On continental margins, upward migration of fluids from various sources and various subsurface accumulations, through the sedimentary column to the seafloor, leads to the development of cold seeps where chemical compounds are discharged into the water column. MarsiteCruise was undertaken in November 2014 to investigate the dynamics of cold seeps characterized by vigorous gas emissions in the Sea of Marmara (SoM). Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site. seventeen seeps consist of variable mixtures of different components from two or three sources.

in the Sea of Marmara to gain detailed insight into the fate of fluids migrating within the sedimentary column and partially released into the water column. The overall objective of the project was to achieve a more global understanding of cold-seep dynamics in the context of a major active strike-slip fault. Five remotely operated vehicle (ROV) dives were performed at selected areas along the North Anatolian Fault and inherited faults. To efficiently detect, select and sample the gas seeps, we applied an original procedure. It combines sequentially (1) the acquisition of ship-borne multibeam acoustic data from the water column prior to each dive to detect gas emission sites and to design the tracks of the ROV dives, (2) in situ and real-time Raman spectroscopy analysis of the gas stream, and (3) onboard determination of molecular and isotopic compositions of the

Abstract:The knowledge of the phase behavior of carbon dioxide (CO 2 )-rich mixtures is a key factor to understand the chemistry and migration of natural volcanic CO 2 seeps in the marine environment, as well as to develop engineering processes for CO 2 sequestration coupled to methane (CH 4 ) production from gas hydrate deposits. In both cases, it is important to gain insights into the interactions of the CO 2 -rich phase-liquid or gas-with the aqueous medium (H 2 O) in the pore space below the seafloor or in the ocean. Thus, the CH 4 -CO 2 binary and CH 4 -CO 2 -H 2 O ternary mixtures were investigated at relevant pressure and temperature conditions. The solubility of CH 4 in liquid CO 2 (vapor-liquid equilibrium) was determined in laboratory experiments and then modelled with the Soave-Redlich-Kwong equation of state (EoS) consisting of an optimized binary interaction parameter k ij(CH 4 -CO 2 ) = 1.32 × 10 −3 × T − 0.251 describing the non-ideality of the mixture. The hydrate-liquid-liquid equilibrium (HLLE) was measured in addition to the composition of the CO 2 -rich fluid phase in the presence of H 2 O. In contrast to the behavior in the presence of vapor, gas hydrates become more stable when increasing the CH 4 content, and the relative proportion of CH 4 to CO 2 decreases in the CO 2 -rich phase after gas hydrate formation.