Item
Ministerio de Ciencia e InnovaciÃ³n (Espanya)  
Mittelstaedt, Eric
EscartÃn, Javier Olive, JeanArthur Barreyre, Thibaut Davaille, Anne Cannat, Mathilde GarcÃa Campos, Rafael 

The relative heat carried by diffuse versus discrete venting of hydrothermal fluids at midocean ridges is poorly constrained and likely varies among vent sites. Estimates of the proportion of heat carried by diffuse flow range from 0% to 100% of the total axial heat flux. Here, we present an approach that integrates imagery, video, and temperature measurements to accurately estimate this partitioning at a single vent site, Tour Eiffel in the Lucky Strike hydrothermal field along the MidAtlantic Ridge. Fluid temperatures, photographic mosaics of the vent site, and video sequences of fluid flow were acquired during the Bathyluckâ€™09 cruise (Fall, 2009) and the Momarsatâ€™10 cruise (Summer, 2010) to the Lucky Strike hydrothermal field by the ROV Victor6000 aboard the French research vessel the â€˜Pourquoi Pasâ€™? (IFREMER, France). We use two optical methods to calculate the velocities of imaged hydrothermal fluids: (1) for diffuse venting, Diffuse Flow Velocimetry tracks the displacement of refractive index anomalies through time, and (2) for discrete jets, Particle Image Velocimetry tracks eddies by crosscorrelation of pixel intensities between subsequent images. To circumvent video blurring associated with rapid velocities at vent orifices, exit velocities at discrete vents are calculated from the best fit of the observed velocity field to a model of a steady state turbulent plume where we vary the model vent radius and fluid exit velocity. Our results yield vertical velocities of diffuse effluent between 0.9 cm s1 and 11.1 cm s1 for fluid temperatures between 3Â°C and 33.5Â°C above that of ambient seawater, and exit velocities of discrete jets between 22 cm s1 and 119 cm s1 for fluid temperatures between 200Â°C and 301Â°C above ambient seawater. Using the calculated fluid velocities, temperature measurements, and photo mosaics of the actively venting areas, we calculate a heat flux due to diffuse venting from thin fractures of 3.15 Â±2.22 MW, discrete venting of 1.07Â± 0.66 MW, and, by incorporating previous estimates of diffuse heat flux density from Tour Eiffel, diffuse flux from the main sulfide mound of ~15.6 MW. We estimate that the total integrated heat flux from the Tour Eiffel site is 19.82 Â± 2.88MWand that the ratio of diffuse to discrete heat flux is ~18. We discuss the implication of these results for the characterization of different vent sites within Lucky Strike and in the context of a compilation of all available measurements of the ratio of diffuse to discrete heat flux Funding for the 2006, 2008, 2009, and 2010 cruises was provided by CNRS/IFREMER through the MoMAR program (France), by ANR (France), the Mothseim Project NT05â€“3 42213 to J. EscartÃn and by grant CTM2010â€“15216/MAR from the Spanish Ministry of Science to R. Garcia and J. EscartÃn 

http://hdl.handle.net/2072/294886  
eng  
American Geophysical Union  
Tots els drets reservats  
Geologia submarina
Submarine geology GeofÃsica Geophysics 

Quantifying diffuse and discrete venting at the Tour Eiffel vent site, Lucky Strike hydrothermal field  
info:eurepo/semantics/article  
Recercat 