The Discovery and Preliminary Geological and Faunal Descriptions of Three New Steinahóll Vent Sites, Reykjanes Ridge, Iceland

During RV MS Merian expedition MSM75, an international, multidisciplinary team explored the Reykjanes Ridge from June to August 2018. The first area of study, Steinahóll (150–350 m depth), was chosen based on previous seismic data indicating hydrothermal activity. The sampling strategy included ship- and AUV-mounted multibeam surveys, Remotely Operated Vehicle (ROV), Epibenthic Sledge (EBS), and van Veen grab (vV) deployments. Upon returning to Steinahóll during the final days of MSM75, hydrothermal vent sites were discovered using the ROV Phoca (Kiel, GEOMAR). Here we describe and name three new, distinct hydrothermal vent site vulnerable marine ecosystems (VMEs); Hafgufa, Stökkull, Lyngbakr. The hydrothermal vent sites consisted of multiple anhydrite chimneys with large quantities of bacterial mats visible. The largest of the three sites (Hafgufa) was mapped, and reconstructed in 3D. In total 23,310 individual biological specimens were sampled comprising 41 higher taxa. Unique fauna located in the hydrothermally venting areas included two putative new species of harpacticoid copepod (Tisbe sp. nov. and Amphiascus sp. nov.), as well as the sponge Lycopodina cupressiformis (Carter, 1874). Capitellidae Grube, 1862 and Dorvilleidae Chamberlin, 1919 families dominated hydrothermally influenced samples for polychaetes. Around the hydrothermally influenced sites we observed a notable lack of megafauna, with only a few species being present. While we observed hydrothermal associations, the overall species composition is very similar to that seen at other shallow water vent sites in the north of Iceland, such as the Mohns Ridge vent fields, particularly with peracarid crustaceans. We therefore conclude the community overall reflects the usual “background” fauna of Iceland rather than consisting of “vent endemic” communities as is observed in deeper vent systems, with a few opportunistic species capable of utilizing this specialist environment.

Heterogeneity around CO2 vents obscures the effects of ocean acidification on shallow reef communities

Studies that use CO2 vents as natural laboratories to investigate the impacts of ocean acidification (OA) typically employ control-impact designs or local-scale gradients in pH or pCO2, where impacted sites are compared to reference sites. While these strategies can accurately represent well-defined and stable vent systems in relatively homogenous environments, it may not adequately encompass the natural variability of heterogeneous coastal environments where many CO2 vents exist. Here, we assess the influence of spatial heterogeneity on the perceived impacts of OA at a vent system well established in the OA literature. Specifically, we use a multi-scale approach to investigate and map the spatial variability in seawater pH and benthic communities surrounding vents at Whakaari-White Island, New Zealand to better understand the scale and complexity of ecological impacts of an acidified environment. We found a network of vents embedded in complex topography throughout the study area, and spatially variable pH and pCO2 levels. The distribution of habitats (i.e. macroalgal forests and turfing algae) was most strongly related to substratum type and sea urchin densities, rather than pH. Epifaunal communities within turfing algae differed with sampling distance from vents, but this pattern was driven by higher abundances of a number of taxa immediately adjacent to vents, where pH and temperature gradients are steep and white bacterial mats are prevalent. Our results contrast with previous studies at White Island that have used a control-impact design and suggested significant impacts of elevated CO2 on benthic communities. Instead, we demonstrate a highly heterogeneous reef where it is difficult to separate effects of reduced pH from spatial variation in reef communities. We urge that future research carefully considers and quantifies the biological and physical complexity of venting environments, and suggest that in dynamic systems, such as White Island, the use of control-impact designs can oversimplify and potentially overestimate the future impacts of OA.

Development of an Easy-to-Operate Underwater Raman System for Deep-Sea Cold Seep and Hydrothermal Vent In Situ Detection

As a powerful in situ detection technique, Raman spectroscopy is becoming a popular underwater investigation method, especially in deep-sea research. In this paper, an easy-to-operate underwater Raman system with a compact design and competitive sensitivity is introduced. All the components, including the optical module and the electronic module, were packaged in an L362 × Φ172 mm titanium capsule with a weight of 20 kg in the air (about 12 kg in water). By optimising the laser coupling mode and focusing lens parameters, a competitive sensitivity was achieved with the detection limit of SO42− being 0.7 mmol/L. The first sea trial was carried out with the aid of a 3000 m grade remotely operated vehicle (ROV) “FCV3000” in October 2018. Over 20,000 spectra were captured from the targets interested, including methane hydrate, clamshell in the area of cold seep, and bacterial mats around a hydrothermal vent, with a maximum depth of 1038 m. A Raman peak at 2592 cm−1 was found in the methane hydrate spectra, which revealed the presence of hydrogen sulfide in the seeping gas. In addition, we also found sulfur in the bacterial mats, confirming the involvement of micro-organisms in the sulfur cycle in the hydrothermal field. It is expected that the system can be developed as a universal deep-sea survey and detection equipment in the near future.

Study of Deep-Ocean Ferromanganese Crusts Ore Components

A complex layer-by-layer morphology and phase analysis of a ferromanganese crust aged about 70 million years, extracted from the rise of the Magellan Mountains of the Pacific Ocean, was carried out using several physics methods: digital optical microscopy, scanning electron microscopy with high resolution, X-ray fluorescence and diffraction analysis and Mossbauer spectroscopy. This analysis showed that the crust is an association of several minerals with various dispersion and crystallization degree, between which fossilized bacterial mats with Fe- and Mn- oxides are located. These phenomena indicate the biogenic nature of the crust. Changes in the crusts phase composition from the lower layer to the upper layer indicate changes in the external environmental conditions during their formation.

Tectonic constraints on submarine hydrothermal activity, degassing, and subseafloor gas storage (Milos Shallow Water Hydrothermal System, Greece)

<p>The Milos hydrothermal field is one of the largest known shallow water hydrothermal systems, and shows both fluid and gas outflow through the seafloor. Recent studies based on imagery acquired by both aerial and submarine drones (Puzenat et al., submitted) reveal several types of fluid outflow associated with bacterial mats along the SE coast of the island (Paleochori, Spathi, and Agia Kyriaki bays). From these observations? include: a) zones of polygonal hydrothermal outflow and associated bacterial mats, b) extended white (bacterial) patches, and c) isolated ones. Subseafloor hydrothermal circulation is hosted in sediments with subseafloor temperatures >50°C, and there is a clear association between hydrothermal circulation and active degassing.</p><p>To understand the controls on and relationships between fluid and gas outflow in the area, we need to characterise: a) the nature of the subseafloor (sediment thickness, composition & permeability); b) the distribution of gas and subseafloor fluids, and c) the distribution of gas flares emanating from the seafloor. In November 2020, we conducted a short pilot geophysical study at Paleochori Bay, deploying a towed catamaran with a multibeam echo sounder (iXblue Seapix) to obtain seafloor bathymetry, acoustic backscatter and water column detection of gas flares. We also deployed a sub-bottom profiler (iXblue Echoes 3500 T1) to image sediment architecture and gas/fluid diffusion within the sediment. Our survey focused on Paleochori Bay, surveing areas from ~5 m (nearshore) to ~100 m waterdepth (offshore).</p><p>Preliminary results of this geophysical survey suggest that subseafloor gas accumulations play a major role on the nature and structure of hydrothermal activity at Milos. These gas accumulations within the sediments develop along an onshore/offshore fault system, and likely control the shallow subseafloor thermal structure, establishing a thin thermal conductive layer between the roof of gas pockets and the seafloor.[GJ1] [je2]   We will report on the link between the distribution and geometry (extent, depth, acoustic nature of the accumulations) of gas pockets, fluid outflows, and gas outflows, all of which will be characterised from both seafloor imagery and subsurface geophysical surveys. We will also discuss how gas pocket geometry may be linked to both fluid flow and subseafloor temperature structure. [HA3] </p><div> <div> <div> </div> </div> <div> <div> </div> </div> <div> <div> </div> </div> </div>

Identification and interpretation of seismic short-duration events inside the Kolumbo submarine volcano in the Southern Aegean

<p>Kolumbo represents one of the most hazardous, currently active, volcanoes in the eastern Mediterranean. Its last eruption in 1650 AD was associated with a vast explosion, causing a tsunami of regionally devastating impact. The eruption was also associated with the voluminous and rapid release of toxic gases asphyxiating humans and animals on the nearby Islands. Earthquake records from the recent decades document on-going unrest beneath the volcano. Remotely operated vehicle dives revealed several hydrothermal vent sites and bacterial mats at the crater floor, which are concentrated near the northern crater wall. The vents emit mainly CO<sub>2</sub>, leading to the accumulation of acidic waters in the crater. Accordingly, one of the main volcanic hazards associated with Kolumbo is that rapid overturning of water in the crater may release harmful amounts of toxic gases. Monitoring the hydrothermal processes inside the Kolumbo crater will provide an important contribution to the understanding and evaluation of this and other volcanic hazards.</p><p>In October 2019, we deployed an ocean bottom seismometer and hydrophone (OBS/H) inside the Kolumbo crater. During the four days of passive recording we identified about 100 so-called short duration seismic events, which were only present on the seismometer channels, while generally being absent on the hydrophone channels. The events have durations of less than one second with dominant frequencies between 5 to 30 Hz. Most of the events represent well-polarized seismic phases, which enables us to determine their azimuth angle (with a 180-degree bias) and angle of incidence at the OBS/H. We cross-correlated all polarized seismic waveforms and subsequently used the cross-correlation coefficients for a hierarchical cluster analysis to elaborate whether the events have a random origin or originated from a common origin. Our analysis revealed that the majority of events is associated with two clusters. The azimuth angles of all events in the largest cluster coincide with the azimuth angle between station and the field of hydrothermal vents and bacterial mats inside the crater. This coincidence suggests that the origin of the short duration events is associated with the sub-seafloor migration of fluids or the fluid discharge process at the crater floor. In fact, short-duration events of similar characteristics, recorded by OBS/H, were previously attributed to sub-seafloor fluid migration and the discharge of fluids at the seafloor. Our analyses indicate that seismic monitoring of submarine volcanoes should include the detection and analysis of short duration events, which may act as a novel tool in the characterization of volcanic unrests and volcanogenic geohazard monitoring in general.</p>

Biogeochemical characteristics of shallow methane seeps of Crimean coastal areas in comparison with deep-sea seeps of the Black Sea

Methane gas bubble emissions (seeps) are widespread phenomenon in the World Ocean, inter alia in Black Sea basin. The relevance of the research of methane seeps is due to their important role as a source of methane – greenhouse and environment-forming gas – for water column and atmosphere. The article presents a comparative analysis of the data from our biogeochemical 10-year studies of shallow gas seeps of the Crimean Peninsula and data on deep-sea gas seeps of the Black Sea. During 10-year period, apart from carrying out hydroacoustic research, the following parameters were determined: bubble gas component composition, methane carbon isotopic composition, microbial community structure of bacterial mats, covering gas bubble emission sites, and gas fluxes from separate seeps. During long-term monitoring, 14 separate gas bubble emission sites were detected and described in Crimean coastal areas; they were located from Cape Tarkhankut in the west of the peninsula to the Dvuyakornaya Bay in the southeast. Crimean coastal seeps were mostly of biogenic origin, with a seasonal type of gas bubble emission. Laspi Bay seeps were classified as emissions of deep gas of thermocatalytic genesis. A significant variation was recorded in values of isotopic composition of methane carbon δ13C-CH4 of bubble gas in coastal shallow areas (−94…−34 ‰), which indicates different conditions for bubble gas generation and maturation in seabed sediments. Similar to deep-sea seeps, coastal gas bubble emissions were accompanied by bacterial mats of diverse structure, with different dominating species. As shown, formation of stable bacterial biomass, usually consisting of sulfide- and sulfur-oxidizing bacteria, requires a fluid flux of reduced dissolved gases, while pointwise bubble gas discharge does not provide sufficient concentration gradients and can mechanically disrupt community structure. Various methods were used to estimate the size spectra of bubbles, as well as fluxes from separate seeps. Gas flux values varied from 1.8 L·day−1 (the Martynova Bay) to 40 L·day−1 (the Laspi Bay). The environment-forming effects, related to gas bubble emission in coastal areas, are discussed: effect of seeps on oxygen conditions in seabed sediments and in water column above gas emission sites, vertical water mixing due to gas lift effect, and fluid discharge at gas emission sites.

Integrated regional scale view of Milos submarine hydrothermalism

<p>Submarine hydrothermal activity is common at the flanks of volcanic islands, and in some cases, occurring at very shallow water (0-100 meter depth). These sites are a key target for systematic seafloor mapping to understand the location, geometry and nature of hydrothermal discharge. These data are also critical for monitoring the temporal variability of these dynamic systems, while providing a context for instrumental measurements, sampling and other observations (e.g., temperature of outflow, chemistry, etc.). Here we present a systematic mapping of the Milos hydrothermal system in the Hellenic volcanic Arc, characterized by submarine gas emissions, high-temperature outflow, bacterial mats, precipitation of hydrothermal minerals, and small hydrothermal constructs and edifices. We have mapped this site at regional scales using satellite imagery (World-View2 images from the DigitalGlobe foundation), complemented with aerial photography acquired with drones, and high-resolution seafloor photomosaics (<1 cm resolution) from underwater imagery acquired by the autonomous underwater vehicle Sparus II (University of Girona). </p><p>Our drone and AUV mapping ground truths the correlation between patterns in satellite imagery and hydrothermal outflow, associated to mineral precipitates and/or bacterial mats at the seafloor. This mapping also reveals a clear organization of the hydrothermal outflow in sandy areas. In particular, polygonal patterns are common and often associated with inactive or actively bubbling pockmarks. These areas, showing white bacterial mats and hydrothermal precipitates, are rippled, suggesting that the hydrothermal precipitates do not consolidate the sediment. White precipitates display subseafloor temperatures >50°C at depths of 10 to 50 cm. The white areas are bound by bands of seafloor with a hummocky structure due to intense bioturbation, that obliterates the ripples, with widths of up to a few meters. This area shows subseafloor temperatures of 20-40°C, and corresponds to a transition from the high-temperature white zones and the seafloor with ripples and no hydrothermal precipitates. This area exhibits subseafloor temperatures similar to those of seawater, and can be associated with seagrass. These patterns reveal a clear organization of a narrowly focused hydrothermal outflow that controls the biological communities at the seafloor and subseafloor. We will discuss the implications of these observations to quantify hydrothermal fluxes in the study area.</p><p><br><br></p>

Volcanic submarine hydrothermal activity from satellites : regional mapping and temporal evolution in shallow water systems

<p>Risk assessment at active volcanic islands link to populated areas is of first importance. We evaluate the potential of satellite imagery to map and monitor the activity of shallow-water hydrothermal systems, which are often found at volcanic islands. For this study, we used publicly available data and proprietary WorldView-2 satellites images, with spectral bands that can penetrate up to water depths of 30 m. Shallow water hydrothermal sites are visible on satellite imagery, primarily with publicly available data, demonstrating the potential of satellite imagery to study and monitor shallow water hydrothermal activity. We focus our work on volcanic islands, showing intense near-shore, shallow-water hydrothermal activity, and distinct styles of hydrothermal venting. Satellite imagery constrains regional outflow geometry and the temporal variability or stability of these systems. Milos Island shows hydrothermal outflow associated with reflective mineral precipitates and/or bacterial mats, which are stable over time (2010-2014). These outflows locally define polygonal patterns likely associated with hydrothermal convection in porous media. In Kueishantao Island individual hydrothermal plumes charged with particles are visible at the sea surface, and display great variability in intensity and distribution of plume sources (2002-2019). Worldwide we have identified ~15 shallow water hydrothermal sites with satellite imagery, that are similar to either the Milos system (e.g., Vulcano and Panarea, Italy), or the Kueishantao system (numerous sites in Pacific volcanic islands). This study demonstrates that satellite imagery can be used to map and monitor different types of shallow-water hydrothermal systems, at regional scale, and monitor their evolution. Satellite data provides not only regional and temporal information on these systems, unavailable to date, but also the regional context for follow-up in situ field data and observations (e.g., instrumental monitoring, sampling, observations and mapping with divers or AUVs) to understand both the nature and dynamics of these systems, and ultimately the associated fluxes.</p>