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Prestonellinae – validation of the name as a new subfamily of Bothriembryontidae (Mollusca, Gastropoda, Orthalicoidea)
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RBINS Staff Publications 2016
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Hydroclimatic conditions and fishing practices at Late Paleolithic Makhadma 4 (Egypt) inferred from stable isotope analysis of otoliths
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The late Paleolithic site of Makhadma 4, located along the Nile River in Upper Egypt, yielded an important ichthyofauna characterized by a very high proportion of tilapia (Oreochromis niloticus). We used isotopic analysis (d18O) of well-preserved otoliths (“ear stones”) of tilapia to reconstruct the former hydrological conditions, as well as the fishing strategies of the site's inhabitants. Otoliths from two modern fish captured in the Nile River near Esna were also examined to test how accurately tilapia otoliths reflect their ambient environment. All otoliths were sequentially micromilled to recover high resolution isotopic profiles along the main growth axis. Comparison of the modern otolith profiles with environmental data shows that tilapia d18O values record seasonal variations of the modern Nile hydroclimate but that their values are offset. The archaeological otoliths record very large intraindividual cyclical variations in d18O values, with relatively consistent amplitude, as well as very high seasonal maximum values (up to þ8.3‰), compared with the modern otoliths. The hydrological regime of the water body in which the archaeological fish lived was characterized by a reduced Nile water inflow that could not negate the effect of local evaporation during spring. The reconstructed hydrological conditions are in accordance with a new model of Nilotic behavior that assumes the creation of lakes by damming of the Nile as a result of a high eolian activity during hyper-arid periods of the Late Pleistocene. Although large seasonal evaporation may have resulted in a severe seasonal reduction in the lake's volume and extent, the lake was, nevertheless, maintained for several years. Cyclic variations in otolith d18O values permit reconstruction of the period of the hydrological cycle during which the fish were captured. Fishing of young individuals occurred mostly after the maximum input of inflow water from the Nile, when evaporitic conditions were at their lowest, i.e. during fall.
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RBINS Staff Publications 2017
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Sequence stratigraphy and palaeontology of the upper Miocene Pisco Formation along the western side of the lower Ica Valley (Ica Desert, Peru)
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RBINS Staff Publications 2017
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Anatomy, life-history and phylogeny of an exceptionally preserved hadrosaur from the Judith River Formation of Montana (USA)
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RBINS Staff Publications 2017
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Remains of Atsinganosaurus from the Late Cretaceous Site of Velaux-La Bastide Neuve (Southern France)
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RBINS Staff Publications 2017
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Spatial and seasonal variation of biomineral suspended particulate matter properties in high-turbid nearshore and low-turbid offshore zones
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Suspended particulate matter (SPM) is abundant and essential in marine and coastal waters, and comprises a wide variety of biomineral particles, which are practically grouped into organic biomass and inorganic sediments. Such biomass and sediments interact with each other and build large biomineral aggregates via flocculation, therefore controlling the fate and transport of SPM in marine and coastal waters. Despite its importance, flocculation mediated by biomass-sediment interactions is not fully understood. Thus, the aim of this research was to explain biologically mediated flocculation and SPM dynamics in different locations and seasons in marine and coastal waters. Field measurement campaigns followed by physical and biochemical analyses had been carried out from 2004 to 2011 in the Belgian coastal area to investigate bio-mediated flocculation and SPM dynamics. Although SPM had the same mineralogical composition, it encountered different fates in the turbidity maximum zone (TMZ) and in the offshore zone (OSZ), regarding bio-mediated flocculation. SPM in the TMZ built sediment-enriched, dense, and settleable biomineral aggregates, whereas SPM in the OSZ composed biomass-enriched, less dense, and less settleable marine snow. Biological proliferation, such as an algal bloom, was also found to facilitate SPM in building biomass-enriched marine snow, even in the TMZ. In short, bio-mediated flocculation and SPM dynamics varied spatially and seasonally, owing to biomass-sediment interactions and bio-mediated flocculation.
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RBINS Staff Publications 2017
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Comparison of Chelex based resins in diffusive gradients in thin-film for high resolution assessment of metals
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The passive sampling technique of diffusive gradients in thin-film (DGT) is widely used to determine 1D profiles (using Chelex-100 resin) and 2D images (using suspended particulate reagent-iminodiacetate resin, abbreviated as SPR-IDA resin) of metals in sediment pore waters and in oxic/anoxic soils. However, when deployed in anoxic sediments with high metal concentrations, Fe and Mn concentrations determined with the Chelex-100 resin gel were ~ 5 times higher than concentrations measured with the SPR-IDA resin gel. This discrepancy suggests that the SPR-IDA resin gel is saturated faster than the Chelex-100 resin gel. Here, we tested the adsorption capacity of the SPR-IDA resin gel and compared it to the Chelex-100 resin gel. Fe and Mn binding capacities on a SPR-IDA gel disc are less than 0.1 μmoles, which means that they are far below those on a Chelex-100 gel disc (around 3.2 μmoles), while competition with stronger binding metals such as Cu and Cd further lowers Fe and Mn capacities. This restricts the SPR-IDA resin gel to be used in contaminated marine sediments. We propose the use of a ground Chelex-100 resin, which is prepared by grinding Chelex-100 resin in a ball-mill prior to gel preparation. The capacities of Fe and Mn on a ground Chelex-100 resin gel disc are around 1.6 μmoles, more than 16 times higher than the capacity on SPR-IDA gel disc. In addition, the bead size of the ground Chelex-100 resin is small enough (~ 10 μm) to allow high resolution LA-ICP-MS imaging of Fe, Mn and trace metals in sediment pore waters as well as soils.
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Transient bottom water oxygenation creates a niche for cable bacteria in long-term anoxic sediments of the Eastern Gotland Basin
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Cable bacteria have been reported in sediments from marine and freshwater locations, but the environmental factors that regulate their growth in natural settings are not well understood. Most prominently, the physiological limit of cable bacteria in terms of oxygen availability remains poorly constrained. In this study, we investigated the presence, activity and diversity of cable bacteria in relation to a natural gradient in bottom water oxygenation in a depth transect of the Eastern Gotland Basin (Baltic Sea). Cable bacteria were identified by FISH at the oxic and transiently oxic sites, but not at the permanently anoxic site. Three species of the candidate genus Electrothrix, i.e. marina, aarhusiensis and communis were found coexisting within one site. The highest filament density (33 m cm−2) was associated with a 6.3 mm wide zone depleted in both oxygen and free sulphide, and the presence of an electric field resulting from the electrogenic sulphur oxidizing metabolism of cable bacteria. However, the measured filament densities and metabolic activities remained low overall, suggesting a limited impact of cable bacteria at the basin level. The observed bottom water oxygen levels (< 5 μM) are the lowest so far reported for cable bacteria, thus expanding their known environmental distribution.
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Early Palaeozoic ocean anoxia and global warming driven by the evolution of shallow burrowing
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The evolution of burrowing animals forms a defining event in the history of the Earth. It has been hypothesised that the expansion of seafloor burrowing during the Palaeozoic altered the biogeochemistry of the oceans and atmosphere. However, whilst potential impacts of bioturbation on the individual phosphorus, oxygen and sulphur cycles have been considered, combined effects have not been investigated, leading to major uncertainty over the timing and magnitude of the Earth system response to the evolution of bioturbation. Here we integrate the evolution of bioturbation into the COPSE model of global biogeochemical cycling, and compare quantitative model predictions to multiple geochemical proxies. Our results suggest that the advent of shallow burrowing in the early Cambrian contributed to a global low-oxygen state, which prevailed for ~100 million years. This impact of bioturbation on global biogeochemistry likely affected animal evolution through expanded ocean anoxia, high atmospheric CO2 levels and global warming.
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Carbon, iron and sulphur cycling in the sediments of a Mediterranean lagoon (Ghar El Melh, Tunisia)
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Coastal lagoon sediments are important for the biogeochemical carbon cycle at the land-ocean transition, as they form hotspots for organic carbon burial, as well as potential sites for authigenic carbonate formation. Here, we employ an early diagenetic model to quantify the coupled redox cycling of carbon, iron and sulphur in the sediments of the shallow Ghar El Melh (GEM) lagoon (Tunisia). The model simulated depth profiles show a good correspondence with available pore water data (dissolved inorganic carbon, NH4+, total alkalinity, Ca2+, Fe2+ and SO42−) and solid phase data (organic matter, pyrite, calcium carbonate and iron (oxyhydr)oxides). This indicates that the model is able to capture the dominant processes influencing the sedimentary biogeochemical cycling. Our results show that sediment of the GEM lagoon is an efficient reactor for organic matter breakdown (burial efficiency < 10%), with an important role for aerobic respiration (32%) and sulphate reduction (61%). Despite high rates of sulphate reduction, free sulphide does not accumulate in the pore water, due to a large terrestrial input of reactive iron oxides and the efficient sequestration of free sulphide into iron sulphide phases. High pyrite burial (2.2 mmol FeS2 m−2 d−1) prevents the reoxidation of reduced sulphide, thus resulting in a low total oxygen uptake (4.7 mmol m−2 d−1) of the sediment and a relatively high oxygen penetration depth. The formation of pyrite also generates high amounts of alkalinity in the pore water, which stimulates authigenic carbonate precipitation (2.7 mmol m−2 d−1) and leads to alkalinity release to the overlying water (3.4 mmol m−2 d−1). Model simulations with and without an N-cycle reveal a limited influence of nitrification and denitrification on overall organic matter diagenesis. Overall, our study highlights the potential role of coastal lagoons for the global carbon and sulphur cycle, and their possible contribution to shelf alkalinity, which increases the buffering capacity of the coastal ocean for CO2 uptake.
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