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Experimental Constraints on Hydrothermal Circulation in Mid-Ocean Ridges

March 10, 2020 @ 3:00 pm - 4:30 pm

Nick Pester, Research Scientist

What to Expect

Magmatic activity beneath the seafloor drives hydrothermal circulation, promoting heat transfer and chemical exchange between newly forming ocean crust and seawater. This process results in the seafloor discharge of fluids that have been compositionally modified, exerting a major control on the chemistry of seawater. Hydrothermal venting also creates large metallic mineral deposits, and provides chemosynthetic energy for primitive microbes. A key problem in studying the chemical evolution of seawater into hydrothermal fluid is understanding the physical conditions under which fluid-mineral reactions occur. Interpreting the chemical composition of deep-sea hydrothermal fluids frequently relies upon experimental observations and empirical models because the prediction of thermodynamic and kinetic parameters at the near-critical and two-phase conditions relevant to these systems is dubious. As an example, experimentally calibrated vapor-liquid partition coefficients and geothermobarometry using Fe-Mn-Si solubility at near-critical conditions can be used to infer how the subsurface structure of a hydrothermal system evolves in response to magmatic events using a 17 yr time-series of fluid chemistry from the East Pacific Rise (EPR). Broader application of these proxies to a global array of hydrothermal fluids reveals transition metal fluxes into the ocean may be governed by the pressure and temperature at which fluids intersect the NaCl-H2O critical curve. One implication is that changes in hydrostatic pressure due to glaciation could impact reaction temperatures and, consequently, the hydrothermal flux of bio-available Fe and Mn (the solubility of these metals increases 600-fold between 300 and 450°C). Calculations of how historic changes in sea level might have affected the Fe flux from vents typical of the EPR compare reasonably well to Fe flux estimates from EPR, 11°S sediments over the last 150 Ka.

Speaker Bio

Nick Pester is an aqueous geochemist and oceanographer with specific expertise in fluid-mineral exchange reactions and chemical mass transport in natural hydrothermal systems. He is currently a research scientist in the Department of Earth and Planetary Science at UC Berkeley. He received a Ph.D. in Geology/Chemistry from the University of Minnesota, followed by post-doctoral work in energy geosciences at the Lawrence Berkeley National Laboratory. He has been a team member of six interdisciplinary oceanographic expeditions focused on characterizing the diversity of seafloor hot springs throughout the Pacific, Atlantic and Indian Oceans. He runs the hydrothermal laboratory at LBNL, conducting experiments with broad implications for modeling chemical/isotope exchange between fluids, minerals and gases in the Earth’s crust and the subsurface oceans of icy satellites.

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