Sponge Spicules Research Articles

Late Ordovician sponge spicules from the Yangtze Platform, South China: Biostratigraphical and palaeobiogeographical significance

A diverse and abundant isolated sponge spicule assemblage of Late Ordovician age is first reported from the western margin of the Yangtze Platform in South China. The spicule assemblage was recovered from argillaceous limestone sampled for conodonts. It includes 14 types which can be split into two categories: hexactinellid spicules and demosponge spicules. The assemblage primarily comprises hexactines and their derivatives, including not only some distinctive types such as Kometia cruciformis, but also large numbers of morphotypes that are quite common and diagnostic for hexactinellids, e.g. swollen hexactines, curved hexactines, and stauractines. Demosponge spicule types are represented by tetraxons, and various desmas typical for lithistids also occur. A highly modified hexactine, Kometia cruciformis, is recovered from China for the first time. This record represents currently the only recovery of such spicules from strata outside of Australia, and is coeval to the assemblage known from the Malongulli Formation. The presence of such unique modified hexactines (Kometia) in both time-equivalent assemblages suggests that certain spicules may have potential importance in biostratigraphic correlations and palaeobiogeographical interpretations, demonstrating the dispersal of taxa and their migration along the peri-Gondwana shelf areas during the Ordovician, driven by ocean current systems. The Late Ordovician sponge spicule assemblage from the Yangtze Platform provides new perspectives for investigating phylogeny, biostratigraphy, and palaeobiogeography of Palaeozoic sponges, and promotes some understanding of macroevolution in siliceous sponges.

Biogenic silica dynamics in coastal wetland sediments: A key driver of silicon and carbon biogeochemical cycling

AbstractBiogenic silica (biogenic Si) is a bioactive component crucial for the biogeochemical cycling of Si in terrestrial and aquatic ecosystems. Its formation and dissolution dynamics are intricately linked to carbon (C) cycling. However, knowledge about the source, composition, and factors controlling the distribution of biogenic Si in coastal wetland sedimentary environments is still limited. To address this lack of knowledge, we introduced a suite of geometric models for biogenic Si biovolume calculation and investigated biogenic Si assemblages, along with biogenic Si and biogenic Si‐occluded C contents, in sediments from representative coastal wetlands along the west coast of Bohai Bay. Our analysis showed that sedimentary biogenic Si predominantly derived from phytoliths (78.1% ± 5.8%), diatoms (18.2% ± 4.8%), and sponge spicules (3.7% ± 2.9%). Notably, phytolith assemblages were primarily composed of forms derived from the Poaceae family. The biogenic Si‐occluded C content (0.035–1.870 g kg−1) within these wetland sediments was consistent across both sites, accounting for 0.97–5.71% of the total organic C pool. Structural equation modeling indicated that total organic C, pH, and amorphous aluminum oxides either directly or indirectly influenced the biogenic Si content in coastal wetlands sediments. These results demonstrate the critical role that biogenic Si plays in the Si biogeochemical cycle and provide valuable information that advances our understanding of the biogeochemical interactions between Si and C in coastal wetland ecosystems.

Palaeoenvironmental analysis of the Langshan Formation in the Xiongba area

The mid-Cretaceous Langshan Formation is a massive limestone unit, outcropping typically in the northern Lhasa block. A Xiongba section, measured near the type section of the Langshan Formation, is here described. The succession consists of orbitolinids limestone, where eight microfacies have been recognized. The lower part of the Langshan Formation consists of discoidal orbitolinids with other heterotrophic associations, including echinoderms, sponge spicules, and bivalves. In contrast, the upper part of the Langshan Formation features conical orbitolinids with an abundance of green algae and small benthic foraminifers. We interpret the morphological changes in orbitolinids as being influenced by bathymetry. Consequently, the microfacies variations in the Langshan Formation in the Xiongba section represent a shallowing upward sequence.

A regularized variational mechanics theory for modeling the evolution of brittle crack networks in composite materials with sharp interfaces

In the design of structural materials, there is traditionally a tradeoff between achieving high strength and achieving high toughness. Nature offers creative solutions to this problem in the form of structural biomaterials (SBs), intelligent arrangements of mineral and organic phases which possess greater strength and toughness than the constituents. The micro-architecture of SBs like nacre and sea sponge spicules are characterized by weak organic interfaces between brittle mineral phases. To better understand the toughening mechanisms in SBs requires simulation techniques which can resolve arbitrary interface and bulk fracture patterns.In this work, we present a modified regularization of Variational Fracture Theory (VFT) that allows for simulation of fracture in materials and structures with weak interfaces. The core of our approach is to widen the weak interfaces on a length scale proportional to that of the diffuse damage field, and assign a reduced fracture toughness therein. We show that in 2D the modified regularized functionals Γ-converge to that for sharp cracks. The resulting thin weak interfaces have fracture toughness which depends on the bulk material fracture toughness, the widened interface fracture toughness, and the ratio of the widened interface length scale to the crack regularization length scale. We next apply our modified regularization within a computer implementation of regularized VFT, which we term RVFTI. We assess the performance of RVFTI in 2D by reproducing the effective interface fracture toughness predicted by the Γ-convergence theory and simulating crack trapping at a bi-material interface. We then use RVFTI to study toughening in SB-inspired microarchitectures, namely layered materials and materials with wavy interfaces.

The topical application of Sphistin12-38 in combination with sponge spicules for the acne treatment.

We demonstrated for the first time that a marine-derived antimicrobial peptide (AMP), Sph12-38, exhibit high antimicrobial activity against P. acnes with a minimum bactericidal concentration (MBC) value of 7μM. Meanwhile, Sph12-38 has no significant cytotoxicity to human keratinocytes (HKs) at its high concentration (33.5μM). The topical application of sponge Haliclona sp. spicules (SHS) dramatically enhanced the skin penetration of Sph12-38 up to 40.9 ± 5.9% (p < 0.01), which was 6.1 ± 0.9-fold higher than that of Sph12-38 alone. Further, SHS resulted in the accumulation of most Sph12-38 in viable epidermis and dermis. Further, the combined use of Sph12-38 and SHS resulted in a cure rate of 100% for rabbit ear acne treatment in vivo for two weeks, while the one induced by other groups was 40%, 0% and 0% for SHS alone, Sph12-38 alone and control group, respectively. The strategy of combined using AMP and SHS can also be applied in a rational designed topical delivery system for the management of other deep infection of the skin. The effectiveness of SHS by itself on the treatment of acne was also demonstrated by clinical trials. After 14days of treatment by 1% SHS gel. The number of skin lesions decreased by 51.4%.

Biogenic opal δ18O in marine deep-sea sediments through the Cenozoic Era and implications for ocean cooling

Benthic foraminifera δ18O increased by 5.4 ‰ through the Cenozoic Era, the past 65 million years of Earth's history. This increase is attributed to growth of global ice sheets and global ocean cooling. On the other hand, δ18O measurements of planktonic foraminifera do not exhibit significant change. These measurements initially were interpreted to suggest cool tropical and subtropical temperatures and introduced the concept of the “cool tropics paradox”, in which global bottomwater temperatures were significantly warmer but tropical surface temperatures were not during the early Cenozoic. This lack of change in δ18O of planktonic foraminifera was explained by secondary postburial alteration of the primary planktonic isotope signal.We provide an alternative record of sea surface water characteristics of Cenozoic Era by measuring δ18O of siliceous microfossils. This scarce phase of marine silica, unaltered biogenic opal-A, composed of diatoms, radiolaria and sponge spicules, was separated and purified from deep-sea Cenozoic sediments. We measured δ18O of siliceous microfossils from a set of drilled cores: DSDP 278 from the South Pacific, DSDP 513 from the South Atlantic, and ODP 1050–1053 and DSDP 391 from the subtropical North Atlantic. The purity of the biogenic opal and its mineralogical phase was assessed with SEM, SEM/EDS, XPS, and XRD.The δ18O of biogenic opal-A fluctuates around an average value of 43.0 ‰ through the Cenozoic Era, comparable to the Southern Ocean average of 43.2 ‰ of diatoms and radiolaria from the last 30,000 years which represent the last glacial and interglacial period and suggesting cold surface temperatures of 2–7 °C, both in the subtropical and polar latitudes. Taking into consideration changes in δ18O associated with bottomwater interaction with the lower crust and changes in sea level associated with waxing and waning of ice sheets, we conclude lack of or minimal change in the surface water temperature through the Cenozoic Era. This revives the original idea of the “cool tropics” paradox with a carbonate independent δ18O record and without issues associated with diagenesis of benthic and planktonic foraminifera.

Mineralogy of Quaternary Sediments from the Valley of Vema Fracture Zone (Central Atlantic)

The content of sediment forming minerals in two cores from the eastern (ANS45-37) and western (ANS45-48) parts of the Vema transform fault valley is studied using the semi-quantitative XRD analysis of bulk powder sediment samples. The mineral composition of deep-sea sediments from the Amazone cone is also analyzed for comparison. It appeared that the average composition of the terrigenous component of both cores (according to prevailing quartz, secondary mica, plagioclase and potassium feldspar, as well as smectite, chlorite, kaolinite, illite) is quite similar and approximately corresponds to the composition of sediments from the Amazon cone. The ratio of four clay minerals suggests the supply of terrigenous material to the Amazon and Orinoco due to the erosion of the Andes and humid tropical weathering in the lower course of the rivers with further transportation of the suspended load to the ocean. This material was transported to the Vema transform valley due to the interplay between the gravity flows from the South American continental slope and the current of the Antarctic Bottom Water. Data on biogenic calcite (planktic foraminiferal tests, nannofossils) and opal A (radiolarians, sponge spicules) are obtained in addition. In the study area, several authigenic (diagenetic) minerals are identified. In particular, siderite and greigite are first found in the sediments from the Vema valley and Amazon cone, respectively.

Geochemistry of cherts from the northern Jiangxi region, South China: Implication for paleoenvironment

The extensive bedded cherts deposited during the Ediacaran–Cambrian (E–C) transition period play a crucial role in understanding the geological evolution of this period, yet the origin of these cherts remains disputed. Here, we present new geochemical data for cherts of the Piyuancun (PYC) Formation deposited during the Late Ediacaran and the Hetang (HT) Formation deposited during the Early Cambrian in northern Jiangxi region, Lower Yangtze region, South China. The PYC cherts contain a small amount of monaxons sponge spicules and radiolarian fragments, while the HT cherts lack siliceous organism evidence. Major and trace element analysis, coupled with discriminant diagrams, indicate a possible shift in redox conditions of seawater during the E–C transition in the northern Jiangxi region. The shift suggests a change from weakly–moderately restricted euxinic conditions to strongly restricted euxinic conditions. Furthermore, the location of both cherts are distant from the source area of siliceous organisms. Fossil evidence, as well as the values of Fe/Ti and Fe/(Mn+Ti), Eu anomalies, Post-Archean Australian Shale (PAAS) normalized REE+Y patterns, and various discriminant diagrams, support the conclusion that the PYC and HT cherts originated primarily from direct seawater precipitation, with the PYC cherts exhibiting weak hydrothermal evidence. Upwelling contributes to the formation of HT cherts and organic matter (OM) accumulation. Ocean acidification, triggered by OM degradation and biodegradation processes during the E–C transition period, leads to the extensive silica precipitation and preservation. These results enhance our understanding of the geological processes during the E–C transition.

Pre-Jurassic weathering crust of the Kalinovoe hydrocarbon deposit, Tomsk region: composition and structure characteristics

Abstract. The study of pre-Jurassic deposits in the southwestern part of Western Siberia is highly relevant due to their potential of increasing hydrocarbon resources. These deposits are considered prospective targets for the discovery of hydrocarbon accumulations. Weathering crusts developed on the upper part of the Paleozoic rocks in the Tomsk region exhibit a complex composition and structure, reflecting the interplay of various factors, including primary sedimentary processes and later alteration processes, including fracture-controlled fluid flow and metasomatism. Aim. To establish the characteristics of the mineralogical composition and structure of the Paleozoic weathering crust formations developed at the Kalinovoe oil-gas-condensate field. Methods. Optical microscopy, X-ray diffraction, scanning electron microscopy. Results and conclusions. The composition and structure of the deposits at the boundary zone between the Paleozoic and Mesozoic successions have been studied in detail in the section of one of the wells at the Kalinovoe oil-gas-condensate field. The factual material is represented by core and thin sections of weathering crust deposits. The primary rock-forming minerals are silica minerals (quartz, chalcedony and opal) and clay minerals, with a lesser amount of carbonate minerals (siderite). Different lithological units were identified based on the content of minerals and bioclast (radiolarians and sponge spicules), indicating their formation under marine conditions. The protoliths of the altered rocks were carbonate-siliceous rocks, argillaceous limestones, and radiolarian cherts, which as a result of multiple stages of hydrothermal alteration and metasomatic processes were transformed into argillaceous-silicified rocks. In these rocks, with intense post-alteration overprinting, good reservoir quality porosity can develop. This porosity includes biogenic voids, microcavities, micropores, and open fractures.

Nested structure role in the mechanical response of spicule inspired fibers

Euplectella aspergillum marine sponge spicules are renowned for their remarkable strength and toughness. These spicules exhibit a unique concentric layering structure, which contributes to their exceptional mechanical resistance. In this study, finite element method simulations were used to comprehensively investigate the effect of nested cylindrical structures on the mechanical properties of spicules. This investigation leveraged scanning electron microscopy images to guide the computational modeling of the microstructure and the results were validated by three-point bending tests of 3D-printed spicule-inspired structures. The numerical analyses showed that the nested structure of spicules induces stress and strain jumps on the layer interfaces, reducing the load on critical zones of the fiber and increasing its toughness. It was found that this effect shows a tapering enhancement as the number of layers increases, which combines with a threshold related to the 3D-printing manufacturability to suggest a compromise for optimal performance. A comprehensive evaluation of the mechanical properties of these fibers can assist in developing a new generation of bioinspired structures with practical real-world applications.

APPLICATION OF MICROBIOMORPHIC AND TOTAL PHOSPHORUS ANALYSES TO THE ARCHAEOLOGICAL STUDY OF THE SREDNY ZELENCHUK TEMPLE, NIZHNY ARKHYZ HILLFORT

The article presents the results of the first geoarchaeological study of the materials of Christian burials identified in the interior of the Middle Zelenchuk temple of the 10th century in the Nizhne-Arkhyz ancient settlement (Republic of Karachay-Cherkessia). The results of microbiomorphic (phytolith) and total phosphorus content analyses allowed us to reveal previously unknown features of the funeral rites of the multicultural and multi-ethnic Christian population of one of the largest cities of the North Caucasus in the Middle Ages. The differences in funerary practices between the 11th and 13th centuries became evident when studying even a small group of funerary complexes in which people of the same social group – representatives of the social elite of Western Alania – were buried. The geoarchaeological study showed an abundance of plant and animal organic matter in the burials. The complex analysis of archaeological materials and data obtained during the microbiomorphic study allowed us to conclude that members of the urban Christian community had several burial traditions: in stone boxes (tombs), in wooden frames, and a mixed ritual when a wooden structure was placed in a stone box. The presence of wooden bark particles in the burials seems to be related not so much to the material from which the burial structures were made as to the presence in the graves of bark or bast objects (bast caskets or boxes, birch bark amulets, toys, etc.). The tradition known from pagan Alanian burials of placing the head of the deceased on a “stone cushion” (more typical for male burials) was preserved in early Christian burials. In one of the four women’s graves studied, the analysis showed the presence of a “hay pillow.” Probably, before the burial, a ritual of washing the deceased was performed, as evidenced by the presence of diatoms and sponge spicules in the samples.

First record of Chelonian coprolites from the Early-Middle Miocene Kutch Basin, western India, and their palaeodietary and palaeobiological implications

In this paper, we provide the first data on large (cm-sized) coprolites (represented by three morphotypes) comprising a rare occurrence of eight specimens from a total of three vertebrate-bearing horizons identified within the Early Miocene (Aquitanian) Khari Nadi Formation and Middle Miocene (Burdigalian-Langhian) Chassra Formation, Kutch Basin, western India. The geochemical data confirm the phosphatic character of the investigated ichnofossils. The dominance of partly digested bone matter and presence of plant remains in all the three coprolite morphotypes reflects the omnivorous diet of the producers, which were most likely chelonians. The occurrence of an inclusion (in a coprolite specimen recorded in this study) showcasing an ultrastructure similar to mammalian dental enamel is a rarity in Neogene coprolite records. Additional biotic inclusions observed in the investigated coprolites include ostracods (assigned to genera Paractinocythereis, Hermanites, and Propontocypris); large planispiral benthic foraminifera including the genus Quinqueloculina; uniserial and biserial benthic foraminifera belonging to genus Textularia; marine calcareous algae genus Actinoporella; chrysophytes (resting spores or cysts of planktonic algae); sponge spicules (represented by the morphotypes Acanthoxea and Strongyle); freshwater diatom genus Aulacoseira; unidentified fungal remains; and phytoliths. Taken together, the biotic and abiotic (e.g., pyrite) inclusions, geochemical data and associated microbiota suggest that these ichnofossils were deposited in a dominantly coastal marine (intertidal) setting linked to a lacustrine/palustrine environment.

The depositional record of the French Flemish Coastal plain since antiquity: Impacts of land reclamation in a tide‐dominated estuary

AbstractThe French Flemish Coastal Plain, which extends from Denmark to France, is characterised by a topography close to sea level and protected by a system of coastal dunes. Quaternary sediments, comprised of marine, estuarine and continental deposits, accumulated by infilling and then prograding above a network of incised valleys. This study focusses on the Holocene infill of the Denna palaeoestuary, south‐west to Dunkerque. Surface geophysics (electrical conductivity and ground‐penetrating radar) and vibrocore data are used to reconstruct the landscape evolution during the last stages of sedimentation. The conductivity map highlights the last network of tidal channels, ditches and dikes of the eastern side of the palaeoestuary. Over the upper 4 m of the infill, the ground‐penetrating radar profiles show two superimposed units. The bottom unit is composed of meandering channel bars and the top unit of flat strata intersected by sparse channels, mostly infilled in place. The sediment analysis of the vibrocores shows a predominantly sandy filling of marine to estuarine origin, evidenced by sponge spicules and a fauna of bivalves and foraminifera adapted to brackish settings. The uppermost deposit exhibits an oxidation profile which marks the groundwater zone transition. Clayey sediments are also present, infilling the uppermost channels and ditches dug during reclamation, in increasing proportions towards the axis of the estuarine palaeovalley. The tidal signature of sedimentary dynamics is evidenced by heterolithic facies in some channel fills and tidal rhythmites infilling scour depressions linked to dike breaching. The abrupt decrease in channel dynamics across the unit boundary, although sedimentation remained sandy in the upper unit, coincides with the development of embankment of the estuarine border and is tentatively interpreted as a result of reclamation.

Biosediment assemblages reveal disrupted silica cycling and redox conditions throughout the Rhaetian Stage: Evidence for a precursor event to the end-Triassic mass extinction

The Norian–Rhaetian boundary (Late Triassic) represents an important precursor extinction event to the end-Triassic mass extinction, but the biotic and geochemical shifts are not well-understood due to poor stratigraphic constraints. Here we examine the microfossil record for metazoans and protists on a Panthalassan carbonate ramp (Gabbs Formation, Nevada, U.S.A.) during the late Norian to mid-Rhaetian, and correlate changes in these assemblages with macrofossil shifts and geochemical data (strontium and carbon isotopes). In the latest Norian, demosponge spicules represent a small proportion of shallow marine biosediments. Demosponges are joined in the earliest Rhaetian by increasingly abundant hypersilicified sponge spicules and silica-limited hexactinellid sponge spicules synchronous with a negative strontium isotope excursion indicating increased hydrothermal or volcanic activity. Common carbonate microfossils such as echinoderm ossicles and ostracods are typically silicified in these deposits as well, suggesting increased silicic porewater. The source for increased dissolved silica in shallow marine systems is suggested to be hydrothermal vent degassing, likely associated with increased tectonic rifting activity. Mid-Rhaetian microfossil assemblages exhibit evidence for intermitted anoxia in reducing conditions, supporting a scenario in which environmental stress was a prolonged feature of much of the Rhaetian Stage, rather than a short-term event in the terminal Rhaetian. While there is no marine sedimentary record of volcanism recognized for this interval, biosedimentary assemblages may serve as proxies for geochemical conditions associated with rifting.

Anomalies of Sponge Spicules: Exploring Links to Environmental Pollution

The aim of this study was to assess the frequency of spicule malformations in freshwater sponges in relation to selected environmental parameters of the streams and the presence of river pollutants. A total of 50 sponge samples were collected from ten rivers in Serbia. Selected parameters of the water varied considerably at every site where sponges were found. After spicule preparation, the samples were subjected to morphological analysis by light and scanning electron microscopy, and the number of anomalies were recorded (spicules with bulbous enlargements, sharply bent, bifurcated, scissor- and cross-like, and t-shaped). The frequencies and types of malformations within the analyzed specimens varied from 1 to 100 per 1000 spicules, with an average number of 12 per 1000. The main types of anomalies were single- and double-bent spicules. The highest number of anomalies was found in a specimen of Eunapius fragilis collected at Markovac (Velika Morava River), and the lowest number was found in a specimen of Ephydatia fluviatilis from Kanjiža (Tisa River). The sites with the lowest and the highest numbers of anomalies showed statistically significant differences in concentrations of ammonia, orthophosphates, sodium, chloride, manganese, and lead. This study indicates that several pollutants potentially affect the occurrence of spicule anomalies.

Response of Siliceous Marine Organisms to the Permian‐Triassic Climate Crisis Based on New Findings From Central Spitsbergen, Svalbard

AbstractSiliceous marine ecosystems play a critical role in shaping the Earth's climate system by influencing rates of organic carbon burial and marine authigenic clay formation (i.e., reverse weathering). The ecological demise of silicifying organisms associated with the Permian‐Triassic mass extinction is postulated to have elevated marine authigenic clay formation rates, resulting in a prolonged greenhouse climate during the Early Triassic. Yet, our understanding of the response of siliceous marine organisms during this critical interval is poor. Whilst radiolarians experienced the strongest diversity loss in their evolutionary history and perhaps also the greatest population decline of silica‐secreting organisms during this event, only a small number of Griesbachian (post‐extinction) localities that record siliceous organisms are known. Here, we report newly discovered latest Changhsingian to early Griesbachian (Clarkina meishanensis ‐ Hindeodus parvus Zone) radiolarians and siliceous sponge spicules from Svalbard. This fauna documents the survival of a low‐diversity radiolarian assemblage alongside stem‐group hexactinellid sponges making this the first described account of post‐extinction silica‐secreting organisms from the Permian/Triassic boundary in a shallow marine shelf environment and a mid‐northern paleolatitudinal setting. Our findings indicate that latitudinal diversity gradients for silica‐secreting organisms following the mass extinction were significantly altered, and that silica productivity was restricted to high latitude and deep water thermal refugia. This result has potential to further shape our understanding of changes in marine dissolved silica levels and in turn rates of reverse weathering, with implications for our understanding of carbon cycle dynamics during this interval.

Two natural toughening strategies may inspire sustainable structures

Contemporary designs of engineering structures strive to minimize the use of material in order to reduce cost and weight. However, the approach taken by focusing on materials selection and on the design of the exterior shape of structures has reached its limits. By contrast, nature implements bottom-up designs based on a multiple-level hierarchy, spanning from nanoscale to macroscale, which evolved over millions of years in an environmentally sustainable manner given limited resources. Natural structures often appear as laminates in wood, bone, plants, exoskeletons, etc., and employ elaborate micro-structural mechanisms to generate simultaneous strength and toughness. One such mechanism, observed in the scorpion cuticle and in the sponge spicule, is the grading (gradual change) of properties like layers thickness, stiffness, strength and toughness. We show that grading is a biological design tradeoff, which optimizes the use of material to enhance survival traits such as endurance against impending detrimental cracks. We found that such design, when applied in a more vulnerable direction of the laminate, has the potential to restrain propagation of hazardous cracks by deflecting or bifurcating them. This is achieved by shifting material from non-critical regions to more critical regions, making the design sustainable in the sense of efficient use of building resources. We investigate how such a mechanism functions in nature and how it can be implemented in synthetic structures, by means of a generic analytical model for crack deflection in a general laminate. Such a mechanical model may help optimize the design of bioinspired structures for specific applications and, eventually, reduce material waste.

Miocene sponge assemblages in the face of the Messinian Salinity Crisis-new data from the Atlanto-Mediterranean seaway.

The Messinian Salinity Crisis is considered as one of the most influential Cenozoic events that impacted negatively on the benthic fauna of the Mediterranean area. Changing environmental conditions, including a sharp reduction of water exchange between the Mediterranean Sea and the Atlantic Ocean, altered the geographical ranges of many organisms, including sponges (Porifera). Here, we report a unique assemblage of isolated sponge spicules from the upper Miocene of southwestern Spain. The newly recognized sponge fauna was inhabiting the Guadalquivir Basin-the corridor between the Mediterranean and the Atlantic Ocean at that time. It represents a taxonomically rich sponge community that consisted of members of "soft" and "lithistid" demosponges and hexactinellids. Demosponges are represented by at least thirty-four taxa, while hexactinellids are significantly rarer; only six taxa have been identified. From among eighteen taxa recognized to the species level, at least eight seem to be inhabiting this area to these days; six are recorded from adjacent areas, such as the Western Mediterranean, South European Atlantic Shelf, and the Azores, and three are present in the Red Sea and/or the Northern Atlantic. Intriguingly, some taxa seem to have their closest relatives in distant areas, such as the Indo-Pacific and Japanese waters which suggests that the range of some once widely-distributed populations shrunk after the isolation of the Mediterranean and the Messinian Salinity Crisis, surviving to the present day only in refugia.

Drivers of pelagic and benthic microbial communities on Central Arctic seamounts

Seamounts are abundant features on the seafloor that serve as hotspots and barriers for the dispersal of benthic organisms. The primary focus of seamount ecology has typically been on the composition and distribution of faunal communities, with far less attention given to microbial communities. Here, we investigated the microbial communities in the water column (0-3400 m depth) and sediments (619-3883 m depth, 0-16 cm below seafloor) along the ice-covered Arctic ridge system called the Langseth Ridge. We contextualized the microbial community composition with data on the benthic trophic state (i.e., organic matter, chlorophyll-a content, and porewater geochemistry) and substrate type (i.e., sponge mats, sediments, basaltic pebbles). Our results showed slow current velocities throughout the water column, a shift in the pelagic microbial community from a dominance of Bacteroidia in the 0-10 m depth towards Proteobacteria and Nitrososphaeria below the epipelagic zone. In general, the pelagic microbial communities showed a high degree of similarity between the Langseth Ridge seamounts to a northern reference site. The only notable differences were decreases in richness between ~600 m and the bottom waters (~10 m above the seafloor) that suggest a pelagic-benthic coupling mediated by filter feeding of sponges living on the seamount summits. On the seafloor, the sponge spicule mats, and polychaete worms were the principal source of variation in sedimentary biogeochemistry and the benthic microbial community structure. The porewater signature suggested that low organic matter degradation rates are accompanied by a microbial community typical of deep-sea oligotrophic environments, such as Proteobacteria, Acidimicrobiia, Dehalococcoidia, Nitrospira, and archaeal Nitrososphaeria. The combined analysis of biogeochemical parameters and the microbial community suggests that the sponges play a significant role for pelagic-benthic coupling and acted as ecosystem engineers on the seafloor of ice-covered seamounts in the oligotrophic central Arctic Ocean.

Ecosystem recovery after the Early Jurassic T-OAE in the Châabet El Attaris section of the Tunisian Atlas

The flooding of the Pliensbachian shelf of the North-South Axis of Central Tunisia during the early Toarcian favoured the development of organic-rich facies in the most subsiding areas, such as that represented by the Châabet El Attaris section. The lower Toarcian strata in this section is represented by organic matter-rich sediments (dark laminated marls with low carbonate content) and the negative carbon isotope excursion (CIE) of the Jenkyns Event. The relatively high TOC values, increase of redox sensitive elements, and the absence of benthic organisms confirm the adverse conditions for life at the sea floor (suboxic to anoxic conditions) during the polymorphum Biozone and lower part of the levisoni Biozone. This indicates that the Jenkyns Event is expressed in this setting as the so-called Toarcian Oceanic Anoxic Event (T-OAE). The diversity and abundance of the calcareous nannoplankton was very low during the early Toarcian.After the T-OAE, the decrease in TOC and the low values of the geochemical redox proxies indicate a re‑oxygenation of the bottom waters, parallel with an increase of the carbonate content of the facies. After the negative CIE, the record of benthic macroinvertebrates (such as brachiopods, bivalves, ophiuroids and echinoids) and trace fossils (Zoophycos, Thalassinoides, Planolites, Chondrites, and locally Trichichnus) confirms the re‑oxygenation of the sea floor with increased diversity and abundance from the upper levisoni Biozone and bifrons Biozone. Benthic foraminifera colonization of the sea floor is evidenced by assemblages dominated by infaunal taxa, specially opportunist forms, such as Lenticulina, and progressive increase of diversity and abundance that confirms oxic pore-waters from the levisoni-bifrons biozone boundary. Planktic organisms attest to a progressive recovery of environmental conditions in the photic zone with increasing diversity and abundance of calcareous nannoplankton and radiolarians from the uppermost part of the levisoni Biozone and the bifrons Biozone. A first pulse after the negative CIE is represented by placoliths of the genus Lotharingius (shallow dweller) interpreted as a renewed input of nutrients to surface waters. The subsequent dominance of muroliths, especially of Crepidolithus crassus (a deep dweller), suggests a successive restoration of the deep-photic zone communities. These observations point towards enhanced oxygen availability in deep waters and pore waters due to improved basin ventilation.Taphonomic features of foraminifera pointing to dissolution in the bifrons Biozone are related to a lowered pH below the redox boundary within the sediment. In the same way, the presence of ferruginous moulds of microfossils (gastropods, bivalves, brachiopods, foraminifera, sponge spicules and radiolarians) with framboidal texture, actually preserved as goethite but originally pyrite, confirm the presence of reducing conditions within the sediment below the redox boundary. The record of Trichichnus confirms the reducing conditions in the deepest infaunal environments during the bifrons Biozone and is consistent with the development of pyrite moulds of microfossils early in the diagenesis.