Deep-sea Settings Research Articles

Bacterial Diversity in Deep-Sea Sediment of West Pacific Nodule Province

Dense polymetallic nodule fields are found in different areas of the Pacific and Indian Oceans. However, limited knowledge exists about microbial diversity, processes and functions in deep-sea polymetallic nodule sediments. This study investigated microbial diversity, composition and function in sediments from various locations and depths in a western Pacific polymetallic nodule province. Sediment cores were collected, DNA extracted, and the V3–V4 regions of the 16S rRNA gene were sequenced using Illumina MiSeq. The test results show that the abundance and diversity of microbial communities in sediments from different sites vary significantly. The dominant microbial communities at the family level in the three sediment samples were all mainly Marinobacteraceae and Alcanivoracaceae. Sediment samples from core 1 had similar microbial structures and microbial community functions. Surface sediment had higher species richness, diversity and evenness than the middle layer. The dominant phylum at different depths was consistent. There was significant spatial heterogeneity in the microbial community within sediments from polymetallic nodule regions. This study expands on our knowledge of the spatial and vertical distribution of microbial community diversity beneath polymetallic nodules in deep-sea settings.

The latest shallow-sea isocrinids from the Miocene of Paratethys and implications to the Mesozoic marine revolution

The predation-driven Mesozoic marine revolution (MMR) is believed to have induced a dramatic change in the bathymetric distribution of many shallow marine invertebrates since the late Mesozoic. For instance, stalked crinoids – isocrinids (Isocrinida) have undergone a striking decline in shallow-sea environments and today they are restricted to deep-sea settings (below 100 m depth). However, the timing and synchronicity of this shift are a matter of debate. A delayed onset of MMR and/or shifts to a retrograde, low-predation community structure during the Paleogene in the Southern Ocean were invoked. In particular, recent data from the Southern Hemisphere suggest that the environmental restriction of isocrinids to the deep-sea settings may have occurred at the end of the Eocene around Antarctica and Australia, and later in the early Miocene in New Zealand. Here, we report the anomalous occurrence of the isocrinids in shallow nearshore marine facies from the middle Miocene of Poland (Northern Hemisphere, Central Paratethys). Thus, globally, this is the youngest record of shallow-sea stalked crinoids. This finding suggests that some relict stalked crinoids may have been able to live in the shallow-water environments by the middle Miocene, and further confirms that the depth restriction of isocrinids to offshore environments was not synchronous on a global scale.

Strong linkage between benthic oxygen uptake and bacterial tetraether lipids in deep-sea trench regions

Oxygen in marine sediments regulates many key biogeochemical processes, playing a crucial role in shaping Earth’s climate and benthic ecosystems. In this context, branched glycerol dialkyl glycerol tetraethers (brGDGTs), essential biomarkers in paleoenvironmental research, exhibit an as-yet-unresolved association with sediment oxygen conditions. Here, we investigated brGDGTs in sediments from three deep-sea regions (4045 to 10,100 m water depth) dominated by three respective trench systems and integrated the results with in situ oxygen microprofile data. Our results demonstrate robust correlations between diffusive oxygen uptake (DOU) obtained from microprofiles and brGDGT methylation and isomerization degrees, indicating their primary production within sediments and their strong linkage with microbial diagenetic activity. We establish a quantitative relationship between the Isomerization and Methylation index of Branched Tetraethers (IMBT) and DOU, suggesting its potential validity across deep-sea environments. Increased brGDGT methylation and isomerization likely enhance the fitness of source organisms in deep-sea habitats. Our study positions brGDGTs as a promising tool for quantifying benthic DOU in deep-sea settings, where DOU is a key metric for assessing sedimentary organic carbon degradation and microbial activity.

Two New Taxa of Goniasteridae (Asteroidea, Echinodermata) and Noteworthy Observations of Deep-Sea Asteroidea by the NOAA Ship Okeanos Explorer in the North and Tropical Atlantic

Two new species and one new genus, collected by NOAA ship Okeanos Explorer, Bathyceramaster kelliottae n. sp. and Rhianastra isosceles n. gen., n. sp. (Goniasteridae; Asteroidea) are described from deep-sea settings in the North Atlantic. Two potentially undescribed species are observed from imagery and new in situ observations further elucidate life modes and feeding behavior of several species from North Atlantic deep-sea habitats. New occurrences of Atlantic Neomorphaster are presented and Neomorphaster forcipatus is synonymized with Neomorphaster margaritaceus.

New Goniasteridae and in situ observations significant to deep-sea coral predation

Eight new species, including one new genus, Armaster chondros n. gen. sp., Atheraster luma n. sp., Atheraster phaeos n. sp., Atheraster umbo n. sp., Circeaster dux n. sp., Evoplosoma besseyae n. sp., Evoplosoma mystrion n. sp. and Evoplosoma pharos n. sp. are newly described from Australian waters. Atheraster, Circeaster and Evoplosoma have been reported previously as predators on deep-sea octocorals. Evoplosoma, Gilbertaster and Hippasteria are members of the Hippasterinae, which have also been reported as predators on deep-sea corals and other cnidarians, suggesting that this interaction occurs in Australian deep-sea settings. Atheraster, Circeaster and Armaster are referred to a new subfamily, the Circeasterinae. Ecological and systematic implications for the Goniasteridae are discussed. An in situ observation of a myxasterid predating upon an octocoral is also reported.

Probing the optical and molecular properties of sedimentary dissolved organic matter in the laminated diatom mats from the southern Mariana Trench

Laminated diatom mats (LDMs) deposition, formed by the aggregation of giant diatoms (e.g., Ethmodiscus rex), are recognized as a crucial driver of the global carbon and silicon cycles due to their substantial contribution to the flux of organic carbon and biogenic silica. The biogenic silica-rich sediment is one of the typical sediment types in the deep-sea setting of the tropical Pacific Ocean. Here, we analyzed the concentrations of pore-water dissolved organic carbon (DOC) and phosphate (PO43−), the optical properties, and molecular compositions of dissolved organic matter (DOM) in the two LDMs cores and one non-LDMs core retrieved from the southern Mariana Trench. Our results showed that the LDMs sediments with higher total organic carbon (TOC) contents have lower concentrations of DOC and chromophoric dissolved organic matter (CDOM), compared to the non-LDMs core. Meanwhile, the LDMs samples exhibited lower relative intensity of fluorescent proteins-like, molecular lability boundary (MLBL%) and higher values for humification index (HIX) and aromaticity modification (AImod) compared to the non-LDM core, indicating a higher level of stability and recalcitrance of DOM likely resulting from microbial degradation of relatively labile DOM compounds. Furthermore, the LDMs samples were characterized by a high abundance of CHO-containing DOM components and a low abundance of nitrogen- and sulfur-containing components, potentially linked to microbial degradation of hydrocarbon compounds that were enriched in the LDMs sediments. Additionally, the unique formulas in the LDMs samples demonstrated higher degree of recalcitrance suggested by higher aromaticity and fraction of CRAM, which may be attributed to microbial transformation of DOM. These findings add to our limited knowledge of the optical properties and molecular composition of DOM in the deep-sea opal-rich sediments, and have implications for understanding DOM cycling in the deep oceans.

Effect of Size Fractions of Foraminifera on Reconstructing the Paleoceanography of Cretaceous Oceanic Anoxic Event 2

Abstract The globally recognized Cretaceous Oceanic Anoxic Event 2 was recorded at Integrated Ocean Drilling Program Site U1407 in the North Atlantic in sediments that were deposited under varying oxygen concentrations, conditions often associated with decreased foraminiferal test size. A >63-µm size fraction is typically used for collecting foraminifera that live in low-oxygen and deep-sea settings, particularly for paleoceanographic reconstructions where key environmental indicator species may be under-represented or absent in coarser sizes. Using 31 sediment samples from the site, we test the best size fraction to utilize when exploring biotic responses to an oceanic anoxic event. Counts of benthic and biserial (heterohelicid) planktic foraminifera from the standard >63-µm and finer 38–63-µm sieve sizes are compared to determine if critical information is lost if the smaller size fraction is not used. Results show similar trends in relative abundances for both size fractions. There are higher abundances in 38–63-µm residues, but species identification and counts are overly time-consuming for obtaining the general trends. We recommend the use of >63-µm sieves for foraminifera collected from low-oxygen sediments but encourage examination of the 38–63-µm fraction to verify intervals recognized as barren are truly absent of foraminifera.

Systematics of deep-sea starfish order Brisingida (Echinodermata: Asteroidea), with a revised classification and assessments of morphological characters

Brisingida Fisher 1928 is one of the seven currently recognised starfish orders, and one of the least known taxa as being exclusive deep-sea inhabitants. Modern deep-sea expeditions revealed their common occurrences in various deep-sea settings including seamounts, basins and hydrothermal vent peripheral, underlining the necessity of clarifying their global diversity and phylogeny. In this study, we present a comprehensive molecular phylogeny of Brisingida which encompasses the highest taxonomic diversity to date. DNA sequences (COI, 16S, 12S and 28S) were obtained from 225 specimens collected in the global ocean, identified as 58 species spanning 15 of the 17 extant genera. Phylogenetic relationship was inferred using both maximum likelihood and Bayesian inference methods, revealing polyphyletic families and genera and indicating nonnegligible bias in prior morphology-based systematics. Based on the new phylogeny, a novel classification of the order, consisting of 5 families and 17 genera, is proposed. Families Odinellidae, Brisingasteridae and Novodiniidae (sensu Clark and Mah, 2001) were resurrected to encompass the genera Odinella, Brisingaster and Novodinia. Brisingidae and Freyellidae were revised to include 11 and 3 genera, respectively. A new genus and species, two new subgenera and seven new combinations are described and a key to each genus and family is provided. Transformations of morphological traits were evaluated under the present phylogenetic hypothesis. A series of paedomorphic characters were found in many genera and species, which led to a high degree of homoplasy across phylogenetically distant groups. Our results provide new insights in the phylogeny and ontogeny of the order, and highlight the necessity to evaluate character convergence under sound phylogenetic hypothesis.

Depth-Dependent Distribution of Prokaryotes in Sediments of the Manganese Crust on Nazimov Guyots of the Magellan Seamounts.

Deep ocean polymetallic nodules, rich in cobalt, nickel, and titanium which are commonly used in high-technology and biotechnology applications, are being eyed for green energy transition through deep-sea mining operations. Prokaryotic communities underneath polymetallic nodules could participate in deep-sea biogeochemical cycling, however, are not fully described. To address this gap, we collected sediment cores from Nazimov guyots, where polymetallic nodules exist, to explore the diversity and vertical distribution of prokaryotic communities. Our 16S rRNA amplicon sequencing data, quantitative PCR results, and phylogenetic beta diversity indices showed that prokaryotic diversity in the surficial layers (0-8 cm) was > 4-fold higher compared to deeper horizons (8-26 cm), while heterotrophs dominated in all sediment horizons. Proteobacteria was the most abundant taxon (32-82%) across all sediment depths, followed by Thaumarchaeota (4-37%), Firmicutes (2-18%), and Planctomycetes (1-6%). Depth was the key factor controlling prokaryotic distribution, while heavy metals (e.g., iron, copper, nickel, cobalt, zinc) can also influence significantly the downcore distribution of prokaryotic communities. Analyses of phylogenetic diversity showed that deterministic processes governing prokaryotic assembly in surficial layers, contrasting with stochastic influences in deep layers. This was further supported from the detection of a more complex prokaryotic co-occurrence network in the surficial layer which suggested more diverse prokaryotic communities existed in the surface vs. deeper sediments. This study expands current knowledge on the vertical distribution of benthic prokaryotic diversity in deep sea settings underneath polymetallic nodules, and the results reported might set a baseline for future mining decisions.

New occurrence of Poraniidae (Valvatacea, Asteroidea) in Australia with a new genus and species from deep-sea settings

The Poraniidae (Asteroidea, Valvatacea) is recorded for the first time from Australian waters at deep-sea (>200m) depths, including, at present, Australia’s deepest known asteroid occurrence from 3850 m. Three genera are reviewed, each represented by a single species, Poraniomorpha tartarus n. sp., Marginaster paucispinus Fisher 1913, and Marginaster patriciae McKnight 2006, which is reassigned to the new genus, Bathymarginaster. Comparisons with other asteroid groups similar to the Poraniidae in Australian waters is made and a key to genera of the Poraniidae is provided.

New Genera, Species, and observations on the biology of Antarctic Valvatida (Asteroidea).

Assessment of Antarctic taxonomic diversity for asteroids and other taxa for poorly studied or unknown regions, such as the deep-sea, will be important for our understanding of these understudied habitats. Eleven new species and a new genus are described from three families (Asterinidae, Goniasteridae, Solasteridae) within the Valvatida, nearly all of which were collected from deep-sea settings below 1000 m by the US Antarctic Research Program in the 1960s. A new subfamily, the Kampylasterinae subfam. nov. is designated for Kampylaster and Astrotholus nov. gen. which were supported as sister taxa on a monophyletic clade within the Asterinidae. Astrotholus nov. gen. is described to accommodate "Anseropoda" antarctica and four new bathyal and abyssal species, which are a significant morphological divergence from the typological definition of Anseropoda. New species of the goniasterid Notioceramus and the solasterid Paralophaster are also described from bathyal depths (2000-3000 m). Paralophaster ferax n. sp. is among the deepest asteroids known to brood, is the first brooding species within Paralophaster and the second species in the Solasteridae known to brood. Following examination of the type and molecular data, Lophaster densus is found to be included within Paralophaster. A review of Antarctic Lophaster species shows additional specimens of Lophaster abbreviatus which support it as a distinct species from Lophaster stellans. New occurrence data for bathyal Antarctic Asteroidea as well as unusual-gut content observations of shallower-water species are also included.

Northernmost (Subarctic) and deepest record of Paleodictyon: paleoecological and biological implications

Paleodictyon is one of the most iconic and widespread of trace fossils in the geological record. However, modern examples are less well known and restricted to deep-sea settings at relatively low latitudes. Here, we report the distribution of Paleodictyon at six abyssal sites near the Aleutian Trench. This study reveals for the first time the presence of Paleodictyon at Subarctic latitudes (51°–53°N) and at depths over 4500 m, although the traces were not observed at stations deeper than 5000 m suggesting that there is some bathymetric constraint for the trace maker. Two small Paleodictyon morphotypes were recognized (average mesh size of 1.81 cm), one having a central hexagonal pattern, the other being characterized by a non-hexagonal pattern. Within the study area, Paleodictyon shows no apparent correlation with local environmental parameters. Finally, based on a worldwide morphological comparison, we conclude that the new Paleodictyon specimens represent distinct ichnospecies that are associated with the relatively eutrophic conditions in this region. Their smaller size may reflect this more eutrophic setting in which sufficient food can be obtained from a smaller area in order to satisfy the energetic requirements of the tracemakers. If so, then Paleodictyon size may provide some assistance when interpreting paleoenvironmental conditions.

Comparison of rosette-shape traces in abyssal terrains: Environmental and faunal implications

Biogenic traces (lebensspuren) result from the activity of benthic organisms on and within the seafloor and are a common feature of deep-sea environments. Rosette-shape traces (RSTs), also referred to as spoke burrows, are a commonly observed and distinctive trace, likely created by echiuran worms during feeding and burrowing. We conduct a quantitative morphometric assessment of RSTs from two contrasting sites at the Porcupine Abyssal Plain Sustained Observatory (PAP-SO; Northeast Atlantic) with similar physico-chemical conditions except for relative sediment compaction, but substantive differences in their megabenthic communities. We quantified RST abundance (numerical density and seafloor cover) and morphological characteristics (spoke number and overlap, spoke length and width, trace area and relative completeness) for 148 individual RSTs observed in some 6800 seafloor photograph (8788 m−2 seafloor area) captured with an autonomous underwater vehicle. We derived two primary results between study sites: (a) individual spoke morphology exhibited no statistically significant differences, while (b) individual trace completeness was significantly different. The consistency in spoke morphometrics reflects our identification of a single RST morphotype, potentially representing a single functional group of echiurans. The difference in trace completeness between sites may have resulted from differences in competition for resource with other megabenthic surface deposit feeders, and not to be directly related to relative sediment compaction. By reference to literature data and observations of similar traces in other deep-sea settings, we further suggest that this connection between trace completeness and resource availability may be more generally applicable in both contemporary ecology and paleoichnology.

A Review on Structural Failure of Composite Pressure Hulls in Deep Sea

With the increasing application and study of lightweight and high strength fiber reinforced polymer composites in ocean industry, the structural failure problem of composite pressure hulls has attracted great attention from many researchers in China and globally. Analysis of the structural failure mechanisms is foundational to the design of deep-sea composite pressure hulls, since nowadays the design rules of pressurized vessels is mostly formulated according to their failure modes. Hence, this paper aims to review the research on the structural failure of composite pressure hulls in deep sea settings. First of all, the applied research status on composite material in marine equipment is analyzed, including inspection modalities for composite pressure hulls. The review then focuses on the three main failure modes, namely overall buckling, material failure and snap buckling of the deep-sea composite pressure hulls. The study identifies further problems of composite pressure hulls to be solved through the application of the deep sea equipment research, aiming to provide a reference for the study of mechanical behavior, ultimate strength computation, and design of thick composite pressure hulls for deep sea equipment.

Machine learning applied to big data from marine cabled observatories: A case study of sablefish monitoring in the NE Pacific

Ocean observatories collect large volumes of video data, with some data archives now spanning well over a few decades, and bringing the challenges of analytical capacity beyond conventional processing tools. The analysis of such vast and complex datasets can only be achieved with appropriate machine learning and Artificial Intelligence (AI) tools. The implementation of AI monitoring programs for animal tracking and classification becomes necessary in the particular case of deep-sea cabled observatories, as those operated by Ocean Networks Canada (ONC), where Petabytes of data are now collected each and every year since their installation. Here, we present a machine-learning and computer vision automated pipeline to detect and count sablefish (Anoplopoma fimbria), a key commercially exploited species in the N-NE Pacific. We used 651 hours of video footage obtained from three long-term monitoring sites in the NEPTUNE cabled observatory, in Barkley Canyon, on the nearby slope, and at depths ranging from 420 to 985 m. Our proposed AI sablefish detection and classification pipeline was tested and validated for an initial 4.5 month period (Sep 18 2019-Jan 2 2020), and was a first step towards validation for future processing of the now decade-long video archives from Barkley Canyon. For the validation period, we trained a YOLO neural network on 2917 manually annotated frames containing sablefish images to obtain an automatic detector with a 92% Average Precision (AP) on 730 test images, and a 5-fold cross-validation AP of 93% (± 3.7%). We then ran the detector on all video material (i.e., 651 hours from a 4.5 month period), to automatically detect and annotate sablefish. We finally applied a tracking algorithm on detection results, to approximate counts of individual fishes moving on scene and obtain a time series of proxy sablefish abundance. Those proxy abundance estimates are among the first to be made using such a large volume of video data from deep-sea settings. We discuss our AI results for application on a decade-long video monitoring program, and particularly with potential for complementing fisheries management practices of a commercially important species.

Depositional environment and genesis of the Paleoproterozoic Astingbulake banded iron formations from the Quruqtagh Block, northeast Tarim Craton

As common marine chemical sedimentary rocks in sequences of Precambrian cratons worldwide, banded iron formations (BIFs) are key repositories of the early Earth’s geological and environmental evolution. The Tarim Craton is one of the major cratons in China and Central Asia, however, little attention has been paid on the BIFs of the Tarim Craton. Here we present new petrographic, bulk rock geochemical and Sm-Nd isotopic data from the poorly-studied Paleoproterozoic Astingbulake BIF in the Quruqtagh Block, north Tarim. The BIF is hosted in the Plaeoproterozoic Xingditage Group and exhibits typical banded structure with layered magnetite- and quartz-rich bands. The elemental composition of the Astingbulake BIF indicates that it is a chemical sediment with a low terrigenous input, but terrigenous materials do not have significant control on the all geochemical budgets of BIF. The positive Eu anomalies (Eu/Eu* = 1.31) and chondritic Y/Ho ratios of 26.4 to 31.4 indicate a hydrothermal fluid contribution to the BIF. The significant negative εNd(t) values (average of −8.0) suggest significant input of older and isotopically evolved continental flux. Therefore, combined with rare earth elementandyttrium and Nd isotope signatures, a mixture of significant contribution from continental-sourced iron source with minor hydrothermal source was suggested. The Astingbulake BIF shows affinity to Superior–type BIFs and was likely deposited on a continental shelf slope where sediments extended from shelf to deep sea settings and distal from the hydrothermal fluid systems. The absence of negative Ce anomalies, coupled with the positive Eu anomalies, indicate deposition in suboxic to anoxic environments. The deposition of the Astingbulake BIF indicates that ferruginous (anoxic and iron-rich) seawater redox conditions were still established in the Paleoproterozoic Tarim basin.

Impact of green clay authigenesis on element sequestration in marine settings

Retrograde clay mineral reactions (reverse weathering), including glauconite formation, are first-order controls on element sequestration in marine sediments. Here, we report substantial element sequestration by glauconite formation in shallow marine settings from the Triassic to the Holocene, averaging 3 ± 2 mmol·cm−²·kyr−1 for K, Mg and Al, 16 ± 9 mmol·cm−²·kyr−1 for Si and 6 ± 3 mmol·cm−²·kyr−1 for Fe, which is ~2 orders of magnitude higher than estimates for deep-sea settings. Upscaling of glauconite abundances in shallow-water (0–200 m) environments predicts a present-day global uptake of ~≤ 0.1 Tmol·yr−1 of K, Mg and Al, and ~0.1–0.4 Tmol·yr−1 of Fe and Si, which is ~half of the estimated Mesozoic elemental flux. Clay mineral authigenesis had a large impact on the global marine element cycles throughout Earth’s history, in particular during ‘greenhouse’ periods with sea level highstand, and is key for better understanding past and present geochemical cycling in marine sediments.

A deep-sea foraminiferal assemblage scattered through the late Cenozoic of Antarctic Peninsula and its biostratigraphic and biogeographic implications

AbstractOur knowledge of the foraminiferal fossil record of Antarctica is notoriously patchy but still offers us an overview of its Cenozoic faunas. Few occurrences have been reported for the continent, with deep-sea assemblages described mainly for its eastern portion. Here we describe 21 taxa of large agglutinated foraminifers from the Miocene Hobbs Glacier Formation and the Plio-Pleistocene Weddell Sea Formation on Seymour Island, West Antarctica, including the gigantic Ammodiscus vastus new species. Most of them consist of genera or species typical of deep-sea agglutinated assemblages. All specimens are completely filled and partially covered by lithified micrite. This, along with the postfill fragmentation of some tests, indicates their re-elaboration from older deposits. Because all of these foraminifers share the same taphonomic features and most of them represent taxa associated with deep-sea settings, they probably represent a flysch-type assemblage from an unknown deposit that was eroded and had its microfossils scattered through post-Paleogene sediments. A Paleocene age for this putative assemblage is indicated by the presence of Reticulophragmiun garcilassoi (Frizzell, 1943), a Paleocene index fossil, and by its association with the Cretaceous–Paleocene Ammodiscus pennyi Cushman and Jarvis, 1928. If taken as a coherent foraminiferal assemblage, it represents one of the few deep-sea assemblages known for West Antarctica, and the first flysch-type assemblage recognized for the Antarctic Cenozoic. In addition, it would show that the Paleocene foraminiferal communities of the West Antarctica's deep-sea floor were more like their Pacific counterparts than their Atlantic equivalents.UUID: http://zoobank.org/0d281489-c0c6-47b4-9884-f820806485b7

Umber as a lithified REY-rich mud in Japanese accretionary complexes and its implications for the osmium isotopic composition of Middle Cretaceous seawater

We report geochemical and isotopic data for umber and related greenstone samples from the Aki umber deposit in the Northern Shimanto Belt, central Shikoku, southwest Japan. The greenstone underlying the umber deposit shows a geochemical signature typical for mid-ocean ridge basalts. Umber samples are characterized by notable enrichments in Fe, Mn, P, V, Co, Ni, and Zn relative to post-Archean average Australian Shale (PAAS). In addition, rare-earth elements and yttrium (REY) are markedly enriched in the umber samples (up to 1120 ppm total REY), and their PAAS-normalized REY patterns are almost identical to those of hydrothermal ferromanganese plume fall-out precipitates (suspended particulates) emanating from a mid-oceanic ridge. These geochemical features suggest that the Aki umber represents a hydrothermal iron oxyhydroxide-type REY-rich mud deposited originally in a pelagic deep-sea setting during the Middle Cretaceous (113.2–100.5 Ma), which was subsequently accreted onto the proto-Japanese Island arc. The initial 187Os/188Os ratios of the Aki umber samples range from 0.554 to 0.668. Because the umbers preserve the primary geochemical signature of hydrothermal Fe-oxyhydroxide-type REY-rich mud deposited near a mid-oceanic ridge, their Os isotopic ratios can be regarded as the marine 187Os/188Os ratios at the time of deposition (Middle Cretaceous). Our results indicate that the Cretaceous marine 187Os/188Os ratios were lower than the present day ratio, probably reflecting more intense hydrothermal activity and/or a lower continental weathering flux during that period. We also suggest that marine Os isotopic compositions during the Middle to Late Cretaceous were relatively constant (0.4–0.6), except during ocean anoxic events.

COMPARATIVE TAPHONOMY OF DEEP-SEA AND SHALLOW-MARINE ECHINOIDS OF THE GENUS ECHINOCYAMUS

ABSTRACT The infaunal living clypeasteroid echinoid genus Echinocyamus is considered a model organism for various ecological and paleontological studies since its distribution ranges from the polar regions to the tropics, and from shallow-marine settings to the deep-sea. Deep-sea analyses of this genus are rare, but imperative for the understanding and function of these important ecosystems. During the 2012 Southern Surveyor expedition, 35 seamounts off the east coast of Australia were dredged in depths greater than 800 m. Of these, six dredges contained a total of 18 deep-sea Echinocyamus tests. The tests have been analyzed for taphonomic alterations including abrasion patterns, macro-borings, micro-borings, depressions on the test, test staining, test filling, encrustation, and fragmentation. Findings are interpreted in the context of the deep-sea setting and are compared to Echinocyamus samples from shallow-water environments. Results show that abrasion in deep-sea environments is generally high, especially in ambulacral and genital pores indicating that tests can persist for a long time on the seafloor. This contrasts with shallow-water Echinocyamus that show lower abrasion due to early test destruction. Macro-borings are present as single or paired holes with straight vertical profiles resembling Lithophaga borings. Micro-borings are abundant and most likely the result of sponge or fungal activity. Depressions on the tests, such as scars or pits, are likely the result of trauma or malformation during ontogeny. Test staining is common, but variable, and is associated with FE/Mn oxidation and authigenic clays based on elemental analyses. Test filling occurs as loose or lithified sediment. Encrustation is present in the form of rudimentary crusts and biofilms. No macro-organisms were found on the tests. Biofilm composition differs from shallow-water environments in that organisms captured in the biofilm reflect aphotic conditions or sedimentation of particles from higher in the water column (e.g., coccoliths). Fragmentation is restricted to the apical system and pore regions. Results of this first comparative study on deep-sea Echinocyamus from Australian seamounts show that the minute tests can survive for a long time in these settings and undergo environmental specific taphonomic processes reflected in various taphonomic alterations.