Intellectual Merit: The concentration of chloride ion is a master variable in controlling the chemical composition of high temperature hydrothermal fluids. Chloride concentration affects this control via its importance in determining mineral solubility. It has become apparent in recent years that the chloride concentration in hydrothermal fluids is controlled primarily by phase separation. Phase separation is, in turn controlled by the nature of the heat source. Short term and very dramatic temporal changes in the nature and degree of phase separation and the resultant changes in chloride concentration in hydrothermal fluids as a result of magmatic diking and eruptive events have been observed in recent years. Tectonic cracking events have also been seen to cause temporal changes in both temperature and chloride concentration. Most of these events have been observed and documented by infrequent ship-based sampling efforts and the temporal nature of the events is poorly defined. We have developed an in-situ instrument that is capable of measuring temperature and fluid resistivity as a proxy for chloride concentration. This instrument has so far been deployed at two RIDGE 2000 Program Integrated Study Sites (Endeavour and 9ºN) for periods of several months, with excellent results. These data records indicate short term changes in chloride concentration on a temporal scale which was unexpected and that we have not had the ability to observe previously. In this project we will evaluate existing data sets of temperature and vent fluid resistivity in the context of the Endeavour seismic data set. Under support of this project, we will deploy these instruments at the High Rise vent field to augment data that will be collected at the Main Endeavour and Mothra vent fields by instruments connected to the NEPTUNE Canada fiber optic cable.
Broader Impacts: In-situ sensors are becoming increasingly important as we shift toward trying to better understand the temporal nature of processes working in hydrothermal systems as well as oceanography in general. The insights gained during the development of sensors capable of operating in the hostile environment of hydrothermal vents is likely to be useful in many fields, in particular the efforts to develop seafloor observatories in hydrothermal environments will be greatly aided by the successful continued deployment of this sensor.
