Carbon and Nutrient Dynamics in Cool Ridge-Flank Hydrothermal Springs: The Dorado Outcrop of the Eastern Pacific.

Abstract:

The Dorado outcrop is a basaltic edifice that protrudes through the marine sediments that cover the seafloor along the eastern flank of the East Pacific Rise. This outcrop is an exit conduit for cool, chemically altered crustal fluids. We sampled exiting fluids using a variety of techniques including autonomous, time-series samplers (OsmoSamplers) and discrete sampling using the DSV Alvin. We also collected and analyzed pore fluids from a series of short sediment cores in the vicinity of hydrothermal springs. Samples for the major nutrients show that silicic acid is significantly enriched within the venting fluids relative to the concentration in bottom seawater, whereas dissolved phosphate is depleted within these fluids. Concentrations of dissolved inorganic carbon appear to be slightly elevated in hydrothermal fluids relative to bottom seawater. Pore fluids are highly variable in their concentrations for the major nutrients, perhaps because of variable exchange between these fluids and the underlying crustal fluids. Our results indicate that the fluids within this crustal aquifer system undergo alteration during their rapid transit within the volcanic crust. The chemical composition of these fluids appears to be influenced by exchange with the overlying sediment pore fluids as well as reactions internal to the volcanic crustal reservoir.