First documented record of a living solemyid bivalve in a pockmark of the Nile Deep-sea Fan (eastern Mediterranean Sea)

A living specimen of a solemyid bivalve was collected at bathyal depths near a pockmark in the Nile Deep-sea Fan (eastern Mediterranean) and is here presented. Both taxonomic and molecular results suggest a Solemya species but due to the small size of the animal and the lack of molecular data for other solemyid species the species cannot be determined. This is the first record of a living solemyid from deep-sea cold seeps in the Mediterranean Basin.FCT - SFRH/ BPD/64154/2009ANR DEEP-OASES - ANRO6BDV005CHEMECO ESF EURODEEPMPG-CNRS-GDRE - DIWOO

Episodic methane concentrations at seep sites on the upper slope Opouawe Bank, southern Hikurangi Margin, New Zealand

Along many active and some passive margins cold seeps are abundant and play an important role in the mechanisms of methane supply from the subsurface into seawater and atmosphere. With numerous cold seeps already known, the convergent Hikurangi Margin east of North Island, New Zealand, was selected as a target area for further detailed, multidisciplinary investigation of cold seeps within the New Vents and associated projects. Methane and temperature sensors (METS) were deployed at selected seep sites on the Opouawe Bank off the southeastern tip of North Island and near the southern end of the imbricate-thrust Hikurangi Margin, together with seismic ocean bottom stations. They remained in place for about 48 h while seismic data were collected. The seeps were associated with seep-related seismic structures. Methane concentrations were differing by an order of magnitude between neighbouring stations. The large differences at sites only 300 m apart, demonstrate that the seeps were small scale structures, and that plumes of discharged methane were very localised within the bottom water. High methane concentrations recorded at active seep sites at anticlinal structures indicate focused fluid flow. Methane discharge from the seafloor was episodic, which may result from enhanced fluid flow facilitated by reduced hydrostatic load at low tides. The strong semi-diurnal tidal currents also contribute to the fast dilution and mixing of the discharged methane in the seawater. Despite dispersal by currents, fluid flow through fissures, fractures, and faults close to the METS positions and tidal fluctuations are believed to explain most of the elevated methane concentrations registered by the METS. Small earthquakes do not appear to be correlated with seawater methane anomalies

Tubular carbonate concretions as hydrocarbon migration pathways? Examples from North Island, New Zealand

Cold seep carbonate deposits are associated with the development on the sea floor of distinctive chemosyn¬thetic animal communities and carbonate minerali¬sation as a consequence of microbially mediated anaerobic oxidation of methane. Several possible sources of the methane exist, identifiable from the carbon isotope values of the carbonate precipitates. In the modern, seep carbonates can occur on the sea floor above petroleum reservoirs where an important origin can be from ascending thermogenic hydrocar¬bons. The character of geological structures marking the ascent pathways from deep in the subsurface to shallow subsurface levels are poorly understood, but one such structure resulting from focused fluid flow may be tubular carbonate concretions. Several mudrock-dominated Cenozoic (especially Miocene) sedimentary formations in the North Island of New Zealand include carbonate concretions having a wide range of tubular morphologies. The concretions are typically oriented at high angles to bedding, and often have a central conduit that is either empty or filled with late stage cements. Stable isotope analyses (δ13C, δ18O) suggest that the carbonate cements in the concretions precipitated mainly from ascending methane, likely sourced from a mixture of deep thermogenic and shallow biogenic sources. A clear link between the tubular concretions and overlying paleo-sea floor seep-carbonate deposits exists at some sites. We suggest that the tubular carbonate concretions mark the subsurface plumbing network of cold seep systems. When exposed and accessible in outcrop, they afford an opportunity to investigate the geochemical evolution of cold seeps, and possibly also the nature of linkages between subsurface and surface portions of such a system. Seep field development has implications for the characterisation of fluid flow in sedimentary basins, for the global carbon cycle, for exerting a biogeochemical influence on the development of marine communities, and for the evaluation of future hydrocarbon resources, recovery, and drilling and production hazards. These matters remain to be fully assessed within a petroleum systems framework for New Zealand’s Cenozoic sedimentary basins

Discovery and mapping of the Triton seep site, Redondo Knoll: fluid flow and microbial colonization within an oxygen minimum zone

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Wagner, J. K. S., Smart, C., & German, C. R. Discovery and mapping of the Triton seep site, Redondo Knoll: fluid flow and microbial colonization within an oxygen minimum zone. Frontiers in Marine Science, 7, (2020): 108, doi:10.3389/fmars.2020.00108.This paper examines a deep-water (∼900 m) cold-seep discovered in a low oxygen environment ∼30 km off the California coast in 2015 during an E/V Nautilus telepresence-enabled cruise. This Triton site was initially detected from bubble flares identified via shipboard multibeam sonar and was then confirmed visually using the remotely operated vehicle (ROV) Hercules. High resolution mapping (to 1 cm resolution) and co-registered imaging has provided us with a comprehensive site overview – both of the geologic setting and the extent of the associated microbial colonization. The Triton site represents an active cold-seep where microorganisms can act as primary producers at the base of a chemosynthesis-driven food chain. But it is also located near the core of a local oxygen minimum zone (OMZ), averaging 100 m across the seafloor, dominate the site, while typical seep-endemic macro-fauna were noticeably absent from our co-registered photographic and high-resolution mapping surveys – especially when compared to all adjacent seep sites within the same California Borderlands region. While such absences of abundant macro-fauna could be attributable to variations in the availability of dissolved oxygen in the overlying water column this need not necessarily be the case. An alternate possibility is that the zonation in microbial activity that is readily observable at the seafloor at Triton reflects, instead, a concentric pattern of radially diminishing fluxes of reductants from the underlying seafloor. This unusual but readily accessible discovery, in close proximity to Los Angeles harbor, provides an intriguing new natural laboratory at which to examine biogeochemical and microbiological interactions associated with the functioning of cold seep ecosystems within an OMZ.Ship time was funded by NOAA – Office of Exploration and Research and the Ocean Exploration Trust. This material is based upon work supported by a National Science Foundation Graduate Research Fellowship (to JW), the Office of Naval Research (to CS), and NASA’s Astrobiology program (to CG)

Quantification of methane fluxes and authigenic carbonate formation at cold seeps along the continental margin offshore Costa Rica: A numerical modeling approach

The expulsion of liquids, gases and fluids at continental margins covers a wide range of processes including not only mud volcanism, mud diapirism and gas flares, but also continuously seeping methane-rich fluids leading to cold vent sites and even outbursts of over-pressured gases. Seepage of fluids frequently leads to precipitation of authigenic carbonates that modify sedimentary processes along the margin, and finally, the fluids constitute the energy source for a number of diverse and complex ecosystems. During the last two decades, researchers gained significant knowledge about the impact of fluid seepage on local ecosystems and the biogeochemical processes that result in carbonate formation via the anaerobic oxidation of methane (AOM). However, all the knowledge was gained in different areas and geological settings of the world ocean but left a regional gap in our knowledge about seeps at the continental margin offshore Costa Rica. Those processes including authigenic carbonate precipitation, quantification of the impact of fluid seepage and methane budgets are documented in the present thesis. Chapter II presents comprehensive results from five cold seep structures at the Costa Rican continental margin addressing the relationship between fluid advection, dissolved calcium concentrations in upward migrating fluids, and authigenic calcium carbonate precipitation. A numerical transport-reaction model was used to determine rates of AOM, CaCO3 precipitation, and benthic fluxes of solutes. Production of carbonate alkalinity and formation of authigenic carbonates is most intense at intermediate flow rates (3-40 cm a-1) and reduced under low and high flux conditions (0.1 and 200 cm a-1). Systematic model runs showed that high Ca concentrations in ascending fluids enhance the rate of authigenic carbonate production at moderate flow rates leading to an almost quantitative fixation of deeply derived Ca in authigenic carbonates. Hence, CaCO3 precipitation is not only controlled by Ca diffusing into the sediment from bottom water, but also by the Ca concentration in ascending fluids. Based on average precipitation rates deduced from the systematic model runs the global Ca-fixation at cold seeps (~2·1010 mol Ca a-1) suggesting that cold seeps are most likely not of key importance with respect to Ca cycling in the ocean. Chapter 3 comprises the quantitative estimates of dissolved methane discharge from wellstudied mud mounds (Mound 11 and Mound 12) at the submarine section of the Costa Rica fore-arc combining geochemical and geoacoustic data. The study is supported by 75 kHz sidescan sonar data, pore-water analysis and visual sea-floor observations by remotely operated vehicle (ROV). A numerical transport reaction model was applied to determine dissolved methane fluxes considering AOM and upward fluid flow. Model results reveal that a significant portion of methane from greater depth is discharged into the bottom water only at high fluid flow velocities that are not sufficiently moderate to allow for AOM. The overall amount of dissolved methane released from the entire mud mounds into the water column was moderate with a discharge of 0.36·106 mol a-1 at Mound 11 whereas it was calculated as 0.58·106 mol a-1 at Mound 12. Compared to other active cold seeps (mainly mud volcanoes), mud mounds at the submarine section of the Costa Rica fore arc do not represent a pathway for significant methane discharge from the seafloor. Sea floor methane emissions from bacterial mat sites of a submarine slide at the Costa Rica continental margin are presented in Chapter IV. The estimates of methane fluxes into the water column are based on (i) detailed mapping in order to determine the abundance of seeps, and thus the spatial validity of the flux measurements; and (ii) application of numerical model to estimate the amount of methane that is transported into the bottom water. Model results illustrate that the majority of the studied seeps transport rather limited amount of methane into the water column due to medium to low advection rates (average 10 cm a-1 ) allowing high methane consumption by AOM (average 45%) and limiting the methane discharge into the water column. Depth-integrated AOM rates (56-1538 μmol CH4 cm-2 a-1) are comparable with the values reported at other very active vents sites, suggesting that the Quepos Slide should be regarded as one of the most active sites at the seafloor. The overall amount of dissolved methane released from the entire bacterial mat sites into the water column is determined as 0.56·106 mol a-1. This conservative estimate, relying on rather accurate determinations of sea floor methane fluxes out of bacterial mats emphasizes the importance of submarine slides as sites of natural methane seepage

Biotechnological aspects of sulfate reduction with methane as electron donor

Biological sulfate reduction can be used for the removal and recovery of oxidized sulfur compounds and metals from waste streams. However, the costs of conventional electron donors, like hydrogen and ethanol, limit the application possibilities. Methane from natural gas or biogas would be a more attractive electron donor. Sulfate reduction with methane as electron donor prevails in marine sediments. Recently, several authors succeeded in cultivating the responsible microorganisms in vitro. In addition, the process has been studied in bioreactors. These studies have opened up the possibility to use methane as electron donor for sulfate reduction in wastewater and gas treatment. However, the obtained growth rates of the responsible microorganisms are extremely low, which would be a major limitation for applications. Therefore, further research should focus on novel cultivation technique

Geochemistry of cold seeps - Fluid sources and systematics

Emanation of fluids at cold seeps, mud volcanoes, and other types of submarine seepage structures is a typical phenomenon occurring at continental margins worldwide. They represent pathways along which volatiles and solutes are recycled from deeply buried sediments into the global ocean, and hence they may be considered as a potentially important link in global geochemical cycles. In this contribution we present geochemical data from various geological and tectonic settings such as the Gulf of Cadiz, the convergent margin off Central America, and/or the Black Sea and provide approaches how to systemize available data sets. Clay-mineral dewatering plays a central role in terms of fluid-mobilization from greater depth, however, resulting cold seep fluids are typically very different from each other and cover a large range of geochemical signatures. This is is due to variations in control parameters such as the type and thickness of the sediment cover, thermal conditions, extension of fluid pathways, and the potential for secondary overprinting. For example, freshened fluids emanating at cold seeps off Costa Rica indicate dewatering and related geochemical reactions in subducting sediments, while fluids sampled at mud volcanoes in the Gulf of Cadiz provide evidence for a high-temperature fluid source originating in the underlying oceanic basement. The latter finding provides evidence for a hydrological connection between buried oceanic crust and the water column even at old crustal ages. Varius geochemical tracers were proposed in the past to decipher relevant processes in the subsurface. In a recent systematic study, Scholz et al. [1] demonstrated the general use of Li, reflecting the temperature-dependent isotope fractionation during early diagenetic Li uptake and burial diagenetic Li release from sediments. However, additional approaches are required in order to provide robust geochmical interpretations of cold seep fluids

Evidence of microbial activity from a shallow water whale fall (Voghera, northern Italy)

The fossil bones, associated carbonate cements and enclosing concretion of a Miocene mysticete from inner shelf deposits (Monte Vallassa Formation, northern Italy) were analyzed for evidence of microbial activity. Optical and scanning electron microscopy, Raman spectroscopy, and stable C and O isotope geochemistry were used for high spatial resolution microfacies and biosedimentological analyses. Whale cancellous bones were filled by different carbonate cements including microcrystalline dolomite, rhombohedral dolomite and sparry calcite. Biofabric and biominerals such as microbial peloids, clotted textures and pyrite framboids were associated with the dolomite cements. Dolomite inside cancellous bones and in the enclosing concretion showed similar isotopic values (avg δ 13C: -7.12‰; avg δ 18O: +3.81‰), depleted with respect to the (late) sparry calcite cement (avg δ 13C: -0.55‰; avg δ 18O: -0.98‰). Microcrystalline barite (BaSO 4) was observed on the external surface of the bones. In addition, two different types of microborings were recognized, distinguished by their size and morphology and were ascribed respectively to prokaryote and fungal trace makers. Our results testify for the development of a diverse microbial ecosystem during the decay of a shallow water whale carcass, which could be detected in the fossil record. However, none of the observed biosignatures (e.g., microbial peloids, clotted textures) can be used alone as a positive fossil evidence of the general development of a sulfophilic stage of whale fall ecological succession. The occurrence of the hard parts of chemosynthetic invertebrates associated with fossil whale bones is still the more convincing proof of the development of a sulfide-base chemoautotrophic ecosystem. © 2011 Elsevier B.V

Acoustic and visual characterisation of methane-rich seabed seeps at Omakere Ridge on the Hikurangi Margin, New Zealand

Six active methane seeps and one cold-water reef that may represent a relict seep were mapped at Omakere Ridge on New Zealand's Hikurangi Margin during cruises SO191 and TAN0616. Hydroacoustic flares, interpreted to be bubbles of methane rising through the water column were identified in the area. The seep sites and the cold-water reef were characterised by regions of high backscatter intensity on sidescan sonar records, or moderate backscatter intensity where the seep was located directly below the path of the sidescan towfish. The majority of sites appear as elevated features (2–4 m) in multibeam swath data. Gas blanking and acoustic turbidity were observed in sub-bottom profiles through the sites. A seismic section across two of the sites (Bear's Paw and LM-9) shows a BSR suggesting the presence of gas hydrate as well as spots of high amplitudes underneath and above the BSR indicating free gas. All sites were ground truthed with underwater video observations, which showed the acoustic features to represent authigenic carbonate rock structures. Live chemosynthetic biotic assemblages, including siboglinid tube worms, vesicomyid clams, bathymodiolin mussels, and bacterial mats, were observed at the seeps. Cold-water corals were the most conspicuous biota of the cold-water reef but widespread vesicomyid clam shells indicated past seep activity at all sites. The correlation between strong backscatter features in sidescan sonar images and seep-related seabed features is a powerful tool for seep exploration, but differentiating the acoustic features as either modern or relict seeps requires judicial analysis and is most effective when supported by visual observations