Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are bacterial lipids that have been largely used as environmental proxies in continental paleorecords. Another group of related lipids, branched glycerol monoalkyl glycerol tetraethers (brGMGTs), has recently been proposed as a potential paleotemperature proxy. Nevertheless, the sources and environmental dependencies of both brGDGTs and brGMGTs along the river-sea continuum are still poorly understood, complicating their application as paleoenvironmental proxies in aquatic settings. In this study, the sources of brGDGTs and brGMGTs and the potential factors controlling their distributions are explored across the Seine River basin (NW France), which encompasses the freshwater to seawater continuum. To this aim, brGDGTs and brGMGTs were analyzed in soils, Suspended Particulate Matter (SPM) and sediments (n=237) collected all along this basin, from land to sea. Both types of compounds are shown to be produced in situ, in freshwater as well as saltwater. Redundancy analysis further shows that both salinity and nitrogen loadings dominantly control the brGDGT distributions. Furthermore, the relative abundance of 6-methyl vs. 5-methyl brGDGTs (IR6Me ratio), Total Nitrogen (TN), δ15N and chlorophyll a concentration co-vary in a specific zone with low salinity, suggesting that 6-methyl brGDGTs are preferentially produced under low-salinity and high-productivity conditions. In contrast with brGDGTs, brGMGT distribution appears to be primarily regulated by salinity, with a distinct influence on the individual homologues. Salinity is positively correlated with homologues H1020a and H1020b, and negatively correlated with compounds H1020c and H1034b. This suggests that bacteria thriving in freshwater preferentially produce compounds H1020c and H1034b, whereas bacteria primarily growing in saltwater appear to be predominantly responsible for the production of homologues H1020a and H1020b. Based on the abundance ratio of the freshwater-derived compounds (H1020c and H1034b) vs. saltwater-derived homologues (H1020a and H1020b), a novel proxy, Riverine IndeX (RIX) is proposed to trace riverine organic matter inputs, with high values (>0.5) indicating higher riverine contribution. RIX was then applied to the Godavari River basin (India) and a paleorecord across the upper Paleocene and lower Eocene, showing its potential applicability in both modern samples and in paleorecords.

wBranched glycerol dialkyl glycerol tetraethers (brGDGTs) are a family of bacterial lipids which have emerged over time as robust temperature and pH paleoproxies in continental settings. Nevertheless, it was previously shown that other parameters than temperature and pH, such as soil moisture, thermal regime or vegetation can also influence the relative distribution of brGDGTs in soils and peats. This can explain a large part of the residual scatter in the global brGDGT calibrations with mean annual air temperature (MAAT) and pH in these settings. Despite improvements in brGDGT analytical methods and development of refined models, the root-mean-square error (RMSE) associated with global calibrations between brGDGT distribution and MAAT in soils and peats remains high (similar to 5 degrees C). The aim of the present study was to develop a new global terrestrial brGDGT temperature calibration from a worldwide extended dataset (i.e. 775 soil and peat samples, i.e. 112 samples added to the previously available global calibration) using a machine learning algorithm. Statistical analyses highlighted five clusters with different effects of potential confounding factors in addition to MAAT on the relative abundances of brGDGTs. The results also revealed the limitations of using a single index and a simple linear regression model to capture the response of brGDGTs to temperature changes. A new improved calibration based on a random forest algorithm was thus proposed, the so-called random Forest Regression for PaleOMAAT using brGDGTs (FROG). This multi-factorial and non-parametric model allows to overcome the use of a single index, and to be more representative of the environmental complexity by taking into account the non-linear relationships between MAAT and the relative abundances of the individual brGDGTs. The FROG model represents a refined brGDGT temperature calibration (R-2 = 0.8; RMSE = 4.01 degrees C) for soils and peats, more robust and accurate than previous global soil calibrations while being proposed on an extended dataset. This novel improved calibration was further applied and validated on two paleo archives covering the last 110 kyr and the Pliocene, respectively. (C) 2021 Elsevier Ltd. All rights reserved.

Gram-negative bacteria produce specific membrane lipids, i.e. 3-hydroxy fatty acids with 10 to 18 C atoms. They have been recently proposed as temperature and pH proxies in terrestrial settings. Nevertheless, the existing correlations between pH or temperature and indices derived from 3-OH FA distribution are based on a small soil dataset (ca. 70 samples) and only applicable regionally. The aim of this study was to investigate the applicability of 3-OH FAs as mean annual air temperature (MAAT) and pH proxies at the global level. This was achieved using an extended soil dataset of 168 topsoils distributed worldwide, covering a wide range of temperatures (5 to 30 ∘C) and pH (3 to 8). The response of 3-OH FAs to temperature and pH was compared to that of established branched glycerol dialkyl glycerol tetraether (GDGT)-based proxies (MBT'5Me/CBT). Strong linear relationships between 3-OH-FA-derived indices (RAN15, RAN17 and RIAN) and MAAT or pH could only be obtained locally for some of the individual transects. This suggests that these indices cannot be used as palaeoproxies at the global scale using simple linear regression models, in contrast with the MBT'5Me and CBT. However, strong global correlations between 3-OH FA relative abundances and MAAT or pH were shown by using other algorithms (multiple linear regression, k-NN and random forest models). The applicability of the three aforementioned models for palaeotemperature reconstruction was tested and compared with the MAAT record from a Chinese speleothem. The calibration based on the random forest model appeared to be the most robust. It generally showed similar trends with previously available records and highlighted known climatic events poorly visible when using local 3-OH FA calibrations. Altogether, these results demonstrate the potential of 3-OH FAs as palaeoproxies in terrestrial settings.

Summary 3-hydroxy fatty acids (3-OH FA), produced by Gram-negative bacteria, were recently proposed as promising temperature and pH proxies in terrestrial settings. Nevertheless, the existing correlations between pH/temperature and indices derived from 3-OH FA distribution are based on a small soil dataset (ca. 70 samples) only applicable regionally. The aim of this study was to investigate the applicability of 3-OH FAs as mean annual air temperature (MAAT) and pH proxies at the global level using an extended dataset of 168 surficial soils from 8 globally distributed elevational transects. Strong linear relationships between 3-OH FA-derived indices and MAAT/pH could only be obtained locally, for some of the individual transects. In addition to linear regressions, non-parametric, machine learning models were used to improve the global relationships between 3-OH FA distribution and MAAT/pH. Strong global correlations between MAAT/pH and 3-OH FA relative abundances were obtained by using multiple linear regression, k-NN and random forest models. The applicability of the k-NN and random forest models for paleotemperature reconstruction was tested with the MAAT record from a Chinese speleothem. The calibration based on the random forest model appeared to be the most robust. These results demonstrate the potential of 3-OH FAs as paleoproxies in terrestrial settings.

To test the extent to which sediments accumulated in sewers may serve as high-resolution archives of urban evolution, this study examined a sedimentary succession deposited in a decantation tank of the combined sewer network of Orléans (France). The focus was on a 1.43 m sediment core drilled after 10 months of operation since the last cleaning. Sediments were stratigraphically organised into three distinct facies. The lower unit comprised organic remains, the middle unit gravels and sands and the upper unit was fine sands. The evolution of radionuclide activities, bile acid concentrations, and glass microspheres enabled sediments from wastewater and stormwater inputs to be distinguished. Precipitation events that affected the area were the main control on sediment deposition with organic-rich sediments accumulating from wastewater during dry weather and coarser, mineral sediments accumulating from stormwater during precipitation events. These results enable development of a chronological framework for sediment deposition. These findings reveal the potential of sewer sediment accumulations to record relevant information on the evolution of urban socio-ecosystems on monthly to annual scales with a relatively high time resolution.

Peruvian Andes and Chilean Andes.Data from

Estuaries are key ecosystems from economical and ecological points of view. This is especially true for the Seine Estuary, its watershed representing 12% of the France area (78 600 km2) in which 30% of the French population, 40% of the industry and 25% of the agriculture are concentrated. Estuaries transfer material from the continent to the oceans, including organic matter (OM), for which they are highly reactive zones. Elucidating the estuarine OM dynamics remains challenging, due to (i) the high variability of environmental parameters, such as salinity, light penetration and tidal range, (ii) the intrinsic heterogeneity and molecular diversity of OM and (iii) the permanently changing nature of this material. Estuarine OM can originate from various sources (transported from rivers or coastal ocean or be produced within the estuary itself) with a different composition, and thus a different behaviour in the ecosystem. The aim of this work was to better constrain the sources of OM in the Seine Estuary. In order to take into account the spatiotemporal variability of OM characteristics, water and sediment samples (10 cm-long cores) were collected all along the estuary, i.e. in the upstream, maximum turbidity and downstream zones, during 5 campaigns with different tidal intensities and river flows. Elemental (C, N) and isotopic composition (δ13C and δ15N) as well as lipid biomarkers were analyzed in both particulate (POM) and sediment OM. This allows comparing the bulk and molecular composition as well as sources of OM in the particulate and sediment pools. Several lipid biomarkers (n-alkanes, fatty acids, n-alcohols, sterols/stanols, GDGTs) were investigated in this study, as they provide complementary information of the sources and degradation degree of OM. Lipids from terrigenous sources were predominant in all samples, even though the concentrations of these compounds as well as those of anthropogenic origin were shown to decrease towards the mouth of the Seine Estuary. In addition, significant differences in bulk and molecular composition were observed between the particulate and sediment pool, especially with a higher abundance of aquatic (i.e. algal/bacterial) vs. terrigenous lipids in POM than sediment OM. Last, bulk and molecular analyses both showed the strong seasonal and spatial variability (along the estuary and with depth) of OM composition in the water column and sediment, which has to be taken into account when investigating estuarine OM dynamics.

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Estuaries are important ecosystems from environmental and economical point of views and are the place of numerous transformations of organic matter (OM) during the transfer from land to the ocean. The dynamics of OM in estuarine systems is complex and was only rarely investigated at the structural or molecular level, even though OM transformation in the estuarine aquatic and sediment compartments involves processes taking place at this level. The aim of this study was to constrain the sources and fate of the OM in the Seine Estuary, one of the largest estuaries in France. The spatiotemporal dynamics of the OM along the estuary was investigated by comparing the bulk (elemental and isotopic composition) and structural (solid state 13C nuclear magnetic resonance) features of the different pools of OM – dissolved OM (DOM), particulate OM (POM) and sediment OM collected during five sampling campaigns. Reverse osmosis coupled with electrodialysis (RO/ED) was used to concentrate and isolate DOM, yielding an average organic carbon recovery of 59% (± 15%). RO/ED had a limited effect on DOM properties, DOM showing >75% of similarity with initial estuarine samples based on 3D fluorescence measurements. Bulk and structural analyses of DOM, POM and sedimentary OM showed that OM is mainly of aquatic origin in the Seine Estuary, regardless the OM pool. Nevertheless, significant differences in chemical composition between the three OM pools were observed: higher C/N ratios, carbohydrate, lipid and protein content as well as lower char and lignin contents in DOM than in the other two compartments. Spatial variations of OM properties, for POM and to a lesser extent DOM, were observed along the Seine Estuary based on δ13C and Δ14C analyses and 13C NMR-derived protein and lipid contents, showing the transition from a riverine to a marine-dominated system. In the mixing zone of the estuary, the Δ14C composition of the sediment OM was related to the tidal strength, with strong tides leading to the resuspension of recent sediment OM and weak tides allowing the deposition of recent aquatic OM. Altogether, the combination of bulk and structural techniques showed that the Seine Estuary OM quality is mainly related to the compartment (DOM/POM/sediment) and to a lesser extent to the sampling zone (upstream/maximum turbidity zone/downstream). The approach proposed for the characterization of the Seine Estuary OM could be applied to other estuaries, allowing a better understanding of the complex OM dynamics in such ecosystems.

Les actions de l’Homme sur son environnement (par exemple deforestation, reforestation, culture,....) affectent l’evolution des surfaces continentales en jouant un role sur le cycle mondial du carbone. La reconstruction et l’evolution des paysages passes constituent des lors un defi pour les approches paleoenvironnementales (Dearing, 2006). Les biomarqueurs moleculaires detectes dans les sols peuvent fournir des informations sur la vegetation locale passee, et donc sur l’utilisation des terres passees. En outre, si ces biomarqueurs sont transferes des sols vers les archives sedimentaires, ils peuvent etre utilises pour reconstruire l’evolution des ecosystemes a travers le temps. Parmi ceux-ci, les triterpenes pentacycliques de vegetaux superieurs representent une famille de lipides tres repandue chez les angiospermes et se situent essentiellement au niveau des cires cuticulaires et des ecorces des vegetaux superieurs. En raison de leur large diversite de structures, de fonctions et de configurations, ils peuvent constituer des marqueurs specifiques de certaines plantes, notamment s’ils sont preserves dans les archives naturelles. Par exemple, les ethers methyliques de triterpenes pentacycliques peu- vent etre lies a la presence de graminees (Jacob et al., 2005; Zocatelli et al., 2010), alors que les acetates de triterpenyle sont principalement produits par des asteracees (Lavrieux et al., 2011). Tous deux refletent le developpement de la vegetation en milieu “ ouvert ” (par exemple prairie, jachere), soit dans le cadre de l’influence du climat, soit en raison d’activites humaines. L’evolution des milieux “ fermes ”, et notamment les forets de coniferes, est quant a elle suivie par le suivi des concentrations en diterpenes, famille de lipides synthetises par les gymnospermes. Recemment, une famille de triterpenes pentacycliques insatures presentant une structure de type serratane, un groupement methoxyle et divers fonctions oxygenees supplementaires (methoxy, acetoxy, cetone ou de l’alcool) ont ete detectees dans des sols d’une foret d’epiceas (Le Milbeau et al., 2013). Les composes possedant un squelette serratane sont synthetises par de nombreuses plantes comme les pins, les epiceas, les sapins, les fougeres et les lycopodes, mais seuls ceux possedant un groupement methoxyle n’ont, jusqu’a present, ete signales que dans les pinacees. Ces composes ont egalement ete observes dans d’autres archives, telles des tourbes, des sediments lacustres (naturels et artificiels) et attestent de la contribution de pinacees a ces archives.

Les sediments naturels recents ont toujours attise la curiosite des scientifiques. Lessediments urbains, temoins privilegies de notre histoire recente, sont encore meconnus dessedimentologues. Pourtant ces sediments accumules dans les reseaux d’assainissement sont uneopportunite pour mieux comprendre la dynamique de sedimentation dans ces milieux particuliersafin d’eventuellement les exploiter pour retracer l’histoire recente de la ville mais egalement pourassurer une meilleure gestion de ces ouvrages.La chambre a sable d’Orleans est un ouvrage de decantation situe en amont des stationsd’epuration, d’environ 17 m de profondeur. Elle draine la majeure partie de la zone nord del’agglomeration orleanaise, a travers un reseau unitaire collectant a la fois les eaux pluviales etusees. Les sediments qui s’y sont accumules depuis 1942 n’ont jamais ete cures. Ils formentpotentiellement une archive a tres haute resolution temporelle. Une premiere carotte d’environ 70cm a ete prelevee dans les sediments pour comprendre les modes d’accumulations de ces matiereset verifier si ces sediments constituent effectivement des “archives sedimentaires”, ici c’est-a-dired’enregistrement diachronique du reseau d’ecoulement des eaux de la ville. Pour ces raisons, nousavons effectue des datations aux radioelements courtes periodes (7Be, 137Cs, 210Pb) sur la carotte,associes a 10 datations au radiocarbone sur des graines.Au meme titre que des sediments classiques, les sediments de la chambre a sable sontstratifies, avec d’epais depots de graviers ou de niveaux de graines, et indiquent une mise en placede type evenementielle, en accord avec la dynamique sedimentaire dans ce type de reseau. Lesanalyses en radioelements indiquent la presence de 7Be (demi-vie de 53,7 jours) uniquement dansle premier echantillon confirmant le caractere recent des depots superficiels. Alors qu’elles sontquasi-nulles dans les sediments les plus grossiers du haut de la carotte, les activites en 137Csatteignent quelques dizaines de mBq/g dans les sediments les plus fins de la base de carotte. Enfinle 210Pb en exces presente une activite fortement variable en fonction de la profondeur. Lesradioelements se fixant principalement sur les particules fines une correction a l’aide de lagranulometrie a ete tentee pour normaliser le 210Pb en exces (210Pbex), mais cette correction n’estpas satisfaisante ce qui indique que le 210Pbex initial est variable au cours du temps rendant cettemethode inutilisable a des fins chronologiques. De plus, cette normalisation fait disparaitre le picde 137Cs, artificiellement present a cause d’une augmentation en profondeur des fractions les plusfines du sediment. Il s’avere donc que le depot sedimentaire est posterieur a 1986 (rejets lies al’accident de Tchernobyl). Les datations au radiocarbone confirment ces resultats et nousindiquent des dates entre 2012 et 1995, posterieures au pic des bombes. Une seule inversion est anoter dans le bas de la carotte, resultant sans doute de remobilisations. Au total, ces resultats nouspermettent de confirmer que les sediments des reseaux d’assainissement sont deposes suivant unelogique temporelle, rendant possible des reconstructions paleoenvironnementales en contextesfortement anthropises, sur des gammes de temps et resolutions rarement atteints.

Urban socio-ecosystems can be defined according to sociological, economic, political, philosophic or historical criteria. For geologists, cities can also be considered as hydrological catchments subjected to biogeochemical cycles of elements, molecules and minerals that are produced, transported and deposited. In this case, most of the transfers are realized at the surface (for stormwater) and underground (for the stormwater and wastewater systems), and can be combined or separative. Materials deposited in sewer networks are considered as an issue for sediment management but, from a paleoenvironemental, they constitute potential archives for the Anthropocene (i.e since AD 1950; Zalasiewicz et al., 2015), allowing an integrated retro-observation of urban metabolism. Similarly, most materials that transit in sewer systems are considered as pollutants, but paleoenvironmentalists could use them as tracers for urban metabolism. Depending on the type of materials preserved in the sedimentary archives (drugs such as analgesics or antibiotics, illict drugs, alcohol residues, pesticides, hydrocarbons, specific molecular biomarkers…), the recent history of a large spectrum of thematics (health, food consumption, biodiversity, transport, energy…) could be reconstructed at the city scale, affording local authorities diagnostic tools for evaluating past public policies.In order to test whether paleoenvironmental approaches could be transposed to urban socio-ecosystems, we have analysed the sediments of short sedimentary cores drilled in a decantation tank located in Orleans (France; Figure 1). This decantation tank was built in 1942, is 17m deep and is presently saturated in sediments so that it does not properly filter sewer waters that are then directed towards wastewater treatment plants. To this respect, local authorities plan to clean out the tank and are undertaking various improvements. The tank is at the outlet of the sewer network that collects combined stormwater and wastewater over the whole hydrological catchment of Orleans and its suburb. A preliminary drilling afforded sedimentary sequences of maximum 1m length characterized by coarse grain silicoclastic deposits, sometimes sorted, interspaced with organic-rich layers (Figure 1). Some objects of evident anthropic origin could be distinguished such as a padlock, a coin dated back to 1999, and plastic and metallic residues of various origins. We also indentified in some layers grape and lemon seeds, and plant remains. XRF core scanner analyses performed on the whole cores revealed high levels of Zn, Pu and Cu all over the section, with organic layers being enriched. Ongoing work is focused on the analysis of “natural” and xenobiotic biomarkers that are studied through classical organic geochemistry analyses for natural biomarkers and through standard techniques employed in pollution studies for xenobiotics. The challenge, is off course, to transfer those techniques to a material of unprecented and extreme organic, elemental and mineral complexity. From the combined sedimentological, elemental and organic analyses, accompanied by radioelement dating, we will be able not only to discuss the nature of the materials (source, preservation…), but also the potential for these original archives to record the recent history of urban metabolism.

Nous avons etudie la distribution et l'evolution des biomarqueurs moleculaires dans les sediments du Maar de Menat (Massif Central), site paleontologique du Paleocene (51-64 Ma), repute, entre autres, pour la qualite de preservation de la flore (feuilles et fleurs). Nous avons preleve 12 echantillons (selon un pas de 4 m) provenant d'un forage de pres de 50 m realise par le BRGM en 2008. Ces echantillons ont ete analyses par pyrolyse Rock-Eval puis les biomarqueurs lipidiques ont ete extraits, separes sur mini-colonnes et identifies et quantifies par CPG-SM. Les sediments se sont reveles tres riches en matiere organique (MO), avec des COT entre 15 et 30 %. La faible maturite thermique des MOs est indiquee par un Tmax inferieur a 440°C. Les valeurs d'IH et d'IO temoigneraient a priori d'un melange de MOs provenant d'algues et de vegetaux vasculaires terrestres. Toutefois, ces valeurs sont tres semblables a celles mesures dans le Maar d'Enspel pour lequel des IH eleves ont ete attribues a une forte contribution de cires de feuilles. Les n-alcanes ne permettent pas de trancher sur la source de MO, bien que leur distribution soit dominee par des homologues a longue chaine, mais avec une CPI faible. A l'inverse, les cetones a longue chaine affichent des CPI elevees, indiquant leur bonne preservation. De nombreux triterpenes pentacycliques de vegetaux superieurs ont pu etre identifies. En particulier le sediment contient des derives diagenetiques varies tels que des des-A-arborenes et des-A-fernenes, des des-A-monoaromatiques, des des-A-triaromatiques, et des triterpenes pentacycliques mono-, tri-, tetra- et penta-aromatiques. Ce cortege confirme la forte contribution des vegetaux vasculaires au sediment. L'evolution comparee de ces biomarqueurs permet de distinguer differents facies moleculaires qui semblent temoigner de changements majeurs des conditions physico-chimiques qui regnaient dans le lac et dans son bassin versant.