Joachim Schöpfel
email: joachim.schopfel@univ-lille3.fr

Coline Ferrant

Francis André

Renaud Fabre

Ready for the Future? A Survey on Open Access with Scientists from the French National Research Center (CNRS)

Keywords: Open access, open repositories, open science, self-archiving, OA publishing, research management. Article Classification: Research paper

The paper presents empirical evidence on the opinion and behaviour of French scientists (senior management level) regarding open access to scientific and technical information. Approach: The results are part of a nationwide survey on scientific information and documentation with 432 directors of French public research laboratories conducted by the French Research Center CNRS in 2014. Findings: 1. The CNRS senior research managers (laboratory directors) globally share the positive opinion towards open access revealed by other studies with researchers from the UK, Germany, the United States and other countries. However, they are more supportive of open repositories (green road) than of OA journal publishing (gold). 2. The response patterns reveal a gap between generally positive opinions about open access and less supportive behaviours, principally publishing articles with APCs. 3. A small group of senior research managers does not seem to be interested in green or gold open access and reluctant to self-archiving and OA publishing. 4. Similar to other studies, the French survey confirms disciplinary differences, i.e. a stronger support for self-archiving of records and documents in HAL by scientists from Mathematics, Physics and Informatics than from Biology, Earth Sciences and Chemistry; and more experience and positive feelings with open access publishing and payment of APCs in Biology than in Mathematics or in Social Sciences and Humanities. Disciplinary differences 2/16

and specific French factors are discussed, in particular in the context of the new European policy in favour of Open Science. Originality: For the first time, a nationwide survey was conducted with the senior research management level from all scientific disciplines. The response rate was high (>30%), and the results provide good insight into the real awareness, support and uptake of open access by senior research managers who provide both models (examples for good practice) and opinion leadership.

Introduction

"Winds of change are blowing throughout scholarly communicationsit has culminated in a so-called 'perfect storm' (which) arises from the confluence of several largely unrelated trends" (Brown 2016, p.22). One of these trends is openness, a "broad social movement involving significant cultural change" (ibid, p.340).

Open Science

Openness to science, or Open Science, is at the top of the research agenda of the European Union. In Horizon 2020, the European Research and Innovation Framework Programme running from 2014 to 2020 open access to publications has become mandatory. Also, the European Commission is commencing a policy process on Open Science, considered as "the transformation, opening up and democratisation of science, research and innovation, with the objective of making science more efficient, transparent and interdisciplinary, of changing the interaction between science and society, and of enabling broader societal impact and innovation" (Ramjoué 2015, p.169). Open access is, together with open research data, a key component for the emergence of a new ecosystem of standards and services of scientific information.

More recently, the European commitment to Open Science was confirmed and reinforced by the Amsterdam Call for Action on Open Science1 which formulates a "multi-actor approach (…) to reach two important pan-European goals for 2020", i.e. full open access for all scientific publications and a fundamentally new approach towards optimal reuse of research data. The Amsterdam Call for Action describes twelve concrete action items to be taken by the European Commission, the EU Member States and the stakeholders, such as research funders, national authorities, publishers and private partners. Research performing organisations and the research communities play a central role to agree on open access principles, promote mutual understanding, put in place new policies, set new standards and coordinate activities in favour of open access and open data. Scientists and their organisations and institutions are not the only stakeholders. But without their support and involvement, the ambitious goals will not be reached, neither in 2020 nor later on.

The French National Center for Scientific Research (CNRS)

In terms of scientific output (articles, citations) and innovation (patents), France is one of the leading Member States of the European Union, together with the United Kingdom and Germany. In 2014, French scientists published nearly 105,000 articles2 , and France spent 2.3% of its GDP on research and innovation, a sector with about 366,000 researchers3 . The National Center for Scientific Research, or CNRS4 , is a public organization under the responsibility of the French Ministry of Education and Research. As the largest fundamental research organization in Europe, the CNRS carries out research in all fields of knowledge, through its ten institutes (life sciences, chemistry, physics etc.) and 32,500 staff members in more than 1,000 research units (laboratories).

One of the first signatories of the Berlin Declaration on Open Access, the CNRS is deeply committed to open access, in particular through funding of the national HAL repository with 388,771 documents5 and of the OpenEdition platform with 431 journals and 2,719 monographs in open access6 . Also, the CNRS supports national, European and international initiatives and projects in favour of open access and Open Science, with a clear preference for self-archiving of publications and data in open repositories (green road).

One

Recent surveys

In recent years, a couple of surveys have assessed the researchers' understanding and awareness of open access and their attitudes and motivation towards the green and gold road, as key factors of the success of open access. More than ten years ago, in an international study with 1,296 authors, 49% of the respondent population had self-archived at least one article during the last three years but a substantial proportion of authors was still unaware of the possibility of providing open access to their work by self-archiving [START_REF] Swan | Open access self-archiving: An author study[END_REF]. These results were corroborated by a 2008 survey with UK researchers that revealed some "suspicion of open access publications" and ignorance about open access and the role of institutional repositories, and suggested that a degree of culture change may be needed [START_REF] Creaser | Open access to research Outputs-Institutional policies and researchers' views: Results from two complementary surveys[END_REF].

On the other side, based on a sample of over 3,000 European scholars, [START_REF] Fry | PEER behavioural research: Authors and users vis-à-vis journals and repositories[END_REF] reported not only a good understanding and appreciation of the ethos of open access in general but also clear differences between disciplines. This was confirmed by [START_REF] Eger | The determinants of open access publishing: Survey evidence from Germany[END_REF] in a study with 2,151 researchers in Germany that revealed significant differences between the scientific disciplines with respect to researchers' awareness of and experience with OA journals and self-archiving. "The perceived relevance and reputation of OA within one's discipline may explain why researchers from particular disciplines (do not) publish in OA journals. Besides, several determinants like age, profession or the discipline specific reward system play a role. In general, discipline-specific incentives matter" (p.4).

In 2014, the European University Association conducted a survey on the development and degree of implementation of institutional policies on open access with 106 universities (EUA 4/16 2015). About 60% reported that the main element in their institutional policy was encouraging researchers to deposit their publications in an open repository. Concerns over copyright infringement were identified as the most frequent barrier regarding self-archiving, and the researchers' awareness of the journal publishers' policies on open access was generally considered as low. [START_REF] Morris | Learned society members and open access[END_REF] surveyed individual members of 35 UK learned societies on their attitudes to open access. Most of their 1,368 respondents were aware of OA and in favour of increased access through OA journals, even if their real knowledge and practice were lagging behind. The access and convenience of self-archiving repositories were seen as positive but there was "less support in principle for self-archiving than for OA journals -36.37% of respondents are in favour, compared with 74.11% for OA journals" (p.237). However, only one quarter of the authors claimed to self-archive at least some of their articles, and the major concerns expressed were about workload, "lack of quality control, and proliferation of multiple versions of articles" (ibid).

Further studies of author perceptions on open access reveal general features as well as domain specific aspects (see overviews by [START_REF] Björk | Open access to the scientific journal literature: Situation 2009[END_REF][START_REF] Nariani | Open access publishing: What authors want[END_REF][START_REF] Nariani | Open access publishing: What authors want[END_REF]). Among the general features are a globally favourable stance towards open access, yet little awareness of OA in general and journal publishing in particular, especially outside of physics, and a general reluctance to pay article processing charges (APCs), mainly in the absence of institutional support. The same response patterns were found by the large SOAP survey with 38,358 authors -89% answered that OA journal publishing was beneficial to their field but only 52% had already published in OA; funding and journal quality were identified as the main barriers [START_REF] Dallmeier-Tiessen | Highlights from the SOAP project survey. What scientists think about open access publishing[END_REF]. In a smaller survey with 481 researchers, 85% liked the idea of open access publishing; "almost two-thirds (66%) of the respondents have used Open Access publication media for accessing research results at least once in their academic career. But only about one quarter (28%) of the researchers have used them for actual publishing the results of their work" (Mann et al. 2009, p.136).

In the Mann et al. survey, "despite their positive general attitude, the majority of the survey participants (61%) fear that Open Access publishing might jeopardize their chances of promotion and tenure. At the same time, 63% worry about Open Access publishing damaging their chances for research funds" (ibid.). Still, reputation and prestige are more important factors for the choice of a journal than openness or business modelsin other words, career prevails when it comes to deciding where and how to disseminate research results.

Reviewing recent surveys on authors' attitudes towards open access and journal publishing, the 2015 STM Report puts it this way: "That there are benefits of open access seem generally accepted: only 11% said OA had no fundamental benefits" (Ware & Mabe 2015, p.71); also, "authors believe journals will remain as the principal publication outlet, demarcating quality research, but a significant proportion of research papers will be published only in subject or institutional repositories that will coexist with journals" (p.72). The "main factors affecting author choice of journal (remain) the journal's quality, its relevance, and speed of publication (in that order)" (p.71).

Questions

All survey results converge towards the fact that the researchers have generally accepted the idea of open access and that they consider it as globally beneficial for their field, even if their information and publishing behaviour may be somewhat delayed. In Europe, 461 research organisations and funders have adopted open access mandates and policies that require or request their researchers to provide open access to their peer-reviewed research article output by depositing it in an open access repository 7 ; many have signed national or international statements on open access, such as the Berlin Declaration. Both, individual awareness and uptake and institutional, political commitment are crucial for the further progress of open access.

Senior researchers, especially research managers and directors of research centres, are key stakeholders in this process in two ways:

 They are appointed by their peers, coordinate the research activities and represent their colleagues in the executive and advisory bodies; as such, they act as a kind of transmission belt of the researchers' opinions and demands, including reporting (bottom-up).  At the same time, they stand for the research organisation and are the guardians of the application of institutional decisions and rules within the local laboratory, including supervision, follow-up and control (top-down). This intermediary or middle function may not always be an easy situation, as a latent source of conflict, but it makes them particularly interesting and influential as opinion leaders and even as potential models for good practice.

Methodology

The survey was conducted between July and September 2014 by the CNRS Scientific and Technical Information Department (DIST)8 . A questionnaire with 91 items was sent to the directors of the 1,250 CNRS research laboratories representing all areas of fundamental science. The survey was a component of an internal audit on the CNRS STI policy and service development. Part of the demand analysis, the items' objective was to assess attitudes and needs expressed by research managers regarding four particular functions of scientific information: access to scientific information, publishing of research results, analysis of scientific information (scientometrics), and other research support services, including ethics and legal advice.

432 laboratory directors completed the questionnaire (35%). The respondents are a representative sample of the CNRS research institutes (social sciences and humanities, life sciences, chemistry, engineering and systems sciences etc.) and of the geographical distribution (Paris, regions).

Fifteen items dealt with different aspects of open access to scientific information -access as well as dissemination, green road as well as gold road, legal advice as well as technical assistance, and global questions on open access alternated with specific items related to the French open access infrastructure, i.e. the HAL repository (see appendix 1).

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The raw results were published in March 20159 . This paper reports a re-analysis of the survey data in particular:

 to explore experiences with green and gold open access,  to assess the general attitudes of French research managers to open access,  to evaluate specific needs and demands, and  to analyse the differences between scientific disciplines. The findings will be discussed from three different points of view: Are French research managers different from those of other countries when it comes to open access? Do they form a relatively homogeneous group or can we distinguish different "clusters"? And in particular, is there a clearly reluctant or even hostile group of researchers opposed to open access as an alternative to traditional publishing? The discussion will also mention the progress made toward open access in France since 2014.

Findings

As indicated above, 432 research unit directors (senior managers) completed the questionnaire. No question was mandatory. The response rates per question are relatively high and range from 0.73 to 0.97 (median 0.91).

Seven questions assess past experiences with open access, e.g. deposit of records and documents in HAL or the payment of APCs. Three questions evaluate the respondents' global attitudes towards open access, in particular towards resource sharing, European networking and APCs. Finally, five questions explore specific demands and needs, such as the promotion and future development of HAL, including a mandatory policy (for more details see Appendix 1 and footnote 9). For each question, the responses can be analysed as "positive" (in favour of OA, interested, experience with HAL or OA publishing) or "negative" (opposed to OA, no experience, not interested, no priority). In other terms, "positive" means "experience/practice with OA", "positive attitude" or "interested in strengthening OA", according to each question.

Consensus

The survey reveals a large consensus on three questions, with about 90% affirmative responses and a high response rate of 0.95. Nine out of ten respondents are willing to share their scientific results with scientists from other laboratories (#25) and are in favour of the sharing of open access deposits through an European or international network (#37), and they think that the national open repository HAL should be better known and promoted (#30). These responses reflect a general scientific attitude (community, internationality) together with a large global support in favour of the HAL repository.

Majority opinion and practice

A majority of respondents -50-70% -declares actual usage of the HAL repository (#26), including deposit of metadata (records, #27) and documents (full text, #28) and demands further development of the HAL services (#31).

Between 65% and 70% of the respondents also demand that HAL should improve on the distinction between preprints (unpublished) and other items, i.e. published articles (#32), and should put open access management on the top of the wish list for new service developments (#84).

Minority opinion and practice

Other questions about open access did not receive a majority of affirmative or positive answers. Here, four different aspects can be distinguished:

Mandate: Nearly 40% of the respondents are in favour of an institutional mandate, in other words, they ask that the deposit in HAL should become mandatory (#36). This is not a small group but nevertheless, it does not express a majority opinion.

APCs: Only 30% declare having paid APCs so far for an open access article (#38), and less than 20% of the others say that they intend to do so in the future (#39). Even when both groups are taken together, they don't reach a majority and remain below 50%.

Usage of other repositories: HAL is the dominant French open repository in the heart of the academic ICT infrastructure. Only 30% of the respondents say that they (also) use other repositories than HAL for their publications (#29), which confirms the central role of HAL for the CNRS laboratories.

Other issues: About 30% have already had legal problems with the deposit of copyrighted material in an open repository (#88), and as many say that they would use an open repository for the referencing of their scientific output (#41), for scientometrics, evaluation and so on.

Disciplinary differences

As mentioned above, the 432 senior managers come from all ten research institutes. Each institute representing a specific research field or discipline (see Appendix 2), the results can also be analysed against the different disciplines. Our observations of differences between disciplines are based on Pearson's chi-squared (Χ 2 ) tests of the response patterns per institute. The fifteen questions were ranked according to their level of confidence in the Χ 2 test (figure 2). Again, three groups of questions can be distinguished. Four questions have a low Χ 2 with a confidence level p between 0.131 and 0.925. For these items, there are few or no differences between the institutesall are convinced of the need for open access management (#84) and for more promotion and further development of the CNRS open access services and tools (#30), in particular HAL (#31), and all are willing to share their digital resources with other scientists (#25).

For three other questions, the confidence levels p range from 0.022 to 0.039, i.e. there are significant differences between the institutes at the 0.05 level. Three items are related to green open access in general (#37 European networking) and HAL in particular (#32 distinction of preprints and #36 mandate).

Together, these seven questions have in common the fact that they all assess either opinions (attitudes) or needs (demands, interest). Obviously, the disciplinary differences have more to do with experiences, behaviours and practice of open access. Except for one item (#39 intention to pay APCs), all questions statistically significant at the 0.001 level are related to past experiences and/or real behaviour. For these questions, we can describe some particular OA patterns (Table 1).

Table 1: Disciplinary differences (the institutes have been replaced by the disciplines, see appendix 2)

The most salient results can be summarized under three different aspects: HAL: Contrary to its multidisciplinary vocation and positioning, but just like its initial model, i.e. arXiv, the part of scientists from Nuclear Physics, Informatics and Mathematics using the national repository HAL is significantly higher than the part of scientists from Biology, Chemistry or Earth Sciences and Astronomy. This does not change the multidisciplinary character of HAL's deposits and usage but shifts the focus on the fact that its relative importance differs between the CNRS scientific communities.

APCs: Especially scientists and laboratories in life sciences (Biology) but also in Physics and environmental research (Ecology) have already published articles with APCs and/or intend to do so while scientists from Mathematics and Social Sciences and Humanities are more reluctant than others to publish their articles in this way.

Legal problems: Researchers from the social sciences and humanities report having experienced legal problems more often with the deposit of copyrighted material in an open repository than colleagues from other disciplines, in particular from Mathematics.

Discussion

Attitude towards open access and behavioural gap

The survey reveals a globally positive and favourable attitude towards resource sharing and the development and promotion of the national open access infrastructure HAL amongst scientists from the French Research Center. This globally positive attitude towards open access, and in particular with the green road (self-archiving) is consistent among the whole sample, without significant differences between disciplines.

Focussing on the gold road (OA journals), the large scale survey of the Study of Open Access Publishing (SOAP) has shown similar response patterns: "One of the key questions asked in the survey is whether respondents considered open access publishing beneficial for their research field (...). In total 89% of published researchers answering to the survey thought that journals publishing open access articles were beneficial for their field" (Dallmeier-Tiessen et al. 2011, p.3). [START_REF] Fry | PEER behavioural research: Authors and users vis-à-vis journals and repositories[END_REF] reported that two-thirds of respondents were convinced that there is a role for open repositories in scholarly communication. This is not self-evident or normal. Based on two surveys, [START_REF] Creaser | Open access to research Outputs-Institutional policies and researchers' views: Results from two complementary surveys[END_REF] regretted that "many researchers" maintained a suspicion of open access publications. Such a global suspicion cannot be detected in the French sample. A more critical stance, and also disciplinary differences, are related not to expressed opinions but to real practice. The CNRS survey shows a gap between generally positive attitudes and less supportive behaviours, i.e. self-archiving and above all APCs. In spite of globally constructive opinions on open access, French scientists are more reluctant when it comes to "acting out"probably because they discover the "costs" of open access, in terms of APCs and time.

It may be that disciplinary, community traditions of scientific communication impact information behaviours more than attitudes. Or it may also be that the survey itself encouraged a positive bias towards open access. Even so, this "behavioural gap" can be interpreted as a cognitive dissonance and exploited as such when promoting self-archiving and open access publishing. At least, this bias will be helpful to convince scientists to adapt their practice to their expressed opinions and attitudes, closing the gap and reducing the dissonance.

Open access clusters?

The French survey does not reveal any significant "OA clusters" among the scientists. One particular question was whether an "OA-reluctant group" could be identified. While [START_REF] Creaser | Open access to research Outputs-Institutional policies and researchers' views: Results from two complementary surveys[END_REF] mentioned "many researchers" with suspicion of open access publishing, [START_REF] Fry | PEER behavioural research: Authors and users vis-à-vis journals and repositories[END_REF] identified only a small group of 4% authors opposed to self-archiving, and 30% respondents without a strong or definite opinion. Regarding mandatory open access, [START_REF] Swan | Open access self-archiving: An author study[END_REF] had come to a comparable result: " (…) the great majority of authorsin the whole population, in each subject area and in each region of the worldhave no objection to a mandate to self-archive imposed by their employer or research funder and would willingly comply with it. Most of the rest (13%) would comply reluctantly. Only a very small percentage (5%) would not comply at all" (p.66).

In the French sample, the part of reluctant respondents, with consistently non-supportive or negative response patterns is 2% for opinions and expressed needs and 4% for reported behaviours. The others, if not clearly favourable and supportive towards open access, are hesitant or undecided. However, two or three aspects need attention: nearly two-thirds are opposed to mandatory self-archiving in HAL (63%); more than the half do not and will not pay APCs (57%); and only a small group of scientists express consistently favourable opinions about open access (9%) and/or show positive interest in open access (14%).

The opposition to mandatory self-archiving can perhaps be explained by the way some scientists perceive the national repository HALbecause some institutions adopted mandatory policies with obligatory self-archiving in HAL, some scientists do not consider any longer HAL as a tool for direct communication but rather as a tool for scientometrics and evaluation, i.e. as a tool of institutional control which they reject.

Concerning APCs, the survey does not distinguish between full open access journals and hybrid journals. One part of the opposition to APCs may have its reason in the fact that some disciplines are now accustomed to full OA journals and very rapid publishing (in particular life sciences with journals like BMC and PLoS) while others like Mathematics or Social Sciences and Humanities did not up to now adopt this way of publishing research.

Taken together, this means that a large part of the scientists -80-85% -are somewhere "inbetween", with positive experiences and opinions but also with some doubts, suspicions and questions. They represent the real challenge of the future communication and promotion of open access, HAL and OA publishing. [START_REF] Fry | PEER behavioural research: Authors and users vis-à-vis journals and repositories[END_REF] described a favourable stance towards open repositories in Social Sciences and Humanities, in Physics and Mathematics while researchers from life sciences (Biology) showed less enthusiasm for self-archiving. A high support for open access in most of the humanities and social sciences (>90%) and in Chemistry, Astronomy, Physics, Engineering and related disciplines (around 80%) was also reported by Dallmeier-Thiessen et al. (2010). [START_REF] Eger | The determinants of open access publishing: Survey evidence from Germany[END_REF] asserted "remarkable differences" between disciplines -a larger share of open access publishing in natural science disciplines, in particular in Biology, and more support for self-archiving in Physics and Mathematics.

The impact of disciplines

The French survey confirms similar disciplinary differencesa stronger support for selfarchiving of records and documents in HAL by scientists from Mathematics, Physics and Informatics than from Biology, Earth Sciences and Chemistry; and more experience and positive feelings with open access publishing and payment of APCs in Biology than in Mathematics or in Social Sciences and Humanities.

Why is this so? [START_REF] Björk | Open access to the scientific journal literature: Situation 2009[END_REF] believe that "possible reasons for the differences between disciplines (…) include uneven spread of available OA journals across disciplines, unequal possibilities for financing author charges, availability of well-established subject based repositories in some disciplines (and) traditions of making preprints available in some subjects". Eger et al (2010) mention academic experience (seniority and status) as another potential determinant. All are convinced that because of these factors and differences a "onesize-fits-all" approach is not appropriate.

Especially in Biology, there are very few preprints and the rapid publishing and exchange of research results is organized thru full OA journals like BMC and PLoS. Non usage of HAM from these three disciplines. Thus their position probably does not reflect a disciplinary usage but rather an average of different behaviours.

However, the figures must be interpreted with caution because of the large categories and because of the small numbers in the subsamples, especially in questions with lower response rates.

What about document supply?

As mentioned above, the CNRS survey was not limited to open access but covered a large scale of information services and needs. Two-thirds of the respondents are satisfied with the digital resources (journals, monographs, databases…) available through the large disciplinary CNRS portals 10 even if many would like a unique gateway, more inter-disciplinary portals and also more specialised, domain-specific content. They are aware of open access and use all kinds of information freely available on the Internet. Many ask for further development and promotion of open access infrastructures.

However they do not explicitly ask for document supply, and most of them do not rely on the CNRS Refdoc service 11 . For them, document supply obviously remains "in a time warp (…) on the periphery of traditional STM publishing" (Brown 2016, p.207). Will the future development of the French academic inter-lending and document supply change the situation? [START_REF] Bérard | Academia and document supply: unsustainable contradictions at INIST?[END_REF] admit that "the development of resources in OA, by the deposit of the researcher or the investments of the publishers in dedicated journals, can only accelerate the end (…) of the 'industrial' supply of article copies" (p.136) and describe a realistic approach to cope with this situation, a "policy of small steps", such as free reciprocal arrangements with some universities or, in the context of the new "CollEx" project 12 , a redesigned and labelled system of document supply with large specialized libraries. The coming years will show the results of this difficult "transition from industrial model to a mediation/identification and retrieval service" (loc.cit.) and its place in Open Science.

Conclusion

The EU Competitiveness Council has confirmed the strategy of the Amsterdam Call for Action at its meeting on May 27 th 2016, and adopted conclusions on the transition towards an Open Science system 13 . The outcome document of the Council Meeting highlights that the "Member states agreed to common goals on Open Science and to pursue concerted actions together with the Commission and stakeholders" and that they "committed to open access to scientific publications as the option by default by 2020 and to the best possible re-use of research data as a way to accelerate the transition towards an Open Science system". It says, too, that "Open Science involves moving from a system in which it is difficult to access and locate the results of scientific research to one that openly disseminates results to all kinds of users, such as researchers, knowledge institutions, companies, patient organisations, teachers, students, farmers and citizens in general. Humanities. The French survey uncovers attitudes, needs and behaviours similar to other countries, except for OA publishing with APCs where French scientists appear more reluctant and hesitant than their colleagues from other European countries. One explanation may be the fact that France globally spends less for scientific information than other similar countries; also APCs may appear less affordable. However, these differences should not be over-interpreted. Since 2014, the situation has changed in France as well as in other European countries, and open access to scientific information is fast becoming the dominant model of academic communication.

Today, the debate is no longer on pros and cons of open access. In 2016 the French parliament will probably adopt a new law ("Loi pour une République Numérique") granting secondary exploitation rights to scientists, similar to German, Austrian and Dutch legislation. Together with the other EU Member States, France is committed to Open Science and will continue to increase the availability of French research results. The challenge today is how to get there. For more than 15 years, France has developed an open access infrastructure with national operating agents, a large open repository (HAL) and public OA journal and book platforms especially in social sciences and humanities. This public infrastructure is now in competition with OA publishing and APCs mainly controlled by large corporate publishers.

One challenge is the control over dissemination, access and preservation of research results, and over innovation in the field of academic publishing. Another challenge is the exploitation of the growing volume of research results through content mining, and the control of these technologies and tools. Will the research community maintain (or regain) control over its data, over usage, impact, evaluation etc.? Who will add value to content, who will provide metrics for research output, for networks, experts, emerging topics etc.? Will the dysfunctional scientific information market survive, with its oligopolies, mergers and benefits? Should it?

Open Science is a great and exciting idea, and the European countries are right to set a short-term goal of full open access in 2020. French scientists appear ready and willing to meet the challengebut not at any cost. The survey points to the fact that one size will not fit all. The development of services to researchers for better sharing of knowledge across a smoother flow of scientific production must respect the specific characteristics of scientific communities. Not only do significant differences persist between scientific disciplines, which exclude and condemns to failure any "easy solution", but significant differences exist also between countries and their specific investments, infrastructures, organisations, research policies and scientific cultures. Seeking to impose the same approach to open access may lead to a dead end or simply elsewhere and definitely not to Open Science.

  For this reason, instead of a new assessment of scientists' attitudes and behaviours towards open access, the CNRS conducted an exploratory survey on Scientific and Technological Information (STI) specifically at the senior management level, i.e. the directors of the CNRS research units (laboratories). One part of this survey was about open access. Our paper reports the survey results on open access, in particular to obtain answers to four questions: 1. Do the CNRS senior research managers (laboratory directors) share the positive opinion towards open access revealed by recent studies with researchers from the UK, Germany, the United States and other countries? Are they supportive of open repositories and OA journal publishing? 2. Does their information behaviour, i.e. use and production of open access publications, meet the challenge of open access or does it lag behind their opinions? 3. Like in other studies, will this survey identify a group of unaware or even reluctant senior research managers not interested in open access? 4. And finally, what can be said about differences between scientific disciplines?

Figure 1 :

 1 Figure 1: OA affirmative responses (with response rates)

Figure 2 :

 2 Figure 2: Disciplinary differences in questions (Χ 2 test, P-values)

  part of the CNRS scientific output (annual average 35,500 publications) is freely available through HAL, arXiv and other open repositories, and in commercial or non-profit open access or hybrid journals. The exact percentage is hard to estimate, but it is probably at a comparable level with other European research organisations, i.e. about 20 to 30%. With the European Council defining a 100% open access goal for 2020, it still has a long way to go. Is the CNRS willing to meet the challenge? Are the CNRS researchers ready to move forward?

  It aims at transforming science through ICT tools, networks and media, to make research more open, global, collaborative, creative and closer to society". The survey with more than 400 CNRS research centres provides an instant photo of the open access attitudes and behaviours of French senior research managers in 2014. In particular the results show that: 1. The CNRS senior research managers (laboratory directors) globally share the positive opinion towards open access revealed by other studies with researchers Germany, the United States and other countries. However, they are more supportive of open repositories (green road) than of OA journal publishing (gold). 2. The response patterns reveal a gap between generally positive opinions about open access and less supportive behaviours, principally publishing articles with APCs. 3. A small group of senior research managers does not seem to be interested in green or gold open access and reluctant to self-archiving and OA publishing. 4. Similar to other studies, the French survey confirms disciplinary differences, i.e. a stronger support for self-archiving of records and documents in HAL by scientists from Mathematics, Physics and Informatics than from Biology, Earth Sciences and Chemistry; and more experience and positive feelings with open access publishing and payment of APCs in Biology than in Mathematics or in Social Sciences and

10 Source: INIST http://www.inist.fr/?-Portals-&lang=en 11 Source: INIST http://www.refdoc.fr/ 12 Source: Ministry of Higher Education and Research http://www.enseignementsuprecherche.gouv.fr/cid99665/collections-d-excellence-pour-la-recherche-%E2%80%93-persee-collex-persee.html 13 Source: European Council http://www.consilium.europa.eu/en/meetings/compet/2016/05/26-27/ 13/16 from the UK,

Source: The Netherlands EU Presidency

2016, April 2016 http://english.eu2016.nl/documents/reports/2016/04/04/amsterdam-call-for-action-on-open-science

Source: SCImago Lab, http://www.scimagojr.com/

Source: OECD https://data.oecd.org

Source: CNRS http://www.cnrs.fr/

Source: HAL https://hal.archives-ouvertes.fr/ (13 May 2016)

Source: OpenEdition http://www.openedition.org/ (7 May2016)

Source: ROARMAP http://roarmap.eprints.org/ (14 May 2016)

Direction de l'Information Scientifique et Technique http://www.cnrs.fr/dist/

http://www.cnrs.fr/dist/z-outils/documents/Enquête%20DU%20-%20DIST%20mars%202015.pdf

does not necessarily mean rejection. Earth Sciences and Chemistry, on the other side, probably are (still) more attached to traditional journal publishing and "their" preferred publishers like ACS or Springer.

Figure 3 shows the ten CNRS institutes on a map with two variablesthe usage of HAL (green road, horizontal axis, #26) and the payment of APCs (gold road with payment, vertical axis, #38). The relative size of the ten institutes in the survey sample is represented through the size of the dot. : committed to self-archiving but not to OA publishing with APCs. Scientists from Chemistry, Biology and Physics have in common their opposition to mandatory self-archiving. One explanation may be that they remain strongly committed to "their" international journals of excellence for the dissemination of their works and papers.

Mathematicians are rather untypical in this sample in the way they use HAL (and other repositories), but are not interested in further development. Perhaps the reason is that for 10-15 years now the French Mathematics communityan excellence cluster in the landscape of French science, led by the CNRS INSMIhas developed its own digital library and OA tools, in partnership with their traditional publishers and with French and European learned societies.

The position of INEE (Environmental Sciences) somewhere in the middle (barycentre) between Biology, Earth Sciences and Social Sciences and Humanities may find an explanation in the fact that this research institute was recently created with scientists mainly

Appendix 1 -The survey questions

The complete survey (French version) is available online (see footnote 8). This is the list of the fifteen items re-analysed for the purpose of our study:

Experience with open access

#26 Do you use HAL?

Appendix 2 -The CNRS research institutes

The complete list of the CNRS research laboratories can be consulted at the following address: http://www.cnrs.fr/fr/recherche/labos.htm All web sites visited in May 2016.

Biographical Details:

IN2P3

Institut national de physique nucléaire et de physique des particules Nuclear and particle physics

INC


Adoum Mahamat Ahmat

Mohammed Boussafir

Claude Le Milbeau

Régis Guégan

Tiago De Oliveira

Lydie Le Forestier

Organic matter and clay interaction in a meromictic lake: Implications for source rock OM preservation (Lac Pavin, Puy-de-Dôme, France)

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

Introduction

Organic Matter (OM) preservation and burial mechanisms in sedimentary environments are still debated, despite the importance they have in oil source rock formation, biomarker fossilization and carbon cycle issues. At the water/sediment interface, OM preservation has been investigated through several approaches: O 2 exposure time [START_REF] Keil | Organic matter preservation through the oxygen-deficient zone of the NE Arabian Sea as discerned by organic carbon:mineral surface area ratios[END_REF][START_REF] Mayer | The inertness of being organic[END_REF][START_REF] Keil | Mineral matrices and organic matter[END_REF]Hernandez-Sanchez et al., 2014), inherited bioresistance [START_REF] Largeau | Formation of botryococcusderived kerogens. Comparative study of immature torbanites and of the extant alga Botryococcus braunii[END_REF][START_REF] Mayer | The inertness of being organic[END_REF], natural sulfurization [START_REF] Tegelaar | A reappraisal of kerogen formation[END_REF][START_REF] Sinninghe Damsté | Analysis, structure and geochemical significance of organically-bound sulphur in the geosphere: state of the art and future research[END_REF][START_REF] Boussafir | Electron microscopy and pyrolysis of kerogen from the Kimmeridgian Clay Formation, UK: Source organisms, preservation processes, and origin of the microcycles[END_REF][START_REF] Werne | Timing of early diagenetic sulfurization of organic matter: a precursor-product relationship in Holocene sediments of the anoxic Cariaco Basin, Venezuela[END_REF][START_REF] Van Dongen | Sulfurization of carbohydrates results in a S-rich, unresolved complex mixture in kerogen pyrolysates[END_REF][START_REF] Van Dongen | Preservation of carbohydrates through sulfurization in a Jurassic euxinic shelf sea: Examination of the black stone band TOC cycle in the Kimmeridge Clay Formation, UK[END_REF], biodegradation of biopolymers and hetero-polycondensation [START_REF] Tissot | Petroleum Formation and Occurrence, 2nd edition[END_REF] and iron oxide/hydroxide co-precipitation [START_REF] Eglinton | A rusty carbon sink[END_REF]Lalondes et al., 2012). The extensive occurrence of OM/mineral phase association in recent marine sediments and in mature and immature source rocks, led to the hypothesis that sorption onto mineral phases significantly promotes OM preservation [START_REF] Hedges | Sedimentary organic matter preservation: an assessment and speculative synthesis[END_REF]. It is now assumed that OM preservation in sediments arises from the combination of the above mechanisms, whose importance depends on the bio-resistance of the produced OM and the physico-chemical characteristics of the water column, as well as the sedimentation rate. These parameters depend on the sub-aquatic morphology and the depth of the sedimentary basin in question.

Studies of the mechanism of mineral protection have been motivated by the observation for many depositional systems of a significant correlation between OM content and the specific surface area of the mineral fraction [START_REF] Keil | Pollen in marine sediments as an indicator of oxidation of organic matter[END_REF]Mayer, 1994 a,b), suggesting the important role of grain size and associated specific surface area during the sorption process. Indeed, the finest mineral phase, especially clay, is recognized as the most efficient sorbent. In addition to granulometry, the importance of mineralogy has also been mentioned, highlighting the role of physico-chemical properties, notably the cationic exchange capacity (CEC) of phyllosilicate micro-particles [START_REF] Drouin | In vitro experiments of carboxylic acids sorption on synthetic clays in natural marine water. Implication on organic clayey rich sedimentation[END_REF]. Besides, the intrinsic features of the OM, such as degree of cyclization and presence of polar functionalities enhance the sorption rate by promoting strong bonding [START_REF] Drouin | In vitro experiments of carboxylic acids sorption on synthetic clays in natural marine water. Implication on organic clayey rich sedimentation[END_REF][START_REF] Mahamat-Ahmat | Organic matter-clay interaction along a seawater column of the Eastern Pacific upwelling system (Antofagasta bay, Chile): implications for source rock organic matter preservation[END_REF].

On a molecular scale, diverse physical and chemical bonding mechanisms have been proposed to explain the linking of organic compounds to clay minerals: hydrophobic effects, H bonding, cation bridges, ligand and ion exchange and Van der Waal effects [START_REF] Arnarson | Mechanisms of pore water organic matter adsorption to montmorillonite[END_REF][START_REF] Keil | Mineral matrices and organic matter[END_REF]. Low energy bonding, such as Van der Waal effects, hydrophobic effects and H bonding are reversible [START_REF] Plante | Changes in clay-associated organic matter quality in a C depletion sequence as measured by differential thermal analyses[END_REF][START_REF] Lutzow | Stabilization of organic matter in temperate soils: Mechanisms and their relevance under different soil conditions-A review[END_REF], while cationic bridges and ligand and ion exchange are considered stable, thereby allowing effective protection [START_REF] Arnarson | Mechanisms of pore water organic matter adsorption to montmorillonite[END_REF][START_REF] Drouin | Rôle des Argiles dans la Préservation et la Fossilisation de la Matière Organique Pétroligène[END_REF]. The relative importance of the mechanisms depends on the organic functional groups, environmental parameters like temperature, pH and the concentration of cationic elements [START_REF] Arnarson | Mechanisms of pore water organic matter adsorption to montmorillonite[END_REF].

Among them, metallic ions play a significant catalytic role during sorption [START_REF] Cervini-Silva | Adsorption kinetics of pentachloroethane by iron-bearing smectites[END_REF]Saidy et al., 2013). In addition to simple surface sorption, other studies have suggested that encapsulation into micro pore and nano pore spaces can also prevent bacterial enzyme access, aiding the preservation of "metabolizable" OM [START_REF] Kaiser | Sorptive stabilization of organic matter by microporous goethite: Sorption into small pores vs. surface complexation[END_REF][START_REF] Curry | Direct visualization of clay microfabric signatures driving organic matter preservation in fine-grained sediment[END_REF]Mayer,2004). Others suggest that OM intercalation in expandable clay interlayer spaces is also an effective preservation mechanism [START_REF] Kennedy | Mineral surface control of organic carbon in black shale[END_REF][START_REF] Kennedy | Clay mineral continental amplifier for marine carbon sequestration in a greenhouse ocean[END_REF][START_REF] Arndt | Quantifying the degradation of organic matter in marine sediments: A review and synthesis[END_REF].

Most of the studies dealing with the issue of mineral sorption for OM preservation do not consider its occurrence during the water column transfer. Mineral protection models have been proposed for settled OM [START_REF] Suess | Interaction of organic compounds with calcium carbonate 2. Organocarbonate associations in recent sediments[END_REF]Mayer, 1994a;[START_REF] Ransom | Organic matter preservation on continental slopes: Importance of mineralogy and surface area[END_REF][START_REF] Keil | Organic matter preservation through the oxygen-deficient zone of the NE Arabian Sea as discerned by organic carbon:mineral surface area ratios[END_REF][START_REF] Keil | Mineral matrices and organic matter[END_REF], without taking account of interaction occurring during the period of sedimentation. There is in fact a gap in the understanding of the fate of OM between the senescence of biological producers and sedimentary integration. We aimed to study the process of OM/clay aggregation interaction in the water column of a permanently stratified lake (Lake Pavin, France). In this analogue of a sedimentary euxinic environment, surface water is oxygenated and the lake is subject to seasonal mixing, while the deep zone is stable and permanently anoxic [START_REF] Michard | Geochemical study of a crater lake: Pavin Lake, France. Identification, location and quantification of the chemical reactions in the lake[END_REF][START_REF] Albéric | Carbon cycling and organic radiocarbon reservoir effect in a meromictic crater lake (Lac Pavin, Puy-de-Dôme, France[END_REF][START_REF] Cosmidis | Biomineralization of iron-phosphates in the water column of Lake Pavin (Massif Central, France)[END_REF]. Stratification involves changing the physico-chemical conditions in the water column, permitting a study of organo-clay aggregation in different redox conditions. OM-clay interaction experiments were performed using natural montmorillonite and kaolinite immersed at 3 conditions of oxygenation in order to understand the role of clay minerology and the influence of different water column physico-chemical conditions on the sorption process.

Prior to performing in situ OM-clay interaction experiments, authigenic organic sources (diatoms and cyanobacteria) and possible pedological OM sources were characterized in order to identify the major lipid contributor pool in the sorption processes.

Material and methods

Study site

Lake Pavin (Puy de Dôme, France) is a volcanic lake generated after a primary explosive eruption and consecutive phreato-magmatic phases [START_REF] Bourdier | Contribution à l'´Etude Volcanologique de Deux Secteurs d'Intérêt Géothermique dans le Mont Dore: Le Groupe Holocène du Pavin et le Massif du Sancy[END_REF][START_REF] Boivin | Le point sur l'éruption du lac Pavin il y a 7000 ans[END_REF]. The maximum depth is 92 m [START_REF] Chapron | Multidisciplinary characterization of sedimentary processes in a recent maar lake (Lake Pavin, French Massif Central) and implication for natural hazards[END_REF], with an oxygenated upper zone (0-52 m), subject to winter water mixing, and a permanently anoxic deep zone (52-92 m; [START_REF] Viollier | Geochemical study of a crater lake: Lake Pavin, Puy de Dôme, France. Constraints afforded by the particulate matter distribution in the element cycling within the lake[END_REF][START_REF] Michard | Geochemical study of a crater lake: Pavin Lake, France. Identification, location and quantification of the chemical reactions in the lake[END_REF]. The O 2 profile has its highest value at ca. 15 m and decreases continuously before reaching total anoxia at ca. 60 m [START_REF] Drouin | Rôle des Argiles dans la Préservation et la Fossilisation de la Matière Organique Pétroligène[END_REF][START_REF] Cosmidis | Biomineralization of iron-phosphates in the water column of Lake Pavin (Massif Central, France)[END_REF]. Deep cold water input sustains this meromictic system [START_REF] Bonhomme | Maintaining meromixis in Lake Pavin (Auvergne, France): The key role of a sublacustrine spring[END_REF].

Soil sampling and water column in situ experiments

Sampling and in situ experiments

Soil samples (10) were taken every 310 m around the lake from 10 cm depth (Fig. 1) and dried at 50 °C for two days. The soil sampling spots were located at ca. 25m from the lake edge. Water samples were taken every 10 m down the water column in order to characterize dissolved organic carbon (DOC) variation. Natural smectite used was the SWy-2 Wyoming montmorillonite (Na MMt) supplied by the Source Clay Minerals Repository of the Clay Minerals Society. The kaolinite (Kaol) was from the same provider. The Na MMt and Kaol samples were first treated with H 2 O 2 and HCl to remove residual OM and carbonate.

Cylindrical clay containers (36) made for previous experiments [START_REF] Drouin | Rôle des Argiles dans la Préservation et la Fossilisation de la Matière Organique Pétroligène[END_REF] were used as in situ traps. Both sides of the containers were edged with porous membranes (0.45 µm). Each sterile trap contained one clay type (150 mg) and Milli-Q water (30 ml) was added before immersion.

Immersion depths (15, 55 and 80 m) were chosen according to the dissolved O 2 profiles and corresponded respectively to oxic, redox front and anoxic zones. The clay traps and blanks were immersed for 6, 12, 24 and 48 h. Afterwards, the traps were removed and the clay collected after immediate centrifugation at 5000 rpm for 10 min. Separated aqueous and solid phases were kept cold (4 °C). The aqueous phase was stabilized with H 3 PO 4 .

Experiments were conducted in April 2014 following the low organic productivity winter period and repeated in July 2014 during the summer algal bloom period.

Analytical methods

Soil analysis

Soil lipids were extracted using accelerated solvent extraction (ASE 200,Dionex©) with CH 2 Cl 2 :MeOH (9:1 v/v) at 100 ° C and1000 psi. The extract was separated into neutral, acidic and polar fractions using solid phase extraction on aminopropyl bonded silica [START_REF] Logan | Biogeochemistry of the Miocene deposit, at Clarika, northern Idaho[END_REF][START_REF] Jacob | Pentacyclic triterpene methyl ethers in recent lacustrine sediments (Lagoa do Caçó, Brazil)[END_REF]. The neutral fraction was silylated by reaction with 80 µl NO-bis(trimethylsilyl)trifluoroacetamide (BSTFA) in 120 µl pyridine at 60 °C for 1 h. The acid fraction was methylated with anhydrous MeOH/MeCOCl by heating at 55 °C for 1 h. An internal standard (5α-cholestane, 100 µl) was added to each fraction for quantification. Both silylated and esterified fractions were analyzed using gas chromatography-mass spectrometry (GC-MS; Trace GC Ultra equipped with AS 3000 autosampler and coupled to a TSQ Quantum XLS mass spectrometer; Thermo-Scientific, Bremen, Germany). The GC instrument was fitted with a TG-5 MS column (60 m, 0.25 mm i.d., 0.25µm film thickness) from Thermo®. The oven temperature program was 40 °C (1 min) to 120 °C at 30 °C/min and then to 300 °C (held 46 min) at 3 °C/min. Each sample (2 µl) was injected in splitless mode at 280 °C and He was the carrier gas at 1.0 ml/min. The MS instrument was operated in electron ionization (EI) mode at 70 eV and scanned from m/z 50 to 600.

Microalgae analysis

Lipids were extracted from a mixture of diatoms and cyanophycea sampled from the superficial photic zone of the water column (2m). The samples were harvested along a stable cable previously immersed. Organic solvent soluble compounds were extracted from dried algae (492 mg) following a modified Bligh and Dyer (1959) method where CHCl 3 had been substituted with CH 2 Cl 2 and base hydrolysis was performed on the resistant residue. The extract was separated into neutral, acid and polar fractions as described in the previous section. Neutral and acid fraction were analyzed using the same GC-MS device and temperature program as used for soil extract analysis.

Water column DOC analysis

DOC concentration was determined using a Shimadzu© TOC 5000A total organic carbon analyzer, which is a high temperature catalytic oxidation type of device with infrared detection and equipped with an ASI 5000A 20 auto sampler.

Immersed clay characterization

Molecular analysis of sorbed compounds

Sorbed lipids were analyzed using a CDS Pyroprobe 5150. An aliquot of sample (15 mg) was placed in a quartz tube (1.5 mm x 2 cm). Tetramethylammonium hydroxide (TMAH; 2 in MeOH; 30 µl) and 10 µl of the internal standard (5α-cholestane, 96 mg/l) were added and the mixture kept at room temperature for 12 h. Pyrolysis (Py) was carried out at 650 °C for 30 s, with a heating rate of 20 °C/ms. The transfer line was maintained at 300 °C. For Py-GC-MS, a GC-TRACE ® (THERMOQUEST ® ) chromatograph coupled to a POLARIS Q (FINNIGAN ® ) mass spectrometer was used. A RESTEK RTX-5Sil MS column (30 m, 0.25mm i.d, 0.25µm film thickness and 5m guard column) was used with He as carrier gas (1ml/min). Electron ionization at 70 eV was used with a scan range of m/z 50-600.

Compounds amounts were quantified using the following relation: Q

(x) = [(A (x) /A (Std) ) x m (std) ]/m (samp) With Q (x) :

XRD analysis of OM-clay aggregates

The d 001 spacing of the immersed clays was determined from the first 001 reflection from the X-ray diffraction patterns, which were recorded with a conventional θ-θ Bragg-Brentano configuration. A Thermo Electron ARL'XTRA diffractometer equipped with a Cu anode (Cu K α1,2 = 1.5418 Å) coupled to a Si(Li) solid detector was used. The X-ray diffractograms from dry samples (100 °C, 24 h) were performed between 1 and 26° (2θ) with an angular step and time step of 0.04° and 10 s respectively.

Results

Organic source characterization

The sampled wmicroalgae were principally diatoms and cyanobacteria. The neutral fraction of each lipid extract was composed of sterols, isoprenoids and n-alkanes (cf. Supplementary data), among which cholesterol, phytone and octacosane were the most abundant. The acid fraction was composed principally of saturated fatty acids (FAs; Fig. 2B), characterized by the classic predominance of hexadecanoic and octadecanoic acids. The neutral fraction of the soil extracts showed the presence of triterpenoids, sterols, aliphatic alcohols and n-alkanes of various chain lengths (cf. supplementary data). The relative abundance varied according to the vegetation around the lake, which is dominated by Betula pubescens and Pinaceae. Docosanoic acid (C 22 ) was the most abundant FA in soil extracts (Fig. 2A and2A'), providing a different signature from the distribution of microalgal lipids.

DOC evolution

DOC analysis of water samples allowed determination of OC evolution every 10 m (Fig. 3). The DOC profile had a slight increase at ca. 20 m, where photosynthetic activity was usually intensive. At this depth, different molecular and particulate biodegradation products such as metabolic exudates and senescent organisms led to an increase in DOC concentration.

Deeper, at ca. 80 m, the high DOC concentration was induced by the diffusion of stored carbon from the underlying sediment. Indeed, at the sediment interface anoxia weakens biodegradation rate, thereby favouring OM accumulation [START_REF] Albéric | Carbon cycling and organic radiocarbon reservoir effect in a meromictic crater lake (Lac Pavin, Puy-de-Dôme, France[END_REF][START_REF] Drouin | Rôle des Argiles dans la Préservation et la Fossilisation de la Matière Organique Pétroligène[END_REF], the ascending diffusive flux of which increases DOC.

The concentration of DOC in the photic zone traps was higher than the external natural lacustrine water values (Fig. 3A), suggesting labile OM enrichment within these traps.

However, this over-concentration was not noticed for the chambers immersed in the deep zone (transition and anoxic depths). As said above, anoxia prevailing beyond 52 m lowers OM degradation rate within the sediment, involving high organic accumulation. Indeed, [START_REF] Schettler | A 700-year record of climate change based on geochemical and palynological data from varved sediments (Lac Pavin, France)[END_REF] and [START_REF] Chassiot | Forçages Naturels et Anthropiques sur la Sédimentation Holocène des Lacs d'Auvergne et des Réservoirs des Bassins Versants de la Loire et d[END_REF] reported an organic concentration ranging between 3 and 6% of OC in the sediment, which enriches deep water via DOC ascending fluxes [START_REF] Albéric | Carbon cycling and organic radiocarbon reservoir effect in a meromictic crater lake (Lac Pavin, Puy-de-Dôme, France[END_REF]. These sedimentary storage effects on the water column can be observed on Fig. 3A, where DOC concentration significantly heightened from 52 m to the bottom. At 52 m and deeper, excess of DOC in the lake did not allow interpretation of the role of clay on organic flux within the chambers. In fac,t clay-attracted DOC concentrations cannot exceed the background values in this zone.

The excess noticed in the photic zone is similar to the trend in lacustrine experiments [START_REF] Drouin | Rôle des Argiles dans la Préservation et la Fossilisation de la Matière Organique Pétroligène[END_REF] and in a marine context [START_REF] Mahamat-Ahmat | Organic matter-clay interaction along a seawater column of the Eastern Pacific upwelling system (Antofagasta bay, Chile): implications for source rock organic matter preservation[END_REF], confirming the capacity of natural clays to over concentrate OC from the nearest aqueous environment. The attraction varied with immersion time, physicochemical immersion zone and clay mineralogy.

As an example, in the photic zone, OC was over-concentrated for 12 h and 48 h of immersion in Na MMt traps, describing an anti-correlation trend compared with the evolution of sorbed amount (Fig. 3B). Water DOC concentration appeared to closely depend on sorption.

Organo-clay complex analysis

Na MMt sorbed lipids

Results stressed the sorption of three main lipid groups during clay lacustrine immersion: benzene alkyls, n-alkanes and FAs, in addition to a pool of nitrogenous and nonidentifiable compounds (Fig. 4). The benzene compounds were probably produced in the water column by microbial precursors that we did not investigate here. FAs were predominantly sorbed during clay lacustrine immersion, excepting for two times (6 h and 12 h, before the algal bloom) where n-alkanes and benzene alkyls were mainly sorbed Labile lipids were sorbed mainly in the transition zone (55 m), where dissolved Fe concentratio started to increase [START_REF] Michard | Geochemical study of a crater lake: Pavin Lake, France. Identification, location and quantification of the chemical reactions in the lake[END_REF]. The anoxic zone was less propitious for aggregation (Fig. 5). Our approach showed that the sorbed amount was substantially higher before the algal bloom period. For this period, we also observed, surprisingly, that the shortest interaction time (6 h) showed the best sorption rate, while no notable hierarchy was observed for the following immersion times: 12, 24 and 48 h. FAs were the most sorbed lipid group (Fig. 6), with a high abundance of hexadecanoic acid (C 16 ) and octadecanoic acid (C 18 ; Fig. 6B). Dodecanoic acid (C 22 ), although highly concentrated in the soil extracts, was not represented, foreshadowing an authigenic source for sorbed FAs. Organo-clay interaction was globally less efficient during the algal bloom season, probably as a result of the clay minerals lack of reactivity with the new input of fresh organic molecules to the lacustrine column.

Sorption on Kaol

Benzene alkyls, n-alkanes and FAs were also the main lipid groups sorbed onto kaolinite samples during immersion (Fig. 4).

The transition zone (55 m) was likewise the most efficient for Kaol interaction, with greater sorbed amount before the algal bloom period (Fig. 5). Sorbed lipid amount was clearly less on Kaol than Na MMt, highlighting the relative efficiency of smectites during organoclay aggregation vs. a 1:1 clay. Besides, from a qualitative point of view, FAs were the most reactive group (Fig. 4), with the same high abundance of hexadecanoic acid and octadecanoic acid. Considering immersion time, the results did not point to any significant favorable interaction time. As observed above for Na MMt, the interaction was less efficient during the post bloom experiments, probably involving the lack of reactivity of freshly inputted compounds.

Electronic microprobe mapping of metallic elements

The Pavin water column contains several types of dissolved mineral elements inherited from its magmatic origin and volcanic basement [START_REF] Michard | Geochemical study of a crater lake: Pavin Lake, France. Identification, location and quantification of the chemical reactions in the lake[END_REF][START_REF] Takayangi | Vertical distribution of Sb(III) and Sb(V) in Pavin lake, France[END_REF][START_REF] Viollier | Geochemical study of a crater lake: Lake Pavin, Puy de Dôme, France. Constraints afforded by the particulate matter distribution in the element cycling within the lake[END_REF]. Among the metallic ones, e.g Fe and Mg were admitted to inducing a catalytic effect during organic compound sorption [START_REF] Cervini-Silva | Adsorption kinetics of pentachloroethane by iron-bearing smectites[END_REF]Saidy et al., 2013). Electronic microprobe mapping of these elements was performed on clay samples immersed in the transition zone, where Fe and Mg concentrations start to considerably increase [START_REF] Michard | Geochemical study of a crater lake: Pavin Lake, France. Identification, location and quantification of the chemical reactions in the lake[END_REF][START_REF] Drouin | Rôle des Argiles dans la Préservation et la Fossilisation de la Matière Organique Pétroligène[END_REF]. Identical analyses were conducted on a non-immersed Na MMt sample, considered a reference (Fig. 7). The results suggest a significant enrichment of Al, Fe and Mg, which were also included in the initial clay composition [(Na, Ca) 0.3 (Al, Fe, Mg) 2 Si 4 O 10 (OH) 2 nH 2 O]. Ionic exchange probably occurred during electrical charge compensation mechanisms during the immersion, highlighting the high reactivity of Na MMt in this environment.

Swelling of clay minerals

X ray diffraction (XRD) analysis was performed on the resultant in-situ organo-clay complexes in order to characterize the interlayer distance fluctuation during time in the water column. Since kaolinite is non-swelling, analysis focused only on the Na MMt samples. The XRD patterns from Na MMt before immersion showed a 00l reflection 8.88 ° (Fig. 8A), corresponding to 10.01 Å for the d 001 interlayer spacing. Computer simulation and previous X-ray diffraction experiments showed that swelling of Na-MMt below the osmotic pressure corresponds to four stable states at basal spacing of 9.7, 12.0, 15.5 and 18.3 Å, due to the hydration of on 1, 2, 3 and 4 layers of water around the exchangeable Na + ions, respectively [START_REF] Cadars | New insights into the molecular structures, compositions, and cation distributions in synthetic and natural montmorillonite clays[END_REF][START_REF] Balme | Structure, orientation and stability of lysozyme confined in layered materials[END_REF]. The value of 10.0 Å for the non-immersed Na-MMt confirms the dehydration of the samples before XRD. For the immersed clay samples, the XRD patterns exhibited several 00l reflections at lower angular values than the non-immersed Na-MMt. It is interesting to note a second order of the 00l reflections for the sample with the longest immersion time, which underlines the existence of a good ordering in the silicate layers. This demonstrates intercalation and the formation of ordered structures within the interlayer space of the silicate layers. The expansion of the d 001 interlayer spacing was observed for all the immersed samples (Fig. 8B) and reached an average value of 14.28 and 15.26 Å for the samples immersed for 6 h and 48 h, respectively.

Discussion

DOC was concentrated in the clay traps, with values often higher than the water column background concentration (Fig. 3A). This organic influx underlined the ability Na MMt and Kaol to attract dissolved environmental organic compounds, probably via electrostatic attraction. Indeed, the clay layers are negatively charged, resulting mainly from Al/Mg or Fe 3+ /Mg substitutions in the octahedral sheet, which offer possible electrostatic interaction with oppositely charged organic compounds, e.g. amino acids. Besides, incorporated metallic elements (Fig. 7) allow cation bridge interactions. In this case, electrostatic attraction can occur between positive ionic sites and negatively charged organic compounds, i.e. FAs. In fact, due to the basic conditions (pH ca.8) in the upper layers of the water column (Alberic et al., 2013), FAs were in the COO -state.

DOC fluctuation in photic zone traps water was intrinsically associated with a sorption/desorption dynamic, as the clay-sorbed amount evolved in an anti-correlated trend with water DOC concentration (Fig. 3B). The trend highlighted the instability of a portion of sorbed compounds with no polar functionality, such as n-alkanes. They cannot develop strong bonding and were probably associated with the clay surface via low energy links such as Van der Waals bonding and H bonding.

Py-GC-MS performed on the immersed clays showed that sorbed amount was particularly high in the transition zone (Fig. 5), suggesting that this zone was the most propitious for organo-clay interaction. This depth (55 m) was also the place where the redox front had been located [START_REF] Cosmidis | Biomineralization of iron-phosphates in the water column of Lake Pavin (Massif Central, France)[END_REF]. Dissolved metallic element concentration (Fe, Al, Mg, Mn) started to rise considerably in this zone, adopting the reduced forms [START_REF] Michard | Geochemical study of a crater lake: Pavin Lake, France. Identification, location and quantification of the chemical reactions in the lake[END_REF][START_REF] Viollier | Geochemical study of a crater lake: Lake Pavin, Puy de Dôme, France. Constraints afforded by the particulate matter distribution in the element cycling within the lake[END_REF] favored by rising anoxia [START_REF] Drouin | Rôle des Argiles dans la Préservation et la Fossilisation de la Matière Organique Pétroligène[END_REF]. These elements had probably been incorporated into clay crystallographic networks via ionic exchange, leading to the enrichment in microprobe mapping (Fig. 7). Batch experiments and field approaches demonstrated that the presence of metallic elements enhances organo-clay association [START_REF] Cervini-Silva | Adsorption kinetics of pentachloroethane by iron-bearing smectites[END_REF]Saidy et al., 2013), underlining in particular the great catalytic effect of dissolved Fe and Fe carrier phases.

So, the sorption in the transition zone samples was probably driven by the presence of precipitated and dissolved catalytic elements. Particular physicochemical conditions prevailing at the oxic-anoxic transition zone involved the formation of oxy-hydroxide flocks and organo-metallic complexes increasing water turbidity at this depth [START_REF] Cosmidis | Biomineralization of iron-phosphates in the water column of Lake Pavin (Massif Central, France)[END_REF]. These conditions probably amplified the OM sorption, which explains the large sorbed amount noticed in this zone of the water column. Supplementary factors, such as the decrease in pH and the cold temperature at this depth [START_REF] Assayag | Hydrological budget, carbon sources and biogeochemical processes in Lac Pavin (France): Constraints from δ 18 O of water and δ 13 C of dissolved inorganic carbon[END_REF][START_REF] Albéric | Carbon cycling and organic radiocarbon reservoir effect in a meromictic crater lake (Lac Pavin, Puy-de-Dôme, France[END_REF] also enhanced sorption and contributed to the high sorption rate. These parameters are indeed known to favor organic sorption on clay minerals [START_REF] Arnarson | Mechanisms of pore water organic matter adsorption to montmorillonite[END_REF][START_REF] Keil | Mineral matrices and organic matter[END_REF].

Photosynthetic organic input to the upper layers and stored carbon diffusion from the bottom enriched DOC concentration respectively in the photic (20 m) and anoxic (80 m) zones, conferring on them higher organic values vs. the transitional zone (Fig. 3). However, the sorbed amounts were greater on the clay samples immersed in the transition zone (Fig. 5). This excluded, de facto, organic availability as a controlling parameter during the sorption process and highlighted the preponderant role of the redoxcline position.

In addition, analysis of pelagic microalgae (cf. Supplementary data), littoral macrophytes [START_REF] Drouin | Rôle des Argiles dans la Préservation et la Fossilisation de la Matière Organique Pétroligène[END_REF] and soil extractable lipids showed a wide diversity of compounds potentially soluble in the water. GC-MS demonstrated that these 3 organic pools produced varied compounds such as isoprenoids, triterpenoids, sterols, stanols and aliphatic alcohols, which were not involved in organo-clay interaction. Py GC-MS conducted on the aggregated organo-clay complexes showed that FAs were the predominant group sorbed, followed by nalkanes. This highlighted selective behavior of the clay minerals. Indeed, they clearly exhibited a greater affinity for these linear molecules vs. isoprenoids and polycyclic compounds also available in the water column. Note that aliphatic alcohols, ubiquitous in the OM sources (cf. Supplementary data), were not sorbed onto the immersed Kaol and Na MMt. This means that linearity was not the only factor required during sorption and underlines the key role of carboxylic functions.

Among the sorbed FAs (Fig. 6), hexadecanoic and octadecanoic acids were the most common. These two dominant acids are ubiquitous and non-specific. However, the FA distribution was closer to that in the autochthonous phytoplankton from the water column (Fig 2B) than to the surrounding soil watershed. In addition, the clay sorbed FA distribution lacked docosanoic acid, the most represented acid in the soil extracts (Fig. 2A and2A'). This confirms the algal influence on the sorbed OM. Nevertheless, a slight difference was observed between algal FA distribution and sorbed FA distribution. Contrary to the planktonic distribution (Fig. 2B), octadecanoic acid concentration was higher than that of hexadecanoic acid in the organo-clay complexes (Fig. 6). Thus, the clay sample probably had a second order of selectivity, favoring a specific carbon length among the FAs. In vitro experiments are necessary to demonstrate this hypothesis.

Overall, Na MMt exhibited higher sorption rate than Kaol (Fig. 6), confirming the hierarchy observed in a marine context [START_REF] Mahamat-Ahmat | Organic matter-clay interaction along a seawater column of the Eastern Pacific upwelling system (Antofagasta bay, Chile): implications for source rock organic matter preservation[END_REF] and in batch experiments [START_REF] Feng | Chemical and mineralogical controls on humic acid sorption to clay mineral surfaces[END_REF], whereby 2:1 clays were more efficient than 1:1 clays.

Physical characteristics, such as specific area and CEC differences could explain such heterogeneous behavior during sorption. Indeed, Na MMt, with a large surface specific area (Table 1), enhances sorption rate by way of numerous accessible sites [START_REF] Keil | Mineral matrices and organic matter[END_REF], and the high CEC value promotes physico-chemical interaction mechanisms such as cation bridging and/or ligand exchange [START_REF] Drouin | In vitro experiments of carboxylic acids sorption on synthetic clays in natural marine water. Implication on organic clayey rich sedimentation[END_REF]. Besides, organic sorption on Na MMt was possibly enhanced by way of possible exfoliation from, or a large opening in the interlayer space. XRD results showed a significant increase in the d 001 interlayer spacing (Fig. 8) during immersion in the lake, suggesting intercalation of dissolved compounds. Yet, this contribution was probably quantitatively low, as inorganic compounds like dissolved metals and metalloids (Al, Fe, Mg, Mn, Sb…) inherited from the magmatic genesis at the site [START_REF] Michard | Geochemical study of a crater lake: Pavin Lake, France. Identification, location and quantification of the chemical reactions in the lake[END_REF][START_REF] Viollier | Geochemical study of a crater lake: Lake Pavin, Puy de Dôme, France. Constraints afforded by the particulate matter distribution in the element cycling within the lake[END_REF]Takayanagi and Cossa, 2007) were probably also incorporated in the interlayer spaces by way of exchange mechanisms (i.e. cationic exchange).

These elements, with high electronegativity, might be more competitive than organic molecules for intercalation, suggesting that sheet edges and external surfaces were the main accessible adsorption sites involved in the adsorption of OM.

The total amount of OC sorbed on both montmorillonite and kaolinte was comparable to that sorbed in a marine water column using a similar in situ experimental approach [START_REF] Mahamat-Ahmat | Organic matter-clay interaction along a seawater column of the Eastern Pacific upwelling system (Antofagasta bay, Chile): implications for source rock organic matter preservation[END_REF]. Indeed, for the same immersion time (24 h), the richest samples had ca.700 µg/g of organic compounds in both contexts, representing 0.07% of the organo-clay complexes. These values are clearly inferior to those found at sediment interfaces. Indeed, TOC measurements of Pavin sediments highlighted a TOC value of 6% [START_REF] Schettler | A 700-year record of climate change based on geochemical and palynological data from varved sediments (Lac Pavin, France)[END_REF], while 2% was measured for recent Antofagasta Bay sediments [START_REF] Niggemann | How depositional conditions control input, composition, and degradation of organic matter in sediments from the Chilean coastal upwelling region[END_REF]. Pavin basin configuration and productivity explain the higher TOC values than for the upwelling zone sediments. Its restricted sedimentary interface leads to OM accumulation. In all types of environment, a huge difference exists between the suspended OM in the water column and the preserved OM in sediments. This suggests that intra column sorption alone cannot explain sedimentary OM preservation, implying further mechanisms assisting OM burial. Processes such as natural sulfurization occurring in the anoxic zone (Sinninghe Damsté and de [START_REF] Sinninghe Damsté | Analysis, structure and geochemical significance of organically-bound sulphur in the geosphere: state of the art and future research[END_REF][START_REF] Boussafir | Electron microscopy and pyrolysis of kerogen from the Kimmeridgian Clay Formation, UK: Source organisms, preservation processes, and origin of the microcycles[END_REF][START_REF] Boussafir | Accumulation of organic matter in the Kimmeridge Clay formation (KCF): an update fossilisation model for marine petroleum sourcerocks[END_REF], which make natural OM recalcitrant to benthos assimilation, play a preponderant role.

Other pathways, such as the selective preservation of bio-resistant OM (Largeau et al., 1986;[START_REF] Riboulleau | Origin of contrasting features and preservation pathways in kerogens from the Kashpir oil shales (Upper Jurassic, Russian Platform)[END_REF][START_REF] Mayer | The inertness of being organic[END_REF], the polycondensation phenomenon leading to recalcitrant geopolymers [START_REF] Tissot | Petroleum Formation and Occurrence, 2nd edition[END_REF], as well as iron oxide co-precipitation [START_REF] Eglinton | A rusty carbon sink[END_REF]Lalondes et al., 2012), should be considered. They confer steric protection, contributing to the global preservation of aliphatic rich material, thereby allowing its later thermal evolution.

Furthermore, this study has shown again that the sorption of dissolved OM is alone insufficient to explain the monolayer equivalent (ME) theory described by Mayer (1994a) or [START_REF] Hedges | Sedimentary organic matter preservation: an assessment and speculative synthesis[END_REF]. Our results are far from the expected 0.5 to 0.8 mg/m 2 of OM sorbed onto mineral surface area proposed via the ME. Sedimentary OM described by the ME model is certainly preserved, but also with the participation of other mechanisms. The ME coating was probably reached because the role of clay minerals was twofold: (i) Adsorption affecting both the dissolved fraction and organic aggregates formed by biodegradation and polycondensation and (ii) steric shielding. Within the sediment, steric protection prevented OM trapped in mesopores from bacterial and enzymatic degradation. The combination of these two processes may lead to a level of OC in clays as high as that evoked in the ME theory.

Conclusions

Organo-clay interaction experiments performed in a stratified lacustrine column demonstrated that FAs were the most reactive lipid group. This underlined a selective behavior, as different types of compounds (isoprenoids, sterols, stanols, triterpenoids, aliphatic alcohols, etc.) were available in the water column. Acidic pH prevailing down through the photic zone suggested that FA reactivity was promoted by the difference in electrical potential between their charged function and the clay surface. Interaction was probably enhanced by dissolved metallic elements (Fe, Al, Mg), which are reported to be catalysts for organo-clay reactions. The transition zone (55 m), where previous authors characterized a dramatic increase in metallic and metalloids concentration [START_REF] Michard | Geochemical study of a crater lake: Pavin Lake, France. Identification, location and quantification of the chemical reactions in the lake[END_REF]Viollier et al., 1997, Takayangi and[START_REF] Takayangi | Vertical distribution of Sb(III) and Sb(V) in Pavin lake, France[END_REF], was also the most propitious zone for sorption. Association down the water column between natural OM and metallic oxyhydroxides (resulting from the oxidation of reduced metallic elements falling back into the anoxic zone) was probably responsible for the increase in water turbidity in the redox-front area of the lake water column [START_REF] Cosmidis | Biomineralization of iron-phosphates in the water column of Lake Pavin (Massif Central, France)[END_REF].

In addition, organic concentration evaluated for the in situ aggregated complexes highlighted the idea that montmorillonites were the most favorable clay type, confirming a hierarchical order observed in batch experiments [START_REF] Feng | Chemical and mineralogical controls on humic acid sorption to clay mineral surfaces[END_REF] and in a marine water column context [START_REF] Mahamat-Ahmat | Organic matter-clay interaction along a seawater column of the Eastern Pacific upwelling system (Antofagasta bay, Chile): implications for source rock organic matter preservation[END_REF]. Although montmorillonite showed an increase in its interlayer space, no OM was intercalated but was preferentially adsorbed onto both the external surface and edges of the phyllosilicate sheets.

However, the amount of sorbed compounds was relatively low compared with the amount of settled OM. Previous studies reported values of OC oscillating between 3 and 6% within recent sediments [START_REF] Schettler | A 700-year record of climate change based on geochemical and palynological data from varved sediments (Lac Pavin, France)[END_REF][START_REF] Chassiot | Forçages Naturels et Anthropiques sur la Sédimentation Holocène des Lacs d'Auvergne et des Réservoirs des Bassins Versants de la Loire et d[END_REF]. To explain the preservation the amount of OM settled in such environments, further concepts relating to preservation, such as inherited resistance, polycondensation and natural sulfurization and the flux of particulate OM have to be considered. We suggest that the concentration of settled OM arises from the combination of these different preservation mechanisms, in addition to the water column protective sorption.

  Concentration of a given molecule (x) expressed in µg/g of sample. A (X) : Peak area of the molecule (x) on the chromatogram (dimensionless). A (Std): Peak area of the internal standard on the chromatogram (dimensionless). m (std) : Internal standard mass (µg) m (samp): Pyrolysed sample mass (g)

Fig. 1 .

 1 Figure captions

Fig. 2 .

 2 Fig. 2. Saturated FA distribution in soil (A, A') and microalgae extracts (B).

Fig. 3 .

 3 Fig. 3. DOC in clay traps (side bars) compared with water column DOC profile (continuous line). Fig. B presents sorbed OM amount and DOC concentration in the same trap according to immersion time.

Fig. 4 .

 4 Fig. 4. Main lipid groups sorbed on montmorillonite and kaolinite samples immersed in the photic (PH), transition (TR) and anoxic (AN) zones of the lacustrine column during 6, 12, 24 and 48 h. Graphs on the left present the results obtained before the algal bloom and those on the right represent sorbed amounts during the algal bloom.

Fig. 5 .

 5 Fig. 5. Clay sorbed lipids (vertical bars) vs. immersion zone (PH, photic zone; TR, transition zone; AN, anoxic zone). Dashed lines represent Fe (II) concentration along the water column (data from[START_REF] Michard | Geochemical study of a crater lake: Pavin Lake, France. Identification, location and quantification of the chemical reactions in the lake[END_REF]. The sorption results are shown for before and after algal bloom experiments.

Fig. 6 .

 6 Fig. 6. Sorbed FA distribution on Na MMt and Kaol. Results obtained from before-bloom experiments. A similar distribution was observed for the post-bloom experiments

Fig. 8 .

 8 Fig. 8. XRD diffractograms of Na MMt immersed samples (PH, photic zone; TR, transition zone; AN, anoxic zone) and non-immersed blank samples (NI). Fig. B shows interlayer basal distance (d 001 ) for immersed samples and referential one.

Table captions Table 1 .

 captions1 Experimental clay mineral physico-chemical characteristics (CEC, cationic exchange

		of clay)		Before algal bloom		During algal bloom
	Na MMt Montmorillonite	85	Oxic zone	736.8	Oxic zone Kaolinite	Montmorillonite	Kaolinite
	Kaol	5		15
			Anoxic		Anoxic
			zone		zone
	capacity).
		CEC (meq/100 g	Specific area (m 2 /g)

Acknowledgements

The study was supported by the CESSUR project funded by the French INSU/CNRS (AO2011-b5017). A.M.A benefitted from a Ph.D. grant provided by the Région Centre Valde-Loire, France. We thank Ms Rowley-Jolivet for her linguistic contribution. We are also