated with diminished vertical mixing because of its tolerance to oxygen deficient conditions, as found in the Newfoundland slope (eastern coast of Canada) in finegrained sediment and low bottom current velocities.

In the borehole GDEC-4-2 the genus Polycope is very abundant (50% of the total ostracoda fauna) during MIS 5 and MIS 1 (Table 1), as previously observed in the core MD01-2472 by Angue Minto 'o et al. (2015) where up to 70 % of the total ostracoda consists of Polycope sp. during MIS 1. This suggests low current velocities and lower bottom water oxygenation during the current interglacial. In the North Atlantic, Polycope sp. abundance reaches the maximum during the glacial periods (Didié and Bauch, 2000;[START_REF] Alvarez Zarikian | Glacial-interglacial variability in deep sea ostracod assemblage composition at IODP Site U1314 in the subpolar North Atlantic[END_REF]. Considering that Polycope sp. is not a temperature marker, its inverse distribution between Atlantic and Mediterranean Ocean would explain by a reverse bottom paleoceanographic conditions. During cold intervals, Atlantic Meridional Overturning Circulation (AMOC) is highly reduced in North Atlantic [START_REF] Labeyrie | Surface and deep hydrology of the northern Atlantic ocean during the past 150,000 years[END_REF][START_REF] Mccave | Circulation in the glacial North Atlantic inferred from grain-size measurements[END_REF][START_REF] Cortijo | Changes in sea-surface hydrology associated with Heinrich event 4 in the North Atlantic Ocean between 40° and 60°N[END_REF][START_REF] Cortijo | Changes in sea-surface hydrology associated with Heinrich event 4 in the North Atlantic Ocean between 40° and 60°N[END_REF][START_REF] Healey | Millennial-scale variability in western subtropical North Atlantic surface and deep water circulation during marine isotope stages 11 and 12[END_REF][START_REF] Stanford | A new concept for the paleoceanographic evolution of Heinrich event 1 in the North Atlantic[END_REF], while an higher bottom current velocity is observed in the Mediterranean Sea during cold climatic intervals [START_REF] Cacho | Evidence for enhanced Mediterranean thermohaline circulation during rapid climatic coolings[END_REF][START_REF] Sierro | Impact of iceberg melting on Mediterranean thermohaline circulation during Heinrich events[END_REF][START_REF] Cacho | Glacial rapid variability in deep-water temperature and δ 18 O from the Western Mediterranean Sea[END_REF]Toucanne et al., 2012). E. echinata is part of glacial ostracod group (Fig. 2). [START_REF] Bassetti | Response of ostracods to abrupt climate changes in the Western Mediterranean (Gulf of Lions) during the last 30 kyr[END_REF] observed in the Gulf of Lions () the same pattern, where E. echinata is particularly abundant during cold stadials (Heinrich events). In the subpolar regions and North Atlantic, E. echinata has been associated with interglacial group [START_REF] Alvarez Zarikian | Glacial-interglacial variability in deep sea ostracod assemblage composition at IODP Site U1314 in the subpolar North Atlantic[END_REF][START_REF] Cronin | Deep-sea ostracode species diversity: response to late Quaternary climate change[END_REF]Didié and Bauch, 2000). E. echinata is considered as probably an indicator of well-ventilated bottom water and sufficient food supply [START_REF] Bassetti | Response of ostracods to abrupt climate changes in the Western Mediterranean (Gulf of Lions) during the last 30 kyr[END_REF]. As Polycope, the reverse distribution shown by E. echinata between Mediterranean Sea and Atlantic Ocean can be linked to trophic level and dissolved oxygen content related to thermohaline circulation [START_REF] Marchitto | Millennial-scale changes in North Atlantic circulation since the last glaciation[END_REF].

Benthic foraminifera species distribution over the last 550 kyr in the East-Corsica basin: bottom trophic conditions

Autochthonous benthic foraminifera are grouped into three main groups. 1) species with continuous distribution composed of 23 species where the most abundant are M. barleeanus (45%), U. mediterranea (36%), T. angulosa (36%) and C. pachyderma (29%, Table 2). 2) group of 16 species that show a discontinuous distribution (Table 2). 3) group of 24 benthic foraminifera species whose distribution allows a characterization glacial/interglacial periods. The first two groups do not allow a clear interpretation of the paleo-environmental conditions of the last 550 kyr. As a result, discussion is focus on the third group.

The interglacial benthic foraminifera group (Fig. 2) is marked by the predominance of H. elegans, S. schlumbergeri, B. nodosaria (MIS 11,MIS 9,MIS 7,and MIS 1) and H.balthica (MIS 5). H. elegans is often observed in meso-oligotrophic sediments, at elevated water depth [START_REF] Mojtahid | Live benthic foraminiferal faunas along a bathymetrical transect (140-4800 m) in the Bay of Biscay(NE Atlantic)[END_REF][START_REF] Duros | Live (stained) benthic foraminifera in the Whittard Canyon, Celtic margin (NE Atlantic). Deep-Sea Res[END_REF][START_REF] Dessandier | Lateral and vertical distributions of living benthic foraminifera off the Douro River (western Iberian margin): Impact of the organic matter quality[END_REF] but with variable quantity of organic fluxes [START_REF] Altenbach | Scaling percentages and distributional patterns of benthic foraminifera with flux rates of organic carbon[END_REF]. Its dominance at deep environment (up to 2000 m) suggests that it tolerates low quality organic matter, often found in well-oxygenated sediments (e.g. [START_REF] Mojtahid | Live benthic foraminiferal faunas along a bathymetrical transect (140-4800 m) in the Bay of Biscay(NE Atlantic)[END_REF]. More recently, [START_REF] Dessandier | Lateral and vertical distributions of living benthic foraminifera off the Douro River (western Iberian margin): Impact of the organic matter quality[END_REF] shown that H. elegans is part of deeper environments that correlate to fairly abundant but low quality organic matter. In the Adriatic Sea, S. schlumbergeri is known to positively correlate with the percentage of organic matter, while it shows a negative correlation with the coarseness of the substrate and percentage of calcium carbonate [START_REF] Jorissen | The distribution of benthic foraminifera in the Adriatic Sea[END_REF]. B. nodosaria was observed as having an opportunistic behaviour in the outer shelf of the Bay of Biscay when it grows after a phytoplankton bloom [START_REF] Duchemin | Seasonal variability of living benthic foraminifera from the outer continental shelf of the Bay of Biscay[END_REF]. This species is also observed in the upper slope of the Gulf of Lions and in the Bay of Biscay suggesting its dependence to marine phytodetritus [START_REF] Fontanier | Live foraminifera from the open slope between Grand Rhône and Petit Rhône Canyons (Gulf of Lions, NW Mediterranean)[END_REF]. High oxygen and labile organic matter are necessary for feeding H. balthica [START_REF] Fontanier | Live benthic foraminiferal faunas from the Bay of Biscay: faunal density, composition, and microhabitats[END_REF][START_REF] Fontanier | Live foraminifera from the open slope between Grand Rhône and Petit Rhône Canyons (Gulf of Lions, NW Mediterranean)[END_REF] which is abundant particularly during MIS 5. At the borehole GDEC-4-2 site, the abundance increase of H. elegans, S. schlumbergeri, B. nodosaria during the interglacials (MIS 11, MIS 9, MIS 7, and MIS 1) and H. balthica during the MIS 5 can be linked to important supply of organic matter.

It might be related to increasing surface productivity, allowing an enhanced export of organic matter to sea floor at the GDEC-4-2 site.

The glacial benthic foraminifera group (Fig. 2) is characterised by the predominance of B. spathulata, B. costata, and B. marginata with higher abundance especially observed during MIS 12 and MIS 6 (and on lesser extent MIS 10 and MIS 2). These species known as opportunistic taxa [START_REF] Gooday | A response by benthic foraminifera to the deposition of phytodetritus in deep sea[END_REF], can be indicative of organic matter abundance, even of low quality (pytodetritus and detrital organic flux). Their abundance in the glacial intervals can possibly link to an enhanced flux of continental detritus (i.e., sediment and organic matter) via runoff at the GDEC-4-2 site. In fact, glacial intervals (sea level lowstand periods) are characterized by the proximity of river mouths conducting to an important sediment flux transfer to the seafloor (e.g. [START_REF] Bonneau | Millennial-Scale Response of a Western Mediterranean River to Late Quaternary Climate Changes: A View from the Deep Sea[END_REF][START_REF] Lombo Tombo | Sea-level control on turbidite activity in the Rhone canyon and the upper fan during the Last Glacial Maximum and early Deglacial[END_REF] for the Western Mediterranean). The abundance of opportunistic benthic foraminifera during the MIS 12, MIS 10, MIS 6 and MIS 2 could be explained by the direct connection between the Golo River and Golo canyon heads leading to important sedimentary inputs associated to well quantity of refractory organic matter.

Benthic foraminifera turnover system: the last three climate cycles bottom conditions

Based on the distribution of benthic foraminifera in both glacial/interglacial group, the last three climatic cycles (MIS 8-9, MIS 6-7, MIS 1-5, Fig. 3) can be characterised in a relatively good detail. The MIS 8-9 interval is marked by the occurrence of G. altiformis, S.tenuis, S. eckisi B. dilatata (especially abundant during the MIS 9, Fig. 3). During the MIS 6-7 interval, these taxa are replaced by R. phlegeri,G. affinis,V. bradyana,C. bradyi,B. albatrossi,N. turgida and U. auberiana (Figs. 3 and Fig. 6). The last climatic cycle is characterised by the occurrence of A. scalaris, R. zitteli, H. balthica and P. crostata (Figs. 3 and7).

The δ 18 O plots (Fig. 3) show that during MIS 9 stable oceanic condition in term of temperature and salinity at the bottom may have prevailed, causing long-term water stratification. The occurrence of B. dilatata, tolerating relatively high bottom water salinity (Figs. 3 and5), [START_REF] Van Der Zwaan | Paleoecology of late Miocene Mediterranean foraminifera[END_REF][START_REF] Jorissen | Vertical distribution of benthic foraminifera in the northern Adriatic Sea: The relation with the organic flux[END_REF] or G. altiformis (Figs. 3 and5), tolerating slightly suboxic conditions [START_REF] Kaiho | Effect of organic carbon flux and dissolved oxygen on the benthic foraminiferal oxygen index (BFOI)[END_REF], is an indication of reduced vertical mixing.

Later on, during MIS 7 and MIS 6, bottom and surface water temperatures (and salinities?) change "quickly" (δ 18 O plots in Fig. 3 show high amplitude of values variation on a short-term time scale). We think that the presence of V. bradyana, R. phlegeri and G. affinis might be significant in this group (Figs. 3 and6). R. phlegeri is known to inhabit shallow water settings in the Mediterranean Sea, in organic-rich sediment [START_REF] Jorissen | The distribution of benthic foraminifera in the Adriatic Sea[END_REF][START_REF] Frezza | Distribution of recent foraminiferal assemblages near the Ombrone River mouth (Northern Tyrrhenian Sea, Italy)[END_REF]. Similarly, V. bradyana and G. affinis are considered as opportunistic species living in organic-matter rich bottoms, including low-quality organic detritus [START_REF] Fontanier | Live benthic foraminiferal faunas from the Bay of Biscay: faunal density, composition, and microhabitats[END_REF]. V. bradyana is also observed to prefer silt sized sediments [START_REF] Frezza | Distribution of recent foraminiferal assemblages near the Ombrone River mouth (Northern Tyrrhenian Sea, Italy)[END_REF] and has been described in low oxygen sediments from the center of the Adriatic Sea mud belt [START_REF] Jorissen | The distribution of benthic foraminifera in the Adriatic Sea[END_REF][START_REF] Van Der Zwaan | Biofacial patterns in river-induced shelf anoxia[END_REF]. We suppose that this distribution can be strongly related to mechanisms of sediments dispersion (downslope transport and lateral advection) and linked to changing intensity in bottom currents during climate oscillations.

High oxygen and labile organic matter are correlated with the occurrence of H. balthica and A. scalaris [START_REF] Fontanier | Live benthic foraminiferal faunas from the Bay of Biscay: faunal density, composition, and microhabitats[END_REF][START_REF] Fontanier | Live foraminifera from the open slope between Grand Rhône and Petit Rhône Canyons (Gulf of Lions, NW Mediterranean)[END_REF] that are abundant particularly during MIS 5 (Fig. 7). In the Corsica Trough (northwestern Tyrrhenian Sea), P. crustata, was especially found during the MIS 1 (Holocene) where bottom conditions was characterized by oligo-mesotrophic trophic level and low-energy bottom conditions [START_REF] Minto'o | Levantine intermediate water hydrodynamic and bottom water ventilation in the northern Tyrrhenian Sea over the past 56,000 years: New insights from benthic foraminifera and ostracods[END_REF]. P. crustata presents the same distribution in this study (Fig. 7). During the last climate cycle (MIS 5-MIS 1), several factors (climate/sea level) interplay for determining the characteristic of the bottom water conditions [START_REF] Minto'o | Enregistrments sédimentaires des changements climatiques et environnementaux pendant le Quaternaire terminal sur la marge Est-Corse[END_REF]. However, we think that changes in surface productivity probably associated to changes in the bottom current could have play an important role in the occurrence of A. scalaris, R. zitteli, H. balthica and P. crostata during the last climate cycle.

In this study, both ostracoda and benthic foraminifera abundances show glacialinterglacial swings. Although, ostracod-foraminiferal differences in relationships between environmental drivers and trophic change can be observed in the borehole GDEC-4-2. The use of both benthic microfossils is very useful because this allows complementarity in interpretation of different environmental parameters. High abundances of allochthonous ostracoda during these intervals are observed on the basis of cumulative abundance of (post-mortem) species.

The last three climate cycles (MIS 8-9, MIS 6-7, MIS 1-5) show a turnover system for benthic foraminifera specific groups. Ostracoda as Polycope sp. and E. echinata show a reverse distribution between Mediterranean and the Atlantic oceans during glacial-interglacial oscillations. This can be linked to the opposite paleooceanographic conditions between the two areas during climatic oscillations.

Figures captions

Tables captions

Table 1:

Table of actual counts of all ostracoda taxa identified in the 291 analysed samples collected in the borehole GDEC-4-2.

Table 2:

Table of actual counts of all benthic foraminifera taxa identified in the 291 analysed samples collected in the borehole GDEC-4-2.

Depth (m)

:

  Cassidulina carinata Silvestri, 1896, Fissurina cucullata Silvestri, 1902, Uvigerina mediterranea Hofker, 1932, Planulina ariminensis d'Orbigny, 1826, Cibicides sp., Melonis barleeanus Williamson, 1858, Cycloforina contorta d'Orbigny, 1839, Cyclogyra sp., Trifarina angulosa Williamson, 1858, Cassidulina minuta Nørvang, 1945, Pullenia sp., Bulimina elegans d'Orbigny, 1826, Bulimina aculeata d'Orbigny, 1826, Cibicides pachyderma Rzehak, 1886, Triloculina sp., Uvigerina peregrina Cushman, 1923, Chilostomella sp., Pyrgo sp.. However species such as C. minuta, C. contorta, F. cucullata, Cyclogyra sp., Pyrgo sp., and Pullenia sp., are poorly represented along the borehole with relative abundances less than 5%. The most abundant species are M. barleeanus (45%), U. mediterranea (36%), T.

  Fig. 2): Bolivina spathulata Williamson, 1858, Bulimina costata d'Orbigny, 1852, Gyroidina orbicularis d'Orbigny, 1826, and Bulimina marginata d'Orbigny, 1826, Pyrgo elongata d'Orbigny, 1826, Pyrgo murrhina Schwager, 1866, Cibicides wuellerstorfi Schwager, 1866, , Fissurina apiculata Reuss, 1851, Eggerella bradyi Cushman, 1911, Suggrunda eckisi Natland, 1950, Spirosigmoilina tenuis Czjzek, 1848, Globobulimina affinis d'Orbigny, 1839, Valvulineria bradyana Fornasini, 1900, Cassidulinoides bradyi Norman, 1881. The dominant species in this group are B. spathulata, B. costata, and B. marginata.

Paradoxostoma

  specie such as Paradoxostoma abbreviatum, Paradoxostoma ensiforme, Paradoxostoma tenuissimum (see references in Faranda and Gliozzi, 2011). Martínez-García et al. (2015) used the presence of C. testudo together with Acanthocythereis dunelmensis and Trachyleberis sp. to evidence the occasional input of cold bottom waters coming from the circumpolar area of the North Atlantic Ocean into the Basque shelf during late Quaternary.

  Interglacial periods are characterized by the increase of ostracoda group mainly composed of the A. acuminata, C. alatum, Henryhowella sp. Polycope sp. and Cytherella sp. indicating an enhanced surface productivity and possibly high bottom water temperature during these warm periods. Benthic foraminifera representing interglacial intervals are H. elegans, S. schlumbergeri, B. nodosaria and H. balthica. They also show an increasing surface productivity which allowed an enhanced export of organic matter to sea floor at the GDEC-4-2 site during these interglacial periods. The abundance increase of ostracoda as Paradoxostoma sp., C. testudo, B. vanstraateni, Macrocypris sp., E. echinata during glacial intervals (MIS 12, MIS 8 and MIS 2) at GDEC-4-2 borehole site, is interpreted as related to bottom temperature drop, but coupled with the trophic level of hosting waters. Higher abundance show by benthic foraminifera as B. spathulata, B. costata, and B. marginata (especially during MIS 12, MIS 10, MIS 6 and MIS 2) indicate that this trophic level is characterized by important sedimentary input associated to high quantity of refractory organic matter. Glacial periods are characterized by an enhanced of the shelf-basin sediment transfer.

Figure 1 :

 1 Figure 1: Bathymetry of northern part of East-Corsica margin and location of studied borehole GDEC-4-2 drilled at water depth of 492 m. The dash lines indicate the Levantine Intermediate Water (LIW) path.

Figure 2 :

 2 Figure 2:Distribution along borehole GDEC-4-2 of δ 18 O curves, cumulative abundance of interglacial ostracod group, allochthonuous ostracod group, glacial ostracod group, and of interglacialglacial benthic foraminifera groups. Oxygen stable isotope measurements were performed on Globigerinoides ruber, Neogloboquadrina pachyderma and Globigerina bulloides (for planktonic foraminifer) and on Cibicides wuellerstorfi, Cibicidoides pachyderma and Cibicidoides kullenbergi (for benthic foraminifera plot,[START_REF] Toucanne | Tracking rainfall in the northern Mediterranean borderlands during sapropel deposition[END_REF].

Figure 3 :

 3 Figure 3: Distribution of benthic foraminifer groups describing a turnover system along the GDEC-4 borehole and allowed the characterization of climate cycles. And δ 18 O curves whose

Figure 4 :

 4 Figure 4: Distribution of benthic foraminifera group whose highest relative abundances are recorded during the climate cycle including the MIS 11-MIS 10, the MIS 9-MIS 8 and the MIS 7-MIS 6. The two dominant species in this group are: S. schlumbergeri and B. nodosaria with percentages up to 20%.

Figure 5 :

 5 Figure 5: Distribution of benthic foraminifera group whose highest relative abundances are recorded during the climatic cycle including the MIS 9 and the MIS 8.

Figure 6 :

 6 Figure 6: Distribution of benthic foraminifera group whose highest relative abundances are recorded during the climatic cycle including the MIS 7 and the MIS 6.

Figure 7 :

 7 Figure 7: Distribution of benthic foraminifera group whose highest relative abundances are recorded during the last climatic cycle.

  Fig. 2 Angue Minto'o et al.

  Fig. 4 Angue Minto'o et al.

  This group consist ofArgilloecia acuminata Mueller, 1894, Cytheropteron alatum Sars, 1866, Henryhowella sp., Rectobuntonia inflataColalongo and Pasini, 1980, Cytherella sp., Carinocythereis carinata Roemer, 1838, Krithe keyi Breman, 1978, Polycopes sp.,

	Bosquetina dentata Mueller, 1894; show higher relative abundance during interglacial
	intervals (Table 1, Fig. 2). In this interglacial group, the most abundant taxa are A. acuminata
	(55%), C. alatum (50 %), Polycope sp. (50 %), Henryhowella sp. (45 %), Cytherella sp.
	(25%). The genus Polycope is rare along borehole except during Marine Isotopic Stage (MIS)
	5 (130-71 kyr BP) and MIS 1 (14 kyr to present).

Bathycythere vanstraateni Sissingh, 1971 and Cytheropteron testudo Sars,1869, Bythoceratina reticulata Bonaduce, Ciampo and Masoli, 1976, (Table 1, Fig. 2). The dominant

  taxa in this ostracod glacial group are: Paradoxostoma sp., Macrocypris sp., E.

	, Paradoxostoma
	sp., Cytheropteron monoceros Bonaduce, Ciampo & Masoli, 1976, Cytheropteron zinzulusae
	Bonaduce, Ciampo & Masoli, 1976, Macrocypris sp., Echinocythereis echinata Sars, 1866,
	echinata and B. vanstraateni, C. testudo.

discontinuous distribution is observed for the 16 following benthic foraminifera

	species Gyroidina umbonata Silvestri, 1898, Lagena hexagona Williamson, 1848, Lagena
	sulcata Walker and Jacob, 1798, Bolivina alata Seguenza, 1862, Bolivina sp., Lagenosolenia
	sigmoidella Cushman, 1933, Lagena hispida Reuss, 1858, Uvigerina bifurcata d'Orbigny,
	1839, Fissurina sp., Lagena sp., Lagena striata d'Orbigny, 1839, Neoeponides schreibersii
	d'Orbigny, 1846, Fissurina apiculata Reuss, 1851, Bulimina elongata d'Orbigny, 1826.
	(Table 2).

Table 2 ,

 2 Fig. 2): Hoeglundina elegans d'Orbigny, 1878, Lenticulina sp., Neolenticulina sp., Sigmoilopsis schlumbergeri Silvestri, 1904, Robulus sp., Bigenerina nodosaria d'Orbigny, 1826, Siphonina reticulata Czjzek, 1884, Spiroloculina sp., Gyroidina altiformis Stewart and Stewart, 1930, Bolivina dilatata Reuss, 1850, Rectuvigerina phlegeri Le Calvez, 1958, Nonionella turgida Williamson, 1858, Uvigerina auberiana d'Orbigny, 1839, Amphicoryna scalaris Batsch, 1791, Rectobolivina zitteli Karrer, 1878, Hyalinea Bigenerina nodosaria (20%) and H. balthica (55%, Table 2). This latter is especially abundant during the MIS 5, while H. elegans, S. schlumbergeri, B.nodosaria are present during MIS 11, MIS 9, MIS 7 and MIS 1.

balthica Schröter, 1783 and Pseudoclavulina crustata Cushman, 1936. However, the dominant species in this group are: H.elegans (16%), S. schlumbergeri (20%),

Acknowledgments

The authors also thank the crew and scientific team (G. Calvès, G. Dan-Unterseh, L. Droz, I. Jégou, G. Lericolais, E. Marchès, T.Marsset) of the GOLODRILL cruise (R/V 'Bavenit' -FUGRO) for the recovery of the GDEC-4-2 borehole. This study has been realized in the frame of the "GOLO PROGRAM", a research consortium between IFREMER, TOTAL, EXXONMOBIL and FUGRO. The authors are very grateful to IFREMER technical staff for sampling and samples treatment and to the two anonymous reviewers who provide helpful review of the manuscript.