3.2. Fluid-escape features and chemosynthetic ecosystems
As well as mapping and monitoring of deep-water hydrothermal
processes, AUVs have played an important role in investigating lowtemperature
fluid escape features. Paull et al. (2008) used the MBARI
D. Allan B. AUV to collect high-resolution MBES (lateral resolution 1.5
m), SBP (0.1mvertical resolution) and SSS data over a series of fluid escape
mounds and surrounding swells at 800–900 m WD in Santa
Monica Basin, offshore California. These mapping data provided broader
geological context for detailed ROV sampling,while SBP profiles provided
indications for small-scale active faulting extending to the seafloor
(supported by ROV data showing elevated methane concentrations,
chemosynthetic fauna and seafloor alteration in these areas). The
high-resolution AUV data contributed to the interpretation that the features
are ‘blisters’ formed by expansion associated with gas hydrate accumulation
in the subsurface; this interpretation supported the
‘submarine pingo’ hypothesis previously developed by Hovland and
Svensen (2006) for seafloor blisters on the Norwegian margin.
Newman et al. (2008) used theWHOI SeaBED AUV to investigate a series
of giant km-scale seafloor pockmarks along the shelf edge (~100mWD)
off the east coast of the US. The AUV flewat an altitude of ~3 m, andwas
carrying a methane sensor to measure in situ dissolved methane
concentrations across the pockmarks. High-resolution MBES, CTD and
colour photography data (44,000 images) were also collected with the
AUV. The results indicated that active methane venting is occurring at
present and is focused along pockmark walls, and provided new information
on spatial and temporal variations in methane concentrations.