U.S. Dept. of Commerce / NOAA / OAR / PMEL / Publications

Episodic venting of hydrothermal fluids From the Juan de Fuca Ridge

E.T. Baker, J.W. Lavelle, R.A. Feely, G.J. Massoth, and S.L. Walker

Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration, Seattle, Washington

J.E. Lupton

Marine Science Institute and Department of Geological Sciences, University of California, Santa Barbara

Journal of Geophysical Research, 94, 9237–9250 (1989)
Copyright ©1989 by the American Geophysical Union. Further electronic distribution is not allowed.


Both megaplume discoveries have come during extensive hydrographic and chemical surveys designed to map the distribution of hydrothermal emissions over and around the crest of the southern JDFR. Deep-two data were collected by a Sea-Bird conductivity-temperature-depth sensor (CTD) and a Sea Tech 0.25-m path length transmissometer continuously cycled through the bottom 400–1000 m of the water column while towed from a surface ship. Effective precision of the measurements was ±0.001°C for temperature, ±0.002‰ for salinity, and ±0.001 m−1 for light attenuation. Hydrothermal plumes were identified in real time by the presence of light attenuation and temperature anomalies. The plume temperature anomaly (ΔT) is the deviation along the potential temperature (θ ) axis from the normally linear relationship between potential density (σθ) and θ [Lupton et al., 1985]. The temperature anomaly thus calculated is relative to ambient water of the same potential density as the neutrally buoyant plume.

Primary navigation was by Loran C; position relative to the axial bathymetry was determined by Sea Beam and by acoustic navigation where transponders were within range. The time, duration, and distance of each tow is given in Table 1.

If your browser cannot view the following table correctly, click this link for a GIF image of Table 1.
TABLE 1. Sequence and Duration of CTD Tows

Tow   Beginning   Beginning Ending Ending  Distance, 
Time, UT Date    Time, UT    Date km

S2 0730 Aug. 20, 1986 1048 Aug. 21, 1986 121  
S3 1745 Aug. 21, 1986 0440 Aug. 22, 1986 21
  S23 0740 Aug. 23, 1986 1500 Aug. 23, 1986 16
T5 1230 Sept. 12, 1987 1803 Sept. 13, 1987 79
T9 0630 Sept. 19, 1987 1540 Sept. 19, 1987 24
  T10 1805 Sept. 19, 1987 0110 Sept. 20, 1987 14
  T11 0303 Sept. 20, 1987 0850 Sept. 20, 1987 16
  T14 0220 Sept. 23, 1987 1507 Sept. 23, 1987 35

Water samples were collected during some of the tows by rosette-mounted 30-L Niskin bottles internally coated with Teflon and with silicon tubing springs. The suspended particles were isolated by N2 pressure filtration through 0.4-μm pore size Nuclepore polycarbonate filters. Elemental particulate chemistry was determined by X ray primary and secondary emission spectrometry using a Kevex Super 8000-770 X ray spectrometer with a Rh source and a Ge secondary target [Feely et al., 1987]. Individual grain identification and sizing were performed on an International Scientific Instruments DS130S scanning electron microscope coupled to the Kevex spectrometer. Dissolved Mn in acidified samples was determined onshore by flameless atomic absorption spectrometry after Klinkhammer [1980]. Nutrient samples were collected in 250-mL plastic amber bottles and analyzed spectrophotometrically at sea using a Technicon Autoanalyzer. Helium samples were collected and stored in copper tubes after cold-weld sealing [Young and Lupton, 1983] and measured by mass spectrometry at the University of California, Santa Barbara.

Go back to previous section or forward to next section

PMEL Outstanding Papers

PMEL Publications Search

PMEL Homepage