Cold seeps associated with a submarine debris avalanche deposit at Kick’em Jenny volcano,Grenada (Lesser Antilles)

Remotely operated vehicle (ROV) exploration at the distal margins of a debris avalanche deposit from Kick’em Jenny submarine volcano in Grenada has revealed areas of cold seeps with chemosynthetic-based ecosystems. The seeps occur on steep slopes of deformed, unconsolidated hemipelagic sediments in water depths between 1952 and 2042 m. Two main areas consist of anastomosing systems of fluid flow that have incised local sediments by several tens of centimeters. No temperature anomalies were observed in the vent areas and no active flow was visually observed, suggesting that the venting may be waning. An Eh sensor deployed on a miniature autonomous plume recorder (MAPR) recorded a positive signal and the presence of live organisms indicates at least some venting is still occurring. The chemosynthetic-based ecosystem included giant mussels (Bathymodiolus sp.) with commensal polychaetes (Branchipolynoe sp.) and cocculinid epibionts, other bivalves, Siboglinida (vestimentiferan) tubeworms, other polychaetes, and shrimp, as well as associated heterotrophs, including gastropods, anemones, crabs, fish, octopods, brittle stars, and holothurians. The origin of the seeps may be related to fluid overpressure generated during the collapse of an ancestral Kick’em Jenny volcano. We suggest that deformation and burial of hemipelagic sediment at the front and base of the advancing debris avalanche led to fluid venting at the distal margin. Such deformation may be a common feature of marine avalanches in a variety of geological environments especially along continental margins, raising the possibility of creating large numbers of ephemeral seep-based ecosystems.     

Characterization of bacterial symbioses in Myrtea sp. (Bivalvia: Lucinidae) and Thyasira sp. (Bivalvia: Thyasiridae) from a cold seep in the Eastern Mediterranean

Cold seeps have recently been discovered in the Nile deep‐sea fan (Eastern Mediterranean), and data regarding associated fauna are still scarce. In this study, two bivalve species associated with carbonate crusts and reduced sediment are identified based on sequence analysis of their 18S and 28S rRNA‐encoding genes, and associated bacterial symbioses are investigated using 16S rRNA gene sequencing and microscopy‐based approaches. The specimens are closely related to Myrtea spinifera and Thyasira flexuosa, two species previously documented at various depths from other regions but not yet reported from the Eastern Mediterranean. Both species harbour abundant gammaproteobacterial endosymbionts in specialized gill epithelial cells. The Myrtea‐associated bacterium is closely related to lucinid symbionts from both deep‐sea and coastal species, whereas the Thyasira‐associated bacterium is closely related to the symbiont of a T. flexuosa from coastal waters off the U.K. An epsilonproteobacterial sequence has also been identified in Thyasira which could correspond to a helicoid‐shaped morphotype observed by electron microscopy, but this was not confirmed using fluorescent in situ hybridization. Virus‐like particles were observed within some symbionts in Thyasira, mostly in bacteriocytes localized close to the ciliated zone of the gill filament. Overall, results indicate that very close relatives of shallow species M. spinifera and T. flexuosa occur at cold seeps in the Eastern Mediterranean and harbour chemoautotrophic symbioses similar to those found in their coastal relatives.     

Morphology and structure of a landslide complex in an active margin setting: The Waitawhiti complex, North Island, New Zealand

Multi-scale gravitational instabilities are widespread in the Coastal Ranges of the North Island of New Zealand. We document here a detailed analysis of the Waitawhiti landslide complex, located in the core of the Tawhero syncline, and investigate the potential landslides triggering factors in the area. Four contiguous large slides form the Waitawhiti complex. These slides involve fine-grained Miocene sandstones and massive fractured siltstones. Sliding occurs mostly along nearly horizontal strata. All slides are bounded laterally and/or distally by deep-incised valleys. Three gas seeps evidencing thermogenic gas release have been discovered in the vicinity of the slides. We propose that river incision, continuously removing distal buttresses, is the main destabilizing factor in the area. However, additional factors, such as tectonic activity and intense rainfall, cannot be excluded. We also propose that fluid overpressure, reducing the effective shear strength at the base of low-permeability layers, may have influenced the triggering of landslides in the Waitawhiti area.     

Long‐term variability of proglacial groundwater‐fed hydrological systems in an area of glacier retreat,Skeiðarársandur,Iceland

Proglacial groundwater‐fed features, such as seeps, substantially impact proglacial geomorphology, hydrology, and ecology. However, there is a paucity of research on the impacts of climate change and glacier retreat on the extent of these important features. This paper aims to investigate the impact of glacier retreat on proglacial groundwater levels and on the extent of groundwater‐fed seeps. Research has taken place in western Skeiðarársandur, the large proglacial outwash plain of Skeiðarárjökull, a retreating temperate glacier in southeast Iceland. Changes in the extent of proglacial groundwater seeps were mapped using historical aerial photographs from 1986, 1997, and 2012. Proglacial groundwater levels were monitored in shallow boreholes between 2000 and 2012. The western margin of Skeiðarárjökull has retreated approximately 1 km beyond its position in 1986. However, this retreat was punctuated by short periods of readvance. The geomorphology and groundwater systems at the site were substantially impacted by the November 1996 jökulhlaup, whose deposits altered approximately 18% of the area of groundwater seeps. The surface areas of groundwater seeps and lakes in the study area have declined by ~97% between 1986 and 2012. Most of the decline took place after 1997, when the mean annual rate of retreat increased three‐fold. Groundwater levels also declined substantially between 2000 and 2012, although this trend varies spatially. The paper provides a conceptual model of the controls on proglacial shallow groundwater systems. Direct impacts of glacier retreat are suggested as the main cause for the declines in proglacial groundwater levels and in the extent of groundwater seeps. These declines are expected to adversely impact sandur ecology. Copyright © 2014 John Wiley & Sons, Ltd.     

Methane gas Seeps Along the Oxic/Anoxic Gradient in the Black Sea: Manifestations, Biogenic Sediment Compounds and Preliminary Results on Benthic Ecology

Abstract. Sediment parameters (grain size, organic content, chloroplastic pigments, Adenylates, Potential hydrolytic activity and electron transport system activity) and benthic biota were studied in methane seep area south-west of the Crimean Peninsula in the Black Sea over a depth range from 60 to 260m. A control transect with similar depths was performed in an adjacent nonseep area. Methane seepage in this region occurs from 35 to ˜ 85m depth, passing the oxic anoxic interface zone at 130 to 180m. The methane seep areas were characterized by abundant carbonate precipitates which occurred in various shapes from small, flat structures to tall chimneys with increasing anoxia. The carbonates were associated with distinct bacterial mats. Most of the measured biochemical parameters in the sediment were quite similar in the seep and nonseep areas. The content of organic matter was higher and grain size was more uniform in the nonseep areas. However, the seep areas were charaterized by highter proportions of the larger fauna (size classes 0.5–1 mm and ≥ 1mm) as well as increased total numbers of benthic fauna in the suboxic and upper anoxic zone. The animals did not show any seep-specific adaptations. In addition to methane seepage, highly variable hydrochemical and sedimentary conditions on the lower shelf and upper slope may also play an important role in structuring the composition and distribution of the benthic fauna.     

Spatial scale and habitat-dependent diversity patterns in nematode communities in three seepage related sites along the Norwegian Sea margin

Assessing the relative contribution of local diversity to regional biodiversity may be the key to understanding large-scale and even global patterns in species diversity. Here, the contribution of habitat heterogeneity of cold seeps at three spatial scales [micro-scale (ms), macro-scale (10 to 100s of ms), and mega-scale (10 to 100s of km)] to the total nematode biodiversity (genus level) along the Norwegian continental margin is evaluated. Due to the development of higher resolution bathymetry and increased bottom sampling in recent years, continental margins, once regarded as monotonous landscapes, are now acknowledged to have a high degree of habitat complexity and diversity. By calculating the additive partitioning of gamma diversity in alpha and beta fractions, we examined to what extent habitat diversity of seep sites significantly increases the nematode genus composition and diversity at different spatial scales. Siboglinidae patches and control sediments yielded comparably high levels of nematode genus richness. They exhibited low turnover rates within and across the different seep sites. In contrast, the bacterial mats at Håkon Mosby Mud Volcano (HMMV) and the reduced sediments at the Nyegga pockmarks harboured genus-poor nematode communities with an equally high dominance of one or two species, which were different for each seep. Different habitats, in particular at the HMMV, contributed significantly to the seep nematode richness. This study demonstrates that the presence of distinct habitat types within multiple seep sites contributes to the high diversity of nematode communities inhabiting the seeps in the Norwegian deep sea.     

Diversity patterns along and across the Chilean margin: a continental slope encompassing oxygen gradients and methane seep benthic habitats

In the present study we review datasets available for the Chilean margin to assess the relationship between environmental (or habitat) heterogeneity and benthic diversity. Several factors, such as the presence of different water masses, including the oxygen-deficient Equatorial Sub-surface Waters (ESSW) at the continental shelf and upper slope, and the Antarctic Intermediate Waters (AIW) at mid slope depths appear to control the bathymetric distribution of benthic communities. The presence of methane seeps and an extended oxygen minimum zone (OMZ) add complexity to the benthic distribution patterns observed. All these factors generate environmental heterogeneity, which is predicted to affect the diversity patterns both along and across the Chilean continental margin. The response to these factors differs among different faunal size groups: meio-, macro-, and megafauna. Physiological adaptations to oxygen deficiency and constraints related to body size of each group seem to explain the larger-scale patterns observed, while sediment/habitat heterogeneity ( e.g. at water mass boundaries, hardgrounds, biogeochemical patchiness, sediment organic content, grain size) may influence the local fauna diversity patterns.     

Submarine hydrothermal brine seeps off Milos, Greece. Observations and geochemistry

A shallow hydrothermal brine seep located off the Greek island of Milos in the Aegean Sea was studied. The brine fluid outcropped as a pool of water in a seabed depression and was detected in the surrounding pore-waters of sediments colonised by the sulphur bacterium Achromatium volutans. The seep fluid was highly saline and sulphidic, depleted in Mg²⁺ and SO₄²⁻, but enriched over seawater in Na⁺, Ca²⁺, K⁺, Cl⁻, SiO₂, reduced species and dissolved gases. The high concentrations of Na⁺, Ca²⁺ and K⁺ were consistent with the Milos tectonic setting. Na-K and Na-K-Ca geothermometers predicted a reservoir temperature of 300–325 °C for the most concentrated seep samples. The deep geothermal reservoir within the metamorphic basement of Milos island has already been located and studied and may represent the source of the seep fluid. Faunal diversity was lowest in seep-influenced sediments, but a sulphide-intolerant species was found in areas of the bacterial mat where salinity and temperature were much lower. Pressure-induced variations in the vertical depth of the brine interface may be occurring in the sediment.     

Early diagenetic formation of carbonates in a clastic-dominated ramp environment impacted by synsedimentary faulting-induced fluid seepage – Evidence from the Late Jurassic Boulonnais Basin (N France)

The Late Jurassic deposits of the Boulonnais area (N-France) represents the proximal lateral-equivalent of the Kimmeridge Clay Formation; they accumulated on a clastic-dominated ramp subject to synsedimentary faulting in relation with the northward propagation of the Atlantic rifting. Within the terrigenous accumulations, some carbonate objects are visible at various conspicuous levels: oyster patch reefs and fine-grained carbonate beds, either continuous, or more or less nodular. Preliminary studies demonstrated that the carbonate beds of the Bancs Jumeaux Formation as well as the carbonate matrix of the oyster patch reefs are of diagenetic origin. In this paper, we extend the study to many other limestone beds of the Boulonnais with mud- or wackestone texture, examining facies and microfacies through various techniques as well as geochemical data (O, C and S stable isotopes, major and trace elements). We conclude that all examined carbonate bodies are of early diagenetic origin and that they precipitated at, or close to, the sea bed, from seawater mixing with ascending fluids containing isotopically light carbon of organic origin. Fluid circulation was probably induced by the extensional block-faulting segmentation of the northern margin of the Boulonnais Basin in Late Jurassic times. Fluid seepages were either channelized along fault planes or more diffuse, as illustrated by the model we propose.