Organic Acids and Amino Acids in Serpentinization Related Fluids from the Atlantis Massif

Serpentinization is a low temperature, low pressure process that occurs when water reacts with ultramafic rocks. Fluids that have interacted with serpentinites have elevated concentrations of hydrogen and reduced carbon species that can fuel chemolithoautotrophy. International Ocean Discovery Program Expedition 357 drilled a series of boreholes into the Atlantis Massif with the goal of investigating how serpentinization impacts carbon cycling and sustains life in the subseafloor. Bottom water samples (CTD), fluids flushed from the boreholes during drilling (Rock Drill), and fluids that were trapped in the liners of the cores (Liner fluids) were collected. The changes and distributions of organic acids and amino acids in these fluids were analyzed to investigate the outcome of water-rock reactions and potential areas of microbial activity in the subsurface of the Atlantis Massif. Liner fluids contained formate (0 – 93 μM) and acetate (0 – 1,791 μM) concentrations that reached as high as those in pure hydrothermal fluids from the nearby Lost City field (formate: 36 – 158 μM; acetate: 1 – 35 μM). Fluids from the Western and Northern portions of the Massif had elevated concentrations of both acetate and formate, while those from the Central region had the highest acetate concentrations, but low formate. Organic acids were lowest in samples from the Eastern drill sites. Organic acid concentrations in the CTD and Rock Drill fluid samples were below detection limit, indicating they are rapidly diluted or removed in the water column. The amino acid concentrations from the Rock Drill (71 - 170 nmol/L) and CTD (64 - 129 nmol/L) samples were in range for ocean waters at the depths of collection (768 - 1585 m). The total hydrolyzed amino acid (THAA) concentrations were higher in the Rock Drill samples, with the highest THAA concentrations in the Central, Western, and Northern locations of the Atlantis Massif. The higher THAA concentrations in the Rock Drill samples, and the distribution of acetate and formate concentrations in the liner fluids suggest that there is potential for enhanced microbial activity in the Western, Central, and Northern portions of the Atlantis Massif