Minerals Report - International Seabed Authority

seabed but, instead, are dispersed within the neutrally-buoyant hydrothermal
plume which, therefore, has the characteristic of being optically much more
cloudy than the remainder of the (both underlying and overlying) deep-ocean
(Figure 9).
Figure 9 Examples of nephelometry (optical back-scatter) cross-sections detected from a deepsea
hydrothermal plume at the Rainbow vent-site, 36°N, MAR
This characteristic of hydrothermal plumes was first demonstrated by
Nelsen et al (1997) who used an in situ optical back-scatter instrument (a
nephelometer) connected to a standard water-sampling instrument package to
show a linear correlation with shipboard dissolved Mn analysis of the water
samples taken - but with the added advantage that the nephelometer data
were obtained both continuously and in real-time. For obvious reasons, use of
in situ optical sensors has subsequently become a staple method or
preliminary investigation for seafloor hydrothermal circulation.
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