Ra. Feely et al., HYDROTHERMAL PLUMES ALONG THE EAST PACIFIC RISE, 8-DEGREES-40' TO 11-DEGREES-50'N - PARTICLE DISTRIBUTION AND COMPOSITION, Earth and planetary science letters, 128(1-2), 1994, pp. 19-36
The discovery of a volcanic eruption at the 9-degrees-45.52'N site on
the East Pacific Rise (EPR) led us to investigate how the composition
of suspended matter in hydrothermal plumes may be used to provide a be
tter understanding of the relative age and vent fluid characteristics
of a ridge crest system during surface ship surveys. During the TROUGH
S (Tropical Ridge Observations of Underwater Geochemical Hydrothermal
Signals) expedition we collected hydrothermal plume particles along a
350 km section, extending from approximately 8-degrees-40'N to 11-degr
ees-50'N, of the EPR north and south of the Clipperton Transform Fault
. Over the segment south of the Clipperton Transform Fault, the S/Fe r
atio in the particles ranged from about 0.9 to 10, with the highest va
lues immediately over the new vent field at the 9-degrees-45.52'N site
. These enrichments exactly coincide with the elevated He-3/heat and C
H4/Mn ratios in the plumes over the same vent field. The S-rich partic
les are primarily organic and may be related to the 'bacteria blizzard
' associated with the eruption. In addition, very high Cu/Fe and Zn/Fe
ratios were observed in the hydrothermal plumes south of the Clippert
on Transform Fault. These high ratios are indicative of the predominan
ce of high-temperature, H2S-rich vents between 9-degrees-35'N and 9-de
grees-50'N. In contrast, the samples from the segment north of Clipper
ton Transform Fault had S/Fe ratios which ranged from 0.04 to 0.82, ty
pical of mature, Fe-rich hydrothermal plumes. These results suggest th
at the gas-rich vent fluids at the 9-degrees-45.52'N site produced the
sulfur-enriched particles in the water column. Gas-rich plumes and su
lfur-enriched plume particles were also observed underneath the 1986 M
egaplume on the Juan de Fuca Ridge (JdFR), suggesting a similar mode o
f formation. North of the Clipperton Transform Fault, the hydrothermal
particles are dominated by Fe-rich oxyhydroxide particles, characteri
stic of mature high-temperature vent fields. The plume maximum is cent
ered at 11-degrees-08'N. The Fe oxyhydroxide particles scavenge Ca, Si
, P, V, Cr and As from seawater. For P and V the mean element/Fe ratio
in the EPR hydrothermal particles are intermediate between JdFR and T
AG hydrothermal systems. For As the mean element/Fe ratios of all thre
e systems are about the same. New evidence for Si scavenging by hydrot
hermal Fe oxyhydroxide particles indicates that this sink for dissolve
d Si in the oceans is small.