Effect of
Current Variability on Temperatures Measured in a Non-buoyant Hydrothermal
Plume
Wetzler,
M.A., and J.W. Lavelle
Marine Geophysical Researches, 20, 505-516, 1998.
Abstract:
Temperature and currents were measured just downstream of the prodigiously
discharging Pipe Organ vent field on the Juan de Fuca Ridge to look at the
temporal variability of the hydrothermal signal passing a single site. Temperatures
(theta) at three depths were sampled every 15 s while current speed and
direction at a single depth was sampled hourly over a 4 day interval in
September 1997 from a taut-wire mooring located ~100 m south of Pipe Organ.
The high temporal variability of temperature, and hen ce inferred heat flux,
is due in large part to current variations. An analytic model of heat transport
and the measured currents were used to extrapolate the measured data in
to two-dimensional time-dependent fields. The effort first required matching
the modeled temperature time series to the measured series at the mooring
site. This extrapolation of the measurements to two dimensions with model,
when animated, demonstrates the pooling of effluent over the vent at various
times, and streaming of ef fluent as a very narrow plume away from the vent
at others, and spawning of boluses of heated fluid and their transport away
from the vent region when a pooling period is followed by a streaming period.
The model temperature fields also allows the comparison of methods used
in calculating heat flux via moored instruments and CTD's; heat flux estimates
are shown to vary widely depending upon analysis assumptions. When the measured
theta time series showed peaks that could not be accounted for by discharge Pipe Organ alone, time reversed trajectories of currents were used to
suggest the location of other contributory vent fields. A contribution to
the measured theta at the mooring site by significant heat flux at or near
Cavern vent field, some 2 km upstream, was thus indicated.
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