Weathering and biodegradation of hydrothermal petroleum in the north rift of Guaymas Basin, Gulf of California

Abstract

The Guaymas Basin, Gulf of California, is an actively spreading ocean basin, part of the system of spreading axes and transform faults extending from the East Pacific Rise to the San Andreas fault. Upward migration of hydrothermal petroleum in the basin rifts occurs by both bulk transport and high temperature/pressure aqueous and supercritical gaseous (e.g. CO2, CH4) fluid phases into the seabed sediments. The resulting mounds are laden with the youngest hydrothermal petroleum known to date. The north rift hydrothermal system has been dormant for ~ 3000 years, and organic geochemical analyses of sediment samples collected by both piston and push corers and by dredging operations from various cruises to the Gulf of California show that the organic matter is composed primarily of autochthonous lipids from marine biota, overprinted by hydrothermal petroleum. The chemical composition of this petroleum indicates severe biodegradation for exposed samples, based on the contents of aliphatic, aromatic, steroid, and hopanoid biomarkers. Sulfurized lipids are enriched in the biodegraded oils. Both hydrothermal minerals and petroleum in the mounds of the north rift seabed have been weathered by oxidative/microbial processes.

Metagenomic profiles of archaea and bacteria within thermal and geochemical gradients of the Guaymas Basin deep subsurface

“…An ideal natural laboratory for such a research task is Guaymas Basin, a hydrothermally-active ocean spreading center in the Gulf of California, covered by several hundred meters of sediment that host basaltic sill intrusions 7 and strong geothermal heat flow 8 . Pyrolysis of buried organic carbon in these organic-rich sediments produces a complex milieu of petroleum hydrocarbons, including light hydrocarbons and methane, alkanes, and aromatic compounds, as well as carboxylic acids, and ammonia 9 , 10 . These compounds are transported via hydrothermal fluids through Guaymas Basin’s thick sediments, supporting diverse and active microbial communities 11 .…”

Metagenomic Profiles of Archaea and Bacteria within Thermal and Geochemical Gradients of the Guaymas Basin Deep Subsurface

“…Guaymas Basin is a hydrothermally-active ocean spreading center in the central Gulf of California, covered by several hundred meters of sediment that host basaltic sill intrusions (Lizarralde et al 2023) and strong geothermal heat flow (Neumann et al 2023). Pyrolysis of buried organic carbon in these organic-rich sediments produces a complex milieu of petroleum hydrocarbons, including light hydrocarbons and methane, alkanes, and aromatic compounds, as well as carboxylic acids, and ammonia (Von Damm et al, 1985, Simoneit et al 1995. These compounds are transported via hydrothermal fluids through Guaymas Basin's thick sediments, supporting diverse and active microbial communities (Cruaud et al 2017;Ramírez et al, 2021).…”