Abstract

International Ocean Discovery Program (IODP) Expedition 357 recently drilled 17 holes into the Atlantis Massif, the ocean core complex that hosts the serpentinite-dominated Lost City Hydrothermal field. Multiple types of fluid samples were collected before, during, and after drilling to characterize the biogeochemical regime of the system. These samples collectively represent the first window into the habitats of the Atlantis Massif subsurface. Fluids were analyzed for concentrations of organic acids, dissolved organic carbon, and amino acids. Elevated concentrations of organic acids were found in multiple subsurface fluids across the Massif. Locations that were drilled in the Northern and Western portions of the Massif had formate and acetate present in similar abundances. Fluids from boreholes drilled in the Central portion of the Massif, closest to the Lost City hydrothermal field, had substantially higher concentrations of acetate than of formate. Distinct regions of high acetate/high formate and high acetate/low formate may reflect differences in the physiochemical characteristics of the locations and/or differences in metabolic strategies of subseafloor life. The highest concentrations of dissolved organic carbon were found in a series of boreholes drilled on the Western portion of the Massif (M0071), where there was also evidence of advective flow emanating from one of the boreholes after drilling. Samples from the Central and Northern portion of the Massif had higher total hydrolizable amino acid concentrations and lower relative abundances of D- amino acids compared to samples from the Eastern sites, possibly reflecting differences in subseafloor biological activity.

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