Gravity complexes as a focus of seafloor fluid seepage: the Rio Grande Cone, SE Brazil

• Published in: Scientific Reports
• Main Authors: Ketzer, M., Praeg, Daniel, Augustin, A., Rodrigues, L., Steiger, A., Rahmati-Abkenar, M., Viana, A., Miller, D., Malinverno, A., Dickens, G., Cupertino, J.
• Other Authors: Linneaus University, Géoazur (GEOAZUR 7329), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD France-Sud ), Institut des Sciences de la Terre de Paris (iSTeP), Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Pontifícia Universidade Católica do Rio Grande do Sul Brasil = Pontifical Catholic University of Rio Grande do Sul Brazil = Université catholique pontificale de Rio Grande do Sul Brésil (PUC-RS), Universidade Federal do Rio Grande (FURG), Petrobras Rio de Janeiro, Lamont-Doherty Earth Observatory (LDEO), Columbia University New York, Trinity College Dublin, European Project: 656821,H2020,H2020-MSCA-IF-2014,SEAGAS(2016)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2023
• Subjects: [SDU]Sciences of the Universe [physics]; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; North Atlantic
• Online Access: https://hal.science/hal-04080037; https://hal.science/hal-04080037/document; https://hal.science/hal-04080037/file/s41598-023-31815-1.pdf; https://doi.org/10.1038/s41598-023-31815-1

International audience Seafloor methane emissions can affect Earth’s climate and ocean chemistry. Vast quantities of methane formed by microbial decomposition of organic matter are locked within gas hydrate and free gas on continental slopes, particularly in large areas with high sediment accumulations such as deep-sea fans. The release of methane in slope environments has frequently been associated with dissociation of gas hydrates near the edge of the gas hydrate stability zone on the upper slope, with discharges in greater water depths less understood. Here we show, using data from the Rio Grande Cone (western South Atlantic), that the intrinsic, gravity-induced downslope collapse of thick slope sediment accumulations creates structures that serve as pathways for gas migration, unlocking methane and causing seafloor emissions via giant gas flares in the water column. The observed emissions in the study region (up to 310 Mg year −1 ) are three times greater than estimates for the entire US North Atlantic margin and reveal the importance of collapsing sediment accumulations for ocean carbon cycling. Similar outgassing systems on the Amazon and Niger fans suggest that gravity tectonics on passive margins is a common yet overlooked mechanism driving massive seafloor methane emissions in sediment-laden continental slopes.