Shallow-water hydrothermal vents in the Azores (Portugal)

Couto, Ruben P.; Rodrigues, Armindo; Neto, Ana I.

doi:10.5894/rgci584

Cited by 14 publications

(14 citation statements)

References 45 publications

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“…The two examples of shallow intraplate vent sites are within the Azores archipelago in the North Atlantic, associated with the Azores hotspot, and the basaltic McDonald seamount in the South Pacific, associated with the McDonald hotspot. The Azores archipelago hosts nine vents degassing bubbles composed of ~90% CO 2 (Aguiar & Costa, ; Couto et al, ; Rajasabapathy et al, ), including shallow (~35 m depth) low‐temperature bubble emissions (Munaro et al, ). The McDonald seamount also has extensive shallow gas (methane, CO 2 , and SO 4 ) release observed exiting shallow (156 m) seafloor sediments (Cheminée et al, ).…”

Section: Discussionmentioning

confidence: 99%

“…Of more than 600 identified submarine gas vents (Beaulieu et al, 2013), 61 (~10%) are found in shallow (<200 m) waters. Of the 61 shallow sites reported by Beaulieu et al (2013) (Aguiar & Costa, 2010;Couto et al, 2015;Rajasabapathy et al, 2015), including shallow (~35 m depth) low-temperature bubble emissions (Munaro et al, 2010). The McDonald seamount also has extensive shallow gas (methane, CO 2 , and SO 4 ) release observed exiting shallow (156 m) seafloor sediments (Cheminée et al, 1991).…”

Section: Implications For Mcdonald Islands Flaresmentioning

confidence: 99%

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Shallow Seafloor Gas emissions Near Heard and McDonald Islands on the Kerguelen Plateau, Southern Indian Ocean

Spain

Johnson

Hutton³

et al. 2020

Earth and Space Science

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Bubble emission mechanisms from submerged large igneous provinces remains enigmatic. The Kerguelen Plateau, a large igneous province in the southern Indian Ocean, has a long sustained history of active volcanism and glacial/interglacial cycles of sedimentation, both of which may cause seafloor bubble production. We present the results of hydroacoustic flare observations around the underexplored volcanically active Heard Island and McDonald Islands on the Central Kerguelen Plateau. Flares were observed with a split‐beam echosounder and characterized using multifrequency decibel differencing. Deep‐tow camera footage, water properties, water column δ3He, subbottom profile, and sediment δ13C and δ34S data were analyzed to consider flare mechanisms. Excess δ3He near McDonald Islands seeps, indicating mantle‐derived input, suggests proximal hydrothermal activity; McDonald Islands flares may thus indicate CO2, methane, and other minor gas bubbles associated with shallow diffuse hydrothermal venting. The Heard Island seep environment, with subbottom acoustic blanking in thick sediment, muted 3He signal, and δ13C and δ34S fractionation factors, suggest that Heard Island seeps may either be methane gas (possibly both shallow biogenic methane and deeper‐sourced thermogenic methane related to geothermal heat from onshore volcanism) or a combination of methane and CO2, such as seen in sediment‐hosted geothermal systems. These data provide the first evidence of submarine gas escape on the Central Kerguelen Plateau and expand our understanding of seafloor processes and carbon cycling in the data‐poor southern Indian Ocean. Extensive sedimentation of the Kerguelen Plateau and additional zones of submarine volcanic activity mean additional seeps or vents may lie outside the small survey area proximal to the islands.

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Section: Discussionmentioning

confidence: 99%

Section: Implications For Mcdonald Islands Flaresmentioning

confidence: 99%

Shallow Seafloor Gas emissions Near Heard and McDonald Islands on the Kerguelen Plateau, Southern Indian Ocean

Spain

Johnson

Hutton³

et al. 2020

Earth and Space Science

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“…Nevertheless, very small hydrozoan colonies began to colonize the hard substrates of those habitats, and were also detected on the newly formed hard substrates away from the crater. Hydroids have also been detected as common components in shallow hydrothermal vents (<200 m depth) in the NE Atlantic [24,39,40]. These could represent early colonizers of extremophilous environments.…”

Section: Discussionmentioning

confidence: 99%

“…In general, the metazoan biodiversity in these vents and sulphurous fields was very low when compared to the remaining habitats. Usually, hydrothermal vents are impoverished in comparison to other substrates located at similar depths, due to toxic and extremophilous environments that are noxious to most metazoans [40,41].…”

Section: Discussionmentioning

confidence: 99%

First Macro-Colonizers and Survivors Around Tagoro Submarine Volcano, Canary Islands, Spain

et al. 2019

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Tagoro, the youngest submarine volcano of the Canary Islands, erupted in 2011 South of El Hierro Island. Pre-existing sea floor and inhabiting biological communities were buried by the newly erupted material, promoting the appearance of new habitats. The present study pursues to describe the first metazoans colonizing different new habitats formed during the eruption and to create precedent on this field. Through dredge and remote operated vehicle samplings, five main habitat types have been detected based on the substrate type and burial status after the eruption. Inside the Tagoro volcanic complex (TVC), two new habitats are located in and around the summit and main craters—hydrothermal vents with bacterial mats and sulfurous-like fields mainly colonized by small hydrozoan colonies. Two other habitats are located downslope the TVC; new hard substrate and new mixed substrate, holding the highest biodiversity of the TVC, especially at the mixed bottoms with annelids (Chloeia cf. venusta), arthropods (Monodaeus couchii and Alpheus sp.), cnidarians (Sertularella cf. tenella), and molluscs (Neopycnodonte cochlear) as the first colonizers. An impact evaluation was done comparing the communities of those habitats with the complex and well-established community described at the stable hard substrate outside the TVC, which is constituted of highly abundant hydrozoans (Aglaophenia sp.), antipatharians (Stichopates setacea and Antipathes furcata), and colonizing epibionts (e.g., Neopycnodonte cochlear). Three years after the eruption, species numbers at Tagoro were still low compared to those occurring at similar depths outside the TVC. The first dominant species at the TVC included a large proportion of common suspension feeders of the circalittoral and bathyal hard bottoms of the area, which could have exploited the uncolonized hard bottoms and the post eruptive fertilization of water masses.

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“…Cutting through the Azores Plateau, the TR comprises four basins and passes through three volcanic islands of the Azores Archipelago (Figure 1). Albeit ongoing magmatic activity in this region, only nine onshore hydrothermal springs (Couto et al, 2015), and one offshore submarine vent, located at the D. João de Castro seamount (Figure 1), have been reported to date (Figure 1; Cardigos et al, 2005). However, during a previous Meteor expedition (M 128) in 2016 no signs of hydrothermal activity was detected at this location (Beier, 2016).…”

Section: Introductionmentioning

confidence: 97%

Origin of High Mg and SO₄ Fluids in Sediments of the Terceira Rift, Azores‐Indications for Caminite Dissolution in a Waning Hydrothermal System

Schmidt

Hensen

Wallmann

et al. 2019

Geochem Geophys Geosyst

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During R/V Meteor cruise 141/1, pore fluids of near surface sediments were investigated to find indications for hydrothermal activity in the Terceira Rift (TR), a hyperslow spreading center in the Central North Atlantic Ocean. To date, submarine hydrothermal fluid venting in the TR has only been reported for the D. João de Castro seamount, which presently seems to be inactive. Pore fluids sampled close to a volcanic cone at 2,800-m water depth show an anomalous composition with Mg, SO 4 , and total alkalinity concentrations significantly higher than seawater and a nearby reference core. The most straightforward way of interpreting these deviations is the dissolution of the hydrothermally formed mineral caminite (MgSO 4 0.25 Mg (OH) 2 0.2H 2 O). This interpretation is corroborated by a thorough investigation of fluid isotope systems (δ 26 Mg, δ 30 Si, δ 34 S, δ 44/42 Ca, and 87 Sr/ 86 Sr). Caminite is known from mineral assemblages with anhydrite and forms in hydrothermal recharge zones only under specific conditions such as high fluid temperatures and in altered oceanic crust, which are conditions generally met at the TR. We hypothesize that caminite was formed during hydrothermal activity and is now dissolving during the waning state of the hydrothermal system, so that caminite mineralization is shifted out of its stability zone. Ongoing fluid circulation through the basement is transporting the geochemical signal via slow advection toward the seafloor.Plain Language Summary Hydrothermal vents are a common phenomenon in oceanic spreading centers worldwide. During Meteor cruise 141/1 we sampled sediments and extracted pore fluids to find the first indications for hydrothermal activity in the Terceira Rift. The results indicate that a hydrothermal vent close to a major volcanic cone formed in the past and seems to be in a waning state at present. Sampled fluids are enriched in total alkalinity, Mg and SO 4 . We found that the most straightforward explanation for this unusual finding is the dissolution of the hydrothermally formed mineral caminite, a magnesium-sulfate-hydroxidehydrate. Caminite is a rare mineral but suggested to be abundant under specific conditions in hydrothermal recharge zones. We propose that caminite formed in the Terceira Rift is now dissolving as temperatures decline, and fluids enriched in Mg and SO 4 are transported along deep-rooted faults to the seafloor.

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Shallow-water hydrothermal vents in the Azores (Portugal)

Cited by 14 publications

References 45 publications

Shallow Seafloor Gas emissions Near Heard and McDonald Islands on the Kerguelen Plateau, Southern Indian Ocean

Shallow Seafloor Gas emissions Near Heard and McDonald Islands on the Kerguelen Plateau, Southern Indian Ocean

First Macro-Colonizers and Survivors Around Tagoro Submarine Volcano, Canary Islands, Spain

Origin of High Mg and SO₄ Fluids in Sediments of the Terceira Rift, Azores‐Indications for Caminite Dissolution in a Waning Hydrothermal System

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Shallow-water hydrothermal vents in the Azores (Portugal)

Cited by 14 publications

References 45 publications

Shallow Seafloor Gas emissions Near Heard and McDonald Islands on the Kerguelen Plateau, Southern Indian Ocean

Shallow Seafloor Gas emissions Near Heard and McDonald Islands on the Kerguelen Plateau, Southern Indian Ocean

First Macro-Colonizers and Survivors Around Tagoro Submarine Volcano, Canary Islands, Spain

Origin of High Mg and SO4 Fluids in Sediments of the Terceira Rift, Azores‐Indications for Caminite Dissolution in a Waning Hydrothermal System

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Origin of High Mg and SO₄ Fluids in Sediments of the Terceira Rift, Azores‐Indications for Caminite Dissolution in a Waning Hydrothermal System