Seafloor Conditions Research Articles

Benthic foraminiferal turnover across the Dan-C2 event in the eastern South Atlantic Ocean (ODP Site 1262)

The Paleogene was punctuated by perturbations of the global carbon cycle, many associated with transient global warming events (hyperthermals). The Dan-C2 event (~160 kyr after Cretaceous/Paleogene boundary; K/Pg) was the oldest of these eccentricity-linked carbon cycle disturbances (ELCD). In contrast to other hyperthermals, the Dan-C2 event was not characterised by bottom water warming, and surface water warming probably was not global. Benthic foraminiferal assemblages across Dan-C2 at SE Atlantic Ocean Drilling Program (ODP) Site 1262 are diverse and strongly dominated by calcareous species. Epifaunal and infaunal morphogroups are equally abundant, suggesting meso-oligotrophic seafloor conditions. Assemblages decreased in diversity gradually before Dan-C2, and Nuttallides truempyi decreased in relative abundance while Stensioeina beccariiformis and the agglutinant Spiroplectammina spectabilis increased, suggesting enhanced food supply to the seafloor. Benthic foraminifera were not highly affected by the Dan-C2 event. An increase in relative abundance of the opportunistic species Bulimina kugleri and Seabrookia cretacea after Dan-C2 points to a change in the type of organic matter arriving at the seafloor. These changes may have been caused by ongoing environmental and/or evolutionary instability following K/Pg mass extinction of oceanic plankton. Variability in composition of pelagic ecosystems, thus the type and/or amount of food arriving at the seafloor, may have been caused by the gradual recovery of pelagic ecosystems after that extinction, possibly affected by warming and pH changes due to Deccan volcanism.

Estimation of layer coefficients of cubipod homogeneous low-crested structures using physical and numerical model placement tests

Homogeneous low-crested structures (HLCSs) on hard seabed are designed to protect beaches and regenerate coral reefs. The height of a HLCS depends on the placement grid which determines the crest freeboard, wave transmission and concrete consumption. In real seafloor conditions, it is not easy to define feasible placement grids for HLCSs on uneven sea bottoms. In this study, the parameters of the numerical model Bullet Physics Engine (BPE) are calibrated and validated using the results of small-scale physical model placement tests of five-layer Cubipod HLCSs on horizontal rigid bottom. The BPE model showed a low sensitivity to variations in the calibrated parameters; the numerical model estimated the layer coefficients with global mean relative errors of 1.04% and 1.39% in the triangular and rectangular placements grids, respectively. Once the numerical model was calibrated, new numerical and physical model tests on a 4% rigid bottom slope were compared for validation. A five-layer Cubipod HLCS on a 4% bottom slope was simulated using the BPE numerical model showing a global mean relative error of 2.75% compared to the small-scale physical model tests. A good agreement was found between numerical and physical model tests of five-layer Cubipod HLCSs on both horizontal as well as 4% rigid bottom slope. The BPE numerical model was found a suitable tool to estimate the structure height of HLCSs and to optimize placement grids of HLCSs on real cases with hard sea bottom.

Physicochemical properties of the Portland cement-based mortar exposed to deep seafloor conditions at a depth of 1680 m

Achieving breakthroughs in marine technologies requires the development of infrastructures submerged in deep-sea environments, whose physicochemical effects on cement-based materials considerably differ from those of shallow seas. However, very few studies focused on the cement-based materials subjected to deep-sea conditions. This work investigates the changes in the compressive strength and phase composition of the cement mortar kept on the seafloor with a depth of 1680 m for 608 d. The mortar specimens salvaged from the seafloor exhibited severe visible damages, including softened mashy structures and significantly decreased compressive strengths. The obtained X-ray diffraction, scanning electron microscopy, and nuclear magnetic resonance data revealed that the dissolution of portlandite, decalcification of calcium (alumino) silicate hydrate, and formation of brucite, magnesium (alumino) silicate hydrate, a hydrotalcite-like phase, thaumasite, and ettringite likely contributed to the disintegration of mortar, which could be further accelerated by the low temperature of the deep-sea environment.

Using Silica Activity to Model Redox-dependent Fluid Compositions in Serpentinites from 100 to 700 °C and from 1 to 20 kbar

AbstractSerpentinization is a metamorphic process that can stabilize highly reduced hydrogen-rich fluids. Previous measurements of elevated CH4 and H2 concentrations in ultramafic-hosted submarine springs indicate that active serpentinization occurs along mid-ocean ridge systems at seafloor pressures (∼<500 bar) and temperatures (∼<350 °C). Serpentinites also exist at higher pressures in subduction zones; for example, during retrograde hydration of the forearc mantle wedge and during prograde deserpentinization within the subducted slab. However, many studies demonstrating the thermodynamic stability of reduced serpentinite fluids have been limited to terrestrial seafloor conditions. To investigate the redox state of serpentinite fluids at elevated pressures, phase equilibria and fluid compositions were computed for 100–700 °C and 1–20 kbar using aqueous silica activity (aSiO2(aq)) as a governing parameter. Silica-sensitive, redox-buffering assemblages were selected to be consistent with previously proposed reactions: SiO2(aq)–fayalite–magnetite (QFM), SiO2(aq)–Fe-brucite–cronstedtite, SiO2(aq)–Fe-brucite–Fe3+-serpentine, plus the silica-free buffer Fe-brucite–magnetite. Fluid species are limited to simple, zerovalent compounds. For silica-bearing redox reactions, aSiO2(aq) is buffered by coexisting ultramafic mineral assemblages in the system MgO–SiO2–H2O. Silica activity and fO2 are directly correlated, with the most reduced fluids stabilized by the least siliceous assemblages. Silica activity and fO2 increase with pressure, but are more strongly dependent on temperature, leading to greater silica enrichment and more oxidized conditions along shallow, warm subduction paths than along steeper, colder paths. Reduced fluids with mCH4/mCO2 > 1 and fO2 below QFM are present only when serpentine is stable, and are favored along all subduction trajectories except shallow P–T paths at eclogite-grade. Values of mH2 and mCO/mCO2 depend strongly on P and T, but also on the choice of redox buffer, especially whether the Fe-serpentine component is cronstedtite or Fe3+-serpentine. Methane and H2S production are thermodynamically favored throughout the P–T range of the serpentinized forearc mantle and in other settings with similar conditions; for example, deep planetary seafloors. The model offers a generalized technique for estimating the redox state of a fluid-saturated serpentinite at elevated P and T, and yields results consistent with previous petrographic and thermodynamic analyses. High-pressure serpentinization may be an important source of reduced species that could influence prebiotic chemistry, support microbial life in the deep biosphere or in deep planetary oceans, or promote greenhouse warming on early Earth.

Integrated micropaleontological study of the Messinian diatomaceous deposits of the Monferrato Arc (Piedmont basin, NW Italy): New insights into the paleoceanographic evolution of the northernmost Mediterranean region

Abstract The upper Miocene diatom-bearing section of Pecetto di Valenza (Piedmont, NW Italy) represents a unique site for reconstructing the paleoceanographic processes that occurred before the onset of the Messinian salinity crisis in the northernmost Mediterranean basin. The combined analysis of foraminifera, calcareous nannofossils, diatoms and other siliceous microfossils observed in the marly and diatomaceous sediments allowed us to define four main evolutionary stages of the biogenic sedimentation. Each stage was typified by specific water column and seafloor conditions, tentatively correlated to the precession/insolation variability. In particular, the variation of the benthic assemblages allowed us to distinguish two stages in the evolution of the diatomaceous deposition, which would be otherwise impossible from the lithology. The accumulation of the diatomaceous sediments was likely controlled by the interplay between riverine runoff, water column stratification and convective mixing, rather than with upwelling and seafloor anoxia as inferred for the Western and Eastern sectors of the Mediterranean.

Sound Velocity Estimation of Seabed Sediment Based on Parametric Array Sonar

Backscattered sound waves of seabed sediments are important information carriers in seafloor detection and acoustic characteristic parameters inversion. Most of the existing methods for estimating geoacoustic parameters are based on multiangle seabed backscattered signal processing and suitable for flat seafloor conditions with uniform sediment thickness. This usually deviates from the real field conditions and affects the accuracy of parameter estimation. In this paper, the sound ray propagation theory is studied and analysed under the condition of sloping seabed and uneven sediment thickness. Based on the phased parameter array sonar system, a method of acoustic parameters estimation of the sediment under inclined seabed conditions is proposed. The simulation results show that the new method shows good adaptability to different inclination angles of the seabed and solves the problem of accuracy of acoustic parameter estimation of the inclined seabed sediments. The model will greatly reduce the seafloor topography requirements in the sediment acoustic parameter inversion, such as velocity, layer thickness, and acoustic impedance.

Seawater motion-induced electromagnetic noise reduction in marine magnetotelluric data using current meters

Seawater motion-induced electromagnetic (EM) noise along the seafloor has a large impact on marine magnetotelluric (MT) data quality. Although the mechanical stability of ocean bottom electromagnetic receivers (OBEMs) has improved due to buoyancy optimization, completely eliminating EM noise generated by seafloor currents as a result of instrument rocking or induction from the Earth’s magnetic field is still not possible. The velocity of the current represents the quantification of seafloor conditions. To mitigate this problem, we installed a current meter on an OBEM to measure the synchronous current velocity along with the OBEM data logger. For the marine EM surveys, we conducted two surveys composed of 42 marine EM data acquisition sites in the South China Sea. We observed a strong correlation between induced EM noise and current velocity when the speed was greater than 2 cm/s. Furthermore, we developed an adaptive correlation noise-canceling filter to reduce the induced EM noise, using the current meter data as a reference signal. The filter refined the coefficients using a least-mean-squares algorithm. We were able to reduce the induced EM noise by pre-filtering the raw time series data with an adaptive correlation noise-canceling filter and using current meter data from nearby sites. Since seafloor currents are clearly an issue that limits MT data quality, special efforts are necessary to reduce seawater motion-induced EM noise in marine MT surveys.

High-resolution paired carbon isotopic records from the Meishucun section in South China: Implications for carbon cycling and environmental changes during the Ediacaran-Cambrian transition

Several prominent negative carbon isotope (δ13C) excursions are observed during the Ediacaran-Cambrian (E-C) transition, reflecting large perturbations of the carbon cycle in the ocean–atmosphere system. These negative δ13C excursions have been linked to dramatic paleoenvironmental changes and been widely used as regional and global chemostratigraphic correlation tools. However, there is still much debate about their causes and mechanisms. In this study, we report high-resolution δ13C records of both carbonate (δ13Ccarb) and organic carbon (δ13Corg) from the Meishucun section in South China. Combined with lithological variations and intrabasinal correlations, we find that the negative δ13C excursions during the E-C transition in South China are tightly linked with transgressive events. The existence of a large vertical (surface-to-deep water) δ13C gradient in a stratified ocean, and episodic incursions of 13C-depleted anoxic/euxinic deep waters into shallow water environment through enhanced upwelling or shoaling of the chemocline, may have contributed to these negative δ13C excursions. In addition, our results also imply a large reduction in the vertical δ13Corg gradient during the E-C transition, which may reflect the ventilation and oxygenation of the deep ocean. The corresponding expansion of oxic seafloor conditions and a large increase in the extent of habitable space for animals may have facilitated the radiation of metazoans during the Cambrian explosion.

A Novel Framework for Evaluating Performance-Estimation Models

A general framework for quantifying the worth of a performance-estimation model is proposed. The purpose of the model is to predict the performance of an automatic target recognition algorithm on a given set of test data, while the purpose of the framework is to quantify how well the model fulfills its task. To this end, a quantity referred to as the utility, which is based on the Kullback–Leibler divergence, is introduced. A key aspect of the framework is the inclusion of a significance function that specifies the relative importance of each point in the performance space, here assumed to be defined in terms of false alarm rate and probability of detection. Example significance functions are suggested and discussed. The functionality of the proposed framework is demonstrated on an underwater target detection application involving measured synthetic aperture sonar data. In this context, an image complexity metric is exploited to enable the development of models corresponding to different seafloor conditions and mine-hunting difficulty. The appeal of the framework is its ability to quantitatively assess the utility of competing performance-estimation models and to fairly compare the utility of a model on different test data sets.

Chitinozoan biostratigraphy of the Rheidol Gorge Section, Central Wales, UK: a GSSP replacement candidate for the Rhuddanian–Aeronian boundary

AbstractAs part of an international effort to evaluate potential replacement sections for the current Aeronian GSSP, the stratigraphy of the Rheidol Gorge section (central Wales, UK) is being restudied. A total of 28 samples from the Rhuddanian–Aeronian boundary interval at Rheidol Gorge were studied for chitinozoans. This famous Welsh Basin section, its stratigraphy rooted in the work of O.T. Jones and M. Sudbury, comprises a series of laminated black shales with abundant graptolites, alternating with grey mudstone intervals, deposited in anoxic to dysoxic/oxic seafloor conditions, respectively. The exposed section of c. 20 m spans the middle part of the upper Rhuddanian Pernerograptus revolutus Biozone through the lower Aeronian Neodiplograptus magnus Biozone of the lower to mid‐Llandovery Series (Cwmere and Derwenlas formations). Our chitinozoan analysis yielded an assemblage of over 2300 specimens distributed approximately uniformly throughout the entire succession. A total of 16 different taxa are identified, of which 12 remain in open nomenclature, reflecting the poor to moderately intact preservation of the specimens. Based on the presence of key species such as Spinachitina maennili and Conochitina iklaensis, the Rheidol Gorge section is referred to the Spinachitina maennili Biozone. This observation is in perfect alignment with the typical signature of other Rhuddanian–Aeronian boundary successions in the Welsh Basin and in other parts of the world.

Paleoenvironmental signature of the Selandian-Thanetian Transition Event (STTE) and Early Late Paleocene Event (ELPE) in the Contessa Road section (western Neo-Tethys)

Sedimentary records of the Early Cenozoic indicate a series of events with climatic and carbon cycle variability known as hyperthermals. A ~350-kyr-long event of environmental disruption during the Paleocene, not described before and here named Selandian–Thanetian Transition Event (STTE), has been recognized and well constrained in the western Tethys Contessa Road section (Gubbio, Italy) through high-resolution biostratigraphic, geochemical, and rock-magnetic data. The STTE exhibits peculiar stressed ecological responses among calcareous nannofossils and foraminifera, which highlight marked environmental perturbation affecting the biosphere. The environmental instability is not confined within the photic zone but extends to the seafloor leading to little more trophic conditions of the sea surface waters with an enhanced, but of short measure, nutrient availability on the seafloor conditions and marked rise of lysocline. Magnetic Susceptibly (MS) is dominantly controlled by the balance between carbonate productivity and detrital supply, as evidenced by the strong correlation between MS and CaCO3 (%) (r2 = −0.72). However, we also document two components in the isothermal remanent magnetization (IRM) and first-order reversal curves (FORC) diagrams that prove the occurrence of biogenic magnetite throughout the STTE. Systematic variations in bio-geochemical and magnetic parameters show the relative abundance of carbonate production (or inversely dissolution of carbonate) versus detrital supply during the STTE, which induced higher populations of magnetotactic bacteria through increased terrigenous input and, therefore, increased nutrient supply. Noteworthy, the uppermost part of the STTE includes the equivalent of the suspected hyperthermal, short-lived Early Late Paleocene Event (ELPE). The ELPE event shows an episode of increase in magnetic properties of the sediments, including an increase in magnetofossil concentration, as indicated by IRM components and FORC diagrams. The comparison of biotic and abiotic records throughout the STTE at Contessa Road section with available data across the ELPE from former investigated ocean and land-based sites provides lines of evidence that this latter event might be indeed only the terminal part of a long-lasting environmental change than hitherto supposed.

Implications of Microbial Thiosulfate Utilization in Red Clay Sediments of the Central Indian Basin: The Martian Analogy

AbstractMicrobial thiosulfate utilization and S‐disproportionation could be important mechanisms of sulfate‐formations on Earth and Mars. Sulfates on Mars date back to late‐Noachian to Hesperian period. In contrast, the large sulfur/sulfate formations on Earth evolved under different chronological sequences. The S‐cycle was provoked intermittently, permitting multiple appearances of the S‐oxidizers on an evolutionary timescale. Hydrothermally altered deep‐oceanic red clay sediments of the Central Indian Basin were examined as potential analogue for sulfur (S) oxidation on Mars. The basin sediments supported an active microbial S‐metabolism that exhibited S‐disproportionation coupled to microbial carbon‐fixation through intermediate processes like thiosulfate utilization. Sulfur‐oxidizers/thiotrophic denitrifiers were isolated in large numbers at circum‐neutral pH, from these cold and dark abyssal Fe‐oxide dominated organic‐C starved clay. Experimental simulations under psychrophilic and thermo‐tolerant conditions revealed the coexistence of an anaerobic, thermal component under the predominantly oxic, circum‐neutral seafloor conditions. Multiple causative factors like hydrothermal seafloor circulation, in situ volcanism, and fracture zone reactivation could drive the widespread S‐cycle activity in the Central Indian Basin, albeit at a low scale. It is postulated that these conditions are analogous to Great Oxidation Event situations on Earth, when S‐oxidizers evolved and flourished. Experimental studies on microbial thiosulfate flux are few in spite of intense scientific interest in microbial S‐disproportionation. To the best of our knowledge, this is a new report on regression model development for microbial thiosulfate flux. These clay‐systems and their component microbes could serve as analogue to the ancient well‐hydrated Noachian Mars and throw light on planetary hydration and desiccation mechanisms.

Chapter 11 Geochemistry used to infer source characteristics and provenance of mudrocks of the Permian–Triassic Maitai Group and the associated Patuki Melange, South Island, New Zealand

Abstract Chemical and mineralogical evidence is reported, first for mudrocks from the Mid-Permian–Mid-Triassic Maitai Group and, secondly, for Late Permian(?) mudrocks from the structurally underlying Patuki Melange. Weathering and alteration indices indicate increased source weathering and aluminosilicate input stratigraphically upwards in the Maitai Group. The Maitai Group exhibits an upward change from a relatively enriched continental magmatic arc source (and related country rocks) during the Late Permian, to a relatively depleted continental magmatic arc source (and related country rocks) during the Triassic. The melange mudrocks have a similar provenance to the Late Permian mudrocks of the Maitai Group. The melange mudrocks are, however, generally less altered, probably because of additional, local, ophiolite-related input. Red iron-rich mudrocks accumulated widely in two Triassic Maitai Group formations and also locally in the Patuki Melange. The iron oxide was derived by continental weathering under warm conditions, and then accumulated relatively slowly under oxidizing seafloor conditions. The chemical evidence, as a whole, indicates sources for all of the mudrocks similar to the Median Batholith and associated country rocks, or non-exposed equivalents along the SE Gondwana active continental margin. Accumulation took place during a change from an icehouse to a hothouse world.

Morphological changes due to marine aggregate extraction for beach nourishment in the German Bight (SE North Sea)

Facing the predicted rise in global sea level, sandy shorelines are under increasing pressure. In order to counteract the loss of material at eroding coastlines, beach nourishment is considered to be an environmentally friendly approach worldwide. This has resulted in a rising demand for aggregates, which are frequently extracted from the seafloor near the coast. In order to explore the long- and short-term morphological changes of such mining on the seabed, the largest extraction area in the German Bight (Westerland Dredging Area, established in 1984) was investigated in this study. Several measurement campaigns were conducted between the years 1994 and 2017 using a set of hydroacoustic techniques. The measurements revealed that up to 20-m-deep pits with diameters of more than 1 km were dredged into the seafloor. The depressions caused by this sand mining are still detectable more than 30 years later. Because of slope failures that mainly consist of fine sand, the formerly steep rims at fresh dredging pits smoothed within a few months. However, after approximately 1 year, muddy sediments dominated the deposition. Since the sedimentation rates are slow, a complete backfill of the post-dredging pits is likely to take many decades. A natural regeneration towards the former seafloor conditions is only visible at the shallow rims of the oldest dredging pits.

The influence of pressure on crude oil biodegradation in shallow and deep Gulf of Mexico sediments.

A significant portion of oil released during the Deepwater Horizon disaster reached the Gulf of Mexico (GOM) seafloor. Predicting the long-term fate of this oil is hindered by a lack of data about the combined influences of pressure, temperature, and sediment composition on microbial hydrocarbon remineralization in deep-sea sediments. To investigate crude oil biodegradation by native GOM microbial communities, we incubated core-top sediments from 13 GOM sites at water depths from 60–1500 m with crude oil under simulated aerobic seafloor conditions. Biodegradation occurred in all samples and followed a predictable compound class sequence dictated by molecular weight and structure. 45 to ~100% of total n-alkane and 3 to 60% of total polycyclic aromatic hydrocarbons (PAH) were depleted. In reactors incubated at 4°C and at pressures of 6–15 MPa, the depletion in total n-alkane was inversely correlated to pressure (R2 ~ 0.85), equivalent to a 4% decrease in total n-alkane depletion for every 1 MPa increase. Our results indicated a modest inhibitory effect of pressure on biodegradation over our experimental range. However, the expansion of oil exploration to deeper waters (e.g., 5000 m) opens the risk of spills at conditions at which pressure might have a more pronounced effect.

Marine climate and hydrography of the Coralline Crag (early Pliocene, UK): isotopic evidence from 16 benthic invertebrate taxa

The taxonomic composition of the biota of the Coralline Crag Formation (early Pliocene, eastern England) provides conflicting evidence of seawater temperature during deposition, some taxa indicating cool temperate conditions by analogy with modern representatives or relatives, others warm temperate to subtropical/tropical conditions. Previous isotopic (δ18O) evidence of seasonal seafloor temperatures from serial ontogenetic sampling of bivalve mollusk shells indicated cool temperate winter (<10 °C) and/or summer (<20 °C) conditions but was limited to nine profiles from two species, one ranging into and one occurring exclusively in cool temperate settings at present. We supplement these results with six further profiles from the species concerned and supply seven more from three other taxa (two supposedly indicative of warm waters) to provide an expanded and more balanced database. We also supply isotopic temperature estimates from 81 spot and whole-shell samples from these five taxa and 11 others, encompassing ‘warm’, ‘cool’ and ‘eurythermal’ forms by analogy with modern representatives or relatives. Preservation tests show no shell alteration. Subject to reasonable assumptions about water δ18O, the shell δ18O data either strongly indicate or are at least consistent with cool temperate seafloor conditions. The subtropical/tropical conditions suggested by the presence of the bryozoan Metrarabdotos did not exist. Microgrowth-increment and δ13C evidence indicate summer water-column stratification during deposition of the Ramsholt Member, unlike in the adjacent southern North Sea at present (well mixed due to shallow depth and strong tidal currents). Summer maximum surface temperature was probably about 5 °C above seafloor temperature and thus often slightly higher than now (17–19 °C rather than 16–17 °C), but only sometimes in the warm temperate range. Winter minimum surface temperature was below 10 °C and possibly the same as at present (6–7 °C). An expanded surface temperature range compared to now may reflect withdrawal of oceanic heat supply in conjunction with higher global temperature.

Benthic Foraminifera and Geochemistry Across the Paleocene–eocene Thermal Maximum Interval in Jordan

AbstractThis study presents benthic foraminiferal data from two sedimentary successions across the Paleocene–Eocene Thermal Maximum (PETM) from Jordan. Calcareous nannofossil biozones NP9a, NP9b, and NP10 of latest Paleocene and earliest Eocene age were encountered in proximal (core OS–01) and distal (core OS–28) sites. Lithologically, the investigated sequence consists of marls, shales, and limestones attributed to the Muwaqqar Chalk-Marl Formation and the Um Rijam Chert Limestone Formation. The δ13Corg curve records the typical carbon isotope excursion (CIE) and shows four distinctive intervals (pre-CIE, CIE-“core”, CIE-“recovery”, post-CIE) over the entire PETM interval in both cores.In the pre-CIE interval, the more proximal site (OS–01) shows high abundances of Neoeponides duwi co-occurring with an outer neritic Midway-type fauna. The fauna indicates meso- to eutrophic conditions in a middle- to outer-neritic setting. The more distal site (OS–28) is characterized by outer-neritic to upper-bathyal taxa (e.g., Cibicides pseudoacutus, Gavelinella beccariiformis, Nuttallides truempyi) suggesting well-ventilated, oligo- to mesotrophic seafloor conditions.The earliest Eocene corresponds to the CIE-“core” interval and is marked by a negative δ13Corg signal, high TOC, low CaCO3 contents, and near absence of benthic foraminifera. Oxygen deficiency in bottom waters with increased organic flux is the most likely scenario to explain the elevated organic content at the seafloor.The subsequent CIE-“recovery” interval of early Eocene age is marked by a restoration of oxygenated seafloor conditions. The proximal site is characterized by a relatively elevated TOC content and high abundance of Lenticulina spp., Valvulineria scrobiculata and common Anomalinoides zitteli, suggesting moderate oxygen conditions and mesotrophic bottom waters. The distal site is characterized by low TOC content and the presence of Lenticulina spp., Valvulineria scrobiculata, Anomalinoides zitteli and Oridorsalis plummerae, indicating a normalization of the organic flux and moderate oxygen concentrations near the seafloor.The post-CIE interval is marked by low TOC content in both cores. Benthic foraminifera include abundant Anomalinoides zitteli and common Lenticulina spp., Valvulineria scrobiculata, Oridorsalis plummerae, Cibicidoides rigidus, Cibicidoides pharaonis, and Anomalinoides praeacutus in the proximal setting. Mesotrophic conditions and a better ventilation of bottom waters are suggested for this interval. Lenticulina spp., Valvulineria scrobiculata, and Oridorsalis plummerae are also associated with the post-CIE interval in the distal site, suggesting similar mesotrophic conditions with renewed oxygenation in bottom waters.

Visual evidence of reduced seafloor conditions and indications of a cold-seep ecosystem from the Hatton–Rockall basin (NE Atlantic)

High definition video from a towed camera system was used to describe the deep-sea benthic habitats within an elongate depression located at the western margin of Rockall Bank in the Hatton–Rockall Basin. At depths greater than 1190 m, an extensive area (10 km long by 1.5 km wide) of what appeared to be reduced sediments, bacterial mats and flocculent matter indicated possible cold-seep habitat. Plumes of sediment-rich fluid were observed alongside raised elongate features that gave topographic relief to the otherwise flat seafloor. In the deepest section of the depression (1215 m) dense flocculent matter was observed suspended in the water column, in places obscuring the seabed. Away from the bacterial mats, the habitat changed rapidly to sediments dominated by tube-dwelling polychaete worms and then to deep-sea sedimentary habitats more typical for the water depth (sponges and burrowing megafauna in areas of gentle slopes, and coral gardens on steeper slopes).

The hidden biology of the pockmarks located at Estremadura Spur (NE Atlantic)

Event Abstract Back to Event The hidden biology of the pockmarks located at Estremadura Spur (NE Atlantic) Clara F. Rodrigues1*, Sofia P. Ramalho1, Vitor Magalhães2 and Marina R. Cunha1 1 University of Aveiro, Departamento de Biologia & CESAM, Portugal 2 Instituto Português do Mar e da Atmosfera (IPMA), Marine Geology and Georesources Division (DivGM), Portugal Pockmarks are crater-like geomorphic features that occur in the seafloor worldwide along both passive and active margins. Their association with subsurface oil and gas makes them interesting features for gas/oil industry. Pockmarks are thought to be formed rapidly, as a consequence of the sudden release of pressurized subsurface gas or pore-water. They can remain active, microseeping gas over long periods of time, or display periods of quiescence between eruptions. Both active and inactive pockmarks show geological and biological characteristics distinct from the surrounding seafloor. The PES project proposes a comprehensive interdisciplinary study of the Estremadura Spur (NE Atlantic) pockmark field. Here we present the first results on the macrofaunal and microbial assemblages in their geologic context. Our investigations indicate that these pockmarks are, at present, inactive. The microbial assemblages comprise several phylotypes associated with the cycling of sulphur and nitrate compounds, as well as numerous known hydrocarbon degraders underlining the variable and reduced activity of the individual pockmarks. The macrofaunal assemblages are composed mainly by detritivores and some of the dominant taxa suggest the occurrence of reduced seafloor conditions. Inactive pockmarks have been studied to a limited extent and our results contribute to ascertain their ecological significance for the biological assemblages in the Portuguese margin. Acknowledgements This work was supported by the PES project (PTDC/GEOFIQ/5162/2014), financed by National funding through the Portuguese Science Foundation (FCT), Financial support to CESAM (UID/AMB/50017 - POCI-01-0145-FEDER-007638), to FCT/MCTES through national funds (PIDDAC), and the co-funding by the FEDER, within the PT2020 Partnership Agreement and Compete 2020. CFR was supported by the FCT grant (SFRH/BPD/107805/2015). Keywords: macrofauna, Microbes, pockmarks, Reduced environments, assemblages Conference: IMMR'18 | International Meeting on Marine Research 2018, Peniche, Portugal, 5 Jul - 6 Jul, 2018. Presentation Type: Oral Presentation Topic: Biodiversity, Conservation and Coastal Management Citation: Rodrigues CF, Ramalho SP, Magalhães V and Cunha MR (2019). The hidden biology of the pockmarks located at Estremadura Spur (NE Atlantic). Front. Mar. Sci. Conference Abstract: IMMR'18 | International Meeting on Marine Research 2018. doi: 10.3389/conf.FMARS.2018.06.00047 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 23 Apr 2018; Published Online: 07 Jan 2019. * Correspondence: Dr. Clara F Rodrigues, University of Aveiro, Departamento de Biologia & CESAM, Aveiro, Portugal, Portugal, clara.rodrigues@ua.pt Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Clara F Rodrigues Sofia P Ramalho Vitor Magalhães Marina R Cunha Google Clara F Rodrigues Sofia P Ramalho Vitor Magalhães Marina R Cunha Google Scholar Clara F Rodrigues Sofia P Ramalho Vitor Magalhães Marina R Cunha PubMed Clara F Rodrigues Sofia P Ramalho Vitor Magalhães Marina R Cunha Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Reliability of Local Scale Human Pressure Modeling at the Seafloor of the Baltic Sea

ABSTRACTEfforts to understand anthropogenic stress in marine environments have introduced methods of cumulative human pressure modeling in the broad-scale mapping of large sea areas. This paper examines the usability of such modeling in the shallow seafloor and complex shoreline conditions of the Archipelago Sea in the northern Baltic Sea. We employed public spatial data sources to describe the spatial patterns of 24 different human pressures with their normalized values in a 20 m × 20 m pixel size. Public data were also used to classify the seafloor into six different environmental types. The model output was assessed against environmental data from regular seafloor monitoring. Visual examination shows general agreement between the cumulative human pressure model and the health of the benthic fauna, seabed oxygen and, to a degree, also the tributyltin. However, although none of these field parameters show high statistical correlation with the cumulative pressure status, multiple parameters assessed simultaneously could provide a sufficient reference. Local-scale disagreements between the cumulative model and the field parameters particularly occur near the largest harbor in the region where regular dredging is practiced. Model sensitivity to different input variables was further tested by comparing 36 dissimilar variants. The comparisons reveal a general stability across the inclusion, exclusion, or modification of such spatially restricted human pressure data, which only induced local-scale details. High instabilities occurred when the tested input data had a large spatial coverage. As the cumulative human impact model reduces several human pressures into one index, it should be considered as a broad scale descriptor of the likely overall health status of the sea. When implemented with accurate local-scale data it can help coastal and marine spatial planning but it should not be considered as a predictive depiction of any particular environmental characteristic. The cumulative pressure map is particularly powerful in providing unforeseen insights into the distributions of overall anthropogenic influences within the study region, and through these it can also contribute to environmental policies.