Minerals Report - International Seabed Authority

flattens out. He drew an analogy with the smoke coming out of a factory
chimney on a windy day. He pointed out that when the smoke first comes
out of a chimney, it is very hot; it starts rising up and then it slows down. As
it slows down, if there is any wind (current) blowing on a given day, it bends
the smoke (plume) over, and disburses it downstream. The level at which the
plume is no longer buoyant, according to Dr. German is called the level of
neutral buoyancy. Depending on which way the current is moving; the
plume is transported in that direction. Dr. German said that typically, plumes
rise somewhere between a hundred and 300 metres above the sea floor as they
are diluting themselves. He also said that this dilution factor tends to be
about 10,000 to 1, making it very difficult to find any temperature or heat
anomalies in the water column associated with them. On the other hand, he
said that although the plumes have been diluted 10,000 fold, since the fluid
itself was a million fold enriched in the first place, the material that rises and
starts being blown away by deep ocean currents, is still a hundred times
richer in all kinds of different chemicals than ordinary seawater. It is this
characteristic that is employed in prospecting for manifestations of
hydrothermal activity and thus associated massive sulphides deposits. Dr
German identified four chemical anomalies commonly used in this search.
These are helium, methane, manganese and iron.
Starting with helium Dr. German said that it is a noble gas; whose
most common form is He4 isotope, which is produced from radioactive decay.
He said that there is also He3 that is trapped inside the interior of the earth
coming out where volcanoes erupt. One of the prime places it can therefore
be found is in association with smokers from hydrothermal vents, and
ultimately the plumes that they produce. Dr. German informed participants
that helium in this form is inert and through measurements of its
concentrations, one obtains an excellent tracer for hydrothermal activity.
According to Dr. German, the drawback with this prospecting method
is the need to analyse samples with a noble gas mass spectrometer, which is a
specialist piece of equipment not available on research vessels. This means
that all samples have to be analysed at a land-based facility resulting in the
loss of valuable ship time, and a delay in determining the precise location of a
given anomaly. He noted that it could take up to six months to obtain the
results of analysis and for the search to continue. To facilitate better use of
INTERNATIONAL SEABED AUTHORITY 417