Gas Geochemistry at Grande Comore and Mayotte Volcanic Islands (Comoros Archipelago), Indian Ocean

Liuzzo, Marco; Muro, Andréa Di; Rizzo, Andrea Luca; Caracausi, Antonio; Grassa, Fausto; Fournier, N.; Shafik, Bafakih; Boudoire, Guillaume; Coltorti, Massimo; Moreira, Manuel; Italiano, Francesco

doi:10.1029/2021gc009870

Cited by 9 publications

(8 citation statements)

References 104 publications

(290 reference statements)

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“…1, Supplementary Video 2). Fluid composition indicates that magmatic/hydrothermal gases are composed primarily of CO 2 and CH 4 with small contribution of H 2 (Table 1A), consistent with emissions at most other volcanoes 9,[30][31][32] and in subaerial volcanic gasses from Mayotte Petite Terre 33 . The isotopic composition of CO 2 indicates a typical mantle 34 signature (δ 13 C-CO 2 = -3.7 ± 0.2‰, Δ 14 C CO2 < -990‰).…”

Section: The Horseshoe Edi Ce: a Large Liquid Co2 Venting And Hydrate...supporting

confidence: 63%

Large CO2 seeps and hydrates field in the Indian Ocean (Mayotte Island)

Cathalot,

Rinnert,

Scalabrin

et al. 2024

Preprint

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About 80% of Earth volcanic activity occurs underwater, releasing deep carbon to submarine environments and impacting Earth’s climate over geological timescales. The CO2 emitted during submarine eruptions and/or hydrothermal degassing creates local ocean acidification, affecting the seawater carbonate equilibrium and oceanic ecosystems at large regional scales. Here, we report for the first time the existence of a major CO2 hydrates field at the seafloor offshore Mayotte Island (Indian Ocean) associated with liquid CO2 venting, following the submarine eruption that occurred in 2018. Using detailed acoustic surveys and in situ Raman spectroscopy, we reveal multiple hydrate mounds and seep zones distributed over an area of 0.06 km². We show that the gas seeps are mainly composed of CO2, with minor contributions of CH4 and H2, with noble gas ratios and stable and radio-carbon isotopes clearly demonstrating their magmatic origin. Estimates of the CO2 emitted over the entire area represent about 0.5% of the global magmatic carbon flux. Our discovery also suggests that CO2 hydrates may potentially be stable at the seafloor at the right pressure-temperature conditions, bringing new prospects into CO2 sequestration and decarbonization pathways in the ocean, in particular regarding kinetics of hydrates dissolution and environmental impacts.

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Section: The Horseshoe Edi Ce: a Large Liquid Co2 Venting And Hydrate...supporting

confidence: 63%

Large CO2 seeps and hydrates field in the Indian Ocean (Mayotte Island)

Cathalot,

Rinnert,

Scalabrin

et al. 2024

Preprint

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“…The average depth of the Dziani Dzaha Lake is about 3 m with a narrow depression reaching 18 m depth (Figure 1), likely related to the chimney of the phreatomagmatic eruption at the origin of this lake. Magmatic gases bubble through the water column in several locations [Milesi et al, 2020, Liuzzo et al, 2021 mostly in shallow areas of the lake, with one bubbling site in the central part for which a strong increase in the bubbling activity has been observed since 2020 compared to our last observations from 2012 to 2017 (Figure 1).…”

Section: Study Sitementioning

confidence: 52%

“…Before the beginning of the seismo-volcanic crisis offshore Mayotte, several bubbling areas were identified at the water-air interface of the Dziani Dzaha Lake. The volcanic origin of these degassing into the atmosphere was confirmed by the CO 2 carbon isotopic composition, which was typically of magmatic origin [around −3 , Milesi et al, 2020, Liuzzo et al, 2021]. Yet, since a large part of these degassing was ebullitive, the contribution of this carbon source to the lake water column was difficult to estimate [Cadeau et al, 2020].…”

Section: Physical and Chemical Features In The Water Columnmentioning

confidence: 99%

“…Before the seismovolcanic crisis, the physical, chemical and biological features of this ecosystem were far from those observed in a modern oceanic or lacustrine environment (details in Study site section). The ongoing seismo-volcanic crisis offshore Mayotte could have a significant impact on the stability and the functioning of this ecosystem through the reactivation of fractures in the crater/basement, the infiltration of fresh/sea water and/or the increase in magmatic bubbling and degassing through its waters [Liuzzo et al, 2021].…”

Section: Introductionmentioning

confidence: 99%

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Impact of the seismo-volcanic crisis offshore Mayotte on the Dziani Dzaha Lake

Cadeau¹,

Jézéquel²,

Groleau³

et al. 2023

Comptes Rendus. Géoscience

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Since May 2018, an unexpected long and intense seismic crisis started offshore Mayotte (Indian Ocean, France). This ongoing seismic sequence is associated with the birth of a newly discovered submarine volcano 50 km east of Petite Terre. Here, we investigate the indirect impact of this crisis on the stability of an atypical ecosystem located in Mayotte, the Dziani Dzaha Lake. This lacustrine system presented physical, chemical and biogeochemical characteristics that were distinct from those classically observed in modern lakes or seawater, e.g. high salinity (up to 70 psu), lack of nitrate, sulfate content below 3 mM, and permanent water column anoxia below ca. 1.5 m depth (2012-2017 period). Based on three surveys conducted in 2020 and 2021, we documented an episode of water column oxygenation, a significant pH decrease and an impressive change in the carbon isotope signatures. These preliminary data suggest that the functioning of biogeochemical cycles in the Dziani Dzaha Lake is impacted by increased CO 2 inputs and the changes in the lake mixing dynamics, which is an indirect consequence of the ongoing seismo-volcanic crisis.

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“…Prolonging the airport beach, is a thick ash sequence (tens of meters) with a bulk rock permeability of ∼10 −5 to 10 −6 m 2 (Guilbert et al., 2008), lower than in La Réunion. Yet, on top of this ash sequence, there are high CO 2 concentrations in the soil with a magmatic geochemical signature (Liuzzo et al., 2021) indicating that the degassing at the beach is prolonged diffusely through the soil. We infer that the fracture network which is visible at the beach is continued in the ash sequence.…”

Section: Soil Co2 Monitoring Stations: Data and Settingmentioning

confidence: 99%

Seasonal Environmental Controls on Soil CO₂ Dynamics at a High CO₂ Flux Sites (Piton de la Fournaise and Mayotte Volcanoes)

et al. 2023

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Environmental parameters drive seasonal soil CO2 efflux toward the atmosphere. However, their influence is not fully understood in contexts of high CO2 fluxes where CO2 accumulates in the subsurface. A prime example are volcanoes subject to continuous CO2 diffuse degassing rising from deep magmatic reservoirs, through the subsurface and up to the atmosphere. For many of these volcanoes where soil CO2 is monitored, a seasonal influence of the atmosphere and water table is observed but not characterized. Here, we compare variations of air temperature, atmospheric pressure, rainfall and water table level with near‐surface soil CO2 concentration by performing a time‐lagged detrended cross‐correlation analysis on years‐long time series from the volcanoes of Piton de la Fournaise and Mayotte. At Piton de la Fournaise, soil CO2 variations correlate best with air temperature variations (0.81) and water table variations (0.74). In Mayotte, soil CO2 variations correlate best with atmospheric pressure variations (−0.95). We propose that at Piton de la Fournaise, the thick vadose zone and high permeability favor CO2 transfer by thermal convection. Additionally, energy transfer is decoupled from mass transfer. Slow heat transfer from the atmosphere down to the accumulated CO2 layers in the subsurface results in a delayed influence of air temperature and of the water table level on the thermal gradient between the subsurface and the atmosphere, and consequently on the efficiency of the CO2 transfer. In Mayotte, we propose that the thin vadose zone and the presence of a network of large fractures favor CO2 transfer by barometric pumping.

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Gas Geochemistry at Grande Comore and Mayotte Volcanic Islands (Comoros Archipelago), Indian Ocean

Cited by 9 publications

References 104 publications

Large CO2 seeps and hydrates field in the Indian Ocean (Mayotte Island)

Large CO2 seeps and hydrates field in the Indian Ocean (Mayotte Island)

Impact of the seismo-volcanic crisis offshore Mayotte on the Dziani Dzaha Lake

Seasonal Environmental Controls on Soil CO₂ Dynamics at a High CO₂ Flux Sites (Piton de la Fournaise and Mayotte Volcanoes)

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Gas Geochemistry at Grande Comore and Mayotte Volcanic Islands (Comoros Archipelago), Indian Ocean

Cited by 9 publications

References 104 publications

Large CO2 seeps and hydrates field in the Indian Ocean (Mayotte Island)

Large CO2 seeps and hydrates field in the Indian Ocean (Mayotte Island)

Impact of the seismo-volcanic crisis offshore Mayotte on the Dziani Dzaha Lake

Seasonal Environmental Controls on Soil CO2 Dynamics at a High CO2 Flux Sites (Piton de la Fournaise and Mayotte Volcanoes)

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Seasonal Environmental Controls on Soil CO₂ Dynamics at a High CO₂ Flux Sites (Piton de la Fournaise and Mayotte Volcanoes)