ARGO II near bottom photographic and DSL-120 kHz sonar
surveys were conducted along the S. EPR in October-
November 1996 to study the narrow axial zone of the ultrafast-
spreading EPR (145 mm/yr) at 17 18'S. Both the ARGO II
camera sled and the DSL-120 were equipped with plume
detecting instruments that collected temperature, salinity, and
particle abundance data simultaneously with photographic and
acoustic coverage. The ARGO II, DSL-120, and plume-detection
instruments were used to map the distribution of
hydrothermal plumes with respect to volcanic-tectonic features
on the ridge. The CTD and transmissometer were mounted on
the sleds and therefore collected data approximately 10 m and
75 m off the seafloor during the ARGO II and DSL-120 surveys,
respectively. The two MAPRs were suspended on the cable,
one at 50m and one at 100 m above the sled.
Plume mapping consisted of two DSL-120 lowerings,
five ARGO lowerings with the CTD, transmissometer, and
MAPRs, totaling 17 days of near bottom data collection and ten
vertical profiles acquired during vehicle deployment and
recovery. The morphologically distinct Spike (17 24-26'S) and
Hump (19 23-29'S) segments and were the principal survey
areas but plume data coverage is continuous from 17 12' -
18 30S. We also ran a sawtooth CTD tow-yo for a short
distance (17.68 - 17.60'S) along the ridge to obtain local
hydrographic data.
Nephelometer and temperature data show that a high
percentage (~75%) of the northern survey area (17 12-55'S)
and ~45% of the southern survey area (17 55' - 18 35'S) are
covered by plume 150m above the seafloor. The most intense
plumes are concentrated at the center of and at the southern
end of the Spike area (near 17 26.5'S and from 17 35-42'S).
Both plumes coincide with other activity indicators (animal
communities, smokers) detected with the ARGO II cameras. In
the Spike Area there is a one-to-one correlation between areas
where seafloor hydrothermal indicators are present, and areas
where plumes are detected, although plume contributions
from individual seafloor vents were not always resolvable.
Further work is being done on this data set to estimate heat
flux from this very hydrothermally active area.