Laure Favier
email: lfavier@cgfl.fr

Nathalie Bremaud

Zoé Tharin

Julie Blanc

Aurélie Bertaut

Véronique Alavoine

A Dubief

Gilles Truc

Christine Dorlean

Bruno Coudert

RCP soins de support : 12 ans d'expérience d'un centre de lutte contre le cancer

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

Résumé

En 2006, à la suite de la circulaire DHOS 2005/101, nous avons créé une réunion multidisciplinaire de soins de support. Il existe très peu de données dans la littérature dans ce domaine et nous avons souhaité reporter ici notre expérience. Pour cela, les dossiers présentés sur les six premiers mois de l'année 2006,2008,2010,2012,2014,2016 et 2018 ont été analysés, soit 405 situations correspondant à 352 patients. La majorité était constituée de femmes (55,7 %, N = 196) et l'âge médian lors de la présentation était de 66 ans . Dans 8 % (n = 32) des situations, la prise en charge était curative, dans 58 % (n = 233) des cas, palliative avec traitement spécifique en cours, dans 31,3 % (n = 126) palliative exclusive et enfin 2,7 % (n = 11) des discussions concernaient l'après cancer. Le nombre médian de participants était de 10 avec une présence régulière des oncologues, de l'équipe de soins palliatifs, de l'assistante sociale, la diététicienne, la kinésithérapeute et la psychologue. Les deux motifs les plus fréquents de présentation étaient le devenir et une demande d'intervention de l'équipe mobile de soins palliatifs. La décision de la réunion était relativement bien appliquée avec un taux de conformité de 81,8 %. Cependant, on peut regretter le délai court de 1,5 mois entre le décès et la concertation. La création d'un département transversal de soins de support a fait prendre de l'ampleur à cette réunion et il serait pertinent dans un avenir proche de vérifier si elle permet une meilleure anticipation.

Mots clés : soins de support -réunion de concertation pluridisciplinaire soins palliatifsoncologie -interdisciplinarité-transversalité

Abstract

In 2006, in response to DHOS Circular 2005/101, we have created a multidisciplinary supportive care meeting. As available literature covering this subject is rare, we report here our own experience. For this purpose, available files from the six initial months of 2006, 2008, 2010, 2012, 2014, 2016 and 2018 were analyzed, representing 405 situations corresponding to 352 patients. The majority of patients were women (55,7 % , n = 196) and the median age was 66 years old . Treatment was curative in 8 % (n = 32) of the situations, palliative in 58 % (n = 233), exclusively palliative in 31.3 % (n = 128) and concerned post-cancer situations in 2.7 % (n = 11). The median number of participants in multidisciplinary team meeting was 10, with a regular presence of oncologists, palliative care team members, social workers, dietician, physiotherapist and psychologist. The two most common reasons for case presentation were advice on follow-up and support on a precise palliative situation. Multidisciplinary support care meeting decisions were relatively well implemented, with a compliance rate of 81.8 %. Nevertheless, cases were presented late with a median time of 1.5 months from presentation to patient death. The creation of a crosssupportive care department has increased this meeting relevance and it would be important in the near future to evaluate whether this organization allows a better foresight of supportive care. Nous avons choisi de conserver l'appellation « RCP ». Les RCP sont définies par la Haute Autorité de Santé (HAS) comme un regroupement « des professionnels de santé de différentes disciplines dont les compétences sont indispensables pour prendre une décision accordant aux patients la meilleure prise en charge en fonction de l'état de la science». Ainsi même si la RCP soins de support ne concerne pas ou très rarement des décisions médicales ou des prises en charge en fonction de l'état de la science, on retrouve en revanche la notion de regroupement professionnel et de réflexion pour améliorer la prise en charge pour le patient. Toujours selon la définition de l'HAS, pour justifier du terme RCP, trois spécialités médicales différentes doivent participer. Dans notre cas, cela ne représente que 22 % des réunions sur la globalité de la période analysée et 61,3 % des réunions en 2018. Le terme de staff pluriprofessionnel comme défini par Chantal Bauchetet (6) paraît sans doute plus adapté. Cependant, aucune valorisation n'est à ce jour active pour ces staffs qui sont pourtant inscrits comme critère de certification 13a de la V32010 de l'HAS pour les patients en soins palliatifs.

Keywords

Enfin, les différentes spécialités paramédicales piliers des soins de support (diététicienne, assistante sociale et psychologue) sont très assidues, témoignant du caractère multidisciplinaire de la réunion et de son importance pour l'équipe. Il est important de souligner que c'est la seule RCP à laquelle, dans établissement tout au moins, participent conjointement et activement les médecins et les paramédicaux.

Bien que maintenant reconnue et essentielle à notre structure de soins, notre réunion soins de support a encore de nombreuses faiblesses. La plupart des patients étaient en situation palliative. Comme expliqué en introduction, nous avons choisi de regrouper les situations en curatif, palliatif, palliatif exclusif et après cancer. Cette dichotomie peut paraître erronée mais sur un recueil rétrospectif à partir de dossiers médicaux, elle nous a permis une certaine reproductivité et objectivité. Le délai médian entre la présentation en RCP et le décès était de 1,5 mois (0,0 -144,3 mois) témoignant de patients en situation palliative terminale et d'un manque d'anticipation dans la prise en charge. Depuis la création du DT2S, nous avons choisi de présenter systématiquement certains parcours complexes (les patients AJA, les patients suivis pour une pathologie ORL pour lesquels une radio chimiothérapie a été retenue, demande d'HJ SOS). Enfin, une UMSP propre à l'établissement a été créée en 2015. Il est encore prématuré pour juger de l'impact de ces mesures mais il sera intéressant à l'avenir de refaire cette analyse dans quelques années pour voir si les choses ont évolué.

Concernant les pathologies présentées, les carcinomes bronchiques (n = 80, soit 19,8 %) représentent la majorité des discussions, suivies par les carcinomes gynécologiques (n = 67, soit 19 %), les carcinomes mammaires (n = 56, soit 13,9 %) et les tumeurs cérébrales primitives (n = 29, soit 7,2 %). Si l'on regarde l'activité du centre Leclerc, on a une distribution complètement différente avec une majorité d'adénocarcinomes mammaires (32,9 %), les cancers digestifs (15,2 %) et les tumeurs génito urinaires (13,1 %). Le médecin oncologue responsable des soins de support s'occupe en particulier de pathologies pulmonaires et gynécologiques ; ceci pourrait être une explication. Deuxième hypothèse, les patients suivis pour une pathologie bronchique sont souvent plus altérés et nécessitent un accès rapide aux soins de support. Pour les pathologies gynécologiques, on a souvent à faire à des patientes en occlusion parfois pendant plusieurs semaines voire plusieurs mois, avec un devenir complexe. Cette hypothèse est corroborée par le fait que les patientes porteuses d'un cancer de l'ovaire constituent une activité importante de notre hospitalisation à domicile [START_REF]Etude des symptômes et prescriptions chez les patients en soins palliatifs pris en charge en hospitalisation à domicile du centre Geogres François Leclerc[END_REF].

En ce qui concerne les gliomes et les glioblastomes, compte tenu des répercussions et du handicap engendré par la pathologie, on comprend l'importance du nombre de cas discutés.

Pour les participants en RCP, les différentes spécialités paramédicales (psychologues, assistante sociale, diététicienne, kinésithérapeute) sont bien représentées. Quant aux médecins, un oncologue médical assiste régulièrement à la réunion et il en va de même pour le médecin de soins palliatifs depuis la création de l'UMSP en 2015 avec un taux de participation respectivement de 77,3 % et 96 %.

Si l'on regarde le motif de discussion en RCP, ce qui revient le plus fréquemment est un problème de devenir suivi d'une aide lors d'une prise en charge palliative. Les questions éthiques (poursuite ou non de la chimiothérapie, poursuite ou non d'une nutrition artificielle) restent exceptionnelles, ce que l'on peut regretter. La place accordée aux professionnels de soins de support en RCP d'oncologie est relativement faible, voire nulle (8). Goldwasser et al. conseillent donc la présentation systématique des dossiers en staff entre l'oncologue référent et le médecin de soins palliatifs à partir de la troisième ligne de chimiothérapie [START_REF] Goldwasser | La reunion de concertation pluridisciplinaire onco-pallaitive : objectifs et préconisations pratiques[END_REF].On peut donc s'étonner que ces discussions ne soient pas plus fréquentes dans notre établissement. Le délai court entre la discussion en RCP et le décès est également un reflet d'un manque d'anticipation et d'échange. Ce phénomène ainsi que le recours tardif aux soins palliatifs en France ont déjà été reportés [START_REF] Vinant | Integration and activity of hospital-based palliative care consultation team: the INSIGHT multicentric cohort study[END_REF]. Il est pourtant maintenant clairement établi qu'une intégration de l'équipe de soins palliatifs, parfois même dès le diagnostic, est bénéfique pour le patient [START_REF] Temel | Phase II study : integreated palliative care in newly diagnosed advanced non small cell lung cancer[END_REF][START_REF] Bakitas | Effects of a palliative care intervention on clinical outcomes in patients with advanced cancer: the Project ENABLE II randomized controlled trial[END_REF][START_REF] Temel | Early palliative care for patients with metastatic non-small-cell lung cancer[END_REF][START_REF] Zimmermann | Early palliative care for patients with advanced cancer: a clusterrandomised controlled trial[END_REF][START_REF] Bakitas | Early Versus Delayed Initiation of Concurrent Palliative Oncology Care: Patient Outcomes in the ENABLE III Randomized Controlled Trial[END_REF].

Conclusion

Au fil du temps, la RCP soins de support crée en 2006 au centre Georges François Leclerc est devenue un rendez-vous important au sein de l'établissement, comme en témoignent l'augmentation du nombre de dossiers présentés et la participation de membres extérieurs à notre établissement. Sa pertinence semble également acquise aux vues du taux de conformité entre la proposition de la RCP et la décision prise par les cliniciens ainsi que par la représentativité de diverses spécialités médicales et paramédicales. Restent à améliorer l'anticipation de la prise en charge palliative, avec présentation plus précoce des dossiers en RCP, et peut être un meilleur repérage des dossiers à discuter. La création d'un département transversal de soins de support en 2018 a clairement fait augmenter notre activité. Il serait donc intéressant de refaire cette revue dans quelques années et d'évaluer l'impact de cette nouvelle organisation des soins de support au sein du département.

Les auteurs souhaitent remercier Isabelle Grégoire et Hanaya Blitot pour leur aide technique et leur relecture.

Bibliographie

Trois mois avant décès 0,0% (0) 0,0 (0) 0,0%(0) 0,0%(0) 14,3%(1) 14,3%(1) 0,0% (0) 2,9%

> 3 mois 14,3 (1) 13%(3) 20%(1) 16,7%(1) 14,3%(1) 42,9%(3) 28,6% (4) 20,3% [START_REF] Zimmermann | Early palliative care for patients with advanced cancer: a clusterrandomised controlled trial[END_REF]

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  supportive care -multidisciplinary team meeting-palliative careinterdisciplinary-transdisciplinary La notion de soins de support est née dans les années 90 avec le « supportive care » défini par la Multidisciplinary Association of Supportive Care in Cancer (MASCC) comme « the total medical, nursing and psychological help which the patients need besides the specific treatment » (1). En France, il faudra attendre le premier plan cancer en 2003 pour voir les choses évoluer et c'est en réponse aux premiers états généraux du cancer mettant en exergue le manque d'information, de communication et de coordination dans la prise charge que l'accent a été mis sur le développement des soins de support. La circulaire de la direction générale de l'offre de soins (DHOS) 2005/101 du 22 février 2005 (2) relative à l'organisation des soins en cancérologie les a définis comme « l'ensemble des soins et soutiens nécessaires aux personnes malades tout au long de la maladie conjointement aux traitements onco hématologiques spécifiques lorsqu'il y en a » ; ils ne constituent donc pas une nouvelle discipline mais une coordination de compétences au service du patient et de ses proches. On a ainsi vu naître la notion d'interdisciplinarité, de coordination et de transversalité au sein d'une spécialité médicale, l'oncologie, où la prise en charge tend à devenir de plus en plus spécifique et scientifique (3). Cette même circulaire DHOS 2005/101 stipule que c'est dans le cadre de réunions de concertation pluridisciplinaire (RCP) que cette coordination est actée par la représentation et l'implication des différents acteurs qui après discussion et concertation proposent aux patients la prise en charge la plus adaptée à leur situation. Par la suite, Le développement de des réunions de soins de support a été soutenu par les différents Plan cancer et le plan cancer 2014-2019 « recommande le développement des temps de réunion de concertation, associant des personnels médicaux, paramédicaux, et des équipes de soins de support. » Aussi, certains établissements ont créé des RCP dédiées aux soins de support. En effet, il semble difficilement concevable de travailler ensemble sans se réunir et échanger autour du patient. Cependant, peu de données ou même de retours d'expérience sur ces RCP ont été publiés dans la littérature (4-5). Quelles sont les questions posées lors de ces réunions ? Quels en sont les participants ? Peut-on parler de RCP ? Depuis 2006, une réunion multidisciplinaire regroupant à la fois l'équipe de soins de support et les équipes d'oncologie au sens large (chirurgie, médecine ou radiothérapie) pour discuter de dossiers et de situations complexes. D'un rythme bi mensuel, elle est rapidement devenue hebdomadaire témoignant de son intérêt pour l'équipe soins de support. L'objectif de notre travail est d'analyser et de présenter l'évolution de notre réunion de concertation pluridisciplinaire entre 2006 et 2018. Méthode et matériel Design de l'étude Il s'agit d'une étude rétrospective monocentrique. Nous avons analysé les situations discutées en RCP soins de support les six premiers mois des années 2006, 2008, 2010, 2012, 2014 et 2018. La liste des patients a été obtenue par le département d'information médicale (DIM) du centre hospitalier. Notre établissement de santé est un centre régional de lutte contre le cancer français. Il comprend 193 lits d'hospitalisation et l'activité annuelle correspond à 4 528 hospitalisations, type existe depuis 2006 et a été remis à jour en 2018. Depuis cette date, il est pré rempli par la secrétaire de soins de support puis complété et validé par le médecin responsable de la RCP. Il est enregistré dans le dossier médical et envoyé au son médecin généraliste et éventuellement au réseau de soins palliatifs ou à l'équipe de soins palliatifs qui prend en charge ou prendra en charge le patient si cela est indiqué. Jusqu'en 2017, date à laquelle les dossiers sont devenus intégralement informatisés, un compte rendu papier était également envoyé au médecin référent du patient. La liste des dossiers présentés en RCP est envoyée par mail à tous les membres du DT2S, au médecin référent, au cadre de santé des différentes unités de l'établissement, aux différentes HAD et réseaux de soins palliatifs de la région. Nous n'avons par contre pas rédigé de règlement intérieur définissant le quorum de participants nécessaires mais initialement, ce rendez-vous a été instauré sous l'impulsion de quatre soins de support essentiels dans l'établissement : le service social, l'unité de psycho oncologie, les diététiciennes et les kinésithérapeutes. La réunion est animée par notre médecin de soins palliatif et un oncologue formé aux soins de support. Le patient n'est pas systématiquement informé que son dossier sera discuté spécifiquement en RCP soins de support mais il est expliqué dans le livret d'accueil remis à chaque patient lors de sa prise en charge initiale que son dossier peut être présenté dans les différentes RCP de l'établissement. Design de l'étude Ont été recueillies : 1/ des données cliniques et démographiques (date de naissance, sexe, date de la prise en charge initiale par l'institution, date du décès) 2/ des données sur la prise en charge carcinologique. Nous avons ainsi relevé le type de primitif, le suivi médian et le type de prise en charge : traitement curatif, traitement spécifique à visée palliative et soins palliatifs exclusifs. Le traitement a été classé en palliatif lorsque l'objectif n'était pas la guérison et palliatifs exclusifs lorsque le traitement spécifique (à l'exclusion de la radiothérapie antalgique) a été définitivement stoppé. Il nous paraissait en effet difficile de classer uniquement sur le dossier le stade de la maladie (palliatif initial, avancé) et l'espérance de vie du malade. 3/ des données spécifiques à la RCP : les participants à la RCP (spécialités représentées, intervenants extérieurs, le nombre de personnes assistant à la RCP), le motif de présentation en RCP, la proposition faite et comment a été appliquée la décision de la RCP, le délai médian entre la prise en charge et la RCP ainsi que le délai médian entre la présentation en RCP et le décès. Analyse statistique Les analyses réalisées étaient uniquement descriptives. Les variables qualitatives ont été décrites par leur effectif et leur fréquence, tandis que les variables quantitatives ont été décrites par la médiane et l'étendue. Toutes les analyses ont été réalisées grâce au logiciel SAS version 9.4. Résultats Mille quatre cent quatre-vingt-dix situations ont été discutées en RCP soins de support entre janvier 2006 et juin 2018. L'évolution a été crescendo, passant de 41 dossiers sur l'année 2006 à 257 sur la totalité de l'année 2018. La création du DT2S apparaît comme un tremplin pour la RCP avec une centaine de situations discutées les années précédentes (108 en 2016, 142 en 2017) et 257 sur l'année 2018. Pour cette étude, nous avons analysé 405 situations soit 352 dossiers. Les femmes constituaient 55,7 % (n = 196) de la population et les hommes 44,3 % (n = 156) (tableau 1). L'âge médian à la prise en charge au centre était de 63 ans [16-93 ans] et de 66 ans [20-93 ans] lors de la présentation en RCP. Le suivi médian depuis la première consultation était de 18,2 mois [0,0 -233,6 mois] et le délai entre la prise en charge initiale et le décès de 16,8 mois [0,0-241,9 mois]. Dans 8 % (n = 32) des situations, la prise en charge était curative, dans 58 % (n = 233) palliative, dans 31,3 % (n = 126) palliative exclusive et enfin 2,7 % (n = 11) des situations analysées concernait l'après cancer. Le délai médian entre la prise en charge initiale et la présentation en RCP était de 11,5 mois [0,0 -211,8 mois] et celui entre la présentation en RCP et le décès était de 1,5 mois [0,0 -144,3 mois]. Pour 37,8 % des patients, la première présentation en RCP a lieu dans le mois qui précède le décès. Concernant les pathologies représentées, on observe un nombre important de carcinomes bronchiques (n = 80, soit 19,8 %), de carcinomes gynécologiques (n = 67, soit 19 %), de carcinomes mammaires (n = 56, soit 13,9 %), des tumeurs cérébrales primitives (n = 29, soit 7,2 %). Le nombre médian de participants à la RCP est de dix personnes sur la période de 2006 à juin 2018 avec une augmentation progressive de ce chiffre au fil du temps qui est passé de six en 2006 à treize en 2018. Quant aux spécialités médicales assistant aux RCP (tableau 2), c'est bien l'oncologie médicale qui est le mieux représentée (77,3 % des discussions, n = 313) suivie par les soins palliatifs (58,5 % sur la totalité de la période mais 100 % sur 2016 et 96,4 % sur 2018, création d'une unité mobile de soins palliatifs en 2015). Pour 74,8 % des cas (n =303), c'est un oncologue senior qui est présent et pour 44,4 % (n = 180), c'est l'oncologue référent senior qui présente le dossier. En ce qui concerne la participation des internes, celleci était pratiquement nulle jusqu'en 2018, date à laquelle leur présence est retrouvée pour 34,2 % des dossiers (n = 38). La chirurgie est en revanche très peu représentée avec aucune participation des médecins et une présence des cadres de chirurgie relativement faible nulle jusqu'en 2018 (2,7 % des réunions sur l'année 2018). La présence d'un représentant soignant du service qui prend en charge est retrouvée dans 44,3 % (n =178) des cas. Trois spécialités médicales différentes ont participé simultanément à seulement 21,7 % des 405 discussions pour la globalité de la période étudiée. En revanche, sur l'année 2018, on a une représentativité de trois spécialités différentes pour 61,3 % (n = 68) des situations. Les spécialités paramédicales les plus assidues sont les psychologues et les diététiciennes avec un taux de participation respectif de 92,8 % (n = 376) et de 81,7 % (n = 331). Une psychologue, une diététicienne, une assistante sociale, d'un kinésithérapeute ont assisté conjointement à 54,1 % (n = 219) des discussions (70,3 %, n = 78 pour l'année 2018). À partir de 2010, des participants extérieurs à notre établissement [HAD taux de participation de 48,6 % (n = 156) et unité mobile de soins palliatifs (UMSP) du centre hospitalier universitaire (CHU) 53,3 % (n =171)] ont régulièrement assisté à nos réunions, témoignant de la pertinence de la RCP. Le motif de présentation en RCP retrouvé le plus fréquemment est une difficulté d'orientation d'aval chez un patient hospitalisé ou un maintien à domicile difficile (66,4 %, n = 269), suivi d'une demande d'intervention de l'équipe mobile de soins palliatifs (20,7 %, n = 84). Nous avons regroupé sous le terme « demande d'intervention de l'équipe mobile de soins palliatifs »: une demande d'intervention de l'UMSP pour gérer un symptôme ou prise en charge à l'arrêt des traitements spécifiques. Depuis 2018, toutes les demandes d'hôpital de jour soins de support sont systématiquement discutées en réunion lorsque le patient n'est pas connu de l'équipe afin de s'assurer de la pertinence de la proposition et de décider des interventions nécessaires. Il en va de même pour tous les adultes jeunes (AJA, définis comme un âge inférieur à 30 ans) Cela a concerné 12,6 % (n = 14) des discussions en 2018 pour les HJ soins de support et 5,4 % (n = 6) pour les AJA. Enfin, nous avons noté quelques questions éthiques (poursuite de la chimiothérapie, mise en place d'une nutrition artificielle) (n = 13, soit 3,2 %). Suite à la RCP, il a été proposé 85 consultations vers les assistantes sociales (21 %) et 73 consultations vers les psychologues (18 %), 49 vers les diététiciennes (12,1 %) et 99 évaluations par une UMSP (24,4 %), une HAD a été proposée pour 81 situations (20 %). Enfin, nous avons voulu nous assurer de la pertinence de la RCP en vérifiant si la proposition de la RCP a été appliquée et si les personnes compétentes pour répondre aux questions posées étaient là. Ainsi, la décision prise par les cliniciens était totalement conforme à la préconisation de la RCP dans 68,7 % des cas (n = 263) et partiellement conforme dans 13,1 % (n = 50). Nous avons tenté de savoir pourquoi la décision de la RCP n'a pas été suivie. Dans 43,4 % (n = 49) des cas, nous n'avons pas pu retrouver ou identifier la cause exacte. Parmi les raisons identifiées de non-respect des réponses apportées par la RCP, on retrouve le décès du patient (n =22 soit 19,5 %), une évolution de la situation clinique (n = 20 soit 17,7 %) ou un refus du patient de la proposition faite (n =15 soit 13,3 %). Lorsque les interrogations concernaient un problème de devenir, le service social et le service d'hospitalisation à domicile étaient présents dans 73,2 % des cas (n =197), lorsqu'il s'agissait d'un trouble touchant l'alimentation, les diététiciennes assistaient à la discussion dans 85,3 % des cas (n =29), et les psychologues pour 93,1 % des souffrances psychologiques (n = 54). Si le motif d'inscription en RCP était les soins palliatifs, une personne de l'équipe de soins palliatifs participait aux échanges dans 52,8 % des cas (n =42) et le délai entre la discussion et le décès était de 0,8 mois (0,0 -11,6 mois), la présence conjointe d'un médecin de soins palliatifs, de l'oncologue référent et d'un représentant soignant du service qui prend en charge le patient n'est retrouvée que dans 16,7 % des cas (n=14). Cependant là encore on note une évolution avec un taux qui atteint 38,5 % en 2018 (n= 10). Pour ce qui est du délai entre la présentation en RCP et le décès, lorsque le motif de discussion en RCP est une question pour une prise en charge palliative, pour 56,5 % des patients (n = 39), la première présentation en RCP a lieu le mois qui précède le décès. Cependant, si l'on regarde l'évolution de ce chiffre entre 2006 et 2018, on a l'impression d'une meilleure anticipation depuis 2018 (tableau 4). Discussion À la suite des préconisations de la circulaire de la DHOS 2005/101, le médecin désigné comme responsable des soins de support à l'époque a créé dans notre établissement une RCP soins de support. L'objectif de notre travail était donc dans un premier temps de dresser un tableau de notre RCP et de tenter d'en estimer l'impact et la pertinence. Ainsi, sur 1 490 situations présentées, nous en avons analysé 405. Si l'on s'intéresse à l'évolution de la RCP au fil des années, on note une évolution croissante du nombre de dossiers présentés (passant de 27 sur les six premiers mois de 2006 à 111 sur la même période pour 2018). Le nombre de participants a également augmenté au cours des années passant de 6,2 à 15 avec une présence régulière d'intervenants extérieurs. Ces chiffres témoignent de la faisabilité et de l'intérêt d'une réunion soins de support. Leur explosion en 2018 souligne l'importance de se structurer en département soins de support et de l'existence d'une unité mobile de soins palliatifs.

Demande prise en charge HJ soins de support

  Tableau 2 : Représentativité des différentes professions sur l'ensemble de la période Tableau 4 : Délai de première presentation en RCP / décès

			Tableau 1: caractéristiques de la population Tableau 3 : motifs de présentation en RCP
			Age médian	63.0 [16.0 -93.0] Représentativité sur l'ensemble de la période
		Représentant HAD	Sexe	92.3% (374)
	Mois avant décès Deux mois avant décès Trois mois avant décès > 3 mois Manquant	Feminin Masculin Motifs de présentation en RCP 196 (55.7%) 77,3% (313) 156 (44.3%) 44.4% (180) 269 (66.4%) % (N) Pathologie Cancer du sein Cancer du poumon Cancer du colon Cancer de prostate Cancer de l'ovaire Cancer col de l'utérus Cancer de l'endomètre Gliomes et gliobastome Sarcome Cancer ORL Cancer du rein Cancer de la vessie Cancer du pancréas 56 (13.9%) 80 (19.8%) 12 (3%) 23 (5.7%) 38 (9.4%) 15 (3.7%) 92.8% (376) 81.7% (331) 78.0 % (316) 73.3% (287) 84 (20.7%) Prise en charge palliative Oncologue médical Oncologue référent Devenir Psychologue Diététicienne Assistante sociale Kinésithérapeute Soins palliatifs 58 (14.3%) Population globale Difficulté ou souffrance psychologique 2006 2008 2010 2012 2014 2016 Prise en charge pluridisciplinaire de soins de support 46 (11.4%) Situation sociale complexe 41 (10.1%) 42,1% (8) 42,9%(21) 25,0% (7) 37,2% (16) 40% (12) 36,1% (13) 34,7% (17) 2018 58.5% (237) Représentant soignant du service 44.3% (178 ) Soutien nutritionnel 38 (8.4%) Douleur 22 (5.4%) 10,5% (2) 14,3% (7) 10,7% (3) 20,9% (9) 13,3% (4) 22,2% (8) 26,5%(13) 14 (3.5%) 29 (7.2%) 7 (1.7%) 43 (10.6%) 15 (3.7%) 12 (3.0%) 11 (2.7%) Médecin généraliste 4.7% (19) IDE plaie et cicatrisation 8,4% (34) Radiothérapeute 7.4% (30) Anesthésiste 1.7% (7) Geriatre 0,7% (3) 14 (3.5%) 13 (3.2%) 5,3% (1) 0,0 % (0) 3,6% (1) 9,3 % (4) 3,3% (1) 5,6% (2) 8,2% (4) Question éthique 6 (1.5%) 42,1% (8) 42,9% (21) 60,7% (17) 32,6% (14) 43,3% (13) 36,1% (13) 30,6% (15) Adulte jeune 6 (1.5%) 0 0 2 0 0 2 0 Evaluation kinésithérapie Autre 10 (2.5%) Population	2006-2018 37,8% (94) 18,5% (46) 5,2% (13) 38,6% (96) 4
			Autre	49 (12.1%)
			Valeurs manquantes	1
			Stade de la maladie
			Curatif	32 (8.0%)
			Chimiothérapie palliative	233 (58.0%)
			Soins palliatifs exclusifs	126 (31.3%)
			Après cancer	11 (2.7%)
			Valeurs manquantes	3

dont le motif de présentation est une prise en charge palliative

		2006	2008	2010	2012	2014	2016	2018	2006-2018
	Mois avant décès	71,4% (5) 65,2% (15)	60%(3)	66,7%(4)	71,4%(5)	42,9% (3)	28,6%(4)	56,5% (39)
	Deux mois avant décès	14,3% (1)	21,7% (5)	20%(1)	16,7%(1)	0,0%(0)	0,0% (0)	42,9% (6)	20,3%

448 séjours d'hôpital de jour, et 4 850 journées en hospitalisation à domicile (HAD). La structure s'est dotée d'une unité mobile de soins palliatifs en 2015. Un département transversal de soins de support (DT2S) a été créé en novembre 2017, avec ouverture d'un hôpital de jour soins de support en janvier 2018. Enfin, l'établissement dispose depuis de nombreuses années d'une petite hospitalisation à domicile de 12 lits. L'inscription d'un dossier de patient en RCP est faite auprès du secrétariat du département transversal de soins de support par n'importe quel professionnel de santé. Un compte rendu


Livio Ruffine
email: livio.ruffine@ifremer.fr

Christian Deusner

Matthias Haeckel

Elke Kossel

Samuel Toucanne

Sandrine Chéron

Audrey Boissier

Mark Schmidt

Jean-Pierre Donval

Florian Scholz

Vivien Guyader

Stéphan Ker

Vincent Riboulot

Effects of postglacial seawater intrusion on sediment geochemical characteristics in the Romanian sector of the Black Sea

Keywords: Black sea, clay minerals, Danube delta, gas seeps, iron reduction, methane oxidation, sulfate reduction

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

Introduction

The Black Sea has been investigated for decades, primarily because it is the largest anoxic basin on Earth and it represents a large hydrocarbon-producing province [START_REF] Kosarev | The Black Sea Environment[END_REF][START_REF] Robinson | Petroleum geology of the Black Sea[END_REF][START_REF] Robinson | Regional and Petroleum Geology of the Black Sea and Surrounding Region: AAPG Memoir[END_REF]. Previous investigations were diverse and integrated physical oceanography, petroleum geology, tectonics, paleoceanography, hydrology, and marine biology and ecosystem studies to reconstruct the history of the basin, capture its current dynamics and preserve its environmental quality and biodiversity. The Black Sea is connected to the Atlantic Ocean through the Marmara and the Mediterranean seas, and is characterized by two water masses: a salty water mass at the bottom supplied from the ocean, and a fresh water mass at the surface delivered by the rivers. The Black Sea hosts a large number of vigorous methane-rich seeps from the continental shelf to the deepest part of its basins that release gas high into the water column (Hillman et al., 2018a;Kessler et al., 2006a;[START_REF] Kessler | Controls on methane concentration and stable isotope (delta H-2-CH4 and delta C-13-CH4) distributions in the water columns of the Black Sea and Cariaco Basin[END_REF][START_REF] Naudts | Geological and morphological setting of 2778 methane seeps in the Dnepr paleo-delta, northwestern Black Sea[END_REF][START_REF] Roemer | Geological control and magnitude of methane ebullition from a high-flux seep area in the Black Seathe Kerch seep area[END_REF]Schmale et al., 2010a;[START_REF] Schmale | Methane emission from high-intensity marine gas seeps in the Black Sea into the atmosphere[END_REF][START_REF] Schmale | Response of the Black Sea methane budget to massive short-term submarine inputs of methane[END_REF]Schmale et al., 2010b). These seeps play a pivotal role in the Black Sea methane cycling [START_REF] Pape | Marine Methane Biogeochemistry of the Black Sea: A Review[END_REF][START_REF] Reeburgh | Blacksea methane geochemistry[END_REF]Schmale et al., 2010a) and are the major methane source responsible for the high concentrations measured in the water column (Greinert et al., 2006;[START_REF] Greinert | Atmospheric methane flux from bubbling seeps: Spatially extrapolated quantification from a Black Sea shelf area[END_REF][START_REF] Reeburgh | Oceanic methane biogeochemistry[END_REF]. However, a significant amount of methane generated in the sediment does not reach the water column [START_REF] Wallmann | Methane discharge into the Black Sea and the global ocean via fluid flow through submarine mud volcanoes[END_REF] as it is partly stored as gas hydrates [START_REF] Blinova | Hydrocarbon gases in deposits from mud volcanoes in the Sorokin Trough, north-eastern Black Sea[END_REF][START_REF] Bohrmann | Mud volcanoes and gas hydrates in the Black Sea: new data from Dvurechenskii and Odessa mud volcanoes[END_REF][START_REF] Heeschen | Quantifying in-situ gas hydrates at active seep sites in the eastern Black Sea using pressure coring technique[END_REF][START_REF] Ker | Anomalously Deep BSR Related to a Transient State of the Gas Hydrate System in the Western Black Sea[END_REF][START_REF] Popescu | Seismic expression of gas and gas hydrates across the western Black Sea[END_REF][START_REF] Zander | On the origin of multiple BSRs in the Danube deep-sea fan, Black Sea[END_REF] or oxidized within the anoxic sediment [START_REF] Holmkvist | Sulfate reduction below the sulfate-methane transition in Black Sea sediments[END_REF][START_REF] Jorgensen | Anaerobic methane oxidation and a deep H2S sink generate isotopically heavy sulfides in Black Sea sediments[END_REF][START_REF] Jorgensen | Sulfate reduction and anaerobic methane oxidation in Black Sea sediments[END_REF][START_REF] Meister | Control of sulphate and methane distributions in marine sediments by organic matter reactivity[END_REF][START_REF] Niewohner | Deep sulfate reduction completely mediated by anaerobic methane oxidation in sediments of the upwelling area off Namibia[END_REF][START_REF] Reeburgh | Blacksea methane geochemistry[END_REF][START_REF] Regnier | Quantitative analysis of anaerobic oxidation of methane (AOM) in marine sediments: A modeling perspective[END_REF][START_REF] Reitz | Sources of fluids and gases expelled at cold seeps offshore Georgia, eastern Black Sea[END_REF][START_REF] Wallmann | Methane discharge into the Black Sea and the global ocean via fluid flow through submarine mud volcanoes[END_REF][START_REF] Zander | New insights into geology and geochemistry of the Kerch seep area in the Black Sea[END_REF].

The chemical composition of pore water in the anoxic Black Sea surface sediments is significantly affected by the onset of the intrusion of seawater into the basin approximately 9 ka BP (Soulet et al., 2011b), giving rise to transient-state diffusion profiles and nonequilibrium chemical conditions. Thus, the natural setting is ideal to provide mechanistic insight and characterize dynamics of important diagenetic processes related to mineral dissolution, alteration or secondary mineral formation. Previous geochemical studies have shown that the sedimentary column of the Black Sea is highly reactive and particulate organic carbon (POC) degradation largely occurs in the upper part of the sediment [START_REF] Egger | Anaerobic oxidation of methane alters sediment records of sulfur, iron and phosphorus in the Black Sea[END_REF][START_REF] Henkel | Diagenetic barium cycling in Black Sea sediments -A case study for anoxic marine environments[END_REF][START_REF] Schouten | Evidence for anaerobic methane oxidation by archaea in euxinic waters of the Black Sea[END_REF]. Methanogenesis, organoclastic sulfate reduction (SR) and anaerobic oxidation of methane (AOM) represent key reactions central to the Black Sea carbon cycling amongst the broad range of redox reactions that commonly lead to the vertical zonation of the sediment. Microbial iron and manganese reduction below the Sulfate Methane Transition Zone (SMTZ) contribute to organic matter degradation, and it is a topic of ongoing discussion if the reactions are driven by methane oxidation or the turnover of other organic or inorganic substrates [START_REF] Egger | Anaerobic oxidation of methane alters sediment records of sulfur, iron and phosphorus in the Black Sea[END_REF]. Previous studies have demonstrated the strong link between carbon, sulfur, iron and phosphate cycling and also suggest a strong coupling between methane turnover and silicate weathering (Aloisi et al., 2004a;Aloisi et al., 2004b;[START_REF] Egger | Iron oxide reduction in methane-rich deep Baltic Sea sediments[END_REF][START_REF] Egger | Anaerobic oxidation of methane alters sediment records of sulfur, iron and phosphorus in the Black Sea[END_REF][START_REF] Henkel | Diagenetic barium cycling in Black Sea sediments -A case study for anoxic marine environments[END_REF][START_REF] Reitz | Sources of fluids and gases expelled at cold seeps offshore Georgia, eastern Black Sea[END_REF][START_REF] Wallmann | Methane discharge into the Black Sea and the global ocean via fluid flow through submarine mud volcanoes[END_REF]. All of the aforementioned microbially influenced geochemical processes can significantly alter the chemistry of pore waters and sediment mineral composition.

Northern hemisphere climate variations during the last glacial and the Holocene strongly influenced the size of continental ice sheets and glaciers, and the global sea level.

This affected the water level of the Black Sea/Lake as well as the sources and intensity of riverine input, resulting in varying accumulation of terrigeneous sediments from different sources and with different rates [START_REF] Huvaj | Clay mineralogy and geochemistry of three offshore wells in the southwestern Black Sea, northern Turkey: the effect of burial diagenesis on the conversion of smectite to illite[END_REF][START_REF] Özsoy | Oceanography of the Black Sea: a review of some recent results[END_REF][START_REF] Piper | Holocene and late glacial palaeoceanography and palaeolimnology of the Black Sea: changing sediment provenance and basin hydrography over the past 20,000 years[END_REF][START_REF] Stoffers | Clay mineralogy of Black Sea sediments[END_REF][START_REF] Wegwerth | Northern hemisphere climate control on the environmental dynamics in the glacial Black Sea "Lake[END_REF]. In addition to input dynamics, local lithostratigraphy is influenced by internal dynamics resulting from sediment mobilization and re-deposition, slumping and slope failure events and the complicated functioning of the Danube deep sea fan [START_REF] Constantinescu | Evolution of the Danube Deep-Sea Fan since the Last Glacial Maximum: new insights into Black Sea water-level fluctuations[END_REF]Hillman et al., 2018b;[START_REF] Popescu | The Danube submarine canyon (Black Sea): morphology and sedimentary processes[END_REF][START_REF] Xu | The Character and Formation of Elongated Depressions on the Upper Bulgarian Slope[END_REF], which connects the upper shelf with the deep basin.

Historically, three sedimentary units were identified describing the general stratigraphy of Late Pleistocene and Holocene sediments in the Black Sea (e.g., Degens and Ross, 1972): a microlaminated coccolith ooze (Unit I, since ca. 2.76 ka BP; Lamy et al., 2006); an organic matter rich sapropel (Unit II, since ca. 8.5 ka BP; Soulet et al., 2011); and (Unit III) a banded lacustrine lutite. Recent efforts provided more detailed lithological and chronostratigraphical information from different parts of the Black Sea (e.g. Lamy et al., 2006;Kwiecien et al., 2008;Soulet et al., 2011;Nowaczyk et al., 2012;Soulet et al., 2018), still highlighting the complexity of building age model frameworks due to problems of constraining reservoir ages and sediment input on local and regional scales (Kwiecien et al., 2008;Soulet et al., 2011).

The Danube River is considered to be the major source of sediment to the north-western margin of the Black Sea [START_REF] Lericolais | Late Quaternary deep-sea sedimentation in the western Black Sea: New insights from recent coring and seismic data in the deep basin[END_REF], especially during the ca. 32-17 ka period [START_REF] Martinez-Lamas | Linking Danube River activity to Alpine Ice-Sheet fluctuations during the last glacial (ca. 33-17 ka BP): Insights into the continental signature of Heinrich Stadials[END_REF]. Over this period, the river was characterized by high flood activity supplying huge amounts of sediment to the margin and the deep basin. [START_REF] Martinez-Lamas | Linking Danube River activity to Alpine Ice-Sheet fluctuations during the last glacial (ca. 33-17 ka BP): Insights into the continental signature of Heinrich Stadials[END_REF] demonstrated that the major sources of sediment have changed over that period, primarily because of the dynamics of the Alpine Ice sheets (AIS), but also that of the Fennoscandian Ice Sheet (FIS) [START_REF] Soulet | Abrupt drainage cycles of the Fennoscandian Ice Sheet[END_REF]. Changes in the chemical composition and mineralogy of the deposited sediment are controlled by the relative inputs from the Danube tributaries connected to three main zones of the drainage basin [START_REF] Martinez-Lamas | Linking Danube River activity to Alpine Ice-Sheet fluctuations during the last glacial (ca. 33-17 ka BP): Insights into the continental signature of Heinrich Stadials[END_REF].

Thus, unlike the North-Eastern Alps, the Carpathians and the Dinarides are characterized by an abundance of kaolinite, and a low dolomite content. The Alpine glaciers provide illite-rich sediment, with a significant amount of smectite, chlorite, and dolomite; the two latter being mainly supplied from the inner Alpine.

In 2015, a study in the Romanian sector of the Black Sea has been undertaken on board the R/V Pourquoi pas? to map the distribution of fluid seeps and gas hydrates in the area, and to identify relationships between fluid migration and sediment destabilization, which could be observed from features apparently related to slumping and slope failure [START_REF] Ballas | Influence of early diagenesis on geotechnical properties of clay sediments (Romania, Black Sea)[END_REF][START_REF] Riboulot | Control of the geomorphology and gas hydrate extent on widespread gas emissions offshore Romania[END_REF][START_REF] Riboulot | Freshwater lake to salt-water sea causing widespread hydrate dissociation in the Black Sea[END_REF]. Special attention was also given to the understanding of the dynamics of the gas hydrate deposits [START_REF] Ker | Anomalously Deep BSR Related to a Transient State of the Gas Hydrate System in the Western Black Sea[END_REF], and the occurrence of multiple BSRs [START_REF] Zander | On the origin of multiple BSRs in the Danube deep-sea fan, Black Sea[END_REF]. The area was previously investigated, mainly to reconstruct its past climate and the functioning of the Danube delta [START_REF] Constantinescu | Evolution of the Danube Deep-Sea Fan since the Last Glacial Maximum: new insights into Black Sea water-level fluctuations[END_REF][START_REF] Major | The coevolution of Black Sea level and composition through the last deglaciation and its paleoclimatic significance[END_REF][START_REF] Popescu | Multiple bottom-simulating reflections in the Black Sea: Potential proxies of past climate conditions[END_REF][START_REF] Soulet | Glacial hydrologic conditions in the Black Sea reconstructed using geochemical pore water profiles[END_REF]. However, unlike other sectors of the Black Sea (Aloisi et al., 2004a;Aloisi et al., 2004b;[START_REF] Reitz | Sources of fluids and gases expelled at cold seeps offshore Georgia, eastern Black Sea[END_REF][START_REF] Wallmann | Methane discharge into the Black Sea and the global ocean via fluid flow through submarine mud volcanoes[END_REF], there are only few studies in this dynamic area (e.g. [START_REF] Jorgensen | Sulfate reduction and anaerobic methane oxidation in Black Sea sediments[END_REF][START_REF] Knab | Regulation of anaerobic methane oxidation in sediments of the black sea[END_REF][START_REF] Egger | Anaerobic oxidation of methane alters sediment records of sulfur, iron and phosphorus in the Black Sea[END_REF] aimed to document geochemical processes in response to seawater intrusion and gas seepage. Hence, the purpose of this study is to contribute towards filling this gap by integrating geochemical analyses of pore water and sediment samples to decipher the coupling of element cycling in the upper tens of meters of the sedimentary column.

Description of the study area

Our study area is located in the Romanian water sector (Fig. 1) at the eastern part of the main Danube canyon, where several other canyons have developed. In this area, evidence for sediment instability and mass movement was found during cruise MSM-34 in 2013 [START_REF] Bialas | FS MARIA S. MERIAN Fahrtbericht / Cruise Report MSM34/1 & 2 -SUGAR Site[END_REF][START_REF] Haeckel | Gas hydrate occurrences in the Black Sea-new observations from the German SUGAR project[END_REF] and GHASS cruise in 2015 (doi: 10.17600/15000500). Acoustic surveys of the water column on both cruises showed that this area is characterized by a large number of widespread gas expulsion sites at the seafloor, bubbling up to several tens to hundreds of meters into the water column [START_REF] Riboulot | Control of the geomorphology and gas hydrate extent on widespread gas emissions offshore Romania[END_REF]. Sites of intense gas seepage indicate strong upward methane migration and discharge in and from the anoxic Black Sea sediments. Accordingly, they have served for guiding coring operation during the GHASS cruise. The cores were collected from water depths between 240 m and 822 m. Core GAS-CS01 was collected at the shelf edge, and GAS-CS07, 08 and 14 along a crest, and the remaining ones on landslide scars or small seafloor depressions. [START_REF] Riboulot | Freshwater lake to salt-water sea causing widespread hydrate dissociation in the Black Sea[END_REF] have shown that the pattern of the seep distribution is related to the gas hydrate stability zone (GHSZ). Indeed the gas flares are primarily located on the shelf and at the upper border of the GHSZ. Within the GHSZ seeps are positioned only at the rim of landslide scars, and at specific location where faults reach the seafloor [START_REF] Ker | Anomalously Deep BSR Related to a Transient State of the Gas Hydrate System in the Western Black Sea[END_REF].

Fig. 1: A) Bathymetric map of the Romanian sector of the Black Sea showing the Danube canyon and the location of all cores recovered on the continental slope. The blue dots highlight the acoustic gas flares identified in the water column during the GHASS cruise [START_REF] Riboulot | Control of the geomorphology and gas hydrate extent on widespread gas emissions offshore Romania[END_REF]. B and C) Detailed views of the study area with location of the cores. Core positioning was guided by the presence of gas flares, or other indications or topographical features attributable to potential presence of shallow gas hydrates.

Sampling and analyses

Coring and sampling

During the GHASS cruise, the coring locations together with Penfeld measurements were selected from previous acoustic and seismic surveys. A Calypso piston-corer was deployed to collect long sediment cores with a length of up to ~35m. A total of 11 cores were collected (Table 1) for geochemical, geophysical and geotechnical analysis. Once retrieved, the Calypso cores were cut into 1m long round sections and transferred to the shipboard laboratory for pore water sampling and processing at sea bottom temperature. The sediment cores were sampled for pore water analyses immediately after the recovery. Pore water was sampled using two different methods. Rhizon samplers were used as long as the sediment was soft enough to insert the plastic tip of the sampler. A Rhizon sampler (Rhizosphere Research Products, Netherlands) is a narrow elongated cylindrical filter (0.2 µm pore size; 5 cm long; 130 µL volume) with a stiff plastic core [START_REF] Seeberg-Elverfeldt | Rhizon sampling of pore waters near the sediment/water interface of aquatic systems[END_REF]. Prior to use, the samplers were conditioned in distilled water ("MilliQ") for several hours. Rhizon samplers are used to draw fluid from the sediment under vacuum, which is applied by attaching the samplers to 10 mL or 20 mL all-plastic syringes. The sampling took less than 12 hours. In addition to using Rhizon samplers, pore water was extracted using a pore water squeezer with N2 gas of up to 5 bar as pressurizing agent and filtering the pore water through 0.2 µm Nuclepore cellulose acetate filters. The use of a second pore-water sampling method was necessary to recover sufficient water volumes for all analyses.

Sediment samples for pore water pressing and sediment analysis were taken directly after recovery of the core from round sections or opened core halves. A 4-cm thick slice of sediment was removed from the working half at either the top or the bottom of the core section. Subsamples of the wet sediment were taken for measurement of sediment porosity, as well as for chemical and mineralogical analyses.

Geochemical analysis

Aliquots of the extracted pore water were sub-sampled for various onboard and shorebased analyses. Analyses for the nutrients NH4 + , PO4 3 -, SiO4 4 -as well as H2S were completed onboard using a Hitachi UV/VIS spectrophotometer. The respective chemical analyses followed standard procedures [START_REF] Grasshoff | Methods of seawater analysis[END_REF], i.e. NH4 + was measured as indophenol blue, PO4 3 -and SiO4 4 -as molybdenum blue, and H2S as methylene blue. Total alkalinity (TA)

was determined by titration with 0.02 N HCl using a mixture of methyl red and methylene blue as indicator. IAPSO seawater standard was used for calibration. Cl -, Br -and SO4 2- concentrations were determined by ion chromatography (METROHM 761 Compact). Cations were analyzed using ICP-OES (VARIAN 720-ES). Subsamples for ICP-OES analysis were acidified with 20 μl of conc. suprapure HNO3 per 2 ml of porewater sample (i.e., pH < 1). All samples for shore-based analyses were stored refrigerated. Further analytical details, including analytical accuracies, precisions and detection limits, can be found in a previous study [START_REF] Haffert | Fluid evolution and authigenic mineral paragenesis related to salt diapirism -The Mercator mud volcano in the Gulf of Cadiz[END_REF].

Dissolved methane concentration was determined from a poisoned aliquot of wet sediment (10 µL of NaN3) by head-space coupled gas chromatography (Agilent GC-7890A coupled with a sampler HP7694). Stable carbon isotopic ratio of methane (δ 13 C/ 12 C) was measured by using a continuous flow isotope ratio mass spectrometer (Thermo MAT253).

Prior to oxidation of methane in a 1150 °C furnace, methane was separated from other gases in a coupled Thermo Trace GC (carrier gas: He; packed column: ShinCarbon, 1.5 m). Stable isotope ratios are reported in the δ-notation with respect to Vienna Pee Dee Belemnite (VPDB). Analytical precision of the reported isotopic composition is ± 0.3 ‰.

Wet sediment was collected for shore-based porosity, carbonate and element CNS analyses. Analyses were carried out using a EURO Element Analyzer (C/N/S configuration), prior and after removal of inorganic carbon with 1 M HCl. The analytical data are presented in percent of the total weight of dried sediment with an accuracy of 3%. Bulk chemical composition analysis of the sediment was carried out with a wavelength dispersive X-ray fluorescence spectrometer S8-Tiger from BRUKER. Mineral composition analysis of sediment samples was performed by X-ray diffractometry (XRD) using a D8 Advance model from BRUKER. Qualitative analysis of the diffraction pattern was carried out with the EVA software (BRUKER) for phase identification of unknown samples, while quantitative analyses were performed according to the Rietveld refinement method with the program TOPAS (BRUKER). Specific analyses were done to determine the clay mineral content according to a validated method commonly used for clay analysis [START_REF] Holtzappel | Les minéraux argileux, préparation, analyse diffractométrique et détermination[END_REF]. The clay content was calculated by applying specific coefficients for the identified clays minerals [START_REF] Underwood | Clay-mineral provenance, sediment dispersal patterns, and mudrock diagenesis in the Nankai accretionary prism, southwest Japan[END_REF]. The results are given with an uncertainty of 10%. X-ray absorption near edge structure spectroscopy (XANES) [START_REF] Calvin | XAFS for Everyone[END_REF] was performed to investigate the mineralogy and the oxidation state of the mineral-bound iron. XANES spectra were recorded at beamline P64 of the synchrotron radiation source PETRA [START_REF] Caliebe | High-flux XAFS-beamline P64 at PETRA III[END_REF], which is operated by the Helmholtz research centre DESY in Hamburg, Germany. For the determination of the mineralogy, a set of reference spectra of iron-containing silicates (augite, biotite, montmorillonite, nontronite and olivine), oxides (ferrihydrite, goethite and hematite) and an iron sulfide (pyrite) were measured. The software package Athena [START_REF] Ravel | HEPHAESTUS: data analysis for X-ray absorption spectroscopy using IFEFFIT[END_REF] was then used for linear fitting of the reference spectra to the XANES spectra of sediments from core GAS-CS01 [START_REF] Scholz | Nitrate-dependent iron oxidation limits iron transport in anoxic ocean regions[END_REF]. The mean oxidation state of the sediments (fraction of ferric Fe, Fe(III)/∑(Fe)) was obtained from the centroid position of the pre-edge structure [START_REF] Scholz | Nitrate-dependent iron oxidation limits iron transport in anoxic ocean regions[END_REF][START_REF] Wilke | Oxidation state and coordination of Fe in minerals: An Fe K-XANES spectroscopic study[END_REF].

Results

Geochemical composition of pore water

Pore water profiles of dissolved elements (Cl -, SO4 2-, Ca 2+ , Mg 2+ , Na + , K + , Ba 2+ , Sr 2+ , NH4 + , Br -, PO4 3-, SiO4 4-, HS -, Fe 2+ and Mn 2+ ) and total alkalinity (TA) are presented in Fig. 2.

Chemical and isotope data of methane (CH4) are shown in Fig. 3, and sediment geochemical composition and mineralogy in Fig. 4 and 5. Overall, pore water geochemical profiles show similar trends, and there is no significant effect of water depth or sample location on pore water profiles in Calypso cores retrieved on the slope, both close to and far from the shelf, for Cl -, SO4 2-, Ca 2+ , Mg 2+ , Na + , K + , Ba 2+ , Sr 2+ . However, pore water profiles from cores GAS-CS13 and GAS-CS14 appear as shifted and show significantly lower concentrations of dissolved elements compared to the other cores. The concentrations of Cl -, Mg 2+ , Na + , K + , TA and Br -decrease non-linearly with depth, resulting in profiles with a concave-down curvature, whereas concentrations of Ca 2+ , Ba 2+ , NH4 + , and Sr 2+ increase to a clear and pronounced maximum followed by a decrease with increasing depth. Among major cations K + , Mg 2+ and Na + , the relative uptake of Na + in the sediment is lowest, thus the shape of the Na + profile is most similar to the Cl -profile, whereas K + is taken up within the upper 10 m of the sediment column. The Mg 2+ profiles are characterized by different gradients with a near linear decrease in Mg 2+ in the upper 11 -13 m below seafloor (mbsf), whereas with greater sediment depth the gradient becomes less steep. Sulfate concentration decreases nearly linearly from values above 15 mM to values < 1 mM. The SMTZ is reached for all cores at a depth shallower than 6 mbsf. The SMTZ depth is even shallower than 1mbsf for cores GAS-CS07, 08, 13 and 14, which are the cores retrieved on crests. Elevated CH4 concentrations were measured over the entire length of the cores, and in few cases, increased CH4 concentrations were found even above the SMTZ. Regardless of the sample locations, methane is extremely depleted in 13 C, with δ 13 C-CH4 ranging between -62.71 and -72.11 ‰ (Fig. 3). The profiles of NH4 + , PO4 3-, SiO4 4-, Fe 2+ and Mn 2+ are very different from one core to another, and values show a large scattering. It has to be noted that the sampling and analytical procedures were not optimized for redox-sensitive species, thus the scatter could be related to procedural artefacts from handling of individual samples. However, this implies that elevated Fe 2+ and Mn 2+ concentrations must be considered as lowest estimates, and in situ concentrations likely were higher. Nevertheless, clear Fe 2+ and Mn 2+ maxima were observed in most of the cores at depths between 8 and 15 mbsf. NH4 + concentrations reached maximum values in the interval 15 -22 mbsf, with large differences in absolute NH4 + concentrations in individual cores.

Geochemical composition of sediment

The organic carbon content decreases rapidly from more than 6 to less than 1 wt-% within the upper first meter of the sampled cores (Fig. 4). The same rapid decrease is observed for the TIC content, which again increases within the horizon ~2.5 -4 mbsf, and continues to increase throughout the sampled interval. The sediment shows high and stable contents of Al, Si and Ti along the cores (Fig. 5). Na and K contents are low but relatively constant throughout the sediment column. However, Fe and Mn contents, and also Mg and Ca contents, show larger relative differences within each individual core and in between cores.

Sediment mineralogical analysis from cores GAS-CS01, CS03, CS07, CS12 and CS14 shows that clay minerals including mica account for 40 to 75 wt-%. This is followed by silicate minerals (feldspar, plagioclase, and quartz) and carbonate phases (mainly calcite and dolomite). The calcite content remains relatively constant except for few samples collected at the upper part of cores GAS-CS01 and GAS-CS12. The dolomite content is slightly lower than that of calcite and decreases towards the water-sediment interface. Amongst clay minerals, illite is the dominant species and accounts for more than 60% of the total clay mineral fraction (Fig. 4). Smectite accounts for 5-20 % of the total clay mineral fraction, and kaolinite and chlorite both usually contribute to less than 10 %. For individual cores, we observe variable trends in clay mineralogy. In GAS-CS01, highest illite (> 90 %) and lowest smectite contents (<10 %) are observed in the narrow interval 4 -6 mbsf. Below this interval, down to a depth of 22 -24 mbsf, lower illite (70 %) and higher smectite (20 %) and kaolinite contents (8 %) are found. Below 24 mbsf, this trend is again reversed with higher illite (80 %), and lower smectite (10 %) and kaolinite contents (2 %). In CS01, the chlorite content increases continuously with depth. However, these relations between clay mineralogy and depth cannot easily be transferred to other cores, which clearly indicates differences in lithology and sediment deposition histories between core locations. Mineral data variability is partly reflected in solid phase element profiles. In GAS-CS01, the element composition profile (Fig. 5) shows a change in Mg content, which smoothly shift from lower to higher values at a depth of 22 -24 mbsf. This trend appears to be associated with shifts in Si, Al, K, and Fe contents. Ca contents show considerable variability when comparing different cores, which is not reflected in pore water profiles. ( [START_REF] Bernard | Light-hydrocarbons in recent texas continental-shelf and slope sediments[END_REF]. For the color code of Fig. 3a, the reader should refer to Fig. 2.

Discussion

Lithology and stratigraphic alignment

In accordance to known lithological variability, Calypso cores from this study showed substantially different solid phase element and mineral profiles (Figs. 4 & 5). To better distinguish geochemical effects in response to seawater intrusion from lithological changes, we compared specific time windows with known climatic and environmental conditions for four cores from different locations across the northwest Black Sea margin (Fig. 6), GAS-CS01, GAS-CS03, GAS-CS07 and GAS-CS12. A detailed analysis of core GAS-CS01 collected at the shallowest site was recently presented in Martinez-Lamas et al. ( 2020), with a detailed age model based on the evaluation of chemical, mineralogical and sedimentological markers in comparison with the well-studied core MD04-2790 (Soulet et al., 2011a). The study showed that core GAS-CS01 contains sediments of up to 33 ka BP, belonging to Unit III. The lacustrine-marine (L-M) transition Unit II and the marine Unit I were not clearly identified. However, although it is not well resolved, Unit II was recovered in core GAS-CS12 suggesting the L-M transition at very shallow depth in the first tens of centimeters of cored sediment (Fig. 6). Sedimentary Ca-XRF counts and Ca/Ti ratios, together with the clay mineralogy, allowed the stratigraphic correlation of three additional cores (GAS-CS03, CS07 & CS12) against the well-dated sediment core GAS-CS01 (Fig. 6). The correlations were realized, for example, through the recognition of (i) the Red Layers deposited ca. 17 [START_REF] Wegwerth | Black Sea temperature response to glacial millennial-scale climate variability[END_REF] (Fig. 6). One can clearly see that the cores GAS-CS03 and GAS-CS07 are characterized by a much lower sedimentation rate compared to GAS-CS01

and GAS-CS12. Furthermore, in agreement with previous studies [START_REF] Soulet | Abrupt drainage cycles of the Fennoscandian Ice Sheet[END_REF]Soulet et al., 2011a), Martinez-Lamas et al. ( 2020) showed that sediment deposition on the NW Black Sea margin was highly variable at the end of the last glacial period due to the waxing and waning of the AIS and FIS in response to northern hemisphere climate variability. For the time interval prior to the deposition of the red layers during ca. 17.2-15.7 ka BP, hyperpycnal floods from the Danube River were identified as the main sediment source, and sediment deposition and burial of reactive minerals under lacustrine oxic bottom water conditions was much more rapid than modern sedimentation. The analysis of clay mineralogy and Nd isotope signatures of the Danube and its main tributaries suggested that early periods of meltwater release during 32.5-30.5 ka BP supplied smectite-poor, chlorite and dolomite-rich sediments from Eastern Alpine domains [START_REF] Martinez-Lamas | Linking Danube River activity to Alpine Ice-Sheet fluctuations during the last glacial (ca. 33-17 ka BP): Insights into the continental signature of Heinrich Stadials[END_REF]. Thereafter between 30 and 29 ka

Transport-reaction characteristics of major ions

The shape of the pore water profiles illustrates the transport of dissolved species from today's Black Sea marine bottom waters into the lacustrine sediment since the reconnection with the Mediterranean Sea about 9 ka ago (Soulet et al., 2011b). The Cl --profiles have a slightly concave down shape and show a continuous decrease in salt concentration indicating the transient state of seawater infiltration. Diffusion is the dominant transport process of pore water species at most locations, and clear evidence for disturbances of profiles by recent sediment mass movement through slumping and slope failure events (Hillman et al., 2018b;[START_REF] Riboulot | Control of the geomorphology and gas hydrate extent on widespread gas emissions offshore Romania[END_REF] is not found for most cores. Gas hydrates were recovered throughout core GAS-CS14, therefore the concentrations of dissolved elements might be affected by gas hydrate dissociation after core recovery. However, a dilution effect is clearly visible only for Ca and Sr in the upper 5 m of sediment, and not for the other dissolved elements. Therefore, hydrate dissolution is not responsible for the low Ca and Sr concentrations. Other processes that we are unable to identify from our dataset might have affected pore water profiles at this location. Core GAS-CS13 also shows characteristically different pore water profiles, especially when comparing with core GAS-CS06, the closest core that is located less than 1 km away. Unlike in core GAS-CS14, there was no evidence for gas hydrates in core GAS-CS13, which was located on an erosional feature (Fig. 1). Thus, one possible explanation for the difference of the pore water profiles is that the erosion process has led to loss of surficial sediment, shifting dissolved element concentration to lower values. In principal, upward fluid migration and gas emission could have affected the pore water profiles; however, none of these impacts is obvious from our geochemical data. Another explanation for the difference in pore water profiles from cores GAS-CS13 and GAS-CS06 could be disturbances from the coring operation resulting in the loss of the surficial part. Indeed, the measured chloride concentrations at the uppermost part of all collected cores are lower than the Black Sea bottom water [START_REF] Bohrmann | Mud volcanoes and gas hydrates in the Black Sea: new data from Dvurechenskii and Odessa mud volcanoes[END_REF][START_REF] Soulet | Glacial hydrologic conditions in the Black Sea reconstructed using geochemical pore water profiles[END_REF][START_REF] Zander | New insights into geology and geochemistry of the Kerch seep area in the Black Sea[END_REF], and vary between 319 and 339 mM. Core depths have been corrected based on the response of the sensors monitoring the displacement of the piston, which provides a measure of reliability and quality of the coring. However, the loss of the upper sediment cannot be discarded, and comparison with the long piston core studied by [START_REF] Soulet | Glacial hydrologic conditions in the Black Sea reconstructed using geochemical pore water profiles[END_REF] showed the lowest chloride concentrations of 311, 319 and 297 mM in cores GAS-CS01, GAS-CS08 and GAS-CS13 at ~1.5 mbsf, 2 mbsf, and 3 mbsf, respectively. For our present study, such an additional depth correction due to sediment loss has not been applied, as it does not change the sediment zonation proposed below. Profiles from core GAS-CS16 include two outlying data points at the bottom that likely result from seawater contamination.

The pore water profiles exhibit three intervals where significant changes of element gradients are observed; at 8 -15 mbsf with distinct maxima of Ca 2+ , Fe 2+ and Mn 2+ concentrations, at 22 -24 mbsf, which coincides with a change of the marine water Na + gradient, and at 31 -33 mbsf as the current depth of marine Cl -penetration (Fig. 2). In this transient-state transport-reaction scenario, Cl -is considered as the most conservative dissolved species. Thus, the change of dissolved element:Cl -ratios indicates the diagenetic release or retention of reactive species (Fig. 7). Decreasing K + :Cl -and Mg 2+ :Cl -ratios in the upper sediment column (shallower than 11 -13 mbsf) indicate the uptake of K + and Mg 2+ by the sediment. Ca 2+ :Cl -and Sr 2+ :Cl -ratios steadily increase with depth, showing the relative enrichment of Ca 2+ and Sr 2+ in the pore water. Below the Ca 2+ maxima (11 -13 mbsf), Sr 2+ :Ca 2+ and Mg 2+ :Ca 2+ ratios remain constant, suggesting a tightly coupled release of Ca 2+ , Mg 2+ and Sr 2+ . These observations provide evidence for pronounced ion exchange capacities of lacustrine clay minerals, which mainly results in the uptake of K + and Mg 2+ , and the release of Ca 2+ and Sr 2+ . Further, the simultaneous release of Ca 2+ and Mg 2+ in the deeper sediment column (below 11 -13 mbsf) indicates dissolution or alteration of silicate and/or carbonate minerals, which could not be constrained in this study. Organic matter degradation and terminal electron-accepting processes NH4 + profiles suggest that organic matter degradation and carbon remineralization are more pronounced in the upper 15 mbsf of the cored sediments than below. The organic matter degradation is coupled to organoclastic sulfate reduction (Eq.1).

(CH2O)(NH3)N/C(H3PO4)P/C + 0.5 SO4 2-→ 0.5 HS -+ 0.632 HCO3 -+ (N/C) NH4 + + (P/C) HPO4 2-+ 0.368 CO2 + 0.368 H2O (1)

However, anaerobic oxidation of methane (AOM) largely contributes to sulfate turnover in Black Sea sediments (Eq.2), and defines the depth of the SMTZ [START_REF] Borowski | Global and local variations of interstitial sulfate gradients in deep-water, continental margin sediments: Sensitivity to underlying methane and gas hydrates[END_REF].

O H HS HCO SO CH 2 3 2 4 4 + + → + - - - (2)
The correspondence of the depths of SO4 2-depletion and TA maxima suggests a dominant role of sulfate-dependent AOM, which is driven by upward diffusion of microbial methane produced by intense methanogenesis. This observation is corroborated by former studies estimating that AOM accounts for nearly 70% of total SO4 2-turnover in typical Black Sea sediments [START_REF] Egger | Anaerobic oxidation of methane alters sediment records of sulfur, iron and phosphorus in the Black Sea[END_REF][START_REF] Jorgensen | Sulfate reduction and anaerobic methane oxidation in Black Sea sediments[END_REF]. Closer to methane seeps, AOM becomes even more dominant. The sulfate-depleted sediment below the SMTZ is undersaturated with respect to barite. Therefore, barite undergoes dissolution releasing Ba 2+ into the pore water in the interval 5-9 mbsf, beneath the AOM interval [START_REF] Haeckel | A transport-reaction model of the hydrological systems of the Costa Rica subduction zone[END_REF][START_REF] Henkel | Diagenetic barium cycling in Black Sea sediments -A case study for anoxic marine environments[END_REF][START_REF] Noethen | Reconstructing changes in seep activity by means of pore water and solid phase Sr/Ca and Mg/Ca ratios in pockmark sediments of the Northern Congo Fan[END_REF]. Very shallow SMTZ depths were determined for cores GAS-CS07, CS08, CS13 and CS14, suggesting enhanced upward methane migration at these sites [START_REF] Jorgensen | Anaerobic methane oxidation and a deep H2S sink generate isotopically heavy sulfides in Black Sea sediments[END_REF][START_REF] Jorgensen | Sulfate reduction and anaerobic methane oxidation in Black Sea sediments[END_REF][START_REF] Zander | New insights into geology and geochemistry of the Kerch seep area in the Black Sea[END_REF]. This is supported by evidence of both gas hydrates and gas emission at the crests, where these four cores were retrieved. The elevated methane concentrations observed above the SMTZ also indicate enhanced upward CH4 transport or limited AOM efficiency [START_REF] Knab | Regulation of anaerobic methane oxidation in sediments of the black sea[END_REF]. Sulfide (HS -) becomes fully depleted below 1 mbsf in all cores although values as high as 3.4 mM were measured at the first meter of sediment (Fig. 2), which indicates efficient sulfide removal through iron sulfide precipitation. Usually sedimentary iron acts as the dominant sulfide sink, leading to the accumulation of pyrite and other iron-sulfur minerals [START_REF] Canfield | The reactivity of sedimentary iron minerals toward sulfide[END_REF][START_REF] Gregory | The formation 27 mechanisms of sedimentary pyrite nodules determined by trace element and sulfur isotope microanalysis[END_REF][START_REF] Jorgensen | Anaerobic methane oxidation and a deep H2S sink generate isotopically heavy sulfides in Black Sea sediments[END_REF][START_REF] Lyons | Sulfur isotopic trends and pathways of iron sulfide formation in upper Holocene sediments of the anoxic Black Sea[END_REF][START_REF] Meister | Sulphur and carbon isotopes as tracers of past sub-seafloor microbial activity[END_REF][START_REF] Neretin | A sulfur budget for the Black Sea anoxic zone[END_REF].

Thus, the transient increase of dissolved Fe 2+ and Mn 2+ concentrations below the SMTZ observed in this study (Fig. 7) is not clearly related to HS -profiles as found from previous studies [START_REF] Jorgensen | Anaerobic methane oxidation and a deep H2S sink generate isotopically heavy sulfides in Black Sea sediments[END_REF][START_REF] Jorgensen | Sulfate reduction and anaerobic methane oxidation in Black Sea sediments[END_REF][START_REF] Zander | New insights into geology and geochemistry of the Kerch seep area in the Black Sea[END_REF], which indicates high iron and manganese reduction activities and confirms bioavailability of Fe(III) below the SMTZ, similar to recent findings [START_REF] Egger | Anaerobic oxidation of methane alters sediment records of sulfur, iron and phosphorus in the Black Sea[END_REF][START_REF] Jorgensen | Anaerobic methane oxidation and a deep H2S sink generate isotopically heavy sulfides in Black Sea sediments[END_REF][START_REF] Kraal | Turbidite deposition and diagenesis in the southwestern Black Sea: Implications for biogeochemical cycling in an anoxic basin[END_REF]. The presence of Fe(III) is in accordance with sedimentation characteristics and oxic bottom water conditions during the last glacial, and rapid burial of Fe(III)-bearing minerals may explain the positioning of the deep iron reduction zone. However, it is neither obvious which electron donor is used for deep iron reduction, nor if the positioning of the iron reduction zone is linked to the lacustrine-marine transition or to the presence of a distinct iron pool. Microbial iron reduction was likely an important process prior to seawater inflow under methanogenic conditions, since methanogenesis and iron reduction are largely compatible, and there is evidence that methanogenic organisms can shift metabolic capabilities towards iron reduction in case of iron availability [START_REF] Bar-Or | Iron-coupled anaerobic oxidation of methane performed by a mixed bacterial-archaeal community based on poorly reactive minerals[END_REF][START_REF] Oni | Distinct microbial populations are tightly linked to the profile of dissolved iron in the methanic sediments of the Helgoland mud area, North Sea[END_REF][START_REF] Van Bodegom | Direct inhibition of methanogenesis by ferric iron[END_REF][START_REF] Vigderovich | Evidence for microbial iron reduction in the methanic sediments of the oligotrophic southeastern Mediterranean continental shelf[END_REF][START_REF] Zhang | Microbial reduction of Fe (III) in illite-smectite minerals by methanogen Methanosarcina mazei[END_REF]. Thus, the deep iron reduction activity below the SMTZ strongly suggests iron mobilization from a former refractory iron pool, or a distinct shift in spatial electron donor availability.

POC degradation and methane oxidation could potentially fuel iron reduction at greater depths [START_REF] Beal | Manganese-and iron-dependent marine methane oxidation[END_REF][START_REF] Egger | Iron oxide reduction in methane-rich deep Baltic Sea sediments[END_REF][START_REF] Egger | Anaerobic oxidation of methane alters sediment records of sulfur, iron and phosphorus in the Black Sea[END_REF], and prevent the development of well-constrained reaction zones and distinct iron peaks. However, in most cases high Fe 2+ concentrations are constrained to particular intervals with distinct maxima, thus Fe(III) reduction appears to be controlled by diffusive transport of reactive species to some extent.

Iron reduction could also be driven by DOC degradation. To become available at greater depths, organic compounds must escape from the sulfate reduction zone. DOC supply to greater depths could become possible from an excess availability of DOC compared to sulfate, availability of methane as substrate for sulfate reduction, kinetic limitations of syntrophic substrate transfer, inhibition of sulfate reduction by high sulfide concentrations, or the release of non-competing intermediates, which are not available for microbial sulfate reduction. In principal, the absence of sulfate-reducing microorganisms in lacustrine sediments could explain DOC transport to greater depth, away from the sulfate reduction zone. However, so far there is no evidence for this assumption [START_REF] Leloup | Diversity and abundance of sulfate-reducing microorganisms in the sulfate and methane zones of a marine sediment, Black Sea[END_REF]. Clearly, the overall balance (Eq.1) provides very limited mechanistic insight, since sulfate-reducing microorganisms only metabolize small organic molecules (e.g. volatile fatty acids: VFA) or H2, which are products of hydrolytic and fermentative microbial reactions. Thus, organic matter degradation and the concomitant release of DOC close to the sediment-water interface, especially during the high productivity period, could potentially supply substrates for microbial metabolism at greater depths. Whereas seawater intrusion certainly initiated a marked shift of the terminal electron-accepting step to microbial sulfate reduction, it is less clear if and to what extent earlier steps of organic matter degradation have changed, that means, hydrolysis and fermentation.

Diagenetic reactions in response to seawater intrusion

Complementary to interval definition from pore water profiles, diagenetic reactions are assigned to 3 specific intervals: (1) AOM and microbial sulfate reduction is located in the interval 0 to 6 mbsf with sulfate depletion to near zero values at the SMTZ, whereas POC is distributed over the upper 15 mbsf. This upper zone is further characterized by silica dissolution leading to SiO4 4-peaks close to the sediment-water interface. (2) Ion exchange processes with lacustrine clay minerals likely control concentrations of major cations in the sediment column above 22-24 mbsf, which results in the net uptake of K + , Mg 2+ and Na + , and the net release of Ca 2+ and Sr 2+ above 11-13 mbsf. (3) In addition to ion exchange reactions, the interval 8-15 mbsf shows clear evidence for reverse weathering reactions and dissolution of silicate and/ or carbonate phases, with a net release of Mg 2+ in a 1:1 ratio with Ca 2+ in the interval 11-13 mbsf. Further, Fe 2+ and Mn 2+ are released between 8-15 mbsf (Fig. 2), which indicates that microbial iron and manganese reduction are linked to these mineral reactions.

Since no alkalinity increase is observed below the SMTZ, TA release from mineral weathering or dissolution needs to be balanced by TA consumption. Reverse silicate weathering (Eq.3) could consume TA, alkaline and alkaline earth metals, and release Ca 2+ (Aloisi et al., 2004a;[START_REF] Kim | Marine silicate weathering in the anoxic sediment of the Ulleung Basin: Evidence and consequences[END_REF][START_REF] Spivack | The sedimentary cycle of the boron isotopes[END_REF][START_REF] Vigier | Quantifying Li isotope fractionation during smectite formation and implications for the Li cycle[END_REF].

Aluminosilicates such as plagioclase and K-feldspar, which are sufficiently abundant in the sediment, are good candidates for marine reverse weathering reactions such as:

Sr-Ca-Al-Silicate + SiO2 + (K + + Mg 2+ + Li + + B 3+ ) + HCO3 -→ K-Mg-Li-B-Al-Silicate + Ca 2+ + Sr 2+ + CO2 + H2O (3)
From comparing element budgets over depth from cores GAS-CS01, CS03 and CS07 (Fig. 8c, f and i, respectively), it is suggested that the progress of diagenetic processes since the Holocene seawater intrusion is not visible in the sediment element or mineral composition, and the chemical signals could not overprint lithological variability. Budgets from all cores are evaluated as relative changes compared to element contents in the lower parts of GAS-CS01, and unlike pore water profiles, normalized sediment element profiles can be linked to stratigraphical features (see supplementary materials for the core logs).

The considerable variability in sediment stratigraphy and mineral composition at different locations does not have a clear effect on reactive transport and pore water profiles of major cations. This could be related to the large pool of reactive minerals or the dominance of kinetic controls of slow geochemical reactions. However, the similarity of pore water profiles could also be linked to microbial metabolism, which would be regulated by substrate availability rather than sediment mineralogy, as discussed above referring to microbial iron reduction. Interestingly, the depletion of seawater cations at 22 -24 mbsf coincides with changes in clay mineral composition (Fig. 4, GAS-CS01). While these changes appear to be sufficiently explained by variability of sediment sources and input rates during the Late Pleistocene and Holocene, as discussed above, we cannot exclude that ion exchange reactions or other diagenetic processes triggered after seawater intrusion contribute to these conspicuous shifts.

Fig. 8: Dissolved Fe and Mn profiles (a: GAS-CS01, d: GAS-CS03, g: GAS-CS07), clay mineral composition (b: GAS-CS01, e: GAS-CS03, h: GAS-CS07) and sediment composition changes relative to steady state compositions below seawater penetration depth at 31-33 mbsf based on Cl -profiles in GAS-CS01 (c: GAS-CS01, f: GAS-CS03, i: GAS-CS07).

We hypothesize that the release of Fe 2+ and Mn 2+ through microbial iron and manganese reduction was stimulated by the iron and organic substrate availability in response to seawater intrusion. Preliminary X-ray absorption data analyses suggest that iron is strongly associated with phyllosilicates in interval 2, above 22-24 mbsf (Fig. 9a). The actual Fe(III) source, however, is not fully resolved. The analysis of Fe(III):Fe(II) ratios shows a trend of increasing Fe(III) content towards shallower sediments depths (Fig. 9b), which is counterintuitive to expected increased contents of Fe(II) in the iron reduction zone. However, smectite-bound Fe(II) is readily oxidized under atmospheric conditions [START_REF] Rozenson | Reduction and oxidation of Fe 3+ in dioctahedral smectites-III. Oxidation of octahedral iron in montmorillonite[END_REF], which would explain the Fe(III):Fe(II) ratios. Sampling and chemical procedures in this study were not focused on iron analysis, thus redox effects and long-time storage artefacts could influence iron concentration measurements and mineral speciation analysis. Iron speciation analysis further suggests, that at greater depths higher amounts of iron are associated with other minerals (among our reference minerals, goethite, biotite and olivine gave the best results for fitting the deviations from the pure montmorillonite spectrum), and Fe(II) contents were better preserved during storage and analysis.

Since iron at relevant depths is associated with clay minerals rather than with oxyhydroxide phases, it appears that its reduction could have contributed to clay mineral alteration in a direct or indirect way [START_REF] Kim | Naturally occurring, microbially induced smectite-to-illite reaction[END_REF][START_REF] Kostka | Growth of iron (III)-reducing bacteria on clay minerals as the sole electron acceptor and comparison of growth yields on a variety of oxidized iron forms[END_REF][START_REF] Liu | Biological reduction of structural Fe(III) in smectites by a marine bacterium at 0.1 and 20 MPa[END_REF][START_REF] Liu | Microbial reduction of Fe(III)bearing clay minerals in the presence of humic acids[END_REF][START_REF] Pentráková | A review of microbial redox interactions with structural Fe in clay minerals[END_REF][START_REF] Vorhies | Microbial dissolution of clay minerals as a source of iron and silica in marine sediments[END_REF]. Thus, clay mineral alteration in the study area could have been influenced by reduction of structurally coordinated Fe(III), which would change charge balances and could trigger changes of the mineral structure or ion exchange capacities [START_REF] Meunier | The glauconite-Fe-illite-Fe-smectite problem: A critical review[END_REF]. Alternatively, if Fe(III) was supplied from an iron oxy-hydroxide phase (e.g. goethite), clay mineral alteration could become driven by equilibration of solid solutions with dissolved Fe 2+ or dissolutioninduced formation of Fe(II)-rich secondary clay minerals. Summarizing our discussion in a conceptual model (Fig. 10), we propose that chemical shifts resulting from seawater intrusion and salt diffusion drive reverse weathering reactions and contribute to the chemical alteration of phyllosilicates. Since iron appears to be largely associated with clay minerals, the alteration of clay minerals could influence iron bioavailability, thus opening up a refractory iron pool. In particular, our conceptual model considers that a redox zonation shift in response to seawater intrusion controls the electron donor supply for microbial iron reduction, acting as the actual driver for iron reduction at depth. processes in Black Sea "lake" sediments. In response to seawater intrusion, ion exchange, dissolution and reverse weathering reactions change the composition of minerals in the lacustrine sediment. In addition to that, the development of a shallow sulfate reduction zone shifts microbial iron reduction to greater depths. We hypothesize that both organoclastic and methanotrophic sulfate reduction contribute to the overall sulfate turnover, and that, however, the organic carbon turnover has not become fully adapted to sulfate reduction under transient state conditions. Thus, dissolved organic compounds (i.e. DOC) escape from the sulfate reduction zone and fuel microbial iron reduction at depth.

Conclusion

Pore water data show the progress of reactive-transport processes in lacustrine sediments at the Black Sea western slope after seawater intrusion into the basin 9 ka BP. Intense sulfate reduction and cation exchange at shallow depths provide clear evidence of ongoing dynamic alteration of the lacustrine sediments. The seawater intrusion drives the release of Ca 2+ and Sr 2+ , and the uptake of K + , Mg 2+ and Na+ in the sediment through reverse weathering and ion exchange, and affects clay mineral pools and iron bioavailability below the SMTZ. Postdepositional disturbances are not clearly visible, and strong sediment and pore water evidence for mass movement events and slope destabilization is lacking. Similarly, the intense gas seepage, which guided the choice of coring locations, was not significantly reflected in pore water profiles, except for a shoaling of the SMTZ. However, the large variability of sediment composition and mineralogy, which results from highly dynamic changes in solids transport and deposition rates during the last glacial period and Holocene, strongly complicates the geochemical interpretations.

Fig. 2 :

 2 Fig. 2: Pore water depth profiles of dissolved ion concentrations. Grey layer indicates the SMTZ, and yellow layer corresponds to the interval of increased iron concentrations.

Fig. 4 :Fig. 5 :

 45 Fig. 4: Solid phase depth profiles of porosity, carbon fractions and mineralogy. Note that the clay fractions were calculated from the total amount of clay only after separation from the other minerals present in the sediment.

  .2-15.7 ka (very low XRF-Ca values;[START_REF] Soulet | Abrupt drainage cycles of the Fennoscandian Ice Sheet[END_REF] Soulet et al., 2011a)); (ii) Peaks in dolomite content (green bold lines) indicating the influence of the Eastern Alps on the local sedimentation at the MIS 3/2 transition (Martinez-Lamas et al., 2020) and possibly during MIS 4, with potential contribution from low-temperature proto-dolomitization (Liu et al., 2019); (iii) the regional imprint of the Dansgaard/ Oeschger (D/O) variability of MIS 3 recognized in the SE Black Sea during ca. 35-60 ka through large variations in the carbonate content

  BP, higher smectite and kaolinite contents suggest that the signals of the sediment contribution from the Danube drainage basin with Dinarides and Carpathians were not overprinted by the Alpine contribution[START_REF] Martinez-Lamas | Linking Danube River activity to Alpine Ice-Sheet fluctuations during the last glacial (ca. 33-17 ka BP): Insights into the continental signature of Heinrich Stadials[END_REF]. Meltwater pulses from the Dniepr basin during the red layer interval supplied illite-rich sediments[START_REF] Soulet | Abrupt drainage cycles of the Fennoscandian Ice Sheet[END_REF].

Fig. 6 :

 6 Fig.6: Age-depth model derived from tentative stratigraphic correlations between cores GAS-CS01 (Martinez-Lamas et al. 2020), GAS-CS03, GAS-CS07 and GAS-CS12 (this study). The upper part of core GAS-CS07 was heavily charged in gas and not reliable for XRF analysis. Ages older that ~33.5 ka (i.e. base of GAS-CS01; in italic) are given according to the recognition of stratigraphical features observed in the SE Black Sea[START_REF] Wegwerth | Black Sea temperature response to glacial millennial-scale climate variability[END_REF]. Peaks in dolomite content (green bold lines) indicate the influence of the Eastern Alps on the local sedimentation (see Martinez-Lamas et al., 2020 for details). All the sedimentary sequences studied here correspond to the lacustrine Unit III of Ross & Degens (1974). BA: Bölling-Alleröd; E.Hol.: Early Holocene; MIS: Marine Isotope Stage; YD: Younger Dryas.

Fig. 7 :

 7 Fig. 7: Ratio of selected pore water species relative to chloride, calcium and bromide (For the color code, the reader should refer to Fig.2)

Fig. 9 :

 9 Fig. 9: (a) Solid phase iron speciation and (b) Fe(III) content for core GAS-CS01. Fe(III) content determination by XANES pre-edge fitting is prone to errors and we had not enough suitable reference samples available for a

Fig. 10 :

 10 Fig. 10: Conceptual model scheme for coupling of biogeochemical processes and element cycling before (a) and after (b) seawater inflow. Prior to seawater intrusion, methanogenesis and microbial Fe reduction were key

Table 1 :

 1 List of cores recovered and sampled for pore water analyses

	Core name	Coordinates	Length/ cm	Water depth/ m
	GAS-CS01	N44°05.188'; E30° 47.961'	3337	240
	GAS-CS03	N43°58.030'; E31° 03.107'	2246	842
	GAS-CS05	59.7349' N43°58.3944'; E30°	1179	794
	GAS-CS06 N43°59.4985'; E30°57.3139'	1970	650
	GAS-CS07	N43°56.048'; E30°50.6635'	1234	822
	GAS-CS08	N43°56.048'; E30°50.6635'	2080	821
	GAS-CS12	N43°57.994'; E30°45.020'	2464	547
	GAS-CS13	N43°59.298'; E30°57.234'	1381	660
	GAS-CS14	N43°56.361'; E30°51.044'	542	738
	GAS-CS16	N43°55.450'; E30°45.427'	2564	685
	GAS-CS18	N43°55.777'; E30°45.301'	2740	638

Acknowledgements

We thank the captain and his crew on-board the RV Pourquoi pas? crew for their technical support and advices. Financial support for the cruise was provided by Ifremer and the European project Midas (grant agreement 603418). This work is also a contribution to the BLAME project sponsored by the French National Research Agency (ANR-18-CE01-0007) and the SUGAR project funded by the German Federal Ministry of Economic Affairs and Energy (grant no. 03SX320A) and the German Federal Ministry of Education and Research (grant nos. 03G0819A and 03G0856A). We acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for the provision of experimental facilities. Parts of this research were carried out at beamline P64 and we would like to thank Wolfgang A.

Caliebe (DESY) for assistance in operating the beamline and Anna-Kathrin Retschko (GEOMAR) for sample preparation. We thank Andrea Bodenbinder, Bettina Domeyer, Anke Bleyer and Regina Surberg for the excellent support with shore-based analyses, as well as Dr.

Guillaume Soulet for constructive discussion. We also thank two anonymous reviewers for their valuable comments, which significantly improved the content of the paper.