Rona
Acoustic imaging and quantification of plume and diffuse flow at vent clusters in the Endeavour Integrated Study Site (ISS): Integration with in situ measurements
P.A. Rona¹*, K.G. Bemis¹, C. Jones², D.R. Jackson², K. Mitsuzawa³, D.R. Palmer⁴, & D. Silver⁵
Corresponding author: rona@imcs.rutgers.edu
¹Rutgers University, IMCS, New Brunswick, NJ 08901-8521
²University of Washington, Applied Physics Lab, Seattle, WA 98105
³JAMSTEC, Yokosuka, Japan 237-0061
⁴NOAA, AOML, Miami, FL 33149
⁵Rutgers University, CAIP, Piscataway, NJ 08855-1390
Abstract:
Integration of remote sensing with direct in situ measurements at a seafloor hydrothermal site is an ideal that is seldom achieved. We use our acoustic images and in situ measurements of a major plume and surrounding diffuse flow discharging from the Grotto vent cluster in the Main Endeavour Field to demonstrate the importance and limitations of coordinating remote sensing with direct measurements to determine fluxes (volume and heat) of plume and diffuse flow. The measurements were made on our Vent Imaging Pacific (VIP) cruise in July 2000. Our measurements and estimates of volume and heat flux are presented in the following table:
| Location | Flow rate (m/s) |
Flow area (m²) |
Volume flux (m³/s) |
Temperature (ºC) |
Heat flux (MW) |
| Main plume, Grotto N tower (at vent) |
1.0 | 0.033 | 0.033 | 340 –360 range at 5 source vents |
5..5—5.9 |
| Main plume, Grotto N tower (16 m above vent) |
0.25 | 79 | 5.5 +/- 0.4 | Not measured | Unknown |
| Diffuse flow surrounding plume on Grotto N tower |
0.07-0.28 | 107 | 8-30 | 6-23 | (209- 3x10³) |
Keywords:
Endeavour ISS, hydrothermal, plumes, diffuse flow, fluxes.
Contributions to Integration and Synthesis:
Our direct measurement of flow rate, flow area (cumulative area of vent orifices), and temperature of discharge at the source vents of the Grotto plume constrained the heat flux to an estimated +/- 20 percent. Acoustic measurement of area of diffuse flow is estimated at +/- 20 percent. Much larger uncertainties exist in measurement of diffuse flow related to variability (over an order of magnitude) in direct point measurements of temperature and flow rate over the area of diffuse flow. These uncertainties result in a large range of volume and heat flux estimates for the diffuse flow (see Table). Advection rates related to tidally driven reversing near-bottom currents add additional uncertainties to the diffuse flow. Coordination of remote and in situ methods to measure volume and heat flux is basic to characterizing seafloor hydrothermal sites, with inherently greater uncertainties with reference to diffuse than to focused flow.