Deep-sea Sites Research Articles

An Assessment of Environmental Metabarcoding Protocols Aiming at Favoring Contemporary Biodiversity in Inventories of Deep-Sea Communities

The abyssal seafloor covers more than 50% of planet Earth and is a large reservoir of still mostly undescribed biodiversity. It is increasingly targeted by resource-extraction industries and yet is drastically understudied. In such remote and hard-to-access ecosystems, environmental DNA (eDNA) metabarcoding is a useful and efficient tool for studying biodiversity and implementing environmental impact assessments. Yet, eDNA analysis outcomes may be biased toward describing past rather than present communities as sediments contain both contemporary and ancient DNA. Using commercially available kits, we investigated the impacts of five molecular processing methods on eDNA metabarcoding biodiversity inventories targeting prokaryotes (16S), unicellular eukaryotes (18S-V4), and metazoans (18S-V1, COI). As the size distribution of ancient DNA is skewed toward small fragments, we evaluated the effect of removingshort DNA fragments via size selection and ethanol reconcentration using eDNA extracted from 10 g of sediment at five deep-sea sites. We also compare communities revealed by eDNA and environmental RNA (eRNA) co-extracted from ∼2 g of sedimen at the same sites. Results show that removing short DNA fragments does not affect alpha and beta diversity estimates in any of the biological compartments investigated. Results also confirm doubts regarding the possibility to better describe live communities using eRNA. With ribosomal loci, eRNA, while resolving similar spatial patterns than co-extracted eDNA, resulted in significantly higher richness estimates, supporting hypotheses of increased persistence of ribosomal RNA (rRNA) in the environment and unmeasured bias due to overabundance of rRNA and RNA release. With the mitochondrial locus, eRNA detected lower metazoan richness and resolved fewer spatial patterns than co-extracted eDNA, reflecting high messenger RNA lability. Results also highlight the importance of using large amounts of sediment (≥10 g) for accurately surveying eukaryotic diversity. We conclude that eDNA should be favored over eRNA for logistically realistic, repeatable, and reliable surveys and confirm that large sediment samples (≥10 g) deliver more complete and accurate assessments of benthic eukaryotic biodiversity and that increasing the number of biological rather than technical replicates is important to infer robust ecological patterns.

New records of family Hormathiidae (Cnidaria: Actiniaria) from Brazilian coast with description of Paraphelliactis labiata n. sp.

The family Hormathiidae Carlgren, 1932 is one of the largest families of sea anemones with ca. 130 species around the world, mostly in the deep sea. In Brazilian waters, only six species have been reported so far. Herein we record four hormathiids from deep-sea sites at the Potiguar Basin continental slope at Northeast Brazil. Monactis vestita (Gravier, 1918) and Phelliactis robusta Carlgren, 1928 represent the first records of both genera for the Brazilian coast. The new species Paraphelliactis labiata n. sp. is described. We also found another species of the genus, Phelliactis sp. The new species possesses fourth and fifth cycles of incomplete mesenteries, unlike all other Paraphelliactis species. These results increase the total number of hormathiid sea anemones in Brazil to nine and contribute to the knowledge of the Brazilian deep sea, still little explored.

Rethinking the chronology of early Paleogene sediments in the western North Atlantic using diatom biostratigraphy

Ocean Drilling Program (ODP) Site 1051 (Blake Nose, western North Atlantic) is of crucial importance for reconstructing diatom evolution and biosiliceous sedimentation patterns through the early Cenozoic period of extreme greenhouse warmth followed by the progressive global cooling. The magnetostratigraphy in Hole 1051A, however, has been subject to divergent interpretations resulting in multi-million-year age control uncertainties, especially for events surrounding the early to middle Eocene transition. To resolve these uncertainties, we compare the stratigraphy of Hole 1051A to the neighboring Holes 1050A, C. We compile the published biomagnetostratigraphic data for both sites and identify three possible magnetostratigraphic solutions for Hole 1051A, the difference being the number of hiati and their duration. In order to identify the most plausible magnetostratigraphic solution for Hole 1051A, we employ the graphic correlation method, in which we compare the depth of individual magnetic reversals in both study sites against an independent proxy, i.e., 49 diatom evolutionary events identified in Holes 1050A,C and 1051A. The distribution of diatom bioevents lends strong support to the presence of two major hiati in both study sites: the upper hiatus juxtaposes magnetozone C21n on C22n, and the lower hiatus juxtaposes magnetozone C23n on C24n, eliminating the record of the initial part of the Early Eocene Climatic Optimum. Diatom, calcareous nannofossil and foraminiferal biostratigraphic markers also indicate that Hole 1051A terminated within magnetozone C28n rather than C27n. This age interpretation is strongly supported by the alignment of high-resolution weight percent biogenic SiO2 records from both study sites. The revised age models developed here for Holes 1050A,C and 1051A have profound consequences for interpretations of western North Atlantic paleoceanographic and paleoclimatic history through the early Paleogene. We propose a revised labelling of the early Eocene carbon cycle perturbations identified to date in Hole 1051A, and show how published Blake Nose δ30Si records change when data from Sites 1050 and 1051 are rescaled to the age models proposed herein. We emphasize that these refinements to the stratigraphy of Sites 1050 and 1051 are based on a study of diatom bioevents, which are here identified and calibrated to the Geomagnetic Polarity Timescale. This successful application of diatom biostratigraphy is a substantial advance toward their future utility in providing high-resolution age control for Paleogene deep-sea sites.

Coccolithophore export in three deep-sea sites of the Aegean and Ionian Seas (Eastern Mediterranean): Biogeographical patterns and biogenic carbonate fluxes

Coccolithophore export fluxes were investigated via the analysis of sinking matter, obtained from Eastern Mediterranean time-series sediment traps moored in three open sites of the north-eastern Mediterranean Sea located in the Athos Basin of North Aegean (M2 site), Cretan Sea of South Aegean (M3 site) and at Ionian Sea (Nestor site). The aim of our study was to determine the spatial, temporal and seasonal variability in coccolithophore fluxes, as well as to estimate coccolith biogenic carbonate contribution to the sedimentation process. Data from an additional time-series sediment trap located in the southwestern Black Sea were also considered for the comparison of the oligotrophic Eastern Mediterranean setting with the eutrophic Black Sea. Coccolithophore fluxes revealed a highly seasonal pattern during February–March in the North Aegean (peak in late February 2015: 85.6 x 105 coccospheres m−2 day−1; 27.9 x 108 coccoliths m−2 day−1), during March–May in the Cretan Sea (peak in late March 2015: 33.7 x 105 coccospheres m−2 day−1; 19.5 x 108 coccoliths m−2 day−1) and during February–March and May–June in the Ionian Sea (peak in late May 2012: 14.3 x 105 coccospheres m−2 day−1; 1.53 x 108 coccoliths m−2 day−1). The recorded maxima coincide with low sea surface temperatures, increased precipitation and high PIC fluxes. Coccosphere fluxes were dominated by Emiliania huxleyi comprising ~70% of the total abundance, in the North Aegean and ~50% in the Cretan and Ionian Seas. Syracosphaera pulchra was also prominent in the study sites, where its abundance reached 14% in the North Aegean and ~10% in the Cretan and Ionian Seas respectively. Florisphaera profunda represented one of the major taxa in the coccolith fluxes of all three Eastern Mediterranean sites (~25% in North Aegean, ~20% in Cretan and Ionian Seas), while Algirosphaera robusta and Umbilicosphaera sibogae were the most abundant among the minor taxa. The North Aegean Sea exhibited a considerably higher coccolith flux when compared to other sediment traps due to the prominent seasonal peak of E. huxleyi during winter (February–March) (>95% of the total abundance). In contrast to the Eastern Mediterranean sediment traps, the time-series data from the Black Sea showed presence of monospecific E. huxleyi assemblage increasing its abundance during late September–November (max 320 x 105 coccospheres m−2 day−1; at least 7.79 x 108 coccoliths m−2 day−1, coccolith flux derived only from coccospheres converted to coccoliths). In the Eastern Mediterranean, biogenic carbonate fluxes followed the general pattern of the total mass flux in all investigated areas, with the Black Sea coccolithophore CaCO3 flux being the lowest due to low the E. huxleyi coccolith mass. Overall, in the North Aegean Sea, coccolithophore fluxes are strongly dependent on surface waters nutrients enrichment due to winter vertical water column mixing, riverine inputs and Black Sea water inflows, while the fertilization and/or formation of fast-sinking aggregates due to episodic dust input event are affecting the coccolithophore fluxes in the Cretan and Ionian Seas. The intercomparison of the coccolith export fluxes in the studied NE-SW mooring transects implies a north-south and east-west decreasing pattern, depending on the variable oceanographic regimes and the associated environmental factors controlling the investigated areas.

A lower to middle Eocene astrochronology for the Mentelle Basin (Australia) and its implications for the geologic time scale

The geologic time scale for the Cenozoic Era has been notably improved over the last decades by virtue of integrated stratigraphy, combining high-resolution astrochronologies, biostratigraphy and magnetostratigraphy with high-precision radioisotopic dates. However, the middle Eocene remains a weak link. The so-called “Eocene time scale gap” reflects the scarcity of suitable study sections with clear astronomically-forced variations in carbonate content, primarily because large parts of the oceans were starved of carbonate during the Eocene greenhouse. International Ocean Discovery Program (IODP) Expedition 369 cored a carbonate-rich sedimentary sequence of Eocene age in the Mentelle Basin (Site U1514, offshore southwest Australia). The sequence consists of nannofossil chalk and exhibits rhythmic clay content variability. Here, we show that IODP Site U1514 allows for the extraction of an astronomical signal and the construction of an Eocene astrochronology, using 3-cm resolution X-Ray fluorescence (XRF) core scans. The XRF-derived ratio between calcium and iron content (Ca/Fe) tracks the lithologic variability and serves as the basis for our U1514 astrochronology. We present a 16 million-year-long (40-56 Ma) nearly continuous history of Eocene sedimentation with variations paced by eccentricity and obliquity. We supplement the high-resolution XRF data with low-resolution bulk carbon and oxygen isotopes, recording the long-term cooling trend from the Paleocene-Eocene Thermal Maximum (PETM – ca. 56 Ma) into the middle Eocene (ca. 40 Ma). Our early Eocene astrochronology corroborates existing chronologies based on deep-sea sites and Italian land sections. For the middle Eocene, the sedimentological record at U1514 provides a single-site geochemical backbone and thus offers a further step towards a fully integrated Cenozoic geologic time scale at orbital resolution.

Heterotrophic metabolism of C1 and C2 low molecular weight compounds in northern Gulf of Mexico sediments: Controlling factors and implications for organic carbon degradation

Low molecular weight (LMW) compounds are key intermediates in organic matter degradation and their metabolism supports a diverse microbial community in anoxic sediments. Much remains to be learned about the metabolic pathways and turnover rates of LMW compounds as well as the factors that influence their metabolism in the environment. We studied the microbial metabolism of acetate, methanol and methylamine in sediments from Northern Gulf of Mexico to elucidate their role as energy and carbon sources for microorganisms mediating terminal metabolic processes and to constrain the importance of C1 and C2 metabolism in the sedimentary carbon cycle. In terms of carbon flow, methanogenesis was a minor process in sulfate-rich sediments; acetate and methanol were oxidized primarily by non-methanogenic heterotrophs as an energy source. A large fraction of utilized acetate (20–76%) was assimilated into biomass, suggesting that acetate was a significant biomass-building source. In situ thermodynamic calculations suggested the utilization of acetate and methanol by sulfate-reducing bacteria was more favorable than the utilization by methanogens, consistent with the observed higher oxidation rates than methanogenesis rates as well as results from inhibitor experiments employing 2-bromoethanesulfonate and molybdate. Methylamine, by contrast, was utilized for methane production (up to 100%), but its utilization was not limited to methanogens. At an organic-poor deep-sea site, elevated acetate and methanol oxidation rates in the absence of sulfate-reducing and methanogenic activity indicated that metabolism of LMW compounds was coupled to other electron accepting processes, such as denitrification. Heterotrophic carbon assimilation was an important pathway for generating biomass at this site, as evidenced by comparable rates of acetate assimilation to bicarbonate incorporation. The oxidation and assimilation rates of LMW compounds generally decreased with sediment depth, following the trend of organic carbon degradation rates. Environmental factor, such as temperature but not pressure, affected the metabolism of LMW compounds; the oxidation of acetate, methanol and methylamine exhibited distinct responses to changes in temperature. In seep sediments, the oxidation of acetate and methanol accounted for 5% and 0.9%, respectively, of the total organic carbon oxidation. Collectively, this assessment of C1 and C2 LMW compound utilization shows that these compounds serve as energetic substrates to fuel methanogens, sulfate reducers and other microbes.

The planktonic foraminiferal response to the Paleocene-Eocene thermal maximum on the Atlantic coastal plain

Abstract Planktonic foraminiferal assemblages in two cores from Maryland and New Jersey show evidence for significant changes in surface ocean habitats on the continental shelf during the Paleocene-Eocene Thermal Maximum (PETM). At both sites, significant assemblage shifts occur immediately before the onset of the event. These changes include the appearance of abundant triserial/biserial species as well as rare excursion taxa, which are limited to the interval of the carbon isotope excursion at deep-sea sites. The assemblage shifts signal the development of new habitats immediately prior to the onset of the PETM, likely involving warming, surface ocean acidification, increased stratification and oligotrophy. A sharp increase in diversity at the onset of the event is interpreted as a further increase in stratification and warming, as well as increased water depth and more eutrophic conditions. Finally, we observe variant morphologies of several planktonic foraminifera, which may also signal the response of the assemblage to environmental perturbation.

Slope-shelf faunal link and unreported diversity off Nova Scotia: Evidence from polychaete data

Deep-water sedimentary habitats off Nova Scotia have only rarely been explored. The topographically and oceanographically complex shelf of Nova Scotia harbours two interesting topographic features, Emerald Basin, a sedimentary habitat reaching greater depths (max of 270 m) than the surrounding shelf and the Gully, the largest canyon in NW Atlantic. Emerald Basin is exposed to upwellings of slope water and harbours predominantly deep-sea hexactinellid sponges. Such distributional pattern resembles “deep-water emergence”. In this study an abundant benthic group, the polychaetes, were selected to test for such deep-water faunal link. Qualitative boxcores were collected from Emerald Basin (180 m depth, N = 5) and the adjacent Gully Canyon (1600 m, N = 3). At species level, there was no overlap in distribution between Emerald Basin (N = 73, S=29) and Gully Canyon (N = 351, S = 60) fauna based on morphological assessment of all specimens and molecular analysis (COI and 16S markers) of selected morphotypes. In an alternative approach, Multivariate analysis (nMDS, Cluster Analysis) of incidence data for polychaete genera (N = 179) from 24 Atlantic sites (5–1600 m) was carried out. These results showed a greater similarity of Emerald Basin polychaetes to bathyal sites (400–1000 m), particularly the 680 m site off Nova Scotia rather than shelf sites (5–80 m), including those on the Nova Scotia shelf. Thus, at 1600 m, the Gully Canyon samples were likely “too deep” for our comparative purposes and depths of < 1000 m should be targeted in the future.Our data also provide the first published assessment of polychaete diversity from the Gully Canyon, suggesting the presence of a diverse assemblage (S = 60). Unusually for a deep-sea site, the Gully Canyon polychaetes are mostly known taxa with wider distribution across bathyal NW Atlantic. Additionally, our molecular data provide an interesting insights into the distribution of several polychaete species commonly found in deep-sea (e.g Aurospio dibranchiata Maciolek, 1981; Ophelina abranchiata Støp-Bowitz, 1948) suggesting wide geographical distribution for some but revealing species complexes for others.

Successive transitory distribution of Thaumarchaeota and partitioned distribution of Bathyarchaeota from the Pearl River estuary to the northern South China Sea.

Thaumarchaeota and Bathyarchaeota (formerly named Miscellaneous Crenarchaeotal Group, MCG) are globally occurring archaea playing potential roles in nitrogen and carbon cycling, especially in marine benthic biogeochemical cycle. Information on their distributional and compositional patterns could provide critical clues to further delineate their physiological and biochemical characteristics. Profiles of thaumarchaeotal and the total archaeal community in the northern South China Sea surface sediments revealed a successively transitional pattern of Thaumarchaeota composition using MiSeq sequencing. Shallow-sea sediment enriched phylotypes decreased gradually along the slope from estuarine and coastal marine region to the deep-sea, while deep-sea sediment enriched phylotypes showed a trend of increasing. Proportion of Thaumarchaeota within the total archaea increased with seawater depth. Phylotypes enriched in shallow- and deep-sea sediments were affiliated to OTUs originated from similar niches, suggesting that physiological adaption not geographical distance shaped the distribution of Thaumarchaeota lineages. Quantitative PCR also depicted a successive decrease of thaumarchaeotal 16S rRNA gene abundance from the highest at shallow-sea sites E708S and E709S (2.57 × 106 and 2.73 × 106genecopies/g of dry sediment) to the lowest at deep-sea sites E525S and E407S (1.97 × 106 and 2.14 × 106genecopies/g of dry sediment). Both of the abundance fractions of Bathyarchaeota subgroups (including subgroups 1, 6, 8, 10, 13, 15, 17, and ungrouped Bathyarchaeota) and the total Bathyarchaeota in the total archaea showed a negative distribution to seawater depth. Partitioned distribution of Bathyarchaeota fraction in the total archaea is documented for the first time in this study, and the shallow- and deep-sea Bathyarchaeota could account for 17.8 and 0.8%, respectively, on average. Subgroups 6 and 8, enriched subgroups in shallow-sea sediments, largely explained this partitioned distribution pattern according to seawater depth. Their prevalence in shallow-sea and suboxic estuarine sediments rather than deep-sea sediments hints that their metabolic properties of carbon metabolism are adapted to carbon substrates in these environments.

The benthic Copepoda (Crustacea) of Anaximenes Seamount (eastern Mediterranean Sea)—Community structure and species distribution

During research cruise M71/1 of German FV METEOR in winter 2006, meiofauna sampling was undertaken on the eastern Mediterranean Anaximenes Seamount at six sites (the summit, northern slope, north-western slope, north-western base, north-eastern slope and eastern base). Analysis of the benthic Copepoda (i.e. Harpacticoida and Canuelloida) revealed a highly diverse fauna. This is in contrast to what is generally considered an impoverished bathyal and abyssal fauna in the surrounding eastern Mediterranean Sea: It is regarded as one of the most oligotrophic regions of the world’s oceans. This is attested to by comparison of the seamount fauna with that of a remote deep-sea (“Far-field”) site in the Rhodes Basin, which presented a clearly impoverished fauna with respect to abundance, higher-taxon diversity and species diversity. Comparison of sites across the seamount found no overall “seamount community” of benthic Copepoda. Instead, three different assemblages could be detected, with abundance and species diversity comparable to north-eastern Atlantic seamounts and islands. Regarding species composition, however, only four of the recorded species are shared with other Mediterranean and Atlantic elevations. The benthic copepod fauna at Anaximenes Seamount is composed mostly by “typical” deep-sea and eurybathic species, whilst “typical” shallow-water species were absent. Thus, it is concluded that Anaximenes Seamount does not play a role in the dispersal of shallow-water benthic Copepoda. Nonetheless, it appears important for the establishment of abundant and diverse deep-sea communities. Moreover, it constitutes no barrier for the dispersal of deep-sea benthic Copepoda in the Mediterranean.

Integration and Curation of At-Risk Collections into the Scripps Institution of Oceanography Collections

The Scripps Institution of Oceanography (SIO) at the University of California, San Diego maintains one of the largest combined oceanographic collections in the world comprising four collections: Geological (sediment cores and dredged rocks), Pelagic Invertebrates, Benthic Invertebrates and Marine Vertebrates. After surviving threats of dissolution, the SIO Collections are now securely funded and have been able to make other collections available to the scientific community. Over the last few years, both the Marine Vertebrate (SIO-MVC) and Benthic Invertebrate (SIO-BIC) Collections have received National Science Foundation (NSF) and institutional funding to integrate important at-risk collections from University of California, Los Angeles (UCLA), the Monterey Bay Aquarium Research Institute (MBARI) and the University of Victoria. The UCLA Ichthyological Collection, around 9000 lots, was at risk of disposal due to hazardous material concerns and lack of institutional support. The collection, accumulated primarily under Boyd Walker (1949-1980) and later Don Buth (1980-), contains material from extensive surveys of the near-shore fishes of Southern California, Baja California and the Tropical Eastern Pacific including remote oceanic islands such as the Revillagigedos, Clipperton and the Galapagos. The UCLA collection also contains over 150 secondary types and over 100 species new to the SIO-MVC. Due to lack of support, the collection records were never digitized and the collection was minimally curated and its holdings were poorly known. For over two years, the collection manager and student employees have physically re-curated and integrated this material into the SIO-MVC. These data are now available online via iDigBio and VertNet and have already been used in numerous studies. The SIO-BIC, holding 45,000 lots, is accepting ownership of two deep-sea animal collections from Verena Tunnicliffe at the University of Victoria and Robert Vrijenhoek at MBARI. These collections include 10,900+ lots, largely from hydrothermal vents across the Pacific. Collected over 35 years from remote deep-sea sites that are difficult and expensive to access, these collections represent a major resource for systematics, genetics, and ecology. With Dr. Vrijenhoek now retired and Dr. Tunnicliffe nearing retirement, their collections were at risk of being lost. This material will be made discoverable online through the SIO-BIC database and iDigBio, and will be available for loan and examination. In the last year, the collection manager and five undergraduate employees have integrated some 3,000 lots. With support from the institution and the NSF, the SIO collections are solidifying their roles as central repositories for deep-sea and Eastern Pacific fauna.

The last Eocene hyperthermal (Chron C19r event, ~41.5 Ma): Chronological and paleoenvironmental insights from a continental margin (Cape Oyambre, N Spain)

The last hyperthermal event in the Eocene, the Late Lutetian Thermal Maximum or Chron C19r event, took place at ~41.5 Ma, during a long-term global cooling phase which occurred between the warm Early Eocene Climatic Optimum and the icehouse Oligocene Epoch. This paleoclimatic event was first identified in the Equatorial Atlantic Ocean Drilling Program (ODP) Site 1260 as an abrupt peak in bulk Fe content and a short-lived decline in stable isotopes (δ13C, δ18O) and carbonate content. Additional studies have recently been carried from the Southern Atlantic ODP sites 702 and 1263. However, many issues were not addressed at these deep-sea sites and no land-based record of the event had been studied. Therefore, the beach cliff at Cape Oyambre (N Spain) was analyzed with the aim of identifying the C19r event and investigating its paleoenvironmental impact. Using magnetostratigraphic and biostratigraphic information, the astronomically tuned cyclo-stratigraphic record from Oyambre was accurately correlated with ODP Site 1260. This, combined with stable isotope data, allowed identification of the event in a conspicuous dark marl bed. Given that the associated negative carbon isotope excursion extends for 2/3 of a precession-driven hemicouplet, a 7–11 kyr duration was estimated, which agrees with recent estimates from the Atlantic deep-sea sites. Exceptional insolation conditions were found to have accelerated the hydrological cycle, increasing rainfall and runoff on land and terrestrial sediment input to the sea, which resulted in relatively low carbonate content in the deep-sea sediments. The terrestrial input also caused seawater eutrophication and freshening, leading to low δ13C and δ18O values, increased abundance of autochthonous and reworked calcareous nannofossil taxa, peaks in the abundance of opportunistic Reticulofenestra <5 μm and opportunistic benthic foraminifera, and a reduction in the abundance of the oligotrophic calcareous nannofossil Zygrhablithus bijugatus. However, neither intensified carbon-gas driven greenhouse effect nor warming over and above natural fluctuations could be demonstrated from the Oyambre data.

The rise and fall of the Cretaceous Hot Greenhouse climate

Abstract A compilation of foraminiferal stable isotope measurements from southern high latitude (SHL) deep-sea sites provides a novel perspective important for understanding Earth's paleotemperature and paleoceanographic changes across the rise and fall of the Cretaceous Hot Greenhouse climate and the subsequent Paleogene climatic optimum. Both new and previously published results are placed within an improved chronostratigraphic framework for southern South Atlantic and southern Indian Ocean sites. Sites studied were located between 58° and 65°S paleolatitude and were deposited at middle to upper bathyal paleodepths. Oxygen isotope records suggest similar trends in both bottom and surface water temperatures in the southern sectors of the South Atlantic and in the Indian Ocean basins. Warm conditions were present throughout the Albian, extreme warmth existed during the Cretaceous Thermal Maximum (early-mid-Turonian) through late Santonian, and long-term cooling began in the Campanian and culminated in Cretaceous temperature minima during the Maastrichtian. Gradients between surface and seafloor δ18O and δ13C values were unusually high throughout the 11.5 m.y. of extreme warmth during the Turonian-early Campanian, but these vertical gradients nearly disappeared by the early Maastrichtian. In absolute terms, paleotemperature estimates that use standard assumptions for pre-glacial seawater suggest sub-Antarctic bottom waters were ≥21 °C and sub-Antarctic surface waters were ≥27 °C during the Turonian, values warmer than published climate models support. Alternatively, estimated temperatures can be reduced to the upper limits of model results through freshening of high latitude waters but only if there were enhanced precipitation of water with quite low δ18O values. Regardless, Turonian planktonic δ18O values are ~1.5‰ lower than minimum values reported for the Paleocene-Eocene Thermal Maximum (PETM) from the same region, a difference which corresponds to Turonian surface temperatures ~6 °C warmer than peak PETM temperatures if Turonian and Paleocene temperatures are estimated using the same assumptions. It is likely that warm oceans surrounding and penetrating interior Antarctica (given higher relative sea level) prevented growth of Antarctic ice sheets at all but the highest elevations from the late Aptian through late Campanian; however, Maastrichtian temperatures may have been cool enough to allow growth of small, ephemeral ice sheets. The standard explanation for the sustained warmth during Cretaceous Hot Greenhouse climate invokes higher atmospheric CO2 levels from volcanic outgassing, but correlation among temperature estimates, proxy estimates of pCO2, and intervals of high fluxes of both mafic and silicic volcanism are mostly poor. This comparison demonstrates that the relative timing between events and their putative consequences need to be better constrained to test and more fully understand relationships among volcanism, pCO2, temperature ocean circulation, Earth's biota and the carbon cycle.

Reverse weathering in marine sediments and the geochemical cycle of potassium in seawater: Insights from the K isotopic composition (41K/39K) of deep-sea pore-fluids

In situ Al-silicate formation, also known as “reverse weathering,” is an important sink of many of the major and minor cations in seawater (e.g. Mg, K, and Li). However, the importance of this sink in global geochemical cycles and isotopic budgets of these elements remains poorly constrained. Here, we report on the potassium isotopic composition (41K/39K) of deep-sea sediment pore-fluids from four (Integrated) Ocean Drilling Program sites (1052, U1378, U1395 and U1403) to characterize potassium isotopic fractionation associated with the formation of authigenic Al-silicate minerals in marine sediments and its role in elevating the 41K/39K of seawater relative to bulk silicate Earth. Isotopic ratios are obtained by high-resolution multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) in cold plasma conditions with a long-term external reproducibility of ca. 0.17‰. We find that, although all sites are characterized by pore-fluid K concentrations that decline with increasing depth, their K isotopic profiles vary systematically from site-to-site; at sites characterized by rapid sedimentation rates, pore-fluid profiles of 41K/39K are relatively invariant whereas at sites characterized by slow sedimentation rates, 41K/39K declines with depth by up to 1.8‰. Results from 1-D diffusion-advection-reaction models suggest that these differences may result from a complex interplay between sedimentation rate and fractionation of K isotopes during diffusion, Al-silicate authigenesis, and ion exchange. Model simulations suggest fractionation factors between 0.9980 and 1.0000 for reverse weathering reactions in deep-sea sediments. Although deep-sea sites do not constitute major sinks of K in seawater, some of the processes responsible for K isotopic fractionation at these sites (diffusion and Al-silicate authigenesis) likely play a role in determining the 41K/39K of seawater.

Living (stained) deep-sea foraminifera from the Sea of Marmara: A preliminary study

In this preliminary study, we investigate living (stained) foraminifera from the Sea of Marmara. We focus on the faunal composition and geochemical signatures (trace elements, carbon and oxygen stable isotopes) in foraminiferal tests at two deep-sea sites (329 and ~ 1240m depth respectively). Documented by ROV observations and sampling, both study areas are heterogeneous (including bacterial mats and carbonate concretions), proximal to cold seeps and consist of dysoxic bottom water (O2 < 20µmol/L). The prevailing dysoxia at both study areas restricts foraminiferal diversity to very low values (S < 9, H’ < 0.97). Stress-tolerant species Bolivina vadescens and Globobulimina affinis dominate living faunas at both sites. The highest foraminiferal standing stock is recorded at the shallowest site underneath a spreading bacterial mat. No benthic foraminifera from either site possess geochemical signatures of methane seepage. Our biogeochemical results show that use of foraminiferal Mn/Ca ratios as a proxy for bottom water oxygenation depends strongly on regional physiography, sedimentary processes and water column structure.

From virus isolation to metagenome generation for investigating viral diversity in deep-sea sediments

Viruses are the most abundant and, likely, one of the most diverse biological components in the oceans. By infecting their hosts, they play key roles in biogeochemical cycles and ecosystem functioning at a global scale. The ocean interior hosts most of the microbial life, and, despite deep-sea sediments represent the main repository of this component and the largest biome on Earth, viral diversity in these ecosystems remains almost completely unknown. We compared a physical-chemical procedure and a previously published sediment washing-based procedure for isolating viruses from benthic deep-sea ecosystems to generate viromes through high-throughput sequencing. The procedure based on a physical-chemical dislodgment of viral particles from the sediments, followed by vacuum filtration was much more efficient allowing us to recover >85% of the extractable viruses. By using this procedure, a high fraction of viral DNA was recovered and new viromes from different benthic deep-sea sites were generated. Such viromes were diversified in terms of both viral families and putative functions. Overall, the results presented here provide new insights for evaluating benthic deep-sea viral diversity through metagenomic analyses, and reveal that deep-sea sediments are a hot spot of novel viral genotypes and functions.

Authigenic minerals from the Paola Ridge (southern Tyrrhenian Sea): Evidences of episodic methane seepage

Paola Ridge, along the NW Calabrian margin (southern Tyrrhenian Sea), is one of the few reported deep sea sites of precipitation of authigenic carbonates in the Tyrrhenian Sea. Here, the changing composition of the seeping fluids and the dynamic nature of the seepage induced the precipitation of pyrite, siderite and other carbonate phases. The occurrence of this array of authigenic precipitates is thought to be related to fluctuation of the sulfate-methane transition zone (SMTZ).Concretions of authigenic minerals formed in the near sub-bottom sediments of the Paola Ridge were investigated for their geochemical and isotopic composition. These concretions were collected in an area characterized by the presence of two alleged mud volcanoes and three mud diapirs. The mud diapirs are dotted by pockmarks and dissected by normal faults, and are known for having been a site of fluid seepage for at least the past 40 kyrs. Present-day venting activity occurs alongside the two alleged mud volcanoes and is dominated by CO2-rich discharging fluids. This discover led us to question the hypothesis of the mud volcanoes and investigate the origin of the fluids in each different domed structure of the study area.In this study, we used stable isotopes (carbon and oxygen) of carbonates coupled with rare earth element (REE) composition of different carbonate and non-carbonate phases for tracing fluid composition and early diagenesis of authigenic precipitates. The analyses on authigenic precipitates were coupled with chemical investigation of venting gas and sea-water.Authigenic calcite/aragonite concretions, from surficial sediments on diapiric structures, have depleted 13C isotopic composition and slightly positive δ18O values. By contrast, siderite concretions, generally found within the first 6 m of sediments on the alleged mud volcanoes, yielded positive δ13C and δ18O values. The siderite REE pattern shows consistent LREE (light REE) fractionation, MREE (medium REE) enrichment and positive Gd and La anomalies. As shown by the REE distribution, the 13C-depleted composition and their association with chemosymbiotic fauna, calcite/aragonite precipitated at time of moderate to high methane flux close to the seafloor, under the influence of bottom seawater. Authigenic siderite, on the other hand, formed in the subseafloor, during periods of lower gas discharges under prolonged anoxic conditions within sediments in equilibrium with 13C-rich dissolved inorganic carbon (DIC) and 18O-rich water, likely related to methanogenesis and intermittent venting of deep-sourced CO2.

Complexity in Matuyama–Brunhes polarity transitions from North Atlantic IODP/ODP deep-sea sites

Integrated Ocean Drilling Program (IODP) Expedition 303 to the North Atlantic provided 16 records of the Matuyama–Brunhes polarity transition (MBT), based on u-channel and discrete samples, from holes drilled at three sites (Sites U1304, U1305 and U1306) that have mean Brunhes sedimentation rates of 16–18 cm/kyr. The MBT occurs during the transition from marine isotope stage (MIS) 19c to MIS 18e, with mid-point at ∼773 ka, and a transition duration of ∼8 kyr. Combining the new MBT records, including one new record for the top Jaramillo, with previously published North Atlantic MBT records (ODP Sites 983, 984 and 1063) yields a total of more than 20 high-sedimentation-rate polarity transition records. The MBT yields a repetitive pattern of transitional field states as virtual geomagnetic poles (VGPs) move from high southern latitudes to loop over the Pacific, group in NE Asia, and transit into the mid-latitude South Atlantic before reaching high latitudes in the Northern Hemisphere. The VGPs for the top Jaramillo transition feature a loop over the Pacific, then a NE Asia group before transit over the Indian Ocean to high southerly latitudes. The North Atlantic MBT records described here contrast with longitudinally-constrained VGP paths for the MBT, indicating that relatively low sedimentation rate (∼4 cm/kyr) records of the MBT are heavily smoothed by the remanence acquisition process and do not adequately represent the MBT field. The VGPs at the MBT and top Jaramillo, as measured in the North Atlantic, have similarities with excursion (Iceland Basin) VGP paths, and were apparently guided by maxima in downward vertical flux similar to those seen in the modern non-dipole (ND) field, implying longevity in ND features through time.

Local effects of large food-falls on nematode diversity at an arctic deep-sea site: Results from an in situ experiment at the deep-sea observatory HAUSGARTEN

To study the response of the smaller benthic biota to larger food-falls and their possible effects on the biodiversity at the deep seafloor, we deployed the halves of a sagittally bisected porpoise (1.3m in length; each half approximately 18kg) at 2500m and 5400m water depth at the LTER (Long-Term Ecological Research) observatory HAUSGARTEN in the eastern Fram Strait. Five weeks after the porpoise deployment, sediments beneath the carcasses and at different distances (0, 20, 40cm) from these artificial food-falls were sampled with push-corers handled by a Remotely Operated Vehicle. The samples provided empirical evidence for a quick response by sediment-inhabiting bacteria and metazoan meiofauna to the carcasses at both water depths. Compared to control sediments, the substantial pulse of organic matter also led to generally increased meiofauna/nematode densities around the artificial food-falls. The comparison of nematode communities in sediments affected by the carcasses with those in control sediments exhibited shifts in the structural composition and the associated trophic and functional diversity of the nematodes. Our results confirmed that the impact of large food-falls on the deep benthic community largely depend on environmental factors (water depth, alternative food sources) as well as the background species composition, i.e., the structure of the prevailing meiofauna/nematode assemblages and the composition of the necrophagous community present in the wider area.

Results and simulation of the prototype detection unit of KM3NeT-ARCA

KM3NeT-ARCA is a deep sea high energy neutrino detector. A detection unit prototype was deployed in the future KM3NeT-ARCA deep-sea site, off of the Sicilian coast. This detection unit is composed of a line of 3 digital optical modules with 31 photomultiplier tubes on each one. The prototype detection unit was operated since its deployment in May 2014 until its decommissioning in July 2015. The results of the calibration of this detection unit and its simulation are presented and discussed.