Hydrothermal areas, microbial mats and sea grass in Paleochori Bay, Milos, Greece

Khimasia, A.; Pichler, Thomas

doi:10.1080/17445647.2020.1748131

Cited by 10 publications

(17 citation statements)

References 44 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Venting activity around the eastern part of Milos island, including Paleochori Bay, occurs over an area of approximately 35 km 2 from onshore to about 100 m water depth, and is characterized by gas-and liquid-dominated fluids that are emitted through the unconsolidated volcaniclastic cover [40,41,[45][46][47]50,53,63,81] (Figure 3). The hydrothermal fluids are highly sulfidic (up to 3 mM H 2 S) and reach temperatures of up to 122 • C [41,82]. The active submarine hydrothermal system of Paleochori Bay discharges vapor-and liquiddominated aqueous fluids with average temperatures (91 ± 23 • C).…”

Section: Hydrothermal Ventingmentioning

confidence: 99%

Arsenian Pyrite and Cinnabar from Active Submarine Nearshore Vents, Paleochori Bay, Milos Island, Greece

et al. 2020

View full text Add to dashboard Cite

Active, shallow-water (2–10 m below sea level) and low temperature (up to 115 °C) hydrothermal venting at Paleochori Bay, nearshore Milos Island, Greece, discharges CO2 and H2S rich vapors (e.g., low-Cl fluid) and high-salinity liquids, which leads to a diverse assemblage of sulfide and alteration phases in an area of approximately 1 km2. Volcaniclastic detritus recovered from the seafloor is cemented by hydrothermal pyrite and marcasite, while semi-massive to massive pyrite-marcasite constitute mounds and chimney-like edifices. Paragenetic relationships indicate deposition of two distinct mineralogical assemblages related to the venting of high-Cl and low-Cl fluids, respectively: (1) colloform As- and Hg-bearing pyrite (Py I), associated with marcasite, calcite, and apatite, as well as (2) porous and/or massive As-rich pyrite (Py II), associated with barite, alunite/jarosite, and late-stage hydrous ferric oxides. Mercury, in the form of cinnabar, occurs within the As-rich pyrite (Py I) layers, usually forming distinct cinnabar-enriched micro-layers. Arsenic in colloform pyrite I shows a negative correlation with S indicating that As1− dominates in the pyrite structure suggesting formation from a relatively reducing As-rich fluid at conditions similar to low-sulfidation epithermal systems. On the contrary, As3+ dominates in the structure of porous to massive pyrite II suggesting deposition from a sulfate-dominated fluid with lower pH and higher fO2. Bulk sulfide data of pyrite-bearing hydrothermal precipitates also show elevated As (up to 2587 ppm) together with various epithermal-type elements, such as Sb (up to 274 ppm), Tl (up to 513 ppm), and Hg (up to 34 ppm) suggesting an epithermal nature for the hydrothermal activity at Paleochori Bay. Textural relationships indicate a contemporaneous deposition of As and Hg, which is suggested to be the result of venting from both high-salinity, liquid-dominated, as well as CO2- and H2S-rich vapor-dominated fluids that formed during fluid boiling. The CO2- and H2S-rich vapor that physically separated during fluid boiling from the high-salinity liquid led to calcite formation upon condensation in seawater together with the precipitation of As- and Hg-bearing pyrite I. This also led to the formation of sulfuric acid, thereby causing leaching and dissolution of primary iron-rich minerals in the volcaniclastic sediments, finally resulting in pyrite II precipitation in association with alunite/jarosite. The Paleochori vents contain the first documented occurrence of cinnabar on the seafloor in the Mediterranean area and provide an important link between offshore hydrothermal activity and the onshore mercury and arsenic mineralizing system on Milos Island. The results of this study therefore demonstrate that metal and metalloid precipitation in shallow-water continental arc environments is controlled by epithermal processes known from their subaerial analogues.

show abstract

Section: Hydrothermal Ventingmentioning

confidence: 99%

Arsenian Pyrite and Cinnabar from Active Submarine Nearshore Vents, Paleochori Bay, Milos Island, Greece

et al. 2020

View full text Add to dashboard Cite

show abstract

“…While abundant and particularly ubiquitous at volcanically active areas (e.g., Tarasov et al, 2005;Price and Giovannelli, 2017;Martelat et al, 2020), their geometry, temporal evolution, and associated fluxes are yet not well constrained. Systematic and comprehensive mapping of shallow-water systems to date is therefore partial and limited to a few sites (e.g., Khimasia et al, 2020;2021).…”

Section: Introductionmentioning

confidence: 99%

“…While earlier studies have provided maps with distribution of active venting areas extending from the shore to deep regions (e.g., Dando et al, 1995b), the actual geometry and distribution of sites and venting areas are poorly constrained. Only recently we have obtained detailed and accurate mapping of the Milos hydrothermal system to depths of ~20 m using satellite imagery (Martelat et al, 2020), and drone aerial imagery coupled with both temperature measurements and fluid chemistry (Khimasia et al, 2020;2021). Here we use underwater surveys to adequately ground truth interpretation of drone imagery, and to provide a detailed context where temperature measurements can be precisely linked to the observed seafloor patterns.…”

Section: Introductionmentioning

confidence: 99%

Shallow-water hydrothermalism at Milos (Greece): Nature, distribution, heat fluxes and impact on ecosystems

et al. 2021

View full text Add to dashboard Cite

Submarine hydrothermal activity is responsible for heat and chemical exchanges through the seafloor. Shallow-water hydrothermal systems (SWHS), while identified around the globe, are often studied in a way that is less comprehensive than their deep-ocean counterparts (e.g., along ridges), where systematic optical and acoustic mapping is more prevalent and coupled to in situ observations and sampling. Using aerial drones, an AUV, and temperature measurements at 10-40 cm subseafloor, we investigated in 2019 one of the most extensive SWHS known to date, in Paleochori (south of Milos, Greece). Hydrothermal venting, found from the shore to water depths of almost 500 m, shows emissions of gases and high-temperature fluids, often associated with bacterial mats and/or hydrothermal mineral precipitates. This study provides extensive drone mapping coupled with local AUV surveys for seafloor characterization and ground-truthing from the shore to ~20 m water depth. Seafloor photomosaics also provide a detailed context to samples, measurements and observations carried in situ. We interpret the photomosaics to define distinct seafloor types, linked to this hydrothermal activity. White hydrothermal patches (WHPs) often show a clear polygonal organization, together with outflow areas that are both more dispersed and distributed. Polygonal patterns likely result from fluid convection in a sandy porous medium heated from below. These WHPs display elevated subseafloor temperatures, typically >50 °C, with maximum values of ~75 °C. Photomosaics also display textures of biological origin, including seagrass and bioturbation patterns. Widespread bioturbation by burrowing shrimps is often associated with WHPs, bounding them, but also occurs on sandy seafloor away from hydrothermal patterns. Subseafloor temperatures at these bioturbated areas are of ~30-40 °C, and are thus transitional between hot WHPs and sedimented seafloor unaffected by hydrothermal activity (~24 °C). In addition to linking subseafloor temperature data and interpreted seafloor 4 photomosaics, our results provide a comprehensive general overview of this SWHS, of the organization of its hydrothermal outflow through the seafloor, and of the underlying subseafloor fluid circulation. This paper also gives the first perspectives on the heat fluxes of the system, and constitutes a background for other studies on the nature and distribution of microbial communities, controlled by this hydrothermal activity.

show abstract

“…This led to a comparatively good understanding of the geochemistry and geomicrobiology of these sites, particularly in Paleochori Bay. The western part of the Bay is described as being hydrothermally more active (Khimasia et al, 2020), with hydrothermal fluids percolating through permeable sediment, creating distinct zones on the sediment surface. Yellow-orange patches can be found in the center, surrounded by white and brown areas, often occurring in concentric circles of about 2 m in diameter (Sievert et al, 1999;Wenzhöfer et al, 2000;Khimasia et al, 2020).…”

Section: Aegean Islands (Greece)mentioning

confidence: 99%

“…The western part of the Bay is described as being hydrothermally more active (Khimasia et al, 2020), with hydrothermal fluids percolating through permeable sediment, creating distinct zones on the sediment surface. Yellow-orange patches can be found in the center, surrounded by white and brown areas, often occurring in concentric circles of about 2 m in diameter (Sievert et al, 1999;Wenzhöfer et al, 2000;Khimasia et al, 2020). The yellow-orange precipitates are mainly composed of amorphous orpiment-like As-sulfides (As 2 S 3 ) (Godelitsas et al, 2015), occurring in the hottest areas (≥ 85 • C).…”

Section: Aegean Islands (Greece)mentioning

confidence: 99%

Submarine Shallow-Water Fluid Emissions and Their Geomicrobiological Imprint: A Global Overview

Caramanna¹,

Sievert

Bühring

2021

Front. Mar. Sci.

View full text Add to dashboard Cite

Submarine fluids emissions in the form of geothermal vents are widespread in a variety of geological settings ranging from volcanic to tectonically active areas. This overview aims to describe representative examples of submarine vents in shallow-water areas around the globe. The areas described include: Iceland, Azores, Mediterranean Sea (Italy and Greece), Caribbean, Baja California, Japan, Papua, New Zealand, Taiwan. Common and divergent characteristics in terms of origin and geochemistry of the emitted fluids and their impact on the indigenous organisms and the surrounding environment have been identified. In the hottest vents seawater concentration is common as well as some water vapor phase separation. Carbon dioxide is the most common gas often associated with compounds of sulfur and methane. In several vents precipitation of minerals can be identified in the surrounding sediments. The analyses of the microbial communities often revealed putative chemoautotrophs, with Campylobacteria abundantly present at many vents where reduced sulfur compounds are available. The techniques that can be used for the detection and quantification of underwater vents are also described, including geophysical and geochemical tools. Finally, the main geobiological effects due to the presence of the hydrothermal activity and the induced changes in water chemistry are assessed.

show abstract

Hydrothermal areas, microbial mats and sea grass in Paleochori Bay, Milos, Greece

Cited by 10 publications

References 44 publications

Arsenian Pyrite and Cinnabar from Active Submarine Nearshore Vents, Paleochori Bay, Milos Island, Greece

Arsenian Pyrite and Cinnabar from Active Submarine Nearshore Vents, Paleochori Bay, Milos Island, Greece

Shallow-water hydrothermalism at Milos (Greece): Nature, distribution, heat fluxes and impact on ecosystems

Submarine Shallow-Water Fluid Emissions and Their Geomicrobiological Imprint: A Global Overview

Contact Info

Product

Resources

About