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Communication Dans Un Congrès Année : 2017

Carbon leakage from the deep sea

Résumé

Marine sediments store large quantities of organic carbon derived both from the drainage basins of rivers on land and from life in the oceans. The Amazon is the world's largest river, from which sediment supply to the Atlantic Ocean has resulted over the last millions of years in the build-up of a vast deep-sea fan up to 10 km thick. Since the last glacial maximum (ca. 24,000 years before present), the fan has accumulated a mass of organic carbon comparable to that contained in the presentday Amazon Forest. Over geological timescales, the process of sedimentary burial in the Amazon and other marine depocentres sequesters organic carbon, but also allows microbial methanogenesis to convert some of it to mobile methane. Methane moving through sediments may be oxidized and converted into CO2, trapped as dissolved or free gas or, where stability conditions permit (in water depths greater than 500 m), as gas hydrates. Reservoirs of gas hydrates are favoured by high sedimentation rates, and it has been suggested that the Amazon and other rapidly deposited deep-sea fans are net carbon sinks. Here we present evidence that carbon stored in and beneath gas hydrates is escaping to the ocean through seafloor venting features. The distribution of these features suggests them to form along faults created by the gravitational collapse of the fan, and along the upper limit of the gas hydrate stability zone in response to changes in pressure (depth) and/or temperatures influenced by climate. Our findings support recent studies suggesting that seafloor gas venting in deep-sea settings where gas hydrates are stable is a more widespread phenomenon than previously recognised, suggesting estimates of global methane emissions to be conservative. A more accurate knowledge of seafloor methane emissions is thus of paramount importance for our understanding of the effects of ongoing climate-driven changes on ocean processes, as well as for the effective management of marine resources.
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Dates et versions

hal-02155745 , version 1 (17-06-2019)

Identifiants

  • HAL Id : hal-02155745 , version 1

Citer

J M M Ketzer, D Praeg, A Augustin, F Rodrigues, R Oliveira, et al.. Carbon leakage from the deep sea. 8th Brazil-Germany Symposium for Sustainable Development, Oct 2017, Porto Alegre, Brazil. pp.65. ⟨hal-02155745⟩
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