Southeast Coastal Ocean Report
16
spanning the Straits of Florida
(Fig. 3b.1). The undersea cable
voltages can be converted to
physically meaningful transport
estimates (i.e., intensity of the
flow), using electromagnetic
induction theory and data from
calibration cruises (cross-stream
sections). These transport
records contain decadal changes,
of the order of 10-25% of the
long-term mean transport, that
track the North Atlantic
Oscillation Index. By extension,
the strong correlation of Florida
Current transport variability with
the North Atlantic Oscillation
indicates a correlation with the
large-scale sea-surface
temperature patterns associated
with the North Atlantic
Oscillation. This suggests
connections to tropical Atlantic
variability on climatically
significant time scales. Numerous societally significant weather and climate phenomena
are thought to be related through large scale ocean-atmosphere patterns in the Atlantic,
including decadal and inter-decadal variations in fisheries, rainfall, and hurricane activity.
The present funding for the WBTS provides for continuous collection of cable voltages
(every minute) and automated processing of simple geomagnetic corrections. In addition
to the cable measurements, quarterly calibration cruises are required. Four two-day small
boat calibration cruises on the (R/V F. G. Walton Smith) are conducted each year. These
measurements complement a related project that measures the upper ocean thermal
structure in the Atlantic through high-density Volunteer Observing Ship (VOS)
expendable bathythermograph (XBT) observations.
At Eight Mile Rock, Grand Bahamas Island and in West Palm Beach, Florida, electrode
equipment provides a stable reference voltage (i.e., grounds) at either end of the
submerged telephone cable (owned by AT&T) that extends across the Straits of Florida
(Fig. 3b.1). Recording instruments for the cable measurements are located at Eight Mile
Rock. Data acquisition was interrupted in the late summer of 2004 when Hurricane
Frances and then Hurricane Jeanne substantially damaged infrastructure on the Bahamas,
including telephone service and electricity. Some data are likely to be unrecoverable. A
temporary recording system was installed on October 28, 2004 to begin acquiring new
data while a permanent replacement was being built; the latter was installed on January
19, 2005. Within the past fiscal year, considerable progress has been made with the
ΧFigure
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Fig. 3b.1. Locations of submarine telephone cables
running beneath the Florida Current (solid lines)
and stations (red) occupied during calibration
cruises.