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Background
Natural Iron Enrichment
Occurring to a measurable extent in coastal upwelling zones, certain
processes control the transformation of resuspended iron into bioavailable
iron. The "natural iron enrichment experiment" looked at
the entrainment in upwelled water of iron-rich sediment from the
continental shelf. This iron is important to phytoplankton growth,
but only two previous experiments have tracked it. Using a single
ship to track a patch of water in a Lagrangian reference frame while
concurrently mapping filament boundaries in an absolute reference frame
led investigators to use AUVs to map off-shore frontal boundaries using
primary physical measurements. Several AUV surveys were sent along
drifter tracks, thus along frontal boundaries.
Frontal Processes
Off the California coast, frontal instabilities develop along the cyclonic
boundary of upwelling filaments, and strong local upwelling occurs in
association with these instabilities. The dynamics of this upwelling
are not understood and the biological effects of the upwelling have not
been examined. Strong local upwelling significantly impacts cycling
of nutrients and particles within the evolving filament. AUVs were
used to investigate the spatial structure of upwelling and down-welling
along filament fronts in Monterey Bay, to define the dynamical basis for
the vertical motions, to quantitatively assess the flux of water and
chemicals along these boundaries, and to define relationships between
biological distributions and physical processes associated with these
instabilities.
Iron from Seafloor Venting
Remote sensing studies of the San Gregorio Fault Zone have identified this
area as being associated with gas and perhaps fluid discharging that is
adequate to produce acoustically detectable water-column plumes. AUV
surveys were used to help establish whether these acoustical plumes are,
in fact, associated with seafloor venting.
The Dorado / MBARI autonomous underwater vehicle (AUV) program is an engineering lead program combining several elements from the various groups here at MBARI and
collaborations with external research institutions. The
AUVs used in MUSE hosted a number of instruments, including a prototype
methane sensor on the daytime vehicle and a bioluminescence sensor on the
nighttime vehicle.
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