This study on the Nootka Fault at the Cascadia Margin of the Juan de Fuca plate is a collaborative effort
with University of Washington and Woods Hole Oceanographic Institution, and is funded by National Science
Foundation and the W.M. Keck Foundation. Check back for further real-time results at an upcoming Keck website.
The Optical Tracer Injection System (OTIS), an electronic data
logging version of the Chemical and Aqueous Transport (CAT) flow
meter also developed in the
Hydrogeology and Tectonics Studies Laboratory at the Scripps
Institution of Oceanography, is designed for high resolution
measurements in higher flow rate regimes, 0.2-1000m/yr, and has
potential for real time data acquisition. Like the CAT meter
(Tryon et al.,2001) the OTIS Meter measures aqueous flux at
the seafloor by sealing around an area of the sediment surface and
channeling the flow from this area through the instrument's flow
tube. They differ, however, in the method of flow measurement.
The OTIS, using the Persistor CF1 computer, injects 50uL pulses of
fluorescent rhodamine tracer at 10-45 minute intervals into the
flow tube, figure 1. The pulse of tracer
will travel with the same velocity as the ambient flow through the
flow tube. In the case of fluid discharge from the sediment, as
displayed in figure 1, the tracer will flow out of the instrument
past the upflow detection station. Alternatively the tracer may
pass the downflow detection station during fluid recharge. In this
manner, the OTIS can be used to determine flow rate in both upflow
and downflow regimes. The computer records photodiode measurements
of transmittance and fluorescence at both detection stations as an
LED shines through the flow tube. In the case of the instrument
currently collecting data on the Nootka fault intersecting the
Cascadia margin, data is transmitted via satellite buoy or
for a description of how to interpret OTIS meter data.
Figure 1: The Optical Flow Meter placed on sedimented seafloor
focuses flow through a clear tube. Tracer is injected between
downflow and upflow detection stations.