Hydrothermal circulation in the upper part of the igneous (volcanic) seafloor feeds submarine hot springs that support vigorous biological communities and causes an exchange of chemical elements between the rocks and sea water the affects the chemistry of the oceans in important ways, yet understanding these hydrothermal systems has been hampered by the difficulty of measuring heat flow and fluid flow. Heat flow blankets developed by one of the proponents of this projects are designed for deployment on bare rock, and thus hold the potential of providing improved and more detailed heat flow values. This deployment of heat flow blankets in combination with magnetic gradiometer and high-resolution bathymetry data seeks to characterize hydrothermal circulation at the RAVEN in detail. In additional to developing a heat flow method and contribution important new data to the field, broader impacts of this work include student participation, and outreach through teaching and public lectures.
Deep sea hydrothermal vent sites are graphic demonstrations of the effect of the circulation of hot fluid within the ocean seafloor crust resulting in spectacular metal-rich mineral deposits along with unique biological communities. The vertical and lateral extent of this hydrothermal circulation is a major question that affects both the distibution of these mineral rich deposits and the extent of life in these extreme environments. The primary objective of this project was to define the pattern of fluid circulation within the seafloor crust in and around an active hydrothermal system. For the experiment we chose the Raven hydrothermal field, located just north of Main Endeavour Field on the northern Juan de Fuca Ridge in the Northeast Pacific ocean. We used innovative thermal blanket technology to measure the seafloor heat flux (i.e. the amount of heat coming out of the seafloor by conduction) in an area of 400 x 800 meters around a single vent site. This survey included high resolution magnetic field measurements which can be used as a proxy of past hydrothermal fluid circulation. The magnetism of upper ocean crust is attenuated and even destroyed by the circulating hot fluids and results in magnetic low areas or "burnholes" that preserve the past history of vent fluid circulation. Our surveys document that the hydrothermal circulation is vigorous in the shallow upper few hundred meters of the seafloor and has lateral variations of less than a 100 meters in scale. The major faults that bound the rift axis act as recharge areas for fluid circulating in this environment. The primary impact on human resources of this research program was the contribution to the educational development of students, both graduate and undergraduates at the University of Washington (UW). Several graduate and undergraduate students from other institutions actively participated in the 2011 field program and gained valuable at-sea experience. Three UW students acquired specific data sets from the cruise, analyzed and interpreted it, resulting in first-author publications in the reviewed scientific literature. In the course of their projects, the students interacted extensively with the Co-PIs of this program and acquired valuable tools that will be important to their professional development. High resolution marine magnetic surveys of the type carried out in this program are part of a exploration suite of geophysical sensing methods that play an important role in defining the extent of subsurface marine hydrothermal systems and related mineral resources. The incipient deep sea mining industry under the auspices of the United Nations International Seabed Authority (new regulations now allow for exploration in "the area") will be using magnetism as one of their tools for defining exploration prospects for eventual exploitation of subsea metallic mineral resources.
