The study of the geological processes associated with the formation of the ocean floor is fundamental to understand hydrothermal systems in terms of genesis, evolution, duration, cyclicity and spatial distribution as well as the colonization of these systems by living beings. In this project, we will use music to communicate about these processes to the public. The ocean floor is constructed by the interaction in time and space of three major processes: volcanism, tectonics and hydrothermalism. This last process is fundamental in the cooling and transformation, through the alteration of rocks, of the oceanic floor. Finally, sedimentation gradually covers the floor constructed by these three processes. Instabilities and landslides will affect the sedimentary cover and volcanoes and thus modify the underwater landscape. Time is fundamental when studying these processes. The ocean floor is constantly changing. Eruptions occur suddenly, last a few hours or extend over several days. A fault can rupture, producing earthquakes which may cause major landslides. All of these processes have a direct impact on the distribution and dynamics of hydrothermal circulations. An earthquake can open new fractures allowing seawater to penetrate into the crust, creating new vents. Another earthquake or volcanic eruption can seal these circulation paths, leading to the cessation of the outflow of fluids and the death of the associated ecosystem. The lifespan of a hydrothermal site is therefore strongly dependent on this dynamic. In this dynamic landscape, organisms evolve, move, colonize chimneys, multiply and eventually disappear when the fluid output stops. It is this constant mutation, on variable time scales, ranging from a few years to a few tens of thousands of years, that we wish to transcribe into music. Over the years, our team built an immense collection of images of the ocean floor and hydrothermal vents. These documents are rarely released to the general public. When exposed, they often speak little because even if the images are beautiful and impressive, the processes and time scales behind them are difficult to grasp. The idea of this project is to create a musical piece telling the stories of the formation of the ocean floor and of hydrothermal fields, on different time scales. We will tell a story of a changing landscape, of the creation of oases of life, from their beginning until the death of the colonies. We will interact with the composer through videos and images, accompanied by explanations of the processes. The exchanges allow the composer to explain his musical choices which will be his way of perceiving these complex developments. The production of this piece will be entrusted to the orchestra of the University of Brest. Here too, the interaction between researchers and the musicians is at the heart of the project. Discussions and scientific explanations of the images will accompany the musical work. The work will therefore be the result of group construction. It will be presented during the university Art & Science festival and during scientific events or maritime festivals.

Ecosystems face various pressures, often leading to loss of biodiversity. Understanding how biodiversity is spatially structured, what are the driving factors, and the ecological and evolutionary processes involved is essential to assess communities' resilience to disturbances and guide efficient conservation measures. Hydrothermal vents from national waters of the West Pacific are targeted by mining industries for their mineral resources that include metals used in high-tech equipment. Although exploitation has not yet started, such activity could significantly affect ecosystem biodiversity and functioning. Here, we describe the distribution of hydrothermal biodiversity in the Southwest Pacific back-arc basins and the Futuna Volcanic Arc at different spatial scales in relation to environmental conditions and geography. We focused on three assemblages dominated by symbiotic megafauna: snails (Alviniconcha spp. and Ifremeria nautilei) and mussels (Bathymodiolus spp.). Faunal assemblages exhibit strong spatial structuring: between habitats along the dilution gradient of the hydrothermal fluid, and between geographic basins, with a faunal split between the Western and the Eastern basins of this region, and to a lesser extent, between fields in a basin. Species replacement along the chemical gradient drives faunal changes between Ifremeria and Bathymodiolus assemblages, while a drop in the number of species is noted when making this comparison with the Alviniconcha assemblage. While these local changes may result from environmental filtering along the diffuse flow gradient, geological settings and current geographic barriers, which drive colonization and speciation at larger scales, are likely shaping the vent community changes between the Eastern and Western basins. This result has significant implications for biodiversity conservation, especially in this mineral-rich setting. The Manus Basin is isolated and displays the highest proportion of endemism while the Woodlark Basin represents an important stepping-stone between the Eastern basins and Manus Basin, making them potentially highly vulnerable to mining with a risk of biodiversity loss.

In 2018, the island of Mayotte located in the western Indian ocean, has experienced a seismo-volcanic crisis linked to the birth of an impressive intraplate submarine volcano at the east of the island. This volcano, named Fani Maoré, which has not yet been the subject of microbiological studies, triggered the largest submarine eruptive event ever recorded. Close to the volcano’s summit is a singular meter-size structure containing abundant native sulfur mineralizations. While a wide variety of ecosystems, with more or less well documented microbial communities, are found in active volcanoes on the ocean floor, knowledge on microbial communities hosted in habitats such as sulfur-rich intraplate volcanoes, that are not located on hotspots, remains limited. Genome-resolved metagenomics, culture-based functional approaches, geochemical and mineralogical analyses were combined to characterize the geological and physico-chemical constraints of the environment surrounding the yellow deposit part of this hotspot volcano and the composition and functions of its microbial community. Geological and geochemical analyses indicated that this volcanic habitat had high concentrations in various sulfur species, including native sulfur, hydrogen sulfide and sulfate. Twenty-three Metagenome Assembled Genomes (MAGs) belonging to 8 different bacterial phyla, mainly Pseudomonadota, Bacteroidota and Campylobacterota, were reconstructed from the sulfur-rich deposit and analyzed. The vast majority of MAGs encoded genes for complete sulfur cycling metabolic pathways, in particular sulfur oxidation. Estimation of the cultivable microbial fraction revealed a diversity of microorganisms, with high growth rates for sulfur reduction, sulfate reduction with dihydrogen, and sulfur oxidation. Sulfur compound (S0, SO32− and S2O32−) disproportionation was also observed in cultures. The versatile genus Sulfurimonas was prevalent in culture at 6 and 20 °C, in the presence of different sulfur redox couples. Microbial communities, including taxa commonly found in ridge hydrothermal systems, were composed of autotrophic, heterotrophic or mixotrophic taxa using a large range of electron donors and acceptors to fuel their catabolism, particularly sulfur compounds in all common oxidation states. They had the genetic potential and physiological capacity to carry out all the metabolic reactions of the microbial sulfur cycle using the abiotic sulfur compounds present in their habitat. Representatives of the Sulfurimonas genus were among the main chemoautotrophs, since they predominated in eleven different temperature-redox pair culture combinations. Based on the observations, a conceptual model was proposed to describe the interactions in this sulfur-rich deposit that may occur between the microorganisms, the physico-chemical conditions and the sulfur compounds supplied by the environment.

This chapter investigates the complexities surrounding the iron biogeochemical cycle from the Archean to present, with a focus on assessing the balance between iron sources and sinks during long periods of Earth's history with relatively invariable redox conditions, when steady state can be safely assumed. Currently, the residence time of iron in the ocean may be as short as approximately 5 years. The input flux of iron is highly sensitive to redox cycling in sediments, while its removal primarily occurs through dispersed processes of oxidation and precipitation. In the Archean, we find a significant imbalance between continental and hydrothermal inputs, which collectively contribute between 61,500 to 263,000 Gg/yr of dissolved iron to the oceans, and the most obvious sinks such as iron formations (IFs), which sequester up to 43,000 Gg/yr of iron. A possible solution to this imbalance involves the dispersed abiotic precipitation and removal of iron as silicates, sulfides, and carbonates in marine basins. Additionally, we calculate the residence time of dissolved iron in the Archean oceans to be between 6 kyr and 3 Myr, which is significantly longer than the ocean mixing timescale. Our estimates indicate that under the anoxic Archean atmosphere, the iron cycle was more protracted than today, and the isotopic compositions and concentrations of dissolved iron were likely more uniform. Distinct water bodies were likely confined to limited areas or specific, dynamic systems with intense iron turnover, such as regions where deep-sea upwelling currents brought hydrothermal iron to photic zones rich in biotic or abiotic oxidants.

Submarine volcanic eruptions impact ocean and sediment geochemistry by generating hydrothermal plumes, fluid expulsion, lava flows, and tephra deposition. The amount and impact of such inputs on the sediment composition and biogeochemistry, on short temporal scales, is yet to be quantified. To this end, the multidisciplinary GEOFLAMME cruise was conducted in May 2021 on board the R/V Pourquoi Pas? to study the Fani Maore edifice, a newly born volcano located on the eastern submarine flank of Mayotte (Comoros archipelago, Indian Ocean). The strategy was to sample sediment cores along two eastward transects from this volcano towards the open ocean. This study aims for a comprehensive overview of the diagenetic alterations occurring within sediments in response to this volcanic event. Solid phase characterization using X-ray fluorescence and diffraction, particulate organic carbon (POC) content, carbon isotopic signature (delta 13C-POC; Delta 14C-POC) and pore water analysis (dissolved inorganic carbon-DIC; Alkalinity; NO3- + NO2-; SO42-; dFe; dMn) reveals low organic matter mineralization and low volcanic material alteration throughout the area. However, close to the volcano and lava flows, DIC, alkalinity and Mg2+ in the sediment show a strong increase at depth while Ca2+ and Sr2+ show a strong depletion. We attribute these concentration gradients to the diffusion of a magmatic CO2-rich fluid with a geochemical signature reflecting strong fluid-rock interactions as evidenced by carbon isotopic signature of DIC (delta 13C-DIC; Delta 14C-DIC) and 87Sr/86Sr ratio followed by carbonate precipitation at depth in the sedimentary pile. This study demonstrated that the interaction between magmatic CO2 degassing and volcanic rocks leads to natural carbonation at depth, as evidence by vertical profiles that differ from those that can be described in more established volcanic systems. These findings enhance our understanding of the sediment biogeochemistry in a volcanic eruptive context, and offers perspective for a better use and development of new volcanic proxies in marine sediments.

The concentration of redox sensitive trace metals (RSTEs) and their isotopic composition preserved in Precambrian marine sediments, are critical for the reconstruction of ocean-atmosphere oxygenation history. Particularly, the concentration of Fe, its redox speciation, and isotopic distribution, have gained widespread use for inferring the biogeochemical processes that controlled Fe cycling in Precambrian oceans linked to the reconstruction of Earth surface redox budget. However, questions remain about the biotic and abiotic processes involved in Fe cycling in these ancient oceans, including the impact of post-depositional alterative processes on the reliability of the Fe redox proxy. Here we present a multi-proxy mineralogical and geochemical study of the 1.1 Ga Atar and El Mreiti strata of the Taoudeni Basin in Mauritania, to better constrain pathways involved in Fe cycling, linked to Fe mineralogy, redox speciation, isotopic ratios during this time and metamorphism. We compare unmetamorphosed sedimentary deposits with facies metamorphosed by dolerite sill intrusion. The results reveal the occurrence of diagenetic Fe minerals in the basal unmetamorphosed samples associated with light S56Fe signatures, reflecting dominant anoxic conditions that promoted microbial dissimilatory Fe reduction. Notably, S56Fe composition of these rocks reveal several fluctuations in evolving seawater redox state from oxic to anoxic/sulfidic conditions associated with changes in sea level stand and periods of full bottom water oxygenation and redox stratification. Overall, Ce anomalies suggest a general up sequence increase in seawater oxygen content. Metamorphosed rocks display heterogeneous S56Fe distribution, consisting of light and heavy signatures associated with secondary Fe-bearing minerals produced by metamorphic and metasomatic overprinting of carbonated rocks by hot circulating fluids. The results thus indicate metamorphic overprinting of primary seawater S56Fe promoted by increased mobility of reactive Fe during post-depositional metamorphic transformation. They show that post-depositional metamorphic/metasomatic overprinting complicates direct reconstruction of seawater biogeochemical Fe cycling and redox state using S56Fe systematics. (c) 2024 International Association for Gondwana Research. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

Deep-sea hydrothermal vent systems are under investigation for base and precious metal exploitations. The impact of mining will depend critically on the ability of larval dispersal to connect and replenish endemic populations. However, assessing connectivity is extremely challenging, especially in the deep sea. Here, we investigate the potential of elemental fingerprinting of mollusk larval shells to discriminate larval origins between multiple hydrothermal sites in the southwest Pacific Ocean. The gastropod Shinkailepas tollmanni represents a suitable candidate as it uses capsules to hold larvae before dispersal, which facilitates sampling and ensures mineralization occurs on the site of origin. Multielemental microchemistry was performed using cutting-edge femtosecond laser ablation inductively coupled plasma mass spectrometry analysis to obtain individual measurements on 600 encapsulated larval shells. We used classification methods to discriminate the origin of individuals from 14 hydrothermal sites spanning over 3500 km, with an overall success rate of 70 %. When considering fewer sites within more restricted areas, reflecting dispersal distances reported by genetic and modeling approaches, the success rate increased up to 86 %. We conclude that individual larval shells register site-specific elemental signatures that can be used to assess their origin. These results open new perspectives to get direct estimates on population connectivity from the geochemistry of pre-dispersal shells of recently settled juveniles.

Mineralogy, geochemistry and sulfur (S) isotope composition of native sulfur (S-0) precipitated at intraoceanic and intracontinental back-arc rift, submarine and subaerial volcanic arc, sediment and sediment-free mid-ocean ridge, hot spot, accretionary wedge, and submarine and continental cave settings were investigated with a main goal to understand the mode of formation of all the types of native S at the modern seafloor. Native S occurs as various depositional forms: chimneys, colloform flows, liquid ponds, slabs; fills in cavities and pore space of the sediment, vesicles and cracks in volcanic rocks; cements and coats the sediment; stains the conduits or fills in pores of the sulfide chimneys; forms fine-grained layers within the sediment; coats the walls, stalactites and stalagmites in the caves. Mineralogically, the native S from the seafloor is pure rhombic S-0 with negligible impurities of metal sulfides, aluminosilicates, and carbonates inferred from the chemistry data. Mineral interrelations and S isotope data suggest that native S from different geologic settings has different origin. In the sulfide chimneys and mounds at the mid-ocean ridges, native S appears to be a result of oxidative alteration of primary pyrrhotite. The native S from back-arc rifts, volcanic arcs and hot spots can be a result of either disproportionation of magmatic SO2 (delta S-34 < 0 parts per thousand), or synproportionation of magmatic SO2 and H2S (delta S-34 > 0 parts per thousand). The native S from the sediments in anoxic brine-filled deeps (accretionary wedge setting) is a result of bacterial sulfate reduction and consequent sulfide (delta S-34 < 0 parts per thousand) oxidation. The native S coating the cave walls and forms also has a bacterial origin (delta S-34 < 0 parts per thousand).

About 80% of Earth volcanic activity occurs underwater, releasing deep carbon to submarine environments and impacting Earth’s climate over geological timescales. The CO2 emitted during submarine eruptions and/or hydrothermal degassing creates local ocean acidification, affecting the seawater carbonate equilibrium and oceanic ecosystems at large regional scales. Here, we report for the first time the existence of a major CO2 hydrates field at the seafloor offshore Mayotte Island (Indian Ocean) associated with liquid CO2 venting, following the submarine eruption that occurred in 2018. Using detailed acoustic surveys and in situ Raman spectroscopy, we reveal multiple hydrate mounds and seep zones distributed over an area of 0.06 km². We show that the gas seeps are mainly composed of CO2, with minor contributions of CH4 and H2, with noble gas ratios and stable and radio-carbon isotopes clearly demonstrating their magmatic origin. Estimates of the CO2 emitted over the entire area represent about 0.5% of the global magmatic carbon flux. Our discovery also suggests that CO2 hydrates may potentially be stable at the seafloor at the right pressure-temperature conditions, bringing new prospects into CO2 sequestration and decarbonization pathways in the ocean, in particular regarding kinetics of hydrates dissolution and environmental impacts.

Abstract Copper isotopes (δ65Cu) in hydrothermal fluids have the potential to provide information on ore‐forming processes occurring below the seafloor, but Cu isotope data from high‐temperature fluids are scarce. Here, we examine the extent to which coexisting sulfide minerals in a hydrothermal chimney can preserve fluid Cu isotope ratios using a fluid‐solid pair of a black smoker (333°C) from the Roman Ruins vent area (PACMANUS) in the Manus Basin. Two ca. 3 cm long transects through the chalcopyrite‐rich chimney wall show an increase in δ65Cu from 0.48 to 2.28‰ from the interior to the exterior, coupled with limited variation in sulfide δ34S (1.52–4.72‰). The Cu isotopic composition of chalcopyrite from the innermost wall closely resembles the δ65Cu value of the paired hydrothermal fluid, indicating that chalcopyrite in the inner ∼5 mm of the chimney records the Cu isotope ratio of the venting fluid. Beyond this, an increase in sulfide δ65Cu toward the exterior correlates with an increase in the relative abundance of secondary Cu sulfides. The appearance of bornite coincides with the presence of small barite crystals, suggesting this represents a redox gradient between reduced hydrothermal fluids and oxidized seawater admixing inwards. Elevated δ65Cu in this zone can be explained by the precipitation of secondary Cu sulfides from 65Cu‐enriched fluids formed during oxidative chalcopyrite dissolution. Our findings indicate that interactions with oxidizing seawater shift chalcopyrite δ65Cu values over small spatial scales, and that caution must be applied if chimney sulfides are used to reconstruct δ65Cu values of high‐temperature hydrothermal fluids.

The 2.4Ga Hotazel Formation is a cyclically interlayered sequence of banded iron formation (BIF) and manganese-rich sedimentary rock at the uppermost part of the Neoarchaean-Palaeoproterozoic Transvaal Supergroup in South Africa. It represents an unusual stratigraphic association in the context of the origin of BIF and the coevolution of oxygen and life on early Earth and hence bears special relevance to the environmental conditions and processes that characterized the period leading up to the Great Oxidation Event (GOE) at ca. 2.3Ga. The mineral assemblages that characterize the Hotazel rocks are dominated by carbonate, silicate and oxide minerals, which are traditionally interpreted as predominantly diagenetic in origin, particularly the carbonates. By contrast, primary mineral assemblages are inferred to have been dominated by ferric oxyhydroxides and tetravalent manganese oxides, which show no preservation in the rock record and consequently hinder reconstruction of environmental conditions during sedimentation. Here, we revisit the Hotazel succession with a focus on its bulk-rock and carbonate-specific mineralogical, geochemical and stable isotope (C, Fe) composition by applying for the first time a high-resolution stratigraphic approach to sampling and analysis. Our main aim is to constrain the precursor mineralogy to the Fe- and Mn-rich facies in the Hotazel strata in order to unravel the redox conditions behind the massive cyclic deposition of Fe and Mn at the onset of the GOE. Our carbonate-specific results question traditional diagenetic models for the development of the carbonate fraction of the rocks and instead place the origin of much of the present mineralogy on water-column processes in a stratified basin characterized by successive redox pathways with changing water depth. These pathways exploited a series of thermodynamically predictable electron acceptors for organic carbon recycling, which included – probably for the first time in Earth history – aqueous Mn(III) and O2 as electron acceptors for the oxidation of both Fe(II) and organic carbon. The emergence of Mn(III) was also critical for the development of a Mn redox shuttle, which led to effective water-column stratification between aqueous Mn and Fe in the depositional basin. We conclude that the first known record of Mn(II) to Mn(III) oxidation as recorded in the Hotazel Formation must be a fundamentally diagnostic step in the redox evolution of the oceans and atmosphere in the lead-up to the GOE.