- 1Institute of Paleoceanography and Climate Change, University of the Sinos River Valley, Technological, Porto Alegre, Brazil
- 2Institute of Marine and Atmospheric Research Utrecht, Utrecht University, Utrecht, Netherlands
- 3Earth and Planetary Science Department, Institute of Science Tokyo
- 4Linnaeus University, Faculty of Health and Life Sciences, Kalmar, Sweden
- 5PETROBRAS, Leopoldo Américo Miguez de Mello Research, Development and Innovation Center, Rio de Janeiro, Brazil
The studies of deep-sea gas venting associated with occurrences of gas hydrates in the Amazon Cone has increased the interest of the world scientific community in understanding the role of the Amazon region in the Earth's climate system. Gas plumes have been observed to align along the edge of the regional gas hydrate stability zone in several areas, suggesting the climate-driven dissociation of gas hydrates, and along faults related to the gravitational collapse of the fan. The gas that migrates toward the seabed is stored in gas hydrates and/or authigenic carbonates or released to the oceans by seafloor venting.
Here, we present data from gas hydrates that were sampled during the AMAGAS campaign offshore Brazil in May-June 2023. Five samples of methane hydrates were sampled and their dD and d13C measured. In addition, the abundance of doubly substituted isotopologues of methane (13CH3D and 12CH2D2) were measured for one sample. It is very important to mention that if the compounds have reached equilibrium with respect to their distributions of isotopes among all possible isotopologues, the proportions of 13CH3D and 12CH2D2 will be a function of temperature.
Results of the methane stable isotopes (δ13C and δD) of hydrate-bound for the Amazon fan indicated the dominant microbial origin of methane via carbon dioxide reduction, in which 13C and deuterium isotopes were depleted (δ13C and δD of -90% to -70% V-PDB and -250 to -150% V-SMOW, respectively). Regarding clumped isotopes, Δ13CH3D and Δ12CH2D2 values from +5.5 ‰ and +16.6 ‰, respectively. The hydrate samples are located around the thermodynamic equilibrium line in the Δ13CH3D vs. Δ12CH2D2 space, and their isotopic compositions correspond to apparent temperatures of °C and °C for Δ13CH3D and for Δ12CH2D2, respectively.
Given the geothermal gradient in the area, this temperature corresponds to a depth of about 1000 meters suggesting methane is migrating upwards with deeper fluids. These observations concur with seismic evidence of signal wipe-outs consistent with the rise of gas-bearing fluids along the faults.
How to cite: Rodrigues, L. F., Gilbert, A., Nakagawa, M., Ketzer, J. M., Sivan, M., Röckmann, T., Augustin, A. H., Miller, D., Cupertino, J. A., and Junior, F. C.: Clumped isotope constraints on the origin of methane hydrate from the Amazon Cone, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21093, https://doi.org/10.5194/egusphere-egu25-21093, 2025.
