To the vent field at 48°N on the Endeavour segment of the Juan de Fuca Ridge, That venting extends more than 20 km along the ridge axis with a vigour comparable Values along the tow track-lines and at the vertical cast locations. In the steady-state plume created by plotting and contouring maximum T
Vertical distribution of temperature anomaly.
Temperature anomalies go to zero at the same depth, supporting our interpretation of the Steady-state plume maximum was ~2,100 m each year. Increased anomalies above 1,950 m in 1986 indicate the megaplume presence. Vertical profiles of the temperature and light-attenuation (proportional to theĬoncentration of fine-grained hydrothermal precipitates) anomalies for each cast. The background trend along an isopycnal, was about the same on each cast. The maximum temperature anomaly, defined as the temperature deviation from Lowermost 1,000 m by the megaplume discharge. Density of the water in theĪxial valley was significantly lower in 1986 because of enhanced vertical mixing of the Thin horizon of ambient water (~27.635-27.640 )īetween the steady-state plume and the overlying megaplume. 1986 casts in the axial valley sampled only a Line) except where hydrothermally affected. Each curve has a slope of -4.865☌ m Kg (shown by the straight Potential density plotted against potential temperature for selected axial Of plume entrainment processes and vent-fluid salinity.įig. Other because the consistency of the ambient hydrographic structure and the Despite some uncertainty in the absolute value of T, we assume that the year-to-year values are correct relative to each Substantially different from that of ambient sea water. Values may be an underestimate of the true hydrothermal heating by as much asĪ factor of two owing to cooling of the plume by entrainment of cold bottomĪnd Rona, 1989], and hydrographic aliasing if vent waters have a salinity 1).Īrising from annual variations of ☐.002 in the Hydrothermal emissions is negligible ( Fig. Plume relative to ambient water of the same potential density is calculatedĪre the potential temperature and potential density, respectively, in the plume,Īnd m and b are the slope and intercept, respectively, of theĬurve of water immediately above the plume where the hydrographic effect of Near-bottom conductivity-temperature-depth transmissometer (CTDT) tows and casts,Īnd sampled for He and other constituents using rosette-mounted Niskin bottles. The steady-state plume has been annually mapped by Plume was also found at the same location. Ridge was discovered in August 1986, an extensive steady-state hydrothermal When the megaplume at the north end of the Cleft segment of the Juan de Fuca Ratios may indicate venting created or profoundly perturbed by a magmatic-tectonicĮvent, and lower ratios may typify systems at equilibrium. Magma degassing into a hydrothermal circulation system of high permeabilityĪnd short fluid residence time. He/heat ratio, sampled within days of the megaplume eruption, resulted from To one characteristic of established vent fields on other ridge segments. STP cal, changing from a uniquely high ratio
Ratio in the steady-state plume has progressively decreased from 4.4 to 2.4 That created the Juan de Fuca Ridge 'megaplumes', we have for three years monitored the HeĬoncentration and temperature anomaly of the underlying steady-state plume at Because it is likely that tectonic stretchingĪnd concomitant shallow magmatic activity triggered the cataclysmic venting Further electronic distribution not allowed.Īn important question in submarine hydrothermal research concerns the connectionīetween hydrothermal discharge from a spreading centre and variations in local Lupton Marine Science Institute and Department of Geological Sciences, University ofĬalifornia, Santa Barbara, California 93106, USA Nature, 346, 556-558 (1990)Ĭopyright ©1990 Macmillan Publishers Ltd. Baker Pacific Marine Environmental Laboratory, National Oceanic and AtmosphericĪdministration, 7600 Sand Point Way NE, Seattle, Washington 98115, USA John E. of Commerce / NOAA / OAR / PMEL / PublicationsĬhanges in submarine hydrothermal 3He/heat ratios as an indicator of
0 kommentar(er)
